HomeMy WebLinkAboutEngineer's OWTS Design SpecsJune 14, 2023
502 Main Street • Suite A3 • Carbondale, CO 81623 • (970) 704 -0311 • Fax (970) 704 -0313
S OPRIS E NGINEERING • LLC civil consultants
Jordan Kobielusz
J&C services
Martin Ranch II LLC
PO Box 654,
Carbondale ,CO81624
"Jordan Kobielusz" jcservices21@yahoo.com (970)319-9918
RE: Design Report, On-site Wastewater Treatment System (OWTS), 3602 County RD 108, Carbondale
Garfield County, CO, Lot 2. AKA Parcel 1 Martin Exemption
SE Job No. 33027.01, Parcel No: 239536400152. Garfield County EHD Permit #______________
Dear Jordan:
This letter report presents the applicable findings in regard to the design and construction of an Onsite
Wastewater Treatment System (OWTS) at the above referenced Site. A new OWTS construction permit is
required for the proposed OWTS construction with respect to proposed usage on the subject property.
The OWTS design is based on our evaluation of the site conditions for use in obtaining a County OWTS
construction permit. We have evaluated the existing and proposed site conditions with respect to the
operation and installation of site specific system design in accordance with County OWTS Regulations and
State of Colorado Regulation 43 in support of your building permit application. The proposed system meets
all required setback requirements and operational demands for residential usage. Based on the physical site
features, soils, and existing building layout, we have prepared a civil OWTS design plan with construction
details for permit approval that was prepared with GIS, Survey Plat information and aerial mapping. The
design criteria and system sizing information is summarized below. The design and construction
recommendations with specifications are delineated on the civil design plans, C3-OWTS Plan dated 06-16-
2023, by Sopris Engineering.
OWTS Conditions and Design Criteria
Proposed OWTS System
The system will be constructed to provide for demand dosing of septic tank effluent to an engineered soil
treatment area (STA) pursuant to Regulation 43 design criteria. The OWTS will include gravity sewer
service pipe from the proposed dwelling to a new 1,250-gallon concrete 2-compartment septic tank. The
tank lids risers and lids will be extended to the finish surface. The new tank will be equipped with a high
head pump assembly to provide full pressure dosing of the STA field.
The STA system is designed based the current design criteria for the use of pressure dosed chamber trench
system. Specifically the preferred treatment technology is individual pressure dosed gravelless chambers
installed in native soils with custom perforated distribution laterals. The sizing is based on utilizing
applicable multiplier loading rates for pressure dosed chamber distribution in trench configurations per the
estimated design flow capacities. The design is in compliance with area calculations based on the LTAR
loading rate for the in-situ soils utilizing shallow pressure dosed low profile infiltrator chamber trenches set
level on the native soil infiltrative surface .
OWTS Upgrade Design and Construction
3602 County RD 108
SE Job No. 33027.01
June 14, 2023
Page 2
The system will include the installation of an Orenco System bio tube simplex effluent pump assembly for
pressure distribution of septic tank effluent to the pressure dosed chamber trenches. The effluent discharge
piping from the pump assembly will be installed to connect to a distribution tee that will have distribution
pipes connecting to manifold pipes with individual pipes to the head of each chamber trench. Each trench
will have appropriate inspection port cleanouts and appurtenances.
Design Calculations OWTS
The proposed onsite wastewater treatment system (OWTS) is being installed to serve a 3-bedroom
residential fcility .The design flow treatment capacity is calculated as follows for a minimum equivalent 3-
bedroom single family residence.
From the Regulation 43 usage table :
Minimum population based on 3 bedrooms = 6 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 = 6*75=450 gpd
Septic Tank Design:
Use a 1250 gallon, two compartment concrete septic tank with a high head pump assembly in the second
chamber.
Preliminary Sub Surface Conditions and Testing
A subsurface soil investigation and site assessment was performed by Kumar & Associates on February 10,
2023. The soils in the proposed field envelope area were sampled and characterized by application of
hydrometer and sieve analysis from samples from three 4-5 foot deep profile pits the shallow soils in these
excavations were sampled, observed and tested at 2-3, and 4-5 foot depths.
The soils below a foot of topsoil consist of relatively dense, sandy loam with gravels and scattered cobble
size sandstone rock fragments. The soils appear to be consistent across the site from observations in other
excavations. No free water was encountered in the pit excavations and soils were slightly moist to moist.
Seasonal high groundwater levels are expected to be below 15 feet from the existing surface grades in the
area of the proposed field.
The native rocky soils sampled from 2-5 feet below the surface, in the vicinity of the proposed field, are
characterized as a soil type 2 sandy loam with rock content less than 35%. The soils at depth have an
effective loading rate for of 0.6 Gal/S.F./day for a level 1 treatment system. The equivalent percolation
rate is assumed to be 16-25 minutes per inch.
Additional observations and soil evaluation will be performed prior to construction mobilization and during
construction, by Sopris Engineering in the area of the proposed absorption field and tank to confirm the
previous soil evaluation and design criteria. Sopris Engineering will observe new profile pits in the area of
OWTS Upgrade Design and Construction
3602 County RD 108
SE Job No. 33027.01
June 14, 2023
Page 3
the proposed absorption field. The soils will be sampled and characterized by application of the USDA soil
texture methods. The soils will be further evaluated to determine the presence of any limiting soil or
hydrological conditions, appropriate hydraulic loading rate, absorptive surface level capacity and to verify
treatment level design for the in-situ native soils. If soil conditions encountered require adjustments to
design criteria or the design plan notice will be made to County EHD and applicable revisions to
design/construction plans and report will be submitted. The results of the additional soil evaluation and soil
characterization will be included in the As-Constructed documentation.
Soil Treatment Area/ Pressure dosed chamber trench Absorption System Design
The treatment/absorption trenches are designed based on utilizing the effective Long Term Acceptance
Rate (LTAR) for native soils and the application of appropriate loading factors for a new soil treatment
area system utilizing pressure dosed chamber trenches with custom perforated distribution laterals installed
in native soil, in accordance with Regulation 43 design criteria for this technology.
Long Term Acceptance Rate (LTAR)
Considering the allowable application of the OWTS regulation 43 and CDPHE approved Distribution
Product for Infiltrator Water Technologies, Quick4 Infiltrators product:
Receiving septic tank effluent, the treatment level-1 for Quick4 Chambers requires the infiltrative surface
being at least 4-feet above a limiting layer (43.8, Table 7-2.4); Maximum hydraulic loading rate for TL1
effluent is the long term acceptance rate of the Type 2 receiving soil is 0.6 gal./S.F./day) (Table 10-1 &10-
1A.).
A(sf) = Qd x L.F.1 x L.F.2.: A = Area;
LTAR LTAR = 0.6 gal/S.F./day for silt loam
Qd = flow (gal/day) for OWTS = 450 gpd
L.F.1=0.8 pressure dosed trench application
L.F.2=0.7 Gravelless chambers
OWTS: A(sf) = 450 gpd x 0.8 x 0.7 = 420 S.F.
0.6 Gal/S.F./day
Number of Quick-4 LP Infiltrator chambers 4'x3'x8"chambers:
420 S.F = 35 Infiltrator Quick-4 chambers; Use 40 Quick-4 LP chambers
12 S.F./Chamber
Use 40 Quick-4 Low Profile Infiltrator chambers in four trenches. Four 42' long by 3' wide trenches with
10 chambers per row plus end caps, as delineated on the plan. The septic tank effluent will be pressure
distributed to the head of each trench via distribution pipe manifolds from a high head pump discharge
assembly in the second compartment of the 1,250 gallon tank.
Effluent Distribution System
OWTS Upgrade Design and Construction
3602 County RD 108
SE Job No. 33027.01
June 14, 2023
Page 4
Filtered effluent will discharge to the trench laterals via a 1.5 inch diameter transport pipe from the high
head pump biotube discharge assembly to distribution piping manifolds between the septic/dosing tank and
the head of the STA trenches.
The distribution system will be installed to allow for effluent to be equally distributed across the absorption
surface in each trench via individual custom perforated full pressure distribution laterals connected to the
manifold pipes at the head of each pair of trenches installed on the native soil surface along the entire
length of the individual trenches. A ball valve will be installed on the terminal end of each distribution
lateral centered below the 4” inspection port in the chamber end cap. The Inspection port with push on cap
will be installed below the surface, housed in a 6" valve box with lid set 1" above surface grades.
The minimum slope of the transport pipe from the tank's dosing compartment to the distribution piping shall
be installed at a minimum 2% downward slope to allow for drainage of piping into the chambers. The
discharge assembly will have an anti siphon orifice to allow for complete drainage of pipes after each
dosing cycle.
Construction and Inspections
Prior to construction of the permitted system, the engineer should be contacted by the contractor and
construction project manager well in advance to provide adequate time to discuss the system components
with the contractor, answer questions, resolve any conflict issues and schedule inspection site visits based
on construction progress. A pre-OWTS construction meeting and calls are essential and required prior to
installation of the OWTS.
The engineer, prior to excavation shall inspect the staked location, of the proposed treatment/absorption
bed and dosing tank. All system components shall be staked in the field for approval by the Engineer prior
to excavation. During initial construction the engineer will evaluate the soils in the location of the
absorption treatment field to confirm design assumptions made and existing conditions. The engineer will
provide construction recommendations and make adjustments to the field layout and sizing if needed with
discussion of construction procedures.
As necessary a revised Construction document drawing will be submitted to the County as needed if
changes are required. All installations shall be inspected, surveyed, documented and reported/delineated in
the Certification letter and As-Constructed drawing.
County Regulations require that the Design Engineer of record perform site inspections of the permitted
system during construction and provide “As-Built” documentation of the installed system to the County
after construction is complete. Photo documentation during construction and site system inspections is
required to be performed by the contractor and Engineer. System component installation inspection and
review of photo documentation is required of the exposed system components prior to backfilling. Photo
documentation will be included with the As-Built Record drawing submittal package to finalize the OWTS
permit. Therefore the Engineer should be contacted as needed and notified of the construction progress and
scheduling to allow time to schedule specific inspection times.