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Homeowner OSS Design and Installation Guide Goldendale Office Klickitat County Health Department White Salmon Office 228 West Main Street 501 NE Washington St/ PO Box 159 MS-CH 14 White Salmon, WA 98672 Goldendale, WA 98620 [PHONE REDACTED] [PHONE REDACTED] The intent of this packet is to provide as much information for installers and homeowners regarding proper procedures for installing a gravity flow on-site sewage disposal system. Washington State Administrative Code 246-272A requires a detailed design prior to issuance of a septic permit. Klickitat County allows the homeowner to both design and install a standard gravity system if not adjacent to a marine shoreline. WAC 246-272A requires all other treatment levels to be designed by a licensed on-site designer or a professional engineer; all other treatment types must also be installed by a licensed septic installer. ENSURE YOU HAVE COMPLETED THE SITE AND SOIL EVALUATION BEFORE SUBMITTING YOUR ON-SITE SEWAGE DESIGN. Glossary of Terms Absorption area: The soil surface area of a drainfield (trench, bed, subsurface injector area, etc.) that treats and absorbs wastewater. Also known as “subsurface soil absorption area.” Application rate: The rate (in gallons of effluent per day) that is applied to one square foot of soil. Building sewer: That part of the horizontal piping of a drainage system extending from the building drain, which collects sewage from all the drainage pipes inside a building, to an on-site sewage system. Building site: The real property on which a proposed structure will be built or placed. It may include the entire parcel of land. Clean out: A plumbing device that provides access to and is used for inspecting and cleaning building sewers and tight lines. Cut Banks: Any naturally occurring or artificially formed slope greater than 100 percent (forty-five degrees) and extending vertically at least five feet from the toe of the slope to the top of the slope as follows: D-Box (Distribution box): A concrete or plastic container used to equally divide the wastewater flow from a single inlet to between 3 to 6 (or more) outlets. Usually the outlets distribute the flows to different parts of a drain field system. Depth of cover/fill: The amount of soil (usually expressed in inches) placed over the absorption area of a drain field. Design flow or sewage flow: The maximum volume of sewage a residence, structure, or other facility is estimated to generate in a typical twenty-four-hour period. Drainrock: Clean washed gravel or crushed rock ranging in size from three-quarters inch to two and one-half inches, and containing no more than two percent by weight passing a US No. 8 sieve and no more than one percent by weight passing a US No. 200 sieve. Effluent: Liquid discharged from a septic tank of other on-site sewage system component. End cap: A plug attached to the end of the perforated drainpipe. It forces the sewage to go out holes in the drainpipe. Gravel depth below pipe: Inches of gravel between the bottom of the pipe and the bottom of the trench. Gravelless distribution technology: An alternative to using perforated pipe and drainrock for the system drainfield. Gray water: Sewage from bathtubs, showers, bathroom sinks, washing machines, dishwashers and kitchen sinks. ---PAGE BREAK--- Homeowner OSS Design and Installation Guide Goldendale Office Klickitat County Health Department White Salmon Office 228 West Main Street 501 NE Washington St/ PO Box 159 MS-CH 14 White Salmon, WA 98672 Goldendale, WA 98620 [PHONE REDACTED] [PHONE REDACTED] Groundwater: A subsurface water occupying the zone of saturated soil, permanently or seasonally, or as the result of tides. Perforated drainpipe: Also known as drain tile. Four-inch plastic pipe with holes specifically located to permit even dispersal of sewage throughout a drain field. Permeable soils: Soils that will absorb and treat wastewater. These are the useful soils for wastewater treatment and disposal. Plumbing stub out: The pipe (or pipes) that exit the perimeter of a building. It is essential that the plumber know the proper elevation (or height) for the stub-out in order to avoid placement too low to reach the drain field by gravity. If the stub-out is too low, a pump (or re-plumbing) must be used to lift the sewage up to the proper level. Replacement area: An area of the building site reserved for a future drain field when the original drain field fails to function. An area equal in size to the original drain field, without any size reductions from other parts of the regulation, is required. Restrictive layer: A stratum impeding the vertical movement of water, air, and growth of plant roots, such as hardpan, claypan, fragipan, caliche, some compacted soils, bedrock and unstructured clay soils. Septic tank: A watertight treatment receptacle receiving the discharge of sewage from a building sewer or sewers, designed and constructed to permit separation of settle-able and floating solids from the liquid; allows detention and anaerobic digestion of the organic matter prior to discharge of the liquid into the drain field. Sewage: Any urine, feces, and water carrying human wastes, including kitchen, bath, and laundry wastes from residences, buildings, industrial establishments or other places. Soil Barrier: A material used to prevent soil from filtering into the drain rock in gravel drain fields. It is placed over the gravel before soil cover is installed. Soil barrier materials must allow air and water to pass freely. Splash box: a component similar to an effluent break. Used to intercept the effluent pumped or gravity fed to a disposal field and reduce the energy level of the sewage before it enters an alternate distribution method or the first disposal trench. Tight line: Also known as solid pipe or transport line; 4” plastic (PVC) pipe without holes. Used to transport sewage between the septic tank and the drain field. Total trench depth: Depth of drain field from top of the original ground surface to bottom of drain field trench. Trench spacing: The distance between trenches is measured from trench center to trench center and must be a minimum of 8 feet apart center on center. Vertical separation: The depth of unsaturated, original, undisturbed soil of soil types 1-6 between the bottom infiltrative surface of a soil dispersal component and the highest seasonal water table, a restrictive layer, or soil type 7. -Continue to the next page.- ---PAGE BREAK--- Homeowner OSS Design and Installation Guide Goldendale Office Klickitat County Health Department White Salmon Office 228 West Main Street 501 NE Washington St/ PO Box 159 MS-CH 14 White Salmon, WA 98672 Goldendale, WA 98620 [PHONE REDACTED] [PHONE REDACTED] Building Sewer Requirements Building sewer must be 4 inches in diameter and must be schedule 40 or equivalent. The grade on all parts of the building sewer must be 1/8 inch minimum fall per foot, and the last 10 feet of pipe can be 1/4 inch maximum per foot. At least one sewer clean-out must be installed prior to the septic tank. Clean-outs must be installed at 50 foot intervals. If elbows or bends are necessary, they cannot be greater than a 45 degree angle, unless it is a soft or sweeping 90 degree bend. A 90 degree bend must be accompanied by a clean-out. Any pipe crossing under a driveway, parking area, or vehicular encroachment area must be buried 36 inches in the ground or bedded, and encased in 5 inch or 6 inch schedule 40 PVC. Septic Tank Requirements Single family residences with 1- 4 bedrooms are required to have a minimum of a 1,000 gallon septic tank. For each additional room, add 250 gallons. The septic tank must be set on undisturbed soil or by the manufacture’s standards. All pipes connecting to the tank must be water-tight with the proper slope. Access to the tank for inspection and maintenance at finished grade is required. Risers must bring access to the tank to grade. All lids must be secure. All pipe entering and exiting the tank should be bedded and construction practices must prevent the pipes from “sagging” after cover. All septic tanks must be from the approved list provided by the Washington State Department of Health. Transport Lines The transport line from septic tank to d-box must have a minimum grade of 1 inch of fall per 100 feet and be water tight. Absorption areas significantly lower in elevation are required to have a splash box to reduce excessive effluent flows to the d-box. Crossing domestic or irrigation water lines is to be avoided. If this is not possible, contact the Health Department concerning standard practices. Distribution Box (D-Box) All unused outlets in a d-box must be water tight. A method must be utilized to ensure the inlet flow is divided equally to all outlets. This can be done by using “dial-a-flow meters,” or installing a 90 degree sweep faced down toward the bottom of the d-box. The d-box must be set on undisturbed soil and 5 feet minimum from the beginning of the lateral trenches. ---PAGE BREAK--- Homeowner OSS Design and Installation Guide Goldendale Office Klickitat County Health Department White Salmon Office 228 West Main Street 501 NE Washington St/ PO Box 159 MS-CH 14 White Salmon, WA 98672 Goldendale, WA 98620 [PHONE REDACTED] [PHONE REDACTED] Initial and Replacement Absorption Area Requirements A minimum of 36 inches of undisturbed, native soil, is required between the bottom of the trench and the restrictive layer. Gravel absorption beds must be covered with a non-woven geotextile filter fabric before covering. The system replacement area will accommodate 100% of the required square footage with NO reductions. Absorption areas shall not be subject to vehicular traffic, shall not be encroached upon by buildings or structures, or be covered by impervious surfaces; including but not limited to asphalt, concrete, and swimming pools. Absorption areas shall not be located or installed on slopes in excess of 40%. Systems installed on sites with 30-40% slope, will be required to show 5 feet of vertical separation. Absorption areas shall not be located in areas where storm-water, drainage, or surface water accumulates. Storm-water drainage will be directed away from or down slope from the disposal area. Absorption trenches must run perpendicular to the slope of the land, and may need to curve around complicated areas. The final absorption trench must be covered with a minimum of 6 inches of top soil and maximum of 24 inches. The bottom of absorption trenches need to be level, plus or minus ½ an inch. The length of an individual trench for gravity flow must not exceed 100 feet. The standard trench absorption width is 36 inches. The end of perforated pipes must be capped. Equal distribution to each lateral is required. -Continue to the next page.- ---PAGE BREAK--- Homeowner OSS Design and Installation Guide Goldendale Office Klickitat County Health Department White Salmon Office 228 West Main Street 501 NE Washington St/ PO Box 159 MS-CH 14 White Salmon, WA 98672 Goldendale, WA 98620 [PHONE REDACTED] [PHONE REDACTED] Minimum Horizontal Setbacks Items Requiring Setback From edge of soil dispersal component and reserve area From sewage tank and distribution box From building sewer and non- perforated distribution pipe Well or suction line 100 ft. 50 ft. 50 ft. Public drinking water well 100 ft. 100 ft. 100 ft. Public drinking water spring measured from the ordinary high-water mark 200 ft. 200 ft. 100 ft. Spring or surface water used as drinking water source measured from the ordinary high-water mark 100 ft. 50 ft. 50 ft. Pressurized water supply line 10 ft. 10 ft. 10 ft. Decommissioned well (decommissioned in accordance with chapter 173-160 WAC) 10 ft. N/A N/A Surface water measured from the ordinary high- water mark 100 ft. 50 ft. 10 ft. Building foundation/in-ground swimming pool 10 ft. 5 ft. 2 ft. Property or easement line 5 ft. 5 ft. N/A Interceptor/curtain drains/foundation drains/drainage ditches Down-gradient*: 30 ft. 5 ft. N/A Up-gradient*: 10 ft. N/A N/A Other site features that may allow effluent to surface Down-gradient*: 30 ft. 5 ft. N/A Up-gradient*: 10 ft. N/A N/A Down-gradient cuts or banks with at least 5 ft. of original undisturbed soil above a restrictive layer due to a structural or textural change 25 ft. N/A N/A Down-gradient cuts or banks with less than 5 ft. of original undisturbed soil above a restrictive layer due to a structural or textural change 50 ft. N/A N/A Other adjacent soil dispersal components/subsurface storm water infiltration systems 10 ft. N/A N/A *The item is down-gradient when the liquid will flow toward it upon encountering a water table or restrictive layer. The item is up-gradient when the liquid will flow away from it upon entering a water table or restrictive layer. -Continue to the next page.- ---PAGE BREAK--- Homeowner OSS Design and Installation Guide Goldendale Office Klickitat County Health Department White Salmon Office 228 West Main Street 501 NE Washington St/ PO Box 159 MS-CH 14 White Salmon, WA 98672 Goldendale, WA 98620 [PHONE REDACTED] [PHONE REDACTED] Homeowner Design Application A complete application with a design and fees is expected on any proposed NEW SYSTEM, REPLACEMENT, or EXPANDED system. Fees are NON-REFUNDABLE and subject to change by resolution of the County Commissioners. Application Type: New System (less than 1,000 gpd) - $350 New System (greater than 1,000 gpd) - $1250 Drainfield Replacement - $100 Tank Replacement - $50 Waterless Toilet - $30 Applicant Information Name: Mailing Address: City: State: Zip: Phone: Email: Property Information Parcel Number: Site Address: City: State: Zip: Directions to the property: Source of Sewage Residential Multi-family Commercial Food Service Other: -Continue to the next page.- ---PAGE BREAK--- Homeowner OSS Design and Installation Guide Goldendale Office Klickitat County Health Department White Salmon Office 228 West Main Street 501 NE Washington St/ PO Box 159 MS-CH 14 White Salmon, WA 98672 Goldendale, WA 98620 [PHONE REDACTED] [PHONE REDACTED] On-Site Sewage (OSS) Installer Name: Phone: Water Supply Private Public, system Well Spring Shared Well System Calculations (note: you will need your site evaluation for this part) NOTE: These calculations only apply to single family residences. Please contact the Health Department regarding alternative projects. The system design flow is determined by the number of bedrooms multiplied by 120 gallons. The minimum design flow for any on-site sewage system is 240 gpd. Step 1. # of bedrooms: X 120 = gallons per day (design flow) - For a home serving 4 bedrooms or fewer, the minimum septic tank size is 1000 gallons. For homes with more than 4 bedrooms, an additional 250 gallons per bedroom is required. Step 2. # of bedrooms = minimum tank size - Refer to your soil log or site evaluation report to calculate the maximum trench depth. For standard gravity systems there must be 36” of vertical separation from the restrictive layer. Step 3. Depth of test pit or restrictive layer: - 36” = maximum trench depth - Refer to the site evaluation report to determine the square footage necessary to treat sewage. The application rate will be listed. To determine the square footage, divide the design flow by the application rate. Step 4. Design flow / application rate = total square footage - For gravel systems, simply divide the total square footage by 3 to get the total linear length of drainfield needed. Step 5. Total square footage / 3 = total linear feet of gravel drainfield - If you plan to use gravelless product, like EZ Flo or Infiltrator domes, you will need to reduce the total square footage by a percent based on soil type. For soils types 3 through 6, there is a 40% reduction. In soil type 2, there is a 20% reduction. Soil type 1 has no reduction. Step 6. Total square footage X reduction factor = new total square footage New total square footage / 3 = total linear feet of gravelless drainfield -Continue to the next page.- ---PAGE BREAK--- Homeowner OSS Design and Installation Guide Goldendale Office Klickitat County Health Department White Salmon Office 228 West Main Street 501 NE Washington St/ PO Box 159 MS-CH 14 White Salmon, WA 98672 Goldendale, WA 98620 [PHONE REDACTED] [PHONE REDACTED] System Calculations Summary (write n/a if there is no pump chamber) Detailed Site Plan and Design Checklist (Ensure to include these on your drafted design.) Detailed site plan: System layout: □ Show property lines and dimensions □ Length of building sewer out □ General topography (direction of slope and percentage □ Length of all transport lines □ Show buildings (existing and planned) □ Show lines encased or buried under roads □ Show roads, driveways, and parking □ Location of observation/inspection ports □ Setbacks to surface water, season streams, creeks □ Location of clean outs □ Location of drinking water source □ Length of each lateral □ Location of pressurized water lines □ Distinguish type of drainfield material □ Location of septic tank □ Location of any risers □ Location of d-box □ Location of other trenched utilities □ Location of initial and reserve drainfield areas □ List piping material used and diameter □ Locations of test pits □ Show width of drainfield laterals Signature: Design Flow: Septic Tank Size: Soil Type: Application Rate: Trench Width: Total Linear Feet: Max. Trench Depth: Pump Chamber Size: Max. Trench Depth ---PAGE BREAK--- Homeowner OSS Design and Installation Guide Goldendale Office Klickitat County Health Department White Salmon Office 228 West Main Street 501 NE Washington St/ PO Box 159 MS-CH 14 White Salmon, WA 98672 Goldendale, WA 98620 [PHONE REDACTED] [PHONE REDACTED] Typical Trench Cross Sections Examples Native Backfill Standard Gravel Trench Standard Dome-Chamber Trench Standard EZ Flo Trench 36” 4” Perforated Pipe Minimum of 2” of gravel on top of perf. pipe 36” Max. Trench Depth 6” Max. Trench Depth Max. Trench Depth ---PAGE BREAK--- Homeowner OSS Design and Installation Guide Goldendale Office Klickitat County Health Department White Salmon Office 228 West Main Street 501 NE Washington St/ PO Box 159 MS-CH 14 White Salmon, WA 98672 Goldendale, WA 98620 [PHONE REDACTED] [PHONE REDACTED] Example Design PROPERTY LINE: 185' PROPERTY LINE: 250' 8' IRRIGATION EASEMENT 10' UTILITY EASEMENT 33' x 66' THREE BEDROOM HOUSE 40' 90' 75' 127' WELL 50' MIN. TO SEPTIC TANK 100' MIN. TO DRAIN FIELD FUTURE 30' x 20' SHOP 10' DRIVEWAY WATER LINE APPROX. SLOPE 5' MIN. 5' MIN. 10' MIN. 89' 1,000 GALLON SEPTIC TANK (manholes to ground surface) 5' MIN. CLEAN OUT D-BOX (Access point to finished grade) 23' x 89' FUTURE REPLACEMENT AREA SEPTIC TANK WELL D-BOX or GRAVEL DRAIN FIELD TRENCH GRAVELESS DRAIN FIELD TRENCH REPLACEMENT AREA BUILDING SEWER WITH CLEAN OUT TIGHT LINE OR BUILDING SEWER 100' MIN. TO NEIGHBOR'S WELL Inspection Ports