Article 3. Sewage Treatment Works
9VAC25-790-450. Treatment works design.
Article 3
Sewage Treatment Works
A. The sewage treatment process consists of a sequential, upstream to downstream, arrangement of unit operations that remove or modify contaminants through several treatment phases, including (i) primary, (ii) secondary, and (iii) tertiary. A conventional or established secondary treatment process will include primary treatment. Advanced wastewater treatment works include all three phases of treatment. Sewage treatment works should be designed to provide waste water treatment for the tributary sewage flows from either the estimated population 10 years hence or a capacity required by applicable state or federal requirements.
B. Location. A sewage treatment works site shall be located as far as practicable from any existing built-up commercial or residential area, which will probably develop within the design life of the treatment works. The treatment works site shall be (i) protected by a buffer zone, (ii) located to avoid flooding, (iii) provided with year-round access, and (iv) provided with ample area for any future expansion. The minimum distance between the locations of effluent discharges from separate treatment works on the same watershed shall be 500 feet.
C. Restrictions. All new primary and secondary sewage treatment unit operations shall provide the minimum buffer zones as shown in Table 2 (found in 9VAC25-790-460) unless they qualify for reduced requirements as provided in this chapter. Buffer zones for advanced treatment (AWT) and natural treatment operations will be established on a case-by-case basis considering the reliability requirements and process design. Buffer zones are areas of controlled or limited use.
1. Within buffer zones, neither residential uses, high density human activities, nor activities involving food preparation are to be established within the extent of the buffer zone. The extent of the buffer zone perimeter is measured from the treatment units. Buffer zone requirements for sewage sludge incinerator restrictions shall be established in accordance with applicable state and federal regulations.
2. The department may approve a reduction of up to one half of the listed buffer zone requirements based on one or more of the following factors: (i) site topography, (ii) prevailing wind directions, (iii) existence of natural barriers, (iv) establishment of an effective windbreak, (v) type of adjacent development, and (vi) provision of enclosed units, as described in this chapter.
3. The prevailing wind direction should be determined by on-site data. Local weather station records may be utilized if they are demonstrated to be applicable. Attention should be paid to both moderate and high speed winds since the high velocity winds often have a prevailing direction different from the prevailing direction of moderate winds.
4. A windbreak should be located on both sides of the treatment works normal to a line projected through the treatment works and the area that is to be protected, as close to the treatment works as practicable. An effective windbreak may be comprised of man-made or natural barriers that extend from the ground surface to a height of 16 feet. Alternatively, a cultivated tree windbreak may be developed by planting at least four rows of fast-growing evergreen trees (pine family preferred), planted on staggered 10-feet centers. Rows should be spaced no greater than 16 feet apart. The minimum tree height at planting shall be six feet, unless taller trees are required in order to provide a windbreak which will be immediately effective. The variety of tree used should be readily adaptable to the soil and climate at the treatment works site.
5. Reduced buffer distances will be established for enclosed treatment unit operations or processes. Covered units shall be provided with screened intake openings and positive forced draft ventilation and shall have provisions for removal of aerosols and odors from the exhaust.
6. Owners of existing sewage treatment works or those treatment works proposed for upgrading shall take whatever steps possible to provide as much of the required buffer as is reasonably possible under the specific existing conditions at each treatment works site. Wherever a demonstrated nuisance problem does exist, corrective action (wind breaks or odor control measures, for example) shall be undertaken.
7. The required buffer zone shall be maintained by adequate legal instruments such as either ownership, recorded easements, or restrictive zoning throughout the life of the treatment works.
8. The director may consider exceptions to the listed buffer zone requirements in accordance with this chapter.
D. Flooding. All mechanical and electrical equipment that could be damaged or inactivated by contact with or submergence in water (motors, control equipment, blowers, switch-gear, bearings, etc.) shall be physically located above the 100-year level or otherwise protected against the 100-year flood/wave action damage. All components of the treatment works shall be located above or protected against the 25-year flood/wave action level and remain fully operational. Consideration should be given to designing the treatment works in such a way as to facilitate the removal of vital components during more extreme flood events.
E. Closure. A closure plan shall be submitted to the department in accordance with this chapter.
Statutory Authority
§ 62.1-44.19 of the Code of Virginia.
Historical Notes
Former 12VAC5-581-510 derived from Virginia Register Volume 18, Issue 10, eff. February 27, 2002; amended and adopted as 9VAC25-790-450, Virginia Register Volume 20, Issue 9, eff. February 12, 2004.
9VAC25-790-460. Standards.
A. The minimum degree of treatment to be provided shall be adequate in design to produce an effluent in accordance with this chapter, that will comply with the provisions of the State Water Control Law and federal law, and any water quality standards adopted by the State Water Control Board or effluent limitations adopted by the State Water Control Board or Department of Environmental Quality or orders issued by the Department of Environmental Quality. The expected performance levels of conventional treatment processes are described in subsection F of this section.
B. Industrial flows. Treatment works receiving industrial wastewater flows at a rate or volume exceeding 90% of the combined average daily influent flow can be designed and operated through the applicable requirements imposed by the State Water Control Board or Department of Environmental Quality, provided that public health and welfare protection issues are resolved. Otherwise, consideration shall be given to the character of industrial wastes in the design of the treatment works. In such cases, the treatability characteristics of the combined (sewage and industrial) wastewater shall be provided and addressed in the treatment process design. Pilot-scale testing as described in this chapter may be required to predict the full-scale treatment works operations.
C. Design loadings. Design loading refers to the established capacity of a unit operation or treatment process to reliably achieve a target performance level under projected operating conditions. Component parts and unit operations of the treatment works shall be arranged for greatest operating convenience, flexibility, economy, and to facilitate installation of future units.
1. Treatment works to serve existing sewerage systems shall be designed on the basis of established average sewage characteristics with sufficient capacity to process peak loadings. Excessive inflow/infiltration is an indication of deficiencies in the sewerage system and the design engineer shall provide an acceptable plan for eliminating or handling these excessive flows so that there will be no discharge of inadequately treated wastewaters or impairment of the treatment process.
2. A new treatment works must be designed in accordance with anticipated loadings. Table 3, found in this section, presents generally accepted minimum design flows and loadings. Deviations from Table 3 shall be based on sound engineering knowledge, experience and acceptable data substantiated in the design consultant's report. Numbers of persons per dwelling shall be based upon planning projections derived from an official source.
3. The design of treatment process unit operations or equipment shall be based on the average rate of sewage flow per 24 hours except where significant deviation from the normal daily or diurnal flow pattern is noted. The design flow for industrial wastewater flow contributions shall be determined from the observed rate of flow during periods of significant discharge or, in the case of proposed or new contributions, the industrial owner shall provide flow projections based on existing facilities of a similar nature. The following factors shall be included in determining design flows:
a. Peak rates of flow delivered through conduits as influent to the treatment process unit operations.
b. Data from similar municipalities, if applicable.
c. Wet weather flows.
4. The design organic loading should be based on the results of acceptable analytical testing of the wastewater or similar wastewater and shall be computed in the same manner used in determining design flow.
5. All piping and channels shall be designed to carry the maximum expected flow. If possible, the influent interceptor or sewer shall be designed for open channel flow at atmospheric pressure. If a force main is used to transmit the influent to the treatment works, a surge or equalization basin should be provided upstream of biological unit operations to provide a more uniform loading. Bottom corners of flow channels shall be filled and any recessed areas or corners where solids can accumulate shall be eliminated. Suitable gates and valves shall be placed in channels to seal off unused sections which might accumulate solids and to provide for maintenance.
D. Pilot plant studies. Pilot plants are defined as small scale performance models of full size equipment or unit operation design. The physical size of pilot plants varies from laboratory bench-scale reactors, with volumetric capacities of one or more liters up to several gallons, up to larger capacity arrangements of pumps, channels, pipes and tankage capable of processing thousands of gallons per day of wastewater.
Pilot scale studies are to include detailed monitoring of treatment performance under operating conditions similar to design sizes, including the proper loading factors. A sampling and analytical testing program is to be developed by the owner and evaluated by the department in order that the results of pilot plant studies can be utilized to verify full size designs.
E. Grease management. An interceptor basin or basins shall be provided to separate oil and grease from wastewater flows discharged to sewage collection systems whenever such contributions will detrimentally affect the capacity of the collection system or treatment works such that permit violations will actually or potentially occur, or such contributions will result in an actual or a potential threat to the safety of the operational staff. Interceptor basins shall be located in compliance with the Statewide Building Code as close to the source of oil and grease as practical. Interceptor basins shall be sized in accordance with the applicable building codes and local standards but shall be designed as a minimum to retain the volume of flow containing the oil or grease for each continuous discharge occurrence. But interceptor basins shall also provide a minimum volume in accordance with the following:
1. Provide two gallons of volume for each pound of grease received; or
2. Provide a minimum retention period of three hours for the average daily volume of flow received.
Interceptor basins shall be routinely maintained, including the periodic, scheduled removal of accumulations of oil and grease, within a portion of the basin volume as necessary, to prevent detrimental effects on system operation. The oil and grease shall be handled and managed in accordance with state and federal laws and regulations.
F. Expected performance. Conventionally designed sewage treatment unit operations and processes should result in an expected performance level when processing design loadings in accordance with this chapter (see Table 4 of this section). A conventional arrangement of unit operations would include primary and secondary phases. The primary phase involves the use of suspended solids setting basins called primary clarifiers. The secondary phase typically includes a biological reactor and secondary clarifier to maintain a population of microorganisms (biomass) capable of achieving a significant reduction of organic matter (Biochemical Oxygen Demand) contained in the sewage. Advanced treatment processes will include primary, secondary and tertiary phases, typically involving filtration unit operations. Conventional processes can be modified to provide for reduced levels of nutrients in the treated effluent as described in Article 9 (9VAC25-790-870 et seq.) of this part. The use of nonconventional processes to achieve required performance levels shall be considered in accordance with the provisions of Article 2 (9VAC25-790-380 et seq.) of this part.
TABLE 2. | |
A. Unit Operations That Are Totally Enclosed(1) | |
DESIGN FLOW, gpd | BUFFER ZONE(4) |
1. <1,000 | None |
2. >1,000 to <500,000 | 50 feet |
3. Greater than 500,000 | 100 feet |
B. Unit Operations Using Low Intensity Mixing or Quiescent System(2) | |
DESIGN FLOW, gpd | BUFFER ZONE(4) |
1. <40,000 | 200 feet |
2. >40,000 to <500,000 | 300 feet |
3. Greater than 500,000 | 400 feet |
C. Unit Operations Using Turbulent High Intensity Aeration or Mixing(3) | |
DESIGN FLOW, gpd | BUFFER ZONE(4) |
1. <40,000 | 300 feet |
2. >40,000 to <500,000 | 400 feet |
3. Greater than 500,000 | 600 feet |
*Notes: (1)For example, package plant with units totally enclosed as an integral part of its design and manufacture. A package plant treatment works is defined by these regulations as a preengineered and prefabricated structural arrangement of tankage and channels with all necessary components for onsite assembly and installation. The design flow of package plants should be less than 0.1 mgd. Also frequent agricultural use of Class I treated sludge. (2)For example, covered basins, bottom tube aerated facultative lagoons or ponds, or surface flow application of treated effluent. Also, frequent agricultural use of Class II treated sludge. (3)For example, uncovered surface mixed basins or trajectory spray irrigation for land application of treated effluent. Also frequent agricultural use of Class III treated sludge. (4)Discharge locations shall be located no closer than 100 feet and up to 200 feet from any private or public water supply source. | |
TABLE 3. | |||||
Discharge facility(1) | Contributing Design Units | Flow gpd | BOD5 #day(3) | S.S. #day | Flow duration, hours |
Dwellings | Per person | 100(2) | 0.2 | 0.2 | 24 |
Schools w/showers and cafeteria | Per person | 16 | 0.04 | 0.04 | 8 |
Schools w/o showers w/cafeteria | Per person | 10 | 0.025 | 0.025 | 8 |
Boarding Schools | Per person | 75 | 0.2 | 0.2 | 16 |
Motels @ 65 gal. per person (rooms only) | Per room | 130 | 0.26 | 0.26 | 24 |
Trailer courts @ 3 persons/trailer | Per trailer | 300 | 0.6 | 0.6 | 24 |
Restaurants | Per seat | 50 | 0.2 | 0.2 | 16 |
Interstate or through highway restaurants | Per seat | 180 | 0.7 | 0.7 | 16 |
Interstate rest areas | Per person | 5 | 0.01 | 0.01 | 24 |
Service Stations | Per vehicle serviced | 10 | 0.01 | 0.01 | 16 |
Factories | Per person/per 8-hr. shift | 15–35 | 0.03–0.07 | 0.03–0.07 | Oper. Per. |
Shopping centers | Per 1,000 square foot of ultimate floor space | 200–300 | 0.1 | 0.1 | 12 |
Hospitals | Per bed | 300 | 0.6 | 0.6 | 24 |
Nursing Homes | Per bed | 200 | 0.3 | 0.3 | 24 |
Doctor's offices in medical centers | Per 1000 square foot | 500 | 0.1 | 0.1 | 12 |
Laundromats, 9–12 machines | Per machine | 500 | 0.3 | 0.3 | 16 |
Community colleges | Per student & faculty | 15 | 0.03 | 0.03 | 12 |
Swimming pools | Per swimmer | 10 | 0.001 | 0.001 | 12 |
Theaters (drive-in type) | Per car | 5 | 0.01 | 0.01 | 4 |
Theaters (auditorium type) | Per seat | 5 | 0.01 | 0.01 | 12 |
Picnic areas | Per person | 5 | 0.01 | 0.01 | 12 |
Camps, resort day & night w/limited plumbing | Per camp site | 50 | 0.05 | 0.05 | 24 |
Luxury camps w/flush toilets | Per camp site | 100 | 0.1 | 0.1 | 24 |
Notes: (1)Colleges, universities and boarding institutions of special nature to be determined in accordance with subdivision B 2 of this section. (2)Includes minimal infiltrations/inflow (I/I) allowance and minor contributions from small commercial/industrial establishments. (3)#/Day - Denotes pounds per day. | |||||
TABLE 4. Effluent Value Range(1) (mg/l) | |||
A. Primary/secondary treatment process. | |||
BOD5(2) | TSS(2) | ||
1. Primary | 100–180 | 100–150 | |
2. Facultative Aerated Lagoon | 24–45 | 24–30 | |
a. With Clarification | |||
b. Without Clarification | |||
3. Biological contactors | 24–50 | 24–50 | |
4. Activated Sludge | 24–30 | 24–30 | |
5. Biological Plus Filtration(3) | 10–20 | 5–15 | |
6. Primary plus constructed wetlands(4) | 24–40 | 24–40 | |
7. Primary plus Aquatic Ponds(5) | 20–30 | 20–30 | |
B. Advanced treatment process. | ||||||
BOD5 | TSS | PO4-P | NH3-N | |||
1. Physical chemical(6) and | 45–95 | 20–70 | 1–10 | 20–30 | ||
a. F | 20–70 | 1–20 | 1–10 | 20–30 | ||
b. F & AC | 5–10 | 0.1–10 | 1–10 | 20–30 | ||
2. Biological(7) and | ||||||
a. C & S | 12–20 | 12–24 | 0.5–10 | 5–30 | ||
b. C, S, & F | 6–11 | 0.5–15 | 0.5–10 | 5–30 | ||
c. C, S, F & AC | 1–5 | 0.1–5 | 0.1–10 | 5–30 | ||
d. Microscreening | ||||||
(1) 21 microns @ 5 GPM/sq. ft. | 2–14 | 1–14 | 20–30 | 5–30 | ||
(2) 35 microns @ 8 GPM/sq. ft. | 5–20 | 3–17 | 20–30 | 5–30 | ||
3. BNR(8) | 20–30 | 20–30 | 2–4 | 1–3 | ||
4. Other biological and natural treatment processes evaluated on a case-by-case basis. | ||||||
NOTES: (1)Ranges reflect normal expected upper and lower values for process, performance, considering design and operations variability. Upper range value reflects performance expected for conventional loadings. (2)Effluent values for soluble phosphorus and ammonia nitrogen are not given for conventional primary and biological processes since these are not designed as nutrient removal processes. However, phosphorus is removed in biological sludge and ammonia is oxidized to nitrate in biological effluents. Typical effluent values range from 4 to 5 mg/l of total phosphorus and from nearly 0 to more than 30 mg/l ammonia, for fully nitrified to unnitrified effluent. (3)Coagulant and polymer addition prior to filter to be provided. (4)Subsurface flow microbial-plant filter system with a minimum detention of three days, or surface flow system with a minimum retention of six days. (5)Aquatic pond providing one acre of surface area (5-foot depth) per 200 population equivalent or less. (6)Physical - Chemical: means coagulation by aluminum, iron or other metal salts or, precipitation by lime, followed by clarification and may include filtration. Unit processes include, as a minimum, flash mix, flocculation, and sedimentation. Filtration operations will be necessary to achieve effluent TSS levels of 15 mg/l or less. (7)Biological: means any of the biological treatment processes including activated sludge and its process variations, attached growth systems including various filters, and facultative and fully aerated lagoons which are capable of producing a secondary effluent containing 30 mg/l BOD5 and TSS or less. (8)Biological Nutrient Removal performance will be a function of influent levels of nutrients with typical influent values of 4 to 6 mg/l of PO4-P and 20 to 40 mg/l of NH3-N. Additional nitrification operations would be necessary to achieve TKN levels of less than 10 mg/l. Denitrification may produce effluent total nitrogen levels of 5 to 10 mg/l. LEGEND: C = Coagulation S = Sedimentation F = Filtration and AC = Activated Carbon BNR = Biological Nutrient Removal | ||||||
Statutory Authority
§ 62.1-44.15 of the Code of Virginia.
Historical Notes
Former 12VAC5-581-520 derived from Virginia Register Volume 18, Issue 10, eff. February 27, 2002; amended and adopted as 9VAC25-790-460, Virginia Register Volume 20, Issue 9, eff. February 12, 2004; Errata 20:12 VA.R. 1526 February 23, 2004; amended, Virginia Register Volume 39, Issue 5, eff. November 23, 2022.
9VAC25-790-470. Treatment works details.
A. Equipment. The specifications should be so written that the installation and essential items of mechanical equipment will be certified by a representative of the manufacturer. The specifications shall require that the equipment manufacturers provide to the owner one complete set of operational instructions, equipment and maintenance manuals, and emergency procedures for each essential mechanical and electrical equipment item. The manuals shall contain drawings of equipment and a numbered parts list keyed to a list of components.
B. Instrumentation. Insofar as possible, all indicating, recording, and totalizing flow meters shall be identical so that repair components and charts are interchangeable. Recording equipment for dissolved oxygen, temperature, pH, and other operating data, along with flow metering equipment, shall be located in areas free from high humidity, extreme temperatures, and corrosive gases. Instrumentation requirements for each treatment works shall be decided on a case-by-case basis.
Facilities for measuring the volume of sewage flows shall be provided at all treatment works. Treatment works having a capacity of equal to or less than 40,000 gallons per day shall be equipped with a primary metering device such as a Parshall flume with separate float well and staff gauge, weir box with plate and staff gauge, or other approved devices, as a minimum unless nonfluid contact measuring devices are provided. All treatment works having a capacity of greater than 40,000 gallons per day shall be equipped with indication, recording, and totalizing equipment. The recording scale shall be sufficient to accurately record and depict the flow measured. Flows passed through the treatment works and flows passed through controlled diversions shall be measured in a manner that will allow them to be distinguished and separately reported.
C. Component isolation. Properly located and arranged diversion piping or structures shall be provided so that any component of the treatment works process can be independently operated in accordance with the reliability classification, or removed from service independently for inspection, maintenance, and repairs. Adequate access and removal space shall be provided around all components to provide for proper maintenance or removal and replacement without interfering with the operation of other equipment. Due consideration shall be given to the need for lifting and handling equipment available to aid in the maintenance and replacement of all components. In addition, the placement of structures and other devices, such as pad-eyes and hooks to aid handling of heavy or large components, should be considered in the preliminary design. These criteria for adequate access and handling equipment do not apply to the removal or replacement of large tanks, basins, channels, or wells. Lines feeding chemicals or process air to basins, wet wells, and tanks shall be designed to enable repair or replacement without drainage of the basins, wet wells, or tanks.
D. Maintenance provisions. The design of a treatment works should facilitate access for both routine maintenance and equipment failure response.
1. Provisions should be made for flushing, with water or air, all scum lines, sludge lines, lime feed and lime sludge lines, and all other lines that are subject to clogging. All piping subject to accumulation of solids over a long period of time should be arranged in a manner to facilitate mechanical cleaning if possible. The design shall be such that flushing and mechanical cleaning can be accomplished without causing violation of effluent limitations or without cross-connections to the potable water system.
2. Provisions should be made for dewatering each unit. Drain lines should discharge to points within the system such that maximum treatment of the contents of the drained unit is provided. Due consideration shall be given to the possible need for hydrostatic pressure relief devices. Where practicable, all piping shall be sloped or have drains (drain plug or valve) at the low points to permit complete draining. Piping shall not be installed with isolated pockets that cannot be drained.
3. Concrete, metals, control and operating equipment, and safety devices shall, insofar as practical, be designed to protect against corrosion, moisture and heat induced damage.
4. Positive identification of the content of a piping system shall be by lettered legend giving the name of the contents. Arrows should be used to indicate direction of flow. Legends shall be applied close to valves and adjacent to changes in direction, branches and where pipes pass through walls or floors, and at frequent intervals on straight pipe runs. The lettering shall be of such color, size, and location to be clearly visible and readable.
5. A complete outfit of tools and accessories for the treatment works operator's use, such as wrenches, valve keys, rakes, shovels, etc., and such spare parts as may be needed, shall be specified as either contractor or owner furnished. A portable pump is desirable. Readily accessible storage space and work bench facilities shall be specified. Consideration shall be given to provision of a garage area that would also provide space for large equipment maintenance and repair.
6. Concrete, paved, or gravel walkways shall be provided for access to all units. Where possible, steep slopes and narrow stairways shall be avoided to increase access for maintenance. Surface water shall not be permitted to drain into any units. Provision should be made for erosion protection and landscaping, particularly when a treatment works must be located near residential areas.
E. Essential facilities. The design of treatment works shall include both proper physical support for operation personnel and specific safety features to protect operators and visitors from exposure to hazards.
1. A supply of potable water with adequate pressure shall be provided for use in the laboratory and bathroom facilities. All potable water supplies within the treatment works shall be protected with reduced pressure zone backflow prevention devices. To facilitate cleaning wet wells, tanks, basins, and beds, water supplied from a nonpotable water system or the treatment works effluent may be supplied at these points by means of an adequately pressurized water system with hydrants or hose bibs having minimum outlets of one inch in diameter.
The potable water supply line to each treatment works shall be equipped, as a minimum, with an approved reduced-pressure zone backflow preventer. These devices shall be installed in an above-ground location, no more than 36 inches above the ground floor elevation and with adequate clearance for access on all sides, to prevent corrosion and to allow for adequate, quick service and periodic inspections. Designers shall consult with the appropriate field office of the department for such requirements at individual treatment works in accordance with the Waterworks Regulations (12VAC5-590).
Where it is not possible to provide potable water from a public water supply, a separate well may be provided. Location and construction of the well shall comply with requirements of the department.
2. All sewage treatment works shall be provided with or have ready access to a toilet and lavatory. For a treatment works at which the operator is required to be on duty for eight or more hours per day, a shower shall also be provided.
3. Minimum laboratory space for treatment works not performing BOD and suspended solids testing on-site shall be 50 square feet of floor space with 20 square feet of bench area. Treatment works providing on-site BOD, suspended solids, or 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 will be working in the laboratory at any given time, 100 square feet of additional space should be provided for each additional person. Advanced sewage treatment works shall provide a minimum of 100 additional square feet of floor space, with a proportionate increase in bench space. On-site laboratories shall be isolated from treatment works equipment, vehicular traffic, etc., so as to render the laboratory reasonably free from the adverse effects of noise, heat, vibration, and dust in accordance with VOSH requirements.
4. Safety provisions should protect operators and visitors at treatment works from exposure to hazards in accordance with VOSH requirements. The designer should refer to the applicable occupational safety and health standards of the Virginia Department of Labor and Industry for the appropriate requirements. The following shall be required as a minimum, as applicable:
a. Enclosing the treatment works site with a fence designed to discourage the entrance of unauthorized persons and animals.
b. Providing adequate lighting, installing handrails, and establishing access guards, where necessary, and posting "No Smoking" signs in hazardous locations.
c. Providing first aid supplies and safety equipment, including protective clothing and equipment such as gas masks, goggles and gloves.
d. Providing explosion-proof electrical equipment, nonsparking tools, etc. in work areas where hazardous conditions may exist, such as digester vaults and other locations where potentially explosive atmospheres of flammable gas or vapor with air may accumulate.
e. Providing properly grounded and insulated electrical wiring, with no part of the treatment works piping being used for grounding.
f. Providing railroad type manhole steps with slip-proof rungs, unless access is to be provided by lifting devices. The railroad type step is designed to help prevent foot slippage off the ends of the rungs. Also, providing intermediate landings or other suitable protection between height intervals of 10 feet or less, unless adequate lifting devices are to be provided.
g. Providing adequate protective storage for flammable and hazardous materials and safety devices for gas collection piping.
h. Providing adequate ventilation for all areas subject to accumulation of hazardous or toxic gases and providing equipment (accuracy of + or—5%) for measuring the concentration of gases in the atmosphere of confined spaces, enclosed areas, underground areas, or other areas where hazardous gases may accumulate or oxygen deficiencies may occur. Providing a portable blower and hose sufficient to ventilate accessed confined spaces.
i. Locating heating devices with open flames in separate rooms with outside entrances located at grade level or above.
j. Locating laboratory and office space at sewage treatment works to minimize interference from motors, generators, compressors, etc. and providing adequate floor slope to a point of drainage.
k. Providing stairways with a slope of 30° to 50° from the horizontal, with risers all of equal height, and with handrails on the open sides of all exposed stairways and stair platforms.
F. Odor control. The potential for odor problems at new treatment works shall be evaluated. The evaluation shall include possible sources of odors, types of odors, and various methods (i.e., covered units, physical treatment, chemical treatment, or biological treatment) of controlling odors. Provisions for odor control shall be included in the design if the sewerage system is primarily composed of force mains or otherwise provides lengthy retention times (i.e., on the order of two or three days), or if the treatment works will provide raw sludge holding, raw sludge dewatering, or thermal treatment. Odor control provisions should be considered for sludge digestion processes, sludge dewatering processes, preliminary and primary sewage treatment processes, and other processes that provide the opportunity for gas transfer or gas stripping activities to occur.
Statutory Authority
§ 62.1-44.19 of the Code of Virginia.
Historical Notes
Former 12VAC5-581-530 derived from Virginia Register Volume 18, Issue 10, eff. February 27, 2002; amended and adopted as 9VAC25-790-470, Virginia Register Volume 20, Issue 9, eff. February 12, 2004.
9VAC25-790-480. Treatment works outfalls.
A. The effluent discharge line or outfall shall be designed with sufficient capacity to transmit the maximum expected flow in a manner so as to prevent flooding of the treatment process while providing optimum dispersion of the treated effluent into the receiving waters.
B. Velocity. The velocity in the outfall at design average flow shall be a minimum of 1-1/2 feet per second to avoid any settling of solids. Velocities should not exceed the recommendations of the pipe manufacturer with respect to maximum velocities to avoid pipe erosion or scour and should be less than eight feet per second to avoid excessive head loss or disruption of the receiving water channel.
C. Structures. The outlet structure should be submerged during design low flow conditions in the receiving water channel, unless adequate dispersion can be achieved without such submergence. The outlet structure should be designed to provide effective dispersion of effluent into the receiving body of water as established by the certificate or permit issued. Additional provisions for dispersion of effluent may be required, based on public health and welfare protection and water quality considerations in accordance with downstream uses.
1. The outfall, where practicable, shall be of gravity sewer design and extend beyond the design low water level of the receiving body of water and account for coastal erosion if necessary. The effluent discharge shall remain submerged if required to maintain water quality standards or protect public health and welfare.
2. Headwalls may be used where adequate dispersion will be obtained without requiring that the outfall be submerged. The design shall include measures to prevent erosion and foaming problems as a result of the discharge.
3. When a diffuser mechanism is provided, the design shall take into account the range of current velocities and directions in the vicinity of the diffuser.
Diffuser ports shall be spaced and located so as to avoid interference between adjacent jet plumes and sized so as to minimize head loss and maximize initial dispersion of the effluent into the receiving water.
D. Protection. The outfall shall be designed and constructed to protect against the effects of erosion, flood waters, tides, ice, boating and shipping, and other hazards, and to insure structural stability and freedom from stoppage.
Statutory Authority
§ 62.1-44.19 of the Code of Virginia.
Historical Notes
Former 12VAC5-581-540 derived from Virginia Register Volume 18, Issue 10, eff. February 27, 2002; amended and adopted as 9VAC25-790-480, Virginia Register Volume 20, Issue 9, eff. February 12, 2004.
9VAC25-790-490. Reliability protection.
A. Reliability is a measurement of the ability of a component or system to perform its designated function without failure or interruption of service. Overflow criteria, such as a period of discharge, are utilized solely for the establishment of reliability classification for design purposes and are not to be construed as authorization for or defense of an unpermitted discharge to state waters. The treatment works design shall provide for satisfactory operation during power failures, flooding, peak loads, equipment failure, and maintenance shut-down (in accordance with the requirements of the appropriate reliability class). Such design features include: (i) additional electrical power sources; (ii) additional flow storage capacity; and (iii) additional treatment unit operations, that provide for alternate operation in accordance with the issued certificate permit requirements.
B. Power feed. For Class I Reliability, two separate and independent sources of power feed shall be provided. Each source shall be capable of maintaining continuous treatment works operation at peak design flow during power failures, flooding, or equipment malfunction. Certain Reliability Class I treatment works for which it is feasible to shut down or discontinue treatment works operation during periods of power failure without bypassing or violating effluent limitations may be exempt from the alternate feed requirement.
1. Class I Reliability treatment works that may qualify for the alternate feed exemption can be broadly categorized as (i) those that serve facilities or institutions that could be closed during periods of power failure, such as certain industrial plants, schools, and recreational and park areas; (ii) those equipped with an emergency overflow holding basin with sufficient capacity to retain a minimum of one day of treatment works design flow and having provisions for recycle to the treatment works; and (iii) those with sufficient operational resources for which it can be demonstrated that projected power failures will not result in public health problems, water quality damage, or socio-economic resource losses.
2. Single source power feed is acceptable for Reliability Class II and III systems or works.
C. Power source. Electric power shall be provided by alternate feed from distribution lines that are serviced by alternate feed from transmission lines (e.g., 115KV) where possible. The transmission lines shall have alternate feed from the generating source or sources. The requirement for alternate feed can be satisfied by either a loop circuit, a "tie" circuit, or two radial lines. Where alternate feed lines terminate in the same substation, the substation shall be equipped as follows:
1. Reliability Class I: two or more in-place transformers.
2. Reliability Class II and Class III: one in-place transformer and capability for a connection of a mobile transformer.
On-site power generating equipment may be used as a substitute for alternate utility source feed. The capacity of the back-up power source shall be sufficient to operate all components vital to wastewater treatment operations during peak wastewater flow conditions, together with critical lighting and ventilation.
D. Power systems. External power distribution lines to a Class I Reliability Treatment Works shall be completely independent (i.e., both power lines cannot be carried on the same pole, cannot be placed in the same underground conduit, or cannot cross in their route to the treatment works) where possible. Minimum separation between alternate lines of 75 feet for above ground routes and 25 feet for underground routes shall be maintained. This shall also apply to service connections into the sewage treatment works. Devices should be used to protect the system from lightning.
1. Reliability Class I treatment works shall have a final step down transformer on each electrical feed line with adequate physical separation between them to prevent a common mode failure. In addition, Reliability Class I treatment works shall be provided with separate buses for each power source and separate independent internal power distribution systems up to the transfer switch for all critical components. The electrical power transfer to the alternate source should occur within 10 minutes of the time of failure of the primary power source.
2. Breaker settings or fuse ratings shall be coordinated to effect sequential tripping such that the breaker or fuse nearest the fault will clear the fault prior to activation of other breakers or fuses, to the degree practicable.
3. Where practicable, the electric switchgear and motor control centers shall be housed in a separate room from the liquid processing equipment. All outdoor motors shall be adequately protected from the weather. Motors located indoors and near liquid handling piping or equipment shall be, at least, of splash-proof design. Means for heating motors located outdoors or in areas where condensation may occur should be provided. On-site emergency power generating equipment shall be located above grade and be adequately ventilated. Fuel shall be stored in safe locations and in containers specifically designed for fuel storage.
a. All electrical equipment (motors, controls, switches, conduit systems, etc.) located in raw sewage wet wells or in totally or partially enclosed spaces where hazardous concentrations of flammable liquids, gases, vapors, or dusts may be present shall comply with the National Electrical Code, including the requirements for Class I, Group D, Division 1 locations.
b. Three-phase motors and their starters shall be protected from electric overload and short circuits on all three phases.
c. Large motors shall have a low voltage protection device that, on the reduction or failure of voltage, will cause and maintain the interruption of power to that motor.
d. Consideration should be given to the installation of temperature detectors in the stator and bearings of large motors in order to give an indication of overheating problems.
e. Wires in underground conduits or in conduits that can be flooded shall have moisture resistant insulation identified in the National Electrical Code.
4. The means for starting an on-site emergency power generator shall be completely independent of the normal electric power source. Air-starting systems shall have an accumulator tank or tanks with a volume sufficient to furnish air for starting the generator engine a minimum of three times without recharging. Batteries used for starting shall have a sufficient charge to start the generator engine a minimum of three times without recharging. The starting system shall be appropriately alarmed and instrumented to indicate loss of readiness (e.g., loss of charge on batteries, loss of pressure in air accumulators, etc.).
5. Testing provisions shall be included in the design of essential equipment requiring periodic testing to enable the tests to be accomplished while maintaining electric power to all vital components. Such provisions would involve an ability to conduct tests, such as actuating and resetting automatic transfer switches and starting and loading emergency generating equipment without taking essential equipment off-line. The electric power distribution system and equipment shall be designed to facilitate inspection and maintenance of individual items without interruption of operations.
E. Flow Storage. In combination with provisions for electrical power reliability, the use of flow storage and additional unit operations should be evaluated. Additional flow storage capacity should provide up to a 24-hour detention of the peak design flow. Additional unit operations could involve chemical clarification, filtration, additional disinfection capacity, or use of natural treatment technology for enhancing effluent quality.
F. Alarm systems. An audiovisual alarm system to monitor the condition of equipment whose failure could result in a bypass or a violation of effluent limitations shall be provided for all treatment works. Alarms shall also be provided to monitor conditions which could result in damage to vital components.
1. For continuously manned treatment works, the alarm system shall sound and be visible in areas normally manned and in areas near the equipment being monitored.
2. Treatment works not continuously manned shall have, in addition to a local audiovisual alarm, provisions for transmitting an audible alarm to a central location where personnel competent to receive the alarm and initiate corrective action are available 24 hours per day or during the period of time that the treatment works receives influent flow.
3. The following requirements apply to all treatment works:
a. The on-site alarm system should be designed in such a manner that each announced condition is uniquely identified.
b. A back up power supply, such as a battery pack with an automatic switchover feature, shall be provided for the alarm system (such that a failure of the primary power source would not disable the alarm system), unless an adequate alternate or backup power source is provided.
c. Test circuits shall be provided to enable the alarm system to be tested and verified to be working properly.
Statutory Authority
§ 62.1-44.19 of the Code of Virginia.
Historical Notes
Former 12VAC5-581-550 derived from Virginia Register Volume 18, Issue 10, eff. February 27, 2002; amended and adopted as 9VAC25-790-490, Virginia Register Volume 20, Issue 9, eff. February 12, 2004.