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Home My WebLink AboutOWTS Design Report 10.02.190ctober 2,2019 Paul and Marianne Stanek 2980 County Road 311 New Castle Co 81647 RE Design Report-Onsite Wastewater Treatment System (OWTS), 2980 County Road 3l 1, Lot 8, Mineota Ridge Est. 3'd Subdivision, Garfield County, Colorado SE iob No. 19228.01 Parcel Number: 2179-134-00-011Garfield County Permit: Dear Paul and Marianne This letter repoft presents the applicable findings in regard to the design and construction of a replacement Onsite wastewater Treatment System Cowrsl at the ãbove referenced site, in support of your owrs permit application to Garfield County. The design recommendations, specifications and construction details are delineated on the attached owTS permit/constiuction plan that is based on GIS, paritial Plat information, aerial mapping and site assessment observations by Sopris Engineering. The Sopris Engineering OWTS design is based on evaluation of existing physical site features, geotechnical soils investigation und ,it" Jonditions witù respect to the proposed residential usage, building layout and applicable reg,rlatãry design criteria that is in accordance with 3taie and County owTS Regulations' The design criteria and system sizing information is summarized below' Summary Desisn Criteria The existing 3-bedroom residence has split waste flows and is served by two separate oWTS's' The original historic field is failing. The design is to provide for a replacement absorption field based on treatment sized for an equivalent 2-bedroorn'c apacity Jingle family residence onsite wastewater treatment system (owTS). The design flow is calculated as follows for ll2the waste flows of the existing single family. This design is for the replacement of the older existing pipe and gravel field that has historically served the kitchen and original bathroom. The other existing owTS, initalled in 2001, serves the previous house addition's waste including the new bathroom that contrib-utes approximately 712 of thetotal waste flow. The existing system has a design capacity of 450 gpd and will be utilized for continued usage. The replacement 9WTS will utilize the existing 1000 gallon 2-compartment septic tank, located in the existing gravel driveway. New traffic rated risers with access lids at the surface will be installed on the existing tank. The tank has an inlet sanitary tee and a new outlet effluent filter sanitary tee will be installed in the second compartment' The existing gravity ."*". pipe will be maintained from the residential structure to the existing tank. The new replacemenì *it t.åut-""t u"it (STU) will consist of leaching chamber trenches that provide 350 s.F' of total absorption area. The septic tank effluent will be gravity discharged through a new 4-inch schedule-4o or SDR-35, installed at1%o slopeacross the driveway, to the STU via a distribution box. The effluent will be equally distributed from the distribution box via 4" distribution pipes connected to the head end cap in each chamber trench' Observation ports with caps will be installedon each end chamber unit. 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). ihe designed system meets all required setbacks and will be installed within the genãral location indicated àn the plan. The existing well is located south of the development area over 100 feet lom both systems. Our design is outlined below and delineated on the attached C-l plan. Desisn Flow 502 Main Street Carbondale, C0 81623 (e70 Fax (970) 704-031 3704-031 1Su ite A3 aaaa $oPnls ÍttGIltIRIllG o 11G civil consu ltants Alameno, OWTS, 2980 C.R. 311 SE Job No. 19228.01 October 2,2019 Page2 The replacement OWTS is designed for a treatment capacity of 300 gallons per day based on the design wastewater flow tó serve a 2-bedroom capacity residence in accordance with Table 6-2 values, Section 43.6, 4.4. From the Regulation 43 usage table : Minimum population based on 2 bedrooms:4 persons' Gallons per day per person :75 gallperson/day, No peaking factor Max. Design flow (Qd)gallons lday = (# of people) x (avg. flow)galipersonlday. Design flow Qd :4*75:300 gqd Use the existing 1000 gallon, two compartment concrete septic tank. Install with an effluent filter outlet sanitary tee in the second compartÃent. Existing tank usage shall continue with installation of new accesses. Install traffic rated concrete risers and iron ring and covers to the finish grade surfac e (1) 24' dia. x 24" depth and 1 ) 24' dia. x I 8" depth risers). Sub Surface Conditions and Observation A subsurface soil investigation and site assessment was performed by Sopris Engineering on October 1, 2019. The soils in the proposed fielã envelope area were sampled and characterizedby application of the USDA visual/tactile soil texture method analysis. Thé soils below 6 inches of topsoil consist of medium dense slightly sandy silt loam soil with less than 5%o sóattered gravels and cobbles to 8 feet below the surface grades. The soils appear to be consistent across the site from observations in the excavated profile pit' The native soils sampled from 2-3 feetbelow the surface are characterized as a soil type 2 consisting of silt loam texture with granulai structure. This soil has an effective loading rate for conventional soil treatment of 0.6 Gal/S.F./day for a level 1 conventional treatment system. The equivalent percolation rate is assumed to be 20-30 minutes pei inch. No free water was encountered in excavations on site. Seasonal high Groundwater levels are expected to be below 20 feetfrom the existing surface grades. The soils are suitable for a shallow conventional shàllow absorption field consisting of gravelless infiltration chamber units. Treatment-Soil Treatment Unit/ Absorption Svstem Desisn The treatment/absorption field is designed based on utilizing the effective Long Term Acceptance Rate (LTAR) for the native soils and the application ofãppropriate loading factors for a soil treatment unit system utilizing gravity distribution to gravelless^óhamber trenches. The new treatment system and absorption field will consist of gravity distribution of septic tank effluen t via adistribution box to individual chamber trenches with treatment across the native soil absorptive surface. The shallow STU trenches shall be installed with a maximum depth to the absorptive surface of 36 inches from finish surface grades and backfilled with approximately 6-inches of final grading topsoil mounded over the trenches placed to alloi positive drainage away from the surface. Chambers shall be installed level in native soil. Each trench will be constructed levei along the contour with successive trenches installed following natural contour grades accordingly. A minimum separation distance of 4 feet will be maintained between the individual trench sidewalls. The engineer, prior to installation shall inspect the trench excavation to confirm suitable soil conditions. All septic system components and trench installations are to be approved by the Engineer and County prior to backfilling. Field Sizing: Alameno, OWTS,2980 C.R. 311 SE Job No. 19228.01 October 2,2019 Page3 Long Term Acceptance Rate (LTAR) Considering the application of the state regulation 43: Receiving Wastewater Treatment Level 1; Soil type 2loadingrate for a silt loam is (0.6 gal./S.F./day).; Loading factors; (Table l0-2, Gravity application trenches : 1.0 ) and (Table 10-3, gravelless chambers : 0.7) A(sÐ: Qd LTAR A: Area; LTAR : 0.6 Gal/S .F.lday for silt loam Qd: flow (gallday):450 gPd L.F. 1:1.0 GravitY Distribution L.F.2:0.7 Chambers A(sÐ : 300 gpd x 1.0 x 0.7 : 350 S'F 0.6 Gal/S.F./day Number of 5'x3' Bio-Diffuser chambers: 350 S.F :23.3 chambers Use 24 chambers 15 S.F./Chamber rJse Z4Bio-Diffuser chambers in two trenches 60' long by 3' wide with 12 chambers units per trench plus two end caps as delineated on the plan. The septic tank effluent will be gravity distributed to the head of each chamber row via individual distribution pipes from a distribution box' Construction and InsPections prior to construction of the permitted system, the engineer should be contacted by the contractor and owner well in advance to provide adequatå time to discuss the system components with the contractor, answer questions, resolve any conflici issues and schedule inspection site visits based on construction progress. A pre-oWTS construction mðeting is essential and required prior to installation of the OWTS. All septic system components shall be staked in the field for approval by the Engineer prior to excavation' During initial construction the engineer will evaluate the soils in the absorption treatment field excavations to confirm soil conditions and make adjustments as needed. All septic system components and trench installations are to be approved by the Engineer prioi to backfilling. All installation will be inspected, surveyed, reported and delineated in the Certificãtion letter and record drawing. The contractor needs to photo document all OWTS construction phases and supply photos to the Engineer. County Regulations require that the Engineers of record perform site inspections of the permitted system during construction and provide "As-Built" documentation of the installed system to the County after construction is complete. OWS Operation and Maintenance Ownership of the system and responsibility for maintenance and repair will remain with the property Owner. The Owner i, ãn"ou.agãd to retain thè services of qualified personnel to inspect the OWTS and to perform all maintenance and repairs necessary to ensure that the ryrt"- components are maintained in good operating condition and suitable vegetative cover is "rtublirh"d on the fields. The components of the owTS system should inspected within:0 daysãf being placed into operation and should been inspected and maintained bi-annually. The tank, absorption field and other system components should be visually inspected bi-annually for debris, damage,leaks, or Alameno, OWTS, 2980 C.R. 311 SE Job No. 19228.01 October 2,2019 Page4 absorption field and other system components should be visually inspected bi-annually for debris, damage, leaks, or other potential problems. In general, for a properly utilized system, septic tanks should be pumped every 3 - 5years. The effluent filter should be ðleaned every six months and at the time of pumping. Absorption fields should be maintained with suitable vegetative cover and kept free of root invasive plants. Positive surface drainage away from the absorption freld should be maintained. If you have any question or need any additional information, please call. Sincerely, SOPRIS ENGINEERING, LLC Paul E. Rutledge Design Engineer Yancy Nichol, PE Principal 28371 ORE