HomeMy WebLinkAboutOWTS Design 10.21.24129 Cains Lane
Carbondale, CO 81623
970.309.5259
carla.ostberg@gmail.com
October 21, 2024 Project No. C1858
Judy Spasser
c/o Chad Jewell
chadjcdb@gmail.com
Subsurface Investigation and Onsite Wastewater Treatment System Design
3-Bedroom Residence + 1-Bedroom ADU
Lot 8, Wooden Deer Subdivision
Garfield County, Colorado
Judy,
CBO Inc. performed a subsurface investigation and completed an onsite wastewater treatment system
(OWTS) design for the subject residence. The 3.009-acre property is located outside of Carbondale, in
an area where OWTSs are necessary. The house and driveway location have moved slightly from our
original design documents dated February 5, 2024 and July 22, 2024. Updated documents are dated
October 21 , 2024.
Legal Description: Section: 24 Township: 7 Range: 88 Subdivision: WOODEN DEER SUB Lot: 8
Parcel ID: 2393-243-04-008
SITE CONDITIONS
The property is currently undeveloped. A 3-bedroom residence with an attached 1-bedroom Accessory
Dwelling Unit (ADU) above the garage is proposed.
The residence will be served potable water from a community water system. The water tap is not located
on the survey. The water line may not come within 5-feet of any sewer line, 10-feet of the septic tank, or
25-feet of the soil treatment area (STA).
No OWTS component may be placed within the 60’ road easement.
The proposed STA location has an approximate 20 – 25% slope to the south. The proposed area is
vegetated with native grasses and sparse pinion trees.
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 on January 9, 2024 by digging two soil profile test pit excavations (Test
Pits). A visual and tactile soil analysis was completed by Carla Ostberg at the time of excavation.1
1 Carla Ostberg holds a Certificate of Attendance and Examination from the CPOW Visual and Tactile
Evaluation of Soils Training.
Page 2
The materials encountered in Test Pit #1 consisted of dark brown clay loam topsoil to 1-foot, underlain by
tan to light brown calcareous clay matrix to a maximum depth explored of 7.0-feet. No bedrock or
groundwater was encountered.
The materials encountered in Test Pit #2 consisted of dark brown clay loam topsoil to 1-foot, underlain by
tan to light brown calcareous clay matrix to a maximum depth explored of 6.0-feet where digging became
more difficult. No bedrock or groundwater was encountered.
While there was a significant amount of surface rock observed, rock content in the test pits appeared to
be less than 35%.
A sample of the soil was taken from Test Pit #1 at 4-feet below grade. Soil structure grade was
moderate. The soil formed a ball and a ribbon less than 1-inch in length before breaking. Soil structure
shape was blocky and consistence was friable. Soil texture was both gritty and smooth.
The calcareous clay matrix is consistent with Soil Type 2 with moderate structure grade. A long-term
acceptance rate (LTAR) of 0.6 gallons per square foot will be used to design the STA.
The subsurface was investigated by Kumar and Associates, Project No. 23-7-590 and is documented in a
report dated October 12, 2023 (enclosed). Two backhoe test pits dug in the lower portion of the proposed
building area were observed and subsurface conditions were described as “…soils encountered below about
1-foot of topsoil consist of 9 feet of silty sand with scattered gravel and cobble to small boulder size rocks.
Results of consolidation testing performed on a relatively undisturbed sample of the sil ty sand matrix soils…
indicate low compressibility under existing moisture conditions and light loading and low settlement potential
when wetted. The soils were moderately compressible under increased loading after wetting. No free water
was observed in the pits at the time of excavation and soils were slightly moist to moist.”
Test Pit #1
Page 3
Sieved sample
Ribbon approx. 1 -inch in length Test Pit #1
Test Pit #1 just below proposed building area
Page 4
Test Pit #1 Test Pit #2
Test Pit #2 closer to the western property boundary / more surface rock
Page 5
Test Pit #2
DESIGN SPECIFICATIONS
Design Calculations:
Average Design Flow = 75 GPD x 2 people/bedroom x 4 Bedrooms = 600 GPD
LTAR = 0.6 GPD/SF
600 GPD / 0.6 GPD/SF = 1000 SF
1000 SF x 1.0 (gravity trenches) x 0.7 (chambers) = 700 SF
The OWTS design is based on 4-bedrooms. An average daily wastewater flow of 600 GPD will be used.
For the purposes of this OWTS design, Benchmark Elevation at grade 6625.7’ has been established as
100’ (Finished Floor). CBO Inc. should be notified of any discrepancies or problems with grade
elevations of proposed components during installation of the OWTS.
Page 6
OWTS Component Minimum Elevation
Primary Tank Inlet Invert Approximate horizontal distance 16’ / min. 2% fall /
min. 4” fall
Distribution Box Approximate horizontal distance 30’ / min. 1% fall /
min. 3.75” fall
Infiltrative Surface Approximate horizontal distance 33’ to furthest
trench / min. 1% fall to STA / min. 4.125” 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 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 minimum 1250-gallon, two-compartment septic tank with an
Orenco® Biotube effluent filter on the outlet tee. Any state-approved poly or concrete septic tank may be
used. We are specifying a 1500-gallon, poly Infiltrator® septic tank which is typically locally available.
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 bed.
Each trench will consist of 15 ‘Quick 4’ Standard Plus Infiltrator® chambers for a total of 60 chambers
and 720 square feet of infiltrative area. There must be at least 4-feet of undisturbed soil between each
trench, although we recommend greater separation, if possible. We recommend backfilling each trench
as chambers are installed to maintain sidewall integrity. 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.
COMPONENT MANUFACTURER MODEL NO. COMMENTS
Septic Tank
Infiltrator® Item # IM1530-2CP Min. 1250-gallon, 2-
compartment septic tank
Effluent Filter Orenco® 4” diameter full size
effluent filter
Double-walled risers
and lid
Orenco® Risers and Lids
Distribution Box, risers, lid and flow equalizers
Polylok 4 ‘Roto-flow’
Chambers Infiltrator® ‘Quick 4’ Plus Standard 60 chambers
Construction must be according to the jurisdiction’s adopted On-Site Wastewater Treatment System
Regulations, the OWTS Permit, and this design.
Page 7
PERMIT APPLICATION INSTRUCTIONS
An OWTS Permit Application must be submitted to Garfield County Environmental Health Department.
https://www.garfield-county.com/environmental-health/filesgcco/sites/16/OWTS-Application -Complete -
Packet-Dec.-2019.pdf. If the OWTS Permit Application will be submitted with a Building Permit
Application, it should be submitted directly to Garfield County Building Department.
All questions regarding permit submission can be directed to Garfield County Environmental Health
Department, 970-945-6614 x8150.
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.
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.
Page 8
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
October 12, 2023
Crawford Design Build
Attn: Don Glenn
P.O. Box 1236
Carbondale, Colorado 81623
crawforddesignbuild@comcast.net
Project No.23-7-590
Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot 8, Wooden Deer,
Wooden Deer Road, Garfield County, Colorado
Dear Don:
As requested, Kumar & Associates, Inc. observed two backhoe pits for design of foundations at
the subject site. The study was conducted in accordance with our agreement for geotechnical
engineering services to Crawford Design Build dated October 6, 2023. The data obtained and
our recommendations based on the proposed construction and subsurface conditions encountered
are presented in this report.
Proposed Construction: We assume the proposed residence will be a two-story wood frame
structure located in the area of the pits on the site. Ground floor will be with slab-on-grade or
structural crawlspace. Cut depths are expected to range between about 5 to 12 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 undeveloped and slopes moderately steeply down to the east-
southeast. There is a steep road cut down to Wooden Deer Road to the east. Two pits had been
excavated with a mini-excavator in the lower part of the building area. The site is vegetated with
pinon and cedar trees with an understory of grass and weeds.
Subsurface Conditions: The subsurface conditions at the site were evaluated by observing two
backhoe pits previously excavated in the lower portion of the proposed building area. The
subsoils encountered, below about 1 foot of topsoil, consist of 9 feet of silty sand with scattered
gravel and cobble to small boulder size basalt rocks. Results of consolidation testing performed
on a relatively undisturbed sample of the silty sand matrix soils, presented on Figure 1, indicate
low compressibility under existing moisture conditions and light loading and a low settlement
potential when wetted. The soils were moderately compressible under increased loading after
- 2 -
Kumar & Associates, Inc. ® Project No. 23-7-590
wetting. No free water was observed in the pits at the time of excavation and the soils were
slightly moist to 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 the undisturbed natural soil designed for an allowable soil bearing pressure of
1,500 psf for support of the proposed residence. The soils tend to compress after wetting and
there could be some post-construction foundation settlement. Footings should be a minimum
width of 18 inches for continuous walls and 2 feet for columns. Loose and disturbed soils and
existing fill encountered at the foundation bearing level within the excavation should be removed
and the footing bearing level extended down to the undisturbed natural soils. 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 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 50 pcf for the on-site soil as backfill.
Floor Slabs: The natural on-site soils, exclusive of topsoil, are suitable to support lightly to
moderately 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 free-draining gravel should be placed beneath basement level
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
condition. We recommend below-grade construction, such as retaining walls, crawlspace and
basement 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
- 3 -
Kumar & Associates, Inc. ® Project No. 23-7-590
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 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 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 12 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. A swale may be
needed uphill to direct surface runoff around the residence.
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. Consideration should be given to the use of xeriscape to
limit potential wetting of soils below the foundation caused by irrigation.
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
upon the data obtained from the exploratory pits excavated at the site, the proposed type of
construction, and our experience in the area. Our services do not include determining the
presence, prevention or possibility of mold or other biological contaminants (MOBC) developing
in the future. If the client is concerned about MOBC, then a professional in this special field of
practice should be consulted. Our findings include interpolation and extrapolation of the
subsurface conditions identified at the exploratory pits and variations in the subsurface
conditions may not become evident until excavation is performed. If conditions encountered
during construction appear different from those described in this report, we should be notified at
once so re-evaluation of the recommendations may be made.
This report has been prepared for the exclusive use by our client for design purposes. We are not
responsible for technical interpretations by others of our information. As the project evolves, we
Kumar & Associates
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3,5081:
Feet5850
Legend
292
Notes
Location
585
Date Prepared: 2/6/2024 10:37:13 AM
Well Constructed
Final Permit
Ground Water
Geophysical Log
Confluence Point
Source Water Route Framework
County
subject property
Gar eld County, CO
Developed by
Account
Number
R111845
Parcel Number 239324304008
Acres 3
Land SqFt 0
Tax Area 011
2019 Mill Levy 72.5180
Physical
Address
0
CARBONDALE 81623
Owner Address SPASSER, JUDY
39 SWEETGRASS
CARBONDALE CO
81623
2019 Total Actual
Value
$400,000 Last 2 Sales
Date Price
5/30/2023 $425,000
6/18/2021 $245,000
Date created: 2/5/2024
Last Data Uploaded: 2/5/2024 2:09:32 AM
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