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Home My WebLink AboutOWTS Design ReportSeptember 1,2021 Gentry, Alan Bruce & Karen J 141 Donegan Road Glenwood Springs Co 81601 'lBruce Gentry" <gentryb52@gmail.com> RË:Design Report-Onsite Wastewater Treatment System (OWTS), Gentry Residencg 607 Highlands Dr, Glenwood Springs, CO, Lot 4 Glenwood Highlands Estates Amd, Garfield County, Colorado SE Job No. 31182.01 Parcel No: 21-8505113004. Garfield County O\I/TS Permit No. Dear Bruce: This letter report presents the applicable findings in regard to the design and construction of a new Onsite Wastewater Treatment System (OWTS) at the above referenced Site, in support of your OWTS Constnrction permit application to Garfield County. The OWTS desigu is based on recent site assessment observations by Sopris Engineering of existing pþsical site features, conditions, review of previous geotechnical soils evaluation with respect to the proposed residential usage and applicable regulatory design criteria in accordance with State and County OWTS Regulations. The desþ recommendations, specifications and construction details are delineated on the attached OWTS permilconstruction plan that was prepared with current LIS Srnvey Plat information and architectural plans. The design criteria and systern sizing information is summarized below' Pxistine and Pronosqd Conditions The proposed development area is situated on undeveloped l-acre lot neighborrng existing residential development to the East, West, North and agricultural land to the South. The proposed OWTS will serve a new single family residential structure with a design capacþ of up to 4-bedrooms. The subject l-acre residential development area existing topography and site conditions are derived from LIC with topography survey information by Bookcliff survey. The site is situated on sloping meadow land. The proposed developmurt area is in a broad moderateþ sloped (13%to 18 %.) convex meadow that generally trends down gradient to the South. The proposed OWTS field will be constructed parallel to the contours on the southerly faced sloped terrain. The property's water supply is from the City's municipal water supply system. The proposed development will consist of the construction of two-story residential structure with attached garage on a 3,000 S.F. building footprint. The proposed site improvements will include associated driveway, auto court, utilities and a new onsite wastewater treatment system. The development will be based on applicable site design criteria and site construction management. The proposed development improvements and site layout plan is shown on the attached OWTS plan. The site development and building construction is being permitted by the City of Glenwood Springs that does not have municipal sewage infrastructure to serve the lot that is outside of the Sanit¿tion district's service area. Summarv Desisn Criteria The new OWTS is designed for a treatment capacity of 525 gallons per day based on the desrgn wastewater flow to serve a 4-bedroom residence in accordance with Table6-2 values, Section 43.6, ^.4. The new OWTS will utilize a minimum 1,250 gallon two-compartment concrete septic tank to be installed off the south westerly corner of the structure. Sealed concrete or ribbed PVC risers with lids will be installed on the new tånk with Carbondale, C0 81623 031 3 Su ite A3 a aa.a Fax (970) 704-(970) 704-031 1502 Main Street $oPnrs tttcllttnmc o llG civil consultants " OWTS GentrYResidence' 607 Hightands Dr, Glenwood Springs' CO SEJobNo. 31182'01 SePtember l,2O2l Page2 appropriate pipe connection to the new tank utilizing the lpploqlate fittinq adaptT rings for the tank and riser' The new t,ZSO gallon 2-comparfment septic tank will te instatiø wrth appropriate sanitary tees, outlet effluent filter with risers and ti¿s at the surface. A gravity schedule-40 or SDR-35 sewer pipe section with two-way cleanout will be installed betwesn the tank inlet on the gravity sewer line and the accessory structure. The STU will consist of leaching chamber trenches that provide 375 S.F. of total absorption area. The septic tank effluent will be gavity discharged through a new 4-inch schedule-4O or SDR-35, installed at minimum l'5olo slope, to the STU via a concrete distribution box. The effluent will be equally distrib-uted from the distribution boxvia 4" distribution pipes connect"d to the head end cap of each chamber trênch. Observation ports with caps will be installed on the proximal and distal ends of each chamber tre,nch. The desþ is in comptiance with the current County regulations with design calculations based on the soil type, texture and stmcture with an appropriate long term ac-òeptance rate (LTAÐ. The designed system meets all required setbacks and will be installed within the general location indicated on the plan. Our desþ is outlined below and delineated on the attached C-l OWTS plan. Desisn Flow The desþ flow is calculated as follo-ws for the minimum design caqlcitf of an equivalent 4-bedroom residential dwelling. The OWTS is designed for a treatment capacþ of {ZS gãno* per day based on the design wastewater flow in accordance with Table l0-1 values, Section 43.6, A.4. Regulation 43: Minimum population based on 3 bedrooms at 2 persons per bedroom and a fourth bedroom at I person per each additional bedroom o-ver 3, equating to 7 persons' The Design flow is calculated based on reside,lrtial usage of 75 gaUperson/da¡ No PF Max. Design flow (Qd)gallons/day: (# of people) x (avg. flow)gavperson/day. Design flow Qd :7*75:525 Wd Septic Tank Desisn Use a 1250 gallon, two compartment concrete septic tank with an effluent filter outlet sanitary tee in the second chamber. Tank shall be installed with sealed concrete risers and lids to the finish gfade surface. Sub Surface Conditions and Testine A previous Subswface Soil investigations was performed by HP Geotech on August 24 &,25,2009. The result of the soiis evaluation is presented in the Subsoil Study for Foundation Design and Percolation Test, Proposed Residence Lot .GlenwoodHighlands,60T Highlands Drive, Glenwood Springs, CO, dated Se,ptember l6,2009,underproject No 109 266^. The subsurface conditions were evaluated by excavation of two exploratory pits in the building envelope and one profile pit down gradient in the proposed OWTS field area. Three percolation test holes were dug at the bottom of shaiow baıkùoe pits in the area of the proposed OWTS field. The soils encountered in the profile pit and percolation holes consistediandy siþ clay to silty sandy gravel and cobbles ínpercolation hole P-2 of a gravelly silt loam. The gradation and hydrometer performed on a bulk sample of the sandy silty clay soils from the profile pit resulted in the soil composition being 0% gravel, 33o/o sand, 44% sih and2SYo clay indicating that the soils are consistent with a Soil type 2, silt loam. Percolation test resulted in percolation tates ranging from l0 to 20 minutes per inch that is consistent *ittr u soil [pe 2thathas a LTAR of 0.60 gallons per square foot per day. The soils evaluation did not indicate the presence of any limiting soil or hydrological conditions. The report states "Based on the subsurface conditions encountered and the percolation test results, the tested area should be suitable for a conventional infiltration septic disposal systfln". OWTS GentryResidence, 607 Highlands Dr, Glenwood Springs, CO SE Job No. 31182.01 September 1,2021 Page3 Based on the geotechnical report the soils are assumed to be a silt loam with slighty blocþ and granular structure with moderate structural grade having an LTAR of 0.60 g/sfld. Additional observations and soil evaluation will be performedprior to construction mobilization and dwing construction, by Sopris Engineering in the area of the proposed absorption field and tank to confirm the previous soil evaluation and design criteria. Sopris Engineering will observe new profile pits in the area of the proposed absorption field. The soils will be sampled and characterudby application of the USDA soil texture methods. The soils will be further evaluated to determine the presence of any limiting soil or hydrological conditions, appropriate hydraulic loading rate, absorptive surface level capacþ and to verifu treatment level design for the in-situ native soils. If soil conditions encountered require adjustments to design criteria or the design plan notice will be made to County EHD and applicable revisions to design/construction plans and report will be submitted. The results of the additional soil evaluation and soil characterization will be included in the As-Constructed documentation. SoiI Treatment Unit/ Absorytion Svstem Desisn The treatmeirt/absorption field is designed based on utilizing the effective Long Term Acceptance Rate (LTAR) 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 distribution of septic tank efTluent via a distribution box to individual chamber trenches with treatment across the native soil absorptive surface. Lons TermAccentance Rate (LTAR) Considering the application of the state regulation 43: Receiving Wastewater Treatment Level 1; LTAR; (Table 10-l Soil rWe2loading rate for a silt loam is (0.6 gal./S.F./day); Design Flow; Qd: flow (gaVday) : 525 Wd Loading factors; (Table 10-2, Gravity application trenches, l.F.l : 1.0 ) (Table I 0-3, Gravelless chambers, L.F .2 : 0.7) STU absorption treatment area; A: Area S.F.; A(sÐ: Qdx L.F.1 xL.F.2 .: LTAR A(sÐ:525 gpdx 1.0 x 0..7 :612.5 S.F 0.6 GaVS.F./day Number of Quick-4 Infi ltrator chambers 4'x3'x I 2"chambers 612.5 S.F. : 51 chambers; Use 52 chambers l2 S.F./Chamber Number of Equivalent Arc chambers 5'x3'xl2"chambers 612.5 S.F. : 4l chambers; Use42 chambers 15 S.F./Chamber Use 52 Quick-4 Infiltrator chambers in 4 trenches 54' long by 3' wide with 13 chambers units per trench plus two end caps as delineated on the plan. Alternative use 42 Arc chambers in 4 trenches paired a 50' or 55' long by 3' wide with l0 or 11 chambers units respectiveþ per paired trenches with ends caps. The septic tank effluent will be gravtty distributed to the head of each chamber row via individual distribution pipes from a distribution box. OWTS GentrY Residencc, 607 Highlan¡ls Dr. Glenrvood Springs, CO SU iob No. 3 I 182'01 SePtentber 1,2021 Page4 Construction snd I nsP€ctions prior to construction of the pe¡.mifted system. the engineer should be confacted by the contractor and o\ryner well in advance to provide adequate ti*:e to discr.rss the system components with {he contractor, anslv€f questions, resclve any conflict issues and scheåule inspection site visits based on ccnstruction prog¡sss. A pre-OlUTS construction meeting is essential and requir.ed prior to installation of tlrc OWTS. All septic system components shall be staked h the field for approval by the Engi:rær prior to excavation. During initial construction the engineer rvill evaluate the soils io the absolption treatlnent field excavations fo confinn soil conditicns and rnake adjustments as needed. All septic systern compouents and tre*ch installations are 1o be appraved by The Engineer prior to backfilling. County Regulations require that the En-gineers of record perforrn site i*spections of the perrniüe¡ s)¡str¡r during cınstmctio:r and pror.ide "As-Constructed" docunrentation of the installed ,yrt*rr, to the {lounty nfter construction is complete. All installation rvill be irspected, field measured or sun'e.ved, råported a¡rd delineated in the cerlification letter and record ùaw-ing. The contractor needs to photo document all OWTS constructiotì phase; and supply photos Îa the Ëngirteer' The Coçnty Environmental Health department should be contacted at least 48 hours prior to final backfill of components to prcvide advanced notice of construction sclredule in ordcr to perform a final inspection of the in-place coüpone¡ts. Tlæ Gartielcl County contact is: Ted White, P.8., Environme¡ital Health Specialist Ill. Garfield County public Health; r.rrhite@;garfield-county.com. 9?0-945-6614 x 8106 (rnain offrce) or 970-23t-2442 {mobile) OlilS Oreratinn end Mrintenarce Orvnership of the systein and responsibi¡ity for maintena¡rce and repair will rernain with the property Owner. Tlte Owner is encouraged to retain the senices of qualified personnel to inspect the O1VTS and to perfonn all maintenanee and repairs necessary to ensure tlmt the systern coruponents are rnaintained in good operating ccndition and suitable v.ogetative coyer is "itubiir¡*d o¡r the fields. The components af fhe O$/TS system should inspæted withir: 3s days of being placed i¡to operation and should been inspected and rnaintained bi-amiually. The tank, absorption field and other systern componants should be visually inspected bi-annually for debris, danrage. leaks, or cther potential probleins. lg geniral, for a properly. utilized sysTenr, septic tanks should be puniped every 3 - Syears. The effluent filter should be cleaned every six r:rcnths and at the time of purnping, Absorption fields should b'e nraintainecl with suitable vegetative.oo", und kept free cf root invasive plants. Positive surface dr-ainage arvay frotn the absorption fieid should be rnaintair:ed. lf you have any question or need any additional inforrnaticn" please cali Sincerely, SOPRIS ENGTNEERING, LLC tj/. .,/,3¿"tt- f'tfl Paul E. Rurledge Ðesign Engineer Yancy Principal PE