HomeMy WebLinkAboutSubsurface Investigation and OWTS Design 04.26.170tr
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33 Four Whoel Drlve Rd
Corbondole, C0 8ló2t
970-309.5259
April26,2017 Project No. C1102
Phil Vaughan Construction Management, lnc.
PhilVaughan
1038 County Road 323
Rifle, CO 81650
Subsurface lnvestigation and Onsite Wastewater Treatment System Design
Terra Energy Partners - Trail Ridge Employee Housing Facility
Garfield County, Colorado
Phit,
ALL SERVICE septic, LLC performed a subsurface investigation and completed an onsite wastewater
treatment system (OWTS) design for the subject employee housing facility. The Site is located in a rural
area of Garfield County where OWTSs are necessary. Some changes have been made to design
documents dated November 12, 2014. These should be discarded and replaced with design documents
dated April 26,2017.
The legal description of the property is as follows:
Section 3, Township 5 South, Range 97 West of the 6th Principal Meridian, County of Garfield, State of
Colorado.
SITE CONDITIONS
The above-mentioned property (Site) is accessed via Rio Blanco County Road 5 and BLM Road No.
1009. A previously excavated flat pad exists on the Site and a 60' x 125' Storage Building will be
developed on this portion of the Site. The employee housing will consist of six factory-built units with a
footprint of approximately 72'x 58' and will be located east of the excavated pad.
The proposed septic tanks and soil treatment area (STA) will be located south of the employee housing
units. This area slopes to the south and is currently vegetated with sage and native grasses.
Potable water will be hauled to the Site. The 10,000-gallon potable water skid will be located at least 25-
feet from the proposed septic tanks and STA.
Page2
SUBSURFACE
The subsurface was investigated on September 16, 2014 by digging two 8-foot deep soil profile test pit
excavations (Test Pits).
The materials encountered in Test Pit #1 consisted of dark brown, moist, topsoil to 4-inches, underlain by
light tan to brown, hard to very hard, moist, highly fractured bedrock to a maximum depth explored of 8.0-
feet. Fractured bedrock was encountered at 4-inches. No groundwater was encountered.
The materials encountered in Test Pit #2 consisted of dark brown, moist, topsoil to 8-inches, underlain by
light tan to brown, hard to very hard, moist, highly fractured bedrock to a maximum depth explored of 8.0-
feet. Fractured bedrock was encountered at 8-inches. No groundwater was encountered.
Soils surrounding the fractured bedrock in both Test Pits were analyzed at approximately 3-feet below
grade and are classified as a Sandy, Silty Loam.
Additional subsurface information is included in the Geologic Hazard Evaluation and Geotechnical
lnvestigation by CTL Thompson, Project GS05884-1 15, dated October 24,2014 (enclosed).
Test Pits observed September 16,2014
Test Pit #1
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Page 3
Test Pit #2
DESIGN SPECIFICATIONS
A 24-person employee housing facility is proposed. The OWTS design is based on a wastewater flow
(A) of 1999 gallons/day (GPD).
OWTS Calculations:
75 GPD x 24 people = 1800 GPD
Using 1999 GPD
Tank capacity = 199n GPD x 48 hours = minimum 3398 gallons
Using I 500 gallons + 1500 gallons + 1500 gallons = 4500 gallons
STA Pressure Dosed Unlined (Open Bottom) Sand Filter
Long Term Acceptance Rate (LTAR) = 1.0 gal/SF (sand filter media, TLl )
Q / LTAR = 1999 GPD / 1.0 gal/SF = 1999 SF
Q / LTAR pressure dosed bed = 1999 SF / 1.0 9al/SF= 1999 SF
Using four 12' x 42' over-excavated, unlined, pressurized sand filters
A commercial kitchen will be part of the employee housing facility. A grease recycling procedure will be
implemented to minimize grease entering the OWTS. Grease will be collected in a bucket stored in the
kitchen. The grease will then be transferred to a bear-proof recycling container located at the exterior of
the kitchen.
The sewer line exiting Unit MDP is 2 Tz-inches in diameter and 10 %-inches above the ground surface.
The sewer line exiting Unit LP4 is 3 %-inches in diameter and 8-inches above the ground surface. Both
sewer pipes will transition to a 4-inch diameter, schedule 40 sewer line with double-sweep clean outs.
Heat trace and insulation must be installed on all above grade sewer lines.
The OWTS installation will include two 15OO-gallon, single compartment concrete septic tanks, followed
by one 15OO-gallon, two-compartment concrete septic tank with an Orenco@ Biotube Pump Vault and
duplexing Orenco@ PF3005 pumps. Floats should be set to dose approximately 90-gallons per pump
cycle. We recommend Valley Precast, lnc. or another qualified professional company perform start-up of
the Orenco@ pumps. The high-water alarm will connect to "Smart Camp" security system.
Septic tanks must have PVC risers on all manhole access ports brought to grade. Tee posts and fencing
(or metal bollards) must be placed around the tanks to eliminate the possibility of traffic over the area of
the septic tanks.
Page 4
Effluent will be pressure dosed through a 1.5-inch diameter pump line to an Orenco@ Model 64044
automatic distributing valve (ADV), which will be placed at the high point of the system and will distribute
effluent to four unlined sand filters, each 12-feet x 42-feet. The 1.5-inch pump line must maintain a minimum
1% slope to the ADV to allow for proper drain back into the pump chamber.
Excavation for the sand filters will extend approximately S-feet below native grade. The unlined sand
filters will consist of a minimum of 3-feet of sand filter material. Sand filter material must be clean, coarse
sand, all passing a screen having four meshes to the inch. The sand must have an effective size between
0.25 and 0.60 mm. The uniformity coefficient must be 4.0 or less. Material meeting ASTM 33, for concrete
sand, with one percent or less fines passing 200 mesh sieve may be used. Tee posts and fencing must be
placed around the sand filters to eliminate the possibility of traffic or grazing over the STA.
Pipes used to disperse the effluent must be surrounded by washed coarse screened gravel or crushed
stone. All of the gravel or stone must pass a2Tz-inch screen and must be retained on aYt-inch screen. The
manifold must be 1.5-inches in diameter. Laterals must be 1.S-inches in diameter with 5/32-inch diameter
orifices facing down, spaced 3-feet on center. Orifice shields should be installed under each orifice. Laterals
wi¡ be separáted by 3-feet. Each 1.5-inch diameter lateral must end in a sweeping ell facing up with a ball
valve for flushing. A soil separation fabric should be placed over the gravel layer followed by approximately
1-foot of topsoil or other suitable soil able to support vegetative growth.
A minimum 20 mil PVC liner should be placed on the downhill side of each bed, extending the full depth
of the sand filter material.
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.
MINIMUM HORIZONTAL SETBACK REQUIREMENTS
A storm water retention pond will be located to the north west of the OWTS components. The minimum
horizontal distance required from the retention point to the unlined (open bottom) sand filters, in accordance
with Table 7-1 of Garfield County On-Site Wastewater Treatment System Regulations, must be a minimum
of 5oJeet. Footnote 3 of Table 7-1 states an additional 8-feet of distance must be added for each 100
gallons per day over 1000 gallons per day ..."unless ff can be demonstnted by...a hydrologic analysis... that
contamination will be minimized."
Water Resource Consultants, LLC has completed a report dated October 13,2014 regarding the "Effect on
Groundwater and Aquifer Recharge Areas" and letter dated November 14,2014 regarding "OWTS -
Separation Distance from Storm water Retention Pond". Given the hydrology and topography of the Site, jn
addition to the positioning of the retention pond relative to the components of the OWTS, a setback of S0Jeet
between the unlined (open bottom) sand filters and the storm water retention pond satisfies the OWTS
requirements and is suitable for actual conditions at this location.
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 irritation shall be placed over
the STA. Until vegetation is reestablished, erosion and sediment control measures shall be implemented
and maintained on the Site. The owner of the OWTS shall be responsible for maintaining proper vegetation
cover.
Page 5
OPERATION INFORMATION AND MAINTENANCE
Terra Energy Partners shall be respons¡ble for the operation and maintenance of each OWTS servicing the
property. Terra Energy Partners is responsible for maintaining service contracts for manufactured units,
alternating STAs, and any other componenß needing maintenance.
Geo-fabrics or plastics should not be used over the STA. No heavy equipment, machinery, or materials
should be placed on backfilled STAs. 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.
Terra Energy Partners should pump the septic tanks as needed, gauged by measurement of solids in the
tanks. Garbage disposal use should be minimized, and non-biodegradable materials should not be placed
into the OWTS. Grease should not be placed in 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
lf design includes a pump, air release valves and weep holes must be installed to allow pump lines to
drain to minimize risk of freezing. The pumps shall be connected to a control breaker separate from the
high water alarm breaker and from any other control system circuits. 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.
INSTALLATION OBSERVATIONS
ALL SERVICE septic, LLC 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. ALL SERVICE septic,
LLC should be notified 48 hours in advance to observe the installation.
LIMITS:
The design is based on information submitted. lf soil conditions encountered are different from conditions
described in report, ALL SERVICE septic, LLC 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,
ALL SERVICE septic, LLC
Reviewed By:
(p-',[æ tstúxng
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98662
Carla Ostberg, MPH, REHS Richard H.
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