Loading...
HomeMy WebLinkAboutOWTS Design 07.31.15GO'cbtech HEPWORTH-PAWLAK GEOTECHNICAL llcpworth·Pawlnk Gcotcchnica1 , Inc 5020 Coun1y Rond I 54 Glenwood Springs, Colorado 81601 Phone . 970-945-7988 Fax : 970·94S-84S4 Em11il ; hpgco@hpgco1cch com ONSITE WASTEWATER TREATMENT SYSTEM DESIGN PROPOSED RESIDENCE LOT 13, ELK SPRINGS, FILING 2 480 PINON POINT GARFIELD COUNTY, COLORADO JOB NO. 115 0698 JULY 31, 2015 PREPARED FOR: MICHAEL EGAN AND PAULI HA YES 928 BRANCH ROAD SCOTTSVILLE, VIRGINIA 24590 (paillo2@ gmail.com) TABLE OF CONTENTS INTRODUCTION ........................................................................................................... - I - BACKGROlJND INFORMATION ................................................................................ -1 - PROPOSED CONSTRUCTION ..................................................................................... -1 - SITE CONDITIONS ....................................................................................................... -2 - SUBSURFACE CONDITIONS ...................................................................................... -2 - OWTS ANALYSIS ......................................................................................................... - 3 - DESIGN RECOMivrENDATIONS ................................................................................. - 3 - SOIL TREATlvlENT AREA ....................................................................................... -3 - OWTS COMPONENTS .............................................................................................. -4 - OWTS OPERATION AND MAINTENANCE .............................................................. -7- 0WTS HOUSEHOLD OPERATION ................................. : ....................................... -8 - OWTS MAIN'TEN.ANCE ............................................................................................... - 8 - OWTS CONSTRUCTION OBSERVATION ................................................................. -9 - LIMITATIONS ............................................................................................................... -9 - FIGURES FIGURE 1 OWTS SITE PLAN FIGURE 2 USDA GRADATION TEST RESULTS FIGURE 3 SOIL TREATMENT AREA CALCULATIONS FIGURE 4 SOIL TREATMENT AREA PL.AN VIEW FIGURE 5 SOIL TREATMENT AREA CROSS SECTION ATTACHMENTS VALLEY PRECAST SEPTIC TANK DETAIL Job No. 115 0698 INTRODUCTION This report provides the results of an onsite wastewater treatment system (OWTS) design for the proposed residence to be located on Lot 13, Elk Springs, Filing 2, 480 Pinon Point, Garfield County, Colorado. The purpose of this report was to provide design details for an OWTS in accordance with the 2014 Garfield County Onsite Wastewater Treatment System Regulations and the Colorado Department of Public Health and Environment's Regulation #43. The study was perfolllled as part of our agreement for gcotcchnical engineering services to Michael Egan dated February 26, 2015. BACKGROUND INFORMATION Hepworth-Pawlak Geotechnical previously performed a subsoil study and percolation test at the subject lot and reported our findings in a report dated June 28, 1996, Job No. 196 285. We recently completed a subsoiJ study for foundation design and profile pit evaluation for the current proposed residence and presented findings in our report dated June 18, 2015, Job No. 115 069A. Applicable information from these reports has reviewed and incorporated into the subject OWTS design. PROPOSED CONSTRUCTION The residence will be a single story wood frame structure over a walkout basement level located on the lot as shown on Figure 1. The basement and garage floors will be slab-on- grade. Cut depths are expected to range between about 3 to 8 feet. The OWTS soil treatment area (ST A) will be located downhill and to the south/southwest of residence . The OWTS was designed based on a maximum of three bedrooms. If the proposed construction changes, we should be contacted to review our design recommendations. Job No. 115 0698 --------------·--·· ·--·-·-··-·------- -2- SITE CONDITIONS The site is located on a rolling upland mesa above the Roaring Fork River VaJley. The lot is vacant and vegetated with a pinion and juniper forest with a ground cover of grass and weeds. The ground surface on the lot appears mostly natural and slopes down to the southwest at a grade of abouL 10 lo 20%. Numerous basalt cobbles and boulders are . visible on the ground surface. SUBSURFACE CONDITIONS The field exploration was conducted on June 17, 1996 and April 20, 2015 . Two profile pits (Profile Pits 1 and 2) were excavated at the approximate locations shown on Figure 1 to evaluate the subsurface conditions. The logs of the profile pits are provided below. The soils encountered consisted of about 6 inches to 2 feet of topsoil overlying very gravelly loam to the maximum depth explored, 8 feet. A hydrometer and gradation analyses was perfonned on a disturbed bulk sample of the soils (minus 3 inch fraction) from Profile Pit 2 with the results provided on Figure 2. The tested sample classifies a very gravelly loam per the USDA system. Based on the subsurface conditions and laboratory testing, the soils have been classified as Soil Type 2A per State regulations, which equates to a long-term acceptance rate (LT AR) of 0.5 gallons per square foot per day. Log of Profile Pit 1 Depth USDA Classification ....... 0-6" TOPSOIL; organic sandy silt and clay with basalt cobbles and boulders, slightly moist, dark brown. 6"-8' LOAM; very gravelly with basalt cobbles and boulders, massive structure, dense, slightly moist, light brown, calcareous. • Bottom of pit@ 8 feet . • No free water was encountered during excavation . Job No. 115 0698 - 3 - Log of Profile Pit 2 Depth USDA Classification 0-2' TOPSOIL; organic sandy silt and clay with basalt cobbles and boulders, slightly moist, dark brown. 2'-8' LOAM; very gravelly with basalt cobbles and boulders, massive structure, dense, • • • slightly moist, light brown, calcareous. Disturbed bulk sample obtained from 2 to 3 feet . Bottom of pit @ 5 feet . No free water was encountered during excavation . OWTS ANALYSIS Based on the profile pit evaluations and laboratory testing, the base of the soil treatment trenches will be located in loam soils (Soil Type 2A) which are suitable for a conventional infiltration disposal system. The ST A will be sized for three bedrooms using an LT AR of 0.5 gallons per square foot per day. The sewage will gravity flow to the septic tank for primary treatment then gravity flow to the STA for disposal and final treatment. The STA will consist of three trenches with Infiltrator chambers. Equal distribution to the trenches will be provided by a distribution box. 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. If conditions encountered during construction are different than those that are described in this report contact us to re-evaluate our design recommendations. SOIL TREATMENT AREA • The treatment system will consist of three trenches with 18 Infiltrator Quick 4 Plus Standard chambers in each trench (54 chambers total). Equal distribution is Job No. 115 0698 -4- proposed by a Fralo Monster distribution box . The STA layout is shown on Figure 1. • The STA was sized based on an LTAR of0.5 gallons per square feet per day. • Each chamber was allowed 12 square feet of area and a 30% reduction in the STA was allowed per Garfield County regulations. The total STA is 648 square feet. Soil treatment area calculations are shown on Figure 3. • The base and sidewalls of the trench excavations should be scarified prior to chamber placement. Concrete sand can be used in the bottom of the trenches as a leveling course if needed . • 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 ST A and should be sloped at 3 Horizontal to I Vertical maximwn. • 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 absorption area as this may damage the system piping. • Four inch ~iameter inspection ports should be installed vertically into the knockouts provided in the Infiltrator end caps . Install vents at each end of each 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 . • 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. Job No. 115 0698 -5- Septic Tank • A 1,000 gallon, two chamber Valley Precast septic tank is proposed for primary treatment. A copy of the tank detail is provided as an attachment to this report. • An effluent filter should be installed in the tank outlet tee. • 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 gravel or road base bedding material may be necessary to prevent tank damage during placement and act as a leveling course. • Install the tank with 2 feet minimum cover soil for frost protection. Maximwn tank soil cover depth is 4 feet. • The septic lids must extend to final surface grade and made to be easily located. Sewer Pipe • The sewer line from the residence to the septic tank should not be less than the diameter of the building drain and not less than 4 inches in diameter. • The sewer pipe should have a rating ofSDR35 or better. Schedule 40 PVC pipe should be used beneath driveway surfaces. • The sewer p ipe 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 minimwn 36 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. 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% inch road base or native soils provided that the native soils contain no angular rocks or rocks larger than 2~ inches in diameter to help prevent settlement of the pipe. Sags could cause standing effluent to freeze and damage piping. Job No. 115 069B -6- • Install cleanout pipes within 5 feet of the building foundation, where the sewer pipe bends 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 to locate all sewer line exit locations and connections to the septic tank. We should be notified ifthere are other sewer lines exiting the residence . Effluent Transport Piping • The effluent transport pipe should be 4 inch diameter SDR35 piping sloped at a 2% minimwn to flow from the septic tank to the first 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 prevent scouring of the infiltrative soil surface in the chambers. • Serial connections between the rows of should also consist of 4 inch diameter SDR35 piping sloped at a 2% minimum to drain to the next trench. Piping should extend at least 6 inches into the knockout provided in the Infiltrator end caps and be screwed in place. • The effluent transport pipe should be bedded in compacted * inch road base or native soils provided that the native soils contain no angular rocks or rocks larger than 2'h inches in diameter to help prevent settlement of the pipe. Sags in the piping could cause standing effluent to freeze and damage the pipe. • A minimum 24 inches of cover soil should be provided over the effluent transport pipe . Paved areas, patios or other paved area or areas without vegetative cover may be more susceptible to freezing. We recommend 48 inches of soil cover over the pipe in these areas. If adequate cover soil is not possible the effluent pipe should be insulated on top and sides with 2 inch thick foam insulation board, and we should re-evaluate the proposed soil cover prior to installation . • Schedule 40 PVC pipe should be used underneath driveway surfaces and be provided with at least 48 inches of soil cover, and insulated on top and sides with 2 inch thick foam insulation board. Job No. 115 0698 -----· . --··-----· . ---· -- -7- • All 90 degree bends should be installed using a 90 degree long-sweep or by using two 45 degree elbows. Distribution Box • To ensure equal effluent distribution a distribution box will be used to divide effluent flow. We recommend the Fralo Monster distribution box since it is easily accessible from ground surface for maintenance with a Fralo septic tank lid system. • The distribution box must be accessible from ground surface for inspection and maintenance per 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. • We recommend that the distribution box be equipped with Tuf-Tite speed levelers for ease of initial setup and adjustment over time. • The distribution box must be installed level on a compacted granular soil 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 premature failure . The distribution box should be monitored periodically and the speed levelers should be adjusted as necessary. The ground surface above and around the distribution box should be graded to prevent standing water at or near the box. 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 reconunendations for the OWfS O&M. Job No. llS 0698 - 8 - 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 household 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. • 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. • The effiuent in septic tanks can freeze during extended periods of non-use in cold weather. We recommend that a tank heater be installed in this system to help prevent freezing. OWTS MAINTENANCE • Inspect the septic tank, effluent filter and soil treatment area at least annually for problems or signs of failure. Job No . J l S 0698 -------------------------·--- -9- • Tue effluent filter should be cleaned annually by spray washing solids into the first chamber of the septic tank. • 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 soil ST A, which may shorten its life span. • Pumping of the septic tank should take place when the Level of the sludge and sewn layers combined take up 25 to 33% of the capacity of the first chamber of the tank. OWTS CONSTRUCTION OBSERVATION The Garfield County Environmental Building Department requires that the designer of the system provide an As-Built certification of the OWTS construction. We should be provided with at least 48 hour notice prior to the installer needing the As-Built 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. 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, percolation test holes, 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 encoWltered 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 monitor the implementation of our recommendations, and to Job No. 115 069B -10- verify that the recommendations have been appropriately interpreted. Significant design changes may require additional analysis or modifications to our design. It is our opinion that the designed location of the OWTS components does not violate any setback requirements of the current Garfield County Regulations. Below is a table of common minimum horizontal setbacks to OWTS components. Refer to the Garfield County Regulations for a complete list of required setbacks. We recommend the OWTS components be surveyed by a Professional Colorado Land Surveyor and verified by H-P Geotech prior to the system permitting. Table I -Common Minimum Horizontal Setbacks from OWTS Components Water Lined Lake, Dry Wells Supply Occupied Ditch Irrigation Ditch Septic Linc Dwelling or Lake Ditch, or Tank Stream Gulch STA 100' 25' 20 ' 20' 50' 25' 5' Septic 50' 10 ' 5' 10' 50' 10' -Tank Building 50' 10' O' 10' 50' 10' -Sewer Please contact us for any necessary revisions or discussion after review of this report by Garfield County. If you have any questions, or if we may be of further assistance, please let us know Respectfully Submitted, HEPWORTH -PAWLAK GEOTECHNICAL, INC. fa0/V<-~ <@ Jason A. Deem Project Geologist Job No . 115 0698 APPROXIMATE SCALE : 1 INCH = 40 FEET \ 115 0696 ~tech HEPWORTH-PAWLAK GEO"ll:CHNICAL LOT 13, ELK SPRINGS, FILING 2 owrs SITE PLAN FIGURE 1 a w z ~ w a:: I-z w u a:: w a.. SIEVE ANALYSIS I HYOAOMETER ANAL YS!S I CLEAR SQUARE OPENINGS I 2 R. 7 HR Tl~E READINGS 1 MIN. O 4~ ~IN.15 MIN. 60MINl9MIN.4 MIN. #325 U.S. STANDARD SERIES I #60 #35 #18 #10 #4 #140 3/8' 314• 1 1~ 3' 5'6' 8' 100 10 90 20 80 30 70 40 60 50 50 - 60 40 70 30 80 20 90 10 100 .001 .002 .005 .009 .019 .045 0 .106 .025 .500 1.00 2.00 4.75 9.5 19.0 37.5 76 .2 152 203 W.Y I DIAMETER OF PARTICLES IN Mll..LIM:TERS S:Lf GRAVEL 51 % SAND 24 % Passing #1 O Gradation: SAND 49 % USDA SOIL TYPE: Very Gravelly Loam SILT 16 % SILT 33 % CLA.Y 9 % CLA.Y 18 % FROM: Profile Pit 2 at 2 to 3 Feet {.!) z vs U> < a.. I-z l.&J (..) 0:: w a.. 115 0698 ~tech LOT 13, ELK SPRINGS, FILING 2 USDA GRADATION TEST RESULTS FIGURE2 HEPWORTH·PAWLAK GEOTECHNICAL OWTS ABSORPTION AREA CALCULATIONS In accordance wth the current Garfiekf County Onste Wastev.iater Treatment System Regulaoons, the son treabnent area was catulated as folbws: CALCULATION OF OWIS DESIGN FLOW: Q = (F)(B)(N) WHERE: Q = DESIGN FLOW F =AVERAGE FLOW PER PERSON PER DAY B =NUMBER.OF BEDROOMS N = NUMBER OF PERSONS PER BEDROOM F= B= N= Q= CALCULATION OF OWTS SOIL TREATMENT AREA: MINIUMUM TREATMENT AREA• Q + LTAR WHERE: Q• LTAR• MINIMUM ABSORPTION AREA= REDUCTION FACTOR FOR CHAMBERS = MINIMUM ABSORPTION AREA WITH REDUCTION = AREA PER INFILTRATOR QUICK 4 STANDARD CHAMBER= TOT AL CHAMBERS NEEDED = ROWS OF CHAMBERS = CHAMBERS PER ROW = TOTAL SOIL TREATMENT AREA= 75 GALLONS PER DAY 3 BEDROOMS 2 PERSONS PER BEDROOM 450 GALLONS PER DAY 450 GALLONS PER DAY 0.5 GALLONS/FT 2/0AY 900.0 SQUARE FEET 0.70 630 SQUARE FEET 12 SQUARE FEET 53 CHAMBERS 3 CHAMBERS 18 CHAMBERS 648 SQUARE FEET 115 0698 ~tech HEPWORTH·PAWLAK GEOTECHNICAL LOT 13, ELK SPRINGS, FILING 2 SOIL TREATMENT AREA CALCULATIONS FIGURE3 NOTTO SCALE 115 0698 INFILTRATOR QUICK4 PLUS STANDARD CHAMBERS INSTAU.ED LEVEL ALONG CONTOUR. THREE ROWS OF 18 CHAMBERS (54 CHAMBERS TOTAL). 4 INCH DIAMETER PVC INSPECTION POAT INSTALLED VERTICALLY INTO KNOCKOUTS PROVIDED IN END CAPS . INSTALL INSPECTION PORTSAT EACH END OF EACH TRENCH (6 TOTAL INSPECTION PORTS). REMOVABLE LIO TO BE PLACED ON TOP OF PIPE. PIPE MUST STICK UP AT LEAST 8 INCHES ABOVE FINISHED GRADE OR BE INSTALLED IN A VALVE BOX AT GRADE. ~ 4" NON-PERFORATED SOR35 TRANSPORT PIPE SLOPED AT 2% MIN . DOWN TO D·BOX lliEN TO EACH TRENCH TRANSPORT PIPING SHOULD BE INSERTED AT LEAST 6 INCHES INTO THE UPPER KNOCKOUT IN THE CHAMBER END PLATES. INSTALL SPLASH PLATES BENEATH INLET PIPING TO HELP PREVENT SCOURING OF THE INFILTRATIVE SURFACE. INFILTRATOR QUICK4 PLUS STANDARD END CAPS AT EACH END OF EACH TRENCH 1. Chambers should be installed lever on a scarified ground surface. 2. AU piping should have a rating of SDA35 or stronger. 3. Changes to this design should not be made without consultat ion and approval by HP Geotech . ~£tech H!?PWORTH-PAWL.AK GEOT£CHNICAL LOT 13, ELK SPRINGS, FILING 2 SOIL TREATMENT AREA PLAN VIEW FIGURE4 -- Net:vo SOI 12" min. 24" max . Cover Soil Graded to Deflect Surface Water ) APPROXIMATE SCALE : 1 INCH = 5 FEET 115 0698 ~cbtech Infiltrator Quick 4 Plus Standard End Cap Notes: S'mi n. -Urdisturbed Soil Between-- Trenches Infiltrator Quick 4 Standard Chamber Installed Level Appg, E.ls lina ~ \ N•M~ l Scarify bottom and sides of trenches before chamber installation T°Chambers should be inslalled level on a scarified ground sur1ace The ba se and side of the trenches should be scarified prior lo chamber inslallation 2. Care should be taken by the contractor to avoid compaction ol the native soils in the tre nc h areas . 3. Changes to this design should not be made without consu tat1on and approval by HP Geotech. FIGURE 5 HS:PWORTl+PA WLAK GEOTEC HMICAL LOT 13, ELK SPRINGS, FILING 2 SOIL TREATMENT AREA CROSS SECTION ' ' Item# 1000T-2CP QES!GN NOJES • De:slgn p1111r performance test per ASTM C1227 • Top surface area 46.25 ft1 • ( c 0 28 doy.i; concrete "' 6,000 PSI Mio. lns!gl!gl!on• • Tonk to be set on s• min. aond bed or pea grovel • Tonk to be backfilled uniformly on oil sides In llfls IHs than 24" ond mechonlcolly compacted • Excavated moterlol may be used for bockflll, pro\4ded large stones are removed • Exeavotlori should bG dewotered and tonk fnled with waler prior to being put In aervlce for lnstctllotlon with water table less than 2' below CJl'Ode • Meeta C164+-06 far resQlent connectors • Inlet and Outlet Identified 01>0119 pips • Delivered complete with lnlemol pfplng • PVC or concrete rls81'$ 0YC1lloble • Secondary safety screen available wllh PVC riser • Option of pump or siphon Installed ALLOWABLE BURY (Based on Water Tobie) WAlER TAB1£ AU.urrABI.£ £AR11'1 RLL O' -o• 2· -o· 1· -o· 3' -o· 2· -o· 3' -Cl' 3' -o· 4' -0- DRY 4' -Cl' 1000 Gallon Top Seam Two Compartment 6 • .... Top View Section View [-·---·--·-··-·--·-·,-----------~---------·--1 Digging Spm '"""'' Dlmml~• Net Copocity ;J Net Weight ;l l~~~~~~~~t ~.'~: _~~.-~~~~f~;~p~'f ::~:·1t~~l~~·~ .~~~:1;~~~·.I~:, .. ! Water & (71I) 395-8784 28005Co. Rd. 317 Wastewater P.O. Balc925 . 0 v ALLEY : =: Fax: (719) 395-3727 BuenaVlsl1\ 0081211 J 0 PRECAST Inc o Service Webde: W\W/.vallsyprecastcom ' • Emal: fmntdesk@valfeyprecast.com •