The URL can be used to link to this page

Home My WebLink AboutOWTS Design 195 Panoramic Drive Repair Onsite Wastewater Treatment System Design 3-BR Single-Family Residence Existing Single-Family OWTS System Silt, CO 81652 Parcel No. 2127-363-00-008 Prepared for: George Strong 195 Panoramic Dr. Silt, CO 81652 June 2022 Prepared By: Page 1 1.0 SITE CONDITIONS The proposed repair onsite wastewater treatment system (OWTS) will serve an existing 3-BR single-family residence located on a 3.05-acre parcel created as Lot 5 of the Panoramic Mesa Subdivision located at 195 Panoramic Drive, Silt, Colorado (Figure A1). The existing 1,250 gallon septic tank and leachfield is comprised of twenty-one Quick4 Infiltrator units in three trenches in a fallow field located south of the existing dwelling. The repair OWTS serving existing 3-BR single-family dwelling will use a total of 44 Quick4 Plus Infiltrators® configured in four (4) Q4 trenches each with eleven (11) units in a minimum 24’ x 47’ footprint (Figure A2). Proposed soil treatment area (STA)/leachfield is south of the existing dwelling and east of existing failed leachfield in an area sloping approximately 10-12 % south-southwest. Soil information was collected by WestWater Engineering May 22, 2022 to determine the long- term acceptance rate of the soil in accordance with Garfield County On-Site Wastewater Treatment Regulations (Regulations). Soil profile in 9.0-foot exploratory pit located approximately 100 feet southeast of the existing garage. Soil observation pit showed a uniform soil profile of strong brown (7.5YR 5/6) silty sand with clay (silty sand loam) which Garfield County assigned a 17 minute per inch percolation rate for a repair leachfield design June 24, 2004 (Appendix A). Groundwater was not encountered in soils observation pit, high seasonal groundwater table is estimated to be greater than 9.0 feet below ground surface (bgs). Based on the comparative tactile soil evaluation, site soils providing secondary wastewater treatment are classified as Soil Type 2 in accordance with the Table 10-1 of the Regulations. This is based on the following soil characteristics: silty sand loam texture, granular structure and estimated percolation rates falling within the 16-25 min/in range. Long-term acceptance rate (LTAR) used to design the OWTS (Table 10-1 Regulations) is 0.60 gallons per day per square foot area (gpd/ft2). 2.0 WASTEWATER FLOWS Average Flow Maximum Daily Wastewater Flow (gpd): 3-BR Single-Family Dwelling 3 x 150 gallons = 450 gpd Septic Tank Septic tank capacity required for a 3-BR dwelling is 1,000 gallons in accordance with Table 9-1 of the Regulations. Septic tank volume corresponds with a 48-hour (2 day) particle detention time for design capacity of proposed OWTS. The 3-BR Tank Capacity: 450 gpd x 2 (48 hour/2 day detention time) = 900 gallons (minimum). Retain the existing 1,250 gallon, two-compartment septic tank previously approved by Garfield County per Regulations. Page 2 3.0 OWTS DESIGN Silty sand loam occurring at the 2.0 to 5.0-foot depth interval will be used for upper infiltrative surface for proposed STA (Figure A3). Maximum trench depth for repair OWTSs must not exceed 5.0 feet in accordance with the Regulations. Trench excavation will remove approximately 2.0 to 5.0 feet of soil and upper root mass to prepare level surface for installing infiltrators on receiving soil infiltrative surface providing secondary treatment of discharged wastewater. Soil should not be wet at time of excavation. Silty sand loam covering STA must be crowned over proposed trenches or match existing grade so water runs off, and is not ponded over any area of STA/leachfield. Prior to backfilling final soil cover, a pervious soil barrier of non-woven geotextile fabric or similar pervious material shall be installed over the STA to prohibit soil intrusion. All setback distances in accordance with the Regulations are applicable to septic system installation. The septic tank must be at least 5 feet and STA at least 20 feet from existing and future plumbed structure(s) to be served. STA’s must be outside any easements and at least 10 feet from property lines. Setback distances also apply to natural and artificial waterways, including a 50-foot setback from STA to open irrigation ditches, creeks, and ponds. The existing shared water well or any future proposed water well must be at least 50 feet from the septic tank and 100 feet from the leachfield. Existing potable water supply line must be located at least 25 feet from nearest corner of the leachfield. Designated repair leachfield area must be retained per Regulations as idle land set aside for future use once primary leachfield fails and no longer accepts wastewater. The existing septic tank will be maintained to provide at least 48 hours detention time for received wastewater flow from the structures they serve. Internal septic tank inlet and outlet tees must be installed per Regulations. An effluent filter must be installed instead of tee on the septic tank outlet. Use the Orenco Systems Biotube Effluent Filter OSI Model FTW0444-36. Effluent filters typically require cleaning and maintenance every 6 months. The following design calculations propose to discharge septic tank effluent to four (4) Quick 4 Plus Infiltrator trenches each with eleven (11) units for a total minimum disturbed area of about 24 feet by 47 feet. A total of 44 Quick 4 Standard Plus Infiltrator units will be installed in the four (4) proposed trench configuration generally oriented northwest to southeast conforming with topographic contours. Soil Absorption Area Calculations STA Area (A) = Design Flow (Q)/LTAR Field percolation rate (t): 17 min/in Leachfield Area: A = Q/LTAR, Page 3 Where: A = Leachfield area square feet Q = Design Flow/maximum daily wastewater flow = maximum daily wastewater flow for total of 3-BRs = 3 x 150 gpd/bedroom = 450 gpd LTAR = Long Term Acceptance Rate (max. hydraulic loading rate) = 0.60 gallons per day/ft2 A = 450 gpd/0.60 gpd/ft2 = 750 ft2 Quick4 Trench Configuration: 750 ft2 x 1.0 (app. method adjustment1) x 0.7 (distribution media adjustment2) = 525 ft2; 525 ft2 /12 ft2 = 43.75 Q4 units; Use 44 units. 1 Regulations Table 10-2 size adjustment factor for Methods of Application in STA 2 Regulations Table 10-3 size adjustment factor for Types of Media in STA Note: County and State approved bottom chamber area for Quick 4 Plus Standard Infiltrator Unit = 12 ft2. The four (4) Quick 4 Infiltrator trenches will use a total of forty-four (44) units. The trenches will have eleven (11) Q4 chamber units in each trench. Wastewater flow into the proposed 4- trench system will be split using a distribution box. Use the top port of Infiltrator faceplate for all influent piping. Each trench must be covered with geotextile fabric or similar material to prohibit soil intrusion into chamber unit louver vents. 4.0 SYSTEM INSTALLATION REQUIREMENTS Minimum setback requirements must be in accordance with the Regulations. All sewer pipe couplings must be completed with solvent weld or bell and spigot joints using 4-inch SDR 35 PVC pipe. Schedule 40 PVC 4-inch pipe with a minimum 1-foot soil cover must be used if pipe is installed in a vehicular traffic crossing. Drain-waste-vent (DWV) rated Schedule 40 PVC pipe is called out for crossings but may also be used instead of SDR 35 PVC pipe. Building sewer pipe must be set at a slope between ⅛-inch and ¼-inch per foot slope (1 to 2%), preferably using the ¼-inch per foot slope as recommended by the International Plumbing Code (IPC) as administered by the County. Fittings should use sweep 90-degee curves or two (2) 45- degree elbows at all influent pipe turns. Fittings must be DWV for schedule 40 PVC pipe. Page 4 Clean-outs (2-way) are required between dwelling and tank and beyond tank where pipe lengths exceed 100 feet from tank to STA/leachfield. Installer must adhere to minimum depth requirements for leachfield and ensure gravity drainage into all septic system components to avoid using a lift pump. System components must be placed on native soils or re-stabilized soils in excavated areas. Trenches must be dug level to ensure prepared infiltrative surface is level along entire length of STA. Solid 4-inch pipe is used in the header network out of distribution box. The owner will ultimately be responsible for septic system maintenance including pumping septic tank once every 3-4 years and cleaning effluent filter every 6 months. 5.0 SYSTEM INSPECTION WestWater Engineering is responsible for inspecting OWTS to ensure construction conforms to design plan and meets all aspects of County Regulations to include:  Inspect system prior to backfilling including piping and septic system components.  Complete as-built drawing of system. 6.0 DESIGN LIMITATIONS The OWTS design is based on site specific soil conditions and percolation data collected in vicinity of proposed leachfield and local experience of designing OWTS’s in Colorado. The design is only valid for proposed new OWTS serving the existing single-family residence at referenced location provided in this report. WestWater Engineering assumes no liability for inaccurate information or conditions that vary from design assumptions listed above. Notify WestWater Engineering and/or the Garfield County official immediately if actual site conditions differ from those assumed here in. Please do not hesitate to contact us if you have any questions regarding this report. Respectfully, Dean Goebel, M.S., P.G. Hydrogeologist Reviewed By: Keith Mendenhall, P.E. APPENDIX A SOILS AND PERCOLATION DATA