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HomeMy WebLinkAboutOWTS Installation Observations 06.07.2024June 7, 2024 502 Main Street • Suite A3 • Carbondale, CO 81623 • (970) 704 -0311 • Fax (970) 704 -0313 S OPRIS E NGINEERING • LLC civil consultants Lee Krauth 4E Cross, LLC 304 Fass Ranch Road New Castle, CO 81647 "Lee Krauth" <leekrauth@gmail.com> RE: As-Constructed–Report –Onsite Wastewater Treatment System (OWTS), 1777 C.R. 241, East Elk Creek, New Castle, Garfield County, CO 81647 SE Job No. 33143.01, Parcel No: 212513200040, County EHD Permit # REVISED SEPT 7757 Dear Lee: Pursuant to County requirements, this letter provides documentation that the Onsite Wastewater Treatment System (OWTS) upgraded components recently installed at the above referenced site is in compliance with the permitted design. Sopris Engineering inspected the excavations, soils, materials and the installation of the system components during construction, prior to final backfill and after all installations were completed. Sopris Engineering performed site visits to inspect and document the as-constructed conditions of the OWTS. Inspections were coordinated with the property owner, electrician and the earthmoving contractor (James Martinez and Company) that installed the system components. The as-constructed conditions and installation of the new OWTS components is in compliance with Garfield County Regulations; the recommendations and specifications delineated on the civil design plan, C1-OWTS-C1-SITE Plan, dated 08-29-2023, by Sopris Engineering. The design criteria and system sizing information is summarized below. OWTS Design Criteria and Sizing The new system is designed for the maximum design flow capacity for a 3-bedroom single family residence. The system is designed based on the current County design criteria and the design criteria approved for the use of a pressure dosed sand filter (SF) system. The design is in compliance with the current County Regulation No. 43 with area calculations based on the LTAR loading rate for ASTM-33 filter sand per a minimum equivalent 4-bedroom residential design flow capacity. A two-compartment 1,500 gallon concrete septic tank was installed equipped with an Orenco Systems simplex high head pump (P300511) in a Biotube vault (PVU57-1819-L) installed in the second compartment with associated piping and controls installed. A full pressure dosed Sand Filter (SF) bed system was installed to provide for equal pressure distribution of effluent across a 720 S.F. treatment/absorption SF field with 24-inches of filter sand below gravelless chamber spray shield units. The effluent is dosed across the three distribution rows via individual custom perforated pressure distribution pipe running the length of the single 60’ feet by 12’ feet sand filter bed. The pump operation is controlled by an Orenco Systems S-1 control panel. The control panel and electrical supply sub-panel is mounted on a strut frame set adjacent to the 2nd ta nk compartment access riser. The operation demand dose to the field is approximately 50 gallons per dose cycle. OWTS As-Constructed Krauth, 4E Cross LLC, 1777 C.R. 241 SE Job No. 33143.01 June 7, 2024 Page 2 Design Calculations OWTS Installation of an OWTS with a minimum 3-bedroom capacity. Minimum population based on 3 bedrooms = 6 persons. Gallons per day per person =75 gal/person/day, No peaking factor Max. Design flow (Qd) gallons/day = (# of people) x (avg. flow) gal/person/day. Design flow Qd = 6*75=450 gpd Septic Tank Design: 2-Day detention time = 450 x 2 = 900 gallons required. Septic Tank Design: Installed a1500 gallon two compartment concrete tank with a Biotube high head pump assembly in second compartment, Tank was installed with risers and lids set slightly above surface grade, adjacent to the treatment field. The first compartment of the tank has a 1002 gallon capacity. Sub Surface Soil Conditions and Testing A site specific subsurface soil evaluation was performed by Sopris Engineering, on August 26, 2023, in the vicinity of the proposed OWTS field. The soils encountered in two excavated profile pits, locations shown on the plan, were sampled and characterized by application of the USDA soil texture method test. Profile pit-1 near the northwesterly corner of the proposed field is assumed to be one of the same pits excavated for the previous SGM soil evaluation. Profile pit-2 near the south easterly corner of the proposed field is assumed to be approximately 20 feet east of the second previously excavated profile pit referenced in the SGM soil evaluation. The soils were tested to determine the presence of any limiting soil or hydrological conditions, assess appropriate hydraulic loading rate and to assess appropriate treatment level design alternatives for installation of sand media treatment/absorption systems set above in-situ native soils. The soils below nil to 4 inches of topsoil consist of medium dense slightly clayey fine sandy loam from 4 to 48- inches below the surface. The soil appears to be consistent in both profile excavations and across the site. The average existing ground slope across the proposed field area is 16%. The native soils sampled from 2 to 3 feet below the surface are characterized as a soil type 2 to type 3 consisting of slightly clayey sandy loam texture of moderate slightly blocky granular structure with rock content less than 35%. The tactile soil test ribbons were 1-inch to 1 ¼ inch long. Soil types 2 and 3 has an effective loading rate for conventional soil treatment of 0.6 and 0.35 Gal/S.F./day, respectively for a level 1 conventional treatment syste m. The equivalent percolation rate is assumed to be 25-50 minutes per inch. The soils become increasingly rocky at depths below 3.5 feet. Soils below 4 to 5 feet refusal depth are characterized as a USDA rocky soil R1 type 2 to consisting of dense rocky sandy loam texture of granular structure with approximately 40% rock and gravel being less than 3/4 inch and containing less than 20% cobbles and small boulders in the sandy loam matrix. Weathered silt/sandstone bedrock is present at 4-4.5 feet in both excavation pits presenting a limiting condition. No evidence of free water was encountered or observed in the profile pit excavations on site. Groundwater levels are expected to be below 10 feet from the existing surface grades. Sopris Engineering has determined based on visual and tactile evaluation that the soils are best characterized as a type 2, sandy loam to Type 3 sandy clay loam. For design purposes the soils are OWTS As-Constructed Krauth, 4E Cross LLC, 1777 C.R. 241 SE Job No. 33143.01 June 7, 2024 Page 3 classified as a Type 3 sandy clay loam due to the tactile ribbon lengths over 1-inch up to 1.25 inches. The friable sandy loam soils have a blocky/granular structure shape, moderate structural grade and contain less than 35% rock content. The fractured bedrock limiting layer is 4-feet below the surface. Soil Treatment Area/ Pressure dosed chamber trench Absorption System Design The treatment/absorption field is designed based on utilizing the effective Long Term Acceptanc e Rate (LTAR) for an intermittent sand filter treatment system utilizing pressure dosed distribution laterals and gravelless chamber units as spray shields. The new treatment system will consist of a fully pressure dosed sand filter Treatment bed System with a 24-inch layer of filter sand ("washed ASTM-33 Concrete sand"). Long Term Acceptance Rate (LTAR) Considering the application of regulation 43 design criteria of unlined sand filters receiving septic tank effluent, pressure dosed sand filter results in the applied effluent to be treated to Wastewater Treatment Level 3 quality prior to infiltration into native soils: The design basal area for a treatment level 3 STA is sized per the maximum LTAR of (0.65 gal./S.F./day) for type 3 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 0.65 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. A = Area; LTAR LTAR = 0.65 Gal/S.F./day for secondary sand, ASTM-33, " Concrete sand" Qd = flow (gal/day) = 450 gpd L.F.1=1.0 pressure dosing A(sf) = 450 gpd x 1.0 = 692.3 S.F. 0.65 Gal/S.F./day Constructed a single 60’ by 12' mounded sand filter bed with 24-inch depth of ASTM-33, concrete sand placed over the shallow native soils to the specified top of sand level. The 12-feet width of sand media is contained on the sloped terrain by placement of an embankment consisting of native soil and/or imported Class-3 pit run material placed over the native soil along the down gradient perimeter of the bed to the specified height of 24-inches above the top of sand level. Installed 3 rows of custom perforated 1.5 inch distribution laterals on top of sand layer and cover with 14 Quick-4 LP chambers per row for use as pressure dose spray shields, as delineated on the plan. The sand and chamber are covered with non-woven filter fabric, (Mirfi N-140). The entire bed was backfilled with native soil 8 to 12 inches above the top of chambers. Effluent Distribution System