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Home My WebLink AboutOWTS Design Report 02.29.16Bridger Smith Smith.bridger@gmail.com Onsite Wastewater Treatment System (OWTS) Design 2-Bedroom Additional Dwelling Unit (ADU) 4110 CR 243 Garfield County, Colorado Bridger, Project No. C1192 ' ALL SERVICE septic, LLC has completed an onsite wastewater treatment system (OWTS) design for the subject proposed additional dwelling unit (ADU). The 54.413-acre property is located outside of New Castle, Colorado, in an area where OWTSs and wells are necessary. Legal Description: Section: 36 Township: 4 Range: 91 PT OF HES #38 IN THE E2E2 OF SEC. 35 & W2W2, SEC. 36. EXCEPT A TR CONT. 2 .439AC, EXCEPT A TR CONT. 2 .168 AC. EXCEPT PARCEL A REED SUB-DIV EX. EXCEPT A TR CONT. 1.055 AC AS DESC IN BK 1250 PG 422. Parcel ID : 1925-363-00-064 SITE CONDITIONS A subject property is currently developed with a Shop, Barn, and residence . An existing OWTS (ALL SERVICE septic Project C1001) serves the existing structures. This proposed OWTS design will serve the proposed ADU on the property. There is a private well located on the property. The well is located greater than 50-feet from the proposed septic tank and greater than 100-feet from the proposed soil treatment area (STA). A ditch currently runs to the west of the proposed STA. This ditch will be re-aligned , as it currently runs through the area of the proposed ADU . This ditch will either be aligned to achieve a minimum 50-foot separation distance from the proposed STA OR the ditch will be lined or placed in culvert and will be at least 10-feet from the proposed STA. This setback must be verified at the time of the installation observation inspection and documented in the installation observation documents. The proposed ST A location has approximately a 10 to 15% percent slope across the proposed STA. The site slopes to the east toward Main Elk Creek. SUBSURFACE The subsurface was investigated on April 25, 2015 by HP Geotech . Subsurface conditions are documented in a report dated April 30, 2015 under Job Number 112 088A (enclosed). Three percolation test holes were excavated and one profile pit boring was drilled approximately 200-feet east and up-gradient of the proposed STA. Page2 Additional soil profile test pits are required prior to installation of the proposed STA. This office must be contacted and testing coordinated to verify soils are consistent with sizing criteria used in this design, in addition to confirmation of depth to groundwater and/or bedrock. Percolation rates of 60 minutes per inch (MPI), 30 MPI, and 2 MPI were documented in the HP Geotech report. No groundwater or bedrock was encountered in the Profile Boring drilled at elevation 6032'. The profile consisted of slightly sandy gravel with cobbles, loose to medium dense, slightly moist, brown fill to approximately 2-feet, underlain by gravelly, silty to slightly clayey, loose, moist brown sand to a maximum depth explored of 9-feet. A sample was obtained from the Profile Boring at 2.5-feet below grade. A USDA Gradation was pertormed on this sample resulting in 5% gravel , 45% sand, 43% silt. and 7% clay. The soil has been classified as Loam. STA sizing is conservatively based on Soil Type 2A. A long term acceptance rate (LTAR) of 0.5 gallons per square foot will be used to design the OWTS, in accordance with Table 10-1, presented in the Garfield County On-Site Wastewater Treatment System Regulations, adopted April 14, 2014. DESIGN SPECIFICATIONS Design Calculations: Average Design Flow = 75 x 2 x 2 Bedrooms = 300 GPO LTAR = 0.5 GPO/SF 300 GPO I 0.5 GPO/SF x 1.0 (gravity trenches) x 0.7 (chambers)= 420 SF The new OWTS design is based on 2-bedrooms. An average daily wastewater flow of 300 GPO will be used. The system installation will include a new 1000-gallon, two-compartment concrete septic tank with an effluent filter (or screen) installed on the outlet tee of the septic tank . Effluent will gravity flow to a distribution box, which must be accessible from grade. Flow equalizers or similar product must be installed on the outlet of each pipe leaving the distribution box to assure equal flow to each trench . The STA will consist of three trenches of 12 'Quick 4' Infiltrator® chambers for a total of 36 'Quick 4' Infiltrator® chambers and 432 square feet of infiltrative area . Trenches must have a minimum of 6-feet of undisturbed soil between them . Installation depth of the chambers must be at least 2-feet below native grade and may not exceed 4-feet below native grade. Fill over the chambers must be 3-inch minus. Inspection ports must be installed at both the beginning and end of each trench. Inspection ports may be cut to grade and covered with a sprinkler box for access. 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. Page 3 REVEGETATION REQUIREMENTS An adequate layer of good quality topsoil capable of supporting revegetation shall be placed over the entire disturbed area of the owrs 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 ST A. Until vegetation is reestablished, erosion and sediment control measures shall be implemented and maintained on site. The owner of the owrs shall be responsible for maintaining proper vegetation cover. OPERATION INFORMATION ANO MAINTENANCE The property owner shall be responsible for the operation and maintenance of each owrs servicing the property. The property owner is responsible for maintaining service contracts for manufactured units, alternating ST As, and any other components needing maintenance. Geo-fabrics or plastics should not be used over the absorption area. No heavy equipment, machinery, or materials should be placed on backfilled ST As. Livestock should not graze on the ST A. Plumbing fixtures should be checked to ensure that no additional water is being discharged to owrs. For example, a running toilet or leaky faucet can discharge hundreds of gallons of water a day and harm a ST A. If an effluent filter or screen has been installed in the owrs, we recommend this filter or screen be cleaned annually, or as needed. If the owrs 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 OWfS. Grease should not be placed in household drains. Loading from a water softener should not be discharged into the OWfS. No hazardous wastes should be directed into the OWfS. Mechanical room drains should not discharge into the owrs. 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. 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. Page4 LIMITS : The design is based on information submitted. If 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: ~~ J _ ')'",,.___" Carla Ostberg, MPH , REHS