HomeMy WebLinkAboutOWTS Design Packet 06.15.2020CBO.I
June 15, 2020
Tony Choma
Tcho1 anvahoo.com
33 FOUR WHEEL DRIVE ROAD
CARBONDALE, CO 81 623
970.309.5259
CARLA.OSTBERG@GMAI L. COM
Subsurface Investigation and Onsite Wastewater Treatment System Design
2-Bedroom Residence + Future 3-Bedrrom Residence
TBD Homestead Road
Garfield County, Colorado
Tony,
Project No. C1528
CBO Inc. performed a subsurface investigation and completed an onsite wastewater treatment system
(OWTS) design for the subject residence. The 39.89-acre property is located outside of Glenwood
Springs, in an area where OWTSs and wells are necessary.
Legal Description: Section: 23 Township: 6 Range: 88 Subdivision: HOMESTEAD EST. Lot: 21 39.890
ACRES
Parcel ID: 2187-234-00-021
SITE CONDITIONS
The property is currently undeveloped with the exception of a driveway and well. A 2-bedroom residence
is proposed.
The residence will be served by a private well located to the southeast of the proposed residence. The
well will be greater than 50-feet from the proposed septic tank and greater than 100-feet from the
proposed soil treatment area (STA). The water line will not come within 25-feet of any OWTS
component.
The proposed STA location has an approximate ten percent slope to the southwest. No topographic map
was provided for this design; therefore, the installer must align the trenches to follow the topography.
The proposed area is vegetated with native grasses and bushes.
You also reported observing seasonal drainage in the area of the proposed STA. We are recommending
an interceptor trench drain be installed upgradient of the proposed STA. Details are provided in this letter
and enclosed W5.0. We recommend a civil engineer be contracted to address drainage on the property.
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.
Page 2
SUBSURFACE
The subsurface was investigated on June 4, 2020 by digging two soil profile test pit excavation (Test Pit). A
visual and tactile soil analysis was completed by Carla Ostberg at the time of excavation.'
The materials encountered in the Test Pit #1 consisted of medium brown silt loam to a maximum depth
explored 6.0-feet. Below 6.0-feet, digging became difficult. No bedrock or groundwater was encountered.
The materials encountered in Test Pit #2 were similar to those in Test Pit #1. Test Pit #2 was excavated
to a maximum depth explored of 6.0-feet where digging became difficult.
A sample of the soils was taken from Test Pit #1 at 3-feet below grade. Soil structure grade was
moderate. The soil formed a ball and a ribbon approximately 1-inch in length before breaking. Soil
structure shape was blocky and consistence was friable. Soil texture was more smooth than gritty.
Conservative STA sizing is based on Soil Type 2A, Silt Loam, although soil structure grade was
moderate. A long term acceptance rate (LTAR) of 0.5 gallons per square foot will be used to
design the OWTS.
View of Test Pit #1
backfill
' Carla Ostberg holds a Certificate of Attendance and Examination from the CPOW Visual and Tactile
Evaluation of Soils Training.
Page 3
Test Pit #2
Sieved sample
backfill
ribbon
DESIGN SPECIFICATIONS
Design Calculations:
Proposed 2-bedroom residence = 75 GPD x 2 people/bedroom x 2 Bedrooms = 300 GPD
Proposed 3-bedroom residence = 75 GPD x 2 people/bedroom x 2 Bedrooms = 450 GPD
Average Design Flow = 300 GPD = 450 GPD = 750 GPD
Min. 1500 gallons
LTAR = 0.5 GPD/SF
750 GPD / 0.5 GPD/SF x 1.0 (gravity trenches) x 0.7 (chambers) = 1050 SF
The new OWTS design is based on 2-bedrooms + 3 future bedrooms for a total of 5-bedrooms. An
average daily wastewater flow of 750 GPD will be used.
Page 4
For the purposes of this OWTS design, Benchmark Elevation at grade 8465' has been established as
100' the elevation of finished floor of the proposed 2-bedroom residence. 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
Approx. horizontal distance 40' / min. 2% fall / Min.
10" fall
Distribution Box
Approx. horizontal distance 32' / min. 1 % fall / Min.
4" fall
Infiltrative Surface
Approx. horizontal distance to upper -most trench 5'
/ Min. 1% fall / Min. 1" fall
The 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 1500-gallon, two -compartment concrete Valley Precast septic tank
with an effluent filter on the outlet tee. 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 six 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 1080 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.
In order to protect the STA from potential upgradient drainage due to spring runoff, we suggest an
interceptor trench drain be installed at least 5-feet upgradient of the upper STA trench. The interceptor
drain trench must extend approximately 1-foot below the elevation of the infiltrative area of the upper-
most STA trench. The interceptor trench drain must be 18-inches wide with clean aggregate material
surrounding the pipe. Aggregate material to be installed within 1-foot of native grade, covered with a
mirifi or soil separation fabric, and capped with native materials (low permeation). A 20 mil PVC liner
must be installed on the downhill side of the trench. See W5.0 Interceptor Trench Section Detail. The
trench running parallel with the STA should be 4-inch diameter perforated pipe, and the outlets to the
north and south of the STA should be 4-inch diameter solid pipe gravity flowing toward the driveway
drainage. A cutoff wall (concrete or flow fill) should be constructed at the point where the distribution
lines cross the interceptor trench drain. These are recommendations and outside of our typical scope of
work. We recommend contracting with a civil engineer for management of drainage on the property.
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 5
COMPONENT
MANUFACTURER
MODEL NO.
COMMENTS
Septic Tank
Infiltrator®
IM-1500-2CP
1500-gallon, 2-
compartment poly septic
tank
Biotube Effluent Filter
Orenco®
Full Size Effluent Filter and
housing
Tank Risers and Lids
Orenco®
Double -walled PVC Risers and
Lids (24" diameter)
Distribution Box
Valley Precast
D-Box 8C
Concrete distribution box
Flow Equalizers
3049 Equalizer
6 Flow Equalizers
Chambers
Infiltrator®
Low Profile
90 `Quick 4' Low Profile
Chambers
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
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 6
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 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.
ov-ivAg
Carla Ostberg, MPH, REHS
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