Full Text
Homeowner Design and Installation Guide for Standard Gravity Systems Revised 3/11/2015 ---PAGE BREAK--- HOMEOWNER DESIGN AND INSTALLATION GUIDE FOR ON-SITE SEWAGE SYSTEM REQUIREMENTS COVERING STANDARD AND CAP SYSTEMS. Washington State Administrative Code (WAC 246-272A) for on-site sewage systems requires a system design for all on-site sewage disposal systems. Prior to obtaining your permit, a detailed design must be submitted to and approved by the Klickitat County Health Department. If you have completed the soil and site evaluation process and your site has been approved for a treatment level E system, you may choose to complete the design as the homeowner or hire a Certified Designer or Professional Engineer to complete the design. Washington State requires that all other treatment levels be designed by a Certified Designer or a licensed Professional Engineer. THE SOIL AND SITE EVALUATION MUST BE COMPLETED BEFORE STARTING THE ON-SITE SEWAGE DISPOSAL DESIGN. INFORMATION PROVIDED IN THE SOIL AND SITE EVALUATION WILL BE NEEDED TO COMPLETE THIS DESIGN WORKBOOK. The goal of this workbook is to aid homeowners in designing and installing their single family residential system. This packet includes the following: Glossary of terms Specifications & construction guidelines Horizontal setback requirements Design flow calculation worksheet Cross section worksheet Sample design A final checklist for your design GENERAL INFORMATION AND A GLOSSARY OF TERMS Absorption area: The soil surface area of a drain field (trench, bed, subsurface injector area, etc.) that treats and absorbs wastewater. Usually the trench bottom. 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. It begins two feet outside the building wall and conveys sewage from the building drain to the remaining portions of the 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. White Salmon Office 501 NE Washington/PO Box 159 White Salmon, WA 98672 Phone (509) 493‐1558 FAX (509) 493‐4025 Goldendale Office 228 W Main MSCH‐14 Goldendale, WA 98620 Phone (509) 773‐4565 FAX (509) 773‐5991 ---PAGE BREAK--- Depth of cover: 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. It incorporates both an operating capacity and a surge capacity for the system during periodic heavy use events. The sizing and design of the on-site sewage system components are based on the design flow. 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. It includes sewage from any source in a residence or structure that has not come into contact with toilet wastes. 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 replumbing) 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. This soil can’t be counted as absorption area. Wrapped Perforated Pipe Dome or Chambers ---PAGE BREAK--- Septic tank: A watertight treatment receptacle receiving the discharge of sewage from a building sewer or sewers, designed and constructed to permit separation of settleable and floating solids from the liquid, 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. 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 ft apart. 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. Typical residential standard or cap on-site sewage system: A. Clean Out B. Building Sewer (carries all sewage to the tank) C. Septic Tank D. Tight Line E. Distribution Box (d-box) F. Tight Line G. Drainfield Trench H. Gravel or Gravelless Disposal method I. Inspection Port TOP VIEW A B C D E F I H G A B C D E F G H I ---PAGE BREAK--- IMPORTANT SPECIFICATIONS & GENERAL CONSTRUCTION GUIDLNES General Notes Shoot elevation grades and stake drainfield location prior to excavating. Start from the drainfield towards the structure to determine exact elevation to set tank and stub-out for plumbing. Roof and surface water runoff or discharge must be directed away from or down slope from the sewage disposal system by means of footing and/or foundation drains, or surface diversion ditches. Do not pipe runoff into the septic system. At a minimum, 4” pipe shall be used. This pipe must schedule 40 or equivalent. All pipe joints must be water tight with no exceptions. It is recommended that the bells be on the upgrade side when possible. All or any portions of the sewage disposal system must be inspected and approved before it is covered with soil, otherwise uncovering will be required for visual verification that standards have been met. Building Sewer Building sewer must be 4 inches in diameter. The grade on all parts of the building sewer must be 1/8 inch minimum fall per foot, and the last 10 foot section of pipe can be 1/4 inch maximum fall per foot. At least one clean-out must be installed on this line outside of the structure. If the building sewer exceeds 50 feet in length, clean-outs must be installed at 50 foot intervals. If elbows or bends are used, they cannot be greater than a 45 degree angle, but a sweeping 90 degree may be used if a cleanout is installed. Any pipe crossing under a drive- way, parking area, or vehicular encroachment area must be buried 36” deep or bedded and en- cased in 5 or 6” Sch 40 PVC, steel, concrete pipe, or other traffic rated culvert or piping. Septic Tank The septic tank must be set on undisturbed soil or by manufacturer’s standards if other than a concrete tank is used. All pipe connections to the tank must be watertight with proper slope. Access to the tank for inspection and maintenance at finished grade is required. However, on gravity flow systems, the Health Officer may allow access for these tanks to be a maximum of six inches below finished grade provided a marker showing the location of the tank access is installed at finished grade, or be other means approved by the Health Officer. All access points to the septic tank must be brought to ground surface with risers. All lids must be secured. All pipe entering and exiting the tank must be bedded on compacted soil. The tank must be approved through the Washington State Department of Health. All tanks must be marked with both the size and the manufacture. Please see the Washington State Department of Health's List of Approved On-Site Sewage Tanks for a complete list of approved tanks. ---PAGE BREAK--- Tight lines or distribution lines The grade on the pipes must be 1 inch minimum downward fall per 100 feet from the tank outlet. The pipe must have a watertight connection to the distribution box (sealed, grouted, or manufactured fittings). The pipes must be bedded with ASTM rating, facing up, and have glued/watertight joints. All pipes must be installed so that the bell end is up-slope. Crossing of the line with domestic or irrigation lines is to be avoided. If necessary, such crossings must comply with the requirements of the Washington State Department of Ecology Criteria for Sewage Works Design. Any pipe under driving/parking or vehicular encroachment areas must be bedded and enclosed in 5 or 6 inch pvc, steel, or concrete pipe which meets or exceeds the crush strength of ASTM 3034. The pipe length must exceed the drive width. At a minimum, 4” pipe shall be used. This pipe must schedule 40 or equivalent. Verification of standards must be provided by the system designer. Distribution Box (D-Box) All unused outlets must be watertight. A method must be utilized to ensure inlet flow is equally directed into all outlets This can be done by the installation of a 90 degree sweep installed on the inlet to direct the effluent to the floor of the box or the use of flow equalizers (such as dial-a-flow inserts). The flow equalizers must be set to allow liquid to enter all lines with equal flow simultaneously. The D-box must be set on undisturbed soil 5 feet minimum from the beginning of trench, gravel, and perforated pipe and must be set level. Drainfields, absorption beds, SSAS (Sub-surface Absorption Systems) Drainfields must run perpendicular to the slope (across/right angles or 90 degrees) and may need to be contoured or curved to accomplish this. The bottom of the trench must be level within + or – ½ an inch. The required maximum installation depth identified in the design is critical. This maximum installation depth is measured from the upslope side of the trench. This is one of most common installation mistakes and results in system failing to pass inspection. The ends of all perforated pipes must be capped. If gravel is used in drainfields it must be clean, washed, and ¾” to 2 ½” in diameter. The soil barrier over the drainfield must be filter fabric (for example, type 3301 & 3341 or approved equivalent, 3.0 to 4.0 oz/square yard and spun-bonded (not woven) material without petroleum/oil properties. Drainfields and replacement area must be protected from encroachment or damage by vehicular and equipment traffic, livestock, heavy weights or objects, impervious coverings (asphalt or concrete), or anything that can obstruct aeration of the system. No cutting or filling with soil is allowed in the drainfield area (replacement area included). The drainfield must be in original undisturbed soil, otherwise permit may be void unless alternative suitable location is found. The length of an individual drainfield line cannot exceed 100 feet. The standard drainfield trench width is 3 feet. ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- JOE HOMEOWNER 123 NEWLANE WAY MRS. JOE HOMEOWNER 123456-12345 1-1-98 LOCATION: FOR: PREPARED BY: PARCEL NUMBER DATE: PROPERTY LINE: 185' PROPERTY LINE: 250' 1 INCH = 30 FEET 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 ATTACHEMENT C - SAMPLE DESIGN 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 Sample Design ---PAGE BREAK--- Section Two: Calculation Worksheet STEP 1 – CALCULATE THE DESIGN FLOW, OR MAXIMUM DAILY SEWAGE FLOW Calculate the design flow based on the number of bedrooms in the home: The number of bedrooms x 120 gallons per day = design flow The minimum design flow for any system is 240 gallons per day (note: These calculations only apply to single family residences. Please contact the Health Department for other building projects.) Calculate The Maximum Daily Sewage Flow # of bedrooms: x 120 = gpd (gallons per day) Minimum allowable design flow = 240 gpd Example: # of bedrooms: 3 x 120 (per bedroom) = 360 gpd The maximum daily sewage flow for a 3 bedroom home is 360 gallons per day. STEP 2- CALCULATE SEPTIC TANK SIZE • For a home serving 4 bedrooms or fewer, the minimum septic tank size is 1000 gallons. • For homes with more than 4 bedrooms, add 250 gallons of capacity per bedroom. Tank Size # of bedrooms: Minimum tank size: gallons Example: # of bedrooms: 3 Minimum tank size: 1,000 gallons The minimum septic tank size for a 3 bedroom home is 1000 gallons STEP 3- CALCULATE THE MAXIMUM DEPTH OF THE DRAINFIELD TRENCH Refer to the soil log/ site evaluation report provided by the Health Department. Locate the depth to the restrictive layer for the approved test pits. For gravity flow systems, subtract 36” from the restrictive layer to establish maximum trench depth. Calculate The Maximum Trench Depth Depth of test pit or to restrictive layer: – 36” = Trench Depth A Standard absorption trench (18” to 36” total depth) Example: 46 in. to restrictive layer less 36 in. required vertical separation = 10 inches trench depth If the soil log indicates a trench depth of 46 inches to the restrictive layer or bottom of test pit, the maximum total depth of the drainfield trenches will be 10 inches. ---PAGE BREAK--- STEP 4- CALCULATE THE ABSORPTION AREA AND RESERVE AREA Refer to the soil log/ site evaluation report provided by the Health Department. The soil loading rate will be listed. For example, based on the soil evaluation of the test pits the approved soil loading rate may be Divide the design flow by the soil loading rate. This will provide the square feet of absorption area needed for a standard gravity system using perforated pipe and gravel. To calculate trench length requirements, divide the square feet by the trench width (maximum width Calculate The Absorption Area Needed On This Site: = estimated peak flow application rate square feet of (from step one above) (from site/soil report) absorption area Example: 360 .4 = 900 estimated peak flow application rate square feet of (from step one above) (from site/soil report) absorption area STEP 5- CALCULATE THE DRAINFIELD LENGTH If you are using gravel/ drain rock divide the square feet of absorption area above by 3 to determine the required lineal feet of drainfield needed. Standard/Shallow Gravity Drainfield Length = square feet of absorption area trench width Total Length of (from step one above) Standard 3’ Trench Example: 900 square feet 3 feet = 300 feet square feet of absorption area trench width Total Length of (from step one above) Standard 3’ Trench If you are using an approved gravelless distribution system the required size of the drainfield can be reduced by 40%. The width of many gravelless distribution products is less than 36 inches therefore the absorption area is divided by 2.82. Standard/Shallow Gravelless Distribution Gravity Drainfield Length X = = square feet of Reduction Total Trench Width Total Length absorption area Factor Of Trench Example: 900 X .6 = 540 2.82 = 191.28ft square feet of Reduction Total Trench Width Total Length absorption area Factor Of Trench ---PAGE BREAK--- JOE HOMEOWNER 123 NEWLANE WAY MRS. JOE HOMEOWNER 123456-12345 1-1-98 LOCATION: FOR: PREPARED BY: PARCEL NUMBER DATE: PROPERTY LINE: 185' PROPERTY LINE: 250' 1 INCH = 30 FEET 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 ATTACHEMENT C - SAMPLE DESIGN 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 Your Design ---PAGE BREAK--- Property Owner For sewage designs submitted to Klickitat County Health Department and installation of on-site sewage systems, the definition of the property owner is expanded. The Health Department will allow on-site sewage system design and installation by the property owner and/or his/her immediate family member. Immediate family member is defined as: parents, children, brothers, sisters, grandparents, or grandchildren. The following statement must be signed by the property owner and the immediate family member. I, property owner of the parcel of land described as in Klickitat County, Washington, have prepared and designed the on-site septic system for this site. I have hired to install the on-site sewage system.