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HomeMy WebLinkAboutEngineer's OWTS ReportOctober 19, 2023 502 Main Street • Suite A3 • Carbond ale, CO 81623 • (970) 704 -0311 • Fax (970) 704 -0313 S OPRIS E NGINEERING • LLC civil consultants Mark Fergen 111 Creekside Drive Rifle, CO 81650 Mjf@mountainair.biz RE: Design Report, On-site Wastewater Treatment System (OWTS), 111 Creekside Drive, Garfield County, CO, Rifle Creek Ranch Block: 2 Lot s: 1-5 and Common Area SE Job No. 32137, Parcel No: 2127-193-01-006. Previous EHD Permit #3516 Dear Mark: This letter report presents the applicable findings in regard to the design and construction of a replacement Onsite Wastewater Treatment System (OWTS) at the above referenced Site, in support of your building permit application to Garfield County. An OWTS Major Repair 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 repair 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 system 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 construction details for repair permit approval. The design drawing is based on the USGS Topo Map for Rifle. The design and construction recommendations with specifications are delineated on the civil design plans, C1-OWTS Plan dated 10-17-2023, by Sopris Engineering. OWTS Conditions and Design Criteria Existing OWTS Components: The current OWTS system serves the existing residential dwelling that currently has five bedrooms. The OWTS components consist of gravity service pipes, a 1,500-gallon septic tank, that discharges ST effluent to a 1,250 S.F. pipe and gravel absorption field consisting of 3 trenches approximately 100' long by 4' wide with 4" perforated pipe distribution laterals assumed to be connected with a header pipe. The absorption field was installed in 1979; under County EHD permit no. 79004. The absorption field sizing was calculated to require 1248 S.F. at the time of permitting. The existing trenches will be abandoned in place The new proposed OWTS Geomat beds in the general vicinity will be located south of the existing field. Proposed OWTS System Replacement Proposed site improvements and expected usage result in a design flow of 600 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 a new 2,000-gal concrete 2-compartment septic tank. The new septic tank will be installed with an Orenco System bio tube high head pump effluent discharge system in the tank’s 500-gallon second compartment. The OWTS will include a OWTS Design and Construction Fergen, 012 Creekside Drive, Rifle SE Job No. 32137.01 October 19, 2023 Page 2 new extension of gravity service pipe from the existing sewer pipe that discharges waste from the entire dwelling to a new 500 gallon one compartment concrete tank with a duplex low head sewage pump assembly that lifts raw sewage to the 2,000 gallon tank. The tanks will be installed in series located adjacent to the existing septic and dosing basin in a landscape area west of the dwelling. The existing septic tank and pump basin with be cleaned, breached and backfilled for abandonment in place. 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 calculations 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 shallow pressure dosed beds per the estimated design flow capacities The replacement 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 existing septic tank will be abandoned in place and new gravity service pipes will be installed from the existing pipe to connect to the new sewage pump basin. The pumped sewage will discharge into the new septic tank. The septic tank effluent discharge piping will be installed to connect to an automatic distribution valve that will have individual distribution pipes connecting to a manifold pipe at the head of each Geomat treatment zone bed each containing a pair of rows with custom perforated distribution laterals. Each paired bed row will have appropriate inspection port cleanouts and appurtenances. Design Calculations OWTS The proposed residential structure has 5 bedrooms, proposed with a design flow based on a total peak residential population of 8 persons. From County adopted State Regulation 43, Design Flow Criteria: Minimum population based on 2 people per first 3 bedrooms and 1 for all successive bedroom. 5-bedroom Design capacity = 3 x 2 +2 = 8 persons @ 75 gal/person/day, Max. Design flow (Qd) gallons/day = (# of people) x (avg. flow) gal/person/day. Design flow Qd = 8 * 75 = 600 gpd Septic Tank Design: 2-Day detention time = 600 x 2 = 1,200 gallons required. Use a 2,000 gallon (total 2066 gal capacity), two-compartment primary septic tank with a with high head pump assembly. OWTS Design and Construction Fergen, 012 Creekside Drive, Rifle SE Job No. 32137.01 October 19, 2023 Page 3 Sub Surface Conditions and Testing Subsurface soil investigations and USDA soil texture method tests were performed by Sopris Engineering on May 4, 2022. The soils in the area of the proposed absorption field were sampled and characterized by application of the USDA soil texture method test. The soils were tested to determine the presence of any limiting soil or hydrological conditions, appropriate hydraulic loading rate, absorptive surface level capacity and to assess appropriate treatment level design for the in-situ native soils. The soils below the inch of topsoil consist of medium dense clay loam. The soils appear to be consistent across the site. The native soils sampled from below the topsoil are characterized as a soil type 3 soil consisting of clay loam texture with moderate blocky to granular structure. This soil has an effective loading rate for conventional soil treatment of 0.35 Gal/S.F./day for a level 1 conventional treatment system. No rocky soils or change of texture was encountered at depth. In order to provide optimal treatment with respect to soil conditions, a pressure dosed STA utilizing enhanced manufactured media overly filter sand will be installed to provide for an enhanced treatment level TL-1 system. No free water is expected to be encountered within the field excavations. Groundwater levels are expected to be below 3 feet from the existing surface grades. Additional observations and soil evaluation will be performed during construction prior to placement of the distribution and sand filter media materials, by Sopris Engineering in the area of the proposed treatment/absorption field and tank to inspect the soils and provide installation guidance. The soils will be further observed to determine the presence of any unsuitable soil or other conditions in order to assist the contractor in installing the design material in the in-situ native soils. If any adjustments to design or installation recommendations are necessary notice will be made to County EHD and applicable revisions to design/construction plans and report will be submitted. All conditions and installations will be included in the As-Constructed documentation. GeoMat™ Treatment Unit/ Absorption System Design 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 10-2 and Table 10-3 as approved by CDPHE for this technology. Long Term Acceptance 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-1 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, Table 7-2.4); Maximum hydraulic loading rate for TL1 effluent is the long-term acceptance rate of the receiving soil Type 3 is 0.35 gal./S.F./day) (Table 10-1 &10-1A.). OWTS Design and Construction Fergen, 012 Creekside Drive, Rifle SE Job No. 32137.01 October 19, 2023 Page 4 A(sf) = Qd x L.F.1 x L.F.2 .: A = Area; LTAR LTAR = 0.35 gal/S.F./day for clay loam Qd = flow (gal/day) for OWTS = 600 gpd L.F.1=1.0 pressure dosed bed application L.F.2=0.7 Enhanced Manufactured Media OWTS: A(sf) = 600 gpd x 1.0 x 0.7 = 1,200 S.F. 0.35 Gal/S.F./day Excavate the individual beds to a minimum 18” depth below finish grade. Scarify surface, remove any random large cobbles or boulders and backfill with 6" 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 specified orifices on top of the GeoMat material. The distribution laterals to be installed per manufacturer’s 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 3 inches above the surrounding surface grades. The treatment field will consist of four 48 feet long by 6.5 feet wide pressure dosed Geomat sand filter beds with 1200+ square feet of absorption treatment area with (8) 48' long rows of 39-inch wide GeoMat model 3900 manufactured treatment/distribution media. Each bed will be installed with 2 paired perforated distribution laterals connected by a common 1.5" manifold pipe connected at the head of each lateral in each bed. The bed will be constructed with 6-inches of washed filter sand below the 8 rows of 39-inch wide GeoMat distribution media. Sewage Pump Basin Sewage from the existing dwelling is collected from the main and lower levels via a single sewage service pipe. The existing sewage service pipe will be recovered up stream of the existing septic tank. A new sewer pipe extension will be installed to route sewer directly to the new 500 gallon concrete septic tank pump station. The 500 gallon structure with a 5 foot riser, will be equipped with a duplex sewage pump assembly to lift the raw sewage to the primary septic tank. The pumped raw sewage will connect into the gravity inlet pipe of the new 2-compartment septic tank for conventional primary treatment. The duplex solids handling sewage pumps will alternate and deliver approximately 50 gallons of raw sewage to the primary septic tank per pump cycle. The tank and pump controls will be sized and set to allow for adequate storage in the event of electrical power outage or equipment failure. The vault will have a sealed access lid adequate for efficient system monitoring and maintenance. The primary septic tank effluent will be pressure dosed to the field from a simplex effluent discharge assembly installed in the second compartment of the septic tank for controlled discharge to the field. OWTS Design and Construction Fergen, 012 Creekside Drive, Rifle SE Job No. 32137.01 October 19, 2023 Page 5 Effluent Distribution System 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 custom perforated 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 a 6" valve box with lid set above surface grades. The minimum slope of the transport pipe from the tank's dosing compartment to the ADV shall be installed at a minimum 2.5% upward slope to allow for drain back to the tank. The individual distribution pipes from the 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 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, answer 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. 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 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 letter and As-Constructed 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 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 Design and Construction Fergen, 012 Creekside Drive, Rifle SE Job No. 32137.01 October 19, 2023 Page 6 OWTS Operation and Maintenance All components of the engineered OWTS shall be inspected on a regular basis and be properly maintained. The responsibility for repair and maintenance of the system will remain with t he property Owner. The owner shall retain the services of qualified personnel to inspect 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 performance requirements. The operating components of the OWTS shall be inspected by the engineer within 30 days of being placed into operation and thereafter every six months by the owner or qualified service provider. In general, for a properly utilized system, septic tanks should be pumped every 3 - 5 years. The effluent filter should be cleaned 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 field should be maintained. If you have any question or need any additional information, please call. Sincerely, SOPRIS ENGINEERING, LLC Paul E. Rutledge Yancy Nichol, PE Design Engineer Principal OWTS Design and Construction Fergen, 012 Creekside Drive, Rifle SE Job No. 32137.01 October 19, 2023 Page 2 new extension of gravity service pipe from the existing sewer pipe that discharges waste from the entire dwelling to a new 500 gallon one compartment concrete tank with a duplex low head sewage pump assembly that lifts raw sewage to the 2,000 gallon tank. The tanks will be installed in series located adjacent to the existing septic and dosing basin in a landscape area west of the dwelling. The existing septic tank and pump basin with be cleaned, breached and backfilled for abandonment in place. 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 calculations 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 shallow pressure dosed beds per the estimated design flow capacities The replacement 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 existing septic tank will be abandoned in place and new gravity service pipes will be installed from the existing pipe to connect to the new sewage pump basin. The pumped sewage will discharge into the new septic tank. The septic tank effluent discharge piping will be installed to connect to an automatic distribution valve that will have individual distribution pipes connecting to a manifold pipe at the head of each Geomat treatment zone bed each containing a pair of rows with custom perforated distribution laterals. Each paired bed row will have appropriate inspection port cleanouts and appurtenances. Design Calculations OWTS The proposed residential structure has 5 bedrooms, proposed with a design flow based on a total peak residential population of 8 persons. From County adopted State Regulation 43, Design Flow Criteria: Minimum population based on 2 people per first 3 bedrooms and 1 for all successive bedroom. 5-bedroom Design capacity = 3 x 2 +2 = 8 persons @ 75 gal/person/day, Max. Design flow (Qd) gallons/day = (# of people) x (avg. flow) gal/person/day. Design flow Qd = 8 * 75 = 600 gpd Septic Tank Design: 2-Day detention time = 600 x 2 = 1,200 gallons required. Use a 2,000 gallon (total 2066 gal capacity), two-compartment primary septic tank with a with high head pump assembly. OWTS Design and Construction Fergen, 012 Creekside Drive, Rifle SE Job No. 32137.01 October 19, 2023 Page 3 Sub Surface Conditions and Testing Subsurface soil investigations and USDA soil texture method tests were performed by Sopris Engineering on May 4, 2022. The soils in the area of the proposed absorption field were sampled and characterized by application of the USDA soil texture method test. The soils were tested to determine the presence of any limiting soil or hydrological conditions, appropriate hydraulic loading rate, absorptive surface level capacity and to assess appropriate treatment level design for the in-situ native soils. The soils below the inch of topsoil consist of medium dense clay loam. The soils appear to be consistent across the site. The native soils sampled from below the topsoil are characterized as a soil type 3 soil consisting of clay loam texture with moderate blocky to granular structure. This soil has an effective loading rate for conventional soil treatment of 0.35 Gal/S.F./day for a level 1 conventional treatment system. No rocky soils or change of texture was encountered at depth. In order to provide optimal treatment with respect to soil conditions, a pressure dosed STA utilizing enhanced manufactured media overly filter sand will be installed to provide for an enhanced treatment level TL-1 system. No free water is expected to be encountered within the field excavations. Groundwater levels are expected to be below 3 feet from the existing surface grades. Additional observations and soil evaluation will be performed during construction prior to placement of the distribution and sand filter media materials, by Sopris Engineering in the area of the proposed treatment/absorption field and tank to inspect the soils and provide installation guidance. The soils will be further observed to determine the presence of any unsuitable soil or other conditions in order to assist the contractor in installing the design material in the in-situ native soils. If any adjustments to design or installation recommendations are necessary notice will be made to County EHD and applicable revisions to design/construction plans and report will be submitted. All conditions and installations will be included in the As-Constructed documentation. GeoMat™ Treatment Unit/ Absorption System Design 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 10-2 and Table 10-3 as approved by CDPHE for this technology. Long Term Acceptance 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-1 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, Table 7-2.4); Maximum hydraulic loading rate for TL1 effluent is the long-term acceptance rate of the receiving soil Type 3 is 0.35 gal./S.F./day) (Table 10-1 &10-1A.). OWTS Design and Construction Fergen, 012 Creekside Drive, Rifle SE Job No. 32137.01 October 19, 2023 Page 4 A(sf) = Qd x L.F.1 x L.F.2 .: A = Area; LTAR LTAR = 0.35 gal/S.F./day for clay loam Qd = flow (gal/day) for OWTS = 600 gpd L.F.1=1.0 pressure dosed bed application L.F.2=0.7 Enhanced Manufactured Media OWTS: A(sf) = 600 gpd x 1.0 x 0.7 = 1,200 S.F. 0.35 Gal/S.F./day Excavate the individual beds to a minimum 18” depth below finish grade. Scarify surface, remove any random large cobbles or boulders and backfill with 6" 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 specified orifices on top of the GeoMat material. The distribution laterals to be installed per manufacturer’s 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 3 inches above the surrounding surface grades. The treatment field will consist of four 48 feet long by 6.5 feet wide pressure dosed Geomat sand filter beds with 1200+ square feet of absorption treatment area with (8) 48' long rows of 39-inch wide GeoMat model 3900 manufactured treatment/distribution media. Each bed will be installed with 2 paired perforated distribution laterals connected by a common 1.5" manifold pipe connected at the head of each lateral in each bed. The bed will be constructed with 6-inches of washed filter sand below the 8 rows of 39-inch wide GeoMat distribution media. Sewage Pump Basin Sewage from the existing dwelling is collected from the main and lower levels via a single sewage service pipe. The existing sewage service pipe will be recovered up stream of the existing septic tank. A new sewer pipe extension will be installed to route sewer directly to the new 500 gallon concrete septic tank pump station. The 500 gallon structure with a 5 foot riser, will be equipped with a duplex sewage pump assembly to lift the raw sewage to the primary septic tank. The pumped raw sewage will connect into the gravity inlet pipe of the new 2-compartment septic tank for conventional primary treatment. The duplex solids handling sewage pumps will alternate and deliver approximately 50 gallons of raw sewage to the primary septic tank per pump cycle. The tank and pump controls will be sized and set to allow for adequate storage in the event of electrical power outage or equipment failure. The vault will have a sealed access lid adequate for efficient system monitoring and maintenance. The primary septic tank effluent will be pressure dosed to the field from a simplex effluent discharge assembly installed in the second compartment of the septic tank for controlled discharge to the field. OWTS Design and Construction Fergen, 012 Creekside Drive, Rifle SE Job No. 32137.01 October 19, 2023 Page 5 Effluent Distribution System 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 custom perforated 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 a 6" valve box with lid set above surface grades. The minimum slope of the transport pipe from the tank's dosing compartment to the ADV shall be installed at a minimum 2.5% upward slope to allow for drain back to the tank. The individual distribution pipes from the 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 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, answer 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. 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 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 letter and As-Constructed 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 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.