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Home My WebLink AboutOWTS Design Report 08.27.2009Gtech HEPWORTH - PAWLAK GEOTECHNICAL Hepworth-Pawlak Geotechnical, Inc. P. 0. Drawer 1887 Silverthorne, Colorado 80498 Phone: 970-468-1989 Fax: 970-468-5891 email: hpgeo4@hpgeotech.com ONSITE WASTEWATER TREATMENT SYSTEM DESIGN EXISTING RESIDENCE 0151 OAKCREST LANE GARFIELD COUNTY, COLORADO JOB NO. 409 172A AUGUST 27, 2009 PREPARED FOR: ADAM MCPHERSON 0151 OAKCREST LANE GLENWOOD SPRINGS, COLORADO 81601 Glenwood Springs 970-945-7988 • Parker 303-841-7119 • Colorado Springs 719-633-5562 TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY - 1 - SITE CONDITIONS - 1 - SUBSURFACE CONDITIONS - 1 - OWTS ANALYSIS - 2 - SEPTIC TANK - 2 - SEWER AND EFFLUENT PIPING - 3 - DISTRIBUTION BOX - 4 - ABSORPTION AREA - 4 - SUBSURFACE DRAINAGE - 5 - OWTS MAINTENANCE - 5 - LIMITATIONS - 6 - FIGURES FIGURE 1- OWTS SITE PLAN FIGURE 2 - LOG OF PROFILE PIT FIGURE 3 - GRADATION TEST RESULTS FIGURE 4 - ABSORPTION AREA CALCULATIONS FIGURE 5 - ABSORPTION AREA PLAN VIEW FIGURE 6 - ABSORPTION AREA CROSS SECTION ATTACHMENTS VALLEY PRECAST SEPTIC TANK DETAIL Job No. 409 172A PURPOSE AND SCOPE OF STUDY As requested, I lepworth-l'awlak Geotechnical, Inc. has designed an Onsite Wastewater Treatment System (OWTS), based on the subsurface conditions, observed for the existing residence located at 0151 Oakcrest Lane in Garfield County, Colorado. The study was conducted in accordance with our written agreement to Adam McPherson dated June 25, 2009. The data obtained and our OWTS design recommendations based on the proposed construction and subsurface conditions encountered are presented in this report. SITE CONDITIONS The project site slopes gently to steeply down to the west and site vegetation consists primarily of scrub oak trees and grasses. Water service is provided to the residence by a community water supply system. The existing residence has three bedrooms and an OWTS that was designed by Garfield County that is 481 square feet consisting of three trenches with seven Infiltrator chambers in each trench. The OWTS also contains a two chamber 1,000 gallon septic tank. The residence is being expanded to a total of five bedrooms. SUBSURFACE CONDITIONS A representative of H -P Geotech observed a profile pit at the subject property on June 26, 2009. The soils exposed in the profile pit consist of about 2 feet of topsoil overlying slightly gravelly, slightly sandy, clayey silt to the depth explored of about 8 feet. A graphic log of the subsurface conditions encountered in the profile pit is shown on Figure 2. A bulk composite sample of the subsoils was collected from the profile pit at 3 to 4 feet below ground surface. Results of gradation analyses performed on small diameter hand drive samples (minus 1.5 inch fraction) are shown on Figure 3. Due the high percentages of silt and clay in the sample, percolation tests were not considered feasible; therefore, a subsurface sand filter will be constructed at the site. Sizing of the sand filter will be based on a sand filter loading rate for a residence with a garbage grinder of 0.95 gallons per square foot per day. Absorption area calculations are shown on Figure 4. Job No. 409 172A -2- OWTS ANALYSIS Based on the subsurface conditions encountered and the LTAR, the tested area is suitable for an OWTS utilizing a subsurface sand filter for the treatment and dispersal of effluent. A site plan showing the approximate location of the existing OWTS, proposed OWTS, existing residence and the minimum horizontal setback distances of site features relative to the OWTS components is shown on Figure 1. The OWTS was designed for a total of five bedrooms. All materials and installation should meet the requirements of the current Colorado State Board of Health's Guidelines on Individual Sewage Disposal Systems SEPTIC TANK A two chamber, 1,000 gallon concrete septic tank is currently in place at the residence; however, it is not large enough to meet the requirements of the additional bedrooms. The existing tank should be abandoned by first pumping the tank, then breaking the bottom and backfilling with onsite soil. A new concrete 1,500 gallon, two chamber Valley Precast septic tank, or equivalent, will be used for primary treatment of sewage from the residence. A copy of the Valley Precast tank detail has been provided as an attachment. An effluent filter will be installed on the outlet of the second chamber of the septic tank. Sewage will gravity feed from the residence to the septic tank and effluent will be gravity fed to the absorption area. If the septic tank access riser lids will be installed at grade, with no backfill cover, then the lids should be insulated with foam insulation board to provide frost protection. The sewer pipe inlet tee in the first chamber of the septic tank should be installed beneath the access lid of the first chamber of the septic tank so that it can be reached for service should it become clogged. The PVC handle on the effluent filter should be extended up to within reach of the septic tank access riser lid. This will allow for easy access and maintenance of the filter. Approximately 2 feet of soil backfill cover should be placed over the tops of the septic tank to allow for easy access and frost protection. For maintenance reasons, deep tank installations should be avoided and we should be contacted to evaluate this OWTS design should it appear that a deep tank installation involving more than 4 feet of backfill soil over the top of the septic tank will be required. Job No. 409 172A -3 - SEWER AND EFFLUENT PIPING The sewer line from the proposed residence to the septic tank should not be less than the diameter of the building drain and not less than 4 inches in diameter and will service all levels of the residence. The sewer pipe should be adequately bedded in 3/4 inch or smaller washed or screened aggregate or native soils provided that the native soils contain no angular rocks or rocks larger than 2 %2 inches in diameter. Backfill of aggregate or native soils must be compacted to prevent settlement of the pipe. The sewer pipe should be installed in landscape areas with at least 40 inches of soil backfill covering the pipe, or the pipe should be insulated on the top and sides with 2 inch thick rigid foam insulation board for frost protection. Beneath driven surfaces we recommend using Schedule 40 PVC sewer pipe. The pipe should be insulated if it will be installed with less than 40 inches of backfill soil cover. We recommend using Schedule 40 PVC pipe between the residence and the septic tank, though this is not required by local regulations. The portion of the sewer pipe extending from 5 feet outside the building foundation should have a slope of at least 2% except for the last 10 feet of sewer pipe immediately preceding the septic tank which should be sloped between 1% and 2%. Cleanout pipes should be installed in the sewer line adjacent from the building foundation, adjacent to the inlet of the septic tank, where the sewer pipe bends at 90 degrees or more and at least one cleanout should be installed at least every 100 linear feet of non - pressurized sewer or effluent pipe throughout its length. We recommend that a straight section of pipe be installed between the residence foundation and the septic tank. Any required 90 degree bends in the sewer pipe should be accomplished through the use of a series of 45 degree smooth elbows or a 90 degree long sweep to help prevent clogging of the pipe. The 4 inch diameter PVC transport pipe should be sloped at 2% minimum to drain to the distribution box. It is critical that the effluent transport pipe be properly bedded to reduce settlement in the pipe. Sags in the transport pipe will increase the risk of effluent freezing. Job No. 409 172A -7 - should be installed including: sewer pipe, effluent pipe, septic tank, effluent filter, inlet and outlet tees, sand, Infiltrator chambers and distribution and manifold piping. No components of the OWTS should be backfilled prior to our performing the OWTS As - built evaluation. Please contact us for any necessary revisions or discussion after review of this report by the Garfield County Environmental Building and Sanitation Department. If you have any questions, or if we may be of further assistance, please let us know. Sincerely, HEPWORTH - PAWLAK GEOTECHNICAL, INC. Jason Deem Project Geologist Reviewed by: Ronald J. Uhle, P.E. Associate Job No. 409 172A FIELD TO: PROPERTY UNES TANK HOUSE WATER UNES SURFACE WATER DRY DITCHES WELLS IRRIGATION DITCH EXISTING FIELDS CUT BANKS Oak Crest Lane North Lasting Indy:sped Wane Existing &Newsy EXISTING ABSORPTION AREA CONSISTING OF THREE ROWS OF SEVEN CHAMBERS. EXACT LOCATION AND ORIENTATION IS UNKNOWN. PROPOSED SUBSURFACE SAND FILTER ABSORPTION BED 6 CHAMBERS WIDE BY 13 CHAMBERS LONG SEPARATED INTO TWO ZONES 0 EXISTING SEPTIC TANK TO BE ABANDONED 0 4,M14.v .t MINIMUM HORIZONTAL DISTANCES TANK TO: 10' HOUSE 6' WATER UNES SURFACE WATER DRY DITCHES WELLS PROPERTY UNES 20' 25' 50' • 25' • 100' • 50' ■ 20' 4X VERT. CUT HEIGHT 5' 10' 50' 10' 50' 10' BUILDING SEWER T0: WATER UNES 10' WELLS 50' • ADD 6 FT. FOR EACH 100 GAL / DAY DESIGN FLOW OVER 1,000 GAL / DAY. DISTRIBUTION BOX --- WITH ONE INLET AND THREE OUTLETS PROPOSED VALLEY PRECAST 1,500 GALLON, TWO CHAMBER SEPTIC TANK EQUIPPED WITH AN EFFLUENT FILTER AT THE OUTLET OF THE SECOND CHAMBER CLEANOUT (TYP.) APPROXIMATE SCALE 1 INCH = 30 FEET 0151 OAKCREST LANE OWTS SITE PLAN Gtech HEPWORTH-PAWLAK GEOTECHNICAL 409 172A FIGURE 1 Depth - Feet 0 5 PROFILE PIT Composi!e Sample + 4=7 -200=82 0 5 10 10 15 15 LEGEND: TOPSOIL; silty, clayey with organics, stiff, moist, dark brown. Sl 2" Diameter hand driven liner sample. -L Depth - Feet SILT (ML); clayey, sandy with scattered basalt cobbles and boulders, stiff, moist, brown. NOTES: 1. The profile pit was excavated on June 26, 2009 with a trackhoe. 2. The location of profile pit was measured approximately by taping from features shown on the site plan provided. 3. The elevation of profile pit was not measured and the log is drawn to depth. 4. The profile pit location should be considered accurate only to the degree implied by the method used. 5. The lines between materials shown on the profile pit log represent the approximate boundaries between material types and transitions may be gradual. 6. No free water was encountered in the pit at the time of excavation. Fluctuation in water level may occur with time. 7. Laboratory Testing Results: +4 = Percent retained on the No. 4 sieve -200 = Percent passing No. 200 sieve 409172A Gtech HEPWORTH-PAWLAK GEOTECHNICAL 0151 OAKCREST LANE LOG OF PROFILE PIT FIGURE 2 SIEVE ANALYSIS HYDROMETER ANALYSIS CLEAR SQUARE OPENINGS 100 6" es. 3" 90 60 70 80 50 40 30 20 10 0 1.5' .75" •5"3 S" U.S. STANDARD SERIES e Cd 116 (30 0 f 00 TIME READINGS 7FR 24HR 200 1 MIN. 4 MIN. 19 MIN. 60 MIN. 15 MIN 45 MN VMM 203 152 76.2 37.5 19.0 9.5 4.75 2.36 1.18 .800 .300 .150 .074 .037 .019 .009 .005 127 COBBLES 12.5 GRAVEL COARSE 1 FINE GRAVEL 7% DIAMETER OF PARTICLES IN MILLIMETERS SAND COARSE_1 MEDIUM 1 SAND 11% FINE CLAY TO SILT SILT 53% CLAY 29% .002 10 20 30 40 50 60 70 80 90 100 IgMganaX 11 AC SAMPLE OF: Slightly Sandy, Slightly Gravelly, Clayey Silt (ML) FROM: Profile Pit, Composite Sample 3 to 4' 409 172A Gtech HEPWORTH-PAWLAK GEOTECHNICAL 0151 OAKCREST LANE GRADATION TEST RESULTS FIGURE 3 OWTS ABSORPTION AREA CALCULATIONS In accordance with the current Colorado State Board of Health's Guidelines on Individual Sewage Disposal Systems, the required absorption area was calculated as follows: Q = (F)(B)(N)(1.5) TOTAL DESIGN FLOW: F = AVERAGE FLOW PER PERSON PER DAY= B = TOTAL NUMBER BEDROOMS = N = ESTIMATED NUMBER OF PERSONS PER BEDROOM = ESTIMATED DESIGN FLOW EQUAL TO 150% OF AVERAGE DAILY SEWAGE FLOW IN GALLONS PER DAY = Q = TOTAL DESIGN FLOW = \BSORPTION AREA CALCULATIONS: LOADING RATE FOR SUBSURFACE SAND FILTER W/ GARBAGE GRINDER = ABSORPTION AREA INCREASE FACTOR OF SAFETY= -- A= Q(l.5) LTAR = MINIMUM ABSORPTION AREA SIZE = ABSORPTION BED DIMENSIONS: AMOUNT OF ABSORPTION AREA GIVEN TO EACH CHAMBER= MINIMUM NUMBER OF CHAMBERS = NUMBER OF ROWS = NUMBER OF CHAMBERS PER ROW = TOTAL NUMBER OF CHAMBERS = A =ACTUAL ABSORPTION AREA SIZE= NOTE: 1. INFILTRATOR QUICK 4 STANDARD CHAMBERS WILL BE USED. 75 GALLONS PER DAY 2 1.5 450 GALLONS PER DAY 0.95 GALLONS PER DAY PER SQI A RE FOOT 1.5 711 SQUAREFEEI' 9.2 SQUARE FEET 78 6. 13 78 718 SQUAREFEEI' 409 172A Gtech HEPWORTH-PAWLAK GEOTECHNICAL 0151 OAKCREST LANE ABSORPTION AREA CALCULATIONS FIGURE 4 (TYP.) 4" DIAMETER PVC AIR VENT INSTALLED VERTICALLY IN THE KNOCKOUTS PROVIDED IN THE CHAMBERS AT EACH CORNER OF THE ABSORPTION BED. REMOVABLE COVER TO BE PLACED ON TOP OF PIPE. TOP OF PIPE TO BE VENTILATED WITH AT LEAST TWELVE, Y2" INCH HOLES. VENT SHOULD STICK UP AT LEAST 8" FROM FINISHED GRADE. DISTRIBUTION LATERALS CONSISTING OF 4 INCH DIAMETER PERFORATED PVC PIPE WITH Y2 INCH DIAMETER ROUND HOLES SPACED 6 INCHES APART. TWO ROWS OF PERFORATIONS PLACED SYMETRICALLY ON BOTH SIDES OF PIPE IN ACCORDANCE WITH ASTM D-3034 SPECIFICATIONS. SEE DETAIL BELOW. DRILL ONE Y2 INCH DIAMETER HOLE AT EACH END OF EACH LATERAL FOR DRAINAGE. CROSS-SECTION DISTRIBUTION LATERAL PERFORATION PERFORATION 120 DEGREES BETWEEN PERFORATIONS PROPOSED SUBSURFACE SAND FILTER ABSORPTION BED 6 CHAMBERS WIDE BY 13 CHAMBERS LONG SEPARATED INTO TWO ZONES. CHAMBERS TO BE INSTALLED LEVEL. 4 INCH DIAMETER PVC MANIFOLD PIPE INSTALLED LEVEL 4 INCH DIAMETER PVC PIPE SLOPED AT 2% MIN. TO EACH MANIFOLD DISTRIBUTION BOX WITH ONE INLET AND THREE OUTLETS INSTALLED LEVEL APPROXIMATE SCALE 1 INCH = 10 FEET NOTES: 1. ALL MATERIALS AND INSTALLATION METHODS SHOULD MEET THE CURRENT COLORADO STATE BOARD OF HEALTH'S GUIDELINES ON INDIVIDUAL SEWAGE DISPOSAL SYSTEMS. 2. INFILTRATOR QUICK 4 STANDARD CHAMBERS WILL BE USED UNLESS OTHERWISE APPROVED BY H -P GEOTECH. 3. ALL PIPING TO BE SDR 35 OR STRONGER. 0151 OAKCREST LANE ABSORPTION AREA PLAN VIEW Gtech HEPWORTH-PAWLAK GEOTECHNICAL 409 172A FIGURE 5 Item# 1500T-2CP 1500 Gallon Tank Two Compartment - Top Seam Top View Section View 132" r 1 Butyl Rubber Sealant 20" Clear Access (Big Hole Lid & Riser) \Flexible Boot 1 4" 5" n 0) ❖Meets ASTM C-1227 spec including the new C-1644-06 for resilient connectors • 4000 psi concrete • Delivered complete with internal piping • PVC or concrete risers available • Can be ordered with a pump or dosing siphon installed IFF VALLEY PRECAST, inc. 129" Digging Specs Invert Dimensions 13' Long x 8' Wide 56" below inlet Inlet Outlet Len th Width Hei ht 56" 53" 132" 68" 68" Net Capacity Net Weight Lid Tank Total 1,509 gallons 3,600 lbs 10,840 lbs 14,440 lbs Water & Wastewater • Systems • Products • Service (719) 395-6764 28105 County Road 317 P.O. Box 925 Fax: (719) 395-3727 Buena Vista, CO 81211 Website: http://valleyprecast.com/ Email: frontdesk@valleyprecast.com