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HomeMy WebLinkAboutOWTS DesignJuly 19,2022 James Matlock RECEIVED P.O. Box 483 silt, co 816s2 .iijl I ll ,¿ilt:r "james mtlck" <james_mtlck@yahoo.com> GARFIËLD COUNTy COMMUNITY DEVELOPMENT RE: Design Report, On-site Wastewater Treatment System (OWTS), Parcel I R.N. 776476, Silt, Garfield County, CO SE Job No. 32156, Parcel No:212724200394. New Garfield CountyPermit # Dear James: This letter report presents the applicable findings in regard to the design and construction of a new Onsite Wastewater Treatment System (OWTS) at the above referenced Site, in support of your building permit application to Garfield County. A new OWTS construction permit is required for the proposed usage on the subject property. The OWTS design is based on our evaluation of the site conditions for use in obtaining a Garfield County OWTS construction permit. We have evaluated the existing and proposed site conditions with respect to the operation and installation of a new OWTS in accordance with County OWTS Regulations and State of Colorado Regulation 43. The new s¡rstem meets all required setback requirements and operational demands for the proposed usage. Based on the physical site features, soils, and proposed building layout, we have prepared a civil OWTS design plan with construotion details for permit approval. The design drawing is based on a recent Topographic Survey, by,Boundaries Unlimited, dated 04-2022. The design and construction recommendations with specifications are delineated on the civil design plans, Cl-OWTS Plan dated 07-19 -2022, by Sopris Engineering. OWTS Conditions and Desisn Criteria Proposed OWTS System Proposed site improvements and expected usage result in a design flow of 450 gpd. The system will be constructed to provide for demand dosing of septic tank effluent to an engineered enhanced media soil treatment area (STA) pursuant to Regulation 43 design criteria. The OWTS will include gravity service pipe from the new dwelling to a new 1060-gal plastic 2-compartment septic tank and a 540-gallon dosing tank, installed in series equþed with a high head effluent pump assembly. The system is designed based the current design criteria approved, on February 19,2020, by CDPHE for the use of a pressure dosed geotextile sand filter (GSF) type system. Specifically, the preferred treatment technology is Geomatrix System, LLC "Geomat" system approved by CDPHE for use as a proprietary distribution product for use in Colorado OWTS's utilizing applicable multiplier loading rates for enhanced manufactured media. The design is in compliance with area calcllations based on the LTAR loading rate for the in-situ soils utilizing Geomat material installed over a 6-inch layer of ASTM-33 filter sand in shallowpressure dosed beds per the estimated design flow capacities The system will include the installation of an Orenco System bio tube effluent pump assembly for pressure distribution of septic tank effluent to a new Geotextile Sand filter (GSF) bed system consisting of Geomat enhanced manufactured media, filter sand and custom perforated distribution laterals. The effluent discharge piping will be installed to connect to an automatic distribution valve that will have individual distribution pipes connecting to a 502 Main Street . Su ite A3 I Carbondale c0 81 623 !9i0 704-0311 ! Fax (970) i04-0313 SOPRI$ TITGIlITTRI]IG o 11G civil consultants OWTS Design and Construction Matlock, Parcel I R.N. 776476 SE Job No. 32156.01 Jr'úy t9,2022 Page2 manifold pipe at the head of each Geomat treatment zoned bed each containing a pair of rows with custom perforated distribution laterals. Eachpaired bed rowwill have appropriate inqpectionport cleanouts and appurtenances. Desisn Calculations OWTS The proposed residential structure curently has 2 bedrooms; however, the system is designed for a minimum 3- bedroom residential capacity. The design flow is based on a total single family residential population of 6 persons. From County adopted State Regulation43, Design Flow Criteria: Minimumpopulation is based on 2 persons per bedroom for the first 3 bedrooms: 6 persons and I personper bedroom for each additional bedroom. Design capacity:3 x2: 6 persons @75 gaVpersorVday, Max. Design flow (Qd)gallons/day: (# of people) x (avg. flow) gallperson/day. Design flow Qd :6 * 75:450 gpd Septic Tank Design:2-Day detention time: 450 x2: 900 gallons required. Use a 1060 gallon, two compartment plastic tank with a 540 gallonplastic tank with a high head pump assernbly in series. The preferred alternative if available and feasible for installation, is use of a, 1,250 gallon, two-compartment concrete septic tank with a high head pump assembly in the second compartment. Sub Surface Conditions and Testins: Based on the site assessment that included soil evaluations from shallow excavations and consideration of preliminary findings from recent site specific geotechnical evaluations the site will support an STA with imported distribution and treatment media. The final geotechnical report by Kumar is still pending. Soil samples obtained in the area of the proposed OWTS field at variable shallow depths were evaluated by SE on June 23,2022by performance of USDA soil texture and structure chaructenzation methods. The soils below l-3 inches of topsoil consist of silt loam texture soils that have moderate dense granular structure. This soil Wpe 2 has an effective loading rate for conventional soil treatment of 0.6 gallS.F./day for a level 1 conventional treatment system. The We 2 soils within proposed soil treatment area (STA) are assumed to be relatively consistent over the moderately sloped vegetated area. In order to provide optimal treatment a pressure dosed STA utilizing enhanced manufactured media will be installed to provide for a treatment level TL-l system. No free water is expected to be encountered within the field excavations and preliminary geotechnical finding do not indicate the presence of ground water. Additional observations and soil evaluations will be performed prior to construction mobilization and during construction, by Sopris Engineering in the area ofthe proposed absorption field and tank to confirm the previous soil evaluation and design criteria. Sopris Engineering will observe new profile pits in the area of the proposed absorption field. The soils will be sampled and characterizedby application of the USDA soil texture methods. The soils will be fi.rther evaluated to determine the presence of any limiting soil or hydrological conditions, appropriate hydraulic loading rate, absorptive surface level capacity and to veriff treatment level design for the in-situ native soils. If soil conditions encountered require adjustments to design criteria or the design plan notice will be made to County EHD and applicable revisions to design/construction plans and report will be submitted. The results of the additional soil evaluation and soil characterizationwill be included in the As-Constructed documentation. OWTS Design and Conskuction Matlock, Parcel I R.N. 776476 SE Job No. 32156.01 Júy 19,2022 Page 3 GeoMatrM Treatment Unit/ Absorntion Svstem Desien The treatment/absorption fields are designed based on utilizing the effective Long Term Acceptance Rate (LTAR) for a geotextile sand filter (GSF) treatment system utilizing pressure dosed distribution laterals. The new treatment systems will consist of pressure dosed GeoMat sand filter treatment beds with 6-inches of washed filter sand (ASTM-C33, "Concrete sand") below 2 rows of 39-inch wide GeoMat model 3900 manufactured treatment/distribution media, in accordance with Regulation 42 sections (43.10(C), 43. 13.E.1.d, Table l0-2 and Table 10-3 as approved by CDPHE for this technology. Long TermAcceptance Rate (LTAR) Considering the allowable application of the OWTS regulation 43 and CDPHE approved proprietary Distribution Product for Geomatrix Systems, GeoMat product: Receiving septic tank effluent, the treatment level-l for GeoMat requires a minimum 6" depth of filter sand media with the bottom of the sand layer defined as the infiltrative surface being at least 4-feet above a limiting layer (43.8,Table7-2.\;MaximumhydraulicloadingrateforTLl effluentisthelongtermacceptancerateofthe receiving soil Type 2 is0.6gal.ls.F./day) (Table l0-l &10-lA.). A(sÐ: QdxL.F.l xL.F.2 LTAR A: Area; LTAR : 0.6 gaVS.F.lday for silt loam Qd: flow (gal/day) for OWTS:450 gpd L.F.1:1.0 pressure dosed bed application L.F .2:0.7 Enhanced Manufactured Media OWTS A(sÐ:450 gpd x 1.0 x 0.7 :525 S.F 0.6 Gal/S.F./day Excavate the beds to a minimum 16" depth below finish grade. Scariff surface, remove any cobbles and backfill with 6-inches of ASTM-C33, "Concrete sand". Install the specified length of GeoMat rows with the specified custom perforated distribution laterals and manufacturer supplied orifice shields below the qpecified orifices on top of the GeoMat material. The distribution laterals to be installed per manufacturers recommendations below the top geofabric cover. Backfill the completed geo mat beds with suitable excavated materials to finish top of bed grade slightly mounded approximately 4 to 6 inches above the surrounding zurface grades. A 4" piezometer monitoring pipe riser with cap will be installed at down gradient corner at the head of each bed in the field. The monitoring port will extend down to the excavated surface depth at the bottom of the placed sand and extend to a minimum 3" above finish grade to serye as a location marker in line with the distribution manifold. The treatment field will consist of four 2l feet long by 6.5 feet wide pressure dosed Geom¿t sand filter beds each with of 13 6.5 square feet of absorption treatmertt area. The 546 S.F. treatment field will be installed with 4 zones that will be altemately pressured dosed by use of an automatic distribution valve (ADV). Each zone will be constructed with 6-inches of washed filter sand below 2 paired rows of 39-inch wide GeoMat model 3900 manufactured treatmenVdistribution media. An ADV assembly will be installed at a high point between the septic/dosing tank and the field to provide for equal pressure distribution ofeffluent across each treatmenlabsorptionbed zone. The septic tank effluent will be dosed across eachzone via 2 individual 1.5" custom perforated pressure distribution pipes running the length of each bed centered on each paired row of 3 9" GeoMat material. Effluent Distribution Svstem OWTS Design and Construction Matlock, Parcel I R.N. 776476 SE Job No. 32156.01 Júy 19,2022 Page4 Filtered effluent will discharge to the Geomat field laterals via a high head pump biotube discharge assembly to an automatic distribution valve between the septic/dosing tank and the head of the STU beds. The distribution system will be installed to allow for effluent to be alternately and equally distributed across the absorption surface in each pair of bed rows via individual customperforated full pressure distribution laterals connected to the manifold pipe at the head of each pair of geo mat rows installed on the enhanced manufactured media surface along the entire length of the individual beds. A ball valve will be installed on the terminal end of each distribution lateral centered below and housed in an 8" valve box with lid set 2" above surface grades. The minimum slope of the tranqport pipe from the tank's dosing compartment to the ADV shall be installed at a minimum 2.5o/oupward slope to allow for drainback to the tank. The individual distributionpipes fromthe ADV shall be installed at a minimum 1% downward slope and will connect to the distribution lateral manifold at the head of each paired Geomat row. Construction and Inspections Prior to construction of the permitted systenl 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, answer questions, resolve any conflict issues and schedule inqpection site visits based on construction progtess. 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. 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 location of the absorption treatment field to confirm design assumptions made and existing conditions. The engineer will provide construction recofirmendations 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 inqpected, surveyed, documented and reported/delineated in the Certification letter and As-Constructed drawing. County Regulations require that the Design Engineer of record perform site inqpections 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 inqpections 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 backfilling. 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 Oneration and Maintenance All components of the engineered OWTS shall be inqpected on a regular basis and be properly maintained. The reqponsibility for repair and maintenance of the system will remain with the property Owner. The owner shall retain the services of qualified personnel to inqpect the OWTS and to perform all maintenance and repairs necessary to ensure that the system is in good operating condition and is in compliance with the manufacturer's OïYTS Design and Construction Matlock, Parcel 1 R.N. 776476 SE Job No. 32156.01 July 19,2022 Page 5 performance requirements, The operatiag components of the OWTS shall be inspected by the engineer within 30 days of being placed into operation and therealler every six months by the owner or qualified seryice provider. ln general, for a properly utilized $ystem, sÊptic tenks should be punped every 3 - 5 years. The elTluent filter should be cleared every six months and a: the time of pumping. Absorption fields should be maint¿inçd with suitable vegetative cover and kept free of root invasive plants. Positive surf¿ce drainage away from the absoqption field should be maintained. If ycu have any question or nsed any additional information, please call. Sincerely. SOPRIS EN{ìINEERING, LtC r83?T îç, ¿ç2? Paul E. Rutledge Design Engineer YancyNichol, PE Principal