Loading...
HomeMy WebLinkAbout287 Hunt Ranch Rd-AC-OWTS-Cert-Report-082525August 25, 2025 502 Main Street • Suite A3 • Carbondale, CO 81623 • (970) 704-0311 • Fax (970) 704-0313 S OPRIS E NGINEERING • LLC civil consultants Anne and Laurence Sperry, West S Ranch LLC 33 Sunhill Lane, Newton Center, MA 02459 lsperry@sperryinc.com RE: As-Constructed Report –Onsite Wastewater Treatment System (OWTS), Sperry Residence, 287 Hunt Ranch Rd, Carbondale, CO, Lot 2 Hunt Ranch, Garfield County, Colorado SE Job No. 34042.01 Parcel No: 239120100278. Garfield County OWTS Permit # SEPT-8811 Dear Laurence and Anne: Pursuant to County requirements, this letter provides documentation that the Onsite Wastewater Treatment System (OWTS) components recently installed at the above referenced site is in compliance with the permitted design. Sopris Engineering inspected the excavations, soils, materials and the installation of the system components during construction, prior to final backfill and after all installations were completed. The installed absorption field and tank were designed and constructed to serve the new 4-bedroom single family residence and a future garage/workshop with a two-bedroom ADU. Sopris Engineering performed site visits in coordination with the owner and contractor (E&L Excavation) that installed the system components. The as-constructed conditions and installation of the new OWTS components are in compliance with Garfield County Regulations; the recommendations and specifications delineated on the OWTS permit/construction plan “C6-OWTS Plan”, dated 06-24-2024 and report by Sopris Engineering. The As- Constructed OWTS conditions, design criteria and components installed are delineated on the attached AC OWTS Record Drawing. The design criteria and system sizing information is summarized below. As-Constructed OWTS and Proposed Conditions The proposed OWTS will serve a new 4-bedroom single family residence with additional capacity for a two- bedroom ADU in a future Garage/workshop to be situated Southwest of the newly constructed dwelling. A sanitary sewer service pipe was installed east of the dwelling with cleanout and capped stubout to connect to the future facility. The sanitary sewer service pipe that crosses under the gravel drive was installed with Schedule -40 PVC bedded and backfilled with Class- 6 ABC. Summary Design Criteria The new OWTS was designed for a treatment capacity of 675 gallons per day based on the design wastewater flow to serve a minimum 6-bedroom residence in accordance with Table 6-2 values, Section 43.6, A.4. A new 2,000 gallon two-compartment concrete tank was installed off the northside of the dwelling. Sealed ribbed PVC risers with lids were installed on the new septic tank along with appropriate pipe connections to the new tank utilizing the appropriate fitting adaptor rings for the tank and riser. The new 2,000 gallon 2-compartment septic tank was installed with appropriate sanitary tees, outlet effluent filter with extension handle and risers and lids at the surface. Sanitary sewer service pipes consisting of SDR-35 and schedule-40 sewer pipe sections were installed with two- way cleanouts adjacent to the dwelling and at wye fitting junctions. Additional in-line cleanouts were installed along the service pipe to the future barn. Piping and cleanouts are delineated on the Record drawing. The STA consist of leaching chamber trenches that provide 960 S.F. of total absorption area in a trench configuration. The septic tank effluent is gravity discharged through a new 4-inch SDR-35 PVC pipe, installed at minimum 1.5% slope, to a 7-port concrete distribution box with risers and lid at the surface. The effluent is equally distributed from the distribution box via 4” distribution pipes connected to the head end cap of each chamber trench. OWTS, Sperry Residence 287 Hunt Ranch Rd, Carbondale, CO OWTS PERMIT #: SEPT-8811, SE Job No. 34042.01 August 25, 2025 Page2 Observation ports with caps are installed on the proximal and distal ends of each chamber trench and housed in valve boxes set just above finish surface grade. The design is in compliance with the current County regulations with design calculations based on the soil type, texture and structure with an appropriate long term acceptance rate (LTAR). The designed system meets all required setbacks and will be installed within the general location indicated on the plan. Design Flow The design flow is calculated as follows for the minimum design capacity of an equivalent 6-bedroom residential dwelling. The OWTS is designed for a treatment capacity of 675 gallons per day based on the design wastewater flow in accordance with Table 10-1 values, Section 43.6, A.4. Regulation 43: Minimum population based on 3 bedrooms at 2 persons per bedroom equating to 6 persons plus three bedrooms at 1 person per bedroom equating to a total of 9 persons. The Design flow is calculated based on residential usage of 75 gal/person/day, Max. Design flow (Qd) gallons/day = (# of people) x (avg. flow) gal/person/day. Design flow Qd = 9*75 = 675 gpd Septic Tank Design The septic tank capacity required for a minimum 48 hour retention time is calculated as follows: V = 675 gal/day * 2 day = 1350 gallons. Use a minimum 2,000 gallon 2-compartment concrete septic tank. The tank to be installed with ribbed PVC risers and access lids set a minimum 3 inches above finish grade surface. Sub Surface Conditions and Testing Subsurface soil investigations and USDA soil texture method tests were performed by Kumar, USA and Sopris Engineering on May 29, 2024. The soils from three profile pits, in the vicinity of the proposed STA field area were sampled and characterized by application of the USDA visual/tactile soil texture method analysis. The soils were tested to determine the presence of any limiting soil or hydrological conditions, appropriate hydraulic loading rate, absorptive surface level capacity and to assess appropriate treatment level design for the in-situ native soils. The soils below 9" of topsoil consist of dense slit loam with less than 2% scattered gravel or rock content to 7 feet below the surface grades. The soils appear to be generally consistent across the site. The native soils sampled from 2-3 feet below the surface are characterized as a soil type 2A soil consisting of silt loam texture with fine granular structure shape with massive grade. This soil has an effective loading rate for conventional soil treatment of 0.5 Gal/S.F./day for a level 1 conventional treatment system. No rocky soils or significant change of texture was encountered at depth. Some evidence of thin scattered lenses of calcareous deposits at variable depths was encountered in Profile pit 1 and 3. A 6 to 9 inch layer of calcareous deposits at variable pitched depth from 18 to 30" below surface grade was encountered in Profile pit 2 that was excavated from existing surface grades approximately 3' below the the other pits. Based on this evidence the proposed STA was situated on the slightly higher ground. No free water was encountered in excavations observed on site. Normal Groundwater levels are expected to be below 8 feet from the existing surface grades. The soils are suitable for the installation of an STA consisting of multiple gravelless chamber trenches. Additional soil evaluations were performed during construction to verify the soils in the entire field excavation. The soils in the tank, pipline and STA trench excavations were observed and found to have consistent relatively dense silt loam soils with fine granular structure shape with massive grade without the presence of rock or gravels.