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HomeMy WebLinkAboutEngineer's Report.pdf July 11, 2014 Project No. C1081 Tamar Mattorano 1164 CR 106 Carbondale, CO 81623 Subsurface Investigation and Onsite Wastewater Treatment System Design 3-Bedroom Residence 1164 CR 106 Garfield County, Colorado Tamar, ALL SERVICE septic, LLC performed a subsurface investigation and completed an onsite wastewater treatment system (OWTS) design for the subject residence. The property is located in Satank, outside of Carbondale, in an area where OWTSs are necessary. SITE CONDITIONS A 3-bedroom, single-family residence presently exists and is utilizing an existing OWTS which includes a cinder block septic tank and soil treatment area (STA) located on the neighboring property. The STA has failed and there is a desire to upgrade and relocate the OWTS. There is a private well located on the property which is not currently in use. This well will be abandoned. The residence is served by a community water system. A minimum setback of 50-feet must be maintained from the ditch on the west property boundary to the STA. A 10-foot setback will be maintained from any OWTS component to the property line. SUBSURFACE The subsurface was investigated on July 2, 2014 by digging two 8-foot soil profile test pit excavations (Test Pits) and taking a soil sample from approximately 3 to 4-feet below grade in Test Pit #2. A gradation analysis was run by HP Geotech and results are detailed in a report dated July 7, 2014, Job No 114 021L. The materials encountered in the Test Pit #1 consisted of dark brown, firm, moist, clayey, silty sand to 4-feet, underlain by medium brown, loose, moist, gravelly, silty sand with 2 to 6-inch cobbles to a maximum depth explored of 8.0-feet. No bedrock or groundwater was encountered. The materials encountered in Test Pit #2 consisted of dark brown, firm, moist, clayey, silty sand to 2.5-feet, underlain by light brown, loose, moist gravelly sand with 2 to 10-inch cobbles to a maximum depth explored of 7.0-feet. No bedrock or groundwater was encountered. The gradation analysis performed by HP Geotech shows the soil consists of 36% gravel, 50% sand, 14% silt and clay. The USDA soil type is classified as Very Gravelly Sandy Loam. Utilizing the USDA Soil Triangle, this could also be interpreted as a Very Gravelly Loamy Sand. A long term acceptance rate (LTAR) of 0.8 gallons per square foot, will be used to design the OWTS, in accordance with Table 10-1 Soil Type 1 presented in the Garfield County On-Site Wastewater Treatment System Regulations, adopted April 14, 2014. Page 2 Test Pits observed July 2, 2014 Test Pit #1 Note the dark brown, firm horizon from 0 to 4-feet Test Pit #2 Dark brown, firm horizon in Test Pit #2 extends only 2.5-feet DESIGN SPECIFICATIONS The existing septic tank and STA will be abandoned in place or removed. If abandoned in place, the septic tank must be collapsed and remaining void filled with gravel, sand, or compacted soil. The new OWTS design is based on 3-bedrooms. An average daily wastewater flow of 450 GPD will be used. The system installation will include a new 1000-gallon, two-compartment concrete septic tank with an H-20 rated lid for installation under an existing driveway. An effluent filter must be installed on the outlet tee of the septic tank. The STA will consist of four rows of 10 ‘Quick 4’ Infiltrator® chambers connected with a level manifold, for a total of 40 chambers and 480 square feet of infiltrative area. The infiltrative area may not exceed 4-feet below native grade. If the firm dark brown horizon is encountered at a depth shallower than 4-feet (most probable at the west end of the bed), this office must be contacted. The bed may NOT be installed in this material. If encountered, the material must be over-excavated and removed. It must be replaced with the more suitable, loamy sand on-site Page 3 material. The over-excavation material must be 3-inch minus and installed in one-foot lifts to the bottom of the infiltrative area. 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. REVEGETATION REQUIREMENTS An adequate layer of good quality topsoil capable of supporting revegetation shall be placed over the entire disturbed are 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 plated over the area. 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 absorption systems, 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 absorption area. Livestock should not graze on the absorption area. 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. 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 OWTS. The OWTS is engineered for domestic waste only. ADDITIONAL CONSTRUCTION NOTES If design includes a pump, air release valves and weep holes must be installed to allow pump lines to drain to minimize risk of freezing. 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 Page 4 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. If soil conditions encountered are different from conditions described in report, ALL SERVICE septic, LLC should be notified. All OW TS 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: Carla Ostberg, MPH, REHS Liability Clause: Under no circumstances whatsoever shall the liability of ALL SERVICE septic, LLC, in connection with any contract, directly or indirectly, exceed the total amount paid by the cl ient to ALL SERVICE septic, LLC for the services and/or goods which are the subject of the contract in connection with which the liability arises.