HomeMy WebLinkAboutOWTS Installation Observations 12.10.24December 10, 2024
502 Main Street • Suite A3 • Carbondale, CO 81623 • (970) 704-0311 • Fax (970) 704-0313
S OPRIS E NGINEERING • LLC civil consultants
Hansen, Linda S
3290 CR 210,
Rifle, CO 81650
C/O Jose Gonzalez
J. Caliber Construction
(970) 314-0489
RE: As-Constructed Report –Onsite Wastewater Treatment System (OWTS), Hansen Residence, 3290 County
Rd 210, Rifle, CO, Garfield County, Colorado
SE Job No. 34058 Parcel No: 217906300068. Garfield County OWTS Permit No. SEPT- 8623
Dear Linda:
Pursuant to County requirements, this letter provides documentation that the Onsite Wastewater Treatment System
(OWTS) components recently installed at the above referenced site is in compliance with the permitted design.
Sopris Engineering inspected the excavations, soils, materials and the installation of the system components during
construction, prior to final backfill and after all installations were completed. The installed absorption field and tank
were designed and constructed to serve the new garage structure and 1-bedroom ADU.
Sopris Engineering performed site visits in coordination with the owner and contractor (J. Caliber Construction) that
installed the system components. The as-constructed conditions and installation of the new OWTS components are
in compliance with Garfield County Regulations; the recommendations and specifications delineated on the OWTS
permit/construction plan “C1-OWTS Plan”, dated 05-15-2024 by Sopris Engineering. The As-Constructed OWTS
conditions, design criteria and components installed are delineated on the attached AC OWTS Record Drawing.
Summary OWTS As-Constructed Conditions and Design Criteria
The new OWTS is designed for a treatment capacity of 300 gallons per day based on the design wastewater flow to
serve a minimum 2-bedroom residence in accordance with Table 6-2 values, Section 43.6, A.4. A new 1,000 gallon
2-compartment septic tank was installed with appropriate sanitary tees, outlet effluent filter and plastic risers and lids
set at the finish surface grade. A 4” SDR-35 sewer service pipe section with two-way cleanout adjacent to the
accessory structure was installed to the septic tank inlet.
The soil treatment area (STA) consists of leaching chamber trenches that provide 360 S.F. of total absorption area.
The septic tank effluent is gravity discharged through a new 4-inch SDR-35, installed at minimum 1.5% slope, to the
STA via a distribution box located at the proximal end of the trenches. The plastic distribution box with inlet baffle
fitting was set level on compacted earth and has risers and lid set at the finish surface grade. The effluent is equally
distributed from the distribution box via two 4” distribution pipes connected to the head end cap of each chamber
trench. Observation ports with caps are installed on the proximal and distal ends of the two chamber trenches.
The STA sizing was based on the design criteria for gravity dosed chambers based on the soil type, texture and
structure with the appropriate long term acceptance rate (LTAR) of 0.6 g/d/SF. A total of 24 ADS Arc-36 gravelless
leaching chambers were installed in the 2 trenches with 12 chamber units per trench. The installed system meets all
required setbacks and is installed within the general location indicated on the record drawing.
Hansen Residence As-Constructed OWTS
3209 County Rd 210, Rifle, CO
SE Job No. 34058.01
December 10, 2024
Page2
Design Flow
The design flow is 300 gallons per day based on the calculated minimum design capacity of an equivalent 2-
bedroom residential dwelling in accordance with Table 10-1 values, Section 43.6, A.4. Regulation 43:
Minimum population based on 2 bedrooms at 2 persons per bedroom equating to 4 persons. The Design flow is
calculated based on residential usage of 75 gal/person/day.
Max. Design flow (Qd) gallons/day = (# of people) x (avg. flow) gal/person/day.
Design flow Qd = 4*75=300 gpd
Septic Tank Design
The septic tank capacity required for a minimum 48 hour retention time:
V = 300 gal/day * 2 = 600 gallons. Installed a 1,060 gallon 2-compartment reinforced plastic septic tank.
Sub Surface Conditions and Testing
A subsurface soil investigation and site assessment was performed by Sopris Engineering on May 9th, 2024. The
soils in the proposed field envelope area were sampled and characterized by application of the USDA visual/tactile
soil texture method analysis from samples in two profile pits. Generally the soils below approximately 6 inches of
topsoil consist of medium dense sandy silt loam texture soil with slightly blocky to granular structure to the profile
pit depth of 8 feet. The soils contain less than 10% scattered gravel or rock content to the 8-feet depth explored
below the surface grades. No free water was encountered in the pit excavations. No evidence of seasonal high
ground water or redox conditions was observed in the profile pits. Seasonal high groundwater levels are expected to
be below 10 feet from the existing surface grades on the relatively flat terrain.
The native soils sampled from 2-3 feet below the surface, in the vicinity of the proposed field, are characterized as a
soil type 2 consisting of sandy silt loam texture with granular structure. This soil has an effective loading rate for
conventional soil treatment of 0.6 Gal/S.F./day for a level 1 conventional treatment system. Additional observations
of the soils encountered in the excavations during construction are consistent with the previously described soil
characterization from the initial soil evaluation.
Long Term Acceptance Rate (LTAR)
Receiving Wastewater Treatment Level 1;
LTAR; (Table 10-1 Soil type 2 loading rate for a sandy silt loam is (0.6 gal./S.F./day);
Design Flow; Qd = flow (gal/day) = 300 gpd
Loading factors; (Table 10-2, Gravity application trenches, L.F.1 = 1.0)
(Table 10-3, Gravelless chambers, L.F.2 = 0.7)
STA absorption treatment area; A = Area S.F.;
A(sf) = Qd x L.F.1 x L.F.2 .: A(sf) = 300 gpd x 1.0 x 0.7 = 350 S.F.
LTAR 0.6 Gal/S.F./day
Number of Arc chambers 5'x3'x12"chambers:
350 S.F. = 23 chambers; Use 24 chambers
15 S.F./Chamber
24 ADS Arc-36 gravelless leaching chamber were installed in 2 trenches 60' long by 3' wide with 12 chambers units
per trench plus two end caps as delineated on the plan.