HomeMy WebLinkAboutRevised OWTS Plan
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
email: kaglenwood@kumarusa.com
www.kumarusa.com
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
ONSITE WASTEWATER TREATMENT SYSTEM DESIGN
PROPOSED RESIDENCE
TBD MAMM CREEK ROAD
GARFIELD COUNTY, COLORADO
PROJECT NO. 25-7-508.02
DECEMBER 10, 2025
REVISED: JULY 21, 2026
PREPARED FOR:
TORREY & SONS, LLC
ATTN: TORREY BYMAN
854 ANTLER POINT LANE
SILT, COLORADO 81652
torreybyman@outlook.com
Kumar & Associates, Inc. ® Project No. 25-7-508.02
TABLE OF CONTENTS
INTRODUCTION ................................................................................................................... - 1 -
PROPOSED CONSTRUCTION ............................................................................................. - 1 -
SITE CONDITIONS ............................................................................................................... - 1 -
SUBSURFACE CONDITIONS ............................................................................................... - 1 -
OWTS ANALYSIS .................................................................................................................. - 2 -
DESIGN RECOMMENDATIONS ........................................................................................... - 2 -
SOIL TREATMENT AREA ............................................................................................. - 2 -
OWTS COMPONENTS ................................................................................................. - 3 -
OWTS OPERATION AND MAINTENANCE ........................................................................... - 6 -
OWTS HOUSEHOLD OPERATION .............................................................................. - 6 -
OWTS MAINTENANCE ................................................................................................. - 6 -
OWTS CONSTRUCTION OBSERVATION ............................................................................ - 6 -
LIMITATIONS ........................................................................................................................ - 7 -
FIGURES
FIGURE 1 – OWTS SITE PLAN
FIGURE 2 – SOIL TREATMENT AREA CALCULATIONS
FIGURE 3 – SOIL TREATMENT AREA PLAN VIEW
FIGURE 4 – SOIL TREATMENT AREA CROSS-SECTION
FIGURE 5 – DISTRIBUTION LINE CLEANOUT DETAIL
ATTACHMENTS
VALLEY PRECAST 1,500 GALLON, THREE-COMPARTMENT SEPTIC TANK DETAIL
ORENCO PF3005 PUMP PERFORMANCE CURVE
Kumar & Associates, Inc. ® Project No. 25-7-508.02
INTRODUCTION
This report provides the results of a design for an onsite wastewater treatment system (OWTS)
for the proposed residence to be located at TBD Mamm Creek Road (County Road 315), Parcel
240108100200, Garfield County, Colorado. The project site is shown on Figure 1. The purpose
of the report is to provide design details for the OWTS in accordance with Garfield County
Environmental Health Department Onsite Wastewater Treatment System Regulations and the
Colorado Department of Public Health and Environmental Regulation #43. The services are in
accordance with our agreement for professional services to Torrey & Sons, LLC dated August 4,
2025. The design was revised to a pressure-dosed system due to the elevation of the residence.
PROPOSED CONSTRUCTION
The proposed residence will be a one to two story structure with an attached garage located on
the parcel as shown on Figure 1. The residence will have four bedrooms and the OWTS will be
designed for four bedrooms. The proposed soil treatment area (STA) for the OWTS will be located
southwest of the residence. Water service will be provided by an onsite well far from the residence
and OWTS. The route of the water supply line has not been designed at the time of this report
on Figure 1.
If proposed construction is different than that described, we should be contacted to re-evaluate
our design recommendations.
SITE CONDITIONS
The parcel is located west/northwest of Mamm Creek and Mamm Creek Road just south of County
Road 322. The site, shown on Figure 1, was vacant at the time of field exploration. The terrain
in the building area is gently sloping down to the south and west towards West Mamm Creek.
West Mamm Creek is approximately 70 feet southeast of the proposed STA. Vegetation consists
of grass, sagebrush, weeds and pinon and juniper trees.
SUBSURFACE CONDITIONS
The field exploration for the OWTS was conducted on August 28, 2025. Two profile pits were
excavated with a mini-excavator at the approximate locations shown on Figure 1 to evaluate the
subsurface conditions at the soil treatment area for the OWTS. The pits were logged by a
representative of Kumar & Associates. The logs of the profile pits are provided below.
Log of Profile Pit 1
Depth USDA Classification
0’-½’ TOPSOIL; organic Loam, firm, moist, dark brown.
½’-8’ SANDY LOAM; moderate blocky structure, medium dense, slightly moist to moist, brown.
• Disturbed bulk sample obtained from 4 to 5 feet.
• Bottom of pit @ 8 feet depth.
• No groundwater or redoximorphic features observed at the time of pit excavation.
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Kumar & Associates, Inc. ® Project No. 25-7-508.02
Log of Profile Pit 2
Depth USDA Classification
0’-½’ TOPSOIL; organic Sandy Loam, firm, moist, brown.
½’-8’ SANDY LOAM; moderate blocky structure, medium dense, slightly moist to moist, brown.
• Bottom of pit @ 8 feet depth.
• No groundwater or redoximorphic features observed at the time of pit excavation.
The soils encountered in the profile pits, below about ½ foot of organic topsoil, consisted of Sandy
Loam down to the pit depths of 8 feet. No free water was encountered in the pits nor indications
of seasonal high groundwater were observed at the time of the pit excavations.
Based on the subsurface conditions and laboratory testing, the design soils have been classified
as Type 2 per State regulations, which equates to a long-term acceptance rate (LTAR) of 0.60
gallons per square foot per day.
OWTS ANALYSIS
Based on the site conditions and profile pit evaluation, the evaluated area should be suitable for
a pressure-dosed infiltration disposal system. Pressure-dosing is required because there is
inadequate elevation difference from the septic tank to the STA for gravity flow. The STA will
consist of chambers in a trench configuration based in the Sandy Loam soils. The STA will be
sized for four bedrooms and seven persons and an average daily flow of 75 gallons per person,
and an LTAR of 0.60 gallons per square foot per day in the natural soils.
The effluent will gravity flow from the residence to the septic tank for primary treatment and then
be pressure-dosed from the septic tank to the STA for dispersal and final treatment. The STA will
consist of three trenches with Infiltrator Quick 4 Plus Standard chambers. Equal distribution will
be provided to the chambers by an automatic distributing valve (ADV).
The route of the water supply line should be outside of any required setbacks. The required
setback of the water line from the septic tank is 10 feet, 5 feet for sewer and effluent lines, and 25
feet from the STA. We should be notified for additional recommendations if any of the setbacks
cannot be met.
DESIGN RECOMMENDATIONS
The design recommendations presented below are based on the proposed construction, the site
and subsurface conditions encountered, and our experience in the area. A layout of the proposed
OWTS components is provided on Figure 1. If conditions encountered during construction are
different than those that are described in this report, we should be contacted to re-evaluate our
design recommendations.
SOIL TREATMENT AREA
• The STA will consist of the three trenches with 14 Infiltrator Quick4 Plus Standard
chambers placed in each trench (42 chambers total) based in the natural soils. Equal
distribution will be provided to the trenches by a distribution box.
• The STA was sized based on an LTAR of 0.60 gallons per square foot per day.
• Each chamber was allowed 12 square feet of area. A 30% reduction for use of Infiltrator
chambers and a 20% reduction for pressure-dosing in a trench configuration were applied
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Kumar & Associates, Inc. ® Project No. 25-7-508.02
to the size of the STA. The total STA design size is 504 square feet. Soil treatment area
calculations are shown on Figure 2.
• Distribution lines, consisting of 1.5-inch diameter, Schedule 40 piping, with 3/16-inch orifice
holes drilled at 4-foot centers near the center of the chambers, should be installed along
the complete length of the chambers (see Figure 4). The distribution lines should be
suspended approximately 2 inches from the top surface of the infiltrators by pipe ties. The
orifice holes should face up toward the chamber surface above.
• An ⅛-inch hole should be drilled on the bottom of each end of the distribution pipe to allow
for complete drainage of the distribution line following pressure dosing. Install splash
plates below drain holes.
• A minimum of four feet of undisturbed soil between the trenches is required.
• Trenches should be cut a maximum of 4 feet deep at the up-slope side.
• The trenches should be oriented along ground contours to minimize soil cut and cover.
• The base and sidewalls of the trench excavations should be scarified prior to the chamber
placement.
• A minimum of 12 inches and a maximum of 36 inches of cover soil should be placed over
the chambers.
• Backfill should be graded to deflect surface water away from the STA and should be
sloped at 3 horizontal to 1 vertical or flatter. A swale to divert surface water flow away
from the STA may be needed upslope of the STA.
• Disturbed soil should be re-vegetated as soon as possible with a native grass mix. No
trees, shrubs or other plants with deep roots should be planted on or near the STA as this
may damage the system piping.
• Four-inch diameter inspection ports should be installed vertically into the knockouts
provided in the chamber end caps. Install ports at each end of the trench. The inspection
port piping should be screwed into the top to the chambers and should not extend down
to the ground surface inside the chambers. The inspection ports should extend at least 8
inches above the finished ground surface or be protected in a valve box at finished grade.
• Care should be taken to ensure that the STA is not driven before and after construction.
• The STA must be a minimum of 20 feet from the residence.
• The STA must be a minimum of 50 feet from the creek.
• The STA must be a minimum of 5 feet from the septic tank.
• The STA must be a minimum of 10 feet from the property lines.
• The STA must be a minimum of 25 feet from potable water supply lines.
• A plan view of the STA is presented on Figure 3 and a cross section of the STA is
presented on Figure 4.
OWTS COMPONENTS
Recommended OWTS components provided below are based on our design details and our
experience with the specific component manufacturers. Equivalent components may be feasible
but need to be approved by us prior to construction.
Septic Tank
• A Valley Precast 1,500-gallon, three-chamber septic tank should be used for primary
treatment and dosing to the STA. The first two chambers will be utilized for treatment and
the settling and the third chamber will contain the effluent pump. A detail of the tank is
provided as an attachment to the report.
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Kumar & Associates, Inc. ® Project No. 25-7-508.02
• A submersible effluent pump enclosed in a Biotube Pump Vault will be installed in the
dosing chamber.
• The tank must be a minimum of 5 feet from the residence.
• The tank must be a minimum of 10 feet from potable water supply.
• The tank must be a minimum of 5 feet from the STA.
• The tank must be a minimum of 50 feet from the creek.
• The tank must be set level. The excavation bottom must be free of large rocks or other
objects that could damage the tank during placement. A road base or gravel bedding
material may be needed to prevent tank damage during placement and act as a leveling
course.
• The tank lids must extend to final surface grade and made to be easily located.
• Install the tanks with 2 feet minimum cover soil for frost protection. Maximum tank soil
cover is 4 feet.
Sewer Pipe
• The sewer line to the septic tank should not be less than the diameter of the building or
other drains and not less than 4 inches in diameter.
• The sewer pipe should have a rating of SDR35 or stronger. Schedule 40 PVC pipe is
required beneath any driveway or gravel surfaces.
• The sewer pipe should be sloped between 2% to 4% to help limit disturbance of solids in
the tank and potential sewage bypass of the first chamber of the tank. If a steeper slope
is needed, this can be accomplished with vertical step-downs in the sewer line.
• A minimum 36 inches of cover soil should be provided over the sewer pipe. Paved or
graveled areas, patios or other areas without vegetative cover may be more susceptible
to frost and we recommend 48 inches of soil cover over the sewer pipe in these areas,
and the pipe be insulated on top and sides with 2-inch-thick blue foam insulation board. If
adequate soil cover is not possible, we should be contacted for re-evaluation prior to
installation.
• The sewer pipe should be bedded in compacted ¾-inch road base or native soils provided
that the native soils contain no angular rocks or rocks larger than 2½ inches in diameter
to help prevent settlement of the pipe. Sags in the pipe could cause standing effluent to
freeze and damage the piping.
• Install cleanout pipes within 5 feet of the building foundation, where the sewer pipe bends
90 degrees or more and every 100 feet of sewer pipe.
• All 90-degree bends should be installed using a 90-degree long-sweep or by using two
45-degree elbows.
• The sewer line must be a minimum of 5 feet from any potable water supply lines.
• The sewer line must be a minimum of 50 feet from the creek.
• The sewer line location shown on Figure 1 is considered conceptual. We assume that
there will be only one sewer line exiting the residence. It is the responsibility of the
owner/contractors to locate all sewer line exit locations and connections to the septic tank.
We should be notified if there are other sewer lines exiting the building.
Effluent Transport Piping
• The effluent transport pipe should be 1.5-inch diameter Schedule 40 piping sloped at 2%
minimum to drain back from the ADV to the dose tank and from the ADV to each trench.
The ADV must be the high point of the system.
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Kumar & Associates, Inc. ® Project No. 25-7-508.02
• The effluent transport pipe should be bedded in compacted ¾-inch road base or native
soils provided that the native soils contain no angular rocks or rocks larger than 2½ inches
in diameter to help prevent settlement of the pipe. Sags could cause standing effluent to
freeze and damage to the piping.
• A minimum 18 inches of cover soil should be provided over the effluent transport pipe.
Paved areas, patios or other areas without vegetative cover may be more susceptible to
frost. We recommend 48 inches of soil cover over the effluent pipe and insulation with at
least 2 inches of rigid foam insulation in these areas. If adequate cover soil is not possible,
we should re-evaluate the condition prior to installation.
• The effluent pipe should be provided with at least 48 inches of soil cover and be insulated
on top and sides with 2-inch-thick foam insulation board underneath driveway surfaces.
• All 90-degree bends should be installed using a 90 degree long-sweep or by using two
45-degree elbows.
Effluent Pumping System
• An Orenco PF3005, 115-volt, submersible effluent pump with a 1.5-inch diameter
discharge assembly, or equivalent, will be required for effluent pumping
• The maximum effluent transport distance from the pump discharge to the ADV is
estimated to be 45 feet and from the ADV to the STA is estimated to be 14 feet.
• The elevation difference from pump discharge up to the STA is estimated to be 5 feet.
• The pump should be enclosed in an Orenco Biotube Pump Vault for effluent filtering and
protection of the pump from vibration.
• An equivalent pump must be capable of operating at 14.7 gallons per minute at 14.8 feet
of total dynamic head. A pump performance curve is provided as an attachment to this
report.
• The floats should be set to provide a dose volume of approximately 27 gallons. The actual
dose volume will be about 22 gallons assuming 5 gallons of drainback in the transport line.
To achieve the desired dose volume, the upper (“ON”) and lower (“OFF”) floats should be
set approximately 2¾ inches apart.
• The flow differential between the first and last orifices is estimated to be 2.6%.
• The high-water alarm float should be placed approximately 3 inches above the “ON” float
in the dose tank. The high-water alarm must be wired on a separate electrical circuit from
the pump.
• A ⅛-inch diameter weep hole should be drilled in the effluent transport line prior to exiting
the dose tank so the transport line can drain after each pumping cycle.
Automatic Distributing Valve (ADV)
• An Orenco V6403 Automatic Distributing Valve (ADV) will be used to distribute effluent to
the trenches.
• The ADV must be installed level and must be the high point in the system.
• The ADV should be installed in a sprinkler box, or equivalent, such that it is serviceable
and protected from freezing. We recommend the ADV be equipped with heat tape for
additional frost protection during winter months.
• We recommend the ground surface be graded away from the ADV in all directions.
Improper surface drainage could cause standing water to freeze and damage the valve
and/or piping.
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Kumar & Associates, Inc. ® Project No. 25-7-508.02
• The valve has clear sections of pipe that should be inspected at least annually to ensure
that it is alternating doses to each trench.
OWTS OPERATION AND MAINTENANCE
The OWTS will require periodic inspection and maintenance to function properly. A properly
designed, installed and maintained system can greatly increase its lifespan. The level of
maintenance will vary depending on the complexity of the system and water use habits of the
residents. We recommend that an OWTS Operation and Maintenance (O&M) Manual be
developed. Below are some basic recommendations for the OWTS O&M.
OWTS HOUSEHOLD OPERATION
• Use of high efficiency water fixtures is recommended to decrease the hydraulic load on
the OWTS system.
• Fix plumbing leaks immediately as this may cause a hydraulic overload of the soil
absorption system.
• Do not irrigate the area on top of or directly upgradient of the soil absorption field as this
may cause a hydraulic overload.
• Do not dispose of household waste down drains as this may clog or damage OWTS
components. Examples of household waste includes: dental floss, cotton swabs, coffee
grounds, paper towels, feminine products and many other kitchen and bath items.
• Use of kitchen garbage disposals is not recommended. If a garbage disposal is utilized,
kitchen wastewater should be screened thoroughly. Many kitchen solids are not
decomposed in the septic tank and may cause increased tank pumping frequency.
• Do not dispose of household chemicals, greases, oils, paints, hot tub water or water
softener backwash in household drains. A separate drywell, if feasible, may be necessary
for hot tub water or water softener backwash disposal.
• Limit the use of bleach as this may harm useful bacteria in the septic tank and soil
absorption system.
• Liquid dishwasher and clothes washer detergent is recommended for households served
by an OWTS. Clay substances used as fillers in powder detergents may result in clogging
of the soils absorption system.
OWTS MAINTENANCE
• Inspect the septic tank, pump, pump vault filter, ADV, and STA at least annually for
problems or signs of failure.
• The effluent filter should be cleaned at least annually by spray washing solids into the first
chamber of the septic tank.
• The septic tank should be pumped and cleaned every 3 to 5 years depending on use.
Longer pumping intervals may increase the amount of solids that reach the STA, which
may shorten its life span.
• Pumping of the septic tank should take place when the level of the sludge and scum layers
combined take up 25 to 33% of the capacity of the first chamber of the tank.
OWTS CONSTRUCTION OBSERVATION
The Garfield County Environmental Health Department requires that the designer of the system
provide a record drawing and certification of the OWTS construction (As-Built inspection). We
should be provided with at least 48-hour notice prior to the installer needing the inspections. Prior
to issuance of our certification letter, we require observation of all system components prior to
Kumar & Associates
Kumar & Associates
Kumar & Associates
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Pump Selection for a Pressurized System - Single Family Residence Project
25-7-508.02 / TBD Mamm Creek Road
Parameters
Discharge Assembly Size
Transport Length Before Valve
Transport Pipe Class
Transport Line Size
Distributing Valve Model
Transport Length After Valve
Transport Pipe Class
Transport Pipe Size
Max Elevation Lift
Manifold Length
Manifold Pipe Class
Manifold Pipe Size
Number of Laterals per Cell
Lateral Length
Lateral Pipe Class
Lateral Pipe Size
Orifice Size
Orifice Spacing
Residual Head
Flow Meter
'Add-on' Friction Losses
1.50
45
40
1.50
6403
14
40
1.50
5
0
40
1.50
3
56
40
1.50
3/16
4
5
None
0
inches
feet
inches
feet
inches
feet
feet
inches
feet
inches
inches
feet
feet
inches
feet
Calculations
Minimum Flow Rate per Orifice
Number of Orifices per Zone
Total Flow Rate per Zone
Number of Laterals per Zone
% Flow Differential 1st/Last Orifice
Transport Velocity Before Valve
Transport Velocity After Valve
0.97
15
14.7
1
2.6
2.3
2.3
gpm
gpm
%
fps
fps
Frictional Head Losses
Loss through Discharge
Loss in Transport Before Valve
Loss through Valve
Loss in Transport after Valve
Loss in Manifold
Loss in Laterals
Loss through Flowmeter
'Add-on' Friction Losses
0.6
0.6
3.0
0.2
0.0
0.3
0.0
0.0
feet
feet
feet
feet
feet
feet
feet
feet
Pipe Volumes
Vol of Transport Line Before Valve
Vol of Transport Line After Valve
Vol of Manifold
Vol of Laterals per Zone
Total Vol Before Valve
Total Vol After Valve
4.8
1.5
0.0
5.9
4.8
7.4
gals
gals
gals
gals
gals
gals
Minimum Pump Requirements
Design Flow Rate
Total Dynamic Head
14.7
14.8
gpm
feet
0 5 10 15 20 25 30 35 400
50
100
150
200
250
300
Net Discharge (gpm)
PumpData
PF3005 High Head Effluent Pump
30 GPM, 1/2HP
115/230V 1Ø 60Hz, 200V 3Ø 60Hz
Legend
System Curve:
Pump Curve:
Pump Optimal Range:
Operating Point:
Design Point: