Geotech Report V1SITE Post Office Box 190537 - Boise, Idaho 83719
!I site.consulting.idaho@gmail.com - 208-440-6276
tOINSULTING, LLC
Matt Schultz January 31, 2022
Schultz Development Page 1 of 17
Post Office Box 1115 File 22805-A
Meridian, Idaho 83680
Re: Geotechnical Recommendation Report
Proposed Grayson Subdivision
1710 East Amity Road
Meridian, Idaho
Matt:
Thank you for retaining SITE to assist with your geotechnical engineering requirements
for your proposed Grayson Subdivision project in Meridian, Idaho. This report is based
upon onsite test pits and labwork generated on samples gathered during test pit
excavation. It is noted that SITE previously provided geotechnical services for Wells,
Warrick, and Paisley Subdivisions all just east of this property on Amity Road. Based
upon the information herein, and our experience in the immediate vicinity of this project,
construction of the planned residential subdivision is feasible. Our research and
recommendations are included herein. We appreciate this opportunity to be of service.
Should you have any questions or require additional information, please contact our
office at your convenience.
Respectfully submitted;
SITE Consulting, LLC
Bob J. Arnold, PE
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Geotechnica/Services /Soil Testing & Inspection Services
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Post Office Box 190537 - Boise, Idaho 83719
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Geotechnical Recommendation Report
Proposed Grayson Subdivision
1710 East Amity Road - Meridian, Idaho
PURPOSE
The purpose of this investigation was to evaluate the onsite soil conditions, observe the
groundwater's elevation, and determine the soil's engineering properties. SITE was
retained to provide construction recommendations for the client who is the property
developer. Specific items requested and included herein are earthwork
recommendations, pavement and stormwater recommendations, allowable foundation
pressures, and construction inspection / testing recommendations.
AUTHORIZATION
Verbal authorization to proceed with this geotechnical investigation was received from
the client on or about December 15, 2021. Authorization to proceed and the use of the
recommendations provided herein indicate the client's acceptance of the scope of work,
warranty, limitations, and general conditions provided herein and within the submitted
proposal.
WARRANTY AND LIMITATIONS
The exploration and evaluation of subsurface conditions documented herein is
considered sufficient to form a basis for the provided recommendations. The provided
recommendations are based on the available soil information and preliminary design
details either assumed or furnished by the client. It is warranted that these
recommendations have been promulgated after being prepared in accordance with
locally accepted professional engineering and geotechnical engineering practice. No
other warranties are implied or expressed.
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GENERALBACKGROUND
Post Office Box 190537 - Boise, Idaho 83719
site.consulting.idaho@gmail.com - 208-440-6276
The project site is located on the north side of East Amity Road and is the second
parcel east of Locust Grove Road in Meridian, Idaho. A tax parcel number of S-
1129336360 and address of 1710 East Amity Road was found for this 3.1-acre property
within the Ada County Assessors Records using land prodata.com. The provided
Concept Design Drawing indicates the planned subdivision will include approximately
15 lots for single family residences, numerous open spaces, and a single public (ACHD)
right of way. East Grayson Street will be extended from Estancia Subdivision to the
east. A standard subsurface seepage trench is planned for storm water re -injection.
The subject property is on the north side of Amity Road just east of Locust Grove Road.
Estancia Subdivision is currently both east and north of the subject property. A single
rural property is to the west, between this property and Locust Grove Road. At the time
of our site visits the west half of the property was covered with structures and vehicles.
Ada County records indicate that a 1995 Manufactured Home is the principal residence
on the property. Ada County records indicate that four structures are present. As many
as six can be seen in the most current aerial photo.
Ada County Assessor File Goo le Earth Aerial Photo
Building Sketch
Ad - 40'
GP Storage 12'
936.0 sf
30' GPB 30'
1200.0 sf
built in 1977
40'� .
40'
960.0 sf
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ITE Post Office Box 190537 - Boise, Idaho 83719
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Sf1LT�N�a LLe
Also visible in the aerial photo are the large number of vehicles, boats, and trailers
abandoned or inventoried on the subject property. Google Earth historical aerial photos
did not indicate the property has been historically used as farmland. In the 2017 aerial
photo a pond (approximately 50' diameter) is visible just north of Amity Road and east
of the main driveway to the property. While no such records were located it is assumed
the property includes both a domestic water well and a sanitary sewer system. Well
Logs for two nearby properties, one to the south and one to the west, were found in the
IDWR database and are included in the Appendix.
INVESTIGATION
On January 22, 2022, SITE observed the excavation of two test pits at locations
intended to provide full coverage of the subject property. Test pit logs and an aerial
photo with test pit locations are included in the Appendix. In general, soils were
observed to be similar across the planned development and consisted of a non -plastic
Sandy Silt or Silty Sand with a four -to -eight inch rootzone or organic layer. The
overburden layer varied from four to five feet thick in our test pit locations. At this depth
a very firm, cemented, silt -hardpan layer was encountered. This layer was difficult to
excavate and did not breakdown is water during lab testing. This layer sat atop deeper
sand and gravel that extends to depths greater than our twelve feet deep test pits. At
this depth sand and gravel material was sloughing faster than it could be removed. No
groundwater was encountered in any of our test pits within the area of the subject
property.
Since groundwater was not encountered, well logs for the immediate area were
reviewed on the IDWR website. Two well logs were selected and are included in the
Appendix. These logs are for the properties adjacent to the south and west of the
subject property. The logs indicate the static groundwater is greater than thirty feet
below the ground surface at the well locations.
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RECOMMENDATIONS
Demolition
Numerous structures are planned for demolition. Inspection and the time of demo
should confirm removal of all foundation and slab on grade concrete. Any well or septic
system encountered is to be closed as per IDEA and IDWR requirements. Septic tanks
and drain fields below future home foundations are to be removed.
Site Work
Grubbing depths of up to six inches can be anticipated to remove most organic
materials in the east end of the property. Deeper removal may be required where large
trees or bushes are present and along ditches and fence lines. The former pond is to be
explored and evaluated at the time of earthwork operations to determine if re -excavation
and backfilling with structural fill is required.
Excavations caused by grubbing and removal of ditches, or over excavation of organic
materials, or soft/wet areas are to be backfilled with structural fill. All subgrade soils
present on the property can be used as structural fill on building lots and within right of
ways. Blending lean clay surface soils with other onsite soils including the cemented or
hardpan soils will improve surface drainage.
Compaction of any fill placed within building pads or right of ways must exceed 95% of
the maximum dry density as determined by Standard Proctor testing. It should be
anticipated that the Meridian City Engineering and / or Building Department will request
these test results prior to or at the time of home construction. Structural fill must pass
compaction testing and visual inspection for stability. Fill that passes compaction but is
observed to rut or deflect under construction traffic is to be rejected and repaired.
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Pavement Sections
Post Office Box 190537 - Boise, Idaho 83719
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An R-Value sample has been sent to a specialty soil lab for testing. Based upon soils
classification tests performed in our inhouse laboratory we anticipate an R-Value result
greater than R=20. Based upon a Traffic Index of TI=6 and R-value or R=20 the
following pavement section is recommended for East Grayson Drive.
Traffic Index
TI=6
H MA
2.5"
%" Base
4.0"
Subbase
10.0"
All materials and methods used in the construction of streets and sidewalks are to
comply with ISPWC and ACHD requirements.
Residential Foundation System
The proposed single-family residential structures may be supported on conventional,
continuous, and isolated pad foundations founded upon the native soils or upon
structural fill extending to these soils. Based upon proper placement and compaction of
structural fill, bearing pressures of up to 1500 psf are allowed for foundations founded
on the native soils or upon properly placed and compacted structural fill. Either
crawlspaces or slab on grade floors are acceptable. If fat clay is revealed at the
foundation bearing elevation, a geotechnical engineer should be consulted.
Slab on Grade Concrete
Care must be taken so that all excavations below both interior and exterior slab on
grade concrete are properly backfilled in accordance with the structural fill
recommendations. Trenches and wall backfill areas are to be filled in lifts and benched
each lift so that fill is not placed against a vertical soil face greater than three feet tall.
Slab on grade floors, sidewalks and pavements should be placed atop a mat of at least
four inches of granular structural fill materials. Mat material should meet ISPWC 3/4"
base specifications. The mat shall be compacted to the requirement for structural fill. �.o
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Storm Water
The proposed seepage bed must extend at least two feet into the native sand and
gravel layer encountered in both test pits. The top of this layer contains clay fines and
has not performed well in prior perc tests at near -by Warrick and Wells Subdivisions.
Once the top of the sand and gravel layer is penetrated the perc rate increases. A
design perc rate of P=4 in./hr. is recommended for this project. This is to be confirmed
with onsite testing at the time of construction.
Inspection & Testing
A qualified engineer or his representative should monitor fill placement to ensure the
work is performed in accordance with these recommendations. Testing should be
performed in accordance with ASTM Test Methods D3017-88 and D2922-91 (nuclear
densometer). For mass filling, compaction testing shall be performed on each lift of
compacted fill with at least one test on each filled lot. Trench-backfill and right of ways
are to be tested to Nampa / ISPWC requirements. It is noted that structural fill can pass
compaction tests and still be unacceptable if pumping, rutting, or deflecting under
vehicle or foot traffic.
General Comments
Testing and inspection services are recommended herein. Proper quality control during
construction is required to confirm materials and methods and thereby obtain a
desirable finished product. Monitoring and testing should also be performed to verify
suitability of materials used for structural fills and to confirm proper demolition, subgrade
grubbing, subgrade stability, and proper placement and compaction of fills. Any
deviations from the herein described subsurface conditions must be brought to the
attention of this consultant. This report has been prepared for the exclusive use of the
client and their retained design consultants. Findings and recommendations within this
report are for specific application to the proposed construction described herein and
apply only to the property identified.
APPENDIX FOLLOWS
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APPENDIX A
Location Map
Project Concept Drawing
Aerial Photo with Test Pit Locations
Test Pit Logs (2)
Contracted R-Value
Pavement Section Calc Sheets (1)
Adjacent Well Logs (2)
Geotechnica/Services/Soil Testing& Inspection Services
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Google Earth
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concept uesign urawin
FUTURE
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Supplied by Client
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Aerial Photo with Test Pit Location
Image from Google Earth
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TEST PIT LOG
Test Pit:
TP-1
File #:
22085-A
Client:
Schultz Development
Date Excavated:
01/27/22
Project:
Grayson Sub
Excavated By:
SC Excavation
Location:
See Aerial Photo
Logged By:
J. Meusch-SITE
DEPTH
SOILS DESCRIPTION
(feet)
3/4"
1/2"
3/8"
# 4
# 10
# 40
#100
#200
%M
LL
PI
0.0-1.0
Brown, Moist, Firm, Sand & Silt
1.0-4.0
Brown/Red, Moist, Firm, Silty, Sand (SM)
3.0
100
1 87
1 68
1 50 1
32
26
23.3
19.9
NP
NP
4.0-5.0
Brown/Tan, Moist, Very Firm, Cemented, SILT, Hardpan
4.5
22.3
NP
NP
5.0-7.0
Brown/Red, Moist, Firm, Sand and Gravel
7.0-12.0
Brown/Red, Moist, Firm, Sand & Gravel with Cobble
12.0
Bottom of Excavation @ 12.0'
No Ground Water Encountered
No Monitoring Well in Place
CV
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TEST PIT LOG
Test Pit:
TP-2
File #:
22085-A
Client:
Schultz Development
Date Excavated:
01/27/22
Project:
Grayson Sub
Excavated By:
SC Excavation
Location:
See Aerial Photo
Logged By:
J. Meusch-SITE
DEPTH
SOILS DESCRIPTION
(feet)
3/4"
1/2"
3/8"
# 4
# 10
# 40
#100
#200
%M
LL
PI
0.0-1.0
Brown, Moist, Firm, Sand & Silt
1.0-3.0
Brown/Red, Moist, Firm, Sticky, Sandy, Silt (ML)
2.0
1
100
1 99 1
97
92
88.6
24.4
1 37
14
3.0-5.0
Brown/Tan, Moist, Firm, Silty, Sand (SM)
4.0
1 100
1 98
1 93
1 73 1
43
39
29.3
1-9-3—r
NP
NP
5.0-6.0
Brown/Tan, Moist, Firm, Cemented, silt Hardpan
6.0-8.0
Brown/Red, Moist, Firm, Silty, Sand & Gravel
7.0
100
1 98 1
71
1 55 1
32
1 28
23.8
18.3
NP
NP
820-9.0
Brown!Red, Moist, Firm; Silty; Sand and Gravel
8.5
91 1
81
1 77
70 1
61 1
35 1
17
15.1
8.6
NP
NP
9.0-12.0
Brown/Tan, Moist, Firm, Sand, Silt, Cobble
12.0
Bottom of Excavation @ 12.0'
No Ground Water Encountered
Monitoring Well in Place
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Contracted R-Value
Pending
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Pavement Section
Ulrdvbgn 3upu1v1510n interior .5zreet
DESIGN SECTION CALCULATIONS
(ACHD R-Value Method)
Project: Grayson Subdivision File No.: 22085-A
Amity at Victory Caic By: B. Arnold
Client: Schults Development Date: 01/30/22
Design Thickness Equation:
T = 0.0032 (TI) (100-R)(12) = GE (inches)
T= Design Thickness TI = Traffic Index = 5 By Agency
GE = Gravel Equivalent R = R-Value = 20 Soil Test
GE= 18.9Inches
ACHD HMA, 3/4" Base and Aggregate Subbase
Actual Thickness Equivalent Thickness
HMAThickness= 2.5 Inches HMA= 5.0 Inches
3/4" Base Thickness = 4.0 Inches RBE= 4.4 Inches
Calculated Aggregate Subbase Thickness Equation:
Subbase Thickness=SB=GE-HMA-RBE
SB= 9.5 Inches
CALCULATED DESIGN SECTION
HMA= 2.5 inches
3/4" Base = 4.0 inches
Subbase = 10.0 inches
RECOMMENDED DESIGN SECTION
HMA = 2.5 inches
3/4" BASE = 4.0 inches
SUBBASE = 10.0 inches
R=20 is maximun R-Value used by SITE for ACHD subdivisions
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IDWR Well Log — Adjacent West
4715 S Locust Grove Road
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Geotechnical Services ISoll Testing & Inspection Services
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IDWR Well Log -Adjacent Property
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