Soils and Stormwater Control
677 Woodland Square Lp SE
Lacey, WA 98503
P.O. Box 3485
Lacey, WA 98509-3485
(360) 493-6002
(888) 493-6002 Toll Free
(360) 493-2476 Fax
December 18,1997
Ken Garmann
Public Works Director
105 Yelm Avenue West
Yelm, WA 98597
RE. Yelm Center; Senior Assisted Living and Children's Daycare Facility
SCA #97110
Dear Ken.
The following is a brief description of our initial soils and stormwater control analysis for the Yelm
Center Project. We have elected to usethe Thurston County Drainage Design and Erosion
Control Manual (DDECM) to size the onsite stormwater treatment and storage facilities
Infiltration Rates/Soils
The Soil Conservation Service (SCS) soil survey of lhurston County classifies the on-site soils
as Spanaway very gravelly sandy loam SCA's analysis of three on-site soil test pits confirmed
the SCS Classification. A copy of SCA's soil logs are included in Appendix "B"
Spanaway soils are very deep, excessively drained soils formed in glacial outwash Spanaway
soils are well suited,for stormwater infiltration systems due to their rapid permeability However,
care needs to be taken to remove silt and sediment from storm water to minimize cloggihg of
infiltration systems
Double Ring Infiltrometer Tests were performed in test hole's #1 and #3 to determine the project
site infiltration rate An average infiltration rate of 960 inches/hour was recorded by SCA staff
However, the DDECM maximum allowed infiltration rate of 20 inches/hour must be used for
design. A copy of SCA's infiltration test results is included in Appendix "B"
Stormwater Control
The proposal is to develop the 5 acre site for a Senior Assisted Living and Children's Daycare
Facility Access to the facility will be from two locations off Burnett Road Water and sewer
service will be provided by the City of Yelm
The completed project will create approximately 0 88 acres of new on-site impervious, roadway
and parking area, 2.97 acres of disturbed pervious area, and 0 95 acres of roof area.
Approximately 0.20 acres of off-site impervious road,way area are tributary to the project.
C I V I L
TRANSPORTATION
PLANNING
SURVEYING
Ken Garmann
December 18, 1997
Page 2
On-site Development Coverage Summary
Existing
Proposed
Off-site Impervious Roadway Area
Impervious Roof Area
Impervious Roadway Area
Disturbed Pervious Area
TOTAL.
o 07 ac
o 00 ac
o 00 ac
4.83 ac
5 '00 ac
0.20 ac
o 95 ac
o 88 ac
2.97 ac
5 00 ac
A. Stormwater Treatment:
Stormwater runoff from Burnett Road and the new on,..site parking lot and roadway areas
will require treatment. To determine the treatment requirements for the on and off-site
impervious roadway surfaces, the'roqdway surfac~s were divided into three separate
basins. These basins are sho\l\fn on the preliminary drainage and grading plan in
Appendix "C" Stormwater runoff from the north basin sheet ijows along a raised
asphalt curb and is collected by a Type 1 catch basin for discharge into the proposed
wetpond of the northwest corner of the property The south basin will collect stormwater
runoff from the south entrance road and the small portion of the off-site tributary area
-along Burnett Road Runoff will discharged into the proposed wetpond in the southwest
corner of the property The third basin consists of the main parking area in front of the
proposed facility, stormwater will sheet flow east to west and thence onto a 10-foot by
200-foot biofiltration filter strip All treatment facilities discharge into the dual stormwater
infiltration pond configuration as shown on the map in Appendix "D"
Stormwater runoff from proposed building roofs does not require treatment prior to
discharge into the groundwater Therefore, all roof stormwater will be tightlined directly
to the site's infiltration facility
B. Stormwater Storage:
Stormwater runoff will be stored and infiltrated on-site via infiltration pond The dual
pond configuration has a capacity to store 10,270 cubic feet of stormwater which
\
exceeds the minimum required storage volume of 9,060 cubic feet. In addition, -we have
modeled the storm pond using Waterworks modeling software The required storage
,
C I V I L
T RAN ,S P 0 R TAT ION
PLANNING
SURVEYING
-
~lii:;
ENGINEERING
Ken Garmann
December 18, 1997
Page 3_
per our Waterworks modeling was 6,397 cubic feet which results in a peak water
surface elevation of 298.4 feet. Our modeling utilizes a 20 inches/hour infiltration rate
applied to only the bottom area (297 contour) off the ponds A copy of the Waterworks
modeling output is included in Appendix "A"
f
If you have any questions during your review of the preliminary drainage and grading
plan, call me at 493-6002,
Sincerely,
SeA Engineering
~d &/%'
RWB/sw
(f.\text\corres\deq-97\7110d17.1tr)
Robert W Balmelli, P E.
Project Manager
C I V I L
TRANSPORTATION
PLANNING
SURVEYING
11II
~11f!;
ENGINEERING
DRAINAGE CALCULATIONS
The following calculations are based on requirements contained in the Drainage Design and Erosion
Control Manual (DDECM) for Thurston County, 1994 Edition.
DESIGN AND BASIN INFORMATION SUMMARY
Site Area (Developed Condition)
Total off-site impervious area.
Total impervious roadway area.
Total impervious roof area.
Total disturbed pervious area.
TOTAL SITE AREA.
Soil Classification
SCS soil classification.
Hydrologic Group
Site infiltration rate (design):
Site infiltration rate (field tests)"
Rainfall Design Storms:
6 month storm - 2/3 x 2 yr storm
2 yr./24 hr storm
10 yr./24 hr storm
100 yr./24 hr storm
Curve Number"
Lawns/Landscape
Paved surface
CN = 85
CN = 98
Minimum Storage Requirements:
0.20 ac
o 88 ac
o 95 ac
2.97 ac
5 00 ac
Spanaway gravelly sandy loam
B
20 inches/hour
960 inches/hour
= 1.33"
= 2.00"
=3.00"
=400"
Reference
Table 4 1 DDECM - 20 incheslhour
Minimum storage volume (disturbed pervious):
1,000 cflac disturbed pervious
Minimum storage volume (impervious)
3,000 cf/ac impervious
SUB-BASIN CALCULA liONS
Treatment Facility Design Calculations.
North Road impervious area.
South Road impervious area.
Main parking impervious area.
TOTAL.
o 47 ac
o 15 ac
0.26 ac
0.88 ac
Filter Strip Design
DDECM
2,000 S F./ac x 0 88 ac = 1,760 S F (required treatment area)
use 200 ft. wide by 10ft. long filter strip
200 ft. x 10 ft. = 2,000 SF> 1,760 S F OK
Wetpond - North Design.
DDECM
0025 x 0 47 ac x 43,560 S F./ac = 511 SF (bottom area)
proposed bottom area = 515 S.F > 511 SF OK
Wetpond - South Design
DDECM
0.25 x 0 15 ac x 43,560 S F./ac = 163 S F (bottom area)
proposed bottom area = 212 SF> 163 S F OK
Stormwater Storage Volume Required
Two Double Ring Infiltrometer Tests were performed on-site. The average infiltration rate was 960
incheslhour Therefore, a maximum design infiltration rate of 20 inches/hour must be used to determine
the storage volume requirements.
From Table 4 1 and 20 incheslhour, the minimum storage volume required per acre of'
Disturbed pervious surface = 1,000 cf/ac
Impervious roadway surface = 3,000 cf/ac
Total disturbed pervious area = 2.97 ac
Total impervious area = 0.20 ac (off-site) + 0 95 ac (roof) + 0.88 ac (on-site) = 2.03 ac
Required storage volume
2.97 ac (1,000 cf/ac) + 2.03 ac(3,000 cf/ac) = 9,060 cf
Dual Pond Stage Storage Table
Description
Elevation
Storage
Pond Bottom
297 ft,
298 ft.
298 4 ft.
299 ft.
300 ft.
o cf
3,694 cf
6,397 cf
10,270 cf
*Design storm
Max. W S Elevation
l' Freeboard
*Using "Waterworks" modeling software (100 year storm)
6,397 cf (model) < 9,060 cf (DDECM) OK
9,060 cf (DDECM) < 10,270 cf (pond storage) OK
Appendix A
Waterworks Output
12/18/97 11:22:4 am S Chamberlain & Assoc. Inc.
YELM CENTER: SENIOR LIVING CENTER
WETPOND SIZING - 6 MONTH STORM
NORTH AND SOUTH AREA WETPONDS
page
1
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BASIN ID: N_wtpond
SCS METHODOLOGY
TOTAL AREA.......:
RAINFALL TyPE....:
PRECIPITATION....:
TIME INTERVAL....:
BASIN SUMMARY
NAME: Q6 MONTH STORM ANALYSIS
0.44 Acres BASEFLOWS: 0.00 cfs
TYPE1A PERV
1.28 inches AREA. . : 0.00 Acres
15.00 min eN . . . . : 0.00
TC. . . . : 0.00 min
ABSTRACTION COEFF: 0.20
PEAK RATE: 0.11 cfs VOL:
BASIN ID: S_wtpond
SCS METHODOLOGY
TOTAL AREA.......:
RAINFALL TyPE....:
PRECIPITATION....:
TIME INTERVAL....:
0.04 Ac-ft TIME:
495 min
NAME: Q6 MONTH STORM ANALYSIS
0.13 Acres
TYPE1A
1.28 inches
15.00 min
BASEFLOWS: 0.00 cfs
PERV
AREA..: 0.00 Acres
CN....: 0.00
TC....: 0.00 min
ABSTRACTION COEFF: 0.20
PEAK RATE: 0.03 cfs VOL:
0.01 Ac-ft TIME:
495 min
IMP
0.44 Acres
98.00
5.00 min
IMP
0.13 Acres
98.00
5.00 min
12/18/97 11:22:52 am
YELM
STORM POND ANALYSIS
Q100 YR STORM EVENT
S Chamberlain & Assoc. Inc.
CENTER: SENIOR LIVING CENTER
page
1
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BASIN ID: N_wtpond
SCS METHODOLOGY
TOTAL AREA.......:
RAINFALL TyPE....:
PRECIPITATION....:
TIME INTERVAL....:
BASIN SUMMARY
NAME: Q6 MONTH STORM ANALYSIS
0.44 Acres BASEFLOWS: 0.00 cfs
TYPE1A PERV
1. 28 inches AREA. . : 0.00 Acres
15.00 min eN....: 0.00
TC. . . . : 0.00 min
ABSTRACTION COEFF: 0.20
PEAK RATE: 0.11 cfs VOL:
BASIN ID: S_wtpond
SCS METHODOLOGY
TOTAL AREA.......:
RAINFALL TyPE....:
PRECIPITATION....:
TIME INTERVAL....:
0.04 Ac-ft TIME:
495 min
NAME: Q6 MONTH STORM ANALYSIS
0.13 Acres BASEFLOWS: 0.00 cfs
TYPE1A PERV
1.28 inches AREA. . : 0.00 Acres
15.00 min CN .. .. : 0.00
TC. . . . : 0.00 min
ABSTRACTION COEFF: 0.20
PEAK RATE: 0.03 cfs VOL:
0.01 Ac-ft TIME:
495 min
IMP
0.44 Acres
98.00
5.00 min
IMP
0.13 Acres
98.00
5.00 min
12/18/97 11:22:52 am
YELM
STORM POND ANALYSIS
Q100 YR STORM EVENT
S Chamberlain & Assoc. Inc.
CENTER: SENIOR LIVING CENTER
page
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STAGE STORAGE TABLE
CUSTOM STORAGE 10 No. ST01
Description: STAGE STORAGE BOTH PONDS
STAGE <----STORAGE----> STAGE <----STORAGE----> STAGE <----STORAGE----> STAGE <----STORAGE---->
(ft) ---cfn- --Ac- Ft- (ft) -ncf--- nAc- Ft- (ft) -ncf--- --Ac- Ft- (ft) -ncfn- nAc- Ft-
--------------------------------------------------------------------------------------------------------
--------------------------------------------------------------------------------------------------------
297.00 0.0000 o 0000 297 60 2216 o 0509 298.20 5009 0.1150 298.80 8955 0.2056
297. 10 369 40 0.0085 297.70 2586 0.0594 298 30 5667 0.1301 298 90 9612 o 2207
297.20 738.80 0.0170 297.80 2955 0.0678 298 40 6324 0.1452 299 00 10270 o 2358
297.30 1108 0.0254 297.90 3325 o 0763 298.50 6982 0.1603
297 40 1478 o 0339 298 00 3694 0.0848 298.60 7640 0.1754
297.50 1847 0.0424 298 10 4352 o 0999 298 70 8297 0 1905
12/18/97 11:22:52 am
YELM
STORM POND ANALYSIS
Q100 YR STORM EVENT
S Chamberlain & Assoc. Inc.
CENTER: SENIOR LIVING CENTER
page
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STAGE DISCHARGE TABLE
DISCHARGE LIST ID No. DIS1
Description: POND DISCHARGE @ 20"/HR
STAGE <--DISCHARGE---> STAGE <--DISCHARGE---> STAGE <--DISCHARGE---> STAGE <--DISCHARGE--->
eft) ---cfs-- ------- eft) ---cfs-- ------- eft) ---cfs-- ------- eft) ---cfs-- -------
--------------------------------------------------------------------------------------------------------
--------------------------------------------------------------------------------------------------------
297.00 1. 1000 297.60 1 1000 298.20 1.1000 298.80 1.1000
297.10 1.1000 297.70 1. 1000 298 30 1.1000 298.90 1. 1000
297.20 1.1000 297.80 1.1000 298.40 1.1000 299 00 1 1000
297.30 1.1000 297.90 1 1000 298.50 1. 1000
297.40 1.1000 298 00 1 1000 298.60 1.1000
297.50 1.1000 298 10 1.1000 298 70 1.1000
12/18/97 11:22:53 am
YELM
STORM POND ANALYSIS
Q100 YR STORM EVENT
S Chamberlain & Assoc. Inc.
CENTER: SENIOR LIVING CENTER
page
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LEVEL POOL TABLE SUMMARY
MATCH INFLOW -STO- -DIS- <-PEAK-> STORAGE
<--------DESCRIPTION---------> (cfs) (cfs) --id- --id- <-STAGE> id VOL (cf)
-----------------------------------------------------------------------------
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Q100 YR STORM
0.00 3.49 ST01 DIS1
298 41 1 6397 05 cf
Appendix B
Soil Logs & Infiltration Test Results
FORM 1 GENERAL SITE INFORMATION
PROJECT TITLE. Yelm Center SHEET 1 OF 1
PROJECT NO 97110 DATE December 16, 1997
PREPARED BY William W Parnell, P E.
1 SITE ADDRESS OR LEGAL DESCRIPTION Burnett Road, Tax Parcel Number 21713402000
2, PROJECT DESCRIPTION' Develop parcel for a convalescent center
3 SITE DESCRIPTION: The project site is currently undeveloped The 5 acre parcel is covered with
Scott's bloom of medium density with a few 12"-18" diameter Fir trees sparesely spaced on the front
one-third of the site Topography is level to gently sloping with relief varying from 0-10% slopes The
site is distinguished by a plateau approximately 200' east of the west property line from which the
terrain slopes to the west, north and east at approximately 6-9% slopes. The eastern one-third of the
site is relatively flat. The extreme north-eastern corner of the site rises at a 10% slope for 60' to the
northeast property corner
4 SUMMARY OF SOILS WORK PERFORMED' Three test pits were excavated by backhoe and
ranged in depth from 108" to 120" below existing grade. Soils were inspected by entering and visually
logging each test hole to a depth of 6 feet. Hole tailings were examined for soils excavated below 6
feet in depth Double ring infiltration tests were completed in test pits #1 and #3 Test results and soil
log data are included in this report.
5 ADDITIONAL SOILS WORK RECOMMENDED' Additional on-site soils work will not be
necessary unless drainage infiltration facilities are located at appreciable distances from those soils
logged in this report,
6 FINDINGS The on-site soils for this site were mapped by the Thurston County Soil Conservation
Service (SCS) as a Spanaway (110), The on-site soils logged in the three test pits confirmed this
designation. Double ring infiltration tests in test pits #1 and #3 revealed infiltration rates greater than 20
inches/hour, at depths of 48"+ below the existing ground
7 RECOMMENDATIONS The Spanaway series soils are very permeable and very suitable for
drainage infiltration facilities. Such facilities should be a minimum of 48" in depth and designed for an
infiltration rate of 20 incheslhour During construction, care must be taken to prevent erosion of the
upper horizon soils that could contaminate the facilities infiltration surface area and adversely affect the
infiltration rate as designed
I hereby certify that I prepared this report, and conducted or supervised the performance of related
work. I certify that I am qualified to do this work. I represent my work to be complete an accurate
within the bounds of uncertainty inherent to the practice of soils science, and to be suitable for its
intended use.
SIGNED'
DATE.
SOIL EVALUATION REPORT
FORM 2: SOIL LOG INFORMATION
PROJECT TITLE Yelm Center SHEET 1 OF 3
PROJECT NO 97110 DATE. December 11, 1997
PREPARED BY William W Parnell, P E.
SOIL LOG. #1
LOCATION See Site Plan
1 TYPES OF TEST DONE. 2. SCS SOILS SERIES 3 LAND FORM:
Double Ring Infiltration Spanaway - 110 Terrace
4 DEPOSITION HISTORY 5 HYDROLOGIC SOIL 6 DEPTH OF SEASONAL HW
GROUp.
Glacial Outwash B Greater than bottom of hole
7 CURRENT WATER DEPTH 8. DEPTH TO IMPERVIOUS 9 MISCELLANEOUS
LAYER:
Greater than bottom of hole Greater than bottom of hole Linear, level
10 POTENTIAL FOR. EROSION RUNOFF PONDING
Slight Slow Minimal
K = 015
11 SOIL STRATA DESCRIPTION See Following chart
12. SITE PERCOLATION RATE Assume 20 inches/hour at a depth of 30" or greater below
existing grade
13 FINDINGS & RECOMMENDATIONS Double ring infiltration test revealed an infiltration
rate equal to 960 inches/hour For design purposes, use 20 inches/hour for all infiltration
facilities with bottoms greater than 30" below existing grade
Soils Strata Description
Soil Log #1
Horz Depth Color Texture %CL %ORG CF STR MOT IND CEM ROO <X> FSP
A 0-20 10 YR 2/1 GRViFiSaLm <5 <10 <15 1SBK CF 2-6 6
Moist
Bw 20-30 10 YR 3/2 SaG Rw/Cobbles <5 <5 <15 1SBK CF 2-6 6
Moist
C, 30-60 2.5Y 5/4 SaG Rw/Cobbles >75 SG. >20 20
Moist
Cz 60-108 2.5Y 5/3 SaGRw/Cobbles >75 SG. >20 20
Moist
SOIL EVALUATION REPORT
FORM 2. SOIL LOG INFORMATION
PROJECT TITLE. Yelm Center SHEET 2 OF 3
PROJECT NO 97110 DATE, December 11, 1997
PREPARED BY William W Parnell, P,E
SOIL LOG. #2
LOCATION See Site Plan
1 TYPES OF TEST DONE. 2 SCS SOILS SERIES 3 LAND FORM.
None Spanaway - 110 Terrace
4 DEPOSITION HISTORY 5 HYDROLOGIC SOIL 6 DEPTH OF SEASONAL HW
GROUP'
Glacial Outwash B Greater than bottom of hole
7 CURRENT WATER DEPTH 8 DEPTH TO IMPERVIOUS 9 MISCELLANEOUS
LAYER:
Greater than bottom of hole Greater than bottom of hole Linear, level
10 POTENTIAL FOR: EROSION RUNOFF PONDING
Slight Slow Minimal
K = 015
11 SOIL STRATA DESCRIPTION See Following chart
12. SITE PERCOLATION RATE Assume 20 inches/hour at a depth of 33" or greater below
existing grade
13 FINDINGS & RECOMMENDATIONS Assume 20 inches/hour for infiltration facilities in
this area
Soils Strata Description
Soil Log #2
Horz Depth Color Texture %CL %ORG CF STR MOT IND CEM ROO <X> FSP
A 0-21 10 YR 2/1 GRViFiSaLm <5 <10 <15 1SBK CF 2-6 6
Moist
Bw 21-33 10 YR 3/2 GRViFiSaLm <5 <5 <15 1SBK CF 2-6 6
Moist
C, 33-48 10YR 5/4 SaGRw/Cobbles >75 SG >20 20
Moist
C2 48-120 2.5Y 5/3 SaGRw/Cobbles >75 SG, >20 20
Moist
SOIL EVALUATION REPORT
FORM 2: SOIL LOG INFORMATION
PROJECT TITLE Yelm Center SHEET 3 OF 3
PROJECT NO 97110 DATE, December 11, 1997
PREPARED BY William W Parnell, P E.
SOIL LOG. #3
LOCATION See Site Plan
1 TYPES OF TEST DONE 2. SCS SOILS SERIES 3 LAND FORM
Double ring infiltration Spanaway - 110 Terrace
4 DEPOSITION HISTORY 5 HYDROLOGIC SOIL 6 DEPTH OF SEASONAL HW
GROUP'
Glacial Outwash B Greater than bottom of hole
7 CURRENT WATER DEPTH 8 DEPTH TO IMPERVIOUS 9 MISCELLANEOUS
LAYER.
Greater than bottom of hole Greater than bottom of hole Linear, level
10 POTENTIAL FOR. EROSION RUNOFF PONDING
Slight Slow Minimal
K = 015
11 SOIL STRATA DESCRIPTION See Following chart
12 SITE PERCOLATION RATE Assume 20 inches/hour at a depth of 43" or greater below
existing grade
13 FINDINGS & RECOMMENDATIONS Double ring infiltration test revealed an infiltration
rate equal to 960 inches/hour For design purposes, use 20 inches/hour for all infiltration
facilities with bottoms greater than 43" below existing grade
Soils Strata Description
Soil Log #3
Horz Depth Color Texture %CL %ORG CF STR MOT IND CEM ROO <X> FSP
A 0-29 10 YR 2/1 GRViFiSaLm <5 <10 <15 1SBK CF 2-6 6
Bw 29-43 10 YR 3/2 GRViFiSaLm <5 <5 <15 1SBK CF 2-6 6
C, 43-70 10YR 5/4 SaGRw/Cobbles >75 SG. >20 20
C2 70-114 2.5Y 5/3 GRw/Si, ViFiSa <5 >75 SG >20 20
Jackets
YELM CENTER
DOUBLE RINGINFILTROMETER TEST
December 12, 1997
SCA#97110
Completed By' Brad Shea
INFILTRATION RESULTS
Test Hole #1 (Depth 58")
Time (seconds) Depth of Water Change in Water Level Stabilized Percolation Rate
(inches) (inches) (inches per hour)
0 4
15 0 4 960
0 4
15 0 4 960
INFILTRATION RESULTS
Test Hole #3 (Depth 70")
Time (seconds) Depth of Water Change in Water Level Stabilized PercolatlOn Rate
(inches) (inches) (inches per hour)
0 4
15 0 4 960
0 5
15 0 4 960
(Abbreviations)
Textural Class Structure Grades of Structure
Gravelly - GR Granular - Gr Strong -3
Sandy - Sa Blocky - Blky Moderate - 2
Loamy -Lm Platy - PI Weak - 1
Silty - Si Massive - Mas
Clayey - CI Single Grained - SG
Coarse -C Sub-Angular Blocky - SBK
Very -V
Fine - F
Medium - M
Mottles
1 Letter Abundance 1st Number Size 2nd Letter Contrast
Few -F Fine - 1 Faint -F
Common -C Medium -2 Distinct -0
Many -M Coarse -3 Prominent -P
Roots
1 st Letter Abundance 2nd Letter Size
Few - f Fine - f
Common -c Medium -m
Many -m Coarse -c
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Appendix C
Preliminary Drainage and Grading Plan