HomeMy WebLinkAboutEX06_Drainage and TIRDeccio 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
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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
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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
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Figure 1: TIR Worksheet
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Figure 1: TIR Worksheet
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Figure 1: TIR Worksheet
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Figure 1: TIR Worksheet
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Figure 1: TIR Worksheet
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Figure 2: Site Location Map
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Figure 3: Drainage Basins, Sub-basins and Site Characteristics
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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.
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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.
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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 cu rbs, 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.
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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.
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Figure 5: Upstream Area and Downstream Flow Map
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Figure 6: Downstream System Table
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5
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Drainage Complaints
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Sensitives Areas
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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.
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Figure 7: Developed Conditions
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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
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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 pla stic 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.
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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 precipit ation. 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”
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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.
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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
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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.
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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.
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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
2
30
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.