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Home My WebLink AboutEngineer's OWTS Design ReportProposed Single-FamilY OWTS Onsite Wastewater Treatment System Design 3-BR Single-Family Residence Harvey Gap Road/CR 237 ^ùdress TBD silt, co 81652 Parcel N o. 2127 -241,'01-002 Prepared for: CMH Homes Tnc. 5000 Clayton Road Maryville, TN 37804 October 2023 Prepared By: ôNest Water E n g i n eeri n g ê consulting Engineers & Scientisìs 2s1 6 FORESIGHT CIRCLE, f1 GRAND JUNCTION, COLORADO 8l 505 197 O) 241 -7 07 6 - F N (97 Ol 241 -7 O97 I.O SITE CONDITIONS The proposed onsite wastewater treatment system (OWTS) will serve a 3-BR single-family residince ona2.43-acre vacant parcel located at Harvey Gap Road CR237 Address TBD, Silt, CO (Figure Al). Proposed 3-BR dwelling will be served by a new 1,000-gallon septic tank and tftt.È (:J trenches eacL with fifteen (15) Q4 Standard Plus units for a minimum 77' x 64' footprint with end caps (Figure A2). The trenches will be configured in serial distribution using a total of 45 Standutd pt.6Qnick4 Infiltrator@ units generally oriented north to south parallel to topographic contours in a soil treatment area (STA)/leachfield sloping approximately l8% east. Soils and percolation data were collected by WestWater Engineering Septembet 19,2023 in accordancè with Garfield County On-Site Wastewater Treatment System (OWTS) Regulations (Regulations). Soil profile in the vicinity of proposed STA shows dark yellowish brown silty Àand with some tabular gravel-sized sandstone clasts from 0.0 to 2.3 feet overlying dark yellowish brown silty sand interbedded with colluvial soil with sub-angular to angular tabular ólasts gravel to smaliboulder sized from 2.3-4.0 feet. Dark yellowish brown mix of colluvial and alluvial soils with a pebbly sand matrix supporting sub-angular to sub-rounded tabular reddish brown sandstonó clasts (up to 50o/o volume rock near 6.0-foot depth interval) from 4.0- g.0 feet maximum depth of excavation. The high seasonal water table is estimated to be greater than 8.0 feet below ground surface (bgs). percolation rates for the 5 percolation test holes completed in the silty sand and colluvial-alluvial soils range from 6 to 26 minutes per inch (min/in) with a 15 min/in average. Site soils are classifieã as soil Type2 in accordance with Table 10-1 of the Regulations based on silty sand texture, granular structure, and percolation rates generally faster than the 16-25 minlin range. The long-lsrm acceptance rate (LTAR) used to design the OWTS (Table 10-l Regulations) is 0.60 gall,ons per day per square foot area (WdlfÒ' 2.0 WASTEWATER FLOWS Maximum Daily Wastewater Flow (gpd): 3-BR Single-Fam.ily Dwelling 3 bedrooms x 150 gpd/bedroom :450 gpd Septic Tank rn"ãtti-.ttn required septic tank capacity for a 3-BR plumbed structure is 1,000 gallons (Table 9-1 Regulations). For this design, use a two-compartment 1,000 gallon septic tank approved for use in Garfield. The proposed new 1,OO0-gallon septic tank will provide at least 48 hours of detention time for influent wastewater flow from the proposed dwelling. The 48 hour (2-day) particle detention time volume requirement is 900 gallons (a50 gpd x 2-days : 900 gallons). The intemal septic tank outlet effluent filter and inlet tee must be installed per Regulations. 3.0 OWTS DESIGN Silty sand and colluvial-alluvial soils occurring at the 2.0 to 4.0 feet depth interval will be used for itre upper infiltrative surface for the proposed STA (Figure A3). Shallow STAs promote secondary effluent treatment due to available soil oxygen optimizing bacteria and fungi pro..rr... Trench excavation will remove approximately 2.0 to 4.0 feet of soil and upper root Page I mass to prepare a level surface for installing the infiltrators in the three (3) trenches configured in serial distribution. Soil should not be wet at the time of excavation. Place approximately 1.5- foot of frnal cover (1g-inches minimum per Regulations) using the silty sand soil' Final grade shall match existing grade over proposed trenches so water runs off and will not pond over any area of STA"/leachfield. Prior to backfilling, cover the Q4 infiltrator trenches with non-woven geotextile fabric or similar permeable material to prohibit soil intrusion into the chamber louver vents. All setback distances in accordance with the Regulations are applicable to septic system installation. The septic tank must be at least 5 feet, and STA at least 20 feet from plumbed modular structure(sjwith a basement, crawl space, and or footing drains. STA's must be outside of any easements and at least 10 feet from property lines. Setback distances also apply to natural and artificial waterways, including a 50-foot setback from STA/leachfield to natural waterways or open irrigation ditcles. Propoied water supply cistern located north of the 3-BR dwelling ,ourì b" at lèast 100 feet from the leachfield and 50 feet minimum to the septic tank. A variance by the Board of Examiners of Water Well Construction and Pump lnstallation Contractors can ,ðd.r"" this setback to a minimum of 25 feet. Potable water lines serving the residence must be 25 feetfrom the STA/leachfield and 5 feet from building sewer or effluent lines. Designated leachfield repair area must be retained per Regulations as idle land set aside for future use once primary fields fail and no longer accepts wastewater' The new 1,ggg-gallon septic tank will provide at least 48 hours of detention time for influent wastewater flow from thå proposed dwelling. Intemal septic tank inlet tee must be installed per Regulations. An effluent filter must be installed instead of tee on the septic tank outlet. Effluent filtãrs typically require cleaning and maintenance every 6 months. If chosen, use the Orenco Systems-Biotube Effluent Filter OSI Model FTW0444-36 (or equivalent). The following design calculations propose to discharge septic tank effluent to three (3) Quick 4 plus trenches each using fifteen (15) Q4 units for a total minimum disturbed area of approximat ely 17 feet by 64 feetwith infiltrator end caps. A total of 45 Quick 4 Standard Plus Inirltrator uniis will be installed in the 3-Trench Serial Distribution System generally oriented north-south. Soil Absorption Area Calculations Absorption Area (A) : Design Flow (Q)/LTAR Field percolation rate (t): 6 to 26 min/in Leachfield Area: 4: Q/LTAR, Where: A: Leachfield area square feet Q: Design Flow/maximum daily wastewater flow : max. daily wastewater flow 3-BRs @ 150 gpd/bedroom Page2 : 3 bedrooms x 150 gpd/bedroom:450 gpd LTAR: Long Term Acceptance Rate (max. hydraulic loading rate) :0.60 gallons per day/ft:2 A:450 gpd/0.60 Wdlft2 : 750 ff Ouick4 Trench Confizuration: 750 f& x 1.0 (appl. method adjustmentl¡ x 0.7 (distribution media adjustment2): 525 ff 525 ff lI2 ftz : 43.75 Q4 units; Use 45 units. I Regulations Table l0-2 size adjustment factor for Methods of Application in STAs 2 Regulations Table l0-3 size adjustment factor for Types of Media in STAs Note: County and State approved bottom chamber area for Quick 4 Plus Standard lnfiltrator Unit : 12ft2. The 3-Trench Q4 Infiltrator Serial Distribution System will use a total of forty-five (45) units. Each trench will have fifteen (15) Q4 Plus chamber units. Wastewater flow into the proposed trenches will be in serial distribution. Use the top port of the Infiltrator faceplate for all influent piping. 4.0 SYSTEMINSTALLATIONREOUIREMENTS Minimum setback requirements must be in accordance with the Regulations. All sewer pipe couplings must be completed with primed and glued or bell and spigot joints using 4-inch SDR ¡S pVCpipe. Schedule 40 PVC 4-inch pipe with a minimum l-foot soil cover must be used if pipe is insølled in a vehicular traffic crossing. Drain-waste-vent (DWV) rated Schedule 40 PVC pipe is called out for crossings but may also be used instead of SDR 35 PVC pipe. Building sewer pipe must be installed at a slope between Y*-inch and Yo-inch per foot slope (1 to 2yo),préferably uiing the Yo-inchper foot slope as recommended by the International Plumbing CoáelIfC¡ as administered by the County. Fittings shall be sweep 9O-degree curves or two (2) 45-degree elbows at all influent pipe turns. Fittings must be DWV for schedule 40 PVC pipe' Cleariouts (2-way) are required between dwelling and tank and beyond tank where pipe lengths exceed 100 feet from tank to STA/leachfield and at all pipe bends greater than 45 degrees. The installer must adhere to minimum depth requirements for leachfield and ensure gravity drainage into all septic system components to avoid using a lift pump. System components must be placed on native soils or re-stabilized soils in excavated areas. Infiltrator trenches must be excavated level to ensure the prepared infiltrative surface is level along the entire length of STA. Solid 4-inch pipe is used in the header network and sanitary tees. Page 3 The owner will ultimately be responsible for septic system maintenance including pumping the septic tank once every 3-4 years and cleaning the effluent filter every 6 months. 5.0 SYSTEM INSPECTION WestWater Engineering is responsible for inspecting OWTS to ensure construction conforms to the design plan and meets all aspects of County Regulations including: o Inspect system prior to backfilling including piping and septic system components. o Complete an as-built drawing of the system. 6.0 DESIGN LIMITATIONS The OWTS design is based on site-specific soil conditions and percolation data collected in the vicinity of the proposed STA/leachfield and local experience of designing OWTS's in Colorado. The design is only valid for the proposed new OWTS serving the proposed single-family residence at the referenced location provided in this report. 'WestVy'ater Engineering assumes no liability for inaccurate information or conditions that vary from the design assumptions listed above. Netify WustWater Engineering and/or thc Gorfield County official immediately if actual site conditions differ from those assumed herein. please do not hesitate to contact us if you have any questions regarding this report. Respectfully, Dean Goebel, M.S., P.G. Hydrogeologist Reviewed By: Keith ONAL Page 4 APPENDIX A SOILS AND PERCOLATION DATA ôNest Water E n g i n eeri n g ê consulting Engineers & scientisìs 251 6 FORESIGHT ClRCLE, #1 GRAND JUNCTION, COLORADO 8'1505 (97 Ol 241 -7 07 6 - F AX 197 Ol 241 -7 O97 AI. SOILS AND PERCOLATION REPORT Date: September 19,2023 Consultant Dean Goebel, M.S., P.G. Hydrogeologist WestWater Engineering 2516 Foresight Circle #1 Grand Junction, CO 81505 (e70) 24r-7076 Client:CMH Homes lnc. 5000 Clayton Road Maryville, TN 37804 Land Parcel: Harvey Gap Rd CR237 Address TBD, Silt, CO 81652 2127-241-01-002 A2. SOLS LOG Site soils were invcstigatcd úthe 2.43-acre vacant parcel to collect site-spec.ific design criteria for an onsite wastewater treatment system (OWTS) to serve a proposed 3-BR single-family dwelling located at Harvey Gap Road/CR237 address TBD. Percolation testing procedures were conducted in accordance with Garfield County On-Site Wastewater Treatment System (OWTS) Regulations (Regulations). The Percolation Test Site is located approximately 80 feet west of the east property line and 340 feet north of the south property line (Figure Al). The proposed soil treatment area (STA)/leachfield is located in the east-central portion of the parcel approximately 30 feet east of proposed 3-BR dwelling in anarea sloping approximately l8% east. Harvey Gap Reservoir is located approximately Yo-mile north-northeast of the proposed building site. The excavated soils observation pit shows silty sand interbedded with colluvium and alluvial sediments supporting tabular sub-angular to sub-rounded pebble- to small boulder-sized sandstone clasts down to 8.0 feet maximum depth of the excavation. Groundwater was not encountered in the 8.0-foot soils observation pit. Estimated high seasonal groundwater is greater than 8.0 feet. The soils profile log is summarizedbelow and in Table Al. Dark yellowish brown (lOYR 3/4) silty sand with some sub-angular reddish brown (5YR 5/6) sandstone clasts up to gravel size from 0.0-2.3 feet. Dark yellowish brown (1OYR 3/4) silty sand with sub-angular to angular gravel- to small boulder-sized clasts occurs from2.3-4.0 feet overlying colluvial and alluvial soils with pebbly sand matrix from 4.0-8.0 feet maximum depth of excavation. Groundwater was not encountered in the 8.Q-foot soils observation pit with an estimated seasonal high water table greater than 8.0 feet. The lack of antecedent soil moisture and redoximorphic soil coloring indicating prolonged saturation near the 7.5-foot depth interval supports the greater than 8.0 feet estimate for high seasonal groundwater. A1 Table Al. Soil Log Descrþtion vf : very fine; f : fine; m: medium and; crs: coarse for sand sized particles percolation rates summanzedin Table A2 show a range from 6 to 26 minutes per inch (mir/in) with a 15 min/in Ðvcr&ge. Bosed on percolation data, macroscopic/tac.tile soil analysis and lack of shallow groundwater or bedrock, the bottom of leachfield (top of infiltrative surface) should be no deeper than 4.0 feet per Regulations. Site soils are categorized as Type 2 soils based on silty sandy loam alluvial matrix texture, granular structure, and percolation rates predominantly less than the 16-25 min/in range. Soils should not be excavated under wet conditions to avoid compaction and smearing leading to a reduction in permeability. Table A2. Percolation Test Results Depth Interval (ft)Soil Description 0-2.3 1OYR 3 (vÐ some clasts up to gravel slze;moderate OM;granular structure;dty;sagebrush, greasewood,and rabbitbrush desert vegetation 2.3-4.0 Dark with colluvium with to angular gravel-to small sandstone clasts; granular strucfure;dry brown ) pebbly sand (Ð supporting sub-angular to sub-rounded tabularmatnx reddish brown structure, dry (5YR st6)sandstone up to 50%volume rock;granular 0-8.0 ID Depth (ft) Time Final Drop (in) Percolation Rate (min/in) ll:25 (start) I 1:40 12:10 12:40 12:55 (end) I 2.0-2.8 3.25"4.25"5.75"6.75" @r2:25 dry 3.5 l8 2 3.0-3.7 3.25"6.0"dry dry dry 2.75 6 J 2.s-3.3 3.75-5.5"8.0"dry dry 4.25 11 4 3.0-3.6 3.5"4.25"5.375"6.375"dry 2.875 26 5 3.0-3.8 3.75"s.75"8.25"dry dry 4.5 l0 A2 APPENDIX B FIGURES a f F ¡, .i'ç ¿ F\ {J ,'lt .. 1 ¡ ,4 .'Ò.t.t .l '.,'* rr I ,l ú ! b $i t !.4 ¡ d .t È$è N |¡ ìlI t ú'# ! v b a tr $P gF tc¡ ri;ôñi:E ={ - X "'t \r=I ?Iaø o ô5 - o æã- fll)(r=gll> ãH_okı =lc, 5Øl> m Øl.o > -ttÞo -loflÈz.' , a' a 1 t ir¡ I t' J t 1¿ .t.',1t. \ \ \ }rr I aair t \ \ J\ "f t ftt / N- + ì{r Eì I Ò- .r\ t1, t t 1 { nortfl rio ll r{;I. n1rqæz,>nR .\ ,a -{ or Joz -lm i\ \'hF \_-_-+,-_ *t -r.¡þ ¡\)-(¡' t t rrl -t 7)o >< {rrl .-\ €n'o ll *Ë r z. o,q noÉ n I FI U) oÐñ(¡¡ -__ \ t ! r"r--i t :fr'Y¡r. ' & t .¡ --- I {t I *fl .. ..s'i *1 t t N)OO OO O f\)OO (n c) t-If il N)O ,53 { åI ù. PROP { 1( AREA TY OLATI rYP)TEST SITE L F RST 64' ILS P Q4 IN HES W co TREN TEX REP 17' FIGURE A2 HARVEY GAP ROAD PROPOSED OWTS LAY-OUT ^\ìþstUJ¡ate¡êEnglneering 25 l6 Foresight Circle, #l Grand Junction, CO 8 I 505 (970) 24t-7076 www.westwaterco.com NOTE: 3 INFILTRATOR TRENCHES 15 Q4 UNITS EACH 45 TOTAL Q4 CHAMBERS SERIAL DISTRIBUTION EXI LINE E 2 -TRA PROPOSED ATER- SUPPLY C POTABLE & TER- LINE TO H SE OPOSED c N_OUT D\1,000 G SEP C TANK 5 TILITIES 4.9' T NOTE: MINIM M DWELLING SETBACKS 20'LEACHFIELD 5'SEPTIC TANK Iq ,-({' c)st-() ,-- . I¿, S:= 40200 SCALE: 1":40' 40 ^\ñlêstlt/hter:ãEnglneerlng 2516 Foresight Circl€, #l Gmd Junction, CO 81505 (9701 24t-7016 w.wosfivâterco,com FIGURE A5 HAR\EY GAP ROAD OWTS CROSS SECTION 3 INFILTRATOR TRENCHES SERIAL DISTRIBUTION USE TOP FACEPLATE PORT COVER INFILTRATORS WTH GEOTEXTLE FABRIC MAÏCH GRADE BACKFILL OVER TRENCHES EXISTING GROUND @ 4' þI MAXIMUM DEPTH 4.0 FEET MINIMUM DEPTH 2.0 FEET SCALE 1":5' INSTALLATION NOTES: 1) FOLLOW MANUFACTURERS INSTRUCTION www. in fil trotors¡ætem s. com 2) SCREW P|PE TOP PORT CHAMBER FACEPLATE 5) SCREW FACEPLATES AND UNITS TOGETHER 4) TNSTALL MONITORING PORTS END OF TRENCH ALL FOUR BED CORNERS \