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HomeMy WebLinkAboutOWTS Design 5020 County Road 154 Glenwood Springs, CO 81601 phone: (970) 945-7988 fax: (970) 945-8454 email: kaglenwood@kumarusa.com www.kumarusa.com Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, C olorado ONSITE WASTEWATER TREATMENT SYSTEM DESIGN PROPOSED RESIDENCE LOT 17-A, MINEOTA ESTATES SENECA DRIVE GARFIELD COUNTY, COLORADO PROJECT NO. 20-7-744.02 JUNE 2, 2021 PREPARED FOR: SIGI MARIONI 198 COMANCHERO TRAIL NEW CASTLE, COLORADO 81647 sigi.marioni@gmail.com Kumar & Associates, Inc. Project No. 20-7-744.02 TABLE OF CONTENTS INTRODUCTION ...................................................................................................................... - 1 - PROPOSED CONSTRUCTION ................................................................................................ - 1 - SITE CONDITIONS ................................................................................................................... - 1 - SUBSURFACE CONDITIONS ................................................................................................. - 1 - OWTS ANALYSIS .................................................................................................................... - 3 - DESIGN RECOMMENDATIONS ............................................................................................ - 3 - SOIL TREATMENT AREA................................................................................................... - 3 - OWTS COMPONENTS ......................................................................................................... - 4 - OWTS OPERATION AND MAINTENANCE.......................................................................... - 7 - OWTS HOUSEHOLD OPERATION .................................................................................... - 7 - OWTS MAINTENANCE ....................................................................................................... - 8 - OWTS CONSTRUCTION OBSERVATION ............................................................................ - 8 - LIMITATIONS ........................................................................................................................... - 8 - FIGURES FIGURE 1A – VICINITY MAP FIGURE 1B – OWTS SITE PLAN FIGURES 2A & B – USDA GRADATION TEST RESULTS FIGURE 3 – SOIL TREATMENT AREA CALCULATIONS FIGURE 4 – SOIL TREATMENT AREA PLAN VIEW FIGURE 5 – SOIL TREATMENT AREA CROSS SECTION ATTACHMENTS VALLEY PRECAST 1,250 GALLON, TWO-CHAMBER SEPTIC TANK DETAIL TUF-TITE 4-HOLE DISTRIBUTION BOX Kumar & Associates, Inc. Project No. 20-7-744.02 INTRODUCTION This report provides the results of an onsite wastewater treatment system (OWTS) design for the proposed residence located on Lot 17-A, Mineota Estates, Seneca Drive, Garfield County, Colorado. The purpose of the report is to provide design details for the OWTS in accordance with the Garfield County Environmental Health Department Onsite Wastewater Treatment System Regulations and the Colorado Department of Public Health and Environmental Regulation #43. The services are supplemental to our agreement for professional services to Sigi Marioni dated December 2, 2020. PROPOSED CONSTRUCTION The residence will be a single-family structure located on the lot as shown on Figures 1A and B. The residence will have four bedrooms. The OWTS will be designed for a total of four bedrooms. The proposed soil treatment area (STA) for the OWTS will be located to the southeast of the residence as shown on Figure 1B. Water service will be provided by a public water supply from a water tank about 1200 feet to the north of the residence. The route of the water supply line to the residence has not been designed at the time of this report. If proposed construction is different than that described, we should be contacted to re-evaluate our design recommendations. SITE CONDITIONS The lot was vacant with a rough-cut driveway leading to the building site (marked by corner stakes) at the time of our field exploration. The ground surface is moderately sloping down to the southeast at grades from about 8 to 10%. Vegetation consists of juniper trees, sage brush, grass and weeds. About 1 to 2 inches of snow covered the ground at the time of our field exploration. SUBSURFACE CONDITIONS The field exploration for the OWTS was conducted on December 15, 2020. Two profile pits (Profile Pits 1 and 2) were excavated with a mini-excavator at the approximate locations shown on Figures 1A and B to evaluate the subsurface conditions at the planned soil treatment area for the OWTS. The pits were logged by a representative of Kumar & Associates. Logs of the profile pits are provided below. - 2 - Kumar & Associates, Inc. Project No. 20-7-744.02 Log of Profile Pit 1 Depth USDA Classification 0-1’ TOPSOIL; organic Loam, firm, moist/frozen, brown. 1’-5’ LOAM; strong blocky structure, very stiff, slightly moist, light brown to brown. • Disturbed bulk sample obtained from 3 to 4 feet. • Bottom of pit @ 5 feet, where digging refusal with the mini-excavator occurred. • No groundwater or redoximorphic features observed at time of pit excavation. Log of Profile Pit 2 Depth USDA Classification 0-1’ TOPSOIL; organic Loam, firm, moist/frozen, brown. 1’-2½’ LOAM; strong blocky structure, very stiff, slightly moist, brown. 2½’-7’ SANDY LOAM; gravelly, moderate blocky structure, very stiff, slightly moist, light brown. • Disturbed bulk sample obtained from 4 to 5 feet. • Bottom of pit @ 7 feet. • No groundwater or redoximorphic features observed at time of pit excavation. The soils encountered in Profile Pit 1, below about 1 feet of organic topsoil, consisted of Loam down to the pit depth of 5 feet. Practical digging refusal was encountered with the mini- excavator in the Loam due to its hardness. The soils encountered in Profile Pit 2, below about 1 feet of organic topsoil, consisted of about 1½ feet of Loam overlying gravelly Sandy Loam down to the pit depth of 7 feet. Hydrometer and gradation analyses were performed on a disturbed bulk sample of the soils from Profile Pit 1 from 3 to 4 feet depth and Profile Pit 2 from 4 to 5 feet depth with the results provided on Figures 2A and 2B, respectively. The tested sample from Profile Pit 1 (minus No.10 size sieve fraction) classifies as Loam per the USDA system. The tested sample from Profile Pit 2 (minus No.10 size sieve fraction) classifies as gravelly Sandy Loam per the USDA system. No free water was encountered in the pits nor indications of seasonal high groundwater were observed at the time of the pit excavations. Based on the subsurface conditions and laboratory testing, the soils at the STA have been classified as Type 2 per State regulations, which equates to a long-term acceptance rate (LTAR) of 0.60 gallons per square foot per day. - 3 - Kumar & Associates, Inc. Project No. 20-7-744.02 OWTS ANALYSIS Based on the site conditions and profile pit evaluations, the evaluated area should be suitable for a conventional infiltration disposal system. There is adequate elevation difference from the ground floor of the residence down to the STA for gravity flow of the sewer effluent. The STA will consist of chambers in a trench configuration based in the Loam and Sandy Loam soils. The STA will be sized for four bedrooms (seven persons) and an average daily flow of 75 gallons per person, and an LTAR of 0.60 gallons per square foot per day for the natural soils. The effluent will gravity flow from the residence to a septic tank for primary treatment and then gravity flow to the STA for dispersal and final treatment. The STA will consist of three trenches with Infiltrator Quick 4 Plus Standard chambers. Equal distribution will be provided to the chambers and trenches by a distribution box. There are no known water supply lines or wells in the vicinity of the proposed STA. The required setback to the water supply line from the septic tank is 10 feet, 5 feet for sewer and effluent lines, and 25 feet from the STA. We should be notified for additional recommendations if any component of the OWTS is within these minimum setbacks. DESIGN RECOMMENDATIONS The design recommendations presented below are based on the proposed construction, the site and subsurface conditions encountered, and our experience in the area. A layout of the proposed OWTS components is provided on Figure 1B. If conditions encountered during construction are different than those that are described in this report, we should be contacted to re-evaluate our design recommendations. SOIL TREATMENT AREA • The STA will consist of three trenches with 18 Infiltrator Quick 4 Plus Standard chambers placed in each trench (54 chambers total) in the native soils. Equal distribution will be provided to the trenches by a distribution box. • The STA was sized based on an LTAR of 0.60 gallons per square feet per day. • Each chamber was allowed 12 square feet of area. A 30% reduction of the STA size was applied for use of Infiltrator chambers in a trench configuration. The total STA design size is 648 square feet. Soil treatment area calculations are shown on Figure 3. • A minimum of four feet of undisturbed soil between trenches is required. • Trench cut depths should be a maximum of 4 feet deep. • The trenches should be oriented along ground contours to minimize soil cut and cover. - 4 - Kumar & Associates, Inc. Project No. 20-7-744.02 • The base and sidewalls of the trench excavations should be scarified prior to the chamber placement. • A minimum of 12 inches and a maximum of 24 inches of cover soil should be placed over the chambers. • Backfill should be graded to deflect surface water away from the STA and should be sloped at 3 horizontal to 1 vertical or flatter. A swale to divert surface water flow away from the STA may be needed along the upslope side. The swale should be at least 10 feet from the STA. • Disturbed soil should be re-vegetated as soon as possible with a native grass mix. No trees, shrubs or other plants with deep roots should be planted on or near the STA as this may damage the system piping. • Four-inch diameter inspection ports should be installed vertically into the knockouts provided in the chamber end caps. Install ports at each end of the trench. The inspection port piping should be screwed into the top to the chambers and should not extend down to the ground surface inside the chambers. The inspection ports should extend at least 8 inches above the finished ground surface or be protected in a valve box at finished grade. • The STA must be a minimum of 25 feet from any potable water supply lines. • The STA must be a minimum of 20 feet from the residence. • The STA must be a minimum of 100 feet from any well or cistern. • A plan view of the STA is presented on Figure 4 and a cross section of the STA is presented on Figure 5. OWTS COMPONENTS Recommended OWTS components provided below are based on our design details and our experience with the specific component manufacturers. Equivalent components may be feasible but need to be approved by us prior to construction. Septic Tank • A Valley Precast 1,250 gallon, two-chamber septic tank should be used for primary treatment. A detail of the tank is provided as an attachment. • An effluent filter should be installed in the tank outlet tee. • The tank must be a minimum of 5 feet from the residence. • The tank must be a minimum of 10 feet from any potable water supply lines. • The tank must be a minimum of 50 feet from any well or cistern. - 5 - Kumar & Associates, Inc. Project No. 20-7-744.02 • The tank must be set level. The excavation bottom must be free of large rocks or other objects that could damage the tank during placement. A road base or gravel bedding material may be needed to prevent tank damage during placement and act as a leveling course. • The tank lids must extend to final surface grade and made to be easily located. • Install the tank with 2 feet minimum cover soil for frost protection. Maximum tank soil cover is 4 feet. Sewer Pipe • The sewer line to the septic tank should not be less than the diameter of the building drains and not less than 4 inches in diameter. • The sewer pipe should have a rating of SDR35 or stronger. Schedule 40 PVC pipe is required beneath any driveway surfaces. • The sewer pipe should be sloped between 2% to 4% to help limit disturbance of solids in the tank and potential sewage bypass of the first chamber of the tank. If a steeper slope is needed, this can be accomplished with vertical step-downs in the sewer line. • A minimum 24 inches of cover soil should be provided over the sewer pipe. Paved areas, patios or other areas without vegetative cover may be more susceptible to frost and we recommend 48 inches of soil cover over the sewer pipe in these areas, and the pipe be insulated on top and sides with 2-inch-thick blue foam insulation board. If adequate soil cover is not possible, we should be contacted for re-evaluation prior to installation. • The sewer pipe should be bedded in compacted ¾-inch road base or native soils provided that the native soils contain no angular rocks or rocks larger than 2½ inches in diameter to help prevent settlement of the pipe. Sags in the pipe could cause standing effluent to freeze and damage the piping. • Install cleanout pipes within 5 feet of the building foundation, where the sewer pipes bend 90 degrees or more and every 100 feet of sewer pipe. • All 90-degree bends should be installed using a 90-degree long-sweep or by using two 45-degree elbows. • The sewer line location shown on Figure 1 is considered conceptual. We assume that there will be only one sewer line exiting the residence. It is the responsibility of the owner/contractors to locate all sewer line exit locations and connections to the septic tank. We should be notified if there are other sewer lines exiting the building. - 6 - Kumar & Associates, Inc. Project No. 20-7-744.02 Effluent Transport Piping • The effluent transport pipe should be 4-inch diameter SDR35 piping sloped at a 2% minimum to flow from the septic tank to the distribution box and from the distribution box to each trench. Piping should extend at least 6 inches into the top knockout provided in the Infiltrator end caps and be screwed in place. Splash plates should be installed beneath the inlet piping to help limit scouring of the infiltrative soil surface in the chambers. • The effluent transport pipe should be bedded in compacted ¾-inch road base or native soils provided that the native soils contain no angular rocks or rocks larger than 2½ inches in diameter to help prevent settlement of the pipe. Sags could cause standing effluent to freeze and damage to the piping. • A minimum 18 inches of cover soil should be provided over the effluent transport pipe. Paved areas, patios or other areas without vegetative cover may be more susceptible to frost. We recommend 48 inches of soil cover over the effluent pipe and insulation with at least 2 inches of rigid foam insulation in these areas. If adequate cover soil is not possible, we should re-evaluate the condition prior to installation. • Schedule 40 PVC pipe is required underneath driveway surfaces and should be provided with at least 48 inches of soil cover, and be insulated on top and sides with 2-inch-thick rigid foam insulation board. • All 90-degree bends should be installed using a 90 degree long-sweep or by using two 45-degree elbows. Distribution Box • The distribution box will be used to equally divide effluent flow between the trenches. We recommend the Tuf-Tite 4-Hole Distribution Box since it is easily accessible from ground surface for maintenance. A copy of the distribution box detail is provided as an attachment to this report. • The distribution box outlet pipes should be equipped with Tuf-Tite speed levelers for ease of initial setup and adjustment over time. • The distribution box should be a minimum of 18 inches below grade with risers and an access lid at or above grade. • The distribution box must be accessible from ground surface for inspection and maintenance per the State guidelines. • The effluent line from the septic tank should be directed downward into the distribution box with a 90-degree elbow inside the box. - 7 - Kumar & Associates, Inc. Project No. 20-7-744.02 • The distribution box must be installed level on a compacted road base subgrade to ensure equal effluent distribution. If settlement of the distribution box occurs, unequal effluent distribution may take place which could cause hydraulic overload of one of the trenches and potential failure. The distribution box should be monitored periodically, and the speed levelers should be adjusted as necessary for leveling. • The ground surface above and around the distribution box should be graded to drain away surface water to prevent standing water near the distribution box which could freeze or cause settlement. OWTS OPERATION AND MAINTENANCE The OWTS will require periodic inspection and maintenance to function properly. A properly designed, installed and maintained system can greatly increase its lifespan. The level of maintenance will vary depending on the complexity of the system and water use habits of the residents. We recommend that an OWTS Operation and Maintenance (O&M) Manual be developed. Depending on the complexity of the system, a contract with an OWTS maintenance provider may be prudent. Below are some basic recommendations for the OWTS O&M. OWTS HOUSEHOLD OPERATION • Use of high efficiency water fixtures is recommended to decrease the hydraulic load on the OWTS system. • Fix plumbing leaks immediately as this may cause a hydraulic overload of the soil absorption system. • Do not irrigate the area on top of or directly upgradient of the soil absorption field as this may cause a hydraulic overload. • Do not dispose of household waste down drains as this may clog or damage OWTS components. Examples of household waste includes: dental floss, cotton swabs, coffee grounds, paper towels, feminine products and many other kitchen and bath items. • Use of kitchen garbage disposals is not recommended. If a garbage disposal is utilized, kitchen wastewater should be screened thoroughly. Many kitchen solids are not decomposed in the septic tank and may cause increased tank pumping frequency. • Do not dispose of household chemicals, greases, oils, paints, hot tub water or water softener backwash in household drains. A separate drywell, if feasible, may be necessary for hot tub water or water softener backwash disposal. • Limit the use of bleach as this may harm useful bacteria in the septic tank and soil absorption system. - 8 - Kumar & Associates, Inc. Project No. 20-7-744.02 • Liquid dishwasher and clothes washer detergent is recommended for households served by an OWTS. Clay substances used as fillers in powder detergents may result in clogging of the soils absorption system. OWTS MAINTENANCE • Inspect the septic tank, distribution box and STA at least annually for problems or signs of failure. • The effluent filter for the tank should be cleaned at least annually by spray washing solids into the first chamber of the septic tank. • The septic tank should be pumped and cleaned every 3 to 5 years depending on use. Longer pumping intervals may increase the amount of solids that reach the STA, which may shorten its life span. • Pumping of the septic tank should take place when the level of the sludge and scum layers combined take up 25 to 33% of the capacity of the first chamber of the tank. OWTS CONSTRUCTION OBSERVATION The Garfield County Environmental Health Department requires that the designer of the system provide a record drawing and certification of the OWTS construction (As-Built inspection). We should be provided with at least 48-hour notice prior to the installer needing the inspections. Prior to issuance of our certification letter, we require observation of all system components prior to backfill. The number of site visits required for the inspection will depend on the installer’s construction schedule. We should be provided the tank inspection report prior to or at the time of our inspection. LIMITATIONS We have conducted this design in accordance with generally accepted engineering principles and practices in this area at this time. We make no warranty either expressed or implied. The recommendations provided in this report are based on the site conditions, profile pit evaluations and soil texture analysis, the proposed construction and our experience in the area. Variations in the subsurface conditions may not become evident until excavation is performed. If conditions encountered during construction appear different from those described in this report, we should be notified so that re-evaluation of the recommendations may be made. This report has been prepared for the exclusive use by our client for design purposes. We are not responsible for technical interpretations by others of our information. As the project evolves, we should provide continued consultation and field services during construction to review and SILT COBBLES COARSE GRAVEL MEDIUMMEDIUMV. FINE SAND CLAY FINE CO.FINEV. CO.CO.FINE Kumar & Associates SILT COBBLES COARSE GRAVEL MEDIUMMEDIUMV. FINE SAND CLAY FINE CO.FINEV. CO.CO.FINE Kumar & Associates Kumar & Associates Kumar & Associates Notes: &KDPEeUssKoXOGEeLQstDOOeGOeYeOoQDsFDULILeGJUoXQGsXUIDFe&oQFUetesDQGPD\EeXseGDsDOeYeOLQJFoXUseLI QeFessDU\ &DUesKoXOGEetDNeQE\tKeFoQtUDFtoUtoDYoLGFoPSDFtLoQoItKeQDtLYesoLOsLQtKetUeQFKDUeDs7KeEDseDQGsLGeZDOOsoI tUeQFKe[FDYDtLoQssKoXOGEesFDULILeGSULoUtoFKDPEeULQstDOODtLoQ $OOSLSLQJsKoXOGKDYeDUDtLQJoI6'5oUstUoQJeU &KDQJestotKLsGesLJQsKoXOGQotEePDGeZLtKoXtFoQsXOtDtLoQDQGDSSUoYDOE\.XPDU $ssoFLDtes 5eIeUtotKe*DUILeOG&oXQt\2QsLte:DsteZDteU6\steP5eJXODtLoQsIoUotKeUDSSOLFDEOesSeFLILFDtLoQs Infiltrator Quick 4 Plus Standard Chamber Installed Level Scarify bottom and sides of trench prior to chamber placement. Excavate 36" Wide Trench Approx. Existing Grou n d S u r f a c e 12" min. 24" max. Cover Soil Graded to Deflect Surface Water Native Soil 4' Min. Undisturbed Soil Between Trenches Kumar & Associates Notes 1.Chambers should be installed level on a scarified ground surface. Concrete sand may be used as a leveling course if necessary. 2.Care should be taken by the contractor to avoid compaction of the native soils in the trench areas. The base and side walls of trench excavations should be scarified prior to chamber installation. 3.Changes to this design should not be made without consultation and approval by Kumar & Associates. Tough Problem Providing a simple, reliable, and permanent means for dividing septic tank effluent flow. TUF-TITE Solution A strong, stable, permanent, non-corrosive Tuf-Tite Distribution Box, with a Tuf-Tite Speed Leveler in each outlet. Snap-in pipe seals They’re patented. Simply insert your PVC pipe and push it through the flexible, polyethylene Tuf-Tite seal. Pipes fit watertight. Installation couldn’t be easier. Tuf-Tite® Distribution Box. THE TOUGH ONE! n Injection molded HDPE n Non-corrosive n Simple to install n Easy to level In a septic environment, no other material can match High Density Polyethylene in delivering a lifetime of trouble-free service. Tuf-Tite Distribution Boxes are injection molded, using only premium HDPE which contains no fillers or foam. They’re permanent Unlike cement-based pipe grout, Tuf-Tite seals will not crack or corrode in septic conditions. They stay pliable and watertight permanently. 4-Hole Distribution Box4-Hole Dist Cat Sheet 11/8/01 8:09 AM Page 1 nInjection molded.Exceptionallystrong.nHDPE is non-corrosive in a septic environment. nPatented snap-in pipe seals simplify installation. Interlocking Lid. Heavy-dutyHDPE Lid is ribbed for addedstrength and rigidity. Slottedsides interlock on theDistribution Box to assure atight fit.The 4HD2 Distribution Box comes complete with a Regular Lid or an Inspection Port Lid, and 5 snap-in fittings of your choice. Model B1 Riser. For series B1 Box. Stackable HDPE Risers extend to grade in 6” increments. Accept 11” x 11” lids and grates. 11” S-35 S-40 P-10 11” 11” 11” 11” 151/2” 2” Drop INSTALLATION IS JUST THIS SIMPLE 1.Position the Distribution Box on level virgin soil. Do not place box on a concrete slab. 2.Install the inlet pipe and outlet pipes. Be sure the bottoms of all pipes rest on virgin soil. 3.Level the Distribution Box and all pipes as needed. 4.Backfill the pipes to within two feet of the Distribution Box. Recheck the level of the box, then backfill up to the top lid ridge. 5.Install and adjust Tuf-Tite Speed Levelers. 6.Place lid on the Distribution Box and finish backfilling. Choice of Fittings S-35 Pipe Seal, for: n Sewer and Drain n SDR 35 n ASTM 3034 n Thin Wall n 1500 Lb. Crush S-40 Pipe Seal, for: n Schedule 40 n 4” Corrugated P-10 Plug, for unused holes Choice of Lids Regular Lid. Molded of rugged HDPE. Inspection Port Lid. For easy access and inspection. Models available to accept either 4” or 6” extension pipes. Tuf-Tite Speed Levelers™ Control the flow of effluent from the Distribution Box. Simply insert a Speed Leveler into each outlet pipe. Rotate each Speed Leveler so the flow is distributed as desired. Available for 3” or 4” PVC pipe. ©1999 Tuf-Tite® Corporation Form 4HD2-3. Printed in USA A full line of innovations for better septic systems 11” 6” 7” 14” Drainage and Septic Products Tuf-Tite®Corporation 1200 Flex Court Lake Zurich, Illinois 60047 4-Hole Distribution Box 4HD24-Hole Dist Cat Sheet 11/8/01 8:09 AM Page 2