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HomeMy WebLinkAboutOWTS Design Report 06.02.16Jason Anthony Clearwater Construction Management Inc. PO Box 6236 Snowmass Village, CO, 81615 janthony@ccmaspen.com June 21 2016 1 RE: Design Report-Onsite Wastewater Treatment System (OWTS) -Anthony Residence, Lot 16 Callicotte Ranch Subdivision, C.R. I 03, Garfield County, Colorado SE Job No. 16090.01 Parcel Number: Parcel Number: 2393-242-06-016 Dear Jason: This Jetter report presents the applicable findings in regard to the design and constrnction of an Onsite Wastewater Tl'eatment System (OWTS) at the above referenced Site, in support of your OWTS pennit application to Garfield County. The OWTS design discussed in this report is delineated on the attached permit/construction plan that is based on the survey and building drawing that was sent to us. The OWTS design is based on om evaluation of the site conditions with information provided by others for use in obtaining a Garfield County OWTS construction permit. We have evaluated the existing and proposed site conditions with respect to the operation and installation of a new OWTS in accordance with Garfield County OWTS Regulations and State of Colorado Regulation 43. Based on the physical site features, soils, and proposed building layout, we have prepared the OWTS design plan with construction details. Conclusions The new OWTS will serve a small ranch style residential structure with a combined total dwelling space of approximately 3000 S.F. The basis of our design is for n 4-bedroom l'esidence. A 1250-gallon septic tank shall be installed that will dischal'ge effluent to a 612 square foot soil tl'entment unit (STU) absorption trench system. The soil absotption system will consist of gravelless leaching chambers installed in trenches . An effluent filtel' will be installed on the sanitary outlet tee in the secondary chamber of the septic tank. The filtered tank effluent will be gmvity discharged to the STU via a distribution box. The effluent will be equally distributed from the distribution box to the end caps at the first leaching chamber in each trench. The designed system meets all required setbacks and will be installed within the general location indicated on the plan. Our design is outlined below and delineated on the attached Cl plan. Existing Site Location and Conditions The subject site is located on Lot 16, Callicotte Ranch Subdivision in Section: 24 Township: 7 Range: 88 of the 6111 P.M., Garfield County, Colorndo. The site is located on a relatively flat dry land area with a slight slope downward toward the Southeast. Vegetation consists of sagebmsh, sluubs and grasses. The Site comprises approximately 3.3 acres. An irrigation ditch traverses through the property along the easterly property boundary. The existing ground I 502 Main Street • Suite A3 • Carbondale, CO 81623 • (970) 704-0311 • Fax (970) 704-0313 ~11D111e S11e1111:1a111e • 111! Jason Anthony SE Job No. 16090.0 I June 2, 2016 Page 5 Dudng initinl construction the engineer will evaluate the soils in the absorption treatment field excavations to confirm soil conditions and make adjustments as needed. All installation will be inspected, surveyed, reported and delineated in the Ce11ification Jetter and As-built drawing. County Regulations require that the Engineers ofrecord perform site inspections of the penuitted system during construction and provide "As-Built" documentation of the installed system to the County after constrnction is complete. OWS Onc1·ntion and Maintenance All components of the engineered OWTS 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 Lot Owner. The owner shall retain the services of qualified personnel to inspect the OWTS and to perform all maintenance and repairs necessary to ensure that the system is in good operating condition and is in compliance with the manufacturer's performance requirements. The components of the OWTS system will be inspected within 30 days of being placed into operation and thereafter arumally. The tank, absorption field and other system components should be visually inspected annually for debris, damage, leaks, or other potential problems. In general, for a properly utilized system, septic tanks should be pumped every 3 -5 years. The effluent filter should be cleaned every six months and at the time of pumping. Absorption fields should be maintained with suitable vegetative cove1· and kept free ofroot invasive plants. Positive surface drainage away from the absorption field should be maintained. Our design and recommendations are based om· site assessment, soils evaluation and upon data supplied to us by others. If subsurface or site conditions are found to be different from those presented in this report, we should be notified to evaluate the effect it may have on the proposed OWTS. If the County Environmental Health Depm1ment requests changes or modifications to this design, we should be contacted to evaluate the effect on the OWTS. Jason Anthony SE Job No. 16090.01 June 2, 2016 Page2 surface in the proposed absorption field area has average 20%. Slope. Domestic water is supplied by an existing community water system. The site has an existing gravel surfaced driveway that traverses tlu-ough the property from the primmy access from Sopris Lane. Proposed Site Conditions The proposed site improvements include the construction of a 3000 S.F. footprint residential stmcture with an attached garage. A new OWTS will be constmcted that is designed for a 4-bedroom residential capacity. The proposed site improvements will include appropriate site grading around the residence, OWTS, and dl'iveway improvements within the development area. Subsm·fnce Conditions Subsurface soil investigations and USDA soil texture method tests were performed by Sopris Engineering on April 22, 2016. The soils in the area of the proposed absorption field were sampled and characterized by application of the USDA soil texture method analysis. The soils were tested to determine the hydraulic loading rate and the approprfate absorptive surface depth in the native soils. A shallow and deep excavated pit was observed in the North central portion of the site. The soils below 6 to 12 inches of topsoil consist of medium dense silt loam with granular structure to the 8 foot depth explored. The native soils sampled from 1-3 feet below the smface are characterized as a soil type 2 consisting of silt loam texture with granular slrncture. This soil has an effective loading rate for conventional soil treatment of 0.60 gaUS.F.lday for a level 1 conventional treatment system. The equivalent percolation rate is approximately 16-25 minutes per inch. No free water was encountered in excavations on site. Groundwater levels are expected to be well below l 0 feet from the existing smface grndes along down gradient North central portion of the site. The soils appear suitable for a conventional shallow absorption field consisting of gravelless infiltration chmnber units. OWTS Design The new system was designed based the current County design criteria and the design criteria approved in the adopted Regulation 43. The design is in compliance with the current County regulations with area calculations based on the soil type and texture with an appropriate long term acceptance rate (LTAR). Design recommendations include the installation of a three compartment 1250-gallon two-compa11ment concrete septic tank with concrete access riser and lid installed to the surface. The tank will be equipped with an outlet effluent filter sanitary tee. The soil treatment unit (STU) will consist of three leaching chamber trenches installed to provide for equal gravity distribution of effluent across a 612 S.F. treatment/absorption STU field installed in the native soils. The effluent will be distributed through a concrete distribution box with individual distribution pipes connected to the head of each trench. The SDR"26 or schedule 40 PVC sewer pipes will be installed with respect to existing grades. The gravity pipes routed to the 2-compartment septic tank and to the STU will be bedded and backfilled with Class~6 base. The installation will be documented and included with the AS-Built ce11ification drawing to be Jason Anthony SE Job No. 16090.01 June 2; 2016 Page 3 submitted after construction is completed. The system will meet all required setbacks nnd be installed within the general location indicated on the plan. Our design is outlined below and delineated on the attached design and construction plan. Design Flow Criteria The design flow is calculated as follows: The new OWTS shall be based on a minimum 4-bedroom capacity for single family residence. From the Garfield County OWTS Regulation 43 ; Minimum population based on 2 persons per bedroom for first 3 bedrooms & 1 person per bedroom for each additional bedroom 3 bedrooms @ 2 person /bedroom = 6 persons. 1 bedrooms @ 1 person /bedroom = 1 persons. Gallons per day per person =75 gal/perso~t/day, No peaking factor Max. Design flow (Qd) gallons/day=(# of people) x (avg. flow)gal/person/day. Design flow Qd = 7"'"75=525 gpd The septic tank capacity required for a minimum 48 hour detention time is calculated as follows: V = 525_gal/day + 2 =1050 gallons (Per Reg 43 a 1250 gallon capacity is required). Use a 1250 gallon 2-compartment concrete septic tank. The tank shall have inlet and outlet sanitary tees with an effluent filter on the outlet. The tank access shall be maintained with riser and lid to the surface grade. Soil T1·catment Unit/ Absorption System Design The sizing of the STU system is per the guidelines by the manufactmer and as approved by the County based on Regulation 43, for sizing of absorption fields utilizing gravelless leaching chambers. The STU trenches will be excavated in native soil allowing placement of the chamber at relatively shallow depths over a scarified level native soil surface. The chambers will be covered with filter fabric and shall be carefully backfilled with excavated material. The treatment/absorption field is designed based on utilizing the effective Long Term Acceptance Rate (LT AR) 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 distdbution of septic tank effiuent via a distribution box to individual chamber trenches with treatment across the native soil absorptive surface. Long Term Acceptance Rate (LTAR) Considering the application of the new state regulation 43: Receiving Wastewater Treatment Level 1; loading rate for silt loam is (0.60 gal./S.F./day) for soil type 2.; Loading factors; (Table 10-2, Gravity application trenches = 1.0 ) and (Table 10-3, gravelless chambers= 0.7) A(sf) = Qd x L.F.: LTAR A=Area; LTAR = 0.60 Gal/S.F./day for silt loam Qd = flow (gal/day) = 525 gpd L.F.1=1.0 Gravity Distribution L.F.2=0.7 Chambers A(st) = 525 gpd x 1.0 x 0.7 = 612 S.F. 0.60 Gal/S.F./day Number of quick-4 chambers: 6128.F = 51 chambers Use 51chambers 12 S.F./Chamber Jason Anthony SE Job No. 16090.01 June 2, 2016 Page4 Use 51 Quick-4 chambers in three trenches 70' long by 3' wide with 17 chambers units per trench plus two end caps as delineated on the plan. The septic tank effluent will be gravity distributed to the head of each chamber row via individual distribution pipes from a distribution box. Additional soil evaluation will be performed during construction to verify the soils in the excavation. The trenches need to be shallow with a maximum excavation depth of 36-inches and approximately 6- inches of final grading topsoil mounded over the trenches placed to allow positive drainage away from the trench surface. Each trench will be constmcted level with successive trenches installed following natural contour grades accordingly. A minimum separation distance of 6 feet will be maintained between the individual trench sidewalls. An inspection port should be installed on the top cutout at each head and end chamber. This will allow for location of the field and for checking the performance of the system over time. A 4u discharge line will discharge effluent to a distl'ibution box installed up gradient and adjacent to the field. The 4" PVC effiuent discharge line will be installed with a minimum I% slope. The distribution box will incorporate a riser section and access lid at the surface. The effiuent will be equally distributed from the distribution box through individual 411 solid distribution pipes to the head of each trench. The invert out of the distribution box shall be at a level above or equal to the top of the chambers end cap. The engineer, prior to installation shall inspect the trench excavation to confirm suitable soil conditions. All septic system components and trench installations are to be approved by the Engineer prior to backfilling. Consh·uction and Inspections Prior to construction of the pem1itted 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.