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HomeMy WebLinkAboutOWTS Design Plan 04.17.2026129 CAWS LANE CARBONDALE, CO 81 623 970.309.5259 CARLA.OSTBERG@GMAIL.COM SI:YTIC; C'ONSi'I: l`ING April 17, 2026 Alberto Pizarro Apizarro1980[�gmail.com Subsurface Investigation and Onsite Wastewater Treatment System Design 2-Bedroom Accessory Dwelling Unit 208 CR 236 Garfield County, Colorado Alberto, Project No. C2033 CBO Inc. performed a subsurface investigation and completed an onsite wastewater treatment system (OWTS) design for the subject residence. The 7.05-acre property is located outside of Silt, in an area where OWTSs and wells are necessary. Legal Description: Section: 4 Township: 6 Range: 92 A TR IN SESW CONT. 7.05 AC. AKA TRACT B AMENDED JOHNSON SUBDIVISION EXEMPTION. Parcel ID: 2179-043-00-412 SITE CONDITIONS The property is currently developed with two non-residential buildings. A 2-bedroom accessory dwelling unit (ADU) is proposed. The residence will be served by a well. The well is located south of the proposed ADU. The well is greater than 50-feet from the proposed septic tank and greater than 100-feet from the proposed soil treatment area (STA). The approximate waterline is depicted on the site plan. The waterline must be located prior to construction. The STA must be at least 25-feet from the STA and the sewer line must be properly encased 5-feet on each side of the waterline crossing (see Encasement Detail W4.0/4). A creek meanders to the east of the proposed development. The creek was not identified on the site plan provided to us. We have estimated the location based on arial images. The creek must be at least. 50-feet from the proposed STA. The proposed soil treatment area (STA) location has an approximate five percent slope to the southeast. The proposed area is sparsely vegetated. 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 March 19, 2026 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.' ' 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 light brown, dense sandy loam to a maximum depth explored of 7.0-feet. No bedrock or groundwater was encountered. The materials encountered in Test Pit #2 consisted of light brown, dense sandy loam to a maximum depth explored of 7.0-feet. No bedrock or groundwater was encountered. A sample of the soil was taken from Test Pit #1 at 3-feet below grade. Soil structure grade was moderate; however, digging was difficult. The soil formed a ball and a ribbon approximately 1-inch in length before breaking. Soil structure shape was blocky and consistence was friable to firm. Soil texture was more gritty than smooth. The soil is consistent with Soil Type 2, Sandy Loam, with moderate structure grade; however, digging was difficult and soil appeared to be dense, so sizing of the STA will be based on Soil Type 2A. A long- term acceptance rate (LTAR) of 0.5 gallons per square foot will be used to size the STA. Sk Test Pit #1 ": OF - Sieved sample Backfill Ribbon approx. 1" I Test Pit #1 Test Pit #2 Page 3 Page 4 Backfill DESIGN SPECIFICATIONS Design Calculations: Average Design Flow = 75 GPD x 2 people/bedroom x 2 Bedrooms = 300 GPD LTAR = 0.5 GPD/SF 300 GPD / 0.5 GPD/SF = 600 SF x 1.2 (gravity bed) x 0.7 (chambers) = 504 SF / 12 SF/chamber = min. 42 `Quick 4' Infiltrator® chambers The OWTS design is based on 2-bedrooms. An average daily wastewater flow of 300 GPD will be used. For the purposes of this OWTS design, Benchmark Elevation 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. OWTS Component Minimum Elevation Primary Tank Inlet Invert Approximate horizontal distance 15' / min. 2% fall / min. 3.75" fall Distribution Box Approximate horizontal distance 75' / min. 1 % fall / min. 9.375" fall Infiltrative Surface Approximate horizontal distance 15' to furthest row / min. 1 % fall to STA / min. 1.875" 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 1000-gallon, two -compartment Infiltrator® poly septic tank with an Orenco@ Biotube effluent filter on the outlet tee. Minimum Schedule 40 sewer line must be used 5-feet before and after 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. Safety Page 5 grates must be placed in each accessible riser. Any state -approved concrete or poly septic tank may be substituted. The sewer line must be minimum Schedule 40 in any area subject to traffic. Additionally, the water line must be accurately located and the sewer line must be encased with minimum Schedule 40 5-feet on each side of the crossing. See Encasement Detail W4.0/4. Effluent will gravity flow to a distribution box, and then to four gravelless chamber rows. 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 trench. A level manifold may be substituted for the distribution box. The chamber bed will consist of 4 rows of 11 'Quick 4' Infiltrator® chambers for a total of 44 chambers and 528 square feet of infiltrative area. Inspection ports must be installed at each corner of the bed. 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® IM-1060-2CP 1000-gallon, two - compartment poly septic tank Effluent Filter Orenco® Full size, 4-inch diameter effluent filter Tank Risers and Lids Orenco® Double -walled PVC Risers and Lids (24" diameter) EZSNAP Safety Star installed in each manhole riser (2) EZ Snap Safety Star Infiltrator® SNAPSAFT-2400 (Risers and safety grate must work together, so substitutions may be necessary) Distribution Box Polylok Distribution box, lid, risers, flow equalizers (4) Chambers Infiltrator® J,Quick 4' Plus Standard 4 `Quick 4' chambers Construction must be according to the jurisdiction's adopted On -Site Wastewater Treatment System Regulations, the OWTS Permit, and this design. 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. Page 6 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. 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 Page 7 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 H w r f { rOp D m m z z 0�U O z C En A 4 1 W =2m •b 1Z n D r m 1 o - voNo N O c o o o m� .N-. v Y m o °i `�' O O ? n m M NET oz 0 w '� I' •) - 1. �O yO. 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