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Geotechnical Engineering Water Resources ., ••• • • ••• . , : '•,, .. ,, .. ,. ' ' .. "' '· .. , . ',. ·:~•; ~'i ·-~-,~--·,, ·. ~;.;.··' Environmental Assessments and Remediation Sustainable Development Services Geologic Assessments Associated Earth Sciences, Inc. ~Jbl"t'lllJ:.f u't1i1r 2_j' ~t'ln' o/Jem1ci1 Subsurface Exploration, Geologic Hazard, and Preliminary Geotechnical Engineering Report WELMAN PLAT Renton, Washington Prepared for MJF Holdings, Inc. c/o Centurion Development Services Project No. KE100030A February 24, 2010 I Associated Earth Sciences, Inc. ~[i]~~~ CefeGrafirJJ Over 251fea~· of.Service February 24, 2010 Project No. KE100030A MJF Holdings, Inc. c/o Centurion Development Services P.O. Box 2668 Redmond, Washington 98073-2668 Attention: Mr. Mike Romano Subject: Subsurface Exploration, Geologic Hazard, and Preliminary Geotechnical Engineering Report Welman Plat Renton, Washington Dear Mr. Romano: We are pleased to present the enclosed copies of the above-referenced report. This report summarizes the results of our subsurface exploration, geologic hazard, and geotechnical engineering studies and offers recommendations for the preliminary design and development of the proposed project. Our recommendations are preliminary in that definite building locations and construction details have not been finalized at the time of this report. 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. ashington I ; Bruce L. Blyton, P. Principal Engineer BLB/tb KE100030A2 Projects\20100030\KE\ WP Kirkland • Everett • Tacoma 425-827-7701 425-259-0522 253-722-2992 www.aesgeo.com SUBSURFACE EXPLORATION, GEOLOGIC HAZARD, AND PRELIMINARY GEOTECHNICAL ENGINEERING REPORT WELMAN PLAT Renton, Washington Prepared for: MJF Holdings, Inc. c/o Centurion Development Services P.O. Box 2668 Redmond, Washington 98073-2668 Prepared by: Associated Earth Sciences, Inc. 911 5"' Avenue, Suite 100 Kirkland, Washington 98033 425-827-7701 Fax: 425-827-5424 February 24, 2010 Project No. KE100030A Welman Plat Renton, Washington Subswface Exploration, Geologic Hazard, and Preliminary Geotechnical Engineering Report Project and Site Conditions I. PROJECT AND SITE CONDITIONS 1.0 INTRODUCTION This report presents the results of Associated Earth Sciences, Inc. 's (AESI's) subsurface exploration, geologic hazard, and preliminary geotechnical engineering study for the property (King County Parcel No. 3223059033) located in Renton, Washington (Figure I). The approximate locations of the explorations accomplished for this study are presented on the "Site and Exploration Plan," Figure 2. If any changes in the nature, design, or locations of the site development improvements are planned, the conclusions and recommendations in this report should be reviewed and modified, or verified. The recommendations in this report are preliminary because grading plans and construction details were not finalized at the time of this report. Once development plans are substantially complete, the conclusions and recommendations in this report should be reviewed and modified, or verified, as appropriate. 1.1 Purpose and Scope The purpose of this study was to provide subsurface data and design recommendations for preliminary design and development of the subject project. This study included a review of available geologic literature, excavation of exploration pits, and performing geologic studies to assess the type, thickness, distribution, and physical properties of the subsurface sediments and shallow ground water conditions. Geologic studies were completed to identify geologic hazards associated with the site. Where warranted, geologic hazard mitigations are recommended. Geotechnical engineering studies were also conducted to recommend the type of suitable foundations, allowable foundation soil bearing pressure, anticipated foundation settlements, retaining wall lateral pressures, floor support recommendations, drainage considerations, and erosion mitigation recommendations. This report summarizes our current fieldwork and offers development recommendations based on our present understanding of the project. 1. 2 Authorization Written authorization to proceed with this study was granted by MJF Holdings, Inc. Our study was accomplished in general accordance with our proposal dated January 20, 2010. This report has been prepared for the exclusive use of MJF Holdings, Inc. and its 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 and February 24, 2010 ASSOCIATED EARTH SCIENCES, INC. JPUlb -KEJ()()()30A2 -Projectsl20100030\KEIWP Page 1 I Welman Plat Renton, Washington Subsu,jace Exploration, Geologic Hazard, and Preliminary Geotechnical Engineering Repor1 Project and Site Conditions engineering geology 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 2 .1 Site Description The subject site consists of a rectangular-shaped parcel of approximately 3.24 acres at 18417 116'" Avenue SE in Renton, Washington (Figure 1). The site is bordered by existing single- family residences on the south and west sides, by 116"' Avenue SE on the east side, and by a gravel road to the north. An existing home, garage, and carport structures currently occupy the central portion of the property. The remainder of the site is cleared for pasture with scattered trees. The topography of the site includes level to gently sloping terrain, with a moderately sloping swale feature that trends roughly east-west across the northern portion of the property. A wetland, delineated by others, is located along the bottom of this swale feature. 2.2 Project Description Our understanding of the project is based on a layout of the plat, prepared by Centurion · Development Services, received via e-mail on January 19, 2010. We understand that development of the subject property will include a 25-lot, residential subdivision with associated road and underground utility improvements. An underground storm water detention vault will be located in the northwest corner of the property. The proposed detention vault is anticipated to require cuts of approximately 12 feet below existing site grades in this area. Grading for the site is anticipated to be limited since current topographic relief is approximately 16 feet. Although not shown on the plans, low rockeries may be used for grade separation in some areas. 3.0 SUBSURFACE EXPLORATION Our field study included excavating a series of exploration pits to gain subsurface information about the site. The various types of sediments, as well as the depths where characteristics of the sediments changed, are indicated on the exploration logs presented in the Appendix. The depths indicated on the logs where conditions changed may represent gradational variations between sediment types. Our explorations were approximately located in the field by measuring from known site features shown on a topographic site plan provided by the client. February 24, 2010 ASSOCIATED EARTH SCIENCES, INC. JPUlb -KE100030A2 -Projec1sl20J()(X}30\KE\WP Page 2 Welman Plat Renton, Washington Subsuiface Exploration, Geologic Hazard, and Preliminary Geotechnical Engineering Report Project and Site Conditions The conclusions and recommendations presented in this report are based, in part, on the conditions encountered in the exploration pits completed for this study. The number, locations, and depths of the explorations were completed within site and budgetary constraints. Because of the nature of exploratory work below ground, interpolation of subsurface conditions between the field explorations is necessary. Differing subsurface conditions may be present outside of the area of the field explorations 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. If variations are observed at that time, it may be necessary to re-evaluate specific recommendations in this report and make appropriate changes. 3 .1 Exploration Pits Exploration pits were excavated with a rubber-tired backhoe. The pits permitted direct, visual observation of subsurface conditions. Materials encountered in the exploration pits were studied and classified in the field by an engineering geologist from our firm. Disturbed soil samples were collected from the pits, placed in moisture-tight containers, and transported to our laboratory for further visual classification and testing. Testing was generally limited to visual-manual classification of the collected samples in general accordance with American Society for Testing and Materials (ASTM) standard practices. After logging the exposed soils, all of the exploration pits were backfilled with the excavated soil and lightly tamped with the excavator bucket. 4.0 SUBSURFACE CONDITIONS Subsurface conditions at the project site were inferred from the exploration pits accomplished for this study, visual reconnaissance of the site, and review of topography provided on the topographic site plan. As shown on the exploration logs, the exploration pits generally encountered consolidated, granular, glacial sediments overlain by a few feet of weathered soils of similar textural composition. The following section presents more detailed subsurface information organized from the youngest to the oldest sediment types. 4 .1 Stratigraphy Fill Fill soils (soils not naturally placed) were encountered at the location of exploration pit EP-1, and generally consisted of loose silty sand with gravel, organic material, and plastic debris. The fill encountered at exploration pit EP-1 was roughly 3 feet in depth and appeared to have February 24, 2010 ASSOCIATED EARTH SCIENCES, INC. JPUrb -KEJ00030A2 -Projec1sl20J00030\KEIWP Page 3 Welman Plat Renton, Washington Subsuiface Exploration, Geologic Hazard, and Preliminary Geotechnical Engineering Report Project and Site Conditions been placed to create a level area across a portion of the east-west trending swale feature. Fill is also expected in unexplored areas of the site, such as the area surrounding and under the existing structure foundations, in existing utility trenches, and in landscape areas and driveways. Due to their variable density and organic debris content, the existing fill soils are not suitable for foundation support. Topsoil A surficial organic topsoil layer was encountered below the fill at exploration pit EP-1, and below the ground surface and exploration pits EP-2 through EP-6. The thickness of the topsoil layer ranged from approximately 6 inches to 1 foot. The organic topsoil is not suitable for foundation support or for use in a structural fill. Colluvium Medium dense silty fine to medium sand was encountered below the topsoil at exploration pit EB-1. This material also contained trace amounts of organic material and a brecciated texture, suggesting that this deposit was derived from past earth movement, likely from minor sloughing at the base of the partially filled east-west trending swale feature. The degree of weathering displayed in the topmost 2 feet of the colluvium, combined with the medium dense nature of this soil unit at depth, suggests that this deposit has been in place for some time, possibly since the time of the last glacial retreat from the region approximately 13,500 years ago. Vashon Lodgement Till Sediments encountered below the topsoil at the locations of exploration pits EP-2 through EP-6 generally consisted of loose to medium dense, silty sand with gravel. These sediments were observed to generally become dense to very dense below depths of approximately 3 to 5 feet. We interpret these sediments to be representative of Vashon lodgement till. The Vashon lodgement till was deposited directly from basal, debris-laden glacial ice during the Vashon Stade of the Fraser Glaciation approximately 12,500 to 15,000 years ago. The reduced density observed within 3 to 5 feet of the ground surface is interpreted to be due to weathering. The high relative density of the unweathered till is due to its consolidation by the massive weight of the glacial ice from which it was deposited. At the locations of exploration pits EP-2 through EP-6, the till extended beyond the maximum depths explored. February 24, 2010 ASSOCIATED EARTH SCIENCES, INC. JPL/tb-KEIOOOJOA2-Projecrs120l(X)()30\KE\'WP Page 4 Welmnn Plat Renton, Washington 4.2 Geologic Mapping Subsu,face Exploration, Geologic Hazard, and Preliminary Geotechnical Engineering Report Proiect and Site Conditions Review of the regional geologic map titled Geologic Map of King County, compiled by D.B. Booth, K.A. Troost, and A.P. Wisher (2006) indicates that the area of the subject site is underlain by Vashon lodgement till (Qvt). Our interpretation of the sediments encountered at the subject site is in general agreement with the regional geologic map. 4.3 Hydrology Ground water seepage was encountered in exploration pits EP-1, EP-2, and EP-5, with significant seepage noted at EP-1. The seepage was generally limited to a thin zone directly atop the unweathered till surface, and is interpreted to be representative of interflow. Interflow occurs when surface water percolates down through the surficial weathered sediments and becomes perched atop underlying, lower-permeability sediments. It should be noted that the occurrence and level of ground water seepage at the site may vary in response to such factors as changes in season, precipitation, and site use. The seepage observed at exploration pit EP-1 may be associated with the delineated wetland at the bottom of the east-west trending swale feature. Ground water seepage is also common in the vicinity of wetlands or local depressions that are outside the representative areas of our exploration pits. Exploration for this study was conducted during the month of February when ground water levels are typically at or near their seasonal high. February 24, 2010 ASSOCIATED EARTH SCIENCES, INC. JPUtb -KEJ00030A2 -Projectsl20100030\KE\WP Page 5 Welman Plat Renton, Washington Subsurface Exploration, Geologic Hazard, and Preliminary Geotechnical Engineering Report Geologic Hazards and Mitigations II. GEOLOGIC HAZARDS AND MITIGATIONS The following discussion of potential geologic hazards is based on the geologic, topographic, and shallow ground water conditions, as observed and discussed herein. 5.0 SEISMIC HAZARDS AND MITIGATION Earthquakes occur in the Puget Lowland with great regularity. The vast majority of these events are small and are usually not felt by people. However, large earthquakes do occur, as evidenced by the 1949, 7.2-magnitude event; the 2001, 6.8-magnitude event; and the 1965, 6.5-magnitude event. The 1949 earthquake appears to have been the largest in this region during recorded history and was centered in the Olympia area. Evaluation of earthquake return rates indicates that an earthquake of the magnitude between 5.5 and 6.0 is likely within a given 20-year period. Generally, there are four types of potential geologic hazards associated with large seismic events: 1) surficial ground rupture, 2) seismically induced landslides, 3) liquefaction, and 4) ground motion. The potential for each of these hazards to adversely impact the proposed project is discussed below. 5 .1 Surficial Ground Rupture The nearest known fault trace to the project site is the Seattle Fault Zone located approximately 6 miles to the north. Recent studies by the United States Geological Survey (USGS) (e.g., Johnson et al., 1994, Origin and Evolution of the Seattle Fault and Seattle Basin, Washington, Geology, v. 22, p.71-74; and Johnson et al., 1999, Active Tectonics of the Seattle Fault and Central Puget Sound Washington -Implications for Eanhquake Hazards, Geological Society of America Bulletin, July 1999, v. 111, n. 7, p. 1042-1053) have provided evidence of surficial ground rupture along a northern splay of the Seattle Fault. The recognition of this fault is relatively new, and data pertaining to it are limited, with the studies still ongoing. According to the USGS studies, the latest movement of this fault was about 1,100 years ago when about 20 feet of surficial displacement took place. This displacement can presently be seen in the form of raised, wave-cut beach terraces along Alki Point in West Seattle and Restoration Point at the south end of Bainbridge Island. The recurrence interval of movement along this fault system is still unknown, although it is hypothesized to be in excess of several thousand years. Due to the suspected long recurrence interval, the potential for surficial ground rupture is considered to be low during the expected life of the structures. February 24, 2010 ASSOCIATED EARTH SCIENCES, INC. JPU1b -KEJOfXJ30A2 -Projects\20100030\KE\WP Page 6 Welman Plat Remon, Washington 5 .2 Seismically Induced Landslides Subswface Exploration, Geologic Hazard, and Preliminary Geotechnica/ Engineering Repon Geologic Hazards and Mitigations The lodgement till is a high-shear strength, relatively low-permeability material and is not prone to landsliding given the topographic conditions at the site. In addition, no evidence of historical landslide activity was observed, such as landslide scarps, hummocky topography, tension cracks, or unusually distorted or leaning tree trunks. Given the subsurface and topographic conditions within and adjacent to the proposed development area, and the apparent lack of historical landslide activity, it is our opinion that the risk of damage to the proposed project by landsliding under either static or seismic conditions is low. This opinion is dependent upon site grading and construction practices being completed in accordance with the geotechnical recommendations presented in this report. 5. 3 Liquefaction The encountered stratigraphy has a low potential for liquefaction due _to its dense state and lack of adverse ground water conditions. No mitigation of liquefaction hazards is warranted. 5 .4 Ground Motion It is our opinion that any earthquake damage to the proposed structures, when founded on suitable bearing strata in accordance with the recommendations contained herein, would likely be caused by the intensity and acceleration associated with the event and not any of the above- discussed impacts. Structural design should follow the 2006 International Building Code IBC. Information presented by the USGS Earthquake Hazards Program indicates a spectral acceleration for the project area for short periods (0.2 seconds) of Ss = 1.357 and for a I-second period of S, = 0 .463. Based on the results of subsurface exploration and on an estimation of soil properties at depth utilizing available geologic data, Site Class "C", in conformance with Table 1613.5.2 of the IBC, may be used. 6.0 EROSION HAZARDS AND MITIGATION As of October 1, 2008, the Washington State Department of Ecology (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 and turbidity monitoring of site runoff for all sites 1 or more acres in size that discharge storm water to surface waters of the state. The TESC inspections and turbidity monitoring of runoff must be completed by a Certified Erosion and Sediment Control Lead (CESCL) for the duration of the construction. The weekly TESC reports do not need to be sent to Ecology, but should be logged into the project Storm Water Pollution Prevention Plan February 24, 2010 ASSOCIATED EARTH SCIENCES, INC. JPL/tb -KEJ(X)()30A2 -Projects\201(X)()30\KE\WP Page 7 Welman Plat Renton, Washington Subswface Exploration, Geologic Hazard, and Preliminary Geotechnical Engineering Report Geologic Hazards and Mitigations (SWPPP). Ecology requires a monthly summary report of the turbidity monitoring results signed by the NPDES permit holder. If the monitored turbidity equals or exceeds 25 nephelometric turbidity units (NTU) (Ecology benchmark standard), the project best management practices (BMPs) should be modified to decrease the turbidity of storm water leaving the site. Changes and upgrades to the BMPs should be documented in the weekly TESC reports and continued until the weekly turbidity reading is 25 NTU or lower. If the monitored turbidity exceeds 250 NTU, the results must be reported to Ecology via phone within 24 hours and corrective actions should be implemented as soon as possible. Daily turbidity monitoring is continued until the corrective actions lower the turbidity to below 25 NTU, or until the discharge stops. This description of the sampling benchmarks and reporting requirements is a brief summary of the Construction Storm Water General Permit conditions. The general permit is available on the internet1. In order to meet the current Ecology requirements, a properly developed, constructed, and maintained erosion control plan consistent with local standards and best management erosion control practices will be required for this project. AESI is available to assist the project civil engineer in developing site-specific erosion control plans. Adjustments and additional measures to the TESC plan are often required to optimize its effectiveness. Ultimately, the success of the TESC plan depends on a proactive approach to project planning and contractor implementation and maintenance. Maintaining cover measures atop disturbed ground provides the greatest reduction to the potential generation of turbid runoff and sediment transport. During the local wet season (October I" 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. Surface drainage control measures are also essential for collecting and controlling the site runoff. Flow paths across slopes should be kept to Jess than 50 feet in order to reduce the erosion and sediment transport potential of concentrated flow. Ditch/ swale spacing should be shortened with increasing slope gradient. Ditches and swales that exceed a gradient of 7 to 10 percent, depending on their flow length, should have check dams installed to reduce the flow velocity of the runoff. Flow paths that are constructed at gradients between 10 to 15 percent should be placed in a riprap-lined swale. Flow paths constructed on slope gradients steeper than 15 percent should be placed in a pipe slope drain. AESI is available to assist the project civil engineer in developing a suitable erosion control plan with proper flow control. 1 http://www.ecy. wa. gov /programs/wq/stormwater /construction/constructionfinalpermit. pdf February 24, 2010 ASSOCIATED EARTH SCIENCES, INC. JPL!rb -KEJ00030A2 -Projectsl20100030\KE\WP Page 8 Welman Plat Renton, Washington Subswface Exploration, Geologic Hazard, and Preliminary Geotechnical Engineering Report Geologic Hazards and Mitigations Once very fine sediment is suspended in water, the settling times of the smallest particles are on the order of weeks and months. Therefore, the typical retention times of sediment traps or ponds will not reduce the turbidity of highly turbid site runoff to the benchmark turbidity of 25 NTU. Reduction of turbidity from a construction site is almost entirely a function of cover measures and drainage control that have been implemented prior to rain events. Temporary sediment traps and ponds are necessary to control the release rate of the runoff and to provide a catchment for sand-sized and larger soil particles, but are ineffective at reducing the turbidity of the runoff. Silt fencing should be utilized as buffer protection and not as a flow-control measure. Silt fencing should be placed parallel with topographic contours to prevent sediment-laden runoff from leaving a work area or entering a sensitive area. Silt fences should not be placed to cross contour lines without having separate flow control in front of the silt fence. A swale/berm combination should be constructed to provide flow control. 6.1 Erosion Hazard Mitigations To mitigate the erosion hazards and potential for off-site sediment transport, we recommend the following: 1. Construction activity should be scheduled or phased as much as possible to reduce the amount of earthwork activity that is performed during the winter months. 2. The winter performance of a site is dependent on a well-conceived plan for control of site erosion and storm water runoff. The site TESC plan should include ground-cover measures, access roads, and staging areas. The selected contractor must implement and maintain the required measures to reduce the amount of exposed ground. A site maintenance plan should be in place in the event storm water turbidity measurements are greater than the Ecology standards. 3. TESC measures for a given area to be graded or otherwise worked should be installed soon after ground clearing or tree removal. The recommended sequence of construction within a given area after clearing would be to install sediment traps and/ or ponds and establish perimeter flow control prior to starting mass grading. 4. During the wetter months of the year, or when large storm events are predicted during the summer months, each work area should be stabilized so that if showers occur, the work area can receive the rainfall without excessive erosion or sediment transport. The required measures for an area to be "buttoned-up" will depend on the time of year and the duration the area will be left un-worked. During the winter months, areas that are February 24, 2010 ASSOCIATED EARTH SCIENCES. INC. JPLltb -KE100030A2 -Projects\20100030\KE\WP Page 9 Welman Plat Renton, Washington Subsuiface Exploration, Geologic Hazard, and Preliminary Geotechnical Engineering Repon Geologic Hazards and Mitigations to be left un-worked for more than 2 days should be mulched or covered with plastic. During the summer months, stabilization will usually consist of seal-rolling the subgrade. Such measures will aid in the contractor's ability to get back into a work area after a storm event. The stabilization process also includes establishing temporary storm water conveyance channels through work areas to route runoff to the approved treatment facilities. 5. All disturbed areas should be revegetated as soon as possible. If it is outside of the growing season, the disturbed areas should be covered with mulch, as recommended in the erosion control plan. Straw mulch provides a cover measure and can be made wind-resistant with the application of a tackifier after it is placed. 6. Surface runoff and discharge should be controlled during and following development. Uncontrolled discharge may promote erosion and sediment transport. Under no circumstances should concentrated discharges be allowed to flow over the top of steep slopes. 7. Soils that are to be reused around the site should be stored in such a manner as to reduce erosion from the stockpile. Protective measures may include, but are not limited to, covering with plastic sheeting, the use of low stockpiles in flat areas, or the use of silt fences around pile perimeters. During the period between October 1" and March 31", these measures are required. 8. On-site erosion control inspections and turbidity monitoring (if required) should be performed in accordance with Ecology requirements. Weekly and monthly reporting to Ecology should be performed on a regularly scheduled basis. A discussion of temporary erosion control and site runoff monitoring should be part of the weekly construction team meetings. Temporary and permanent erosion control and drainage measures should be adjusted and maintained, as necessary, for the duration of project construction. It is our opinion that with the proper implementation of the TESC plans and by field-adjusting appropriate mitigation elements (BMPs) throughout construction, as recommended by the erosion control inspector, the potential adverse impacts from erosion hazards on the project may be mitigated. February 24, 2010 ASSOCIATED EARTH SCIENCES, INC. JPL/tb -KEJCXXJ30A2 -Projecrs120l(XJ()301KE'1WP Page 10 Welman Plat Renton, Washington Subsuiface Exploration, Geologic Hazard, and Preliminary Geotechnical Engineering Report Preliminary Design Recommendations III. PRELIMINARY DESIGN RECOMMENDATIONS 7.0 INTRODUCTION Our exploration indicates that, from a geotechnical standpoint, the parcel is suitable for the proposed development provided the recommendations contained herein are properly followed. The foundation bearing stratum is relatively shallow, and conventional spread footing foundations may be utilized for the residences. Consequently, foundations bearing on either the medium dense to very dense, natural sediments, or on structural fill placed over these sediments, are capable of providing suitable building support. 8.0 SITE PREPARATION 8.1 Clearing and Stripping Site preparation of the planned building and pavement areas should include removal of all trees, brush, debris, and any other deleterious materials. These unsuitable materials should be properly disposed of off-site. Additionally, any areas of organic topsoil should be removed and the remaining roots grubbed. Topsoil thicknesses in our exploration pits ranged from 6 inches to 12 inches, but may vary outside this range, particularly in the vicinity of wetlands or any previously disturbed graded areas. Topsoil should be expected to swell by approximately 25 percent relative to in-place volumes. Areas where loose surficial soils exist due to grubbing operations or previously filled/disturbed areas (e.g., EP-1) should be considered as fill to the depth of disturbance and treated as subsequently recommended for structural fill placement. Any buried utilities should be removed or relocated if they are under development areas. The resulting depressions should be backfilled with structural fill, as discussed under the "Structural Fill" section of this report. After stripping of the organic topsoil layer and removal of roots, we recommend that the soil exposed in the proposed roadway areas be recompacted to a firm and unyielding condition. The recompacted area should then be proof-rolled with a fully loaded, tandem-axle dump truck. Any soft or yielding areas identified during proof-rolling should be overexcavated and backfilled with structural fill. 8.2 Temporary Cut Slopes In our opinion, stable construction slopes should be the responsibility of the contractor and should be determined during construction based on the local conditions encountered at that time. For planning purposes, we anticipate that temporary, unsupported cut slopes in the loose February 24, 2010 ASSOCIATED EARTH SCIENCES, INC. JPUtb -KEIOOOJOA2 -Projects\2010003DIKE\WP Page 11 Welman Plat Renton, Washington Subsurface Exploration, Geologic Hazard, and Preliminary Geotechnical Engineering Repon Preliminary Design Recommendations to medium dense, weathered till or colluvial sediments can be made at a maximum slope of I.SH: 1 V (Horizontal:Vertical). Temporary cut slopes within the dense to very dense, unweathered lodgement till up to a IH:IV inclination may be planned. As is typical with earthwork operations, some sloughing and raveling may occur, and cut slopes may have to be adjusted in the field. Flatter, temporary cut slopes should be anticipated in areas of ground water seepage. In addition, WISHA/OSHA regulations should be followed at all times. 8.3 Site Disturbance The shallow-depth site soils contain a high percentage of fine-grained material, which makes them moisture-sensitive and subject to disturbance when wet. The contractor must use care during site preparation and excavation operations so that the underlying soils are not softened. If disturbance occurs, the softened soils should be removed and the area brought to grade with structural fill. If crushed rock is considered for the access and staging areas, it should be underlain by stabilization fabric (such as Mirafi 500X or approved equivalent) to reduce the potential of fine-grained materials pumping up through the rock and turning the area to mud. The fabric will also aid in supporting construction equipment, thus reducing the amount of crushed rock required. We recommend that at least 10 inches of rock be placed over the fabric; however, due to the variable nature of the near-surface soils and differences in wheel loads, this thickness may have to be adjusted by the contractor in the field. 9.0 STRUCTURAL FILL We anticipate that structural fill will be necessary to establish desired grades in some areas and to re-establish grade after unsuitable soils are removed. All references to structural fill in this report refer to subgrade 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. 9.1 Subgrade Compaction After overexcavation/stripping have been performed to the satisfaction of the geotechnical engineer/engineering geologist, the upper 12 inches of exposed ground should be compacted to a firm and unyielding condition. If the subgrade contains too much moisture, suitable compaction may be difficult or impossible to obtain and should probably not be attempted. In lieu of compaction of the subgrade surface, 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. The filled area in the vicinity of EP-1 February 24, 2010 ASSOCIATED EARTH SCIENCES, INC. JPUtb -KE100030A2 -Projects\201000301KE\WP Page 12 Subswface Exploration, Geologic Hazard, and Welman Plat Preliminary Geotechnical Engineering Report Renton, Washington Preliminary Design Recommendations will likely require a rock fill zone and geotextile filter fabric to provide drainage and separation of the fill from the wet subgrade soils. After compaction 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. 9 .2 Structural Fill Compaction 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 at least 95 percent of the modified Proctor maximum dry density using ASTM:D 1557 as the standard. Roadway and utility trench backfill should be placed and compacted in accordance with applicable municipal codes and standards. The top of the compacted fill should extend horizontally a minimum distance of 3 feet beyond the perimeter footings or pavement edges before sloping down at an angle no steeper than 2H: 1 V. Fill slopes should either be overbuilt and trimmed back to final grade or surface-compacted to the specified density. 9. 3 Moisture-Sensitive Fill 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 near-optimum subgrade moisture. The on-site lodgement till sediments are suitable for use as structural fill, but contain significant amounts of silt and are considered highly moisture-sensitive. In addition, construction equipment traversing the site when the soils are wet can cause considerable disturbance. If fill is placed during wet weather or if proper compaction cannot be 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. 9 .4 Structural Fill Testing 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 at least 3 business days in advance to perform a Proctor test and determine its field compaction standard. A representative from our firm should inspect the stripped subgrade 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 February 24, 2010 ASSOCIATED EARTH SCIENCES, INC. JPUtb -KEIIXXBOA2 -Projectsl20100030\KE\WP Page 13 I Welman Plat Renton, Washington Subsuiface Exploration, Geologic Hazard, and Preliminary Geotechnical Engineering Report Preliminary Design Recommendations acceptable performance of a fill. As such, we are available to aid the owner in developing a suitable monitoring and testing frequency. 10.0 FOUNDATIONS IO. I Allowable Soil Bearing Pressure Spread footings may be used for building support when founded either directly on the medium dense to very dense, natural glacial sediments, or on structural fill placed over these materials, as described under the "Site Preparation" and "Structural Fill" sections of this report. For footings founded either directly upon the medium dense to very dense natural sediments, or on structural fill as described above, we recommend that an allowable bearing pressure of 2,500 pounds per square foot (pst) be used for design purposes, including both dead and live loads. An allowable bearing pressure of 4,000 psf is possible for deeper structures, such as the proposed detention vault, where all foundation elements are founded on undisturbed dense to very dense till. An increase of one-third may be used for short-term wind or seismic loading. 10.2 Footing Depths Perimeter footings for the proposed buildings should be buried a minimum of 18 inches into the surrounding soil for frost protection. No minimum burial depth is required for interior footings; however, all footings must penetrate to the prescribed strata, and no footings should be founded in or above loose, organic, or existing fill soils. Sediments suitable for foundation support were encountered in most of our explorations at depths of approximately 2 to 5 feet. 10.3 Footings Adjacent to Cuts The area bounded by lines extending downward at lH: 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 I.SH: 1 V 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 edges of steps or cuts in the bearing soils. 10.4 Footing Settlement Anticipated settlement of footings founded as described above should be on the order of 1 inch or less. However, disturbed soil not removed from footing excavations prior to footing placement could result in increased settlements. February 24, 2010 ASSOCIATED EARTH SCIENCES, INC. JPL/tb-KE100030A2 -Projects\20J(Xl()30\KEIWP Page 14 Welman Plat Renton, Washington 10.5 Footing Subgrade Bearing Verification Subsurface Exploration, Geologic Hazard, and Preliminary Geotechnical Engineering Repon Preliminary Design Recommendations All footing areas should be observed by AESI prior to placing concrete to verify that the exposed soils can support the design foundation bearing capacity and that construction conforms with the recommendations in this report. Foundation bearing verification may also be required by the governing municipality. 10.6 Foundation Drainage Perimeter footing drains should be provided, as discussed under the "Drainage Considerations" section of this report. If gravity drainage is not possible, the portion of the structure below the drain level must be designed for combined soil and hydrostatic/buoyant forces. 11.0 LATERAL WALL PRESSURES All backfill behind walls or around foundations should be placed following our recommendations for structural fill and as described in this section of the report. Horizontally backfilled walls, which are free to yield laterally at least 0.1 percent of their height, may be designed using an equivalent fluid equal to 35 pounds per cubic foot (pcf). Fully restrained, horizontally backfilled, rigid walls that cannot yield should be designed for an equivalent fluid of 50 pcf. Walls that retain sloping backfill at a maximum angle of 2H: 1 V should be designed for 55 pcf for yielding conditions and 75 pcf for 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. Undrained walls/structures must be designed for combined soil and hydrostatic pressures (85 pcf for yielding walls, 100 pcf for unyielding walls with horizontal backfill) and for buoyant/uplift forces. In accordance with the 2006 IBC, retaining wall design should include seismic design parameters. Based on the site soils and assumed wall backfill materials, we recommend a seismic surcharge pressure in addition to the equivalent fluid pressures presented above. A rectangular pressure distribution of 4H and 8H psf (where H is the height of the wall in feet) should be included in design for "active" and "at-rest" loading conditions, respectively. The resultant of the rectangular seismic surcharge should be applied at the midpoint of the walls. 11. l Wall Backfill The lateral pressures presented above are based on the conditions of a uniform backfill consisting of either the on-site glacial sediments, or imported sand and gravel compacted to 92 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 unacceptable February 24, 2010 ASSOCIATED EARTH SCIENCES, INC. JPUtb -KEIOOOJOA2-Projects\20J()(X)30\KEIWP Page 15 Welman Plat Renton, Washington Subsurface Exploration, Geologic Hazard, and Preliminary Geotechnical Engineering Report Preliminary Design Recommendations settlement behind the walls. Thus, the compaction level is critical and must be tested by our firm during placement. The recommended compaction of 92 percent of ASTM:D 1557 applies to any structural fill placed behind the wall within a distance equal to the wall height and up to the elevation of the top of the wall. Structural fill used to construct slopes behind retaining walls should be compacted to at least 95 percent of ASTM:D 1557 if the fill is placed above the elevation of the top of the wall. Surcharges from adjacent footings, heavy construction equipment, or sloping ground must be added to the above-recommended lateral pressures. Footing drains should be provided for all retaining walls, as discussed under the "Drainage Considerations" section of this report. 11. 2 Wall Drainage 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, I-foot-wide blanket drain for the full wall height (excluding the uppermost 1 foot of backfill) using imported washed gravel against the walls. The wall drain material must be hydraulically connected to the footing drain pipe. Wall foundation drains are discussed in Section 14.0 of this report. 11. 3 Passive Resistance and Friction Factor Lateral loads can be resisted by friction between the foundation and the natural, medium dense to very dense sediments or supporting structural fill soils, or by passive earth pressure acting on the buried portions of the foundations. The foundations must be backfilled with compacted structural fill to achieve the passive resistance provided below. We recommend the following allowable design parameters. • Passive equivalent fluid = 250 pcf • Coefficient of friction = 0. 30 12.0 ROCKERIES Rockeries may be used to prevent erosion of slopes; however, they are not engineered structures and should not be used in place of retaining walls. Buildings and roads should be set back from rockeries so that a lH: 1 V line extending up from the rear base of the rockery does not intersect the footing or pavement. Rockery construction quality depends largely on the skill of the builder. Although rockeries are commonly used, they should be considered a long-term maintenance item. Care must be exercised in selecting a rock source since some of the material presently being supplied is soft and disintegrates in a relatively short period of time. Samples of rock can be tested by AESI prior to their use in rockeries. February 24, 2010 ASSOCIATED EARTH SCIENCES, INC. JPL/tb -KEJ()(X)30A2-Projecrsl20/CXXJ30\KEIWP Page 16 Welman Plat Renton, Washington Subsurface Exploration, Geologic Hazard, and Preliminary Geotechnical Engineering Repon Preliminary Design Recommendations It is our understanding that rockery walls will be placed to provide erosion control for excavations and will also be used as a facing for geogrid-reinforced fill slopes. The following notes present rockery design and construction considerations. A typical rockery detail for cut slopes (Figure 3) and for geogrid-reinforced slopes (Figure 4) are included in this report. In addition, the contractor should confirm that his configuration conforms to current Municipal specifications. A) The base of the rockery should be started by excavating a trench to a minimum depth of 12 inches below subgrade into firm, undisturbed ground. If loose, soft, or disturbed materials exist at the base rock location, they should be removed and replaced with free-draining sand and gravel or crushed rock. This backfill material should be compacted to a minimum of 90 percent of ASTM:D 1557. The gradation of the sand and gravel should be such that not more than 5 percent by weight should be finer than the No. 200 sieve, based on the minus No. 4 sieve. B) The base rock should have a minimum width (perpendicular to the line of the rockery) of 40 percent of the height of the rockery. All rocks should also meet the following weight requirements: Height of Rockery Above 5 feet 5 feet or less Minimum Weight of Rock 200/4,000 pounds, graded, top/bottom rocks 200/700 pounds, graded, top/bottom rocks C) The rock material should all be as nearly rectangular as possible. No stone should be used which does not extend through the wall. The rock material should be hard, sound, durable, and free from weathered portions, seams, cracks, or other defects. The rock density should be a minimum of 160 pcf. D) Rock selection and placement should be such that there will be minimum voids and, in the exposed face of the wall, no open voids over 8 inches across in any direction. The rocks should be placed in a manner such that the longitudinal axis of the rock will be at right angles or perpendicular to the rockery face. Each rock should be placed so as to lock into two rocks in the lower tier. After setting each rock course, all voids between the rocks should be chinked on the back with quarry rock to eliminate any void sufficient to pass a 2-inch-square probe. The rockery should be limited to 8 feet in height. February 24, 2010 ASSOCIATED EARTH SCIENCES, INC. JPUtb -KE]()(X)JOA2-Projeas\20100030\KEIWP Page 17 I Welman Plat Renton, Washington Subswface ExploraJion, Geologic Hazard, and Preliminary Geotechnical Engineering Repon Preliminary Design Recommendations E) F) A drain consisting of rigid, perforated, polyvinyl chloride (PVC) pipe enclosed in a 12-inch-wide pea gravel trench should be placed behind the lower course of rock to remove water and prevent the buildup of hydrostatic pressure behind the wall. The remainder of the wall backfill should consist of quarry spalls with a maximum size of 4 inches and a minimum size of 2 inches. This material should be placed to a 12-inch-minimum thickness between the entire wall and the cut material. The backfill material should be placed in lifts to an elevation approximately 6 inches below the top of each course of rocks as they are placed until the uppermost course is placed. Any backfill material falling onto the bearing surface of a rock course should be removed before the setting of the next course. Any asphalt paving should be sloped to drain away from the rockery. In addition, the areas above rockeries should be planted with grass as soon as possible after rockery construction to reduce erosion. 13.0 FLOOR SUPPORT Slab-on-grade floors may be constructed either directly on the medium dense to very dense natural sediments, or on structural fill placed over these materials. Areas of the slab subgrade that are disturbed (loosened) during construction should be recompacted to an unyielding condition prior to placing the pea gravel, as described below. If moisture intrusion through slab-on-grade floors is to be limited, the floors should be constructed atop a capillary break consisting of a minimum thickness of 4 inches of washed pea gravel. The pea gravel should be overlain by a 10-mil (minimum thickness) plastic vapor retarder. 14.0 DRAINAGE CONSIDERATIONS The unweathered till sediments encountered in our explorations at depths of approximately 3 to 5 feet below ground surface are relatively impermeable, and water will tend to perch atop this stratum. Additionally, traffic across the till sediments when they are very moist or wet will result in disturbance of the otherwise firm stratum. Therefore, prior to site work and construction, the contractor should be prepared to provide drainage and subgrade protection, as necessary. February 24, 2010 ASSOCIATED EARTH SCIENCES, INC. JPL/1b -KE100030A2 -Projects\20100030\KEIWP Page 18 Welman Plat Renton, Washington 14.1 Wall/Foundation Drains Subsuiface Exploration, Geologic Hazard, and Preliminary Geotechnical Engineering Repol1 Preliminary Design Recommendations All retaining and perimeter footing walls should be provided with a drain at the footing elevation. The drains should consist of rigid, perforated, polyvinyl chloride (PVC) pipe surrounded by washed pea gravel. The level of the perforations in the pipe should be set approximately 2 inches below the bottom of the footing, and the drains should be constructed with sufficient gradient to allow gravity discharge away from the structures. All retaining walls should be lined with a minimum, 12-inch-thick, washed gravel blanket provided to within 1 foot of finish grade, and which ties into the footing drain. Roof and surface runoff should not discharge into the footing drain system, but should be handled by a separate, rigid, tightline drain. Exterior grades adjacent to walls should be sloped downward away from the structures to achieve surface drainage. Final exterior grades should promote free and positive drainage away from the buildings at all times. Water must not be allowed to pond or to collect adjacent to foundations or within the immediate building areas. It is recommended that a gradient of at least 3 percent for a minimum distance of 10 feet from the building perimeters be provided, except in paved locations. In paved locations, a minimum gradient of 1 percent should be provided unless provisions are included for collection and disposal of surface water adjacent to the structures. Additionally, pavement sub grades should be crowned to provide drainage toward catch basins and pavement edges. Crawl space areas should be provided with drains at low points to prevent water from accumulating. 15.0 PROJECT DESIGN AND CONSTRUCTION MONITORING The recommendations in this report are preliminary because grading plans and construction details were not finalized at the time of t!J.is report. We are available to provide additional geotechnical consultation as the project design develops and possibly changes from that upon which this report is based. If significant changes in grading are made, we recommend that AESI perform a geotechnical review of the plans prior to final design completion. In this way, our earthwork and foundation recommendations may be properly interpreted and implemented in the design. We are also available to provide geotechnical engineering and monitoring services during construction. The integrity of the foundations depends on proper site preparation and construction procedures. In addition, engineering decisions may have to be made in the field in the event that variations in subsurface conditions become apparent. 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 proposal. February 24, 2010 ASSOCIATED EARTH SCIENCES, INC. JPUlb -KEJOlXJ30A2 -Projects120J(X)(J30IKE\WP Page 19 Welman Plat Renton, Washington Subsu,face Exploration, Geologic Hazard, and Preliminary Geotechnical Engineering Report Preliminary Design Recommendations We have enjoyed working with you on this study and are confident that these reconunendations 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 Attachments: February 24, 2010 . , L.E.G. Figure 1: Figure 2: Figure 3: Figure 4: Appendix: Vicinity Map Site and Exploration Plan Unreinforced Rockery Detail Geogrid Reinforced Rockery Detail Exploration Logs JPUtb -KE100030A2 -Projects\20/(XJ()JOIKE\WP Bruce L. Blyton, P.E . Principal Engineer ASSOCIATED EARTH SCIENCES, INC. Page 20 REFERENCE: USGS TOPO! J Associated Earth Sciences, Inc. • [I] ~ iii eJ VICINITY MAP WELMAN PLAT RENTON, WASHINGTON N A FEET FIGURE 1 DATE 2/10 PROJ. NO. KE100030A FILL ENCOUNTERED AT EXPLORATION PIT EP-1 FILL ALSO INFERRED TO BE PRESENT IN SHADED AREA -FILL MAY ALSO OCCUR AT UNEXPLORED AREAS OF THE SITE, PARTICULARLY AROUND STRUCTURES AND UTILITIES -SEE REPORT TEXT ___ iii' ___ _ l .EP-1 \ \_ ''"' ---""--"' -j I I : ;~··~ ./ • I ... • -~ ,,. 11 S43;)SF .. • EP-5 • t 1 •14i8F .EP-4 I 12 L ___ ._~_: .... - •• • • • ~17TS'F i h - ' 315351' ' _,, ., ' ~"' " 51:!J!lSf' APPROXIMATE LOCATION OF EXPLORATION PIT TYP • • • • • '" " m,~ EP-3 " ..... " REFERENCE: CENTURION DEVELOPMENT SERVICES Associated Earth Sciences, Inc. SITE AND EXPLORATION PLAN WELMAN PLAT RENTON, WASHINGTON ·/ I · 1 I ~ I 0 : .. I I I I I I / I N A 30 FEET r I 60 FIGURE 2 DATE 2/10 PROJ. NO. KE100030A ] ~ I => ~ => ~ { I i l 0 12" FIRM UNDISTURBED SOIL SEE NOTE 2 NOTES: NO ROADWAY, PARKING LOTS OR BUILDING FOOTINGS IN THIS AREA 1---1-1' MIN I I I I / MIN 1' WIDE LAYER OF 2"-4" QUARRY / SPALLS ADJACENT TO ROCKERY I_J1 / 1 / STABLE CUT FACE IN NATURAL MATERIAL SEE NOTE 5 ~--1" OR LESS DIAMETER WASHED GRAVEL MIN 6" COVER OVER PIPE, 2" GRAVEL UNDER PIPE MIN 4" DIAMETER PERFORATED RIGID PVC PIPE MIN 1 % CONTINUOUS SLOPE TO OUTLET 1. ROCKERIES HIGHER THAN 5' SHALL BE CONSTRUCTED OF ROCKS OF GRADUATED SIZES FROM 5-MAN TO 2-MAN, FROM BOTIOM TO TOP. ROCKERIES OF 5' OR LOWER SHALL BE CONSTRUCTED OF 3-MAN TO 2-MAN, FROM BOTIOM TO TOP. 2. INSPECTION OF SUBGRADE, PLACEMENT OF BASE COURSE AND DRAINAGE, AND FINISHED ROCKERY BY ENGINEER IS REQUIRED. 3. ROCK SHALL BE SOUND AND HAVE A MINIMUM DENSITY OF 160 POUNDS PER CUBIC FOOT. 4. THE LONG DIMENSION OF ALL ROCKS SHALL BE PLACED PERPENDICULAR TO THE WALL. EACH ROCK SHOULD BEAR ON TWO ROCKS IN THE TIER BELOW. 5. ROCKERIES ARE EROSION-CONTROL STRUCTURES, NOT RETAINING WALLS. NATURAL MATERIAL MUST BE STABLE AND FREE STANDING IN CUT FACE. MAXIMUM HEIGHT OF 3 FEET FOR ROCKERIES FACING UNREINFORCED FILL SOILS. 6. SEE TEXT OF REPORT FOR ADDITIONAL RECOMMENDATIONS. ROCK LB. AVG. DIMENSION CIN.l 1-MAN 50-200 12 TO 18 2-MAN 200-700 18 TO 28 3-MAN 700-2000 28 T036 4-MAN 2000-4000 36 T048 5-MAN 4000-6000 48 T054 ~========================================= ~ Associated Earth Sciences, Inc. UNREINFORCED ROCKERY DETAIL FIGURE 3 ; ~ I :f\l ~ ~ ~ REN~~'::;~~~TON DATE 2/10 PROJECT NO. KE100030A MIN 1' WIDE LAYER OF 2"-4" QUARRY SPALLS ADJACENT TO ROCKERY 1 UPPERS' i 4-3 MAN ROCKS b ~ :s >-I Cl iiJ LOWERS' I 5-MAN j RICKS 12" FIRM UNDISTURBED SOIL OR STRUCTURAL FILL SEE NOTE2 NOTES: NO WALLS, ROCKERIES, OR FOOTINGS IN THIS AREA [ 1'MIN 20RFLATIER i / / -.__ _ /.:J1 / 1 STRUCTURAL FILL COMPACTED TO 95% OF ASTM D-1557 ---- 12" THICK CHIMNEY DRAIN 213 H FREE DRAINING CLEAN CRUSHED ROCK WITH LESS THAN 5% FINES GEOGRID REINFORCEMENT LAYERS MIRAFI 5XT, SYNTEEN SF35, STRATA SG350, OR ENGINEER APPROVED EQUAL -TYP MIN 4" DIAMETER PERFORATED RIGID PVC PIPE WITI-16" COVER AND 2" BEDDING OF 1" WASHED ROCK -PROVIDE MIN 1 % CONTINUOUS SLOPE TO APPROVED OUTLET 1. ROCKERIES HIGHER THAN 5' SHALL BE CONSTRUCTED OF ROCKS OF GRADUATED SIZES FROM 5-MAN TO 2-MAN, FROM BOTIOM TO TOP. ROCKERIES OF 5' OR LOWER SHALL BE CONSTRUCTED OF 3-MAN TO 2-MAN, FROM BOTIOM TO TOP. 2. INSPECTION OF SUBGRADE SOILS, GEOGRID PLACEMENT, COMPACTION OF STRUCTURAL FILL, ROCK PLACEMENT AND DRAINAGE BY GEOTECHNICAL ENGINEER IS REQUIRED. 3. ROCK SHALL BE SOUND AND HAVE A MINIMUM DENSITY OF 160 POUNDS PER CUBIC FOOT. 4. THE LONG DIMENSION OF ALL ROCKS SHALL BE PLACED PERPENDICULAR TO THE WALL. EACH ROCK SHOULD BEAR ON TWO ROCKS IN THE TIER BELOW. 5. MAXIMUM HEIGHT OF 3 FEET FOR ROCKERIES FACING UNREINFORCED FILL SOILS. 6. SEE TEXT OF REPORT FOR ADDITIONAL RECOMMENDATIONS. ROCK LB. AVG. DIMENSION CIN.l 1-MAN 50-200 12 TO 18 2-MAN 200-700 18 TO 28 3-MAN 700-2000 28 TO 36 4-MAN 2000-4000 36 T048 5-MAN 4000-6000 48 T054 ~========================================= FIGURE 4 Associated Earth Sciences, Inc. GEOGRID REINFORCED ROCKERY DETAIL WELMAN PLAT RENTON, WASHINGTON DATE 2110 PROJECT NO. KE100030A APPENDIX w > w cij 0 0 N 0 z C 0 "O w C 1B w "' ,e 0 "' C rn = ~ 0 :, w > w ul 0 0 N 0 z ~ w ~ ~ rn a. w i5 :, • 0 • 0 Well-graded gravel and GW gravel with sand. little to no fines GP Poorly-graded gravel and gravel with sand, little to no fines Silty gravel and silty GM gravel with sand Clayey gravel and GC clayey gravel with sand Terms Describing Relative Density and Consistency Coarse- Grained Soils Fine- Grained Soils Density SPT('1blows/foot Very Loose O to 4 Loose 4 to 10 Medium Dense Dense Very Dense Consistency Very Soft Soft Medium Stiff Stiff Very Stiff Hard 10 lo 30 30 to SO >50 SPT 121 blows/foot a to 2 2 to 4 4 to 8 8 ID 15 15 to 30 >30 Test Symbols G = Grain Size M = Moisture Content A = Atterberg Limits C = Chemical DD -Dry Density K = Permeability Component Definitions c Well-graded sand and Descriptive Term Size Range and Sieve Number 0 t5 §: SW sand with gravel, litt!e Boulders Larger than 12M !t to no fines Cobbles 3~ to 12" (3 ) Estimated Percentage ~ *-Gravel 3" to No. 4 (4.75 mm) ro ~ in Poorly-graded sand Coarse Gravel 3" to 3/4" ~ ~ ,... :-SP and sand with gravel, Fine Gravel 3/4" to No. 4 {4.75 mm) a -sr little to no fines 11) • Sand No. 4 (4.75 mm) to No. 200 (0.075 mm) 0 ~ f--h-'i-,--rl---+--------------1 Coarse Sand No. 4 (4.75 mm) to No. 10 (2.00 mm) ! * '° Silty sand and Medium Sand No. 1 a (2.00 mm) to No. 40 (0.425 mm) gi -II) . SM silty sand with Fine Sand No. 40 (0.425 mm) to No. 200 {0.075 mm) -;f!. a.. ~ gravel ~ U:::V· ·/J;'//IIL----:--:-----1-_S_ilt_a_n_d_c_1_ay:_ ____ s_m_a_11_er_1n_an_N_o_. _20_0_:_(0_.0_1_s_m_m_:_J _________ _j Clayey sand and SC clayey sand with gravel Component Percentage by Weight <5 Moisture Content Dry -Absence of moisture, dusty. diy to the touch Slightly Moist -Perceptible moisture Silt, sandy silt, gravelly silt, ML silt with sand or gravel CL Clay of low to medium plasticity; silty, sandy, or gravelly clay, lean clay Trace Few Little With Sampler Type Elastic silt, clayey silt, silt 2.0"0D Organic clay or silt of low OL plasticity MH with micaceous or Split-Spoon diatomaceous fine sand or Sampler tJ:-----1r's=ilt_-:-:--:-c--:--c-c------i (SPT) Clay of high plasticity, CH sandy or gravelly clay, fat clay with sand or gravel Organic clay or silt of OH medium to high plasticity Bulk sample S to 10 151025 -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 Blo"WS/6'' or portion of 6" I • " • Sampler Type Description 3.0" OD Split-Spoon Sampler r,, Cement grout surface seal Bentonite seal 3.25" OD Split-Spoon Ring Sampler :: Filter pack with =·:· blank casing :-· section 3.0" OD Thin-Watl Tube Sampler (including Shelby tube) :: Screened casing . -: or Hydrotip ·_. with fitter pack O Portion not recovered . :. End cap ( 4l Depth of ground water .Y ATD = At time of drilling Sl.. Static waler /eve! (date) Standard Practice for Description (S) Combined uses symbols used for fines between 5% and 15% 'el~----- and Identification of Soils (ASTM D-2488) g, Classifications of soils in this report are based on visual field and/or laboratory observations, which include density/consistency, moisture condition, grain size, and _j plasticity estimates and should not be construed to imply field or laboratory testing unless presented herein. Visual~manual and/or laboratory classification 5 methods of ASTM D-2487 and D-2488 were used as an identification guide for the Unified Soil Classification System. 0 >-, 5 Associated Earth Sciences, Inc. EXPLORATION LOG KEY g .c C. ID 0 LOG OF EXPLORATION PIT NO. EP-1 This log is part of the report prepared by Associated Earth Sciences, Inc. (AES1) for the named project and should be read together with that report for complete interpretation. This summary applies 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 simplfication of actual conditions encountered. DESCRIPTION Fill Loose, moist, brown, silty SAND, with gravel, organics, and plastic debris/refuse. 1 - 2 - 3 Topsoil \LIL_o_o_se_,:.._m_o_is--'t,_d_a_r_k...:.b_ro:.._w_n_c,_s_il_,.ty_S...:.A_N_D_:_,_w_it_h_o_rg!<a_n_i_cs_. _________________ _Jr 4 -Weathered Colluvium Loose to medium dense, moist to wet, reddish brown, silty SAND, with gravel, brecciated texture. 5 -Medium dense, moist to wet, rust-stained brownish gray, silty fine to medium SAND, with gravel. Colluvium 6 -Medium dense, moist, brownish gray, silty fine to medium SAND, with gravel. 7 - 8 - 9 - 10 - 11 - 12 - 13 - 14 - 15 - 16 - 17 - 18 - 19 - Bottom of exploration pit at depth 8 1 /2 feet. Significant seepage at 31/2'. Slight caving 31/2' to 5'. ~----:26--------------------------------------------N _____________________________________________ _ ;i ~ 1 • ~ 0: " I M ~ Logged by: JPL Approved by: Welman Plat Renton, WA Associated Earth Sciences, Inc. Project No. KE100030A 2/10/10 ~---------------------------------------------- 2 3 4 - 5 - 6 - 7 .. 8 - 9 - 11 - 12 - 13 - 14 - 15 - 16 - 17 - 18 - 19 - LOG OF EXPLORATION PIT NO. EP-2 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 report for complete interpretation. This summary applies 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 simplfication of actual conditions encountered. DESCRIPTION Topsoil Loose, moist, dark brown, silty SAND, with organics and roots. Weathered Vashon Lodgement Till Loose to medium dense, moist, reddish brown, silty SAND, with gravel and roots. Medium dense to dense, moist, rust-stained brownish gray, silty fine to medium SAND, with gravel. Vashon Lodgement Till Dense to very dense, moist, brownish gray, silty fine to medium SAND, with gravel, fine sand lenses. Bottom of exploration pit at depth 10 feet. Slight seepage at 3 feet. No caving. ~---9-Ar-----------------------------------------__:_-N _____________________________________________ _ N ~ j • ~ ~ ~ " I M ~ >- Logged by: JPL Approved by: Welman Plat Renton, WA Associated Earth Sciences, Inc. II ~-'·"".. Ii'' a·· : 111-~ .~· .. --· . . . Project No. KE100030A 2/10/10 ~---------------------------------------------- g .c Q. "' 0 2 - 3 - 4 5 - 6 - 7 8 - 9 - 10 - 11 - 12 13 - 14 - 15 - 16 - 17 - 18 - 19 - LOG OF EXPLORATION PIT NO. EP-3 This log is part of the report prepared by Associated Earth Sciences, Jnc. (AESI) for the named project and should be read together with that report for complete interpretation. This summary applies 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 simplfication of actual conditions encountered. DESCRIPTION Topsoil Loose, moist, dark brown, silty SAND, with organics and roots. Weathered Vashon Lodgement Till Loose to medium dense, moist, reddish brown, silty SAND, with gravel and roots. Medium dense to dense, moist, rust-stained brownish gray, silty fine to medium SAND, with gravel. Vashon Lodgement Till Dense to very dense, moist, brownish gray, silty fine to medium SAND, with gravel, fine sand lenses. Bottom of exploration pit at depth 7 feet. No seepage or caving. 0 ~--s>B------------------------------------------- ~ f ~ o'. " I M ~ r Logged by: JPL Approved by: Welman Plat Renton, WA Associated Earth Sciences, Inc. Project No. KE100030A 2/10/10 !.! _____________________________________________ _ 0 ~ :,: " ~ " ~ ~ ~ " ~ § ~ ~ LOG OF EXPLORATION PIT NO. EP-4 -g This Jog is part of the report prepared by Associated Earth Sciences, Inc. (AESI) for the named ftroject and should be ~ read together with that report for comftlete interpretation. This summary a~plies only to the loca ion of this trench at the a. <l) time of excavation. Subsurface condi ions may change at this location wit the passage of time. The data presented are 0 a simplfication of actual conditions encountered. DESCRIPTION Topsoil 1 Loose, moist, dark brown, silty SAND, with organics and roots. Weathered Vashon Lodgement Till 2 -Loose to medium dense, moist, reddish brown, silty SAND, with gravel and roots. 3 Medium dense to dense, moist, rust-stained brownish gray, silty fine to medium SAND, with gravel. 4 Vashon Lodgement Till 5 -Dense to very dense, moist, brownish gray, silty fine to medium SAND, with gravel, fine sand lenses. 6 - 7 Bottom of exploration pit at depth 61/2 feet. No seepage or caving. 8 - 9 - 10 - 11 - 12 - 13 14 - 15 - 16 - 17 - 18 - 19 - ---------------------------------------------- Logged by: JPL Approved by: Welman Plat Renton, WA Associated Earth Sciences, Inc. Project No. KE100030A 2/10/10 "---------------------------------------------- LOG OF EXPLORATION PIT NO. EP-5 g This log is part of the report prepared by Associated Earth Sciences, Inc. (AESI) for the named firoject and should be ~ read together with that report for comfllete interpretation. This summary a~plfes only to the loca ion of this trench at the 15. time of excavation. Subsurface condi lons may change at this location wit the passage of time. The data presented are <I> 0 a simplfication of actual conditions encountered. DESCRIPTION Topsoil 1 Loose, moist, dark brown, silty SAND, with organics and roots. Weathered Vashon Lodgement Till 2 -Loose to medium dense, moist, reddish brown, silty SAND, with gravel and roots. 3 -Medium dense to dense, moist, rust-stained brownish gray, silty fine to medium SAND, with gravel. 4 Vashon Lodgement Till 5 -Dense to very dense, moist, brownish gray, silty fine to medium SAND, with gravel, fine sand r \lenses. 6 -Bottom of exploration pit at depth 5 feet. Moderate seepage at 3 1/2 feet. No caving. 7 - 8 - 9 - 10 - 11 - 12 - 13 - 14 - 15 - 16 - 17 - 18 - 19 - ~--~-------------------------------------------"' _____________________________________________ _ N [ ~ • ~ ~ " I M ~ ~ Logged by: J PL Approved by: Welman Plat Renton, WA Associated Earth Sciences, Inc. Project No. KE100030A 2/10/10 ------------------------------------- g cg_ w 0 2 - 3 - 4 - 5 - 6 - 7 - 8 - 9 - 10 - 11 - 12 - 13 - 14 - 15 - 16 - 17 - 18 - 19 - LOG OF EXPLORATION PIT NO. EP-6 This log is part of the report prepared by Associated Earth Sciences, lnc. (AESI) for the named project and should be read together with that report for complete interpretation. This summary applies 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 simplfication of actual conditions encountered. DESCRIPTION Topsoil Loose, moist, dark brown, silty SAND, with organics and roots. Weathered Vashon Lodgement Till Loose to medium dense, moist, reddish brown, silty SAND, with gravel and roots. Medium dense to dense, moist, rust-stained brownish gray, silty fine to medium SAND, with gravel. Vashon Lodgement Till Dense to very dense, moist, brownish gray, silty fine to medium SAND, with gravel, fine sand lenses. Bottom of exploration pit at depth 5 1/2 feet. No seepage or caving. ~--20------------------------------------------- ,i • & • ~ ~ " I M ~ Logged by: JPL Approved by: Welman Plat Renton, WA Associated Earth Sciences, Inc. Project No. KE100030A 2/10/10 \! _____________________________________________ _ Prepared By: J3ME Welman Plat Technical Information Report City of Renton March 15, 201 O June 23, 2010 (revised) Prepared for: Centurion Development Services, Inc. P.O. Box 2668 Redmond, WA98073-2668 Jerrit Jo/ma P.E. .13ME .Job No. M.JF-004 Technical Information Report -Welman Plat TABLE OF CONTENTS SECTION 1 PROJECT OVERVIEW ....................................................................................... 1 SECTION 2 CONDITIONS & REQUIREMENTS SUMMARY .................................................. 6 SECTION 3 OFF-SITE ANALYSIS ......................................................................................... 8 SECTION 4 FLOW CONTROL & WATER QUALITY ANALYSIS AND DESIGN .................... 9 SECTION 5 CONVEYANCE SYSTEM ANALYSIS AND DESIGN ........................................ 14 SECTION 6 SPECIAL REPORTS AND STUDIES ................................................................ 16 SECTION 7 OTHER PERMITS ............................................................................................. 17 SECTION 8 ESC ANALYSIS AND DESIGN ......................................................................... 18 SECTION 9 BOND QUANTITIES AND FACILITY SUMMARIES ......................................... 19 SECTION 10 OPERATIONS AND MAINTENANCE MANUAL ............................................... 20 APPENDIX A: KCRTS ANALYSIS & CONVEYANCE KCSWDM Table 3.2.2.B Rainfall Regions and Regional Scale Factor KCRTS Output: -Existing Conditions -Developed Conditions -Detention Vault -Sediment Pond Sizing Figure 5.3.4.H Riser Inflow Curves Storm Sewers Output Outfall Design Calculations APPENDIX B: Welman Subdivision Level One Downstream Analysis by Site Development Associates, LLC dated June 13, 2007 King County Stormwater Adjustment LIST OF FIGURES: Figure 1: Vicinity Map Figure 2: Existing Conditions Map Figure 3: SCS Soils Map Figure 4: Developed Conditions Map Figure 5: Conveyance Basins Map BME ~ Technical Information Report -Welman Plat SECTION 1: PROJECT OVERVIEW The proposed project is the subdivision of approximately 3.24 acres into 25 single- family detached residences. The Welman Plat is located at 18417 1161h Ave SE, in Renton. Tax parcel number 3223059033 which is sited within the NE Y., SE Y., Section 32, T 23, R 5 E. Please see Figure 1: Vicinity Map. Existing Site Conditions: The site is currently developed with a single family residence that contains a garage and carport. The site vegetation can be generally characterized as a grass with scattered trees. The majority of the site slopes toward a swale located in the northwest portion of the parcel which is classified as a Class 4 wetland. This wetland drains toward an existing subdivision located west of the site, see Figure 2: Existing Conditions Map. The existing onsite soils are mapped as Alderwood gravelly sandy loam per the Natural Resources Conservation Service -Web Soil Survey. Please see Figure 3: SCS Soils Map. Table 3.2.2.B of the KCSWDM classifies the soils as Till, a copy of the table is included in Appendix A for reference. Developed Site Conditions: The project consists of the subdivision of the property into 25 single-family detached residences. Access to the residences will be provided a public road extending off of SE 134th St. Frontage improvements will consist of improvements to 115th Ave SE and construction of a portion of SE 1841h St west of 115th Ave SE, see Figure 4: Developed Conditions Map. Stormwater runoff from the project will be collected and routed to a detention vault that will be located in the northwest corner of the site. The detention vault will outfall into the existing Class 4 wetland, which is the sites natural discharge location. Water quality will be provided via dead storage in the proposed detention vault. J3ME 1 J N SE 176TH ST ------NORTH BENSON CENTER SE 180TH ST ijj SE 180TH PL ~ ( < SE 181ST ST r w w ls w w SE 182ND ST ~ ~ r r § § 515 SITE SE 1MTHST SE 186TH ST VICINITY MAP NE 1/4, SE1/4, SEC. 32, T.23 N., R. 5 E., W.M. WELMAN PLAT • 1375 NW Moll Street, Suite 3 DWN. BY: DATE: JOB NO. I ssoquoh, WA 9802 7 TAM 1/16/10 MJF-004 Tel (425) 313-1078 CHKD. BY: SCALE: J3ME Fax(425)313-1077 J. JOLMA NTS FIGURE 1 -~ u s 6 J! ,: a $ s " e ' ~ f, ~ ~ ' ~ ~ 5 ...J Cl. :,:: ,r1 • f-. "' / ~I w CJ) J' I /, " y' -H0--- _-,_-• < .~:-:---:-• :-:·-=-·~ .~ ~~, "---:,C.:.--;--L--.,.:..::..._-r_::<~-;·~/::'.,_~-.::-~·--:---:. ----=-....:... y 1,<t,, /-. / / ./ / / CAT. AREA TO REMAIN UNCHANGED 0.25 ac \ <..::, ::..\ I_ --\?;o/' I 1.J : ~ / ff I I ' / / / .7 / .. ; /./ .. / /• ••• ;I /-: ... / .,,< ••• ·/ / .. ~ -~ ./ <· ,,.--· ----· -.:- -/ ' r .~iv, . .,,, '---- '~ EXISTING WETLAND ·, ' -L '·._ "--_r .... -------~-...,...~--~ //7,?7777/7' r ;, r ;i " / y /, ·/ ,1 !"'f ;:1 1:,·r 1 .,,, . /--( ~ ' .-, V '/-,.·;··/ r / Y.t . ...:.< / / ___ ,,_ OFFSITE AREA C GRAVEUIMPERVIOUS = 0.08 ac PASTURE = 0.06 ac \ ·, ' • \ \;,, ' \ : ~ .· / · •. ,, I ui I / CJ) / u.i ( > <( :,:: f- "' - / . .;,;,; ---·----- S.E. 184TH ST. 0 25 SCALE IN FEET OFFSITE AREA A PAVEMENT/IMPERVIOUS= 0.13 ac PASTURE = 0.08 ac 50 ONSITE AREA TO VAULT 3.24 ac -0.25 ac = 2.99 ac ALL ONSITE AREAS TO BE CONSIDERED FOREST PER 2005 KCSMDM KCRTS EXISTING AREAS Forest :;::: 2.99 ac Impervious : 0.21 ac Pasture = 0.14 ac Total = 3.34 ac OFFSITE AREA B 2,708 SF TO OFFSITE BASIN 6 ·-------- i < " a N <<J<J<<l <l<l<l<i<l i ~ ~ I ~ ! ::'.!! ', ~ ~ ~ 0. I" ~ ii~li --~~ -~-~-~.~ .}} ~ ~ l.lJ i§ :,:; ,5: ~ i=:: ~ 8 (:, ~ hC C/) ~ I.ti .... q: ~ =t ; iit s: STAMP NOT VALID UNLESS SIGNED ANO DATED • J3ME 1375 NW Moll Street, Suite 3 lmquuh, WA 98027 Tel (425) Jl J. J 078 Fox (425) 31 J. \077 " 2 (0 ~ ~ ~ ~ is i: G JOB NUMBER MJF-004 FIGURE 2 Soil Map-King County Area , Washington (We lman Plat) FIGURE 3-SCS SC>ILS 47' 26' 17" Map Unit Legend 5613~ King County Area, Washington (WA633) Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI AgB Alderwood gravelly sandy loam, 0 to 6 4.7 73 .8% percent slopes AgC Alderwood gravelly sandy loam, 6 to 15 1.7 - 26 .2% percent slopes -- Totals for Area of Interest 6.3 100.0% -·------ IVIAP 561300 561390 56f420 1-- "' ~ 0 ;! -:!, ~ S! ~ g 0 '(J, ~ g 0 -:!, ~ ~ '(J, ~ 7/15/2009 Page 1 of 3 47° 26' 17" 47 ' 26' 11 · 6 = ' . ' C ; 0 " 8 ~ u ~ ~ ' : i $ " LOT IMPERVIOUS CALCULATIONS SF OF IMPERVIOUS/LOT, LOT#, TOTALS 2,200 2,275 2,550 2, 3, 6, 9, 10, 11, 13, 16-24 35,200 1,4, 12, 14, 15 11,375 5, 7,8,25 __J Cl. I ~I w "' l I < 10,200 TOTAL 56,775 (1.30 ac) C.A.T. AREA TO REMAIN UNCHANGED = 0.25 ac . BACKYARDS OF LOTS 6-8 TO BYPASS DETENTION · (0.1 ac.) / / ·;:, OFFSITE AREA C----.. IMPERVIOUS = 0.08 ac P/\STURE -0.06 ac 8 TRACT 'P CAiAUL T ROOF ASSUMED ' 25% IMPERV. (0.04 ac), 75% G~SS (0.11 ac) 9 10 11 12 .--·"'."'. µ ,-' c :,. -;;,, / bi 13 OFF VAULT GRASS-CRETE ASSUMED IMPERVIOUS 14 4',;(f-- / 2 "" 3 4. I -- (' 7~t"7/"T7) ·1 A ,r'..<L.:..t / 1../,:J ,L 15 ~J >'; I c:f·I " !I '?·1 25 24 23 11 500 '\l 17 ONSITE AREA T TO OFFSITE AR (IMPERVIOUS= 0.04 ac· :· 21 T CTS = 0.50 a •. 1ij IBUTARY B .01 ac) l?l,:; s -+-~,----+--~--·so2 I 'Sq, 16 f 502---' ~o, ,,\< >1 ii 11 ;I ;1 • iJ ' u.i en u.i > <( i': <O ~ '. ' i - S.E. 18,4TH ST. fH; OFFSITE AREA A IMPERVIOUS= 0.17 ac GRASS = O.Q4 ac SITE: TOTAL SITE = 3.24 ac -C.A.T. AREA = 0.25 ac -TO OFFSITE B = 0.01 ac ONSITE TO VAULT = 2.98 ac BYPASS: BACKYARD LOTS 6-8 GRASS = 0.10 ac ONSITE: IMPERVIOUS ASPHALT = 0.50 ac SIDEWALK = 0.11 ac LOT IMPRV = 1.30 ac VAULT LID = 0.04 ac ;:.i,: N 0 25 SCALE IN FEET (SEE LOT IMPERVIOUS CALCS THIS SHEED TOTAL = 1.95 ac PERVIOUS YI\ULT LIQ -o.11ac 50 GRASS TOTAL = (2.98-(1.95+0.11+0.10)) = 0.82 ac = 0.93 ac OFFSITE: AREA A IMPERVIOUS GRASS AREAC IMPERVIOUS PASTURE = 0.17 ac ::: 0.04 ac ::: 0.08 ac = 0.06 ac KCRTS DEVELOPED CONDITIONS TO VAULT IMPERVIOUS PASTURE GRASS TOTAL = 2.20 ac ::: 0.06 ac = 0.97 ac ::: 3.23 ac OFFSITE AREA B TRIBUTARY TO OFFSITE BASIN = 0.06 ac , ' . ~ ~ ~ • a ~<.] <.] <.] <.] <.]<.] <.]<.] <1'1<.l ~~~ . ". I H I" •I ' I ~Ii 2t~ ~'-~Ea o,i;; ~ ~ ~ t,.g ~1, • a. \ll(-;~i-,~-;~ 1§~~ i j::: ~ 8 @ @s [jj ::,; ~ .... ~ Q.; :it: ~ ~ s: STAMP NOT VALID UNLESS SIGNED ANO DATED • J3ME 1375 NW Mall S1mt, Suite 3 lmquch, WA 9BD27 Tel (425)313-1078 Fa~ (425) 313-1077 >: :2 I ~ ~ ~ is r: \] JOBNUMBER MJF-004 FIGURE 4 Technical Information Report -Welman Plat SECTION 2: CONDITIONS & REQUIREMENTS SUMMARY King County Surface Water Design Manual Core Requirements: 1. Discharge at the Natural Location The existing drainage patterns of the site will be emulated and maintained in the developed conditions by conveying stormwater to the existing wetland located in the northwest corner of the site. 2. Off-site Analysis An offsite analysis has been prepared for the project; please see Section 3 of this report. 3. Flow Control The site is located within a Conservation Flow Control Area, per King County, calculations are provided in Section 4: Flow Control and Water Quality Analysis, which conform to the requirements set forth in the 2005 KCSWDM. 4. Conveyance System All proposed conveyance systems conform to the 2005 KCSWDM requirements. See Section 5: Conveyance System Analysis and Design. 5. Temporary Erosion & Sediment Control An erosion and sediment control plan which will serve to control soil erosion and sedimentation during the proposed site construction activities will be prepared for approval by the City. See Section 9: ESC Analysis and Design of this report for further details of the Best Management Practices to be implemented for the project. 6. Maintenance & Operations Standard King County maintenance and Operation guidelines have been included in Section 10: Operations and Maintenance Manual. 7. Financial Guarantees & Liability Financial Guarantee & Liability commitments between the property developer and The City of Renton will be established at the time of permit issuance. 8. Water Quality J3ME The project site is subject to provide Basic Water Quality as outlined by the Water Quality Applications Map in the 2005 KCSWDM. Water quality will be provided by incorporating a wet vault into the proposed detention vault sized to conform to King County standards. See Section 4: Flow Control and Water Quality Analysis. 6 Technical Information Report -Welman Plat King County Surface Water Design Manual Special Requirements: 1 . Other Adopted Area-Specific Requirements The project is located within the Duwamish-Green River Watershed, Water Resources Inventory Area (WRIA) 9. No know area-specific plans are applicable to this site. 2. Floodplain/Floodway Delineation 3. 4. The site is not located within a 100-year floodplain, zero-rise flood fringe, zero- rise floodway, FEMA floodway, or channel migration zone as described in KCC 21 A.24. Concurrently, the site is not adjacent to any such area. Flood Protection Facilities The site is not located in a floodplain or adjacent to a flood protection facility. Source Control This site does not meet the threshold for source control requirements, therefore, source control is not proposed for the completion of this project. 5. Oil Control BME This site does not meet the threshold for oil control requirements, therefore, oil control is not proposed for the completion of this project. 7 Technical Information Report -Welman Plat SECTION 3: OFF-SITE ANALYSIS A Level -1 Offsite Analysis was prepared for the site by Site Development Associates, LLC dated June 13, 2007. This analysis was reviewed and approved with the preliminary engineering and is included in Appendix B for reference. J3ME 8 Technical Information Report -Welman Plat SECTION 4: FLOW CONTROL & WATER QUALITY ANALYSIS AND DESIGN A hydrologic analysis of the site was completed in order to determine the required detention and water quality treatment volume necessary. The site was analyzed for the pre-developed and developed conditions using the King County Continuous Runoff Time Series (KCRTS) hydrograph model using the KCRTS software developed and provided by the King County Surface Water Management Division. Part A -Existing Site Hydrology The site is currently developed with a single family residence that contains a garage and carport. The site vegetation can be generally characterized as grass with scattered trees. The southerly portion of the site is fairly flat with slopes less than 5%, while the northwest portion of the site slopes to an existing swale at approximately 20%. This swale is classified as a Class 4 wetland which drains westerly toward an existing subdivision located west of the site; see Figure 2: Existing Conditions Map. As described in the downstream analysis, the southerly portion of the site sheet flows toward the west where it eventually joins runoff from swale/wetland portion of the site. Therefore, the site is a single threshold discharge area. A Stormwater Adjustment was approved by King County during preliminary review, which allows all stormwater to be directed to the existing swale/wetland. A copy of the approved Adjustment has been included in Appendix B for reference. A small amount of offsite road shoulder area along 1161h Ave SE near SE 1841h St. will be included in the existing conditions due to the construction of the frontage improvements (Offsite Area A). The southerly portion of the 1161h Ave SE frontage improvements will be collected and conveyed to the roadside ditch on the east side of the street (Offsite Area B). This area is less than 5,000 sf and therefore does not require detention, as approved with the Preliminary Design by King County. Additionally a small amount of upstream tributary area will flow onto the site from the north (Offsite Area C). This will be collected and passed through the detention vault. The detention system is designed to meet the 2005 King County Stormwater Requirements for Conservation Flow Control. Therefore, the existing conditions are required to be modeled as forest. As a conservative assumption, the wetland area within future Lots 1 and 2 was also considered to be forest rather than wetland. The area within C.A.T. G (0.25 ac) was excluded from the calculations as it will be downstream of the development and stormwater system, and can be considered unchanged in the developed conditions. KCRTS Hydrologic Parameters J3ME Soil Type Location Rain Region Scale Factor = = = = Till Black River Subbasin of the Green River Drainage Basin SeaTac 1.0 9 Technical Information Report -Welman Plat Basin Areas Forest= 2.99 ac Pasture= 0.14 ac Impervious= 0.21 ac Please see Figure 2: Existing Basin Map for the complete area breakdown. Flow Frequency Analysis Time Series File:ex-1.tsf Project Location:Sea-Tac ---Annual Peak Flow Rates--- Flow Rate Rank Time of Peak (CFS) 0.231 2 2/09/01 18:00 0.097 7 1/05/02 16:00 0.202 3 2/28/03 3:00 0.053 8 8/26/04 2:00 0.121 6 1/05/05 8:00 0 .195 4 1/18/06 16:00 0.179 5 11/24/06 4:00 0.339 ~ 1 1/09/08 9:00 Computed Peaks Part B -Develo12ed Site Hydrology -----Flow Frequency Analysis------- --Peaks --Rank Return Prob (CFS) Period 0.339& 1 100.00 0.231 2 25.00 0.202 3 10.00 0.195 4 5.00 0.990 0.960 0.900 0.800 0.179 5 3.00 0.667 0.121 6 2.00 0.500 0.097 7 1.30 0.053 8 1.10 0.303 50.00 0.231 0.091 0. 980 The project consists of the subdivision of the site into 25 single-family detached residences. Access to the residences will be provided a public road extending off of SE 184th St. Frontage improvements will consist of improvements to 115th Ave SE and construction of a portion of SE 184th St west of 1161h Ave SE, see Figure 4: Developed Conditions Map. Stormwater runoff from the site will be collected and routed to a detention vault that will be located in the northwest corner of the site. The detention vault will outfall into the existing Class 4 wetland, which is the sites natural discharge location. Critical Areas Track G will remain unchanged and therefore not included in the analysis. Approximately 0.1 ac of backyard grass area from Lots 6-8 will be bypassed in the developed condition. This bypass area is accounted for by using the Point of Compliance Analysis method in KCRTS modeling. Water quality will be provided via dead storage in the proposed detention vault. KCRTS Hydrologic Parameters Soil Type Location Rain Region Scale Factor BME = = = = Till Black River Subbasin of the Green River Drainage Basin SeaTac 1.0 10 Technical Information Report -Welman Plat Basin Areas -To Vault Grass= 0.97 ac Pasture = 0.06 ac Impervious= 2.20 ac Please see Figure 4: Developed Conditions Map for the complete area breakdown. Flow Frequency Analysis Time Series File:de-1.tsf Project Location:Sea-Tac ---Annual Peak Flow Rates--- Flow Rate Rank Time of Peak (CFS) 0.620< 6 2/09/01 2:00 0.514 8 1/05/02 16:00 0.743 3 2/27 /03 7:00 0.566 7 8/26/04 2:00 0.678 4 10/28/04 16:00 0.659 5 1/18/06 16:00 0.823.k---2 10/26/06 0:00 1. 24&-1 1/09/08 6: 00 Computed Peaks Bypass Area Grass = 0. 1 ac Flow Frequency Analysis Time Series File:bypass.tsf Project Location:Sea-Tac ---Annual Peak Flow Rates--- Flow Rate Rank Time of Peak (CFS) 0.009 3 2/09/01 2:00 0.005 6 1/05/02 16:00 0. 011 2 2/27 /03 7:00 0.002 8 8/26/04 2:00 0.005 7 1/05/05 8:00 0.009 4 1/18/06 16:00 0.008 5 11/24/06 3:00 Ot... o. 021 £-1 1/09/08 6: 00 Computed Peaks Part C -Performance Standards -----Flow Frequency Analysis------- --Peaks --Rank Return Prob (CFS) Period l.24e--° 1 100.00 0.823~ 2 25.00 0.743 3 10.00 0.678 4 5.00 0.659 5 3.00 0.620'=:--- 0.566 0.514 1.10 6 7 8 2.00 1. 30 1.10 50.00 0.990 0. 960 0.900 0.800 0.667 0.500 0.231 0.091 0.980 -----Flow Frequency Analysis------- --Peaks --Rank Return Prob (CFS) Period 0.02~ DI:. 1 100.00 0.990 0. 011 2 25.00 0. 960 0.009 3 10.00 0.900 0.009 4 5.00 0.800 0.008 5 3.00 0.667 0.005 6 2.00 0.500 0.005 7 1. 30 0.231 0.002 8 1.10 0. 091 0.018 50.00 0.980 The project site is located in the Black River Basin which is within the Green River Watershed. The design will meet the Conservation Flow Control Standard set forth in the 2005 King County Surface Water Design Manual (KCSWDM) Section 1.2.3.1.B. This standard mandates maintaining the durations of high flows at their predevelopment levels for all flows greater than one-half of the 2-year peak flow, up to the 50-year peak J3ME 11 Technical Information Report -Welman Plat flow and matching the 2 and 10-year predeveloped peak flows. The predevelopment conditions are to be modeled usirig the historic site conditions (forested) in order to provide a hydrologic regime that more closely resembles the conditions to which local aquatic species have adapted. The area-specific water quality treatment was determined to be Basic Water Quality per the Water Quality Applications Map in the 2005 KCSWDM. This standard is generally applied to areas outside of the drainage basin of sensitive lakes or sphagnum bog wetlands. Water quality treatment facilities are designed to treat flows up to and including the water quality design flow and provide minimum 80 percent Total Suspended Solids removal. Part D -Flow Control System The detention/water quality vault system was designed for the project site and provides 6 feet of active storage depth. The vault outfall will be via a 12-inch pipe to a level spreader that will disperse flows into the onsite wetland. Retention/Detention Facility Type of Facility: Facility Length: Facility Width: Facility Area: Effective Storage Depth: Stage O Elevation: Storage Volume: Riser Head: Riser Diameter: Number of orifices: Orifice # Height (ft) 1 0.00 2 3.50 3 4.75 Top Notch Weir: Outflow Rating Curve: Detention Vault 58.67 ft V 104.00 ft - 6102. Sq. ft v 6. 00 ft 489.00 ft 36610. cu. ft 6.00 ft · 12.00 inches 3 Full Head Diameter Discharge (in) (CFS) 1. 05 0. 073 1. 45 0.090 1. 40 0.059 None None Pipe Diameter (in) 4.0 4.0 The volume required to adequately detail runoff generated by the project site is 35L6AO cubic feet. The proposed vault will provide 6 feet of active storage depth and will be 104 feet long and 60 feet wide, which will provide ~s (volume utilized by internal walls subtracted). This will provide a 3% factor of safety. See Appendix A for complete KCRTS vault sizing output. Part E -Water Quality System Water quality for the proposed development will be provided by a wet vault sized per King County standards. Wet vaults maintain a permanent pool of water and treat stormwater during the relatively long residence time within the vault. J3ME 12 Technical Information Report -Welman Plat Wet Vault Sizing (Area Tributary to Vault Only): V, = [0.9At + 0.25A1 9 J(R) = (0.9(95,832)+0.25(43, 124)](0.0392) = 3,804 = 3.0 (3,804) = 11 412 ft3 Where: V, = Runoff Volume from Mean Annual Storm ( cf) A, = Area of Impervious Surface (sf) A,9 = Area of Till Grass + Pasture ( sf) V 0 = Required Wetpool Volume (cf) f = Volume Factor (3.0 for basic ponds) R = Rainfall from Mean Annual Storm (ft) (from KCSWDM Figure 6.4.1.A) Through the analysis, the required volume of the wetpool was determined to be 11,412 cubic feet. This volume will be provided under the live storage volume within the proposed detention/water quality vault. J3ME 13 Technical Information Report -Welman Plat SECTION 5: CONVEYANCE SYSTEM ANALYSIS AND DESIGN The onsite conveyance system contains 14 catchments with 3.23 acres of total tributary area. Please see Figure 5: Conveyance Basins Map. The analysis was completed using the Storm Sewers 2005 computer analysis model, which calculates flows in accordance with the Rational Method. The runoff coefficient for each catchment was calculated using a weighted average, assuming 0.9 for impervious and 0.25 for grass, which results in an overall C value of 0.69. AC value of 0.7 was used as a conservative assumption in the model. This accounts for all areas within the project, including roadway, yards, footing drains, driveways and roof downspouts. The conveyance modeling demonstrates that the proposed system is capable of conveying the 100-year runoff from the site without overtopping any of the catch basins. This exceeds the required performance of conveying the 25-year event without overtopping. Please see the Storm Sewers output in Appendix A, which demonstrates the freeboard available at each structure. Riser Design The detention vault will use a 12-inch riser to control flows. Using Figure 5.3.4.H of the 2005 KCSWDM, the riser flow rate can be determined during an overflow condition. The figure shows that a 12-inch riser with 0.5 feet of head can flow approximately 1. 75 cfs, which is greater then the modeled flowrate of 1.24 cfs. The KCSWDM Figure is included in Appendix A. Outfall Design All flows exiting the detention vault will be dispersed into the onsite wetland using two level spreaders and an energy dissipater. The level spreaders will be constructed in accordance with Figure 4.2.2.N of the KCSWDM and be limited to 0.5 cfs by using orifice plates. Any flows beyond 1.0 cfs will overtop the energy dissipater as weir flow. During a 100-year event less than 0.3 cfs will flow over the dissipater rim with an approximate height of 0.12 feet. Complete design calculations are included in Appendix A. J3ME 14 /,,,-···· / 1 l I '/>/ ~ s ' • C 0 ~ ] £ g ~ s ~ ~ / / , / / / , '., .I I f h./j 5' ______ ,.~,. {J I l l CB 12 0.30 ac. TRACT'F' 9 CB 1 '0.48 ac. --· _,., p ri . 1' ,1 il • • ..!>-• ._ --'.{J--- 2-i -4~>- 2 ·---. --· --· 'T: CB 6 4 0;19 ac. 'f[T 7T7 7777'.'' 7 ;'"7/_7 -,cl .. / . ·' 5 Y-i ,: _____ .,_. CB8 0.13 aQ. ' ----------," -i 25 CB 3 0.23 ac. ,.. /~-."' ' • 2J ·, . • ' ·. CB 7'& . \ 22 Q.24 ac.'. 21 . . 1§1 CB14 0.4alac. ~ i' I ,. J <f ,1 er.~~ I ,j I ,I I ·/ '·I 'II :·~ I .\1 , I :!·;· ·,; 1 ,1 CB 5 0.24 ac. i } ''/ '! i1 ;j ii :'1 ''I I I ' /1 V JI ' ii -J ( / / "".; a /",,. -4~ . 25 50 SCALE IN FffT CATCH BASIN AREAS CB# AREA 1 0.48 ac. 2 0.11 ac. 3 0.23 ac. 4 0.03 ac. 5 0.24 ac. 6 0.19 ac. 7 0.24 ac. 8 0.13 ac. 9 0.09 ac. 10 0.30 ac. 11 0.37 ac. 12 0.30 ac. 13 0.04 ac. 14 0.48 ac. TOTAL 3.23 ac. s ~ ~ .-- ! ~<] <J <J <J <J <J <J <J <] <! <J I ~ '. § "--~ , '!. i ii !Ii !I~ !II ,J\! i§ ~ it Q.. ~ ~ ~ I 2 o ... ~ ~ ~ iii ~ 2 l ~ ~ f... ~ ti r:: (j 10 CB 10 0.30 ac. 1 11.· \1 COMPOSITE C VALUE (ASSUME ALL PERVIOUS IS GRASS) 11 CB 11 0.37 ac. 1: 13 14 I I ·. i1 ' J 1 1 r n .11: 15 •, -.~:':11·---······-·-·· .. -,.--·-·-.. 16 ! 12 I "-. .......... -----Sn2-··"··-··"··-····-) l 1 -~--_j ,..,---------------,---~:-"--f--",.,....'. .. ~~~~. "•'·-----------------··-·······-··...::,-!.... .. -----------··---~------j '."~) ~-" Ul15 I ; I C = (0.9 x 2.20) 3~i~.25 x 0.99) = 0.60 ASSUME C = 0.7 STAMP NOT VALID UNLESS SIGNED AND DATED • J3ME 1375 NW Mall Street, Suite 3 lmquah, WA 98027 Tel (425) 313-1078 Fax (425)313-1077 J()i!NUMBER MJF-004 FIGURE 5 l1 -~ Technical Information Report -Welman Plat SECTION 6: SPECIAL REPORTS AND STUDIES A soils investigation was completed and will be submitted under separate cover. J3ME 16 Technical Information Report -Welman Plat SECTION 7: OTHER PERMITS The following permits are anticipated as part of the approval process: NPDES Building Permit -Detention Vault J3ME 17 Technical Information Report -Welman Plat SECTION 8: ESC ANALYSIS AND DESIGN To develop the project site, several Best Management Practices (BMP's) will be implemented. Other temporary erosion and sediment control may occur during the duration of the project depending on weather conditions, clearing operations, and excavation and fill placement. The on-site soils are mapped as Alderwood series. Alderwood material have slow permeability, runoff potential is slow to medium, and a moderate to severe erosion hazard. Specific TESC measures to be implemented include the following: • Filter fabric fencing • Temporary Catch Basin Filters will be installed inside the catch basins downstream of the site. • Rock construction entrance may be constructed at the entrance to the project area. Given that the existing driveway is covered with hard packed gravel, a note has been added to the construction plan that allows this BMP to be waived pending the approval of the City Inspector. • The proposed detention vault will be utilized as a temporary sediment control facility. A temporary flow control riser utilizing a float system will be installed. Please see the TESC plans for additional details and sizing calculations. • Rock lined interceptor swales will be provided to direct flows to the TESC pond while slowing flow velocity to below erosive levels. • Seeding with an appropriated City approved seed mix will be performed on all areas of the project site not covered with impervious surfaces. • A construction sequence is provided to help direct the contractor as to the appropriate construction steps that will help minimize erosion. A KCRTS runoff analysis was completed to size the proposed sediment pond. The model output is included in Appendix A. J3ME 18 Technical Information Report -Welman Plat SECTION 9: BOND QUANTITIES AND FACILITY SUMMARIES This section is not required under Renton processing requirements. J3ME 19 Technical Information Report -Welman Plat SECTION 10: OPERATIONS AND MAINTENANCE MANUAL The following maintenance requirements should be followed to insure the stormwater system continues to function adequately. J3ME 20 APPENDIX A MAT1'TE'lANCE REQUIREMENTS FLOW CONTROL, CONVEYANCE, AND WQ FACTLTTIES NO. 3-DETENTION TANKS AND VAULTS Maintenance Defect or Problem Conditions When Maintenance is Needed Results Expected When Component Maintenance is Perlormed Storage Area Plugged Air Vents One-half of the cross section of a vent is blocked Vents free of debris and sediment at any point with debris and sediment. Debris and Sediment Accumulated sediment depth exceeds 10% of All sediment and debris removed the diameter of the storage area for % length of from storage area. storage vault or any point depth exceeds 15% of diameter. Example: 72-inch storage tank would require cleaning when sediment reaches depth of 7 inches for more than 1.h length of tank. Joints Between Any crack allowing material to be transported into All joint between tank/pipe sections Tank/Pipe Section facility. are sealed Tank Pipe Bent Out of Any part of tank/pipe is bent out of shape more Tank/pipe repaired or replaced to Shape than 10% of its design shape. design. Vault Structure Damage to Wall, Cracks wider than Y:z-inch and any evidence of Vault replaced or repaired to design Frame, Bottom. soil particles entering the structure through the specifications. and/or Top Slab cracks, or maintenance inspection personnel determines that the vault is not structurally sound. Damaged Pipe Joints Cracks wider than Yrinch at the joint of any No cracks more than ~-inch wide at inlet/outlet pipe or any evidence of soil particles the joint of the inleUout1et pipe. entering the vault through the walls. Manhole Cover Not in Place Cover is missing or only partially in place. Any Manhole is closed. open manhole requires maintenance. Locking Mechanism Mechanism cannot be opened by one Mechanism opens with proper tools. Not Working maintenance person with proper tools. Bolts into frame have less th8n % inch of thread (may not apply to self-locking lids.) Cover Difficult to One maintenance person cannot remove lid after Cover can be removed and Remove applying BOlbs of lift. Intent is to keep cover from reinstalled by one maintenance sealing off access to maintenance. person. Ladder Rungs Unsafe King County Safety Office and/or maintenance Ladder meets design standards. person judges that ladder is unsafe due to Allows maintenance person safe missing rungs, misalignment, rust, or cracks. access. Large access Gaps, Doesn't Cover Large access doors not flat and/or access hole Doors closes flat and covers access doors/plate Completely not completely covered. NOTE however that hole completely. grated doors are acceptable. Lifting Rings Missing, Lifting rings not capable of lifting weight of door Lifting rings sufficient to remove lid. Rusted or lid. l/24/2005 2005 Surface Water Design Manual -Appendix A A-4 APPENDIX A MAINTENANCE REQUIREMENTS FOR FLOW CONTROL, CONVEY A'ICE, AND WQ F ACJUTIES NO. 4 -CONTROL STRUCTURE/FLOW RESTRICTOR ( Maintenance Defect or Problem Condition When Maintenance is Needed Results Expected When Component Maintenance is Performed General Trash and Debris Distance between debris build-up and bottom of All trash and debris removed. (Includes Sediment) orifice plate is less than 1.5 feet. Structural Damage Structure is not securely attached to manhole Structure securely attached to wall wall and outlet pipe structure should support at and outlet pipe. least 1,000 lbs of up or down pressure. Structure is not in upright position (allow up to Structure in correct position. 10% from plumb). Connections to outlet pipe are not watertight and Connections to outlet pipe are water show signs of rust. tight; structure repaired or replaced and works as designed. Any holes-other than designed holes-in the Structure has no holes other than structure. designed holes. C/eanout Gate Damaged or Missing Cleanout gate is not watertight or is missing. Gate is watertight and works as designed. Gate cannot be moved up and down by one Gate moves up and down easily and maintenance person. is watertight. Chain/rod leading to gate is missing or damaged. Chain is in place and works as designed. Gate is rusted over 50% of its surface area. Gate is repaired or replaced to meet design standards. Orifice Plate Damaged or Missing Control device is not working properly due to Plate is in place and works as missing, out of place, or bent orifice plate. designed. Obstructions Any trash, debris, sediment, or vegetation Plate is free of all obstructions and blocking the plate. works as designed. Overflow Pipe Obstructions Any trash or debris blocking (or having the Pipe is free of all obstructions and potential of blocking) the overflow pipe. works as designed. Manhole See "Detention Tanks See "Detention Tanks and Vaults" Table No. 3 See "Detention Tanks and Vaults" and Vaults" Table No. 3 2005 Surface Water Design Manual -Appendix A 1/24/2005 A-5 APPENDIX A MAINTENANCE REQUIREMENTS FLOW CONTROL, CO'IVEY ANCE, AND WQ F AC!LlT!ES NO. 5 -CATCH BASINS Maintenance Defect or Problem Conditions When Maintenance is Needed Results Expected When Component Maintenance is perlormed General Trash & Debris Trash or debris of more than Y.t cubic foot which No Trash or debris located (Includes Sediment) is located immediately in front of the catch basin immediately in front of catch basin opening or is blocking capacity of the basin by opening. more than 10%. Trash or debris (in the basin) that exceeds 1/3 the No trash or debris in the catch depth from the bottom of basin to invert the basin. lowest pipe into or out of the basin. Trash or debris in any inlet or outlet pipe blocking Inlet and outlet pipes free of trash or more than 1 /3 of its height. debris. Dead animals or vegetation that could generate No dead animals or vegetation odors that could cause complaints or dangerous present within the catch basin. gases (e.g., methane). Deposits of garbage exceeding 1 cubic foot in No condition present which would volume. attract or support the breeding of insects or rodents. Structure Damage to Comer of frame extends more than % inch past Frame is even with curb. Frame and/or Top curb face into the street (If applicable). Slab Top slab has holes larger than 2 square inches Top slab is free of holes and cracks. or cracks wider than 114 inch (intent is to make sure all material is running into basin). Frame not sitting flush on top slab, i.e., Frame is sitting flush on top slab. separation of more than :Y. inch of the frame from the top slab. Cracks in Basin Cracks wider than X inch and longer than 3 feet, Basin replaced or repaired to design Walls/Bottom any evidence of soil particles entering catch standards. basin through cracks, or maintenance person judges that structure is unsound. Cracks wider than X inch and longer than 1 foot No cracks more than 1/4 inch wide at at the joint of any inleVoutlet pipe or any the joint of inleVoutlet pipe. evidence of soil particles entering catch basin through cracks. Settlement/ Basin has settled more than 1 inch or has rotated Basin replaced or repaired to design Misalignment more than 2 inches out of alignment. standards. Fire Hazard Presence of chemicals such as natural gas, oil No flammable chemicals present. and gasoline. Vegetation Vegetation growing across and blocking more No vegetation blocking opening to than 10% of the basin opening. basin. Vegetation growing in inleVoutlet pipe joints that No vegetation or root growth is more than 6 inches tall and less than 6 inches present. apart. Pollution Nonflammable chemicals of more than Y2 cubic No pollution present other than foot per three feet of basin length. surface film. Catch Basin Cover Cover Not in Place Cover is missing or only partially in place. Any Catch basin cover is closed open catch basin requires maintenance. Locking Mechanism Mechanism cannot be opened by on Mechanism opens with proper tools. Not Working maintenance person with proper tools. Bolts into frame have less than % inch of thread. Cover Difficult to One maintenance person cannot remove lid after Cover can be removed by one Remove applying BO lbs. of lift; intent is keep cover from maintenance person. sealing off access to maintenance. Ladder Ladder Rungs Unsafe Ladder is unsafe due to missing rungs, Ladder meets design standards and misalignment. rust, cracks, or sharp edges. allows maintenance person safe access. 1/24/2005 2005 Surface Water Design Manual -Appendix A A-6 APPEI\DIX A MA[]';TENANCE REQU!REMENTS FOR FLOW CONTROL, CONVEYANCE. AND WQ F ACJUTTES NO. 5 -CATCH BASINS ( Maintenance Defect or Problem Conditions When Maintenance is Needed Results Expected When Component Maintenance is performed Metal Grates Unsafe Grate Grate with opening wider than 7 Is inch. Grate opening meets design (If Applicable) Opening standards. Trash and Debris Trash and debris that is blocking more than 20% Grate free of trash and debris. of grate surface. Damaged or Missing. Grate missing or broken member(s) of the grate. Grate is in place and meets design standards. NO. 6 -DEBRIS BARRIERS (E.G., TRASH RACKS) Maintenance Defect or Problem Condition When Maintenance is Needed Results Expected When Component Maintenance Is Performed. General Trash and Debris Trash or debris that is plugging more than 20% Barrier clear to receive capacity of the openings in the barrier. flow. Metal Damaged/Missing Bars are bent out of shape more than 3 inches. Bars in place with no bends more Bars. than% inch. Bars are missing or entire barrier missing. Bars in place according to design. Bars are loose and rust is causing 50% Repair or replace barrier to design deterioration to any part of barrier. standards. NO. 7 -ENERGY DISSIPATERS Maintenance Defect or Problem Conditions When Maintenance Is Needed Results Expected When Component Maintenance Is Perfonned. Extemal: Rock Pad Missing or Moved Only one layer of rock exists above native soil in Replace rocks to design standards. Rock area five square feet or larger, or any exposure of native soil. Dispersion Trench Pipe Plugged with Accumulated sediment that exceeds 20% of the Pipe cleaned/flushed so that it Sediment design depth. matches design. Not Discharging Visual evidence of water discharging at Trench must be redesigned or Water Properiy concentrated points along trench (normal rebuilt to standards. condition is a "sheet flow" of water along trench}. Intent is to prevent erosion damage. Perforations Plugged. Over Yi of perforations in pipe are plugged with Clean or replace perforated pipe. debris and sediment. Water Flows Out Top Maintenance person observes water flowing out Facility must be rebuilt or of "Distributor~ Catch during any storm less than the design storm or redesigned to standards. Basin. its causing or appears likely to cause damage. Receiving Area over· Water in receiving area is causing or has No danger of landslides. Saturated potential of causing landslide problems. Internal: Manhole/Chamber Worn or Damaged Structure dissipating flow deteriorates to X or Replace structure to design Post. Baffles, Side of original size or any concentrated worn spot standards. Chamber exceeding one square foot which would make structure unsound. 2005 Surface Water Design Manual -Appendix A J/24/2005 A-7 APPENDIX A MAINTDIANCE REQUIREMENTS FLOW CONTROL. CONVEYANCE. AND WQ F.~CILITIES NO. 8 -FENCING Maintenance Defect or Problem Conditions When Maintenance is Needed Results Expected When Component Maintenance is Performed General Missing or Broken Any defect in the fence that permits easy entry to Parts in place to provide adequate Parts a facility. security. Erosion Erosion more than 4 inches high and 12-18 No opening under the fence that inches wide permitting an opening under a fence. exceeds 4 inches in height. Wire Fences Damaged Parts Post out of plumb more than 6 inches. Post plumb to within 1 i'2 inches. Top rails bent more than 6 inches. Top rail free of bends greater than 1 inch. Any part of fence (including post, top rails, and Fence is aligned and meets design fabric) more than 1 foot out of design alignment. standards. Missing or loose tension wire. Tension wire in place and holding fabric. Missing or loose barbed wire that is sagging Barbed wire in place with less than more than 21h. inches between posts. % inch sag between post. Extension arm missing, broken, or bent out of Extension arm in place with no shape more than 1 Yz inches. bends larger than :Y. inch. Deteriorated Paint or Part or parts that have a rusting or scaling Structurally adequate posts or parts Protective Coating condition that has affected structural adequacy. with a uniform protective coating. Openings in Fabric Openings in fabric are such that an 8-inch No openings in fabric. diameter ball could fit through. N0.9-GATES Maintenance Defect or Problem Conditions When Maintenance is Needed Results Expected When Component Maintenance is Performed General Damaged or Missing Missing gate or locking devices. Gates and Locking devices in place. Members Broken or missing hinges such that gate cannot Hinges intact and lubed. Gate is be easily opened and closed by a maintenance working freely. person. Gate is out of plumb more than 6 inches and Gate is aligned and vertical. more than 1 foot out of design alignment. Missing stretcher bar, stretcher bands, and ties. Stretcher bar, bands, and ties in place. Openings in Fabric See "Fencing~ Table No. 8 See "Fencing" Table No. 8 1/24/2005 2005 Surface Water Design Manual-· Appendix A A-8 APPENDIX J\ MAfNTENANCE REQUIREMENTS FOR FLOW CONTROL CONVEYANCE. AND WQ FACILITIES NO. 10 -CONVEYANCE PIPES AND DITCHES ( Maintenance Defect or Problem Conditions When Maintenance is Needed Results Expected When Component Maintenance is Performed Pipes Sediment & Debris Accumulated sediment that exceeds 20% of the Pipe cleaned of all sediment and diameter of the pipe. debris. Vegetation Vegetation that reduces free movement of water AU vegetation removed so water through pipes. flows freely through pipes. Damaged Protective coating is damaged; rust is causing Pipe repaired or replaced. more than 50% deterioration to any part of pipe. Any dent that decreases the cross section area Pipe repaired or replaced. of pipe by more than 20%. Open Ditches Trash & Debris Trash and debris exceeds 1 cubic foot per 1,000 Trash and debris cleared from square feet of ditch and slopes. ditches. Sediment Accumulated sediment that exceeds 20% of the Ditch cleaned/flushed of all design depth. sediment and debris so that it matches design. Vegetation Vegetation that reduces free movement of water Water flows freely through ditdies. through ditches. Erosion Damage to See woetention Pondsn TabJe No. 1 See ~Detention Ponds~ Table No. 1 Slopes Rock Lining Out of Maintenance person can see native soil beneath Replace rocks to design standards. Place or Missing (If the rock lining. Applicable). NO. 11 -GROUNDS (LANDSCAPING) Maintenance Defect or Problem Conditions When Maintenance is Needed Results Expected When Component Maintenance Is Performed General Weeds Weeds growing in more than 20% of the Weeds present in less than 5% of (Nonpoisonous, not landscaped area (trees and shrubs only). the landscaped area. noxious) Safety Hazard Any presence of poison ivy or other poisonous No poisonous vegetation present in vegetation. landscaped area. Trash or Litter Paper, cans, bottles, totaling more than 1 cubic Area clear of litter. foot within a landscaped area (trees and shrubs only) of 1,000 square feet. Trees and Shrubs Damaged Limbs or parts of trees or shrubs that are split or Trees and shrubs with less than 5% broken INhich affect more than 25% of the total of total foliage with split or broken foliage of the tree or shrub. limbs. Trees or shrubs that have been blown down or Tree or shrub in place free of injury. knocked over. Trees or shrubs which are not adequately Tree or shrub in place and supported or are leaning over, causing exposure adequately supported; remove any of the roots. dead or diseased trees. 2005 Surface Water Design Manual -Appendix A J/2412005 A-9 APPENDIX A MAINTENANCE REQUIRE:v!ENTS FLOW CONTROL. CONVEYA:'ICE, AND WQ FACILITIES N0.12-ACCESS ROADS Maintenance Defect or Problem Condition When Maintenance is Needed Results Expected When Component Maintenance is Performed General Trash and Debris Trash and debris exceeds 1 cubic foot per 1,000 Roadway free of debris which could square feet (i.e., trash and debris would fill up damage tires. one standards size garbage can). Blocked Roadway Debris which could damage vehicle tires (glass Roadway free of debris which could or metal). damage tires. Any obstruction which reduces clearance above Roadway overhead clear to 14 feet road surface to less than 14 feet. high. Any obstruction restricting the access to a 10-to Obstruction removed to allow at 12-foot width for a distance of more than 12 feet least a 12-foot access. or any point restricting access to less than a 1 O· foot width. Road Surface Settlement, Potholes, When any surface defect exceeds 6 inches in Road surface uniformly smooth with Mush Spots, Ruts depth and 6 square feet in area. In general, any no evidence of settlement, potholes, surface defect 'IM'lich hinders or prevents mush spots, or ruts. maintenance access. Vegetation in Road Weeds growing in the road surface that are more Road surtace free of weeds taller Surface than 6 inches tall and less than 6 inches tall and than 2 inches. less than 6 inches apart within a 4QQ.square foot area. Modular Grid Build·UP of sediment mildly contaminated with Removal of sediment and disposal Pavement petroleum hydrocarbons. in keeping with Health Department recommendations for mildly contaminated soils or catch basin sediments. Shoulders and Erosion Damage Erosion within 1 foot of the roadway more than 8 Shoulder free of erosion and Ditches inches wide and 6 inches deep. matching the surrounding road. Weeds and Brush Weeds and brush exceed 18 inches in height or Weeds and brush cut to 2 inches in hinder maintenance access. height or cleared in such a way as to allow maintenance access. 1/24/2005 2005 Surface Water Design Manual -Appendix A A-JO APPENDIX A MAINTENANCE REQUIREMENTS FLOW CONTROL. CONVEYANCE, AND WQ FACILITIES N0.17-WETVAULT Maintenance Defect or Problem Condition When Maintenance is Needed Recommended Maintenance to Component Correct Problem Vault Area Trash/Debris Trash and debris accumulated in vault (includes Remove trash and debris. Accumulation floatables and non-floatables). Sediment Sediment accumulation in vault bottom exceeds Remove sediment from vault. Accumulation the depth of the sediment zone plus 6 inches. Ventilation Ventilation area blocked or plugged Remove or clear blocking material from ventilation area. A specified % of the vault suriace area must provide ventilation to the vault interior (seep. 6-82 for required%). Vault Structure Damage to Wall, Cracks wider than %-inch and any evidence of Vault replaced or repaired to design Frame, Bottom, soil particles entering the structure through the specifications. and/or Top Slab cracks, or maintenance inspection personnel determines that the vault is not structurally sound. Damaged Pipe Joints Cracks wider than %-inch at the joint of any No cracks more than 1.4-inch wide at inlet/outlet pipe or any evidence of soil particles the joint of the inleUoutlet pipe. entering the vault through the walls. Baffles Damaged/Defective Baffles corroding, cracking, warping and/or Repair or replace baffles to showing signs of failure as determined by specifications. maintenance/inspection staff. lnleUOutlet Damaged Pipes tnleUoutlet piping damaged or broken and in Pipe repaired and/or replaced. need of repair. Trash/Debris Trash and debris accumulated in pipe or Remove trash and debris. Accumulation inlet/outlet (includes floatables and nonw ftoatables). Access Cover Damaged/Not Cover cannot be opened or removed, especially Pipe repaired or replaced to proper Working by one person. working specifications. Access Ladder Damaged Ladder is corroded or deteriorated, not Ladder replaced or repaired to functioning properly, missing rungs, has cracks specifications, and is safe to use as and/or misaligned. Confined space warning sign determined by inspection personnel. missing. Replace sign warning of confined space entry requirements. 1/24/2005 2005 Surface Water Design Manual -Appendix A A-14 APPENDIX A MATNTENANCE REQUIREMENTS FLOW CO:'-!TROL. CONVEYANCE, AND WQ FACILITIES NO. 24 -CATCHBASIN INSERT Maintenance Defect or Problem . Conditions When Maintenance is Needed Results Expected When Component Maintenance is Performed Catch Basin Inspection Inspection of media insert is required. Effluent water from media insert is free of oils and has no visible sheen. Sediment When sediment fonns a cap over the insert No sediment cap on the insert Accumulation media of the insert and/or unit. media and its unit. Trash and Debris Trash and debris accumulates on insert unit Trash and debris removed from Accumulation creating a blockage/restriction. insert unit. Runoff freely flows into catch basin. Media Insert Water Saturated Catch basin insert is saturated with water, which Remove and replace media insert no longer has the capacity to absorb. Oil Saturated Media oil saturated due to petroleum spill that Remove and replace media insert. drains into catch basin. Service Life Exceeded Regular interval replacement due to typical Remove and replace media at average life of media insert product. regular intervals, depending on insert product. 1/24/2005 2005 Surface Water Design Manual -Appendix A A-20 APPENDIX A 3.2.2 KC'RTS.'RU"OFF FILES METHOD-GE,\ER.IT!.VG Tl\/£ SERIES TABLE 3.2.2.B EQUIVALENCE BETWEEN SCS SOIL TYPES AND KCRTS SOIL TYPES SCS Soil Type scs KCRTS Soil Notes Hydrologic Group Soil Group Alderwood (AgB, AgC, AgD) C Till Arents, Alderwood Material (AmB, AmC) C Till Arents, Everett Material (An) B Outwash 1 Beausite (BeC, BeD, BeF) C Till 2 Bellingham (Bh) D Till 3 Brisco! (Br) D Till 3 Buckley (Bu) D Till 4 Earlmont (Eal D Till 3 Edgewick (Ed) C Till 3 Everett (EvB, EvC, EvD, EwC) A/B Outwash 1 Indianola (lnC, lnA, lnD) A Outwash 1 Kitsap (KpB, Kl')C, KpD) C Till Klaus (KsC) C Outwash 1 Neilton (NeC) A Outwash 1 Newberg (Ng) B Till 3 Nooksack (Nk) C Till 3 Norma (No) D Till 3 Orcas (Or) D Wetland Oridia (Os) D Till 3 Ovall (OvC, OvD, OvF) C Till 2 Pilchuck (Pc) C Till 3 Puoet (Pu) D Till 3 Puyallup (Py) B Till 3 Ragnar (Rae. RaD, RaC, RaE) B Outwash 1 Renton /Re) D Till 3 Salal (Sa) C Till 3 Sammamish (Sh) D Till 3 Seattle (Sk) D Wetland Shalcar (Sm) D Till 3 Si (Sn) C Till 3 Snohomish (So, Sr) D Till 3 Sultan /Su) C Till 3 Tukwila (Tu) D Till 3 Woodinville /Wo) D Till 3 Notes: 1. Where outwash soils are saturated or underlain at shallow depth (<5 feet) by glacial till, they should be treated as till soils. 2. These are bedrock soils, but calibration of HSPF by King County DNRP shows bedrock soils to have similar hydrologic response to till soils. 3. These are alluvial soils, some of which are underlain by glacial till or have a seasonally high water table. In the absence of detailed study, these soils should be treated as till soils. 4. Buckley soils are formed on the low-permeability Osceola mudflow. Hydrologic response is assumed to be similar to that of till soils. 2005 Surface Water Design Manual 1/24/2005 3-25 SECTION 3.2 RL'NOFF COMPUTATION AND A!\ALYSIS METHODS WESTERN KING COUNTY 2-Year 24-Hour Precipitation in Inches 1/24/2005 FIGURE 3.2.1.A 2-YEAR 24-HOUR ISOPLUVIALS ' _- ""~. ~Si:.\. ~!/ , / ... ~· -------,,: r-,, ---1 ,~./ /' ,, O 2 4 Miles 3-14 ----3.5 2005 Surface Water Design Manual WESTERN KING COUNTY 10-Year 24-Hour Precipitation in Inches 2005 Surface Water Design Manual 3.::'. I RATIONAL METHOD FIGURE 3.2.1.B JO-YEAR 24-HOUR ISOPLU\'IALS 4.5 --... iD 4.0 / ... O 2 4 Miles ' .,, "'~ 3-15 l/2412005 SECTIO'> 3 .2 RUNOFF COMPUTATION AND ANALYSIS METHODS FIGURE 3.2.1.C 25-YEAR 24-HOUR ISOPLUVIALS WESTERN KING COUNTY 25-Year 24-Hour Precipitation in Inches 1/24/2005 0 2 4 Miles 3-16 ~ .. HQ/.,oS!i CCUNTY -7i .. o. cc~ .. "7'; S.s S.o 411 4.s ·. . . ,.,::;;..., -----,.. .. (' -\__F-..... -c-.:.7 2005 Surface Water Design Manual FIGURE 3.2.1.D JOO-YEAR 24-HOUR ISOPLUVIALS WESTERN KING COUNTY 100-Vear 24-Hour Precipitation in Inches 2005 Surface Water Design Manual --,-----.s---- D 0 2 4 Miles 3-17 3.2.1 RATIONAL METHOD 1/24/2005 SECTION 3.2 RUNOFF COMPUTA TJON ANO ANALYSIS METHODS FIGURE 3.2.2.A RAINFALL REGIONS AND REGIONAL SCALE FACTORS ST 1.1 ST 1.1 ST1.0 Rainfall Regions and Regional Scale Factors D r~::::-::.1 Incorporated AreaD -= River/LakeD Major RoadD D 112412005 LA 1.0 LA 1.2 s,.o,.ou1 l'l OUNT• LA 1.0 2005 Surface Water Design Manual 3-22 Flow Frequency Analysis Time Series File:ex-1.tsf Project Location:sea-Tac ex-1 ---Annual Peak Flow Rates--------Flow Frequency Analysis------- Flow Rate Rank Time of Peak --Peaks --Rank Return Prob (CFS) 0.231 2 2/09/01 18:00 0.097 7 1/05/02 16:00 0.202 3 2/28/03 3:00 0.053 8 8/26/04 2:00 0.121 6 1/05/05 8:00 0.195 4 1/18/06 16:00 0.179 5 11/24/06 0.339 1 1/09/08 Computed Peaks ':>I -/. 0 It I I fo( ps_-/- JW< ?-· 2 '77 ac..... o 2: I "'-'-- ()./'-/a c_ 3 :s ~ <;.c__ 4:00 9:00 I - (CFS) 0. 339 0.231 0.202 0.195 0.179 0.121 0.097 0.053 0. 303 z_ '/ r2-O.S-x._ V, SD~ -J_x./2 I 2--' Page 1 Period 1 100.00 0.990 2 25 .00 0.960 3 10.00 0.900 4 5.00 0.800 5 3.00 0.667 6 2.00 0. 500 7 1.30 0.231 8 1.10 0.091 50.00 0.980 \ 2 I a 007 Flow Frequency Analysis Time Series File:bypass.tsf Project Location:sea-Tac ---Annual Flow Rate (CFS) 0.009 0.005 0.011 0.002 0.005 0.009 0.008 0.021 Peak Flow Rates--- Rank Time of Peak 3 6 2 8 7 4 5 1 2/09/01 2:00 1/05/02 16:00 2/27 /03 7: 00 8/26/04 2:00 1/05/05 8:00 1/18/06 16:00 11/24/06 3:00 1/09/08 6:00 computed Peaks St -I u T7// br'd::..S. -o, f «c bypass -----Flow Frequency Analysis------- --Peaks Rank Return Prob (CFS) Period 0.021 1 100.00 0. 011 2 2 5 . 00 0.009 3 10.00 0.009 4 5.00 o. 008 5 3 .oo 0.005 6 2.00 0. 005 7 1. 30 0.002 8 1.10 0.018 50.00 Page 1 0.990 0.960 0.900 0.800 0.667 o. 500 0.231 0.091 0.980 Flow Frequency Analysis Time series File:de-1.tsf Project Location:Sea-Tac ---Annual Peak Flow Rates--- Flow Rate Rank Time of Peak (CFS) 0. 620 6 0. 514 8 o. 743 3 o. 566 7 0. 678 4 0. 659 5 0. 823 2 1. 24 ..:;:._.-...1 computed Peaks 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 :;-r -;, a "°Tr I I 2. Z "'c... () ,Q(b C{(_ O, 17ecc de-1 -----Flow Frequency Analysis------- --Peaks --Rank Return Prob (CFS) Period 1. 24 1.: 1 100. 00 0.823 2 25.00 0.743 3 10.00 0.678 4 5.00 0.659 5 3.00 0.620 6 2.00 0. 566 7 1. 30 0.514 8 1.10 1.10 50.00 Page 1 0.990 0.960 0.900 0.800 0.667 0. 500 0.231 0.091 0.980 Retention/Detention Facility Type of Facility: Detention Vault ' Facility ::..ength: 58.67 ft ~ ~ \\AV '::i. (V\.•k/'\A_C,( l tA .. hLl\.S, Facility Width: 104.00 ft Facility Area: 6102. sq. ft -'ID\ s Effective Storage Depth: 6.00 ft tr<o9 t Lt -, Stage 0 Elevation: 489.00 ft Storage Volume: 36610. cu. ft Riser Head: 6. 00 ft Riser Diameter: 12.00 inches Number of orifices: 3 Full Head Pipe Orifice # Height Diameter Discharge Diameter (ft) (in) (CFS) (in) 1 0.00 1. 05 0.073 2 3.50 1. 45 0.090 4.0 3 4.75 1. 40 0.059 4.0 Top Notch Weir: None Outflow Rating Curve: None Stage Elevation Storage Discharge Percolation (ft) (ft) (cu. ft) (ac-ft) (cfs) (cfs) 0.00 4 8 9. 00 0. 0.000 0.000 0.00 0.01 489.01 61. 0.001 0.003 0.00 0.02 489.02 122. 0.003 0.004 0.00 0.03 489.03 183. 0.004 0.005 0.00 0.04 489.04 24 4. 0.006 0.006 0.00 0.05 489.05 305. 0.007 0.007 0.00 0.07 4 8 9. 07 427. 0.010 0.008 0.00 0.08 489.08 488. 0. 011 0.008 0.00 0.09 489.09 54 9. 0.013 0.009 0.00 0.10 489.10 610. 0. 014 0.009 0.00 0.22 489.22 1342. 0.031 0.014 0.00 0.33 489.33 2014. 0.046 0.017 0.00 0.45 489.45 2746. 0.063 0.020 0.00 0.57 489.57 3478. 0.080 0.023 0.00 0.69 489.69 4210. 0.097 0.025 0.00 0.80 489.80 4881. 0 .112 0.027 0.00 0.92 489.92 5614. 0.129 0.029 0.00 1. 04 490.04 6346. 0 .146 0.030 0.00 1.16 490.16 7078. 0.162 0.032 0.00 1. 27 490.27 7749. 0.178 0.034 0.00 1. 39 490.39 8481. 0.195 0.035 0.00 1. 51 490.51 9214. 0.212 0.037 0.00 1. 63 490.63 9946. 0.228 0.038 0.00 1. 75 490. 75 10 67 8. 0.245 0.040 0.00 1. 86 490.86 1134 9. 0.261 0.041 0.00 1. 98 490.98 12081. 0. 277 0.042 0.00 2.10 491.10 12814. 0.294 0.043 0.00 2.22 4 91. 22 1354 6. 0. 311 0.045 0.00 2.33 491.33 14217. 0.326 0.046 0.00 2.45 4 91. 4 5 14 94 9. 0.343 0.047 0.00 2.57 4 91. 5 7 15681. 0.360 0.048 0.00 2.69 491.69 16414. 0.377 0. 04 9 0.00 2.80 491.80 17085. 0. 392 0.050 0.00 2. 92 4 91. 92 17817. 0.409 0.051 0.00 3.04 492.04 18549. 0.426 0.052 C.00 3.16 4 92. 16 19281. 0.443 0.053 0.00 3. 27 4 92. 27 19952. 0.458 0.054 0.00 3.39 4 92. 3 9 20685. 0.475 0.055 0.00 3.50 4 92. 50 21356. 0. 4 90 0.056 0.00 3.52 4 92. 52 21478. 0. 4 93 0.056 0.00 3.53 4 92. 53 21539. 0. 4 94 0.058 0.00 3.55 4 92. 55 21661. 0. 4 97 0.060 0.00 3.56 4 92. 5 6 21722. 0. 4 99 0.063 0.00 3.58 4 92. 58 21844. 0.501 0.067 0.00 3.59 4 92. 5 9 21905. 0.503 0. 072 0.00 3.61 4 92. 61 22027. 0.506 0.075 0.00 3.62 4 92. 62 22088. 0.507 0. 077 0.00 3.64 4 92. 64 22210. 0.510 0.078 0.00 3. 7 5 4 92. 7 5 22881. 0.525 0.087 0.00 3.87 492.87 23614. 0.542 0.094 0.00 3.99 4 92. 99 24346. 0.559 0.100 0.00 4 .11 4 93. 11 25078. 0.576 0.105 0.00 4.22 493.22 25749. 0.591 0 .110 0.00 4. 34 493.34 26481. 0.608 0 .115 0.00 4.46 4 93. 4 6 27213. 0.625 0 .119 0.00 4.58 493.58 27 94 6. 0. 642 0.123 0.00 4.69 4 93. 69 28617. 0. 657 0.127 0.00 4.75 493. 75 28983. 0.665 0 .129 0.00 4.76 4 93. 7 6 29044. 0. 667 0.130 0.00 4.78 4 93. 7 8 29166. 0.670 0.131 0.00 4.79 493. 79 29227. 0. 671 0.134 0.00 4.81 493.81 29349. 0.674 0.137 0.00 4.82 493.82 29410. 0.675 0.141 0.00 4.84 493.84 29532. 0.678 0.146 0.00 4.85 493.85 29593. 0.679 0. 14 9 0.00 4.87 493.87 29715. 0.682 0.151 0.00 4.88 493.88 2 977 6. 0.684 0.152 0.00 5.00 494.00 30508. 0.700 0.163 0.00 5 .12 494.12 31241. 0. 717 0.172 0.00 5.23 494.23 31912. 0.733 0.181 0.00 5.35 494.35 3264 4. 0.749 0.188 0.00 5.47 494.47 33376. 0.766 0.195 0.00 5.59 494.59 34108. 0.783 0.202 0.00 5.70 494.70 34780. 0.798 0.208 0.00 5.82 494.82 35512. 0.815 0.214 0.00 5.94 494.94 36244. 0.832 0.220 0.00 6.00 4 95. 00 36610. 0.840 0.223 0.00 6. 10 495.10 37220. 0.854 0.536 0.00 6.20 495.20 37830. 0.868 1.100 0.00 6.30 495.30 38 4 41. 0.882 1. 8 4 0 0.00 6. 40 495.40 39051. 0. 896 2.630 0.00 6. 50 495.50 39661. 0. 910 2.920 0.00 6.60 495.60 4 0271. 0. 924 3.180 0.00 6.70 495.70 40881. 0.939 3. 420 0.00 6. 80 495.80 41491. 0.953 3.640 0.00 6.90 4 95. 90 42102. 0. 967 3. 850 0.00 7.00 4 96. 00 42712. 0.981 4. 050 0.00 7.10 4 96 .10 43322. 0.995 4.240 0.00 7.20 496.20 43932. 1. 009 4.420 0.00 7.30 496.30 44542. 1. 023 4. 5 90 0.00 7.40 496.40 45152. 1.037 4.760 0.00 7.50 4 96. 50 45763. 1. 051 4.920 0.00 7.60 4 96. 60 46373. 1. 065 5.070 0.00 7.70 496. 70 46983. 1. 079 5.220 0.00 7.80 496.80 47593. 1. 093 5.370 0.00 Hyd Inflow Outflow Peak Storage Stage Elev (Cu-Ft) (Ac-Ft) ---->1 1. 24 0.82 6. 15 495.15 2 0.62 0.22 5.84 494.84 3--";>0 . 6 3 0.18 5.22 4 94. 22 4 0.74 0.14 4.82 493.82 5 0.66 0.12 4.46 493.46 6 ---;Si. 39 . 06 3.51 492.51 7 0.51 0.05 2.98 491.98 8 0.57 0.05 2.41 491.41 Hyd R/D Facility Tributary Reservoir Outflow Inflow Inflow 1 0.82 0.02 ******** 2 0.22 0.01 ******** 3 0.18 0.01 ******** 4 0.14 0.01 ******** 5 0.12 0.01 ******** 6 0.06 0.00 ******** 7 0.05 0.00 ******** 8 0.05 0.00 ******** Route Time Series through Facility Inflow Time Series File:de-1.tsf Outflow Time Series File:rdout POC Time Series File:dsout Inflow/Outflow Analysis Peak Inflow Discharge: 1. 24 CFS Peak Outflow Discharge: 0.823 CFS Peak Reservoir Stage: 6.15 Ft Peak Reservoir Elev: 495.15 Ft 37529. 0.862 35640. 0.818 31870. 2 9411. 27193. 21402. 18162. 14684. POC Outflow Target/ Cale _0.34 0.83 ******* 0.22 ******* 0.19 ******* 0.15 ******* 0.12 ******* 0.06 ******* 0.05 ******* 0.05 at 6:00 on Jan at 10:00 on Jan 0.732 0.675 0.624 0.491 0.417 0.337 9 in 9 in Peak Reservoir Storage: 37 52 9. Cu-Ft 0. 8 62 Ac-Ft Add Time Series:bypass.tsf Year 8 Year 8 Peak Summed Discharge: 0.829 CFS at 10:00 on Jan 9 in Year 8 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) 0.215 2 2/09/01 20:00 0.051 7 12/29/01 10:00 0. 141 4 3/06/03 22:00 -----Flow Frequency Analysis------- --Peaks --Rank Return Prob (CFS) (ft) Period 0.823 6.15 1 100.00 0.215 5.84 2 25.00 0.180 5.22 3 10.00 0.990 o. 960 0.900 0.047 8 3/26/04 7:00 0. 141 4.82 4 5.00 0.800 0.056 6 1/05/05 17:00 0.119 4. 4 6 5 3.00 0.667 0.119 5 1/18/06 23:00 0.056 3.51 6 2.00 0.500 0.180 3 11/24/06 8:00 0.051 2. 98 7 1. 30 0.231 0. 823 1 1/09/08 10:00 0.047 2.41 8 1.10 0. 091 Computed Peaks 0.620 6.11 50.00 0.980 Flow Frequency Analysis Time Series File :_d;,i,mt tsf ~~'-" -t-'iS-j f'""',. Project Location:Sea-Tac ---Annual Peak Flow Rates--------Flow Frequency Analysis------- Flow Rate Rank Time of Peak --Peaks Rank Return Prob C l..i ,K \"'" ,i«-> (CFS) (CFS) Period -z.. / 10 '(ti!- 0.222 2 2/09/01 20:00 0. 829 1 100.00 0.990 0.053 7 12/28/01 17:00 0.222 2 25.00 0. 960 L .es.s. ti,, "-'-\ 0. 14 6 4 3/06/03 22:00 0.186 3 10.00 0.900 ~ O.LCL 0.048 8 8/26/04 6:00 0. 14 6 4 5.00 0.800 0.060 6 1/05/05 16:00 0.125 5 3.00 0. 667 0.125 5 1/18/06 23:00 0.060 6 2.00 0.500 ~ LJ?>> fl-..-.,-., 0. 18 6 3 11/24/06 8:00 0.053 7 1. 30 0.231 0. l2 \ 0. 829 1 1/09/08 10:00 0.048 8 1.10 0.091 Computed Peaks 0.627 50.00 0.980 Flow Duration from Time Series File:rdout.tsf Cutoff Count Frequency CDF Exceedence Probability CFS % % % 0.003 33474 54.589 54.589 45.411 0.454E+OO 0.009 6200 10 .111 64.700 35.300 0.353E+OO 0.015 5238 8.542 73.242 26.758 0.268E+OO 0.021 4 710 7.681 80.923 19.077 0 .191E+OO 0.027 3970 6.474 87.397 12.603 0.126E+OO 0.033 3017 4.920 92.317 7.683 0.768E-01 0.039 1633 2.663 94.980 5.020 0.502E-01 0.045 1229 2.004 96. 985 3.015 0.302E-01 0.051 1004 1. 637 98.622 1.378 0.138E-01 0.057 541 0.882 99.504 0. 496 0.496E-02 0.063 17 0.028 99.532 0. 4 68 0.468E-02 0.069 13 0.021 99.553 0.447 0.447E-02 0.075 12 0.020 99.573 0.427 0.427E-02 0.081 21 0.034 99.607 0.393 0.393E-02 0.087 26 0.042 99.649 0.351 0.351E-02 0. 094 28 0.046 99.695 0.305 0.305E-02 0.100 16 0. 026 99. 721 0. 279 0. 279E-02 0.106 27 0.044 99.765 0.235 0.235E-02 0.112 28 0. 046 99.811 0.189 0.189E-02 0.118 32 0.052 99.863 0.137 0.137E-02 0.124 18 0.029 99.892 0.108 0.108E-02 0.130 16 0.026 99.918 0.082 0.815E-03 0 .136 6 0.010 99.928 0.072 0. 718E-03 0.142 3 0.005 99.933 0.067 0.669E-03 0.148 2 0.003 99.936 0.064 0.636E-03 0.154 4 0.007 99.943 0.057 0.571E-03 0.160 5 0.008 99.951 0.049 0.489E-03 0.166 5 0.008 99.959 0.041 0.408E-03 0.172 3 0.005 99. 964 0.036 0.359E-03 0.178 5 0.008 99. 972 0.028 0.277E-03 0.184 3 0.005 99.977 0.023 0.228E-03 0.190 2 0.003 99.980 0.020 0 .196E-03 0 .196 2 0.003 99.984 0.016 0.163E-03 0.202 2 0.003 99.987 0.013 0.130E-03 0.208 4 0.007 99.993 0.007 0.652E-04 0.214 3 0.005 99.998 0.002 0.163E-04 Flow Duration from Time Series File:dsout.tsf Cutoff Count Frequency CDF Exceedence Probability CFS % % % 0.003 33584 54.768 54.768 45.232 0.452E+OO 0.009 6247 10.188 64.956 35.044 0.350E+OO 0.016 5518 8.999 73.955 26.045 0.260E+OO 0.022 4569 7.451 81.406 18.594 0.186E+OO 0.028 3961 6. 4 60 87.865 12.135 0 .121E+OO 0.034 2868 4. 677 92. 542 7.458 0.746E-01 0. 041 1590 2.593 95. 135 4. 8 65 0.486E-01 0.047 1207 1. 968 97.104 2. 896 0.290E-01 0.053 945 1. 541 98.645 1. 355 0 .136E-01 0.059 522 0.851 99.496 0.504 0.504E-02 0.065 23 0.038 99.534 0.466 0.466E-02 0. 072 13 0.021 99.555 0.445 0.445E-02 0.078 13 0.021 99.576 0.424 0.424E-02 0.084 22 0.036 99.612 0.388 0.388E-02 0.090 26 0.042 99.654 0.346 0.346E-02 0.097 23 0.038 99.692 0.308 0.308E-02 0.103 20 0.033 99. 724 0.276 0. 276E-02 0 .109 23 0.038 99.762 0.238 0.238E-02 0.115 30 0.049 99. 811 0.189 0.189E-02 0.122 30 0.049 99.860 0.140 0. 14 OE-02 0.128 18 0.029 99.889 0.111 0.111E-02 0.134 17 0.028 99. 917 0.083 0.832E-03 0 .140 7 0. 011 99.928 0. 072 0. 718E-03 0.146 3 0.005 99.933 0. 067 0.669E-03 0.153 2 0.003 99.936 0. 064 0.636E-03 0.159 5 0.008 99.945 0.055 0.554E-03 0.165 5 0.008 99.953 0.047 0.473E-03 0. 1 71 4 0.007 99.959 0.041 0.408E-03 0.178 3 0.005 99. 964 0.036 0.359E-03 0.184 4 0.007 99.971 0.029 0.294E-03 0.190 4 0.007 99. 977 0.023 0.228E-03 0.196 2 0.003 99.980 0.020 0 .196E-03 0.203 2 0.003 9 9. 98 4 0.016 0.163E-03 0.209 2 0.003 99.987 0. 013 0 .130E-03 0.215 3 0.005 99.992 0.008 0.815E-04 0. 221 4 0.007 99.998 0.002 0.163E-04 Duration Comparison Anaylsis Base File: ex-1. tsf New File: dsout.tsf Cutoff Units: Discharge in CFS -----Fraction of Time--------------Check of Tolerance------- Cutoff Base New %Change Probability Base New %Change 0.060 0. 72E-02 0.50E-02 -30.5 I 0. 72E-02 0.060 0.057 -4.9 0.073 0.52E-02 0.45E-02 -15.0 I 0.52E-02 0.073 0.059 -19.4 0.086 0.41E-02 0.38E-02 -8.3 I 0.41E-02 0. 086 0.081 -6. 4 0.099 0.30E-02 0.30E-02 -3.2 I 0.30E-02 0.099 0.097 -2.6 0.112 0.22E-02 0.21E-02 -3.7 I 0.22E-02 0 .112 0.111 -1.1 0.126 0.16E-02 0.12E-02 -24.7 0.16E-02 0 .139 O.llE-02 0.75E-03 -34.3 0. llE-02 0.152 O.BBE-03 0.64E-03 -27. 8 O.BBE-03 0.165 0.60E-03 O.OE-03 -21. 6 0.60E-03 0.178 0.39E-03 0.36E-03 -8.3 0.39E-03 0 .191 O.lBE-03 0.23E-03 27. 3 0.18E-03 0.204 0.98E-04 0.16E-03 66. 7 0.98E-04 0.218 0.49E-04 0.65E-04 33.3 0.49E-04 0.231 0.16E-04 O.OOE+OO -100.0 0.16E-04 Maximum positive excursion -0. 014 cfs ( 7. 1%) occurring at 0 .195 cfs on the Base Data:ex-1.tsf and at 0.209 cfs on the New Data:dsout.tsf Maximum negative excursion= 0.016 cfs (-21.6%) occurring at 0.076 cfs on the Base Data:ex-1.tsf and at 0.060 cfs on the New Data:dsout.tsf .,;-v,.. +-C v+ o G1 )I.Ac,._.;.. p,,sJ,~r l)A. o<e. -0---o."'-Yz. > 0.126 0 .119 -5.2 0.139 0.127 -8. 7 0.152 0 .133 -12. 3 0 .165 0.158 -4. 2 0 .178 0.175 -1. 6 0.191 0.201 4. 9 0.204 0. 214 4. 6 0.218 0.220 1. 1 0.231 0.222 -3.7 I 10 . r;; .. !!. • 10·1 " • li iS . 10·~ 1 = !'4u,~d • ~ 0 ~ 0 ~ 0 1l ci ~ 0 0 ~ 0 0 0 0 0 . rd out >·ks in ·~,;,c:,. l ~. ,,cu11t rJ ~ ,•c ,a.'. I r•~ ' ' 5 flu ~!Ion .,41)"" !I lllS 000 00 0 10 -~ 0 • 10 _, • '° 2Q JO 10 ·3 I ..~ .. ' -~ ·-- R 000 0 • M 40 C 50 60 umulative Probability Probability E , x<..:eedence ' --,. lO 10 _, R91:ur1 Period llf, 5 ·o -~ 0 ; • - so 90 ' 10 ., 20 • zt,11J ' 95 , 50 100 • ' 1)'5>0J1 ~ 98 99 "-,-'x rdout our dsou'. dur • t.a,·g~l dur L. .~ Flow Frequency Analysis Time series File:tesc.tsf Project Location:sea-Tac ---Annual Flow Rate (CFS) 1.05 0.738 2 .22 0.844 1. 24 1. 24 1.46 3.15 Peak Flow Rates--- Rank Time of Peak 6 8 2 7 5 4 3 1 8/27/01 18:00 1/05/02 15: 00 12/08/02 17:15 8/23/04 14: 30 11/17 /04 5: 00 10/27/05 10:45 10/25/06 22:45 1/09/08 6: 30 computed Peaks s-r. 1.0 15 IS'•\/\ "fiv,,.12. S:k~~ ..lMt' -2, ,ZO Ci.<._ 'Fu.:s~vtf' b o!Qc..<..._ Cir~ a. c;~ <uo-- CD2. --:: I. oS-c.-A, TESC -----Flow Frequency Analysis------- --Peaks Rank Return Prob (CFS) Period 3.15 1 100.00 2.22 2 25.00 1.46 3 10.00 1. 24 4 5. 00 1.24 5 3.00 1.05 6 2.00 0. 844 7 1. 30 0.738 8 1.10 2.84 50.00 0.990 0.960 0.900 0.800 0.667 0.500~ 0.231 0.091 0.980 /(0'--L;'i)i).I\. ii) -S 5. -Z -Sec.A,"W'-<'-"--\-" ?0~J .. <;,--z'.vtj 2 J.. qyo oocjl.p 2 X I ,:,~ / 0. oco I \o 2l'is"'il >+ ~ TD-le:..\ 'S.,\e_ C(-ecd~J ! \Jsc D,,.\e.._--1-,~., Vuvli-- Vctv I+ l\t.e<>c 'S.. 4,() )(. 1 o<-/-=-~ZlfD ,,.i ..--c, ((_ W h, le \Ja.v\--1--IS I/ r . : ~ O..c.-Ste.( l,_) ,_\ \ ~-C [ac,,rec,(. A-\.0 I \ \_ If.) --€_ u ~, I 1cfd !) a o 2.1~ Page 1 SECTIO~ 5.J DETENTJOJ\ FACILITIES l/24/2005 Riser Overflow The nomograph in Figure 5.3.4.H may be used to detennine the head (in feet) above a riser of given diameter and for a given fiow (usually the 100-year peak fiow for developed conditions). FIGURE 5.3.4.H RISER INFLOW CURVES I 'c § .. "' ~ 8. j 10 u :is ::, ~ a 1.7> 1 . T (measured from crest of nser) 10 Q-1,=9.739 DH312 Q 011flc9=3.782 D 2 H 1r.z Q in cfs, D and H In feet Slope change occurs at weir-orifice transition 2005 Surface Water Design Manual 5-48 s: Cl) > C "' -D.. s: 0 -,a I., ,, >, :::c • • ~r • • '.!l ;!_ • • '!l • := • 0 " • a ~ a N • ~ N co a ;,; Q) C: :.::; 0 z - E "1 "'" a a ~ E .; ii: t, Q) '5' ~ a.. Storm Sewer Inventory Report Page 1 ' Line Alignment Flow Data Physical Data line ID No. Dnstr Line Defl June Known Drng Runoff Inlet Invert Line Invert Line Line N J-loss Inlet/ line length angle type Q area coeff time EIDn slope El Up size type value coeff Rim El No. (ft) (deg) (cfs) (ac) (C) (min) (ft) (%) (It) (In) (n) (K) (ft) 1 End 11.7 -20.4 MH 0.00 0.48 0.70 5.0 487.75 18.76 489.95 15 Cir 0.013 0.50 497.03 1 2 1 96.1 26.5 MH 0.00 0.11 0.70 5.0 489.95 5.00 494.75 15 Cir 0.013 1.00 497.26 1 3 2 33.6 22.6 MH 0.00 0.23 0.70 5.0 495.00 0.63 495.21 12 Cir 0.013 0.79 497.45 1 4 3 48.1 -48.8 MH 0.00 0.03 0.70 5.0 495.21 0.50 495.45 12 Cir 0.013 0.66 497.71 1 5 4 46.7 37.5 MH 0.00 0.24 0.70 5.0 495.45 0.51 495.69 12 Cir 0.013 1.00 498.20 1 6 2 119.9 85.9 MH 0.00 0.19 0.70 5.0 494.75 0.46 495.30 15 Cir 0.013 1.00 498.32 1 7 6 24.4 -89.9 MH 0.00 0.24 0.70 5.0 495.60 0.53 495.73 12 Cir 0.013 1.00 498.23 1 8 2 19.3 -93.0 MH 0.00 0.04 0.70 5.0 495.00 0.52 495.10 12 Cir 0.013 1.00 497.88 1 9 6 73.1 0.6 MH 0.00 0.13 0.70 5.0 495.60 0.51 495.97 12 Cir 0.013 0.76 499.07 1 10 9 43.2 45.6 MH 0.00 0.09 0.70 5.0 495.97 0.51 496.19 12 Cir 0.013 0.54 499.49 1 11 10 33.4 -29.2 MH 0.00 0.30 0.70 5.0 496.19 0.51 496.36 12 Cir 0.013 0.82 499.86 1 12 11 84.1 51.3 MH 0.00 0.37 0.70 5.0 496.36 0.70 496.95 12 Cir 0.013 1.00 500.91 1 13 12 55.0 86.7 MH 0.00 0.30 0.70 5.0 496.95 0.53 497.24 12 Cir 0.013 1.00 501.21 1 14 9 33.7 -24.1 MH 0.00 0.48 0.70 5.0 495.97 0.50 496.14 12 Cir 0.013 1.00 499.31 1 I I Project File: mjf-004.stm Number of lines: 14 Date: 06-21-2010 Hydraflow Storm Sewers 2005 Welman Plat Conveyance Model -100-Year Event Line Toline Linelength Iner.Area TotalArea RunoffCoeff. lncrC x A TotalC x A lnletTime TimeConc Rnfallnt TotalRunoff TotalFlow CapacFull Veloc PipeSize PipeSlope Inv ElevUp Inv ElevDn HGLUp HGLDn Grnd/RlmUp Gmd/RimDn Freeboard CB I] (fl) (ac) (ac) (Cl (mm) (mmJ lmmrJ \CTSJ ll:,l5J \\.151 t•u~, \1111 'IDJ \UJ \OL/ ,.u ... , ,·-, ,--, .. 1 Outfall 11.73 0.48 3.23 0.7 0.34 2.26 5 8.4 2.7 6.14 6.14 27.97 5 15 18.76 489.95 487.75 495.11 495 497.03 495 1.92 1 2 1 96.06 0.11 2.75 0.7 0.08 1.93 5 8.1 2.8 5.34 5.34 14.43 4.35 15 5 494.75 489.95 495.84 495.4 497.26 497.03 1.42 2 3 2 33.58 0.23 0.5 0.7 0.16 0.35 5 6.6 3 1.06 1.06 2.82 1.36 12 0.63 495.21 495 496.16 496.14 497.45 497.26 1.29 3 4 3 48.14 0.03 0.27 0.7 0.02 0.19 5 5.7 3.2 0.61 0.61 2.51 0.87 12 0.5 495.45 495.21 496.2 496.19 497.71 497.45 1.51 4 5 4 46.66 0.24 0.24 0.7 0.17 0.17 5 5 3.4 0.57 0.57 2.55 1.11 12 0.51 495.69 495.45 496.22 496.21 498.2 497.71 1.98 5 6 2 119.86 0.19 2.1 0.7 0.13 1.47 5 7.5 2.9 4.22 4.22 4.37 3.44 15 0.46 495.3 494.75 496.65 496.14 498.32 497.26 1.67 6 7 6 24.4 0.24 0.24 0.7 0.17 0.17 5 5 3.4 0.57 0.57 2.6 0.73 12 0.53 495.73 495.6 497.01 497.01 498.23 498.32 1.22 7 -8 2 19.32 0.04 0.04 0.7 0.03 0.03 5 5 3.4 0.09 0.09 2.56 0.12 12 0.52 495.1 495 496.14 496.14 497.88 497.26 1.74 13 9 6 73.1 0.13 1.67 0.7 0.09 1.17 5 7.2 2.9 3.41 3.41 2.53 4.34 12 0.51 495.97 495.6 497.5 496.83 499.07 498.32 1.57 8 10 9 43.21 0.09 1.06 0.7 0.06 0.74 5 7 3 2.2 2.2 2.54 2.8 12 0.51 496.19 495.97 498.06 497.9 499.49 499.07 1.43 9 11 10 33.42 0.3 0.97 0.7 0.21 0.68 5 6.8 3 2.04 2.04 2.54 2.6 12 0.51 496.36 496.19 498.26 498.15 499.86 499.49 1.6 10 12 11 84.05 0.37 0.67 0.7 0.26 0.47 5 6 3.2 1.48 1.48 2.98 1.89 12 0.7 496.95 496.36 498.54 498.39 500.91 499.86 2.37 11 13 12 55 0.3 0.3 0.7 0.21 0.21 5 5 3.4 0.71 0.71 2.59 0.91 12 0.53 497.24 496.95 498.66 498.63 501.21 500.91 2.55 12 14 9 33.71 0.48 0.48 0.7 0.34 0.34 5 5 3.4 1.14 1.14 2.53 1.45 12 0.5 496.14 495.97 498.02 497.99 499.31 499.07 1.29 14 Q (cfs) C A (sf) d (in) H (ft) Input 000 0.62 0.00 3.75 1.50 Job: Welman By: J3 Output 0.47 0.62 0.08 3.75 1.50 Orifice Q-Flow C -Orifice Coefficient A -Area of Orifice d -Diameter of Orifice H -Head 3 12 /16 inches Date: 12/4/2009 Page 1 Q (cfs) C L (ft) h (ft) p (ft) H (ft) Input 0.30 0.60 12.56 0.00 2.50 3 Job: Job Name By: Designer L Output 0.30 0.60 12.56 0.12~ 2.50 3.00 Hit 'Solve for h' Date: Date Notch Weir I Page 1 Notch Weir Area Velocity I 1.464 sf 0.205 ft/s APPENDIX B ••• SiteDevEllQpment Associates,. LLC Project Location: 18417 1161h Avenue SE Renton, WA Prepared For: Dreamcraft Homes 3502 "B" Street NW Auburn, WA 98001 (253) 859-9697 Prepared by: Site Development Associates, LLC Ken McIntyre, P.E. 10117 Main Street Bothell, WA 98011 Date: June 13, 2007 Project Number: 136-005-05 WELMAN SUBDIVISION Level One Downstream Analysis Project Location: 184171161h Avenue SE Renton, WA Prepared For: Dreamcraft Homes 3502 ·s· Street NW Auburn, WA 98001 (253) 859-9697 Prepared by: Site Development Associates. LLC Ken McIntyre, P.E. 10117 Main Street Bothell, WA98011 Date: June 13, 2007 Project Number: 136-005-05 WELMAN SUBDIVISION Level One Downstream Analysis TABLE OF CONTENTS Project Description 1 Core Requirement No. 1 1 Core Requirement No. 2 1 Core Requirement No. 3 4 Core Requirement No. 4 4 Core Requirement No. 5 4 Core Requirement No. 6 4 Core Requirement No. 7 4 Core Requirement No. 8 4 Special Requirement No. 1 4 Special Requirement No. 2 4 Special Requirement No. 3 5 Special Requirement No. 4 5 Special Requirement No. 5 5 Appendix A -Figures Appendix B -Downstream Analysis Appendix C -Calculations Appendix D -Operations and Maintenance Manual WELMAN SUBDIVISION Level One Downstream Analysis Project Description The purpose of this report is to present-a Level one downstream analysis of Welman Subdivision in accordance with King County requirements. The proposed project will subdivide the site into 25 single-family housing lots. In addition to the roadways, the proposed project will include all utilities and other improvements necessary to accommodate the new lots. Detention will be provided for in a vault on site. Water quality will be done with a wet vault under the proposed detention vault. This report addresses the storm drainage issues associated with the subdivision of the property, and construction of the new homes and access roads. The design standards addressed for this report are contained in King County Code and the King County Surface Water Design Manual. Review of the 8 Core Requirements and 5 Special Requirements of the 1998 King County Surface Water Design Manual SDA has reviewed the Core and Special Requirements in Chapter 1 of the King County Surface Water Design Manual, and addresses each of the requirements as follows: Core Requirement No. 1 -Discharge at Natural Location Currently the site discharges to the northwest and southwest comers of the site. Discharge to the northwest is through a small swale, which drains into the Emerald Glen subdivision, adjacent and to the west. This swale has been identified as a Class 4 Wetland. Discharge from the southwest corner of the site travels via overland flow to the southwest corner of the site. From here stormwater travels via overland flow through an adjacent residential Joi in the Walhaven Plat, before entering the conveyance system located within SE 186"' Street. From here runoff travels west down SE 186"' Street to 114th Avenue SE, where ii turns north and joins with the runoff that exits the site along the northwest corner. Runoff is then routed through a slormwater detention facility built for the Emerald Glen subdivision. This is a multiple natural discharge and a single threshold discharge area. Runoff from the developed site will be collected and conveyed via a light line system to a detention vault located in the northwest corner of the site. The runoff will exit this vault and be conveyed to the northwest property line and discharged into the existing Class 4 Wefland. The proposed project will discharge stormwater from the entire site to the northwest corner of the properly. A drainage adjustment will be requested for this change. Core Requirement No. 2 -Offsite Analysis Task 1: Define and Map Study Area This project is located west of 1161h Avenue SE, in unincorporated King County, Washington. The property address is 18417 116th Avenue SE, Renton. The project consists of one tax parcel; 3223059033. The property is approximately 3.24 acres. The property will be divided into 25 residential lots. All of these lots will gain access from a newly constructed public road that runs through the subdivision, one access on 116h Ave SE. The properties to the north, west, and south are zoned R-8. The property adjacent and to the west, known as Emerald Glen, was platted in 1996, and is fully built out. The properties to the south, along SE 186th Street, have been developed into single-family residential lots. To the north, there are some larger, undeveloped parcels, which are also zoned R-8. The properties to the east of 1161h Ave SE are zoned R-6, and are partially developed, with several homes on large parcels. The analysis of the basin boundary indicates that the project is in the Black River Drainage Basin. See Figure 1 for a vicinity map of the project and Figure 2 in (both in Appendix A) for an existing site survey of the project. Figure 3 in WELMAN SUBDIVISION Level One Downstream Analysis 1 Appendix A shows the proposed site plan for the development. There is an existing houses and associated outbuildings located on several parcels. All of the existing structures are lo be demolished during plat construction. Task 2: Review all Available Information on the Study Area Critical Drainage Area Map • Black River Drainage Basin • Duwamish -Green River Watershed • Duwamish-Green WRIA (9) Flood plain/floodway (FEMA) Maps • There are no mapped floodplains in the immediate area per the available FEMA map. The site is located in Zone X per the Flood Insurance Rate Map (FIRM) map number 53033C0991 F. See Figure 5 in Appendix A for a copy of the FIRM map. Sensitive Areas • Wetlands -Recent site investigations conducted indicate that there is a wetland located on the site. A wetland report, completed in April 2005 by Habitat Technologies, was provided to us by the property owner. The wetland report indicates that a small Category 4 Wetland is present on the site. Altmanri Oliver Associates (AOA) was retained to conduct a field visit, and to review the wetland report and address the wetland classification and provide guidance related to wetland buffers and potential impact and mitigation alternatives. It appears that the wetland could be filled, with mitigation measures on site (creation of additional wetlands), and that the buffer width could be reduced lo 25' with buffer enhancements. From our site visit, there does not appear to be any streams, steep slopes, or wildlife habitat on the site . • Streams and 100 Year Flood Plains -There are no streams or flood plains mapped on site. • Erosion Hazard Areas -There are no mapped erosion hazard areas ori site. • Landslide Hazard Areas -There are no landslide hazard areas mapped in this area. • Seismic Hazard Areas -This site is not within in a mapped seismic hazard area. • Coal Mine Hazard Areas -None mapped in this area. U.S. Department of Agriculture, King County Soils Survey • The soil on the site is Ground Moraine Deposits (Qgt). Figure 4 in Appendix A presents the soil survey for the project area. Flow Control Applications Map • The site is located in a Level 2 area of Flow Control. Waler Quality Applications Map • The site is located in a Basic Water Quality Treatment Area. Landslide Hazard Drainage Area Map • The site is not located in a landslide hazard drainage area. WELMAN SUBDIVISION Level One Downstream Analysis Task 3: Field Inspect the Study Area A representative of Site Development Associates, LLC (SDA) made a site visit to the property on December 15, 2005. The weather conditions were dry, 35 degrees and cloudy. The field investigation covered approximately Y. mile downstream of the site. Task 4: Describe the Drainage System, and its Existing and Predicted Problems Upstream Drainage Analysis: This site is located near the edge of the Black River Drainage Basin. There is no upstream runoff that enters the site. On-Site Drainage Analysis: The property is approximately 3.24 acres in size, and has approximately 400 LF of frontage on 1161h Avenue SE. The site generally slopes to the north and west. The southern half of the site is on a relatively flat, grassy plateau and contains an existing house, a garage, and a carport, which are located in the center of the property. The northern half of the property is also characterized by largely grass areas, and slopes down from the southern plateau toward a small swale, which drains into the subdivision adjacent and to the west. This swale has been identified as a Class 4 Wetland, and is addressed in the following pages of this report. The majority of the site is grassy pasture, with scattered trees of varying size throughout the site. Please see Figures 2 & 3 for aerial views and general topographical information. The property appears to be frequently maintained, and the grass mowed regularly. Downstream Drainage Analysis: The project site and surrounding vicinity was visited on July 14, 2006. The weather conditions were warm and dry, and no precipitation having recently occurred. No surface flow was visible during the site visit. A brief description of the downstream drainage path is included below. See the Appendix B for an off-site Analysis Drainage System Table and map. The majority of the site drains towards the northwest to a swale classified as a Class 4 wetland, located near the western boundary of the site. These wetlands drain offsite to the west (see photo #'s 1 & 2) where they drain into the enclosed drainage system for the Emerald Glen Plat. This system flows southwesterly SE 185th Place, to 114th Ave. SE, which lies approximately 400 feet downstream of the project site. From this point, runoff continues southerly along 114th Ave. SE for a short distance, then turns westerly (see photo #3), beneath an access driveway, before entering a detention facility (see photo #4) approximately 625 feet downstream of the site .. The outfall from this pond could not be located, but from the regional topography, and from a prior drainage investigation, it appears that the pond outfalls to. the west. A 1 O' drainage easement exists along the back of the lots adjacent to SE 186th Street. It is likely that this easement contains a conveyance pipe, however, no pipe could be located. It appears that flow continues westerly from the detention facility to 112'h Ave. SE. Upon reaching 112th Ave. SE, the runoff is intercepted by the public storm drainage system, and is conveyed northerly to a catch basin which lies just north of SE 1841 h Pl. From this catch basin, runoff is conveyed westerly to a second, larger detention facility (see photo #'s 5 & 6), approximately 1,400 feet downstream of the project site. The outfall from this detention pond appears to be at the southwest corner of the pond, and runoff appears to be conveyed to the west from this outfall (see photo #7). The remainder of the downstream flowpath is beyond the Y.-mile distance required for this analysis. WELMAN SUBDIVISION Level One Downstream Analysis Drainage Complaints: Review of the King County Drainage complaints indicates that there are two relevant drainage complaints recorded downstream of the site within the last 10 years. These complaints are included in Appendix B of this report.· Task 5: Addressing Mitigation of Existing and Potential Problems The development of this project is not expected to have an adverse impact to the downstream drainage system. Drainage for the 25 lot subdivision will meet King County requirements for detention and water quality. Portions of the Class 4 wetland will be filled as a result of this project. Mitigation measures will be employed to ensure that the remaining wetland will continue to operate hydraulically in the same manor as before the subdivision. A sensitive area tract for the wetland and buffers is provided. There should be no impact to the downstream system as a direct result of this project. Core Requirement No. 3 -Flow Control The proposed project is located in a Level 2 Flow Control Area. The Level 2 Flow Control requires the developed flow rates discharge to the predeveloped flow rates ranging from 50% of the 2-year peak flow up to the full 50-year peak flow. See Appendix C for preliminary detention calculations. The project currently contains two separate discharge locations, however, the two discharge points converge within Y.- mile of the site, so the project is assumed to be contained within a single basin. The project proposes the re-aligning of an existing intersection, on the east side of 116"' Avenue SE, near the northeast comer of the site. This improvement is being completed in order to align the intersection with the project's proposed intersection. The east side of 116"' Avenue SE lies in a separate basin than the project, and the proposed improvements there will add less than 5,000 square feet of new imprervious surface, so no flow control is proposed there. Core Requirement No. 4 -Conveyance System As part of the final engineering design for this project, it will be required to demonstrate that the storm drainage system can convey the peak flow from 25-year storm event, and that the 100-year storm event does not create or aggravate a "severe flooding problem". Core Requirement No. 5 -Erosion and Sediment Control In order to protect the downstream conditions from sediments, several erosion control Best Management Practices (BMP's) from the King County Surface Water Design Manual will be utilized. During and after grading, and during house construction, the site will be stabilized with appropriate BMP's consisting of silt fencing, mulching and hydroseeding. A temporary construction entrance will be installed for construction related traffic. Filter fabric will be placed over catch basin grates. All yard areas will be landscaped. Additionally, limiting earthwork and utility construction activities to dry weather conditions, minimizing area and duration of soil exposure, construction of temporary storage basins and protective dikes to control storm runoff, and stockpiling and sheathing of strippings, will further reduce the potential for silt-laden runoff. Interim measures to be employed during construction will include the construction of sediment basins, the installation of silt fences along the low side of the areas to be cleared and graded, and mulching and hydroseeding of exposed soils after attainment of final grade. Stockpiles will be covered with polyethylene sheathing. Additional erosion control measures by individual builders are recommended during construction of houses. These should include installation of a silt fence at the roadside, placing a bed of builder's sand between the house and the street, and covering stockpiles. WELMAN SUBDIVISION Level One Downstream Analysis Core Requirement No. 6 -Maintenance and Operations See AppendixD for the Maintenance and Operations Manual for the Welman Subdivision. Core Requirement No. 7 -Financial Guarantees and Liability The Financial Guarantees and Liabilities will be required prior to the project being finalized by King County. Core Requirement No. 8 -Water Quality The project will provide basic water quality prior to discharge to the class 4 wetland on the project site. Water quality will be accomplished in a wet vault under the project detention vault. See Appendix C for preliminary water quality calculations. Special Requirement No. 1 -Other Adopted Area-Specific Requirements The project is located within the Duwamish-Green River Watershed, Water Resource Inventory Area (WRIA) 9. Special Requirement No. 2 -Floodplain/Floodway Delineation This requirement does not apply. Special Requirement No. 3 -Flood Protection Facilities This requirement does not apply. Special Requirement No. 4 -Source Controls This requirement does not apply because the project is located in the basic water quality treatment area. Special Requirement No. 5 -Oil Control This requirement does not apply. WELMAN SUBOIVISION Level One Downstream Analysis APPENDIX A -FIGURES Vicinity Map 1 Existing Site Survey 2 Proposed Site Plan 3 Soils Map 4 Flood Insurance Rate Map 5 Flow Control Applications Map 6 Water Quality Applications Map 7 Landslide Hazard Drainage Areas Map 8 WELMAN SUBDIVISION Level One Downstream Analysis ni.wn 3/5/2000 1!!1111! site Development Assoclates,LLC _1_113;22~.W..,l'e . .,.,..,_~ ~I OC!lcr,c.5~ Pai:t-G&AN.~ ~~ WELMAN PROPERTY N.T.S, 1-----------------l 8oale VICINTY MAP 1 Figure No. I "' I --CS..------,-X __,_.,__ EXISTING SITE CONDITIONS TOTAL BASIN AREA = 2.96 AC. (ASSUME 100% FORESTED) SAM Design NKJ Drawn 3/5/2008 Date 136-005-05 Project No. ••• Site Development Associates, LLC 18322 aothel Way Hf: lolhel, Wastmgfon 'PflDl I WELMAN PROPERTY 1-------------l Soale EXISTING HYDROLOGY 2 Figure No. t ! E9N 1 ~= .. . -.... ~~;;:;, --------------------------------------------\~_-_ 3----:::,--=--~---____ -------..::.:__---------==--=---------- \ \ SAM Design NKJ -. ) ) C\© 0 /0 .-+'6-498,0 -·-F'G-49S.O / ----,...... ----___,,.,. "' "" I ( -- ( -©'"" ,-©~ I f.l1'- 1 --:l=J=lc=-="=="='dfl FG=-502.0 fG•502.0 I r rG\ -....@ __,. re-so~ "' )TRACT F J.U.D.T. I i \ ~/ ~2) @) @ @ F'G=\2.0 FG-502( fC=502r \ ! L ® FG•502.0 502 500 .... "' I I DEVELOPED SITE CONDITIONS TOTAL BASIN AREA = 2.96 AC. TOTAL LOT AREA = 1.90 AC. PERVIOUS LOT AREA = 0.47 AC. IMPERVIOUS LOT AREA = 1.43 AC. (ASSUME 75% IMPERVIOUS PER ZONING CODE) ••• ~\ ( ,..____ @ l ro-502.0 @ FG-502.0 @ e @) FG=502.0 FG:502.0 rn-so2.o (i I I IMPERVIOUS LOT AREA = 1.43 PVMT/WALK AREA= 0.58 TOTAL IMPERVIOUS AREA = 2.01 TOTAL PERVIOUS AREA = 0.95 WELMAN PROPERTY w "' w > < :r t- CD -- AC. AC. AC. AC. Site Development Associates, LlC 18322aothelWO'f NE: lofflel, Wastinglon ?Slll >-----------------< Scale PROPOSED HYDROLOGY 3 Drawn 3/5/2006 bate 138-005-05 Project No. Figure No. r I 0 . i ~ ~ ~ ~ ~ a g ~ ~ 0 m 0 i ~ I ~ 56122D N A Soil Map-King County Area, Washington (Welman Subdivision) 56f240 561°260 561300 561280 ---c:===-------======:::::, Meters 60 0 10 :..:u 40 ';., __ .:;;._,='.;===;:~••;,;;,•-••••~;==========; 300 ~Feet u 50 100 200 tiSDA Natural Resources -Conservation Service Web Soil Survey 2.0 National Cooperative Soil Survey 561320 561340 56f360 6113/2007 Page 1 of3 !Iii Soll Ma1>-Klng County Area, Washington (Welman SubdMsion) MAP LEGEND MAP INFORMATION Area of Interest (AOI) D Area of Interest (AOI) Soll• D Soil Map Units Special Point Features I.,> Blowout 181 Borrow Pit * Clay Spot • Closed Depression ;x: Gravel Pit Gravelly Spot 0 Landfill A. Lava Flow ... Marsh 'Ji' Mine or Quarry ® Miscellaneous Water ® Perennial Water V Rock Outcrop + Saline Spot Sandy Spot SE, Severely Eroded Spot 9 SlnkhoJe 9 Slide or Slip II Sodlc Spot !ii Spoil Area 0 Stony Spot Natural Resources Conservation Service (I) Very Stony Spot t W.t Spot ... Other Special Line Features ~ Gully 1:11 Short Steep Slope z Other PoUUcal Features Munlclpalltles • Cities m Urban Areas Water Featuraa • Oceans -Sb-earns and Canals Transportation m Rails Roads -Interstate Highways -US Routes a State Highways a local Roads z Other Roads Ortginal soil survey map sheets -e prepared at publication scale. Viewing scale and printing scale, however, may vary from the original. Please rely on the bar scale on each map sheet for proper map measurements. Source of Map: Natural Resources Conservation Service Web Soll Survey URL: http://websoilsurvey.nrcs.usda.gov Coordinate System: UTM Zone 10N This product Is generated from the USOA-NRCS certified data as of the version date(s) listed below. Soll Survey Area: Survey Area Data: King County Area, Washington Version 4, Nov 21, 2006 Date(s) aenal images were photographed: 7/10/1990; 7/18/1990 The orthophoto or other base map on whlch the soil lines were compiled and digitized probably differs from the background Imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident. Web Soil Survey 2.0 National Cooperative Soil Survey 6/13/2007 Page 2 of 3 I Soil Map-King County Area, Washington Map Unit Legend AgB AgC j Totals for Area of Interest (AOI) Natural Resources Conservation Service AJderwood gravelly sandy loam, O to 6 percent slopes Alderwood gravelly sandy foam, 6 to 15 percent slopes Web Soll Survey 2.0 National Cooperative SoU Survey 3.1 0.9 4.01 Welman Subdivision 77.6% 22.4% 100.0% I 6/13/2007 Page 3 of3 ( - 122011·15·• 47"26'15" r-----f1$1 .Sn€ SOl(n<~ 32 T23N SOU!liEASr T22N i W8,Wt),!,. Si,/8IJ'.JJjOI\J !S1~v~ ~~· ...... Z'ONE X j _1881ll STilEgf .! -.~ ..JP~AS1 192~0 ! § c' "' i',._ .. - l .&T!IElif ~ i "'- ~; .. .,., "' !l APPROXIMATE SCALE JN FEET 500 0 5(10 ea ea F3 I NATIONAi. ~Q IIISIIRANCE PROGRAM FIRM fl.OIID INSUJIANti RATE MAP JmG COU!lr,'rY, WASHINGTON' ANO lNOORPOBATED ARliWl - -!!I!!. .!!!!!I -... ' ~~r,, MAP ROISEII: MAT 18, 1995 ( 1hl•· ts art·-'• C:o;A' .a(•~ r.l thf~· ..-.r,ced,tood fflap. it w. extnleted'Ul;lfiQF~fT.Oh:U"-, -m• ~p dol9;not_ret1.ct•ng,a o,•m~enls:.'M'lch·ma)' ftM.t..n·m•-•~to:ti.it._·on·t~ utr. blook. ·Far thlr 1at.~~1rtf0rraatjori-•bixit Nattonllf Ffood!IMW'mm•· p.n, -IOC11;1,·1t1i1P.9 ctiecl!:,Ul!J ~-flood·Map St*!9. ,t WNW..tM'C.lwtt.-.vev ltMA M~ + Flow Control Applications Map Benin B""'ndory fthicl,e, line de1fgru:1!•:u o,&a$ w',th pubfohed Basin Plorn) LJrbon Growlh Ar&a Bo,mdory ~ ln-::orporoted Ar~a ~ ft-res/ Pr~clion Zone A,ea @King county ~ent or Nanual Resources ilnd Parks Watm-and Utnd Resourt:es Dhr;,s;ion iiffllB ~ruic fk,w ~ ~ -C:c,fln,,vutt,;m Flow C(llnli'ol At«.$ -Flood PnSblftm Fk,w cat'ttrQI h..u \o'Jl,ot> 1.n~,, Lnl• 0..1 .... M)"t><. l,,k~, m,d llo"""°r l.<>~J A, '"~'°"',.,.,, ...,,l<'n ol .,;,. m<>p it .....,a,,,l,l,o on,.,.. :1<;,-,,,~>>.:;,p:;,;,.,o;~,:;,. .... iyWl<>pltl Nip//,,._,:--"'~-!i'<'\'/g;,l,,:,,:,,,pc:\rl<'l/,MAP_,,,.,.,,.,""" Moforll:~ngW~ s-Lore R•qu_i,ffllfflf Number 3 o;rw DtKhi;,rge Cz-1t..r1._. i c..i,,;.,.- i.?..........,,;,~~- l, ............ ':;,v,:\~ ~.s.,...it,r...icM,.i.-tJ.L-.., 5. 1.,,i,..,.,:. n. ,;:;.-;,,ri--....i.1i... bo'-lM!~~r., 11 + Kin:J Counfy Water Quality Applications ~v1ap 8a!i'1 8our,dory [t+iiclo.e, line designot.i,~ orcos with publllhed Bosin Plon5I Biiiii; Lake M.o.n,;,gement f'fon Bounclory Urban Growth A,(,o Boundmy ~ lncnrporoled Ar~o .. foie:,,1 Pmd'.fdion l,onD Ar~a ® King County Department of N.iti_1ral Rp..so,,rces and Pork\ W;ater and Lllnd Rnour-ces Division -Sensifi,,,., L..,;,ke Treatmer,t Antos• S.,nsilr,t& to~es: B"""-l.o~~(<,,>,/J..dopi.d .v,,,.,"'111111'"'~ Pion ,,,..1,n "'"'• II'~ WO g<><>I,/ Co"<>?~ 101• L<>,~ c,..,.,. lo"' ("...,,,..., Ile.•• H,chJ t .. ,~s.,..,.,..,_,,,h le,~· "><>"'Y"' $f,,,1Ja, ... 1d.~ • Fnhon~.,d B,:u,r_-Wplef Ouolity T reo•m"'M Areas .,11 ~ ,t,,,~,e:,. "r,g\e "1m,ft, .. va-i-,;,,, c<>•,;,-,,;,ot, ,,,..; IN/,-r•ia! .,,~,. ,,. -" o• ,.,...,. •,,co;h, ""' ,..,t,"°"' 1<> Er.'>u,..,_.,,;! ~""' Wu-O""'l-1yT,...,,-., ~~,p~,,,,._.N,. Sn;,,. M"~"'-'' !,.,· """'" ,~'k ,,,,,...;., A~ Jal~<~<~"" ~·•f1<1~ .,I,,,~ .ru<1 ,1 .,...,,,k,oi, ¢~ '"" :;,,,..,.-,,N .' ... <>f' •,.,, (..,~ t·o"'">y ,.....,p"' i,"r.··//~'-· ,,..,,..,:Jc G'"'/(;;,/~,.~,'1.v.,.,.p ""''" """ Noni!,· c-tlt-j, JA...,.L,t.,4 iS"l N<l,C-. ti,-" 1&.i,~•:c,...i, 3,1'11. ~i.«,-43.$2 bo,,,1".-,l.V,1'/, )IO;b t~._.i::.-tt.,ll,2,) G,,jl[.,.,:""1, l! ~-· ildOi>-6 -""'· ~~ ,. ,-...,~-~ ·--~~,,,-... .. -~ ¥clo.,.-.o,-., ,..., ___ .... ..,,....,,.. ... ""'1-~ ...... ,,,,_!n..,j -~~rn t~CreMa f<ou-v .. --3 -M.,j,J .. -,...,19 t-~l ......... 11..,i.,.. ~-!<:> + Landslide Hazard Drainage Areas Map Bes.in. Bovndory (thtck,u lino de-signoto$ oreo~ with publiohed'6as'•n Plon~I UrOOn Gt-owth Area Boundary l!i'ifffi ln~orpol"Otf!d Area mm Unineo,pom,,d A,oo ~ for,ul P1odvetion Zone Area ® King County Department of Natural Resoorces and Parks Water and Land Resources PiviSlon ( }.ill!..D lar.dsfode Hozord On,inol}* T),.'--. .... ,... .. ·~ ---·· .,,.._ .,,, __ , .-...~,... _ .. . ~.,, .................. ,.,..,.._,,,_ .. "-'1,, ... ._..~ .... . -·--,.~ ........ ~~--, .... ..,.,_....,, ............... ....._ . .. ~ ... ,,,.,t,..__ ........... 1;,,....-.., ..... v,-i~~ """"',_· ,.....,_ ,-~ ,.,.....,._, ~""' ,--. "-'o-......,~, -<.:.,,..~.....,._.. •• ; ....................................... ... ............ ......... ~ ........ -......................... ,~ ......• ~.,,..d >~p.,-~ ... ,._, .... ~-·-<.:-.:,o.o,pk ........ .,,,, ... -........,.., .. __._"'..._,, .. ___ , An '".....,ci'•• '"'''"'" ,,1 ,~1, "'"r '• a,.,;k,I~ :r,;,.. ~,,,,..,.,,.,,.Mor"<'· i(.,,1 C»tl"'• ~.....,,,,,. hep /1..,.,.,,,, ,,...1, ,,, ,1--· 'g;,/,_,,,,.,....,,.,v.v.,' ,,...,,,.,,,., APPENDIX B -DOWNSTREAM ANALYSIS Downstream Analysis Basin Map 1 Downstream System Table 2 Downstream Analysis Key Map 3 Downstream Analysis Photographs 4 Drainage Complaints 8 WELMAN SUBDNISION Level One Downstream Analysis : .. : ( ) l \ 1¥1 a u r y '"'-., / ·lstand ) '~--- ' ' " A i'fr . Pug.et :so·und -,-. .. ----- ::-i: --~ ,--'\,__.!' ~- \. / \ I · i \ II \...i_ I',; "''· i, ' Lo~r;;,)/f#J-, - ·J"uget · ) Ii. · Sound-, . ( ', ' ,.,._,. /~ ·,: '·,. -· .\ ', ;; ,f ./· "' f'''."'.' ,. ' ' ' ~ r .. ~,__ . .. --··~ L:· . '!. ( .. ' G'•.i<.."'! ; '· L-r·s·" ··~_.,I_. :"J;..~L ·. , . ..1 _ ] "i ) ~RiVIJf' , ; "·;/ · > f ' •· .• ":,l~J, ... \:, :,~~,~--(:· ', lower Cedar.'\ River · Po, . \ ro.i.-1;.t,1,-. Ra y . ... i. '). ... .. ,., w', l '·' ·,. \.~---. .... ~. IA" • ' ·v , .. , r· ' -·. (\~-~-""--·,,.·+; , .... : I 1 .. .1 \ ri,,m·r'~,1 -· ( :~1':r( ;Ei1\. /{-·, f »ll, ,.,,1., . .!.,.l_J ' ... ~;~· /'.': \' .. <t\ ~\ i }·1: .(! fyENf'( ·1 ·} ~-\:. ' ' -~ . ' ::( \ ., ~ t· "' ' ' ', ·~ Soos Creek. "" .. .,,.-.-\--, ·z\~, . • '\!· ·t,, (·....... _''I'"" ,.;·. '-~-, · ... ,. ;,..._···-··· ··-· .. 11 '\<_ : < I j\ r i fl >, '!-~~-,.. Mill Creek· \ r:· H st ' ' (\_' ti .£=::~...,,A: ' • 1 Re_" __ ton · Mapte ( :" . ' ,._ < ' .! (. ~t. ")~ ., ~··:""-- -~·- ' . AJ_ ,i "'.;j .., ~ Jenk,i{ls ._ Ci'ecR __ .,.. ..,, ~~lnt:. ~M19ie~ Rd ~"' Coving.ton -~ ... _'1:. ~.' Creok Basin: Black River Symbol Drainage Component Type, Name, and Size Type; sheet flow, swale, see map stream, channel, pipe, pond; size: diameter, surface area 1 sheet flow 2 pipe flow 3 Detention Facility 4 Overland Flow 5 pipe flow 6 Detention Facility OFF-SITE ANALYSIS DRAINAGE SYSTEM TABLE Surface Water Design Manual, Core Requirement #2 Subbasin Name: Drainage Component Slope Distance Existing Potential Description from site Problems Problems discilarge constrictions, under capacity, ponding, drainage basin, vegetation, cover % 1/4 mi= 1,320 ft overtopplng, flooding, habitat or organism depth, type of sensitive area, volume destruction, scouring, bank sloughing, sedimentation, incision, other erosion Wetland Area / Swale Varies O' • 80' No apparent None problems Pipe Flow through Emerald Glen Varies 80' -625' No apparent None Subdivision problems Emerald Glen Detention Facility N/A 625' • 700' No apparent None problems Flow between Emerald Glen No apparent (see comment at Varies 700' -1100' Subdivision & 112111 Ave. SE problems right) No apparent Flow beneath 112th Ave Se Varies 1100' -1400' problems None Detention Facility at intersection of N/A 1400' -> No apparent None 112th Ave. SE & Se 184111 Pl. problems Subbasin Number: Observations of field inspector resource reviewer, or reSldent tributary area, likelyhood of problem, overflow pathways, potential l.mpacts. . No pote.ntial impacts assuming proper operation of proposed detention facility None None This reach was on private property anc could not be inspected. No well~ defined flowpalh was observed . . None None . ®King County DOWNSTREAM ANALYSIS KEY MAP iMAP I -:,.., i ),-,!;pl I / ~ I ~ I I ~'~ ~ • : • ~ ' t ~ \J '.'.J ~. j ~ -·-~-== --3_ ) = ':) = =-~~ :1 =\.--!~----~------------4 I I > ~~ -;i-l :; ~ ) I-. s. ~. 0~ 0 Pn. .,,.,,1c.-r S,rlf!. . - I-' ;,/ ... • • ... ~ N' ,, 1111 OotJnly Boundary OontotJm (511] Pubic Land SuM!y Section& Slleets H--._ l.Oben G-Alea u,o Lakes entl large -... ;./ --0 Pa ..... '3ml lnlXifPOll>led ,,,,,. Legend D /'ltO:TECr s:,rE ~ P£rG.vr~ /"'...VP --,a. /"',rt£ ~e.-.;, (A,,-x . RP'N) -+-··-+ ~ERM.VP ...,..,.._..,. ("' .ff',~. ?4TW',) 0-+ ;',.,.;,r::, t4>eAru,,,u !' J?11z.tt~T1e>;J lltfl P,u,,u-4,;c C:,,,..;ou,pr $c~£! / ": ~/ ~Pl"-lj 'he infonnati?" l~cl~ded ~n !his map has been complied by King County staff from a variety of sources and is subject to change without notice. King County makes no representations or warranties, express Or Implied, as to accuracy, completeness, timeliness; or rights to the use of such infonnation. King County shall not be liable for. ;eneral, special, indirect, inc1den.tal, or consequential damages including, but not limited to, lost revenues or lost profits resulting from the use or misuse of the lnfonnation contained on thls map. Any sale of this map or information on this map is prohibited exCE1pt by written pennission of King County. Date: 7-13-2006 Source: King County IMAP -Pro.2_erty lnfonnatlon (http://www.metrokc.gov/GIS/iMAP DOWNSTREAM PHOTOGRAPHS PHOT0#1 (Looking East along West Property Line) PHOT0#2 (Looking South along West Property Line) WELMAN SUBDIVISION Level One Downstream Analysis PHOT0#3 (Looking West from 114 h Ave SE)) PHOT0#4 (Looking southwest at detention pond) WELMAN SUBDIVISION Level One Downstream Analysis PHOTO #5 (Looking North along 112th Ave SE) PHOT0#6 (Looking West at detention pond) WELMAN SUBDIVISION Level One Downstream Analysis PHOTO#? (Looking East along SE 1841h Pl.) WELMAN SUBDIVISION Level One Downstream Analysis Drainage Complaint Number 2002-0314 This drainage complaint applies to the property at 18524 114'" Ave. SE. The complaint appears to be a Type 1 (nuissance) complaint. The property owner claims that an adjacent property is discharging flow to the complaintant property. King County listed the complaint as a private drainage dispute, and issued standard handouts to the property owner. No further action appears to have been taken by the County. The subject property and tributary properties are in the general vicinity of the downstream analysis, however, neither property appear to be directly in the downstream flowpath. Flow from the Welman subdivision is collected and conveyed around the complaintant property, and it does not appear that the Welman development will have any affect on this drainage complaint. WELMAN SUBDIVISION Level One Downstream Analysis KING COUNTY WATER AND LAND RESOURCES DIVISION DRAINAGE INVESTIGATION REPORT -~ ''-RECEIVED BY~ Received from: INVESTIGATION REQUEST Date: (Day) (t/;);5} PHONE J.d-j" ~'J-W ~ TYPe c:. 200 (Eve) ( -----NAME: ~JmaA., 'W,<)VV) ADDRESS: /1)5 £. 4 II tJl'h (l»e__ c)f; City State. __ Zip LOCATION OF PROBLEM, IF DIFFERENT: Platname:~.G~ Othera enoiesinvolved: RDP RESPONSE: Lot No: Block No: uired DISPOSITION: Turned to on -~/-~/'---by__ OR: No further action recommended became,: /ii ) __ Lead agency has beM notified: . ____ _ __ Problem has been corrected. __ No problem has been identified. __ Prior investigation addresses problem: S)tEFILE II _ _)SjPrivate prob!eAJ NDAP will not consider becau_se: · W. ater originates onsite an.A. or;: on j n · ghboring parcel. DATECLOSED: 51,'J 1VZ....By: _::__f!J/ . !°Vt ,#(q)-6 ___ Other (Specify): -- . ---·------··------- Complaint 2002-0314 Irwin Investigated by Andrew McDonald on April 25, 2002 Visited site and met with Deborah Irwin and discussed her property's rear yard drainage problem. Ms. Irwin experiences a wet rear yard during the rainy season and complains that water is flowing from properties to the east onto her property. In particular, she says, water is draining from a paved area serving Lot 11 to the east. Ms. Irwin assumed the driveway, which accesses Lot 11, was a County right-of-way and therefore we were responsible for water coming from the east. I explained to her that it was a private driveway that serves Lot 11 and therefore was a private drainage problem between two property owners. I told her I would look at the design of the drainage system for her development and if there weie'.any lines in or near her rear yard I would be back out to investigate. There are no drainags, lines in or near her rear yard per the as- built for the development of Emerald Glen. At the time of my site visit there was no water in the rear yard. However, there Was saturation of the rear yard. Grass growth·was moderate in its density and half of it was yellow. Per the complainant, water "gushes" out of an area of plantings along her rear property line. I could find no direct source outletting water. From the way the property behind her is graded it is possible that water is sheetflowing across their lots and onto hers . ..... ..... , .. ~ i I\ • \ • • \ \ • • ' • + • • ' • • • • . p.,,.,,n,m:ff,,.. ho"-7 ;:;z,,,., ~"~-4µ $£.>;JP/VIS,..,.., Drainage Complaint 18504 1121h Ave SE No formal drainage complaints are on file at King County for this property. However, during King County's field review for the Welman Subdivision, County staff were apparently approached by the property owner regarding a drainage problem on the property. King County has requested that the property owner be contacted and interviewed regarding their drainage complaint. Site Development Associates contacted Judy Bryant, the property owner, in June of 2007. She indicated that her property was experiencing periodic Type 1 (nuissance) flooding problems. Based on the local hydrologic features, and topographical information available in the area, it is likely that the flooding problem originates east of her property, possibly near the discharge of an upstream detention facility. Ms. Bryant indicated that she had previously lived in the house immediately south of her current residence, and recalls that there is a 10' drainage easement across the back of the lots adjacent to her. This was verified on King County Assesor mapping. This easement most-likely contains a conveyance pipe, which is intended to carry flow from west from the upstream detention facility. A pipe could not be localed during the field-investigation, and it's possible that ii is buried, and not functioning correctly. From my conversation with Ms. Bryant, it appears that flooding has been limited to her yard, and that flooding events are periodic. It was unclear whether a flooding event had taken place within the past year. The property in question lies directly in the downstream flowpath of the proposed Welman development. However, the property is required to meet King County Level-Two flow control standards. This standard is intended to ensure that peak flows and peak flow durations are not exceeded for all flows ranging up to the 50-yr design storm event. With this in mind, the drainage is not likely lo be further aggravated by the proposed development. Location and maintenance of the existing detention pipe in the adjacent lots would be the logical first step in alleviating the problem. WELMAN SUBDIVISION Level One Downstream Analysis ®King County he information included on this map has been compiled by King County staff from a variety of sources and is subject to change without notiae. King C makes no representations or warranties, express or implied, as to accuracy, completeness, timeliness, or rights to the use of such information. King Cc shall not be liable for any general, special, indirect, incidental, or consequential damages including, but not limited to, lost revenues or lost profits result he 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 c APPENDIX C-CALCULATIONS Preliminary Detention Calculations 1 Preliminary Water Quality Calculations 2 WELMAN SUBDIVISION Level One Downstream Analysis PRELIMINARY DETENTION CALCULATIONS WELMAN SUBDIVISION Level One Downstream Analysis Existing Hydrologic Conditions Flow Frequency Analysis Time Series File:predev.tsf Project Location:Sea-Tac ---Annual Peak Flow Rates--- Flow Rate Rank Time of Peak (CFS) 0.187 2 2/09/01 18:00 0.051 7 l/06/02 3:00 0.138 4 2/28/03 3: 00 0.005 B 3/24/04 20:00 0.082 6 1/05/05 8:00 0.143 3 1/18/06 21: 00 0 .121 5 11/24/06 4:00 0.239 l 1/09/08 9:00 Computed Peaks -----Flow Frequency Analysis------- -Peaks Rank Return Prob (CFS) Period 0.239 1 100.00 0.990 0 .187 2 25.0D 0.960 0.143 3 10.00 0,900 0,138 4 5.00 0. BOO 0.121 5 3.00 0.667 0.082 6 2.00 0.500 0.051 7 1.30 0.231 0.005 8 1.10 0.091 0.221 so.co 0.980 I Developed Hydrologic Conditions Flow Frequency Analysis Time Series File:dev.tsf Project Location:Sea-Tac ---Annual Peak Flow Rates--- Flow Rate Rank Time of Peak (CFS) 0. 572 6 2/09/01 2:00 0.473 8 1/05/02 16:00 0.686 3 2/27/03 7:00 0.519 7 8/26/04 2:00 0.622 4 10/28/04 16:00 0.608 5 1/18/06 16 :00 0.754 2 10/26/06 0:00 1.15 1 1/09/08 6:00 Computed Peaks -----Flow Frequency Analysis------- -Peaks Rank Return Prob (CFS) Period 1.15 1 100.00 0.990 0.754 2 25.00 0.960 Q.686 3 10.00 Q.900 0.622 4 s.oo 0.800 0.608 5 3-00 0.667 0. 572 6 2.00 0.500 0.519 7 1.30 0 .231 0.473 8 1.10 0.091 1. 02 SO.DO 0.980 Detention Facility Design Calculations Type of Facility: Facility Length: Facility Width: Facility Area: Effective Storage Depth: Stage O Elevation: Storage Volume: Riser Head: ~iser Diameter: Number of orifices: Detention Vault 220. 00 ft 23.00 ft 5060. sq. ft 8 .so ft 488.50 ft 43010. cu. ft 8. so ft 12. 00 inches 2 Full Head Pipe Orifice # Height Diameter Discharge Diameter (ft) (in) (CFS) (in) 1 0 .oo 0.75 0.044 2 5.25 1.63 0.129 4.0 Top Notch Weir: None outflow Rating Curve: None Stage I Storage I Discharge Performance Stage Elevation Storage Discharge Percolation {ft) {ft) (cu. ft) {ac-ft) (cfs} (cfs) Stage Elevation Storage Discharge Percolation (ft) {ft) {cu. ft) {ac-ft) (cfs) (cfs) 0.00 488.50 0. 0.000 0 .ooo o.oo 0.01 488.51 51. 0.001 0.001 0.00 0.02 488.52 101. 0.002 0.002 0.00 0.03 4BB.53 152. 0.003 0.003 0.00 0.04 488.54 202. 0.005 0.003 0.00 0.05 488.55 253, 0.006 0.004 0.00 0.06 488.56 304, 0.007 0.004 0 .00 0.21 488.71 1063. 0.024 0,007 o.oo 0.35 468.85 1771. 0.041 0.009 0.00 0.49 488.99 2479. 0.057 0.011 0.00 0 .64 489.14 3238. 0 .074 0.012 0.00 0.78 489.28 3947. 0.091 0 .013 0.00 0.93 489-43 4706. O.lQB 0,015 0 .oo 1.07 489.57 5414. 0.124 0. 016 0.00 1.22 489.72 6173. 0.142 0.017 0.00 1.36 489.86 6882. 0.158 0.018 0.00 1.50 490.00 7590. 0 .174 Q.019 0.00 l.65 490.15 8349. 0.192 0.020 0.00 1.79 490.29 9057. 0 .208 0.020 0 .oo 1.94 490.44 9816. 0.225 0. 021 0 .00 2.08 490,58 10525. 0.242 0.022 0 .oo 2.22 490.72 11233. 0.258 0.023 o.oo 2 .37 490.87 11992, 0.275 0.023 0.00 2.51 491. 01 12701. 0 .292 0.024 0.00 2.66 491.16 13460. 0.309 0.02s 0 .oo 2.80 491.30 14168. 0.325 0.026 0 .oo 2. 94 491.44 14876. 0.342 0.026 0.00 3.09 491. 59 15635. 0.359 0.027 0.00 3.23 491. 73 16344, 0 .375 0.027 0.00 3.38 491.88 17103. 0.393 0.028 0 .00 3.52 492.02 1 7811. 0.409 0.029 0 .00 3.66 492.16 18520. 0.425 Q.029 0.00 3.81 492-31 19279. 0.443 0.030 0 .00 3.95 492,45 19987. 0.459 0.030 0.00 4.10 492.60 20746, 0.476 0 .031 0.00 4.24 492.74 21454. 0.493 0. 031 0.00 4 .38 492. 88 22163. 0.509 0.032 0 .OD 4.53 493.03 22922. 0.526 0.032 0.00 Stage (ft) Elevation (ft) Storage (cu. ft) (ac-ft) Discharge (cfs) Percolation {cfs) 4.67 4.82 4.96 5.10 5.25 5.27 5.28 5.30 5.32 5.33 5 .35 5.37 5.39 5.53 5.67 5. 82 5.96 6.11 6 .25 6.39 6.54 6.68 6 .83 6.97 7.11 7.26 7.40 7.55 7.69 7.83 7.98 8.12 8.27 8.41 8.50 493 .. 17 493.32 493.46 493.60 493. 75 493.77 493. 78 493,BO 493. 82 493.83 493.85 493.87 493.89 494.03 494.17 494.32 494.46 494.61 494. 75 494-89 495.04 495.18 495. 33 495.47 495.61 495.76 495.90 496.05 496.19 496. 33 496.48 496.62 496.77 496. 91 497.00 23630 .. 24389. 25098. 25806. 26565, 26666. 26717. 26818. 26919. 26970. 27071. 27172. 27273. 27982. 28690. 29449. 30158. 30917. 31625. 32333. 33092. 33801. 34560, 35268. 35977. 36736. 37444. 38203. 38911. 39620. 40379. 41087. 41846. 42555. 43010. .0.542 .. 0.033. 0.560 0.576 0 .592 0.610 0.612 0.613 0 .616 0.618 0.619 0.621 0.624 0.626 0 .642 0 .659 0.676 0.692 0.710 0. 726 0.742 0.760 0.776 0.793 0.810 0.826 0 .843 0.860 0.877 0.893 0.910 0.927 0.943 0.961 0.977 0.987 0.033 0.034 0.034 0.035 0.036 0.037 0 .040 0.044 0.049 0.055 0.060 0 .062 0.074 0.083 0.091 0.098 0.104 0.110 0.115 0.120 0.125 0.130 0 .134 0.138 0.143 0.147 0.150 0.154 0.158 0.161 0.165 0.168 0.172 0.174 Stage I Storage I Discharge Performance at Significant Stonn Events Inflow Peak Storage 0. 0.0 0. 00 0.00 0.00 0.00 0.00 0.00 o.oo 0.00 0.00 0. 00 0.00 0.00 o.oo 0.00 0.00 0.00 o.oo o.oo 0.00 0.00 0.00 o.oo 0.00 0.00 o.oo 0.00 0.00 0.00 o.oo 0. 00 0.00 0.00 0.00 0.00 Hyd l 2 3 4 5 6 7 B outflow Target Cale 0.33 0.16 0.14 0.13 0.08 0.03 0.04 0.03 Stage 8.55 7. 82 7.21 6.93 5.57 5.17 5.26 3.25 Elev 497.05 496.32 495.71 495.43 494. 07 493. 67 493.76 491. 75 {Cu-Ft) (Ac-Ft) 1.15 0.57 0.69 0 .58 0.61 0.36 0.47 0.52 0.24 43271. 0 .993 ******* ******* ******* ******* ******* ******* ******* KCRTS Routing Instructions Route Time Series through Facility Inflow Time Series File:dev.tsf Outflow Time Series File:RDOut 39547. 36483. 35066. 28174. 26179. 26617. 16447. Inflow/Outflow Analysis Peak Inflow Discharge: Peak Outflow Discharge: 1.15 CFS at 6:00 on Jan 0.334 CFS at 11:00 on Jan Peak Reservoir Stage: Peak Reservoir Blev: Peak Reservoir Storage: B .55 497.05 43271. 0.993 Ft Ft CU-Ft Ac-Ft 0.908 0.838 0.805 0 .647 0.601 0.611 0 .378 9 in Year 8 9 in Year 8 Duration Com~arison Anal~ls Duration Comparison Anayleie Base File: pr~q..ev. tsf New File: rdout.tsf cutoff Units: Discharge in CFS -----Fraction of Time--------------Check of Tolerance------- Cutoff Base New .\Change Probability 0.042 0. 91E-02 0.64E-02 -29.7 I 0.91E-02 0.053 0.62E-02 0.57E-02 -7.7 I 0.62E-02 0.064 0.48E-02 0.50E-02 4.8 I 0.48B-02 0.075 0.36E-02 0.38E-02 3.6 I 0.36E-02 0.087 0.28E-02 0,2BE-02 -1. 7 I 0.2BE-02 0.09B 0.22E-02 0.21E-02 -2.3 I 0.22E-02 0.109 O.lSE-02 0.17E-02 19.1 I O.lSE-02 0.120 0.96E-03 0 .13E-02 33.9 I 0.96B-03 0.132 0.60E-03 0.91E-03 51.4 I 0.608-03 0.143 0.33E-03 0.52E-03 60.0 I 0.33E-03 0.154 0.21E-03 0.26E-03 23.1 I 0.21E-03 0.165 0.16E-03 0.llE-03 -30. 0 I 0.16E-03 0.176 0. 82E-04 O.OOE+OO -100.0 I 0.82B-04 Maximum positive excursion e 0.011 cfs ( 9.lt) occurring at 0.122 cfs on the Base Oata:predev.tsf and at 0.133 cfs on the New Data:rdout.tsf Maximum negative excursion= 0.012 cfs (-24.3%) occurring at 0.048 cfs on the Base Data:predev.tsf and at 0.036 cfs on the New Data:rdout.tsf in IL ~ .. 2' a, Base New \Change 0.042 0.035 -17.1 0 .053 0.043 -18.2 0.064 0.067 4.1 0.075 0.077 1. 9 0.087 0.086 -1.0 0.09B 0.096 -1.6 0.109 0.118 a.o 0.120 0.130 a.s 0 .132 0.141 7.3 0.143 0.149 ••• 0.154 0.159 3.4 0.165 0.162 -2.1 0.176 0.167 -5.2 .. .c u i5 Cl t----------,-----,-----,-,.,--~-'ls---------c-'--'--'------'---'----'-----'--'---' 0 Prob~bility Exceedence PRELIMINARY WATER QUALITY CALCULATIONS WELMAN SUBDIVISION Level One Downstream Analysis WETVAULT DESIGN ProJ11ctJ>larr11,: Pro ect Numf>l!r, DRAINAGE CRITERIA: RAINFALL METHOD: st11p 21 Detarmlnp rainfall R tor mean annual litonn R = r"'~)mf ft See Figure 6.4., .A Step 31 Calculate runoff frorn me.an annual stonn Vr = (0.9Al t 0.25Alg + 0.10 Atl + 0.01 Aog) • R Al= Area of impeNlous· surface Atg = Area of till grass Alf: Area of till forest Aog = Area of outwash grass R= Ralnfalfftom·mean annual81orm Yr= Vol. runoff from lruilan annual storm st,,p 41 balcuhite wetpool.)IO!ume Vb= fVr f = Volume factor Vr = Vol. runoff from mean annual storm Vb = Volume of wetpool Step 51 Detennlne wetpool dimensions a)· Oelennfne geometry of Wetvautt V(!lumil of Wetpool Deplhh .Provided dimensions: width length Provided Volume sf . sf . sf . sf 0.039 ft 3722 cf J 3722 cf 11167 cf 11167 cf ''.. '.>'.,;Aft Fl'(jm Step.2 . From Step 1 From Sti!p 3 3 to 6 feet Vprov'd > Vreq'd APPENDIX D -MAINTENANCE AND OPERATIONS MANUAL WELMAN SUBDIVISION Level One Downstream Analysis Operation & Maintenance Manual NO. 1 • CLOSED DETENTION SYSTEMS (Vaults) Maintenance Defect .Conditions When Maintenance_ is ... Needed Component Storage Area Plugged Air Vents Debris and Sediment Joints Between Tank/Pipe Section Tank Pipe Bent Out of Shape One-half of the cross section of a vent is blocked at any point with debris and sediment Accumulated sediment depth exceeds 10% of the diameter of the storage area for X length of storage vault or any point depth exceeds 15% of diameter. Example: 72-inch storage tank would require cleaning when sediment reaches depth of 7 inches for more than Y;i; length of tank. Any crack allowing material to be transported into facility Any part of tank/pipe is bent out of shape more than 10% of it's design shape Manhole Cover Not in Place Cover Is missing or only partially In place. Any open manhole requires maintenance. Catch Basins Locking Mechanism Not Working Cover Difficult to Remove Ladder Rungs Unsafe WELMAN SUBDIVISION Level One Downstream Analysis Mechanism cannot be opened by one maintenance person with proper tools. Bolts into frame have less than X inch of thread (may not apply to self~locking lids.) One maintenance person cannot remove lid after applying 80lbs of 11ft. Intent ls to keep cover from sealing off access to maintenance. King County Safety Office and/or maintenance person judges that ladder Is unsafe due to missing rungs, misalignment, rust, or cracks. See "Catch Basins" Standards No. 3 Results.Expected When Maintenance Is Performed Vents free of debris and sediment All sediment and debris removed from storage area. All joint between tank /pipe sections are Sealed Tank/ pipe repaired or replaced to design. Manhole is closed. Mechanism opens with proper tools. Cover can be removed and reinstalled by one maintenance person. Ladder meets design standards allows maintenance person safe access. See "Catch Basins" Standards No.3 0.1 NO. 2 • CONTROL STRUCTURE/FLOW RESTRICTOR Maintenance Defect component General Trash and Debris (Includes Sediment) Structural Damage Cfeanout Gate Damaged or Missing Orifice Plate Damaged or Missing Obstructions Overflow Pipe Obstructions Manhole Catch Basin WELMAN SUBDIVISION Level One Downstream Anal)ISis Condition When Maintenance is Needed Distance between debris build-up and bottom of orifice plate is less than 1-112 feet. Structure is not securely attached to manhole wall and outlet pipe structure should support at least 1,000 lbs of up or down pressure. Structure is not in upright position (allow up to 10% from plumb). Connections to outlet pipe are not watertight and show signs of rust. Any holes--other than designed holes-in the structure. Cleanout gate is not watertight or is missing. Gate cannot be moved up and down by one maintenance person. Chain leading to gate is mlssfng or damaged. Gate fs rusted over 50% of its surface area. Control device is not working properly due to missing, out of place, or bent orifice plate. Any trash, debris, sediment, or vegetation blocking the plate. Any trash or debris blocking (or having the potential of blocking) the overflow pipe. Results Expected When Maintenance is Performed All trash and debris removed. Structure securely attached to wall and outlet pipe. Structure in correct position. Connections to outlet pipe are water tight; structure repaired or replaced and works as designed. Structure has no holes other than designed holes. Gate is watertight and works as designed. Gate moves up and down easily and is watertight. Chain Is in place and works as designed. Gate is repaired or replaced to meet design standards. Plate is in place and works as designed. Plate is free of all obstructions and works as designed. Pipe is free of all obstructions and works as designed. See "Closed Detention SystemsQ Standards No. 1 See ~Closed Detention Systems' Standards No. 1 See "Catch Basins" Standards No. 3 See 'Catch Basins" Standards No. 3 D.2 NO. 3 • CATCH BASINS Maintenance COmponettt' · " General Defect Trash & Debris (Includes Sediment) Struch.Jre Damage to Frame and/or Top Slab Cracks in Basin Walls/ Bottom SedimenU Misalignment WELMAN SUBDIVISION Level One Downstream Analysis Conditions When Maintenance Is Needed Trash or debris of more than 1/2 cubic foot which is located Immediately in front of the catch basin opening or is blocking capacity of the basin by more than 10% Trash or debrts (In the basin) that exceeds 113 the depth from the bottom of basin to invert the lowest pipe into or out of the basin. Trash or debris In any Inlet or outlet pipe blocking more than 1/3 of its height. ' Dead animals or vegetation that could generate odors that could cause complaints or dangerous gases (e.g., methane). Deposits of garbage exceeding 1 cubic foot ln volume Comer of frame extends more than 3/4 Inch past curb face into the street (If applicable). Top slab has holes larger than 2 square inches or cracks wider than 1/4 incti (Intent ls to make sure all material Is running into basin)- Frame not sitting flush on top slab, Le., separation of more than 3/4 inch of the frame from the top slab. Cracks wider than 1/2 inch and longer than 3 feet, any evidence of soil particles entering catch-basin through cracks, or maintenance person judges that structure ls unsound. Cracks wider than 1/2 inch and longer than 1 foot at the joint of any inlet/ outlet pipe or any evidence of soil particles entering catch basln through cracks. Basin has settled more than 1 Inch or has rotated more than 2 inches out of alignment. Results Expected When Maintenance·is performed No Trash or debris located immediately in front of catch basin opening. No trash or debris in the catch basin. Inlet and outlet pipes free of trash or debris. No dead animals or vegetation present within the catch basin. No condition present which would attract or support the breeding of insects or rodents. Frame is even with curb. Top slab is free of holes and cracks. Frame is sitting flush on top slab. Basin replaced or repaired to design standards. No cracks more than 1/4 Inch wide at the joint of inle'Voutlet pipe. Basin replaced or repaired to design standards. D.3 I NO. 3 -CATCH BASINS (Continued) Maintenance Defect Conditions When Maintenance is Needed Com])onent Catch Basin Cover Ladder Metal Grates (If Applicable) Fire Hazard Vegetation Pollution Cover Not In Place Locking Mechanism Not Working Cover Difficult to Remove Ladder Rungs Unsafe Trash and Debris Damaged or Missing. Presence of chemicals such as natural gas, oil and gasoline. Vegetation growlng across and blocking more than 10% of the basin opening. Vegetation growing In inleVoutlet pipe joints that is more than six Inches tall and less than six inches apart. Nonflammable chemicals of more than 1/2 cubic foot per three feet of basin length. Cover is missing or only partially In place. Any open catch basin requires maintenance. Mechanism cannot be opened by on maintenance person with proper tools. Bolts into frame have less lhan 112 inch of thread. One maintenance person cannot remove Ud after applying 80 lbs. of lift; Intent is keep cover from sealing off access to maintenance. Ladder is unsafe due to missing rungs. misallgnment, rust, cracks, or sharp edges. Grate with opening wider than 7/8 inch. Trash and debris that is blocking more than 20% of grate surface. Grate missing or broken member{s} of the grate. NO. 4 DEBRIS BARRIERS (e.g., Trash Racks) Maintenance Defect Condition When Maintenance is Needed Components General Metal Trash and Debris Damaged/ Missing Bars. WELMAN SUBDIVISION Level One Downstream Analysis Trash or debris !hat is plugging more than 20% of the openings in the barrier. Bars are bent out of shape more than 3 inches. Bars are missing or entire barrier missing. Bars are loose and rust Is causing 50% deterioration to any part of barrier. Results Expected When Maintenance is perfonned No flammable chemicals present. No vegetation blocking opening to basin. No vegetation or root growth present No pollution present other than surface film. Catch basin cover is closed Mechanism opens with proper tools. Cover can be removed by one maintenance person. Ladder meets design standards and allows maintenance person safe access. Grate opening meets design standards. Grate free of trash and debns. Grate is in place and meets design standards. Results Expected When Maintenance is Performed. Barrier clear to receive capacity flow. Bars In place with no bends more lhan 314 inch. Bars in place according to design. Repair or replace barrier to design standards. D.4 N0 .. 5 -ENERGY DISSIPATERS Maintenance Components External: Rock Pad Dispersion Trench Internal: Manhole/ Chamber Defect Missing or Moved Rock Pipe Plugged with Sediment Not Discharging Water Property Perforations Plugged. Water Flows Out Top of "Distributor" Catch Basin. Receiving Area Over-Saturated Worn or Damaged Post. Baffles, Side of Chamber Other Defects WELMAN SUBDIVISION Level One Downstream Analysis Conditions When Maintenance is Needed Only one layer of rock exists above nafive soil in area five square feet or larger, or any exposure of native soil. Accumulated sediment that exceeds 20% of the design depth. Visual evidence of water discharging at concentrated points along trench (normal condition is a "sheet flow' of water along trench). Intent is to prevent erosion damage. Over 1/2 of perforations in pipe are plugged with debris and sediment. Maintenance person observes water flowing out during any storm less than the design storm or Its causing or appears likely to cause damage. Water in receiving area Is causing or has potential of causing landslide problems. Structure dissipating flow deteriorates to 1/2 or original size or any concentrated worn spot exceeding one square foot which would make structure unsound. See "Catch Basins· Standard No. 2 Results Expected When --Maintenance is Performed. Replace rocks to design standards. Pipe cleaned/ flushed so that it matches design. Trench must be redesigned or rebuilt to standards. Clean or replace perforated pipe. Faclllty must be rebuilt or redesigned to standards. No danger of landslides. Replace structure to design standards. See "Catch Basins" Standard No. 3 D.5 NO. 6 -FENCING Maintenance Components General Wire Fences NO. 7-GATES Maintenance Component General Defect Missing or Broken Parts Erosion Damaged Parts Deteriorated Paint or Protective Coating Openings In Fabric Defect Damaged or Missing Members Openings in Fabric WELMAN SUBDIVISION Level One Downstream Analysis Conditions When Maintenance is Needed Any defect in the fence that permits easy entry to a facility. Erosion more than 4 inches high and 12·18 inches wide permitting an opening under a fence. Post out of plumb more than 6 Inches. Top rails bent more Ulan 6 inches. Any part offence Onctuding post, top rails, and fabric) more than 1 foot out of design alignment. Missing or loose tension wire. Missin~ or loose barbed wire that ls sagging more than 2-1/2 lnches between posts. Extension arm missing, broken, or bent out of shape more than 1 1/2 inches. Part or parts that have a rusting or scaling condition that has affected structural adequacy. Openings In fabric are such that an 8-inch- dlameter ball could fit through. Conditions When Maintenance is Needed Missing gate or locking devices. Broken or missing hinges such that gate cannot be easily opened and closed by a maintenance person. Gate Is out of plumb more than 6 lnches and more Ulan 1 foot out of design alignment. Missing slretcher bar, stretcher bands, and ties. See "Fencing" Standard No. 5 Results Expected When Maintenance is Performed Parts in place to provide adequate security. No opening under the fence that exceeds 4 inches In height. Post plumb to within 1-1/2 Inches. Top rail free of bends greater than 1 inch, Fence is aligned and meets design standards. Tension wfre in place and holding fabric. Barbed wire in place with less than 3/4 inch sag between post. Extension arm ln place with no bends.larger than 3/4 inch. Structurally adequate posts or parts with a unifoITTt protective ooaUng. No openings In fabric. Results Expected When Malntenarice Is Performed Gates and Locking devices In place. Hinges intact and lubed. Gate Is working freely. Gate is aligned and vertical. Stretcher bar, bands and ties in place. See "Fencing" Standard No. 6 D.6 NO. 8 -CONVEYANCE SYSTEMS (Pipes & Ditches) Maintenance Defect Conditions When Maintenance is Needed COfllponeni: Pipes Sediment & Debris Vegetation Damaged Accumulated sediment that exceeds 20% of the diameter of the pipe. Vegetation that reduces free movement of water through pipes. Protectlve coating Is damaged; rust is causing more than 50% deterioration to any part of pipe. Results Expected When M3int&"rlaince is ·performed Pipe cleaned of all sediment and debris. All vegetation removed so water flows freely through pipes. Pipe repaired or replaced. Any dent that decreases the cross section area of Pipe repaired or replaced. Open Ditches Catch Basins Debris Barriers (e.g., Trash Rack) Trash & Debris Sediment Vegetation Rock Lining Out of Place or Missing (If Applicable). NO. 9 -GROUNDS (Landscaping) Maintenance Defect Component General Trees and Shrubs Weeds (Nonpoisonous) Safety Hazard Trash or Utter Damaged WELMAN SUBDIVISION Level One Downstream Analysis pipe by more than 20%. Trash and debris exceeds 1 cubic foot per 1.000 square feet of ditch and slopes. Accumulated sed'1ment that exceeds 20 % of the design depth. Vegetation that reduces free movement of water through ditches. Maintenance person can see native soil beneath the rock lining. See ~catch Basfns: Standard No. 2 See "Debrts Barners" Standard No.3 Conditions When Maintenance Is Needed Weeds growing in more than 20% of the landscaped area {trees and shrubs only). Any presence of poison Ivy or other poisonous vegetation. Paper, cans, bottles, totaling more than 1 cubic foot within a landscaped area {trees and shrubs only) of 1,000 square feet. Limbs or parts of trees or shrubs that are split or broken which affect more than 25% of the total foliage of the tree or shrub. Trees or shrubs that have been blown down or knacked over. Trees or shrubs which are not adequately supported or are leaning over, causing exposure of the roots. Trash and debris cleared from ditches. Ditch deaned/ flushed of all sediment and debris so that it matches design, Water flows freely through ditches. Replace rocks to design standards. See "Catch Basins" Standard No.3 See "Debris Barriers" Standard No. 4 Results Expected When Maintenance is Perlormed Weeds present in less than 5% of the landscaped area. No poisonous vegetation present in landscaped area. Area clear of litter. Trees and shrubs with Jess than 5% of total foliage with split or broken limbs. Tree or shrub in place free of injury. Tree or shrub in place and adequately supported; remove any dead or diseased trees. D.7 N0.10 -ACCESS ROADS/ EASEMENTS Maintenance Componant General Road Surface Shoulders and Ditches Defect Trash and Debris Blocked Roadway Settlement, Potholes, Mush Spots, Ruts Vegetation in Road Surface Modular Grid Pavement Erosion Damage Weeds and Bnish WELMAN SUBDIVISION Level One Downstream Analysis Condition When Maintenance is Needed Trash and debris exceeds 1 cubic foot per 1,000 square feet i.e., trash and debris would fill up one standards size garbage can. Debris which could damage vehlcle tires (glass or metal). Any obstruction whidl reduces clearance above road surface to Jess than 14 feet. Any obstruction restricting the access to a 10 to 12 foot width for a distance of more than 12 feet or any point resbicting access to less than a 1 O foot width. When any surface defect exceeds 6 inches in depth and 6 square feet In area. In general, any surface defect which hinders or prevents maintenance access. Weeds growing In the road surface that are more than 6 inches tall and less than 6 inches tall and less than 6 inches apart within a 400- square foot area. Build-up of sediment mildly contaminated with petroleum hydrocarbons. Erosion within 1 foot of the roadway more than 8 inches wide and 6 inches deep. Weeds and brush exceed 18 inches in height or hinder maintenance access. Results Expected When Maintenance· ls Performed Roadway free of debris which could damage tires. Roadway free of debris which could damage tires. Roadway overhead clear to 14 feet high. Obstruction removed to allow at least a 12 foot access. Road surface unlformly smooth with no evidence of settlement, potholes, mush spots. or ruts. Road surface free of weeds taller than 2 Inches. Removal of sediment and disposal in keeping with Health Department recommendations for mildly contaminated solls or catch basin sediments. Shoulder free of erosion and matching the surrounding road. Weeds and brush cut to 2 inches In height or cleared in such a way as to allow maintenance access. D.8 ~ King County · Department of Development and Environmental Services 900 Oakesdale Avenue Southwest Renton, WA 98057-5212 206-29.6-6600 TIY .206-296-7217 www. kloaeountv goy - January 24, 2008 MJF Holdings 3502 "B" Street NW Auburn, WA 98001 Attn: Michael Feuerborn · Site Development Associates, LLC 1 0117 Main Street Bothell; WA 98011 Attn: Ken McIntyre, P.E. RE: Welman Subdivision 2005 KCSWDM Adjustment Request (File No. L07V0085) Dear Applicant and Engineer: The Department of Development and Environmental Services (ODES), Land Use Services Division (LUSD), Site Engineering Review Section, has completed review of the adjustment request for the Welman Subdivision. You are requesting approval for an adjustment from the 2005 King County Surface Water Design Manual (SWDM) Section 1.2.1, Discharge at the Natural Location. Our review of the infonnation provides the following findings: I. The proposed Welman subdivision is located at 18417 116th Avenue SE in Renton. The 25 lot, 3.24 acre, proposed subdivision is filed under Land Use Services Division(LUSD) file number L06P0009. 2 .. The Welman subdivision isJocated in the Black River Drainage Basin. The site is . subject to the Conservation flow control and Basic water quality requirements of the 2005 KCSWDM. 3. Currently the site discharges to the northwest, southwest, and south. • Discharge from the north portion of the site travels via overland flow to the northwest through a small swale, which drains into the Emerald Glen subdivision, adjacent and to the west. This swale has· been identified as a Class 4 Wetland. · • Discharge from the southwest portion of the site travels via overland flow to the southwest corner of the site. Runoff then travels west down SE 186th Street to 114th Ave SE, where it turns north and joins with the runoff that exits the site along the · northwest comer. • Discharge from the southeast portion of the site travels via overland flow to the south. Runoff then travels west down SE 186th Street to I l 4th Ave SE, wl:iere it turns north and joins with the runoff that exits the site along the northwest corner. L07V0085 January 24, 2008 Page2 • All runoff from the site is routed through an infiltration facility built for the Emerald Glen subdivision. The point where the three downstream flow paths combine is less than 400 feet downstream of the site. There is no upstreanJ runoff that enters the site. 4. The proposal is to collect most runoff from the project site and direct it to a single detention and water quality facility.located at the northwest comer of the property. The allowed release would then be discharged to the existing Class 4 Wetland. The diversion would eliminate flows to the southwest and south of the project. 5. No decorative ponds or shallow wells have been identified that would be affected by the proposed diversion. 6. The Level One Downstream Analysis identified the following drainage complaints: • A drainage complaint at 18504 ! 12th Ave SE (Parcel# 3223059287) was made on January 2, 1997 dwing construction of the Emerald Glen Infiltration Pond (EGIP). The EGIP was confirmed to experience an overflow event while under construction. The EGIP final corrected plans show a plan revision to the pond. which called for the replacement of the sand-filter media at the bottom of the pond and drilling ofsevei-al bore-holes, and backfill of the holes with drain tock. There have been no further drainage complaints regarding this specific facility since the date of the plan revision .. • Five drainage complaints dating from December 20, 1994 to January 30, 1997 describe the Ruddell Detention Pond (Facility #D90914) overflowing or backing- up, inundating the adjacent roads and lots. King County performed a capital improvement project on this facility, and the nearby tributary pipe system several years ago. . There have been no drainage complaints in this vicinity logged since January 30, 1997. Additionally, the site was visited on Deceinber 3, 2007. On this day, the Puget Sound area experienced a significant storm event which caused localized flooding within the region and approached a I 00-year design storm event in most local event -'based hydrologic models. The site was visited just a few hours after the peak intensity of this storm had passed, and there was no standing water observed in the EGIS or in the surrounding vicinity and the Riddell pond appeared to be at a normal operating level. 7. A consolidation of facilities for the proposed subdivision will be rnore economical in long term maintenance. Based on these findings, we hereby approve this adjustment to allow the diversion of runoff to on-site facility (draining to SE 312th Street) with the following conditions: 1. The release rates for the detention facility will be based on the land naturally draining from the site in all directions. L07V0085 January 24, 2008 Page 3 2._. The volume fo~ the detention facility will be based -0n-a!Hlows directed to the facility at · full development under currerrt zoning. The allowed release rate will be reduced by any undetained flows that would bypass the proposed subdivision.drainage facilities. The detention volume shall be sized using the Conservation flow control standard in the 2005 KCSWDM. The design Technical Information Report shall state the factor of safety selected and the basis of that determination. · 3. Water quality facilities must be sized based on the entire proposed subdivision draining to the facilities including any required frontage improvements. 4. The onsite drainage facilities must be located in a public right-of-way, recreation space tract with easement or storm drainage tract dedicated to King County. 5. Conveyance (from the RID facility) in a closed pipe system must be in accordance with Core Requirement #4. 6. Additional storm drainage requirements identified by SEPA or the plat hearing ·review will apply to this project. The applicant retains all rights and privileges afforded in Section I .4. ' · · · If you have any further questions regarding the SWDM variance or the design requirements, please contact Claire Jonson at (206) 296-6641. · Sincerely, Jim Sanders, P.E., Supervising Development Engineer Land Use Services Division .IA&l<f~~ Mark Bergam, P.E. Site Engineering and Planning Supervisor Building Services Division cc: Curt Crawford, P .E., Supervising Engineer, Local Drainage Services, KCDNR Bruce Whittaker, Engineer III, Engineering Review Section, LUSD Trishah Bull, Project/Program Manager III, Current PI~g Section, LUSD Claire Jonson, P.E., Engineer III, Engineering Review Section, LUSD ® ls lLa J \VJ~ IQ) AUG 2 7 2007 l!dJ K.C. D.D.E.S. King County Department of Development and Environmental Services 900 Oakesdale Avenue Southwest -, Renton, Washington 98055-1219 206-296-6600 TIY 206-296-7217 For alternate formats, call 206-296-6600. Project Name: ODES Project FHe No: L06P0009 Loi V oovs ODES Engineer/Pia nner Name: Tri shah Bull Welman Subdivision Project Address: Design Engineer. Phone: 18417 116th Avenue SB; Renton, WA Ken McIntyre, P.B. (425) 486-6533 Applicant/Agent*"': Phone: sjz:re oA::W· (t/.;,07 Michael Feuerborn (253) 859-9697 Signature of Applicant/Agent Date: Engineering Firm Name: Site Development ·Associates, LLC Address: City, State, ZIP: Address: City, State, ZIP: 3502 •s• Street NW Auburn, WA 98001 10117 Main Street Bothell, WA 98011 INSTRUCTIONS TO APPLICANT/DESIGN ENGINEER: Please be sure to include all materials (Level One Downstream Analysis, Certification of Applicant Status, sketches, photos, and maps) that may assist in complete review and conslderafio/J of this adjustment request. FaHure lo provide all perfinenl information may result in delayed processing or denial of request. Please submit two complete copies of thjs request application form, and appr.cable fee lo th& Department of Development and Environmental Services, 900 Oakesdale Ave. SW, Renton, WA 98055-1219. For more information, contact Mark Bergam, P.E., al 206-296-7270. -Applicant/Agent Is the lndlVtdual financially responsible for all fees ~ 11li,_, .. _ .. , .. ·•"·•'•. .e' ., < , , ' ,• 'I' . ' '/ I v ' . I' ·--·-,=r.-j/ ,, ~, •cfrt~Jj~ J ,,, .• Jj'' r,f,, 'I-,,,],' I ,j I\'-,, ) ,,, • 1 t ,, )f ,.-' f 1 1'' • ,'' ',\' \ ., ) !1 '•r<~ ••li'>{ ~c,0 :,~J~.:-~1,-~>1•s J,•1. '.,"' I 1 '•• ,'<•' • ,IIJ', • I~'' _'lt;..'.!.<!i;:.P',.i, DESCRIPTION OF ADJUSTMENT REQUEST: (ly Stsndard O Complex O Expertmental O Blanket O Pre-application APPLICABLE VERSION KCSWDM: D 1990 (11195)* D 1998 (9198! 00 2005 c1105J *(Nole: the term 'variance· replaced by "adjustmenr) APPLICABLE SECTION(S) OF STANDARDS: Core Requirement #1 JUSTJFICA TJON PER KCSWDM SECTION 1.4.2: 0 See attachments fisted below. Both existing downstream flow paths combine within 1/4 mile from the site, so the project lies within a single threshold discharge basin. see attached juStification. AUTHORIZATION SIGNATURES: DETERMINATION: 0 Approval onditional Approval (sae below) D Denial 0 DNRP/WLRD Approval Signed: , ----=,...-,-----Date: ---------(Experiments! & Blanke! only) ODES Staff Recommendation Signed: Date: /~ 24--aJ/ Conditions of Approval: ODES,BS glneertng & Planning Supervisor Dale:. Signed: . Date: / pf tJj' Check out the ODES Web site at www.metrokc.gov/ddes ·suii\Natert)esManReqStdsAdJReqFORM.doc le-lnfo.surwa-adj.pdf 11/16/2005 Page 1 of1 I EXISTING SITE CONDITIONS TOTAL BASIN AREA = (ASSUME 100% FORESTED) 2.96 AC. Drawn S/6/2008 0•1• 138-006-05 Project No, 1111111 Site Development Associates, LLC 11322 lolhlil War te lodMII ~. 9901 T Ol'llc:e:.tt5.4&.6531 f'IIC: Cl5AIU5'3 WWW~~ WELMAN PROPERTY . j . f I I /" I I 1---------------l Scale I r ~---; . I h .. ··· A'. I I ·. 1 1 . I I I . i i ! ' : I I [ I f ! 2 EXISTING .HYDROLOGY Figure No, z <( ::E ...J w ~· a a N g a l .; -2? "' 0 u ~ ~ ;; ~ ~ ~ I is • • ... 'I; • ' I n 0 ' n 0 t ~ 0 , J ' " I. \ SAM beatgn / / ( "1TRACT F ' J.U.D.T. ! , ® ,/@ FU•502f' fG .. 502!Ji,r, ' J l....' ,00 ,., '-· @ ® F"G•.502.0 FG•S02.0 </ -, ' '~ '-, ) DEVELOPED SITE CONDITIONS T.OTAL BASIN AREA = TOTAL LOT AREA= PERVIOUS LOT AREA = . IMPERVIOUS LOT AREA = 2.96 AC. 1.90 AC: 0.47 AC. 1.43 AC. (ASSUME 75% IMPERVIOUS PER ZONING CODE) ~ ' I , i J I ' r---~ I f J 11 r . I I I ' I "; 0 -502.0 ) \ I ro~o \ . I I * f :r l ' -- \ " ' ---.:::i. ! TRACT E J.U.0.T, ® rG•.502.D ( @) ~ l ;: I ' I I/;:~-:; l•, <"J I J ''·,, _J r·- 1 I i I I : : I I ! I J I l I @ ® F"C•50Z.0 F(; .. 502.0 rc ... scn.o t I I I ! IMPERVIOUS LOT AREA = PVMT/WALK AREA.= TOTAL IMPERVIOUS AREA = TOTAL PERVIOUS AREA = WELMAN PROPERTY 1.43 AC. 0.58 AC. 2.01 AC. 0.95 AC. I ! ~KJ rawn 3/5/2008 Date 138-005•05 PtoJeot No. ••• Site Development Associates. LLC l!:m'°"'91WoyN!;lollal,W~ V!Dll -·-·--·- Oflk:9: ~2.S.4&6.6S» F'IJIC 425,.W.&5'3 www.Jdo~.(;Cm i------------------1 Soale PROPOSED HYDROLOGY Figure No. 3