HomeMy WebLinkAboutEngineer's OWTS Design Plan2789 Riverside Parkway
Grand Junction, Colorado 81501
Phone: 970-255-8005
Info@huddlestonberry.com
July 14, 2025
Project#02997-0001
Stephen and Jennifer Wells
540 Panoramic Drive
Silt, Colorado 81652
Subject: OWTS Design
540 Panoramic Drive ADU
Silt, Colorado
References: Geotechnical Investigation, 540 Panoramic Drive ADU, Silt, Colorado, by
Huddelston-Berry Engineering & Testing for Stephen and Jennifer Wells, April
21, 2025.
Dear Mr. and Mrs. Wells,
At your request, Huddleston-Berry Engineering & Testing, LLC completed design of an Onsite
Wastewater Treatment System (OWTS) for a new Accessory Dwelling Unit (ADU) at 540
Panoramic Drive in Silt, Colorado. The site location is shown on Figure 1 – Site Location Map.
A site plan is included as Figure 2.
Site Conditions
At the time of the investigation, the western and eastern portions of the site were occupied by an
existing residence and a pond, respectively. The remainder of the site was open and generally
sloping down from the west and east to the south of the pond. Site topography is shown on
Figure 2. Vegetation consisted primarily of weeds, grasses, and sparse trees. The site was
bordered to the north, west, and east by rural residential/agricultural properties, and to the south
by Panoramic Drive.
Subsurface Investigation
In accordance with Garfield County regulations, two test pits were excavated in the vicinity of
the Soil Treatment Area (STA). Using visual-tactile classification methods, the soil profile
consisted of 1.0 foot of topsoil above brown to reddish-brown, moist, medium dense to loose
sandy loam soils with a weak granular structure (Soil Type 2A) that extended to depths of 4.0
and 5.0 feet below the existing ground surface. The sandy loam soils were underlain by brown,
moist to wet, medium stiff to soft, structureless sandy clay loam soils (Restrictive Layer) that
extended to the bottoms of the excavations.
Groundwater was encountered at depths of 4.0 and 5.0 feet in the subsurface at the time of the
investigation. In general, based upon time of year and the results of the subsurface investigation,
HBET believes that the seasonal high groundwater elevation is 4.0 feet below the existing grade
at this site.
540 Panoramic Dr.
#02997-0001
07/14/25
V:\2008 ALL PROJECTS\02997 - Stephen and Jennifer Wells\02997-0001 540 Panoramic Drive\200 - Geo\02997-0001 OWTS062425.doc 2
The locations of the test pits are shown on Figure 2. Copies of the test pit logs are included in
Appendix A.
Onsite Wastewater Treatment System
The seasonal high groundwater elevation is an important factor in determining the suitability of
the site for Onsite Wastewater Treatment Systems. For OWTS suitability, the seasonal high
groundwater elevation should be at least four feet below the bottom of the proposed Soil
Treatment Area (STA). As discussed previously, HBET believes the seasonal high groundwater
elevation is deeper than 4.0 feet below the existing grade at this site. As a result, the bottom of
the STA can be no deeper than existing grade at this site. Therefore, a mounded system will be
required at this site. This should be considered when establishing the elevation of the ADU to
make certain that adequate fall to the STA can be achieved.
Seepage Bed Design
The design of the absorption system generally follows the requirements of the Garfield County
Department of Public Works as outlined in the Garfield County On-Site Wastewater Treatment
System Regulations, effective July 2018. The proposed construction at the site is anticipated to
include a two-bedroom ADU.
Based upon the visual tactile classification of the soils, a Long-Term Acceptance Rate (LTAR)
of 0.5 will be utilized for the absorption field design. Infiltrator Systems Quick4 Standard
Chambers are proposed. The daily flow of the sewage disposal system is calculated below and a
plan and profile of the absorption system are shown on Figure 3.
Average Daily Flow = (4 persons)(75 GPD/person)
= 300 GPD
Soil Treatment Area = (300 GPD / 0.5) = 600 Square Feet
Adjusted Soil Treatment Area = (600 SF)(1.2)(0.7) = 504 Square Feet
# of Quick4 Chambers = (504 / 12) = 42 Chambers; Use 44 Chambers
System Installation
The installation of the septic tank, plumbing lines, Infiltrators, etc. should be completed in
accordance with the Garfield County On-Site Wastewater Treatment System Regulations and
Infiltrator Systems, Inc. specifications. In addition, the following construction procedures are
recommended:
The septic tank and distribution box should be placed level over native soils that have
been scarified to a depth of 8 to 12 inches, moisture conditioned, and recompacted to
a minimum of 95% of the standard Proctor maximum dry density, within ±2% of
optimum moisture content. However, up to 3-inches of washed rock or pipe bedding
passing the 1-inch sieve may be used as a leveling course under the septic tank and/or
distribution box.
The bottoms of trenches and backfill around the septic tank and distribution box
which will support sewer or effluent lines should be compacted to at least 90 percent
of the standard Proctor maximum dry density, within ±2% of optimum moisture
content. Pipe bedding should have a maximum particle size of 1-inch.
540 Panoramic Dr.
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07/14/25
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Vehicular or heavy equipment traffic and placement of structures should not encroach
within 10 feet of the septic tank or distribution box.
Inspection Schedule
Huddleston-Berry Engineering & Testing LLC should be retained to monitor the construction of
the OWTS. The following schedule of observation and/or testing should be followed:
Observe the absorption bed excavation prior to placement of Infiltrator chambers.
Observe placement of the septic tank, distribution box, and all connecting sewer and
effluent lines prior to backfill. Verify proper fall between inverts.
Observe and verify installation of the absorption bed prior to placement of cover and
backfill.
In conformance with Garfield County regulations, HBET will be required to provide the Garfield
County Health Department with documentation certifying that the OWTS was placed in
conformance to the plan and profile and Garfield County regulations.
General Notes
The OWTS design was based upon the results of the subsurface investigation and on our local
experience. The design is valid only for the proposed construction.
We are pleased to be of service to your project. Please contact us if you have any questions or
comments regarding the contents of this report.
Respectfully Submitted:
Huddleston-Berry Engineering and Testing, LLC
Wayne D. Anderson, P.E.
Project Engineer
FIGURES
Gar eld County, CO
Developed by
Date created: 4/16/2025
Last Data Uploaded: 4/16/2025 2:07:16 AM
971 ft
2789 Riverside Parkway
Grand Junction, CO 81501
Project No.: 02997-0001
Date: 07/14/25
By: WDA
540 PANORAMIC DRIVE
PARCEL#212736400013
FIGURE 2 - SITE PLANTEST PIT
C.I. = 2 FT
SCALE: 1" = 50'
**NOTE:TANK AND BED LOCATIONS APPROXIMATE AND MAY SHIFT SOME DURING
CONSTRUCTION BASED UPON SITE TOPOGRAPHY, OWNER PREFERENCE, AND/OR OTHER
FACTORS AS LONG AS APPLICABLE SETBACKS ARE MET. ACTUAL LOCATION OF TANK AND
BED WILL BE INDICATED ON AS-BUILT DRAWINGS.**
575
0
TP-5
TP-6
576
0
575
8
575
4
5752
575
2
575
4
575
6
~82'
~33'
~63'
~28'
~56'
~84'
~109'
~30'
42'
~32'
~20'~443'
33'
47'
5' MIN 20' MIN
50'
1' MIN
44'
12'
~51'
~62'
NEW
ADU
NEW
STA
SEPTIC TANK
WITH MINIMUM
1,000 GALLON
CAPACITY
EXISTING
POND
EXISTING HOME
EXISTING SHED
EXISTING SHED
EXISTING
CISTERN
EXISTING TANK
EXISTING
STA
EXISTING BARN
NEW DRIVEWAY
**ASSUMED WATER
LINE LOCATION
PORTION OF 15'
UTILITY EASEMENT
15' DRAINAGE EASEMENT15' UTILITY EASEMENT 30' DRAINAGE EASEMENT
EXISTING DRIVEWAY
**NOTE:
REPAIR AREA AT
STA LOCATION**
2789 Riverside Parkway
Grand Junction, CO 81501
Project No.: 02997-0001
Date: 07/14/25
By: WDA
MINIMUM SETBACKS
(UNITS = FT)
**OTHER SETBACKS NOT LISTED HERE SHOULD BE IN ACCORDANCE WITH GARFIELD COUNTY OWTS REGULATIONS
**USE SWEEP 90'S OR
TWO 45'S AT 90
DEGREE BENDS**
DETAIL AREA
SCALE: 1" = 20'
540 PANORAMIC DRIVE
PARCEL#212736400013
FIGURE 3 - SEPTIC SYSTEM
DETAILS
INSPECTION PORTS
44'
5' MIN
20' MIN
SEPTIC TANK WITH
MINIMUM 1,000
GALLON CAPACITY
NEW
ADU
4-INCH DIAMETER SEWER AND
EFFLUENT PIPE MEETING ASTM D1785,
SCHEDULE 40 OR SDR 35
WATER LINE
12'
SYSTEM MOUND ENVELOPE
3H:1V SLOPES FROM SPECIFIED
2-FOOT SHOULDER
TOP OF SLOPE
BOTTOM OF SLOPE
GENERALIZED SYSTEM PROFILE
GENERALIZED BED PROFILE
COVER SOIL; NATIVE SOILS OR OTHER SUITABLE
TOPSOIL. GRADE TO CARRY SURFACE WATER
AWAY FROM BED.
NONWOVEN, NEEDLE PUNCHED, GEOTEXTILE
FABRIC IMMEDIATELY ABOVE CHAMBERS
INFILTRATOR SYSTEMS QUICK4
STANDARD CHAMBERS
**BOTTOMS OF CHAMBERS
AT EXISTING GRADE
FILTER BED DIMENSIONS = ONE 12'X36' BED
4 ROWS OF 9 QUICK4 STANDARD INFILTRATORS OR
ENGINEER APPROVED EQUAL
2'
MIN
MAX. 3H:1V SLOPE
NATIVE NON-FREE
DRAINING MATERIAL
2'
MIN
MAX. 3H:1V SLOPE
DISTRIBUTION BOX THAT
ENSURES EVEN DISTRIBUTION
OF EFFLUENT
4 ROWS OF 11 QUICK4
STANDARD INFILTRATORS OR
ENGINEER APPROVED EQUAL
INSPECTION PORTS
APPENDIX A
Typed Test Pit Logs
Sandy Loam with Organics (TOPSOIL)
Sandy Loam, brown to reddish-brown, moist, medium dense to
loose, weak granular structure (Soil Type 2A)
Sandy Clay Loam, brown, moist to wet, medium stiff to soft,
structureless (**Restrictive Layer**)
Bottom of test pit at 6.0 feet.
NOTES
GROUND ELEVATION
LOGGED BY TC
EXCAVATION METHOD Trackh/Backhoe AT TIME OF EXCAVATION 5.0 ft
AT END OF EXCAVATION 5.0 ft
AFTER EXCAVATION ---
TEST PIT SIZE
EXCAVATION CONTRACTOR Wiseland GROUND WATER LEVELS:
CHECKED BY MAB
DATE STARTED 3/18/25 COMPLETED 3/18/25
DE
P
T
H
(f
t
)
0.0
2.5
5.0
GR
A
P
H
I
C
LO
G
ATTERBERG
LIMITS
MATERIAL DESCRIPTION
SA
M
P
L
E
T
Y
P
E
NU
M
B
E
R
FI
N
E
S
C
O
N
T
E
N
T
(%
)
RE
C
O
V
E
R
Y
%
(R
Q
D
)
BL
O
W
CO
U
N
T
S
(N
V
A
L
U
E
)
PO
C
K
E
T
P
E
N
.
(t
s
f
)
DR
Y
U
N
I
T
W
T
.
(p
c
f
)
MO
I
S
T
U
R
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N
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(
%
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IN
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PL
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X
PAGE 1 OF 1
TEST PIT NUMBER TP-5
CLIENT Stephen and Jennifer Wells
PROJECT NUMBER 02997-0001
PROJECT NAME 540 Panoramic Drive
PROJECT LOCATION Silt, CO
GE
O
T
E
C
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B
H
C
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0
2
9
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6
/
2
5
Huddleston-Berry Engineering & Testing, LLC
2789 Riverside Parkway
Grand Junction, CO 81501
970-255-8005
Sandy Loam with Organics (TOPSOIL)
Sandy Loam, brown to reddish-brown, moist, medium dense to
loose, weak granular structure (Soil Type 2A)
Sandy Clay Loam, brown, moist to wet, medium stiff to soft,
structureless (**Restrictive Layer**)
Bottom of test pit at 7.0 feet.
NOTES
GROUND ELEVATION
LOGGED BY TC
EXCAVATION METHOD Trackh/Backhoe AT TIME OF EXCAVATION 6.0 ft
AT END OF EXCAVATION 6.0 ft
AFTER EXCAVATION ---
TEST PIT SIZE
EXCAVATION CONTRACTOR Wiseland GROUND WATER LEVELS:
CHECKED BY MAB
DATE STARTED 3/18/25 COMPLETED 3/18/25
DE
P
T
H
(f
t
)
0.0
2.5
5.0
GR
A
P
H
I
C
LO
G
ATTERBERG
LIMITS
MATERIAL DESCRIPTION
SA
M
P
L
E
T
Y
P
E
NU
M
B
E
R
FI
N
E
S
C
O
N
T
E
N
T
(%
)
RE
C
O
V
E
R
Y
%
(R
Q
D
)
BL
O
W
CO
U
N
T
S
(N
V
A
L
U
E
)
PO
C
K
E
T
P
E
N
.
(t
s
f
)
DR
Y
U
N
I
T
W
T
.
(p
c
f
)
MO
I
S
T
U
R
E
CO
N
T
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N
T
(
%
)
LI
Q
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LI
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PL
A
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M
I
T
PL
A
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I
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Y
IN
D
E
X
PL
A
S
T
I
C
I
T
Y
IN
D
E
X
PAGE 1 OF 1
TEST PIT NUMBER TP-6
CLIENT Stephen and Jennifer Wells
PROJECT NUMBER 02997-0001
PROJECT NAME 540 Panoramic Drive
PROJECT LOCATION Silt, CO
GE
O
T
E
C
H
B
H
C
O
L
U
M
N
S
0
2
9
9
7
-
0
0
0
1
5
4
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-
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S
.
G
P
J
G
I
N
T
U
S
L
A
B
.
G
D
T
4
/
1
6
/
2
5
Huddleston-Berry Engineering & Testing, LLC
2789 Riverside Parkway
Grand Junction, CO 81501
970-255-8005