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HomeMy WebLinkAboutRS FINAL TIR REPORT 201002Deccio Engineering Inc. 17217 7th Avenue W. Bothell, WA. 98012 (206) 390-8374 Fax: (425) 741-8214 Mahal 2-Lot Short Plat PR19- Drainage Design Report, O&M Manual & SWPP Report Property Location: 13436 156th Ave SE Renton, WA February 9, 2019 Prepared for: Ralraj Mahal Drainage Technical Information Report February 9, 2019 1 | P a g e TABLE OF CONTENTS SECTION 1 PROJECT OVERVIEW 1 o Figure 1: TIR Worksheet 2 o Figure 2: Site Location Map 7 o Figure 3: Existing Site Characteristic, Drainage Basins, and Sub-Basins 8 SECTION 2 CONDITIONS & REQUIREMENTS SUMMARY 9  King County Requirements SECTION 3 OFF-SITE ANALYSIS 10  Sensitive Areas Map 11  Drainage Complaint Map 12 o Figure 4: Upstream and Downstream Flow Map 14 o Figure 5: Downstream System Table 15 SECTION 4 FLOW CONTROL & WATER QUALITY ANALYSIS AND DESIGN 15 o Figure 6: Soils Logs 16 o Figure 7: Developed Conditions Map 16 o Infiltration Requirements 17 o Soil Management Plan 18 SECTION 5 CONVEYANCE SYSTEM ANALYSIS AND DESIGN 18 SECTION 6 SPECIAL REPORTS AND STUDIES 21 SECTION 7 OTHER PERMITS 21 SECTION 8 SWPPP ANALYSIS AND DESIGN 21 SECTION 9 BONDS, SUMMARIES AND COVENANTS 23 SECTION 10 OPERATIONS AND MAINTENANCE MANUAL 23  Operations and Maintenance Procedures Appendix A  O&M Requirements  WWHM3 Results  South Sound Infiltration Assessment  Engineers Cost Evaluation Package Drainage Technical Information Report February 9, 2019 2 | P a g e TIR SECTION 1 PROJECT OVERVIEW Project: Mahal 2-lot Short Plat Site Information: The proposed project is the construction of a 2-lot short plat. The site is located 13436 156th Ave SE Renton. More generally the site is located within SW ¼ of the NE ¼ of Section 24, Township 23 North, Range 05 East, W.M., see Figure 2: Vicinity Map. The site is bordered by residential lots on the north, south, east, and west sides of the site. Pre-developed Site Conditions: The site is 29,105 sf in size and contains an existing home, driveway, patio and walkway and landscaping with a total existing impervious area of 4,254 sf. The lot slopes from east to west with all runoff leaving the site along the west property line. There are no known sensitive areas on site. The soils report prepared for the site show the site soils are suitable infiltration. Please refer to Figure 3: Existing Conditions Map.. Developed Site Conditions: The project will consist of construction of a 2-lot short plat with two single family dwellings and driveways. Half Street frontage improvements in the form of curbs, gutters, sidewalks and landscape strip will be required on 156th Ave SE. Please refer to Figure 7: Developed Conditions Map Since the impervious area exceeds the 5,000 sf threshold, flow control will be addressed through infiltration of the runoff from the proposed site improvements. (See TIR Section 4 of this report) The project will use the Design Requirement’s under “Appendix C” of the 2017 City of Renton Surface Water Design Manual. Specifically, Section C.1.3.2 for lots over 22,000 sf Drainage Technical Information Report February 9, 2019 3 | P a g e Figure 1: TIR Worksheet Drainage Technical Information Report February 9, 2019 4 | P a g e Figure 1: TIR Worksheet Drainage Technical Information Report February 9, 2019 5 | P a g e Figure 1: TIR Worksheet Drainage Technical Information Report February 9, 2019 6 | P a g e Figure 1: TIR Worksheet Drainage Technical Information Report February 9, 2019 7 | P a g e Figure 1: TIR Worksheet Drainage Technical Information Report February 9, 2019 8 | P a g e Figure 2: Site Location Map Drainage Technical Information Report February 9, 2019 9 | P a g e Figure 3: Drainage Basins, Sub-basins and Site Characteristics Drainage Technical Information Report February 9, 2019 10 | P a g e TIR SECTION 2 CONDITIONS & REQUIREMENTS SUMMARY The City of Renton has adopted the City of Renton 2017 storm water manual which governs the design of stormwater systems to serve this project. The Core and Special Requirements are being met in the following manner: City of Renton 2017 storm water manual Core Requirements: 1. Discharge at the Natural Location Under 1.2.1-2, The surveyed contours show all runoff leaves the site towards west. The drainage design proposes to use BMP’s to address the runoff through infiltration with any over flow leaving the site along the west side maintaining the natural discharge location. 2. Off-site Analysis The Level 1 downstream analysis showed that there will be minimal impacts on the downstream conditions, since the site proposes to use small site BMP’s to address all stormwater runoff. 3. Flow Control The site will provide flow control in the form of infiltration and will provide BMP’s as outlined in Appendix C Small Site Drainage requirements. 4. Conveyance System None proposed on-site. 156th Ave SE contains existing 12” storm . 5. Temporary Erosion & Sediment Control All TESC measures proposed will conform to the 2009 KCSWDM during construction, Refer to Section 9 of this TIR for additional information. The measures shown on the TESC plans include: Clearing limits, sediment control, soil stabilization, BMP’s maintenance and construction sequence 6. Maintenance & Operations Maintenance and Operations manual has been provided. Note that a “Declaration of Covenant” may be required. See Section 10. 7. Financial Guarantees & Liability A completed bond quantity worksheet will be provided at the time of preparation of construction plans 8. Water Quality Since new pollution generating impervious surface is less than 5,000 sf, water quality is not required. Refer to Section 4 of this report. Drainage Technical Information Report February 9, 2019 11 | P a g e City of Renton 2017 storm water manual Special Requirements: 1. Other Adopted Area-Specific Requirements There are no area-specific requirements for this project site. 2. Floodplain/Floodway Delineation A review of the FEMA FIRM panels for the site, shows that the site and area of work is outside any floodplain areas and site does not contain any floodplain/floodway delineations. 3. Flood Protection Facilities There are no flood protection facilities located on or directly adjacent to the site. 4. Source Control This final site does not meet the threshold for source control requirements. 5. Oil Control This final site does not meet the threshold for oil control requirements. 6. Aquifer Protection Area None known. Drainage Technical Information Report February 9, 2019 12 | P a g e City of Renton Conditions FINDINGS/CONCLUSIONS: To be determined TIR SECTION 3 OFF-SITE ANALYSIS TASK 1 – STUDY AREA DEFINITIONS AND MAPS Overview This section of the TIR is a Level 1 Downstream Analysis per the City of Renton 2017 storm water manual Section 2.3. The project will consist of construction of a 2-lot short plat with two single family dwellings and driveways. Half Street frontage improvements in the form of curbs, gutters, sidewalks and landscape strip will be required on 156th Ave SE., see Figure 2: Vicinity Map. The site is bordered by residential lots on the north, south, east, and west sides of the site. Upstream Drainage Analysis / Upstream Contributing Area Based on the site contours, there is minimal off-site drainage from upstream areas draining onto the site from the east. The site slopes from east to west eliminating any off-site runoff from the north and south sides of the site. Therefore the drainage is basically limited to the site itself. TASK 2 – RESOURCE REVIEW Adopted Basin Plan The site is located in the Cedar River Basin and East Lake Washington Basin which flows into Puget Sound. Community Plan The site is located in the East Lake Washington Basin Planning Area. Basin Reconnaissance Summary Report We are not aware of a current Basin Reconnaissance Summary Report for this area. Critical Drainage Area The site is not considered to be within a critical drainage area as defined by the 2009 KCSWDM. Sensitive Area Maps Per City of Renton the site does contain areas of steep slope with a potential for landslide hazard sensitive areas. (See “Sensitive Areas Map”) Soils Survey The soils logs for the site show the site soils to be a silty sand and suitable for infiltration. Drainage Technical Information Report February 9, 2019 13 | P a g e Wetland / Stream Inventory No known wetlands or streams exist with-in the site. A review of the FEMA FIRM panels for the site, shows that the site and area of work is outside any floodplain areas and site does not contain any floodplain/floodway delineations. Drainage Complaints There appeared to be several drainage complaints downstream. All were minor and all were over 17-years old. (See “Drainage Complaints Map”) TASK 3 – FIELD INSPECTION A Level 1 site inspection was performed on January 20, 2019. The weather was overcast with temperatures around the 40’s degrees. The inspection focused on identifying potential downstream drainage and water quality problems As previously indicated, the site slopes to the east to west with all runoff leaving along the west side of the site TASK 4 – DRAINAGE SYSTEM DESCRIPTION, AND PREDICTED DRAINAGE AND WATER QUALITY PROBLEMS OFFSITE LEVEL ONE DOWNSTREAM ANALYSIS 1. The runoff leaves the property along the west side and into the storm system serving 156th Ave SE. from here it flows south for a distance of 2,000 ft to SE 142nd Place before discharging into an unnamed stream 2. This stream flows for a distance of 1,200 feet south and into the Cedar River. 3. The Cedar River then flows west over 1-mile before discharging into the south end of Lake Washington. The total distance covered is just over 1-mile Basin 1 Predicted Drainage and Water Quality Problems The steep slopes located along the stream and river may have erosion issues. However, since most of the downstream including the discharge locations were on private property and not accessible to inspection, no drainage issues could be confirmed. TASK 5 MITIGATION OF EXISTING OR POTENTIAL PROBLEMS The project proposes to use infiltration to address the storm water runoff from the proposed site improvements, thus mitigating any downstream impacts. Drainage Technical Information Report February 9, 2019 14 | P a g e Figure 5: Upstream Area and Downstream Flow Map Drainage Technical Information Report February 9, 2019 15 | P a g e Figure 6: Downstream System Table F i g u r e 5 Drainage Technical Information Report February 9, 2019 16 | P a g e Drainage Complaints Drainage Technical Information Report February 9, 2019 17 | P a g e Sensitives Areas Drainage Technical Information Report February 9, 2019 18 | P a g e TIR SECTION 4 FLOW CONTROL & WATER QUALITY ANALYSIS AND DESIGN (PRELIMINARY) Per Appendix C Section C.1.3.1, the following BMP’s were reviewed and analyzed for use:  Full Infiltration: The soils were found to be suitable for infiltration. ROOF INFILTRATION FACILITIES DESIGN The infiltration trenches were designed using the requirements outline in Chapter 5.4.5 “Infiltration Facilities” of the King County Surface Water Design Manual. The “South Sound” Geotech report prepared for the site (Appendix B) identified the site soils in in the area of Test Pit-1 (PIT-1) as a Silty Sand w/Gravel with a field infiltration rate of 6.0 inches per hour and recommended infiltration design rate of 1.70 inches per hour. Gravel Trench Calculation Results: The sizing of the Gravel Trench to infiltrate the 100-year developed flows was designed using the WWHM3 under Section 7.2.6 Gravel Trenches. The results for the trench sizing are included in Appendix C. The estimated roof areas for both lots is 5,300 sf (0.12 acres) and the trenches will be designed using the 1.70 inch per hour rate. The WWHM3 program was then used to size the trenches with the following results:  Total Impervious Roof Area: 5,300 sf (0.12 acres)  Design Infiltration rate: 1.70 in/hr (See “South Sound” Infiltration Results)  Correction Factor: 1.0  WWHM3 Trench Size Req’d: 80-ft x 5-ft wide x 2.5-ft deep @ 400 sf area (See WWHM3 Results) The trenches they will be place in each lot on the site as follows:  Lot 1; Trench 1: 40 lf x 5-ft x 2.5-ft deep (Picks up 2,650 sf of roof area)  Lot 2; Trench 2: 40 lf x 5-ft x 2.5-ft deep (Picks up 2,650 sf of roof area) PAVEMENT TRENCHES Since the total new PGHS will be under 5,000 sf, infiltration trenches will be designed and located along the sides of the driveway and access drive to address the runoff from the pavement. WATER QUALITY FACILITY On-Site Water Quality: Parking & Driveways: Since the total PGHS area is estimated at 3,800 sf, and is well under the 5,000 sf threshold and is exempt from water quality. Drainage Technical Information Report February 9, 2019 19 | P a g e Figure 7: Developed Conditions Drainage Technical Information Report February 9, 2019 20 | P a g e TIR SECTION 5 CONVEYANCE SYSTEM ANALYSIS AND DESIGN PIPE CAPACITY: None Required all storm pipe is existing. TIR SECTION 6 SPECIAL REPORTS AND STUDIES None Required. TIR SECTION 7 OTHER PERMITS Below is the list of anticipated permits required for this project. Other permits may be required that are not mentioned below. Building Permit – New Single Family Residence Right of Way- construction permit Drainage Technical Information Report February 9, 2019 21 | P a g e TIR SECTION 8 CSWPPP ANALYSIS AND DESIGN For the purposes of this report, several standard erosion control procedures will be utilized by the contractor to minimize the amount of erosion and sedimentation perpetuated by the construction of the site. Furthermore, these techniques are proposed for the Construction Stormwater Pollution Prevention Plan (CSWPPP) and should be reviewed and instituted by the onsite contractor. Some of the measures include filter fabric fence, and standard ground cover practices, A construction sequence will also be used to minimize the impacts of erosion due to construction. ESC Plan Analysis and Design (Part A) 1. At just under 12,000 sf the site is small requiring only minimal ESC measures. The 12- Elements of a Construction CSWPPP listed below, discuss and describe the appropriate ESC measure to be used. 2. Due to the small size of the site, no ESC facilities are proposed. Therefore, no analysis of the site’s ESC facilities was required. The proposed BMPs consist of standard items including: filter fences, construction entrance, CB inlet protection and plastic cover, etc. No sediment traps are proposed. 3. The site is fairly flat and the areas of high erosion are minimal and will be controlled by the filter fence around the perimeter of the site. 4. There were no special reports done for the site. 5. No exceptions or modifications are proposed of the “Erosion and Sedimentation Control Standards” ESC Plan Analysis and Design (Part B) A full SWPP Plan and report will be prepared for the site after preliminary approval is received. THE 12 ELEMENTS OF A CONSTRUCTION CSWPPP 1. Preserve Vegetation/Mark Clearing Limits: The clearing limits are indicated on the plan sheet. Furthermore, clearing and grading will be limited to only areas that need to be disturbed for grading/construction of the road surface to preserve as much natural vegetation as possible. Field marking the clearing limits shall be completed prior to clearing and grubbing activities. BMP's: Preserve Natural Vegetation (VEG) Field Marking Clearing Limits (CL) 2. Establish Construction Access: Access to the construction site shall be limited to the rock construction entrance. The construction entrance shall be extended to provide access to the construction vehicle/equipment staging and employee parking areas. BMP's: Stabilized Construction Entrance (CE) 3. Control of Flow Rates: Storm water detention: No detention is proposed for the site since the increase in volume is minimal 4. Installation of Perimeter Sediment Controls: Sediment control will be provided through a combination of filtration through the surround on-site vegetation, filter fence, straw bails, BMP's: Silt Fence (FF) 5. Soils Stabilization: Temporary and permanent soil stabilization will be provided. Temporary stabilization will be provided through the application of straw and/or plastic sheeting to exposed, worked earth. From October 1 until April 30, no exposed soil may remain exposed and unworked for more than two days; after May 1, no exposed soil may remain exposed and unworked for more than seven days. Drainage Technical Information Report February 9, 2019 22 | P a g e BMP's: Plastic Sheeting, 6. Slope Protection: Slopes shall be protected from erosion through cover and prevention of concentrated surface runoff flows. BMP's: Plastic Sheeting, 7. Protection of Permanent Drain Inlets and Dust/Mud Control: Inlet protection will be provided for all catch basins. BMP’s: Inlet Protection BMP’s: Street Sweeping and watering of dust areas 8. Stabilization of Channels and Outlets: All channel slopes shall be constructed and protected against erosion in accordance with City of Renton BMP's: None required 9. Pollutant Control: Pollutants shall be controlled as described in the Potential Pollutants section of this SWPPP. 10. Dewatering Control: De-watering: Interception of the water table is not expected to occur, even if there is an increase in precipitation. However, should ground water flows be encountered, the flows can be directed to on site native vegetation for cleanup. BMP's: Native vegetation (As Required) 11. BMP Maintenance: All BMP's and SWPPP elements shall be inspected daily and maintained as required. 12. Project Management: The project shall be managed in a cooperative effort by the project manager, contractor, engineer, and the county inspector. During the construction process, if unforeseen issues arise that cannot be resolved on site, construction activity (other than SWPPP maintenance) shall be halted and the county inspector and the project engineer are to be contacted and informed of the situation. The Erosion Control Lead TBD Since the project is for residential lots, under SCC 30.63 A.530, (2) the project does not fall under the “High Use Sites” covering commercial or industrial sites. BMP C-151: Concrete Handling (Design and Installation Specifications) Concrete truck chutes, pumps, and internals shall be washed out only into formed areas awaiting installation of concrete or asphalt. Unused concrete remaining in the truck and pump shall be returned to the originating batch plant for recycling. Hand tools including, but not limited to, screeds, shovels, rakes, floats, and trowels shall be washed off only into formed areas awaiting installation of concrete or asphalt. Equipment that cannot be easily moved, such as concrete pavers, shall only be washed in areas that do not directly drain to natural or constructed stormwater conveyances. Washdown from areas such as concrete aggregate driveways shall not drain directly to natural or constructed stormwater conveyances. When no formed areas are available, washwater and leftover product shall be contained in a lined container. Contained concrete shall be disposed of in a manner that does not violate groundwater or surface water quality standards Maintenance Standards: Containers shall be checked for holes in the liner daily during concrete pours and repaired the same day Soil Management Plan for “Post Construction Soil Standard” Drainage Technical Information Report February 9, 2019 23 | P a g e The top soils will be stockpile on-site and reused per “Implementation Options #4b “Amend existing soil in place per the Post Construction Soil Standard” which requires “Stockpile existing top soils during grading and replace it prior to planting…” In addition, the soils will be required to be tested for organic compliance. See the following requirements. Drainage Technical Information Report February 9, 2019 24 | P a g e Drainage Technical Information Report February 9, 2019 25 | P a g e Amend Existing Soils, Purpose and Definition Naturally occurring (undisturbed) soil and vegetation provide important stormwater functions including: water infiltration; nutrient, sediment, and pollutant adsorption; sediment and pollutant biofiltration; water interflow storage and transmission; and pollutant decomposition. These functions are largely lost when development strips away native soil and vegetation and replaces it with minimal topsoil and sod. Not only are these important stormwater functions lost, but such landscapes themselves become pollution- generating pervious surfaces due to increased use of pesticides, fertilizers and other landscaping and household/industrial chemicals, the concentration of pet wastes, and pollutants that accompany roadside litter. Establishing soil quality and depth regains greater stormwater functions in the post development landscape, provides increased treatment of pollutants and sediments that result from development and habitation, and minimizes the need for some landscaping chemicals, thus reducing pollution through prevention. Applications and Limitations Establishing a minimum soil quality and depth is not the same as preservation of naturally occurring soil and vegetation. However, establishing a minimum soil quality and depth will provide improved on-site management of stormwater flow and water quality. Soil organic matter can be attained through numerous materials such as compost, composted woody material, biosolids, and forest product residuals. It is important that the materials used to meet the soil quality and depth BMP be appropriate and beneficial to the plant cover to be established. Likewise, it is important that imported topsoils improve soil conditions and do not have an excessive percent of clay fines. Design Guidelines Soil retention. The duff layer and native topsoil should be retained in an undisturbed state to the maximum extent practicable. In any areas requiring grading remove and stockpile the duff layer and topsoil on site in a designated, controlled area, not adjacent to public resources and critical areas, to be reapplied to other portions of the site where feasible. Soil quality. All areas subject to clearing and grading that have not been covered by impervious surface, incorporated into a drainage facility or engineered as structural fill or slope shall, at project completion, demonstrate the following: I. A topsoil layer with a minimum organic matter content of ten percent dry weight in planting beds, and 5% organic matter content (based on a loss-on-ignition test) in turf areas, and a pH from 6.0 to 8.0 or matching the pH of the original undisturbed soil. The topsoil layer shall have a minimum depth of eight inches except where tree roots limit the depth of incorporation of amendments needed to meet the criteria. Subsoils below the topsoil layer should be scarified at least 4 inches with some incorporation of the upper material to avoid stratified layers, where feasible. 2. Planting beds must be mulched with 2 inches of organic material 3. Quality of compost and other materials used to meet the organic content requirements: a. The organic content for -pre-approved” amendment rates can be met only using compost that meets the definition of -composted materials” in WAC I73-350-220. This code is available online at: http://www.ecy.wa.gov/programs/swfa/facilities/350.html. Compost used in bioretention areas should be stable, mature and derived from yard debris, wood waste, or other organic materials that meet the intent of the organic soil amendment specification. Biosolids and manure composts can be higher in bio-available phosphorus than compost derived from yard or plant waste and therefore Drainage Technical Information Report February 9, 2019 26 | P a g e are not allowed in bioretention areas due to the possibility of exporting bio-available phosphorus in effluent. The compost must also have an organic matter content of 35% to 65%, and a carbon to nitrogen ratio below 25:I. The carbon to nitrogen ratio may be as high as 35:I for plantings composed entirely of plants native to the Puget Sound Lowlands region. b. Calculated amendment rates may be met through use of composted materials as defined above; or other organic materials amended to meet the carbon to nitrogen ratio requirements, and meeting the contaminant standards of Grade A Compost. The resulting soil should be conducive to the type of vegetation to be established. Implementation Options: The soil quality design guidelines listed above can be met by using one of the methods listed below. I. Leave undisturbed native vegetation and soil, and protect from compaction during construction. 2.Amend disturbed soil according to the following procedures: b. Scarify subsoil to a depth of one foot c. In planting beds, place three inches of compost and till in to an eight-inch depth. d. In turf areas, place two inches of compost and till in to an eight-inch depth. e. Apply two to four inches of arborist wood chip, coarse bark mulch, or compost mulch to planting beds after final planting. Alternatively, disturbed soil can be amended on a site-customized manner so that it meets the soil quality criteria set forth above, as determined by a licensed engineer, geologist, landscape architect, or other person as approved by City of Renton. 3. Stockpile existing topsoil during grading, and replace it prior to planting. Stockpiled topsoil must be amended if needed to meet the organic matter and depth requirements by following the procedures in method (2) above). 4. Import topsoil mix of sufficient organic content and depth to meet the organic matter and depth requirements. 5. More than one method may be used on different portions of the same site. Soil that already meets the depth and organic matter quality standards, and is not compacted, does not need to be amended. Maintenance Soil quality and depth should be established toward the end of construction and once established, should be protected from compaction, such as from large machinery use, and from erosion. Soil should be planted and mulched after installation. Plant debris or its equivalent should be left on the soil surface to replenish organic matter. Drainage Technical Information Report February 9, 2019 27 | P a g e TIR SECTION 9 BONDS, SUMMARIES AND COVENANTS All the necessary documents listed below will be included in the Full TIR report after preliminary approval is received. These will include:  Bond Quantities,  Flow Control and Water Quality Facility Summary Sheet and Sketch  Declaration of Covenant for Privately Maintained Flow Control and WQ Facilities  Declaration of Covenant for Privately Maintained Flow Control BMPs TIR SECTION 10 OPERATIONS AND MAINTENANCE MANUAL Stormwater System Description The stormwater system for the site is fairly basic and contains the following elements:  On-site Infiltration Trenches  Catch basins The stormwater runoff from the site improvements flows over to catch basins then to the on-site infiltration trenches. Water quality treatment is not a requirement for the site since it is under the 5,000 sf threshold. Drainage Technical Information Report February 9, 2019 28 | P a g e Appendix A  O&M Requirements  WWHM3 Results  South Sound Geotechnical Infiltration Assessment  Engineers Cost Evaluation Package WWHM3 INFILTRATION TRENCH RESULTS WWHM3 INFILTRATION TRENCH RESULTS Western Washington Hydrology Model PROJECT REPORT ___________________________________________________________________ Project Name: SINGH SFD Site Address: City : Report Date : 2/5/2019 Gage : Seatac Data Start : 1948/10/01 Data End : 1998/09/30 Precip Scale: 1.00 WWHM3 Pro Version: ___________________________________________________________________ PREDEVELOPED LAND USE Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use Acres C, Forest, Mod .12 Impervious Land Use Acres ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use Acres Impervious Land Use Acres ROOF TOPS FLAT 0.12 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater Gravel Trench Bed 1, Gravel Trench Bed 1, ___________________________________________________________________ Name : Gravel Trench Bed 1 Bottom Length: 80ft. Bottom Width : 5ft. Trench bottom slope 1: 0.01 To 1 Trench Left side slope 0: 0.01 To 1 Trench right side slope 2: 0.01 To 1 Material thickness of first layer : 2.5 Pour Space of material for first layer : 0.35 Material thickness of second layer : 0 Pour Space of material for second layer : 0 Material thickness of third layer : 0 Pour Space of material for third layer : 0 Infiltration On Infiltration rate : 1.70 Infiltration saftey factor : 1 Wetted surface area On Discharge Structure Riser Height: 2.4 ft. Riser Diameter: 12 in. Element Flows To: Outlet 1 Outlet 2 ___________________________________________________________________ Gravel Trench Bed Hydraulic Table Stage(ft) Area(acr) Volume(acr-ft) Dschrg(cfs) Infilt(cfs) 0.000 0.009 0.000 0.000 0.000 0.028 0.009 0.000 0.000 0.016 0.056 0.009 0.000 0.000 0.016 0.083 0.009 0.000 0.000 0.016 0.111 0.009 0.000 0.000 0.016 0.139 0.009 0.000 0.000 0.016 0.167 0.009 0.001 0.000 0.017 0.194 0.009 0.001 0.000 0.017 0.222 0.009 0.001 0.000 0.017 0.250 0.009 0.001 0.000 0.017 0.278 0.009 0.001 0.000 0.017 0.306 0.009 0.001 0.000 0.018 0.333 0.009 0.001 0.000 0.018 0.361 0.009 0.001 0.000 0.018 0.389 0.009 0.001 0.000 0.018 0.417 0.009 0.001 0.000 0.018 0.444 0.009 0.001 0.000 0.018 0.472 0.009 0.002 0.000 0.019 0.500 0.009 0.002 0.000 0.019 0.528 0.009 0.002 0.000 0.019 0.556 0.009 0.002 0.000 0.019 0.583 0.009 0.002 0.000 0.019 0.611 0.009 0.002 0.000 0.020 0.639 0.009 0.002 0.000 0.020 0.667 0.009 0.002 0.000 0.020 0.694 0.009 0.002 0.000 0.020 0.722 0.009 0.002 0.000 0.020 0.750 0.009 0.002 0.000 0.021 0.778 0.009 0.003 0.000 0.021 0.806 0.009 0.003 0.000 0.021 0.833 0.009 0.003 0.000 0.021 0.861 0.009 0.003 0.000 0.021 0.889 0.009 0.003 0.000 0.021 0.917 0.009 0.003 0.000 0.022 0.944 0.009 0.003 0.000 0.022 0.972 0.009 0.003 0.000 0.022 1.000 0.009 0.003 0.000 0.022 1.028 0.009 0.003 0.000 0.022 1.056 0.009 0.003 0.000 0.023 1.083 0.009 0.003 0.000 0.023 1.111 0.009 0.004 0.000 0.023 1.139 0.009 0.004 0.000 0.023 1.167 0.009 0.004 0.000 0.023 1.194 0.009 0.004 0.000 0.023 1.222 0.009 0.004 0.000 0.024 1.250 0.009 0.004 0.000 0.024 1.278 0.009 0.004 0.000 0.024 1.306 0.009 0.004 0.000 0.024 1.333 0.009 0.004 0.000 0.024 1.361 0.009 0.004 0.000 0.025 1.389 0.009 0.004 0.000 0.025 1.417 0.009 0.005 0.000 0.025 1.444 0.009 0.005 0.000 0.025 1.472 0.009 0.005 0.000 0.025 1.500 0.009 0.005 0.000 0.025 1.528 0.009 0.005 0.000 0.026 1.556 0.009 0.005 0.000 0.026 1.583 0.009 0.005 0.000 0.026 1.611 0.009 0.005 0.000 0.026 1.639 0.009 0.005 0.000 0.026 1.667 0.009 0.005 0.000 0.027 1.694 0.009 0.005 0.000 0.027 1.722 0.009 0.006 0.000 0.027 1.750 0.009 0.006 0.000 0.027 1.778 0.009 0.006 0.000 0.027 1.806 0.009 0.006 0.000 0.027 1.833 0.009 0.006 0.000 0.028 1.861 0.009 0.006 0.000 0.028 1.889 0.009 0.006 0.000 0.028 1.917 0.009 0.006 0.000 0.028 1.944 0.009 0.006 0.000 0.028 1.972 0.009 0.006 0.000 0.029 2.000 0.009 0.006 0.000 0.029 2.028 0.009 0.007 0.000 0.029 2.056 0.009 0.007 0.000 0.029 2.083 0.009 0.007 0.000 0.029 2.111 0.009 0.007 0.000 0.030 2.139 0.009 0.007 0.000 0.030 2.167 0.009 0.007 0.000 0.030 2.194 0.009 0.007 0.000 0.030 2.222 0.009 0.007 0.000 0.030 2.250 0.009 0.007 0.000 0.030 2.278 0.009 0.007 0.000 0.031 2.306 0.009 0.007 0.000 0.031 2.333 0.009 0.008 0.000 0.031 2.361 0.009 0.008 0.000 0.031 2.389 0.009 0.008 0.000 0.031 2.417 0.009 0.008 0.021 0.032 2.444 0.009 0.008 0.091 0.032 2.472 0.009 0.008 0.189 0.032 2.500 0.009 0.008 0.308 0.032 ___________________________________________________________________ MITIGATED LAND USE ___________________________________________________________________ ANALYSIS RESULTS Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.003069 5 year 0.004786 10 year 0.005721 25 year 0.006673 50 year 0.00724 100 year 0.007705 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0 5 year 0 10 year 0 25 year 0 50 year 0 100 year 0 ___________________________________________________________________ Yearly Peaks for Predeveloped and Mitigated. POC #1 Year Predeveloped Mitigated 1950 0.004 0.000 1951 0.007 0.000 1952 0.008 0.000 1953 0.002 0.000 1954 0.002 0.000 1955 0.003 0.000 1956 0.005 0.000 1957 0.004 0.000 1958 0.003 0.000 1959 0.003 0.000 1960 0.003 0.000 1961 0.005 0.000 1962 0.003 0.000 1963 0.002 0.000 1964 0.002 0.000 1965 0.003 0.000 1966 0.002 0.000 1967 0.002 0.000 1968 0.005 0.000 1969 0.003 0.000 1970 0.003 0.000 1971 0.002 0.000 1972 0.002 0.000 1973 0.006 0.000 1974 0.002 0.000 1975 0.003 0.000 1976 0.004 0.000 1977 0.002 0.000 1978 0.000 0.000 1979 0.002 0.000 1980 0.001 0.000 1981 0.004 0.000 1982 0.002 0.000 1983 0.004 0.000 1984 0.003 0.000 1985 0.002 0.000 1986 0.001 0.000 1987 0.006 0.000 1988 0.005 0.000 1989 0.002 0.000 1990 0.001 0.000 1991 0.008 0.002 1992 0.007 0.000 1993 0.002 0.000 1994 0.003 0.000 1995 0.001 0.000 1996 0.004 0.000 1997 0.007 0.000 1998 0.007 0.000 1999 0.001 0.000 ___________________________________________________________________ Ranked Yearly Peaks for Predeveloped and Mitigated. POC #1 Rank Predeveloped Mitigated 1 0.0080 0.0018 2 0.0076 0.0000 3 0.0072 0.0000 4 0.0070 0.0000 5 0.0069 0.0000 6 0.0066 0.0000 7 0.0058 0.0000 8 0.0056 0.0000 9 0.0049 0.0000 10 0.0047 0.0000 11 0.0047 0.0000 12 0.0046 0.0000 13 0.0040 0.0000 14 0.0040 0.0000 15 0.0037 0.0000 16 0.0037 0.0000 17 0.0037 0.0000 18 0.0036 0.0000 19 0.0033 0.0000 20 0.0033 0.0000 21 0.0030 0.0000 22 0.0028 0.0000 23 0.0027 0.0000 24 0.0027 0.0000 25 0.0027 0.0000 26 0.0027 0.0000 27 0.0026 0.0000 28 0.0026 0.0000 29 0.0026 0.0000 30 0.0025 0.0000 31 0.0025 0.0000 32 0.0023 0.0000 33 0.0023 0.0000 34 0.0022 0.0000 35 0.0022 0.0000 36 0.0022 0.0000 37 0.0021 0.0000 38 0.0021 0.0000 39 0.0020 0.0000 40 0.0020 0.0000 41 0.0019 0.0000 42 0.0018 0.0000 43 0.0018 0.0000 44 0.0016 0.0000 45 0.0013 0.0000 46 0.0013 0.0000 47 0.0012 0.0000 48 0.0011 0.0000 49 0.0006 0.0000 50 0.0002 0.0000 ___________________________________________________________________ POC #1 The Facility PASSED The Facility PASSED. Flow(CFS) Predev Dev Percentage Pass/Fail 0.0015 3775 2 0 Pass 0.0016 3490 2 0 Pass 0.0016 3244 2 0 Pass 0.0017 3037 2 0 Pass 0.0018 2831 2 0 Pass 0.0018 2633 0 0 Pass 0.0019 2452 0 0 Pass 0.0019 2276 0 0 Pass 0.0020 2129 0 0 Pass 0.0021 1998 0 0 Pass 0.0021 1885 0 0 Pass 0.0022 1771 0 0 Pass 0.0022 1678 0 0 Pass 0.0023 1584 0 0 Pass 0.0023 1490 0 0 Pass 0.0024 1398 0 0 Pass 0.0025 1318 0 0 Pass 0.0025 1238 0 0 Pass 0.0026 1187 0 0 Pass 0.0026 1114 0 0 Pass 0.0027 1055 0 0 Pass 0.0027 1004 0 0 Pass 0.0028 954 0 0 Pass 0.0029 902 0 0 Pass 0.0029 861 0 0 Pass 0.0030 818 0 0 Pass 0.0030 775 0 0 Pass 0.0031 738 0 0 Pass 0.0031 710 0 0 Pass 0.0032 669 0 0 Pass 0.0033 643 0 0 Pass 0.0033 616 0 0 Pass 0.0034 586 0 0 Pass 0.0034 566 0 0 Pass 0.0035 533 0 0 Pass 0.0036 508 0 0 Pass 0.0036 474 0 0 Pass 0.0037 452 0 0 Pass 0.0037 432 0 0 Pass 0.0038 417 0 0 Pass 0.0038 391 0 0 Pass 0.0039 371 0 0 Pass 0.0040 353 0 0 Pass 0.0040 340 0 0 Pass 0.0041 322 0 0 Pass 0.0041 305 0 0 Pass 0.0042 282 0 0 Pass 0.0042 273 0 0 Pass 0.0043 260 0 0 Pass 0.0044 245 0 0 Pass 0.0044 232 0 0 Pass 0.0045 222 0 0 Pass 0.0045 211 0 0 Pass 0.0046 206 0 0 Pass 0.0046 197 0 0 Pass 0.0047 189 0 0 Pass 0.0048 182 0 0 Pass 0.0048 174 0 0 Pass 0.0049 167 0 0 Pass 0.0049 159 0 0 Pass 0.0050 155 0 0 Pass 0.0051 151 0 0 Pass 0.0051 145 0 0 Pass 0.0052 143 0 0 Pass 0.0052 135 0 0 Pass 0.0053 127 0 0 Pass 0.0053 120 0 0 Pass 0.0054 113 0 0 Pass 0.0055 109 0 0 Pass 0.0055 107 0 0 Pass 0.0056 96 0 0 Pass 0.0056 89 0 0 Pass 0.0057 83 0 0 Pass 0.0057 75 0 0 Pass 0.0058 72 0 0 Pass 0.0059 63 0 0 Pass 0.0059 61 0 0 Pass 0.0060 58 0 0 Pass 0.0060 52 0 0 Pass 0.0061 49 0 0 Pass 0.0061 47 0 0 Pass 0.0062 43 0 0 Pass 0.0063 39 0 0 Pass 0.0063 34 0 0 Pass 0.0064 31 0 0 Pass 0.0064 29 0 0 Pass 0.0065 26 0 0 Pass 0.0065 25 0 0 Pass 0.0066 23 0 0 Pass 0.0067 21 0 0 Pass 0.0067 21 0 0 Pass 0.0068 20 0 0 Pass 0.0068 18 0 0 Pass 0.0069 17 0 0 Pass 0.0070 14 0 0 Pass 0.0070 13 0 0 Pass 0.0071 12 0 0 Pass 0.0071 9 0 0 Pass 0.0072 7 0 0 Pass 0.0072 7 0 0 Pass _____________________________________________________ ___________________________________________________________________ Water Quality BMP Flow and Volume for POC 1. On-line facility volume: 0 acre-feet On-line facility target flow: 0 cfs. Adjusted for 15 min: 0 cfs. Off-line facility target flow: 0 cfs. Adjusted for 15 min: 0 cfs. ___________________________________________________________________ Perlnd and Implnd Changes No changes have been made. ___________________________________________________________________ This program and accompanying documentation is provided 'as-is' without warranty of any kind. The entire risk regarding the performance and results of this program is assumed by the user. Clear Creek Solutions and the Washington State Department of Ecology disclaims all warranties, either expressed or implied, including but not limited to implied warranties of program and accompanying documentation. In no event shall Clear Creek Solutions and/or the Washington State Department of Ecology be liable for any damages whatsoever (including without limitation to damages for loss of business profits, loss of business information, business interruption, and the like) arising out of the use of, or inability to use this program even if Clear Creek Solutions or the Washington State Department of Ecology has been advised of the possibility of such damages. South Sound Geotechnical Infiltration Assessment South Sound Geotechnical Consulting November 10, 2018 Mr. Ralraj Mahal 15816 – 147th Court SE Renton, WA 98058 Subject: Geotechnical Engineering Report – Infiltration Assessment 13436 – 156th Avenue SE Short Plat Renton, Washington SSGC Project No. 18090 Mr. Mahal, South Sound Geotechnical Consulting (SSGC) has completed a geotechnical assessment for the planned residential development on above addressed property in Renton, Washington. Our scope of services included completion of one test pit and two infiltration tests on the site, laboratory testing, engineering analyses, and preparation of this report. PROJECT INFORMATION Development plans include subdividing the existing parcel into two separate lots. An existing single- family residence on the property will be removed. Access to the lots will be from a private driveway off of 156th Avenue SE. SITE CONDITIONS The property is located on level to gently westerly sloping ground. The existing residence and separate shop building are in the southern portion of the two planned lots, surrounded by landscaped lawn. SUBSURFACE CONDITIONS Subsurface conditions were characterized by completing one test pit and two infiltration tests on the site on October 22, 2018. Explorations were advanced to final depths between about 2 and 5.5 feet below existing ground surface. Approximate locations of the explorations are shown on Figure 1, Exploration Plan. Logs of subsurface conditions are provided in Appendix A. A summary description of observed subgrade conditions is provided below. Soil Conditions A thin sod layer was observed over native loose silty fine sand with some roots. This surface soil extended to a depth of about 3 feet and is considered alluvium and/or weathered glacial till. Below this upper soil was silty sand with gravel in a medium dense to dense condition, extending to the termination depth of the test pit. This soil is interpreted to be glacial till. Geotechnical Engineering Report SSGC 13436 – 156th Ave. SE Renton, Washington SSGC Project No. 18090 November 10, 2018 2 Groundwater Conditions Groundwater was not observed in the excavations at the time of digging. However, slight mottling was observed near the base of the upper weathered zone in test pit TP-1. The denser glacial till will limit vertical flow of groundwater and can cause perched groundwater conditions during the wetter seasons of the year. Groundwater levels will fluctuate due to seasonal precipitation variations and on- and off-site drainage patterns. Geologic Setting Soils on the property are mapped as glacial till per the Washington State Department of Natural Resources (DNR) geology map of the area. Soils observed in the excavations appear to confirm the mapped soil type. Infiltration Characteristics Infiltration characteristics of upper soils were assessed in general conformance with 2014 DOE Stormwater Management Manual for Western Washington procedures. Two small-scale Pilot Infiltration Tests (PIT) were completed in the upper native soils with approximate location shown on Figure 1. Field and corrected infiltration rates are provided in Table 1. Table 1. Infiltration Rates Test Site and Depth Soil Type Field Infiltration Rate (in/hr) Corrected Infiltration Rate (in/hr) Correction Factors* (CFt/CFv/CFm) PIT-1, 2 ft Silty Sand 4.0 1.1 (0.5/0.7/0.8) PIT-2, 2 ft Silty Sand 6.0 1.7 (0.5/0.7/0.8) *Correction Factors from the 2016 King County Surface Water Design Manual. The field and corrected infiltration rates are considered appropriate for the upper soil tested. However, due to the presence of dense glacial till at fairly shallow depth, these rates are considered representative of mostly horizontal flow through the upper looser soil towards the west. Shallow dispersion systems will be required on this site to facilitate stormwater control. An average design rate of 1.4 inches per hour (in/hr) would be recommended for design of infiltration facilities located in the upper several feet of soils on the site. Other correction factors per the stormwater manual should be applied to the above recommended long-term rate, as required for the type of infiltration system selected. Cation Exchange Capacity (CEC) and organic content tests were completed on a soil samples from the bottom of the infiltration test holes. Test results are summarized in the table below. Geotechnical Engineering Report SSGC 13436 – 156th Ave. SE Renton, Washington SSGC Project No. 18090 November 10, 2018 3 Table 2. CEC and Organic Content Results Test Location, Sample Number CEC Results (milliequivalents) CEC Required* (milliequivalents) Organic Content Results (%) Organic Content Required* (%) PIT-1, S-1 14.2 ≥ 5 5.4 ≥1.0 PIT-1, S-2 11.8 ≥ 5 4.1 ≥1.0 * Per the 2014 DOE Stormwater Management Manual for Western Washington. CEC and organic content results satisfy DOE requirements at the PIT sites. REPORT CONDITIONS This report has been prepared for the exclusive use of Mr. Ralraj Mahal for specific application to the project discussed, and has been prepared in accordance with generally accepted geotechnical engineering practices in the area. No warranties, either express or implied, are intended or made. The analysis and recommendations presented in this report are based on observed soil conditions and test results at the indicated locations, and from other geologic information discussed. This report does not reflect variations that may occur across the site, or due to the modifying effects of construction or weather. The nature and extent of such variations may not become evident until during or after construction. If variations appear, we should be immediately notified so that further evaluation and supplemental recommendations can be provided. This report was prepared for the planned type of development of the site as discussed herein. It is not valid for third party entities or alternate types of development on the site without the express written consent of SSGC. If development plans change we should be notified to review those changes and modify our recommendations as necessary. The scope of services for this project does not include any environmental or biological assessment of the site including identification or prevention of pollutants, hazardous materials, or conditions. Other studies should be completed if the owner is concerned about the potential for contamination or pollution. N South Sound Geotechnical Consulting P.O. Box 39500 Lakewood, WA 98496 (253) 973-0515 Figure 1 – Exploration Plan 13436 - 156th Avenue SE Renton, WA SSGC Project #18090 Approximate Test Pit Location PIT - 1 TP - 1 PIT - 1 Approximate Infiltration Test Location Scale: NTS Base map from Google Maps PIT-1 TP-1 TP-1 Legend PIT-2 TP-1 Geotechnical Engineering Report SSGC 13436 – 156th Ave. SE Renton, Washington SSGC Project No. 18090 November 10, 2018 A-1 Appendix A Field Exploration Procedures and Test Pit Logs Geotechnical Engineering Report SSGC 13436 – 156th Ave. SE Renton, Washington SSGC Project No. 18090 November 10, 2018 Field Exploration Procedures8 Our field exploration for this project included one test pit and two pilot infiltration tests completed on October 22, 2018. The approximate locations of the explorations are shown on Figure 1, Exploration Plan. The exploration locations were determined by pacing from site features. Ground surface elevations referenced on the logs were inferred from Google Earth Imagery. Exploration locations and elevations should be considered accurate only to the degree implied by the means and methods used. A client provided excavator dug the explorations. Soil samples were collected and stored in moisture tight containers for further assessment and laboratory testing. Explorations were backfilled with excavated soils and tamped when completed. Please note that backfill in the explorations will likely settle with time. Backfill material located in building and pavement areas should be re-excavated and recompacted, or replaced with structural fill. The following logs indicate the observed lithology of soils and other materials observed in the explorations at the time of excavation. Where a soil contact was observed to be gradational, our log indicates the average contact depth. Our logs also indicate the approximate depth to groundwater (where observed at the time of excavation), along with sample numbers and approximate sample depths. Soil descriptions on the logs are based on the Unified Soil Classification System. Project: 13436 - 156th Avenue SE SSGC Job # 18090 EXPLORATION LOGS PAGE 1 OF 2 Location: Renton, WA EXPLORATION LOGS FIGURE A-1 South Sound Geotechnical Consulting TP-1, PIT-1 and PIT-2 Logged by: THR Test Pit TP-1 Depth (feet) Material Description 0 – 0.5 0.5 – 3 3 – 5.5 Sod over silty fine SAND with roots (SM): Loose, dry, brown. Silty SAND with gravel (SM): Loose to medium dense, damp, light brown with slight orange mottling. (Alluvium/Weathered Glacial Till) Silty SAND with gravel (SM): Dense, moist, grayish brown. (Glacial Till) Test pit completed at approximately 5.5 feet on 10/22/18. Groundwater not observed at time of excavation. Approximate surface elevation: 446 feet Pilot Infiltration Test PIT-1 Depth (feet) Material Description 0 – 0.5 0.5 – 2 Sod over silty fine SAND with roots (SM): Loose, dry, brown. Silty SAND with gravel: Loose to medium dense, damp, light brown. (Alluvium/Weathered Glacial Till)(Sample S-1 @ 2 feet) Test completed at approximately 2 feet on 10/22/18. Groundwater not observed at time of excavation. Approximate surface elevation: 447 feet Pilot Infiltration Test PIT-2 Depth (feet) Material Description 0 – 0.5 0.5 – 3 Sod over silty fine SAND with roots (SM): Loose, dry, brown. Silty SAND with gravel: Loose to medium dense, damp, light brown (SM). (Alluvium/Weathered Glacial Till)(Sample S-1 @ 3 feet) Test completed at approximately 3 feet on 10/22/18. Groundwater not observed at time of excavation. Approximate surface elevation: 443 feet Geotechnical Engineering Report SSGC 5411 – 132nd Avenue East Edgewood, Washington SSGC Project No. 18059 July 18, 2018 B-1 Appendix B Laboratory Testing and Results Geotechnical Engineering Report SSGC 13436 – 156th Ave. SE Renton, Washington SSGC Project No. 18090 November 10, 2018 B-1 Laboratory Testing Select soil samples were tested for organic content and cation exchange capacity (CEC) by Northwest Agricultural Consultants of Kennewick, Washington. Results of the laboratory testing are included in this appendix. 2545 W Falls Avenue Kennewick, WA 99336 509.783.7450 www.nwag.com lab@nwag.com Sample ID Organic Matter Cation Exchange Capacity PIT-1, S-1 5.38% 14.2 meq/100g PIT-2, S-1 4.13% 11.8 meq/100g Method ASTM D2974 EPA 9081 South Sound Geotechnical Consulting PO Box 39500 Lakewood, WA 98496 Report: 46725-1 Date: November 8, 2018 Project No: 18090 Project Name: Mahal - 156th Ave SE UNIFIED SOIL CLASSIFICATION SYSTEM Criteria for Assigning Group Symbols and Group Names Using Laboratory TestsA Soil Classification Group Symbol Group NameB Coarse Grained Soils More than 50% retained on No. 200 sieve Gravels More than 50% of coarse fraction retained on No. 4 sieve Clean Gravels Less than 5% finesC Cu  4 and 1  Cc  3E GW Well-graded gravelF Cu  4 and/or 1  Cc  3E GP Poorly graded gravelF Gravels with Fines More than 12% finesC Fines classify as ML or MH GM Silty gravelF,G, H Fines classify as CL or CH GC Clayey gravelF,G,H Sands 50% or more of coarse fraction passes No. 4 sieve Clean Sands Less than 5% finesD Cu  6 and 1  Cc  3E SW Well-graded sandI Cu  6 and/or 1  Cc  3E SP Poorly graded sandI Sands with Fines More than 12% finesD Fines classify as ML or MH SM Silty sandG,H,I Fines Classify as CL or CH SC Clayey sandG,H,I Fine-Grained Soils 50% or more passes the No. 200 sieve Silts and Clays Liquid limit less than 50 inorganic PI  7 and plots on or above “A” lineJ CL Lean clayK,L,M PI  4 or plots below “A” lineJ ML SiltK,L,M organic Liquid limit - oven dried  0.75 OL Organic clayK,L,M,N Liquid limit - not dried Organic siltK,L,M,O Silts and Clays Liquid limit 50 or more inorganic PI plots on or above “A” line CH Fat clayK,L,M PI plots below “A” line MH Elastic SiltK,L,M organic Liquid limit - oven dried  0.75 OH Organic clayK,L,M,P Liquid limit - not dried Organic siltK,L,M,Q Highly organic soils Primarily organic matter, dark in color, and organic odor PT Peat A Based on the material passing the 3-in. (75-mm) sieve B If field sample contained cobbles or boulders, or both, add “with cobbles or boulders, or both” to group name. C Gravels with 5 to 12% fines require dual symbols: GW-GM well-graded gravel with silt, GW-GC well-graded gravel with clay, GP-GM poorly graded gravel with silt, GP-GC poorly graded gravel with clay. D Sands with 5 to 12% fines require dual symbols: SW-SM well-graded sand with silt, SW-SC well-graded sand with clay, SP-SM poorly graded sand with silt, SP-SC poorly graded sand with clay E Cu = D60/D10 Cc = 6010 230 DxD )(D F If soil contains  15% sand, add “with sand” to group name. G If fines classify as CL-ML, use dual symbol GC-GM, or SC-SM. HIf fines are organic, add “with organic fines” to group name. I If soil contains  15% gravel, add “with gravel” to group name. J If Atterberg limits plot in shaded area, soil is a CL-ML, silty clay. K If soil contains 15 to 29% plus No. 200, add “with sand” or “with gravel,” whichever is predominant. L If soil contains  30% plus No. 200 predominantly sand, add “sandy” to group name. M If soil contains  30% plus No. 200, predominantly gravel, add “gravelly” to group name. N PI  4 and plots on or above “A” line. O PI  4 or plots below “A” line. P PI plots on or above “A” line. Q PI plots below “A” line.