HomeMy WebLinkAboutOWTS Design129 Cains Lane
Carbondale, CO 81623
970.309.5259
carla.ostberg@gmail.com
August 12, 2022 Project No. C1744
Emanuel Rivas
armandorivas_19@hotmail.com
Onsite Wastewater Treatment System Design
3-Bedroom Residence
Lot 2, Gobbler’s Knob Amended Exemption
Garfield County, Colorado
Emanuel,
CBO Inc. has completed an onsite wastewater treatment system (OWTS) design for the subject
residence. The 5.281-acre property is located outside of Glenwood Springs, in an area where OWTSs
and wells are necessary.
Legal Description: Section: 5 Township: 6 Range: 89 A PCL IN A PT OF LOTS 1 & 2, & NWSE OF SEC.
5 AKA LOT 2 GOBBLER KNOB AMD EX. 5.281 ACRES
Parcel ID: 2185-051-00-121
SITE CONDITIONS The property is currently undeveloped. A 3-bedroom residence is proposed.
The residence will be served potable water from a private well on the property. The well was not located
on the survey, so we have approximated the location based on information provided to us. The well is
located in the northern corner of the property. The well is greater than 50-feet from the proposed septic
tank and greater than 100-feet from the proposed soil treatment area (STA).
The proposed soil treatment area (STA) location has an approximate 17-18 percent slope to the
southwest. The proposed area is located in an open field. The area is vegetated with native grasses.
There should be no traffic or staging of material over the future STA site to avoid compaction of soils
prior to construction of the STA.
SUBSURFACE
The subsurface was investigated by Kumar and Associates, with findings documented in a report dated
March 2, 2021, Job 21-7-142. Four test pits were excavated to perform a subsoil study for the foundation
and septic design. The report is enclosed.
Test Pits excavated on the property were between 6 and 8.5-feet in depth. No groundwater or bedrock was
encountered, but practical digging refusal was encountered in three of the four test pits.
Page 3 of the Kumar report references the “septic disposal area” and describes Pit 4 of consisting of Gravelly
Sandy Loam. A gradation of the materials sampled from Pit 4 at approximate 4.5’ to 5’ below elevation 6011’
consisted of 20% gravel, 31% sand, 36% silt, and 13% clay.
Page 2
We are sizing of the STA based on Soil Type 2 based on our interpretation of the Kumar and Associates
report. A long term acceptance rate (LTAR) of 0.6 gallons per square foot will be used to design
the OWTS.
DESIGN SPECIFICATIONS
Design Calculations:
Average Design Flow = 75 GPD x 2 people/bedroom x 3 Bedrooms = 450 GPD
LTAR = 0.6 GPD/SF
450 GPD / 0.6 GPD/SF x 1.0 (gravity trenches) x 0.7 (chambers) = 525 SF
The new OWTS design is based on 3-bedrooms. An average daily wastewater flow of 450 GPD will be
used.
For the purposes of this OWTS design, Benchmark Elevation has been established as 100’ as the Lower
Level Finished Floor (FF) elevation of 6006.85’. CBO Inc. should be notified of any discrepancies or
problems with grade elevations of proposed components during installation of the OWTS.
OWTS Component Minimum Elevation
Primary Tank Inlet Invert Approximate horizontal distance 46’ / min. 2% fall /
min. 11.5” fall
Distribution Box Approximate horizontal distance 12’ / min. 1% fall /
min. 1.5” fall
Infiltrative Surface Approximate horizontal distance to furthest trench
29’ / min. 1% fall / min. 3.625” fall
*Elevations are based upon standard OWTS installation practices. Component elevations may change during
installation due to site conditions. Minimum grade refers to piping between components.
The 4-inch diameter SDR-35 sewer line exiting the residence must have a double-sweep clean out and a
minimum 2% grade to the septic tank.
The system installation must include a 1000-gallon, two-compartment septic tank (state-approved
concrete or poly) with an effluent filter on the outlet tee. We have provided specifications for a 1000-
gallon, two-compartment Infiltrator® poly septic tank. Risers must bring the manhole lids to grade for
access. If more than one riser is added to the septic tank, an extension handle must be installed on the
effluent filter.
Effluent will gravity flow to a distribution box, and then to four gravelless chamber trenches. The
distribution box must be accessible from grade and must have flow equalizers, or similar product,
installed on each outlet pipe in the distribution box to assure equal flow to each trench.
Each trench will consist of 11 ‘Quick 4’ Standard Plus Infiltrator® chambers for a total of 44 chambers
and 528 square feet of infiltrative area. There must be at least 4-feet of undisturbed soil between each
trench. Inspection ports must be installed at the beginning and end of each trench. Ports may be cut to
grade and placed in sprinkler boxes for access.
COMPONENT SPECIFICATIONS
The component manufacturers are typical of applications used by contractors and engineers in this area.
CBO Inc. must approve alternative components prior to installation of the OWTS. Requests must
be submitted, in writing, to our office for approval prior to installation. Component technical data
sheets are available upon request.
Page 3
COMPONENT MANUFACTURER MODEL NO. COMMENTS
Septic Tank Valley Precast or
Infiltrator®
Item # 1000T-2CP or
Item # 1060-2CP
1000-gallon, 2-
compartment septic tank
Risers and Lids Orenco® Double-walled PVC
risers and lids
Effluent Filter Orenco® 4-inch diameter Full size
Distribution Box Polylok Distribution box, lids,
rises, and (4) flow
equalizers
Chambers Infiltrator® Standard Plus 44 ‘Quick 4’
Construction must be according to Garfield County On-Site Wastewater Treatment System Regulations, the
OWTS Permit provided by Garfield County Building Department, and this design.
INSTALLATION CONTRACTOR
CBO Inc. expects that the installer be experienced and qualified to perform the scope of work outlined in this
design. The installer must review this design thoroughly and coordinate with our office in advance of
installation. Any additional conditions in this design or county permit must be completed and documented
prior to final approval of the OWTS installation. Communication between the installer and this office is
expected throughout the installation.
INSTALLATION OBSERVATIONS CBO Inc. must view the OWTS during construction. The OWTS observation should be performed before
backfill, after placement of OWTS components. Septic tanks, distribution devices, pumps, dosing
siphons, and other plumbing, as applicable, must also be observed. CBO Inc. should be notified 48 hours
in advance to observe the installation.
In an effort to improve the accuracy of the record drawing, we request that the installer provide a
sketch of the installation, including path of the sewer lines, water line installation (if applicable),
septic tank location, STA location, and measurements from building corners or another fixed
objects on the property. This sketch is most easily provided on Sheet W2.0 of the OWTS Design
Packet. Photographs of the installation and final cover are also requested to supplement our installation
documentation.
REVEGETATION REQUIREMENTS
An adequate layer of good quality topsoil capable of supporting revegetation shall be placed over the entire
disturbed area of the OWTS installation. A mixture of native grass seed that has good soil stabilizing
characteristics (but without taproots), provides a maximum transpiration rate, and competes well with
successional species. No trees or shrubs, or any vegetation requiring regular irrigation shall be placed over
the STA. Until vegetation is reestablished, erosion and sediment control measures shall be implemented
and maintained on site. The owner of the OWTS shall be responsible for maintaining proper vegetation
cover.
OPERATION INFORMATION AND MAINTENANCE
The property owner shall be responsible for the operation and maintenance of each OWTS servicing the
property. The property owner is responsible for maintaining service contracts for manufactured units,
alternating STAs, and any other components needing maintenance.
Page 4
Geo-fabrics or plastics should not be used over the STA. No heavy equipment, machinery, or materials
should be placed on the backfilled STA. Machines with tracks (not wheels) should be used during
construction of the STA for better weight distribution. Livestock should not graze on the STA. Plumbing
fixtures should be checked to ensure that no additional water is being discharged to OWTS. For example, a
running toilet or leaky faucet can discharge hundreds of gallons of water a day and harm a STA.
If an effluent filter or screen has been installed in the OWTS, we recommend this filter or screen be cleaned
annually, or as needed. If the OWTS consists of a pressurized pump system, we recommend the laterals be
flushed annually, or as needed.
The homeowner should pump the septic tank every two years, or as needed gauged by measurement of
solids in the tank. Garbage disposal use should be minimized, and non-biodegradable materials should not
be placed into the OWTS. Grease should not be placed in household drains. Loading from a water softener
should not be discharged into the OWTS. No hazardous wastes should be directed into the OWTS.
Mechanical room drains should not discharge into the OWTS. The OWTS is engineered for domestic waste
only.
ADDITIONAL CONSTRUCTION NOTES If design includes a pump, weep holes must be installed to allow pump lines to drain to minimize risk of
freezing. The pump shall have an audible and visual alarm notification in the event of excessively high-
water conditions and shall be connected to a control breaker separate from the high-water alarm breaker
and from any other control system circuits. The pump system shall have a switch so the pump can be
manually operated.
Excavation equipment must not drive in the excavation of the STA due to the potential to compact soil.
Extensions should be placed on all septic tank components to allow access to them from existing grade.
Backfill over the STA must be uniform and granular with no material greater than minus 3-inch.
LIMITS: The design is based on information submitted. If soil conditions encountered are different from conditions
described in report, CBO Inc. should be notified. All OWTS construction must be according to the county
regulations. Requirements not specified in this report must follow applicable county regulations. The
contractor should have documented and demonstrated knowledge of the requirements and regulations of
the county in which they are working. Licensing of Systems Contractors may be required by county
regulation.
Please call with questions.
Sincerely,
CBO Inc.
Carla Ostberg, MPH, REHS
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email: kaglenwood@kumarusa.com
www.kumarusa.com Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
March 2, 2021
Armando Rivas
P.O. Box 964
Glenwood Springs, Colorado 81602
armandorivas_19@hotmail.com
Job No. 21-7-142
Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot 2, Gobblers Knob,
Donegan Road, Garfield County, Colorado
Dear Mr. Rivas:
As requested, Kumar and Associates, Inc. performed a subsoil study for design of foundations at
the subject site. The study was conducted in accordance with our agreement for geotechnical
engineering services to you dated January 19, 2021. The data obtained and our
recommendations based on the proposed construction and subsurface conditions encountered are
presented in this report.
Proposed Construction: The proposed residence design was conceptual at the time of our
study. In general, it will be a one story, wood frame structure with slab-on-grade floor with an
attached slab-on-grade garage. Cut depths are expected to range between about 3 to 6 feet.
Foundation loadings for this type of construction are assumed to be relatively light and typical of
the proposed type of construction.
If building conditions or foundation loadings are significantly different from those described
above, we should be notified to re-evaluate the recommendations presented in this report.
Site Conditions: The site is situated in a broad, undefined hillside drainage. The lot is vacant
and vegetated with grass and weeds, with juniper and oakbrush on the periphery of the building
area. At the northern, uphill corner, the lot slopes gently to moderately down to the southwest.
In the building area, the lot slopes moderately down to the south with a gentle slope from east
and west toward the center of the lot. The ground surface is relatively smooth and firm with
around 5 to 6 feet of elevation change across the building area.
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating
four exploratory pits at the approximate locations shown on Figure 1. The logs of the pits are
presented on Figure 2. Below about ½ foot of topsoil consisting of organic sandy silty clay, a
very stiff sandy silty clay that became calcareous with depth was encountered. In Pits 2 and 3,
the sandy silty clay continued to the total excavated depth of 6½ feet. In Pits 1 and 4, beneath
from 1 to 4 feet of clay, gravel with cobbles and boulders in a silty, sandy, light brown to white
calcareous clay matrix was encountered down to the maximum excavated depths of 8½ and
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Kumar & Associates, Inc. ® Project No. 21-7-142
6 feet. Digging was difficult due to the very stiff clay and the cobbles and boulders and practical
digging refusal was encountered in both the clay and the gravel deposits. Results of swell-
consolidation testing performed on a relatively undisturbed sample of the sandy silty clay soils,
presented on Figure 3, indicate low compressibility under existing moisture conditions and light
loading, and low to moderate compressibility potential when wetted and additionally loaded.
Results of USDA gradation analyses performed on a sample of the natural coarse granular soils
(minus 5-inch fraction) obtained from the site are presented on Figure 4. The laboratory test
results are summarized in Table 1. No free water was observed in the pits at the time of
excavation and the soils were slightly moist.
Foundation Recommendations: Considering the subsoil conditions encountered in the
exploratory pits and the nature of the proposed construction, we recommend spread footings
placed on either the undisturbed natural clay soils or the undisturbed natural gravel soils, and
designed for an allowable soil bearing pressure of 1,500 psf for support of the proposed
residence. Footings should be a minimum width of 16 inches for continuous walls and 2 feet for
columns. The topsoil and loose disturbed soils encountered at the foundation bearing level
within the excavation should be removed and the footing bearing level extended down to the
undisturbed natural soils. We should observe the completed foundation excavation for bearing
conditions. Exterior footings should be provided with adequate cover above their bearing
elevations for frost protection. Placement of footings at least 36 inches below the exterior grade
is typically used in this area. Continuous foundation walls should be heavily reinforced top and
bottom to span local anomalies such as by assuming an unsupported length of at least 12 feet.
Foundation walls acting as retaining structures should be designed to resist a lateral earth
pressure based on an equivalent fluid unit weight of at least 55 pcf for the on-site soil as backfill,
excluding organics and rock larger than 6 inches.
Floor Slabs: The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded
slab-on-grade construction. To reduce the effects of some differential movement, floor slabs
should be separated from all bearing walls and columns with expansion joints which allow
unrestrained vertical movement. Floor slab control joints should be used to reduce damage due
to shrinkage cracking. The requirements for joint spacing and slab reinforcement should be
established by the designer based on experience and the intended slab use. A minimum 4 inch
layer of road base or free-draining gravel should be placed beneath slabs to facilitate drainage.
This material should consist of minus 2-inch aggregate with less than 50% passing the No. 4
sieve and less than 2% passing the No. 200 sieve.
All fill materials for support of floor slabs should be compacted to at least 95% of maximum
standard Proctor density at a moisture content near optimum. Required fill can consist of the on-
site soils devoid of vegetation, topsoil, and oversized rock.
Underdrain System: Although free water was not encountered during our exploration, it has
been our experience in the area that local perched groundwater can develop during times of
heavy precipitation or seasonal runoff. Frozen ground during spring runoff can create a perched
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Kumar & Associates, Inc. ® Project No. 21-7-142
condition. We recommend below-grade construction, such as retaining walls and crawlspace
areas, be protected from wetting and hydrostatic pressure buildup by an underdrain system.
The drains should consist of drainpipe placed in the bottom of the wall backfill surrounded above
the invert level with free-draining granular material. The drain should be placed at each level of
excavation and at least 1 foot below lowest adjacent finish grade and sloped at a minimum 1% to
a suitable gravity outlet. Free-draining granular material used in the underdrain system should
contain less than 2% passing the No. 200 sieve, less than 50% passing the No. 4 sieve and have a
maximum size of 2 inches. The drain gravel backfill should be at least 1½ feet deep.
Surface Drainage: The following drainage precautions should be observed during construction
and maintained at all times after the residence has been completed:
1) Inundation of the foundation excavations and underslab areas should be avoided
during construction.
2) Exterior backfill should be adjusted to near optimum moisture content and
compacted to at least 95% of the maximum standard Proctor density in pavement
and slab areas and to at least 90% of the maximum standard Proctor density in
landscape areas. Free-draining wall backfill should be covered with filter fabric
and capped with about 2 feet of the on-site, finer graded soils to reduce surface
water infiltration.
3) The ground surface surrounding the exterior of the building should be sloped to
drain away from the foundation in all directions. We recommend a minimum
slope of 6 inches in the first 10 feet in unpaved areas and a minimum slope of
3 inches in the first 10 feet in pavement and walkway areas. Swales should be
constructed upslope of the building area to divert runoff. Water should not be
allowed to pond upslope of the building area which could impact slabs-on-grades
and foundations. Graded swales should have a minimum slope of 2%.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
5) Landscaping which requires regular heavy irrigation should be located at least
5 feet from the building.
Septic Disposal Area: The subsoil conditions in the planned septic disposal area were evaluated
by digging Pit 4 at the location shown on Figure 1. The subsurface profile mainly consists of
gravelly sandy loam. Results of a USDA gradation test performed on a sample of the coarse
grained soils are shown on Figure 4. Based on these findings, the tested area appears suitable for
an infiltration septic disposal system. A civil engineer should be engaged to design the septic
disposal system.
Limitations: This study has been conducted in accordance with generally accepted geotechnical
engineering principles and practices in this area at this time. We make no warranty either
express or implied. The conclusions and recommendations submitted in this report are based
Kumar & Associates
Kumar & Associates
Kumar & Associates
1 MIN.
4 MIN.19MIN.15 MIN.60MIN.#325 #140 3/4"3/8"1 1/2"3"5"6"8"
DIAMETER OF PARTICLES IN MILLIMETERS
U.S. STANDARD SERIES CLEAR SQUARE OPENINGS
SIEVE ANALYSIS
TIME READINGS
HYDROMETER ANALYSIS
#4#10#18#35#60
7 HR
45 MIN.
24 HR.
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20315276.237.519.09.54.752.001.00.500.025.106.045.019.009.005.002.001
SILT COBBLESLARGE
GRAVEL
MEDIUMCOARSEMEDIUMV. FINE
SANDCLAY FINE V. COARSE SMALL
USDA SOIL TYPE:
GRAVEL %SILT %CLAY %
FROM:Pit 4 @ 4.5'-5'
20 31 13SAND %36
Gravelly Sandy Loam
Kumar & Associates
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Project No. 21-7-142
SAMPLE LOCATION NATURAL MOISTURE CONTENT
NATURAL DRY DENSITY
GRADATION USDA SOIL TEXTURE SOIL TYPE PIT DEPTH GRAVEL SAND SILT&CLAY GRAVEL SAND SILT CLAY
(ft) (%) (pcf) (%) (%) (%) (%) (%) (%) (%)
2 3½ 8.4 98 Sandy Silty Clay
4 4½-5 20 31 36 13 Gravelly Sandy Loam
Garfield County, CO
Developed by
Account
Number
R005124
Par cel
Number
218505100121
Acr es 5
Land SqFt 0
T ax Ar ea 004
2019 Mill Levy 79.4730
Physical
Addr ess
0
GLENWO OD SP RINGS 81601
Owner
Addr ess
RIVAS, EMANUEL
P O BOX 964
GLENWO OD SP RINGS C O
81602
2019 T otal A ctual
Va lue
$236,250 Last 2 Sales
Date Pr ice
8/27/2018 $242,500
12/17/2004 $0
Date created: 8/12/2022
Last Data Uploa ded: 8/12/2022 5:24:56 AM
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