Loading...
HomeMy WebLinkAboutEngineer's OWTS Design PlanJune 10, 2025 502 Main Street • Suite A3 • Carbondale, CO 81623 • (970) 704-0311 • Fax (970) 704-0313 S OPRIS E NGINEERING • LLC civil consultants Federico J. Pena El Rancho Sueno 1026 Highway 133 Carbondale CO 81623 Federico J. Pena fpena@soprisliquor.com Bobby Almazan bobby@ramdev.build RE: OWTS Design Report, On-site Wastewater Treatment System (OWTS), El Rancho Sueno, Residence, 00012 Weeping Willow Lane, Carbondale, Garfield County, CO SE Job No. 34142.01, Parcel No: 239336319008. New Garfield County Permit # ____________ Dear Federico: 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 residential building permit application. The new OWTS is designed to serve the required design capacities for the current proposed primary residence and future proposed Barn/ADU usage on the subject property. The OWTS design is based on our evaluation of the existing and proposed site conditions with respect to the operation and installation of a new OWTS in accordance with County OWTS Regulation 43 for use in obtaining a Garfield County OWTS construction permit. The new system meets all required setback requirements and operational demands for the proposed usage. Based on the physical site features, soils, and proposed dwelling layouts, we have prepared a civil OWTS design plan with construction details for permit approval. The design drawing is based on an Improvement Survey Plat, by True North Colorado, LLC and topographic Survey, by Sopris Engineering. The design and construction recommendations with specifications and details are delineated on the civil design plans, C5.0-OWTS Plan and C5.1 dated 06-09- 2025, by Sopris Engineering. OWTS Conditions and Design Criteria The proposed OWTS System will serve the current and future proposed usage for a primary single family dwelling and future proposed barn/ADU, based on a total design flow of 1050 gpd. The OWTS will include gravity sewer service pipes from the currently proposed primary residence to a new 1500 gallon 3- comparment concrete septic tank that will provide for sewage detention of the residential dwelling waste. The third tank compartment will be equipped with a high head effluent duplex pump assembly used for dosing effluent from the primary residence and future ADU to a combined Pressure dosed sand filter soil treatment area (STA). The future proposed barn/ADU will have a 1500-gallon 2-compartment concrete septic tank equipped with a high head effluent pump assembly and 1.5” discharge transport pipe. The 1.5” effluent discharge pipe will transport the ADU septic tank effluent to the Third chamber of the primary residence, 1500-gallon septic/dosing tank. The combined effluent will be dosed to the proposed STA sized to treat the total current and future design flow of both dwellings. The STA dosing system will include the installation of an Orenco Systems effluent pump assembly installed in a bio tube or dual flow inducers for pressure distribution of septic tank effluent to a new Geotextile Sand filter (GSF) bed system consisting of Geomat enhanced manufactured media, filter sand OWTS Design and Construction El Rancho Sueno, 0012 Weeping Willow Lane Carbondale, Garfield County SE Job No. 34142.01 June 10, 2025 Page 2 and custom perforated distribution laterals. The effluent discharge piping will be installed with independent discharge assemblies to alternately dose one of the two beds. Each independent transport pipe will connect to a common manifold pipe at the head of each quad set of distribution lateral rows set in each Geomat treatment bed with custom perforated distribution laterals. Each lateral row will have appropriate inspection ports and appurtenances. The system is designed based on 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 treatment area calculations based on the treatment level 3 LTAR loading rate for a 24-inch layer of ASTM-33 secondary filter sand in shallow pressure dosed beds utilizing Geomat distribution media sized per the estimated total design flow. Design Calculations OWTS Design Flow Criteria: The current proposed residential structure will have 5 bedrooms. The future proposed ADU will have 3 bedrooms. Therefore the OWTS is designed to provide treatment for two single family residences with 5 and 3 bedrooms respectively. Minimum population for the primary residence is 8 persons and 6 persons for the future ADU. Design flows are based on a usage rate of 75 gal/person/day with caculated capacity based on 2 persons per bedroom for the first 3 bedrooms and 1 person per bedroom for each additional bedroom for each dwelling. Max. Design flow (Qd) gallons/day = (# of people) x (avg. flow) gal/person/day. The total system Design capacity = 1050 gpd. Septic Tank Design: The primary residence and ADU will each have a dedicated septic tank that will provide for 2-Day detention time capacity for the respective design flows from each building. Residence : Design flow Qd = 8* 75= 600 gpd x 2hr = 1200 gal detention capacity Barn/ADU: Design flow Qd = 6 * 75 = 450 gpd x 2hr = 900 gal detention capacity . Residence: Install a 1500 gallon three compartment concrete septic tank with a duplex high head pump assembly in the third compartment to dose combined buildings effluent to the soil treatment Area. Barn/ADU: Install a 1500 gallon two compartment concrete septic tank with a high head pump assembly in the second compartment to transfer ADU septic tank effluent to the primary residence tank's 3rd compartment dosing basin. Sub Surface Conditions and Testing A subsurface soil investigation and site assessment was performed by Sopris Engineering on December 4, 2024, to evaluate the soil conditions and determine the effective Long Term Acceptance Rate (LTAR) for OnSite Wastewater Treatment System (OWTS) Soil treatment area (STA). The soils in the development envelope explored were sampled and characterized by application of the USDA visual/tactile soil texture method analysis from samples in four (4) profile pits. Two of the four profile pits were observed in the preferred OWTS field envelope and in the location of the main house. Evidence of seasonal high ground water, gravel, cobbles and possible redox conditions was observed in profile pits at depths from 3.5-ft to OWTS Design and Construction El Rancho Sueno, 0012 Weeping Willow Lane Carbondale, Garfield County SE Job No. 34142.01 June 10, 2025 Page 3 4.5-ft. Seasonal high groundwater levels are expected to be approximately 4-ft from the existing surface grades on the moderately flat terrain. No groundwater was encountered in any of the pit excavations at the time of the observation. However, in our experience, the seasonal high ground water level (SHGL) is typically present in this area in July and August. Profile Pit-1 MHW The soils below approximately 12-inches of topsoil consists of silt loam texture soil with blocky structure of moderate structural grade to a depth of 24-inches containing no scattered gravel or rock content. The underlying soils to a depth of 2.5-ft consist of dense sandy loam with fine granular structure of moderate structural grade underlain by rocky soils consisting of gravels and cobbles in a sandy loam matrix to a depth of 3.25-ft. The soils below 3.25-ft to the 5.25-ft depth explored consist of gravels, cobbles, and small boulder with sandy loam and are characterized as a type R2 soil with 70% rock content. No groundwater was encountered at the time of the observation in the pit excavation. However, seasonal high ground water level (SHGL) is expected to be at 3.25-ft. Profile Pit-2-MH The soils below approximately 12-inches of topsoil consists of silt loam texture soil with blocky structure of moderate structural grade to a depth of 18-inches containing no scattered gravel or rock content. The underlying soils consist of dense sandy loam with fine granular structure of moderate structural grade underlain by slightly rocky soils consisting of less than 35% gravels and cobbles to a depth of 4-ft. The soils below 4-ft to the 5-ft depth explored consist of gravels, cobbles, and small boulders with sandy loam and are characterized as a type R2 soil with 70% rock content. No groundwater was encountered at the time of the observation in the pit excavation. However, seasonal high ground water level (SHGL) is expected to be at 4.0-ft. Profile Pit-3-OWTS NE The soils below approximately 12-inches of topsoil consists of silt loam texture soil with blocky structure of moderate structural grade to a depth of 2.25-ft containing no scattered gravel or rock content. The underlying R-1 soils to a depth of 3-ft consist of sandy loam with fine granular structure of moderate structural grade with gravels and cobbles with an approximate 50% rock content with 50% of rock less than 3/4". The soils below 3-ft to the 6-ft depth explored consist of gravels cobbles and small boulders in a sandy loam matrix and are characterized as a type R2 soil with over 60% rock content. No groundwater was encountered at the time of the observation in the pit excavation. However, seasonal high ground water level (SHGL) is expected to be at 4-ft. Profile Pit-4-OWTS SW The soils below approximately 12-inches of topsoil consists of silt loam texture soil with blocky structure of moderate structural grade to a depth of 2.5-ft containing no scattered gravel or rock content. The underlying R-1 soils to a depth of 3.25-ft consist of sandy loam with fine granular structure of moderate structural grade with gravels and cobbles with an approximate 50% rock content with 50% of rock less than 3/4". The soils below 3.25-ft to the 6-ft depth explored consist of gravels, cobbles, and small boulders in a sandy loam matrix and are characterizes as a type R2 soil with over 60% rock content. No groundwater was encountered at the time of the observation in the pit excavation. However, seasonal high ground water level (SHGL) is expected to be at 4-ft. OWTS Design and Construction El Rancho Sueno, 0012 Weeping Willow Lane Carbondale, Garfield County SE Job No. 34142.01 June 10, 2025 Page 4 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 24- inches of filter sand (ASTM-C33, "Concrete sand") below 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 10-2 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 a treatment level-3 system for an unlined sand filter requires a minimum 24" depth of filter sand media with the infiltrative surface being at least 3-feet above a limiting layer (43.8, Table 7-2.4); A pressure dosed sand filter results in the applied effluent to be treated to Wastewater Treatment Level 3 quality prior to infiltration into native soil: The design basal area for a treatment level 3 STA is sized per the maximum LTAR of (0.9 gal./S.F./day) for type 2A receiving soils or the maximum LTAR of 0.8 gal/S.F./day for the minimum 24" depth of secondary sand treatment media whichever results in the larger area; The maximum Loading rate for this design is therefore 0.8 gal./sq.ft./day The STA is designed utilizing a loading factor of 1: (Table 10-2, pressure dosed application bed = 1.0 ) A(sf) = Qd x L.F.1 .: A = Area; LTAR LTAR = 0.80 gal/S.F./day for secondary sand Qd = flow (gal/day) for OWTS = 1050 gpd A(sf) = 1050 gpd = 1313 S.F. 0.80 Gal/S.F./day Install two 12' by 55' Geomat beds with 4 rows of full pressure dose distribution laterals. The 2 beds will provide 660 S.F. of treatment/absorption area per bed. Excavate the beds to a minimum 32” depth below average existing surface grade. Scarify surface, remove any cobbles and place 24-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 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 geomat beds with suitable excavated materials to finish top of bed grade mounded approximately 24 to 42 inches above the surrounding surface grades graded with 3:1 embankment side slopes. Effluent Distribution System Filtered effluent will discharge to each geomat bed laterals via a duplex high head pump discharge assembly via individual 1.5" transport pipe from each pump to the common manifold on each bed. The duplex pumps will alternate dosing to each bed with individual discharge assemblies. No discharge manifold pipe, check valve or isolation valves are required on the individual discharge assemblies. OWTS Design and Construction El Rancho Sueno, 0012 Weeping Willow Lane Carbondale, Garfield County SE Job No. 34142.01 June 10, 2025 Page 5 The distribution system will be installed to allow for effluent to be alternately and equally distributed across the absorption surface in each bed rows via individual custom perforated full pressure distribution laterals connected to the common manifold pipe at the head of each bed's quad set of geo mat rows installed on the enhanced manufactured media surface along the entire length of the beds. A ball valve will be installed on the distal end of each distribution lateral centered below and housed in a 10" valve box with lid set 2" above surface grades. The minimum slope of the transport pipe from the tank's dosing compartment to the manifold shall be installed at a minimum 2.5% upward slope to allow for drainback to the tank. The transport pipe will connect to the distribution lateral mainifold at a slight high point to allow drainage into the manifold and laterals at the head of each geomat bed. 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-Constructedt” 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. The engineer should be contacted to perform inspection of components prior to backfill. The county environmental health department should be contacted at least 48 hours prior to final backfill of components in order to perform a final inspection of the in-place components.