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RS_Geotech Report_Sandhu Short Plat_200921_v1.pdf
GEOTECHNICAL ENGINEERING REPORT AND INFILTRATION FEASIBILITY EVALUATION PROPOSED SHORT PLAT 13952 SOUTHEAST 159TH PLACE RENTON, WASHINGTON KING COUNTY TAX PARCEL # 2223059022 PREPARED FOR: MR. KULWANT SANDHU BY: OTTO ROSENAU & ASSOCIATES, INC. ORA JOB NO. 19-0616, REPORT NO. 1 OTTO ROSENAU & ASSOCIATES, INC. Geotechnical Engineering, Construction Inspection & Materials Testing TABLE OF CONTENTS 1. INTRODUCTION ..................................................................................................................... 1 2. PROJECT DESCRIPTION ....................................................................................................... 1 3. SCOPE OF SERVICES ........................................................................................................... 2 4. SURFACE CONDITIONS ........................................................................................................ 2 5. SITE CHARACTERIZATION ................................................................................................... 3 6. SUBSURFACE CONDITIONS ................................................................................................. 3 7. INFILTRATION TESTING ........................................................................................................ 4 8. LABORATORY TESTING ........................................................................................................ 6 9. DISCUSSION ........................................................................................................................... 6 10. CONCLUSIONS AND RECOMMENDATIONS ...................................................................... 6 10.1 General .......................................................................................................................... 6 10.2 Seismic Considerations .................................................................................................. 7 10.3 Conventional Foundation System .................................................................................. 8 10.4 Concrete Slabs-On-Grade ............................................................................................. 9 10.5 Below-Grade Walls and Retaining Walls ....................................................................... 9 10.6 Earthwork ..................................................................................................................... 10 10.6.1 Foundation and Slab Subgrade Preparation ....................................................... 10 10.6.2 Structural Fill – Material, Placement and Compaction ........................................ 10 10.6.3 Temporary Excavations ...................................................................................... 11 10.6.4 Erosion and Sedimentation Control .................................................................... 12 10.7 Drainage....................................................................................................................... 12 10.7.1 Dewatering .......................................................................................................... 12 10.7.2 Below-Grade Wall Drainage ................................................................................ 12 11. REPORT LIMITATIONS ...................................................................................................... 13 12. REFERENCE ....................................................................................................................... 13 APPENDIX Vicinity Map .............................................................................................................................. A-1 Site Plan ................................................................................................................................... A-2 Geologic Map ........................................................................................................................... A-3 NRCS Web Soil Survey ........................................................................................................... A-4 Test Pit Log Notes ................................................................................................................... A-5 Unified Soil Classification System ............................................................................................ A-7 Test Pit Logs ............................................................................................................................ A-8 Photo of Simple Infiltration Test (TP-1) .................................................................................. A-11 Photo of Simple Infiltration Test (TP-3) .................................................................................. A-12 Particle Size Distribution Results ........................................................................................... A-13 USDA Soil Classification ........................................................................................................ A-14 Cation Exchange Capacity (CEC) and Organic Content Determinations (by AMTEST Laboratories) .......................................................................................................................... A-15 2016 KCSWDM Figure C.2.4.A Typical Splash Block For Basic Dispersion .......................... A-16 2016 KCSWDM Figure C.2.4.B Typical Gravel-Filled Trench For Basic Dispersion .............. A-17 GEOTECHNICAL ENGINEERING REPORT AND INFILTRATION FEASIBILITY EVALAUTION PROPOSED SHORT PLAT 13952 SOUTHEAST 159TH PLACE RENTON, WASHINGTON KING COUNTY PARCEL # 2223059022 PREPARED FOR MR. KULWANT SANDHU BY OTTO ROSENAU & ASSOCIATES, INC. NOVEMBER 25, 2019 1. INTRODUCTION This report presents the results of our geotechnical engineering services for the proposed short plat development to be located at 13592 Southeast 159th Place in Renton, Washington (King County Parcel #2223059022), which we understand and will create two new lots from the existing single lot. Infiltration tests were performed at a total of two locations on the existing 0.65-acre parcel to evaluate the feasibility of onsite infiltration of stormwater runoff. We understand that one of the proposed infiltration facilities will be used to provide infiltration of roof runoff water from the roof of the proposed single-family residence that would be located on the western portion of the property. The other infiltration facility will consist of a permeable asphalt or concrete pavement driveway located on the western portion of the site. See the figure entitled “Vicinity Map” located on page A-1 of the appendix. 2. PROJECT DESCRIPTION We understand that the existing parcel (K.C. # 2223059022) will be short platted to create two new lots for single-family residences. The existing single-family residence will be located on the eastern lot of the future short plat, and a new single-family residence will be built on the new western lot. The Site Plan on page A-2 of the appendix shows the layout of the proposed short plat with the new eastern 15,727 square foot lot to be designated as Lot C and include the existing single-family residence. The new, western Lot D will be 12,632 square feet in area, and will be the location of the new single-family residence. Otto Rosenau & Associates, Incorporated Geotechnical Engineering, Construction Inspection & Materials Testing 13952 Southeast 159th Place Short Plat ORA Project No.: 19-0616 November 25, 2019 Page 2 of 12 3. SCOPE OF SERVICES The scope of services included a reconnaissance of the site by a geotechnical engineer, a review of geologic literature, and the witnessing of the completion of three (3) exploratory test pits at the approximate locations shown on the Site Plan on page A-2 of the appendix. The geotechnical engineering services were performed by Otto Rosenau and Associates, Inc. (ORA) to provide the following information: A summary of the observed soil and groundwater conditions, An evaluation of the existing site conditions, A review of available geologic information, Infiltration testing and the capability of the onsite soils to support infiltration on site for surface water drainage Seismic design considerations including liquefaction potential of the underlying soils, Suitable foundation systems with estimated settlements, Allowable bearing capacity for conventional foundation systems, Lateral earth pressures and friction coefficients, Consideration of the effect of the proposed development on the regulated slopes, Influence of groundwater on the proposed construction, and Limited site preparation and earthwork. 4. SURFACE CONDITIONS The site consists of a rectangular-shaped parcel with an area of approximately 28,360 square feet (0.65 acres). The site is bounded by Southeast 159th Place to the south and single-family residences to the west, north and east. An existing, two-story single-family residence with a basement that daylights to the north is present at the eastern portion of the site. The existing residence has an attached three-car garage located at the southeast side of the existing residence. An accessory building or detached garage is located at the middle of the west side of the site. A paved loop driveway is present at the central portion of the site to provide vehicular access to the attached 3-car garage and the detached garage with access at two locations along SE 159th Place. The driveway is paved with asphalt concrete closest to the SE 159th Place and portland concrete cement between the two garages. Concrete stairs are located west of the existing residence. See figure titled “Site Plan” on page A-2 of the appendix showing configuration and the locations of the existing structures on the site. The topography of the site slopes downward from the southwest corner of the site with an approximate elevation of 445 feet (NAVD 88) to an approximate elevation of 430 feet (NAVD 88), located along the north side of the site. The northwest portion of the site is heavily covered with ivy and blackberry bushes. Otto Rosenau & Associates, Incorporated Geotechnical Engineering, Construction Inspection & Materials Testing 13952 Southeast 159th Place Short Plat ORA Project No.: 19-0616 November 25, 2019 Page 3 of 12 5. SITE CHARACTERIZATION We reviewed the geological map on Washington State Department of Natural Resources (DNR), Division of Geology and Earth Resources, Washington State Geologic Information Portal’s website (fortress.wa.gov/dnr/geology). The soils at or near the site are mapped as “Pleistocene age, glacial till deposits” (Qgt). Glacial till (Qgt) deposits generally consist of a glacially-transported and deposited mix of silts, sands, and gravels. These soils have been glacially overridden and typically have a dense to very dense consistency and are typically have very low permeability rates. The mapped soils are shown on the attached figure titled “Geologic Map” on page A-3 of the appendix. We also reviewed the Natural Resources Conservation Service’s (NRCS) “SoilWeb” online mapping (https://websoilsurvey.sc.egov.usda.gov/App/WebSoilSurvey.aspx), which described the soils across the site as Alderwood gravelly sandy loam, 0 to 8 percent slopes (AgB). Please see the attached figure titled “NRCS Web Soil Survey”, which shows the project site on page A-4 of the appendix. Alderwood gravelly sandy loam deposits are described as having originated from glacial drift and/or glacial outwash over dense glaciomarine deposits. Also, we reviewed King County IMAP online GIS website (http://gismaps.kingcounty.gov/iMap), the site is located within a wellhead protection area for areas that would take five and ten year groundwater travel time to a wellhead in the vicinity of the site. No steep slope hazard or landslide hazard areas or slopes that are greater than 40% are mapped on adjacent on the property or on adjacent properties. A mapped mapped erosion hazard area that is approximately 110 square feet in area is present at the northeast corner of the site, on what will be Lot C. No mapped geologic hazard areas are present on the future Lot D. Mapped erosion hazard areas are present on the adjacent parcels located immediately north of the site. 6. SUBSURFACE CONDITIONS Three (3) test pit excavations (TP-1 through TP-3) were completed on July 30, 2019 using a rubber- tracked mini-excavator and hand tools to depths ranging from approximately 1½ to 6 feet below the existing site grades at the approximate locations shown on the Site Plan. Similar soil conditions were encountered at each of the test pit locations with approximately 1 to 1½ feet of topsoil overlying weathered glacial till and glacial till deposits. Weathered glacial till deposits were encountered underlying the topsoil in the test pits designated as TP-1 and TP-2 at approximate depths of 1 to 1½ feet below existing ground surface to a depth of 5 feet below existing ground surface in the test pit designated as TP-2. Glacial till deposits were encountered underlying weathered glacial till deposits in the test pit designated as TP-2 at approximate depth of 5 feet below existing ground surface and underlying topsoil in the test pit designated Otto Rosenau & Associates, Incorporated Geotechnical Engineering, Construction Inspection & Materials Testing 13952 Southeast 159th Place Short Plat ORA Project No.: 19-0616 November 25, 2019 Page 4 of 12 as TP-3 at approximate depth of 1 foot below existing ground surface. The details and explanations of the test pits are presented on pages A-5 to A-10 of the appendix. The topsoil that was encountered in the test pit excavations generally consist of loose, brown, silty SAND (SM) with varying amounts of gravel and organics. The fill material/topsoil was in a dry to slightly moist condition. The weathered glacial till deposits were encountered underlying the topsoil in test pit excavations designated as TP-1 and TP-2 at depths ranging from 1 to 1½ feet below the existing grade. The weathered glacial till deposits generally consist of medium dense to dense, orangish brown, silty SAND (SM) with varying amounts of gravel. The weathered glacial till deposits were in a slightly moist condition. The glacial till deposits that were encountered underlying the topsoil in the test pit designated as TP-3 at approximate depth of 1 foot and underlying the weathered glacial till deposits in the test pit designated as TP-2 at approximate depth of 5 feet below existing ground surface. The glacial till deposits generally consist of very dense, light gray brown, Silty SAND (SM) with some gravel. The glacial till deposits were in a slightly moist to moist condition. Groundwater was not encountered in any our excavations and we anticipate that the groundwater will not affect the proposed development if the recommendations presented in this report are followed. 7. INFILTRATION TESTING Single ring percolation tests were performed at the test pit excavations designated as TP-1 and TP-3 on July 31, 2019 to evaluate the infiltration characteristics in a future permeable pavement area (TP-1) and a future infiltration facility for roof runoff from the future single family residence at the western lot. The single ring percolation tests were performed at depths of approximately 2.7 feet and 1.5 feet below the adjacent ground surface at TP-1 and TP-3 respectively. The base of each excavation was made level using hand tools and was verified with a self-leveling laser level. Single Ring Percolation Test Two (2) single ring percolation tests were performed at the test pit excavations designates as TP-1 and TP-3 using 3-foot diameter, 16-inch tall steel rings that were embedded into the ground approximately 2 to 3 inches to prevent water from flowing underneath. The rings were filled with potable water to depths of 6 inches and maintained at depths of 6 inches for a 4- hour long soaking period on July 30, 2019. Upon completion of the 4-hour long soaking period, we observed that the water did not drain away in less than 10 minutes. As a result, the percolation rates were recorded approximately 18 to 24 hours after the soaking period. The percolation rates were recorded on July 31, 2019, at the end of 30-minute long Otto Rosenau & Associates, Incorporated Geotechnical Engineering, Construction Inspection & Materials Testing 13952 Southeast 159th Place Short Plat ORA Project No.: 19-0616 November 25, 2019 Page 5 of 12 periods for at least 90 minutes with the final water levels drop being used to calculate the percolation rates. The observed final water level drop was 5/8 inches (TP-1) and 0 inches (TP-3) in a 30-minute period, which works out for the measured percolation rates to be 48 minutes per inch for TP-1 and non- measurable for TP-3. The design infiltration rate is calculated using the following formula. Idesign = I measured x Fcorrection x Faggregate Where, I measured = Final measured infiltration rates measured at the test pit locations TP-1 (1.25 inches per hour) and TP-3 (0 inches per hour). Fcorrection = Correction factor for permeable pavement used to meet the LID Performance Standard. = 0.6. Faggregate = Correction factor based on the quality of the aggregate base material. = 0.9. The results are presented in the table below with the preliminary design infiltration rates (Idesign) for each test location for the permeable asphalt or concrete pavement located on the southern portion of the site. Photographs were taken of the single ring percolation procedures are presented on pages A-11 and A- 12 of the appendix. Location Final Measured Infiltration Rate (in / hr) Fcorrection Faggregate Preliminary Design Infiltration Rate (in / hr) TP-1 1.25 0.6 0.9 0.68 TP-3 0 0.6 0.9 0.00 Based on a review of information on King County’s iMAP online mapping service and King County’s KCRTS manual we understand that the site has the following hydrologic characteristics. The project site is located in the SeaTac Rainfall region with a KCRTS scaling factor of 1. The project is located within the Urban Growth Area (UGA). The project site is located within Wellhead Protection areas – 5- and 10-year times of travel. Otto Rosenau & Associates, Incorporated Geotechnical Engineering, Construction Inspection & Materials Testing 13952 Southeast 159th Place Short Plat ORA Project No.: 19-0616 November 25, 2019 Page 6 of 12 8. LABORATORY TESTING We performed moisture content determinations on samples collected during our exploratory borings. The result of the moisture content determination is presented on the test pit logs on pages A-8 to A-10 of the appendix. A particle size analysis, which included the results of results of a hydrometer analysis, is presented on page A-13 of the appendix. The USDA Classification of this sample is presented on page A-14 of the appendix. Cation Exchange Capacity (CEC) determinations (EPA 9081) and Organic Content determinations (ASTM D2974) were performed on a representative sample obtained from depths of approximately 1½ to 2⅓ feet below the adjacent ground surface at the test pit designated as TP-1 are presented on page A-14 of the appendix. The following table summarizes the results. Location Cation Exchange Capacity Organic Content TP-1 13 (5 min) OK 5.6% (1% min) OK TP-3 Not Tested Not Tested 9. DISCUSSION The engineering recommendations and advice presented in this report have been made in accordance with generally accepted geotechnical engineering practices in the area and are based on our understanding of the geology of the area and on our experience with similar projects. Project conditions, regarding type and location of structures and foundation loads, can change and subsurface conditions are not always similar to those encountered during the subsurface exploration. Therefore, if discrepancies are noticed, the geotechnical engineer must be contacted for review and for possible revision of the recommendations. 10. CONCLUSIONS AND RECOMMENDATIONS 10.1 GENERAL Based on the conditions of the underlying soils as encountered during the exploratory test pits, it is our opinion that the foundation systems for the proposed single-family residence on the western portion of the site (future Lot D) can be supported with conventional foundational system that bear directly on the very dense, glacial till deposits that were encountered in the excavations designated as TP-2 (at depth of approximately 5 feet below adjacent ground surface) and TP-3 (at depth of approximately 1 foot below adjacent ground surface). Please refer to the following sections of the report for specific site recommendations. Otto Rosenau & Associates, Incorporated Geotechnical Engineering, Construction Inspection & Materials Testing 13952 Southeast 159th Place Short Plat ORA Project No.: 19-0616 November 25, 2019 Page 7 of 12 Based on the infiltration testing performed at the site, lab test results, and the Water Quality Treatment provisions listed in Section 5.2.1 of KCSWDM, it is our opinion that infiltration located at the southwestern portion of the site is feasible to treat surface water at the proposed permeable asphalt or concrete pavement at or near TP-1 at the southwestern portion of the site. We recommend that a design infiltration rate of 0.68 inches per hour be used to design infiltration BMPs at this location. However, due to the lack of any measured infiltration and the presence of the glacial till deposits (impervious soils) at shallow depth (approximately 1 foot below adjacent ground surface) at TP-3, it is our opinion that infiltration at the northern portion of future Lot D. As a result, we anticipate that a gravel- filled trench basic dispersion system may be a suitable option for dispersing the runoff water from the roof future residence towards the north property line, provided that a 25-foot wide vegetated flow path can be permanently maintained between the gravel filled trench and the north property line. Figure C.2.4.B from the 2015 King County Stormwater Design Manual (KCSWDM) is included on page A-17 of the appendix, which presents several of the details related to a gravel-filled trench basic dispersion system. Figure C.2.4.B from the 2015 KCSWDM is included on page A-16 of the appendix, which presents several of the details related to a typical splash block basic dispersion system. Splash block dispersion systems require a 50-foot long vegetated flow path, which would make it unsuitable for lots with tight property line constraints. If there is insufficient room for a gravel-filled trench or splash block basic dispersion systems, consideration will need to be given to a detention system to handle the stormwater runoff from the future roof of the single-family residence on Lot D. 10.2 SEISMIC CONSIDERATIONS The seismic design of structures in the City of Renton is governed by the requirements of the 2015 International Building Code (IBC). We recommend that the site soils be categorized as Site Class D for design purposes. Risk-targeted Maximum Considered Earthquake (MCER) ground motion response accelerations for this are based on the maps in the IBC (Figures 1613.3.1(1) and 1613.3.1(2)) for 0.2-second and 1-second spectral response accelerations on a bedrock site. The values for SS and S1 are spectral accelerations (SRA) for a maximum considered earthquake event with a 2,475-year return period, or a 2 percent probability of exceedance in 50 years. The values recommended for use in this report were obtained from the Structural Engineers Association of California (SEAOC) and California’s Office of Statewide Health Planning and Development (OSHPD) website at (http://seismicmaps.org). The input parameters used with this website were the latitude and longitude for the project site (47.4603° N, 122.1525° W). The following table presents recommended Otto Rosenau & Associates, Incorporated Geotechnical Engineering, Construction Inspection & Materials Testing 13952 Southeast 159th Place Short Plat ORA Project No.: 19-0616 November 25, 2019 Page 8 of 12 values from the 2015 IBC and ASCE 7-16 “Minimum Design Loads and Associated Criteria for Buildings and Other Structures” for seismic design: RECOMMENDED SEISMIC DESIGN PARAMETERS Site Soil Class Definition (Table 20.3-1 of ASCE 7-16) D Risk-Targeted Max. Considered EQ (MCER) 0.2 s. SRA, Site Class B, SS, g 1.374 Risk-Targeted Max. Considered EQ (MCER) 1.0 s. SRA, Site Class B, S1, g 0.513 Site Coefficient Fa (Table 1613.3.3(1) of the IBC 1.0 Site Coefficient Fv (Table 1613.3.3(2)) of the IBC 1.5 Max. Considered EQ Adjusted for Site Class Effects for Short Periods, SMS, g 1.374 Max. Considered EQ Adjusted for Site Class Effects for Long Periods, SM1, g 0.513 5% Damped Design SRA at Short Periods, SDS, g 0.916 5% Damped Design SRA at Long Periods, SD1, g 0.513 Liquefaction may be defined as the sudden loss of shear strength of soil as the soil is subjected to a rapid back and forth cyclic loading, such as during an earthquake. The mechanism that allows this to occur is the buildup of excess pore water pressures between the soil particles. This excess pore water pressure reduces the frictional contact between the soil particles, and reduces the shear strength of the soil. If the earthquake is of large magnitude and duration, the soil can begin to behave more like a liquid than solid and “liquefy”. In order for liquefaction to occur, several conditions must typically be present. These include the following: Saturated soil. Fine to medium sand matrix containing less than about 10 percent fines (soil that can pass a No. 200 sieve). Very loose to medium dense soil conditions. This is usually defined as soils that have N- values of 15 or less. Based on the observed subsurface soil conditions encountered at the site and our understanding of geologic conditions present at the site, it is our opinion that the potential for the occurrence of liquefaction at the project site is low. 10.3 CONVENTIONAL FOUNDATION SYSTEM It is our opinion that the foundation elements to be built for the new residential structure can be satisfactorily supported on the conventional footings that bear directly onto the native, dense to very dense, glacial till deposits or properly compacted structural fill material. Otto Rosenau & Associates, Incorporated Geotechnical Engineering, Construction Inspection & Materials Testing 13952 Southeast 159th Place Short Plat ORA Project No.: 19-0616 November 25, 2019 Page 9 of 12 We recommend that an allowable bearing capacity of 2,500 pounds per square foot (psf) to be used for the design of conventional spread footings. The allowable bearing capacity may be increased by one- third for wind and seismic loads. If the recommendations in this report are followed, we estimate that maximum post-construction settlements will be less than three-quarters (3/4) of an inch and differential settlements will be less than one-half (1/2) of an inch between comparably loaded column footings. Passive resistance should be evaluated using an equivalent fluid pressure of 300 pounds per cubic foot (pcf) where foundation elements are cast on dense to very dense, native soils or properly compacted structural fill materials. This value of passive pressure includes a factor of safety of 1.5. An allowable coefficient of friction between footings and bearing soils of 0.4 may be used to resist lateral foundation loads. This value includes a factor of safety of about 1.5. 10.4 CONCRETE SLABS-ON-GRADE Structural fill can be placed at future slab-on-grade areas only after the complete removal of any unsuitable soils. All fill placed below future slabs on grade must be placed as structural fill. The slabs-on-grade should bear on a minimum of 6-inch-thick, free-draining, clean, crushed, gravel base (Type 22 material). A robust vapor retarder such as 10-mil polyethylene sheeting shall be included beneath the slab to minimize transmission of moisture through the concrete floor. A minimum, two-inch thick layer of clean sand with less than 3 percent fines may be placed on top of the polyethylene sheeting to protect the sheeting and to enhance the curing of the concrete slabs. The sand must not be saturated at the time of concrete placement in order to enhance concrete curing. If slabs–on-grade are being planned at heated areas, a more robust vapor barrier should be utilized, since the conditioned air in the heated areas will tend to draw moisture from the near-surface groundwater that is present beneath the site. ORA can provide recommendations for vapor barriers upon request. 10.5 BELOW-GRADE WALLS AND RETAINING WALLS The below-grade foundation walls for this project must be designed as retaining walls. Lateral earth pressures for design of permanent retaining walls with no hydrostatic pressures or other surcharge loads, may be calculated using the following equivalent fluid densities in pounds per cubic foot (pcf): Level Back Slope Condition Active (unrestrained): Compacted granular soils or native soils against wall 37 pcf. Level Back Slope Condition Active (restrained): Compacted granular soils or native soils against wall 55 pcf. Passive: Otto Rosenau & Associates, Incorporated Geotechnical Engineering, Construction Inspection & Materials Testing 13952 Southeast 159th Place Short Plat ORA Project No.: 19-0616 November 25, 2019 Page 10 of 12 Embedded Portions of Foundation Elements in native soils 300 pcf. No factor of safety has been applied to the active pressure values listed above. A factor of safety of about 1.5 has been applied to the passive pressure value listed above. The geotechnical engineer should be contacted to determine appropriate lateral earth pressures for situations not described above. Seismic earth pressures were estimated using the Mononobe-Okabe pseudo-static method. We recommend that seismic earth pressures be estimated using a rectangular pressure distribution equal to 6H, where H is the height of the retained soil behind the wall. A total soil unit weight of 125 pounds per cubic foot should be used in design of any permanent below- grade wall or retaining structures. Passive resistance should be evaluated using an equivalent fluid pressure of 300 pounds per cubic foot (pcf) where foundation elements are cast on structural fill and backfilled on both sides with structural fill compacted to at least 95 percent of maximum dry density (MDD). This value of passive pressure includes a factor of safety of 1.5. An allowable coefficient of friction between footings and bearing soils of 0.4 may be used to resist lateral foundation loads. This value includes a factor of safety of about 1.5. 10.6 EARTHWORK The recommendations presented in this report are predicated on fulfillment of the following earthwork recommendations. 10.6.1 Foundation and Slab Subgrade Preparation: All old concrete slabs, undocumented fill, organic debris, and old topsoil must be removed from all new foundation element locations and future slab areas. If construction activities are to be performed during periods of wet weather, we recommend that the exposed foundation subgrade soils be protected with 4 to 6 inches of thoroughly compacted 1-1/4 inch minus crushed rock, quarry spalls, controlled density fill (CDF), or a rat slab of structural concrete. The exposed subgrade soil conditions should be verified by a representative of ORA to ensure that the soils are adequately prepared to provide the required support. 10.6.2 Structural Fill – Material, Placement and Compaction: A granular import should be used as structural fill. All fill and backfill materials should be placed in relatively horizontal loose lifts, not exceeding 10 inches in thickness, and compacted to at least 95 percent of the maximum dry density (MDD) as determined by the modified Proctor test (ASTM D1557). If manually-operated equipment such as a jumping jack compactor is used, the thickness of each loose lift should be no greater than 6 inches. Light vibratory plate compactors are not suitable for the compaction of structural fill. Soils consisting of clay, silt, peat or containing deleterious matter are generally not suitable for use as structural fill. Otto Rosenau & Associates, Incorporated Geotechnical Engineering, Construction Inspection & Materials Testing 13952 Southeast 159th Place Short Plat ORA Project No.: 19-0616 November 25, 2019 Page 11 of 12 Structural fill material should be approved by ORA prior to use. The following table summarizes our recommendations of fill material and compaction requirements for various types of aggregates. Intended Use Specification Compaction Requirements Structural fill below foundation elements Gravel backfill for Foundations (WSDOT 9-03.12(1)) Each lift must be compacted to 95 percent of MDD per ASTM D1557 test procedure. Fill behind below- grade walls (outside of zone of wall drainage material) Gravel Backfill for Walls (WSDOT 9- 03.12(2)) Fill placed within 5 feet of below- grade walls or retaining walls shall be compacted with manually-operated compaction equipment. Fill placed at depths greater than 2 feet below finish subgrade elevation compacted to 90 percent of MDD. Fill placed at depths within 2 feet of finish subgrade elevation must be compacted to 95 percent of MDD, if the area will be supporting pavements or roadway. Fill behind below- grade walls at zone of wall drainage material Gravel Backfill for Drains (WSDOT 9- 03.12(4)) No compaction until at least 18 inches of cover is present above perforated drain pipe. Each subsequent 12-inch lift lightly compacted using manual compaction equipment. Capillary break material below slabs- on-grade Clean, 5/8-inch crushed rock Each lift must be compacted to a firm and unyielding condition over the firm subgrade soils. Structural fill to be compacted to 95 percent of MDD should be moisture-conditioned to within three (3) percent of optimum moisture. Structural fill to be compacted to 90 percent of MDD should be moisture- conditioned to within six (6) percent of optimum moisture content. Placement of frozen soils or placement of soils on frozen ground should not be attempted. 10.6.3 Temporary Excavations: We recommend that the inclination of the temporary cut slopes be no greater than 1.5H:1V (horizontal to vertical) for the fill materials and medium dense, native, weathered till deposits and no greater than 1H:1V for the dense to very dense, native, glacial till deposits. An ORA representative should evaluate the exposed soil conditions at the time of construction to verify that the Otto Rosenau & Associates, Incorporated Geotechnical Engineering, Construction Inspection & Materials Testing 13952 Southeast 159th Place Short Plat ORA Project No.: 19-0616 November 25, 2019 Page 12 of 12 recommended slope inclinations are appropriate for the conditions being encountered. In addition, the configuration for temporary cut slope inclinations may need to be modified during the course of construction if site conditions change. All temporary cut slopes and excavations must comply with the provisions of Washington Administrative Code (WAC) Chapter 296-155, Part N, “Excavation, Trenching and Shoring.” The contractor performing the work has the primary responsibility for protection of workers and adjacent improvements. 10.6.4 Erosion and Sedimentation Control: The migration of sediments from the site must be installed and controlled in accordance with City of Renton requirements. We recommend that the following minimum erosion control measures be employed at the site: Provide silt fencing around the construction area to delineate the construction limits. No construction or soil disturbance should take place outside of the construction limits. Stockpiled soil at the site should be kept to a minimum. Any stockpiled soils should be covered with carefully secured plastic sheeting. Catch basin socks should be installed in nearby catch basins located downhill of the work area that could be impacted by construction activities. All sediment and soil should be removed from adjacent pavements at the end of each day of construction activities. Periodic inspection of the adequacy and condition of the installed erosion control measures by a geotechnical engineer or an experienced representative assigned by the geotechnical engineer. Additional erosion control measures may be required as construction progresses. 10.7 DRAINAGE 10.7.1 Dewatering: Based on our review of the proposed development, we do anticipate that groundwater will not be encountered during construction of the new residential structure. We anticipate that if dewatering is to be needed then it can be satisfactorily completed by routing water through ditches to a low spot or sump in the excavation. We recommend that the sump depths be set to lower groundwater to at least 2 feet below the base of excavation elevation. Runoff water and groundwater collected in temporary excavations should be removed as soon as possible and should be discharged to a location approved by the City of Renton in accordance with City of Renton requirements. 10.7.2 Below-Grade Wall Drainage: Good drainage is an integral part of the performance of earth- supported structures such as foundations and retaining walls. New drainage will need to be provided between the exposed soil at the excavations along the new foundation walls. We anticipate that this may be most easily accomplished using a composite drainage panel such as CCW MiraDrain 6000, or an approved equivalent. The composite drainage panel is installed with the filter fabric side against the soil Otto Rosenau & Associates, Incorporated Geotechnical Engineering, Construction Inspection & Materials Testing 13952 Southeast 159th Place Short Plat ORA Project No.: 19-0616 November 25, 2019 Page 13 of 12 and the plastic, dimpled board facing the interior of the foundation. Water collected by composite drainage panel will need to be routed to the interior of the foundation using a PVC pipe fitting made by the drainage panel manufacturer that is designed for the system being used and passes through the foundation wall or footing into an interior tight line collection system below the future subfloor. The collected water then may be routed to the outfall of the existing foundation drain system, which may require the use of a sump and sump pump, if gravity flow is not feasible. 11. REPORT LIMITATIONS The recommendations presented in this report are for the exclusive use by Mr. Sandhu Kulwant for the proposed development that is to be located at 13952 Southeast 159th Place in Renton, Washington. The recommendations are based on readily-available geologic literature, configuration of the proposed development, and three (3) test pits that were completed on July 30, 2019. The recommendations of this report are not transferable to any other site. If there are any revisions to the plans, or if deviations from the subsurface conditions noted in this report are encountered during construction, Otto Rosenau & Associates, Inc. (ORA) should be notified immediately to determine whether changes to the design recommendations are required. 12. REFERENCE Structural Engineers Association of California (SEAOC) and California’s Office of Statewide Health Planning and Development (OSHPD) website at (http://seismicmaps.org). United States Department of Agriculture, Natural Resources Conservation Service’s (NRCS) “SoilWeb” online mapping (https://websoilsurvey.sc.egov.usda.gov/App/WebSoilSurvey.aspx). Washington State Department of Natural Resources (DNR), Division of Geology and Earth Resources, Washington State Geologic Information Portal’s website (fortress.wa.gov/dnr/geology). APPENDIX 13952 SE 159th PL SHORT PLAT PARCEL # 2223059022 VICINITY MAP OTTO ROSENAU & ASSOCIATES, INC. Reference: ©2019 Microsoft Corporation Bing Mapping Service. ORA Project Number: 19-0616 Project Name: 13952 SE 159th Place Short Plat For: Kulwant Sandhu Location: 13952 SE 159th Place, Renton, Washington Date: November 21, 2019 A-1 TP-3 TP-2 TP-1 13952 SE 159th PLACE MAPPED EROSION HAZARD AREA (KING COUNTY IMAP) SITE PLAN OTTO ROSENAU & ASSOCIATES, INC. KING COUNTY PARCEL NO: 2223059022 REFERENCE: PROPERTY SURVEY PERFORMED BY EDWARD BARNARD, PLS DATED 12/27/2016, AND SITE MEASUREMENTS TAKEN WITH A STEEL TAPE FROM EXISTING SITE FEATURES, KING COUNTY IMPA ONLINE MAPPING SERVICE LEGEND NORTH APPROXIMATE SCALE 1" = 30' TP-1 TEST PIT COMPLETED BY ORA 07/30/2019 ORA Project Number: 19-0616 Project Name: 13952 SE 159th Place Short Plat For: Kulwant Sandhu Location: 13952 SE 159th Place, Renton, Washington Date: November 21, 2019 13952 SOUTHEAST SHORT PLAT 13952 SOUTHEAST 159th PLACE PARCEL # 2223059022 Qgo Qgo(i) Qls Qa Qgt GEOLOGIC MAP OTTO ROSENAU & ASSOCIATES, INC. LEGEND Qgt - Continental Glacial Till, Fraser-Age Qgo - Continental Glacial Outwash, Fraser-Age Qgo(i) - Continental Glacial Outwash, Fraser-Age Qls - Mass-Wasting Deposits, Mostly Landslides Qa - Quaternary Alluvium Note: The location of all features shown is approximate. Reference: Interactive Geologic Map Online Mapping Service By Washingon Department of Natural Resource ORA Project Number: 19-0616 Project Name: 13952 SE 159th Short Plat For: Kulwant Sandhu Location: 13952 SE 159th Place, Renton, Washington Date: November 21, 2019 A-3 A-4 TEST PIT LOG NOTES These notes and hand excavation logs are intended for use with this geotechnical report for the purposes and project described therein. The logs depict ORA’s interpretation of subsurface conditions at the location of the excavation on the date noted. Subsurface conditions may vary, and groundwater levels may change because of seasonal or numerous other factors. Accordingly, the logs should not be made a part of construction plans or be used to define construction conditions. The approximate locations of the excavations are shown on the Site Plan. The excavations were located in the field by measuring from existing site features. “Sample Number and Type” refers to the sampling method and equipment used during exploration. “Moisture Content (MC)” refers to the moisture content of the soil expressed in percent by weight of dry sample as determined in the laboratory. “Grain Size (GS)” refers to a grain size distribution analysis completed in general accordance with the ASTM D422 test procedure. “Fines” is an estimate of the portion of a soil sample passing a No. 200 sieve as determined using the ASTM D422 test procedure. “Atterberg Limits (AL)” refers to a determination of the liquid and plastic limits of a cohesive soil using the ASTM D 4318 test procedure. “Dry Density (DD)“ refers to an estimate of the dry density of a soil sample collected using a Shelby thin-wall sampling tube. “Description and USCS Classification” refer to the materials encountered in the excavation. The descriptions and classifications are generally based on visual examination in the field and laboratory. Where noted, laboratory tests were performed to determine the soil classification. The terms and symbols used in the logs are in general accordance with the Unified Soil Classification System. Laboratory tests are performed in general accordance with applicable procedures described by the American Society for Testing and Materials. “” Indicates location of groundwater at the time noted. A-5 TERMS for RELATIVE DENSITY of NON-COHESIVE SOIL Term Standard Penetration Resistance “N” Very Loose 4 or less Loose 5 to 10 Medium Dense 11 to 30 Dense 31 to 50 Very Dense Over 50 blows/foot TERMS for RELATIVE CONSISTENCY of COHESIVE SOIL Term Unconfined Compressive Strength Very Soft 0 to 0.25 tons/square-foot (tsf) Soft 0.25 to 0.50 tsf Medium Stiff 0.50 to 1.00 tsf Stiff 1.00 to 2.00 tsf Very Stiff 2.00 to 4.00 tsf Hard Over 4.00 tsf DEFINITION of MATERIAL by DIAMETER of PARTICLE Boulder 8-inches+ Cobble 3 to 8 inches Gravel 3 inches to 5mm Coarse Sand 5mm to 0.6mm Medium Sand 0.6mm to 0.2mm Fine Sand 0.2mm to 0.074mm Silt 0.074mm to 0.005mm Clay less than 0.005mm A-6 GW GM GC SW SP SC ML CL OL CH OH PT SOIL CLASSIFICATION CHART MAJOR DIVISIONS SYMBOLS TYPICAL GRAPH LETTER DESCRIPTIONS COARSE GRAINED SOILS MORE THAN 50% OF MATERIAL IS LARGER THAN NO. 200 SIEVE SIZE FINE GRAINED SOILS MORE THAN 50% OF MATERIAL IS SMALLER THAN NO. 200 SIEVE SIZE GRAVEL AND GRAVELLY SOILS MORE THAN 50% OF COARSE FRACTION RETAINED ON NO. 4 SIEVE SAND AND SANDY SOILS MORE THAN 50% OF COARSE FRACTION PASSING ON NO. 4 SIEVE SILTS AND CLAYS SILTS AND CLAYS CLEAN GRAVELS (LITTLE OR NO FINES) GRAVELS WITH FINES (MORE THAN 12% FINES) CLEAN SANDS (LITTLE OR NO FINES) SANDS WITH FINES (MORE THAN 12% FINES) LIQUID LIMIT LESS THAN 50 LIQUID LIMIT GREATER THAN 50 WELL-GRADED GRAVELS, GRAVEL - SAND MIXTURES, LITTLE OR NO FINES POORLY-GRADED GRAVELS, GRAVEL GP - SAND MIXTURES, LITTLE OR NO FINES SILTY GRAVELS, GRAVEL - SAND - SILT MIXTURES CLAYEY GRAVELS, GRAVEL - SAND - CLAY MIXTURES WELL-GRADED SANDS, GRAVELLY SANDS, LITTLE OR NO FINES POORLY-GRADED SANDS, GRAVELLY SAND, LITTLE OR NO FINES SM SILTY SANDS, SAND - SILT MIXTURES CLAYEY SANDS, SAND - CLAY MIXTURES INORGANIC SILTS AND VERY FINE SANDS, ROCK FLOUR, SILTY OR CLAYEY FINE SANDS OR CLAYEY SILTS WITH SLIGHT PLASTICITY INORGANIC CLAYS OF LOW TO MEDIUM PLASTICITY, GRAVELLY CLAYS, SANDY CLAYS, SILTY CLAYS, LEAN CLAYS ORGANIC SILTS AND ORGANIC SILTY CLAYS OF LOW PLASTICITY INORGANIC SILTS, MICACEOUS OR MH DIATOMACEOUS FINE SAND OR SILTY SOILS INORGANIC CLAYS OF HIGH PLASTICITY ORGANIC CLAYS OF MEDIUM TO HIGH PLASTICITY, ORGANIC SILTS HIGHLY ORGANIC SOILS PEAT, HUMUS, SWAMP SOILS WITH HIGH ORGANIC CONTENTS NOTE: FINES ARE MATERIALS PASSING THE NO. 200 SIEVE. COARSE GRAINED SOILS RECEIVE DUAL SYMBOLS IF THEY CONTAIN BETWEEN 5% AND 12% FINES. FINE GRAINED SOILS RECEIVE DUAL SYMBOLS IF THEIR LIMITS PLOT LEFT OF THE "A" LINE WITH A PLASTICITY INDEX (PI) OF 4% TO 7%. A-7 442.5 441.3 GB 1 MC=8% GS, Hydrometer SM SM Loose, brown, Silty SAND with trace gravel and organics (dry to slightly moist) (topsoil) Medium dense, orange-brown, Silty SAND with trace gravel, slightly moist (weathered till) (USDA Classification = Sandy Loam) Bottom of test pit at 2.7 feet. 1.5 2.7 NOTES GROUND ELEVATION 444 ft LOGGED BY Scott Hoobler, P.E. EXCAVATION METHOD Rubber-Track Mini Excavator AT TIME OF EXCAVATION --- AT END OF EXCAVATION --- AFTER EXCAVATION --- TEST PIT SIZE 48"x64" EXCAVATION CONTRACTOR Provided by Owner GROUND WATER LEVELS: CHECKED BY Scott Hoobler, P.E. DATE STARTED 7/30/19 COMPLETED 7/30/19 DEPTH(ft)0 1 2 SAMPLE TYPENUMBERPAGE 1 OF 1 TEST PIT NUMBER TP-1 CLIENT Sandhu, Kulwant PROJECT NUMBER 19-0616 PROJECT NAME 13952 Southeast Short Plat PROJECT LOCATION 13952 Southeast 159th Place GENERAL BH / TP / WELL 13952 SOUTHEAST SHORT PLAT.GPJ GINT US.GDT 11/19/19OTTO ROSENAU & ASSOCIATES, INC. 6747 M.L. King Way South Seattle, WA 98118 Telephone: (206) 725-4600 Fax: (206) 723-2221 TESTS U.S.C.S.GRAPHICLOGMATERIAL DESCRIPTION A-8 441.0 437.0 436.0 GB 1 GB 2 MC=7% MC=7% SM SM SM SM Loose, brown, Silty SAND with organics (dry to slightly moist) (topsoil) Medium dense, orange-brown, Silty SAND with some gravel, slightly moist (weathered till) Becomes dense at 3.5' Very dense, light grayish brown, Silty SAND with some gravel, slightly moist to moist (glacial till) Bottom of test pit at 6.0 feet. 1.0 5.0 6.0 NOTES GROUND ELEVATION 442 ft LOGGED BY Scott Hoobler, P.E. EXCAVATION METHOD Rubber-Track Mini Excavator AT TIME OF EXCAVATION --- AT END OF EXCAVATION --- AFTER EXCAVATION --- TEST PIT SIZE 24"x60" EXCAVATION CONTRACTOR Provided by Owner GROUND WATER LEVELS: CHECKED BY Scott Hoobler, P.E. DATE STARTED 7/30/19 COMPLETED 7/30/19 DEPTH(ft)0.0 2.5 5.0 SAMPLE TYPENUMBERPAGE 1 OF 1 TEST PIT NUMBER TP-2 CLIENT Sandhu, Kulwant PROJECT NUMBER 19-0616 PROJECT NAME 13952 Southeast Short Plat PROJECT LOCATION 13952 Southeast 159th Place GENERAL BH / TP / WELL 13952 SOUTHEAST SHORT PLAT.GPJ GINT US.GDT 11/19/19OTTO ROSENAU & ASSOCIATES, INC. 6747 M.L. King Way South Seattle, WA 98118 Telephone: (206) 725-4600 Fax: (206) 723-2221 TESTS U.S.C.S.GRAPHICLOGMATERIAL DESCRIPTION A-9 432.0 431.5 GB 1 MC=6% SM SM Loose, brown, Silty SAND, with some gravel and organics, dry to slightly moist (topsoil) Very dense, light grayish brown, Silty SAND with some gravel, slightly moist to moist (glacial till) Bottom of test pit at 1.5 feet. 1.0 1.5 NOTES GROUND ELEVATION 433 ft LOGGED BY Scott Hoobler, P.E. EXCAVATION METHOD Manual Excavation AT TIME OF EXCAVATION --- AT END OF EXCAVATION --- AFTER EXCAVATION --- TEST PIT SIZE 36" diameter EXCAVATION CONTRACTOR Provided by Owner GROUND WATER LEVELS: CHECKED BY Scott Hoobler, P.E. DATE STARTED 7/30/19 COMPLETED 7/30/19 DEPTH(ft)0 1 SAMPLE TYPENUMBERPAGE 1 OF 1 TEST PIT NUMBER TP-3 CLIENT Sandhu, Kulwant PROJECT NUMBER 19-0616 PROJECT NAME 13952 Southeast Short Plat PROJECT LOCATION 13952 Southeast 159th Place GENERAL BH / TP / WELL 13952 SOUTHEAST SHORT PLAT.GPJ GINT US.GDT 11/19/19OTTO ROSENAU & ASSOCIATES, INC. 6747 M.L. King Way South Seattle, WA 98118 Telephone: (206) 725-4600 Fax: (206) 723-2221 TESTS U.S.C.S.GRAPHICLOGMATERIAL DESCRIPTION A-10 PHOTO OF SINGLE RING INFILTRATION TEST (TP-1) OTTO ROSENAU & ASSOCIATES, INC.ORA Project Number: 19-0616 Project Name: 13952 SE 159th Place Short Plat For: Kulwant Sandhu Location: 13952 SE 159th Place, Renton, Washington Date: November 21, 2019 INFILTRATION TEST WAS PERFORMED ON 07/31/2019 A-11 PHOTO OF SINGLE RING INFILTRATION TEST (TP-3) OTTO ROSENAU & ASSOCIATES, INC.ORA Project Number: 19-0616 Project Name: 13952 SE 159th Place Short Plat For: Kulwant Sandhu Location: 13952 SE 159th Place, Renton, Washington Date: November 21, 2019 INFILTRATION TEST WAS PERFORMED ON 07/31/2019 This report applies to the items tested or reported and is the exclusive property of Otto Rosenau & Associates, Inc.Reproduction of this report, except in full, without written permission from our firm is strictly prohibited.Classification: ASTM D2487 Natural Moisture: ASTM D2216Particle Size Distribution Report PERCENT FINER0 10 20 30 40 50 60 70 80 90 100 GRAIN SIZE - mm. 0.0010.010.1110100 % +3"Coarse % Gravel Fine Coarse Medium % Sand Fine Silt % Fines Clay 0.0 14.9 21.7 10.7 11.5 21.7 14.4 5.16 in.3 in.2 in.1½ in.1 in.¾ in.½ in.3/8 in.#4#10#20#30#40#60#100#140#200Test Results (ASTM D 422 & ASTM D 1140) Opening Percent Spec. *Pass? Size Finer (Percent) (X=Fail) Material Description Atterberg Limits (ASTM D 4318) Classification Coefficients Date Received:Date Tested: Tested By: Checked By: Title: Date Sampled:Location: TP1 18"-32" Sample Number: 8150 Client: Project: Project No:Figure Sample ID: 8150 Reddish brown (Trace organic) silty sand with gravel 2 1 1/4 1 3/4 5/8 1/2 3/8 1/4 #4 #8 #10 #40 #100 #200 0.0327 mm. 0.0211 mm. 0.0125 mm. 0.0090 mm. 0.0065 mm. 0.0032 mm. 0.0014 mm. 100.0 100.0 94.9 85.1 84.4 78.9 74.4 67.7 63.4 54.6 52.7 41.2 27.0 19.5 13.2 11.4 9.0 7.2 6.0 3.6 1.8 SM A-1-b 22.4517 18.5763 3.6510 1.5155 0.1869 0.0441 0.0153 238.68 0.63 Test equipment ID: Set 5 Was sample soaked: Yes As received MC: 7.5% 7/21/2019 8/15/2019 Andy Duong Anthony Coyne Professional Engineer 7/21/2019 Sandhu, Kulwant 13952 Southeast Short Plat 13952 Southeast 159th Place, Renton 19-0616 PL=LL=PI= USCS (D 2487)=AASHTO (M 145)= D90=D85=D60= D50=D30=D15= D10=Cu=Cc= Remarks *(no specification provided) OTTO ROSENAU & ASSOCIATES, INC.8105 A-13 This report applies to the items tested or reported and is the exclusive property of Otto Rosenau & Associates, Inc.Reproduction of this report, except in full, without written permission from our firm is strictly prohibited.Classification: ASTM D2487 Natural Moisture: ASTM D2216USDA Soil Classification siltloam sand siltyclay loam loam clay loam sandy loam siltyclay sandyclay loam loamy sand clay silt sandy clay 0 1000 10 901 0 20 802 0 30 703 0 40 604 0 50 505 0 60 406 0 70 307 0 80 208 0 90 109 0 100 01 0 0 Percent SandPercent ClayPercen t S i l t SOIL DATA Source Sample Depth ClassificationNo. Percentages From Material Passing a #10 Sieve Sand Silt Clay OTTO ROSENAU & ASSOCIATES, INC. Client: Project: Project No.:Figure Sandhu, Kulwant 13952 Southeast Short Plat 13952 Southeast 159th Place, Renton 19-0616 8150 68.9 26.6 4.6 Sandy loamTP-1, S-1 18" A-14 Am Test Inc. 13600 NE 126TH PL Suite C Kirkland, WA 98034 (425) 885-1664 www.amtestlab.com Professional Analytical Services ANALYSIS REPORT OTTO ROSENAU & ASSOCIATES Date Received: 08/12/19 6747 MARTIN LUTHER KING JR WAY S Date Reported: 9/10/19 SEATTLE, WA 98118 Attention: SCOTT HOOBLER Project Name: 13952 SE SHORT PLAT All results reported on an as received basis. _________________________________________________________________________________________________ AMTEST Identification Number 19-A012025 Client Identification TP-1-1 Sampling Date 07/30/19, 10:00 Conventionals PARAMETER RESULT UNITS Q D.L. METHOD ANALYST DATE Cation Exchange Capacity 13. meq/100g 0.5 SW-846 9081 JDM 09/03/19 Organic Matter 5.6 %0.1 ASTM D 2974 DM 08/21/19 _________________________________ Kathy Fugiel President A-15 FIGURE C.2.4.A TYPICAL SPLASHBLOCK FOR BASIC DISPERSION SIDE VIEW NTS HOUSE DOWNSPOUT EXTENSION SPLASH BLOCK ROOF DOWNSPOUT SERVES UP TO 700 S.F. OF ROOF UNDER BASIC DISPERSION SPLASH BLOCK 50' MIN. VEGETATED FLOWPATH UNDER BASIC DISPERSION A-16 FIGURE C.2.4.B TYPICAL GRAVEL-FILLED DISPERSION TRENCH FOR BASIC DISPERSION MAXIMUM 50-FOOT TRENCH WITH NOTCHED BOARD (SEE FIGURE C.2.1.D) 25-FOOT (MIN.) VEGETATED FLOWPATH SEGMENT 25-FOOT (MIN.) VEGETATED FLOWPATH SEGMENT SIMPLE 10- FOOT TRENCH 24" MIN. MAX 15% SLO P E TRENCH SECTION NTS 3/4" TO 1-1/2" WASHED DRAIN ROCK RIGID PEFORATED PIPE, 4" MIN. DIA. LEVEL OUTLETMAX 20% SLO P E 18" MIN. 6" MIN. = 700 SQ. FT. = 3,500 SQ. FT. SLOPE SMALL CATCH BASIN OR YARD DRAIN TYPE 1 CB PLAN VIEW OF ROOF NTS FLOWPATH SEGMENTS MUST NOT OVERLAP A-17