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III.G. Water Supply
Local governments may be responsible for the operation of a public water system. Public water systems are defined as the central systems or network of facilities that supply drinking water to the public. Public water systems are designed to provide and maintain a reliable, high-quality water source (e.g., groundwater or surface water). The operations necessary to provide and maintain reliable drinking water include water treatment, residuals management, and water distribution.
Chemical, physical, radiological and bacteriological substances in drinking water which pose a health risk to the public are regulated by EPA under the Safe Drinking Water Act (SWDA). Under the SWDA, the federal government develops drinking water regulations to protect public health and welfare. Individual states enforce these regulations for public water systems. Public water systems, therefore, must provide water treatment, as required; ensure drinking water quality through monitoring; and provide public notice of violations or possible contamination.
Water treatment operations include several activities that have the potential to impact the environment and are regulated under U.S. environmental laws and regulations. These activities include the treatment process itself, laboratory operations, management of residuals, storage of chemicals, and hazardous materials management. Typical steps in the treatment process include:
· Screening and Presedimentation. Screening captures large debris such as leaves, logs, plastic bottles, sticks, and fish at the intake where water is drawn into the treatment plant. Presedimentation allows removal of settleable solids in the water by gravity prior to additional treatment.
· Coagulation/Flocculation/Sedimentation. These are three processes commonly used together to remove suspended solids, dissolved chemical substances, and impurities from raw water supplies. Removal of suspended solids and other substances improves the appearance and taste of drinking water and helps remove some of the chemical and microbiological contaminants that might be harmful to humans.
· Filtration. Filtration is another commonly used step in removing solids and fine particles. In filtration, source water passes through granular materials, such as sand, where particles are trapped and removed.
· Disinfection. Disinfection is the process by which pathogenss in the water are inactivated or rendered harmless by the use of chemicals, such as chlorine and ozone, or physical processes such as ultraviolet radiation.
· Softening. Water softening is a process used to remove minerals (primarily calcium and magnesium) that cause hardness of water.
Treatment of drinking water is regulated under the Safe Drinking Water Act. Specifically, SDWA regulations (40 CFR 141) require filtration and disinfection for water systems that use surface water as their source of water.
The following are other activities associated with treatment operations that may be regulated under a section of EPA regulations:
· Activities with aspects regulated under EPCRA/CERCLA/CAA Section 112(r):
- Chemical storage/hazardous materials management
· Activities with aspects regulated under RCRA:
- Laboratory operations
- Residuals management
· Activities with aspects regulated under the CWA:
- Residuals management
- Chemical storage/hazardous materials management.
More detail on the specific activities related to water treatment are provided below.
Chemical Storage/Hazardous Materials Management
If a local government stores or uses specified amounts of certain hazardous chemicals, it may be subject to planning and reporting requirements of EPCRA and Section 112(r) of the CAA. Hazardous chemicals may be used in various water treatment operations, such as disinfection, or other maintenance activities. Specifically, chlorine is commonly used in the disinfection process. Additional chemicals are used for laboratory procedures used to analyze water samples. Facilities must submit hazardous chemical inventory and emergency release information as follows:
A list of hazardous chemicals as defined in EPCRA can be found in 40 CFR 372.65.
· Hazardous Chemical Reporting. Under EPCRA, facilities with chemicals that are present in excess of certain amounts are required to submit either actual copies of MSDSs or lists of MSDS chemicals to the LEPC, SERC, and the local fire department. This reporting requirement has been in effect since October 1987. In addition, these facilities must submit annual inventories (Tier I and Tier II reports) on some hazardous chemicals present in excess of certain quantities to the LEPC, the SERC, and the local fire department. These inventory forms are due on March 1 of each year. LEPCs make this information available to the public, and fire departments and public health officials use the information to plan for and respond to emergencies.
· Emergency Release Notification. Under EPCRA and the CAA Section 112(r), a facility is required to immediately notify the community and the state (e.g., the LEPC and the SERC) of the release of more than a predetermined amount of certain hazardous chemicals. Chemicals covered by this requirement include not only the 366 "extremely hazardous substances," by also more than 700 hazardous substances subject to the emergency notification requirements of the Superfund hazardous waste cleanup law. The emergency release notification activates emergency plans and the information on emergency releases is considered in the LEPC planning process.
Exhibit 53 presents some of the process chemicals used in local government water supply operations.
Exhibit 53. Chemicals Used in Water Supply Activities
|
Activity |
Process Chemicals Utilized |
|
Coagulation, flocculation, and sedimentation |
Alum (aluminum sulfate), ferrous sulfate, ferric chloride, cationic polymers, calcium hydroxide and sodium aluminate |
|
Filtration |
Cationic polymers, anionic polymers, calcium carbonate, and calcium hydroxide |
|
Disinfection |
Chlorine (gas or liquid), sodium hypochlorite, calcium hypochlorite, chloramines, chlorine dioxide, and ozone |
|
Softening |
Lime and calcium carbonate |
|
Residuals management |
Lime and calcium carbonate |
|
Water main repair/replacement |
Sodium hypochlorite, calcium hypochlorite, liquid chlorine |
|
Pump maintenance |
Petroleum-based lubricants and grease |
Laboratory Operations
Some water supply facilities perform analyses of wastewater samples and residuals at onsite laboratories. Laboratory procedures must comply with approved methods and meet SDWA monitoring requirements. Chemicals used in the laboratory include acids (e.g., sulfuric, hydrochloric, nitric), bases (e.g., sodium hydroxide, potassium hydroxide, sodium azide solution), and others such as chlorine, ferric salts, carbon disulfide, and benzene. The quantity of wastes generated is dependent on the number and types of tests performed. The storage and disposal of some wastes generated from laboratory activities may be regulated under the hazardous waste provisions of RCRA.
Water supply facilities are responsible for operating the laboratory safely. To prevent laboratory accidents, chemicals should be stored in a properly ventilated and well lit room. All bottles and reagents should be clearly labeled and dated. Volatile liquids which may escape as a gas, such as ether, must be kept away from heat sources, sunlight, and electrical switches. Cylinders of gas in storage should also be capped and secured to prevent rolling or tipping.
Residuals Management
Residuals management includes managing the wide variety of waste products generated from the treatment of drinking water using screening, presedimentation, coagulation/flocculation/sedimentation, filtration, disinfection, and softening processes. These residuals may be organic and inorganic compounds in liquid, solid, and gaseous forms depending on the source of raw water and the type of treatment processes. Key residuals include the following:
· Sludges from coagulation/flocculation/sedimentation operations
· Sludges from softening operations
· Sludges from iron and manganese removal operations
· Solids in filter backwash water
· Solids from screening and presedimentation, filtering, and other processes.
The primary aspect of residuals that may impact the environment is solid materials that, if discharged to waterways, can lead to increased suspended sediment levels in the water column and deposition at the bottom. Additional aspects include metals and chemical residuals that are attached to the solids. The environmental impacts of these depend on the management method. Management methods include dewatering and landfilling, and discharge to POTW or surface water.
Sludge that is dewatered and placed in a landfill or applied to land has minimal environmental impact if performed properly. Excessive land application, however, can lead to sludge runoff during rain events, increasing sedimentation in water bodies. Liquid sludge that is discharged to a wastewater treatment plant may negatively impact the integrity of the sewer system through excessive buildup of solids in the system. Liquid sludge that is discharged to a water body can increase sedimentation in that water body. Land application or land disposal of sludge may be regulated under RCRA solid waste regulations, or state guidelines, while liquid disposal to a treatment plant or directly to a water body are regulated under the CWA pretreatment and NPDES programs, respectively.
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