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HomeMy WebLinkAboutMisc• Geotec hn ica l Engi nee rin g Geology Env iro nm en tal Sc ient ists Construction Moni torin g GEOTECHNICAL ENGINEERING STUDY AVANARIDGE 10615 SOUTHEAST 172nd STREET RENTON , WASHINGTON ES-4147 PREPARED FOR AVANA RIDGE, LLC December 21,2015 cP~ Keven D. Hoffmann, E.I.T. Project Engineer Raymond A. Coglas, P.E. Principal GEOTECHNICAL ENGINEERING STUDY AVANARIDGE 10615 SOUTHEAST 172ND STREET RENTON, WASHINGTON ES-4147 Earth Solutions NW, LLC 1805 -138111 Place Northeast, Suite 201 Bellevue, Washington 98005 Phone: 425-449-4704 Fax: 425-449-4711 Toll Free: 866-336-8710 Important Information About Your Geotechnical Engineering Report Geotechnical Services APe Perlormed lOr Specific PIII'II0888, Persona, and Projects Geotechnical engineers structure their services to meet the specnic neecs of their clients. A geotechnical engineering study conducted for a civil engi- neer may not fulfill the neecs of a construction contractor or even another civil enginee[ Because each geotechnical engineering study is unique, each geotechnical engineering report is unique, prepared solely for the client No one except you should rely on your geotecllnical engineering report without first conferring with the geotechnical engineer who prepared it. And no one -not even you -should apply the report for any purpose or project except the one originafly contemplated. Read the filii Report Serious problems have occurred because those relying on a geotechnical engineering report did not read it all. Do not rely on an executive summary. Do not read selected elements only. A Geoteclldcal ~ Report Is Based on A U_ Set 01 ~-IIiIcIIIC Factors Geotechnical engineers consider a number of unique, project-specific fac- tors when establishing the scope of a study. Typical factors include: the client's goals, objectives, and risk management preferences; the general nafure of the structure involved, its size, and configuration; the 10catiOll of the structure on the site; and other planned or existing site improvements, such as access roads, parking lots, and underground util~ies. Unless the geotechnical engineer who conducted the study specifically indicates oth- erwise, do not rely on a geotechnical engineering report that was: • not prepared for you, • not prepared for your project, • not prepared for the specific site explored, or • completed before important project changes were made. Typical changes that can erode the reliability of an existing geotechnical engineering report include those that affect: • the tunction of the proposed structure, as when it's changed from a parking garage to an office building, or from a light industrial plant to a refrigerated warehouse, • elevation, configuration, location, orientation, or weight of the proposed structure, • composition of the design team, or • project ownership. As a general rule, always infonn your geotechnical engineer of project change5---1lven minor ones-and request an assessment of their impact. Geotechnical engineers cannot accept fliSponsibility or liability for problems that occur because their reports do not consider developments of which they were not informed. Subsurlace COIIdIllons can CUIQI8 A geotechnical engineering report is based on conditions that existed at the time the study was pertonned. 00 not rely on a geotechnical engineer- ing report whose adequacy may have been affected by: the passage of time; by man-made events, such as construction on or adjacent to the site; or by natural events, such as floods, earthquakes, or groundwaterfluctua- tions. Alw.iys contact the geotechnical engineer before applying the report to detenmine if it is still reliable. A minor amount of additional testing or analysis could prevent major problems. Most Geotechnical findings Are Professional 0tIinIaaI Site exploration identifies subsurtace conditions only at those points where subsurtace tests are conducted or samples are taken. Geotechnical engi- neers review field and laboratolY data and then apply their professional judgment to render an opinion about subsurtace conditions throughout the site. Actual subsurtace conditions may differ-sometimes significanlly- from those indicated in your report Retaining the geotechnical engineer who developed your report to provide construction observation is the most effective method of managing the risks associated with unanticipated conditions. A ReIIOrI's Recommendations Are NI1t final Do not overrely on the construction recommendaffons Included in your report. Those recommendaflons are not final, because geotechnical engi- neers develop them principally from judgment and opinion. Geotechnical engineers can finalize their recommendations only by observing actual subsurtace conditions revealed during construction. The geotechnical engineer who developea your report cannot assume responsibility or liability for the report's recommendations if that engineer doos not perform construction observation. A Geotechnical Englneerilg Report Is Subject to Misinterpretation Other design team members' misinterpretation of geotechnical engineering reports has resulted in costly problems. Lower that risk by having your geo- technical engineer confer with appropriate roomoors of the design team after submitting the report Also retain your geotechnical engineer to review perti- nent elements of tile design team's plans and specifications. Contractors can also misinterpret a geotechnical engineering report. Reduce that risk by having your geotechnical engineer partiCipate in prebid and preconstruction conferences, and by providing construction observation. Do Not Rudraw the Engineer's Logs Geotechnical engineers prepare final boring and testing logs based upon their interpretation of field logs and laboratory data. To prevent errors or omissions, the logs included in a geotechnical engineering report should never be redrawn for inclusion in architectural or other design drawings. Only photographic or electronic reproduction is acceptable, but recognize that sepamting logs from the report can elevate risk. GIve ClntPlctors I Complete Report and GllIdance Some owners and design professionals mistakenly believe they can make contractors liable for unanticipated subsurface conditions by limiting what tIley provide for bid preparation. To help prevent costly problems, give con- tractors the complete geotechnical engineering report, but preface it witll a clearly written letier of transmittal. In tIlat letter, advise contractcrs tIlat the reportwas not prepared for purposes of bid developmert and that the report's accuracy is limited; encourage them to confer with tile geotechnical engineer who prepared the report (a modest fee may be required) and/or to conduct additional study to obtain the specific types of information they need or prefer. A prebid conference can also 00 valuable. Be sum contrac- tors have suIIicient time to pertonffi additional study. Only then might you be in a position to give contractors the best infomnation available to you, while requiring them to at least share some of the financial responsibilities stemming from unanticipated conditions. Read Responsibility Previsions Closely Some clients, design professionals, and contractors do not recognize tIlat geotechnical engineering is far less exact than otller engineering disci- plines. This lack of understanding has created unrealistic expectations that have led to disappointments, claims, and disputes To help reduce the risk at such outcomes, geotechnical engineers commonly include a variety of explanatory provisions in their reports. Sometimes labeled 'limitations" many of these provisions indicate where geotechnical engineers' responsi- bilities begin and end, to help others recognize their own responsibilities and risks. Read tfJese provisions closely Ask questions. Your geotechnical engineer should respond fully and frankly. Geoenvironmental Concerns Are Not Covered The equipment, techniques, and personnel used to pertorm a geoonviron- mental study differ significantly from tIlose used to pertorm a geotechnical study. For t\lat reason, a geotechnical engineering report does not usually relate any geoenvironmental findings, conclusions, or recommendations; e.g., about the likelihood of encountering underground storage tanks or regulated contaminants. Unanticipated environmental problems have lea to numerous project failures If you have not yet obtai ned your own geoen- vironmental information, ask your geotechnical consultant for risk man- agement guidance. Do not rely on an environmental report preparea for someone else. Obtain Professional ASSistance To 0811 with Mold Diverse strategies can be applied during building deSign, construction, operation, and maintenanoe to prevent significant amounts of mold from growing on indoor surfaces. To be effective, all such strategies should be devised for tile express purpose of mold prevention, integrated into a com- prehensive plan, and executed witll diligent oversight by a professional mold prevention consultant. Because just a small amount of water or moisture can lead to the development of severe mold infestations, a num- ber of mold prevention strategies locus on keeping building surfaces dry. While groundwater, water infiltration, and similar issues may have been addressed as part of the geotechnical engineering study whose findings are conveyed irrlhis report, the geotechnical engineer in charge of this project is not a mold prevention consultant; none of the services per- formed In connection with the geotechnical engineer's study were deSigned Of conducted for the purpose of mofd preven- tion_ Proper implementation of /he recommendations conveyed in this report will not of Itself be sufflcient to preVflnt mold from growing in or on the structure involved. =vour ASfE.M8mbar Geotecbnclal for Adlllklnll AssIstIInc8 Membership in ASFE/The Best PeDjJle on Earth exposes geotechnical engineers to a wide array of risk management techniques t\lat can be of genuine benefit for everyone involved with a construction project. Confer with you ASfE-member geotechnical engineer for more information. ASFE t ... ,,( ." .. 1 ... hllll 6611 Cotesville Road/Suite G106, Silver Spring, MD 20910 Telephone' 301/565-2733 Facsimile: 3011589-2017 e-mail: info@aste.org WWII.asfe.org Copyright 2004 by ASFE, frrc. Dupticatlon, reproduction. or copying of this docum6nt, in whom or in part, by any mtIaIlS whats06V6f, Is strictly prohibited, except with ASFf's specific wrfttBn permission. Excerpring, QUo~. or Otli8rwiS6 extracting wording from this docummt IS f)6ITfIitt6d only with the 8X(Jr8SS wrtrren {IfIrm/$$jon of ASFE. and only for pUrpo86S at scholarly f6S88rcll or book review. Only msmbsrs of ASFE may lJSe til's documsrrt as a complement to or as an element of 3 geotechnical enginsering report. Any other firm, individual, or other errtlly tllat so uses this document wftllout lJelng an ASFf member could b8 commfttlng negogent or Intentional (fraudulent) misrepresenfil.tiorl. IIGER06045.!IM December 21, 2015 ES-4147 Avana Ridge, LLC 9675 Southeast 36th Street, Suite 105 Mercer Island, Washington 98040 Attention: Mr. Justin Lagers Dear Mr. Lagers: • Earth Solutions NW LLC • Geotechnical Engineering • Construction Monitoring • Environmental Sciences Earth Solutions ~, LLC (ESNW) is pleased to present this report titled "Geotechnical Engineering Study, Avana Ridge, 10615 Southeast 172nd Street, Renton, Washington". In our opinion, the proposed residential development is feasible from a geotechnical standpoint. Our subsurface exploration indicates the site is primarily underlain by Vashon till and bedrock of the Renton formation. During our subsurface exploration completed on October 1, 2015, groundwater seepage was not encountered at the test pit locations. At the time of Icicle Creek Engineers' most recent subsurface exploration (December 16, 2008), groundwater seepage was reported at one test pit location at approximately one-and-one-half feet below existing grades. In our opinion, discrete, perched seepage zones should be anticipated during construction depending on the time of year grading activities take place. In our opinion, the proposed residential structures may be supported atop conventional continuous and spread footing foundations bearing on competent native soil, recompacted native soil, or new structural fill. In general, competent native soil suitable for support of new foundations will be encountered within the upper two to three feet of existing grades. Where loose or unsuitable soil conditions are exposed at foundation subgrade elevations, compaction of the soils to the specifications of structural fill, or overexcavation and replacement with a suitable structural fill material, will be necessary. Construction of the proposed vault within the southwestern portion of the northem half of the site is feasible from a geotechnical standpoint. We anticipate competent, dense to very dense, undisturbed Vashon till will be encountered within excavations at depth for the vault foundation subgrade elevation. With respect to infiltration, it is our opinion native soils will not accommodate large-scale or full infiltration facility design; however, native soils are a good candidate for limited infiltration and/or bioretention applications. Recommendations for foundation deSign, site preparation, drainage, critical area mitigation, preliminary stormwater detention vault design, and other pertinent development aspects are provided in this study. We appreciate the opportunity to be of service to you on this project. If you have questions regarding the content ofthis geotechnical engineering study, please call. Sincerely, EARTH SOLUTIONS NW, LLC .u:::2~ Keven D. Hoffmann, E.I.T. Project Engineer 1805 -136lh Place N.E., Suile 201 • Bellevue, WA 98005 • (4251449-4704 • FAX (4251449-4711 Table of Contents ES-4147 INTRODUCTION..................................................................... 1 General........................................................................ 1 Proiect Description.................... ....... ............................. 2 SITE CONDITIONS........ ...... .................. ............................. ..... 2 Surface........................................................................ 2 Subsurface............................ ....................................... 3 Topsoil and Fill.................. .................................. 3 Native Soil ........................................................... 3 Geologic Setting.................................................. 4 Groundwater................................................................. 4 Critical Areas................................... ...... ........................ 4 Steep Slope Hazard.............................................. 5 Coal Mine Hazard............ ...... ......... ................. ..... 5 Minimum Risk Statement... ... ... ... . .. .. .. . .. . . . .. .. ... ... ... 6 DISCUSSION AND RECOMMENDATIONS............ ...... ...... .......... 6 General........................................................................ 6 Site Preparation and Earthwork.. ..................................... 6 Temporary Erosion ControL........ ................................ 7 Stripping........ ........... ...... .................................... ............ 7 In-situ Soils........ ..... ...................................... ................. 7 Imported Soils.. ........ ................................. ..................... 8 Subgrade Preparation........................................... 8 Structural Fill.... ........ ...................... ............................... 8 Foundations............................... .................................. 8 Seismic Design............................................................. 9 Slab-on-Grade Floors...... ........ ...................................... 9 Retaining Walls............................................................. 10 Drainage.................................................................................... 10 Infiltration Feasibility.. .... ... ........... ....... .... ...... ....... 11 Preliminary Detention Vault Design............ ............. 11 Excavations and Slopes......... ............ ..................................... 12 Pavement Sections........................................................ 13 Utility Support and Trench Backfill......... .......................... 13 LIMITATIONS............ ...... ...... .................................................. 14 Additional Services............ ............ ............ ............... ..... 14 Earth Solutions MH. LLC Table of Contents Cont'd ES-4147 GRAPHICS Plate 1 Vicinity Map Plate 2 Test Pit Location Plan Plate 3 Retaining Wall Drainage Detail Plate 4 Footing Drain Detail APPENDICES Appendix A Subsurface Exploration Test Pit Logs AppendixB Laboratory Test Results AppendixC Reports by Others Earth Solullons NW, LLC General GEOTECHNICAL ENGINEERING STUDY AVANARIDGE 10615 SOUTHEAST 172NO STREET RENTON, WASHINGTON ES-4147 INTRODUCTION This geotechnical engineering study was prepared for the proposed Avana Ridge apartment complex development to be completed at 10615 Southeast 172nd Street in Renton, Washington. The purpose of this study was to provide geotechnical recommendations for currently proposed development plans. Our scope of services for completing this geotechnical engineering study included the following: • Reviewing site-specific reports, prepared previously by Icicle Creek Engineers, Inc., for geotechnically relevant information pertinent to the proposed development; • Completing subsurface test pits for purposes of characterizing site soils; • Completing laboratory testing of soil samples collected at the test pit locations; • Conducting engineering analyses, and; • Preparation of this report. The following documents and maps were reviewed as part of our report preparation: • Geologic Map of the Renton Quadrangle, King County, Washington, by D. R. Mullineaux, 1965. • Preliminary Coal Mine Hazard Assessment, prepared by Icicle Creek Engineers, Inc., dated June 24, 1999; • Coal Mine Hazard Assessment, prepared by Icicle Creek Engineers, Inc., dated March 22,2004; • Geotechnical Engineering Services Report, prepared by Icicle Creek Engineers, Inc., dated January 20, 2009; • Liquefaction Susceptibility of King County (Map 11-5), prepared by the King County Flood Control District, May 2010; • Sensitive Areas maps for the City of Renton, printed August 2012; • Pre-Application Site Plan, Sheet No. PA-00.1, prepared by Baylis Architects, dated August28,2015, and; • Online Web Soil Survey (WSS) resource, provided by the Natural Resources Conservation Service under the United States Department of Agriculture. Avana Ridge, LLC December 21,2015 Project Description ES-4147 Page 2 We understand the proposed development will include construction of two residential apartment structures, utility improvements, parking and drive areas, and open space areas. Each apartment structure will be four to five stories in height. Rockeries will likely be incorporated into final designs to accommodate grade transitions, where necessary. We anticipate stormwater will be managed likely by a below-grade detention vault (vault) which is proposed for construction within the southwestern portion of the northern half of the site. Site geologic hazards include a stream and associated buffer space (within the central and southern site areas) and a historic coal mine, known as the Springbrook Mine, and its associated opening (near the southern property line). The proposed development will occur across a currently forested, unimproved property, and in general, the southern, geologically sensitive area of the site will not be improved. The site has been explored previously on several occasions by means of both soil borings and exploratory test pits. The referenced reports, prepared previously by Icicle Creek Engineers, Inc. (ICE), are discussed within the text of this report where relevant to the currently proposed development. The collective term "ICE reports" will be used hereafter when referring to these previously prepared reports. For reference, the ICE reports are provided in Appendix C. At the time of report submission, specific grading and building load plans were not available for review; however, based on our experience with similar developments, the proposed residential structures will likely be constructed at grade (following site mass grading) utilizing relatively lightly-loaded wood framing supported on conventional foundations. Based on the information provided, it is our understanding that underground garage levels are not proposed. We anticipate the residential structures will incorporate slab-on-grade floors or crawl space construction at grade. We anticipate perimeter footing loads on the order of 2 to 4 kips per lineal foot (kif). Slab-on-grade loading is anticipated to be on the order of 150 pounds per square foot (psf). If the above design assumptions are incorrect or change, ESNW should be contacted to review the recommendations in this report. ESNW should review final designs to confirm that our geotechnical recommendations have been incorporated into the plans. SITE CONDITIONS Surface The subject site is located north of the intersection between State Route 515 (Benson Drive South) and Benson Road South in Renton, Washington. The site and the surrounding upland area are commonly referred to as Benson Hill. The approximate location of the property is illustrated on Plate 1 (Vicinity Map). The triangular property is comprised of two adjoining tax parcels (King County Parcel Nos. 292305-9009 and -9148) totaling approximately 3.78 acres. The site is enveloped to the north by Southeast 172nd Street, to the southwest by State Route 515, to the southeast by Benson Road South, and to the east by a daycare facility. Earth Solutions NIN. LLC Avana Ridge, LLC December 21, 2015 ES-4147 Page 3 Both the northern and southern tax parcels are currently undeveloped; scattered vagrant camps, as well as associated debris and rubbish, are present across portions of the site. Site topography descends generally from north to south, and we estimate total elevation change to be on the order of 50 feet or less. Existing vegetation is dense and is representative of undisturbed, forested conditions. Subsurface An ESNW representative observed, logged, and sampled seven test pits, excavated at client- specified locations, on October 1, 2015 using a Client-provided excavator and operator. The test pits were completed for purposes of assessing soil conditions, classifying site soils, and investigating the presence of groundwater below the existing ground surface (bgs). The approximate locations of the test pits are depicted on Plate 2 (Test Pit Location Plan). Please refer to the test pit logs provided in Appendix A for a more detailed description of subsurface conditions. Soil samples collected at the test pit locations were analyzed in accordance with both United States Department of Agriculture (USDA) and Unified Soil Classification System (USCS) methods and procedures. Topsoil and Fill In general, topsoil was encountered within the upper 8 to 10 inches of existing grades at the test pit locations. A more significant topsoil depth of 16 inches bgs was observed at test pit (TP) location TP-5. The topsoil was characterized by dark brown color, the presence of fine organic material, and small root intrusions. Fill was not explicitly encountered at the test pit locations during our fieldwork. Based on our review of the ICE reports, fill was also not encountered at previously explored locations of the site, with the exception of ICE TP-9 which was drilled near the suspected former mine entry. Fill at ICE TP-9 was encountered to the terminus of the exploration pit (15 feet bgs). Native Soil Underlying topsoil, native soils at the test pit locations were comprised primarily of silty sand with gravel (USCS: SM), consistent with the typical makeup of Vashon till. In general, the upper two to three feet of the Vashon till was characterized as "weathered" and was encountered in a loose to medium dense state, while the Vashon till at depth was characterized as "unweathered" and was encountered in a dense to very dense state. The presence of iron oxide staining was also considered in our characterization of upper Vashon till deposits as ·weathered". Native soils were primarily encountered in a damp condition and extended to the maximum exploration depth of six-and-one-half feet bgs. Based on our review of the ICE reports, previous soil borings encountered bedrock of the Renton formation at depths of approximately 22 to 43 feet bgs underlying the Vashon till. The bedrock was comprised of sandstone, beds of coal and carbonaceous shale, and Claystone. Earth Solutions NW, LLC Avana Ridge, LLC December 21, 2015 Geologic Setting ES4147 Page 4 The referenced geologic map resource identifies ground moraine deposits (Qgt) , otherwise known as Vashon till, as underlying the site and surrounding areas. According to the geologic map resource, Vashon till is typically a compact, coherent, unsorted mixture of sand, silt, clay, and gravel which is commonly referred to as "hardpan". The referenced WSS resource identifies Alderwood gravelly sandy loam (Map Unit Symbol: AgC) across the site and surrounding parcels. The Alderwood series was formed in hills and ridges. Based on our field observations, native soils underlying the subject site, specifically those likely to be encountered during construction, are consistent with ground moraine deposits (Vashon till) as described in this section. The deposits encountered on site are consistent with those areas across the majority of Benson Hill, which are also mapped to be underlain primarily by Vashon till. As indicated in the previous section of this report, soil boring information outlined in the ICE reports indicate bedrock of the Renton formation is present at depth underlying the Vashon till. Groundwater During our subsurface exploration completed on October 1, 2015, groundwater seepage was not encountered at the test pit locations. Iron oxide staining was observed within the upper two to four feet of existing grades. In our opinion, discrete, perched groundwater seepage zones may be encountered during construction, particularly within excavations at depth for site utilities and the vault. Groundwater seepage rates and elevations fluctuate depending on many factors, including precipitation duration and intensity, the time of year, and soil conditions. In general, groundwater flow rates are higher during the wetter, winter months. Critical Areas The presence of critical areas on the subject site has been investigated by ICE on multiple occasions, and the conclusions of said investigations are summarized within the ICE reports. We also reviewed the referenced sensitive areas maps published by the City of Renton (City) to confirm the presence of critical area hazards within the property boundaries in accordance with Critical Areas Ordinance No. 5137, as adopted by the City. Based on our review, the site is designated as having potential for hazard relating to steep slopes and the historic coal mine. Earth Solution. fiW, LLC Avana Ridge, LLC December 21,2015 Steep Slope Hazard ES-4147 Page 5 The City steep slope hazard map identifies slopes with gradients in excess of 15 percent within the city limits. According to the steep slope hazard map, slopes within the property boundaries maintain gradients of at least 25 percent and equal to or less than 40 percent. Steep slopes, as defined by the City, are present at select locations across the site but are mostly concentrated within the central and southern site areas. In our opinion, with respect to the proposed locations of site improvements, the presence of steep slopes will not interfere with the proposed development. Where slopes of less than 40 percent are encountered during earthwork activities, those slopes may be successfully re-graded in the interest of meeting final project designs and finish grades. The soil strength characteristics of the Vashon till, as well as bedrock at depth, support this opinion from a geotechnical standpoint. Coal Mine Hazard Based on our review of the ICE reports, the following information is pertinent to the historic coal mine and related activity on site: • A coal mine was operated historically within the southern portion of the site, along the southwestern property line. The coal mine is designated by ICE to have high coal mine hazard (City Designation: CH). This designation is consistent with the definition provided within City Ordinance No. 5137 regarding coal mine hazards. • ICE TP-9, completed on December 16, 2008, encountered at least 15 feet of fill at the suspected, former mine entry, which is estimated to be approximately five to eight feet in diameter and inclined at approximately 55 to 60 degrees below horizontal (to the south). • ICE recommended excavation of existing fill soils to a depth of at least 15 feet or to at least five feet below the base of the deepest structural excavation. The excavation was recommended to be widened into native Vashon till areas and backfilled with a structural plug comprised of controlled density fill (CDF) to help stabilize subsurface areas. As indicated in the Project Description section of this report, the proposed development will occur within the northern portion of the site, and in general, the southern, geologically sensitive area of the site will not be improved. The recommendations provided by ICE were based on previous site development intentions, which included construction of a building within the southern site area. As the proposed development will not encroach on the southern area of the site, it is our recommendation no further remediation need be incorporated into the plans. The proposed development is apparently set back from the historic coal mine entry by a minimum distance of approximately 125 to 150 feet. Earth Solutions NW, LLC Avana Ridge, LLC December21,2015 Minimum Risk Statement ES-4147 Page 6 Based on our review of the preliminary project plans, it is our opinion the proposed development can be safely accommodated on site. The proposal will not increase the threat of the geological hazard to adjacent properties beyond pre-development conditions, and the proposal will not adversely impact other critical areas. DISCUSSION AND RECOMMENDATIONS In our opinion, construction of the proposed residential development on the subject site is feasible from a geotechnical standpoint. The primary geotechnical considerations associated with the proposed development include foundation support, slab-on-grade subgrade support, the suitability of using on-site soils as structural fill, and construction of the vault. In our opinion, the proposed residential structures may be supported atop conventional continuous and spread footing foundations bearing on competent native soil, recompacted native soil, or new structural fill. In general, competent native soil suitable for support of new foundations will be encountered within the upper two to three feet of existing grades. Where loose or unsuitable soil conditions are exposed at foundation subgrade elevations, compaction of the soils to the specifications of structural fill, or overexcavation and replacement with a suitable structural fill material, will be necessary. Construction of the proposed vault is feasible from a geotechnical standpoint. We anticipate competent, dense to very dense, undisturbed Vashon till will be encountered within excavations at depth for the vault foundation subgrade elevation. With respect to infiltration, it is our opinion native soils will not accommodate large-scale or full infiltration facility design; however, native soils are a good candidate for limited infiltration and/or bioretention applications. This study has been prepared for the exclusive use of Avana Ridge, LLC and their representatives. No warranty, expressed or implied, is made. This study has been prepared in a manner consistent with the level of care and skill ordinarily exercised by other members of the profession currently practicing under similar conditions in this area. Site Preparetlon and Earthwork Initial site preparation activities will consist of installing temporary erosion control measures, establishing grading limits, and performing clearing and site stripping (as necessary). Subsequent earthwork activities will involve mass site grading and related infrastructure improvements. Earth Solutions NW. LLC Avana Ridge, LLC December 21, 2015 Temporary Erosion Control ES-4147 Page 7 We anticipate entry and egress to the proposed development will be provided off both the Southeast 172nd Street and Benson Road South frontages. Prior to finished pavement installation, temporary construction entrances and drive lanes, consisting of at least six inches of quarry spalls, should be considered in order to minimize off-site soil tracking and to provide a stable access entrance surface. Geotextile fabric may also be considered underlying the quarry spalls for greater stability of the temporary construction entrance. Erosion control measures should consist of silt fencing placed around down gradient margins of the site. Soil stockpiles should be covered or otherwise protected to reduce soil erosion. Temporary approaches for controlling surface water runoff should be established prior to beginning earthwork activities. Additional Best Management Practices (BMPs), as specified by the project civil engineer and indicated on the plans, should be incorporated into construction activities. Stripping In general, topsoil was encountered within the upper 8 to 10 inches of existing grades at the test pit locations; however, a more significant topsoil depth of 16 inches bgs was observed at TP-5. For preliminary estimation purposes, it is our opinion an average topsoil stripping depth of 12 inches should be anticipated. ESNW should be retained to observe site stripping activities at the time of construction in order to thoroughly assess the required degree of stripping. Over-stripping should be avoided as it is unnecessary and may result in increased project development costs. Topsoil and organic-rich soil is neither suitable for foundation support nor for use as structural fill. Topsoil and organic-rich soil may be used in non-structural areas if desired. In-situ Soils From a geotechnical standpoint, in general, our field observations indicate on-site soils likely to be encountered during construction will be suitable for use as structural fill, provided the soil moisture content is at (or slightly above) the optimum level at the time of placement and compaction. Site soils should be considered highly moisture sensitive, and successful use of on-site soils as structural fill will largely be dictated by the moisture content at the time of placement and compaction. In general, soil that is near, or slightly above, the optimum moisture content at the time of placement and compaction may be used as structural fill. Conversely, soil that is found to be dry at the time of installation will likely require moisture conditioning (typically achieved through the application of water) prior to soil compaction. Soil encountered during site excavations that is excessively over the optimum moisture content will likewise require moisture conditioning (typically achieved through soil aeration) prior to placement and compaction. It should be emphasized native material should never be placed and compacted dry of the optimum moisture content, especially in site utility trench applications. If the on-site soils cannot be successfully compacted, the use of an imported soil may be necessary. Earth Solulion. NW, LLC Avana Ridge, LLC December 21,2015 Imported Soils ES-4147 Page B Where necessary, imported soil intended for use as structural fill should consist of a well- graded granular soil with a moisture content that is at or slightly above the optimum level. During wet weather conditions, imported soil intended for use as structural fill should consist of a well-graded granular soil with a fines content of 5 percent or less (defined as the percent passing the Number 200 sieve, based on the minus three-quarter inch fraction). Subgrade Preparation Native and structural fill foundation and slab subgrade surfaces should exhibit firm and stable characteristics. Uniform compaction of the foundation and slab subgrade areas may be necessary to establish a consistent subgrade condition below the foundation and slab elements. ESNW should observe the subgrade areas prior to placing formwork. Supplementary recommendations for subgrade improvement may be provided at the time of construction and would likely include further mechanical compaction or overexcavation and replacement with suitable structural fill. Structural Fill Structural fill is defined as compacted soil placed in foundation, slab-on-grade, and roadway areas. Fills placed to construct permanent slopes and throughout retaining wall and utility trench backfill. areas are also considered structural fill. Soils placed in structural areas should be placed in loose lifts of 12 inches or less and compacted to a relative compaction of at least 90 percent, based on the laboratory maximum dry density as determined by the Modified Proctor Method (ASTM 01557). Soil placed in the upper 12 inches of slab-on-grade, utility trench, and pavement areas should be compacted to a relative compaction of at least 95 percent. More stringent compaction specifications may be required for utility trench backfill zones depending on the responsible utility district or jurisdiction. Foundations In our opinion, the proposed residential structures may be supported atop conventional continuous and spread footing foundations bearing on competent native soil, recompacted native soil, or new structural fill. In general, competent native soil suitable for support of new foundations will be encountered within the upper two to three feet of existing grades. Where loose or unsuitable soil conditions are exposed at foundation subgrade elevations, compaction of the soils to the specifications of structural fill, or overexcavation and replacement with a suitable structural fill material, will be necessary. Provided foundations will be supported as described above, the following parameters may be used for design: • Allowable soil bearing capacity • Passive earth pressure • Coefficient of friction Eartf1 Solutions ~, LLC 2,500 psf 350 pet (equivalent fluid) 0.40 Avana Ridge, LLC December 21,2015 ES-4147 Page 9 A one-third increase in the allowable soil bearing capacity may be assumed for short-term wind and seismic loading conditions. The above passive pressure and friction values include a minimum factor-of-safety of 1.5. With structural loading as expected, total settlement in the range of one inch, as well as differential settlement of approximately one-half inch, is anticipated. The majority of the settlements should occur during construction as dead loads are applied. Seismic Design The 2012 International Building Code recognizes the American Society of Civil Engineers (ASCE) for seismic site class definitions. In accordance with Table 20.3-1 of the ASCE Minimum Design Loads for Buildings and Other Structures manual, Site Class 0 should be used for design. The referenced liquefaction susceptibility map indicates the site and surrounding areas maintain very low liquefaction susceptibility. Liquefaction is a phenomenon where saturated or loose soils suddenly lose internal strength and behave as a fluid. This behavior is in response to increased pore water pressures resulting from an earthquake or other intense ground shaking. Based on our field observations, it is our opinion site susceptibility to liquefaction during a seismic event may be considered negligible. The relatively consistent densities of native soils at depth and the absence of a uniformly established, shallow groundwater table were the primary bases for this opinion. Slab-on-Grade Floors Slab-on-grade floors for the proposed residential structures should be supported on a firm and unyielding subgrade. Where feasible, native soil likely to be exposed at the slab-on-grade subgrade levels can be compacted in situ to the specifications of structural fill. Unstable or yielding areas of the subgrade should be recompacted, or overexcavated and replaced with suitable structural fill, prior to construction of the slab. Highly organic soils exposed at slab-on- grade subgrade elevations will likely require overexcavation and replacement with suitable structural fill. A capillary break consisting of at least four inches of free-draining crushed rock or gravel should be placed below the slab. The free-draining material should have a fines content of 5 percent or less (percent passing the Number 200 sieve, based on the minus three-quarter inch fraction). In areas where slab moisture is undesirable, installation of a vapor barrier below the slab should be considered. If a vapor barrier is to be utilized, it should be a material specifically designed for use as a vapor barrier and should be installed in accordance with the specifications of the manufacturer. Earth Solutions NW, LLC Avana Ridge, LLC December 21,2015 Retaining Walls ES-4147 Page 10 Retaining walls must be designed to resist earth pressures and applicable surcharge loads. The following parameters may be used for design: • Active earth pressure (yielding condition) 35 pet (equivalent fluid) • At-rest earth pressure (restrained condition) 50 pet • Traffic surcharge" (passenger vehicles) 70 psf (rectangular distribution) • Passive earth pressure 350 pet (equivalent fluid) • Coefficient of friction 0.40 • Seismic surcharge 6H psf* • Where applicable; H equals the retained height (In feet) The above design parameters are based on a level backfill condition and level grade at the wall toe. Revised design values will be necessary if sloping grades are to be used above or below retaining walls. Additional surcharge loading from adjacent foundations, sloped backfill, or other relevant loads should be included in the retaining wall design. Retaining walls should be backfilled with free-draining material that extends along the height of the wall and a distance of at least 18 inches behind the wall. The upper 12 inches of the wall backfill can consist of a less permeable soil, if desired. A perforated drain pipe should be placed along the base of the wall and connected to an approved discharge location. A typical retaining wall drainage detail is provided on Plate 3. If drainage is not provided, hydrostatic pressures should be included in the wall design. Drainage Although groundwater was not explicitly encountered at the test pit locations during our fieldwork, it is our opinion discrete, perched groundwater seepage zones should be anticipated within site excavations depending on the time of year grading operations take place, particularly within excavations at depth for site utilities and the vault. Temporary measures to control surface water runoff and groundwater during construction would likely involve interceptor trenches and sumps. ESNW should be consulted during preliminary grading to identify areas of seepage and to provide recommendations to reduce the potential for instability related to seepage effects. Finish grades must be designed to direct surface drain water away from structures and slopes. Water must not be allowed to pond adjacent to structures or slopes. In our opinion, foundation drains should be installed along building perimeter footings. A typical foundation drain detail is provided on Plate 4. Earth Solutions NW. LLC Avana Ridge, LLC December21,2015 Infiltration Feasibility ES-4147 Page 11 As indicated in the Subsurface section of this report, native soils encountered during our fieldwork were characterized primarily as Vashon till. Subsequent to USDA textural analyses, the Vashon till was further classified as either gravelly sandy loam or gravelly loamy sand. From a geotechnical standpoint, the Vashon till should not be considered an ideal geologic feature to accommodate infiltration, especially when encountered in a dense, compact slate. In general, the infiltration capacity of the Vashon till should be considered minimal. It should be noted Vashon till can likely accommodate construction of rain gardens (bioretention) and other limited-infiltration facilities. ESNW can provide further evaluation of, and recommendations for, stormwater flow control BMPs upon request. Preliminary Detention Vault Design We anticipate stormwater will be managed likely by a below-grade detention vault which is proposed for construction within the southwestern portion of the northern half of the site. Specific grading plans for the vault were not available for review at the time of report preparation; however, we anticipate grade cuts on the order of 10 feet will be necessary to achieve the vault foundation subgrade elevation. Based on our field observations, grade cuts for the vault are likely to expose very dense, undisturbed Vashon till. The vault foundation should be supported on competent native soil or crushed rock placed atop competent native soil. The final vault design must incorporate adequate buffer space from property boundaries such that temporary excavations to construct the vault structure may be successfully completed. Perimeter drains should be installed around the vault and conveyed to an approved discharge point. Perched groundwater seepage should be anticipated within excavations for the vauH. The following preliminary design parameters may be used for the vauH: • Allowable soil bearing capacity (dense Vashon till) • Active earth pressure (unrestrained) • Active earth pressure (unrestrained, hydrostatic) • At-rest earth pressure (restrained) • At-rest earth pressure (restrained, hydrostatic) • Coefficient of friction • Passive earth pressure Earth Solutions '"". LLC 5,000 pst 35 pcf 80 pcf 50 pcf 95 pcf 0.40 350 pcf Avana Ridge, LLC December 21,2015 ES-4147 Page 12 Retaining walls should be backfilled with free-draining material or suitable sheet drainage that extends along the height of the walls. The upper one foot of the wall backfill may consist of a less permeable soil, if desired. A perforated drain pipe should be placed along the base of the wall and connected to an approved discharge location. If the elevation of the vault bottom is such that gravity flow to an outlet is not possible, the portion of the vault below the drain should be designed to include hydrostatic pressure. ESNW should observe grading operations for the vault and subgrade conditions prior to concrete forming and pouring. If the soil conditions encountered during construction differ from those anticipated, supplementary recommendations may be provided. ESNW should be contacted to review final vault designs to confirm appropriate geotechnical parameters have been incorporated, as necessary. Excavations and Slopes The Federal Occupation Safety and Health Administration (OSHA) and the Washington Industrial Safety and Health Act (WISHA) provide soil classification in terms of temporary slope inclinations. Soils that exhibit a high compressive strength are allowed steeper temporary slope inclinations than are soils that exhibit a lower compressive strength. Based on the soil conditions encountered at the test pit locations, both loose and medium dense soils, as well as any area where groundwater seepage is exposed, are classified as Type C by OSHA and WISHA. Where encountered, fill should also be considered Type C soil. Temporary slopes over four feet in height in Type C soils must be sloped no steeper than one- and-one-half horizontal to one vertical (1.5H:1V). Dense, undisturbed native deposits encountered without the presence of groundwater may be classified as Type A by OSHA and WISHA. Temporary slopes over four feet in height in Type A soils must be sloped no steeper than 0.75H:1V. Type A soils that are fissured, subjected to vibrations from heavy traffic, or have been otherwise previously disturbed must be classified as Type B by OSHA and WISHA. Temporary slopes over four feet in height in Type B SOils must be sloped no steeper than 1H:1V. Steeper excavations for the vault may be permissible provided the excavations expose very dense, cemented Vashon till. ESNW can provide supplementary recommendations, including field observations of excavations for the vaUlt, during the appropriate phase of construction. Where encountered, the presence of perched groundwater may cause caving of the temporary slopes due to hydrostatic pressure. ESNW should observe site excavations to confirm soil types and allowable slope inclinations. If the recommended temporary slope inclinations cannot be achieved, temporary shoring may be necessary to support excavations. Permanent slopes should be planted with vegetation to enhance stability and to minimize erosion and should maintain a gradient of 2H:1V or flatter. An ESNW representative should observe temporary and permanent slopes to confirm the slope inclinations are suitable for the exposed soil conditions. Supplementary recommendations with respect to excavations and slopes may be provided as conditions warrant. Earth Solutions NW. LLC Avana Ridge, LLC December 21,2015 Pavement Sections ES-4147 Page 13 The performance of site pavements is largely related to the condition of the underlying subgrade. To ensure adequate pavement performance, the subgrade should be in a firm and unyielding condition when subjected to proofrolling with a loaded dump truck. Structural fill in pavement areas should be compacted to the specifications previously detailed in this report. It is possible that soft, wet, or otherwise unsuitable subgrade areas may still exist after base grading activities. Areas containing unsuitable or yielding subgrade conditions will require remedial measures, such as overexcavation and replacement with crushed rock or structural fill, prior to pavement. We anticipate new pavement sections will be subjected primarily to passenger vehicle traffic. For lightly loaded pavement areas subjected primarily to passenger vehicles, the following preliminary pavement sections may be considered: • A minimum of two inches of hot mix asphalt (HMA) placed over four inches of crushed rock base (CRB), or; • A minimum of two inches of HMA placed over three inches of asphalt treated base (ATB). The HMA, ATB and CRB materials should conform to WSDOT specifications. All soil base material should be compacted to a relative compaction of 95 percent, based on the laboratory maximum dry density as determined by ASTM D1557. Final pavement design parameters, including recommendations for heavy traffic areas or access roads, may be provided once final traffic loading has been determined. Road standards utilized by the City of Renton may supersede the recommendations provided in this report. Utility Support ai1d Trench Backfill In our opinion, on-site soils will generally be suitable for support of utilities. Remedial measures may be necessary in some areas in order to provide support for utilities, such as overexcavation and replacement with structural fill, or placement of geotextile fabric. Groundwater seepage may be encountered within utility excavations and caving of trench walls may occur where groundwater is encountered. Depending on the time of year and conditions encountered, dewatering, as well as temporary trench shoring, may be necessary during utility excavation and installation. In general, on-site soils will likely be suitable for use as structural backfill throughout utility trench excavations provided the soil is at or near the optimum moisture content at the time of placement and compaction. Moisture conditioning of the soils may be necessary at some locations prior to use as structural fill. Each section of the utility lines must be adequately supported in the bedding material. Utility trench backfill should be placed and compacted to the specifications of structural fill as previously detailed in this report, or to the applicable specifications of the City of Renton or other responsible jurisdiction or agency. Earth Solutiona mv. LLC Avana Ridge, LLC December 21, 2015 LIMITATIONS ES-4147 Page 14 The recommendations and conclusions provided in this geotechnical engineering study are professional opinions consistent with the level of care and skill that is typical of other members in the profession currently practicing under similar conditions in this area. A warranty is not expressed or implied. Variations in the soil and groundwater conditions observed at the test pit locations may exist and may not become evident until construction. ESNW should reevaluate the conclusions in this geotechnical engineering study if variations are encountered. Additional Services ESNW should have an opportunity to review final project plans with respect to geotechnical recommendations provided in this report. ESNW should also be retained to provide testing and consultation services during construction. Earth Solutions NW, LLC Reference: King County. Washington Map 656 By The Thomas Guide Rand McNally 32nd Edition NORTH • jIlt~ I I ~~ NOTE: This plate may contain areas of color. ESNW cannot be responsible for any subsequent misinterpretation of the information resulting from black & white reproductions of this plate. ~' I :.~'\,!) "IIU I I ........ T~!_ I ~~~ /Ii )/)' TP-7 1 p-..... FaTllyCirde LeamlngC<!nter (prtlschool) ~ ."" ,,-- 0- ( LEGEND I Approximate location of T~1. _ ESNW Test Pit, Proj. No. I ES-4147, Oct 2015 1 ___ I Subject Site D Proposed Building Stream o o 40 BO 160 1~=BO' ~ !""II i~"'''''nr: ..... t NOTEThegr9plucsshownooltll$~f!tenotWltanOOdforde&ign purpoS6sorpre(:isa$calamaasur_I\t$.t.ut~torlluGlratelhe apprO;Qmaie les;!loeations ll.IIa1ive to the approxlmale Iocation& 01 eri8Iingandlorpr~siteleatures.Theinfotmaliooillu8tr3t9d islargelyba&edondalaprovidtldbvtheetienlaltha1imeo/ou[ study. ESNWcamol be respollliibleforsubreqJentde6ign changes ornlarprelation 01 the da!a byolhers. NOTE 'fhj,plalemayoootalnarea~otcolor.ESNWcannotbe responSIble for lItIysublleqoo'ltmismlerprBlationofltle lniormaIJon re8lAtinglrornblacl<.-!.wh~&r~ctIon~olltlispiate C C ~~~ C 01.-o~~ §~~ ::~c ~~~ ~ '" , Sheet Drain --;."'T.~ (See Note) NOTES: • Free-Draining Backfill should consist of soil having less than 5 percent fines. Percent passing #4 should be 25 to 75 percent. • Sheet Drain may be feasible in lieu of Free-Draining Backfill, per ESNW recommendations. • Drain Pipe should consist of perforated, rigid PVC Pipe surrounded with 1-inch Drain Rock. LEGEND: I ~ ~ 0 I Free-Draining Structural Backfill • 0.0 1-inch Drain Rock 18" Min. Structural Fill Perforated Drain Pipe (Surround In Drain Rock) SCHEMATIC ONLY -NOT TO SCALE NOT A CONSTRUCTION DRAWING •• ' . rth Solutions NWLU leal Engineer mg Canstl uetton MOl1lfOIII1? and Envil anmental SCiences RETAINING WALL DRAINAGE DETAIL Avana Ridge Renton, Washington Drwn. MRS Date 12/21/2015 Proj. No. 4147 Checked KDH Date Dec. 2015 Plate 3 Perforated Drain Pipe NOTES: • Do NOT tie roof downspouts to Footing Drain. • Surface Seal to consist of 12" of less permeable, suitable soil. Slope away from building. LEGEND: [0;.:.: 0;. :[ Surface Seal; native soil or : : :: ::: ::: other low permeability materiaL 1" Drain Rock (Surround with 1" Rock) SCHEMATIC ONLY -NOT TO SCALE NOT A CONSTRUCTION DRAWING : h Solutions NWlU mcal Engineering COnstl uctlon MOT1ltol Illg ... : and Envlronment~1 SCiences • Drwn. MRS FOOTING DRAIN DETAIL Avana Ridge Renton, Washington Date1212112015 Proj. No. 4147 Checked KDH Date Dec. 2015 Plate 4 Appendix A Subsurface Exploration Test Pit Logs ES-4147 The subsurface conditions at the site were explored on October 1, 2015 by excavating seven test pits using a client-provided excavator and operator. The approximate locations of the subsurface exploration test pits are illustrated on Plate 2 of this study. The subsurface test pit logs are provided in this Appendix. The test pits were advanced to a maximum depth of six- and-one-half feet bgs. The final logs represent the interpretations of the field logs and the results of laboratory analyses. The stratification lines on the logs represent the approximate boundaries between soil types. In actuality. the transitions may be more gradual. Earth Solutions tom. LLC Earth Solutions NWLLC SOIL CLASSIFICATION CHART MAJOR DIVISIONS TYPICAL DESCRIPTIONS GRAVEL AND GRAVELLY SOILS COARSE GRAINED SOILS MORE THAN SO% OF COARSE FI<ACTION RETAINED ON NO. 4 SIEVE MORE THAN SO'I' SAND OF MATERIAL IS AND lARGER THAN SANDY NO. 200 SIEVE SOILS SIZE MORE THAN 50% OF COARSE FRACTION PASSING ON NO. 4 SIEVE SILTS FINE AND GRAINED CLAYS SOILS MORE THAN SO'I' OF MATERIAl IS SMAllER THAN NO. 200 SIEVE SIZE SILTS AND CLAYS CLEAN GRAVELS (UT11.E OR NO ANES) GRAVELS WITH FINES (APPRECIABlE AMOUNT OF FINES) CLEAN SANDS (UT11.E OR NO FINES) SANDS WITH FINES (APPRECIABLE AMOUNT OF ANES) LIQUtD ut.IT LESSTHANSQ LK)UIDLIMrr GREATER THAN 50 OH WELL-GRAOEO GRAVELS. GRAVEL- SAND MIXTURES, UTIlE OR NO FINES POORL Y~AADEO GRAVELS. GRAVEL-SAND MIXTURES. lrTTlE OR NO FINES SILTY GRAVELS, GRAVEL-SAND- SILT MIXTURES CLAYEY GRAVELS. GRAVEL-SAND- CLAY MIXTURES WELL-GRAOeD SANeS, GRAVELLY SANDS, lrTTLE OR NO FINES POORLY-GRAOEO SANDS, GRAVELLY SAND, LrTTLE OR NO ANES SL TY SANDS. SAND -SILT MIXTURES INORGANIC SILTS. MICACEOUS OR DIATOMACEOUS FINE SAN) OR SILTY SOILS INORGANIC CLAYS OF HIGH PLASTICITY ORGANIC CLAYS OF MEDIUM TO HIGH PlASTICITY, ORGANIC SILTS HIGHLY ORGANIC SOILS PT PEAT, HUMUS, SWAMP SOILS WITH HIGH ORGANIC CONTENTS DUAL SYMBOLS are used to Indicate borderline soil classifications. The discussion in the text of this report is necessary for a proper understanding of the natu re of the material presented in the attached logs. • Earth Sclutions NW TEST PIT NUMBER TP-1 1805 -1361h Place N.E., Suft. 201 Bellevue, W •• hing1On 98005 PAGE 1 OF 1 Telephone: 425-449-4704 Fax: 425-449-4711 CUENT Avana R~, UC PROJECTNAIilE _~ PROJECT NUIllBER 4147 PROJECT LOCATION Remon, Washi!Jgton DATE STARTED 1011/15 COMPLETED 1011115 GROUND ELEVATION TEST PIT SIZE EXCAVATION CONTRACTOR ClientProvi<I<HI GROUND WATER LEVELS: EXCAVATION IIETHOD ATl1l1E OF EXCAVATION LOGGeD BY KDH CHeCKED BY KDH AT END OF EXCAVATION - NOTES IleIlIh ofTopsoil & Sod 10": brush, duff AFTER EXCAVATION - w .. \,! ~g 1:ffi oj w'" TESTS U :1:8 MATERIAL DESCRIPTION ...J:;; vi ~...J C ~~ ;j CI 0 TPSL,: Dark brown TOPSOIL, roots to l' ,1'~ 0.8 Brown silty SAND, medium den .. , moist (Wee-TilQ -scattered cobbles from 1'-2' MC= 9.20% -iron oxide S1aining to 3.5' SM -becomes dense at 2' -becomes VOI)I dense at 3' ..moderate cementation MC= 8.90% 4.5 -trace gravel Test pit terminated at 4.51eet below existing grade due to _red till refusal. No gmundwaterencountered during excavation. Bottom of test pI at 4.5 feet. CUENT AvanaR~~,L~L~C~ ______________________ ___ PROJECT NUMBER DATE STARTED _1,,01"'1"-11"'5'---____ _ C~ETED_1~0I~11~1~5 ____ _ EXCAVATION CONTRACTOR ...,C",I".ien",t"P",rovid"",· ",o",d ______________ _ EXCAVATION METHOD __________________________ _ LOGGED BY ."K"'D"'H-'----________ _ CHECKED BY -'KD=H-'----____ __ NOTES Depth of TopsoO & Sod 9": brush, duff TESTS MC= 5.60% MC= 7.00% Fines. 34.90% TEST PIT NUMBER TP-2 PAGE 1 OF 1 PROJECTNAME~A~d~na~~~·~L_ ________________________ _ PROJECT LOCATION GROUND ELEVATION _________ TEST PIT SIZE _______ _ GROUND WATER LEVELS: AT TIllE OF EXCAVATION -= ______________________ _ ATENDOFEXCAVATION-=~ ____________________ _ AFTER EXCAVATION - MATERIAL DESCRIPTION • Earth Solutions MN TEST PIT NUMBER TP-3 1805 -1361h Place H.E., Suite 201 PAGE 1 OF 1 Bellevue, Washing10n 98005 Telephone: 425-449-4704 Fax: 425-449-4711 CUENT Avana~, LLC .... ".~--"------" ----PROJECT NAME Avana Riclge _______ PROJECT NUMBER 4147 PROJECT LOCAll0N Renton, Washi~ton DATE STARTED 1011115 COIIPLETED 1011115 GROUND ELEVAllON TEST PIT SIZE EXCAVAll0NCONTRACTOR Clien! Provided GROUND WATER LEVELS: EXCAVAll0N METHOD ATllME OF EXCAVAllDN LOGGED BY KOH CHECKED BY KDH AT END OF EXCAVAll0N - NOTES !!!!I!!!! of To~soil & Sod 8": brush duff ~ng boles AFTER EXCAVA lION - w t-~ffi oj u ~'" TESTS d ii:g MATERIAL DESCRIPTION we. 11.:::;; oj ~..J [J ~~ :;j C) 0 rws L /: ' , Darl< broWn TOPSOIL, ro01S to 2,5' ,1.lr 0.8 Brown silty SAND, loose to medium dense, damp (Wea1he1l!d TiIQ -iron oxide staining to 3.5' -becomes medium den .. , trace gravel MC=6.SO% 5M -becomes tan silty SAND with graval, very den .. (unwaathell!d till) -L -moderate cementation MC=6.5O% 5.' T •• t p~ tenminaled at 5.5 feet below existing grade due to unweathell!d tin refusal. No groundwater encountered during excavation. Bottom of test p~ at 5.5 feel ~ • Earth Solutions NW TEST PIT NUMBER TP-4 1805 -136th Place N.E.. Su~. 201 PAGE 1 OF 1 Bellevue. Washington 9IlOO5 Telephone: 425-449-4704 Fax: 425-449-4711 CLIENT Avana Rillge. LLC PROJECT NAME Awn. Ridge PRO.JECT NUMBER 4147 PROJECT LOCAll0N Renton Weshi!Jgton DATE STARTED 1011/15 COMPLETED 1011/15 GROUND ELEVAll0N TEST PIT SIZE EXCAVAll0N CONTRACTOR Client Provided GROUND WATER LEVELS: EXCAVAll0N MEDlOD AT liME OF EXCAVAllON - LOGGED BY KDH CHECKED BY KDH AT END OF EXCAVA110N - NOTES !l!!I!!h ofTaosoil & Sod 6"-8~ cardboard, debris AFTEREXCAVAllDN - w ~g ~ffi en 0 J:C) wID TESTS 0 ~g MATERIAL DESCRIPTION -':::E en c "-:::> oj ~z C) 0 TPS ., , Brown TOPSOIL, roots to 3.5' 0.' Brown silty SAND. loose. damp (Weathered Tdl) -iron oxJde staining to 4' -becomes medium dense MC=8.00% Fines = 22.10% SM [USDA Classification: gravaUy loamy SANDI -becomes tan silty SAND wfih gravel. very danae (unwea!herod til~ r-L -moderate cementation MC = 7.20% ... Teat pn lenninaled at 6.0 feet below existing 9rade due to unweathered till refusal No groundwater encountered during excavation. Bottom of test pfi at 6.0 feet. Earth Solutions NW 1805 -136th Place "'.E., Sui. 201 Bellevue, Washinglon 98005 Te"phon.: 425-449-4704 Fax: 425-449-4711 CUENT Avan. Ridge, LLC PROJECT NUMBER DATE STARTED _1",01""1,,,,/1,,-5 __ _ COMPLETED _1",011'-".11",5,-__ EXCAVATION CONTRACTOR -,C",IIe~nt,-,P-,-ro",v",kI",od,,---______ _ EXCAVAnONMETHOD ______________ ___ LOGGED BY --'K"'D"'H-'-____ _ CHECKED BY ...!K"'O"-H'--__ _ NOTES Depth of Topeoll & Sod 16": brush, dull, YOUng trees TESTS TEST PIT NUMBER TP-5 PAGE 1 OF 1 PROJECT LOCATlON GROUND ELEVATION ____ _ TEST PIT SIZE _____ _ GROUND WATER LEVELS: ATnMEOFEXCAVA11ON~'_ __________ __ AT END OF EXCAVAnoN -= _________ _ AFTER EXCAVATION - UA TERIAl OESCRIPTION -iron oxide staining MC=5.5D% -becomes medium den ... -becomes brownish gray, dense to very dense (unweatherod tilQ ~ I!o ~ I • EarthSolutionsNW 1805 -136111 Place N.E., Suite 201 Bellevue, Washington 98005 Telephone: 425-449-4704 TEST PIT NUMBER TP-6 Fax: 425-449-4711 CUENT Avana Ridge LLC PROJECT NUMBER 4147 PAGE 1 OF 1 PROJECTNAME~A~v~a~n.~Ridge~·~L-________________________ _ PROJECT LOCATION Renton, Washington DATE STARTED .."1,,,0/"'1/"'15"--____ _ COMPLETED -'1"'0/,,1'-'11"'5 ____ __ GROUND ELEVATION ________ _ TEST PIT SIZE __________ _ EXCAVATION CONTRACTOR -'C"'I"'Ie"'nI"'P..cro"'Y1"'·d"'ad"-____________ __ GROUNDWATER LEVELS: EXCAVATION METHOD __________________________ __ AT liME OF EXCAVATION -='--____________________ _ LOGGEDBY-'K~D~H~ ______ ___ CHECKED BY -'KD=H-'-____ __ ATENDOFEXCAVATION~-~ ______________________ _ NOTES Depth 01 Topsoil & Sod 8": bnIsII dull AF1l!R EXCAVATION - W ~e-~ffi .; 0 Will TESTS d rg W-...J::! .; ~...J Cl 0..::J :::j ::!z C> iii MATERIAL DESCRIPTION 0 in'sl '-', '0.7 Dark brown TOPSOIL, roots to 3' SM MC = 6.80% .8.6 Brown silty SAND, lOose to madium dense, damp (Weathered nUl -ron oxide staining -become medium dense to denae -becomes tan (unweathered tilQ -becomes very dense -moderate cementation Test p~ lermln_ at 6.5 feet below existing grade due to unweathered til """sal. No groundwater encountered during excavation. Bottom of .... t pft at 6.5 feet. ~~~--~--------~~~----------------------------------------~ • Earth Solutions NW TEST PIT NUMBER TP-7 1805 -136th Place N.E., Suite 201 PAGE 1 OF 1 Bellevue, Washington 98005 Telephone: 425-449-4704 Fax: 425-449-4711 CUENT Avana Rid!!!,. LLC PROJECT NAME AvorlS Ridge PROJECT NUMBER 4147 PROJECT LOCAll0N Renton, Wa.hi!!ll!on DATE STARTED 1011/15 COMPLETED 1011115 GROUND ELEVA11DN TEST PIT SIZE EXCAVAll0N CONlRACTOR Client Provided GROUND WATER LEVELS: EXCAVAllON METHOD ATTlIIE OF EXCAVAll0N - LOGGED BY KDH CHECKED BY KDH AT END OF EXCAVA110N - NOTES Dell!!! ofT_il& Sod 10": brush, dull AFTER EXCAVA110N - w n. 9 ~g ~'" 0 will TESTS 0 its MATERIAL DESCRIPTION ....r:E 0 ~....r C n.::> ::j :Ez 0 ~ D TPSI ;: ' , Dark brown TOPSOIL, roo1s to 1.5' ,H, 0.' Brown silty SAND with gravel, loose to medium dense, damp (Wealhered Till) -iron oxide staining -becomes tan, medium dense to dense MC = 5.00% SM Anas = 27.40% -weak to moderate cementation [USDA Classlficalion: oIighlty gravelly .andy LOAM] -beoomes very dense (unweathered till) -..L MC. 7.20% 5.0 Test pft termin_ at 5.0 feat below existing glllde due 10 unwealhered til refusal. No groundwater encountered during excawtlon. Bottom of test pft at 5.0 feel Appendix B Laboratory Test Results ES-4147 Earth Solutions NW, LLC • Earth Solutions NW GRAIN SIZE DISTRIBUTION 1805 -1361h Place N.E .• Suite 201 Bellevue. WA 98005 Telephone: 425-284-3300 CLIENT Avan. Ridee. LLC PROJECT NAME Avan. Ridge PROJECT NUMBER ES-4147 PROJECT LOCATION Renlon U,S. SIEVE OPENING IN INCHES I U.S. SIEVE NUMBERS I HYDROMETER 6 4 3 2 1 112318 3 4 6 810 1416 20 30 -40 50 60 100 140200 100 '\ "'\ 95 90 85 \ i'--.., \ 'lit.. 80 75 ~ 70 '---11'-., 65 t\ ... l: (!) 60 ill I\~ ~ ~ 55 t\ \ '" 50 ~ 1\ ~ Ii: ... 45 z .~\ UJ a? 40 UJ 1\\ .. 35 "\ 30 25 20 15 10 5 0 100 10 1 0.1 0,01 0.001 GRAIN SIZE IN MILLIMETERS I COBBLES I GRAVEL I SAND I SILT OR CLAY coarse fine I coo"", medium I fine I Specimen Identification Classification Cc Cu • TP-2 5.0ft. USDA: Brownish Gray Gravelly Fine Sandy Loam. useS: SM with Gravel. .IZI TP-4 3.Oft. USDA: Brownish Gravelly Loamy Sand. uses: SM. .. TP-7 3.Oft. USDA: Tan Slightly Gravelly Sandy Loam. uses: SM. ~ Specimen Identification 0100 060 030 010 LL PL PI 'IoSil! 'IoClay • TP-2 5.0ft. 37.5 0.351 34.9 IZI TP-4 3.Oft. 19 0.398 0.116 22.1 ~ .. ~ TP-7 3.0ft. 19 0.296 0.086 27.4 z AppendixC Reports by Others ES-4147 As indicated in the Project Description section of this report, the site has been previously explored on several occasions by ICE. The following reports, referred to previously within the report text as the "ICE reports", are provided in this Appendix: • Preliminary Coal Mine Hazard Assessment, prepared by Icicle Creek Engineers, Inc., dated June 24, 1999; • Coal Mine Hazard Assessment, prepared by Icicle Creek Engineers, Inc., dated March 22, 2004, and; • Geotechnical Engineering Services Report, prepared by Icicle Creek Engineers, Inc., dated January 20, 2009. Earth Solutions MN I LLC I c E Icicle Creek Engineel'8, Inc. Geotechnical, Geologic and Environmental Services Iune 24, 1999 Phil Davidson Claremont Development Company, Inc. SIS -11611> Avenue NE, Suite 108 Bellevue, Washington 98004 INTRODucnON Report Geological Engineeriug Services Coal Mine Hazard Assessment Cugiui Property 10sth Avenue SE and State Route SIS Renton, (King County), Washington File No. 0336-00 I This report summarizes Icicle Creek Engineers' (ICE's) geological engineering services regarding a preliminary """I mine b87Md assessment of two land parcels located near the intersection of 10Sth Avenue SE and State Route (SR) SIS in Renton (King County), Washington. In this report, the land parcels are referred to as the Southeast and the Northwest Parcels; collectively, the land parcel. are referred to as Ute "Cugini property." Our services have been completed in general accordance with our Services Agn:ement dated June 2, 1999 and were authorized by Alex Cugini on June 4, 1999. The property is situated in southeast Renton in an area where historic underground coal mining has occurred. The property is shown relative to nearby physical features on the Vicinity Map, Figure I. BACKGROUND INFORMATION We understand that this property is being considered for development. The type of development is not known. Portions of this property are underlain by the underground workings of the Springbrook Mine. King County Ordinance No. 13319 describes general policy for land use in "Coal Mine Hazard Areas" within King County. Recently, draft Administrative Guidelines (DAG) have been developed by King County Department of Development and Environmental Services (DOES) that generally outline the requirements for technical review and evaluation of Coal Mine Hazard Areas. SCOPE OF SERlVCES GENERAL The purpose of our services was to conduct a coal mine hazard assessment of lb. Cugini property follOWing the review and evaluation guidelines presenllld in DAG. Our specific scope of services inclUded the following: Icicle C=I< Engineers, Inc., Mcodow Cr<ek Professional C .. tcr. 2252.S SE 64th Pia«, Suilo 202, '_uah, Washington 98027 Tel""" .... : (42S) 557-436& Fax: (42.S) 557-4369 Claremont Development Company, Inc. Iune 24, 1999 Page 2 1. Geologic Information Review -Review available information conceming project site topography, geology, soil conditions and other relevant site c:lwactcristics. Published materials include geologic maps prepan:d by the U.S. Geological Survey (USGS), and a variety of maps publislied by the Washington State Department of Natural Resources. 2. Mioo Records Review -Review of available mine records to evaluate the location of the mined-<lut areas, together with the depth of mining. thickness of zone mined and mining methods. This information wa. reviewed in concen with ground surface topography ID evaluate if there has been any surface expression or collapse of underground openings. 3. Geol. Reco.naIosaDce -Surface reconnaissance mapping ID identi!}l mine openings such as adits or air shafts, IDgether with stockpiles of tailings or other areas in which the original ground surface has been disturbed. In addition, we noted any surface topographic anomaly that might indicate collapse ofunderground workings. 4. MID. Mapping -Mine mapping included superimposing the identified mines onto a projecl site base map. This map was used 10 develop geologic cross-sections showing the depth to mined-<lut areas and a prelimin"'Y interpretation of mine overburden conditions. The cross-sections were used to develop a map showing the estimated depth below the ground surface to the mine workings. 5. EvaluatioD -Based on the findings of Scope Items 1 througb 4, cJassify the mine hawds as either: 1) severe coal mine hazard areas, 2) moderate coal mine hazard areas, or 3) declassified coal mine hazard areas. Evaluate the potential for regional ground subsidence in moderate coal mine hazard areas (vertical ground subsidence, ground tilt and ground strain). 6. M'rtiption -Develop mitigation for development within severe and moderate coal mine hazard areas, as appropriate. 7. Additional Study -Provide recommendations fot' additional study, as appropriate. EXISTING INFORMAll0N The following documents were reviewed regarding the geology, historic coal mining and regulatory status (related to coal mine hazards) in the Cugini property area: • Morri.on Knudsen, JanDlll)' 1985, "Engineering Investigation for the Renton, Wuhington Area," prepared for the U.S. Depanment of Agriculture Office of Surface Mining. • Warren, W.C., Norbisrath, H., Orivetti, RM., and Brown, S.P., 1945, "Prelimialll)' Geologic Map and Brief Dcscription ofllle Coal Fields of King COURty. Washington," United State. Geological Survey, 1 plate. Washington State Department of Natural Resources, 1948, himric map of the Springbrook Mine including surface features and underground mine workings. GEOLOGIC SETI1NG The Cugini propeny is underlain by bedrock of lb. Renton fonnation. Renlon formation bedrock consists of interbedded sandstone, siltstone, shale, claystone, carbonaceous shale and coal beds. SlJUclUrally, the bedrock has been uplifted, folded and faulted over time. This structural deformation of the bedrook has created a northwest trending syncline. "Syncline" is • geologic term refming to a fold in the bedrock layering that is concave up. The "limbs" or layering of the syncline dip at angles ranging from 30 to 70 degrees from horizontal. The bedrock is covered with weathered soil and glacial sediments varying in thickness from a few reet to several tens of reet The glacial sediments are referred to as Vashon age glacial till consisting primari ly of dense to very dense silty sand with gravel. Icicle Creek Etlginccrs 03360011062499 Claremont Development Company, Inc. June 24, 1999 Page 3 GENERAL MINING HISTORY The Springbrook Mine is one of several small underground mines in this area and it underlies portions of the Cugini property as shown on the Underground Mine Map, Figure 2. Presently, there are no active coal mining operations on or adjacent to the Cugini property. MINING METHODS The Springbrook Mine was an underground mine developed using "room-and-pillar" (also ~ferred to as "chutb-arul-pillar") mining methods. Initial development of the mine was from a "water slope" or entry tunnel driven along the strike of the mine to facilitate drainage. The entry tunnel •• rves as the main haulageway for coal out of the mine. The entry tunnel is usually paired with a second tunnel driven parallel to the main slope to serve as an "air shaft." The entry tunnel and air shaft were connected at certain inteNus with cross-cutting tunnels. Air would then he mechanico..lly forced (a fan) down the air shaft to provide air circulation within the mine. Air shafts in other areas were driven depending on the circuIatiOlI requirements fur the mine. Usuo..lly the main slope and air shafts were heavily shored with timber posblbeams or reinfurced concrete to prevent collapse. The main slope was used to remove coal from the mine using coal cars on tracks that were liftod up the main slope using a hoist At specified intervals along the main haulageway, ·chutes" were driven up the coal seam. "Cross- cuts" were then driven between the chutes. The chute, and cross-cuts were then widened until the coallelt in place (pillars) and rooms comprised about a I to I ratio. Most or all of the pillars were removed before abandonment of a level. This mining method is referred to as ''full pillar extraction." Full pillar _ion i, a normal underground mining process designed to maximize coal extraction and to promote short term collapse of Ibe mined-out areas. As designed, the removal of the pillars causes the mincd-out area to collapse within a few days to a few weeks following retreat since backfilling was not intended. Based on engineeting studies of the mines conducted at the time of mining, caving of the mined-out areas (rooms) waS desirable upon retreat of production areas. Room caving was desired to allow the overburden pressures in the mines to adjust If mined-out rooms remained open, then "bumps" became a mllior concern. Bumps occur when a large room remains open for a long period of time followed by a catastrophic collapse sending an air blast through the mine that could injure Ibe miners. SPRINGBROOK MINE The Springbrook Mine was active fium the early 1900. to about 1948. The primary coal seam that was mined in this area is co..Iled the Springbrook Seam. The Springbrook Seam is inclined downward to the south at S4 to 57 degrees at this location; a horizontal line on the coal seam would he oriented roughly east- west The Springbrook Seam was mined for a total thickness of about 5 feet. The percentage of coo..l mined from production room and pillar areas is Dot confidently known. Based on our review oflbe historic mine maps and review of production records, it appears that about 80 percent of the coal was mined from the production Bleas. The mined-out areas are sbown on Figure 2. Geologic cross-sections showing the general orientation oflbe mined-out zones are shown on Figure 3. The depth to the undcrgroUDd mine workings (3S to 450 feet helowthe existing ground surface) is shown on the Depth to Uuderground Mine Workings, Figw-e 4. A surface feature (an airshaft) for Ibe Springbrook Mine (located about 350 feet west ofth. Northwest Parcel) is shown on Figure 4. No other surra .. features such as mine entries, mine rock fill stockpiles or buildings associated with the mining in this area are indicated within the Cugini property on the historic mine map. Icicle Creek Engineen 033600 11062499 Claremont Development Company, Inc. lune 24,1999 Page 4 SURFACE CONDITIONS GENERAL The surface conditions on the Cugini property were evaluated based on detailed geologic reconnaissance on June 17, 1999 by Brian Beaman ofiCE and review of historical mine maps. mSTORIC MINE MAP REVIEW As previously described, no mining-related surf.ce foatu",s were indicated within dle Cugini I""perty based on our review ofthe historic mine maps. The property on the historic mine maps (1948) is shown to be bordered to the east by l08th Avenue SE and to the north by SE 172nd Place. The current location of l()8th Avenue SE where it crosses between the Northwest and Southeast Parcels and SR 515 did not exist in 1948. CURRENT SITE CONDmONS The Cugini property is currently undeveloped and is vegetated with second-growth conifer and deciduous trees and dense brush. The ground surface is level to gently sloping. A shallow drainage swal. (about 10 to IS feet deep) crosses the Northwest Parcel from caslto west. No Ground surfuce depressions (suggesting n mine opening or sinl;hole) were observed on the Cugini property. No surface evidence of mine rock fill was observed on the Cugini property. COAL MINE HAZARD DESCRIPTION GENERAL The principal physical hazards associaled with abandoned coal mines include I) mine openings, sinkholes and related gas emissions or concentrations (Severe Coal Mine Hazards), 2) regional ground subsidence (Moderate and Declassified COlli Mine Hazards), and 3) mine rock fill, Sinkholes form shallow depressions in the ground surface, or in extreme cases, a vertically-sided pit csused by collapse of poorly backfilled mine openings or progressive failure of the mine roof (stoping). Regional ground subsidence occurs as regional plastic deformstion of the ground surface as the mine collapses. Mine rock fill includes stockpile. of mining by-prod""'" consisting of broken rock and coal. Other considerations are the potential for ''wildest" or "gypo" mining (undocumented mining) and the accuracy of the historic mine maps when being used to evaluate the subsurface geometry of these mines and associated development constraints. SEVERE COAL MINE HAZARD AREAS Severe coal mine hazard areas are typically underlain by underground mine wonungs that are Ie •• than 200 feet below the ground surface. In these areas snrface features such a. mine openings, shafts and sinkholes may be present. SiJlkh"les fOIDl because of progressive csving of the mine roof or by the settling of backfill in improperly reclaimed mine openings. Sinkholes are usually preceded by a sag in the ground surface that typicslly deepens during a period ofseveral dsys or weeks before collapse. Sinkholes are genelllUycircular or elongated and are typically a few feet to (more t1II'Cly) tens of feet in diameter, The typicsl effect ofa sinkhole is the loss of ground support of surface structures. No evidence of m ioe openings, shafts or sinkholes w .... observed within the Cugini property at the time of our surface reconnaissance, Oases :JSSOciated with abandoned mines (predominantly methane gas and csrbon dioxide) are typically greatest at mine openings or in "air-traps" within the mine workings. Since methane and other volatile gases are lighter than air, dissipation into the atmosphere occurs rapidly at or slightly below the Icidc CTeek Engineers 03360011062499 Claremont Development Company, Inc. June 24, 1999 Page 5 ground surface. Mines such as the Springbrook Mine have not been undisturbed for morc than 50 years and are not likely to emit gas quantities that arc hazardous. MODERATE AND DECLASSIFIED COAL MINE HAZARD AREAS Moderate IlDd Declassified Coal Mine Hazard Areas are generally areas where the mine workings are more than 200 feet below the ground surface WId are potentially affected by "regional ground subsidence." Regional ground subsidence occurs when the ground surf'ace subsides over a large area. Surface deflection is caused by plastic deformation oftbe strsta overlying the mine as thiroof sags into th. mine. The affected area is expected to be much larger than the vertical projection of the underground m ioe workings. The effects of regional ground subsidence include ground subsidence (settlement), ground tilt and ground strain. Based on case histories in mining districts in other states and countries, regional ground subsidence usually occurs within • few days to years following abandonment of the mines. Regional ground subsidence is Il!!! a public health and safety issue; the potential hazard i. related directly to property damage. The following are the defmitions for Moderate and Declassified Coal Mine Hazards Areas as presented in DAG: • Moderate Coal Miae Hazard Are .. -Moderate Coal Mine Hazard Areas require special engineering or architectural measures to mitigate excessive ground displacement, IlDd ground tilt WId strain. • DeclassIlled eoal MiDe Hazard Areas -Declassified Coal Mine Hazard Areas arc those areas affected by regional ground subsidence, but no special engineering or architectural measures arc needed as mitigation. No manifestation of regional ground subsidence was observed during our reconnaiSSllDce within the Cugini property and adjocent areas. MINE ROCK FILL Mine rock fill consists of loose rock and soil mixed with inferior grade coal from underground workings and fin •• from coal washing operaliOll'. These materials were not compacted and are potentially compressible because of the loose texture and long-tenn air degradation of the coal. No mine rock fill was observed during our surface reconnaissance of the Cugini property. UNDOCUMENTED MlNING No undocumented mining is known to have occurred within the Cugini property. This is based on the detailed surfilce reconnaissance, review of extensive mine records and personal knowledge of this area dating.over 40 years. ANALYSIS OF COAL MINE HAZARDS METHODOLOGY The evaluation of development issues associated with abandoned underground coal mines is based on methods that have evolved over the past several years, primarily in KingCounty. During Ihe past three years, King County ODES bas developed specific policy and has drafted guidelines for technical evaluation of areas underlain by abandoned underground coal m ioes. These draft development guidelines develOped by King County are referred to as the "Administrative Guidelines to Implement Coal Mine Hazard Assessment WId Mitigation Plans," and are referred to in this report as the Draft Administrative Guidelines Iticle Creek Engineers Claremont Development Company, Inc. June 24, 1999 Page 6 (DAG). The method recommended in DAG was used in this study to evaluate these development issues and is consistent with culTent and local standards of engineering practice. The results of our analysis arc attached to this report. ANALYSIS Severe Mine Hazan! Areas The Severe Mine Hazard Areas are underlain by abandoned underground coal mines at a depth of less than 200 feet and are shown on the Mine Hazards Map, Figure 5. These are areas where a risk of sinkholes exist (greater than I percent risk). Moderate Bnd Deelasslfled Coal Mine Hazan! Areas Moderate and Deelassified Coal Mine Hazard Areas are underlain by abandoned underground coal mines at a depth of more than 200 feet. These are areas where regional ground subsidence mayo<:cur, but not sinkhole •. The primary difference between these classifications is that a Deelassi tied Coal Mine Hazard Area does not requite speeial engineering or architectural measure to mitigate for regional ground subsidence. Our evaluation assumes a scenario in which the mined-out zones shallower than 200 feet arc not collapsed and may collapse during the next 100 years. The original miocd height of the Springbrook Seam used in our calculations is 5 feet. Based on our analysis and empirical method. suggested by DAG, total potential ground subsidence is estimated to he up to 27 to 28 inches during the lifetime of the development (assumed to he 100 ~s) on the Cugini property. The predicted distribution of ground subsidence is shown on Figure 5. We also predicted maximum ground strain. Maximum extension and compression of the ground surface is predicled to be more than 0.003 incbes per inch. This excessive ground strain (strain greater than 0.003 inches per inch) occurs south of the Cugini property. The strain values were calculated using methods described in the Subsidence Engineers' Handbook (1975) and suggested by DAG. Predicled ground till values are a function ofth. subsidence prom •. Ground tilt is excessive (les. than 1 V:350H (vertical to horizontal) in the area south of the Springbrook Mine. A IV:3S0H tilt means that there is the potential for differential settlement of the ground surface that may be one foot of vertical senlement in 350 horizontal feet. Developable Areas Developable areas are all other .rees not affected by underground coal mines. 'Ibese areas may have other building constraints such as wetlands, steep slopes, etc., and require additional critical areas review, as appropriate. CONCLUSIONS A.."ID RECOM,.\1ENDATlONS GENERAL Based on OUT review of available information and analysis of coal mine hazards at the Cugini property. we have developed the following conclusions: • Portions of the Cugini property are underlain by the Springbrook Mine as shown on Figure 2. • The depth to the mine workings that underlie the Cugini property varie. from about 35 to 450 feet below the ground surface. • 11IB! portion of the Southeast Parcel nonh of the line on Figure S indicated as having "Less than! inch" cf vertical ground subsidence requires special engineering or IITChiteetural measures for mitigation of •• rtical ground di~plncclne"t. ground tilt and ground strain (Moderate Coal Mine Hazard Area). Icicle Creek. Engineers Claremont Development Company, Inc. June 24, 1999 Page 7 • That portion ofth. Southeast Par1:c,j south of the line on Figure 5 indicated as having "Less than I inch" of vertical ground subsidence does not require special engineering or architectural measures for mitigation of regional ground subsidence (Declassified Coal Mine Hazard Area). • That portion oflbe Northwest Parcel north ofth. area shown on Figure 5 as a "Severe Mine Hazard Area" is not affected by coal mine hazards (Developable Area). SEVERE COAL MINE HAZARD AREAS Based on our review of available information, a portion of the Springbrook Mine underlies tbe Cugini property within 200 feet of the ground surface. Currently, the generally accepted depth or thickoess of overburden for "safe" surface development over underground mines in this area is 200 feet. In our opinion, there iB a high risk of sinkhole development at the Cugini properly within the area shown as • Severe Coal MiDe Hazard Area "n Figure S. The Severe Coal Mille Hazard Area includes a 4S·foot-widc buffer along the updip (north) projection of the coal seam. We recommend against development of buildings, roads, parking lob; or trails in thiB area unless the slatus of mine collapse is evaluated by subsurface exploration and reclamation, as necessary. MODERATE COAL MINE HAZARD AREAS It is our opinion that the areas nortb of the "Less than I inch" contour line and south of the Severe Coal Mine Hazard Area as shown on Figure 5 are Moderate Coal Mine Hazard Areas. ConceptUal mitigaticn measures for structure., roads and utilities within dlis area include the fullowing; • Use of rigid fuundations (conventional reinforced concrete spread footings) supporting a flexible superstructure (wood-frame)_ • Small, square or nearly square-shaped building pad. should be favored over large, irregularly shaped building pads. • Crawl-space construction rather than slab-on-grade. However, slab-on-grade may be used in garage and driveway areas. • Buildings shou Id be constructed such that they could be easily releveled. • No brick or basemCJIt construction. • Edges offuundations should be backfilled with loose soil or other compressible material to allow for potential ground compression. • Underground utilities should be de.igned with flexible andlor teleocopic couplings or fittings. • Utilities tbat depend on gravity for Dow (sewers and S1nnn drain) should be designed to compensate for the potential for ground subsidence. DECLASSIFIED COAL MINE HAZARD AREAS It is our opinion that the area south of the "Less than I inchM contour shown on Figure 5 within the Southeast Parcel is a Declassified Coal Mine Hazard Area. No special engineering or areililccturai measures are needed in this area to mitigate coal mine hazards. DEVELOPABLE AREAS It is our opinion d18t the area north of the Severe Coal Mine Hazand Are. within the Northwest Parcel is a "Developable Area. M Based on available information, this area is not underlain by, or affected by regional ground SUbsidence. The .. areas may have other building constraints sueb as wetlands, steep slopes, etc., and require additional critical areas review, as appropriate. Icicle Creek Engineers 03360011062499 Claremont Development Company. Inc. June 24, 1999 Page 8 MlNE ROCK FILL No mine rock fill occurs within the Cugini property based on our sulface reconnaissance. ICE should be contaeted for review and evaluation if mine rock fill is encountered during site grading GROUND PROOFING (~E. ~ U.£ ,,J ?Pt>tJ) Coal mine hazards exist because of the potential for collapse of the underground mines. No coal mine hazards exist if the mines have collapsed or been properly filled/reclaimed. It i. our opiniollihat severe 0".1 mine hazard areas may be developed without re,triMbn providcJ that the underground mines are demnnstl'Bled to haw collapsed or are properly reclaimed. This may be IIC<lOmplished by a dri lling program (ground proofing). The purpose of ground proofmg is to obtain specific subsurf8ce datil thaI CAn be used to evaluate the status of collapse, assess the risk of sinkholes and to validate historic coal mine map survey accuracy. Ground proofing requires drilling test boles Ihrough the underground workings lo asse.s the overburden character and the condition of!be underground workings. If the cboract:. ofth. ",'«burden can be sh.,wn to be more """'1"-'1.,..,1 than assu.ned, and/or the mille workings arc collapsed or parti.Il~' collapsed, then our assessment of coal mint hazards at the Cugini property will be revised. The ground proofing program, ifundcrfaken, sbould be designed to account for the possibility of drilling through existing pillars ratherthan the mined-out areas. The purpose ofblving sevcnal drill holes is to increase Ihe probability of encountering 8n underground mine, if present, to an acceptable confidence level. USE OF THIS REPORT W. have prepared this report for Claremont Development Company, Inc. for use in evaluating coal mine hazards at the property subject to this consultalion. Our report, conclusions and interpretations sbould not be construed as a warranty of subsurface conditions at the .ite. Within the limilltions of scope, sctiedule and budge!, our services have been executed in accordance with generally a<:<:epted practices in this area at the time the report was prepared. No warranties or other conditions, express or implied, should be understood . •••••••••••••••• (1 ••• leielc Creek Bngineers 0336OOt1062499 Claremont Development Company, Inc. June 24, 1999 Page 9 We trust that this repon provides the information you need at this time. If you have any questions or need additional information, please contact us. I EXPIRES fI) -10 • 0<> Document ID: 03~600I.REP Two copies submitted Attachments lcicle Creek Engineers Youn very truly, Icicle Creek Engineen, Inc. Brian R. Beaman, P.Il., P.O. Principal Engineer/Geologist ~.~~~ Priucipal Geologist 03360011062499 o 2,000 Scale in Feet ~ ~ Icicle Creek Engineers N 4,000 I ! Vicinity Ma -Figure 1 '~ ; EXPlANATION Cross-Section Location ( ... Figure S) : Icicle Creek En ineers J B 7~ .... '~.'~'~,., :: 8' i ~ / ~0 o 150 300 Approximate Scale In Feet A (North) 450- Sever" Mine Hazard,.,.. Declassified and Moderate Mine Hazard Area A' (South) -450 \.... GlacialTtl1 , ...... _ .............. _a. ....................... ___ ............................ __ ...... '" _ ..... _ ........... _--............... _____ ... _ .. '" p , _ 300- ~ £; Ii i .!! w 150· o· 8 (North) 450- Severe Mine Hazard Area ' Bedrock DecI ••• ifllOd and Moderate Mine Hazard Area ·300 m f 5- '" :;- ;r : 150 !l -0 8' (South) -450 \.. GlacialTtIl ..... --........................... ------.......... -_ ...... -........ --..... -...... --_ ................... --................... -......... -"'-"'-.. -300-! .!: :§ 1 w 150~ 0' NDIN:1) loattctlrlCInJI ......... A-A'f8.f1lhownnf1Aue2. 2)~ ...... «*lI'ICIm"'*lIDfIdIIIDr.~an .. _..ec:tiIIII .. beMd'onflYiewof.VIiI .... Wanlillan. AduIl~onIlIkIIII m~VMY. o o 150 300 Horizontal Scale = Vertical Scale Springbrook Mine Icicle Creek Engineers Geologic Cross-Section A-A'/B-B' -Figure 3 EXPLANATION EI .; vertical Projection ofUndergrnund Mine Vlbrt<ings and Depth in Feet J o 150 300 Approximate Scale in Feet Springbrook Mine i Icicle Creek En ineers De th to Underground Mine Workin s -Figure i EXPlANATION -Severe Coal Mine Hazard Area Antal where the underground mine i. lellS than 200 feet below the ground surface (Includes a ~5 foot butler on the north side of hazard a",.~ •···•• .. ·••·· •.• ,O inCh"" Moderate/Declassified Coal Mine Hazard Area ES1imated verticelgraund subsidence of tile 9raund surtilce ceused by regional ground subsidence o 1~ ~O Approximate Scale in Feet J : Icicle Creek En ineers Springbrook Mine Mine Hazards Map -Figure 5 Report Geological Engineering Services Coal Mine Hazard Assessment Cugini Property -Northwest Parcel Renton (King County), Washington March 22, 2004 Project No •. 0336-004 Prepared For: Alex Cugini Prepared By: Icicle Creek Engineers, Inc. ICICLE CREEK ENGINEERS Gl!olechnlClII. Geologic and Environmental 5ervkes March 22, 2004 Alex Cugini clo Claremont Development Company, Inc, 515 -116do AvenueNE, Suite 108 Bellevue, Washington 98004 INTRODUCTION Report Geological Engineering Services Coal Mine Hazard Assessment CUgini Property -Northwest Partel Renton (King County), Washington File No. 0336-004 This report summarizes Icicle Creek Engineers' OCE's) geological engineering services for a coal mine hazard assessment of a portion of the Cugini property referred to as the "Northwest Parcel" located northwest of the intersection of lOS'" Avenue SE and· State Route 515 near Renton in King Couoty, Washington. The Cugini properlY is shown relative to nearby physical features on the Vicinity Map, Figure 1. ICE previously provided a preliminary coal mine hazard assessment or the Cugini Property that is divided into two parcels referred to as the ''Northwest Parcel" IIIlCI the "Southeast Parcel" as shown on Figure I and the Cugini Property Site Plan, Figure 2. The results of the preliminary coal mine hazard assessment of the two parcels are presented in our report dated June 24,1999. Subsequent \0 the lune 1999 study, ICE conducted a detailed coal mine hazard assessment of the Southeast Parcel thai included ground plOOfing (subsurface exploration) to evaluate the collapse status of the abandoned underground coal mines. Theresults of that study for the Southeast Parcel are presented in our report dated November 13,2001. BACKGROUND INFORMATION ICE's Iune 1999 preliminllI)' coal mine hazard assessmentldentified an abandoned underground coal mine, referred to as the "Springbrook Mine," underlying the south portion of the Northwest Parcel. Because no subsurface exploration was conducted to evaluate the collapse status of the abandoned underground coal mines, ICE assumed that the mines were substantially nol collapsed which resulted in a portion of the Northwest Parcel being considered a "Severe" and "Moderate Coal Mine Hazard Area." Severe Coal Mine Hazard Area designation results in relatively restrictiveconditioDS for site development in th~ areas. Severe and Moderate Coal Mine Hazard Areas are described later In this report. Under current King County regulations (Administrative Guidelines for Coal Mine Hazard Areas • Ordinance 13319), development of buildings, roads, parking lots or trails are not allowed within Severe Coal Mine Hazard Areas and mitigation is required in ModerBle Coal Mine Hazard Areas. However, a detailed coal mine hazard assessment may be conducted including "ground proofing" (subsurface exploration) to physically evaluate the character orthe overburden soil and bedrock, and the status of mine collapse. If the overburden is shown to be competent and the mine void is substantially collapsed, then development, ineIuding paved access and parking and possibly building, may be allowed. Alex Cugini c/o Claremont Development Company, Inc. March 22, 2004 Page 2 SCOPE OF SERVICES The purpose of our services was to conduct a detailed coal mine hazard assessment (ground proofing) of the Northwest Parcel. Specifically, our services included: Evaluate subsurface soil, bedrock, voids and ground water conditions and historic mine map accuracy by drilling seven test borings (Borings B-5 through B-I I) to depths ranging from 20 to 160 feet in the Severe Coal Mine Hazard Are. identified in our June 1999 study. These test borings were supplemented by the four test borings (Borings B-J through B-4) completed for ICE's November 2001 study. Based on tile findings ofiCE's June 1999 preliminary coal mine hazard assessment, ICE's November 2001 ground proofing study of the SoUllleast Parcel and the current ground proofing program on the Northwest Parcel, classify the coal mine hazards as either: I) Severe Coal Mine Hazard Areas, 2) Moderate Coal Mine Hazard Areas, or 3) Declassified Coal Mine Areas. Evaluate the potential for regional ground subsidence in Severe and Moderate Coal Mine Hazard Areas (vertical ground subsidence, groWld tilt and ground strain), if appropriate. Develop mitigation for development within Severe and Moderate Coal Mine Hazard Areas, if appropriate .. GEOLOGIC SETTING The Cugini Property is underlain by bedrock oftbe Renton fonnation. Renton formation bedrock consists of interbedded sandstone, siltstone, shale, claystone, carbonaceous shale and coal beds. Structurally, the bedrock has been uplifted, folded and faulted over time. This structural deformation of the bedrock has created a northwest trending syncline. "Syncline" is a geologic term referring to a fold in the bedrock layering that is concave up. The "limbs" or layering of the syncline dip at angles ranging from 30 to 70 degrees from borizontal. The bedrock is typically covered with forest duff"and topsoil, weathered soil and glacial drift (glacial till and outwash) varying in total thickness from a few feet to several tens of feet. Weathered soil typically consists of loose silty sand with gravel and abundant roots. Glacial till typically consistS of dense to very dense silty sand with gravel. Outwash typically consists of dense gravel with variable amounts of sand and silty sand with a trace of gravel. EXISTING INFORMATION The following documents were reviewed regarding the historic coal mining in the Cugini property area: Morrison Knudsen, January 1985, "Engineering Investigation for the Renton, Washington Area," prepared for the U.S. Department of Agriculture OffICe of Surface Mining. Warren, W.C., Norbisrath, H., Griveui, R.M., and Brown, S.P., 1945, "Preliminary Geologic Map and Brief Description of the Coal Fields of King County, Washington," United States Geological Survey, I plate. Washington State Department of Natural Resources, 1948, historic map of the Springbrook Mine including surface features and underground mine workings. SPRINGBROOK MINE DESCRIPTION The Springbrook Mine is one of several small underground mines in this area. Based on our review of historic mine maps, the east end of the Springbrook Mine underlies the south portion of the NorthWest Parcel as shown on the Springbrook Mine Underground Mine Map, Figure 3. Presently, there are no active coal mining operations on or adjacent to the Northwest Parcel. Icicle Crl:tk Engjneers 03360041032204 Alex Cugini clo Claremont Development Company, Inc. March 22, 2004 Page 3 The Springbrook Mine was active fromme.arly 1900s to about 1948 when it Was abandoned. The main entry and airshaft for the Springbrook Mine were located approximately 200 feet southwest of the west end of the Nonhwest Parcel. Based on information ICE has developed for other coal mine hazard studies in this area, the main entry and airshaft to the Springbrook Mfne are collapsed andlor backfilled (not accessible). The Springbrook Mine coal seam is inclined downward to the south at S4 to 57 degrees in this area; a horizontal line on the coal seam would be oriented roughly east-west. The coal seam that was mined is reported to be about 5 feet thick. Based on our review ofthe historic mine maps and review of production records, it appears that about SO to 100 percent of the coal was mined from the production areas. Geologic cross-sections showing the general orientation of the mined-out coal seam are shown on the Springbrook Mine Gecfogic Cross-Sections A-A' and B'B', Figures 4 and 5, respectively. The historic mine maps also s1ww that some of the coal seam was not mined under the Northwest Parcel in areas that contained coal. Notes on the historic mine maps indicate that the coal was not mined because it was highly fractured and the fragments were too small for commercial use. However, for the purpose of our June 1999 study, we assumed this area to be mined out as a conservative approach as no subsurface explorations were conducted at that time. Based on engineering studies of the mines conducted at the time of mining, caving of the mined-out areas (rooms) waS desirable upon retreat of production areas. Room caving was desired to allow the overburden pressures in the mines to adjust. Ifmined-out rooms remained open, then "bumps" became a major concem. Bumps occur when a large room (a "room" is a mined-out area) remains open for a long peri cd of time followed by a catastrophic collapse sending an air blast through the mine that could injure the miners working in other areas of the mine. The term bump is used because during a catastrophic roof fai lure, a vibration, Or "bump" would be felt at the ground surface. SURFACE CONDITIONS GENERAL The surface conditions on the Northwest Parcel were evaluated based on review of historical mine maps and on detailed geologic reconnaissance conducted on June 17, 1999 by Brian Beaman oflCE and on February 16 through 24, 2004 by Brian Beaman and Scort Dobner oflCE. HISTORIC MINE MAP REVIEW No mining-related surface features were indicated within the Northwest Parcel based on our review of the historic mine maps. The property on the historic mine maps (dated 1948) is shown to be bordered to the east by 10Sth Avenue SE (Benson Road) and to the north by the present location ofSE "172'01 Street. The propenies to the west and south were undeveloped in 1948 according to the historic mine maps. Within the past 10 years, 108'" Avenue SE was" modifted resulting in tbe Cugini Property being "split" into the two parcels. CURRENT SITE CONDITIONS The Northwest Parcel is currently undeveloped and is vegetated with second-growth conifer and deciduous trees, and moderately dense brush. The ground surface is level to gently sloping ranging from about Elevation 3 54 feet in the west comer of the site to about Elevation 400 feet in the east comer of the site. A shallow drainage swale (about 10 to IS feet deep) crosses the Northwest Parcel from east to west bl ground surface depressions (suggesting a mine opening or sinkhole) were observed on the Nonhwest Parcel. However, a shallow low area along the southwest property line with rock rubble On the surface suggests an area that was filled or otherwise modified. No surface evidence of mine rock fill (mine rock fill is a waste product consisting of coal fines and rock fragments) was observed on the Northwest Parcel. No surface water JcicJe Creek Engineers 0336004/032204 Alex Cugini c/o Claremont Development Company, Inc. March 22, 2004 Page 4 was observed on the Northwest Parcel at the time of our reconnaissance other than water drainage (less than I gallon per minute) in the floor of the drainage swale that crosses the site. It is likely that the water in the swale varies in volume considerably depellding on rainfall. GROUNDPROOFmG PROGRAM SUMMARY MElliODOWGY The ground proofing program was conducted by drilling seven, 6-inch-diameter borings (Borings B-5 through B-II) to depths ranging from 20 to 160 feet using mud-rotary drilling methods with track-mounted drilling equipment provided and operated by Gregory Drilling, Inc. Thetest borings were supplemented by explorations (Borings B-1 through B-4) conducted during our November 2001 study that were drilled to depths ranging from 91 to 120 feet also using drilling equipment provided and operated by Gregory Drilling. The test borings for the current study were completed between Febnl9ry 16 and 24, 2004 and the lest borings for the November 200 1 study were completed belween October 29 and 31, 2001. The approximate locations of the test boring explorations are shown on Figures :1 and 3. Exploration locations were established by measuring from physical features ofth. site. The number of borings was determined such !hat the probability of drilling through an anomalous tunnel, pillar or caved area was decreased. The subsurface explorations were continuously logged by an engineering geologist from our firm. Representative samples were generally obtained at 5-foot depth intervals either by using a I.5-inch diameter split-spoon standard penetration test (SPT) sampler or "grab" samples, as noted on the logs. When the SPT sampling method was used, the sampler was driven 18 inches, if possible, with a 140-pound weight faIling a vertical distance of approximately 30 inches. The number of blows required to drive the sampler the last 12 inches, or other indicaled distance, is recorded on the boring logs. It sbould be noted that the blow counts may not be. representative (will be overstated) of the formation density when gravel or cobbles are encountered. "Grab" samples were typically obtained at 5-foot depth intetvals by screening soil cuttings from the discharge pipe. In some zones, no soil samples were obtained because of loss of drill circulation. The soil classification system and explanation for the test boring logs are shown in Figure 7. Logs oflbe test borings for the November 2001 study Bnd the current study are included as Figures 8 through 18. Drilling rate, which is an indicator of subsurface conditions associated with lithologic (rock type) changes, caved bedrock and voids, was monitored by Ica We also monitored drilling fluids circulation (drilling fluids, referred to as "mud," is used to convey drill cuttings to the surface). A circulation loss or partial loss would indicate underground fractures, voids and/or caved bedrock. In addition to evaluating subsurface conditions, the ground proofmg program was also used to evaluate historic mine map accuracy. Prior to drilling each test boring, the depth of the coal seam or mine was evaluated based on the historic mine maps. Encountering the coal seam or mine at thaI predetermined depth would allow for an evaluation of the mine map accuracy. Two geologic cross-sections showing the interpreted subsurfuce conditions including geology and the Springbrook Mine geometry across the Northwest Parcel, are sbown on Figures 4 and S. GROUND PROOFING RESULTS Boring B-1 (Southeast Parcel) Boring B-1 encountered overburden soils consistingof6 feet of weathered soil, underlain by glacial till to a depth of 24 feet. Glacial till is an unsoned mixture of silt, sand gravel and cobbles often called "hardpan." Glacial till is In a dense to very dense condition as a result ofheing overridden by approximately 3,000 feet of glacial ice. Bedrock (Renton fonnation) was encountered at24 feet. The bedrock consisted ofcoal from 24 10 54 fee~ layers .of carbonaceous shale and coal from 54 to 60 feet; coal from 60 to 69 feet; and carbonaceous shale Icicle Creek Engineers 0336000032204 Alex Cugini c/o Claremont Development Company, Illc. March 22, 2004 Page S with layers of coal and siltstone from 69 to 76 feet. Carbonaceous shale was observed in the sample at 80 feet. Drilling fluid circulation was lost at a depth of76 feet (indicating bedrock fractures or caved bedrock) and was partially restored to a depth of 82 feet at which time drilling fluid circulation never returned (no bedrock samples from 81 to 110 feet -the bottom of the test boring). Based on the drilling rate, partially caved rock and one 4·inch void (fracture at 78 to 78.3 feet) was encountered from 76 to 90 feet. Caved bedrock was enc(>untered from a depth of 90 feet to the completion depth of the test boring at 110 feet (Springbrook Mine zone -completely caved and collapsed). The Springbrook Mine was encountered within 5 feet of the predicted depth. Boring B-2 (Southeast Parcel) Boring B·2 encountered overburden soils consisting of6 feet of weathered soil, underlain by glacial till to a depth of 23 feet. Bedrock (Renton fonnation) was encountered at 23 feet. The bedrock consisted ofcoa! from 23 to 27 feet; siltstone with layers of coal from 27 to S4 feet; coal with layers of carbonaceous shale from S4 to 58 feet; and coal from 58 to 92 feet . Soft drilling and drilling fluid circulation was lost at a deptb of92 feet (indicating caved bedrock) to the completion depth of at 120 feet (Springbrook Mine zone -completely caved and collapsed). No voids were encountered in Boring B·2. The Springbrook Mine was encountered within 5 feet of !lie predIcted depth. Boring B-3 (Southeast Parcel) Boring B·3 encountered overburden soils consisting of 5 feet of weathered soil. underlain by glacial till to a depth of 28 feet. Bedrock (Renton fonnation) was encountered at :;!8 feet. The bedrock consisted of carbonaceous shale with I ayers of coal from 28 to 34 feet; siltstone with layers of coal from 34 to 48 feet; coal with layers of carbonaceous shale from 48 to 72 feet; and coal (tbe Springbrook Coal Seam -intact -not mined) from 72 feet to tbe completion depth of Boring B-3 at 91 feet. No voids were encountered in Boring B-3. No soft drilling or drilling fluid circulation was lost during !be drilling ofBoring B·3. The Springbrook Coal Seam was intact, as predicted. and within S feet of tbe predicted depth. Boring B-4 (Southeast Parcel) Boring B-4 encountered overburden soils consisting ofS feet of weathered soil. underlain by glacial till to adeptb of22 feet. Bedrock (Renton fonnation) was encountered at 22 feet. The bedrock consisted of coal with layers of siltstone from 22 to 49 feet; coal from 49 to 73 feet; carbonaceous shale with layers of coal from 73 to 79 feet; coal from 79 to 89 feet; siltstonewitb layers of co a! from 89to 91 feet; coal (the Springbrook Coal Seam- intact -not mined) from 91 to 97 feet; and claystone (very hard -caused drilling refusal) from 97 feet to the completion depth at 100.5 reeL No voids were encountered in Boring B-4. No soft drliling or drilling fluid circulation was lost during the drilling of Boring B-4. The Springbrook Coal Seam was intact, as predicted. and within 5 reet of the predicted depth. Iciclf Creck Engineers 0336OOWJ2204 Alex Cugini clo Claremont Development Company, Inc. March 22,2004 Page 6 Boring B-S (Northwest Parcel) Boring 8-5 encountered overburden soils consisting of 4 feet afforest duff, topsoil and weathered soil, underlain by glacial till to a depth of 32.5 feet. The glacial till was underlain by advance outwash to a depth of39 feet. Bedrock (Renton fonnation) was encountered at 39 feel The bedrock consisted of siltstone to a depth of91.5 feet (with a thin layer of carbonaceous shale at47.5 to 48 feet): carbonaceous shale and siltstone with thin layers of coal from 91.S to 110; and siltstone from 110 feet to the completion depth at 120 feet. No voids were encountered in Boring B-5. No soft drilling or drilling fluid circulation was lost during the drilling of Boring B-5. The Springbrook Coal Seam was not encountered in Boring B-5 because of the location of the test boring was slightly "updip" of where tbe Springbrook Coal·Seam was "truncated" (eroded) as shown on Figure S. Boring B-6 (Northwest Parcel) Boring B-6 encountered overburden soils consisting of 6.5 feet of forest duff, topsoil and weathered soil, underlain by glacial till to a depth uf28.5 feet. The glacial tiU was underlain by adv8IICe outwash to a depth of 43 feel Bedrock (Renton fonnation) was encountered at 43 feet. The bedrock consisted of siltstone and carbonaceous shale with thin layers of coal from 43 to 55 feet; coal from SS to 61.5 feet; carbonaceous shale and siltstone with thin layers of coal, and coal from 61.5 to 90.S feet; siltstone from 90.S to 94feet; coal (the Springbrook Coal Seam -intact -not mined) from 94 to 109 reet; carbonaceous shale with thin layers of coal from 109 to 114 feet; and siltstone to the completion depth at 160 feet (with a layer of siltstone with thin layers of coal from 133 to 136.5 feet. No voids were encountered in Boring B-6. No soft drilling or drilling fluid circulation was lost during the drilling of Boring B-6. TIle Springbrook Co:d Seam was intact, as predicted, and within 5 feet of the predicted depth. . ?¥:-' Boring B-7 (Northwest Par«l) Boring B-7 was drilled in the previously mentioned shallow low area along the southwest property line. This location is directly above the north end of a "mine tunnel" of the Springbrook Mine. During drilling, we encountered loose soils and fragments of sandstone rubble in soil that is possibly fill or "caved soil." We were not able to maintain drilling fluid circulation because of the presence ofloose soil therefore the test boring was completed at a depth of 20 reel It is possible that this is a filled "sinkhole" associated with the Springbrook Mine. Boring B-8 (Northwest Parcel) Boring B-8 encountered overburden soils consisting of2 feet of forest duff, topsoil and weathered soil, underlain by glacial till to a depth of34 feet. Bedrock (Renton ronnation) was encountered at 34 feet. The bedrock consisted of sandstone from 34 to 42.5 feet; carbonaceous shale, coal, siltstone and siltstone with thin layers of coal from 42.S to 70.5 feet; coal, carbonaceous shale, siltstone and siltstone with thin layers of coal from 70.5 to 82 reet; coal (the Springbrook Coal Seam -intact -not mined) from 82 to 96 feet; and carbonaceous shale, siltstone and siltstone with thin layers of coal to the completion depth at J 05 feel No voids were encountered in Boring B- 8. No soft drilling or drilling fluid circulation was lost during the drilling of Boring B-S. TIle Springbrook Coal Seam was Intact, 8S predicted, and within 5 reet of the predicted depth. BorIng B-9 (Northwest Parcel) JcJcle Creek En&inec r$ 0336000032204 Alex Cugini cia Claremont Development Company, Inc. March 22, 2004 Page 7 Boring B·9 encountered overburden soils consisting of3.5 feet afforest duff, topsoil and weathered soil, underlain by glacial till to a depth of 35.5 feet. Bedrock (Renton fonnation) was encountered at 35.5 feet The bedrock consisted of siltstone, carbonaceous shale and sandstone from 35.S to 49 feet; coal, carbonaceous shale and siltstone from 49 to 96 feet; coal (the Springbrook Coal Seam-intact-not mined) from 96 to 113 feet; and carbonaceous shale to the completion deptJi at 116 feet. No voids were encountered in Boring B·9. No soft drilling or drilling fluid circulation was lost during the drilling of Boring B·9. The Sprlngbrook Coal Seam was intact, as predicted, and within 5 reet of the predicted depth. Boring 8-10 (Northwest Parcel) Boring B· I 0 encountered overburden soils consisting on.s feet offorestdufi; topsoil and weathered soil, underlain by glacial till to a depth of 34 feet. Bedrock (Renton formation) was encountered at 3 4 feet. The bedrock consisted of siltstone from 34 to S9 feet; "fragments" of siltstone, carbonaceous shale, and coal (the caved/collapsed Springbrook Mine) from 59 to 65.5 feet; and siltstone to the completion depth at 95 feet. The caved/COllapsed zone of the Springbrook Mine was characterized by rough drilling and a rapid (indicating 50ft material) drilling rate. No drilling fluid circulation was lost, including within the caved/collapsed zone of the Springbrook Mine, during the drilling of Boring B·l0. No voids were encountered in BoringB-IO. The Springbrook Mille was encountered, as predicted, and within 5 feet of the predicted depth. Boring 8-11 (Northwest Parcel) Boring B·11 encountered overburden soils consisting of3 feet offorest duff, topsoil and weathered soil, underlain by glacial till to a depth of32 feet. The giacial till was underlain by advance outwash to a depth of36 feet. Bedrock (Renton formation) was encountered at 36 feet. The bedrock consisted of siltstone from 36 to 62.S feet; carbonaceous shale mm 62.S to 72 feet; coal (the Springbrook Coal Seam -intact -not mined) from 72 to 90 feet; and coal. with thin layers of carbonaceous shale and siltstone to the completion depth at 99 feet. No voids were encountered in BoringB·ll. No soft drilling or drilling fluid circulation was lost during the drilling of Boring B.ll. The Springbrook Coal Seam was intact, as predicted, and within 5 feet of the predicted depth. COAL MINE HAZARDS DESCRIPTION Ina coal mine hazard assessment for an area proposed fur development, certain factors must be evaluated to assess the potential for public health and safety issues, and potential property damage conoorns. Fortunately, considerable Information is available in the fonn of historic mine maps, historic aerial photographs, engineers reports and production reporta. Considerable effort has been undertaken by the local geotechnical and geologic professional community during the past IS years to obtain site-specific information regarding the region's abandoned coal mines. As a result of this effort, K ing County adopted Ordinance 13319 (Administrative Guidelines-AG) to provide guidance in conducting coal mine hazard assessments. At this time, the AG is the most current, comprehensive and generally accepted document for assessing coal mine hazards in western Washington. However, additional infonnation is continuing to be developed by direct observations of the condition of the abandoned coal mines, and i. incorporated into ICE's detailed assessment of the Springbrook Mine at the Northwest Parcel. The principal physical hazard classifications described in the AG are I) Severe Coal Mine Hazard Areas and 2) Moderate Coal Mine Hazard Areas. A third classification, not related to hazards, is referred to [citle Creek Engineers 0336004/032204 Alex Cugini clo Claremont Development Company, Inc. March 22, 2004 Page 8 as Declassified Coal Mine Areas. The following are definitions of these classifications as presented in the AG: S~'ere Coal Mine Hazard Arens -Severe Coal Mine Hazard Areas are '"those areas that pose a significant risk of catastrophic grollnd swface col/apse. Severe coal mine ha;ard areas may typically include, hut are not limited 10, areas charocterized by IInmiligated openings such as entries, parta/s. adils. mine shafts. air shafts, limber shajis. sinkholes. improperly filled sillkholes. and oth,rarea. of post or sigllificant probability for catastrophic ground surface collapse. Sev.", coal mine hazard area. typically illclude. but are not limited to, overland surfaces underlain or directly affected by abandoned coal mine workingsfrom a depth of zero 10 one hundredfifly foet." Moderate Coal Mine Hazard Area. -Moderate Coal Mine Hazard Areas are "those areas Ihat pose significanl risks of property damage which can be mitigated by special engineering or architectural recommendations. Moderate coal mine hazard areas may typically include. buJ are not limited to, areas ullderlain or directly qffected by abandoned eoalmine workings from a depth of zero to three hun4red feet Or with overburden-cover-to...seam thickness ratios of less Ihon lell 10 aile dependent on the inclination of the seam. .. • Declassified Coal Mile Areas -Declassified Coal Mine Areas are "those Dreas for which a risk of catastrophic col/apse /Illot significant t1I1d which the hazard assessment report has determined require no special eng/neering Qr architectural recommendatiOns to prevent significant risks of property damage . . Declassified coal millt areas may typically Include. bllt are not limlled 10. areas underlain or directly affected by coal mines III depths greater than three hundredfoet as measured./rom the surface but may often include areas underlain or direclly affected by coal mines at depths less than three hundred foet .• MINE ROCK FILL Mine rock fill consists of loose rm:k and soil mixed with inferior grade coal from underground workings and fmes from coal washing operations. These materials were not compacted and are potentially cOmpressible because of the loose texture and long-term air degradation of the coal. No mine rock fill was observed on the Northwest Parcel. PROSPECTS AND UNDOCUMENTED MINlNG Based on our review of the historic mine maps and site reconnaissance, we do not expect prospects or undocumented mining within the Nonhwest Parcel. CONCLUSIONS GENERAL Our conclusions presented in the following sections are based on our review of available information, site observations, ground proofing and analysis of coal milJe hazards at the Nonhwest Parcel, supplemented by information obtained for a previous study of the Southeast Parcel. Our conclusions, based on our detailed assessment of co a] mine hazards at the Nonhwest Parcel, are described in the following sections of this repon, with the results of reclassification of coal mine hazards shown on the Coal Mine Hazards Map, Figure 6. HISTORIC MINE MAP ACCURACY In our opinion. based on the results oftbe ground proofing program, the historic mine maps for the Springbrook Mine are accurate. This includes the area of the Springbrook Coal Seam that is shown on the maps as being left in place because the coal was "fractured." SEVERE COAL MINE HAZARD AREAS As described above, Severe Coal Mine Hazard Areas are underlain by abandoned underground coal Icicle Creek Engineers 0336004/{J32204 Alex Cugini clo Claremont Development Company, Inc. March 22,2004 Page 9 mines at a depth of less than 150 feet. However, this delineation can be modified as a result of~ground proofing" as was completed for this study. Our ground proofing program indicated that the shallow workings of the Springbrook Mine beneath the Northwest Parcel are substantially collapsed and caved. Howe •• r, Boring B-7 was completed in a "suspicious· low area and encowltered soft drilling and loss of drilling fluids to the degree that dIe boring had to be comploted at a shallow depth of20 feet. It is possible that the loo~e soil may be indicative of rast caving into an underground lunnel of the Springbrook Mine. Based on our knowledge of the site conditions, it is our opinion that dIe "caving" has stabilized (no fulure caving). However, Ihe presence oflhis local area of caved soil or fill does creale a condition where a local area of Severe Coal Mine Hazards should remain as shown on Figure 6. MODERATE COAL MINE HAZARD AREAS Moderate Coal Mine Hazard-1.reas are underlain by abandoned underground L'Oai mines where regional ground subsidence may occur, but nol sinkholes. No explorations were conducted in the deeper zones of the Springbrook Mine. However, with the shallow workings being caved and collapsed, it is our judgement that the deeper mine workings (more than 100 feet below the ground surface) are also caved and collapsed, especially considering the steep inclination afthe mined-oul coal seam (54 to 57 degrees) as shallow cilving tends to fill the deeper sections of the mine. As previously described, our ground proofmg program suggesls tbat tbe Springbrook Mine is caved and collapsed. In our opinion, no Moderate Coal Mine Hazards presently exist within the Northwest Parcel as the regional ground subsidence has likely already occurred. DECLASSIFIED COAL MINE AREAS The surficial overburden soils encountered in our lesl borings on the Northwest Parcel generally consist of about 34 to 43 feel of glacial till and advance olllWash with the exception of the area of Boring B-7 that was not able to advance deeper than 20 feet because of the loss of drilling fluid circulation. Glacial till and advance outwash are relatively high strength soil types that are resistant to caving and sinkhole formation. The areas identified In ICE's June 1999 report as Severe and Moderate Coal Mil)e Hazards in the Northwest Parcel area should be reclassified as a Declassified Coal Mine Area as ~ resuh of this detailed coal mine hazard assessment. witb the exception of the remaining Severe Coal Mirie'HazIird Area in the vicinity of Boring B·7. The Declassified Coal Mine Area is shown on Figure 6. RECOMMENDATro~S In our opinion, the Northwest Parcel can be de\'~loped "'1111 structures and paved roadslaccess without special mitigation or restrictions associated with coal inin~ hazards with the exception of the remaining localized Severe Coal Mine Hazard Area shown on Figure 6. No development should occur in the Severe Coal Mine Hazard Area widlout further evaluation as described below. II is our opinion that the Severe Coal MIne Hazard Area could be developed with paved roads/acceSs and parking provided Ihat the area is funher evaluated by loose soil removal with an excavator to better assess t~.e condition of the soils that underlie this area. As previously mentioned, based on our ground proofing program, it appears that the Springbrook Mine is substantiallY collapsed and the possible CBVed sinkhole area is stable (no further caving expected). In addition, il is also possible that this area may have been a preexisting low area that was tilled with loose soil and is therefore not a sinkhole. Excavation of this area would remove lcic:1e Creek: Engineers 033~0041032204 Alex Cugini c/o Claremont Development Company, Inc. March 22, 2004 Page 10 the loose soil and expose the underlying native, undisturbed soils, if present. The excavation could then be filled with structural fill that would be suitable for support of pavement. USE OF THIS REPORT We have prepared this report for use by Alex Cugini and Claremont Development Company, Inc. and their associates and engineers for tbeir use in planning development oflhe Nonhwest Parcel. The data and report should be provided to pennitting agencies for their information, but our report conclusions and interpretations should not be construed as a warranty of the subsurface conditions. Within the limitations of scope, schedule and budget, our services have been executed in accordance with generally accepted practices in this area at the time the report was prepared. No warranty or other conditions, express or implied, sbould be understood . •••••••••••••••••••• We ~ tllis infonnation meets your present needs. If you bave any questions or if we can be of further assistance to you, please call. I EXPIRES to -I () -alf DoOument JD: 0336004.REP AtIBcbmelllS Four copies submitted le:icJe Creek Engineers Yours very truly, iC10C Scott M. Dobner Staff Geologist Brian R. Beaman, P .E., L.G. Principal Engineer/Geologist 0336OO41lll2204 o 2,000 Scale in Feet ! 8 i ~ ~ Icicle Creek Engineers 4,000 ! I Vicinity Map -Figure 1 ~ ~ ~ .. Ban map _ "Cuglrl Properly T8lC Lots 14819: ... "' ... by Poc-loon E_er1ng.lnc.dalOd Oc1obor7.1994. O _______ 1~50======5300 Approximate Scale in Feet ii' w Icicle Creek En ineers e 2 ~~~~~~~ ____ ~~~ ____________________ -J'-~~-4~-L~ ______ ~~~~~~ ; Icicle Creek Engineers EXPLANATION (;B-6 BorIng Locatlcn for Current study Boring Location for Previous Study Geologic CIOS&-Sec:tion LocaUon (see Figures 4 and 5) o _______ 1~®======~300 Approximate Scale in Feet Springbrook Mine Under ound Mine Ma -Fi re 3 Cugini Prcperty-Northwest Parcel i u. .E c 0 "" ~ ., iii Icicle Creek Engineers AI (South) 400 300 200 100 o III ~ .. g S· ~ a .O ____ ~ __ 10CO~======~O Scale in Feet Horizontal Scale = Vertical Scale Springbrook Mine Geolo . c Cross-Section A-AI -Figure 4 Cugini Property· Northwest Pa~cel.;----f I!l t g :r I o ____ ~~I~OO~=====5~O Scale In Feet Horizontal Scale 0: Vertical Scale Springbrook Mine Icicle Creek Engineers Geolo ic Cross-Section B-B' -Fi re 5 Explanation: I i .! ~ Icicle Creek En ineers Severe Coal Mine Hazard Area ~0IIIl"""""""1.fMlNIowa.fNIUI'Id .,.. .n:w..1ODIi:lalbl.llEwDl"l" ..... lndlObit ..... 01'1 ...... j. . Declassified Coal Mine Area (The .. N .............. ID .. -..bIIInIIIJ~ ......... _--No development restricllons associated with coal mine hazards 0 ..... __ .. 1;,:50====:.3,00 Approximate Scale in Feet Coal Mine Hazards Ma -Fi ure 6 Report Geotechnical Engineering Services Proposed Property Development Springbrook Ridge King County Tax Parcel Nos. 2923059009 and 2023059148 Renton, Washington January 26, 2009 Project No. 0336-004 Prepared For: Alex Cugini Prepared By: Icicle Creek Engineers, Inc. ICICLE CREEK ENGINEERS Geotechnical. Geologic and Environmental Services January 26, 2009 Alex Cugini c/o Jamie Schroeder, P.E. CPH Consultants, LLC 733 -7'· Avenue, Suite 100 Kirkland, Washington 98033 INTRODUCTION Report Geotechnical Engineering Services Proposed Property Development Springbrook Ridge King County Tax Parcel Nos. 2923059009 and 2923059148 Renton, Washington ICE File No. 0336-004 This report summarizes Icicle Creek Engineers' (ICE's) geotechnical engineering services for the proposed development ofan approximately 3.78 acre property (referred to as the Springbrook Ridge property- King County Tax Parcel Nos. 2923059009 and 2923059148) located north of the intersection of! OS'" Avenue SE (Benson Road) and State Route (SR) 515 in Renton, Washington. Our services were completed in general accordance with our Proposal dated April 2, 2008 and were authorized by Alex Cugini Jr., the property owner, on December 8, 2008. ICE previously completed coal mine hazard assessments of the property; the results are presented in our reports dated June 24, 1999 and March 22, 2004. The location of the Springbrook Ridge property is shown relative to nearby physical features on the Vicinity Map, Figure I. PROJECT DESCRIPTION Jamie Schroeder of CPH Consultants, LLC (CPH), the project engineer, provided ICE with the following infonnation regarding the project: CPH, March 4, 2008, "Conceptual Site Plan," sheet I, scale I inch = 100 feet. City of Renton Department of Community & Economic Development, March 27,2008, preapplication meeting notes for the Benson Road Development, 8 pages. • City of Renton Development Services Division, March 2007, "Submittal Requirements, Site Plan Review," 8 pages. Based on our review of the CPH site plan and discussions with Mr. Schroeder, the Springbrook Ridge property will be developed with retail/commercial and residential buildings along with paved parking and access. We understand that the north building (residential) may have below-grade parking. As currently planned, stonnwater will be detained in two underground vaults (Vaults A and B). Site grading will require cuts up to 16-feet deep, primarily for installing Vault B and underground parking for the north building. The balance of the site grading for parking and access areas will require cuts and fill of less than 5 feet. :9335 NE 20th Street. Carnation, Washington 98014 • www.lclclecreekenglneers.com • (425) 333·0093 phone. (425) 996·4036 fax Alex Cugini clo Jamie Schroeder, P.E. CPH Consultants, LLC January 26, 2009 Page 2 A Class 4 stream (classified by others) crosses the site from east to west. The stream includes a 25-to 35-foot wide buffer on either side of the stream channel. An access driveway will cross the stream corridor by installation of a culvert and construction of a fill embankment up to l2-feet thick. The remainder of the stream and buffer will remain undeveloped. The project site, including the proposed site improvements, is shown on the Site Plan, Figure 2. SCOPE OF SERVICES The purpose of our services was to explore subsurface soillbedrock and ground water conditions at the site as a basis for developing geotechnical recommendations and design criteria for the proposed development. Our scope of services was developed, in part, based on our review of the City of Renton documents (referenced above) that included a list of items that should be addressed in the geotechnical report. Our specific scope of services includes the following: Complete a detailed surfuce reconnaissance with particular emphasis on slope areas. Explore shallow subsurface soil, bedrock and ground water conditions by completing nine test pits with a track-mounted excavator. One of the test pit explorations was completed in a Severe (High) Coal Mine Hazard area. We supplemented these explorations with test borings that were completed at the site for a previous study of coal mine hazards. Complete laboratory testing on selected soil samples for moisture content. Evaluate pertinent physical and engineering characteristics of the soilslbedrock based on our observations and site koowledge, and on the results of laboratory tests completed on samples obtained from the test pits. Describe and characterize soil/bedrock and ground water conditions at the site. Evaluate the present stability of the slope areas and the effects of the proposed development on future slope stability. Evaluate the High Coal Mine Hazard area and reclassify, if appropriate, andlor provide recommendations to mitigate the High Coal Mine Hazard condition. Provide recommendations for site preparation and grading including stripping requirements, structural fill criteria and reuse of onsite excavated soils and bedrock for structural fill. Evaluate dewatering and shoring requirements and provide recommendations for excavation and trench side slopes for underground utilities. Provide recommendations for bedrock excavation including excavatability and mechanical splitting (loosening), as appropriate. Provide recommendations for underground utility backfill materials including thc suitability of excavated materials for use as backfill and hedding, including recommendations for placement and compaction of bedding and backfill materials. Provide recommendations for temporary cuts and permanent cut and fill slopes. Provide recommendations for foundation support, including minimum footing dimensions, embedment depths, allowable soil bearing pressures and settlement estimates. Provide recommendations for support of on-grade floor slabs including criteria for a capillary break. Provide recommendations for lateral earth pressures including active pressures for retaining walls and passive earth pressures on footingS, including the coefficient of base friction against sliding. Provide recommendations for pavement subgrade preparation. Provide seismic design criteria based on the 2006 International Building Code (IBC). Provide recommendations for erosion control and surfuce and subsurface drainage requirements, as appropriate. Icicle Creek Engineers 03360041012609 Alex Cugini clo Jamie Schroeder, P.E. CPH Consultants, LLC January 26, 2009 Page 3 ABANDONED UNDERGROUND COAL MINING As previously mentioned, ICE has completed coal mine hazard assessments of the Springbrook Ridge property (June 1999 and March 2004) at a time when the site was within King County. The Springbrook Ridge property was annexed by the City of Renton in November 2007. The June 1999 study was a preliminary assessment that summarized the coal mine hazard conditions; no subsurface explorations were completed for the June 1999 study. The March 2004 coal mine hazard assessment included subsurface exploration of the shallow (less than ISO-foot deep) abandoned coal mine workings. In the March 2004 study we concluded that the abandoned underground coal mines were substantially collapsed and most of the coal mine hazards were "Declassified" (using King County Ordinance 13319 terminology). A Declassified Coal Mine Area is defined by King Countyas "those areas for which a risk of catastrophic collapse is not significant and which the hazard assessment report has determined require no special engineering or architectural recommendations to prevent significant risks of property damage. Declassified coal mine areas may typically include, but are not limited to, areas underlain or directly afficted by coal mines at depths greater than three hundredfoet as measuredfrom the surface but may often include areas underlain or directly affected by coal mines at depths less than three hundred feet. " However, one area remained as a "Severe Coal Mine Hazard" area (equivalent to City of Renton "High Coal Mine Hazard") in the south portion of the Springbrook Ridge property where a fonner mine entry (inaccessible and filled) was roughly located during our March 2004 study. At that time, the specific location of this former mine entry was not known so a relatively wide circle identifying the Severe (High) Coal Mine Hazard area was established to encompass the most probable location of the former mine entry. A full description of the abandoned underground coal mines and results of ICE's subsurface explorations (ground proofmg) of the abandoned underground coal mines is presented in ICE's June 1999 and March 2004 reports. This current study includes a detailed evaluation of the High Coal Mine Hazard area (the former mine entry) that was established in ICE's March 2004 report. GEOLOGIC SETTING Based on regional geologic mapping by U.S. Geological Survey (USGS -Mullineaux, D.R., 1965, ''Geologic Map of the Renton Quadrangle, King County, Washington," Geologic Quadrangle Map GQ-405), the Springbrook Ridge property is underlain by glacial till. Glacial till typically consists of dense to very dense silty sand with gravel. The glaCial till is underlain by bedrock of the Renton formation. Renton formation bedrock consists of interbedded sandstone, siltstone, shale, claystone, carbonaceous shale and coal beds. Structurally, the bedrOck has been uplifted, folded and faulted over time. This structural deformation of the bedrock has created a northwest trending syncline. "Syncline" is a geologic term referring to a fold in the bedrock layering that is concave up (downward curving). The "limbs" or bedrock layering of the syncline dip at angles ranging from 30 to 70 degrees from horizontal. The unweathered glacial till is typically covered with forest duff and topsoil, and weathered glacial till varying in total thickness from a few inches to several feet. Weathered glacial till typically consists of loose silty sand with variable amounts of gravel and roots. In historic coal mining areas, it is possible that "mine rock fill" could exist on the surface of the property. Mine rock fill typically consists ofcoal fines and broken rock. Icicle Creek Engineers 03360041012609 Alex Cugini cia Jamie Schroeder, P.E. CPH Consultants, LLC January 26, 2009 Page 4 SURFACE CONDITIONS SITE CONDITIONS The Springbrook Ridge property is located on an upland area within the central Puget Sound lowlands commonly referred to as "Benson Hill." The roughly triangular-shaped property is bordered to the north by SE 172M Street and residential development, to the northeast by a child care fucility (Family Circle Learning Center), to the southeast by lOB" Avenue SE (Benson Road), undeveloped property and a church, and to the southwest by SR 515 and commercial development. The Springbrook Ridge property is currently undeveloped and is vegetated with mature second-growth conifer and deciduous trees, and dense brush. A stream (the previously mentioned Class 4 stream) within a swale about 10-to IS-feet deep, crosses the property from east to west. The ground surface is gently undulating and ranges from Elevation 366 feet (where the stream exits the property along the southwest property line) to about Elevation 40 I feet in the east corner of the property. Slopes bordering the stream channel range from 10 to 25 percent grade and are up to 15 -feet high. No ground surface depressions (suggesting a mine opening or sinkhole) were observed on the Springbrook Ridge property with the exception of the previously described former mine opening area. No surface evidence of mine rock fill was observed on the Springbrook Ridge property. SUBSURFACE CONDITIONS The March 2004 coal mine hazard assessment included drilling seven, 6-inch-diameter borings (Borings B-5 through B-II) to depths ranging from 20 to 160 feet between February 16 and 24, 2004 using mud-rotary drilling methods with track-mounted drilling equipment owned and operated by Gregory Drilling, Inc. The approximate locations of the test boring explorations are shown on Figure 2. Subsurface conditions for the current study were evaluated by the excavation of nine test pits (Test Pits TP-I through TP-9). The test pits were completed on December 16, 200B to depths ranging from 6 to 15 feet using a track-mounted excavator (Komatsu PC 120) owned and operated by Kelly's Excavatiog, Inc. of Pacific, Washington. The approximate locations of the test pits are shown on Figure 2. The test pit explorations were continuously observed by a geologist from ICE who classified the soils, observed ground water conditions, and prepared a detailed log of each exploration. The soil consistencies noted on the test pit logs are based on conditions observed, our experience and judgment, and the difficulty of excavation. Soils were classified in general accordance with the classification system described in Figure 5. The test pit logs are presented in the Test Pit Logs, Figures 6 through B. Laboratory testing including moisture content, was completed on selected soil samples from the test pits. A summary ofthe moisture content results is shown on the Laboratory Testing Moisture Content Results, Figure 9. The test pit explorations (Test Pits TP-l through TP-B) encountered relatively uniform conditions consisting of approximately y, to I Y2 foot of forest duff and topsoil underlain by approximately I to 3Y2 feet of weathered glacial till consisting ofloose to medium dense silty sand with variable amounts of gravel and roots. The weathered glacial till was underlain by unweathered glacial till to the full depth of the explorations ranging from 6 to 10 feet below the ground surface. The unweathered glacial till consisted of dense to very dense silty sand with variable amounts of gravel and cobbles. Practical digging refusal was encountered in Test Pits TP-3 andTP-5. Test Pit TP-9 was completed in the area of the suspected former mine entry. Test Pit TP-9 encountered fill for the full depth of the exploration to 15 feet below the ground surface. The fill consisted of loose to medium dense silty sand with a trace of gravel and cobbles and abundant wood debris. This fill appears to be nonstructural soil that was placed in the mine opening to prevent entry. Icicle Creek Engineers 0336004/012609 Alex Cugini c/o Jamie Schroeder, P.E. CPH Consultants, LLC January 26, 2009 Page 5 Based on the test borings that were completed for the March 2004 study, the glacial till overlies Renton fonnation bedrock. Renton fonnation bedrock consists of interbedded sandstone, siltstone, shale, claystone, carbonaceous shale and coal beds. The depth to the bedrock ranged from 22 to 43 feet below the ground surface. No ground water was observed in the test pit explorations with the exception of Test Pit TP-4 which encountered rapid ground water seepage at a depth of about I Y, feet. Test Pit TP -4 was completed in a low area with spongy ground that appears to be accumulating in a closed depression. Though ground water was not encountered in the remaining test pit explorations, we expect shallow "perched" ground water to occur within the weathered glacial till along the contact with the underlying, nearly impermeable, glacial till during extended periods of wet weather. The perched ground water is expected to dry out following extended periods of dry weather. CONCLUSIONS AND RECOMMENDATIONS SLOPE STABILITY We did not observe surface evidence of slope instability, primarily along the stream channel which is to remain undeveloped. Based on topographic survey plans and our site observations, slopes within the Springbrook Ridge propertY are less than 2S percent grade and are therefore not regulated as a Sensitive or Protected Slope. mGH COAL MINE HAZARD AREA CONSIDERATIONS Test Pit TP-9 appeared to encounter the former mine entry because of the presence offill to depth (at least IS-feet deep). Currently, this area is planned for parking and an underground stOimwater detention vault (Vault B). In our opinion, this former mine entry, though apparently filled to a depth of at least 15 feet, will need to be excavated during construction to expose the plan dimensions of the tunnel area and to refine our recommendations for reclamation as described below. We expect the former mine entry to be about S-to 8-feet in diameter and inclined at about 55 to 60 degrees below horizontal down to the south. The diameter of the former mine entry should be confinned during site preparation and grading. The reclamation of the mine entry should consist of a structural plug (controlled density ftll-CDF) that will reduce the risk of future caving and support surface facilities such as a parking lot and/or underground stormwater vault. The structural plug should consist of lean concrete that is used to fill a "prepared excavation." A diagram showing the schematic details of this reclamation for a parking lot condition is shown in the High Coal Mine Hazard Reclamation Plan (parking Area), Figure 3 and for an underground stormwater vault in the High Coal Mine Hazard Reclamation Plan (Stormwater Vault), Figure 4. Based on our experience, this type of mine opening reclamation has been used frequently by the U.S. Department of Interior Office of Surface Mining. The prepared excavation should be completed during site grading by removal of existing fill soils to a depth of at least 15 feet or to at least 5 feet below the base of the underground stormwater vault, or as determined by a geotechnical engineer or geologist during excavation. The prepared excavation should be widened into the native glacial till areas that surround the mine opening by at least 5 feet to fonn the ''plug'' and should also be observed by a geotechnical engineer or geologist during excavation The vault, where underlain by the former mine entry, should have the base designed to span at least 10 feet as a design redundancy. Icicle Creek Engineers 03360041012609 Alex Cugini clo Jamie Schroeder, P.E. CPH Consultants, LLC January 26, 2009 Page 6 SITE PREPARATION AND EARTHWORK Site Preparation Conventional site preparation procedures for the type of terrain and forest present on the site are expected. We recommend that all trees, fallen logs, brush, low-growing vegetation and forest duffbe removed from the planned development area. We recommend that any hazardous trees (e.g., trees that lean toward or may eventually fall onto parking or building areas) be removed or trimmed. We expect that stripping will be on the order of 12 to 18 inches unless excessive disturbance is caused by clearing operations. Local areas of brush and tree stumps will require additional stripping. Tree root balls should be removed and replaced with structural fill. Disturbance to a greater depth can be expected if clearing operations are done in wet weather. The excavated weathered and unweathered glacial till soils are moisture-sensitive and difficult to operate on and to compact during wet weather. Rubber-tired vehicles and even foot traffic will disturb this material when it is above-optimum moisture. This material readily absorbs moisture, is difficult to dry out, and also has a fairly high erosion potential. Accordingly, silt fences and other erosion protection measures will be necessary. Structural Fill General -All new fill in bUilding and parking areas should be placed as structural fill. Structural fill material shOUld be free of debris, organic contaminants and rock fragments larger than 6 inches. The suitability of material for use as structural fill will depend on the gradation and moisture content of the soil. As the amount of fines (soil particles passing the u.s. Standard No. 200 sieve) increases, soil becomes increasingly sensitive to small changes in moisture content and adequate compaction becomes more difficult to achieve. Common Borrow -We recommend that common borrow fill confonn with Section 9-03.14(3) of the 2008 WSDOT Standard Specifications for Road, Bridge and Municipal Construction (Standard Specifications). Common borrow will be sensitive to changes in moisture content and compaction will be difficult or impossiblc to achieve during wei weather. We recommend that common borrow be used as structural fill only during dry weather conditions when proper moisture conditioning can be achieved. Gravel Borrow -We recommend that gravel borrow confonn with Section 9-03.14(1) of the 2008 Standard Specifications. We recommend that gravel borrow contain no more than 5 percent fines during wet weather and in wet subgrade conditions. Reuse of On-Site Materials -The native soils (weathered and unweathered glacial till) may be reused for structural fill during periods of extended dry weather. Soil containing more than 20 percent organic matter (roots, forest duff and topsoil) should only be used in landscaping areas or for other purposes where specific compaction criteria is not required. Placement and Compaction -For placement during wet weather or on wet subgrades, structural fill should contain no more than 5 percent fines. Fill placement over wet ground should connnence with an initial lift of about 24 inches of gravel borrow with less than 5 percent fines. This lift should be compacted by rolling without vibration to reduce the potential for inducing "pumping" or "yielding" of the underlying soils. During dry weather, the fines content may be up to about 30 percent, provided that the fill can be moisture-conditioned and compacted to the degree specified below. Structural fill should be compacted to at least 95 percent of the maximum dry density (MOD) obtained from ASTM Test Method D 1557. Tbis applies to all utility trench backfill as well. Waste fill in landscaping areas need only be compacted to the extent required for trafficability of construction equipment. Icicle Creek Engineers 0336004/012609 Alex Cugini c/o Jamie Schroeder, P.E. cpn Consultants, LLC January 26, 2009 Page? As a guideline, we recommend that structural fill be placed in horizontal lifts which are 10 inches or less in loose thickness. The actual lift thickness will depend of the compaction equipment used and the quality of the fill. Each lift should be compacted with vibratory equipment to at lcast 95 percent of the MOD. The moisture content of the fill material should be adjusted as necessary to achieve the required degree of compaction. Each lift should be compacted to the required specification before placing subsequent layers. Nonstructural fill placed in landscape and waste-fill areas where the existing surface slope is no steeper than 4H:IV (horizontal to vertical) needs to be compacted only to the degree required for trafficability of construction equipment and effective surface drainage. All nonstructural fills should be sloped no steeperthan 4H: I V. Nonstructural fill is very susceptible to erosion. Therefore, we recommend that all nonstructural fill areas be immediately seeded, planted, or otherwise protected from erosion. We recommend that a representative from our firm observe the preparation for, placement, and compaction of structural fill. An adequate number of in-place density tests should be completed in the fill to evaluate if the desired degree of compaction is being achieved. Fill Settlement We expect that fill areas will be underlain by medium dense to very dense silty sand with variable amounts of gravel and cobbles (weathered and unweathered glacial till). Settlement of these underlying materials is expected to range from 12 to I inch and should occur rapidly as fill is placed. Some settlement will also occur within the fill itself, especially where the fill thickness is greater than about 5 feet. We estimate that the maximum amount of settlement within the fill will be no more than I percent of the fiU thickness. Thus, for a la-foot thick fiU section, settlements on the order of I to 1.5 inches might occur. EXCAVATIONS In general, most materials encountered in our test pits and borings can be excavated using conventional heavy construction equipment such as a Hitachi EX450LC track-mounted excavator. The unweathered glacial till is generally in a dense to very dense condition and may be difficult to excavate. We expect that occasional boulders will be encountered in the glacial till. Typically, these boulders are less than 6 feet in diameter based on our experience in this area, however it is possible that larger boulders may be present. Bedrock may be encountered locally in deep excavations, especialIy for the storm water detention vaults. The bedrock may be difficult, if not impossible, to excavate if the trench extends greater than 5 feet into the unweathered bedrock. Hard bedrock may require mechanical splitting or blasting to loosen. AlI temporary cut slopes and shoring must comply with the provisions of Title 296 Washington Administrative Code (WAC), Part N, "Excavation, Trenching and Shoring." We recommend that temporary excavations, including any temporary shoring, be made the responsibility of the contractor. The contractor is present at the site continuously and is best able to observe changes in site and soil conditions and monitor the performance of excavations. SHORING It may be necessary to support temporary excavations to maintain the integrity of the surrounding undisturbed soils and minimize disruption of adjacent areas, as well as to protect the personnel worlcing within the excavations. Because of the diversity of available shoring systems and construction techniques, the design of temporary shoring is most appropriately left up to the contractor proposing to complete the instalIation. However, we recommend that the shoring be designed by a licensed professional engineer in Washington, and Icicle Creek Engineers 0336004/012609 Alex Cugini c/o Jamie Schroeder, P.E. CPH Consultants, LLC January 26, 2009 PageS that the PE-stamped shoring plans and calculations be submitted to the proj ect engineer for review and comment prior to construction. The following paragraphs present recommendations for the type of shoring system and design parameters thai we conclude are appropriate for the subsurfuce conditions at the Springbrook Ridge property. The majority of the materials within the project area can be retained using conventional trench shoring systems such as trench shields or sheet piles, with lateral restraint. The design oftemporary shoring should allow for lateral pressures exerted by the adjacent soil, and surcharge loads due to traffic, construction equipment, and temporary stockpiles adjacent to the excavation, etc. Lateral load resistance can be mobilized through the use of braces, tiebacks, anchor blocks and passive pressures on members that extend below the bottom of the excavation. Temporary shoring utilized to support trench excavations typically uses internal bracing such as aluminum hydraulic shoring or trench shield bracing. Temporary trench shoring with internal bracing can be designed using active soil pressures. We recommend that temporary shoring be designed using a lateral pressurc equal to an equivalent fluid density of 40 pounds per cubic foot (pc!), for conditions with a level ground surfuce adjacent to the excavation. If the ground within 5 feet of the excavation rises at an inclination of I H: I V or steeper, the shoring should be designed using an equivalent fluid density of75 pcf. For adj acent slopes flatter than I H: IV, soil pressures can be interpolated between this range of values. Other conditions should be evaluated on a case-by-case basis. These lateral soil pressures do not include traffic or construction surcharges that should be added separately, if appropriate. It is typical for shoring to be designed for a traffic influence equal to a uniform lateral pressure of 240 pounds per square foot (pst) acting over a depth of 10 feet from the ground surface. More conservative pressure values should be used if the designer deems them appropriate. These soil pressure recommendations are predicated upon the construction being essentially dewatered; therefore, hydrostatic water pressures are not included. CONSTRUCTION DEWATERING Based on our test pit explorations and general know ledge of the site area, we do not expect that construction dewatering will be necessary. However, if pockets of ground water seepage are encountered, we expect that pumping from a sump within the trench may be used for smaIl to moderate amounts of ground water seepage. Well points or pumped wells will be necessary if large amounts of ground water seepage are encountered. We recommend that the contractor be required to submit the proposed dewatering system design and plan layout to the project engineer for review and comment prior to beginning construction. UNDERGROUND UTILITY TRENCH BACKFILL All trench backfill should consist of structural fill quality material as previously described in the Structural Fill section of this report. Unless specified otherwise in this report, the following general requirements shall apply to all fill placement, including pipe bedding, and trench backfilling. Underground utilities should be bedded in crushed gravel as specified in the 2008 WSDOT Standard Specifications, Section 9-03.12(3) for "Gravel Backfill for Pipe Zone Bedding." • Pipe zone bedding should be exteuded at least 4 inches below the utility line and 6 inches above the utility line. Bedding should be worked under the pipe haunches using hand tools as required. Bedding material should be tamped or VIbrated (compacted) into place. • Pipe zone bedding for all non-water undergrouud utilities sbould be compacted to at least 90 percent of the MDD (ASTM Test Method D 1557). Pipe zone bedding for all water mains should be compacted to at least 95 percent of the MDD (ASTM Test Method D 1557). Icicle Creek Engineers 0336004/012609 Alex Cugini clo Jamie Schroeder, P.E. CPH Consultants, LLC January 26, 2009 Page 9 Backfill placed above the bedding material should consist of structural fill quality on-site material, or "Common Borrow" as specified in 2008 WSDOT Standard Specifications, Section 9-03.14(3). During wet weather periods, backfill material should have less than 5 percent fines content. As a guideline, backfill should be placed in lifts oflO inches orless (loose thickness). Each lift should be compacted prior to placing the subsequent lift. Prior to compaction, the backflll should be moisture conditioned to near optimum moisture content. All trench backfill should be compacted in lifts to at least 95 percent of the MDD (ASTM Test Method D 1557). Backfill compaction should be achieved by mechanical means. No jetting, ponding, or flooding will be allowed for compaction. During trench backfill placement, in-place density tests should be completed at approximately 100-foot intervals along the trench alignment to evaluate if the required compaction is being achieved. CUT AND FILL SLOPES Cut Slopes It is expected that temporary cuts of up to 16 feet will be required for stormwater Vault B and the underground parking for the north building. The appropriate slope for temporary cuts is dependant on several factors including the presence of ground water, the type and density of soils, the depth of cut, surcharge loading adjacent to the cut and the time of construction. Because many variables are involved, the actual slope required to maintain stability can only be approximated. The following recommendations apply to temporary cuts: Temporary cuts in excess of 4 feet should be sloped no steeper than 1.5H:IV. The cuts rnayhave to be flattened for stability if ground water seepage is ·encountered. Temporary cut-slope inclinations should be made in accordance with applicable OSHA and WISHA regulations. Permanent cut slopes should be inclined no steeper than 2H: I V. The upper portion of cut slopes will expose loose to medium dense weathered glacial till soil that may be several feet thick. The weathered glacial till soil will be subject to localized raveling and sloughing and must therefore be sloped no steeperthan 3H:l V. Fill Slopes Structural fill slopes may be sloped at 2H: I V or flatter. All surfaces which will receive fill should be properly stripped of vegetation and organic matter prior to placing fill. Fill placed on existing slopes which are steeper than 4H: I V should be properly keyed into the native slope surface. This can be accomplished by constructing the fill in a series of 4-to 8-foot-wide horizontal benches cut into the slope. The fill should be placed in horizontal lifts. We recommend that fill be placed on the cut benches as soon as possible following construction of the benches. FOUNDATION SUPPORT We recommend that all footings be founded on either the medium dense or denser weathered or unweathered glacial till, or structural fill overlying g\acial till. If loose weathered glacial till is encountered at footfu.g subgrade levels, it may be necessary to compact the weathered till to structural fill specifications. Continuous strip footings should be at least 18-inches wide; isolated spread footings should have a minimum width of 2 feet. We recommend that all exterior footings be founded at least 18 inches below the lowest 1cicle Creek Engineers 0336004/012609 Alex Cugini clo Jamie Schroeder, P.E. CPH Consultants, LLC January 26, 2009 Page 10 adjacent finished grade. lbe base of interior footings should be founded at least 12 inches below the fmished floor grade. An allowable soil bearing pressure of 2,500 psf may be used for design of isolated and continuous spread footings founded in accordance with our recommendations. An allowable soil bearing pressure of 4,000 psf can be used for footings bearing on the dense or very dense unweathered glacial till. These values apply to the sum of all dead plus long-tenn live loads, excluding the weight of the footing and any overlying backfill. These values may be increased by one-third when earthquake or wind loads are considered. The settlement of foundation elements bearing on dense to very dense glacial till will be nominal (less than l<'. inch). The expected settlement will increase as the structural fill underlying the footings increases. We expect the maximum total settlement of footings founded on structural fill prepared as recommended will be less than about I inch. Therefore, provided there is not an abrupt transition between footings underlain by fill and the unweathered glacial till, we expect differential settlements will be limited to about Y, inch between comparably loaded isolated column footings or within 50 feet along continuous strip footings. If a sharp transition between the fill and the unweathered glacial till is encountered during construction, the transition can be made more gradual by excavating some of the unweathered glacial till and replacing it with structnral fill or taking the footings founded on weathered glacial tilllstructnral fill deeper. We recommend that the preparation ofthe shallow foundation subgrades and structural fill placement be observed by a representative of our staffso that our recommendations can be modified as needed based on the actual field conditions encountered during construction. Lateral loads can be resisted by passive resistance on the sides of the footings and by friction on the base of the footings and floor slab. Passive resistance may be evaluated using an equivalent fluid density of 300 pef, assuming that the soil around the footings for a distance oftwice the footing depth consists of either dense glaciallill or compacted structural fill. The top of the triangular passive pressure distribution should begin at the bottom of adjacent floor slabs or paving or below a depth of 1 foot where the adjacent area is unpaved, as appropriate. Frictional resistance can be evaluated using 0.4 for the coefficient of base friction against footings and the building slab. The above values incorporate a factor of safety of about 1.5. SLAB-ON-GRADE The slab-on-grade subgrade should be prepared in accordance with the previously described SITE PREPARATION AND EARTHWORK recommendations. We recommend that the subgrade surface be compacted such that a minimum compaction of95 percent of the MDD (ASlM Test Method D 1557) is achieved before placing structural fill or capillary break material. We recommend that a compacted base-course layer consisting of at least 4 inches of gravel containing less than 3 percent fines be placed on the sub grade to provide uniform support and act as a capillary break beneath the slab. A vapor retarder should be placed beneath the slab if moisture control in the slab is critical (i.e., where tile or carpeting is to be glued to the slab). This vapor retarder should consist of polyethylene sheeting. A layer of clean sand not more than 2 inches in thickness may be placed over the polyethylene sheeting. The vapor retarder should be placed immediately below the slab. We estimate that the settlement of floor slabs due to uniform areal loads of 150 psf will be less than Y, inch. These settlements are expected to occur rapidly upon load application. STORMWATERDETENTION VAULTS We expect that the stormwater detention vault structures (Vaults A and B) will be supported on undisturbed unweathered glacial till in a dense or denser condition. We estimate that settlement of the vault Icicle Creek Engineers 0336004/012609 Alex Cugini c/o Jamie Schroeder, P.E. CPH Consultants, llC January 26, 2009 Page 11 structures will be less than I inch using an allowable bearing pressure of 4,000 psf. Settlements are expected to occur rapidly as loads are applied. Backfill around the vault structures should be placed in horizontal lifts with a maximum loose thickness of about 8 inches and compacted to at least 90 percent of the MDD (ASTM Test Method D 1557). Only hand-operated compaction equipment should be permitted within 5 feet of the vault structure walls to avoid excessive lateral pressures on the walls. For backfill placed as described, we recommend using a design lateral pressure imposed by an equivalent fluid weighing 55 pcf. The design lateral pressure is based on maintaining drained conditions in the soils surrounding the vault structures. If a drainage system cannot be provided at the base of the vault structures, we recommend designing the stormwater detention vault structures for a lateral pressure resulting from an equivalent fluid weighing 90 pcffrom a depth of2 feet below the ground surface to the bottom of the vault. A rectangular pressure equal to 0.45 times the weight of superimposed dead or live loads at the surface should be added where present. Uplift forces on the underground stormwater vault can be resisted by the weight of soil located above the structure or slabs which protrude beyond the walls and by friction between the wall and the adjacent soil. We recommend that soil weight be computed using a density of 125 pcf above the water table. Friction between the wall and the adjacent backfill soil may be estimated using a coefficient of friction of 0.2. This coefficient of friction value includes a factor of safety of 1.5. If a projecting base slab is used, the perimeter area of the soil on the sides of the prism formed by the base slab and the vertical distance to the ground surface may be used with a coefficient of friction of 0 .25 to calculate resistance to uplift. SUBGRADE (BASEMENT) WAILS Subgrade walls may be required for building construction. The lateral soil pressures acting on subgrade walls depend on the type, density and geometry of the soil behind the wall and the amount oflateral wall movement which can occur as backfill is placed. For walls that are free to yield at the top at least one one-thousandth of the height of the wall, an active pressure oB5, 45, and 60 pcfshould be used for level backslopes, 4H: I V backslopes and 2H: I V backslopes, respectively. These values assume that the soil behind the wall is free draining. For "at rest" conditions where the wall is restrained against movement, an active pressure of 50, 55, and 75 pcf should be used for level backslopes, 4H:l V backslopes and 2H: I V backslopes, respectively. These values assume that the soil behind the wall is free draining. Surcharge effects should be considered as appropriate. In settlement-sensitive areas, the backfill for subgrade walls should be compacted to at least 95 percent of the MDD (ASTM Test Method D 1557). At other locations, wall backfill should be compacted to between 90 and 92 percent of the MDD (ASTM Test Method D 1557). Measures should be taken to prevent the buildup of excess lateral soil pressures due to overcompaction of the backfill behind the wall. Care must be exercised by the contractor to avoid overcompaction. A drainage zone consisting of clean, free-draining granular material containing less than 5 percent fmes at least 1S-inches wide should be placed against the back face of the wall for its full height. Positive drainage behind subgrade walls should also include installing a footing drain at the base of the wall as described in the DRAINAGE CONSIDERATIONS section of this report. LATERAL RESISTANCE Lateral loads can be resisted by passive resistance on the sides ofthe footings and by friction on the base of the footings and floor slab. Passive resistance may be evaluated using an equivalent fluid density of Icicle Creek Engineers 03360041012609 Alex Cugini c/o Jamie Schroeder, P.E. CPH Consultants, LLC January 26, 2009 Page 12 300,240,290 and 150 peffor a level foreslope, 4H:IV foreslope, 3H:IV foreslope and 2H:IV foreslope, respectively, assuming that the soil around the footings for a distance of at least twice the footing depth consists of either medium dense native soil or compacted structural filL The top of the triangular passive pressure distribution should begin at the bottom of adjacent floor slabs, roadway pavement, or below a depth of I foot where the adjacent area is unpaved, as appropriate. Frictional resistance can be evaluated using 0.4 for the coefficient of base friction against footings and the building slab. The above vaJues incorporate a factor of safety of about 15. PAVEMENTSUBGRADE Pavement subgrade should be compacted to at least 95 percent of the MDD (ASTM Test Method D I 557) prior to placing the pavement section. During wet season construction or if the subgrade soils are soft or loose, it may be necessary to excavate soft!loose soils, replace these soils with free-draining, compactable sand and gravel, andlor a suitable geotextile fabric such as Mirafi 500X or other fabric as suggested by the geotechnical engineer. The free- draining sand and gravel should contain less than 5 percent fines. It is critical that all traffic be kept off the subgrade soil if the on-site silty sub grade soils are wet. It is also important that backfill in utility line trenches be compacted to structural fill specifications. We recommend a pavement section consisting of2 inches of Class B asphaltic concrete (AC) surfacing over4 inches of crushed rock base course (CRBC) for automobile parking areas, and 6 inches ofCRBC and 3 inches of AC in main access and truck use areas. Alternatively, a layer of asphalt treated base (ATB) could be placed directly over the prepared subgrade (no CRBC), and a finaJ layer of Class B AC placed over the A TB at a later time. The advantage of using A TB is that it could be used as a relatively durable surface during construction. Prior to placing a fiuish coat of Class B AC, the road surface could be releveled with ATB or CRBe. If ATB is used, we recommend a minimum thickness of4 inches. We recommend a minimum thickness of2 inches of Class B AC over the A TB for a fiuished wearing course for automobile parldng areas, and 3 inches of AC in main access and truck use areas. Any distressed areas in the A TB must be repaired prior to placing the Ae. SEISMIC SITE CLASSIFICATION Based on our review of available geologic information and our site explorations, we interpret the shallow (less than 10 feet) soil conditions to correspond to Seismic Site Class D, as defined by the 2006 mc. This classification pertains to a very stiff soil profile with an average Standard Penetration Test (SPT) value of 15 to 50. EROSION CONTROL AND DRAINAGE CONSIDERATIONS The surficial soils on the site have a high potential for erosion on slopes greater than about 20 percent when disturbed by construction activities. Erosion control measures should be implemented prior to the start of site preparation, including proper control of surface water runoff, use of straw bales or appropriate geotextile filters and temporary sedimentation basins. Erosion control measures should comply with the guidelines of the appropriate regulatory agency. Based on conditions encountered in our test pit explorations, it is possible that ground water may be encountered in temporary excavations or permanent cuts. We expect that seepage may be adequately handled by installation of French drains, open ditches andlor pumping as necessary. The grading should be done to avoid concentration of runoff onto natural slopes. We recommend Icicle Creek Engineers 0336004/012609 Alex Cugini c/o Jamie Schroeder, P.E. CPR Consultants, LLC January 26, 2009 Page 13 sloping the ground surface away from structures. Roof downspouts must be tightlined to an approved disposal area. Other surface runoff may be addressed by using swale drains, drainage ditches or other drainage measures. We recommend that perimeter footing drains be installed adjacent to the outside footings of all structures. These drains should consist of a minimum 4-inch diameter perforated smooth-walled pipe surrounded with at least 6 inches of free-draining sand, sand and gravel or pea gravel, with the perforations down and the base of the pipe at the base of the adjacent footings. The bedding should be enclosed within a nonwoven geotextile fabric to reduce the potential for fines contamination from the native soil. The perimeter footing drain should be connected to a tightline collection system that discharges away from the developed areas. Roof drains on structures should be connected directly to a tightline collection and disposal system, separate from the footing drain. Perched ground water may result in the development of wet areas at finished grades. Interceptor drains or French drains installed in selected locations is an effective way to manage perched ground water. The need for and location of these drains should be a field decision at the time of construction. The drain should consist of a trench at least IS-inches wide and 24-inches deep. A rigid smooth-walled perforated pipe at leJISl4 inches in diameter should be placed in the bottom of the trench, surrounded with at least 6 inches washed rock or pea gravel and wrapped with a nonwoven geotextile fabric such as Mirafi l40N. We recommend that pavement surfaces be sloped away from the building area to route drainage away from foundations and floor slabs and toward the storm drain system. Drainage of the pavement base course and subbase will decrease the risk of pavement distress. Small holes can be provided in that portion of catch basins adjacent to the subbase or base layer, provided that the expected water level within the catch basin will always be below the elevation of the holes. The holes should be covered with a suitable geotextile fabric placed against the outside of the catch basin to prevent piping of the subbase or base material into the catch basin. USE OF TIDS REPORT We have prepared this report for use by Alex Cugini. The data and report should be provided to prospective contractors for their bidding or estimating purposes, but our report, conclusions and interpretations should not be construed as a warranty of the subsurface conditions. If there are changes in the grades, locations, configurations or types of the facilities planned, the conclusions and recommendations presented in this report may not be applicable. If design changes are made, we request that we be given the opportunity to review our conclusions and recommendations and to provide a written modification or verification. When the design has been finalized, we recommend that the final design and specifications be reviewed by our finn to see that our recommendations have been interpreted and implemented as intended. There are possible variations in subsurface conditions between the explorations and also with time. A contingency for unexpected conditions should be included in thc budget and schedule. Sufficient observation, testing and consultation by our firm should be provided during construction to evaluate whether the conditions encountered are consistent with those indicated by the explorations, to provide recommendations for design changes should the conditions encountered during the work differ from those anticipated, and to evaluate whether or not earthwork and foundation installation activities comply with contract plans and specifications and our recommendations. Icicle Creek Engineers 0336004/012609 Alex Cugini c/o Jamie Schroeder, P.E. CPR Consultants, LLC January 26,2009 Page 14 Within the limitations of scope, schedule and budget, our services have been executed in accordance with generally accepted practices in this area at the time the report was prepared. No warranty or other conditions, express or implied, should be understood . .......... **.** ••• ****** We trust this report meets your present needs. If you have any questions or if we can be of further assistance to you, please call. Document!D: 0336004.REP Attachments: Vicinity Map -Figure 1 Site Plan -Fig\lre 2 Inc. R. Beaman, P.E., L.G. Principal Engineer/Geologist ~~:.~ Principal Engineering Geologist High Coal Mine Hazard Reclamation Plan (Parking Area) -Figure 3 High Coal Mine Hazard Reclamation Plan (Stannwal ... Vault) -Figure 4 Soil Classification System -Figure 5 Test Pit Logs -Figures 6, 7 and 8 Moisture Content Results -Figure 9 Eight copies submitted Icicle Creek Engineers 0336004/012609 FIGURES Icicle Creek Engineers .03360041012609 N o 2,000 4,000 i i i Scale in Feel ~ ~ Icicle Creek Engineers Vicinity Map -Figure 1 ICE Ale No. 0336-004 5> ,---::;:,== ; ,-c·~ .... ,,·,~ ./:!-f;;i $t.SE 172nd Street ~~~~~;-~.;~ ----.• '"[ .... ~ . ~"(5I . '?O(l; '&6': 7.s Explanation ta-TP-1 Test Pit Location .{ ~-1 • o Boring Location (ICE previous slu<!y -March 2004) High Coal Mine Hazard Area (tonner mine opening; ICE pmoiou. study -March 2004) 100 200 -"-~'''' ";:'.,j~-" 'i/:"o ~ ""'.,.(3:. '"~~0--~/ " ',,- BRB:Ol!16109 N .,---- Family Circle Learning Center (child care facility) -1 ~ / 0iv ;,0 ~ .J,.'lJ"'~ ---~,,~ .~ ~V'-~·. ~ lOt::' ~::i' .'!:.' , ~ ""'" ..• --~7":~ !II)....K,atC / ,:5/ -' / ! ~ ," I: -Base map provided by Bayliss Architects, undated Approximate Scale in Feet Icicle Creek Engineers Site Plan -Figure 2 ~r--------------------------------------------------------------------------------------------' § ~ ~ OJ I i .I :; ::> o rJ) N_: 1) Not fofCons"'I<;tioo 2) The lIChematle may be used for planning purposes but the actuel dimensions and rnalerlals used in redam8tlon may vary from that shOwn. 3) COF = Corrtro'led Densl1y Fill o 5 to , Approximate Scale in Feet ~ Icicle Creek Engineers Schematic Mine Hazard Reclamation Plan for Parking Area +-Sruc!ural Fill--+ n' , Limit of Excavation . ;' (may vary -to be evaluated '_'o' at the time of construction) <:'~;';:~?»/;, >}~:, ~~ ~'i:: ':~ ~: ';;,:),: " " ,'" Older Filled Mine Tunnel '.: '),. , ' ,', ',':;',~ (condition may vary -to be evaluated :,: , :',<,: y{. at the time of construction) , ,1:-' " DWeathered Glacial TIll D Older Fill (mine opening) [}:-t'S] Unweathered Glacial Till ~ Bedrock (Renton formation) High Coal Mine Hazard Reclamation Plan (Parking Area) -Figure 3 ~~-------------------------------------------------------------------------------------. I Schematic Mine Hazard Reclamation Plan for Stormwater Vault B m lli ,:;-. ;:);;.:,0'· :"l£I'*-(:;oF -Single Lilt·--+~· Noles: 1) Not for Construction 2) The ac::hematJc may be used for ptaMing purposes but the actuaf dimensions end materiels ulSed in reclamation may vary from that snown. 3) CDF -Controlled Den.1ty FYI o 5 10 :fi Approximate Scale in Feet " § Icicle Creek Engineers D Weathered Glacial Till D Older Fill (mine opening) r?2~.:~il Unweathered Glaciallill ~ Bedrock (Renton formation) High Coal Mine Hazard Reclamation Plan (Stonnwater Vault) -Figure 4 Coarse- Grained Soils Unified Soil Classification System --~ --~~-. --Soii Classification and MAJOR DIVISIONS Generalized Group Description ---r ----.~ --1--------------- GRAVEL iCLEANGRAVEL! GW I~ WeU-gra~:<l~vels~ . More than 50% 1 GP I Poorly-graded gravel~ 'o~:~;z~n G~il~~ITH i ~ill ~~~:::::::~;;-i SAND ~I SW WeU~g .. dcd sand j CLEAN SAND SPJI I More than 50% _ Poorly-graded ~a~ i More than 50% of coarse fnwtion SAND WITH SM _~~~ siltmix~ __ ~ ;:~~~~~ ___ ;~~i~___ FINES SC Sandandelaymixtures .1 G':!~:~ SILT AND CLAY INORGANIC ML Low;>lasticity s~_ -~ -1 CL Low-plasticity clays I Soils liquid Limit ORGANIC Ot. -~slcity organiCSiltS less than SO and organic clays I t I SILT AND CLAY MH HIgh-plastiCIty Slits INORGANIC ---I i More than 50% --~-d ~H Htgh.plasticity cla~ - -. 1 ~S~~gs~e I g~:d~:~~ ORGANIC OU :r-~::~~y~C Silts I H~~~~lCS(H'~l_~~~·nL~~~~wt;orgamCOdor !!~ _______ J Nota: I) Soil clJI,uifieation bmcdDn viaual dsuification of soil in peni1 a«9rdanccwithASTM 02488-00. 2) Soill:laslfitalioo. VIIinS Illbort1lQ1y lcals is baxd on ASTM 02487-00. 3)DcscriptklnofloildmlsityorcOll.istCDC)'ist:.-loninterprellllionofblowo;ouoldal'UI~0fk:atdata. SoU Particle Size Definitions Soil Moisture Modifiers Soil Moisture Descriptigon '-D-ry-------~·-A-~-e-~-e-o-fm--o~e Moist Damp, but ro visible~waler Wet Visible water '------'-~-- Icicle Creek Engineers Component Boulders Cobbles Grave] Coarse Fine S.nd Medium Fine Silt and Clay Size futngo I Greater than 12 inch 3 i~h to 12 inch 3 inch to No.4 (4,78 mm) 3 inch to 3/4 inch 3/4 inch to No.4 (4.78 mm) No.4 (4.78 rom) 10 No. 200 i (0.074oun) t No.4 (4.78 mm) 10 No. 10 ' (2.0mm) No. 10 (2.0 mm) 10 No. 40 (0.42 nun) No. 40 (0.42 nun) to No. 200 (0.074 nun) Less lItan No. 200 (0.074 nnn) Soil Classification System -Figure 5 Depth Soil Group Test Pit Description (3) ([eet)(1) Symbol (2) Test PitTP-\ Apl'IOximale Ground Surface Elevation: 400 Feet 0.0 -1.0 Forest duff and topsoil 1.0 -3.0 SM Brown silty fine to medium SAND with occasional gravel and abundant organics and fine roots (loose, moist) (weathered glacial till) 3.0 -4.5 SM Mottled gray and brown silty fine to medium SAND with occasional gravel (medium dense, moist) (weathered glacial till) 4.5 -9.0 SM Gray silty fine to medium SAND with occasional gravel (dense to very dense, moist) (glacial till) Test pit compleled a19.0 reet on 12116/08 Disturbed soil samples obtained at 0.5, 2.5 4.0 and 8.0 feet No ground water seepage observed No caving aftest pit wall observed Test Pit TP-2 Approximate Ground SUrface Elevation: 389 Feet 0.0 -1.0 Forest duff and topsoil 1.0 -3.0 SM Mottled gray and brown silly fine to medium SAND with a trace of gravel (medium dense, moist) (weathered glaciaJ till) 3.0 -10.0 SM Gray silty fine to medium SAND with a trace of gravel (dense to very dense, moist) (glacial till) Test pit completed at 10.0 feet on 12116108 Disturbed soil samples obtained at 2.5 and 5.0 feet No ground water seepage obselved No caving oftest pil wall observed TestPItTP~ AIlD'roX"ih!ateQroiJnd SUiiaU'Efevation: 387. Feet . 0.0 -1.0 Forest duff and topsoil 1.0 -3.5 SM Mottled gray and brown silty fine to medium SAND with a trace of gravel and fine toots (medium dense, moist) (wealhered glacial till) 3.5·10.0 SM Gray silty fine to medium SAND with. trace of gravel and cobbles (dense to very dense, moist) (glacial till) Test pit completed at 10.0 feet on 12/16/08 because of practical digging refusal Disturbed soil samples obtained at 6.0 and 8.5 feel No ground water seepage observed No caving of tesl pit wall observed t .. t PItTP-4 A~~mate·OroundSurt';"'·Elevation: 363 Feel 0.0·1.5 Forest duff and topsoil 1.5 -4.5 SM Mottled gray and brown silty fine to medium SAND with a trace of gravel (1oose to medium dense, weI to moist) (weathered glacial till) 4.5·10.0 SM Gray silty fine to medium SAND with a Irace of gravel and cobbles (medium dense to dense, moisl) (glaciallill) Test pit completed at 10.0 feet on 12/16/08 Disturbed soil sample obtained at 7.0 feet Rapid ground water seepage observed al 1.5 feet Severe caving ofnoMh test pit wall observed above about 2 reet Page I of3 0336-0041012609 Icicle Creek Engineers Test Pit Logs -Figure 6 Depth Soil Group Test Pit Description (3) (feet) (I) Symbol (2) Test Pit TP-5 Approximate Ground Surface Elevation: 380 Feet 0.0-0.8 Forest duff and topsoil 0.8 -2.0 SM Mottled gray and brown silty fine to lnedium SAND with a trace ofgravei (medium dense, moist) (weathered glacial till) 2.0-6.0 SM Gray silty fine to medium SAND wilh a Irace of gravel and cobbles (dense 10 very dense, moist) (glaciallill) Test pil completed at 6.0 feet on 12/16/08 because ofpraclical digging refusal Dislurbed soil sample obtained at 4.0 feet No ground water seepage observed No caving oftesl pil wall observed TestPitTP-6 AJ,,,RiXiniate:Orouili!SufraceEleilation: 390 Feet 0.0 -1.0 Foresl duff and topsoil 1.0-2.0 SM Brown silty fine to medium SAND with a trace gravel and abundant organics and fine rools (loose, moist) (weathered glaciallill) 2.0-3.0 SM Mottled gray and brown silly fine to medium SAND wilh alrace of gravel (medium dense, moisl) (weathered glaciallill) 3.0 -10.0 SM Gray silty tine to medium SAND wilh a trace of gravel (dense 10 very dense, moisl) (glacial till) Grades to occasion.l gravellUld cobbles .1 8 feel Test pil completed at to.O reel on 12116/08 Disturbed soil samples obtained at 1.5 and 2.5 feet No ground water seepage observed No caving oflesl pil w.1I observed Test Pit TP.'f':, _ ...... ...,~ '. ,'A~"Mte""1iiilIlWJ.Stt'_JroVimoil:",388·FeeL .. - 0.0-0.5 Pores! duff and topsoil 0.5·1.5 SM Brown silty fine to medium SAND with occasional gravel and abundant org.nics and fine moll! (loose, moist) (weathered glaciallill) 1.S·4.0 SM Mottled gray and brown silty fine 10 medium SAND with occasion.1 gravel (medium dense, moist) (weathered glacial till) 1.5 -to.O SM Gray silty fine 10 medium SAND with occasional gravel and cobbles (dense to very dense, moisl) (glaciallill) Tesl pit completed at 10.0 feet on 1211 6108 No ground water seepage observed No caving of tesl pil wall observed Test pitTP-8::'~ -.',""""", )'~1i-ro\l'M~~~~:;''38i~~" .. ---. 0.0-1.0 Forest duff and lopsoil 1.0-4.0 SM Mottled gray and brown silty fine to medium SAND with occasional gravel (medium dense, moist) (weathered glaciallill) 4.0-6.0 SM Gray silty fine to medium SAND with occasional gravel and cobbles (dense, moist) (glaciallill) Test pit completed at 6.0 feet on 12116108 No ground water seepage observed No caving of test pil wall observed Page 2 of3 0336-0041012609 Icicle Creek Engineers Test Pit Logs -Figure 7 Depth Soil Group Test Pit Description (3) (feet) (1) Symbol (2) Test Pit TP-9 Approximate Ground Surface Elevation: 376 Feel' 0,0 -0,8 Forest duff and topsoil 0.8 -15,0 8M Brown silty fine to medium SAND with a trace of gravel and cobbles and abund."t wood debris (loose to medium dense, dry to moist) (fill) Test pit completed at 15.0 feet on 04110103 Disturbed soil sample obtained at 4.0 feet No ground water seepage observed No caving of test p_~t walls observed Page 3 00 0336-0041012609 Icicle Creek Engineers Test Pit Logs -Figure 8 Test Pit Sample Sample Moisture Number Number Depth (feet) Content(%) TP-1 S-1 0.5 44 S-2 2.5 15 S-3 4.0 11 S-4 8.0 12 TP-2 S-l 2.5 10 S-2 S.O 8 TP-3 S-1 6.0 9 S-2 8.S 9 TP-4 S-l 7.0 8 TP-S S-1 8.0 12 TP-6 S-l 1.5 19 S-2 2.5 12 TP-9 S-l 4.0 7 0336004/012609 Icicle Creek Engineers Moisture Content Results -Figure 9 D.R. STRONG CONSULTING ENGINEERS Preliminary Technical Information Report (TIR) for AVANA RIDGE PUD 17249 Benson Road Sand 10615 SE 172"d Street Renton, Washington DRS Project No. Renton File No. 15088 PRE15-000611 Owner/Applicant Avana Ridge, LLC 9725 SE 36th Street, Suite 214 Mercer Island, Washington 98040 Report Prepared by -D. R. STRONG Consulting Engineers, Inc. 620 7'h Avenue Kirkland W A 98033. (425) 827-3063 © 2015 D. R. STRONG Consulting Engineers Inc. Report .Issue Date December 28, 2015 PRELIMINARY TECHNICAL INFORMATION REPORT AVANA RIDGE TABLE OF CONTENTS SECTION I .......................................................•••••..••••..••••...•.••..•••...•................................•••..•••...••••..•••••...... 1 PROJECT OVERViEW: ............................................................................................................................ 1 PREDEVELOPED SITE CONDITIONS: ................................................................................................... 1 DEVELOPED SITE CONDITIONS: ........................................................................................................... 1 NATURAL DRAINAGE SYSTEM FUNCTIONS: ....................................................................................... 3 FIGURE 1. TlR WORKSHEET.. .......................................................................................................... 4 FIGURE 2. VICINITY MAP .................................................................................................................. 9 FIGURE 3. DRAINAGE BASINS, SUBBASINS, AND SITE CHARACTERiSTICS ........................... 10 FIGURE 4. SOILS ............................................................................................................................. 11 SECTION II .....................................•..••••..••••...••••..••.•.................................•......••••..••••..•••••..•..•...•....•.•........ 14 CONDITIONS AND REQUIREMENTS SUMMARy ............................................................................... 14 SECTION III .••••..••••.............................••..••••..•••••..•••••..•••...••......•..............................•.................................. 16 OFF·SITE ANALYSIS ............................................................................................................................. 16 SECTION IV .•....••••..•.••...•••..•••••..••••..••••....•...................•...........•.................................................•................ 17 FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN .................................. 17 EXISTING SITE HYDROLOGY .............................................................................................................. 17 FIGURE 5. PREDEVELOPMENT AREA MAP .................................................................................. 18 DEVELOPED SITE HYDROLOGY ......................................................................................................... 19 BYPASS AREA HYDROLOGY ............................................................................................................... 20 FIGURE 6. POST DEVELOPMENT AREA MAP ............................................................................... 21 PERFORMANCE STANDARDS ............................................................................................................. 22 FLOW CONTROL SYSTEM ................................................................................................................... 22 FIGURE 7. DETENTION & WA TER QUALITY FACILITY DETAILS ................................................ 28 SECTION V •.....•.....•...........•...............................•...................•.........•.....•••••..•••••.••••...••••..•••••...........•.......... 29 CONVEYANCE SYSTEM ANALYSIS AND DESIGN .............................................................................. 29 SECTION Vi .............................•......•......•....•••..•••••..••••..••.••..••••..•.••...........................••.....•..•...•••..••••...•••••..• 30 SPECIAL REPORTS AND STUDIES ...................................................................................................... 30 SECTION VII ...................................••...•.•..•••••..•••••..•••....................................•.....•..................•................... 31 OTHER PERMITS, VARIANCES AND ADJUSTMENTS ........................................................................ 31 SECTION VIII .............................................................................................................................................. 32 ESC AND CSWPPP ANALYSIS AND DESIGN ...................................................................................... 32 SECTION IX ................................................................................................................................................ 33 BOND QUANTITIES, FACILITY SUMMARIES, AND DECLARATION OF COVENANT ........................ 33 STORMWATER FACILITY SUMMARY SHEET ..................................................................................... 34 SECTION X ................................................................................................................................................. 35 OPERATIONS AND MAINTENANCE MANUAL ..................................................................................... 35 APPENDIX A ............................................................................................................................................... 36 © 2015 D. R. STRONG Consulting Engineers Inc. Technical Information Report Avana Ridge Renton, Washington SECTION I PROJECT OVERVIEW: The applicant is seeking approval to construct 74 apartment units, surface parking, and amenities on 3.78 acres (Parcel Numbers 292305900 and 292309148) (Project). The Project is located at 17249 Benson Road S in Renton, Washington. PREDEVELOPED SITE CONDITIONS: Total site area is approximately 164,828 s.f. (3.78 acres) (Site). The Parcels are currently undeveloped and are heavily forested with moderate underbrush. The predeveloped Site is contained within one Threshold Discharge Area (TDA). The TDA has two Natural Discharge Areas (NDAs), NDA 1 and NDA 2. Runoff from NDA 1 discharges at the Site's western property line (south of NDA 2) and heads north through the conveyance system in Benson Drive S, where it meets NDA 2. NDA 2 discharges across the western property line (north of NDA 1). Flow from both NDAs eventually crosses under Benson Road S in a westerly direction. Runoff outlets into a ditch between parcels 2923059150 and 2923059134, flowing west. Before reaching Cedar Ave S, flow is conveyed into a system of pipes and catch basins and continues west along S 36 th Street. Runoff is conveyed south between parcels 1441000150 and 1441000170 before moving west -parallel to S 36 th Street along the south side of the parcels. Runoff crosses under Wells Ave Sand outfalls into parcel 144100TRCT - a tract for an adjacent development. Based on available topography, runoff sheet flows west through the tract into another tract (810630TRCT). Runoff appears to continue into a pond in parcel 8106301170. Overflow from the pond travels southwest to Morris Ave S, where it continues south. Runoff continues south, crossing under S 38 th Ct and eventually outfalling into Panther Creek. Panther Creek flows north and eventually becomes a tributary for Black River and the Duwamish River. DEVELOPED SITE CONDITIONS: The applicant is seeking approval to construct a 74-unit apartment complex on 3.78 acres (Project). The developable area (Project Area) is approximately 159,574 s.f. (3.64 acres) (excludes right-of-way dedication area and area of the identified stream from the gross Site area). A total of 66,438 S.F. of impervious area is proposed for the Site - which is less than 75 percent of total Site Area (123,620 S.F.). The remainder of the Project Area will consist of residential landscaping and other pervious surfaces. Per Section 5.2.1 of the 2009 King County Surface Water Design Manual (Manual), projects are required to mitigate for impervious surface by use of Flow Control Best Management Practices (BMP's). The Project falls within the "Large Lot High Impervious" category, as the proposed impervious is approximately 40% of the total Site area and the total project area is larger than 22,000 SF. However, to meet the intent of the Manual, we have analyzed the impervious surface percentage based upon the developable area as approximately one acre of the site is encumbered by sensitive areas. With 1.53 acres of the 2.64 acres of developable area categorized as impervious (58%), it would be prudent to analyze the Project as "Large Lot High © 2015 D. R. STRONG Consulting Engineers Inc. Technical Information Report Avana Ridge Renton, Washington Impervious". For projects that will result in an impervious surface coverage of more than 45% up to 65%, flow control BMPs must be applied to an impervious area equal to at least 20% of the Site area or 40% of the target impervious surface, whichever is less. Projects are required to first analyze the feasibility of dispersal and infiltration before choosing another method. The soils investigation summarized by the project geotechnical report are confined to the upper layers (up to 12 feet deep) of Site soils. That report indicates the presence of glacial till not conducive to infiltration. Further investigation may be conducted to assess infiltration capacity of deeper soils. Until further evaluation occurs, alternative BMPs must be considered. The presence of a stream and buffers provide an opportunity to fully disperse runoff from a portion of the Site. In other areas, rain gardens, Native Growth Retention Credit and dry wells are also possible Flow Control BMP's that may be utilized. These options will be further analyzed at the time of engineering plan review. The Project is located within a Conservation Flow Control and Basic Water Quality Area. However due to the fact that the Project is a multifamily development, it shall be required to adhere to the Enhanced Water Quality Treatment criteria. Runoff will be collected and conveyed to a wet vault at the west end of the Site. The vault will be followed by a media filtration system to accommodate the Enhanced Water Quality Treatment requirements. Preliminary sizing is shown on the engineering plans and final sizing will be performed at the time of engineering plan review. © 2015 D. R. STRONG Consul1ing Engineers Inc. Technical Information Report 2 Avana Ridge Renton, Washington NATURAL DRAINAGE SYSTEM FUNCTIONS: A portion of the Natural Resource Conservation Service (NRCS) soil survey of King County is included as Figure 4 and indicates the presence of Alderwood gravelly sandy loam with 8 to 15 percent slopes (AgC). Per the 2009 King County Surface Water Design Manual, this soil type is classified as "Till" material. The Natural Re Soil series descriptions follow Figure 4. The upstream basin area was evaluated by examining the King County topographic map, City of Renton Mapping Application and by conducting field reconnaissance on December 15, 2015 under overcast conditions. Upstream runoff enters the Site in two locations. Portions of SE 172nd St and 106th Ave SE direct upstream runoff across the northern property line. Runoff from 106th Ave SE and the north side of SE 172 nd Sl. enters a Type 1 catch basin at the intersection of these two streets. An 18-inch diameter concrete pipe conveys runoff south under SE 172nd Sl. and outfalls onto the Site. Runoff from the southern portion of SE 172nd St is intercepted by a ditch along the south side of SE 172nd Sl. and enters the Site where the previously mentioned 18-inch diameter concrete pipe outlets. Upstream runoff from the west side of Benson Rd S flows west into a ditch along the east property line. This ditch conveys upstream runoff southwest along the east property line until it enters a stream about halfway down the property line. This stream conveys water through the Site. The Project proposes to construct a conveyance system to collect runoff from these two upstream tributary areas and bypass the infiltration facility on Site. © 2015 D. R. STRONG Consulting Engineers Inc. Technical Information Report Avana Ridge Renton, Washington I , FIGURE 1. TIR WORKSHEET King County Department of Development and Environmental Services TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 1 PROJECT OWNER AND PROJECT ENGINEER Project Owner: Avana Ridge, LLC Phone: (425) 588-1147 Address: 9675 SE 36th Street, Suite 105 Mercer Island, WA 98040 Project Engineer: Toby Coenen, P.E. Company: D. R. STRONG Consulting Phone: Engineers Inc. (425) 827-3063 Part 3 TYPE OF PERMIT APPLICATION I2J Landuse Services Subdivision! Short Subd. PUD D Building Services M!F ! Commercial! SFR D Clearing and Grading D Right·of-Way D Other: ___________ _ Part 5 PLAN AND REPORT INFORMATION Technical Information Report Drainage Review Type ~ ! Targeted! Large (circle one): Site Date (include revision December 29, 2015 dates): Date of Final: Part 6 ADJUSTMENT APPROVALS Part 2 PROJECT LOCATION AND DESCRIPTION Project Name: DDES Permit#: Location: Township: Range: Section: Site Address: Avana Ridge N!A 23 North 05 East 29 17249 Benson Road S 10615 SE 172nd Street Renton, Washington Part 4 OTHER REVIEWS AND PERMITS I2J DFW HPA D Shoreline Management D COE404 I2J Structural D DOE Dam Safety RockeryNaultlWall D FEMA Floodplain D ESA Section 7 D COE Wetlands D Other: Site Improvement Plan (En gr. Plans) Type ~! Targeted! Small (circle one): Site Date (include revision December 29,2015 dates): Date of Final: Type (circle one): Standard! Complex ! Preapplication ! Experimental ! Blanket Description: (include conditions in TIR Section 2) Date of Approval: © 2015 D. R. STRONG Consulting Engineers Inc. Technical Information Report 4 Avana Ridge Renton, Washington Part 7 MONITORING REQUIREMENTS Monitoring Required: Yes/~ Describe: Start Date: Completion Date Part 8 SITE COMMUNITY AND DRAINAGE BASIN Community Plan: "S"'o""o"'-s-'C!!.r"'ee"'k"----____________________ _ Special District Overlays: ~N!L!!Al-___________________ _ Drainage Basin: Black River, Panther Creek Sub-Basin Stormwater Requirements: Conservation Flow Control, Enhanced WQ Treatment Menu Part 9 ONSITE AND ADJACENT SENSITIVE AREAS o River! Stream Unnamed T)1l2e Ns stream D Steep Slope D Lake D Wetlands: D Closed Depression D Floodplain D Other Part 10 SOILS Soil Type AGC IZI High Groundwater Table (within 5 feet) IZI other Low infiltration rate D Additional Sheets Attached © 2015 D. R. STRONG Consulting Engineers Inc. Technical Information Report D Erosion Hazard D Landslide Hazard IZI Coal Mine Hazard (High} D Seismic Hazard D Habitat Protection Slopes Erosion Potential 8-15% Slight to Moderate IZI Sole Source Aquifer IZI Seeps/Springs Avana Ridge Renton, Washington Part 11 DRAINAGE DESIGN LIMITATIONS REFERENCE LIMITATION I SITE CONSTRAINT D Core 2 -Offsite Analysis None ~ Sensitive I Critical Area Stream and associated buffers through Site ~ SEPA T/B/D D Other Additional Sheet attached Part 12 TIR SUMMARY SHEET (provide one TIR Summary Sheet per Threshold Discharge Area) Threshold Discharge Area: (name or description) Core Requirements (all 8 apply) Discharge of Natural Location ~ Offsite Analysis Flow Control (incl. facility summary sheet Conveyance System Erosion and Sediment Control Maintenance and Operation Financial Guarantees and Liability Water Quality (include facility summary sheet) Special Requirements (as applicable) Area Specific Drainage Requirements Floodplain/Floodway Delineation Flood Protection Facilities Source Control (comm. I industriallanduse) Oil Control Other Drainage Structures Describe: © 2015 D. R. STRONG Consulting Engineers Inc. Technical Information Report Site com!;!rised of single, unnamed TDA Number of Natural Discharge Locations: 2 Level: 112 I 3 dated: 12/15/2015 Level: 1 I g 13 or Exemption Number Small Site BMPS N/A Spill containment located at: Detention facilities ESC Site Supervisor: T/B/D Contact Phone: T/B/D After Hours Phone: T/B/D Responsibility: Private I Public (Both) If Private, Maintenance Log Required: Yes I No Provided: Yes I No Type: Basic I Sens Lake I Enhanced Basic I Bog or exemption No. Landscape Management Plan: Yes I No Type: CDA I SDO I MOP I BP I LMP I Shared I None Name: Type: Major I Minor I Exemption I None 1 ~O-year Base Flood Elevation (or range): Datum: Describe: N/A Describe Landuse: Multi Family Describe any structural controls: covered trash storage, High-use Site: Yes I No Treatment BMP: Maintenance Agreement: Yes I No with whom? N/A Avana Ridge Renton, Washington Part 13 EROSION AND SEDIMENT CONTROL REQUIREMENTS MINIMUM ESC REQUIREMENTS MINIMUM ESC REQUIREMENTS DURING CONSTRUCTION AFTER CONSTRUCTION I2l Clearing Limits I2l Stabilize Exposed Surfaces I2l Remove and Restore Temporary ESC I2l Cover Measures Facilities I2l Perimeter Protection I2l Clean and Remove All Silt and Debris, I2l Traffic Area Stabilization Ensure Operations of Permanent Facilities I2l Sediment Retention 0 Flag Limits of SAO and open space I2l Surface Water Collection Preservation areas 0 Other I2l Dewatering Control I2l Dust control I2l Flow Control Part 14 STORMWATER FACILITY DESCRIPTIONS (Note: Include Facility Summary and Sketch Flow Control Type/Description I2l Detention Vault o Infiltration o Regional Facility o Shared Facility I2l Flow Control Dis!;!ersion, Drll well BMPs o Other Part 15 EASEMENTSITRACTS I2l Drainage Easement 0 Covenant I2l Native Growth Protection Covenant D Tract D Other: © 2015 D. R. STRONG Consulting Engineers Inc. Technical Information Report Water Quality Type/Description o Biofiltration I2l Wetpool Wet vault I2l Media Filtration Contech Storm Filter o Oil Control o Spill Control I2l Flow Control See flow control BMPs o Other Part 16 STRUCTURAL ANALYSIS I2l I2l 0 0 0 Cast in Place Vault Retaining Wall Rockery > 4' High Structural on Steep Slope Other: Avana Ridge Renton, Washington Part 13 SIGNATURE OF PROFESSIONAL ENGINEER I or a civil engineer under my supervision have visited the site. Actual site conditions as observed were incorporated into this worksheet and the attachments. To the best of my knowledge the information provided here is accurate. ~~ © 2015 D. R. STRONG Consul1ing Engineers Inc. Technical Information Report Signed/Date Avana Ridge Renton, Washington FIGURE 2. VICINITY MAP !'~~~:'K~,~~~;~~;.~,.,;~=:%~g}':'~~J;!,~~~~:~:~/I"~~~:t~;'""'" ~·f9'U"'N~"'~I'll1m1i!l(r" T1'J&c(QJ,"""1[~<Q.ne-.Joo""J .. ,,,.~.~elp;oo~ !<:YI1="" .. ~'o!"" .. '"" l'-'~i""'''''' ><>"""'1 M~ hol:Io ... 1 or"'.,..qJ .... ''''IO>'''9<'"n;;~c''' D':'>:It.,., ... ~", I>"'MI''\Je<Of~"'9''~ .. >..II,..,. ~ ~e..,.. or ,,~ .. C(,~ "",<",., .. 0, arc.",,, <r"~,,"P ""i"''''''l"~''''''' ornt.nn,ow,,,,,"p IS ",.bSd"'-:O;.lOwr_'..rn\iott!"',Q--'1Ca.. ... 1 © 2015 D. R. STRONG Consulting Engineers Inc. Technical Information Report Avana Ridge Renton, Washington FIGURE 3. DRAINAGE BASINS, SUBBASINS, AND SITE CHARACTERISTICS © 2015 D. R. STRONG Consulting Engineers Inc. Technical Information Report 10 Avana Ridge Renton, Washington ~~. '- "--- I.IJI (/) . /sYSTEM THEN OUTLETS ONTO ,'jiTE, ,:" .• r. .• ~ .• , •• ... ,'/' . .. :r-, CQL~ .. E.C .. T£D IN PITCH.v4NO>CP«VEYA,.Nix., ..... . . q; / ,"'_ :,) ,,'~1 _~_._ ' .. "_ ,./,,1., J;; ~ ~ ~ u~ f'Xjs~~G UPSTREAM RUNOFF IS ~ .. ~ ":~"~l' ~ '., --;~' SE 172ND ST :g ~c, .' . . ,::,. '" .' '.: ~~;~""1t?:: .,';; ~\,---. ,~~> I .. ,1'/, I~ .,~ ~~ ~ i ~ Iii I < ~ ~ 0 ~ DEVELOPED RUNOFF WILL BE STORED IN AN INFILTRA TlON VAULT WITH EMERGENCY OVERFLOW DISCHARGING INTO THE NORTHEASTERN CONVEYANCE SYSTEM NA ruRAL DISCHARGE POINT FOR THE SITE IS ACROSS THE K£STERN PROPERTY LINE v HIGH POINT DIRECTING RUNOFF NORTH AND flfST / '~ ,'-: ' .... :: .... I .'. I I@ NORTH GRAPHIC SCALE o 40 80 120 , , , , 1 INCH = 80 FT. ~ j::: ~ ffi " to) ~ ~ u ~ (i) ~ '0::( ~ ~ CJj ~ ~ CI) ~ ~ CI) ~ ~ ~ .... ~ t) ~ ~ ~ ~~ l!!~!;g QS):t: Et:q;(/) S:!I)~ ~9~ q;~~ §~ ~Et: ai III ~ ~ DRAFTED BY; GRD D£SICNID BY; PRO.ECT ENGINffR: esc DATE: 12.28.15 PROJECT NO.: 150M F1GUR£-UJ COPYRIGHT@2015, D.R. STRONG CONSULT1NG EN~NEERS INC. King County Area, Washington FIGURE 4. SOILS Web SO~SI.JlO'!lY National CooperalJvB So~ Surwy AgC-Alderwood gravelly sandy loam, 8 to 15 percent slopes Map Unit Setting National map unit symbol: 2t626 Elevation: 50 to 800 feet Mean annual precipitation: 20 to 60 inches Mean annual air temperature: 46 to 52 degrees F Frost-free period: 160 to 240 days Farmland classification: Prime farmland if irrigated Map Unit Composition Alderwood and similar soils: 85 percent Minor components: 15 percent Estimates are based on observations, descriptions, and transects of the mapunit. © 2015 D. R. STRONG Consulting Engineers Inc. Technical Information Report 11 P~ge 1 013 Avana Ridge Renton, Washington Description of Alderwood Setting Landform: Ridges, hills Landform position (two-dimensional): Shoulder Landform position (three-dimensional): Nose slope, tall Down-slope shape: Linear, convex Across-slope shape: Convex Parent material: Glacial drift and/or glacial outwash over dense glaciomar'lne deposits Typical profile A -0 to 7 inches: gravelly sandy loam Bw1 -7 to 21 inches: very gravelly sandy loam Bw2 -21 to 30 inches: very gravelly sandy loam Bg -30 to 35 inches: very gravelly sandy loam 2Cd1 -35 to 43 inches: very gravelly sandy loam 2Cd2 -43 to 59 inches: very gravelly sandy loam Properties and qualities Slope: 8 to 15 percent Depth to restrictive feature: 20 to 39 inches to densic material Natural drainage class: Moderately well drained Capacity of the most limiting layer to transmit water (Ksat): Very low to moderately low (0.00 to 0.06 in/hr) Depth to water table: About 18 to 37 inches Frequency of flooding: None Frequency of ponding: None Available water storage in profile: Very low (about 2.7 inches) Interpretive groups Land capability classification (irrigated): None specified Land capability classification (nonirrigated): 4s Hydrologic Soil Group: B Other vegetative classification: Limited Depth Soils (G002XN302WA), Limited Depth Soils (G002XS301WA), Limited Depth Soils (G002XF303WA) Minor Components Everett Percent of map unit: 5 percent Landform: Eskers, kames, moraines Landform position (two-dimensional): Shoulder, foots lope Landform position (three-dimensional): Crest, base slope Down-slope shape: Convex Across-slope shape: Convex Indianola Percent of map unit: 5 percent Landform: Eskers, kames, terraces Landform position (three-dimensional): Tread Down-slope shape: Linear Across-slope shape: Linear © 2015 D. R. STRONG Consulting Engineers Inc. Technical Information Report 12 Avana Ridge Renton, Washington Shalcar Norma Percent of map unit: 3 percent Landform: Depressions Landform position (three-dimensional): Dip Down-slope shape: Concave Across-slope shape: Concave Percent of map unit: 2 percent Landform: Depressions, drainageways Landform position (three-dimensional): Dip Down-slope shape: Concave, linear Across-slope shape: Concave © 2015 D. R. STRONG Consulting Engineers Inc. Technical Information Report 13 Avana Ridge Renton, Washington SECTION II CONDITIONS AND REQUIREMENTS SUMMARY The Project must comply with the following Core and Special Requirements: • C.R. #1 -Discharge at the Natural Location: Runoff from the Site will discharge at the natural location. • C.R. #2 -Offsite Analysis: An Offsite Analysis is included in Section III. The Analysis describes the Site's runoff patterns in detail. • C.R. #3 -Flow Control: The Project is located in a Conservation Flow Control Area and will therefore adhere to Level 2 Flow Control Standards, forested conditions. A combined detention/wet vault will provide flow control consistent with that standard. The Project is required to "match developed discharge durations to predeveloped durations for the range of predeveloped discharge rates from 50% of the two-year peak flow up to the full 50-year peak flow. Also match developed peak discharge rates to predeveloped peak discharge rates for the 2-and the 10-year return periods. Assum(ing) historic conditions as the predeveloped condition." (KCSWDM, Sec. 1.2) Preliminary flow control calculations were conducted at this time. Final sizing will be completed at time of final engineering. • C.R. #4 -Conveyance System: New pipe systems and ditches/channels are required to be designed with sufficient capacity to convey and contain (at minimum) the 25-year peak flow, assuming developed conditions for onsite tributary areas and existing conditions for any offsite tributary areas. Pipe system structures and ditches/channels may overtop for runoff events that exceed the 25-year design capacity, provided the overflow from a 100-year runoff event does not create or aggravate a "severe flooding problem" or "severe erosion problem" as defined in C.R. #2. Any overflow occurring onsite for runoff events up to and including the 100-year event must discharge at the natural location for the project site. In residential subdivisions, such overflow must be contained within an onsite drainage easement, tract, covenant or public right-of-way. The proposed conveyance system will be analyzed using the KCBW program to determine if the proposed conveyance system is capable of conveying the 100-year peak storm without overtopping any structures or channels. This analysis will be performed at time of construction plan preparation. • C.R. #5 -Erosion and Sediment Control: The Project provides the seven minimum ESC measures. A temporary erosion and sedimentation control plan will be prepared at time of construction plan preparation. • C.R. #6 -Maintenance and Operations: Maintenance of the proposed storm drainage facilities will be the responsibility of the City. An Operation and Maintenance Manual will be included in Section X at the time of construction plan preparation. © 2015 D. R. STRONG Consulting Engineers Inc. Technical Information Report 14 Avana Ridge Renton, Washington • C.R. #7 -Financial Guarantees: Prior to commencing construction, the Applicant must post a drainage facilities restoration and site stabilization financial guarantee. For any constructed or modified drainage facilities to be maintained and operated by the City, the Applicant must: 1) Post a drainage defect and maintenance financial guarantee for a period of two years, and 2) Maintain the drainage facilities during the two-year period following posting of the drainage defect and maintenance financial guarantee. • C.R. #8 -The Project is located in the Enhanced Water Quality Treatment area. A combined detention/wet vault will be followed by a Storm Filter media filtration system to meet water quality requirements. • S.R. #1 -Other Adopted Area-Specific Requirements: Not applicable for this Project. • S.R. #2 -Floodplain/Floodway Delineation: Not applicable for this Project. • S.R. #3 -Flood Protection Facilities: Not applicable for this Project. • S.R. #4 -Source Control: The project shall comply with the 2009 Stormwater Pollution Prevention Manual with such measures as cleaning of the storm drain system, prohibiting illicit connections to the storm drainage system and stenciling the site storm drains among other BMP's. • S.R. #5 -Oil Control: Not applicable to this project. © 2015 D. R. STRONG Consulting Engineers Inc. Technical Information Report 15 Avana Ridge Renton, Washington SECTION III OFF-SITE ANALYSIS A Level One Downstream Analysis was prepared by D.R. STRONG Consulting Engineers Inc. and is included in Appendix A. © 2015 D. R. STRONG Consulting Engineers Inc. Technical Information Report 16 Avana Ridge Renton, Washington SECTION IV FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN The continuous simulation model, the King County Runoff Time Series, KCRTS, was used to analyze the pre and post developed runoff rates. Per Table 3.2.2.b of the Manual, the soil type is modeled as 'Till" for the Alderwood gravelly sandy loam SCS classification as shown in Figure 4. Soils. Results of the KCRTS analysis are included in this section. EXISTING SITE HYDROLOGY Modeling input Pre-Developed Conditions Time Series Predev.tsf Rainfall Gage Seatac Scale Factor: 1.000 Time Step: Hourly --_.---------- Data Type: Reduced Land cover Acres Till Forest 2.870 I-- 0.000 -- Till Grass Wetland 0.000 Impervious 0.035 -- Total Area: 2.905 Modeling results Flow Frequency Analysis Time Series File:predev.tsf Project Location:Sea-Tac ---Annual Peak Flow Rates--- Flow Rate Rank Time of Peak (CFS) 0.186 2 2/09/01 18:00 0.054 7 1/05/02 16:00 0.143 4 2/28/03 3:00 0.009 8 8/26/04 2:00 0.085 6 1/05/05 8:00 0.145 3 1/18/06 20:00 0.125 5 11/24/06 4:00 0.245 1/09/08 9:00 Computed Peaks ©2015 D. R. STRONG Consulling Engineers Inc. Technical Information Report -----Flow Frequency Analysis------- - -Peaks Rank Return Prob 17 (CFS) Period 0.245 1 100.00 0.186 2 25.00 0.145 3 10.00 0.143 4 5.00 0.125 5 3.00 0.085 6 2.00 0.054 1.30 0.009 1.10 0.225 50.00 0.990 0.960 0.900 0.800 0.667 0.500 0.231 0.091 0.980 Avana Ridge Renton, Washington FIGURE 5. PREDEVELOPMENT AREA MAP ©2015 D. R. STRONG Consulting Engineers Inc. Technical Information Report 18 Avana Ridge Renton, Washington ~ ~.----. '-~ .....• "-~ ... "-•.. -'~-... "~l . " '-:'. , ' •. -. . '. '-. . :'-"'" "., , " ' '" . . . LEGEND: ~ PROJECT AREA: t:-:':-:-:-:':-:'I UPSTREAM AREA: :::::::::::::::: (IMPERVIOUS) 125,037 SF 1.509 SF. " '. '~ -"-'-- 1-; ~. f .. :~· ... ;i / .; I "'j ···.i '/'" .w ','\ ; / I@ NORTH GRAPHIC SCALE ~ ___ ~p 8,0 1~0 I ~ ~~ ~5 ~~ ~ o ~ ~ CI:i ~ -=( @ ~ Uj ~ @ 2: I lO tt! ::s Q) Li:: ~ ! ~ ill !Ij ~ : 0 ti ~ ~ .... ~ ""O~ .... f;;:. ~~~ 5:!~:t: 0::'«11) ~II)~ §~;: '«~~ ~~ 11)0:: ~ III 0) ~ .... DRAFmJ BY: Yl..P DESIGNED BY: Yl.P PRO.ECT ENGINEER; esc DATE! 12.28.15 fflO.£CT NO.: 15088 1 INCH = 80 FT. II 5 COPYRIGHT © 2015, D.R. STRONG CONSULTING ENGINEERS INC. fiGURE: DEVELOPED SITE HYDROLOGY Soil type The soil types are unchanged from pre-developed conditions. Land covers KCRTS was used to model the developed peak runoff from the Site. The portions of the Site within the proposed clearing limits tributary to the proposed detention vault were modeled as "Till Grass" and Impervious as appropriate. Results of the KCRTS analysis are included in this section. Modeling input Post-Developed Conditions Time Series Rdin.tsf Rainfall Gage Seatac Scale Factor: 1.000 Time Step: Hourly - - Data Type: Reduced Land cover Acres Till Forest 0.000 Till Grass 0.689 Wetland 0.000 Impervious 1.861 - Total Area: 2.550 Modeling results Flow Frequency Analysis Time Series File:rdin.tsf Project Location:Sea-Tac ---Annual Peak Flow Rates--- Flow Rate Rank Time of Peak (CFS) 0.513 6 2/09/01 2:00 0.429 8 1/05/02 16:00 0.614 3 2/27/03 7:00 0.476 7 8/26/04 2:00 0.571 10/28/04 16:00 0.546 5 1/18/06 16:00 0.693 2 10/26/06 0:00 1. 03 1/09/08 6:00 Computed Peaks ©2015 D. R. STRONG Consulting Engineers Inc. Technical Information Report -----Flow Frequency Analysis------- - -Peaks Rank (CFS) 1. 03 1 0.693 2 0.614 3 0.571 4 0.546 5 0.513 6 0.476 7 0.429 8 0.915 19 Return Prob Period 100.00 0.990 25.00 0.960 10.00 0.900 5.00 0.800 3.00 0.667 2.00 0.500 1. 30 0.231 1.10 0.091 50.00 0.980 Avana Ridge Renton, Washington BYPASS AREA HYDROLOGY Modeling input Bypass Area Time Series Bypass.tsf Rainfall Gage Seatac Scale Factor: 1.000 ------- Time Step: Hourly Data Type: Reduced Land cover Acres Till Forest I 0.000 - Till Grass 0.355 Wetland 0.000 Impervious 0.000 Total Area: 0.355 Modeling results Flow Frequency Analysis Time Series File:bypass.tsf Project Location:Sea-Tac ---Annual Peak Flow Rates--- Flow Rate Rank Time of Peak (CFS) 0.032 2/09/01 2:00 0.016 7 1/05/02 16:00 0.040 2 2/27/03 7:00 0.007 8 3/24/04 19:00 0.017 6 1/05/05 8:00 0.032 3 1/18/06 16:00 0.029 5 11/24/06 3:00 0.075 1 1/09/08 6:00 Computed Peaks ©2015 D. R. STRONG Consul1ing Engineers Inc. Technical Information Report -----Flow Frequency Analysis------- -Peaks Rank (CFS) 0.075 1 0.040 2 0.032 3 0.032 0.029 5 0.017 6 0.016 0.007 0.063 20 Return Prob Period 100.00 0.990 25.00 0.960 10.00 0.900 5.00 0.800 3.00 0.667 2.00 0.500 1. 30 0.231 1.10 0.091 50.00 0.980 Avana Ridge Renton, Washington FIGURE 6. POST DEVELOPMENT AREA MAP ©2015 D. R. STRONG Consulling Engineers Inc. Technical Information Report 21 Avana Ridge Renton, Washington "-... ~ ~. LEGEND: !""8 :.>:-:-:-:-:-:. ........ ................ UPSTREAM AREA: (IMPERVIOUS) 1,509 S.F. ~ LOT AREA: IMPERVIOUS: "-_""-"UL""-"'-' PERVIOUS: 85,798 SF. 60,260 SF. 25,538 SF. ~~~~~~~~~~~~~~~~~~l MITIGA TlON TRADE AREA: 6,541 S.F. IMPERVIOUS; 6,541 SF. ':~#+iil ROW AREA; IF IMPERVIOUS: ~~~~ PERVIOUS: 17,232 SF. 12.744 S.F. 4,488 SF. BYPASS AREA: 22,008 SF. IMPERVIOUS; 6,541 S.F. (MITIGA TlON TRADE AREA) PERVIOUS; 15,467 S.F. OPEN SPACE AREA; 19.795 S.F. (TO 8E FULLY DISPERSED) IMPERVIOUS: 4,685 SF. PERVIOUS: 15,110 SF. _._--- " I@ NOR.TH GRAPHIC SCALE o 40 80 120 ! ! ! ! I ~ ~~ ~5 ~~ ~ o ~ ~ ! ~ ill ! I j ~ : 0 ~ ~ ai ~ ~ ~~ ..... !;!q~ oq: ~§!~ ~ (!j!:lJ: ~ !;;;!:C::CIl Q a::~~ ~ ~~~. :s "«lE~ ~ ~\ii "'r o a:: ~ ~ ~ ~ 0;. ~ 10 .... ti! ~ Li:: DRAfTED BY: 'rlP DESIGNED BY: YLP PRO.£CT ENGINEER; esc DATE! 12.28.15 PRO.ECT NO.: 15088 1 INCH = 80 FT. FIGURE: 6 COPYRIGHT © 2015, D.R. STRONG CONSULTING ENGINEERS INC. PERFORMANCE STANDARDS The Project is located in a Conservation Flow Control Area and will therefore adhere to Level 2 Flow Control Standards, forested conditions. A detention vault will provide flow control as required. The Project is required to "match developed discharge durations to predeveloped durations for the range of predeveloped discharge rates from 50% of the two-year peak flow up to the full 50-year peak flow. Also match developed peak discharge rates to predeveloped peak discharge rates for the 2 and the 10 year return periods. Assum(ing) historic conditions as the predeveloped condition." (KCSWDM, Sec. 1.2). FLOW CONTROL SYSTEM Retention/Detention Facility Type of Facility: Facility Length: Facility Width: Facility Area: Effective Storage Depth: Stage 0 Elevation: Storage Volume: Riser Head: Riser Diameter: Number of orifices: Detention Vault 158.00 ft 30.00 ft 4740. 8.00 352.00 37920. 8.00 18.00 2 sq. ft ft ft cu. ft ft inches Full Head Pipe Orifice # Height (ft) 0.00 5.50 Diameter (in) 0.75 1. 60 Discharge Diameter 1 2 Top Notch Weir: None Outflow Rating Curve: None (CFS) (in) 0.043 0.110 4.0 Stage Elevation Storage Discharge (ft) (ft) (cu. ft) (ac-ft) (cfs) 0.00 352.00 O. 0.000 0.000 0.01 352.01 47. 0.001 0.001 0.02 352.02 95. 0.002 0.002 0.03 352.03 142. 0.003 0.003 0.04 352.04 190. 0.004 0.003 0.05 352.05 237. 0.005 0.004 0.06 352.06 284. 0.007 0.004 0.20 352.20 948. 0.022 0.007 0.33 352.33 1564. 0.036 0.009 0.47 352.47 2228. 0.051 0.010 0.60 352.60 2844. 0.065 0.012 0.74 352.74 3508. 0.081 0.013 0.88 352.88 4171. 0.096 0.014 1. 01 353.01 4787. 0.110 0.015 1.15 353.15 5451. 0.125 0.016 1. 28 353.28 6067. 0.139 0.017 1. 42 353.42 6731. 0.155 0.018 1. 55 353.55 7347. 0.169 0.019 1. 69 353.6,.9 8011. 0.184 0.020 1. 83 353.83 8674. 0.199 0.021 ©2015 D. R. STRONG Consul1ing Engineers Inc. 22 Technical Information Report Percolation (cfs) 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Avana Ridge Renton, Washington 1. 96 353.96 9290. 2.10 354.10 9954. 2.23 354.23 10570. 2.37 354.37 11234. 2.50 354.50 11850. 2.64 354.64 12514. 2.77 354.77 13130. 2.91 354.91 13793. 3.05 355.05 14457. 3.18 355.18 15073. 3.32 355.32 15737. 3.45 355.45 16353. 3.59 355.59 17017. 3.72 355.72 17633. 3.86 355.86 18296. 3.99 355.99 18913. 4.13 356.13 19576. 4.27 356.27 20240. 4.40 356.40 20856. 4.54 356.54 21520. 4.67 356.67 2213 6. 4.81 356.81 22799. 4.94 356.94 23416. 5.08 357.08 24079. 5.22 357.22 24743. 5.35 357.35 25359. 5.49 357.49 26023. 5.50 357.50 26070. 5.52 357.52 26165. 5.53 357.53 26212. 5.55 357.55 26307. 5.57 357.57 26402. 5.58 357.58 26449. 5.60 357.60 26544. 5.62 357.62 26639. 5.63 357.63 26686. 5.77 357.77 27350. 5.90 357.90 27966. 6.04 358.04 28630. 6.18 358.18 29293. 6.31 358.31 29909. 6.45 358.45 30573. 6.58 358.58 31189. 6.72 358.72 31853. 6.85 358.85 32469. 6.99 358.99 33133. 7.12 359.12 33749. 7.26 359.26 34412. 7.40 359.40 35076. 7.53 359.53 35692. 7.67 359.67 36356. 7.80 359.80 36972. 7.94 359.94 37636. 8.00 360.00 37920. 8.10 360.10 38394. 8.20 360.20 38868. ©2015 D. R. STRONG Consulting Engineers Inc. Technical Information Report 0.213 0.021 0.229 0.022 0.243 0.023 0.258 0.023 0.272 0.024 0.287 0.025 0.301 0.025 0.317 0.026 0.332 0.027 0.346 0.027 0.361 0.028 0.375 0.028 0.391 0.029 0.405 0.029 0.420 0.030 0.434 0.030 0.449 0.031 0.465 0.032 0.479 0.032 0.494 0.032 0.508 0.033 0.523 0.033 0.538 0.034 0.553 0.034 0.568 0.035 0.582 0.035 0.597 0.036 0.598 0.036 0.601 0.036 0.602 0.038 0.604 0.041 0.606 0.044 0.607 0.049 0.609 0.055 0.612 0.060 0.613 0.062 0.628 0.073 0.642 0.081 0.657 0.089 0.672 0.095 0.687 0.101 0.702 0.106 0.716 0.111 0.731 0.116 0.745 0.121 0.761 0.125 0.775 0.129 0.790 0.133 0.805 0.137 0.819 0.141 0.835 0.144 0.849 0.148 0.864 0.151 0.871 0.153 0.881 0.617 0.892 1. 460 23 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Avana Ridge Renton, Washington 8.30 360.30 39342. 0.903 2.560 0.00 8.40 360.40 39816. 0.914 3.860 0.00 8.50 360.50 40290. 0.925 5.330 0.00 8.60 360.60 40764. 0.936 6.760 0.00 8.70 360.70 41238. 0.947 7.290 0.00 8.80 360.80 41712. 0.958 7.780 0.00 8.90 360.90 42186. 0.968 8.250 0.00 9.00 361.00 42660. 0.979 8.690 0.00 9.10 361.10 43134. 0.990 9.100 0.00 9.20 361.20 43608. 1.001 9.500 0.00 9.30 361.30 44082. 1. 012 9.880 0.00 9.40 361.40 44556. 1. 023 10.250 0.00 9.50 361.50 45030. 1.034 10.610 0.00 9.60 361.60 45504. 1. 045 10.950 0.00 9.70 361. 70 45978. 1. 056 11.280 0.00 9.80 361.80 46452. 1. 066 11.610 0.00 9.90 361.90 46926. 1.077 11.920 0.00 Hyd Inflow Outflow Peak Storage Stage Elev (Cu-Ft) (Ac-Ft) 1 1. 03 0.30 8.03 360.03 3S073. 0.S74 2 0.51 0.15 7.72 359.72 36616. 0.841 3 0.61 0.13 7.04 359.04 33377. 0.766 4 0.69 0.11 6.60 358.60 31304. 0.719 5 0.55 0.04 5.43 357.43 25738. 0.591 6 0.37 0.03 4.73 356.73 22443. 0.515 0.43 0.03 4.70 356.70 22287. 0.512 0.48 0.03 3.13 355.13 14830. 0.340 Hyd R/D Facility Tributary Reservoir POC Outflow Outflow Inflow Inflow 1 0.30 O.OS ******** 2 0.15 0.03 ******** 3 0.13 0.04 ******** 4 0.11 0.03 ******** 5 0.04 0.03 ******** 6 0.03 0.02 ******** 7 0.03 0.02 ******** 8 0.03 0.01 ******** Route Time Series through Facility Inflow Time Series File:rdin.tsf Outflow Time Series File:rdout poe Time Series File:dsout Inflow/Outflow Analysis Peak Inflow Discharge: Peak Outflow Discharge: Peak Reservoir Stage: Peak Reservoir Elev: 1. 03 CFS 0.303 CFS 8.03 Ft 360.03 Ft Target 0.19 ******* ******* ******* at 6:00 at 11: 00 Peak Reservoir Storage: 38073 . Cu-Ft 0.874 Ac-Ft on on Calc 0.33 0.17 0.14 0.13 0.06 0.05 0.04 0.03 Jan Jan 9 in 9 in Year 8 Year 8 Add Time Series:bypass.tsf Peak Summed Discharge: 0.326 CFS at 11:00 on Jan 9 in Year 8 ©2015 D. R. STRONG Consulting Engineers Inc. Technical Information Report 24 Avana Ridge Renton, Washington Point of Compliance File:dsout.tsf Flow Frequency Analysis Time Series File:rdout.tsf Project Location:Sea-Tac ---Annual Peak Flow Rates--- Flow Rate Rank Time of Peak (CFS) 0.146 2 2/09/01 20:00 0.033 7 1/07/02 4:00 0.127 3 3/06/03 22:00 0.027 8 8/26/04 8:00 0.033 6 1/08/05 5:00 0.036 5 1/19/06 5:00 0.112 11/24/06 8:00 0.303 1/09/08 11: 00 Computed Peaks Flow Frequency Analysis Time Series File:dsout.tsf Project Location:Sea-Tac ---Annual Flow Rate (CFS) o .l70 0.044 0.144 0.031 0.046 0.062 0.132 0.326 Peak Flow Rates--- Rank Time of Peak 2 7 3 8 6 5 4 1 2/09/01 1/05/02 3/06/03 8/26/04 1/05/05 1/18/06 11/24/06 1/09/08 20:00 16:00 22:00 2:00 8:00 16:00 7:00 11: 00 Computed Peaks -----Flow Frequency Analysis------- --Peaks - -Rank Return Prob (CFS) (ft) Period 0.303 8.03 100.00 0.990 0.146 7.73 2 25.00 0.960 0.127 7.04 3 10.00 0.900 0.112 6.60 4 5.00 0.800 0.036 5.43 5 3.00 0.667 0.033 4.74 6 2.00 0.500 0.033 4.70 7 l. 30 0.231 0.027 3.13 8 l.10 0.091 0.251 8.02 50.00 0.980 -----Flow Frequency Analysis------- -Peaks (CFS) 0.326 0.170 0.144 0.132 0.062 0.046 0.044 0.031 0.274 Rank Return Period 1 100.00 2 25.00 3 10.00 4 5.00 5 3.00 6 2.00 l. 30 l.10 50.00 Prob 0.990 0.960 0.900 0.800 0.667 0.500 0.231 0.091 0.980 Flow Duration from Time Series File:rdout.tsf Cutoff Count Frequency CDF Exceedence_Probabi1ity CFS 0.002 0.006 0.010 0.014 0.018 0.023 0.027 0.031 0.035 0.039 27332 6675 7340 5847 4961 3595 2060 2038 1022 232 0.043 12 0.047 5 0.051 5 o . 055 7 0.059 7 0.063 10 0.067 17 0.072 23 0.076 10 % 44.573 10.886 11.970 9.535 8.090 5.863 3.359 3.324 1.667 0.378 0.020 0.008 0.008 0.011 0.011 0.016 0.028 0.038 0.016 ©2015 D. R. STRONG Consulting Engineers Inc. Technical Information Report % 44.573 55.458 67.428 76.963 85.054 90.917 94.276 97.599 99.266 99.644 99.664 99.672 99.680 99.692 99.703 99.720 99.747 99.785 99.801 % 55.427 44.542 32.572 23.037 14.946 25 9.083 5.724 2.401 0.734 0.356 0.336 0.328 0.320 0.308 0.297 0.280 0.253 0.215 0.199 0.554E+00 0.445E+00 0.326E+00 0.230E+00 0.149E+00 0.908E-01 0.572E-01 0.240E-01 0.734E-02 0.356E-02 0.336E-02 0.328E-02 0.320E-02 0.308E-02 0.297E-02 0.280E-02 0.253E-02 0.215E-02 0.199E-02 Avana Ridge Renton, Washington 0.080 11 0.018 99.819 0.181 0.181E-02 0.084 0.010 99.829 0.171 0.171E-02 0.088 5 0.008 99.837 0.163 0.163E-02 0.092 7 0.011 99.848 0.152 0.152E-02 0.096 9 0.015 99.863 0.137 0.137E-02 0.100 8 0.013 99.876 0.124 0.124E-02 0.104 11 0.018 99.894 0.106 0.106E-02 0.108 7 0.011 99.905 0.095 0.946E-03 0.112 11 0.018 99.923 0.077 0.766E-03 0.116 7 0.011 99.935 0.065 0.652E-03 0.120 9 0.015 99.949 0.051 0.506E-03 0.125 10 0.016 99.966 0.034 0.342E-03 0.129 5 0.008 99.974 0.026 0.261E-03 0.133 3 0.005 99.979 0.021 0.212E-03 0.137 3 0.005 99.984 0.016 0.163E-03 0.141 3 0.005 99.989 0.011 o .1l4E-03 0.145 5 0.008 99.997 0.003 0.326E-04 Flow Duration from Time Series File:dsout.tsf Cutoff Count Frequency CFS % 0.002 27637 45.070 0.007 7531 12.281 0.012 7290 11.888 0.017 6628 10.809 0.021 4370 7.127 0.026 3365 5.488 0.031 1978 3.226 0.036 1259 2.053 0.041 738 1. 204 0.045 229 0.373 0.050 44 0.072 0.055 38 0.062 0.060 8 0.013 0.064 16 0.026 0.069 12 0.020 0.074 15 0.024 0.079 14 0.023 0.083 17 0.028 0.088 8 0.013 0.093 12 0.020 0.098 7 0.011 0.102 7 0.011 0.107 8 0.013 0.112 6 0.010 0.117 10 0.016 0.122 10 0.016 0.126 0.010 0.131 11 0.018 0.136 10 0.016 0.141 10 0.016 0.145 8 0.013 0.150 2 0.003 0.155 3 0.005 0.160 0.007 0.164 3 0.005 ©2015 D. R. STRONG Consulling Engineers Inc. Technical Information Report CDF Exceedence_Probability % % 45.070 54.930 0.549E+00 57.352 42.648 0.426E+00 69.240 30.760 0.308E+00 80.049 19.951 0.200E+00 87.17 5 12.825 0.128E+00 92.663 7.337 0.734E-Ol 95.889 4.111 0.4llE-Ol 97.942 2.058 0.206E-Ol 99.145 0.855 0.8S5E-02 99.519 0.481 0.481E-02 99.591 0.409 0.409E-02 99.653 0.347 0.347E-02 99.666 0.334 0.334E-02 99.692 0.308 0.308E-02 99.711 0.289 0.289E-02 99.736 0.264 0.264E-02 99.759 0.241 0.241E-02 99.786 0.214 0.214E-02 99.799 0.201 0.201E-02 99.819 0.181 0.181E-02 99.830 0.170 0.170E-02 99.842 0.158 0.158E-02 99.855 0.145 0.145E-02 99.865 0.135 0.135E-02 99.881 0.119 0.119E-02 99.897 0.103 0.103E-02 99.907 0.093 0.930E-03 99.925 0.075 0.750E-03 99.941 0.059 0.S87E-03 99.958 0.042 0.424E-03 99.971 0.029 0.294E-03 99.974 0.026 0.261E-03 99.979 0.021 0.212E-03 99.985 0.015 0.147E-03 99.990 0.010 0.978E-04 26 Avana Ridge Renton, Washington 0.169 3 0.005 99.995 0.005 0.489E-04 Duration Comparison Anaylsis Base File: predev.tsf New File: dsout.tsf Cutoff Units: Discharge in CFS -----Fraction of Tirne--------------Check of Cutoff Base New %Change Probability 0.043 0.88E-02 0.64E-02 -27 .2 I 0.88E-02 0.054 0.61E-02 o .36E-02 -40.9 I 0.61E-02 0.065 0.47E-02 0.31E-02 -34.6 I 0.47E-02 0.076 0.36E-02 0.26E-02 -29.0 I 0.36E-02 0.087 0.27E-02 0.20E-02 -25.1 I 0.27E-02 0.098 0.21E-02 0.17E-02 -17.5 I 0.21E-02 0.109 0.14E-02 0.14E-02 2.4 I 0.14E-02 0.120 0.99E-03 o . 11E-02 8.2 I 0.99E-03 0.131 0.60E-03 0.75E-03 24.3 I 0.60E-03 0.142 0.34E-03 0.39E-03 14.3 I 0.34E-03 0.153 0.20E-03 0.24E-03 25.0 I 0.20E-03 0.164 0.15E-03 0.98E-04 -33.3 I 0.15E-03 0.175 0.82E-04 O.OOE+OO -100.0 I 0.82E-04 0.186 0.16E-04 O.OOE+OO -100.0 I 0.16E-04 Maximum positive excursion = 0.006 cfs ( 5.2%) occurring at 0.121 cfs on the Base Data:predev.tsf and at 0.127 cfs on the New Data:dsout.tsf Maximum negative excursion ~ 0.020 cfs (-29.9%) occurring at 0.067 cfs on the Base Data:predev.tsf and at 0.047 cfs on the New Data:dsout.tsf Water Quality Treatment Base 0.043 0.054 0.065 0.076 0.087 0.098 0.109 0.120 0.131 0.142 0.153 0.164 0.175 0.186 Tolerance------- New %Change 0.040 -5.2 0.043 -20.2 0.046 -29.5 0.054 -29.2 0.073 -15.9 0.086 -11.7 0.111 1.9 0.122 2.2 0.135 3.4 0.143 0.5 0.159 3.6 0.161 -1.7 0.167 -4.7 0.170 -8.7 The Project is located in the Enhanced Water Quality Treatment area. A wet vault followed by a media filtration system will be utilized. Rainfall (R) of the mean annual storm = 0.52 in. From KCSWDM Fig. 6.4.1.A Area of impervious surface (Ai) = 81,054 s.f. Area of till soil covered with till grass (Atg) = 30,026 s.f. Area of till soil covered with till forest (Art) = 0 s.t. Area of outwash soil covered with grass or forest (Ao) = 0 s.t. Volume factor (f) = 3 N/A From KCSWDM Sec. 6.4.1,1 Calculations Units Notes Volume of runoff from mean annual storm (Vr) = 3486 c.f. =(O,9Ai + O.25Atg + O.10Atl + O,OlAo) • R/12 Minimum Welpool volume required (Vb) = 10,459 c.f, =f' Vr A 72" Storm filter manhole will be installed downstream of the detention facility with 6 ZPG cartridges. ©2015 D. R. STRONG Consulting Engineers Inc. Technical Information Report 27 Avana Ridge Renton, Washington FIGURE 7. DETENTION & WATER QUALITY FACILITY DETAILS To be completed at time of final engineering ©2015 D. R. STRONG Consulting Engineers Inc. Technical Information Report 28 Avana Ridge Renton, Washington SECTION V CONVEYANCE SYSTEM ANALYSIS AND DESIGN Per Core Requirement, #4 of the KCSWDM, the conveyance system must be analyzed and designed for existing tributary and developed onsite runoff from the proposed project. Pipe systems shall be designed to convey the 1 ~O-year design storm. The Rational Method will be used to calculate the Q-Ratio for each pipe node. A conveyance system consisting primarily of pipes and catch basins will be designed for the Project. Onsite runoff from PGIS will be collected by the multiple catch basins. Pipes are typically twelve-inch diameter LCPE material. A backwater analysis will be provided at time of final engineering. ©2015 D. R. STRONG Consul1ing Engineers Inc. Technical Information Report 29 Avana Ridge Renton, Washington SECTION VI SPECIAL REPORTS AND STUDIES A number of reports have been prepared for the project as well as an earlier development proposal (Springbrook Ridge) on this parcel. These include: • Geological Engineering Services, Coal Mine Hazard Assessment. Cugini Property; Icicle Creek Engineers, Inc,; June 24, 1999, • Geological Engineering Services, Coal Mine Hazard Assessment. Cugini Property -Northwest Parcel; Icicle Creek Engineers, Inc,; March 22, 2004. • Geological Engineering Services, Proposed Property Development. Springbrook Ridge; Icicle Creek Engineers, Inc.; January 26, 2009. • Cugini Property wetland and stream delineation study -TWC Ref# 080109, The Watershed Company, January 25, 2009. • Environmental Checklist. Springbrook Ridge PUD; Century Pacific, LP; February 4, 2009. • Geotechnical Engineering Study -Avana Ridge Apartments; Earth Solutions NW, LLC; December 21,2015. • Tree Inspection, Avana Ridge PPUD, Parcel Numbers 292305-9148, -9009, Renton. WA; Greenforest Incorporated; December 16, 2015 • Wetland and Supplemental Stream Study -Avana Ridge PUD; Sewall Wetland Consulting, Inc.; December 22,2015. • Habitat Data Report -Avana Ridge; Sewall Wetland Consulting, Inc.; December 22,2015. • Avana Ridge Apartments. Traffic Impact Analvsis; TraffEx; December 21,2015. ©2015 D. R. STRONG Consulting Engineers Inc. Technical Information Report 30 Avana Ridge Renton, Washington SECTION VII OTHER PERMITS, VARIANCES AND ADJUSTMENTS No other permits have been required as part of this development, as of the date of this report. ©2015 D. R. STRONG Consulting Engineers Inc. Technical Information Report 31 Avana Ridge Renton, Washington SECTION VIII ESC AND CSWPPP ANALYSIS AND DESIGN The Erosion and Sedimentation Control Design meets the seven minimum King County requirements: 1. Areas to remain undisturbed shall be delineated with a high visibility plastic fence prior to any site clearing or grading. 2. Site disturbed areas shall be covered with mulch and seeded, as appropriate, for temporary or permanent measures. 3. Perimeter protection shall consist of a silt fence down slope of any disturbed areas or stockpiles. 4. A stabilized construction entrance will be located at the point of ingress/egress (Le. onsite access road). 5. A sediment pond will be utilized for sediment retention (see calculations below). Perimeter silt fences will provide sediment retention within the bypass areas. 6. Surface water from disturbed areas will sheet flow to the sediment pond for treatment. 7. Dust control shall be provided by spraying exposed soils with water until wet. This is required when exposed soils are dry to the point that wind transport is possible which would impact roadways, drainage ways, surface waters, or neighboring residences. The complete CSWPPP will be completed and submitted at time of final engineering. ©2015 D. R. STRONG Consulting Engineers Inc. Technical Information Report 32 Avana Ridge Renton, Washington SECTION IX BOND QUANTITIES, FACILITY SUMMARIES, AND DECLARATION OF COVENANT 1. Bond Quantity Worksheet -will be submitted at time of final engineering. 2. Facility Summary -will be submitted at time of final engineering. ©2015 D. R. STRONG Consulting Engineers Inc. Technical Information Report 33 Avana Ridge Renton, Washington STORMWATER FACILITY SUMMARY SHEET Number 1 (Detention Vault) (provide one Stormwater Facility Summary Sheet per Natural Discharge Location) Overview: Avana Ridge Project Name Downstream Drainage Basins Black River Major Basin Name Flow Control: Detention Vault Flow Control Facility Name/Number If none, December 29,2015 Date Panther Creek Minor Basin Name Private Parking Lot Facility Location Flow control provided in regional/shared facility (give location) ---'-'N"-'YA-'----_____ _ No flow control required __ Exemption number ____________ _ General Facility Information: Type/Number of detention facilities Ponds Type/Number of infiltration facilities: _1_ Vaults Tanks Ponds Tanks Trenches Control Structure Location Located inside proposed vault Type of Control Structure _F,-,R,-=O.!...P~-T'--__ _ Number of Orifices/Restrictions _2_ Size of Orifice/Restriction: No.1 -""0.,-,-7,,,,5_" __ _ No.2 1.60" No. 3 ____ _ No. 4 ____ _ Flow Control Performance Standard: --=L"'-e-'-'ve~/...:2'--______________ _ Live Storage Volume 37,920 cf Depth ~8..!..!fe~eu.t _________ _ Volume Factor of Safety --'--'1.""0'----___ _ Number of Acres Served -=.2"".5"'5'----___ _ Number of Lots --.!..!N/,u..A-'---_____ _ Dam Safety Regulations (Washington State Department of Ecology) Reservoir Volume above natural grade --<..!N""YA-'-______________ _ Depth of Reservoir above natural grade --'-'N""YA-'----_____________ _ Facility Summary Sheet Sketch All detention, infiltration and water quality facilities must include a detailed sketch. ©2015 D. R. STRONG Consulting Engineers Inc. Technical Information Report 34 Avana Ridge Renton, Washington SECTION X OPERATIONS AND MAINTENANCE MANUAL To be completed at time of final engineering ©2015 D. R. STRONG Consulting Engineers Inc. Technical Information Report 35 Avana Ridge Renton, Washington ©2015 D. R. STRONG Consulting Engineers Inc. Technical Information Report APPENDIX A 36 Avana Ridge Renton, Washington LEVEL ONE DOWNSTREAM ANALYSIS AVANA RIDGE 17249 Benson Road Sand 10615 SE 172"d Street Renton, Washington DRS Project No. 15088 City Of Renton File No. XXXX Owner/Applicant Avana Ridge, LLC 9675 SE 36'h Street, Suite 105 Mercer Island, Washington 98040 Report Prepared by -D. R. STRONG Consulting Engineers, Inc. 620 ih Avenue Kirkland, WA 98033 (425) 827-3063 Report Issue Date December 28, 2015 AVANARIDGE LEVEL ONE DOWNSTREAM ANALYSIS DISCLAIMER: ........................................................................................................................... 1 TASK 1: DEFINE AND MAP STUDY AREA ........................................................................ 1 TASK 2: RESOURCE REViEW ............................................................................................. 1 FIGURE 1. Vicinity Map ................................................................................. 2 FIGURE 2: Site Map ....................................................................................... 3 FIGURE 3. King County iMap Topography .............................................. 4 FIGURE 4. King County Sensitive Area Map .......................................... 5 FIGURE 5. City of Renton Erosion Hazards Map ................................... 6 FIGURE 6. City of Renton Landslide Hazards Map ............................... 7 FIGURE 7. City of Renton Coal Mine Hazards Map ............................... 8 FIGURE 8. City of Renton Steep Slopes .................................................. 9 FIGURE 9. City of Renton Flood Hazard ................................................ 10 FIGURE 10. City of Renton Seismic Hazards ....................................... 11 FIGURE 11. City of Renton Liquefaction Hazards ............................... 12 FIGURE 12. City of Renton Aquifer Protection Zones ........................ 13 FIGURE 13. USDA King County Soils Survey Map ............................. 14 FIGURE 14. FEMA Map ............................................................................... 17 TASK 3: FIELD INSPECTION ............................................................................................. 18 Upstream Tributary Area ........................................................................................... 18 General Onsite and Off site Drainage Description ................................................ 18 TASK 4: DRAINAGE SYSTEM DESCRIPTION AND PROBLEM DESCRIPTIONS ........................................................................................................ 18 Drainage System Description ................................................................................... 18 TASK 5: MITIGATION OF EXISTING OR POTENTIAL PROBLEMS .......................... 20 APPENDIX A OFFSITE ANALYSIS DRAINAGE SYSTEM TABLE & DOWNSTREAM MAP ............................................................................................... 21 © 2015 D. R STRONG Consulting Engineers Inc. Level One Downstream Analysis Avana Ridge Renton, Washington LEVEL ONE DOWNSTREAM ANALYSIS DISCLAIMER: THIS REPORT WAS PREPARED AT THE REQUEST OF PNW HOLDINGS, LLC FOR THE 3.78 ACRE PARCELS KNOWN AS A PORTION OF THE SOUTHEAST QUARTER OF SECTION 29, TOWNSHIP 23 NORTH, RANGE 5 EAST, W.M., IN KING COUNTY, TAX PARCEL NUMBERS 292305900 AND 292309148 (SITE). D. R. STRONG CONSULTING ENGINEERS INC. (DRS) HAS PREPARED THIS REPORT FOR THE EXCLUSIVE USE OF DRS, THE OWNER, AND THEIR AGENTS, FOR SPECIFIC APPLICATION TO THE DEVELOPMENT PROJECT AS DESCRIBED HEREIN. USE OR RELIANCE ON THIS REPORT, OR ANY OF ITS CONTENTS FOR ANY REVISIONS OF THIS PROJECT, OR ANY OTHER PROJECT, OR BY OTHERS NOT DESCRIBED ABOVE, IS FORBIDDEN WITHOUT THE EXPRESSED PERMISSION BY DRS. TASK 1: DEFINE AND MAP STUDY AREA This Offsite Analysis was prepared in accordance with Core Requirement #2, Section 1.2.2 of the 2009 King County Surface Water Design Manual and Section 2.3 of the 2010 City of Renton Amendments to the King County Surface Water Design Manual (Manual). The Site is located at 17249 Benson Road Sand 10615 SE 172 nd Street Renton, Washington. The Project is the development of two parcels into a 74 unit apartment complex. See Figures 1, 2 and 3 for maps of the study area. TASK 2: RESOURCE REVIEW • Adopted Basin Plans: None at this time • Finalized Drainage Studies: None available • Basin Reconnaissance Summary Reports: The Green-Duwamish and Puget Sound Water Resource Inventory Area 9 Habitat Limiting Factors And Reconnaissance Assessment Report is available for the Basin. • Floodplain/Floodway (FEMA) Map: No floodplains exist on site, See Figure 14 • Other Offsite Analysis Reports: Technical Information Report (TIR) for Fieldbrook Commons, dated December 2nd , 2013 by D.R. Strong Consulting Engineers • Sensitive Areas Map: See Figures 4-12 • DNRP Drainage Complaints and Studies: Per King County Water and Land Resources Division, there are no complaints within the downstream path, 1 mile from the Site within the last 10 years. • USDA King County Soils Survey: See Figure 13 • Wetlands Inventory: Vol. 2 East (1990) -The wetland inventory revealed no additional wetlands within one mile along the downstream path, see Appendix C. • Migrating River Studies: None Applicable • King County Designated Water Quality Problems: None at this time © 2015 D. R. STRONG Consulting Engineers Inc Level One Downstream Analysis Avana Ridge Renton, Washington FIGURE 1 -Vicinity Map © 2015 D. R. STRONG Consulting Engineers Inc Level One Downstream Analysis Avana Ridge Renton, Washington © 2015 D. R STRONG Consulting Engineers Inc Level One Downstream Analysis FIGURE 2 -Site Map Avana Ridge Renton, Washington .1S ONW 3:~fio~laHSVM 'N0.1N3!J NVSOVO!JNO 3fJOI!J VNWI V SN38 6Yi:L t dVW 3.LIS -~ 3~nf)I::/ FIGURE 3 -King County iMap Topography III Legend Highlighted Feature .f'/ Incorporated Area -I I- County Boundary Streets X Mountain Peak, "......, C<>ntoun; (5ft d.,1<) ......... f'/ 100;BOII;1(1OO loa! fr ""'a Parcels Highways 0 Lakes and urge Rivers /./ StreaR'l$ © 2015 D. R. STRONG Consulting Engineers Inc Level One Downstream Analysis Avana Ridge Renton, Washington FIGURE 4 -King County Sensitive Area Map II Highlighted Feature S,alected Parcela -I County Boundary ~ I- X MDuntaln Peaks CAO Shorellne Condition # ;0/ ..... ;v' M ....... ;0/ ..... 0 Highw.y. /./ /'/ Irw:orporatsd Area ~ StreCits 0 ~ ......... 1m ........ fI!:l c,"-""' ...... ~ © 2015 D. R. STRONG Consulting Engineers Inc Level One Downstream Analysis Legend Parce!1:. fm SAO Seismic SAO Stream SAO Erosion c .... , Cbiss 2 Pammial Ctal!l2s.r-ud C ..... tJndnsifiDd Lakes and Large Ri~el'1i Streams Floodway 100 Year FlOOdplain SAOWGU.nd SAO Landolldo SAOCo.oI MiN! Avana Ridge Renton, Washington FIGURE 5 -City of Renton Erosion Hazards Map c ~ ~ RENTON SE ce.rr Ro Spring GImJ srlf_ng Cente!! EROSION HAZARDS © 2015 D. R STRONG Consulting Engineers Inc Level One Downstream Analysis Erosion Hazard Areas 6 W III NTS Avana Ridge Renton, Washington FIGURE 6 -City of Renton Landslide Hazards Map ; ii ~ '''~ REtHON S~"G"" S~''"'''''' t;(!<Iftr~ LANDSLIDE HAZARDS © 2015 D. R. STRONG Consulting Engineers Inc level One Downstream Analysis Hazard Severity Moderate _High _ Very High King County Data NTS Avana Ridge Renton, Washington FIGURE 7 -City of Renton Coal Mine Hazards Map ,9 s'i: carrRa COAL MINE HAZARD Severity _HIGH MODERATE L~ UNCLASSIFIED oJ-' I~.!J Renton City Limits NTS SEc Pe!(<l'ilts~y F © 2015 D. R. STRONG Consulting Engineers Inc Avana Ridge Level One Downstream Analysis Renton, Washington ) FIGURE 8 -City of Renton Steep Slopes < ~ @ "' .. . > .. ~ REN10N s'ES co.Tf Rd Steep Slopes Percentage Range >15% & <=25% >25% & <=40% M >40% & <=90% M >90% ~ ~ , n c ~ • NTS © 2015 D. R. STRONG Consulting Engineers Inc Avana Ridge Level One Downstream Analysis Renton, Washington FIGURE 9 -City of Renton Flood Hazard ~ >~ REtHON _~"...,ptl"'" S',..."..,aC_<1<' Hazard Condition © 2015 D. R. STRONG Consulting Engineers Inc Level One Downstream Analysis Flood Hazard 10 NTS Avana Ridge Renton, Washington FIGURE 10 -City of Renton Seismic Hazards " , , SJI!i!hLl REN10N so;:. c&rrRd Hazard Condition © 2015 D. R. STRONG Consulting Engineers Inc Level One Downstream Analysis High Seismic Severity 11 St 16111" ~j NTS Avana Ridge Renton, Washington FIGURE 11 -City of Renton Liquefaction Hazards HAZARD CONDITION Liquefaction Susceptibility ~ high © 2015 D. R STRONG Consulting Engineers Inc Level One Downstream Analysis moderate to high low to moderate 12 Avana Ridge Renton, Washington FIGURE 12 -City of Renton Aquifer Protection Zones Renton Municipal Code Zone 1 Zone 1 Modified Zone 2 ---City Limits © 2015 D. R. STRONG Consulting Engineers Inc Level One Downstream Analysis 13 Avana Ridge Renton, Washington FIGURE 13 -USDA King County Soils Survey Map Web Sol So.roey Nallonal CoopefallYfl Sol s..wy King County Area, Washington AgC-Alderwood gravelly sandy loam, 8 to 15 percent slopes Map Unit Setting National map unit symbol: 2t626 Elevation: 50 to 800 feet Mean annual precipitation: 20 to 60 inches Mean annual air temperature: 46 to 52 degrees F Frost-free period: 160 to 240 days Farmland classification: Prime farmland if irrigated Map Unit Composition Alderwood and similar soils: 85 percent Minor components: 15 percent Estimates are based on observations, descriptions, and transects of the mapunit. Description of Alderwood © 2015 D. R STRONG Consulting Engineers Inc Level One Downstream Analysis 14 1211-4121)15 Pagelof3 Avana Ridge Renton, Washington Setting Landform: Ridges, hills Landform position (twa-dimensional): Shoulder Landform position (three-dimensional): Nose slope, talf Down-slope shape: Linear, convex Across-slope shape: Convex Parent material: Glacial drift andlor glacial outwash over dense glaciomarine deposits Typical profile A -0 to 7 inches: gravelly sandy loam Bw1 -7 to 21 inches: very gravelly sandy loam Bw2 -21 to 30 inches: very gravelly sandy loam Bg -30 to 35 inches: very gravelly sandy loam 2Cd1 -35 to 43 inches: very gravelly sandy loam 2Cd2 -43 to 59 inches: very gravelly sandy loam Properties and qualities Slope: 8 to 15 percent Depth to restrictive feature: 20 to 39 inches to densic material Natural drainage class: Moderately well drained Capacity of the most limiting layer to transmit water (Ksat): Very low to moderately low (0.00 to 0.06 in/hr) Depth to water table: About 18 to 37 inches Frequency of flooding: None Frequency of ponding: None Available water storage in profife: Very low (about 2.7 inches) Interpretive groups Land capability classification (irrigated): None specified Land capability classification (nonirrigated): 4s Hydrologic Soil Group: B Other vegetative classification: Limited Depth Soils (G002XN302WA), Limited Depth Soils (G002XS301WA), Limited Depth Soils (G002XF303WA) Minor Components Everett Percent of map unit: 5 percent Landform: Eskers, kames, moraines Landform position (two-dimensional): Shoulder, footslope Landform position (three-dimensional): Crest, base slope Down-slope shape: Convex Across-slope shape: Convex Indianola Shalcar Percent of map unit: 5 percent Landform: Eskers, kames, terraces Landform position (three-dimensional): Tread Down-slope shape: Linear Across-slope shape: Linear © 2015 D. R. STRONG Consulting Engineers Inc Level One Downstream Analysis 15 Avana Ridge Renton, Washington Norma Percent of map unit: 3 percent Landform: Depressions Landform position (three-dimensional): Dip Down-slope shape: Concave Across-slope shape: Concave Percent of map unit: 2 percent Landform: Depressions, drainageways Landform position (three-dimensional): Dip Down-slope shape: Concave, linear Across-slope shape: Concave © 2015 D. R. STRONG Consulting Engineers Inc level One Downstream Analysis 16 Avana Ridge Renton, Washington -------------------- FIGURE 14 -FEMA Map NTS Revised FEMA Preliminary DFIRM Nov. 2010 r---] L-Renton City Limits [,:.:::1 Potential Annexation Area Boundary o Floodway --Base Flood Elevation (ftl © 2015 D. R STRONG Consulting Engineers Inc Level One Downstream Analysis Regulatory • Zone A Non-Regulatory Zone X Zone A -Special flood hazard areas inundated by 100 year flood (regulatory floodplain) Zone X -Areas of SOO year flood, Areas less than 1-ft depth during 100 year flood, Areas protected by levees from 100 year flood (non-regulatory floodplain) 17 Avana Ridge Renton, Washington TASK 3: FIELD INSPECTION Upstream Tributary Area The upstream basin area was evaluated by examining the King County topographic map (see Figure 3), City of Renton Mapping Application and by conducting field reconnaissance on December 15, 2015 under overcast conditions. Upstream runoff enters the Site in two locations. Portions of SE 172nd St and 106th Ave SE direct upstream runoff across the northern property line. Runoff from 106th Ave SE and the north side of SE 172 nd St. enters a Type 1 catch basin at the intersection of these two streets. An 18-inch diameter concrete pipe conveys runoff south under SE 172 nd St. and outfalls onto the Site. Runoff from the southern portion of SE 172nd St is intercepted by a ditch along the south side of SE 172nd st. and enters the Site where the previously mentioned 18-inch diameter concrete pipe outlets. Upstream runoff from the west side of Benson Rd S flows west into a ditch along the east property line. This ditch conveys upstream runoff southwest along the east property line until it enters a stream about halfway down the property line. This stream conveys water through the Site. The Project proposes to construct a conveyance system to collect runoff from these two upstream tributary areas and bypass the infiltration facility on Site. General Onsite and Off site Drainage Description The Site is contained within one Threshold Discharge Area (TDA) but is divided into two distinct Natural Discharge Areas (NDA's), NDA 1 and NDA 2. See Downstream Analysis Map for the location of each NDA. Natural Discharge Point 1 (NDP 1) is located at approximately the midpoint of the southwestern property line. NDP 2 is northwest of NDP 1. See Appendix A for a map of the NDAs and downstream paths. Runoff exits the Site via an onsite ditch from both NDAs. NDA 1 is approximately 2.65 acres (115,449 SF) and NDA 2 is approximately 1.13 acres (49,378 SF). The flow paths were observed and appear to converge at points 01 and C2. TASK 4: DRAINAGE SYSTEM DESCRIPTION AND PROBLEM DESCRIPTIONS Drainage System Description The downstream area was evaluated by reviewing available resources and by conducting a field reconnaissance on December 15, 2015 under overcast conditions. The analysis is illustrated and detailed in the Downstream Map and Downstream Table located in Appendix A. The downstream path is located within the Black River Drainage Basin; more specifically the Panther Creek Subbasin. For point-to-point descriptions of downstream flow, see Appendix A. Runoff exits the Site via channel flow from an onsite ditch in two locations -NDP 1 and NDP 2. Both NDPs are located along the western property line. Runoff enters box culverts on the northeast side of SR 515, eventually crossing under the road to the southwest. Flows from each NDA converge at a Type 2 catch basin on the southwest side of SR 515, just east of parcel © 2015 D. R. STRONG Consulting Engineers Inc Level One Downstream Analysis 18 Avana Ridge Renton, Washington 2923059150. Runoff continues west through a ditch between parcels 2923059150 and 2923059134 and is conveyed west through a series of catch basins and PVC pipes. Runoff outlets west of Wells Ave S and continues west, eventually outfalling into Panther Creek. A review of the King County Water and Land Resources Division -Drainage Services Section Documented Drainage Complaints within one mile of the downstream flow paths revealed no complaints within the last ten years along all downstream paths for the Site. © 2015 D. R. STRONG Consulting Engineers Inc Level One Downstream Analysis 19 Avana Ridge Renton, Washington TASK 5: MITIGATION OF EXISTING OR POTENTIAL PROBLEMS No drainage complaints were found in Task 4, and therefore no mitigation is required by this Project. All potential maintenance issues should be resolved by either City Maintenance (public systems) or the respective property owners (private systems). No further analysis should be required of this Project. The Project should not create any problems as specified in Section 1.2.2.1 of the Manual and therefore is not required to provide Drainage Problem Impact Mitigation subject to the requirements of Section 1.2.2.2. Project runoff will be collected and released per the Manual's requirements to accommodate Flow Control Duration Standard -Matching Forested Site Conditions (Level 2 Flow Control). The Project is located within a Basic Water Quality Area, but since the Project is a multifamily development, it will adhere to Enhanced Basic Water Quality requirements. During construction, standard sediment and erosion control methods will be utilized. This will include the use of a stabilized construction entrance, perimeter silt fencing, and other necessary measures to minimize soil erosion during construction. © 2015 D. R. STRONG Consulting Engineers Inc Level One Downstream Analysis 20 Avana Ridge Renton, Washington APPENDIXA. OFFSITE ANALYSIS DRAINAGE SYSTEM TABLE & DOWNSTREAM MAP OFFSITE ANALYSIS DRAINAGE SYSTEM TABLE Basin: Black River Symbol Drainage Component Type, Name, and Size Type: sheet flow, See map swale, Stream, channel, pipe, Pond; Size: diameter Surface area Al 2' x 4' Concrete Box Culvert Al-Bl Southwesterly Pipe Flow Bl Type 2 Catch Basin Bl-Cl Southwesterly Pipe Flow Cl Type 2 Catch Basin Cl-0l Northwesterly Pipe Flow 01 Type 2 Catch Basin 01-El Southwesterly Pipe Flow SURFACE WATER DESIGN MANUAL, CORE REQUIREMENT #2 TDA 1: NDA 1 Subbasin Name: Panther Creek Drainage Component Slope Distance Existing Potential Description From site Problems Problems Discharoe Constrictions, under capacity, p~nding, drainage basin, vegetation, cover, % 114 mi=l ,320 ft overtopping, flooding, habitat or organism depth, type of sensitive area, volume destruction, scouring, bank sloughing, sedimentation, incision, other erosion Northeast side of SR 515, approximate ±Q' None Observed Slight potential for midpoint of western property line. blockage from debris/foliaQe 18" Concrete Pipe ±0'-19' None Observed None Anticipated Slightly southwest of box culvert on the ±19' None Observed None Anticipated northeast side of SR 515.18" Cone. (NESW) 18" Concrete Pipe, travels southwest ±19'-74' None Observed None Anticipated under SR515 On the southwest side of SR 515, ±74' None Observed None Anticipated across the street from CB at point 81. 12" Cone. (SE), 18" Cone. (NE, NW) 18" Concrete Pipe, travels northwest ±74'-358' None Observed None Anticipated along the southwestern side of SR 515. Southwestern side of SR 515, just east ±358' None Observed None Anticipated of parcel 2923059150. 18" Cone. (NE,SE), 24" Cone. (Sw) 24" Concrete Pipe, travels southwest ±358'-378' None Observed None Anticipated under the sidewalk and outfalls into ditch. © 2015 D. R. STRONG Consulting Engineers Inc. level One Downstream Analysis 21 Avana Ridge Renton, Washington Subbasin Number: N/A Observations of field inspector resource reviewer, or resident tributary area, likelihood of problem, overflow pathways, potential impacts. Light flow observed Light flow observed Light flow observed Moderate flow observed El Pipe Outlet 24" Concrete Pipe outfalls into ditch on the southwest side of SR 515, heading southwest between parcels 2923059150 and 2923059134 E1-F1 Channel Flow Runoff flows southwesterly between the parcels through a moderately vegetated ditch, approximately 2' wide Fl Culvert Inlet Runoff flows into 30" CMP with trash rack. Flow is separated from the sidewalk by a -2' high concrete wall and chain link fence. Inlet is custom designed and transitions from 30" to 18" pipe. F1-G1 Southwesterly Pipe 18" PVC Pipe Flow G1 Type 1 Catch Basin South side of S 36'" St. 18" (NE, SE, W) G1-H1 Westerly Pipe Flow 18" PVC Pipe H1 Type 2 Catch Basin Solid lid in south side of S 36'" St. 18" PVC{E, NW) H1-11 Northwesterly Pipe 18" PVC Pipe Flow 11 Type 2 Catch Basin Solid lid in south side of S 36th St. 18" PVC (SE, W) 11-J1 Westerly Pipe Flow 18" PVC Pipe J1 Type 2 Catch Basin Solid lid in south side of S 36 th St. 18" PVC (E, SW) J1-K1 Southwesterly Pipe 18" PVC Pipe Flow © 2015 D. R. STRONG Consulting Engineers Inc. Level One Downstream Analysis 22 ±378' ±378'-791, ±791' ±791'-856' ±856' ±856'-954' ±954' ±954'-112T ±1127" ±112T-1264' ±1264' ±1264'-137T None Observed None Observed None Observed None Observed None Observed None Observed None Observed None Observed None Observed None Observed None Observed None Observed Avana Ridge Renton, Washington None Anticipated Moderate flow observed General maintenance and clearing may be necessary in the future Heavy flow may Moderate flow observed erode subgrade of wooden fence near inlet and cause problems None Anticipated None Anticipated Moderate flow observed None Anticipated None Anticipated Moderate flow observed None Anticipated None Anticipated Moderate flow observed None Anticipated None Anticipated Moderate flow observed None Anticipated K1 Type 2 Catch Basin Solid lid in south side of S 36th St. 18" PVC (NE, S). Over % mile downstream -end offield reconnaissance. Runoff continues south between parcels 1441000150 and 1441000160. According to record drawings from the City of Renton, flow enters a CB at the back of parcel 1441000150, moves to another CB at the back of parcel 8106300980, and then moves west towards a CB at the front of parcel 8106300890, ±1866' along the downstream path. This Type 2 CB was observed during field reconnaissance. Moderate flow was observed. 18" pipe (E,W). Runoff outlets to the west. © 2015 D. R. STRONG Consulting Engineers Inc. Level One Downstream Analysis 23 ±1377' None Observed Avana Ridge Renton, Washington None Anticipated Moderate flow observed Basin: Black River Symbol Drainage Component Type, Name, and Size Type: sheet flow, See map swate, Stream, channel, pipe, Pond; Size: diameter Surface area A2 2' x 4' Concrete Box Culvert A2-B2 Southwesterly Pipe Flow B2 Type 2 Catch Basin B2-C2 Westerly Pipe Flow C2 (01) Type 1 CB OFFSITE ANALYSIS DRAINAGE SYSTEM TABLE SURFACE WATER DESIGN MANUAL, CORE REQUIREMENT #2 TDA 1: NDA2 Subbasin Name: Panther Creek Drainage Component Slope Distance Existing Potential Description From site Problems Problems Discharge Constrictions, under capacity, ponding, drainage basin, vegetation, cover, % 1/4 mi=1,320 It overtopping, flooding, habitat or organism depth, type of sensitive area, volume destruction, scouring, bank sloughing, sedimentation, incision, other erosion Northeast side of SR 515, just ±O' None Observed Slight potential for southeast of the northwest property blockage from corner. debrislfoliage 18" Concrete Pipe ±O'-16' None Observed None Anticipated Slightly southwest of box culvert on the ±16' None Observed None Anticipated northeast side of SR 515. 18" Conc. (NE,W) 18" Concrete Pipe, travels west under ±16'-84' None Observed None Anticipated SR515 Southwestern side of SR 515, just east ±84' None Observed None Anticipated of parcel 2923059150.18" Cone. (NE,SE), 24" Cone. (SW). Flow combines at point D1 and continues alon~ path for NOA 1 © 2015 o. R STRONG Consulting Engineers Inc. Level One Downstream Analysis 24 Avana Ridge Renton, Washington Subbasin Number: N/A Observations of field inspector resource reviewer, or resident tributary area, likelihood of problem, overflow pathways, potential impacts. Light Flow Observed Light Flow Observed Moderate Flow Observed tztro:n;n.:I ttIO£"RII"RJ-O &fOfI6lfN1'0NY1>IlIDI3fJN311.yw,-(g ~Rm<Hnd_ Sl/33N/EJN3 DNIJ.7fISN(X) eNOW.$1I"O / NO.1fJNIHS'rfM 'N0.1N3M .1S aNy. ~ 3S 9~90~ aN'rf S attOM NOSN38 6p~L~ 3fJaiM 'rfN'rfl1 'rf dtIW Wtl3~.1SNMOa -t V' 3~nf)ld I I I I I l-~£D~AVESE_ - -J I -------l ( \ \ J ------/ // // I I I I I I 0: ~I I ~I I \ \ \ \ \\ \\ \ \ \ \ \ \