HomeMy WebLinkAboutOWTS Design 10.13.2022129 Cains Lane
Carbondale, CO 81623
970.309.5259
carla.ostberg@gmail.com
October 13, 2022 Project No. C1756
Brian Hanlen
brian@brooksdesignbuild.com
Onsite Wastewater Treatment System Design
4-Bedroom Residence + Future Bunkhouse
TBD CR 108
Garfield County, Colorado
Brian,
CBO Inc. has completed an onsite wastewater treatment system (OWTS) design for the subject
residence. The 35-acre property is located outside of Carbondale, in an area where OWTSs and wells
are necessary.
Legal Description: Section: 32 Township: 7 Range: 88 THAT PARCEL OF LAND IDENTIFIED AS THE
PADGETT HOUSE PARCEL AS PER SUBDIVISION EXEMPTION PLAT RECEPTION NO. 960325 AS
AMENDED PER AMENDED EXEMPTION PLAT RECEPTION NO. 973918 (35 AC)
Parcel ID: 2393-323-00-379
SITE CONDITIONS This large agricultural property is developed with several residences and structures and utilized for
ranching. The proposed development is on an area of the property that is currently undeveloped. A 4-
bedroom residence is proposed, and a bunkhouse is contemplated in the future.
The structures will be served by an onsite well. The well will be located greater than 50-feet from the
proposed septic tank and greater than 110-feet 1 from the proposed soil treatment area (STA).
A ditch runs to the east of the proposed development. There must be a minimum 60-foot 2 setback from
the ditch to the STA.
The proposed STA location has an approximate 7-8 percent slope to the east. The proposed 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
1 The setback calculation is based on a design flow of 1125 gallons/day and the “8-foot rule” applies. Garfield
County OWTS Regulation, Table 7-1, note 3 “Add eight feet additional distance for each 100 gallons per day
of design flows between 1,000 and 2,000 gallons per day…”
2 The same “8-foot rule” setback applies to the ditch setback.
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The subsurface was investigated by Kumar and Associates, Project No. 21-7-382.1 and is documented in a
report dated August 18, 2022. One Profile Pit and three additional Pits were sampled for the evaluation. A
sample was taken from the Profile Pit between 4 and 5-feet below grade. Soils consisted of 43% sand, 36%
silt, and 21% clay.
Kumar and Associates has classified soils as Soil Type 2, Loam. A long term acceptance rate (LTAR) of
0.6 gallons per square foot will be used to design the OWTS.
DESIGN SPECIFICATIONS
Design Calculations:
4-Bedroom Residence = 75 GPD x 2 people/bedroom x 3 Bedrooms + 75 GPD (4th Bedroom) = 525 GPD
Bunkroom = 4 bunk beds = 8 ppl x 75 GPD/person = 600 GPD
Average Design Flow = 525 GPD + 600 GPD = 1125 GPD
LTAR = 0.6 GPD/SF
1125 GPD / 0.6 GPD/SF x 0.8 (pressure dosed trenches) x 0.7 (chambers) = 1050 SF
The OWTS design is based a 4-bedrooms residence and a future Bunkhouse. An average daily
wastewater flow of 1125 GPD will be used.
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For the purposes of this OWTS design, Benchmark Elevation as Finished Floor of the 4-bedroom
residence has been established as 100’ (6492’). 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 53’ / min 2% fall to
septic tank / min. 13.25” fall
Automatic Distributing Valve Approximate horizontal distance 28’ / min. 1% rise
for drain back / min. 3.5” rise
Infiltrative Surface Approximate horizontal distance 38’ / min. 1% fall
to furthest trench / min. 4.25” fall
*Elevations are based upon standard OWTS installation practices. Component elevations may change during
installation due to site conditions.
The sewer line exiting the residence must have a double-sweep clean out and a minimum 2% grade to
the septic tank. The future bunkhouse will be served by a separate septic tank, placed upgradient of the
proposed septic tank. A separate OWTS Permit must be obtained from Garfield County
Environmental Health Department prior to installation of this future septic tank. At the time the
future bunkhouse is constructed, we recommend the dose setting for the pump be re-evaluated based on
the increased design flow.
The system installation will include a 1500-gallon, two-compartment concrete septic tank with an
Orenco® Biotube Pump Vault and an Orenco® PF3005 pump in the second compartment of the 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 and float tree. The floats should be
set to dose approximately 60 gallons each pump cycle, allowing approximately 3 gallons of drain back after
each pump cycle. A pump curve is enclosed. The control panel for the pump must be located within line of
sight of the septic tank. We recommend Valley Precast out of Buena Vista be contracted for start-up of the
pumping system.
Pump Table (based on dose volume for the 4-bedroom residence)
Dose Range Max = 134.25 gal. (525 GPD x
25% + 3 gal drain back)
Min. 49.4 gal. (11.6 gal x 4) + 3
gal drain back
Dose Setting 60 gallons/dose 3 gallons drain back (28’ / 1.5”
diameter pump line)
Float Separation 1500 gallon 2-compartment
Valley Precast concrete septic
tank
6” on/off float separation
Pump Criteria 17.1 gallons per minute (GPM) 17.7 feet total dynamic head
(TDH)
Effluent will be pumped through a 1.5-inch diameter pump line from the pump chamber to an Orenco®
automatic distributing valve (ADV), model 6605. This pump line must have a minimum 1% grade for proper
drain back into the tank after each pump cycle. The ADV must be placed at a high point in the system in an
insulated riser with access from grade. Screened rock must be placed below the ADV to support the ADV
and to assure the clear pipes exiting the ADV remain visible for future inspection and maintenance.
Effluent will be pressure dosed through 1.5-inch diameter pipes to five trenches, each with 18 ‘Quick 4’
Plus Standard Infiltrator® chambers, for a total of 90 chambers and 1080 square feet of infiltrative area.
There must be at least 4-feet of undisturbed soil between each trench. Effluent will be pressure dosed to
1.5-inch diameter laterals, which must be hung with zip ties from the underside of the chambers. Laterals
will have 5/32-inch diameter orifices facing up, with the exception of the first and last holes facing down
for drainage. Orenco® Orifice Shields may be placed under each downward-facing orifice. The orifices
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must be placed 3-feet on center. Each lateral must end in a 90 degree ell facing up with a ball valve for
flushing. Valves may be placed in a valve box, accessible from grade, for access. Inspection ports must
be placed at the beginning and end of each trench. Ports may be cut to grade and covered with a valve
box 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 Valley Precast Item # 1500T-2CP-HH 2-compartment concrete
septic tank with high
head pump
Pump Orenco® PF500511 ½ HP
120 Volt
Biotube ProPak Pump Package Orenco® BPP30DD Vault, Filter, Control Panel (demand dose)
Tank Risers and Lids Orenco® Double-walled PVC Risers and Lids (24” diameter)
ADV Orenco® V6605A 1.5” Inlet and Outlets
ADV Riser and Lid Orenco® Double-walled PVC Risers
and Lids (30” diameter) Chambers Infiltrator® Standard Plus ‘Quick 4’ 90 ‘Quick 4’ chambers Orifice Shields Orenco® 10 Orifice Shields Flushing Assembly Orenco® 1.5” diameter (2) 45° or 90° long sweep only (5 total)
The component manufacturers are typical of applications used by contractors and engineers in this area.
Alternatives may be considered or recommended by contacting our office. 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
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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 the 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 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
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10-25-2022
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. Reviewed By:
Carla Ostberg, MPH, REHS Romeo A. Baylosis, PE
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
August 18, 2022
Brooks Design Build
Attn: Brian Hanlen
231 Robinson Street, #226
Basalt, Colorado 81621
brian@brooksdesignbuild.com
Project No. 21-7-382.1
Subject: Subsoil Study for Foundation Design and Septic Field, Proposed Residence,
Crystal River Ranch, 1508 County Road 108, Garfield County, Colorado
Dear Mr. Hanlen:
As requested, Kumar & Associates, Inc. performed a subsoil study for foundation design and
septic disposal feasibility at the subject site. The study was conducted in accordance with our
agreement for geotechnical engineering services to Brooks Design Build dated June 8, 2022.
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 will be a one story wood frame structure over
a crawlspace located on the site as shown on Figure 1. Ground floors are proposed to be
structural over crawlspace. A detached garage with slab-on-grade floor is proposed to the
northeast of the house. 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. The septic disposal system is proposed to be located about
50 feet east of the house.
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 currently vacant cow pasture which slopes gently down to the east
below an active irrigation ditch, located about a quarter mile northeast of the main ranch area.
The building area is relatively flat with slopes down to the east at about 3% to 5%, down to the
east. Vegetation in the building area consists of grass. There are pinon trees to the west and
uphill of the building area. There is another active irrigation ditch located east and downhill of
the proposed building site.
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating
three exploratory pits in the building area and one pit in the septic disposal area at the
approximate locations shown on Figure 1. The logs of the pits are presented on Figure 2. The
- 2 -
Kumar & Associates, Inc. ® Project No. 21-7-382.1
subsoils encountered, below about 1 foot of topsoil, consist of mostly medium stiff, sandy silty
clay down to the bottom of the pit depths of 7 to 8 feet. Silty, sandy gravel with small cobbles
and rock fragments were encountered in Pit 1, closest to the upper irrigation ditch. Results of
swell-consolidation testing performed on relatively undisturbed samples of the sandy silty clay
soils, presented on Figures 3 and 4, indicate low compressibility under existing low moisture
conditions and light loading and a low to moderate potential under increased loading after
wetting. Results of a gradation analysis performed on a sample of slightly silty sand and gravel
(minus 5-inch fraction) obtained from Pit 1, are presented on Figure 5. A gradation/hydrometer
analysis of the loam soils encountered in the Septic Profile Pit are presented on Figure 6. 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 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 bearing pressure of 1,500 psf for
support of the proposed residence. Footings should be a minimum width of 20 inches for
continuous walls and 2 feet for columns. Loose and 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 to confirm suitable 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.
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
imported granular soils such as ¾-inch road base devoid of vegetation, topsoil and oversized
rock.
- 3 -
Kumar & Associates, Inc. ® Project No. 21-7-382.1
Underdrain System: Although free water was not encountered during our exploration, there is
an active irrigation ditch uphill of the residence. 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 or sump and pump. 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.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
Septic Field: The soils exposed in the Profile Pit consist of USDA Loam soils to a depth of
8 feet. Based on the soil gradation shown on Figure 6, the soils are Type 2. A civil engineer
should design the infiltration 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
upon the data obtained from the exploratory pits excavated at the locations indicated on Figure 1,
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
Kumar & Associates
Kumar & Associates
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Kumar & Associates
Kumar & Associates
Kumar & Associates
Kumar & Associates
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Project No. 21-7-382.1
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) (%) (%) (%) (%) (%) (%) (%)
1 6 to 7 45 45 10 Silty Sand and
Gravel
2 2 19.9 104 Slightly Sandy Silty
Clay
3 20.4 101 Slightly Sandy Silty
Clay
Profile
Pit 4 to 5 43 36 21 Loam
Garfield County, CO
Developed by
Account
Number
R084702
Par cel Number 239332300379
Acr es 35
Land SqFt 0
T ax Ar ea 010
2019 Mill Levy 79.7800
Physica l
Addr ess
0 108 C OUNTY RD
C ARBONDALE 81623
Owner Addr ess C RYSTAL RIVER RANC H
C OMPANY
555 17TH STREET, SUITE 2400
DENVER C O 80202-3941
2019 T otal Actual
V alue
$1,030 Last 2 Sales
Date Pr ice
4/22/2022 $0
4/22/2022 $0
Date created: 10/15/2022
Last Data Uploa ded: 10/13/2022 12:05:15 AM
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