HomeMy WebLinkAbout OWTS Installation Observation Letter 12.31.24December 31, 2024
502 Main Street • Suite A3 • Carbondale, CO 81623 • (970) 704-0311 • Fax (970) 704-0313
S OPRIS E NGINEERING • LLC civil consultants
Dylan Mace
88 Cedar Street,
Carbondale, CO 81623
"dylan mace" <dylawnmace@gmail.com>
RE: Certification Letter, As-Constructed On-site Wastewater Treatment System (OWTS), Mace
Residence, 88 Cedar Street, Lots 15-16, D Blk 9, Cooperton TWNSTE Carbondale, CO
SE Job No. 19219, Parcel No: 2393-284-09-015. County OWTS Permit #SEPT-6424
Dear Dylan:
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 residential system was designed for a maximum 3-bedroom residential capacity.
System Startup
Sopris Engineering adjusted float setting and performed a dry run system startup to test float and control
operations on October 31, 2024. The system floats were wired for correct functionality in compliance with
installation and design specifications. No water was in the tank at the time, however the floats were
manually operated to test the pump on/off activation and high water visual/audible alarm. The high level
visual and audible alarm is active. The testing verified that the system is functioning as designed and can
be set for automatic normal operation once a near normal liquid level is present in the tank. The pump
amperage and voltage was tested and found to be in compliance with manufacturer’s specifications. The
operation demand dose to the field is approximately 40 gallons per dose cycle with an approximate end of
lateral squirt height of 2.5 feet. The high level visual and audible alarm is active.
Sopris Engineering performed a site visit to inspect and document the as-constructed conditions of the
OWTS. 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 C2
OWTS plan drawing dated 08-16-2020 by Sopris Engineering. The design criteria and system sizing
information is summarized below. The As-Constructed OWTS components were completed as delineated
on the design construction document plan previously submitted for permit for a three-bedroom capacity.
OWTS Design Criteria and Sizing
The residential facility includes a 1-bedroom dwelling served by the new OWTS system. The system was designed
based on the current County design criteria and the design criteria approved for the use of a pressure dosed sand
filter (SF) system. The design is in compliance with the current County Regulation No. 43 with area calculations
based on the LTAR loading rate for ASTM-33 filter sand per a minimum equivalent 3-bedroom design flow
capacity.
A two-compartment 1,250 gallon concrete septic tank equipped with an Orenco Systems simplex high head pump
with Biotube vault assembly was installed in the secondary chamber with associated piping and controls. The field
consists of a single 564 S.F. pressure dosed sand filter treatment/absorption bed with 24-inches of filter sand.
OWTS As-Constructed Report
Mace Residence
SE Job No. 19219.01
December 31, 2024
Page 2
The effluent is equally dosed via three individual custom perforated 1.25” PVC pressure distribution pipes, running
the length of the 47 feet by 12 feet sand filter bed. The distribution lateral pipes are covered with Infiltrator Quick-4
Plus chamber units for use as spray shields.
Design Calculations OWTS
Installation of an OWTS with a minimum 3-bedroom capacity.
Minimum population based on 3 bedrooms = 6 persons.
First 3 bedrooms (2 persons/bedroom) Over 3 bedrooms (1 person per bedroom)
Gallons per day per person =75 gal/person/day, No peaking factor
Max. Design flow (Qd) gallons/day = (# of people) x (avg. flow) gal/person/day.
Design flow Qd = 6*75=450 gpd
Septic Tank Design: Used a 1250 gallon, two compartment septic tank with a bio-tube dosing assembly in the
second chamber.
Sub Surface Conditions and Testing
Subsurface soil investigations and USDA soil texture method tests were performed by Sopris Engineering on April
6, 2020. The soils in the area of the proposed absorption field were sampled and characterized by application of the
USDA soil texture method test. The soils were tested to determine the hydraulic loading rate and to confirm the
appropriate absorptive surface level suitable for an intermittent sand filter treatment system in native soils. The soils
below nil to 3 inches of topsoil consist of medium dense gravelly loamy sand to sandy loam material to 0.3 to 4 feet
below the surface. The soil appears to be consistent across the site.
The native soils sampled from 1-2 feet below the surface are characterized as a soil type 1 consisting of loamy sand
to sandy loam texture with moderate granular structure. Soils below 2 feet are increasingly rocky becoming R-1 soils
with more than 30% rock content smaller than 3/4”. This soil has an effective loading rate for conventional soil
treatment of 0.8 Gal/S.F./day for a level 1 conventional treatment system. Due to limited area, rock content and to
provide optimal treatment an intermittent sand filter is recommended. No free water was encountered in excavations
on site. Groundwater levels are expected to be below 10 feet from the existing surface grades.
The soils are suitable for the installation of a sand filter treatment bed system that is fully pressure dosed and utilize
24-inches of washed concrete sand.
Intermittent Sand Filter Treatment Unit/ Absorption System Design
Long Term Acceptance Rate (LTAR)
Receiving Wastewater Treatment Level 1; loading rate for sand filter is (0.8 gal./S.F./day) for the minimum 24"
depth of secondary sand treatment media;
Loading factors; (Table 10-2, pressure dosed application bed = 1.0)
A(sf) = Qd: A = Area;
LTAR LTAR = 10.8 Gal/S.F./day for secondary sand, ASTM-33, "Concrete sand"
Qd = flow (gal/day) = 450 gpd
L.F.1=1.0 pressure dosing
A(sf) = 450 gpd x 1.0 = 562.5 S.F.
0.8 Gal/S.F./day