10_Painted_Hills_Phase_I_Preliminary_Geotechnical_Evaluation_Revised_8-29-16
PRELIMINARY GEOTECHNICAL EVALUATION
PHASE I
PAINTED HILLS GOLF COURSE PROPERTY
4403 SOUTH DISHMAN-MICA ROAD
SPOKANE COUNTY, WASHINGTON
Inland Pacific Engineering Company Project No. 2013-026
December 31, 2013
Revised August 29, 2016
Prepared for:
NAI Black
Spokane, Washington
IPEC
Inland Pacific Engineering Company
Geotechnical Engineering and Consulting
Preliminary Geotechnical Evaluation Project No. 2013-026
Painted Hills Golf Course Property December 31, 2013
4403 South Dishman-Mica Road Spokane County, WA
Inland Pacific Engineering Company Page 3
Geologic maps indicate the soils in this area consist primarily of alluvial and/or glacially
deposited silts, clays, sands, and gravels. According to the Soil Survey of Spokane County, the
site soils are classified by the Natural Resource Conservation Service (NRCS) as Hardesty ashy
silt loam, Narcisse silt loam, Endoaquolls and Fluvaquents, Phoebe ashy sandy loam, and Urban
land-Springdale disturbed complex. The native soils encountered in the test pits were consistent
with the NRCS data.
Field Permeability Testing
We performed five test pit permeability tests at the site. The test pit permeability tests were
performed in accordance with the Spokane Regional Stormwater Manual (SRSM) Appendix 4C
procedures. Test pit permeability tests were performed adjacent to Test Pits TP-3, TP-8, TP-19,
TP-22, and TP-28. The following table summarizes the results of the tests performed.
Test Location Depth
(feet)
USCS
Classification Percent Fines Infiltration
Rate (cfs/ft2)
P-1 (TP-3) 1 – 3 SW-SM 10.8 2.84 x 10-4
P-2 (TP-8) 1.5 – 3.5 SM 12.5 8.36 x 10-4
P-3 (TP-19) 1 – 3 GW 3.0 1.21 x 10-3
P-4 (TP-22) 2 – 4 ML 64.0 1.29 x 10-4
P-5 (TP-28) 2 – 4 SM 47.0 6.93 x 10-5
Attached are data sheets summarizing the results of the tests performed. The above results do
not include a safety factor.
ANALYSIS AND PRELIMINARY RECOMMENDATIONS
Discussion
Based on the data obtained from the test pits, field permeability tests, and laboratory tests
performed, it is our opinion that subsurface infiltration of stormwater is feasible. The most
promising layers are the glacial sands and gravels. These soils would be suitable for infiltration
using standard drywells.
In areas where the alluvial soils are deeper, use of gravel galleries could be considered. These soils
are present in the southern portion of the site south and east of Test Pits TP-18, TP-19, and TP-21.
Glacial sands were encountered at depth in Test Pits TP-29 and TP-30 at the south end of the site. It
is our opinion that drywells could be considered at the south end of the site.
Preliminary Geotechnical Evaluation Project No. 2013-026
Painted Hills Golf Course Property December 31, 2013
4403 South Dishman-Mica Road Spokane County, WA
Inland Pacific Engineering Company Page 4
Drywell Recommendations
We analyzed recommended design rates for drywells using the Spokane 200 Method from the
SRSM (Appendix 4A). The following table summarizes the results of the tests performed.
Test
Pit
Depth
(feet)
USCS
Classification
Percent
Fines
Hydraulic
Conductivity
(cm/s)
Recommended Drywell
Outflow Rate (cfs)
Type A Type B
TP-3 10 – 12 SP 3.5 6.1 x 10-2 0.3 1.0
TP-4 10 – 12 GW 4.4 4.1 x 10-2 0.3 0.8
TP-8 10 – 12 GW 3.6 5.9 x 10-2 0.3 1.0
TP-9 8 – 10 GW 2.1 1.7 x 10-1 0.3 1.0
TP-11 10 – 12 SP 2.3 1.5 x 10-1 0.3 1.0
TP-13 10 – 12 SP 2.2 1.6 x 10-1 0.3 1.0
TP-17 10 – 12 SW 2.9 9.0 x 10-2 0.3 1.0
TP-19 10 – 12 SP 1.6 2.5 x 10-1 0.3 1.0
TP-29 10 – 12 SP 2.3 1.5 x 10-1 0.3 1.0
TP-30 14 – 15 SP 4.3 4.3 x 10-2 0.3 0.8
These recommended design infiltration rates include a safety factor of 1.3 as recommended by the
SRSM. Higher design outflow rates may be possible if full-scale drywell tests are performed.
Gravel Gallery Recommendations
We analyzed gravel gallery design infiltration rates using the data from the test pit permeability tests
performed. The following table summarizes our recommended design infiltration rates for design
of gravel galleries.
Test
Location
Depth
(feet)
USCS
Classification
Percent
Fines
Design Infiltration
Rate (cfs/ft2) Safety Factor
P-1 (TP-3) 1 – 3 SW-SM 10.8 1.13 x 10-4 2.5
P-2 (TP-8) 1.5 – 3.5 SM 12.5 3.34 x 10-4 2.5
P-3 (TP-19) 1 – 3 GW 3.0 1.10 x 10-3 1.1
P-4 (TP-22) 2 – 4 ML 64.0 5.16 x 10-5 2.5
P-5 (TP-28) 2 – 4 SM 47.0 2.77 x 10-5 2.5
Additional Recommendations
We recommend that soil borings be considered to evaluate soil and groundwater conditions at
depth. It may be possible that suitable sands and gravels are present below the alluvial soils in the
southern portion of the site as evidenced by the sands encountered at depth in Test Pits TP-29 and
TP-30. Also, we recommend that additional test pits be excavated for pavement section analysis
when a site development plan and traffic data are available.
FIGURE 3
Test Pit Location Map
Project No. 2013-026
December 30, 2013Painted Hills Golf Course
4403 South Dishman-Mica
Road
Spokane County, WA