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HomeMy WebLinkAbout1.1 Supplemental InfoCHURCH & Associates ENGINEERS & GEOLOGISTS August 12,2004 Marian Nilsen 0489 Rose Lane Carbondale, Colorado 8L623 Subject Subsurface Investigation and OWS Upgrade Design Existing Residences and Proposed Barn 0489 Rose Lane Garfield County, Colorado Job No. 16564 Ms. Nilsen, As requested, an upgraded onsite wastewater system (OWS) for the existing residences and proposed bam has been designed. The subsurface investigation was performed on July 14,2004. SITE CONDITIONS The properry is in a rural residential area of Garfield Counfy, where OWS are required. There is an existing OWS, which is to be properly abandoned. Irrigation ditches and ponds are located to the north and south of the proposed drain field area. The drain field must be located a minimum of 50 feet from any irdgation ditches not shown on the site plan. The area has an approximate slope of LVo to the south. Water is provided by an onsite weil 125+ feet east of the proposed drain field. PROPOSED CONSTRUCTION A 2-bedroom residence and 4-bedroom residence exist at the locations presented on Figure 1. A horse barn is proposed near the location shown on Figure i. The OWS was sized based on 1440 gallon per day (GPD) using Garfield County Buiiding Department (GCBD) loading of 75 GPD per person for 6 bedrooms in the residences and 50 GPD each for i0 horse stalls and 20 GPD each for 2 washing machines to be located in the proposed barn. The sewage loading with a peaking factor of 1.5 is 2160 GPD. This loading includes washing machines and garbage grinders in the residences. If additional bedrooms in unfinished areas are possible, it is suggested that the OWS be constructed to handie the additional loading. The installation of a properly engineered OWS to serve furure buiid-out can be cost effective. SUBSLRFACE CONDITIONS The subsurface investigation was performed by digglng a test pit at the location ind.icated on Figure 1. Subsurface materials in the test pit consisted of siity, -eravelly, sand with scattered alluviai cobbles to the maximum depth explored of 3 feet. Ground water was encountered at 3 feet. Ground water is assumed at 2 feet during spring runoff conditions. A percolation test was nor peCormed due to the high _eroundwater level. A sradation analvsis w DENVER 4501 Wadsworth Boulevard Wheat Ridge, CO 80033 www.geo-ch urch.co m Toll Free - 1.87-1.24€31 n303.463.9317 Fax: 303.463.9321 OWS Upgrade Design Job No. 16564,811A04 Page2 texttrre classification. Results of the gradadon analysis indicate the soil to be a sandy lo1r,.*T..^1.1* . i-ailprrAng long-term acceptance rate (I-TAR) of 0.72 gallons per square foot per day (gdlft'lhy). Gndafr.otanalysis results are included as Figure 8. RECOMMENDATIONS The installation must include three septic tanks with effluent pumps, an automatic distributing valve, and a mounded, pressurized" gravelless cha:nber-bed drain field with imported sand filter material at the locations presented on Figure 2. Imported sand filter material has a percoiation rate of 28 Minutes Per Inch (I4PI1. The OWS design is based on a sewage loading of 1440 GPD, a percolation rate of 28 MPI at the top of the mound, and an LTAR of 0.72 gilft"lday at the bottom of the mound. The installation must include one 1500-gai1on, two-compartment, concrete septic tank with a Biorube@ pump vault at the proposed barn, one 1500-gallon, two-compartrnent, concrete septic tank with a Biotube@ pump vault al the 4-bedroom residence, and one 1000-gallon, two-compartrnent, concrete septic tank with a Biotube@ pump vauit at the 2-bedroom residence. Pump specifications are presented in Figures 5, 6, and 7. The septic tanls must be water tight and weighted down with ballast to reduce the risk of floatation. Pump lines must be schedule 40 PVC, must be properly encased within 10 feet of irrigation ditches or water lines, and be installed below lowest seasonal -round water levels to reduce the risk of freezing. The drain field instaltation consists of mounded graveiless chamber-befu with imported sand filter material. Each bed must have 3 rows of 9 chambers each for a total of 108 chambers and 1674 ftz of infiltrative a.rea. Prior to drain field installation, it must be verified that no wells exist within L25 f.eet and no surface water exists within 50 feet of the proposed drain field area. An automatic dist'ibuting valve is required to distribute effluent to the beds. Based on soii conditions, the use of imported sand filter material, pressurized dosing of the drain field, and evaluation of risk of contamination of surface water and ground waier, it is not necessary to add 8 feet additional distance for each 100 gailons of wastewater per day of desi-sn flow over 1000 gallons per day as specified in the table to prevent contamination. The 125-foot separation between the proposed absorption area and the well and the 50-foot separation between the proposed absorption area and the irrigation ditches and ponds are appropriate to prevent contamination. Vehicle movement over the drain field area during construction shouid be kept at a minimum to reduce compaction of the receiving soils. The bottom of the bed should be scarified with a pick. shovel, or backhoe bucket teeth prior to the addition of the imported sand. Sand must be compacted to avoid sefiling after construction. The surface of *re drain field should be seeded after installation of the system. A native seed mix from the area available at seed stores should be used. These mixes do not require irrigation and deveiop a growth 10 to 15 inches high. No automatic sprinkler system should be installed over the field. OPER{TION AND NfA.INTENANCE The owner must realize an OWS is different from public sewer service. The owner must be aware of and assume responsibility for maintenance of the system. In the absence of a monitoring program, the septic tank should be pumped every fwo yea$ or more frequently if needed. Effiuent filter and screened vaults, as applicable, are to be cleaned during pumping or as needed. There are daiiy considerations such as not puning piastic or other non-biodegradable materiais into the septic system. Garbage disposal use should be minimized to reduce the frequency of pumping. Water use must be monitored so toilets are not allowed to run when seais malfunction. To iliustrate the point, a running OWS Upgrade Design Job No. 16564,8/12/04 Page 3 toilet can use in excess of 1000 GPD. An additional 1000 GPD loading may flood and irreparably harrr the system. We caution against the installation of a water softener. The hydraulic loading from the backwash of a water softener is detrimental to an OWS and a separate drywell should be constructed for the backwash waste, if a softener is installed. No landscaping or plastic can be used over the field, which will reduce performance of the field. Chemically treated water from a swimming pool or spas should not be introduced, to the OWS. The design of the OWS is based on the treatment of domestic sewage only. No industrial or hazardous wastes should be introduced into the OWS. LIMITATIONS A contactor who is experienced in OWS instaliation should install the OWS. Our investigation,layout, design and recommendations are based on d.ata submitted. If subsurface conditions different from those described in this report are encountered, we should be notified to evaluate the effect on the proposed OWS. If the healttr-department makes modifications to this design, we should be contacted to evaluate the impact on the performance of the OWS. The county and our firrn must be contacted upon completion of the OWS Al1 construction is to be in accordance with the ISDS reguiations. Pipe type and size, burial requirements, septic tank construction, and other specifications, which are not depicted in our repor[, arc to conform to the requirements of the ISDS regulations. The installer of the system is to have demonstrated knowled,ee of the ISDS regulations and requirements. If there are questions, please call. The project engineer for this site is Eric Burns. Sincerely, CHLIRCH & Associates, Inc. Reviewed by Eric R. Burns Design Technician EOC/erb 3 copies sent tl ir ti ri s;r& t€-12-t'$*e fua;;a*# -. t Edward O. Church, P o4'e RosE LANE o o SCALE TowN oF oARBoNDALE 1" = 6o' cARFIELD COUNTY, COLORADO I LJf L,AnD\Jl\uliLtr I =LD COUNTY, COLOHADO I/ -- !------ - ---It{! - / rN / rHE LocaTloN oF EXISTING aND PRoPoSED IMPRoVEMENTS SHowN HEREIN AND rHE WELL I I,' AND/6R DRATN FTELD LocATtcNS sraKED AT THE slrE ARE Nor rHE RESULT oF A PRoPERTY / .'l' , suRVEy. tMpRovEMENT LocATtoNS ARE aPPRoxlMATE. lr ls rHE PRoPERTY owNER's / ,' ,' RESPONS|BILITY TO DEFINE PROPERTY BOUNDARIES AND ENSURE ALL ONSITE II1PROVEMENTS / ,', .' / ; ARE LOCATED WITHIN THE PLATTED SITE AND OUT OF INAPPROPRIATE EASEHENTS. ALL / , T f . 'EPARATT.N DrsrANcES ARE ro 8E 'ERIFIED PRI.R ro ExcAVArloN' /rr r, / I ,',/ I I "/ I ''r/ I/'/ IX. LOCATION OF PROPOSED BARN PARTIAL SITE PLAN AND LOCATION OF TEST PIT xrslNc 2-BEDROOM RESTDENCE /." ,"1 | ,",/ | DIRT DRIVEWAY .}r. - EXiSTING DITCH I( -\-- -J I I EXrsrNG 4-BEDR..M RESTDENCE I -\=__-j- ../ | I I EXISTING WELL ._-_.- _--_ r- lt I' I I I I FIGURE 1 APPROX. 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