HomeMy WebLinkAboutOWTS Installation Observations 06.29.2020June 29, 2020
502 Mai n Street • Suite A3 • Carbondale, CO 81623 • (970) 704 -0311 • Fax (970) 704 -0313
S OPRIS E NGINEERING • LLC civil consultants
Lowell Walter
Locabebrem Family Trust
6538 331 County Rd
Silt Co 81652
RE: As-Constructed–Onsite Wastewater Treatment System (OWTS), Walter Ranch Residence, 6538 C.R. 331,
A Parcel In Sec 10 & 11 T7s R92w 6th PM Subdivision, Garfield County, Colorado
SE Job No. 30060.01 Parcel Number: 2401-112-00-206, Garfield County Permit: SEPT-6234
Dear Lowell:
Pursuant to County requirements, this letter provides documentation that the Onsite Wastewater Treatment System
(OWTS) upgraded 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 installatio ns were completed. The replacement
absorption field and tank installations were designed and constructed to serve the existing 5-bedroom residential
structure.
Sopris Engineering performed site visits to inspect and document the as-constructed conditions of the OWTS.
Inspections were coordinated with the property owner and the Contractor, Heyl Construction that installed the
replacement system components. The as-built conditions and installation of the upgraded and new OWTS
components is in compliance with Garfield County Regulations; the recommendations and specifications delineated
on the civil C1 OWTS plan drawing dated 04-14-2020 and the OWTS design Report dated, 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.
Summary Design Criteria
The waste flow from the existing residence ha d been served by an OWTS permitted at the time of building permit in
1995, under County ISDS permit No. 2324 to serve a 3-bedroom residence. The recently installed OWTS provided
for a replacement of the septic tank and absorption field for a treatment capacity of 600 gallons per day based on the
design wastewater flow to serve a 5-bedroom residence in accordance with Table 6-2 values, Section 43.6, A.4. The
new 1,500 gallon 2-compartment concrete septic tank, was installed in the native meadow area west of the dwelling
adjacent to the existing septic tank that was removed. The tank was installed with risers and lids at the surface, an
inlet sanitary tee and an outlet effluent filter sanitary tee in the second compartment. A gravity schedule-40 or
SDR-35 sewer pipe with a cleanout was installed from the existing gravity sewer line from the dwelling upstream of
the existing tank to route raw sewage to the new tank. The existing gravity sewer pipe will be maintained from the
residential structure to the new connection point. A new two cleanout was installed at the pipe connection.
The new replacement soil treatment unit (STU) consists of leaching chamber trenches that provide 700 S.F. of total
absorption area. The septic tank effluent is gravity discharged to the STU via a distribution box. Observation ports
with caps have been installed on each end chamber unit. 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 as-constructed system meets all required setbacks and was installed within the
general location indicated on the OWTS plan. The existing well is located over 200 feet northwest of the field area.
An as-constructed OWTS plan is attached.
Walter Ranch Residence, 6538 C.R. 331
SE Job No. 19228.01 GarcoPermit: SEPT-6234
June 29, 2020
Page2
Design Flow
The replacement OWTS is designed for a treatment capacity of 600 gallons per day based on the following design
criteria:
Minimum population based on 2 person per bedroom for the first 3 bedrooms = 6 persons and 1 person per
bedroom for each additional 2 bedrooms = 2 persons for a total of 8 persons.
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 = 8*75=600 gpd
Septic Tank Design
The septic tank capacity required for a minimum 48 hour retention time is calculated as follows:
V = 600 gal/day * 2 = 1,200 gallons. Use a 1,500 gallon, two compartment concrete septic tank with an inlet
sanitary tee and effluent filter outlet sanitary tee in the second chamber.
Sub Surface Conditions and Observation
A subsurface soil investigation and site assessment was performed by Sopris Engineering in on April 15, 2020. The
soils in the proposed field envelope area were sampled and characterized by application of the USDA visual/tactile
soil texture method analysis. The soils below 6 inches of topsoil consist of medium dense sandy silt loam soil with
less than 2% scattered gravel or rock content to 8 feet below the surface grades. The soils appear to be consistent
across the site from observations in the excavated profile pits.
The native soils sampled from 2-3 feet below the surface are characterized as a soil type 2 consisting of sandy silt
loam texture with fine granular structure. This soil has an e ffective 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 assumed to be 20-30
minutes per inch. No free water was encountered in excavations on site. Seasonal high Groundwater levels are
expected to be below 20 feet from the existing surface grades.
Treatment-Soil Treatment Unit/ Absorption System Design
The treatment/absorption field is designed based on utilizing the effective Long Term Acceptance Rate (LTAR) for
the native soils and the application of appropriate loading factors for a soil treatment unit system utilizing gravity
distribution to gravelless chamber trenches. The shallow STU trenches were installed level to an average absorptive
surface depth of 30 inches from finish surface grades along natural contour grades accordingly.
Field Sizing per Long Term Acceptance Rate (LTAR):
Receiving Wastewater Treatment Level 1; Soil type 2 loading rate for a silt loam is (0.6 gal./S.F./day).; Loading
factors; (Table 10 -2, Gravity application trenches = 1.0 ) and (Table 10-3, gravelless chambers = 0.7)
A(sf) = 600 gpd x 1.0 x 0.7 = 700 S.F.
0.6 Gal/S.F./day
Number of Quick-4 Infiltrator chambers 4'x3'x12"chambers:
700 S.F = 58.3 chambers; Installed 60 chambers
12 S.F./Chamber