A family of six in a five bedroom house would like to treat their wastewater in

Question

A family of six in a five bedroom house would like to treat their wastewater in an onsite septic system, constructed wetland, and tile drainage (leach field) system. They will be generating a maximum of 1.2 m3/d of septic tank effluent. The septic tank effluent characteristics are 140 mg/L BOD, 50 mg/L TSS and 40 mg/L nitrogen (as ammonia nitrogen). They would like their constructed wetland to reduce their BOD to 15 mg/L and their nitrogen to 10 mg/L before the water enters the tile drain/leach field. No treatment objectives are required for TSS or pathogens in the wetland. The available gravel medium has a K of 9,144 m/d, with a porosity of 0.42. Decaying plant matter provides a background BOD concentration (C*) of 7 mg/L. Assume a wastewater temperature in the wetland of 12

Explanation / Answer

) Roof, footing, garage, cellar and surface water drainage must be excluded from the system. Water softener, water recharge and backwash wastes normally are not to be discharged to the system unless a separate subsurface discharge to an area 250 feet from wells or water courses is unavailable. (b) Designs for new construction shall be based upon a minimum daily flow of 110 gallons per day per bedroom. Other design flows listed in Table 1 may be applicable for systems receiving wastewater from dwellings equipped with older plumbing fixtures or waterless toilets. Table 1 Daily Design Flows Plumbing Fixtures (based on manufactured date) Minimum Design Flow (gallons per day per bedroom) Post-1994 Fixtures 1.6 gallons/flush toilets 2.5 gallons/minute faucets & showerheads 110 Pre-1994 Fixtures 3.5 gallons/flush toilets 3.0 gallons/minute faucets & showerheads 130 Pre-1980 Fixtures 3.5+ gallons/flush toilets 3.0+ gallons/minute faucets & showerheads 150 Waterless toilets (e. g., composter) (graywater discharge only) 75 Soil and Site Appraisal (a) Site Investigation. (1) Areas lower than the 10 year flood level are unacceptable for on-site systems. Slopes greater than 15% are also unacceptable. (2) There must be at least four feet of useable soil available above rock, unsuitable soil, and high seasonal groundwater for the installation of a conventional absorption field system (75-A.8(b)). (3) Soils with very rapid percolation rates (faster than one minute per inch) are not suitable for subsurface absorption systems unless the site is modified by blending with a less permeable soil to reduce the infiltration rate throughout the area to be used. (4) Subsurface treatment systems and components of the sewage system shall be separated from buildings, property lines, utilities and wells, to maintain system performance, permit repairs and reduce undesirable effects of underground sewage flow and water bodies dispersion. Table 2 lists the acceptable minimum separation distances from the various components of onsite wastewater treatment systems. (5) Once the required infiltration area is determined by daily flow, percolation tests and soil evaluation, the required useable area of the property for subsurface treatment can be found. An additional useable area of 50 percent shall be set aside for future expansion or replacement whenever possible. (b) Separation Requirements: Table 2 Separation Distances From Wastewater System Components (in feet) System Components Well or Suction Line (e)(g) To Stream, Lake, watercourse (b), or Wetland Dwelling Property Line House sewer (watertight joints) 25if cast iron sewer pipe 50 otherwise 25 3 10 Septic tank or watertight ETU 50 50 10 10 Effluent line to distribution box 50 50 10 10 Distribution box 100 100 20 10 Absorption field(c)(d) 100 (a) 100 20 10 Seepage pit(d) 150 (a) 100 20 10 Raised or Mound system (c)(d) 100 (a) 100 20 10 Intermittent Sand Filter (d) 100 (a)(f) 100(f) 20 10 Non-Waterborne Systems with offsite residual disposal 50 50 20 10 Non-Waterborne Systems with onsite discharge 100 50 20 10 Notes: (a) When wastewater treatment systems are located upgrade and in the direct path of surface water drainage to a well, the closest part of the treatment system shall be at least 200 feet away from the well. (b) Mean high water mark. (c) For all systems involving the placement of fill material, separation distances are measured from the toe of the slope of the fill. (d) Separation distances shall also be measured from the edge of the designated additional usable area as described in Section 75-A.4 (a)(5). (e) The closest part of the wastewater treatment system shall be located at least 10 feet from any water service line (e.g. public water supply main, public water service line or residential well water service line). (f) When sand filters are designed to be watertight and collect all effluent, the separation distance can be reduced to 50 feet. (g) The listed water well separation distances from contaminant sources shall be increased by 50% whenever aquifer water enters the water well at less than 50-feet below grade. If a 50% increase can not be achieved, then the greatest possible increase in separation distance shall be provided with such additional measures as needed to prevent contamination. (c) Soil Investigation. (1) The highest groundwater level shall be determined and shall include the depth to the seasonal high groundwater level and the type of water table - perched, apparent, or artesian. (2) If a subsurface treatment unit such as an absorption field is planned, at least four feet of useable soil shall be available over impermeable deposits (i.e., clay or bedrock). Highest groundwater level shall be at least two feet below the proposed trench bottom. Where systems are to be installed above drinking water aquifers, a greater separation distance to bedrock may be required by the local health department having jurisdiction. At least one test hole at least six feet deep shall be dug within or immediately adjacent to the proposed leaching area to insure that uniform soil and site conditions prevail. If observations reveal differing soil profiles, additional holes shall be dug and tested. These additional holes shall be spaced to indicate whether there is a sufficient area of useable soil to install the system. Treatment systems shall be designed to reflect the most severe conditions encountered. If the percolation tests results are inconsistent with field determined soil conditions, additional percolation tests must be conducted and the more restrictive tests must be the factor used for the system design. (3) Test holes for seepage pits shall extend to at least mid-depth and full depth of the proposed pit bottom. At least three feet of useable soil shall exist between the pit bottom and rock or other impermeable soil layer and the highest groundwater level. This shall be confirmed by extending at least one deep test hole three feet below the deepest proposed pit. (4) A local health department may accept or require other soil tests in lieu of the percolation test when such tests are conducted or observed by local health department personnel. (d) Soil Percolation Test. (1) At least two percolation tests shall be made at the site of each proposed sewage treatment system. (2) For seepage pits, one test shall be conducted at the bottom depth, and the other at half the pit depth. If different soil layers are encountered when digging the test pit, a percolation test shall be performed in each layer with the overall percolation rate being the weighted average of each test based upon the depth of each layer. The local health department having jurisdiction may adopt an alternative procedure for determining the permeability of soil for the installation of seepage pits. (3) A percolation test is only an indicator of soil permeability and must be consistent with the soil classification of the site as determined from the test holes. House Sewer (a) House sewers are laid on firm foundation at a minimum grade of one-quarter inch per foot preferably without bends. At least one cleanout with a properly fitted plug is to be provided. The house sewer shall allow for venting of gases from the sewage system. (b) House sewer construction including materials shall comply with the applicable requirements of the State Uniform Fire Prevention and Building Code, Residential Code, Chapter 30, Sanitary Drainage. (c) A minimum horizontal separation of 10 feet should exist between the house sewer and any water line. Where lines must cross, the water service line shall be at least 12 inches above the house sewer. If a water line must pass below the house sewer, the vertical separation must be at least 18 inches. (d) Suction waterlines shall never cross under house sewers or any other component of the sewage system. Septic Tanks (a) General information. (1) Septic tank capacities shall be based upon the number of household bedrooms. An expansion attic shall be considered as an additional bedroom. Table 3 specifies minimum septic tank capacities and minimum liquid surface areas. Table 3 Minimum Septic Tank Capacities Number of Bedrooms Minimum Tank Capacity (gallons) Minimum Liquid Surface Area (sq. ft.) 1, 2, 3 1,000 27 4 1,250 34 5 1,500 40 6 1,750 47 Note: Tank size requirements for more than six bedrooms shall be calculated by adding 250 gallons and seven square feet of surface area for each additional bedroom. A garbage grinder shall be considered equivalent to an additional bedroom for determining tank size. (2) Septic tank covers shall always be accessible. Where man holes are more than 12 inches below final grade, an extension collar shall be provided over each opening. Extension collars shall not be brought flush with the ground surface unless the cover can be locked to prevent tampering. Driveways or other facilities shall not be constructed above septic tanks unless specially designed and reinforced to safely carry the load imposed. (b) Design and Installation. (1) General Requirements. The following applies to all septic tanks regardless of material. (i) A minimum liquid depth of 30 inches. The maximum depth for determining the allowable design volume of a tank shall be 60 inches. Deeper tanks provide extra sludge storage, but no credit shall be given toward design volume. (ii) he minimum distance between the inlet and outlet shall be six feet. All tanks shall meet the minimum surface area requirement for the specific design volume specified in Table 3. The effective length of rectangular tanks should not be less than two nor greater than four times the effective width. (iii) Tanks must be watertight, constructed of durable material not subject to corrosion, decay, frost damage, or cracking. After installation, all septic tanks shall be able to support at least 300 pounds per square foot (psf). (iv) Tanks with a liquid depth of 48 inches or more shall have a top opening with a minimum of 20 inches in the shortest dimension to allow entry into the tank. Tanks with a liquid depth less than 48 inches shall have a top opening that is at least 12 inches in the shortest dimension. (v) Tanks shall have inlet and outlet baffles, sanitary tees or other devices to prevent the passage of floating solids and to minimize disturbance of settled sludge and floating scum by sewage entering and leaving the tank. Outlet designs such as gas deflection baffles are strongly recommended in all tanks. Inlet and outlet baffles shall extend a minimum of 12 inches and 14 inches respectively, below the liquid level in tanks with a liquid depth of less than 40 inches, and 16 and 18 inches respectively, in tanks with a liquid depth of 40 inches or greater. The distance between the outlet baffle and the outlet shall not exceed six inches. Baffles shall be constructed of a durable material not subject to corrosion, decay or cracking. (vi) There shall be a minimum of one inch clearance between the underside of the top of the tank and the top of all baffles, partition and/or tees to permit venting of tank gases. Multi-chamber and multi-tank systems shall also be designed to permit the venting of tank gases. (vii) Tanks shall be placed on at least a three inch bed of sand or pea gravel. This will provide for proper leveling and bearing. Additional instructions provided by the manufacturer shall also be followed. (viii) There shall be a minimum drop in elevation of two inches between the inverts of the inlet and outlet pipes. (ix) Garbage grinders. An additional 250 gallons of capacity and seven square feet of surface area is required when a garbage grinder can reasonably be expected at the time of construction or in the future. A gas deflection baffle or other acceptable outlet modification, and a dual compartment tank or two tanks in series must also be provided. (2) Multi-compartment tanks or tanks in series. (i) Dual compartments are recommended for all tanks and shall be required on all tanks with an interior length of ten feet or more. (ii) The first compartment or tank (inlet side) shall account for 60 - 75% of the required total design volume. (iii) The baffle separating the compartments shall extend from the bottom of the tank to at least six inches above the invert of the outlet pipe. (iv) Compartments shall be connected by a four inch vertical slot at least 18 inches in width, a six inch elbow, or two 4-inch elbows located at a distance below the liquid level equal to one-third the distance between the invert of the outlet and the bottom of the tank. At least one access manhole shall be provided into each compartment. (v) Tanks in series should be connected by a single pipe with a minimum diameter of four inches. (vi) The volume and surface area for meeting the requirements of Table 3 shall be based upon the total volume and surface areas of all the tanks and chambers. (3) Concrete tanks. (i) Concrete shall have a minimum compressive strength of 2,500 pounds per square inch (psi) at 28 days se

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