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Home My WebLink AboutMiscAssociated Earth Sciences, Inc. ~[l8~~~ Serving tne Pacific Nortnwest Since 19B1 December 20,2013 Project No. TE130561A Iossif Rozenblat 5415 NE 2"" Court Renton, Washington 98509 Subject: Subsurface Exploration and Preliminary Geotechnical Engineering Report Proposed Melrose Short Plat 186XX 108'" Avenue Southeast Renton, Washington Dear Mr. Rozenblat: We are pleased to present these copies of our preliminary geotechnical engineering report for the referenced project. This report summarizes the results of our subsurface exploration, geologic hazards, and geotechnical engineering studies, and offers preliminary recommendations for the design and development of the proposed project. At the time this report was prepared, the site was in the planning stage and no detailed project plans had been formulated. This report is based on a preliminary site layout plan titled "Melrose Short Plat" by Beyler Consulting dated November 14,2013. We recommend that we be allowed to review the recommendations contained in this report and modify them, if necessary, when a detailed project plan has been developed. We have enjoyed working with you on this study and are confident that the recommendations presented in this report will aid in the successful completion of your project. If you should have any questions, or if we can be of additional help to you, please do not hesitate to call. Sincerely, ASSOCIATED EARTH SCIENCES, INC. Tacoma, Washington ~'M~rri~an, P.E. Senior Principal Engineer KDM/pc TE130S6IA3 ProjcctsUOI30561\TE\WP Kirkland 425-827-7701 • Everett • Tacoma 425-259-0522 253-722-2992 www.aesgeo.com (jeotecfinica('Engineering Water 'Resources Environmenta( :Assessments antI 'Remediation Sustainalj(e 1Jeve(oyment Services (jeo(ogic :Assessments Associated Earth Sciences, Inc. Serving the Pacific Northwest Since 19B1 Subsurface Exploration and Preliminary Geotechnical Engineering Report PROPOSED MELROSE SHORT PLAT Renton, Washington Prepared for Iossif Rozenblat Project No. TE130561A December 20,2013 SUBSURFACE EXPLORATION AND PRELIMINARY GEOTECHNICAL ENGINEERING REPORT PROPOSED MELROSE SHORT PLAT Renton, Washington Prepared for: Iossif Rozenblat 5415 NE 2"" Court Renton, Washington 98509 Prepared lJy: Associated Earth Sciences, Inc. 1552 Connnerce Street, Suite 102 Tacoma, Washington 98402 253-722-2992 Fax: 253-722-2993 December 20,2013 Project No. TE130561A Proposed Me/rose Shorl Pial Renton, Washington Subsurface Exploration and Preliminary Geotechnical Engineering Reporl Project and Site Conditions I. PROJECT AND SITE CONDITIONS 1.0 INTRODUCTION This report presents the results of our subsurface exploration, geologic hazards, and preliminary geotechnical engineering studies for the proposed new short plat. The site location is shown on the "Vicinity Map,» Figure 1. The approximate locations of exploration pits completed for this study are shown on the "Site and Exploration Plan,» Figure 2. Logs of the subsurface explorations and copies of laboratory test results completed for this study are included in the Appendix. 1.1 Purpose and Scope The purpose of this study is to provide geotechnical engineering design recommendations to be utilized in the preliminary design of the project. This study included a review of selected available geologic literature, advancing three exploration pits and performing geologic studies to assess the type, thickness, distribution, and physical properties of the subsurface sediments and shallow ground water. Geotechnical engineering studies were completed to formulate recommendations for site preparation, structural fill, pavement subgrade preparation, and drainage. Based on exploration data contained in this report, on-site storm water infiltration using conventional shallow infiltration strategies is not feasible in our opinion. This report summarizes our fieldwork and offers preliminary geotechnical engineering recommendations based on our present understanding of the project. We recommend that we be allowed to review the recommendations presented in this report and revise them, if needed, when a detailed project design has been developed. 1.2 Authorization Authorization to proceed with this study was granted by means of a signed copy of our scope of work and cost proposal dated November 7, 2013, This report has been prepared for the exclusive use of Iossif Rozenblat and his agents for specific application to this project. Within the limitations of scope, schedule, and budget, our services have been performed in accordance with generally accepted geotechnical engineering practices in effect in this area at the time our report was prepared. No other warranty, express or implied, is made. 2,0 PROJECT AND SITE DESCRIPTION The project site is an undeveloped parcel between 18633 and 18647 108th Avenue Southeast in Renton, Washington. The site is rectangnlar in plan view and overall site area is December 20, 2013 ASSOCIATED EARTH SCIENCES, INC. BWG/pc ~ TEl30561A3 -Projectsl2013056111E\WP Page 4 Proposed Melrose ShOJ1 Plat Renton, Washington Subsurface Exploration and Preliminary Geotechnical Engineering Report Pro;ect and Site Conditions approximately 0.4 acres. Site topography generally slopes gently down from west to east, and a rockery along the east edge of the site protects a grade transition of approximately 5 feet descending from west to east. Overall vertical relief across the site is approximately 10 feet. The site does not appear to include Geologic Hazard Areas as described in Remon Municipal Code (RMC) Section 4-3-050 J with the exception of possible Erosion Hazard Areas. At the time of our subsurface investigation, the site was undeveloped except for the existing rockery, and covered with mature trees and moderately dense native understory plants. 3.0 SUBSURFACE EXPLORATION Our subsurface exploration completed for this project included advancing three exploration pits. The conclusions and recommendations presented in this report are based on the explorations completed for this study. The locations and depths of the explorations were completed within site and budget constraints. 3.1 Exploration Pits The exploration pits were excavated using a tracked excavator. The pits permitted direct, visual observation of subsurface conditions. Materials encountered in the exploration pits were studied and classified in the field by geologists from our firm. All exploration pits were backfilled after examination and logging. Selected samples were then transported to our laboratory for further visual classification and testing, as necessary. 4.0 SUBSURFACE CONDITIONS Subsurface conditions at the project site were inferred from the field explorations accomplished for this study, visnal reconnaissance of the site, and review of selected applicable geologic literature. Because of the nature of exploratory work below ground, extrapolation of subsurface conditions between field explorations is necessary, It should be noted that differing subsurface conditions may sometimes be present due to the random nature of deposition and the alteration of topography by past grading and/or fIlling. The nature and extent of any variations between the field explorations may not become fully evident until construction. 4.1 Stratigraphy Surficial Topsoil Exploration pits encountered surficial topsoil approximately 1 foot thick. Topsoil is not suitable for structural support, and should be stripped from structural areas. Excavated topsoil December 20, 2013 ASSOCIATED EAlITH SCIENCES, INC. BWGlpc -TE130561A3 -Projec/sl20J 3056JlTEIWP Page 5 Proposed Melrose Shon Plat Renton, Washington Subsurface Exploration and Preliminary Geotechnical Engineering Repon Project and Site Conditions may be suitable for reuse in landscape areas if allowed by project specifications. Excavated topsoil should be expected to swell 30 percent or more in volume between the in situ condition and the loose condition after stripping. Lodgement Till Each of the exploration pits encountered native sediments consisting of medium dense grading to very dense sand with varying silt and gravel content interpreted as Vashon lodgement till. Lodgement till was deposited at the base of an active continental glacier and was compacted by the weight of the overlying glacial ice. Lodgement till is suitable for structural support when properly prepared. Excavated lodgement till material is suitable for use in structural fill applications if suitable moisture conditions are achieVed prior to compaction and if such reuse is specifically allowed by the owner and project documents. At the time of exploration, we estimate that most or all of the lodgement till soils that we observed were above optimum moisture content for compaction purposes, and therefore, will require drying during favorable weather prior to compaction in structural fill applications. Published Geologic Map We reviewed a published geologic map of the area (Geologic Map of King County, Washington, by Derek B. Booth, Kathy A. Troost, and Aaron P. Wisher, 2006). The referenced map indicates that the site is expected to be underlain at shallow depths by lodgement till. 4.2 Hydrology No ground water seepage was observed in the subsurface explorations completed for this study. Sites underlain by lodgement till often develop shallow "perched" ground water during seasonal wet weather. Perched ground water occurs when vertical infiltration is impeded by less-penrieable soil layers, resulting in horizontal flow. The quantity and duration of perched ground water flow from an excavation will vary, depending on season, soil gradation, and adjacent topography. Ground water conditions should be expected to vary in response to changes in precipitation, on-and off-site land usage, and other factors. 4.3 Laboratory Testing As a part of our investigation of the infiltration potential of the site soils, we completed one laboratory grain-size analysis. A copy of the grain-size analysis report is included in the Appendix. December 20, 2013 ASSOCIATED EARTH SCIENCES. INC. BWG/pc -TE13{)56JA3 -ProjecrsI2013056111E'IWP Page 6 Proposed Melrose Short Plat Renton, Washington 4.4 InfIltration Potential Subsurface Exploration and Preliminary Geotechnical Engineering Report Project and Site Conditions Native sediments at shallow depths below the site consist of lodgement till. The grain-size analysis of lodgement till completed for this project identifIed 23-percent silt in the sample selected for testing. The estimated density of the lodgement till ranged from medium dense near the snrface to very dense at depth. Though the applicable storm water design standards (2009 King County Surface Water Design Manual and 2010 City of Renton Addenda) do not provide a quantitative method for estimating an infIltration rate based on grain-size testing, in our experience the measured infIltration rate of lodgement till is very small, approaching zero. We do not recommend that lodgement till be used as a storm water infIltration receptor. Other best management practices (BMPs) such as splash blocks and storm water dispersion might be feasible at the discretion of the project civil engineer. We do not recommend storm water dispersal in close proximity to the existing rockery on the east side of the site. Ideally any storm water dispersal that is planned on the east lot of the short plat should be positioned on the west side of the proposed home on that lot. December 20, 2013 ASSOCIATED EAKI1l SCIENCES, INC. BWG/pc -TEi30561A3 -Projects12OJ3056J1TEIWP Page 7 Proposed Melrose Short Pklt Renton, Washington Subsuiface Exploration and Preliminary Geotechnical Engineering Report Geologic Hazards and Mitigations n. GEOLOGIC HAZARDS AND MITIGATIONS The following discussion of potential geologic hazards is based on the geologic, slope, and ground and surface water conditions, as observed and discussed herein. The discnssion will be limited to slope stability, seismic, and erosion issues. The site does not appear to contain any areas that meet City of Renton definitions for Geologic Hazard Areas as defined in RMC Section 4-3-050 J with the exception of Erosion Hazard Areas. Individual geologic hazard topics are discussed in further detail below. 5.0 SLOPE HAZARDS AND MITIGATIONS Based on the plat map that was provided to us, it does not appear that any slopes on-site meet City of Renton definitions for treatment as Steep Slope or Landslide Hazard critical areas in our opinion. No detailed assessment of slope stability was prepared as part of this report and none is warranted in our opinion. 6.0 SEISMIC HAZARDS AND MITIGATIONS The site is underlain at shallow depths by unsaturated lodgement till. The site does not contain areas that meet City of Renton definitions for Seismic Hazard areas in our opinion. A detailed assessment of liquefaction risks was not completed, and none is warranted for the currently proposed project in our opinion. 6.1 Surficial Ground Rupture Generally, the largest earthquakes that have occnrred in the Puget Sound area are sub-crustal events with epicenters ranging from 50 to 70 kilometers in depth. Earthquakes that are generated at such depths usually do not result in fault rupture at the ground surface. Current research indicates that surficial ground rupture is possible in areas close to the Seattle Fault Zone, the closest mapped fault zone to the project. Although our current understanding of this fault zone is limited and is an active area of research, the site lies approximately 2 miles south of the currently mapped limits of the Seattle Fault Zone. Therefore, based on current information, the risk of damage to planned improvements as a result of surface rupture due to faulting is low, in our opinion. December 20. 2013 ASSOCIATED EAKI1l SCIENCES, INC. BWG/pc -TEl3056lA.3 -fu:?jects\20J 3056Jl1E\ WP Page 8 Proposed Melrose Short Plat Renton, Washington 6.2 Ground Motion Subsuiface Exploration and Preliminary Geotechnical Engineering Report Geologic Hazards and Mitigations Structural design of the project should be in accordance with the 2012 International Building Code (IBC) using Site Class C. 7.0 EROSION HAZARDS AND MITIGATIONS The following discussion addresses Washington State Department of Ecology (Ecology) erosion control regulations that will be applicable to the project. We anticipate that if the project complies with Washington State requirements, it will also be acceptable with respect to City of Renton requirements. As of October 1, 2008, Ecology Construction Storm Water General Permit (also known as the National Pollutant Discharge Elimination System [NPDES] permit) requires weekly Temporary Erosion and Sedimentation Control (TESC) inspections, turbidity monitoring, and pH monitoring for all sites 1 or more acres in size that discharge storm water to surface waters of the state. Because the proposed project will not require disturbance of more than 1 acre, we anticipate that these inspection and reporting requirements will not be triggered. The following recommendations are related to general erosion potential and mitigation. The erosion potential of the site soils is high. Maintaining cover measures atop disturbed ground typically provides the greatest reduction to the potential generation of turbid runoff and sediment transport. During the local wet season (October 1" through March 31"), exposed soil should not remain uncovered for more than 2 days unless it is actively being worked. Ground-cover measures can include erosion control matting, plastic sheeting, straw mulch, crushed rock or recycled concrete, or mature hydroseed. Project planning and construction should follow local standards of practice with respect to temporary erosion and sedimentation control. BMPs should include but not be limited to: • Provide storm drain inlet protection; • Route surface water away from work areas; • Keep staging areas and travel areas clean and free of track-out; • Cover work areas and stockpiled soils when not in use; • Complete earthwork during dry weather and site conditions, if possible. December 20, 2013 ASSOCIATED EAIIIH SCIENCES, INC. BWG/pc -TElJ056JA3 -Projects120130561lTE1WP Page 9 Proposed Melrose Short Plat Renlon, Washington Subsuiface Exploration and Preliminary Geotechnical Engineering Report Preliminary Design Recommendations m. PRELIMINARY DESIGN RECOMMENDATIONS 8.0 INTRODUCTION The site is underlain at shallow depths by lodgement till that is suitable for structural support with proper preparation. Lodgement till is silty and sensitive to moisture contents above optimum for compaction purposes. Careful preparation and protection of lodgement till bearing surfaces will reduce the potential that remedial preparation will be needed. Aeration and drying of excavated lodgement till sediments is expected to be needed before they can be reused in compacted fill applications. Reuse of excavated lodgement till in structural fill applications is permitted only if explicitly allowed by the owner and project documents. 9.0 SITE PREPARATION Erosion and surface water control should be established around the clearing limits to satisfy local requirements. We are not aware of any existing structures or buried utilities on-site. If any exist they should be removed where they are located below planned construction areas. All disturbed soils resulting from demolition activities should be removed to expose underlying undisturbed native sediments and replaced with structural fill, as needed. All excavations below final grade made for demolition activities should be backfilled, as needed, with structural fill. Existing vegetation and topsoil should be stripped, and tree stumps and roots should be grubbed. Any materials below final grades that are disturbed by stripping and grubbing should be removed and replaced as structural fill as defined in this report. 9.1 Site Drainage and Surface Water Control The site should be graded to prevent water from ponding in construction areas and/or flowing into excavations. Exposed grades should be crowned, sloped, and smooth drum-rolled at the end of each day to facilitate drainage. Accumulated water must be removed from subgrades and work areas immediately prior to performing further work in the area. Equipment access may be limited, and the amount of soil rendered unfit for use as structural fill may be greatly increased, if drainage efforts are not accomplished in a timely sequence. If an effective drainage system is not utilized, project delays and increased costs could be incurred due to the greater quantities of wet and unsuitable fill, or poor access and unstable conditions. December 20, 2013 ASSOCIATED EARTH SCIENCES, INC. BWGIpc -TE130561A1-ProjeclSl20130561lIEIWP Page 10 Proposed Melrose Short Plat Renton, Washington 9.2 Subgrade Protection Subsurface Exploration and Preliminary Geotechnical Engineering Report Preliminary Design Recommendations If construction will proceed during the winter, we recommend the use of a working surface of sand and gravel, crushed rock, or quarry spalls to protect exposed soils, particularly in areas supporting concentrated equipment traffic. In winter construction staging areas and areas that will be subjected to repeated heavy loads, a minimum thickness of 12 inches of quarry spalls or 18 inches of pit run sand and gravel is recommended. If subgrade conditions are soft and silty, a geotextile separation fabric, such as Mirafi 500X or approved equivalent, should be used between the subgrade and the new fill. 9.3 Proof-Rolling and Subgrade Compaction Following the recommended demolition, site stripping, and planned excavation, the stripped sub grade within the planned building and paving areas should be compacted to 95 percent of the modified Proctor maximum dry density and proof-rolled with heavy, rubber-tired construction equipment, such as a fully loaded tandem-axle dump truck. Proof-rolling should be performed prior to structural fill placement or foundation excavation. The proof-roll should be monitored by the geotechnical engineer so that any soft or yielding subgrade soils can be identified. Any soft/loose, yielding soils should be removed to a stable subgrade. The sub grade should then be scarified, adjusted in moisture content, and recompacted to the required density. Proof-rolling should only be attempted if soil moisture contents are at or near optimum moisture content. Proof-rolling of wet subgrades could result in further degradation. Low areas and excavations may then be raised to the planned fmished grade with compacted structural fill. Subgrade preparation and selection, placement, and compaction of structural fIll should be performed under engineering-controlled conditions in accordance with the project specifications. 9.4 Overexcavation/Stabilization Construction during extended wet weather periods could create the need to overexcavate exposed soils if they become disturbed and cannot be recompacted due to elevated moisture content and/or weather conditions. Even during dry weather periods, soft/wet soils, which may need to be overexcavated, may be enconntered in some portions of the site. If overexcavation is necessary, we recommend that overexcavation progress be observed by Associated Earth Sciences, Inc. CAESI). Soils that have become unstable may require remedial measures in the form of one or more of the following: 1. Drying and recompaction. Selective drying may be accomplished by scarifying or windrowing surficial material during extended periods of dry and warm weather. 2. Removal of affected soils to expose a suitable bearing subgrade and replacement with compacted structural fill. December 20, 2013 ASSOCIATED EARTH SCIENCES, INC. 8WG/pc -TE130561A3 -Projecrs\20l305611TEIWP Page 11 Proposed Melrose Short Plat Renton, Washington Subswface Exploration and Preliminary Geotechnical Engineering Report Preliminary Design Recommendations 3. Mechanical stabilization with a coarse-crushed aggregate compacted into the subgrade, possibly in conjunction with a geotextile. 4. Soil/cement admixture stabilization. 9.5 Wet Weather Conditions If construction proceeds during an extended wet-weather construction period and the moisture-sensitive site soils become wet, they will become unstable. Therefore, the bids for site grading operations should be based upon the time of year that construction will proceed. It is expected that in wet conditions additional soils may need to be removed and/or other stabilization methods used, such as a coarse crushed-rock working mat, to develop a stable condition if silty subgrade soils are disturbed in the presence of excess moisture. The severity of construction disturbance will be dependent, in part, on the precautions that are taken by the contractor to protect the moislure-and disturbance-sensitive site soils. If overexcavation is necessary, it should be confirmed through continuous observation and testing by a representative of our firm. 9.6 Temporary and Permanent Cut Slopes In our opinion, stable construction slopes should be the responsibility of the contractor and should be determined during construction. For estimating purposes, however, we anticipate that temporary, unsupported cut slopes in unsaturated surficial weathered lodgement till can be made at a maximum slope of 1.5H:IV (Horizontal:Vertical) or flatter. Temporary slopes in unsaturated lodgement till may be planned at IH: 1 V. As is typical with earthwork operations, some sloughing and raveling may occur, and cut slopes may have to be adjusted in the field. If ground water seepage is encountered in cut slopes, or if surface water is not routed away from temporary cut slope faces, flatter slopes will be required. In addition, WISHAlOSHA regulations should be followed at all times. Permanent cut and structural fIll slopes that are not intended to be exposed to surface water should be designed at inclinations of 2H: 1 V or flatter. All permanent cut or fill slopes should be compacted to at least 95 percent of the modified Proctor maximum dry density, as determined by American Society for Testing and Materials (ASTM):D 1557, and the slopes should be protected from erosion by sheet plastic until vegetation cover can be established during favorable weather. 9.7 Frozen Subgrades If earthwork takes place during freezing conditions, all exposed sub grades should be allowed to thaw and then be recompacted prior to placing subsequent lifts of structural fIll or foundation components. Alternatively, the frozen material could be stripped from the subgrade to reveal unfrozen soil prior to placing subsequent lifts of fill or foundation components. The frozen soil should not be reused as structural fill until allowed to thaw and adjusted to the proper moisture content, which may not be possible during winter months. December 20, 2013 ASSOCIATED EARTH SCIENCES, INC. BWGIpc -TE130561A3 -Projects120lj0S611TE1WP Page 12 Proposed Melrose Short Plat Renton, Washington 10.0 STRUCTURAL FILL Subsurface Exploration and Preliminary Geotechnical Engineering Report Preliminary Design Recommendations All references to structural fIll in this report refer to sub grade preparation, fill type and placement, and compaction of materials, as discussed in this section. If a percentage of compaction is specified under another section of this report, the value given in that section should be used. After stripping, planned excavation, and any required overexcavation have been performed to the satisfaction of the geotechnical engineer, the upper 12 inches of exposed ground in areas to receive fIll should be recompacted to 90 percent of the modified Proctor maximum density using ASTM:D 1557 as the standard. If the subgrade contains silty soils and too much moisture, adequate recompaction may be difficult or impossible to obtain and should probably not be attempted. In lieu of recompaction, the area to receive fill should be blanketed with washed rock or quarry spalls to act as a capillary break between the new fill and the wet subgrade. Where the exposed ground remains soft and further overexcavation is impractical, placement of an engineering stabilization fabric may be necessary to prevent contamination of the free-draining layer by silt migration from below. After recompaction of the exposed ground is tested and approved, or a free-draining rock course is laid, structural fill may be placed to attain desired grades. Structural fill is defined as non-organic soil, acceptable to the geotechnical engineer, placed in maximum 8-inch loose lifts, with each lift being compacted to 95 percent of the modified Proctor maximum density using ASTM:D 1557 as the standard. Use of soils from the site in structural fill applications is acceptable if the material meets the project specifications for the intended use, and if specifically allowed by project specifications. In the case of roadway and utility trench filling, structural fill should be placed and compacted in accordance with current City of Renton codes and standards. The top of the compacted fill should extend horizontally outward a minimum distance of 3 feet beyond the locations of the roadway edges before sloping down at an angle of 2H: I V. Structural fills with sloping faces that cannot be compacted directly by a vibratory roller should be compacted by overbuilding, then cutting back to a compacted slope core. Track walking alone is not an effective means of compacting a structural fill slope. The contractor should note that any proposed fill soils must be evaluated by AESI prior to their use in fills. This would require that we have a sample of the material 72 hours in advance to perform a Proctor test and determine its field compaction standard. Soils in which the amount of fine-grained material (smaller than the No. 200 sieve) is greater than approximately 5 percent (measured on the minus No.4 sieve size) should be considered moisture-sensitive. Use of moisture-sensitive soil in structural fills should be limited to favorable dry weather conditions, and is only permitted if specifically allowed by project plans and specifications. The native soils present on-site contained significant amounts of silt and are considered highly moisture-sensitive. If fill is placed during wet weather or if proper compaction cannot be December 20, 2013 ASSOCIATED EARTH SCIENCES, INC. BWGlpc -TEJ10561A3 -Projecrsl20J305611TEIWP Page 13 Proposed Melrose Shon Plat Renton, Washington Subsurface Exploration and Preliminary Geotechnical Engineering Repon Preliminary Design Recommendations obtained, a select import material consisting of a clean, free-draining gravel and/or sand should be used. Free-draining fill consists of non-organic soil with the amount of fine-grained material limited to 5 percent by weight when measured on the minus No. 4 sieve fraction with at least 25 percent retained on the No.4 sieve. A representative from our firm should inspect the stripped sub grade and be present during placement of structural fill to observe the work and perform a representative number of in-place density tests. In this way, the adequacy of the earthwork may be evaluated as filling progresses, and any problem areas may be corrected at that time. It is important to understand that taking random compaction tests on a part-time basis will not assure uniformity or acceptable performance of a filL As such, we are available to aid the owner in developing a suitable monitoring and testing program. 11.0 FOUNDATIONS Spread footings that are supported on structural fill or a combination of structural fill and native lodgement till sediments may be designed witb an allowable foundation soil bearing pressure of 2,500 pounds per square foot (psf), including both dead and live loads. Higher foundation soil bearing pressures are possible but are not expected to be needed. An increase of one-third may be used for short-term wind or seismic loading. Footings should be buried at least 18 inches into the surrounding soil for frost protection. However, all footings must penetrate to tbe prescribed bearing stratum, and no footing should be founded in or above organic or loose soils. All footings should have a minimum width of 18 inches. It should be noted that the area bound by lines extending downward at IH: 1 V from any footing must not intersect another footing or intersect a filled area that has not been compacted to at least 95 percent of ASTM:D 1557. In addition, a 1.5H:IV line extending down from any footing must not daylight because sloughing or raveling may eventually undermine the footing. Thus, footings should not be placed near the edge of steps or cuts in the bearing soils. Anticipated settlement of footings founded as described above should be on the order of % inch or less. However, disturbed soil not removed from footing excavations prior to footing placement could result in increased settlements. All footing areas should be inspected by AESI prior to placing concrete to verifY that the design bearing capacity of the soils has been attained and that construction conforms to the recommendations contained in this report. Such inspections may be required by the governing municipality. Perimeter footing drains should be provided, as discussed under the "Drainage Considerations" section of this report. December 20, 2013 ASSOCIATED EARm SCIENCES, INC. BWGlpc -TE13056JAJ -Projerul20J3056J1TElWP Page 14 Proposed Melrose Short Plat Renton, Washington 11.1 Drainage Considerations Subsurface Exploration and Preliminary Geotechnical Engineering Report Preliminary Design Recommendations Foundations should be provided with foundation drains. Drains should consist of rigid, perforated, polyvinyl chloride (PVC) pipe surrounded by washed pea gravel. The drains shonld be constructed with sufficient gradient to allow gravity discharge away from the proposed buildings. No other runoff shonld be placed into the footing drain system. 12.0 FOUNDATION WALLS All backfill behind foundation walls or around foundation units should be placed as per our recommendations for structural fill and as described in this section of the report. Horizontally backfilled walls, which are drained and free to yield laterally at least 0.1 percent of their height, may be designed to resist active lateral earth pressure represented by an equivalent fluid equal to 35 pounds per cubic foot (pct). Fully restrained, drained, horizontally backfilled, rigid walls that cannot yield should be designed for an at-rest equivalent fluid of 50 pcf. Walls with sloping backfill up to a maximum gradient of 2H:IV should be designed using an equivalent fluid of 55 pef for yielding conditions or 75 pcf for fully restrained conditions. If parking areas are adjacent to walls, a surcharge equivalent to 2 feet of soil should be added to the wall height in determining lateral design forces. As required by the 2012 mc, retaining wall design should include a seismic surcharge pressure in addition to the equivalent fluid pressures presented above. Considering the site soils and the recommended wall backfill materials, we recommend a seismic surcharge pressure of 5H and lOH psf, where H is the wall height in feet, for the "active" and "at-rest" loading conditions, respectively. The seismic surcharge should be modeled as a rectangular distribution with the resultant applied at the midpoint of the walls. The lateral pressures presented above are based on the conditions of a uniform backfill consisting of excavated on-site soils, or imported structural fill compacted to 90 percent of ASTM:D 1557. A higher degree of compaction is not recommended, as this will increase the pressure acting on the walls. A lower compaction may result in settlement of slab-on-grade floors or other structures supported above the walls. Thus, the compaction level is critical and must be tested by our firm during placement. Surcharges from adjacent footings or heavy construction equipment must be added to the above values. Perimeter footing drains should be provided for all retaining walls, as discussed under the "Drainage Considerations" section of this report. It is imperative that proper drainage be provided so that hydrostatic pressures do not develop against the walls. This would involve installation of a minimum, 1-foot-wide blanket drain to December 20, 2013 ASSOCIATED EAKTH SCIENCES, INC. BWG/pc -TE13056IA3 -Projectsl20130561IIE1WP Page 15 Proposed Melrose Short Plat Renton, Washington Subsurface Exploration and Preliminary Geotechnical Engineering Report Preliminary Design Recommendations within 1 foot of finish grade for the full wall height using imported, washed gravel against the walls. 12.1 Passive Resistance and Friction Factors Lateral loads can be resisted by friction between the foundation and the natural glacial soils or supporting structural fill soils, and by passive earth pressure acting on the buried portions of the foundations. The foundations must be backfilled with structural fill and compacted to at least 95 percent of the maximum dry density to achieve the passive resistance provided below. We recommend the following allowable design parameters: • Passive equivalent fluid = 250 pef • Coefficient of friction = 0.30 13.0 PAVEMENT RECOMMENDATIONS Pavement areas should be prepared in accordance with the "Site Preparation" section of this report. If the stripped native soil subgrade can be compacted to 95 percent of ASTM:D 1557 and is firm and unyielding, no additional preparation is required. Soft or yielding areas should be overexcavated to provide a suitable subgrade and backfilled with structural fill. The pavement sections included in this report section are for driveway and parking areas on-site, and are not applicable to right-of-way improvements. At this time, we are not aware of any planned right-of-way improvements; however, if any new paving of public streets is required, we should be allowed to offer situation-specific recommendations. Pavement areas should be prepared in accordance with the "Site Preparation" section of this report. The exposed ground should be recompacted to 95 percent of ASTM:D 1557. If required, structural fill may then be placed to achieve desired subbase grades. Upon completion of the recompaction and structural fill, a pavement section consisting of 2'h inches of asphaltic concrete pavement (ACP) underlain by 4 inches of 1 \<I-inch crushed surfacing base course is the recommended minimum in areas of planned passenger car driving and parking. Pavement sections for use by heavy vehicles are not expected to be needed for this project. We can provide heavy pavement section recommendations on request. The crushed rock course must be compacted to 95 percent of the maxinrum density, as determined by ASTM:D 1557. All paving materials should meet gradation criteria contained in the current Washington State Department of Transportation (WSDOT) Standard Specifications. December 20, 2013 BWGIpc. -TE1J0561A3 -Projwsl20J30S61\TEIWP ASSOCIATED EARI1I SCIENCES, INC Page 16 Proposed Melrose Shan Plat Renton, Washington Subsurface Exploration and Preliminary Geotechnical Engineering Report Preliminary Design Recommendations 14.0 PROJECT DESIGN AND CONSTRUCTION MONITORING Our report is preliminary since project plans had not been finalized at the time this report was written. We recommend that AESI perform a geotechnical review of the plans prior to final design completion. In this way, we can confirm that our earthwork and foundation recommendations have been properly interpreted and implemented in the design. We are also available to provide geotechnical engineering services during construction. Construction monitoring services are not part of this current scope of work. If these services are desired, please let us know, and we will prepare a cost proposal. We have enjoyed working with you on this study and are confident that these recommendations will aid in the successful completion of your project. If you should have any questions or require further assistance, please do not hesitate to call. Sincerely, ASSOCIATED EARTH SCIENCES, INC. Kirkland, Washington Bruce W. GiIenzler, L.E.G. Senior Project Geologist Attachments: Figure 1: Figure 2: Appendix: December 20, 2013 Vicinity Map Site and Exploration Plan Exploration Logs Laboratory Testing Results BWGlpc -TE]30561A3 -Projects\20/3056/11E1WP Kurt D. Merriman, P.E. Senior Principal Engineer ASSOCIATED EARTH SCIENCES, INC. Page 17 ., toe 1 ..... . " Ill. )\ " " \" I .~ .. ;11 • '""", 1 I ~f.lr "1ii" ~~,ll 'I I :'~, '( ~ ! c, .. ;r-'f ' ., I " j- REFERENCE: USGS TOPO! " , I, Associated Earth Sciences, Inc. ., .. , "i· c,· -, I rill j \ ) -4- ~ ..... , .. , I ". ". .' " . "Co ... ~: ", -". ~ . /:..r ! \, .\; "\.','1 ., L! . i , / S~-: .... ":'·"~·!;." f"·,:.l/~ "'; 1 • , /. J. ',-,"',' '~ " \~t<:,:'> \ . '., ~, _1. , ", K'-';;;;:i.ii~ • io,.,f);. HI - . .. \ . \ ) '., ~ ... _ ,_ ..... ,. . _....r • -'.' , '""'": "_',~ , ( • I .: .,---1' • I - t~~·, '\ . ,( , ~:'-~~ .: . '.\ .. ,",' .tiQIf: BLACK AND WHITE REPRODUCTION OF THIS COLOR ORIGINAL MAY REDUCE ITS EFFECTIVENESS AND lEAD TO INCORRECT INTERPRETATION. VICINITY MAP MELROSE SHORT PLAT RENTON, WASHINGTON a I N A 1000 . FEET 2000 I FIGURE 1 DATE 12113 PROJ_ NO_ TE130561A :Ii .. ~ ~ /1] I I I ~ 'f. \ "- ".9,0 I \ I I \ ~ ( \ \ \. 487 -_-. """ '. \ y.... \.... \ ~O', ASPHALT ''''\. 'd> ~ '\. '\ \ \ \ \ ----~~;----~~----~--.----~ 10BTHAVESE REFERENCE: BEYlER CONSULTING APPROXIMATE LOCATION 4/ OF EXPLORATION PIT TYP • '!i J I \ I , .. , / ~I .: .. \:l .,; *1 ~ o I 15 I FEET 30 ! ~ • Associated Earth Sciences, Inc. SITE AND EXPLORATION PLAN FIGURE 2 I $ .' rAJ IIii:J IZ".iI •. MELROSE SHORT PLAT DATE 12113 ~ _______ ~ _____ ~ _____ I111 ___________________ R_E_N_T_O_N_,\M __ ~_S_H_IN_G_T_O_N ____________ ~P~R~O~J.~N~O~.T~E~I~30~56~I~A __ __ APPENDIX GC gravel and sand, little to gravel gravel with sand, to no fines Clayey gravel and clayey gravel with sand Poorly-graded sand and sand with gravel, little to no fines Silty sand and . SM silty sand with gravel Clayey sand and clayey sand with gravel ---if---------l Silt, sandy silt, gravelly silt, ML slit with sand or gravel medium I pl"stl"lty;; silty, sandy, or gravelly clay, lean clay clay or silt of low Terms Describing Relative Density and Consistency Density SPT~)blows/foot Coarse-Very Loose Oto 4 Grained Soils Loose 4to 10 Medium Dense 10 to 30 Dense 30 to 50 Test Symbols Very Dense >50 G -Graln Size M ~ Moisture Content ConSistent::;' SPT(2t,lows/foot A ~ Atterberg Umlts Fine-Very Soft o t02 C ~ Chemical Grained Soils son 2t04 DD ~ Dry Density Medium Stiff 4 taB K ~ Penneabiilty Stiff B t015 Very Stiff 15 to 30 Hard >30 Descriptive Term Boulders Component Definitions Size Range and Sieve Number Larger tnan 12" Cobbles Gravel Coarse Gravet Rna Gravel Send Coarse Sard Medium Send AneSand SOt and Clay 3' to 12" 3' to No.4 (4.75 mm) 3~ to 3/4- 3/4' to No.4 (4.75 mm) No.4 (4.75 mm) 10 No. 200 (0.075 mm) No.4 (4.75 mm) to No. 10 (2.00 mm) No. 10 (2.00 mm) to No. 40 (0.425 mm) No. 40 (0.425 mm) to No. 200 (0.075 mm) Smaller then No. 200 (0.075 mm) Estimated Percentage Moisture Content Dry ~ Absence of moisture, dusty, dry 10 the IoucIl Slightly Moist -Perceptible moisture Component Percentage by Weight Trace Few UtUe WiIh Sampler Type 2.0'00 Spllt-Spoon Sampler <5 5to 10 15 to 25 ~ Non-primary coarse constituents: .:::. 15% -Fines content between 5% and 15% Moist -Damp but no visible water Very Moist -Water visible but not free draining Wet· Visible free water, usually from below water table Symbols BIows/6~· or portion of 6" I • • • Sampler Type Description 3.0' 00 spin-spoon Sampler ,.) Cement grout surface seal Bentonite seal -~----"':77-:--.-::--I (SPl) high plasticity, 3.25' 00 Spln-spoon Ring Sempler ~ Flter pack with :. btank casing 0.-section or gravelly c1ey, fat Bulk sample clay with sand or gravel ~_+-________ -I Grab Sample • 3.0' 00 thin-Wail Tube Sampler Qncfudlng Shelby tube) :' Screened casing -or Hydrotlp '. ". with liter pack :. Endcap Organic clay or sitt of o Portion not recovered OH medium to high Percentage by dry weight ~-.JL_~~~_!~~' ~ _____ ~ t2) (SPl) Standard Penetration Tesl Peat, muck and other highly organic sQlls (ASTM D-15B6) 13) In General Accordarce with Standard Practice for Deoonption 1'1 Depth of ground water :f ATD ~ At time 01 drilHng ~ Static waler _ (date) (6) Combined uses symbols used for flnes between 5% and 15% end ldentffication of Soils (ASTM ~24BB) I Classifications of solis in this report are based on Vhiual field amilor laboratory observations. which Include density/consistency, moIsture condltrOf\ grain size, and' plastlctty estimates: and should not be construed to lmpJy field or laboratory lestlng unless presented herem. Vlsua1-manual and/or laboratory classification 5 methods of ASTM 0-.2487 and D-24BB were used as an Identfftcatlon guide for the Unified Sol Classtfication System. ~ l============================================ . Associated Earth Sciences, Inc. i ----------------------------------------------------------- EXPLORA liON LOG KEY FIGURE A1 LOG OF EXPLORATION PIT NO. EP-1 S This log Is part of the report rrrepared by Associated Earth Sciences, Inc. (AESI) for the named RrOject and should be t read togetlier with that rsPQ for com;R'ate interpretation. This summary ~p!ies only to the loea Ion of this trench at the '" time of excavation. Subsurface cond' Ions may change at this location wi the passage of time. The data presented are 0 a simplfication of actual conditions encountered. DESCRIPTION Topsoil 1 Vashon Lodgement "" 2 Medium dense, moist, reddish brown, fine SAND, trace medium to coarse sand, little silt, few fine to coarse gravel; weathered (SM). 3 - 4 - 5 -Medium dense, moist to very mOist, mottled brown, fine SAND, trace medium to coarse sand, little silt, few to little fine to coarse gravel, with layers (1 to 2 inches thick) of fine to medium sand, few to 6 - little silt (SM). Medium dense to dense, moist to very moist, brown, fine SAND, trace medium to coarse sand, little 7 - silt, little fine to coarse gravel (diamict) (SM). 8 - 9 - 10 -Very dense, moist to very moist, brown, fine SAND, trace medium to coarse sand, little silt, little fine r\to coarse gravel (diamict) (SM). r 11 - BoHom of exploration pit at depth 10 feet No seepage. No caving. 12 - 13 - 14 - 15 - 16 - 17 - 18 - 19 - 28 M " ;------------------------------------------------------------------------------------ Melrose Short Plat J ~ Logged by: LDM Approved by: Renton, WA Associated Earth Sciences, Inc. Project No. TE130561 A 12/9113 ------------------------------------------------------------------------------------------------------- I LOG OF EXPLORATION PIT NO. EP-2 . -------~ g This log is part of the report rrrepared by Associated Earth Sciences, Inc. (AESJ) for the named ftrOject and should be £i read tqgether with that rePe;? for comftlete interpretation. This summary agplles only to the loea ion of this trench at the "-time of excavation. Subsurface condi ions may change at this location Wit the passage of time. The data presented are <D 0 a simplfication of actual conditions encountered. DESCRIPTION Topsoil 1 Vashon Lodgement Till 2 -Medium dense, very moist, reddish brown, fine SAND, trace medium to coarse sand, little silt, few fine to coarse gravel; weathered (SM). I 3 Medium dense, moist to very mOist, mottled brown, fine SAND, trace medium to coarse sand, little ! silt, few to little fine to coarse gravel, with lenses (1 to 2 inches thick) of fine sand, little to with silt 4 (diamict); stratified (SM). 5 6 -Dense, very moist, brown to gray, fine SAND, trace medium to coarse sand, little to with silt, little 7 -fine to coarse gravel (diamicl), with layers «1 inch thick) of fine to medium sand, few silt(SM). 8 - 9 -Very dense, very moist, gray, fine SAND, trace medium to coarse sand, little silt, few fine to coarse 10 -I\gravel, with layers «1 inch thick) of fine to medium sand, few silt (SM). . r Bottom of exploration pit at depth 9,5 feet No seepage. No caving. 11 - 12 - 13 - 14 - 15 - 16 - 17 - 18 - 19 - I I ~--~2~O~-----------------------------------------------------------------------------e------------------------------------------------------------------------------------ 0 1 Melrose Short Plat • Renton, WA Logged by: LDM Approved by: Associated Earth Sciences, Inc. Project No. TE130561 A 1219113 ~ ------------------------------------------------------------- ~ '" o 2 - 3 - LOG OF EXPLORATION PIT NO. EP-3 This log is part of the report prepared by Associated Earth Sciences, Inc. (AESI) for the named project and should be read together with that repqrt for complete interpretation. This summary aoolies only to the location of this trench at the time of excavation. Subsurface conditions may change at this location with'the passage of time. The data presented are a slmplfication of actual conditions encounterBd. DESCRIPTION Topsoil Vashon Lodgement Till Medium dense, very moist, reddish brown, fine SAND, trace medium to coarse sand, little silt, few fine to coarse gravel; nonstratified; weathered (SM). Dense, moist to very moist, mottled brown, fine SAND, trace to few medium to coarse sand, little 4 -silt, little fine to coarse gravel (diamict) (SM). 5 - 6 -Dense, moist to very moist, brown to gray, fine SAND, trace medium to coarse sand, little silt, few to little fine to coarse gravel, with layers (t to 2 inches thick) of few silt(SM). 7 - 8 - 9 - Very dense, very moist, brown, fine SAND, trace medium to coarse sand, little silt, few fine to 10 -[\,coarse gravel, with layers (1 to 2 inches thick) of fine to medium sand, few silt (SM). r 11 - 12 - 13 - 14 - 15 - 16 - 17 - 18 - 19 - Bottom of exploration pit at depth 10 feet No seepage. No caving. ~--~2~O~----------------------------------------------------------------------------m----------------------------------------------------------- " ~ Logged by: LDM Approved by: Melrose Short Plat Renton, WA Associated Earth Sciences, Inc. Project No. TE130561A 1219113 --------------------------------------------------- GRAIN SIZE ANALYSIS -MECHANICAL Date Sampled Project Project No. Soil Description 12/1112013 Rozenblat TE130561A Sand little gravel little silt Tested Sy Location ESIEP No lDePth MS Onsite EP·2 2' wt. of moisture wet sample + Tare 316. Total Sample Tare Wt. of moisture dry Sample + Tare 286.81 Total Sample wt + tare wt. of Tare .. Total Sample Wt 747.2 Wt. of moisture D Sample 184.77 Total Sample Dry Wt 645.2 Moisture % 16% Sieve No. Dian (mm) Wt (! % % i .1"'" '. ·C>.· 0.0· . " " c u: -c 8 " ~ 100 ; 80 60 40 20 o 100 3" , US STANDARD SIEVE NOS. 314" NO.4 NO.16 NO.40 NO.200 ~ . ~ Ii. "l! "' , .. "' 10 01 Gravel Sand Silt and Clay Coarse I Fine Coarse I Medium I Fine Grain Size, mm ASSOCIA TED EARTH SCIENCES, INC. 911 5th Ave., Suite 100 Kirkland. WA 98033 425-827·no1 FAX425-827-5424 001 iB: BEYLER CONSULTING Prepared for: Prepared by: Reviewed by: CONTACT phone: 253-380-2958 fax. 253-582-5694 landon(ci'beylerconsulting,coM beylerconsultrng.com OFFiCE 10314 lOOth St. SW Lakewood, WA 98498 Plan. Design. Manage. CIVIl. [NGIN[[RIi'.JG I L/\ND Pl/\"INING I rU,SIGUT'! PROJ[CT MI\'-.lI\G['vI[N~ I PC:RMIT =XP[DITI~::; MELROSE SHORT PLAT Preliminary Drainage Report Jossif Rosenblat 5415 NE 2 nd Ct Renton, WA 98509 January 24, 2014 Brandon Loucks, PE Landon C. Beyler, P.E. Beyler Consulting 7602 Bridgeport Way W #3d Lakewood, WA 98499 253.301.4157 IVED FEB 1 0 2014 CITY OF RENTON PLANNING DIVISION TABLE OF CONTENTS I. PROJECT OVERVIEW •••••••..••••••••••••••••••••••••••••••••••••••••••••••••••••••• 3 Project Description ....................................................................... 3 TIR Worksheet ............................................................................. 5 II. CONDITIONS AND REQUIREMENTS SUMMARy ......................... 6 III. OFFSITE ANALYSIS ••••••••••••••••••••••••••..••••••••••••••••••••••••••••• 11 ••••••• 8 3.1.1 Task 1 -Study Area Definition and Maps ............................ 8 3.1.2 Task 2 -Resource Review ................................................ 8 3.1.3 Task 3 -Field Inspection .................................................. 9 3.1.3.1 Upstream and onsite runoff ............................................... 9 3.1.3.2 Downstream ................................................................... 9 3.1.4 Task 4 -Drainage System Description and Problem Descriptions .............................................................................. 10 3.1.5 Task 5 -Mitigation of Existing or Potential Problems .......... 10 IV. FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 10 V. CONVEYANCE SYSTEM ANALYSIS AND DESIGN ...................... 14 VI. SPECIAL REPORTS AND STUDIES ........................................... 14 VII. OTHER PERMITS ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 14 VIII. CSWPPP ANALYSIS AND DESIGN ........................................... 14 IX. BOND QUANTITIES, FACILITY SUMMARIES, AND DECLARATION OF COVENANT .•••••.•••••••••••••••••••••••••••••••••••••••••••••••••••••.•••••••••••••••••••• 14 X. OPERATION AND MAINTENANCE MANUAL .............................. 14 XI. Appendices •••.•••••.•••••.•••••...••.••.••••••••••••..••••••••••••••••••.•••••••.•••••. 15 iB: APPENDIX A -OFFSITE STUDY MAPS APPENDIX B -DOWNSTREAM SYSTEM TABLE AND MAPS APPENDIX C -CSWPPP BEYLER I PROJECT OVERVIEW Project Description This project proposes to short plat a vacant parcel located in Renton Washington. The project is located within the Renton City limits, however does not currently have an assigned address yet (parcel #322305-9202). The current zoning of the parcel is Residential 8 indicating a maximum density of 8 dwelling units per acre. This project proposes 2 lots on the 0.41 acre property, each approximately 8,232 sf. The remaining area will be dedicated for future right- of-way. The short plat proposal includes providing 2 lots for single family residences, a shared use driveway within a access and utility easement, frontage improvements, and appropriate utilities. The futures houses will be permitted at a future date. The property is adjacent to 108th Ave SE (SR 515, Principal Arterial), to the north and south are single family residences, and to the east is a single family residence within the Vista Hills subdivision. The project is keeping consistent with neighboring land use characteristics. It has been requested on the preapplication memorandum, dated October 9, 2013 to provide improvements along 108th Ave SE to meet the City's complete street standards. These improvements include an 8-foot planting strip behind the existing curb, a 12-foot sidewalk, and a 2-foot strip back of the sidewalk. To build this, approximately 12' of right-of-way is proposed for dedication. The site will be accessed off of 108th Ave SE near the southeast corner of the property. The access way will be a 12' paved shared-use driveway within a 20' access and utility easement. The 12' shared driveway will be approximately 80 linear feet. This project is subject to the 2009 King County Surface Water Design Manual (King Manual) and the City of Renton amendments to the Manual (Renton Manual). Per Figure 1.1.2.A of the Renton Manual, the project is subject to a Full drainage review. A subsurface exploration on the project site was conducted by Associated Earth SCiences, Inc (AES) in December 2013. In summary, each of the exploration pits encountered native sediments consisting of medium dense grading to very dense sand with varying silt and gravel content (23% silt). This is interpreted as Vashon Lodgement till. AES does not recommend infiltration as a method for managing storm water. A field study was conducted by EnCo Environmental Corporation to locate any wetlands or streams located on the site and determine any required buffers. Based on observation, review of collected data, and evaluation of readily available maps, the project site does not contain wetlands or streams at this time. The edges of wetland and streams were not identified within 200 feet of the project site. iB: BEYLER 1- / VALLn' "'EOlCAL CENTER 1_ l--- \.-·'~-T·' '., ~:"''-I I -__ l , ----' "---, .. I -'-' FIGURE 1.1 \" . --' -'. --" / '.-' ,-/ . /'/ PROJECT I, // SITE r , .. VICINITY MAP N.T.S t __ Sf 1~6rH ~L TIR Worksheet TlR Worksheet will be completed during final engineering lB: SEYLER Ii. CONDITIONS AND REQUIRElviENTS SUMfJiARv (The plat conditions with responses will be placed here upon receipt of conditions) Review of Eight Core Requirements and Five Special Requirements The following comments are a review of the Core and Special Requirements per the 2009 Ki ng County Surface Water Storm water Manual. Core Requirement No.1 Discharge at the Natural Location The site's topography suggests that stormwater runoff from the site sheets flows to the east through the project parcel to the city drainage system in 108th Ave SE. Under developed conditions, stormwater from the shared driveway will be directed toward 108th Ave SE to an existing catch basin. Core Requirement No 2 Offsite Analysis The project proposes to discharge all stormwater to the existing conveyance system in 108th Ave SE. A Level 1 off site analysis was conducted January 22 2014. No flooding or potential flooding problems were identified downstream of the site. Further narrative of this analysis can be found in Section III of this report. Core Requirement No 3 Flow Control Flow Control Facility (1.2.3.1.Bl: The proposed project is located within the Flow Control Duration Standard -Matching Forested area per the Renton Manual. This is equivalent to Conservation Flow Control in the King Manual which matches requiring runoff from developments to be detained and released at a rate that matches the flow duration of predeveloped rates. The above is required unless an exception applies to the proposed site conditions. The developed conditions of do not exceed a 0.1 ds difference in the sum of developed 100- year peak flows for those target surfaces subject to the flow control facility requirement and the sum of forested site conditions 100-year peak flows for the same surface areas. Thus flow control is not required for this basin per section 1.2.3.1.B of the Renton Manual. See Section N of this report for details and a table of the target areas. Flow Control BMPs: In addition to flow control facility requirements, projects subject to Core Requirement #3 must apply flow control BMPs to impervious surfaces on each individual lot. Flow control BMPs are methods and design for dispersing, infiltrating, or otherwise reducing development increases in runoff. However, implementation of flow control BMPs on indiVidual lot as part of this short plat project is optional per Section 5.2.2.1 of the King Manual. The applicant has chosen to defer implementation of flow control BMPs on the individual lots of the short plat until the building permit is obtained for construction on each lot. Stubs for roof drain connections will be provided as a part of this short plat. Core Requirement No.4 Conveyance System All new pipes systems will be designed with sufficient capacity to convey and contain at minimum the 25-year peak flow. Conveyance design will be completed during final engineering. iB: -1"'-" .. -; .~/ BEYLER Core Requirement No.5 Erosion and Sediment Control This development will be constructed in one phase. A CSWPPP will be prepared during final engineering. Core Requirement No.6 Maintenance and Operations The maintenance and Operations Manual will be included during final engineering. Core Requirement No.7 Financial Guarantees and Liability Financial guarantees will be provided during final engineering. Core Requirement No.8 Water Quality This project falls within a Basic Water Quality treatment land use area as designated by the Renton Manual and is not subject to Enhanced Basic WQ menu per Section 1.2.8.1.A. The goal of Basic WQ treatment is 80% removal of total suspended solids. The project though falls under the Pollution Generating Impervious Surface (PGIS) threshold of 5,000 sf within a threshold discharge area. Stormwater treatment is not required for this project. See Section IV of this report for details and a table of the target areas. Special Requirement No.1 Other Adopted Area-Specific Requirements This project is not in a designated Critical Drainage Area. This special requirement is not applicable. Special Requirement No.2 Flood Hazard Area Delineation The project does not contain or is not adjacent to a flood hazard area for a river, stream, lake, wetland, closed depreSSion, or marine shoreline that is within the 100-year floodplain according to King County and FEMA. Special Requirement No.3 Flood Protection Facilities This project does not rely on any flood protection facility such as a levee or revetment nor will construct a new flood protection facility. Special Requirement No.4 Source Control This project does not require a commercial building or commercial site development permit. This special requirement is not applicable. Special Requirement No.5 Oil Control This project is not defined as a high-use site nor is a redevelopment project proposing $100,000 or more of improvements to an existing high-use site. This special requirement is not applicable. iB: BEYLER ilL OFFSlfE ANALYSIS A preliminary off site analysis report has been prepared per Section 1.2.2, Core Requirement #2. This is to identify and evaluate offsite flooding, erosion, and water quality problems that may be created or aggravated by the proposed project. The primary component of this off site analysis report is the downstream analysis. The second component of the report is to evaluate the upstream drainage system to verify that significant flooding and erosion impact will not occur as a result of the project. 3.1 DOWNSTREAM ANAL YSIS The following Level 1 downstream analysis is a review of the drainage system up to a mile downstream of the site. 3.1.1 The four tasks outlined under this review are: Task 1 -Define and map the study area Task 2 -Review all available information on the study area Task 3 -Field inspect the study area Task 4 -Drainage System Description and Problem Descriptions Task 1 -Study Area Definition and Maps The project is located in the King County Black River Drainage Sub-Basin within the Duwamish-Green water resource inventory area. The drainage study area is approximately a mile long path encompassing the site's downstream corridor. See Appendix A for maps of the basic study area. The site is currently vacant, surrounded by NE 203rd to the South and single family residences to the north, east, and west. 3.1.2 Task 2 -Resource Review The following resources have been reviewed for the downstream analysis. This is a review of all available information on the downstream area at least a mile downstream. Sources include the City of Renton GIS maps, King County GIS maps, geotechnical studies, wetland studies. Sensitive Area (See Appendix A for Sensitive Area Maps) iB: • Erosion-Project site mapped as high erosion potential according to the geotechnical report prepared by AES. However, the downstream path is within a closed conveyance system. • Seismic -None Mapped • Landslide -None Mapped • Coal Mine -None Mapped • Streams and Wetlands Map -None Mapped • Susceptible to Groundwater Contamination -Low • 100 year flood plain -According to King County iMAP and the FEMA Flood Maps, the 100 year flood plain is not located near the project property. BEYLER Drainage complaints and studies 3.1.3 King County -Relevant DNRP drainage complaints within 1 mile of the downstream corridor within the last 10 years were searched. There are currently no open complaints within the corridor, however 3 relevant complaints within the last 10 years has been filed. Refer to drainage complaint map in Appendix A for the location of this complaint. See also Task 4 of this Downstream analysis for a description of the complaint and how it was mitigated. Task 3 -Field Inspection A site visit was performed on January 22, 2012 for the purpose of analyzing the proposed project site and its upstream and downstream corridor at least a quarter mile downstream of the site (1,320 ftJ. The weather conditions were cloudy and partly foggy. A description of the drainage path is described below. See Appendix B for downstream reach locations. 3.1.3.1 Upstream and onsite runoff The project site does not appear to be subject to any significant upstream run-to the project site. The site's topography suggests that that stormwater sheet flows through west to the public storm. Currently the site is heavily forested and most stormwater is absorbed into the duff layer and does not convert to runoff. 3.1.3.2 Downstream The following is a discussion of the downstream corridor from the discharge location of the project. See Appendix B for a Summary of each reach including: pipe size, length, and material as well as a map of each reach's location. City of Renton GIS information was utilized to determine pipe size, slope, and length. Reach 1 0-> 1,535' Storm water from the site and upstream flows is collected in an existing catch basin near the proposed shared access entrance on 10Sth Ave SE and enters the public storm system. From this point stormwater is conveyed in 12" Concrete pipes north along lOSth to the limits of the field inspection analysis. The pipe slopes range from 1% to S.5%. See Appendix B for a Summary of each reach including: pipe size, length, and material as well as a map of each reach's location. iB: SEYLER 3.1.4 Task 4 -Drainage System Description and Problem Descriptions The drainage system is comprised mostly an existing piped conveyance system within 10S th Ave SE. However parcels adjacent to 10Sth Ave SE have had some complaints filed with King County. Two existing relevant drainage complaints are listed below. Existing drainage complaint #2006-0549: This complaint is regarding the regional stormwater facility located at the corner of 10Sth and SE lS2nd St. There was a complaint that the facility was not being maintained, the vegetation was very overgrown, and there were rats. This facility has since been cleaned and is in better working order. Existing drainage complaint #2006-0553: This is a Code enforcement case #E0600791 for the same issue above. 3.1.5 Task 5 -Mitigation of Existing or Potential Problems There does not appear to be any existing or potential problems (other than standard maintenance of the piped conveyance system) associated with the site. IV. FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN The stormwater flow control and water quality facilities were designed in accordance with the 2009 King County Surface Water Design Manual (King Manual) and the City of Renton amendments to the Manual (Renton Manual). Existing Site Hvdrology (Part A) Existing conditions on the project site consists of a vacant 0.41 acre parcel. The project is made up of one sub basin where the site generally slopes down from the west to east over a relatively flat grade. The overall vertical relief of the site is approximately 5 feet. Slopes across the site are generally less than 8 percent. At the eastern edge of the property is rock wall up to 6' in height. The majority of the site is 4 to 6 feet above the Sidewalk and road along lOS th Ave SE. Currently the site is covered with a large amount of deCiduous trees, cottonwoods and alders. Most of the trees are in poor condition. According to the geotechnical report, the topsoil is approximately 1 foot thick. It is likely that with the thick topsoil cover and the large tree canopy cover, most stormwater is absorbed into the soil with very little turning into runoff. Developed Site HYdrology (Part B) The disturbance on Site will include construction clearing and grading, construction the shared use driveway, aSSOCiated utilities, and eventually the two future houses. The future driveways and rooftops have been included in the stormwater calculations. It is proposed that each ilt BEYLER driveway will slope toward the shared use driveway. The shared use driveway will be graded such that it directs runoff to a private catch basin on the shared access. It is then proposed to connect the new CB to the existing catching in 108th Ave SE adjust to the property. A stub for a roof drain connection has been proposed for each lot to tightline rooftop runoff to the new catch basin in the shared driveway. Tables 4.1 and 4.2 break down the historic and developed site conditions TABLE 4 1 -Historic Conditions . Sub-basin Total Area Impervious Till Grass Till Forest sf (ae) Sf (ac) Sf (ac) sf (ac) Site* 16,464 0 0 16J 464 TOTAL 16,464 0 0 16,464 (0.378) (0.378) *The area reflects the site area after ROW dedication . -TABLE 4 2 D eve ope dC d" on Ittons Sub-basin Total Impervious Till Grass PGIS sf (ac) Sf (ac) Sf (ac) (YIn) Site* 16464 Shared Use 936 v 2 Houses 4500 n Lot 1 Conc 834 y Drive Lot 2 Asphalt 777 y Drive Lot 2 Conc 783 Drive Lawn 8634 n TOTAL 16,464 7,830 8,634 (0.378) (0.180) (0.198) TOTAL PGIS 3,330 (0.076) *The area reflects the site area after ROW dedication Performance Standards (part C) Flow Control Facilitv (1 2.3.1.8); The proposed project is located within the Flow Control Duration Standard -Matching Forested area per the Renton Flow Control Application Map Dated 01/09/2014. This is equivalent to Conservation Flow Control in the King Manual which matches requiring runoff from developments to be detained and released at a rate that matches the flow duration of predeveloped rates. This is for a range of predeveloped discharge rates from 50% of the 2- year peak flow up to the full 50-year peak flow and applied to target surfaces only. The above is required unless an exception applies to the proposed Site conditions. The developed conditions do not exceed a 0.1 cfs difference in the sum of developed 100- year peak flows for those target surfaces subject to the flow control facility requirement and the sum of forested site conditions 100-year peak flows for the same surface areas. Thus flow control is not required for this basin per section 1.2.3.1.B of the Renton Manual. Part 0 of this section for analysis output comparing the pre and post flow rates. ill: BEYLER Flow Control BMPs: In addition to flow control facility requirements, projects subject to Core Requirement #3 must apply flow control BMPs to impervious surfaces on each individual lot. Flow control BMPs are methods and design for dispersing, infiltrating, or otherwise reducing development increases in runoff. However, implementation of flow control BMPs on individual lot as part of this short plat project is optional per Section 5.2.2.1 of the King Manual. The applicant has chosen to defer implementation of flow control BMPs on the individual lots of the short plat until the building permit is obtained for construction on each lot. Stubs for roof drain connections will be provided as a part of this plat. Water Qualitv This project falls within a Basic Water Quality treatment land use area as designated by the Renton Manual and is not subject to Enhanced Basic WQ menu per Section 1.2.B.1.A. The goal of Basic WQ treatment is BO% removal of total suspended solids. The project though falls under the Pollution Generating Impervious Surface (PGIS) threshold of 5,000 sf within a threshold discharge area. See Table 4.2. Stormwater treatment is not required for this project. Storm water Conveyance The conveyance system capacity standards require that new conveyance systems contain the 25-year peak flow and ensure that the lOa-year event does not create a severe flooding or erosion problem. See Section V of this report for the conveyance analysis per Core Requirement #4. Flow Control Systems (Part Pl As discussed in Section The developed conditions of do not exceed a 0.1 cfs difference in the sum of developed lOa-year peak flows for those target surfaces subject to the flow control facility requirement and the sum of forested site conditions lOa-year peak flows for the same surface areas. To compare the flow rates, the King County Runoff Time Series (KCRTS) analysis software was used. The project is located in the SeaTac 1 region according to Figure 3.2.2.A of the King Manual. The values in Table 4.2 were input into KCRTS and analysis results are below. All areas are conSidered target as defined in Section 1.2.3.1.B in the Renton Manual. Flow Frequency Analysis [lme Serles Flle:pre.tsTI project Locatlon:Sea-Tac ---Annual Flow Rate (CFS) 0.024 0.006 0.018 0.001 0.011 0.019 0.015 0.031 Peak Flow Rates--- Rank Time of peak 2 7 4 8 6 3 5 1 2/09/01 18:00 1/05/02 16:00 2/28/03 3:00 3/24/04 20:00 1/05/05 8:00 1/18/06 21:00 11/24/06 4:00 1/09/08 9:00 computed peaks ill: SEYLER -----Flow Frequency Analysis------- - -Peaks Rank Return Prob (CFS) peri od 0.019 3 10.00 0.900 0.018 4 5.00 0.800 0.015 5 3.00 0.667 0.011 6 2.00 0.500 0.006 7 1.30 0.231 0.001 8 1.10 0.091 0.028 50.00 0.980 Flow Frequency Analysis [lme serles F1Ie:dev.tsfj ProJect Locatlon:sea-Tac ---Annual Flow Rate (CFS) 0.061 0.047 0.074 0.048 0.059 0.065 0.070 0.127 Peak Flow Rates--- Rank Time of peak 5 8 2 7 6 4 3 1 2/09/01 2:00 1/05/02 16:00 2/27/03 7:00 8/26/04 2:00 10/28/04 16:00 1/18/06 16:00 10/26/06 0:00 1/09/08 6:00 computed peaks Flow Control BMPs -----Flow Frequency Analysis------- - -peaks - -Rank Return prob ~CFS) peri od :s?K ~ ~~:gg g:3g~ 0.070 3 10.00 0.900 0.065 4 5.00 0.800 0.061 5 3.00 0.667 0.059 6 2.00 0.500 0.048 7 1.30 0.231 0.047 8 1.10 0.091 0.109 50.00 0.980 The applicant has chosen to defer implementation of flow control BMPs on the individual lots of the short plat until the building permit is obtained for construction on each lot. Stubs for roof drain connections will be provided as a part of this plat. Water Quality System (Part E) The project is located within a Basic Water Quality treatment area as discussed in Part C in this Section. The project though falls under the Pollution Generating Impervious Surface (PGIS) threshold of 5,000 sf within a threshold discharge area. See Table 4.2. Stormwater treatment is not required for this project. iB: SEYLER v. CONVEl'ANCE SYSTHi ANALYSIS AND DESIGN The conveyance system will be designed per Section 3 and 4 of the King Manual. Table 3.2 of the Manual suggests that the Rational Method of analysis is required for undetained areas for tributary areas less than 10 ac. Further analysis will be provided during final engineering. VI. SPECIAL REPORTS AND STUDIES Geotechnical Report Subsurface Exploration and Preliminary Geotechnical Engineering Report, December 20,2013; Prepared by Associated Earth Sciences Inc. Sensitive Area Study Wetland & Stream Assessment and Certification, November 6, 2013; Prepared by EnCo Environmental Corporation. VII. OTHER PERMITS There are currently no other permits that effect the drai nage submittal or the Technical Information Report. VIII. CSWPPP ANALYSIS AND DESIGN A CSWPPP will be included during final Engineering. IX. BOND QUANTITIES, FACILITY SUMMARIES, AND DECLARATION OF COVENANT A completed Bond Quantities Worksheet can be made available to the County upon request. X. OPERATION AND MAINTENANCE MANUAL The Operations and Maintenance Manual will be submitted at a later date. iB: BEYLER ",,,..',,,,,",0"''''' "'''·'''''IO:~~~~;;;:~,'."':~ '''10'1'''''''"""'' I - .IDC '~I ~1fIrl.JM)N • N a-.. ... ".J ·....,.,1 gJ1 <!yr >-- ''lJ.YQ 'nntI ~ 'UIWOlJ,,' ,~ ....... Y1t<I a:. N01!JNmSVM --:-:;d MrIl'N~~I1~I:/-::-'1oID.i./l3"//Ki .tiD ~ J.\Ild DJOHS 3S0'tJ13W OJ N'Ifld 3.lIS / .13;11-15 "tJ3110:J ~ .... ··c >". ''''''"'''"""'''''' ';.,' ?;~l'UJ.fl()r , - - ~ , , ~t;~~ d:;:' XI. Append Ices APPENDIX A -OFFSITE STUDY MAPS Topography Map Renton , + {C12IOO8Kmog County 01 The informetion indldecl on this map has been compiled by KIng COI.rrty stat'\' rrom II II8Iiely at L'IOIJI'C89 and IS ~ect to d\ange withOut notice. King County makes no represerUtIons or warranties, e~ or impled, 81 to accuracy, completeness, 1irneIrIeas, or rights to the use of SUCh infOrmation. ThIs dOa.iment is not intended tor use 81 a &uI'W)' product King CounIY shall not be ~abI$ for any general, special, Indirea, iocidenIaI, or 00I'IMqU8I"Itia damages i'IcIuding, W not Mmited to, ~ revenues or Io&t profits resutti~ rrom the use or miSuse of the infOrmation contained on this map. Any sale of this map or Information on this map is prohibited except by written permission of King County. Date: 12f2712013 Soutar. King County iMAP -S10rmwatef (http://www.meIrokc.govIGISliMAP) , 110111 til King County Drainage Complaints SL l&iTH Da le : IMAP- APPENDIX B -DOWNSTREAM SYSTEM TABLE AND MAPS Basin: DUWAMISH-GREEN Symbol Drainage Component Type, Name and Size see map Type: sheet flow, swale, stream, channel, pipe, pond; Size: diameter, surface area Reach 1 Pipe Reach 2 Pipe Reach 3 Pipe Reach 4 Pipe Reach 5 Pipe Reach 6 Pipe Reach 7 Pipe OFF-SITE ANALYSIS DRAINAGE SYSTEM TABLE SURFACE WATER DESIGN MANUAL, CORE REQUIREMENT #2 Snbbasin Name: BLACK RIVER Subbasin Number: WRIA #9 Drainage Slope Distance Existing Potential Observations of field I Component from site Problems Problems inspector, resource Description discharae reviewer, or resident I drainage basin, vegetation, % 1,.4 ml -1,320 ft. constrictions, under capacity, ponding, tributary area, likelihood of problem, ! cover, depth, type of sensitive overtopping, flooding, habitat or organism overflow pathways, potential impacts area, volume destrudion, scouring, bank sloughing, i sedimentation, incision, other erosion 57 LF-12" Rep 1% 57' none none 302 LF-12" Rep 4% 359' none none 145 LF-12" Rep 2.8% 504' none none 237 LF-12" Rep 3.2% 741' none none 276 LF-12" Rep 4% 1 ,017' none none 249 LF-12" Rep 8.5% 1,266' none none 269 LF-12" Rep 5% 1,535' none none • 1/9.12009 o 1 : 1,856 155 o 77 155 Feet C ity of RentOD F :" Finan ce & IT Divi s ion Downstream Map 1 Legend City and County Boundary Olher [j Ci, of R,""," Parcels Structu re • Catchbasm -Type 1 • Catchbasin -TypelL • Conaele/Curb !nlet . Type 4 • Orop Inlet • Catchbasm -Type 2 MH Beyler Cons ulting 1212712013 • Calchbasm -Type 1 • Calchbasin -Typel L • Concrete/C urb In let -Type 4 • Drop Inlet Caldlbasm -Type 2 MH c Access Riser Utility Vault • Claanout • Other , Unknown Structure I-'~r IS ,(' , f'ra!f) -!IJJI)I'I ';" ":" ;,-y It:~. (~i~ t!,~ '.ppe9.r ~I'IS ,,'J!(' :l~;; '~ ';; "'J '1'8)' r' , )~ In rv: '(' "ltJi THI S MAP IS NOT TO BE USED FOR NAVIGATION Note s o 1: 1 ,856 155 o 77 155 Feet C ity of Renton Finan c e & IT Division Downstream Map 2 Legend City and County Boundary 0"'" [j C,t, of Ron ton Parcels Structure • Catchb85in -Type 1 • Catctlba sin -Typell • Cooaele/Curt) Inlet -Type 4 • Or op Inlet • CalchOaSin -Type 2 MH Beyler Consulting 12 127/2013 • Catchba5ln • Type 1 • Catchb8Stn -TypelL • ConcretelCurtllnlei . Type 4 • Drop Inlet CatchbaSl n · Type 2 MH • Access Riser Ub li ty Vault • Cleanout • Other .. Unknown Struc1ure tlra' , utf1 I' )rr n nlf r ~r'~ 'l ,~,. Dat "'., 'prJ" r ,,", :t1'~ 1;W;J) 'J~ r:-I .Jt I~ er Ihe'~;:, Jei€ THIS MAP IS NOT TO BE USED FOR NAVIGATION APPENDIX C -CSWPPP Will be submitted at a later date. Mr. Jossef Rozenblat 5415 NE 2nd Court Renton WA 98509 PO Box 1212 Puyallup WA 98371 Telephone: 253.841.9710 www.encoec.com Mr. Gerald Wasser, Associate Planner City of Renton 1055 South Grady Way Renton WA 98057 RE: Wetland & Stream Assessment and Certification Jossef Rozenblat Property November 6, 2013 Address: XXX 108th Avenue SE, Renton, King County, WA 98057 Current Land Use: Undeveloped Proposed Land Use: Residential 1.0 INTRODUCTION & SUMMARY At the request of Mr. Landon Beyler of Beyler Consulting, LLC, EnCo Environmental Corporation (EnCo) performed a wetland and stream assessment on the above-referenced property, herein known as the project site. It is my understanding that the landowner may develop the project site into a 2 lot short plat for two single family residences. Based on observations, review of collected data, and evaluation of readily available maps the project site does not contain wetlands or streams at this time. The edges of wetlands and streams were not identified within 200 feet of the project site. 2.0 DESCRIPTION The project site is located within the jurisdictional boundary of the City of Renton in King County (FIGURE 1 -VICINITY). The lot is situated in the southwest quarter of Section 32, Township 23N, Range 05W of the Willamette Meridian. The property consists of vacant, third grown woodland. The lot is covered with a moderately dense stand of trees with a scrub-shrub and emergent understory. There are no structures on the property. The east boundary of the site is located contiguous with 108th Avenue, SE. The south, west and north boundary of the site is located contiguous to residential properties. There are no other public roads which lie contiguous to the site. The property consists of one separate parcel of land as shown below. Parcel Number Acreage Shape Length eN to S) Width eE to W) A: 322305-9202 0.41 Rectangle 105.54' 168.06' GIS Mapping· Site Assessment • Wetla~d. Remediation· Habitat· stormwateRECEIVED FEB 102014 CITY OF RENTON PLANNING DIVISION 3.0 BACKGROUND Reportedly, a single family dwelling formerly occupied the site. The dwelling has been demolished. A professional land survey was completed on November 1, 2013. 4.0 PURPOSE The purpose of this report is to study and document the presence or non-presence of wetlands and streams on and in the near vicinity to the project site for the City of Renton in support of a proposed application for a 2 lot short plat residential development. 5.0 SCOPE OF WORK EnCo performed the following sub tasks: • Reviewed readily available aerial photographs, agency mapped wetlands, streams, soils, and topography. • Performed one site visit with the landowner or approved representative who is familiar with the project site boundaries, current land use, proposed development, and project envelope. • Established two (2) randomly selected test plots in representative ecological communities as depicted on FIGURE 2 -TEST PLOT LOCATIONS. • Determined the baseline condition of the natural features and land use. • Determined whether or not wetlands exist on the property according to current jurisdictional government agency methodology and within about 200 feet from the project site boundary, proposed development, or change in land use. • Determined whether or not streams or other regulated waterbodies exist on the property according to currently accepted methodology and within about 200 feet from the project site boundary, proposed development, or change in land use. • Determined if wetlands and streams (if identified) are jurisdictional. • Prepared a hand sketch (not to scale) of the test plots over a color aerial photograph. • Prepared this letter on the findings with a PHOTOGRAPHIC LOG (APPENDIX B) documenting current site conditions and the test plots. 6.0 METHODOLOGY The critical area determination was performed using the most current edition of the City of Renton Critical Area Ordinance. The wetland determination method followed the latest version (2008) of the U. S. Army Corps of Engineers Wetland Delineation Manual for Western Mountains, Valleys, and Coast Region and stream determination followed the Washington Department of Natural Resource stream and river dassification system. GIS Mapping· Site Assessment· Wetland' Remediation' Habitat· Stormwater 2 7.0 SCHEDULE & WEATHER CONDITIONS The assessment was performed by Mr. Jonathan Kemp, Professional Wetland Scientist of EnCo on November 4, 2013. The field work took about 4 hours to complete with one project wetland scientist. The site visit was performed during the growing season and weather conditions consisted of mostly clear skies with ambient air temperatures ranging from 44°F to 52°F. No rainfall fell during the field work or within 48 hours. The climatic conditions are considered typical for this time of the year. 8.0 FIELD PROCEDURES Field procedures undertaken followed acceptable industry practices. The assessment included a pedestrian survey over the property, starting at east end and then traveling north, west and south along the property boundary. The survey included walking a transect through the middle of the property. A trenching shovel was used to dig the test holes down to at least 18 inches below the ground surface at 2 discrete locations to study the presence or non-presence of near-surface hydric soil indicators and to measure the presence or non-presence of the near surface ground water level. The assessment included estimating areal cover of dominant vegetation species and looking for indicators of flowing water, scouring, and defined channels. The collected data and indicators were compared to the three wetland criteria and a wetland and stream determination was made. Based on this process a final analysis was made to determine if the area assessed contains jurisdictional wetlands or streams. These data and observations were recorded in a field log book by the wetland scientist. The wetland determination was made by putting equal emphasis on all three wetland indicators; 1) hydric soil indicators, 2) dominant hydrophytic vegetation growth pattems, and 3) wetland hydrology. 9.0 FINDINGS The data collected at the test plots in concert with the pedestrian survey of the lot was used to make the determinations. The project site exhibits normal circumstances for soils, vegetation, and hydrology because these features appear to have remained stable for five years or more. The topography is relatively flat and there are no defined depressions or scoured swales to collect, concentrate or convey surface water. Soils Observed Soil The soils observed at the test plots from the ground surface down to about 5 inches below ground surface (bgs) consists of aerobic dark brown to brown, gravelly (rounded 1/8 th inch), silty medium GIS Mapping· Site Assessment· Wetland· Remediation • Habitat· Stormwater 3 to fine sandy loam underlain with yellow brown gravelly (rounded 1/2 inch to 1.S inch) silty medium sand to the bottom of the test pit at 18 inches bgs. Natural depletions were not observed from the surface down to 18 inches bgs. The soil was slightly moist at the surface down to the bottom of the test holes. The soil layers at P-2 are mixed and blended indicating human disturbance. Observed soil characteristics in the test plots are presented on the data forms. The data forms are kept in the EnCo file for future reference, if needed. A summary of the rationale for making the upland vs. wetland determination for hydric soil indicators (if any) at plots is listed below. Hydric Soil Indicators Identified in Test Plots Test Black Sulfidic Loamy Redox Depleted Depleted Hydric Plot Histic Odor Mucky Dark Matrix Below Dark Soil List Mineral Surface 1 No No No No No No No 2 No No No No No No No Mapped Soil Based on interpretation of the USDA Natural Resources Conservation Service Web Soil Survey map, the original, undisturbed, primary mapped soil series identified at the ground surface and down to about 60 inches bgs on the project site have been mapped as indicated below. Age -Alderwood Gravelly Sandy Loam 6"10 to 15% The soil type mapped on 100 percent of the project site is classified as Alderwood Gravelly Sandy Loam 6-12"10. Note: The actual slope observed at the site ranges from 0% to 6%. The Alderwood series consists of nearly level to undulating soil and is moderately well drained while permeability in the upper soil profile is (if disturbed), is moderately rapid to moderately slow depending upon compaction. Roots penetrate to and tend to mat on the surface of the consolidated substratum. Some roots enter the substratum through cracks. Water moves on top of the substratum in winter. Available water capacity is low. Runoff is slow and the erosion hazard is slight. This soil type formed in ancient lake moraines and till plains from basal till and volcanic ash. Alderwood soils are not listed on the county hydriC soils list. In a typical soil profile the surface layer from 0 to 26 inches is dark-brown (1 OYR 4/3) gravelly sandy loam, pale brown (10YR 6/3) dry, massive, slightly hard, very friable, non-sticky, non-plastic; many roots; medium acid with abrupt and smooth boundary. From 26 inches to 60 inches bgs the soil consists of grayish-brown (2.SY S/2) weakly consolidated to strongly consolidated glacial till, light brownish gray (2.SY 6/2) dry; common, medium, prominent mottles of yellowish brown (10YR S/6) moist, massive, no roots, medium acid. The upper, very friable part of the soil extends to a depth of 20 inches to 40 inches bgs and ranges from dark grayish brown to dark yellowish brown. A restrictive layer of glacial till was observed at or greater than 1.S feet below ground surface in upland test plots. GIS Mapping· Site Assessment· Wetland· Remediation· Habitat· Stormwater 4 Vegetation Observed vegetation species in the test plots are presented on the data forms. Dominance was determined using the using the AGOE 50/20 rule. Hydrophytic plants are those plants listed with indicator status of OSL, FAGW, and/or FAG. A summary of the rationale for making the upland vs. wetland determination for hydrophytic vegetation indicators at the plots is listed in the table below. Dominant Hydrophytic Vegetation Identified in Test Plots Test Common Name Scientific Name Stratum Indicator Plot Status 1,2 Big Leaf Maple Acer macrophyllum Tree FACU 1,2 Red Alder Alnus rubra Tree FAC 1 Bitter Cherry Prunus emarginata -mol/is Tree FACU 1 Beaked Hazelnut Corylus cornuta Shrub FACU 1,2 Himalayan Blackberry Rubus discolor Shrub FACU 1 Holly /lex aquifolium Shrub None 2 Hawthorne Crataegus monogyna Shrub FACU 2 Osoberry Oemleria cerasiformis Shrub FACU 2 Cut/eaf Blackberry Rubus laciniatus Shrub FACU 2 Big Leaf Maple (saplings) Acer macrophy/lum Shrub FACU 2 Thimble Berry Rubus parviflourus Shrub FAC- 1 Bracken Fern Pferidium aquilinum Herb FACU 1 Colonial Bentgrass Agrostis capillaris tenuis Herb FAC 1 Orchard Grass Oactylis glomerata Herb FACU 2 Sword Fern Polystichum munitum Herb FACU 2 Trailing Blackberry Rubus ursinus vitifolius Herb FACU Hydrology Observed hydrology in the test plots are presented on the data forms. A summary of the rationale for making the upland vs. wetland determination for the wetland hydrology indicators at the test plots is listed in the table below. Test Plot 1 2 Inundated Saturated Water Sediment Drainage Stained Stunted (S1' bgs) Marks Deposits Patterns Leaves No No No No No No No No No No No No GIS Mapping· Site Assessment· Wetland· Remediation· Habitat· Stormwater 5 Plants No No The rationale for making the upland and wetland determination after reviewing all indicators is summarized in the table below. WETLAND, STREAM, & UPLAND DETERMINATION RATIONALE Test Problematic Hydric Dominant Wetland Water Wetland Plot Soil Hydrophytic Hydrology Level Stream Indicators Vegetation (bgs) Upland 1 No No No No >1.5' Upland 2 No No No No >1.5' Upland 10.0 EXCLUSIONS The work effort did not include interviewing govemment agencies, attending meetings, applying for or obtaining permits, performing a professional land survey, resolving violations (if any), designing or engineering any structure, or trespassing onto off-site property. 11.0 CONCLUSION Based on observations, review of collected data, and evaluation of readily available maps the project site does not contain wetlands or streams at this time. The edges of wetlands and streams were not identified within 200 feet of the project site. Sincerely, Jonathan M. Kemp Professional Wetland Scientist and Wildlife & Fisheries Biologist EnCo Environmental Corporation Sent via e-mail RozenblaLWetland_Recon_Nov_2013 GIS Mapping· Site Assessment· Wetland • Remediation • Habitat· Stormwater 6 APPENDIX A FIGURE 1 -VICINITY FIGURE 2 -TEST PLOT LOCA nONS GIS Mapping· Site Assessment· Wetland· Remediation· Habitat. Stonnwater ~uno~ SU!>I '" n;?('Yi! ~ I'11iil ~ it ':jDII l4If~r,lfrm l~nttlf!r.,"1·fr , Illln.fj'WI O"CI'I "9;'90 : OH l i69J-S,; i O/r ,ll·,i!'J r!'lG ~ ,--,.. n.· ... r.:rI!h:!lil HI O!l;(IIMNII' III ~ 'iHMnJ'rd 11.',h1I1M:'!t~ ,oHI1U=t .. u: rNlIl11;1=t9!i I >.nli lirrr./Ili I\i e"nnO(Jft99 11i;~IJ(1!1rl!ii .. ~, .. , "'-'" ~:j;J l'(l(,;:l 99 rP/In'Ir.r.~i~r ,. ;;, '" ". <'Innnfrr.nt l "j t;vnJ1i'tr.!J9 'f-r,Mo "r.r.99 n<;,~no)j:f.pjl I'flfl(,.Il"r.tM Ii! It • -----!, IM~rr./'l fr I"till 'lr. ~ or,ltJ'inf.f.j'.S' ,1!OM/'I:"..,.r ~O~690t~~t Nd Al.INI~IJ\ -~ 3~n~l:I tGftV;M-r.t.r: Date : 911212013 Source: FIGURE 2 -TEST PLOT LOCATIONS King County iMAP Map [IN 1m .... ?' :::34-",-"6+ Q •• tQ King County APPENDIX B PHOTOGRAPHIC LOG GIS Mapping· Site Assessment· Wetland· Remediation· Habitat· Stormwater Photo 1 Facing North Project Site Test Plot 1 Up land Plot East-Central Photo 3 Facing South Project Site Sample Plot 1 Upland Plot East-Central Photo 5 Top View Project Site Sample Plot 1 Upland Plot East-Central No Water At 1.5' ) Photo 2 Facing East Project Site Test Plot 1 Upland Plot East-Central Photo 4 Facing West Project Site Sample Plot 1 Upland Plot East-Central Appendi. B 11.4.2013 Rosenblal-Renlon·1 Page 1 Photo 6 F aci ng No rth Pro jec t Site Test Pl ot 2 Up tand Pl ot So uthw est Corner Photo 8 Fa cing South Project Site Test Pl ot 2 Upland Plot Southwest Corner Photo 10 Top Vi ew Test Plot 2 Up land Plot Southwest Corne r No Water At 1,5' Photo 7 Facing East Pr oject Si te Test Plo t 2 Up land Pl ot Southwest Corne r Photo 9 Facing West Project Sit e Test Plot 2 Up land Pl ot Southwest Co rner Appendix B 11.4,2013 Ros en bla!·Renton ·1 Page 2