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HomeMy WebLinkAboutOWTS 4-30-14HEPWORTH-PAWLAK GEOTECHNICAL_ t 11,.l t. .� , , I I .I, ,;, ', :III II ONSITE WASTEWATER TREATMENT SYSTEM DESIGN EXISTING INDUSTRIAL BUILDING LOT 4, COKE OVENS EXEMPTION 0755 AIRPORT ROAD GARFIELD COUNTY, COLORADO JOB NO. 114 080A APRIL 30, 2014 PREPARED FOR: PITKIN IRON ATTN: ROB DELANEY P. O. BOX 1298 GLENWOOD SPRINGS, COLORADO 81602 r0b(r -l)iikin1r on.con huker 303-841-7119 • Culorado Spring=, 719-633-5562 • Sih'ertlitrrne 970-468-1980 TABLE OF CONTENTS INTRODUCTION - 1 - SITE CONDITIONS - I - SUBSURFACE CONDITIONS _ PERCOLATION TESTING 2 2 - OWTS ANALYSIS -2- DESIGN RECOMMENDATIONS SOIL TREATMENT AREA - 3 - OWTS COMPONENTS - 3 Septic Tank 4 Sewer Pipe - 4' Effluent Transport Piping - 4 - - 5 - OWTS OPERATION AND MAINTENANCE OWTS OPERATION - 5 - OWTS MAINTENANCE - 6 - - 6 - OWTS CONSTRUCTION OBSERVATION -7- LIMITATIONS -7- FIGURE 1 — SITE LOCATION PLAN FIGURE 2 — OWTS SITE PLAN FIGURE 3 — ABSOPRTION AREA CALCULATIONS FIGURE 4 — ABSORPTION AREA PLAN VIEW FIGURE 5 — ABSORPTION AREA CROSS SECTION TABLE 1 - PERCOLATION TEST RESULTS ATTACHMENTS PITKIN IRON PUMPING RECORDS Job No. 114 080A Gtech INTRODUCTION This report provides an onsite wastewater treatment system (OWTS) design for the existing commercial building located at 755 Airport Road near Glenwood Springs in Garfield County, Colorado, The purpose of this report was to explore the subsurface conditions at the site and provide design details for an OWTS in accordance with current Garfield County Individual Sewage Disposal System Regulations. DESIGN SUMMARY The existing soil treatment area on the property has failed and the owner is currently utilizing the existing septic tank as a vault. There is no water supply to the property, therefore, water use is limited. We have designed a new gravity flow soil absorption treatment area (STA) that utilizes the existing septic tank. Sewage will continue to flow to the existing septic tank and the effluent will then gravity flow to the soil treatment area. The STA will consist of Infiltrator chambers in a single trench. Design flow was based on the vault tank pumping records provided to us. SITE CONDITIONS The property is the current location of the Pitkin Iron facility, which is a custom steel fabrication business. There is an existing metal office and shop structure on the property that is approximately 120 feet long by 80 feet wide, see Figure 1. There are a variety of other sheds, steel racks and storage areas throughout the property. There is no water service at the property. Water is trucked in to the site for limited use primarily for bathrooms. The site has been generally graded flat. Most of the site is developed with sheds, steel racks and other storage areas. Access roads are located throughout the property. There are no water wells near the site that we are aware of. Job No. 114 080A GecPtech -2 - SUBSURFACE CONDITIONS The field exploration for the project was conducted on March 24, 2013. One Profile Pit and three percolation test holes (P-1, P-2 and P-3) were excavated at the approximate locations shown on Figure 1 to evaluate the subsurface conditions. The pit was logged by a representative of Hepworth-Pawlak Geotechnical (H -P Geotech). No free water was encountered during our observations and the soils were generally moist. A log of the Profile Pit is provided below. 710 Log of Profile Pit 0-7' CS01.. i001.0ps (GreltH '1)61; SAND AND GRAVEL (SC -GC); clayey with cobbles and boulders, medium dense, slightly moist, brown. • Bottom of pit @ 7feet. • No free water was observed in the pit at the time of observation. PERCOLATION TESTING Percolation tests were performed in three test holes by a representative of H -P Geotech on March 24, 2014. The tests were completed at depths of 32 to 42 inches below the adjacent ground surface. The percolation test results, provided in Table 1 indicate an average percolation rates in each test hole of 40 minutes per inch with an overall average design percolation rate of 40 minutes per inch. The design percolation rate corresponds to a Long -Term Acceptance Rate of 0.4 gallons per square foot per day. OWTS ANALYSIS The subsurface subsoil conditions at the site are suitable for a conventional absorption system consisting of infiltrators in a trench configuration using the natural soils for final disposal of the effluent. Based on our site observations and the site contours, it appears gravity flow from the tank to the soil treatment area is feasible. The existing tank appears adequate for incorporation into the system and will be used for primary treatment. A long term acceptance rate (LTAR) of 0.40 will be used to size the absorption field. The system Job No. 114 080A Gtech -3 - will be designed on water usage as approximated from the pumping records for the existing tank being used to collect disposed water from the building. DESIGN RECOMMENDATIONS The recommendations presented below are based on the site and subsurface conditions, the proposed construction and our experience in the area. If conditions encountered during construction are different than those that are described in this report please contact us and we will re-evaluate our recommendations. SOIL TREATMENT AREA • The soil treatment area will be 138 square feet and will consist of one trench with 14 Infiltrator Quick 4 Standard chambers. • Since the site has no water supply and limited water use, the estimated design flows based on the pumping records from January 20, 2012 through September 30, 2013, the 1,000 gallon tank was pumped on average every 28 days. This equates to an average daily flow of 35.7 gallons per day. Design flow is 150% of the average daily flow or 54 gallons per day. Absorption area calculations are presented on Figure 3. • An area of 9.87 square feet was applied for each chamber per Garfield County guidelines. • No reductions in absorption area size were applied. • A minimum of 12 inches and a maximum of 36 inches of cover soil should be placed over the infiltration chambers. • Backfill should be graded to deflect surface water away from the absorption area and should be sloped at 3H:1 V maximum. • The trench backfill and nearby disturbed soil should be re -vegetated immediately 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 infiltrators and piping. • Four inch diameter inspection ports should be installed at each end of the trench. The inspection port piping should be placed in the knockouts provided in the Job No. 114 080A GFPtech -4 - chambers. The inspection ports should extent at least 8 inches above the final graded ground surface. At least twelve, 1/2 inch holes should be drilled in the above grade portion of the inspectionports for ventilation. • A plan view of the design absorption area is provided as shown on Figure 4 and a cross section of the absorption area is presented provided as shown on Figure 5. • Due to the potential for vehicular traffic in the area of the proposed soil treatment area, we recommend the area be protected with bollards or fencing. Vehicular traffic can lead to premature failure of the soil treatment area. OWTS COMPONENTS Recommended OWTS components were based on our design details and our experience with the specific component manufacturers. Equivalent components may be used if desired; however, they must meet our minimum recommendations and should be verified by the design engineer. Septic Tank • There is an existing 1,000 gallon, two chamber concrete septic tank being utilized on the property. We have proposed to continue to utilize the existing septic tank for primary treatment due to limited non -traffic areas for a new tank, and the existing tank appears to be performing adequately. • An effluent filter should be installed in the septic tank outlet tee. • The existing tank does not meet the required 10 foot setback to the property boundary as shown on Figure 2; however, the owner would like to petition for continued use of the previously approved location. D • Due to the potential for vehicular traffic in the area of the existing septic tank, we recommend the location be protected with bollards or fencing. The tank is not likely traffic rated and could become damaged by heavy loads that frequent the property. Sewer Pipe • The existing sewer line from the building to the septic tank will remain. We did not verify the construction or condition of the pipe. Job No. 114 080A Gtech -5- • A cleanout was not observed where the sewer line exits the building. We recommend a cleanout be installed within 5 feet of the structure. It may be desirable to provide a new pipe depending on the condition of the exposed pipe. Effluent Transport Piping • The 4 inch diameter non -perforated SDR35 effluent transport piping should be sloped at 2% minimum to drain to the soil treatment area. • 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 2A inches in diameter to help prevent settlement of the pipe. Sags could cause standing effluent to freeze and damage piping. • A minimum 24 inches of soil cover should be provided over the effluent transport pipe. Paved areas, patiosor other areas without vegetative cover may be more susceptible to frost. We recommend at least 48 inches of soil cover over the sewer pipe in these areas. If adequate cover soil is not possible the sewer pipe should be insulated on top and sides with 2 inch thick foam insulation board and the design engineer should re-evaluate soil cover prior to installation. • The sewer pipe should be double encased with larger diameter Schedule 40 PVC pipe underneath driveway surfaces and be provided with at least 48 inches of soil cover. • All 90 degree bends should be installed using a 90 degree long -sweep or by using two 45 degree elbows. 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 with 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 for the system to ensure that it is properly maintained. Depending on the complexity of the system a contract with an OWTS maintenance provider may also be prudent. Below are some basic recommendations for OWTS O&M. Job No. 114 080A GecPtech -6- OWTS OPERATION • 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 treatment absorption area as this may cause hydraulic overload. • Do not dispose of waste down drains as this may clog or damage OWTS components. Examples of waste that should not be disposed of in drains include: dental floss, cotton swabs, coffee grounds, paper towels, feminine products and many other kitchen and bath items. If a garbage disposal is utilized, wastewater should be screened thoroughly. • Do not dispose of chemicals, greases, oils, paints, hot tub water or water softener backwash in household drains. • Limit the use of bleach as this may harm useful bacteria in the septic tank and soil absorption system. • The water in septic tanks can freeze during extended periods of non-use. A tank heater could be provided to help prevent freezing. OWTS MAINTENANCE • Inspect the septic tank, effluent filter and soil absorption area at least annually for problems or signs of failure. • The effluent filter should be cleaned annually by spray washing solids from the filter 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 absorption area, which may shorten its life span. • Pumping should take place when the level of the sludge and scum layers combined take up about 25 to 33% of the capacity of the first chamber of the septic tank. Job No. 114 080A GecPtech -7- OWTS CONSTRUCTION OBSERVATION Due to the relatively tight setback constraints on the site, we recommend that all OWTS components be field staked and verified by a representative of H -P Geotech prior to starting excavation. Following confirmation of component locations, the Garfield County Building Department requires that the design engineer perform an As -Built inspection of the OWTS. Prior to inspection, all system components should be installed, but not backfilled. No components should be backfilled without prior approval by H -P Geotech. LIMITATIONS This design study has been performed in accordance with generally accepted engineering principles and practices in this area at this time. We make no warranty either expressed or implied. The conclusions and recommendations submitted in this report are based upon the data obtained from the profile pit and percolation test holes, the proposed type of 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 monitor the implementation of our recommendations, and to verify that the recommendations have been appropriately interpreted. Significant design changes may require additional analysis or modifications to the recommendations presented herein. It is our opinion that the designed location of the OWTS does not violate any setback requirements of the current Garfield County Individual Sewage Disposal System (ISDS) Regulations of any features that are offsite. Below is a table of common minimum horizontal setbacks to OWTS components. Refer to the Garfield County ISDS Regulations for a complete list of required setbacks. We recommend the OWTS Job No. 114 080A Gtech -8 - components be surveyed by a Professional Colorado Land Surveyor and verified by H -P Geotech prior to permitting. Table 1 - Common Minimum Horizontal Setbacks from OWTS Components Please contact us for any necessary revisions o • 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. Sincerely, HEPWORTH-PAWLAK GEOTECHNICAL, INC. /r9ea &i Jason A. Deem Project Geologist Reviewed by: David A. Young, P.E. Sr. Project Engineer JAD/ksw Job No. 114 080A ~Ptech Wells Water Supply Line Occupied Dwelling Lined Ditch or Lake Lake, Irrigation Ditch, Stream Dry Ditch or Gulch Septic Tank Absorption Area 100' 25' 20' 20' 75' 25' 6' Septic Tank 50' 10' 5' 10' 50' 10' Building Sewer 50' 10' 0' 10' 50' 10' Please contact us for any necessary revisions o • 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. Sincerely, HEPWORTH-PAWLAK GEOTECHNICAL, INC. /r9ea &i Jason A. Deem Project Geologist Reviewed by: David A. Young, P.E. Sr. Project Engineer JAD/ksw Job No. 114 080A ~Ptech Approximate Scale: 1 inch = 800 feet Drawing adapted from Google Earth Images 114 080A Gtech HE PWORTH-PAW LAK GEOTECFINICAL LOT 4, COKE OVENS EXEMPTION SITE LOCATION PLAN FIGURE 1 -- RCALER PROPOSED SOIL TREATMENT AREA CONSISTING OF ONE ROW OF 14 INFILTRATOR QUICK 4 PLUS CHAMBERS PROPOSED CLEANOUT EXISTING 1,000 GALLON, TWO CHAMBER CONCRETE SEPTIC TANK _ II Profile Pi\ H -P GEOTECH RECOMMENDS THAT THE SOIL TREATMENT AREA AND SEPTIC TANKBE PROTECTED FROM POTENTIAL DAMAGE BY VEHICULAR TRAFFIC BY MEANS OF BOLLARDS OR FENCING APPROXIMATE SCALE: SCALE: 1 INCH = 40 FEET Legend •1 Profile Pit A Percolation Test Hole 114 080A Gtech HEPWORTH-PAWLAK GEOTECHNICAL LOT 4, COKE OVENS EXEMPTION OWTS SITE PLAN FIGURE 2 OWTS ABSORPTION AREA CALCULATIONS In accordance with the current Garfield County Individual Sewage Disposal System Regulations, the absorption area was calculated as follows: CALCULATION OF OWTS DESIGN FLOW: WHERE: Q = AVERAGE DAILY FLOW BASED ON PUMPING RECORDS 1.5 = DESIGN FLOW IS 150% OF AVERAGE DAILY FLOW Q. AVERAGE DAYS PER PUMPING = DESIGN FLOW =Q*1.5= CALCULATION OF OWTS ABSORPTION AREA: MINIUMUM ABSORPTION AREA = Q _ LTAR ;WHERE: ,Q= t - PERCOLATION RATE = COORESPONDING LTAR = ;MINIMUM ABSORPTION AREA = AREA PER INFILTRATOR QUICK 4 PLUS STANDARD CHAMBER; TOTAL CHAMBERS NEEDED = 1000 GALLONS 28.0' 35,7; GALLONS 53.6 GALLONS PER MONTH PER DAY PER DAY 'NUMBER OF TRENCHES = LENGTH (NUMBER OF CHAMBERS PER TRENCH) = TOTAL NUMBER OF CHAMBERS = TOTAL ABSORPTION AREA = 1000 GALLONS PER DAY 40 MINUTES PER INCH 0.4 133.9 SQUARE FEET 9.87 SQUARE FEET 14CHAMBERS 1.TRENCH • 14 CHAMBERS 14 'CHAMBERS 138•, SQUARE FEET 114 080A GPtech HEPWORTH.PAWLAK GEOTECHNICAL LOT 4, COKE OVENS EXEMPTION ABSORPTION AREA CALCULATIONS IFIGURE 3 APPROXIMATE SCALE: 1 INCH = 10 FEET 4 inch diameter PVC air vent installed vertically into knockouts provided in end caps. Install vents at each end of each trench. Removable lid to be placed on top of pipe, Pipe must stick up at least 8 inches above finished grade. Extend 4" non -perforated SDR35 pipe to connection between end plate and first chamber. End of pipe to be open. Fourteen Infiltrator Quick 4 Plus Standard Chambers. 4" diam. non -perforated SDR35 pipe sloped at 2% min. from septic tank to trench j WOJd MOW Bulgy Notes: 1. Chambers should be installed level on a scarified ground surface. A leveling course of concrete sand may be used if necessary. 2. All piping should have a rating of SDR35 or greater. 3. Changes to this design should not be made without consultation and approval by HP Geotech. 114 080A 1 HEPWORTH.PAWLAK GEOTECHNICAL Infiltrator Quick 4 Plus Standard End Caps. Ge Ptech LOT 4, COKE OVENS EXEMPTION ABSORPTION AREA PLAN VIEW IFIGURE 4 APPROXIMATE SCALE: 1 INCH = 4 FEET Infiltrator Quick 4 Plus Standard End Cap Approx. Existing Ground Surface 24-36" Cover Soil Graded to Deflect Surface Water Scarify Ground Surface and Provide Sand Leveling Course as Needed. Prior to Chamber Installation Notes: 1. Chambers should be installed level on a scarified ground surface. 2. All piping should have a rating of SDR35 or greater. 3. Care should be taken by the contractor to avoid compaction of the native soils in the trench areas. 4. Concrete sand may be used as a leveling course beneath the chambers if necessary. 5. Changes to this design should not be made without consultation and approval by HP Geotech. 114 080A Ge Piech HEPWORTH-PAWLAK GEOTECHNICAL LOT 4, COKE OVENS EXEMPTION ABSORPTION AREA CROSS SECTION FIGURE 5 HEPWORTH-PAWLAK GEOTECHNICAL, INC. TABLE 1 PERCOLATION TEST RESULTS JOB NO. 114 080A HOLE NO. HOLE DEPTH (INCHES) LENGTH OF INTERVAL (SEC) WATER DEPTH AT START OF INTERVAL (INCHES) WATER DEPTH AT END OF INTERVAL (INCHES) DROP IN WATER LEVEL (INCHES) AVERAGE PERCOLATION RATE (MIN./INCH) P-1 32 10 5% 5% 40 5% 534 '4 5% 5 5 4' % P-2 36 10 7 61/4 1/4 40 6' 634 14 634 634 y, 634 6 /, P-3 42 10 6% 6 Y: 40 6 5% 24 5:4 5334 34 534 5 Y< Note: Percolation test holes were hand dug in the bottom of backhoe pits and soaked on March 23, 2014. Percolation tests were conducted on March 24, 2014 by a representative of H -P Geotech. The average percolation rates were based on the last two readings of each test.