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Home My WebLink About10.02 Septic Documents18 July 12, 2012 Jeff Johnson Johnson Carter Architects,PC 136 East Third St., Suite B Rifle, CO 81650 RE: As -Built On -Site Wastewater Treatment System (OWTS), Bayou Well Services Building Expansion, Parcel 2, Green Subdivision, Rifle, Colorado SE Job No. 11084.01 Dear Mr. Johnson: Pursuant to County Regulations, this letter provides documentation that the new and expanded Onsite Wastewater Treatment System (OWTS) recently installed is in general compliance with the permitted design. Sopris Engineering has performed site visits to measure, inspect, and document the as built conditions of the constructed system. We have coordinated our efforts with the system installer. The systems were inspected prior to backfilling and after component installations were complete. The as -built conditions and installation of the new OWTS components is in compliance with the permitted design specifications for the new and expanded system. The OWTS systems were constructed in accordance with the design recommendations and specifications delineated on the design plan, C-4, Utility and OWS Plan, by Sopris Engineering, dated 8-23-11. The improved site includes a new East side facility addition with plumbed office space that is served by a new OWTS system. The original West side facility and plumbed office space is served by the existing expanded OWTS system. The combined systems were designed based on an average flow of 1 520 gpd and a peak sewage flow of 2280 gpd calculated by the per capital usage of employees and transient population. Facility Usage Employees/transient daily Capita Facility description Well Service Truck Maintenance Job desription Office, Shop, Crew Drivers, Transient Existing # Max. 24 -hours Proposed # Total # (capita Usage gpolcap Avg Rate QA gpd Peaking Factor # Design QD gpd WEST EAST Combined Daily fulltime office 7 14 21 15 315 1.5 472.5 Infrequent parttime Temporary 8 0 8 5 40 1.5 60 Daily fulltime shop 13 13 26 20 520 1.5 780 Max. Daily Transient Crew & Drivers 20 94 114 5 570 1.5 855 Infrequent Guest visitor Delivery 2 10 12 5 60 1.5 90 Infrequent 0 3 3 5 15 1.5 22.5 Existing + Proposed 50 1520 1.5 2280 Design Calculations The design flow is calculated for the subject facilities as shown in the table above based on usage descriptions and per capita flow rates from the State I. S. D. S. Regulations. 502 Main Street • Suite A3 • Carbondale, CC 81623 • (970) 704-0311 • Fax (970) 704-0313 SOPRISENGINEERINC•LLC civil consultants Jeff Johnson, Bayou Well Services AB-OWTS SE Job No. 11084.01 July 12, 2012 Page 2 The commercial building includes office, shop and maintenance Facilities. The Onsite Wastewater system has been upgraded to include two distribution systems that serve the existing west side facilities and the proposed east side facilities. The total average flow (Regulatory Design Capacity) Qa = 1520 gpd. The total Peak flow (Peak Daily Design Flow) Qd = 2280 gpd. The combined system consists of the existing West side septic tank, distribution system and field and the new East side septic tank, distribution system and field, The two separate collection and tank detention systems discharge effluent to their respective secondary treatment absorption fields. The existing field has been expanded to accommodate projected increase in usage. The West system has a projected peak design flow Qd 772.5 gpd The East system has a projected peak design flow Qd = 1507.5 gpd The total combined systems projected peak design flow Qd = 2280 gpd. Septic Tank Design The volumetric capacity is based on 125% of peak design flow V = Q* 1.25 \Vest Side: Qd 772.5 gpd * 1.25 days = 966 gallons. The existing 1,000 gallon concrete, dual compartment septic tank is adequate. East Side: Qd = 1507.5 gpd * 1.25 days = 1884 gallons. installed a 2,000 gallon concrete, dual compartment septic tank. Sub Surface Conditions and Testing: Percolation testing was performed by All Service Septic, LLC. A percolation rate of 32 minutes per inch has been reported in the location of the existing and proposed treatment/absorption fields. A soil investigation has been performed by CTL Thompson. The soil profile includes approximately 1 foot of top soil overlaying nil to 5 feet of sandy clay underlain by clayey sand. to a depth of 14 feet explored. Free ground water was measured at 8 to 14 feet. Flgen in-DrainlGeotcxtilc Sand Filter (G.S.F.) Treatment System Design The Commercial facility will have variable daily flows typically lower than the projected average. The use of a single pass gravity Secondary treatment system is recommended due to the Geotechnical conditions and the relatively high strength waste water from the facility. Area required for a conventional pipe and gravel absorption system may be appropriately reduced by using a secondary treatment GSF treatment bed system. The maximum reduction is 50% however are design allows for only a 40% reduction over a conventional system. No kitchen facilities are included in the facilities. Using a design percolation rate of 32 minutes per inch with a Design flow of 2280 gpd, The standard absorption area equation yields: A (st) = Qd* t : where A = Area; 5 t = time in minutes per inch=32mpi Qd = flow gpd = 2280 gpd Use 2300 gpd A = = 2280 * 32 = 2580 S.F. 5 Apply sizing credit reduction of 40% for use of single pass secondary geotextile sand filter (GSF) secondary treatment system. A(credit reduction)— A*.60 = ; 2580 * .6 = 1548 S.F. Jeff Johnson, Bayou Well Services AB-OWTS SE Job No. 11084.01 July 12, 2012 Page 3 Each In -drain unit area (Au) is 2 FT wide by 4 FT long (8 S.F. horizontal surface area) with a loading rate (L.R.) of 2.5 gal. per S.F. of G.S.F. Number of Eljen In -Drain units required equals Design Flow QdriL.R./Au # units 2280 S.F. 18 S.F./2.5 gsf = 114 units. Installed 116 total units including the 26 units in the existing West side field. The total field Area is approximately 60% of a conventional field size. Standard Field requires 2580 S.F. with 40% reduction = 1548 S.F. The total design area of the secondary treatment GSF field is 1595 S.F. that is approximately 62% of the size of a conventional system. Separate West and East collection pipes, septic tanks, individual distribution boxes and treatment fields have been installed to treat the flow from each system. The West system Qd = 772.5 gpd In -Drain units Qd/L.R./Au= # units; 772.5 gpd 18 S.F./2.5 gsf = 39 units. Use 40 26 units exists over a total sand basil area of 371 S.F. in two 3.5' wide x 53' long trenches. An additional GSF Bed on the terminal end of the System was installed. The installed Bed contains 14 In -Drain units in two rows of 7 over a 30' long by 7' wide bed with 218 S.F. of additional sand basil area. Therefore the total area is now 581 S.F. The East system Qd = 1507.5 gpd In -Drain units Qd/L.R./Au= # units; 1507.5 gpd 18 S.F.f2.5 gsf 75 units. Use 76 A new GSF Bed System near the existing system was installed per the design plan. The Bed contains 76 In -Drain units in four rows of 19 units each over a 78' long by 13' wide bed with a total 1114 S.F. of sand basil area. Therefore the combined total treatment field area is 581 S.F. + 1014 S.I. = 1595 S.F. as stated above_ The new septic tank was installed near off the Southeast corner of the building. The 2000 -gallon dual compartment concrete septic tank was installed with an effluent filter installed in the outlet tee and with risers with lids to the surface. The effluent Iine from the Building Addition and into the new tank is installed at a 2% slope. A two-way cleanout was installed on the sewer line between the exterior building wall and the tank. A Geotextile Sand Filter (GSF) treatment/absorption systems were installing to provide single pass secondary treatment of the effluent from the tank with ground infiltration of treated effluent into the ground. The GSF field Eljen In -Drain units were installed as shown on the attached As -Built plan over a 12 -inch concrete sand filter Iayer and backfilled with additional sand to approximately 12 -inches above the top of the distribution pipe. A distribution box was installed next to the new field to equally distribute effluent to the trenches via individual 4" distribution lines connected to individual perforated distribution pipes at the head of each row. A 4" perforated distribution piping was placed on the center of each In -Drain row along the entire length of the row. Inspection ports were installed on each end of the perforated distribution pipes. The individual beds were installed level with suitable soil below the In -Drain units and sand filter layer with backfill over and around the In -Drain units. The construction was completed utilizing specified materials installed according to design. The minimum setback distances have been maintained. Observations of the soils within the field were performed during construction indicating that the soils are consistent with the descriptions in the geotechnical report. The soils consisted of uniform sandy clays to clayey sands. A percolation test was performed by All Service Septic, LLC that resulted in an average percolation rate of 32 mpi. Jeff Johnson, Bayou Well Services A13-OWTS SE Job No. 11084.01 July 12, 2012 Page 4 OWS Operation and Maintenance The re establishment of vegetative cover over the field and responsibility for inspection and maintenance of the system will remain with the Lot Owner or the owners representative_ All components of the engineered OWS shall be inspected on a regular basis and be properly maintained. The system and responsibility for repair and maintenance of the system will remain with the Owner. The OWS should require minimal maintenance. Several factors influencing the need for maintenance include: actual wastewater flows versus design flows, the volume waste and amount of cleaning products, chemicals and other toxic liquids. The tank, absorption field and other system components should be visually inspected bi- annually for debris, damage, leaks, or other potential problems. In general, for a properly utilized system, septic tanks should be pumped and inspected every 2 - 4 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. 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