HomeMy WebLinkAboutEngineer's Letter 12.15.2016December 15, 2016
Brett Jolley
1288 County Road 245,
New Castle Co 81647
RE: AS -BUILT, On-site Wastewater Treatment System (OWTS), Parcel B Huber Exemption,
1793 County Road 245, New Castle CO, LLC,
SE Job No. 27163.03, Parcel Number 2125-252-00-132, County OWTS Permit No.SEPT-3882
Dear Brett:
Pursuant to County requirements, this letter provides documentation that the new Onsite Wastewater Treatment
Systems (OWTS) 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 system
constructed on site was designed with a maximum treatment capacity for the 5 -bedroom residence currently
under construction. 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. Inspections were coordinated with the earthmoving contractor, Redneck Excavation. The as -
built conditions and installation of the new OWTS components is in compliance with Garfield County
Regulations and State of Colorado Regulation 43. The recommendations and specifications delineated on the
civil OWTS design plan, C5-OWTS Plan, dated 8-25-2015, by Sopris Engineering and revised construction
document plan, dated 8-9-16. The design criteria and system sizing information is summarized below. An As -
built OWTS record drawing is attached delineating the As -built descriptions and location of the components.
Design Criteria and As -built System Component Installation
The system was designed based on the design criteria approved for use of Soil Treatment Area (STA) systems.
The OWTS includes the installation of a 1250 gallon 2 -compartment concrete septic tank, with concrete risers
and lids installed at the surface and 500 gallon concrete septic/dosing tank in series. The septic tank was
installed with an inlet sanitary tee and an outlet effluent filter sanitary tee. A gravity schedule -40 sewer pipe
with a cleanout is installed from the residence to the primary septic tank. The soil treatment Area (STA),
consists of 4 fully pressure dosed leaching chamber trenches that provides 672 S.F. of total absorption area.
Septic tank effluent is pumped to the dosed chamber soil treatment unit (STU) field located east of the
building within a previously undisturbed land. The primary treated effluent discharges to two slightly mounded
pressure dosed beds consisting of gravelless chambers with custom perforated pressure distribution pipe laterals.
The pressure doses STA system provides secondary treatment of wastewater with infiltration into the underlying
soils. The system meets all required standards and setbacks for a STA chamber trench system.
The 500 gallon concrete septic/dosing tank (pump basin) is installed with an Orenco Systems bio -tube
dosing pump vault. The duplex effluent pump assembly discharges effluent to STA absorption field that
consists of 4 pressure dosed chamber trenches installed in native soils. The pump basin tank system has
been installed with an Orenco Systems Biotube vault duplex effluent pump assembly. A 30" ribbed PVC
riser with lid at the surface was installed over the tank access opening. The pump system transports effluent
from the pump basin tank to a 672 square foot STA configured for alternating pressure distribution over 2
pressure distribution zones through alternating pumps. The dual 1.25 -inch transport lines from each pump
502 Main Street • Suite A3 • Carbondale, CO 81623 • (970) 704-0311 • Fax (970) 704-0313
SOPRIS ENGINEERING • LLC
civil consultants
Brett Jolley
AS -BUILT OWTS
1793 County Road 245
SE Job No. 27163.03
December 15, 2016
Page 2
is bedded in road base and installed to allow gravity drainage of effluent back to the tank from the high
point at the center of the individual distribution zone manifolds installed at the head of each trench pair.
All distribution piping, valves and pump assembly components have been installed and are in operation in
accordance with the design and performance specifications.
Design Criteria and As -built System Component Installation and Sizing
The design flow is calculated as follows for a 5 -bedroom single family residence onsite wastewater
treatment system (OWTS).
From the Regulation 43 usage table:
Minimum population based on the first 3 bedrooms @ 2 persons per bedroom & 2 additional bedrooms
@ 1 person per bedroom= 8 persons.
Gallons per day per person =75 gal/person/day, No peaking factor
Max. Design flow (Qd) gallon per day (GPD) = (# of people) x (avg. flow) gal/person/day.
Design flow Qd = 8 persons*75gal/person/day=600 GPD
Septic Tank Design:
600 GPD x 2 day detention storage = 1200 gallons.
A 1250 gallon, two-compartment concrete septic tank & a 500 gallon dosing tank with a duplex system
effluent pump was installed. Tanks shall be installed with concrete 30" risers and lids to the finish grade
surface.
Sub Surface Conditions and Testing:
Subsurface soil investigations and USDA soil texture method tests were performed by Sopris Engineering.
The soils in the area of the proposed absorption field were sampled and characterized by application of the
USDA soil texture method analysis. The soils were tested to determine the hydraulic loading rate and to
confirm the appropriate absorptive surface level suitable for conventional absorption systems in native
soils. The soils below 6 to 12 inches of topsoil consist of medium dense sandy loam to loam soil with
gravels to 6 feet below the surface. The underlying soils are composed of mixed alluvial materials
consisting of gravels & cobbles in a sand matrix. The soil appears to be consistent across the proposed
STA field.
The native soils sampled from 2-3 feet below the surface are characterized as a soil type 2A consisting of
sandy loam to loans texture with granular structure. This soil has an effective loading rate for conventional
soil treatment of 0.5 Gal/S.F./day for a level 1 conventional treatment system. The equivalent percolation
rate is assumed to be 20-40 minutes per inch.
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 a conventional shallow absorption field
consisting of gravelless infiltration chamber units.
Brett Jolley
AS -BUILT OWTS
1793 County Road 245
SE Job No. 27163.03
December 15, 2016
Page 3
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 pressure dosed distribution to gravelless chamber trenches.
Long Term Acceptance Rate (LTAR) Regulation 43 design criteria:
Receiving Wastewater Treatment Level 1; Loading rate for Sandy loam to loam is (0.5 gal./S.F./day) for
soil type 2A. Reductions in area are based on the applicable Loading factors for Level 1 treatment that
include, (Table 10-2, Pressure Dosed Trenches = 0.8) and (Table 10-3, gravelless chambers = 0.7)
A (sf) = Qd. A = Area;
LTAR = 0.5 Gal/S.F./day for loamy sand
Qd = flow (gal/day) = 600 GPD
L.F.1=0.8 Pressure Dosed Trenches
L.F.2=0.7 Chambers
A (sf) = 600 GPD x .8 x 0.7 = 672 S.F.
0.5 Gal/S.F./day
Number of Infiltrator Quick -4 chambers:
672 S.F = 56 chambers Installed
12 S.F./Chamber
56 Quick -4 chambers were installed in four trenches 58' long by 3' wide with 14 chambers units per trench
plus two end caps as delineated on the plan. The beds are alternately dosed from the duplex high head
pump system installed in the third compartment of the septic tank. Each chamber row has custom
perforated 1.25" PVC distribution laterals with 3/16 inch orifices spaced on 3 -foot centers. The orifices
are oriented upward to spray against the chamber with the first and last orifice at each end oriented
downward to allow for drainage of the pipe between pump cycles.
Distribution Pump System
The system was installed with an Orenco Systems biotube vault w/ duplex dosing pump assembly (PVU-48-2419-L)
vault w/ (PP -300512 pumps) & 1.25 -inch discharge assembly (HV 125XQ-DB).
The dosing assembly is operated by an Orenco Systems strut mounted control panel & alarm installed next to the
dosing tank. The system was installed by Valley Precast, Inc.
OWS Operation and Maintenance
Ownership of the system and responsibility for 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 perform all
maintenance and repairs necessary to insure that the system components are maintained in good operating
condition. The components of the OWTS system should be inspected within 30 days of being placed into operation
Brett Jolley
AS -BUILT OWTS
1793 County Road 245
SE Job No. 27163.03
December 15, 2016
Page 4
and should be inspected and maintained bi-annually. The tank, absorption field and other system components
should be visually inspected annually for debris, damage, leaks, or other potential problems. In general, for a
properly utilized system, septic tanks should be pumped every 3 - 5 years. The system includes an effluent filter in
the primary septic tank and a bio tube filter in the pump vault that should be inspected every six months and cleaned
as needed and at the time of tank 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. Rutle
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