Groundwater Report
208-440-6276 * bjarnoldpe@msn.com * Post Office Box 190537 * Boise, Idaho 83719
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Brad Miller
Ronald Van Auker Inc.
1802 Lanark Street
Meridian, Idaho 83642
January 28, 2016
Page 1 of 9
File # 16016A
Re: Geotechnical Recommendations
Swindell Property
1495 South Locust Grove
Meridian, Idaho
Brad:
As per your authorization and as requested by Matt Munger with WH Pacific, SITE
Consulting, LLC logged and sampled two test pits on the referenced property. WH
Pacific requested that soils profiles be generated, the depth to groundwater be
determined and recommendations for storm water disposal be provided. It was
reported that subsurface infiltration trenches are preferred.
An aerial photo and the address of 1495 South Locust Grove were obtained from the
Ada County Assessor's website. Two parcel numbers S1118449550 & S1119449350
were also listed for the subject property. The test pits were excavated as close to the
planned storm water facilities as possible. Approximate locations are shown on the
included aerial photo. These locations were provided by WH Pacific. During
excavation, soil samples were gathered and the included Test Pit Logs were generated.
Soils were submitted to our in house soil laboratory for analysis. Laboratory test results
and all soil classifications and descriptions are reported on the attached Test Pit Logs.
Our recommendations are based upon the proposed design, the observed conditions
and test results as documented herein.
208-440-6276 * bjarnoldpe@msn.com * Post Office Box 190537 * Boise, Idaho 83719
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GENERAL OBSERVATIONS
It is noted that the surface elevation of the subject property is very irregular with
numerous low area and many large piles of fill material. The Topo Map provided by WH
Pacific indicates there is six feet of elevation change between our two test pits with the
west pit being substantially lower. Both test pit were excavated to the maximum depth
possible with the selected equipment. In both pits, sloughing sands and gravels
prevented deeper excavation.
As indicated, the surface of the site is very irregular. The area between our two test pits
is covered with end dumped stockpiles of soils. According to historical aerial photos
available on Google Earth, these piles have been onsite for over ten years. This source
indicates that earthwork activities have been on going on this property since 2002.
SUBSURFACE CONDITION
At both test pit locations the surface appears to have been graded and filled. This may
have occurred when the prior utility work was done along the west property boundary.
From the existing ground surface to gravel contact varied from 6.5 feet (west) to 9.0 feet
(east). Above the native pitrun was layers of silt and sand and blends of silt and sand
with gravel. No dense clay, hardpan or cemented silt layer was observed in either test
pit. All samples soils were determined to be non plastic by laboratory testing. Soils
varied from 3 inch minus to #4 minus with moisture content ranging from 6.5 to 12.5 %.
Once contacted the native pitrun type sand and gravels graded very quickly to free
draining, free flowing, sands and gravel that are very dry (3.5% moisture). At the
bottom of our test pits these materials were dry and flowing freely into the excavation.
Materials could not be removed fast enough to excavate to deeper depth s.
208-440-6276 * bjarnoldpe@msn.com * Post Office Box 190537 * Boise, Idaho 83719
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GROUNDWATER OBSERVATIONS
Since groundwater was not contacted in our 13 feet deep test pits, additional research
was undertaken. WH Pacific indicated that a well was present in a small pump house,
just east of our east Test Pit. The client was contact and permission received to access
this well by removing the top of the well casing. On January 8, 2016 the static water
level in this well was 38 feet below the pump house concrete floor. A topo map provided
by WH Pacific and included in the Appendix indicates the ground surface is 2642 at the
pump house, 2638 at our east test pit and 2632 at our west test pit. Therefore
groundwater is greater than 14 feet below the bottom of our west (deepest) test pit.
Based upon our experience in the area, this greatly exceeds any season change in the
groundwater.
STORMWATER RECOMMENDATION
The free draining pitrun type sand and gravel encountered in both test pit locations at
ten feet below the surface will accept stormwater and therefore infi ltration trenches are
acceptable. Based upon observed conditions and experience on other project s in the
general vicinity the percolation rate for these soils will greatly exceed the P= 8 in / hr
that is currently the upper limit for storm water design. Confirmation of this assumed
percolation rate at the time of construction is recommended and will likely be required.
GENERAL COMMENTS
Concern must be expressed for construction of roadways on this property. It is
recommended that all undocumented fill materials within planned right of ways be
stripped and then, if acceptable, replaced a s structural fill. Unacceptable material will
include soils with organic matter, large clod or pieces of hardpan, concrete, pavement
and other debris, excessively wet soils, low density soils, and expansive clay. ISPWC
requirements for fill quality, placement methods and inspection are recommended.
208-440-6276 * bjarnoldpe@msn.com * Post Office Box 190537 * Boise, Idaho 83719
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We appreciate this opportunity to be of service. When appropriate, we would like to
discuss continuing our role as geotechnical consultant during construction. Please
contact our office if additional information or services are required.
Respectfully submitted,
Bob J. Arnold, PE
Appendix Follow
208-440-6276 * bjarnoldpe@msn.com * Post Office Box 190537 * Boise, Idaho 83719
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APPENDIX
Test Pit Locations
Topo Map
Test Pit Logs (2)
208-440-6276 * bjarnoldpe@msn.com * Post Office Box 190537 * Boise, Idaho 83719
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Test Pit Locations
Aerial Photo from Ada County Assessor Website
TP-West
TP-East
208-440-6276 * bjarnoldpe@msn.com * Post Office Box 190537 * Boise, Idaho 83719
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TOPO MAP
208-440-6276 * bjarnoldpe@msn.com * Post Office Box 190537 * Boise, Idaho 83719
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TEST PIT LOG
Test pit #: TP-East File: 16016A
Client: Van Auker Date Excavated: 12/6/15
Project: Swindell Property Digger: Culver / Backhoe
Location: East Infiltration Trench Logged By: K. Arnold
DEPTH
SOILS DESCRIPTION
Sample
Type
3/8
#4
#10
#40
200
M
PI
LL
0.0-1.0
FILL - Topsoil - Brown, Moist to
Wet, Silt and Sand
1.0-5.5
Brown, Moist, Sandy SILT (ML)
with Gravel
Bag
2.5
Scalped
100
94
88
68
54.0
10.5
NP
NP
5.5-6.5
Brown, Moist, Firm, SILT (ML)
Bag
6.0
100
92
74
69.9
10.0
NP
NP
6.5-9.0
Brown, Moist, Sandy, SILT (ML)
Bag
8.0
98
93
87
82
62.2
11.5
NP
NP
9.0
Gravel Contact
9.0-12.5
Tan & White, Moist, Coarse,
PITRUN type Sand and Gravel
Free Draining at 10 feet
Bag
12.0
Scalped
65
55
46
18
5.5
2.9
NP
NP
12.5
Bottom of Hole -
Sloughing Soils Prevented
Deeper Exploration
NO GROUNDWATER
ENCOUNTERED
208-440-6276 * bjarnoldpe@msn.com * Post Office Box 190537 * Boise, Idaho 83719
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TEST PIT LOG
Test pit #: TP-West File: 16016A
Client: Van Auker Date Excavated: 12/6/15
Project: Swindell Property Digger: Culver / Backhoe
Location: West Infiltration Trench Logged By: K. Arnold
DEPTH
SOILS DESCRIPTION
Sample
Type
3/8
#4
#10
#40
200
M
PI
LL
0.0-0.8
FILL - Topsoil, Brown, Moist,
Silt and Sand
0.8-3.5
Tan to Light Brown, Moist, Silty
SAND with Gravel
Bag
2.5
97
90
83
61
37.4
7.5
NP
NP
3.5-5.5
Brown, Moist, Firm, Silty, SAND
Bag
5.0
100
98
79
44.4
11.2
NP
NP
5.5-6.5
Brown, Moist, SAND with silt
And gravel
Bag
6.0
76
70
65
45
28.9
6.8
NP
NP
6.5
Gravel Contact
6.5-13.0
Tan & White, Moist, Fine,
PITRUN type Sand and Gravel
FREE DRAINING AT 9.0 FEET
Bag
12.0
Scalped
61
51
42
15
8.4
3.5
NP
NP
13.5
Bottom of Hole -
Sloughing Soils Prevented
Deeper Exploration
NO GROUNDWATER
ENCOUNTERED
Nothing Follows