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Home My WebLink AboutOWTS Design ReportOctober 6,2022 KJS Revocable Living Trust Juan Suarez (Ph: 7 02 3405222) 919 Samoy Street Las Vegas NV 89110 RE:Design Report-Onsite Wastewater Treatment System (OWTS), Harvey Residence,3Tll Grass Mesa Rd, Rifle CO, Lot 44, Grass Mesa Ranch Lot: 44, Garfield County, Colorado SE Job No.32222.01 Parcel No:217734300387. Garfield County OWTS Permit No.- Dear Jaun: 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 OWTS permit application to Garfield County. The OWTS design is based on recent site assessment observations by Sopris Engineering of existing physical site features, conditions, geotechnical soils evaluation with respect to the proposed residential usage and applicable regulatory design criteria in accordance with State and County OWTS Regulations. The design recommendations, specifications and construction details are delineated on the attached OWTS permit/construction planlhat was prepared with GIS, LIDAR, Survey Plat information and aerial mapping. The design criteria and system sizing information is summarized below. Existing and Pronosed Conditions The proposed development area is situated on undeveloped rangeland with adjacent sparsely developed existing rural residential, oil/gas infrastructure, and agricultural development sites surrounded the 4}-acre Parcel. The proposed OWTS will serve a new tiny home structure. The existing topography and site conditions are derived from county GIS data base, aerial mapping, Lidar topography and survey information by Sexton Survey Company. The site is situated in existing agricultural and rangelands lands primarily consisting of sage brush, meadow and hayfield gmsses, The proposed development area is in a broad gently sloped (6% to l0%.) rangeland area that generally trends downgradient to the northeast. The proposed OWTS field will be constructed parallel to the contours to the East southeast of the proposed dwelling. faced sloped terain. The property's water supply is from an existing domestic well (DWR permit number 466181-F located over a 150 feet north of the proposed OWTS field. The proposed development will consist of the construction of a 360 S.F tiny home structure. The proposed site improvements will include associated driveway, auto court, utilities and a new onsite wastewater treatment system. The development will be based on applicable site design criteria and include appropriate grading, drainage, and site construction management. The proposed development improvements are shown on the attached OWTS plan. Summarv l)esign Criteria The new OWTS is designed for a treatment capacity of 150 gallons per day based on the design wastewater flow to serve a minimum l-bedroom residence in accordance with Table 6-2 values, Section 43.6, A.4. The new OWTS will utilize a minimum 1,000 gallon two-compartment concrete or alternative reinforced plastic septic tank to be installed off the northeast corner of the proposed structure. Sealed concrete or ribbed PVC risers with lids will be installed on the new septic tank along with appropriate pipe connection to the new tank utilizing the appropriate 502 Main Street a Suite A3 a Carbondale, C0 81623 a (e70) 704-031 1 o Fax (970 704-031 3 SoPRIS [ttcmttnlle o 11G civil consultants Suarez ProPertY 37l l Grass Mesa Rd' Rifle, CO SE Job No.32222.O1 October 6,2022 Page2 fitting adaptor rings for the tank and riser. The new 1,000 gallon 2-compartment septic tank will be installed with appropriatã sanitary tees, outlet effluent filter with risers and lids at the surface. A gravity schedule-40 or SDR-35 rå*"ipip" section with two-way cleanout will be installed between the tank inlet on the gravity sewer line and the accessory structure. The STA will consist of leaching chamber trenches that provide 300 S.F. of total absorption area. The septic tank effluent will be gravity discharged through a new 4-inch schedule-40 or SDR-35, installed at minimum l% slope, to the STA via a distribution box. The effluent will be equally distributed from the distribution box via 4" distribution pipes connected to the head end cap of each chamber trench. Observation ports with caps will be installed on the þroximal and distal ends of each chamber trench. The designed system meets all required setbacks and will be ìnstalled within the general location indicated on the plan. Our design is outlined below and delineated on the attached C-l OWTS plan. Desisn Flow The design flow is calculated as follows for the minimum design capacity of an equivalent 2-bedroom residential dwelling. The OWTS is desigled for a treatment capacity of 300 gallons per day based on the design wastewater flow in accordance with Table l0-l values, Section 43.6, A.4. Regulation 43: Minimum population based on 2 bedrooms at 2 persons per bedroom equating to 4 persons' The Design flow is calculated based on residential usage of 75 gallperson/day, No PF Max. Design flow (Qd)gallons/day: (# of people) x (avg. flow)gallperson/day. Design flow Qd:4*75:300 gpd Septic Tank DesÍsn The septic tank capacity required for a minimum 48 hour retention time is calculated as follows: V : 1t0 gallday * 2:300 gallons. Use a minimum 1,000 gallon 2-compartment septic tank. The tank to be installed with risers and access lids set a minimum 3 inches above finish grade surface. Sub Surface Conditions and Testins A subsurface soil investigation and site assessment was performed by Sopris Engineering in on Septembet 28,2021. The soils in the vicinity of the proposed development areawere sampled and characterized by application of the USDA visual/tactile soil texture method analysis from samples a six foot profile pit and alarge excavation exposing native soils to an approximateT feet depth below the existing surface grades, located to the south of a utility storage/shop structure under construction Generally the soils below approximately 6 inches of topsoil consist of rnedium dense clay loam texture soil with slightly blocþ to granular structure to the observed excavation depths. The soils contain less than l0olo scattered gravel or rock content to the 6-7-feet depth observed below the surface grades. No free water was encountered in any excavations on site. No evidence of seasonal high ground water or iedox conditions was observed in the excavations. Seasonal high Groundwater levels are expected to be below 20 feet from the existing surface grades on the relatively flat tenain. The native soils sampled from 2-3 feel below the surface are chzracterized as a soil type 3 consisting of clay loam texture with granular structure. This soil has an effective loading rate for conventional soil treatment of 0'35 Ga1/S.F./day-for a level I conventional treatment system. The equivalent percolation rate is assumed to be 40-50 minutes pei inch. The soils are suitable for a shallow conventional absorption field consisting of gravelless infiltration chamber units. Suarez Property 3711 Grass Mesa Rd, Rifle, CO SE Job No.32222.01 October 6,2022 Page3 Soil Treatment Unit/ Absorntion Svstem Design The treatment/absorption field is designed based on utilizing the effective Long Term Acceptance Rate (LTAR) for the native soils and the application of appropriate loading factors for a soil treatment unit system utilizing gravity distribution to gravelless chamber trenches. The new treatment system and absorption field will consist of gravity distribution of septic tank effluent via a distribution box to individual chamber trenches with treatment across the native soil absorptiYe surface. Long Term Acceotance Rate (LTAR) Receiving Wastewater Treatment Level 1; LTAR; (Table 10-l Soil type 3 loading rate for a clay loam is (0.35 ga1./S.F./day); Design Flow; Qd: flow (gallday): 150 gpd Loading factors; (Table l0-2, Gravity application trenches, L.F.I - 1.0 ) (Table l0-3, Gravelless chambers, L.F.2 :0.7) STA absorption treatment area; A: Area S.F.; A(sÐ: Qdx L.F.1 xL.F.2 LTAR A(sÐ : 150 gpd x 1.0 x 0.7 : 300 S.F 0.35 Gal/S.F./day Number of Quick-4 Infiltrator chambers 4'x3'x 1 2"chambers: 300 s.F.: 25 chambers; Use 26 chambers 12 S.F./Chamber Number of Equivalent Arc chambers 5'x3'xl2"chambers 3s0 s.F.: 20 chambers; Use 20 charnbers 15 S.F./Chamber lJse 26 Quick-4 Infiltrator chambers in 2 trenches 52' long by 3' wide with l3 chambers units per trench plus two end caps as delineated on the plan. Alternative use 20 Arc chambers in 2 trenches 50' long by 3'wide with 10 chambers units per trench with ends caps. The septic tank effluent will be gravity distributed to the head of each chamber row via individual distribution pipes from a distribution box. Construction and Inspections Prior to construction of the permitted system, the engineer should be contacted by the contractor and owner 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 is essential and required prior to installation of the OWTS. 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 absorption treatment field excavations to confirm soil conditions and make adjustments as needed. All septic system components and trench installations are to be approved by the Engineer prior to backfilling. County Regulations require that the Engineers of record perform site inspections of the pennitted system during construction and provide "As-Constructed" documentation of the installed system to the County after construction is complete. All installation will be inspected, field measured, reported and delineated in the certification letter and record drawing. The contractor needs to photo document all O'WTS construction phases and supply photos to the Engineer. Suarez ProPerty 3711 Grass Mesa Rd, Rifle, CO SE Job No. 32222.01 October 6,2022 Page4 The County Environmental Health department should be contacted at least 48 hours prior to final backfill of compcnents to provide advanced notice of construction schedule in order to perform a final inspecfion of the in-place components. The County Environmental Health department should be contacted at least 48 hours prior to finat backfill of components to provide advanced nctice of construction schedule in order to perfcrm a final inspection of the in place components" The Garfield County contact is: Ted lVhite, P.8., Ënvironmental Hçalth Specialist lll.Garfield County Public Health; twhite@garfield-county.com, 970-945-6614 x 8106 (main offïce) çr 97t-230-2442 (mobile) OWS Oneration and Maintenance Ownership of the systern and responsibili{y for mainten¿nce and repair will remain with the property Ownor. The Owner is encouraged to retain the services of qualified personnel to inspect the OWTS and to perform all ¡naintenançe and repairs neçessâry to ensure that the system çomponçnts are maintained in good operating condition aad suitable vegeta{ive cover is established on the fields. The components of thc OWTS system should inspected within 30 days of being placed into operation and should been inspected and maintained bi-annually. The tank, absorption ficld and other system components should be visually inspected bi-annually for debris, damage, leaks, or other potential problems, In general, for a properly utilizsd system, septic tanks should be pumped every 3 - Syears, The cffluent filter should be cleancd every six months and at the tirne of punping. Absorption fîclds should be maintained with suitable vegetative cover and kept free of root invasive plants. Pocitive surface drainage away from the absorption ficld should bc maintained" If you have any question or need any additional information, please call. Sincerely, SOPRIS ENGINEERTNG, LLC Paul E. Rutledge Design Eugineer 06, âûîå,; g Ë8377