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HomeMy WebLinkAboutOWTS Final Installation Observations 12.10.2024December 10, 2024 502 Main Street • Suite A3 • Carbondale, 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: As-Constructed–Report, On-site Wastewater Treatment System (OWTS), 111 Creekside Drive, Garfield County, CO, Rifle Creek Ranch Block: 2 Lots: 1-5 and Common Area SE Job No. 32137, Parcel No: 212719301006. Previous Permit #3516 OWTS Permit# SEPT-8392 Dear Mark: Pursuant to County requirements, this letter/report provides documentation that the Onsite Wastewater Treatment System (OWTS) upgraded components recently installed at the above referenced site is incompliance with the permitted design. Sopris Engineering performed several site visits to inspecte the excavations, soils, materials and the installation of the system components during construction, prior to final backfill and after all installations were completed. The replacement OWTS includes a raw sewage pump basin tank and a new primary detention septic tank with effluent pump, Geomat absorption field, dispersal dosing/distribution components and controls designed to treat the total combined wastewater design flow for the existing residence based on an equivalent 5-bedroom residential capacity. Sopris Engineering performed site visits in coordination with the Contractor (Zen Excavation) that installed the replacement system components. The as-constructed conditions and installation of the new OWTS components are in compliance with Garfield County Regulations; the recommendations and specifications delineated on the civil C1 OWTS plan drawing dated 10-17-2023 by Sopris Engineering. The design criteria and system sizing information is summarized below. The As-Constructed OWTS conditions and components installed are delineated on the attached AC OWTS Record Drawing. System Startup Sopris Engineering was on site December 22, 2023, to advise, inspect and coordinate, riser set, discharge piping, control panel set, external splice box and component wiring for pumps and floats. The final distribution piping was installed to the ADV and the geomat bed manifiolds. Sopris engineering performed a follow up inspection on January 26, 2024 to inspect all final distribution piping and pump system installations, to check that system floats were wired for correct functionality. The post-mounted Orenco systems MVP DAX control panel for the sewage pumps and the S-1 control panel for the effluent pump were installed and energized by the electrician. The respective pump and control wires were connected at the panels to the respective external splice boxes. Sopris Engineering performed a dry run system startup to test floats and verified that the systems are functioning as designed compliance with installation and design specifications. No water was in the tank at the time since the water system was not active. The new sewage influent pipe was connected and the system was fully operational on February 1, 2024. Sopris Engineering observed normal liquid levels in sewage pump basin and septic tank dosing compartment, performed manual float operational testing and observed system pump cycle operation. OWTS As-Constructed Report Fergen, 012 Creekside Drive, Rifle SE Job No. 32137.01 December 10, 2024 Page 2 The high level visual and audible alarms for both systems are operational. The pump amperage and voltage was tested and found to be in compliance with manufacturer’s specifications. The operational demand dose to the field is approximately 48 gallons per dose cycle with an approximate end of lateral squirt height of 2.5 feet. OWTS Conditions and Design Criteria Previous OWTS Components: The OWTS components consisted of gravity service pipes, a 1,500-gallon septic tank, that discharged 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 existing components were abandoned in place. Installed OWTS System Replacement The existing 5-bedroom residence has a design flow of 600 gpd. The system was 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 included a new 2,000-gal concrete 2-compartment septic tank. The new septic tank was installed with an Orenco System bio tube high head pump effluent discharge system in the tank’s 500-gallon second compartment. The OWTS included a 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 were 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 was cleaned, breached and backfilled for abandonment in place. The replacement system included 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 was abandoned in place and new gravity service pipes was installed from the existing pipe to connect to the new sewage pump basin. The pumped sewage discharges into the new septic tank. The septic tank effluent discharge piping was installed to connect to an automatic distribution valve that connects each individual distribution pipe 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 has an appropriate inspection port cleanouts and appurtenances. Design Calculations OWTS Design Flow Criteria: The existing residential structure has 5 bedrooms. The minimum design population is based on 2 people per first 3 bedrooms and 1 for all successive bedrooms. 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 OWTS As-Constructed Report Fergen, 012 Creekside Drive, Rifle SE Job No. 32137.01 December 10, 2024 Page 3 Septic Tank Design: 2-Day detention time = 600 x 2 = 1,200 gallons required. Installed a 500 gallon concrete septic tank with a duplex sewage pump assemblies in series with a 2,000 gallon (total 2066 gal capacity), two-compartment primary septic tank with dosing pump assembly. 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. No free water is expected to be encountered within the field excavations. Seasonal high Groundwater levels are expected to be below 5 feet from the existing surface grades. GeoMat™ Treatment Unit/ Absorption System Design The treatment/absorption fields were 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 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.). 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 OWTS As-Constructed Report Fergen, 012 Creekside Drive, Rifle SE Job No. 32137.01 December 10, 2024 Page 4 The individual beds were excavated to a minimum 18” depth below finish grade. The native bed surface was scarified and backfilled with 6" of ASTM-C33, "Concrete sand". The specified length of GeoMat rows was installed with the specified custom perforated distribution laterals and manufacturer supplied orifice shields below the specified orifices on top of the GeoMat material. The completed geo mat beds were backfilled with suitable excavated materials to finished top of bed grade slightly mounded approximately 6 inches above the surrounding surface grades. The treatment field consists 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 was 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 was 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 was recovered up stream of the existing septic tank. A new sewer pipe extension was installed to route sewage directly to the new 500 gallon concrete septic tank pump station. The 500-gallon structure with a 5 foot riser, was equipped with a duplex sewage pump assembly to lift the raw sewage to the primary septic tank. The pumped raw sewage connects into the gravity inlet pipe of the installed 2-compartment septic tank for conventional primary treatment. The duplex solids handling sewage pumps will alternate and deliver approximately 27 gallons of raw sewage to the primary septic tank per pump cycle. The tank and pump controls were sized and set to allow for adequate storage in the event of electrical power outage or equipment failure. The vault has a sealed access lid adequate for efficient system monitoring and maintenance. The primary septic tank effluent is 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. 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 (Orenco model 6404) between the septic/dosing tank and the head of the STU beds. The distribution system was 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 was installed on the terminal end of each distribution lateral and housed in a 8" valve box with lid set above surface grades. The minimum slope of the transport pipe from the tank's dosing compartment to the ADV was installed at a minimum 2.5% upward slope to allow for drain back to the tank. The individual distribution pipes from the ADV were installed at a minimum 1% downward slope and connects to the distribution lateral manifold at the head of each paired Geomat row.