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HomeMy WebLinkAboutOWTS Design129 CAINS LANE cRnaoruoeLE, co a1623 970.309.5259 CARLA. OSTBERG@G MAI L.CO M '¡-t.:''îl Í<: (_:{} i\gÉ t_tI..r ¡ ¡ii (+ September 5,2021 Project No. C1638 Tim Pestotnik tim@pestotnik.com Onsite Wastewater Treatment System Design 6-Bedroom Residence Lot 20, Ranch at Coulter Creek Garfield County, Colorado Tim, CBO lnc. has completed an onsite wastewater treatment system (OWTS) design for the subject residence. The 5.915-acre property is located outside of Glenwood Springs, in an area where OWTSs are necessary. We have changed the location of the septic tank from our original design documents dated August 22,2021. Those should be discarded and replaced with these, dated September 5,2021 Legal Description: Section: 7 Township: 7 Range: 87 Subdivision: RANCH AT COULTER CREEK PUD Lot: 20 AS PER FIRST AMENDED FINAL PLAT RECEPTION NUMBER 889891 5.916 ACRES Parcel lD: 2391-07 1-01-020 SITE CONDITIONS The property is currently undeveloped. A 6-bedroom single-family residence is proposed. The property is served potable water from a community water system. The water line will enter the property from the north and will not come within 2S-feet of any proposed OWTS component. The proposed soil treatment area (STA) location has an approximate 10-12% slope to the southeast. The proposed area is vegetated with native grasses, sage brush, and scattered pinion trees. 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 by Kumar and Associates and findings are documented in a report (enclosed) dated April 12,2021, Project 21-7-256. The report notes ". ..The subsoils encountered below about % to 1 foot of topsoil, consist of 1 to 3 feet of stiff, sandy silty clay overlying mostly whitish, medium dense to stiff, gravelly silt and sand. Basalt rocks in a sand and silt matrix were encountered in Pit 1 at a depth of 2 feet. Resu/fs of a gradation analysis performed on a sample of slightly gravelly sand and silt (minus S-inch fraction) obtained from the site are presented on Figure 3. No free water was obserued in the pits at the time of excavation and the soils were slightly moist to moist." Gradation results from a sample taken from Profile Pit 2 between 6 and 7-feel below grade was 21o/o gravel, 42o/o sand, 27o/o silt, and 10% clay. Page 2 STA sizing is based on Soil Type 2. A long term acceptance rate (LTAR) of 0.6 gallons per square foot will be used to design the OWÏS. DESIGN SPECIFICATIONS Desiqn Calculations: nyerage Oe gn Flow = 75 GPD x 2 people/bedroom x 3 Bedrooms + 225 GPD (4th, 5th, and 6th bedrooms) = 675 GPD LTAR = 0.6 GPD/SF 675 GPD / 0.6 GPD/SF x 1.0 (gravity trenches) x 0.7 (chambers) = 787.5 SF The OWTS design is based on G-bedrooms in a single-family residence. An average daily wastewater flow of 675 GPD will be used. For the purposes of this OWTS design, Benchmark Elevation at grade 7438.5' (Finished Floor) has been established as 100'. The sewer line will exit the residence at approximately 98'. CBO lnc. should be notified of any discrepancies or problems with grade elevations of proposed components during installation of the OWTS. *Elevations are based upon standard OWTS installation practices. Component elevations may change during installation due to site conditions The 4-inch diameter SDR-35 sewer line exiting the residence must have a double-sweep clean out and a minimum 2o/o grade to the septic tank. The system installation must include a minimum 2000-gallon, two-compartment septic tank with an effluent filter on the outlet tee. Risers must bring the manhole lids to grade for access. lf 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 five 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 trench. Each trench will consist of 14 'Quick 4' Standard Plus lnfiltrator@ chambers for a total of 70 chambers and 840 square feet of infiltrative area. There must be at least 4-feet of undisturbed soil between each trench. lnspection 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. COMPONENT SPECIFICATIONS The component manufacturers are typical of applications used by contractors and engineers in this area. CBO lnc. 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. OWTS Component Minimum Elevation Primary Tank lnlet lnvert Approximate horizontal distance 56' / min. 2% fall to septic tank / min. 14" fall Distribution Box Approximate horizontal distance 89' / min. 1o/o fall to distribution box / min. 11.125" falJ. lnfiltrative Surface Approximate horizontal distance to furthest trench 45'l min. 1%fall / min. 5.625" fall Page 3 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 lnc. 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 lnc. 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 lnc. should be notified 48 hours in advance to observe the installation. ln 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 REQUI REMENTS 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 so¡l 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. COMPONENT MANUFACTURER MODEL NO COMMENTS Septic Tank Valley Precast ltem # 2000T-2CP 2000-9allon, 2- ;ompartment concrete septic tank Biotube Effluent Filter Orenco@ Full Size Effluent Filter and rousino Tank Risers and Lids Orenco@ Double-walled PVC Risers and Lids (24" diameter) Distribution Box PolyLok D-Box 8C Poly distribution box, lids, 'isers, and flow equalizers Chambers lnfiltratoKÐ Standard Plus 70 'Quick 4' Chambers Page 4 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. lf an effluent filter or screen has been installed in the OWTS, we recommend this filter or screen be cleaned annually, or as needed. lf 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 OWïS. The OWTS is engineered for domestic waste only. ADDITIONAL CONSTRUCTION NOTES lf 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. lf soil conditions encountered are different from conditions described in report, CBO lnc. 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 lnc. fç"n{*-ts?fu,ç Carla Ostberg, MPH, REHS