HomeMy WebLinkAboutSoils & Perc Test 09.23.2020,WestWater Engineering
7 Consulting Engineers & Scientists
2516 FORESIGHT CIRCLE, #1
GRAND JUNCTION, COLORADO 81505
SOILS AND PERCOLATION REPORT
Date: September 23, 2020
Consultant: Dean Goebel, M.S., P.G. Hydrogeologist
WestWater Engineering
2516 Foresight Circle #1
Grand Junction, CO 81505
(970) 241-7076
Client: Beth Douglas
831 County Road 237
Silt, CO 81652
Land Parcel: 831 CR 237, Silt, CO 81652
2127-363-00-073
SOILS LOG
(970) 241-7076 - FAX (970) 241-7097
Site soils were investigated to collect site -specific data on a I 0-acre lot developed with one 3-BR
single-family residence and outbuildings located on Tract 24 of the Antlers Orchard
Development, 831 County Road 237 Silt, Colorado. The soils and percolation test was
conducted to collect site specific soils data for a proposed secondary accessory dwelling unit
(ADU) onsite wastewater treatment system (OWTS). Percolation testing procedures were
conducted in accordance with Garfield County On -Site Wastewater Treatment System
Regulations (Regulations). The Percolation Test Site is located approximately 120 feet north of
the south property line and 180 feet west of the east property line (see Figure Al).
Site soils were described and percolation tested in an area sloping approximately 4 to 5 % to the
southeast. The 9-foot soils observation pit shows a soil profile comprised of clayey sand to
sandy clay soils with a 6-inch upper silty sand loam epipedon. Groundwater was not
encountered in the 9-foot soils observation pit; high seasonal groundwater is estimated to be
greater than 9.0 feet.
The soils profile log is summarized below and in Table 1. Dark brown (7.5YR 3/2) silty sand
loam with granular structure occurs from 0-0.5 feet overlying dark yellowish brown (l 0YR 4/4)
clayey sand to sandy clay with granular to massive structure from 0.5-9.0 feet maximum depth of
A-1
excavation. The high seasonal water table estimate of 9.0 feet is based on low antecedent soil
moisture content and the lack of soil coloring/redoximorphic features indicative of prolonged soil
saturation via groundwater.
Table 1. Soil Log Description
Depth Interval (ft)
Soil Description
0-0.5
Dark brown (7.5YR 3/2) silty sand (vt 1 loam; moderate -high OM;
granular; dry; sparse vegetation with some weeds
0.5-9.0
Dark yellowish brown (10YR 4/4) clayey sand (f) to sandy (f) clay;
chalky appearance from disseminated gypsum 4-6.7 feet; low OM;
granular to massive; dry
of = very fine; f = fine; m — medium and; crs = coarse for sand sized particles
Percolation rates summarized in Table 2 range from 17 to 33 minutes per inch (min/in).
Excluding the surface test hole 17 min/in percolation rate, the average rate for the four test holes
completed in the sandy clay average 29 min/in. Based on percolation data, macroscopic tactile
soil analysis and estimated depth of the high seasonal water table, the infiltrative surface of the
soil treatment area (STA) /leachfield can occur along a soil depth interval ranging from 2.0 to 4.0
feet depth. Site soils are categorized as Type 3 Soils based on sandy clay loam to clayey sand
textures, granular to massive structure, and percolation rates faster than the 41-60 min/in
percolation rate range. At the time of installing the OWTS, soils should not be excavated under
wet conditions to avoid compaction and smearing leading to reduction in permeability.
Table 2. Percolation Test Results
ID
Depth
(ft)
Time
Final
Drop
(in)
Percolation
Rate
(min/in)
10:07
(start)
10:37
11:07
11:37
12:07
1
1.6-2,6
3.75"
4.75"
5.75"
6.625"
7.5"
3.75
32
2
0.0-1.0
3.375"
5.5"
7.25"
8.875"
1 0.3 75"
7.0
17
3
2.0-3.0
2.75"
4.25"
5.125"
6.25"
7.125"
4.375
27
4
4.0-5.0
3.625"
5.5"
6.5"
7.5"
8.5"
4.875
25
5
2.0-3.0
3.5"
4.625"
5.5"
6.375"
7.125"
3.625
33
A-2
FIGURES
EXISTING 3—BR
MAIN DWELLING
- EXISTING
PROPERTY
LINE
100 50 0
— �— J
EXISTING
ACCESS
�� �EXISTING SHARED
WATER SUPPLY
ROAD ��' ‘.i I WELL APPROXIMATELY
"•• NE PARCEL CORNER
ji. 315 FEET EAST OF
EXISTING OWTS
SEPTIC TANK AND \\ 1
LEACHFIELD AREA
III
1j
\k.. 6
1 j
11t •
• 1
1 I
t I
PERCOLATION 5•
TEST SITE 1 I
SLOPE 4-5% j I
10.0 ACRES SOUTHEAST
I 1
I I
100
SCALE: 1 "=100'
EXISTING POTABLE
WATER LINE SERVING
MAIN DWELLING
EXISTING WATER
METER PIT
PROPOSED 2—BR
SECONDARY ADU
STAKED —OUT
WestWater
Engineering
2516 Foresight Circle, #1
Grand._ Junction, CO 81505
(970) 241-7076
FIGURE Al
831 County Road 237
PROPOSED
CISTERN
2—WAY
CLEANOUT
NEW 1,000
GALLON
SEPTIC TANK
DISTRIBUTION BOX
RISER AT GRAD
PROPOSED POTABLE
WATER LINE CORRIDOR
7
25'
. 1Vi
\g
1 EXISTING
PROPERTY
LINE
M
EXISTING UNPAVED
ACCESS ROAD
Q4 INFILTRATOR TRENCHES
3 TRENCHES EACH WITH
117 INFILTRATOR UNITS
TOTAL OF 51 UNITS
GENERAL LOCATION OF
EXISTING POTABLE
WATER LINE SERVING
MAIN DWELLING
I
COVER Q4 TRENCHES I I
WITH GEOTEXTILE FABRIC
40 20 0 40
SCALE: 1 "=40'
westwater
Engineering
2516 Foresight Circle, 1
Grand Junction, CO 81505
(970) 241-7076
FIGURE A2
PROPOSED OWTS LAY —OUT
813 County Road 237
Silty
Sand Loam
USE TOP PORT
INFILTRATOR FACE PLATE
PROPOSED 3 INFILTRATOR TRENCHES
COVER WITH GEOTEXTILE FABRIC PRIOR BACKFIJLLING
CROWN BACKFILL
OVER TRENCHES
I
Existing
0.5'
3'
17.0'
a
MAXIMUM DEPTH 4.0 FEET
MINIMUM DEPTH 2.0 FEET
LEACH FI ELQ CROSS SECTION
SCALE 1 "=5"
WestlNater
Engineering
2516 Foresight Circle, 11
Grand Junction, CO 81505
(970) 241-7076
FIGURE A3
DWCS CROSS SECTIQM
831 County Road 237