HomeMy WebLinkAboutOWTS Installation ObservationFebruary 20, 2024
502 Main Street • Suite A3 • Carbondale, CO 81623 • (970) 704 -0311 • Fax (970) 704 -0313
S OPRIS E NGINEERING • LLC civil consultants
Harvey, Christopher R & Rebecca J
993 CR 227,
Rifle, CO 81650
C/O Jeff Parrington
President, Tally Ho Construction
www.tallyhoconstruction.com
"jeff" <jeff@tallyhoconstruction.com>
RE: As-Constructed–Onsite Wastewater Treatment System (OWTS), Harvey Residence, 993 County Rd 227,
Silt, CO, Lot 2 Hoffmeister Exemption, Garfield County, Colorado
SE Job No. 31154.01 Parcel No: 217906100631. Garfield County OWTS Permit #:SEPT-7037, issued
09/02/2021
Dear Jeff and Chris:
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 general compliance with the permitted
design. Sopris Engineering inspected the excavations, soils and materials during construction, prior to final backfill.
The soil treatment area (STA) absorption field, septic tank and distribution component installations were designed
and constructed to serve the proposed usage from the garage/apartment structure built on the subject property.
The as -constructed conditions and installation of the new OWTS components is in compliance with Garfield County
Regulations; the recommendations and specifications delineated on the civil design plans, C1-OWTS Plan and the
OWTS design Report dated 08-05-21, by Sopris Engineering. The design criteria and system sizing information is
summarized below.
Summary Design Criteria
The new OWTS was 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. The new OWTS
utilizes a 1,000 gallon two-compartment reinforced plastic septic tank that was installed off the northwesterly wall of
the proposed structure. Sealed plastic risers with lids were installed on the new septic tank along with appropriate
pipe connections to the new tank utilizing the appropriate fitting adaptor rings for the tank and riser. The new 1,000
gallon 2-compartment septic tank was installed with appropriate sanitary tees, outlet effluent filter with risers and lids
at the surface. A gravity schedule-40 sewer pipe section with two-way cleanout will be installed between the tank
inlet on the gravity sewer line and the accessory structure.
The STU consists of leaching chamber trenches that provide 350 S.F. of total absorption area. The septic tank
effluent is gravity discharged through a 4-inch schedule-40 installed at minimum 1.5% slope, to the STU via a
distribution box. The effluent is equally distributed from the distribution box via 4” distribution pipes connected to
the head end cap of each chamber trench. Observation ports with caps were installed on the proximal and distal ends
of each chamber trench. The design is in compliance with the current County regulations with design calculations
based on the soil type, texture and structure with an appropriate long term acceptance rate (LTAR). The designed
system meets all required setbacks and was installed within the general location indicated on the plan. Our design is
outlined below and delineated on the attached C-1 OWTS record drawing.
Harvey Residence
As-Constructed OWTS, 993 County Rd 227, Silt, CO
SE Job No. 31154.01
February 20, 2024
Page2
Design Flow
The design flow is calculated as follows for the minimum design capacity of an equivalent 2-bedroom residential
dwelling. The OWTS is designed for a treatment capacity of 300 gallons per day based on the design wastewater
flow 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, No PF
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 is calculated as follows:
V = 300 gal/day * 2 = 600 gallons. Installed a minimum 1,000 gallon 2-compartment septic tank.
Sub Surface Conditions and Testing
A subsurface soil investigation and site assessment was performed by Sopris Engineering in on July 30, 2021. 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 12 inches of
topsoil consist of medium dense 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 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. The equivalent
percolation rate is as sumed to be 20-30 minutes per inch. The soils are suitable for a shallow conventional
absorption field consisting of gravelless infiltration chamber units.
Long Term Acceptance Rate (LTAR)
Considering the application of the state regulation 43:
Receiving Wastewater Treatment Level 1;
LTAR; (Table 10-1 Soil type 2 loading rate for a 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)
STU 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 Quick-4 Infiltrator chambers 4'x3'x12"chambers: