Section 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.

Historical Notes

Former 12VAC5-581-530 derived from Volume 18, Issue 10, eff. February 27, 2002; amended and adopted as 9VAC25-790-470, Virginia Register Volume 20, Issue 09, eff. February 12, 2004.

Statutory Authority

§ 62.1-44.19 of the Code of Virginia.