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HomeMy WebLinkAboutOWTS Design Report 06.06.18June 6,2018 Keith and Carrie Brand 1327 West Ridge Court, Carbondale,CO 81623 keith @terrali nkstructures.com RE: Design Report, On-site Vy'astewater Treatment System (OWTS), Brand Residence, TBD Cedar Street; LÐt 204 Amended I-ats 12-14. Blk 9, Carbondale, CO SE Job No. 18065, Parcel No: 2393-284-09-020. Dear Keith: This letter report presents the applicable findings in regard to the design and construction of an Onsite Wastewater Treatment System (OWTS) and residential site improvements at the above referenced Site, in support of your building permit application to Garfield County. The proposed improvements include minor grading and drainage, potable water service, OWTS, electric and other utilities to serve the proposed residence shown on the Site Plan prepared by SE in coordination with the property owner. The OV/TS design is based on our evaluation of the site conditions with information provided by others for use in obtaining a Garfield County OV/TS construction permit. We have evaluated the existing and proposed site conditions with respect to the operation and installation of a new O'WTS in accordance with Garfield County O\ryTS Regulations and State of Colorado Regulation 43. The proposed site specific improvements have been designed in accordance with County Regulations and general engineering guidelines regarding grading, drainage, utilities and construction best management practices. Based on the physical site features, soils, and proposed building layout, we have prepared civil site and O\ryTS design plans with construction details for building permit approval. The design and construction recommendations with specifications are delineated on the civil design plans, C1-SITE PLAN and C2-OïVTS Details, dated 6-6-2018, by Sopris Engineering. Existine & Proposed Site Conditions The site is located on Cedar Street, Carbondale, in Section: 28 Township: 7 Range: 88 Subdivision: Cooperton Twnste. Block 9 Lou 12 Thru:- Lot: 14, Garfield County, Colorado. The proposed site includes: a single family home with a detached shop/garage, driveway improvements, and site landscape features. The site comprises 0.3 acres and is located on Cedar Street in Satank northwest of the Town of Carbondale. The site is situated on a flat terrain with slope grades of IVo to 3Eo. The proposed driveway will access from Cedar Street on the East side of the property. The site vegetation consists of grasses, and scattered shrubs. The site has water, electric, gas and phone services available. Draínage Erosion control Best management practices will be utilized to manage onsite drainage. The existing site has vegetated areas, over very porous terrain. The existing conditions provide for natural storm water treatment and attenuation with infiltration. The proposed site will be landscaped to improve the existing vegetation conditions to provide continued attenuation and management of onsite drainage. Appropdate best 502 Main Street a Suite A3 a Carbondale c0 81 623 a 970 704-031 1 a Fax 970 704-031 3 $oPRr$ tnnmrlnurc o llG civil consultants OWTS Design and Construction Brand Residence SE Job No. 18065.01 June 6,2018 Page2 management practices will be installed and utilized during construction and maintained until vegetation is established. OWTS DesÍsn Criteúa and Sizine Based on our findings the design and installation of an engineered OWTS with enhanced treatment is feasible in accordance with applicable County and the State of Colorado Regulation 43. The Residential facility will include a 2-bedroom dwelling to be served by the new OlilTS system. The system is designed based on the current County design criteria and the design criteria approved for the use of a pressure dosed sand filter (SF) system. The design is in compliance with the current County Regulation No. 43 with area calculations based on the LTAR loadingrate for ASTM-33 filter sand per a minimum equivalent 3-bedroom design flow capacity. Design recommendations include the installation of a three compartment 1,250 gallon 2-compartment concrete septic tank that will be equipped with an Orenco Systems simplex high head pump in a Biotube vault installed in the secondary chamber with associated piping and controls. We recommend the use of a full pressure dosed Sand Filter (SF) system to provide good secondary treatment perforrnance in the relatively rocþ soils. The SF field will consist of a single bed installed to provide for equal pressure distribution of effluent across a 450 S.F. treatmenlabsorption SF field with 36-inches of filter sand below gravelless chamber spray shield units. The effluent will be dosed across the three distribution rows via an individual custom perforated pressure distribution pipe running the length of the 38 feet by I 2 feet sand filter bed. Design Calculations OWTS Installation of an OWTS with a minimum 3-bedroom capacity- From County adopted State Regulation 43: Minimum population based on 3 bedrooms = 6 persons. First 3 bedrooms (2 persons/bedroom) Over 3 bedrooms (l person per bedroom) Gallons per day per person =75 gal/person/day, No peaking factor Max. Design flow (Qd)gallons/day = (# of people) x (avg. flow)gaVperson/day. Design flow Qd = 6*75=450 gpd Septic Tank Design: Use a 1250 gallon, two compartment septic tank with a bio-tube dosing assembly in the second chamber.. S\rb Surface Conditions an$ Testine Subsurface soil investigations and USDA soil texture method tests wdre performed by Sopris Engineering on May l7 ,2018. The soils in the area of the proposed absorption field were sampled and charactenzed by application of the USDA soil texture method test. The soils were tested to determine the hydraulic loading rate and to confirm the appropriate absorptive surface level suitable for an intermittent sand filter treatment system in native soils. The soils below nil to 3 inches of topsoil consist of medium dense gravelly loamy sand to sandy loam material to 0.3 to 4 feet below the surface. The soil appears to be consistent across the site. The native soils sampled from 2-3 feet below the surface are characterized as a soil type 1 consisting of loamy sand to sandy loam texture with moderate granular structure. This soil has an effective loading rate for conventional soil treatment of 0.8 Gal/S.F./day for a level I conventional treatment system. Due to limited area and to provide O\ryTS Design and Consffuction Brand Residence SE Job No. 180ó5.01 June 6,2018 Page 3 optimal treatment an intetmitte¡rt sancl filter is recommcruleil. No frEe water was encountered in excavations on site. Groundwater levels are expected to be below 10 feet from the existing surface grades. The soils are suitable for the installation of a sand filter treatment bed system that will be frrlly pressure dosed and utilize 36-inches of washed concrete sand. An additional soil evaluation will be performed during construction to verify the soils in the proposed field excavation and to confirm that appropriate sand filter media is installed. Intermittent Ssnd Filter Treatment UnilAbsorntion Svstem Desien The treatment/absorption field is designed based on utilizing the effective Long Term Acceptance Rate (LTAR) for an intermittent sand filter treatment system utilizing prcssure dosed distribution laterals and gravelless charnber units as spray shields.. The new treamrent system will consist of a fully pressure dosed sand filær Trearment bed System with a 36-inch layer of filter sand (ASTM-33, "washed ASTM-36 Concrete sand"). Long Term Acceptance Rate (LTAR) Considering the application of the new state regulation 43: Receiving'Wastewater Treatment Level l; loading rate for sand filter is (1.0 gal./S.F./day) for the minimum 36" depth of treatment media; Loading factors; (Table l0-2, pressure dosed application bed = 1.0 ) A(sf)= Qd.: A=Area; T-TAR LTAR = 1.0 Gal/S.F./day for ASTM-33, " Washed Concrete sand" Qd = flow (gallday) = 450 gpd L.F.1=1.0 pressure dosing A(sÐ = 450 sDd x 1.0 =450 S.F. 1.0 GallS.F./day Excavate a single 37.5' by l2' bed to a maximum 4.5' depth below finish grade. Backfill with 36-inches of ASTM- 33, washed concrete sand. Install 3 rows of custom perforated 1.25-inch distribution lateral on top of sand layer in the bed and cover with I Quick-4 chambers per row for use as pressure dose spray shields, as delineated on the plan. The standard Quick 4 chamber spray shields shall be installed over the top of the sand on 5 foot centers and bacldlled with a minimum l2-inch depth of cover. Filter fabric shall be placed over the chambers and the entire extents of the sand filter bed. The slightly mounded field shall be constructed with final surface grading at a minimum 6-inches above the up gradient surface grades with a minimum 3-inch topsoil layer placed over the field surface. The chamber rows shall be completed with standard end caps installed at both ends. A piezometer monitoring well pipe riser with threaded cap will be installed near a corner of the field and be extended down to the excavated surface depth at the bottom of the placed sand. Effluent Distribution Svstem The OS/TS field shall be fully pressure dosed along the entire length of the distribution rows. An Orenco Systems Bio Tube pump vault system will be installed with an effluent screen in fhe second compartment of the septic tank. The pump system shall incorporate a single high head pump. The simplex pump assembly will demand dose effluent through a single 1.25-inch diameter PVC transport pipe from the pump assembly and connect to manifold OWTS Design and Construction Brand Residence SE Job No. 18065.01 June 6, 2018 Page 4 pipe that connects to the three custom perforated pipes at the head of the bed. The 1.25" discharge transport pipe shall be installed with a minimum 2.5Vo continuous slope to allow for drainage of the pipe. The effluent will be equally pressure dosed through each 1.25-inch custom perforated distribution lateral running the length of the treatment bed installed on top of the sand filter layer. The pipe will have 3/16-inch orifices drilled every 2.0 feet oriented upward to spray against the interior chamber unit that will broadcast the effluent onto the sand surface. The first and last orifice will be drilled and oriented downward with an orifice shield to allow drainage of the line. Individual l.25 ball valves will be installed at the end of each perforated distribution lateral centered below one of the pair of end cap vertical inspection port penetrations at the terminal end of the field. Two vertical 4-inch inspection ports will be installed from the pair of end cap inspection port penetrations at the terminal end of the field and one 4-inch inspection port will be installed from either end cap penetration at the head of the field. All inspection ports shall extend a minimum 6-inches above the finish grade and be topped with a treaded cap. Pump operations shall be controlled by a wall mounted exterior control panel in direct line of site with the tank. Automatic float switches for on, off and high water with alarm activation shall be installed on a dedicated PVC float tree. Two separâte circuits from the electrical circuit panel and/or junction box shall be routed to the control panel for separate power to the controls and pump. Construction and Inspections Prior to construction of the permitted system, the engineer should be contacted by the contractor and construction project manager well in advance to provide adequate time to discuss the system components with the contractor, anstwer questions, resolve any conflict issues and schedule inspection site visits based on construction progress. A pre-OWTS construction meeting and calls are essential and required prior to installation of the OWTS. The engineer, prior to excavation shall inspect the staked location, of the proposed treatment/absorption bed and tank. AII 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 location of the absorption treatment field to conf;irm design assumptions made and existing conditions. The engineer will provide construction recommendations and make adjustments to the field layout and sizing if needed with discussion of construction procedures. As necessary a revised Construction document drawing will be submitted to the County as needed if changes are required. All installations shall be inspected, surveyed, documented and reported./delineated in the Certification Ietter and As-built drawing. County Regulations require that the Design Engineer 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. Photo documentation during construction and site system inspections is required to be performed by the contractor and Engineer. System component installation inspection and review of photo documentation is required of the exposed system components prior to bacldlling. Photo documentation will be included with the As- Built Record drawing submittal package to finalize the OWTS permit. Therefore the Engineer should be contacted as needed and notified of the construction progress and scheduling to allow time to schedule specific inspection times. OWTS Design and Construction Brand Residence SE Job No. 18065.01 June 6,2018 Page 5 O\ilTS Onelatior¡ and Maintenance All cornponents of the eugineercd OWTS shall be irrspected on a regular basis and be properly maintained. The responsibility for tepair and rnaintenance of tlrc system will re¡nain rvith the properry Orvner. The orvner shall retain the selices of qualified personnel to inspect the OWTS ancl to perfonn all mai¡rtetta¡rce and repairs ¡lecessary to ensurc that the system is in good operating condition and is in cornpliance rvith the manufachrrcr's perfonnance rrg comþöriêntiıf tlie OWTS Shãn be äif¡rèófdt{ by the engiriétü'ivitliiif30 dàtsıf ltêitlg placed into operation ancl thereafter every six months by the orvnel or qualified seryice provider. Lr geneml, fot'a propelly utilizecl system, septic tanks should be pumped evety 3 - 5 yearc. The effluent filter should be clearrecl every six rnonths and at the ti¡ne of pumping. ,4bsorption fielcls shoulcl be uraintaiuecl *'ith suitable vegetative cover ancl kept fiee of loot invasive plants. Positive surface drainage arvay ftom the absorption fteld shot¡ld be ruraintainecl. If you have any question or neecl any additional information, please call. Sincereiy, SOPRIS ENGINEERING, LLC Pat¡l E. Rutleclge Desigrr Engineer Yancy Nichol, PE Pdncipal RE 2ß:t7'.î