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HomeMy WebLinkAboutSubsurface Investigation and OWTS Design 12.09.16 December 9, 2016 Project No. C1261 Steve Ochko sgochko@comcast.net Subsurface Investigation and Onsite Wastewater Treatment System Design 3-Bedroom Residence 4366 CR 100 Garfield County, Colorado Steve, ALL SERVICE septic, LLC performed a subsurface investigation and completed an onsite wastewater treatment system (OWTS) design for the subject residence. The 2.0-acre property is located outside of Carbondale, in an area where OWTSs and wells are necessary. The original design documents dated November 26, 2016 must be discarded and replaced with those dated December 9, 2016. We were alerted of the presence of a well on the property that was not noted on the site plan provided. This well is not currently in service. Additionally, groundwater was encountered during excavation of the seepage pit and design documents dated December 9, 2016 address these issues. Legal Description: Section: 30 Township: 7 Range: 87 A TR IN SEC 30 IN THE SW1/4 OF THE NE1/2. AKA LOT 1 IRENE GREEN EXEMPTION Parcel ID: 239130100028 SITE CONDITIONS A 3-bedroom, single-family residence presently exists. The residence is served by an existing OTWS that is experiencing signs of failure. The metal septic tank is no longer able to hold effluent and the existing soil treatment area (STA) is not sufficient to accommodate a 3-bedroom residence. The existing septic tank will be and STA will be abandoned. There is a spring that serves potable water to the property greater than 50-feet from the proposed septic tank and greater than 100-feet from the proposed STA. There must be at least 10-feet of separation between the property line and any OWTS component. A private well, not currently in use, is located 100-feet southeast of the proposed STA. This distance has been measured and marked on site. The portion of the property available for the STA is covered with an existing driveway. A seepage pit has been designed to accommodate traffic loading over the STA. A dry gulch runs to the west of the proposed STA. The seepage pit will be located at least 25-feet from the dry gulch. Page 2 Note dry gulch with culvert under county road SUBSURFACE The subsurface was investigated on November 25, 2016 by digging one soil profile test pit excavation (Test Pit). A visual and tactile soil analysis was completed by Carla Ostberg at the time of excavation.1 The materials encountered in the Test Pit #1 consisted of medium brown silty loam to a maximum depth explored of 14-feet, which was the maximum depth the backhoe could reach. No bedrock or groundwater was encountered. Soils were consistent throughout the depth of the Test Pit. A tactile analysis of the soils was taken from Test Pit #1 at 8-feet below grade. The soil formed a ball and a very weak ribbon less than 1-inch in length before breaking. Soil structure shape was blocky, soil structure grade was moderate, and consistence was loose to friable. While the soils were consistent Soil Type 2, be believe it is appropriate for purposes of the seepage pit design to size based Soil Type 1. STA sizing is based on Soil Type 1. A long term acceptance rate (LTAR) of 0.8 gallons per square foot will be used to design the OWTS, in accordance with Table 10-1 Soil Type 1 presented in the Garfield County On -Site Wastewater Treatment System Regulations, adopted April 14, 2014. During excavation of the seepage pit, groundwater was encountered at 12-feet. The location of the seepage pit was shifted approximately 30 feet from the test pit location to accommodate the required dry gulch and well setbacks. We have modified the design to accommodate a shallower installation of the seepage pit to allow the required 4-foot separation between groundwater and the infiltrative surface of the STA. 1 Carla Ostberg holds a Certificate of Attendance and Examination from the CPOW Visual and Tactile Evaluation of Soils Training. Page 3 Test Pit #1 View of profile pit Consistent soils top to bottom DESIGN SPECIFICATIONS The existing septic tank must be removed or collapsed and remaining void filled with gravel, sand, or compacted soil. The existing STA will be abandoned in place, Design Calculations: Average Design Flow = 75 GPD x 2 people/bedroom x 3 Bedrooms = 450 GPD LTAR = 0.8 GPD/SF 450 GPD / 0.8 GPD/SF = Min. 562.5 SF 24’ x 24’ x 6’ deep + area under manhole ring = 588 SF (not including majority of bottom area = 576 SF) The OWTS design is based on 3-bedrooms, with tank capacity to accommodate a 4th bedroom. An average daily wastewater flow of 450 GPD will be used. A 4th bedroom may be contemplated in the future. Under current code requirements, the seepage pit is sized to accommodate a 3-bedroom residence. The proposed OWTS regulation from the Colorado Department of Public Health and Environment allows bottom area square footage to count toward the total required square footage, whereas current code does not allow consideration of bottom area into the required square footage. If and when this code amendment is adopted, the seepage pit will be sized properly to accommodate a 4th bedroom in the residence. The installation must include a 1250-gallon two-compartment concrete septic tank with an effluent filter on the outlet tee. Effluent will gravity flow to a seepage pit. Dimensions of the seepage pit will be 24-feet x 24-feet x 6-feet deep below the inlet pipe. A minimum of 2-feet of cover and geotextile fabric is required over the seepage pit for traffic rating (see Seepage Pit Detail 3/W3.0). Page 4 The seepage pit will consist of clean, graded rock ranging from ½” to 2 ½” in diameter surrounding three 4-foot diameter perforated concrete manhole rings. The rock will extend from the bottom of the seepage pit to at least 2-inches above the inlet pipe. The sidewalls of the seepage pit will be scarified. A covering of heavy duty geotextile fabric will be placed over the aggregate, followed by 1-foot of road base and another layer of heavy duty geotextile fabric and another foot of gravel. The backfill material shall be graded to deflect precipitation and surface drainage. While the seepage pit is designed to withstand vehicle traffic, no heavy commercial vehicles including but not limited to dump trucks, concrete trucks, pump trucks, and busses should drive over the seepage pit. The component manufacturers are typical of applications used by contractors and engineers in this area. Alternatives may be considered or recommended by contacting our office. Construction must be according to Garfield County On-Site Wastewater Treatment System Regulations, the OWTS Permit provided by Garfield County Building Department, and this design. 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 irritation shall be placed over 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 absorption area. No heavy equipment, machinery, or materials should be placed on backfilled STAs. 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. Page 5 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 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. INSTALLATION OBSERVATIONS ALL SERVICE septic, LLC 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. ALL SERVICE septic, LLC should be notified 48 hours in advance to observe the installation. LIMITS: The design is based on information submitted. If soil conditions encountered are different from conditions described in report, ALL SERVICE septic, LLC 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. Please call with questions. Sincerely, ALL SERVICE septic, LLC Reviewed By: Carla Ostberg, MPH, REHS • Has 5-10 times more flow area than other brands, so lasts many times longer between clean- ings, increasing homeowner satisfaction • Installs in min- utes inside new or existing tanks; extendible tee handle for easy removal • Easy to clean by simply hosing off whenever the tank needs pumping • Removes about two-thirds of sus- pended solids, on average, extending drainfield life • Corrosion-proof construction, to ensure long life • Lifetime warranty Residential Biotube® Effluent Filters Applications Our patented* 4-in. (100-mm) Biotube Effluent Filters, Biotube Jr., Biotube Insert Filters, and Biotube Base Inlet Filters are ideal for residential septic tanks and have a lifetime warranty. They prevent large solids from leaving the tank, dramatically improving wastewater quality and extending the life of residential drainfields. Standard Features & Benefits • Alarm available, to signal the need for cleaning • Flow modulating discharge orifices available to limit flow rate leaving tank, mitigat- ing surges and increasing retention time • Custom and commercial sizes available Effluent from the relatively clear zone of the septic tank, between the scum and sludge layers, horizontally enters the Biotube Effluent Filter. Effluent then enters the annular space between the housing and the Biotubes, utilizing the Biotubes’ entire surface for filtering. Particles larger than the Biotube’s mesh are prevented from leaving the tank. Optional Features & Benefits Biotube Filtering Process 8-in. (200-mm) Base Inlet Filter 4-in. (100-mm) Insert Filter 4-in. (100-mm) Biotube Jr. (4-in. Biotube cartridge avail- able separately as Insert Filter) Orenco’s superior effluent filters resist clogging better than all other brands. Our stan- dard, full-sized 4-in. (100-mm) Biotube Effluent Filter provides maximum long-term protection in a complete package, with housing. Our 4-in. (100-mm) Biotube Jr., at half the size of our standard model, has more filtering capacity than the full-sized filters sold by other manufacturers. For tanks with existing outlet tees, the Biotube Insert Filter is ideal. And for low-profile tanks, there’s the Base Inlet Filter. * Covered by patent numbers 5,492,635 and 4,439,323 4-in. (100-mm) Biotube Effluent Filter APS-FT-1 Rev. 3.4 © 11/10 Orenco Systems®, Inc. To Order Call your nearest Orenco Systems®, Inc. distributor. For nearest distribu- tor, call Orenco at 800-348-9843 or go to www.orenco.com and click on “Distributor Locator.” Nomenclatures Riser wall Tank wall Filter housing Extendible PVC handle Stainless steel set screws Top seal plate Air vents Biotube® filter cartridge Solid base 4-in. Biotube Effluent Filter 4-in. Biotube Jr. 4-in. Biotube Filter (standard) 4-in. Biotube Jr. (includes cartridge and housing) Distributed By: 8-in. Biotube Filter (base inlet model) 4-in. Biotube Filter Insert (cartridge only) Junior series FT J0418 Biotube effluent filter series Filter diameter (inches) Cartridge height (inches) W = fits Type 3034 outlet tee S = fits Schedule 40 outlet tee Options: Blank = no options M = flow modulation plate installed A = float bracket attached Blank = 1/8" filtration P = 1/16" filtration Insert FT i0418 Biotube effluent filter series Filter diameter (inches) Cartridge height (inches) W = fits Type 3034 outlet tee S = fits Schedule 40 outlet tee - For customized options (e.g., NC indicates North Carolina regions) - Blank = 1/8" filtration P = 1/16" filtration FT 04 Biotube effluent filter series Filter diameter (inches) Housing height: 36" and 44" are standard Options: Blank = no options M = flow modulation plate installed A = float bracket attached Cartridge height: 28" and 36" are standard - Blank = 1/8" filtration P = 1/16" filtration W = fits Type 3034 outlet pipe S = fits Schedule 40 outlet pipe FT 2208 14 B Biotube effluent filter series Housing height: 22" standard Cartridge height: 14" standard Options: A = float bracket FS = 2" outlet orifice FSO = 2" outlet orifice and overflow plate* Base inlet model - Blank = 1/8" filtration P = 1/16" filtration Filter diameter (inches) 08 = 8" * Also available with coupling and sleeve as a “kit”: FT-OVERFLOWKIT