HomeMy WebLinkAboutOWTS Installation ObservationsRE
0ctober 7 ,2022
Paul & Robyn V/haley
1776 CountyRoad24l,
New Castle CO 81647
robyn.whaley 1 3 @gmail.com
As-Constructed Report-Onsite Wastewater Treatment System (OWTS), V/haley Property, 1776 County
Road 2411, New Castle CO, Tr lnBll4 Of Lot 3 Lying Ely of New Harris Ditch, Garfield County
SEJob No. 32219.01 Parcel No: 2 123 I 8300001 . Existing County ISDS Permit No.: 1 777
Dear Paul & Robyn:
Pursuant to County requirements, this letter provides documentation of the usage and as-constructed conditions of
the Onsite Wastewater Treatment System (OWTS) installed at the above referenced site to support obtaining a post
construction permit for the system. The OWTS installations were constructed to serve a detached guest bedroom
suite on the 14 acre rural parcel. The existing bedroom suite contains 2 bedrooms, a3/+bath and basin and does not
have any kitchen or laundry fixtures. Regulatory usage is considered to be equivalent to additional bedrooms in
addition to the existing 3-bedroom residence. The water source for the detached bedroom facility is from a water
storage tank plumbed for use inthe 775 S.F. accessory dwelling unit structure. It is reported by the owners that the
average monthly water use withdraw from the water storage tank equates to approximately 25 gallon per day when
occupied. Sopris Engineering performed site visits to inspect and document the as-constructed conditions of the
OWTS. lnspections were coordinated with the property owner that had the system components installed
approximately 2 years ago.
The as-constructed conditions and installation of the OWTS components are generally in compliance with Garfield
County Regulations in regard to design criteria for usage based on 75 gpd per additional bedroom over the first
three bedrooms. The limited usage of the single guest bedroom suite may be considered equivalent to a hotel room
usage of 75 gpd per unit or a luxury resort room usage of 125 gpd per unit. The field observations and post
installation system sizing/component information is summarized below.
Summarv Existine OWTS Conditions
The installed OWTS has a regulatory treatment capacity of 150 gallons per day based on the design wastewater
flow to serve two additional bedrooms over the first 3, for a total 5-bedroom residential complex in accordance with
Table 6-2 values, Section 43.6, A.4. The OWTS utilizes a 1,060-gallon two compartment reinforced plastic septic
tank and soil treatment area (STA) consisting of a single chamber trench installed west of the westerly corner of the
accessory structure. The system is installed in line, along the edge ofa protected gravel surfaced area adjacent to a
large expansive lawn area. The tank was installed with sealed risers and lids to the finish grade surface, an inlet
sanitary tee and an effluent filter outlet sanitary tee in the second compartment.
The soil treatment unit (STA) consists of 7 Arc-36leaching chamber trenches that provide 105 S.F. of total
absorption area. The septic tank effluent is gravity discharged through a 4-inch assumed schedule-4O gravity sewer
pipe installed to the head of the first trench chamber. Observation ports with threaded PVC caps are installed on the
head and distal end chamber units. The design is in compliance with the current County regulations with design
calculations based on assumed soil type, texture and structure long term acceptance rate (LTAR). The installed
system meets all required setbacks and was installed within the general location indicated on the plan. The existing
well, serving the primary residence, is located over 100 feet east of the existing STA. The back calculated OWTS
design criteria, assumed soil characteristics and system components are further summarized below and delineated
on the attached C-l As-Constructed OWTS Record drawing, dated 10-07-2022 prepared by Sopris Engineering.
502 Main Street a Su ite A3 a Carbondale, C0 81623 a (970) 704-031 1 a Fax (970) 704-031 3
$oPnrs tnGIrrrnrlrc o 11G civil consullants
Whaley Property
AC-OWTS, 1776 Coun|y Road 241
SE Job No. 32219.01
october 7,2022
Page2
Resulatorv Flow
The OWTS is regulatory design flow is 150 gallons per day based on the minimum design wastewater flow to serve
1 person per additional bedroom for a single family residential complex that has a total 5 bedrooms, in accordance
with Table 6-2 values, Section 43.6, A.4. Regulation 43: Minimum population based on I person per bedroom for
the additional 2 bedroom capacity : 2 persons. Gallons per day per person :75 gallperson/day, No peaking factor
Max. Design flow (Qd)gallonslday: (# of people) x (avg. flow)galipersonlday.
Design flow Qd:2*75:150 gpd
Septic Tank Desisn
The existing septic tank has adequate capacity for minimum 48 hour retention time:
V : 150 gallday * 2 : 300 gallons. Installed a minimum 1,060 gallon, two compartment reinforced plastic septic
tank with an inlet sanitary tee and effluent flrlter outlet sanitary tee in the second chamber. Tank was installed with
sealed risers and lids to the finish grade surface.
Sub Surface Conditions and Observation
A site assessment was performed by Sopris Engineering in on October 3,2022. The onsite soils near and adjacent to
the existing STA were sampled and characterizedby application of the USDA visual/tactile soil texture method
analysis from samples obtained in a driveway excavation cut and a shallow hand dug excavation near the distal end
of the trench. The soils below 3-6 inches of topsoil consist of medium dense loamy sand texture soil with slightly
granular structure to a depth of 3 feet. The soils contain scattered gravels and cobbles assumed to be less than 30Yo
in the loamy sand to sandy loam soil matrix. The moderately flat area is situated at higher elevations slightly above
the upper ridgeline of the draw in an area refemed to as the Fenin Heights located at the base of a massive steep
sandstone flat iron feature on the easterly mountainous slope of the East Elk Creek valley and the northerly side of
the upper bench of the U shaped draw. No free water was encountered in the shallow excavations or observed in the
vicinity. The native sandy soils in the immediate area appear to be well drained and our situated at elevation
approximately 100 feet above the agricultural fields to the south located across the broad expanse of the terrain
feature draw. Seasonal high Groundwater levels are expected to be below 20 feef from the existing surface grades
on the moderately slope terrain.
The native soils sampled at 3 feet below the surface grades, in the vicinity, are characterized as a soil type I
consisting of loamy sand texture with slightly granular structure. This soil is assumed to have an effective loading
rate for conventional soil treatment of 0.8 Gal/S.F./day for a level 1 conventional treatment system. The equivalent
percolation rate is assumed to be 5- 1 5 minutes per inch. The soils observed appear to be suitable for the
conventional shallow absorption field consisting of gravelless infiltration chamber units.
Septic tank & Treatment-Soil Treatment Area Existine Conditions
The existing treatment system and absorption field consists of gravity distribution of septic tank effluent to a single
chamber trench with treatment across the native soil absorptive surface. The STA trench was installed to a
maximum depth at the absorptive surface approximately 36 inches from pre-construction existing surface grades
and backfilled with 6 to l2-inches of final grading subgrade soils and imported gravel over the trench placed to
allow positive drainage off the finish grave surface. The trench area is protected from vehicular traffic by a line of
placed embedded boulders installed in a northwesterly line adjacent to the tank and trench parallel to the existing
contours. The trench absorptive surface was dry at the time of inspection. The sludge level in the septic tank fist
compartment was less than 4 inches and no scum was observed in either compartment. A clean out was installed
outside the exterior wall of the bathroom. The effluent filter was clean. No evidence of excessive hydraulic or
organic loading was observed.
Whaley Property
AC-O\ryTS, 1776 County Road 241-"t"T"i"lï'åli
Page3
STA Sizins Lons Term Accentance Rate ILTAR)
Receiving Wastewater Treatment Level l; Soil type I loading rate for a loamy sand is (0.8 gal./S.F./day).;
Loading factors; (Table l0-2, Gravity application trenches = 1.0 ) and
(Table l0-3, gravelless chambers = 0.7)
A(sÐ: Qd x L.F.l x L.F.2
LTAR
A = Area;
LTAR: 0.8 Gal/S.F./day for loamy sand
Qd = flow (gallday): 150 gpd
L.F. l:1 .0 Gravity Distribution
L.F.2=0.7 Chambers
A(sO = 150 gFd x 1.0 x 0.7 = l3l'5 S.F,
0.8 GaUS.F./day
Number of Arc-36 chambers 5'x3'xI2"chambers:
l3l.2s s.F.= 8.75 chambers; Installed 7 chambers 35 L.F. absorption area by 3 feet wide = 105 S.F.
l5 S.F./Chamber
Based on field observations and measurement it appears that 7 Arc-36 chambers were installed in a single trench 35'
long by 3'wide. Based on reported average water usage in the structure of 25 gpd and the limited occupancy of the
bedrooms the effective absorptive area of 105 S.F. is expected to provide adequate treatment for actual usage.
Additional area beyond the distal end of the existing trench is available if expansion of the trench length is to be
considered.
O\ilTS Oneration and Maintenance
Ownership of the system and responsibility for maintenance and repair remains with the property Owner. The
Owner is encouraged to retain the services of qualified personnel to inspect the OWTS and to perform all
maintenance, repairs and any future upgrades as necessary to ensure that the system components are maintained in
good operating condition. The components of the OWTS system should be inspected and maintained bi-annually.
The tank, absorption freld and other system components should be visually inspected for periodic tank pumping,
eflluent frlter cleaning, potential ponding in trenches, leaks from fïxtures, or other potential conditions. In general,
for a properly utilized systom, septic tanks should be pumped every three - five years. The effluent filter should bc
cleaned every six months and at the time of pumping. 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
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