HomeMy WebLinkAboutEngineer's OWTS Design129 Cains Lane Carbondale, CO 81623 970.309.5259 carla.ostberg@gmail.com April 29, 2024 Project No. C1870 Dorothy Bleakley Dbleakley14@gmail.com Subsurface Investigation and Onsite Wastewater Treatment System Design 4-Bedroom Residence 387 Meadow Lane Garfield County, Colorado Dorothy, CBO Inc. performed a subsurface investigation and completed an onsite wastewater treatment system (OWTS) design for the subject residence. The 1.059-acre property is located outside of Glenwood Springs, in an area where OWTSs are necessary. Legal Description: Section: 35 Township: 6 Range: 89 Subdivision: WESTBANK RANCH SUB. #3 Lot: 28 Parcel ID: 2185-354-03-028 SITE CONDITIONS The property is currently developed with a 4-bedroom residence. The residence is served by an existing OWTS that consists of a 1000-gallon, two-compartment concrete septic tank followed by a 12’ x 40’ pipe and gravel soil treatment area (STA) with 3-feet of gravel under the distribution piping. Garfield County Individual Sewage Disposal System Permit 1679 documents this system. The system was sized to accommodate 3-bedrooms. The permit received final approval from Garfield County on December May 31, 1989. The existing STA is experiencing slow draining and must be replaced. The residence is served potable water from a community water system. The new STA must be at least 25-feet from any water line; however, as this is a repair and space on the property for the replacement is limited, we may encroach slightly on the setback to the water line that runs along the eastern side of the property. We have approximated the water line on our site plan, but the water line was located on the property. The proposed soil treatment area (STA) location has an approximate five percent slope to the northeast. The proposed area is vegetated with sage and native grasses. There should be no traffic or staging of material over the future STA site to avoid compaction of soils prior to construction of the STA. Page 2 Waterline as it angles into the house Waterline as it comes up the eastern property line Waterline middle of subdivision road Curb stop Page 3 View of approx. water line Curb stop View of approx. areas for STA SUBSURFACE The subsurface was investigated on March 18, 2024 by digging two soil profile test pit excavations (Test Pits). A visual and tactile soil analysis was completed by Carla Ostberg at the time of excavation.1 Excavation was done in an effort to see if there was a broken sewer line after the septic tank; however, it was evident that the STA was saturated and both excavations encountered saturation in the existing STA. The soils are consistent with Soil Type R-0 with greater than 35% rock. A pressure-dosed, unlined sand filter with a minimum of 3-feet of sand filter material (Secondary Sand) is proposed. A long-term acceptance rate (LTAR) of 0.8 gallons per square foot will be used to design the STA. 1 Carla Ostberg holds a Certificate of Attendance and Examination from the CPOW Visual and Tactile Evaluation of Soils Training. Page 4 Inspection port between septic tank and STA / sewer line between septic tank and STA Trench (sand and gravel) Page 5 Excavation to trouble-shoot Additional test pit to the east Encountered saturation 5-feet Page 6 Test Pit #2 DESIGN SPECIFICATIONS The existing septic tank will be abandoned by pumping the tank and removing it or crushing the top, bottom, and sides and filling in the void with onsite materials. The existing STA will be abandoned in place. Design Calculations: Average Design Flow = 75 GPD x 2 people/bedroom x 3 Bedrooms + 75 GPD (4th Bedroom) = 525 GPD LTAR = 0.8 GPD/SF 525 GPD / 0.8 GPD/SF = 656.25 SF The OWTS design is based on 4-bedrooms. An average daily wastewater flow of 525 GPD will be used. For the purposes of this OWTS design, Benchmark Elevation has been established as 100’ (Finished Floor). CBO Inc. should be notified of any discrepancies or problems with grade elevations of proposed components during installation of the OWTS. OWTS Component Minimum Elevation Primary Tank Inlet Invert (existing sewer line) Approximate horizontal distance 32’ / min. 2% fall / min. 8” fall Automatic Distributing Valve Approximate horizontal distance 6’ / min. 1% rise / min. 0.75” rise Infiltrative Surface Approximate horizontal distance 61’ to furthest bed / min. 1% fall to STA / min. 7.625” fall *Elevations are based upon standard OWTS installation practices. Component elevations may change during installation due to site conditions. Minimum grade refers to piping between components. The 4-inch SDR-35 sewer line exiting the residence must have a double-sweep clean out and a minimum 2% grade to the septic tank. The existing sewer line may remain in use as long as it is in good condition. The system installation will include a 1500-gallon, two-compartment Valley Precast concrete septic tank with an Orenco® Biotube Pump Vault and an Orenco® PF3005 pump in the second compartment of the septic tank. The floats should be set to dose approximately 61 gallons each pump cycle, allowing approximately 1 gallon of drain back. The control panel for the pump must be located within line of sight of the septic tank. An electrician will be responsible for wiring the pumping system and the contractor will be responsible for connecting the plumbing. This office should be contacted for start up of the system to verify its functioning and to perform a squirt test prior to use of the system. Page 7 Pump Table Dose Range Max = 132.25 gal. (525 GPD x 25% + 1 gallon drain back) Min. 53 gal. (13 gal x 4) + 1 gal drain back Dose Setting 61 gallons/dose 1 gallon drain back (6’ / 1.5” diameter pump line) Float Separation 1500 gallon 2-compartment Valley Precast concrete septic tank 6” on/off float separation Pump Criteria 17.6 gallons per minute (GPM) 15.3 feet total dynamic head (TDH) Effluent will be pumped through a 1.5-inch diameter pump line from the pump chamber to an Orenco® automatic distributing valve (ADV), model 6402. This pump line must have a minimum 1% grade for proper drain back into the tank after each pump cycle. The ADV must be placed at a high point in the system in an insulated riser with access from grade. Screened rock must be placed below the ADV to support the ADV and to assure the clear pipes exiting the ADV remain visible for future inspection and maintenance. Effluent will be pressure dosed to through 1.5-inch diameter distribution lines to two 10’ x 33’ beds. A minimum of 3-feet of sand filter material will be installed in the over-excavated footprints. Sand filter material must be clean, coarse sand, all passing a screen having four meshes to the inch. The sand must have an effective size between 0.15 and 0.60 mm. The uniformity coefficient must be 7.0 or less. Material meeting ASTM 33, for concrete sand, with three percent or less fines passing 200 mesh sieve may be used. A gradation of the sand media must be submitted to this office prior to obtaining the sand. Laterals must be 1.5-inches in diameter with 5/32-inch diameter orifices facing down, spaced 2.5-feet on center, installed on the GeoMat™ with the filter fabric over the laterals. Laterals should be placed 2-feet from the edges of the bed with 3.0-feet between the laterals. Laterals will be connected with 1.5-inch diameter level manifolds. Three 39” wide GeoMat™ sheets must be placed on the 10-foot wide bed. All material associated with the GeoMat™ installation must be proprietary products associated with the GeoMat™, including orifice shields and geotextile fabric. Manufacturer instructions must be followed regarding installation of the GeoMat™. Each 1.5-inch diameter lateral must end in a sweeping ell facing up with a ball valve for flushing. Valves should be placed in a 10-inch sprinkler box for access. Laterals must be covered by a soil separation fabric and at least 1-foot of topsoil or other suitable soil able to support vegetative growth. There shall be no cobble-sized (>2.5”) or greater rock in final cover over the GeoMat™. Inspection ports must be placed at each corner of each bed. Ports may be cut to grade and covered with a valve box for access. COMPONENT SPECIFICATIONS The component manufacturers are typical of applications used by contractors and engineers in this area. CBO Inc. must approve alternative components prior to installation of the OWTS. Requests must be submitted, in writing, to our office for approval prior to installation. Component technical data sheets are available upon request. COMPONENT MANUFACTURER MODEL NO. COMMENTS Septic Tank Valley Precast Item # 1500T-2CP-HH 1500-gallon, 2- compartment concrete septic tank with high head pump Pump Orenco® PF300511 ½ HP 120 Volt Page 8 Biotube ProPak Pump Package Orenco® BPP30DD Vault, Filter, Control Panel (demand dose) Tank Risers and Lids Orenco® Double-walled PVC Risers and Lids (24” diameter) ADV Orenco® V6402A 1.5” Inlet and Outlets ADV Riser and Lid Orenco® Double-walled PVC Risers and Lids (30” diameter) Flushing Assembly Orenco® 1.5” diameter (2) 45° or 90° long sweep only (8 total) GeoMat™ GeoMatrix Systems, LLC 198 linear feet 39” wide GeoMat™ and 72 orifice shields Construction must be according to the jurisdiction’s adopted On-Site Wastewater Treatment System Regulations, the OWTS Permit, and this design. PERMIT APPLICATION INSTRUCTIONS An OWTS Permit Application must be submitted to Garfield County Environmental Health Department. https://www.garfield-county.com/environmental-health/filesgcco/sites/16/OWTS-Application-Complete- Packet-Dec.-2019.pdf. If the OWTS Permit Application will be submitted with a Building Permit Application, it should be submitted directly to Garfield County Building Department. All questions regarding permit submission can be directed to Garfield County Environmental Health Department, 970-945-6614 x8150. INSTALLATION CONTRACTOR CBO Inc. expects that the installer be experienced and qualified to perform the scope of work outlined in this design. The installer must review this design thoroughly and coordinate with our office in advance of installation. Any additional conditions in this design or county permit must be completed and documented prior to final approval of the OWTS installation. Communication between the installer and this office is expected throughout the installation. INSTALLATION OBSERVATIONS CBO Inc. must view the OWTS during construction. The OWTS observation should be performed before backfill, after placement of OWTS components. Septic tanks, distribution devices, pumps, dosing siphons, and other plumbing, as applicable, must also be observed. CBO Inc. should be notified 48 hours in advance to observe the installation. In an effort to improve the accuracy of the record drawing, we request that the installer provide a sketch of the installation, including path of the sewer lines, water line installation (if applicable), septic tank location, STA location, and measurements from building corners or another fixed objects on the property. This sketch is most easily provided on Sheet W2.0 of the OWTS Design Packet. Photographs of the installation and final cover are also requested to supplement our installation documentation. REVEGETATION REQUIREMENTS An adequate layer of good quality topsoil capable of supporting revegetation shall be placed over the entire disturbed area of the OWTS installation. A mixture of native grass seed that has good soil stabilizing characteristics (but without taproots), provides a maximum transpiration rate, and competes well with successional species. No trees or shrubs, or any vegetation requiring regular irrigation shall be placed over Page 9 the STA. Until vegetation is reestablished, erosion and sediment control measures shall be implemented and maintained on site. The owner of the OWTS shall be responsible for maintaining proper vegetation cover. OPERATION INFORMATION AND MAINTENANCE The property owner shall be responsible for the operation and maintenance of each OWTS servicing the property. The property owner is responsible for maintaining service contracts for manufactured units, alternating STAs, and any other components needing maintenance. Geo-fabrics or plastics should not be used over the STA. No heavy equipment, machinery, or materials should be placed on the backfilled STA. Machines with tracks (not wheels) should be used during construction of the STA for better weight distribution. Livestock should not graze on the STA. Plumbing fixtures should be checked to ensure that no additional water is being discharged to OWTS. For example, a running toilet or leaky faucet can discharge hundreds of gallons of water a day and harm a STA. If an effluent filter or screen has been installed in the OWTS, we recommend this filter or screen be cleaned annually, or as needed. If the OWTS consists of a pressurized pump system, we recommend the laterals be flushed annually, or as needed. The homeowner should pump the septic tank every two years, or as needed gauged by measurement of solids in the tank. Garbage disposal use should be minimized, and non-biodegradable materials should not be placed into the OWTS. Grease should not be placed in household drains. Loading from a water softener should not be discharged into the OWTS. No hazardous wastes should be directed into the OWTS. Mechanical room drains should not discharge into the OWTS. The OWTS is engineered for domestic waste only. ADDITIONAL CONSTRUCTION NOTES If design includes a pump, weep holes must be installed to allow pump lines to drain to minimize risk of freezing. The pump shall have an audible and visual alarm notification in the event of excessively high- water conditions and shall be connected to a control breaker separate from the high-water alarm breaker and from any other control system circuits. The pump system shall have a switch so the pump can be manually operated. Excavation equipment must not drive in the excavation of the STA due to the potential to compact soil. Extensions should be placed on all septic tank components to allow access to them from existing grade. Backfill over the STA must be uniform and granular with no material greater than minus 3-inch. LIMITS: The design is based on information submitted. If soil conditions encountered are different from conditions described in report, CBO Inc. should be notified. All OWTS construction must be according to the county regulations. Requirements not specified in this report must follow applicable county regulations. The contractor should have documented and demonstrated knowledge of the requirements and regulations of the county in which they are working. Licensing of Systems Contractors may be required by county regulation. Page 10 Please call with questions. Sincerely, CBO Inc. Carla Ostberg, MPH, REHS Pump Selection for a Pressurized System - Single Family Residence Project 387 Meadow Lane Parameters Discharge Assembly Size Transport Length Before Valve Transport Pipe Class Transport Line Size Distributing Valve Model Transport Length After Valve Transport Pipe Class Transport Pipe Size Max Elevation Lift Manifold Length Manifold Pipe Class Manifold Pipe Size Number of Laterals per Cell Lateral Length Lateral Pipe Class Lateral Pipe Size Orifice Size Orifice Spacing Residual Head Flow Meter 'Add-on' Friction Losses 1.25 6 40 1.50 6402 61 40 1.50 3 3 40 1.25 4 31 40 1.50 5/32 2.5 5 None 0 inches feet inches feet inches feet feet inches feet inches inches feet feet inches feet Calculations Minimum Flow Rate per Orifice Number of Orifices per Zone Total Flow Rate per Zone Number of Laterals per Zone % Flow Differential 1st/Last Orifice Transport Velocity Before Valve Transport Velocity After Valve 0.68 26 17.6 2 0.5 2.8 2.8 gpm gpm % fps fps Frictional Head Losses Loss through Discharge Loss in Transport Before Valve Loss through Valve Loss in Transport after Valve Loss in Manifold Loss in Laterals Loss through Flowmeter 'Add-on' Friction Losses 2.2 0.1 3.7 1.2 0.0 0.1 0.0 0.0 feet feet feet feet feet feet feet feet Pipe Volumes Vol of Transport Line Before Valve Vol of Transport Line After Valve Vol of Manifold Vol of Laterals per Zone Total Vol Before Valve Total Vol After Valve 0.6 6.5 0.2 6.6 0.6 13.2 gals gals gals gals gals gals 17.6 15.3 gpm feet 0 5 10 15 20 25 30 35 40 0 50 100 150 200 250 300 Net Discharge (gpm) PumpData PF3005 High Head Effluent Pump 30 GPM, 1/2HP 115/230V 1Ø 60Hz, 200V 3Ø 60Hz PF3007 High Head Effluent Pump 30 GPM, 3/4HP 230V 1Ø 60Hz, 200/460V 3Ø 60Hz PF3010 High Head Effluent Pump 30 GPM, 1HP 230V 1Ø 60Hz, 200/460V 3Ø 60Hz PF3015 High Head Effluent Pump 30 GPM, 1-1/2HP 230V 1Ø 60Hz, 200/230/460V 3Ø 60Hz Legend System Curve: Pump Curve: Pump Optimal Range: Operating Point: Design Point: Gareld County, CO Developed by Account Number   R080475 Parcel Number   218535403028 Acres 1 Land SqFt 0 Tax Area 131 2019 Mill Levy 73.2960 Physical Address   387 MEADOW LN   GLENWOOD SPRINGS 81601 Owner Address   BLEAKLEY, DAVID & DOROTHY 387 MEADOW LN GLENWOOD SPRINGS CO 81601 2019 Total Actual Value   $1,093,240 Last 2 Sales Date  Price   7/14/2006  $525,000   3/15/1989  $37,500   Date created: 2/15/2024 Last Data Uploaded: 2/15/2024 2:11:12 AM 230 ft Overview Legend Parcels Roads Parcel/Account Numbers Owner Name Lakes & Rivers County Boundary Line