HomeMy WebLinkAboutOWTS Design Report 03.19.19March 19, 2019
Dave Heyl
Heyl Construction
6560 C.R. 335
New Castle, CO 81647
" Dave Heyl" <d.heyl@heylcivil.com>
RE: Design Site Engineering Report, On-site Wastewater Treatment System (OWTS), Lot 3, Oak
Meadows Subdivision Filing 3, Oak Crest Drive, Glenwood Springs, Garfield County, CO
SE Job No. 18206, Parcel No: 2395-222-03-007.
Dear Jerome:
This letter report presents the applicable findings in regard to the design and construction of an Onsite
Wastewater Treatment System (OWTS) and residential site improvements at the above referenced Site, in
support of your building permit application to Garfield County. The proposed improvements include
grading and drainage, OWTS, driveway, building construction and utilities shown on the Site Plan
prepared by SE in coordination with the property owner.
The OWTS design is based on our evaluation of the site conditions with information provided by others for
use in obtaining a Garfield County OWTS construction permit. We have evaluated the existing and
proposed site conditions with respect to the operation and installation of a new OWTS in accordance with
County OWTS Regulations and State of Colorado Regulation 43. The proposed site specific
improvements have been designed in accordance with County Regulations and general engineering
guidelines regarding grading, drainage, utilities and construction best management practices. Based on the
physical site features, soils, and proposed building layout, we have prepared civil site and OWTS design
plans with construction details for building permit approval. The design and construction recommendations
with specifications are delineated on the Onsite Wastewater Treatment System Plan, dated 3-19-2019, by Sopris
Engineering.
OWTS Design Criteria and Sizing
Based on our findings the design and installation of an engineered OWTS with enhanced treatment is feasible in
accordance with applicable County and the State of Colorado Regulation 43. The building improvements will
include a 4 -bedroom dwelling with a Shop Garage facility that includes a '/2 bath to be served by the new OWTS
system. The system is designed based on the current County design criteria and the design criteria approved for the
use of a pressure dosed sand filter (SF) system. The design is in compliance with the current County Regulation
No. 43 with area calculations based on the LTAR loading rate for ASTM -33 filter sand per a minimum equivalent
4 -bedroom design flow capacity.
Design recommendations include the installation of a 2,000 gallon3-compartment concrete septic tank that provides
1,500 gallon capacity in the first and second compartments. The tank that will be equipped with an Orenco Systems
duplex high head pumps in a Biotube vault installed in the third chamber with associated piping and controls. We
recommend the use of a full pressure dosed Sand Filter (SF) system to provide good secondary treatment
performance in the relatively rocky soils. The SF field will consist of two beds installed to provide for equal
pressure distribution of effluent across a 672 S.F. treatment/absorption SF field with 36 -inches of filter sand below
502 Main Street • Suite A3 ■ Carbondale, CO 81623 • (970) 704-0311 • Fax (970) 704-0313
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civil consultants
OWTS Design and Construction
Oak Meadows Lot 3
SE Job No. 18206.01
March 19, 2019
Page 2
gravelless chamber spray shield units. The effluent will be dosed across the two distribution rows via an individual
custom perforated pressure distribution pipe running the length of each 42 feet by 8 feet sand filter beds.
OWTS Design Flow Calculations
The onsite wastewater treatment system (OWTS) is designed with the capacity to serve a 4 -bedroom residence. The
design flow is calculated for a four bed -bedroom residential dwelling with less than 6000 S.F. of floor space.
From Garfield County/Regulation 43 usage table :
Minimum population based on 3 bedrooms = 6 persons.
Additional population based on (bedrooms assuming 1 person per bedroom.Gallons per day per person =75
gal/person/day, No peaking factor
3 bedrooms x 2 persons/bedroom + 1 additional bedroom x 1 person/bedroom = 7 persons
Max. Design flow (Qd)gallons/day = (# of persons) x (avg. flow)gal/person/day.
Design flow Qd = 7*75=525 gpd
Septic Tank Design:
Qd = 525 gal/day
Volume (V) of tank = Design Flow x 2 (48 hour -2 day retention time)
V = 525 gal/day * 2 = 1050
Use a 2000 gallon, 3 -compartment septic with 1500 gallons of capacity in the 1st and 2nd chambers, The third
chamber will be equipped with a head duplex dosing pump assembly.
A site specific subsurface soil evaluation was performed by Sopris Engineering, in March, 2019, in the vicinity of
the proposed OWTS field. The soils encountered in two excavated profile pits were sampled and characterized by
application of the USDA soil texture method test. The soils were tested to determine the hydraulic loading rate and
to confirm the appropriate absorptive surface level suitable for an intermittent sand filter treatment system in native
soils. The soils below nil to 12 inches of topsoil consist of medium dense sandy clay loam from 1.0 to 6 feet below
the surface. The soil appears to be consistent in both profile excavations and across the site.
The native soils sampled from 2-3 and at 6 feet below the surface are characterized as a soil type 3 consisting of
sandy clay loam texture with moderate granular structure. The tactile soil test ribbons were over 1 -inch long
however they did not exceed 1 '/4 inch. The type 3 soil has a theoretical effective loading rate for conventional soil
treatment of 0.35 Gal/S.F./day for a level 1 conventional treatment system and 0.65 Gal/S.F./day for a level 3
secondary treatment system. Due to terrain topography and to provide optimal treatment an intermittent sand filter is
recommended that will treat effluent to a Level 3 treatment quality prior to infiltration into the native soil. 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 the installation of a sand filter treatment bed system that will be fully pressure dosed and
utilize 36 -inches of washed concrete sand. An additional soil evaluation will be performed during construction to
verify the soils in the proposed field excavation and to confirm that appropriate sand filter media is installed.
Intermittent Sand Filter Treatment Unit/ Absorption System Design
The treatment/absorption field is designed based on utilizing the effective Long
an intermittent sand filter treatment system utilizing pressure dosed distribution
units as spray shields. The new treatment system will consist of a fully pressure
System with a 36 -inch layer of washed filter sand (ASTM -33, "Concrete sand")
secondary sand.
OWTS Design and Construction
Oak Meadows Lot 3
SE Job No. 18206.01
March 19, 2019
Page 3
Term Acceptance Rate (LTAR) for
laterals and gravelless chamber
dosed sand filter Treatment bed
assuming available as new defined
Long Term Acceptance Rate (LTAR)
Considering the application of regulation 43 for design of unlined sand filters receiving Wastewater Treatment
Level 1; loading rate for sand filter is (0.8 gal./S.F./day-Secondary sand) and the design basal area for effluent
treatment level 3 is (0.65 gal./S.F./day) for Type 3 receiving soils and 0.8 gal/S.F./day for treatment level 3 sand
filter with minimum 36" depth of treatment media ;
Loading factors L.F.; (Table 10-2, pressure dosed bed application = 1.0)
A(sf) = Qd x L.F.: A = Area; Qd = flow (gal/day) = 525 gpd
LTAR L.F.1=1.0 pressure dosing
LTAR = 0.8 gal/S.F./day for treatment level 3 sand
filter utilizing 36" washed ASTM -33, filter secondary sand
A(sf) = 525 gpd x 1.0 = 660 S.F.
0.8 gal/S.F./day
Excavate two 42' by 8' beds to a maximum 5' depth below finish grade to insure that that the absorptive surface, at
the top of the sand layer does not exceed an average 2.5' depth below the finish surface grades across either bed.
Scarify surface and backfill with 36 -inches of ASTM -33, washed concrete sand. Install 2 rows of custom perforated
1.25 -inch distribution lateral on top of sand layer in each bed and cover with 9 Quick -4 chambers per row for use as
pressure dose spray shields, as delineated on the plan. The beds will be alternately dosed from the duplex high head
distribution pump system installed in the second compartment of the new septic tank. See plan for layout of system
beds.
The standard Quick 4 chamber spray shields shall be installed over the top of the sand on 4 -foot centers and
backfilled with a minimum 12 -inch depth of cover. Filter fabric shall be placed over the chambers and the entire
extents of the sand filter bed. The slightly mounded field shall be constructed with final surface grading at a
minimum 6 -inches above the up gradient surface grades with a minimum 3 -inch topsoil layer placed over the field
surface.
The chamber rows shall be completed with standard end caps installed at both ends. A piezometer monitoring well
pipe riser with threaded cap will be installed near a corner of the field and be extended down to the excavated
surface depth at the bottom of the placed sand.
Effluent Distribution System
The OWTS field shall be fully pressure dosed along the entire length of the distribution rows. An Orenco Systems
Bio Tube pump vault system will be installed with an effluent screen in the second compartment of the septic tank.
The pump system shall incorporate a duplex high head pump assembly for alternate dosing to each bed. The duplex
pump assembly will demand dose effluent through the dual 1.25 -inch diameter PVC transport pipes from the pump
OWTS Design and Construction
Oak Meadows Lot 3
SE Job No. 18206.01
March 19, 2019
Page 4
assembly and connect to manifold pipe that connects to the two custom perforated pipes at the head of each bed.
The 1.25" discharge transport pipes shall be installed with a minimum 2.5% continuous slope to allow for drainage
of the pipe.
The effluent will be equally pressure dosed through each 1.25 -inch custom perforated distribution lateral running
the length of the treatment bed installed on top of the sand filter layer. The pipe will have 3/16 -inch orifices drilled
every 2.0 feet oriented upward to spray against the interior chamber unit that will broadcast the effluent onto the
sand surface. The first and last orifice will be drilled and oriented downward with an orifice shield to allow
drainage of the line. Individual 1.25" ball valves will be installed at the end of each perforated distribution lateral
centered below one of the pair of end cap vertical inspection port penetrations at the terminal end of the field. Two
vertical 4 -inch inspection ports will be installed from the pair of end cap inspection port penetrations at the terminal
end of the field and one 4 -inch inspection port will be installed from either end cap penetration at the head of the
field. All inspection ports shall extend a minimum 6 -inches above the finish grade and be topped with a treaded cap.
Pump operations shall be controlled by a wall mounted exterior control panel in direct line of site with the tank.
Automatic float switches for on, off and high water with alarm activation shall be installed on a dedicated PVC float
tree. Two separate circuits from the electrical circuit panel and/or junction box shall be routed to the control panel
for separate power to the controls and pump.
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
tank. All septic 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 -built 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.
OWTS Design and Construction
Oak Meadows Lot 3
SE Job No. 18206.01
March 19, 2019
Page 5
OWTS Operation and Maintenance
All components of the engineered OWTS shall be inspected on a regular basis and be properly maintained. The
responsibility for repair and maintenance of the system will remain with the property Owner. The owner shall
retain the services of qualified personnel to inspect the OWTS and to perform all maintenance and repairs necessary
to ensure that the system is in good operating condition and is in compliance with the manufacturer's performance
requirements. The operating components of the OWTS shall be inspected by the engineer within 30 days of being
placed into operation and thereafter every six months by the owner or qualified service provider. In general, for a
properly utilized system, septic tanks should be pumped every 3 - 5 years. 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
28377
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Paul E. Rutledge Yancy Nichol, PE
Design Engineer Principal