HomeMy WebLinkAboutOWTS Installation Report 11.26.2019November 26, 2019
Marianne Alameno & Paul Stanek
2980 County Road 311
Ness' Castle Co 81647
RE: As-Constructed—Onsite Wastewater Treatment System (OWTS), 2980 County Road 311, Lot 8, Mineota
Ridge Est. 3`d Subdivision, Garfield County, Colorado
SE Job No. 19228.01 Parcel Number: 2179-134-00-01 IGarfield County Permit: SEPT -10-19-5983
Dear Paul and Marianne:
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 at various times during construction, prior to final backfill and after all installations was completed.
The replacement absorption field and existing tank modification installations were designed and constructed to
serve the existing 3 -bedroom residential structure.
Sopris Engineering performed site visits to inspect and document the as -built conditions of the constructed system.
Inspections were coordinated with the property owner that installed the upgraded field and Down Valley Septic and
Drain that installed the tank upgrades. 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 C3 OWTS plan drawing dated 10-2-2019, 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 existing 3 -bedroom residence has split waste flows and is served by two separate OWTS's. The original
historic field was failing. The design provided for a replacement absorption field based on treatment sized for an
equivalent 2 -bedroom capacity single family residence onsite wastewater treatment systems (OWTS). The design
flow was calculated for 1/2 the waste flows of the existing single family. The upgrade consisted of replacement of
the older existing Pipe and gravel field that has historically served the kitchen and original bathroom. The other
existing OWTS, installed in 2001, serves the previous house addition's waste including the new bathroom that
contributes approximately 1/2 of the total waste flow with a design capacity of 450 gpd.
New traffic rated risers with access lids at the surface were installed on the existing 1000 gallon 2 -compartment
concrete septic tank, located in the existing gravel driveway. The tank has an inlet sanitary tee and a new outlet
effluent filter sanitary tee was installed in the second compartment. The existing gravity sewer pipe is maintained
from the residential structure to the existing tank. The new replacement soil treatment unit (STU) consist of
leaching chamber trenches that provide 350 S.F. of total absorption area. The septic tank effluent is gravity
discharged through a new 4 -inch schedule -40 or SDR -35, installed at 2% slope across the driveway, 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 in each chamber trench. Observation ports with caps were installed on each end chamber unit.
The as -constructed field 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. The existing well is
located south of the development area over 100 feet from both systems.
502 Main Street • Suite A3 • Carbondale, CO 81623 • (970) 704-0311 • Fax (970) 704-0313
SOPRIS ENGINEERING •LLC
civil consultants
Alameno, AC-OWTS, 2980 C.R. 311
SE Job No. 19228.01
November 26, 2019
Page2
Design Flow
The replacement OWTS is designed for a treatment capacity of 300 gallons per day based on the design wastewater
flow to serve a 2 -bedroom capacity residence in accordance with Table 6-2 values, Section 43.6, A.4.
From the Regulation 43 usage table :
Minimum population based on 2 bedrooms = 4 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 = 4*75=300 gpd
The existing 1000 gallon, two compartment concrete septic tank was upgraded with the installation of an effluent
filter outlet sanitary tee in the second compartment and addition of traffic rated concrete risers with iron ring and
covers to the finish grade surface.
Sub Surface Conditions and Observation
A subsurface soil investigation and site assessment was performed by Sopris Engineering on October 1, 2019. 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 slightly sandy silt loam
soil with less than 5% scattered gravels and cobbles to 8 feet below the surface grades. The soils appear to be
consistent across the site from observations in the excavated profile pit.
The native soils sampled from 2-3 feet below the surface 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 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. The soils are suitable for a shallow conventional
shallow absorption field consisting of gravelless infiltration chamber units.
Treatment -Soil Treatment Unit/ Absorption System Design
The treatment/absorption field was 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 at a maximum depth
to the absorptive surface of 36 inches from finish surface grades and backfilled with approximately 6 -inches of final
topsoil mounded over the trenches. The field and tank component installations were inspected and approved by the
Engineer prior to backfilling.
Field Sizing:
Long Term Acceptance Rate (LTAR)
Considering the application of the state regulation 43:
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) = Qd .: A = Area;
LTAR LTAR = 0.6 Gal/S.F./day for silt loam
Qd = flow (gal/day) = 450 gpd
Alameno, AC-OWTS, 2980 C.R. 311
SE Job No. 19228.01
November 26, 2019
Page3
L.F.1=1.0 Gravity Distribution
L.F.2=0.7 Chambers
A(sf) = 300 gpd x 1.0 x 0.7 = 350 S.F.
0.6 Gal/S.F./day
Number of 5'x3' Bio -Diffuser chambers:
350 S.F = 23.3 chambers Use 24 chambers
15 S.F./Chamber
Installed 24 Bio -Diffuser chambers in two trenches, 60' long by 3' wide, with 12 chambers units per trench with two
end caps. The septic tank effluent is gravity distributed to the head of each chamber row via individual distribution
pipes from a distribution box.
OWS Operation and Maintenance
Responsibility for OWTS maintenance and repair will remain with the property Owner. The Owner is encouraged
to retain the services of qualified personnel to inspect the OWTS and to perforin all maintenance and repairs
necessary to ensure that the system components are maintained in good operating condition and suitable vegetative
cover is established on the fields. The components of the OWTS system should inspected within 30 days of being
placed into operation and should been inspected and maintained bi-annually. The tank, absorption field and other
system components should be visually inspected bi-annually for debris, damage, Ieaks, or other potential problems.
In general, for a properly utilized system, septic tanks should be pumped every 3 - 5years. The effluent filter should
be cleaned every six months and at the time of pumping. Absorption fields should be maintained with suitable
vegetative cover and kept free of root invasive plants. Positive surface drainage away from the absorption field
should be maintained.
If you have any question or need any additional information, please call.
Sincerely,
SOPRIS ENGINEERING, LLC
Paul E. Rutledge
Design Engineer
dry !ONAI
Yancy Nichol, PE
Principal