W. Va. Code R. § 64-47-5 - Sewage Treatment Works

5.1. General.

5.1.a. The design of sewage treatment plants shall be to provide for an estimated population on July 1, 2042. The design of all treatment plants shall be so that their capacity can readily be increased except when circumstances preclude the probability of expansion.

5.1.b. Plant Location. A sewage treatment plant site shall be as far as practical from any present area being built-up or any area that shall probably be built up within a reasonable future period. There shall be a buffer zone as indicated in Table 64-47-E. at the end of this rule, from any surrounding occupied structure to any new plant site. These buffer zone requirements do not apply to existing treatment works that are being upgraded or expanded. The direction of prevailing winds shall be considered when selecting the plant site. The location of the plants operational units shall be at an elevation that is not subject to the 100-year flood or shall otherwise be adequately protected against 100-year flood damage. The plant shall remain fully operational during a 25-year flood. The plant shall be readily accessible in all seasons. The site shall be of sufficient size to accommodate expansion or addition of facilities to increase the degree of treatment.

5.1.b.1. The Commissioner may wave buffer zone requirements shown in Table 64-47-E. upon receipt of a written request by the applicant and a detailed review by the Commissioner to determine any public health impact. Health, safety, and nuisance considerations shall be the basis of establishing a buffer zone.

5.1.b.2. The distances set forth in Table 64-47-E. are distances to sewage treatment units such as aeration basins, clarifiers, sludge holding tanks, chlorination basins, chlorinator rooms, blower houses and other units as stated in Table 64-47-E. Other buildings that may be part of the plant but are only used for storage or as a laboratory and do not contain chlorine cylinders or blowers, shall not be considered a sewage treatment unit and shall not be subject to buffer zone requirements.

5.1.c. Quality of Effluent.

5.1.c.1. Surface Water Discharge. The stream standards and water quality criteria established by the water resources board and effluent limitations established by the division of water resources shall be the basis of the required degree of wastewater treatment. The Commissioner may establish more stringent requirements if the location of a public water supply intake, a recreational water use area, or an aquaculture is downstream from the discharge point.

5.1.c.2. Land Discharge. See subsection 5.19 of this rule.

5.1.c.3. New Processes, Methods and Equipment. The policy of the Commissioner is to encourage the development of new processes, methods, and equipment for sewage treatment. The Commissioner may require the following:

5.1.c.3.A. Monitoring observations, including test results and engineering evaluations, demonstrating the efficiency of these processes;

5.1.c.3.B. Detailed description of the test methods;

5.1.c.3.C. Testing, including appropriately composited samples, under various ranges of strength and flow rates, including daily variations, and waste temperatures over a sufficient length of time to demonstrate performance under climatic and other conditions that the system may encounter in the area of the proposed installations;

5.1.c.3.D. Testing and evaluations made under the supervision of a competent process engineer other than those employed by the manufacturer or developer; and

5.1.c.3.E. A performance bond.

5.1.d. Design.

5.1.d.1. Industrial Wastes. When treating industrial and institutional wastes in a sewage treatment works, the character of the wastes in the design of the plant shall be considered. In these cases, the Commissioner may require treatability studies on the composite wastewater prior to the plant design.

5.1.d.2. Hydraulic Loading. The design of treatment plant units shall be based on the average rate of sewage flow per 24 hours, except where there are notations of significant deviations from the normal daily flow pattern.

5.1.d.3. Existing Sewage Systems. When there are existing sewers, there shall be a determination as to the volume and strength of sewage flow. Obtaining these data shall be from actual flow measurements, preferably for both wet and dry weather periods. There shall be laboratory analysis made on flow proportional composite samples taken over 24-hour periods. The design of plans and specifications for sewage works to serve existing sewage systems shall be on the basis of characteristics and strength of sewage as shown by results of composite samples examined and gaugings of the present flow plus allowance for estimated increase in population. In addition, they shall include non-excessive infiltration/inflow.

5.1.d.4. New Sewage Systems. For the construction of new sewers, design plans for sewage treatment works shall be made on the basis of 70 gallons per capita per day or estimates based upon a minimum one yearfully documented analysis of water use records adjusted for consumption and losses.

5.1.d.5. Organic Loading. Computation of the design organic loading shall be in the same manner used in determining design flow. Generally, computation of organic loading shall be at 0.17 pounds of five-day BOD per person per day. For package sewage treatment plants, recirculating sand filter systems, stabilization ponds, aerated ponds, and individual sewer systems, treating 50,000 G.P.D. or less, the organic loading design shall increase if proposing garbage grinders.

5.1.d.6. Conduits. The design of all piping and channels shall be to carry the maximum expected flows. The design of the incoming sewer shall be for free discharge. Filleting bottom corners of the channels is required. Eliminating pockets and corners where solids can accumulate is also required. There shall be suitable gates in channels to seal off unused sections that might accumulate solids. The use of shear gates or stop planks shall receive approval when using them in place of gate valves or sluice gates.

5.1.d.7. Arrangement of Units. Arrangement of component parts of the plant shall be for greatest operating convenience, flexibility, economy, and so as to facilitate installation of future units. There shall be multiple treatment units for plants greater than 100,000 gallons in size. There shall be a provision for appurtenances in such a manner that it is possible to temporarily take any unit of service. The remainder of the plant shall be operational with the unit or units out of service. In the case of oxidation ditches, if multiple rotors exist, the above requirements shall be met.

5.1.e. Miscellaneous.

5.1.e.1. Provisions for Taking Units Out of Service. Diversion piping and structures shall be properly located and arranged so that it is possible to independently remove either dual or multiple units of the plant from service for inspection, maintenance, and repairs.

5.1.e.2. Dewatering. There shall be means to dewater each unit. The possible need for hydrostatic pressure relief devices shall be considered.

5.1.e.3. Construction Materials. Because of the possible presence of hydrogen sulfide and other corrosive gases, greases, oils, and similar constituents frequently present in sewage, the materials selected for use in sewage treatment works shall be considered. This is particularly important in the selection of metals and paints. It is essential to avoid using dissimilar metals to minimize galvanic action. Cathodic protection is a requirement for all steel tanks.

5.1.e.4. Covering Units. The use of properly vented covers shall receive approval.

5.1.e.5. Painting. It is important to avoid the use of paints containing lead or mercury. In order to facilitate identification of piping, this rule suggests that the different lines be color-coded. The contents shall be stenciled on the piping in a contrasting color. The color scheme is only required for plants of over 100,000 gallons in size. For purposes of standardization, Table 64-47-F. at the end of this rule contains the recommended color scheme.

5.1.e.6. Operating Equipment. The specifications shall include a complete outfit of tools and accessories for the plant operator's use, such as squeegees, wrenches, valve keys, rakes, shovels, etc. A portable pump is recommended. There shall be readily accessible storage space and work bench facilities and consideration given to provision of a garage area that would also provide space for large equipment, maintenance, and repair.

5.1.e.7. Grading and Landscaping. There shall be concrete, asphalt or gravel walkways for access to all units. Where possible, it is important to avoid steep slopes to prevent erosion. Surface water shall not drain into any unit. There shall be particular care taken to protect trickling filter beds, sludge beds, and intermittent sand filters from surface water. There shall be a provision for landscaping, particularly when a plant location must be near residential areas.

5.1.f. Plant Outfalls.

5.1.f.1. Outlet. The outfall sewer, where practical, shall extend to the low water level of the receiving body of water in a manner to insure satisfactory dispersion of the effluent. It shall not have its outlet submerged and there must be provisions for taking samples of the effluent discharge. This rule permits the use of headwalls where adequate dispersion is obtained without carrying the outfall into the stream.

5.1.f.2. Design and Construction. The construction of the outfall sewer shall be as to protect it against the effects of flood water, ice, or other hazards as to reasonably insure its structural stability and freedom from stoppage.

5.1.g. Essential Facilities.

5.1.g.1. Emergency Power.

5.1.g.1.A. General. All sewage treatment facilities greater than 100,000 gallons in size that require electrical power, shall have an alternate source of electric power to allow continuity of operation during power failures, except as noted below. Methods of providing alternate sources include:

5.1.g.1.A.1. The connection of at least two independent public utility sources, such as substations. This rule recommends a power line from each substation, and it shall be a requirement unless the reviewing agency receives verifying documentation and approves that a duplicate line is not necessary to minimize water quality violations;

5.1.g.1.A.2. Portable or in-place internal combustion engine equipment that shall generate electrical or mechanical energy; and

5.1.g.1.A.3. Portable pumping equipment when only emergency pumping is required.

5.1.g.1.B. Power for Aeration. Standby generating capacity is not a requirement for aeration equipment used in the activated sludge process. When power outages of four hours or more are common, auxiliary power for minimum aeration of the activated sludge is a requirement. The reviewing authority may require full power generating capacity on certain critical stream segments.

5.1.g.1.C. Power for Disinfection. There shall be continuous disinfection, when required, during all power outages.

5.1.g.2. Electrical Equipment. The location of all electrical equipment such as motors and local controls, and electrical conduits shall either be at an elevation above the 100-year flood level or be of waterproof design. There shall be adequate protection for all outdoor equipment from the weather. Motors located indoors, and near liquid handling piping and equipment, shall be of splashproof design. All electrical wires in underground conduits or in conduits that can flood shall have water resistant insulation as identified in the National Electrical Code.

5.1.g.3. Water Supply.

5.1.g.3.A. General. There shall be an adequate supply of drinking water for use in the laboratory and general cleanliness around the plant. No piping or other connections shall exist in any part of the treatment works that, under any condition, might cause the contamination of a drinking water supply. There shall be an examination of the chemical quality for suitability for the intended use in heat exchangers, chlorinators, and other units.

5.1.g.3.B. Direct Connections. The drinking water supply line to each treatment plant shall have, as a minimum, an approved reduced pressure type backflow preventer. The installation of these devices shall be in a location to prevent flooding, corrosion and allow for adequate, quick service and periodic inspections. Installation in below-grade meter type vaults is not acceptable. All water supply take-off points shall follow the devices and, there shall be no allowance for extension of this line to serve the public.

5.1.g.3.C. Indirect Connection. When using a potable water supply for any purpose in a plant, there shall be provisions for a break tank, pressure pump, and pressure tank. Water shall discharge to the break tank through an air-gap at least six inches above the maximum flood line or the spill line of the tank, whichever is higher. There shall be a permanently posted sign at every hose bibb, faucet, or stop clock located on the water system beyond the break tank to indicate that the water is not safe for drinking.

5.1.g.3.D. Separate Drinking Water Supply. When it is not possible to provide drinking water from a public water supply, there shall be a separate well. Location, construction, and testing of the well shall comply with requirements of the Bureau. Requirements governing the use of the supply are those contained in subparagraphs 5.1.g.3.B. and 5.1.g.3.C. of this rule. Prior to construction, an applicant shall obtain approval of the supply from the Commissioner.

5.1.g.3.E. Separate Non-Drinking Water Supply. When there is a provision for a separate non-drinking water supply, there shall be posting of a permanent sign indicating the water is not safe for drinking to stop cocks, hose bibbs, and other water outlets.

5.1.g.4. Sanitary Facilities. All sewage treatment plants with laboratory facilities shall have a shower, toilet, and lavatory. There shall also be a provision for locker facilities.

5.1.g.5. Sewage Flow Measurement. There shall be facilities for measuring the volume of sewage flows at all treatment works greater than 100,000 gallons in size. All plants having a capacity of greater than 100,000 gallons per day shall equip indicating, recording, and totalizing equipment for effluent flow measurement.

5.1.g.6. Floor Slope. There shall be adequate floor surface slope to a point of drainage.

5.1.g.7. Stairways. The installation of stairways shall be with a slope of 30 to 35 degrees from the horizontal to facilitate carrying samples, tools, and other necessaries. All risers in a stairway should be of equal height. All stairways shall have handrails.

5.1.h. Safety. Following are the minimum requirements for all plants:

5.1.h.1. Enclosure of the wastewater treatment works with a minimum six feet high chain link fence with a locked entrance gate designed to discourage the entrance of unauthorized persons and animals. In lieu of a chain link fence, a barbed wire fence with a locked entrance gate can enclose natural systems, such as stabilization ponds, polishing ponds, and wetlands.

5.1.h.2. There shall be handrails, grating, and guardrails installed for safety when installed in open basins, screen channels, mechanical equipment, and other hazardous places. For all extended aeration plants of 50,000 gallons per day or less grating is a requirement.

5.1.h.3. Provision of first-aid equipment.

5.1.h.4. Posting of "No Smoking" signs in hazardous locations.

5.1.h.5. Provision of protective clothing and equipment such as SCBA's, atmospheric testers and gloves.

5.1.h.6. Provision of portable blower and sufficient hose.

5.1.h.7. There shall be explosion proof electrical equipment and non-sparking tools in work areas where hazardous conditions may exist, such as digester vaults and other locations where potentially explosive atmospheres of flammable gas or vapor accumulate.

5.1.h.8. Proper grounding and insulation of all electrical wiring is a requirement. There shall be no part of the plant piping used for grounding.

5.1.h.9. There shall be a provision for portable lighting equipment.

5.1.h.10. All manhole steps shall have slip-proof rungs and the steps shall be of the railroad type that shall help prevent foot slippage off the ends of the rungs.

5.1.h.11. There shall be a provision for separate storage located remotely from the plant for flammable and hazardous material.

5.1.h.12. The location of heating devices with open flames shall be in separate rooms with outside entrances and at grade or above.

5.1.h.13. Installation of particular safety precautions for gas-collection piping is a requirement.

5.1.h.14. There shall be adequate ventilation.

5.1.h.15. Chlorinator rooms and chlorine storage areas shall have heat, light, and a ventilation fan that is capable of being turned on from outside the room. The room shall be at grade or above. There shall be a provision a viewing window from the plant interior; and

5.1.h.16. The treatment works shall comply with the provisions of the Occupational Safety and Health Act (OSHA).

5.1.i. Laboratory Space. All treatment works shall have facilities, either contractual or on-site, for making the necessary analytical determinations and operating control tests. When using an on-site laboratory, isolation shall be done to render the laboratory reasonably free from the adverse effects of noise, heat, vibration, and dust. Minimum laboratory space for facilities not performing BOD and suspended solids testing on-site shall be 100 square feet floor space with 35 square feet bench area. Facilities providing on-site BOD, suspended solids, and fecal coliform analysis shall provide a minimum of 400 square feet of floor space and 150 square feet of bench space. If more than two persons shall be working in the laboratory at any given time, there shall be a provision of 100 square feet of additional space for each additional person. Advanced wastewater treatment plants shall provide a minimum of 100 additional square feet of floor space with proportionate increase in bench space. Lists of laboratory equipment shall be compiled from USEPA approved latest edition of Standard Methods for the Examination of Water & Wastewater, by APHA - AWWA - WPCF.

5.1.j. Laboratory Equipment. All treatment works shall have laboratory equipment determined by the commissioner based upon type and complexity of the treatment process. However, all extended aeration treatment plants of 100,000 gallons per day or less shall have the following:

5.1.j.1. A test kit for pH and for chlorine residual. This test kit shall be of the comparator type as manufactured by Hach, Taylor, Hellige, or Wyandotte;

5.1.j.2. Two one-liter graduated beakers;

5.1.j.3. A secchi disk; and

5.1.j.4. A squeegee with proper length of handle, five-quart bucket and rubber gloves.

5.2. Screening Devices and Comminutors.

5.2.a. Bar Racks and Screens.

5.2.a.1. Either coarse bar racks or bar screens shall provide protection for pumps and other equipment. Coarse bar racks shall provide protection for comminutors.

5.2.a.2. Location.

5.2.a.2.A. Indoors. Screening devices, installed in a building where there is other equipment or offices located, should be accessible only through a separate outside entrance.

5.2.a.2.B. Outdoors. Screening devices installed outside shall have protection from freezing.

5.2.a.2.C. Access. Screening areas shall have stairway access, lighting and ventilation, and a convenient means for removing the screenings.

5.2.a.3. Design and Installation.

5.2.a.3.A. Bar Spacing. Clear openings between bars shall be no less than one inch for manually cleaned screens. Clear openings for mechanically cleaned screens may be as small as 0.5 inch. Maximum clear openings shall be 1.75 inches.

5.2.a.3.B. Slope. The placement of manually cleaned screens, except those for emergency use, shall be on a slope of 30 to 45 degrees from the horizontal.

5.2.a.3.C. Velocities. At normal operating flow conditions, approach velocities shall be no less than 1.25 feet per second, to prevent settling; and no greater than 3 feet per second through the bar screen to prevent forcing material through the openings.

5.2.a.3.D. Channels. For plants of greater than 100,000 gallons per day, there shall be a provision for dual channels and equipped with the necessary gates to isolate flow from any screening unit. There shall also be provisions to facilitate dewatering each unit. The shape of the channel preceding and following the screen shall be to eliminate stranding and settling of solids. Channels shall be three to six inches below the invert of the incoming sewer.

5.2.a.3.E. Mechanical Devices. A positive means of locking out each mechanical device shall be a provision.

5.2.a.4. Control Systems.

5.2.a.4.A. Timing Devices. All mechanical units without timing devices shall run continuously. All mechanical units operated by timing devices shall have auxiliary control that shall set the cleaning mechanism in operation at predetermined high-water elevations.

5.2.a.4.B. Electrical Fixtures and Controls. Electrical fixtures and controls in screening areas where explosive gases may accumulate shall meet the requirements of the National Electrical Code for Class 1, Group D, Division 1 locations.

5.2.a.4.C. Manual Override. A manual override shall supplement automatic controls.

5.2.a.5. Auxiliary Screens. When using mechanically operated screening or comminuting devices, there shall be a provision for auxiliary manually cleaned screens. Design shall include provisions for automatic diversion of the entire sewage flow through the auxiliary screens should the regular units fail.

5.2.a.6. Fine Screens. The use of fine screens in lieu of sedimentation is not permitted. In special cases, if demonstrated that the features peculiar to fine screens may be advantageous, the Bureau may approve the proposed installation on a case-by-case basis.

5.2.a.7. Disposal of Screenings. There shall be facilities for removal, handling, storage, and disposal of screenings in a sanitary manner. Manually cleaned screening facilities shall include an accessible platform from which the operator may rake screenings easily and safely. There shall be a provision for suitable drainage facilities for both the platform and storage areas. This rule prohibits grinding of screenings and return to the sewage flow. This rule prohibits open area disposal. The commissioner shall approve the manner in which applicant buries screens or if permitted, applicant may place them in a landfill.

5.2.b. Comminutors.

5.2.b.1. Location. The location may be a requirement at sewage treatment plants forty thousand (40,000) gallons or greater in size. The location of comminutors shall downstream of any grit removal equipment.

5.2.b.2. Size. The design of comminutors shall be to handle peak flow.

5.2.b.3. Installation. There shall be a bar screen bypass channel. The use of the bypass channel should be automatic at depths of flow exceeding the design capacity of the comminutor.

5.2.b.4. Servicing. There shall be a provision to facilitate servicing units in place and removing units from their location for servicing.

5.2.b.5. Macerators and Grinder Pumps. In lieu of comminutors, applicant may use macerators and grinder pumps or similar devices upon approval by the Commissioner.

5.3. Grit Removal.

5.3.a. General. There shall be grit removal facilities for all sewage treatment plants serving combined sewer systems. There shall be provision made for future installation of grit removal facilities for all plants of greater than 100,000 gallons in size serving new sanitary sewer systems. Grit removal facilities may be a requirement for new plants serving existing sewer systems. All sewage treatment plants having anaerobic digesters require grit removal.

5.3.b. Location. The location of grit removal facilities, except in unusual circumstances shall be ahead of pumps and comminuting devices, and coarse bar racks should be placed ahead of mechanically cleaned grit removal facilities.

5.3.c. Type and Number of Units. Grit removal facilities for plants treating wastes from combined sewers shall have at least two manually cleaned units or one mechanically cleaned unit and one manually cleaned unit. Facilities other than channel-types are desirable for plants 100,000 gallons or greater in size, if provided with flexible controls for agitation or air supply devices and with grit removal equipment.

5.3.d. Velocity-Controlled Grit Removal.

5.3.d.1. Inlet. Inlet turbulence shall be minimal.

5.3.d.2. Velocity and Detention. Design of channel-type chambers shall be to provide a velocity of one foot per second. The detention time shall be based on the size of particles (0.21 mm) to be removed. The design should take into consideration undesirable turbulence and velocities at inlets and outlets.

5.3.d.3. Grit Washing. The method of final grit disposal should determine the need for grit washing.

5.3.d.4. Drains. There shall be a provision for dewatering each unit.

5.3.d.5. Water. For clean up purposes, there shall be an adequate supply of water under pressure.

5.3.d.6. Grit Removal. Grit removal facilities located in deep pits shall have mechanical equipment for pumping or hoisting grit to ground level. The pits shall have a stairway, elevator or manlift, ventilation, and lighting, and have a means of drainage.

5.3.e. Aerated Grit Removal.

5.3.e.1. Air Diffusers. The location of air diffusers shall be on one side of the tank, two to three feet above the tank bottom.

5.3.e.2. Air Supply Rate. There shall be a detention time of three minutes.

5.3.e.3. Inlet and Outlet. Design of the aerated grit chamber shall be such as to prevent short circuiting at the inlet and outlet. The inlet to the chamber shall introduce the wastewater directly into the circulation pattern caused by the air diffusion. The outlet shall be at a right angle to the inlet and a baffle installed near the outlet.

5.3.e.4. Grit Removal. The aerated grit chambers shall have mechanical grit removal equipment.

5.3.f. Grit Handling. Grit handling areas should have impervious surfaces with drains. If transporting grit, the design of the conveying equipment should be to avoid loss of material and to provide protection from freezing.

5.3.g. Grit Disposal. The Commissioner shall approve in advance the manner in which an applicant buries grit or if permitted, applicant may place it in a landfill.

5.4. Pre-aeration.

5.4.a. General. Pre-aeration of sewage to reduce septicity may be a requirement in special cases.

5.5. Flow Equalization.

5.5.a. General. There shall be flow equalization when there are expectations of large daily variations in organic or hydraulic loadings.

5.5.b. Location. The location of equalization basins shall be downstream of pretreatment facilities such as bar screens, comminutors, and grit chambers.

5.5.c. Type. There may be a provision for flow equalization by using separate basins or on-line treatment units, such as aeration tanks. The design of equalization basins may be as either in-line or side-line units.

5.5.d. Design.

5.5.d.1. Mixing. Mixing requirements for normal raw domestic wastewaters shall range from 0.02 to 0.04 hp/1000 gallons of maximum storage volume.

5.5.d.2. Aeration. Maintaining a minimum of 1.0 mg/1 of dissolved oxygen in the mixing basin at all times is required. Air supply rates shall be a minimum of 1.25 cfm/1000 gallons of storage capacity.

5.5.d.3. Storage. There shall be sufficient storage to allow the sections of the plant that follow the storage to operate at or at less than their rated design capacity.

5.5.d.4. Detention/Equalization. Basins designed for a combination of storage of wet weather flows and equalization shall have compartments to allow utilization of a portion of the basins for dry weather flow equalization.

5.5.d.5. Flow Discharge Control. There shall be multiple pumping units capable of delivering the desired flow rate from the equalization basin with the largest pumping unit out of service. All pumps, ejectors and air lifts shall be easily removable.

5.5.d.6. Aeration Support. When pumps have floating surface aerators, there shall be provisions to protect the units when dewatering the tank.

5.5.d.7. Basin Cleaning. There shall be facilities to flush solids and grease accumulations from the basin walls.

5.5.d.8. Scum Control. For plants greater than 100,000 gallons in size there shall be a provision for a high-water-level takeoff for withdrawing floating material when using subsurface diffusers.

5.5.d.9. Controls. Controls shall be a provision for plants greater than 100,000 gallons per day. Inlets and outlets for all basin compartments shall suitably equip accessible external valves, stop plates, weirs, or other devices to permit flow control, level control, and the removal of an individual unit from service. Also, there shall be a provision for facilities to measure and indicate liquid levels and flow rates.

5.6. Settling.

5.6.a. Inlets. The design of inlets should be to dissipate the inlet velocity, to distribute the flow equally, and to prevent short-circuiting. The design of channels should be to maintain a velocity of at least one foot per second at one-half design flow. There shall be provisions for eliminating corner pockets and dead ends and use corner fillets or channeling where necessary. There shall be provisions for elimination or removal of floating materials in inlet structures having submerged ports.

5.6.b. Dimensions. The minimum length of flow from inlet to outlet shall be 10 feet unless special provisions are made to prevent short-circuiting. The liquid depth of mechanically cleaned settling tanks shall be as shallow as practicable, but not less than seven feet. Sidewater depth for final clarifiers for activated sludge shall not be less than 12 feet for plants greater than 100,000 gallons in size.

5.6.c. Scum Removal. There shall be effective scum collection and removal facilities, including baffling, ahead of the outlet weirs on all settling tanks. There may be provisions for discharge of scum with the sludge; other provisions may be necessary to dispose of floating materials that may adversely affect sludge handling and disposal.

5.6.d. Weirs. Overflow weirs shall be adjustable. Weir loadings shall not exceed ten thousand 10,000 gallons per day per linear foot for plants designed for average flows of 1.0 mgd or less. Weir loadings for plants designed for flows in excess of 1.0 mgd shall receive special consideration, but these loadings should not exceed 15,000 gallons per day per linear foot. If pumping is a requirement, pump capacity shall relate to tank design to avoid excessive weir loading.

5.6.e. Submerged Surfaces. The tops of beams and similar construction features submerged shall have a minimum slope of 1.4 vertical to 1 horizontal. The underside of these features shall have a slope of one to one to prevent the accumulation of scum or solids.

5.6.f. Multiple Units. Multiple units capable of independent operation shall exist at all plants having a capacity greater than 100,000 gallons per day.

5.6.g. Protective and Servicing Facilities. In plants greater than 100,000 gallons in size all settling tanks shall have a provision for easy access for maintenance, and protection of operators. These features include stairways, walkways, handrails, etc. If side walls extend some distance above the liquid level to provide flood protection for other purposes, there shall be convenient walkways to facilitate housekeeping and maintenance of weirs.

5.6.h. Surface Settling Rates.

5.6.h.1. Primary Settling Tanks. Surface settling rates for primary tanks shall not exceed 1,000 gallons per day per square foot at design flow or 1,500 gallons per day per square foot for peak hourly flows, whichever is larger, for plants having a design flow of 1.0 mgd or less. The Commissioner may permit higher surface settling rates for larger plants.

5.6.h.2. Intermediate Settling Tanks. Surface settling rates for intermediate settling tanks, when using following fixed film reactors, shall not exceed 1,500 gallons per day per square foot based on their design flow.

5.6.h.3. Final Settling Tanks. Surface settling rates for final settling tanks, based on maximum flow rates, shall be as follows:

5.6.h.3.A. Fixed Film Biological Reactors. Surface settling rates for settling tanks following trickling filters or rotating biological contactors shall not exceed 1,200 gallons per day per square foot based on peak hourly flow.

5.6.h.3.B. Activated Sludge. The hydraulic design of intermediate and final settling tanks following the activated sludge process shall be based upon the anticipated peak hourly rate for the area downstream of the inlet baffle. The hydraulic loadings shall not exceed: 1,200 gallons per day per square foot for conventional, step aeration, contact stabilization and the carbonaceous stage of separate-stage nitrification; 1,000 gallons per day per square foot for extended aeration; and 800 gallons per day per square foot for the separate nitrification stage. The solids loading, that includes the return activated sludge (RAS) concentration volume, for all activated sludge processes shall not exceed 50 pounds of solids per day per square foot at the peak rate. Package plants equal to or smaller than 5,000 gallons per day shall have a minimum of eight hours detention time in the clarifier and plants between five thousand 5,000 and 40,000 gallons per day shall have a minimum six-hours detention time in the clarifier, excluding the bottom 2/3 of the hopper.

5.6.i. Freeboard. The walls of settling tanks shall extend at least six inches above the surrounding ground surface and shall provide not less than 12 inches freeboard. Additional freeboard or the use of wind screens is recommended where larger settling tanks are subject to high velocity wind currents that would cause tank surface waves and inhibit effective scum removal.

5.6.j. Scum Removal. Effective scum collection and removal facilities, including baffling, shall exist for all settling tanks. The design shall recognize unusual characteristics of scum that may adversely affect pumping, piping, sludge handling and disposal. There may be provisions for the discharge of scum with the sludge; however, other special provisions for disposal may be necessary.

5.6.k. Sludge Removal. There shall be provisions to permit continuous sludge removal from settling tanks. Final clarifiers in activated sludge plants greater than 0.25 mgd shall have positive scraping devices except for in-basin clarifiers. Each sludge withdrawal line shall be at least four inches in diameter, if pumped, and, if gravity flow, at least six inches in diameter and individually valved. This does not apply to air lift methods of sludge removal rate. Head available for withdrawal of sludge shall be at least thirty 30 inches. There shall be adequate provisions for rodding or backflushing individual pipe runs. Piping shall also exist to return waste sludge to primary clarifiers.

5.6.l. Sludge Hopper. The minimum slope of the side walls shall be 1.7 vertical to 1 horizontal. Hopper wall surfaces shall be smooth with rounded corners to aid in sludge removal. Hopper bottoms shall have a maximum dimension of two feet.

5.7. Activated Sludge.

5.7.a. General. The use of activated sludge process, and its various modifications, shall be permitted where sewage is amenable to biological treatment.

5.7.b. Settling Tanks. The following requirement is in addition to those set forth in subsection 5.6 of this rule:

5.7.b.1. Bypass. When using a primary settling tank, there also shall be a provision for discharging raw sewage directly to the aeration tanks to facilitate plant start-up and operation during the initial stages of the plant design life.

5.7.c. Aeration.

5.7.c.1. Aeration Tanks.

5.7.c.1.A. General. There shall be multiple tanks capable of independent operation for all plants rated at greater than 100,000 gallons per day. The size of the aeration tank for any particular adaptation of the process shall be based on such factors as the size of the plant, degree of treatment desired, sludge age, mixed liquor suspended solids (MLSS) concentration, BOD loading and food to microorganism ratio (F/M). There shall be calculations submitted to justify the basis of the aeration tank capacity and process efficiency. When not submitting process design calculations, it is a requirement to use the aeration tank capacities and permissible loadings for the several adaptations of the processes shown in Table 64-47-G., found at the end of this rule. These values apply to plants receiving peak to average daily load ratios ranging from about 2-to-1 to 4-to-1. Thus, the Commissioner may consider the utilization of flow equalization facilities to reduce the daily peak organic load as justification to approve organic loading rates that exceed those specified in Table 64-47-G.

5.7.c.1.B. Arrangement of Aeration Tanks. The dimensions of each independent mixed liquor aeration tank shall be such as to maintain effective mixing and utilization of air. Liquid depths shall not be less than 10 feet for plants greater than 100,000 gallons per day. For very small tanks or tanks with special configuration, the shape of the tank and the installation of aeration equipment should provide for elimination of short-circuiting through the tank. Table 64-47-G. at the end of this rule contains Permissible Aeration Tank Capacities and Loadings.

5.7.c.2. Inlets and Outlets. Inlets and outlets for each aeration tank unit shall suitably equip valves, gates, stop plates, weirs, or other devices to permit control of the flow and to maintain reasonably constant liquid level. The hydraulic properties of the system shall permit any single aeration tank unit out of service to carry the maximum instantaneous hydraulic load.

5.7.c.3. Conduits. Design of channels and pipes carrying liquids with solids in suspension shall be to maintain self-cleaning velocities or shall agitate to keep the solids in suspension at all rates of flow within the design limits.

5.7.c.4. Measuring Devices. For plants designed for greater than 100,000 gallons per day, there shall be devices installed for indicating flow rates of influent sewage, return sludge and air to each aeration tank. For plants designed for greater than 1,000,000 gallons per day, there shall be devices installed for totalizing, indicating, and recording influent sewage and returned sludge to each aeration tank. Where the design provides for mixing all returned sludge with the raw sewage, or primary effluent, at one location, then measuring the mixed liquor flow rate to each aeration unit is a requirement.

5.7.c.5. Freeboard and Foam Control.

5.7.c.5.A. Aeration tanks shall have a freeboard of at least 18 inches.

5.7.c.5.B. Aeration tanks shall have foam control devises on all plants greater than 10,000 gallons in size. Suitable spray systems or other appropriate means is acceptable. The spray lines shall have provisions for draining to prevent damage by freezing.

5.7.d. Aeration Equipment.

5.7.d.1. General. Design of aeration equipment shall be to supply sufficient oxygen to maintain a minimum dissolved oxygen concentration of 2 mg/l throughout the mixed liquor at all times. Aeration equipment shall be capable of transferring 1.1 lbs. of oxygen per pound of peak BOD applied to the aeration tank with the exception of the extended aeration process for which the value shall be 1.8. There shall be calculations submitted to justify the oxygen requirements and the aeration equipment capacity for plants greater than 100,000 gallons in size.

5.7.d.2. Nitrification. In the case of nitrification, the oxygen requirement for oxidizing ammonia shall be added to the above requirement for carbonaceous BOD removal. Taking the nitrogen oxygen demand (NOD) as 4.6 times the daily peak TKN content of the influent is a requirement. In addition, there shall be consideration given to the oxygen demands due to recycle flows, heat treatment supernatant, vacuum filtrate, elutriates, and others due to high concentrations of BOD and TKN associated with the flows.

5.7.d.3. Controls. There shall be variable air controls to aeration basins. There may be time clocks, variable speed devices or variable depth weirs for the blowers or aerators used. All extended aeration plants shall have a 24-hour time clock graduated in 15-minute intervals.

5.7.d.4. Diffused Air Systems.

5.7.d.4.A. The design of aeration equipment shall be to provide oxygen requirements as set forth in Table 64-47-H. at the end of this rule.

5.7.d.4.B. The requirements above shall include air volume standards for channels, pumps or other air-use demands.

5.7.d.4.C. The specified capacity of blowers or air compressors, particularly centrifugal blowers, shall take into account that the air intake temperature may reach 40 degrees Celsius or 104 degrees Fahrenheit or higher and the pressure shall be less than atmospheric.

5.7.d.4.D. The blowers shall exist in multiple units, for plants of a capacity greater than 20,000 gallons per day in size, so arranged and in such capacities as to meet the maximum air demand with the single largest unit out of service. The design shall also provide for varying the volume of air delivered in proportion to the load demand of the plant.

5.7.d.4.E. The spacing of diffusers shall be in accordance with the oxygenation requirements through the length of the channel or tank and designed to facilitate adjustments of their spacing without major revision to air header piping. The arrangement of diffusers shall also permit their removal for inspection, maintenance, and replacement without dewatering the tank and without shutting off the air supply to other diffusers in the tank.

5.7.d.4.F. Individual assembly units of diffusers shall equip control valves, preferably with indicator markings for throttling or for complete shut-off. Diffusers in any single assembly shall have substantially uniform pressure loss.

5.7.d.4.G. There shall be air filters to prevent clogging of the diffuser system used and to protect the blowers.

5.7.d.5. Mechanical Aeration System.

5.7.d.5.A. The design of the mechanism and drive unit shall be for the expected conditions in the aeration tank in terms of the power performance. Certified testing shall verify mechanical aerator performance.

5.7.d.5.B. A mechanical aeration system shall also accomplish the following:

5.7.d.5.B.1. Maintain all biological solids in suspension.

5.7.d.5.B.2. Meet maximum oxygen demand and maintain process performance with the largest unit out of service. When system capacity is greater than 20,000 gallons per day and when proposing single unit installations, there shall be a provision for a spare aeration mechanism; and

5.7.d.5.B.3. Provide for varying the amount of oxygen transferred in proportion to the load demand on the plant.

5.7.e. Return Sludge Equipment.

5.7.e.1. Return Sludge Rate. The rate of sludge return shall vary by means of variable speed motors, drivers, air lifts or timers to pump sludge. The rate of sludge return expressed as a percentage of the average design flow of sewage shall generally be variable between the limits shown in Table 64-47-I at the end of this rule.

5.7.e.2. Return Sludge Pumps. If using motor driven return sludge pumps, the largest pump out of service shall obtain the maximum return sludge capacity. Pump suctions shall equip a positive head. Pumps shall have at least three-inch suction and discharge openings. If using air lifts for returning sludge from each settling tank hopper, a standby unit is not a requirement provided the design of the air lifts facilitate rapid and easy cleaning and removal and applicant is providing other standby measures. Air lifts shall be at least 2.5 inches in diameter.

5.7.e.3. Return Sludge Piping. Discharge piping shall be at least three inches in diameter and the design shall be to maintain a velocity of not less than two feet per second when return sludge facilities are operating at normal return sludge rates.

5.7.e.4. Waste Sludge Facilities. Waste sludge control facilities shall have a maximum capacity of not less than 25% of the average rate of sewage flow and function satisfactorily at rates of 0.5% of average sewage flow or a minimum of 10 gallons per minute, whichever is larger, for plants greater than 100,000 gallons per day in size. Aerated sludge holding tanks shall exist for all extended aeration plants up to 100,000 gallons per day in size. The design of sludge holding tanks shall be with a minimum capacity of 10% of the average daily design flow.

5.8. Trickling Filters.

5.8.a. Design. The design of filters shall be so as to provide the reduction in carbonaceous and nitrogenous oxygen demand required, and to properly condition the sewage for subsequent treatment processes. The hydraulic loading on standard rate trickling filters shall be between 2,000,000 and 4,000,000 gallons per acre per day with an organic loading equal to or less than 400 pounds of BOD₅ per acre foot per day.

5.8.b. Dosing Equipment.

5.8.b.1. Distribution. The sewage distribution may be over the filter by rotary distributors or other suitable devices that permit reasonably uniform distribution to the surface area. At design average flow, the deviation from a calculated uniformly distributed volume per square foot of the filter surface shall not exceed plus or minus 10% at any point.

5.8.b.2. Dosing. Sewage application to the filters may be by siphons, pumps, or by gravity discharge preceding treatment units when suitable flow characteristics have been developed. Application of sewage shall be practically continuous. A piping system that permits recirculation shall be considered.

5.8.b.3. Hydraulics. There shall be careful calculation of all hydraulic factors involving proper distribution of sewage on the filters. For reaction type distributors, a minimum head of 25 inches between low water level in siphon chamber and center of arms is a requirement. There shall be surge relief to prevent damage to distributor seals, where pumping sewage directly to the distributors.

5.8.b.4. Clearance. There shall be a minimum clearance of six inches between media and distributor arms. This rule requires greater clearance where icing occurs.

5.8.c. Media.

5.8.c.1. Quality. The media may be crushed rock, slag, or plastic, or specially manufactured material. The media shall be durable, resistant to spalling or flaking and relatively insoluble in sewage. The top 18 inches shall have a loss by the 20-cycle, sodium sulfate soundness test of not more than 10%, as prescribed by ASCE Manual of Engineering Practice No. 13, "Filtering Materials for Sewage Treatment Plants." The balance to pass a 10-cycle test using the same criteria. Slag media shall be free from iron. Manufactured media shall be structurally stable and chemically and biologically inert.

5.8.c.2. Rock or slag filter media shall have a minimum depth of five feet above the underdrains. Manufactured filter media shall have a minimum depth of 10 feet to provide adequate contact time with the wastewater. Rock or slag filter media depths shall not exceed 10 feet and manufactured filter media depths shall not exceed 30 feet.

5.8.c.3. Size and Grading.

5.8.c.3.A. Rock, slag and similar media shall not contain more than 5% by weight of pieces whose longest dimension is three times the least dimension. They shall be free from thin elongated flat pieces, dust, clay, sand, or fine material and shall conform to the size and grading when mechanically graded over vibrating screens with square openings according to Table 64-47-J at the end of this rule.

5.8.c.3.B. Hand Picked Field Stone. The maximum dimensions of stone shall be five inches; and minimum dimensions of stone shall be three inches.

5.8.c.3.C. Manufactured Media. On a case-by-case basis, the Commissioner shall evaluate applications of manufactured media.

5.8.c.3.D. Handling and Placing of Media. Storage of material delivered to the filter site shall be on wood planks or other approved clean, hard surfaced areas. Rehandling of all material shall take place at the filter site and there shall be no dumping of material into the filter. Rescreening and forking crushed rock, slag, and similar media at the filter site to remove all fines is required. Placement of these material shall be by hand to a depth of 12 inches above the tile so as not to damage the underdrains. The engineer may place the remainder of the material. The engineer shall approve how applicant handles and places manufactured media. There shall be no trucks, tractors, or other heavy equipment driven over the filter during or after construction.

5.8.d. Underdrainage System.

5.8.d.1. Arrangement. Underdrains with semi-circular inverts shall exist and the underdrainage system shall cover the entire floor of the filter. Inlet openings into the underdrains shall have an unsubmerged gross combined area equal to at least 15% of surface area of the filter.

5.8.d.2. Slope. The underdrains shall have a minimum slope of 1%. The design of effluent channels shall be to produce a minimum velocity of two feet per second at average daily rate of application to the filter.

5.8.d.3. Flushing. There shall be a provision for flushing the underdrains. The use of a peripheral head channel with vertical vents is acceptable for flushing purposes. There shall be inspection facilities.

5.8.d.4. Ventilation. The design of the underdrainage system, effluent channels and effluent pipe shall be to permit free passage of air. The size of drains, channels, and pipe shall be such that not more than 50% of their cross-sectional area shall be submerged under the design hydraulic loading. There shall be a provision in the design of the effluent channels to allow the possibility of increased hydraulic loading.

5.8.e. Special Features.

5.8.e.1. Flooding. There shall be provisions in the design of filter structures so that they may flood.

5.8.e.2. Maintenance. The installation of all distribution devices, underdrains, channels, and pipes shall be so that an applicant may properly maintain, flush, or drain them.

5.8.e.3. Freeboard. There shall be a freeboard of four feet or more for tall, manufactured media filters to minimize windblown spray.

5.8.e.4. Flow Measurement. There shall be devices to permit measurement of flow to filter, including recirculated flows.

5.8.e.5. Recirculation. The merits of recirculation for various purposes; for example, to prevent drying of a standard rate filter between dosings shall be considered.

5.8.f. Two-Stage Filters. The use of two-stage filters when single stage filters may not accomplish the required removals shall be considered.

5.8.g. Efficiencies. Calculating and documenting expected efficiencies is required. The effect of climatic conditions on the overall filter performance shall be considered.

5.8.h. Rotary Distributor Seals. This rule does not permit the use of mercury seals. Ease of seal replacement shall be a consideration in design.

5.9. Rotating Biological Contactors (RBCs).

5.9.a. Winter Protection. Year-round operation requires covering of rotating contactors to protect the biological growth from cold temperatures and the excessive loss of heat from the wastewater with the resulting loss of performance. Construction of enclosures shall be of a suitable corrosion resistant material. Windows or simple louvered mechanisms shall be installed that can be opened in the summer and closed in the winter to provide ventilation. To minimize condensation, the enclosure shall have insulation or heat.

5.9.b. Required Pretreatment. Primary settling tanks equipped with scum and grease collecting devices shall precede RBCs. Bar screening or comminution are not suitable as the sole means of pretreatment.

5.9.c. Unit Sizing. Unit sizing shall be based on experience at similar full-scale installations or thoroughly documented pilot testing with the particular wastewater. In determining design loading rates, expressed in units of volume per day per unit area of media covered by biological growth, the following parameters shall be considered:

5.9.c.1. Design flow rate and influent waste strength;

5.9.c.2. Percentage of BOD to be removed;

5.9.c.3. Media arrangement, including number of stages and unit area in each stage;

5.9.c.4. Rotational velocity of the media;

5.9.c.5. Retention time within the tank containing the media;

5.9.c.6. Wastewater temperature;

5.9.c.7. Percentage of influent BOD that is soluble; and

5.9.c.8. In addition to the above parameters, loading rates for nitrification shall depend upon influent total Kjeldahl nitrogen (TKN), influent ammonia nitrogen concentration, pH, and the allowable effluent ammonia nitrogen concentration.

5.9.d. Design Safety Factor. Daily load variations affect effluent concentrations of ammonia nitrogen from the RBC process designed for nitrification. Therefore, it may be necessary to increase the design surface area proportional to the ammonia nitrogen daily peaking rates to meet effluent limitations. An alternative is to provide flow equalization sufficient to insure process performance within the required effluent limitations.

5.9.e. Air Driven Units. This rule does not permit air driven units.

5.10. Sequential Batch Reactor (SBR) and Intermittent Wastewater Treatment Systems.

5.10.a. Batch Reactor. Batch reactor and intermittent treatment technologies shall use an alternating multiple-tank system for new installations. Tank applications for renovating existing treatment works or for facilities with flows equal to or less than 50,000 gallons per day shall be considered on a case-by-case basis, by the Commissioner.

5.10.b. Aeration Devises. Blowers or other aeration devices shall exist in multiple units for treatment works that have a capacity of greater than 20,000 gallons per day. The arrangement and capacity of blowers or other aeration devices shall be as to meet the maximum air demand with the largest single unit out of service.

5.10.c. Diffusers. Individual assembly units of diffusers shall have control valves, preferably with indicator markings for throttling or for complete shutoff.

5.10.d. Design Loadings. Five-day biochemical oxygen demand loading and aeration requirements shall be no less than the requirements specified by the manufacturer for each particular proprietary sequencing batch reactor (SBR) process. An applicant shall obtain written concurrence with the proposed design and specifications for a particular installation from the manufacturer of a proprietary system or technology and shall provide it with the project plans. Generally, an applicant should use an average hydraulic detention time of 24 hours as a basis for design.

5.10.e. Operation. Each unit shall be capable of independent operation during low, average, peak, and storm flow.

5.10.f. Decanting. There shall be provisions to ensure that decanting cannot in any way occur during any phase of operation except at the end of the "settle" or the "idle" phase or period.

5.10.g. Pre-treatment. A mechanically cleaned bar screen having maximum clear openings between the bars of a half inch (closer spacings are encouraged) shall precede SBR treatment plants. Comminutors or other sewage grinders are not acceptable substitutes for this requirement.

5.10.h. Scum Removal. Each unit shall have a means of excluding scum and other floatables from entering the decanter.

5.10.i. Design Flow Rate. The design of downstream units and piping shall be based upon the decanter flow rate, not the design flow of the treatment facilities.

5.11. Recirculating Sand Filters (RSF). The design of RSF systems can be to treat flows as small as those generated by the individual home, up to any size for which engineering considerations and economics would indicate the RSF system to be the optimum choice, when comparing the RSF technology to other candidate technologies.

5.11.a. Design Considerations. All piping used in RSF systems shall comply with collection system piping standards. Appropriate cleanouts or access ports shall be available in all piping, to allow operator access for inspection and maintenance purposes.

5.11.b. General Description. The recirculating sand filter treatment system consists of a septic tank, or Imhoff tank, followed by a recirculation tank, and then an open sand filter. An applicant shall provide a pumping system with time clock control mechanisms to provide a recirculation rate that results in fresh liquid being dosed onto the surface of the sand filter. An applicant shall provide float controls to override the time clocks, if flows increase to the point where overflow is imminent, but the time clock is not yet ready to provide power to the pumps.

5.11.c. Septic Tank/Imhoff Tank Design. The design of septic tanks or Imhoff tanks are to be in accordance with established design standards.

5.11.d. Recirculation Tank. Septic tank or Imhoff tank effluents are directed, by gravity if possible, to a recirculation tank. Normally, the tank size is to be equal to the incoming 24-hour flow, assuming that the organic concentrations are within the range of normal domestic sewage i.e., 150 350 mg/l BOD₅. The primary purpose of the recirculation tank is to receive underdrain flows from the sand filter(s), to mix with the septic tank or Imhoff tank effluent. This maintains a positive dissolved oxygen concentration in the recirculation tank, thus eliminating any septic odors from being released when dosing the filters. There shall be a provision for pumps in the recirculation tank to dose the filter(s) on an intermittent basis.

5.11.e. Dosing. A means of dosing the filters can be dosing troughs, spray nozzles, or a central splash pad in the middle of the filter, or a dosing grid system. This rule recommends spray nozzles to optimize distribution onto the filter. All exposed dosing lines shall be self draining to prevent freezing during cold weather periods.

5.11.e.1. Filter dosing normally lasts for several minutes each hour, or half-hour periods. Dosing less frequently than once every two hours is not a recommendation, although applicant may vary the dose interval and dose volume. Dosing shall not occur for more than 50% of a dosing cycle to allow aeration to occur between cycles. This rule recommends a recirculation ratio of at least 12-to-1 (i.e., recirculation ratio equals daily flow dosed onto the filter(s) divided by the average daily flow of sanitary wastes entering the treatment facility). Recirculation ratios up to 25-to-1 may be appropriate, depending on the nature of the wastes being treated.

5.11.e.2. The activation of the recirculation pump(s) shall be by means of a time clock with not greater than 15-minute increment settings. An applicant shall use a 96 pin, 24-hour clock, or another timer approved by the Commissioner.

5.11.e.3. A single recirculation pump is acceptable for a single-family home or smaller RSF system. An RSF system serving a greater design load than a single-family home shall have duplex pumps.

5.11.e.4. This rule recommends volumes equal to one to four inches of depth over the filter during each dosing cycle.

5.11.e.5. Piping between the recirculation tank and filters shall allow dosing of any filter by either duplex pump, via actuation of appropriate valves.

5.11.f. Electrical Controls. All electrical wiring shall be in compliance with the National Electrical Code. This rule recommends a control panel in a NEMA IV housing to preclude damage due to inclement weather conditions unless the location of the controls is inside a secure building.

5.11.f.1. There shall be high and low liquid level control switches (i.e., mercury float switches, or similar) installed in the recirculation tank. The high-level switch shall activate at least one pump by overriding the timer control. The low-level switch shall override the timer control to turn all pumps off. Placement of the high-level switch should be several inches above the normal operating level in the recirculation tank. Placement of the low-level switch should be several inches above the pump intake. Actuation of either the high- or low-level switches shall also cause activation of a visual or audible, or both, alarm indicator to notify the operator of a potential operational problem.

5.11.f.2. Removing pumps and electrical controls (i.e., high- and low-level switches, etc.) located in the recirculation tank, shall be easy via "quick disconnect" piping and electrical connections.

5.11.g. Discharge Valving. The dischargement of treated sewage is only from the filter underdrain piping. All underdrain piping is directed back into the recirculation tank. There shall be a floating ball valve installed inside the recirculation tank. At the maximum operating liquid level in the recirculation tank, the ball valve shall close, and filter effluents shall bypass the tank to disinfection. At lower operating liquid levels, filter effluents shall re-enter the recirculation tank for further treatment.

5.11.h. Filter. Except for a single-family home, all RSF systems shall include at least two filters, with filter alternation accomplished manually. The overall filter area shall be based on a design of [LESS THAN EQUAL TO] four gallons per day per square foot, based on the average daily sewage flow entering the treatment facility.

5.11.h.1. The filter media shall be silica sand, Black Beauty, graded bottom ash from coal-fired power plants, or other media approved by the Commissioner. Filter media shall have a uniformity coefficient of [LESS THAN EQUAL TO] 2.5 with an effective particle size of 0.5 to 1.5 mm.

5.11.h.2. The filter media depth shall be [GREATER THAN EQUALS TO] 24 inches, with three layers of support gravel in the underdrain. Support gravel layers shall be [GREATER THAN EQUALS TO] 3 inches for each layer, with support gravel sizes as follows: bottom layer, 1.5 inches to 0.75 inch; middle layer, 0.75 inch to 0.25 inch; top layer 0.25 inch to 0.125 inch.

5.11.h.3. This rule does not recommend the use of a filter fabric between the filter media and support gravel. A filter fabric placed on top of the filter media may reduce maintenance requirements.

5.11.h.4. Placement of perforated underdrain piping shall be at the bottom of the filter prior to placement of the gravel support material. Underdrain piping shall be [GREATER THAN EQUALS TO] 4 inches in diameter or sized based on system hydraulics. Underdrain piping shall lay on a 1% slope, at a spacing of no greater than 10 feet apart. The upper ends of all underdrain piping shall contain an elbow and non-perforated riser pipe that shall terminate halfway between the top of the filter media and the top of the filter sidewalls. The riser pipe shall be available for inspection and maintenance to the underdrain without necessitating excavation of the filter.

5.11.h.5. There shall be a filter sidewall freeboard of 12 inches above the filter media. Filter sidewalls and bottoms shall be impermeable. The slope of the filter bottoms shall be toward the perforated underdrain piping at a grade of one inch vertical to one foot horizontal.

5.11.h.6. Normal operation of a multiple filter RSF system would allow one or more filters to be "at rest" while the filter-in-use operates until "ponding" occurs; after that the applicant manually alternates the filter-in-use. If ponding of a filter does not occur within a one- to two-month period, this rule recommends manual alternation. After ponding occurs on a filter, there shall be an allowance for the filter to rest, the removal of clogging material from the top of the filter, raking the media, and then releveling it as necessary.

5.11.i. Disinfection. Disinfection of the RSF system effluent is required.

5.12. Constructed Wetlands Wastewater Treatment Systems.

5.12.a. The Commissioner shall review constructed wetlands wastewater treatment systems on a case-by-case basis. Recommended design shall be on the basis of the latest edition of the Tennessee Valley Authority's "General Design, Construction, and Operation Guidelines Constructed Wetlands Wastewater Treatment Systems for Small Users Including Individual Residences." Other acceptable designs are the USEPA and NASA wetlands designs.

5.13. Other Biological & Mechanical Systems.

5.13.a. New Biological & Mechanical Treatment Schemes. New biological and mechanical treatment schemes with promising applicability in wastewater treatment may be considered if the applicant provides the required engineering data for new process evaluation in accordance with paragraph 5.1.c.3. of this rule.

5.14. Sewage Stabilization Ponds, Anaerobic Lagoons, and Aerated Lagoons. This rule does permit the use of stabilization ponds, anaerobic lagoons, and aerated lagoons for treatment of raw sewage, primary sewage effluent or secondary sewage effluent.

5.14.a. Stabilization Ponds.

5.14.a.1. Sizing. Stabilization ponds shall have a minimum capacity of 65,000 gallons.

5.14.a.2. Wind Sweep. The location of stabilization ponds shall be to permit an unobstructed wind sweep across the ponds.

5.14.a.3. Water Supply. The location of stabilization ponds shall be a minimum of 300 feet from public water supplies using wells or springs. Maintaining a minimum distance of 600 feet if the public water supply well is down gradient from or lower in elevation than the bottom of the sewage pond is required.

5.14.a.4. Geology and Soils. An applicant shall obtain borings to determine surface and subsurface characteristics of the pond site for all ponds greater than 2.5 acres in size or where required by the commissioner. The soil conservation service, the U.S. Department of Agriculture, requires a soil report for all pond sites.

5.14.a.5. Pond Shape. The shape of all ponds should be such as to produce a uniform perimeter with no coves, islands or peninsulas permitted. Corners of ponds are required to be round. The most desirable shape of ponds is round, square, or rectangular with the length not exceeding three times the width.

5.14.a.6. Design.

5.14.a.6.A. Loading. The design of stabilization ponds shall be on the basis 34 pounds per day of five-day BOD per acre.

5.14.a.6.B. Ponds in Series. If one or more ponds are added in series with the primary pond, the primary pond shall have a minimum volume of 65,000 gallons.

5.14.a.6.C. Depth. Liquid depth of ponds shall be no less than 3.5 feet or greater than five feet. There shall be a three-foot minimum freeboard.

5.14.a.7. Influent Lines.

5.14.a.7.A. Location of Discharge. Influent lines shall extend 10 feet beyond the maximum pond depth and in no case, more than one-fourth the length of the primary stabilization pond. Ponds following the primary pond or secondary treatment facilities in multiple unit systems shall be edge discharging.

5.14.a.7.B. Gravity. Influent lines from gravity collection systems shall discharge at a point 12 to 18 inches above the pond surface.

5.14.a.7.C. Pressure. Pressure influent lines may discharge either above the pond surface or at a point one foot above the pond bottom. When discharging below the pond surface, the end of the pressure line shall rest upon a concrete apron of two square feet minimum size.

5.14.a.7.D. Pipe Support. Piers or other open structures shall support influent lines. This rule does not permit dikes for pipe support.

5.14.a.8. Pond Details.

5.14.a.8.A. Embankments. The construction of embankments shall be of compacted impervious materials with a minimum top width of eight feet. This rule requires the removal of all vegetation from the area upon which the embankment is to be placed.

5.14.a.8.B. Slope. Embankment slopes shall not be steeper than two feet horizontal to one foot vertical. Minimum slopes shall not be flatter than four feet horizontal to one foot vertical.

5.14.a.8.C. Pond Bottom. Pond bottoms shall be level and cleared of all vegetation and debris.

5.14.a.8.D. Watertightness. If soil characteristics are such that seepage shall take place, ponds shall be watertight through use of a pond liner of man-made materials with a minimum thickness of 60 mil required, or clay or through use of a soil additive, approved by the Commissioner.

5.14.a.9. Effluent Lines.

5.14.a.9.A. Discharge. The design of the effluent line shall be to discharge from a point 18 inches below the surface of the pond. There may be a provision to vent the effluent line to prevent siphoning. The effluent line shall discharge on a concrete slab or rip-rap apron. The placement of effluent lines shall be at the furthest point from the influent line discharge.

5.14.a.9.B. Discharge Structure. For ponds greater than 2.5 acres in size, there shall be discharge structures capable of variable depth control. Depth shall be adjustable between 3.5 and five feet in increments of 0.5 foot or less. Spacing of withdrawal points shall be from 18 inches below the surface to 12 inches above the pond bottom discharge structures. Placement of these structures shall be at a point farthest from the influent line discharge and be readily accessible from the embankment.

5.14.a.9.C. Recirculation. Recirculation should be a consideration for multiple pond facilities. When proposing recirculation, thereby reducing pond size, applicant shall submit calculations justifying the proposed reduction to the commissioner for approval.

5.14.a.10. Drain Lines. This rule does not permit drain lines.

5.14.a.11. Miscellaneous.

5.14.a.11.A. Surface Runoff. There shall be a provision to divert storm and surface water around stabilization ponds.

5.14.a.11.B. Fencing. Enclosing ponds with a stock-tight fence a minimum of six feet in height with a locked entrance gate is a requirement.

5.14.a.11.C. Signs. There shall be several signs stating the nature of the facility installed on the fence.

5.14.a.11.D. Prefilling. This rule requires prefilling stabilization ponds with water to a minimum depth of two feet prior to use.

5.14.a.11.E. Access Road. There shall be an all-weather access road to the pond site.

5.14.b. Anaerobic Lagoons.

5.14.b.1. General. Anaerobic lagoons shall generally be used for animal waste treatment.

5.14.b.2. Location. The location of anaerobic lagoons shall be a minimum of 1,500 feet from the nearest occupied structure.

5.14.b.3. Water Supply. Distance from a drinking water supply shall comply with paragraph 5.14.a.3. of this rule.

5.14.b.4. Geology and Soils. These shall comply with paragraph 5.14.a.4. of this rule.

5.14.b.5. Lagoon Shape. This shall comply with paragraph 5.14.a.5. of this rule.

5.14.b.6. Design. Design shall comply with the Waste Treatment Lagoon Code 359, published October 2017 by the USDA Natural Resources Conservation Service.

5.14.c. Aerated Lagoons.

5.14.c.1. General. Aerated lagoon sewage treatment facility shall consist of the following:

5.14.c.1.A. Pretreatment;

5.14.c.1.B. Aeration basin;

5.14.c.1.C. Settling basin, if required; and

5.14.c.1.D. Supplementary treatment, if required.

5.14.c.2. Water Supply. Distance from a drinking water supply shall comply with paragraph 5.14.a.3. of this rule.

5.14.c.3. Geology and Soils. These shall comply with paragraph 5.14.a.4. of this rule.

5.14.c.4. Shape. The shape shall comply with paragraph 5.14.a.5. of this rule.

5.14.c.5. Design.

5.14.c.5.A. Method. The design of aeration basins is normally based upon the aerated lagoon theory using a K_e of 0.5 (at 20 degrees C). Formulas to be used are: t = % removal/(100-% removed) K_T = days detention where: K_T = 0.5 (1.075)^T-20

T = average year-round air temperature at the site in degrees C.

The dissolved oxygen level should be a minimum of 2 ppm and assumed that ratio of oxygen transfer should be at (0.9). The oxygen requirement should be based upon the removal of 1.5 pounds/pound of BOD₅.

5.14.c.5.B. Depth. The aeration basin shall be of a depth ranging from six to 15 feet. Supplying air to the aeration basin shall be by means of surface aerators or subsurface air diffusers. A 96-pin time clock shall operate each surface aerator. The design of basins shall be to distribute oxygen throughout, but not to keep solids in suspension.

5.14.c.5.C. Settling. A settling pond shall follow the aeration basin. The size of the settling pond shall be based upon BOD₅ remaining after aeration at the loading rate of 34 pounds of BOD₅ per surface acre per day.

5.14.c.6. Lagoon Details. Lagoon shape, dikes, embankments, construction, and effluent lines shall comply with paragraph 5.14.b.6. of this rule.

5.15. Disinfection.

5.15.a. General. There shall be adequate disinfection of all sewage treatment plant effluents prior to discharge. All wastewater treatment works using gas chlorination shall have a Chlorine Institute chlorine repair kit.

5.15.b. Chlorination.

5.15.b.1. Chlorine Terminology. The word "chlorine" whenever used in this section refers to dry chlorine unless otherwise indicated.

5.15.c. Equipment.

5.15.c.1. Feed Equipment Type. This rule generally prefers solution-feed vacuum-type chlorinators for plants greater than 100,000 gallons per day in size. There shall be consideration given to the use of hypochlorite solution feeders of the positive displacement type. For plants of 100,000 gallons per day or less in size, using tablet type chlorinators shall receive approval.

5.15.c.2. Feed Equipment Capacity. Chlorinator capacities required may vary, depending on the use and point of application of the chlorine. For disinfection, the capacity shall be such to produce a residual of 0.5 ppm maximum in the final effluent at peak flow rates.

5.15.c.3. Chlorination Equipment and Spare Parts. It is a requirement to maintain an inventory of parts subject to wear and breakage at all times. This rule requires dual chlorinators for plants over 100,000 gallons per day in size. Each chlorinator shall be able to provide the required chlorination at peak flow rates. If the discharge is within a five-mile distance up-stream from a public water supply, chlorination of the sewage effluent shall be a requirement unless a written waiver is granted by the Commissioner.

5.15.c.3.A. Water Supply. A supply of water shall be available for operating the chlorinators. When a booster pump is required, there shall be duplicate pumping equipment. When a connection is made from the domestic water supplies, there shall be a provision for equipment for backflow prevention. There shall be pressure gauges on chlorinator water supply lines.

5.15.c.3.B. Measurement Equipment. There shall be equipment for measuring the amount of chlorine use.

5.15.c.4. Evaporators. When manifolding of several cylinders is required to feed sufficient chlorine, there shall be consideration given to the installation of evaporators.

5.15.c.5. Leak Detection and Controls. A bottle of ammonium hydroxide solution shall be available for detecting chlorine leaks. Also, there shall be consideration given to the provision of caustic soda solution reaction tanks for absorbing the contents of leaking one-ton cylinders where the cylinders are in use. There shall be installation of automatic leak detectors wherever using gas chlorination.

5.15.d. Piping and Connections.

5.16.d.1. General. Piping systems shall be well supported, adequately sloped to allow drainage and protection from mechanical damage. Due to changes in temperature, there shall be allowance for pipe expansion.

5.15.d.2. Condensation. When a vaporizer does not provide adequate superheat, a pressure reducing valve shall be used to prevent condensation.

5.15.d.3. The arrangement of chlorine solution piping shall be such that any or all chlorinators may pre-chlorinate and post-chlorinate.

5.15.e. Housing.

5.15.e.1. Building. The design and construction of any building to house chlorine equipment or containers shall be to protect all elements of the chlorine system from fire hazards. If storing or processing flammable materials in the same building with chlorination equipment other than that using hypochlorite solutions, there shall be a fire wall erected to separate the two areas.

5.15.e.1.A. If gas chlorination equipment and chlorine cylinders are to be in a building used for other purposes, a gas-tight partition shall separate this room from any other portion of the building. Doors to this room shall equip panic hardware and applicant shall install a chlorine detector/alert system. The rooms shall be at ground level and shall permit easy access to all equipment. Storage area shall be separated from the feed area. This rule does not permit a basement.

5.15.e.1.B. There shall be a means of exit to the outside of the building from each separate room or building in which applicant is storing, handling, or using chlorine, other than hypochlorite.

5.15.e.1.C. There shall be installation of a clear glass, gas-tight window in an exterior door or interior wall of the chlorinator room to permit viewing of the chlorinator without entering the room.

5.15.e.2. Heat. There shall be chlorinator rooms with a means of heating and maintaining a temperature of at least 60 degrees Fahrenheit. The room shall also have protection from excess heat.

5.15.e.3. Ventilation. There shall be installation of forced, mechanical ventilation that provides one complete air change per minute in all chlorine feed rooms and rooms where storing chlorine cylinders. The entrance to the air exhaust duct from the room shall be near the floor and the location of the point of discharge shall be so as not to contaminate the air inlets to any building or inhabited areas. The location of air inlets shall be so as to provide cross ventilation with air and at such a temperature that shall not adversely affect the chlorination equipment. The vent hose shall run without traps from the chlorinator and shall discharge to the outside atmosphere above grade.

5.15.e.4. Electrical Controls. The controls for the fans and lights shall be such that they shall automatically operate when the door is opened and manually operated from the outside without opening the door.

5.15.e.5. Respiratory Protection. Respiratory air-pac protection equipment, meeting the requirements of the National Institute for Occupational Safety and Health (NIOSH), shall be available where the handling of chlorine gas takes place, and stored at a convenient location, but not inside any room when using or storing chlorine. There shall be instructions posted for using the equipment. The units shall use compressed air, have at least a 30-minute capacity, and be compatible with the units used by the fire department responsible for the plant. This rule requires a minimum of two air-pacs.

5.15.f. Application of Chlorine.

5.15.f.1. Mixing with Flow. There shall be provisions to ensure uniform mixing of the chlorine solution with the wastewater flow near the point of application.

5.15.f.2. Contact Period. There shall be a minimum contact period of 40 minutes at average daily flow or 15 minutes at maximum daily flow. Additional contact time may be a requirement if the discharge point is in proximity to a water supply intake, recreational area, or some other similar area.

5.15.f.3. Contact Tank. Design of chlorine contact tanks shall be to minimize "short-circuiting" of flow. There shall be over and under, or end-around, baffling provided. This rule requires air lift sludge returns from the contact tank for all extended aeration sewage treatment plants unless preceded by a filter or polishing pond. This rule requires multiple units for plants over 100,000 gallons in size.

5.15.g. De-chlorination. The removal of all or part of the chlorine residual may be a requirement prior to final discharge, to meet the adopted stream standards or other requirements for particular streams.

5.15.g.1. Other Methods. The Commissioner shall evaluate the use of other methods for disinfection on a case-by-case basis. As a minimum, there shall be an investigation when intending to use other disinfection methods.

5.15.g.2. Minimum effluent conditions, such as clarity, soluble organics and pH are required for adequate disinfection.

5.15.g.3. Methods for dispersion and mixing with the waste stream are required.

5.15.g.4. Other factors, including but not limited to, equipment reliability, safety and application rates are required for varying waste flows.

5.15.g.5. Refer to paragraph 5.1.c.3. of this rule.

5.15.h. Evaluation of Effectiveness.

5.15.h.1. Sampling. There shall be facilities included for securing a sample prior to discharge to determine the effectiveness of the disinfection method.

5.15.h.2. Residual Chlorine Testing and Control. When using chlorine for disinfection, there shall be equipment for measuring chlorine residual. When the discharge occurs in critical areas, the installation of facilities for continuous automatic chlorine residual analysis, recording and proportioning systems may be a requirement.

5.16. Supplementary Treatment.

5.16.a. General. Supplementary treatment shall be a requirement when health considerations or waste load allocations and effluent limitations require treatment more stringent than secondary.

5.16.b. Alternating Surface Sand Filters.

5.16.b.1. General. Normally, an applicant shall use alternating surface sand filters for plants of 100,000 gallons per day or less in size. The commissioner may permit alternating surface sand filters for plants of over 100,000 gallons per day in size on a case-by-case basis. No individual surface sand filter shall exceed 500 square feet.

5.16.b.2. Filter Rate. The design of an alternating sand filter shall be for a filter rate of not more than 20 gallons per square foot per day.

5.16.b.3. Application. The effluent application shall be with either a pump or siphon chamber designed to dose all sections of the filter equally with three to four inches of liquid in 20 minutes or, where elevation differences permit, the Commissioner may permit gravity application of effluent to the filter if the distribution of the effluent is uniform.

5.16.b.4. Location. The location of alternating surface sand filters shall not be within 100 feet of the nearest occupied residence or habitation. The commissioner may waive this distance requirement in the event applicant obtains a release from the neighboring property owner or owners.

5.16.b.5. Media. The sand used in alternating surface sand filters shall be coarse, clean sand of uniform size. Effective size of 0.5 to 1.5 mm in diameter with a uniformity coefficient of no greater than 3.0 and less than 1% fines passing a 100 sieve. The Commissioner may waive this requirement if finding the media is to perform in an adequate manner.

5.16.b.6. Construction. The side walls, dividing partitions and bottom of the sand filters shall be impermeable. General construction shall be as shown in the Portfolio of Drawings.

5.16.b.7. Disinfection. This rule requires disinfection after the filters and before discharge to a stream.

5.16.c. High-Rate Effluent Filtration.

5.16.c.1. General. High-rate filters may be either gravity or pressure.

5.16.c.1.A. Pressure. This rule limits the use of pressure high-rate filters to plants of greater than 100,000 gallons per day in size.

5.16.c.2. Filtration Rates. Allowable rates for gravity filters shall not be greater than one gallon per minute per square foot per day. Filtration rates for pressure filters shall not be greater than five gallons per minute per square foot per day. Rates are based upon the maximum flow rate applied.

5.16.c.3. Number of Units. There shall be total filter area in two or more units, and calculation of the filtration rate shall be on the total available filter area with one unit out of service, for plants of 40,001 gallons per day or more in size.

5.16.c.4. Backwash. Backwash shall include either or both air scouring and positive surface wash. There shall be a provision for using filtered effluent for backwash and waste filter backwash water. It shall return to the head of the plant.

5.16.c.4.A. Backwash Water Storage. Total backwash water storage capacity required shall equal or exceed one complete backwash cycle.

5.16.c.4.B. Backwash Rate. The backwash rate shall not exceed 20 gallons per minute per square foot with a minimum backwash period of 10 minutes.

5.16.c.4.C. Pumps. An applicant shall size and interconnect pumps for backwashing filter units to provide the required rate to any filter with the largest pump out of service.

5.16.c.5. Proprietary Equipment. Where proposing proprietary filtration equipment not conforming to the preceding requirements, an applicant shall provide data that supports the capability of the equipment to meet effluent requirements under design conditions. The Commissioner shall consider the equipment on a case-by-case basis.

5.16.c.6. Equipment Serving Plants with Design Flows of 40,000 Gallons Per Day or Less. When proposing filtration equipment serving plants with design flows of 40,000 gallons per day or less not conforming to the preceding requirements, an applicant shall provide data that supports the capability of the equipment to meet effluent requirements under design conditions. The Commissioner shall consider the equipment on a case-by-case basis.

5.16.d. TKN Removal.

5.16.d.1. General. Consideration shall be given to TKN removal when the total Kjeldahl nitrogen limit as stated in the discharge load allocation is less than 18 mg/l.

5.16.d.2. Methods. Methods used to achieve TKN removal may include, but not be limited to: additional aeration in extended aeration plants; separate stage nitrification; break-point chlorination; nitrification column; and alternating surface sand filters.

5.16.e. Microscreening.

5.16.e.1. General. An applicant may use microscreening units following a biological treatment process for the removal of residual suspended solids.

5.16.e.2. Materials. Microscreen shall be either a specially woven polyester or stainless steel with aperture size of 20 to 30 microns.

5.16.e.3. Design. The hydraulic loading shall not be greater than 10 gallons per minute per square foot of submerged drum surface. Maximum head loss shall be 12 to 18 inches. There shall be an overflow weir to bypass part of the flow when head exceeds six to eight inches. It is recommended that drums be not less than 10 feet in diameter.

5.16.e.4. Backwash. Application of continuous pressurized (60 psig) backwash shall be at a minimum rate of eight gallons per minute per square foot of screen. There shall be dual backwash pumps, with each pump being capable of supplying 100% of the required flow. Backwash water shall return to the head of the plant at a rate not to exceed 15% of the average daily design flow.

5.16.e.5. Reliability. There shall be dual microscreen units with each unit being capable of providing 100% of the design microscreen capacity. There shall be automatic drum speed controls with provision for manual override for each screen. It is a requirement to enclose all units in a heated and ventilated structure.

5.16.f. Polishing Ponds.

5.16.f.1. General. The design of polishing ponds shall be in accordance with Section 5.14.b. of this rule. Polishing ponds shall have a capacity of at least 65,000 gallons or capacity for a detention time of 10 days plant design flow, whichever is greater.

5.16.f.2. Distance Requirements. The location of polishing ponds shall be at least 100 feet from the nearest occupied structure.

5.16.g. Post Aeration. Meeting a discharge load allocation of 6.0 milligrams per liter dissolved oxygen shall be by means of one of the following:

5.16.g.1. Post aeration tank with air added by diffusion or mechanical means;

5.16.g.2. Cascade aeration; or

5.16.g.3. Polishing ponds shall provide the dissolved oxygen requirements.

5.17. Sludge Handling and Disposal.

5.17.a. Anaerobic Sludge Digestion.

5.17.a.1. Multiple Units. This rule recommends multiple tanks. When using a single digestion tank, there shall be an alternate method of sludge processing or emergency storage to maintain continuity of service.

5.17.a.2. Depth. For those units proposed to serve as supernatant separation tanks, the depth shall be sufficient to allow for the formation of a reasonable depth of supernatant liquor. This rule recommends a minimum sidewater depth of 10 feet.

5.17.a.3. Maintenance Provisions. To facilitate draining, cleaning, and maintenance, the following features are desirable:

5.17.a.3.A. Slope. The tank bottom should slope to drain toward the withdrawal pipe. For tanks equipped with a suction mechanism for withdrawal of sludge, this rule recommends a bottom slope not less than 1:12. When the sludge removal is to be by gravity alone, this rule recommends 1:4 slope.

5.17.a.3.B. Access Manholes. In addition to the gas dome, there shall be at least two 36-inch diameter access manholes in the top of the tank. There shall be stairways to reach the access manholes. There shall be a separate sidewall manhole. The opening should be large enough to permit the use of mechanical equipment to remove grit and sand.

5.17.a.3.C. Safety. There shall be non-sparking tools, safety lights, rubber-soled shoes, safety harness, gas detectors for inflammable and toxic gases and at least two self-contained breathing units for emergency use.

5.17.a.4. Sludge Inlets and Outlets.

5.17.a.4.A. Recirculation. There shall be multiple recirculation withdrawal and return points, unless incorporating mixing facilities within the digester. The return shall discharge above the liquid level and the location shall be near the center of the tank.

5.17.a.4.B. Raw Sludge Discharge. Raw sludge discharge to the digester shall be through the sludge heater and recirculation return piping, or directly to the tank if there are internal mixing facilities.

5.17.a.4.C. Withdrawal. Sludge withdrawal to disposal shall be from the bottom of the tank. This pipe shall interconnect with the recirculation piping.

5.17.a.5. Tank Capacity. The determination of the total digestion tank capacity shall be by rational calculations based upon such factors as volume of sludge added, its percent solids and character, the temperature to maintain in the digesters, the degree or extent of mixing to obtain and the degree of volatile solids reduction required. An applicant shall submit calculations to the Commissioner, to justify the basis of design. When the calculations are not based on the above factors, the minimum combined digestion tank capacity design shall be based on: the assumption that a raw sludge evolves from ordinary domestic wastewater, that a maintained digestion temperature is to be in the range of 90 degrees Fahrenheit to 100 degrees Fahrenheit or (32 degrees Celsius and 38 degrees Celsius), that the digested sludge shall maintain 40% to 50% volatile matter, and that there shall be frequent removal of the digested sludge from the system.

5.17.a.5.A. Completely-Mixed Systems. Completely-mixed systems shall provide for effective mixing. Loading the system may be at a rate up to 80 pounds of volatile solids per 1,000 cubic feet of volume per day in the active digestion units. When there are no grit removal facilities, reducing the digester volume due to grit accumulation shall be considered.

5.17.a.5.B. Moderately-Mixed Systems. For digestion systems where accomplishing mixing is only by circulating sludge through an external heat exchanger, loading the system may be at a rate up to 40 pounds of volatile solids per 1,000 cubic feet of volume per day in the active digestion units. Modification to this loading may be upward or downward depending upon the degree of mixing provided.

5.17.a.6. Gas Collection, Piping, and Appurtenances.

5.17.a.6.A. General. The design of all portions of the gas system, including the space above the tank liquor, the storage facilities, and the piping, shall be so that under all normal operating conditions, including sludge withdrawal, the gas shall be maintained under positive pressure. All enclosed areas where any gas leakage might occur shall have adequate ventilation.

5.17.a.6.B. Safety. When producing gas all safety facilities shall be used. There shall be pressure and vacuum relief valves and flame traps, along with automatic safety shutoff valves. This rule does not permit water seal equipment. Housing gas safety equipment and gas compressors shall be in a separate room with an exterior entrance.

5.17.a.6.C. Gas Piping and Condensate. Gas piping shall be of adequate diameter and shall slope to condensate traps at low points. This rule does not permit the use of float-controlled condensate traps.

5.17.a.6.D. Gas Utilization Equipment. The location of gas-fired boilers for heating digesters shall be in a separate room not connected to the digester gallery.

5.17.a.6.E. Electrical Fixtures. Electrical fixtures and controls in places enclosing anaerobic digestion appurtenances, when the tanks and piping normally contain hazardous gases, shall comply with the National Electrical Code for Class 1, Group D, Division 2 locations. An applicant shall isolate digester galleries from normal operating areas to avoid an extension of the hazardous location.

5.17.a.6.F. Waste Gas. Waste gas burners shall be readily accessible and located at least 25 feet away from any plant structure if placed at ground level or located on the roof of the control building if sufficiently removed from the tank. All waste gas burners shall equip an automatic ignition, such as a pilot light or a device using a photoelectrical cell sensor. The use of natural or propane gas to ensure reliability of the pilot light shall be considered. Discharging the gas to the atmosphere through a return-bend screened vent terminating at least 10 feet above the ground surface, provided that the assembly incorporates a flame trap, may be permissible in remote locations.

5.17.a.6.G. Ventilation. Any underground enclosures connecting with digestion tanks, or containing sludge, gas piping or equipment shall be equipped with forced ventilation. The piping gallery for digesters shall not connect to other passages. If self-closing doors are used at connecting passageways and tunnels to minimize the spread of gas, they shall be tightly fitting.

5.17.a.6.H. Meter. There shall be a gas meter with a bypass to meter total gas production.

5.17.a.7. Digester Heating.

5.17.a.7.A. Insulation. Wherever possible, the construction of tanks shall be above ground water level and suitably insulated to minimize heat loss.

5.17.a.7.B. Heating Facilities. Sludge may be heated by circulating it through external heaters or using heating units located inside the digestion tank.

5.17.a.7.B.1. The design of piping for external heating shall be to provide for the preheating of feed sludge before introduction to the digesters. There shall be provisions in the layout of the piping and valving to facilitate cleaning of these lines. The sizing of heat exchanger sludge piping should be for heat transfer requirements.

5.17.a.7.B.2. Other Heating Methods. The Commissioner shall consider other types of heating facilities on their own merits.

5.17.a.7.C. Heating Capacity. There shall be heating capacity sufficient to consistently maintain the design sludge temperature. When using a digester tank gas for sludge heating, an auxiliary fuel supply is required.

5.17.a.7.D. Hot Water Internal Heating Controls.

5.17.a.7.D.1. There shall be an automatic mixing valve to temper the boiler water with return water so that the inlet water to the heat jacket can be held below a temperature at which caking shall be accentuated. In addition, there shall be manual control provided by bypass valves.

5.17.a.7.D.2. The boiler shall equip automatic controls to maintain the boiler temperature at approximately 180 degrees Fahrenheit to shut off the main gas supply in the event of pilot burner or electrical failure, low boiler water level, or excessive temperature.

5.17.a.7.D.3. There shall be thermometers to show temperatures of the sludge, hot water feed, hot water return, and boiler water.

5.17.a.8. Supernatant Withdrawal.

5.17.a.8.A. Piping Size. Supernatant piping shall not be less than six inches in diameter.

5.17.a.8.B. Withdrawal.

5.17.a.8.B.1. Arrangement of piping shall be so that withdrawal can be made from three or more levels in the digester. There shall be a positive unvalved vented overflow.

5.17.a.8.B.2. If providing a supernatant selector, provisions shall be made for at least one other drawoff level located in the supernatant zone of the tank in addition to the unvalved emergency supernatant drawoff pipe. There shall be high pressure backwash facilities.

5.17.a.8.C. Sampling. There shall be provisions for sampling at each supernatant drawoff level. Sampling pipes shall be at least 1.5 inches in diameter and shall terminate at a suitably-sized sampling sink or basin.

5.17.a.8.D. Alternate Supernatant Disposal. An applicant shall give consideration to supernatant conditioning, when appropriate, in relation to its effect on plant performance and effluent quality.

5.17.b. Aerobic Sludge Digestion.

5.17.b.1. General. Using aerobic digestion may stabilize secondary sludge. There shall be digestion in single or multiple tanks, designed to provide effective air mixing, reduction of the organic matter, supernatant separation, and sludge concentration under controlled conditions.

5.17.b.2. Digestion Tanks. This rule recommends multiple tanks. An applicant may use a single sludge digestion tank in the cases of small treatment plants, when making provisions for sludge handling, or when a single unit shall not adversely affect normal plant operations.

5.17.b.3. Mixing and Air Requirements. Design of aerobic sludge digestion tanks shall be for effective mixing by aeration equipment. There shall be sufficient air to keep the solids in suspension and maintain dissolved oxygen between one and two milligrams per liter. There shall be a minimum mixing and oxygen requirement of 30 cfm per 1,000 cubic feet of tank volume with the largest blower out of service. If using diffusers, the non-clog type is a requirement, and their design shall be to permit continuity of service. If using mechanical aerators, there shall be a minimum of 1.0 horsepower per 1,000 cubic feet. This rule discourages the use of mechanical equipment in areas where freezing temperatures are typical.

5.17.b.4. Tank Capacity. The determination of tank capacities shall be based on rational calculations, including such factors as quantity of sludge produced, sludge characteristics, time of aeration, and sludge temperature.

5.17.b.4.A. Volatile Solids Loading. The volatile suspended solids loading shall not exceed 100 pounds per 1,000 cubic feet of volume per day in the digestion units. Lower loading rates may be necessary depending on temperature, type of sludge, and other factors.

5.17.b.4.B. Solids Retention Time. Required minimum solids retention time for stabilization of biological sludges varies depending on type of sludge. Normally, there shall be a minimum of 15 days retention for waste activated sludge and 20 days for combination of primary and waste activated sludge, or primary sludge alone. In areas where sludge temperature is lower than 50 degrees Fahrenheit, additional detention time shall be considered.

5.17.b.5. Supernatant Separation. There shall be facilities for separation and withdrawal of supernatant and for collection and removal of scum and grease.

5.17.b.6. Sludge Thickening. Prior to placement on sludge drying beds, all sludge produced by the activated sludge process shall condition to a minimum solids content of 2% by weight.

5.17.c. Sludge Pumps and Piping.

5.17.c.1. Sludge Pumps.

5.17.c.1.A. Duplicate Units. There shall be duplicate units.

5.17.c.1.B. Type. There shall be plunger pumps, screw feed pumps, recessed impeller type centrifugal pumps, progressive cavity pumps, or other types of pumps capable of solids handling for handling raw sludge.

5.17.c.1.C. Minimum Head. There shall be a minimum positive head of 24 inches at the suction side of centrifugal-type pumps and that minimum is desirable for all types of sludge pumps. Maximum suction lifts shall not exceed 10 feet for plunger pumps.

5.17.c.1.D. Sampling Facilities. Unless sludge sampling valves are installed at the sludge pumps, the size of valve and piping shall be at least 1.5 inches.

5.17.c.2. Sludge Piping.

5.17.c.2.A. Size and Head. Sludge withdrawal piping shall have a minimum diameter of six 6 inches for gravity withdrawal and three inches for pump suction and discharge lines. When withdrawal is by gravity, the available head on the discharge pipe shall be adequate to provide at least 3.0 feet per second velocity.

5.17.c.2.B. Slope. Gravity piping shall be laid on uniform grade and alignment. The slope of gravity discharge piping shall not be less than 3%. There shall be provisions for cleaning, draining and flushing discharge lines.

5.17.c.2.C. Supports. The corrosion resistance and continuing stability of supporting systems located inside the digestion tank shall receive special consideration.

5.17.d. Sludge Dewatering.

5.17.d.1. Sludge Drying Beds. Estimating the sizing of the drying bed shall be on the basis of four-square foot capita when the drying bed is the primary method of dewatering, and one square foot capita if using it as a back-up dewatering unit. Under no circumstances shall surface water enter the bed areas.

5.17.d.2. Design.

5.17.d.2.A. Gravel. An applicant shall grade the lower course of gravel around the underdrains, and it shall be 12 inches in depth, extending at least six inches above the top of the underdrains. It is desirable to place this in two or more layers. The top layer of at least three inches shall consist of gravel one eighth 0.125 inch to 0.25 inch in size.

5.17.d.2.B. Sand. The top course shall consist of six to nine inches of clean washed coarse sand with an effective size of 0.3 to 0.6 mm in diameter with a uniformity coefficient of no greater than 4.0 and less than 1% fines passing number 100 sieve. The Commissioner may waive this requirement if this media performs adequately. The finished sand surface shall be level.

5.17.d.2.C. Underdrains. Underdrains shall be at least four inches in diameter and the spacing of them shall be not more than 20 feet apart.

5.17.d.2.D. Partially Paved Type. The design of the partially paved drying bed shall be with consideration for space requirement to operate mechanical equipment for removing the dried sludge.

5.17.d.2.E. Walls. Walls shall be watertight and extend 15 to 18 inches above and at least six inches below the surface. There shall be curbing of outer walls to prevent soil from washing onto the beds.

5.17.d.2.F. Sludge Removal. There shall be not less than two beds and their arrangement shall be to facilitate sludge removal. There shall be concrete truck tracks for all percolation-type sludge beds.

5.17.d.2.G. Sludge Influent. The sludge pipe to the drying beds shall terminate at least 12 inches above the surface and be arranged so that it shall drain. There shall be concrete splash plates for percolation-type beds at sludge discharge points.

5.17.d.2.H. Protective Enclosure. A protective enclosure shall be considered if winter operation is required.

5.17.d.3. Mechanical Dewatering Facilities. There shall be a provision to maintain continuity of service so that an applicant may dewater sludge without accumulation beyond storage capacity. The number of vacuum filters, vacuum beds, centrifuges, filter presses, belt filters, and other mechanical dewatering facilities shall be sufficient to dewater the sludge produced with the largest unit out of service. Unless other standby facilities are available, there shall be adequate storage facilities. The storage capacity shall be sufficient to handle at least a three-month sludge production.

5.17.d.3.A. Auxiliary Facilities for Vacuum Filters. There shall be back-up vacuum pumps and filtrate pumps. It is permissible to have an uninstalled back-up vacuum pump or filtrate pump for every three or less vacuum filters, provided that the removal or replacement of the installed unit requires little effort.

5.17.d.3.B. Ventilation. There shall be facilities for ventilation of dewatering area. The condition of the exhaust air shall be to avoid odor nuisance.

5.17.d.3.C. Chemical Handling Enclosures. There shall be lime-mixing facilities of lime dust.

5.17.d.4. Drainage and Filtrate Disposal. Drainage from beds or filtrate from dewatering units shall return to the sewage treatment process at appropriate points.

5.17.d.5. Other Dewatering Facilities. If proposing to dewater or dispose of sludge by other methods, a detailed description of the process and design data shall accompany the plans.

5.18. Sewage Sludge, Disposal Methods. When considering sewage sludge disposal methods, such as incineration and landfill, an applicant shall follow appropriate requirements of the solid waste regulations.

5.19. Land Application of Sewage Effluent.

5.19.a. General. Land application shall not be considered as a treatment process, but only a means of disposing of sewage effluent that received secondary treatment. For public health reasons, this rule shall not permit land disposal of effluent that received primary treatment.

5.19.b. Preliminary Considerations.

5.19.b.1. Land application installations are normally used where the waste contains pollutants that can successfully be removed through distribution to the soil mantle. Removal of these pollutants may be through organic decomposition in the vegetation-soil complex and by absorptive, physical, and chemical reactions with earth materials. Preliminary considerations of a site for land application shall be the compatibility of the waste with the organic and earth materials and the percolation rates and exchange capacity of the soils. The land application of wastewater shall eventually recharge the local groundwater. Therefore, the quality, direction and rate of movement, and local use of the groundwater, present and potential, are prime considerations in evaluating a proposed site.

5.19.b.2. It is essential to maintain an aerated zone of at least five feet and preferably more, to provide good vegetation growth conditions and removal of nutrients. A groundwater mound shall develop below a disposal site after it is in use. The major factors in design of ground disposal fields are topography, soils, geology, hydrology, weather, agriculture practice, adjacent land use and equipment selection and installation.

5.19.c. Site Plan and Report. The following shall be considerations and included in a site plan and report:

5.19.c.1. Location Maps. USGS topographic map of the area, a 7.5-minute series where published, showing the location of the total property and proposed land application site; and West Virginia Division of Highways County Maps showing location of the total property.

5.19.c.2. Plan. A topographic map of the entire property at a workable scale showing all buildings, land application area, area of possible expansion, roads, direction of groundwater flow, active and abandoned wells, public water supplies, groundwater monitoring wells, streams, wooded areas, fences or other barriers, visible geologic formations such as sinkholes and rock outcrops, ponds, and all structures, wells, and ponds on adjacent property within 2,000 feet of the boundaries of proposed disposal area.

5.19.c.3. Soil Map. A soil map shall be furnished showing soil types within the land application site. An applicant may incorporate this information on the plan.

5.19.c.4. Report.

5.19.c.4.A. Geology of Site. This includes formations, rock types, degree of weathering of bedrock, local bedrock structure, character and thickness of surficial deposits, solution openings and sinkholes or limestone areas.

5.19.c.4.B. Hydrology of Site. This means the depth to seasonal high-water table and test well data including chemical and bacterial analysis for groundwater quality and depth of well.

5.19.c.4.C. Soils at Site. Cation exchange capacity of the soils, soil types and characteristics, detailed chemical analysis of the soils and thickness of the soils.

5.19.c.4.D. Climatological Data at Site. This includes daily rainfall and daily temperature.

5.19.c.4.E. Agricultural Practices at Site. This includes the present and intended soil-crop management practices, kinds of crops to be grown, harvesting frequency and ultimate use of crop.

5.19.c.4.F. Effluent Characteristics. This is the detailed chemical analysis of effluent to dispose.

5.19.c.4.G. Rate and Frequency of Application. This includes all calculations relating to nitrogen, cadmium and heavy metals and calculations for winter storage.

5.19.c.4.H. Management Practices. These include types of equipment for transport and application; supervision of site; contracts, land easements, land leases, land purchases, monitoring procedures, and emergency procedures in the event of plant or equipment breakdown.

5.19.d. Design.

5.19.d.1. Effluent Requirements. Secondary treatment shall be a requirement (30 mg/1 of BOD₅ and 30 mg/1 of suspended solids). Disinfection shall be a requirement with disinfection occurring after secondary treatment.

5.19.d.2. Holding Pond. There shall be a minimum 90-day storage to store all flow during periods when disposal cannot occur. All storage shall be above a fixed water level to prevent complete draining of the pond. A two-foot residual water depth is a requirement to prevent growth of vegetation.

5.19.d.3. Application Rates. The maximum application rates in terms of depth of effluent are: 0.25 inch per hour; 0.5 inch per day; 2 inches per week. The above are maximum rates and lower application rates may be necessary in some areas due to soil characteristics.

5.19.d.4. Slopes. There shall be a limit on cultivated fields to 4% or less. The limit of slope on sodded fields shall be to 8% or less. The limit on forested slopes shall be 8% for year-round operation but for seasonal operation 14% slopes may be acceptable.

5.19.d.5. Runoff. The design of the system shall be to prevent surface runoff from entering or leaving the project site.

5.19.d.6. Fencing. A fence at least six feet high or a locked entrance gate shall enclose the irrigated area to keep out children and domestic animals.

5.19.d.7. Warning Signs. Appropriate signs shall be posted along the fence around the project boundaries to designate the nature of the facility and advise against trespassing.

5.19.e. Spray Irrigation.

5.19.e.1. Piping to Sprinklers. The arrangement of the piping shall be to allow the irrigation pattern to be varied easily. For a permanent system, facilities shall be designed to allow complete drainage of the pipes to prevent pollution and freezing, and to provide an even distribution over the entire field.

5.19.e.2. Pump Station. There shall be duplicate pumps for delivery to the spray field, with the capacity of each pump sized to handle maximum rate of flow, plus an allowance to deplete stored volumes. The pump station shall have a metering device that shall show the total flow and rates to the irrigation field. The top of the disinfection facility and the wet well of the pumping station shall be at least as high as the maximum holding pond surface elevation, to prevent flooding of the units when the spray irrigation equipment is not in operation. A control valve between the holding pond and the spray irrigation pump station is required.

5.19.e.3. Buffer Zone. Sprinklers shall be located to give a non-irrigated buffer zone around the irrigated area, and the design of the buffer zone shall consider wind transport of the wastewaters. A fence shall be placed at least 50 feet beyond the normal projected spray area. A minimum of 350 feet from the fence of the enclosed irrigated area to the property lines of adjacent areas or highways is required, unless there are:

5.19.e.3.A. Low sprays to reduce wind transport of the effluent; or

5.19.e.3.B. Physical buffers, such as trees, along with low sprays.

5.19.f. Ridge and Furrow.

5.19.f.1. Slopes. The construction of furrows may be down slope on sites up to 1%. The construction of furrows shall be at right angles to the slope on sites up to 8%.

5.19.f.2. Construction. Furrows shall be no more than 1,000 feet in length and spaced from 20 to 40 inches apart.

5.19.g. Overland Flow.

5.19.g.1. Slopes. Slopes shall range from 2% to 8%. Lengths of slopes shall range from 150 to 300 feet.

5.19.g.2. Construction. Slopes may be flooded, or application made by gated pipe or spray.

5.19.h. Monitoring and Reporting. A minimum of one drilled groundwater monitoring well shall be in each dominant direction of groundwater movement, and between the project site and public well(s) or high-capacity private wells, there shall be a provision for sampling at the surface of the water table and at five feet below the water table at each monitoring site. The Commissioner shall approve the location and construction of the monitoring well(s) before construction. These may include one or more of the test wells where appropriate. If crops are used for animal or human consumption, analysis of the crop shall be required at harvest. The Commissioner shall determine frequency of reporting on a case-by-case basis, based on site characteristics.

Notes

W. Va. Code R. § 64-47-5