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Local governments may be responsible for the final system through which water is conveyed and treated. WWTPs are responsible for the treatment, analysis, and discharge of wastewater received from sanitary, or combined sewer systems, and the disposal of sludge generated from the treatment process.
Activities at a WWTP may include:
· Operating and maintaining the plant to assure that discharges meet the facility's NPDES permit requirements and limitations
· Overseeing a pretreatment program to prevent industrial discharges from causing interference or pass through, sludge contamination, or the plant to violate its permit (see Section III.H.)
· Conducting sampling and analysis of wastewater and sludge prior to discharge or disposal to meet NPDES monitoring requirements
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· Managing the biosolids from the treatment processes by landfilling, land application, surface disposal, incineration, or composting
· Maintaining records and submitting discharge monitoring reports (DMRs).
Most of these activities are regulated under the NPDES, pretreatment, or biosolids provisions of the CWA. More detail on the specific activities related to wastewater collection and treatment and the respective regulations is presented below:
· Activities with aspects regulated under the CWA:
- NPDES permit compliance, including monitoring program and laboratory operations.
- Biosolids management and disposal.
· Activities with aspects regulations under RCRA:
- Chemical waste from laboratory operations.
- Disposal of biosolids exhibiting toxic characteristics.
· Activities with aspects regulations under EPCRA/CERCLA:
- Chemical storage/hazardous materials management.
· Activities with aspects regulations under the CAA:
- Chemical storage/hazardous materials management
- Emissions from biosolids incinerators
- Dispensing gasoline/fuel.
Wastewater Treatment Process
Municipal wastewater (sewage) treatment is defined by the extent to which pollutants are removed from the system, and the mechanisms (physical, chemical, or biological) by which they are removed. Wastewater treatment is classified as primary, secondary, and tertiary treatment. Primary treatment consists primarily of physical processes (settling or skimming) that remove a significant percentage of the organic and inorganic solids from wastewater. Secondary treatment depends on biological action to remove fine suspended solids, dispersed solids, and dissolved organic solids. In addition, secondary treatment satisfies much of the oxygen demand of the pollutant(s). Advanced wastewater treatment uses chemical treatment or filtration equipment to reduce nutrients (phosphorous and nitrogen), organic matter, and residual solids and pathogens. Using tertiary treatment can lead to the removal of nearly 99 percent of pollutants from wastewater. Many plants have a disinfection process that follows either the secondary or tertiary treatment process.
Local governments can use "biogas," a product of anaerobic digestion, in several ways. Biogas, a gas composed of methane, carbon dioxide, hydrogen sulfide, and other minor gaseous compounds, has about 60 percent of the heat value of natural gas. Biogas may be used either offsite or within the plant to improve energy efficiency of wastewater treatment processes. If the gas is not reused, it may be flared. Flaring of such gases by the treatment plant may be regulated under the CAA.
NPDES Permit Compliance
Local governments are responsible for complying with federal regulations, both for wastewater plant operation and the collection system (sanitary or combined) that conveys wastewater to the WWTP. Proper operation and maintenance is critical for sewage collection and treatment because the environmental impacts from these processes can severely degrade water resources and ultimately, human health. For these reasons, POTWs receive NPDES permits to ensure that they operate in compliance with federal regulations.
NPDES permits, issued by either EPA or a delegated state (EPA has authorized 42 states to administer the NPDES program), establish effluent limits on the kinds and quantities of pollutants that POTWs can discharge and the pollutant monitoring, recordkeeping, and reporting requirements. Each POTW that intends to discharge into the nation's waters must obtain a NPDES permit prior to initiating its discharge.
To comply with the NPDES permit, local governments are responsible for implementing a NPDES monitoring program at their POTWs. To comply with the program, POTWs must collect samples of effluent discharges at the required frequencies and general locations (e.g., preceding or following chlorination) as specified in their permits and submit monitoring reports to the state or federal EPA. Sampling and analysis is conducted to verify that the amounts and types of pollutants discharged after wastewater treatment systems meet the NPDES permit limits. The parameters that must be monitored are specified in the NPDES permit and vary by plant. Primary parameters in NPDES permits for POTWs include biochemical oxygen demand (BOD), pH, fecal coliform, residual chlorine, and suspended solids. Additional parameters may be included in the NPDES permit, such as flow limits and metals.
If the NPDES permit limits are met, this is generally an indication that the systems at the POTW are operating properly and safely. Failure to comply with these requirements can result in permit suspension, increased monitoring requirements, and/or issuance of fines or other penalties by EPA or the relevant state.
Laboratory Operations
Some POTWs perform analyses of wastewater samples and sludge at onsite laboratories. Laboratory procedures must comply with approved methods and meet NPDES 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.
POTWs are responsible for operating the wastewater 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.
Pretreatment Program
Under the pretreatment regulations (40 CFR 403), POTWs are required to develop and implement local pretreatment programs. Through this program, the POTW is directly responsible for the regulation of certain industrial users discharging to the wastewater treatment system. See Section III.H. for more information.
What are biosolids?
Biosolids (or sewage sludge) are defined as solid, semi-solid, or liquid residue generated during the treatment of domestic sewage in a treatment works.
Biosolids Management and Disposal
Local governments are responsible for managing and disposing of sewage sludge, referred to as biosolids. Biosolids are a primary organic solid product produced by wastewater treatment processes that can be beneficially recycled. (The fact that the biosolids can be recycled does not preclude their being disposed.) Local governments must follow the federal sludge management program (40 CFR Part 503) which establishes requirements for the final use or disposal of biosolids when biosolids are:
· Applied to land to condition the soil or fertilize crops or other vegetation grown in the soil;
· Placed on a surface disposal site for final disposal; or
· Fired in a biosolids incinerator.
A fourth disposal option is landfilling. If biosolids are placed in a municipal solid waste landfill, the local government is responsible for ensuring that the biosolids meet the provisions of 40 CFR Part 258.
For the most part, the requirements of 40 CFR Part 503 are self-implementing and must be followed even without the issuance of a permit. In most cases, Part 503 requirements will be incorporated over time into NPDES permits issued to POTWs. The sludge program includes other facilities that have not been part of the NPDES program because they were not point sources of discharge to waters of the United States. Examples of these facilities that are now regulated and that may eventually receive permits for the use and disposal of sewage sludge include sewage sludge incinerators, composting facilities, and sewage sludge surface disposal sites.
· Land Application. Land application, defined as the spreading of biosolids on or just below the surface of the land, is the most widely employed biosolids use option. Biosolids quality, pollution limits (metals), pathogen reduction and vector attraction requirements, application rates, and environmental conditions under which land application is permitted are specified in the provisions of Part 503. Representative samples of biosolids must be collected and analyzed for inorganic pollutants and pathogens according to methods specified in the Part 503 rule. In addition, the regulations specify recordkeeping requirements for land application facilities.
· Surface Disposal. Surface disposal is defined in the Part 503 regulations as an area of land that contains one or more active biosolids units. A unit is an area of land on which only biosolids are placed for final disposal. Under the provisions of Part 503, facilities using surface disposal must comply with pollutant limits, management practices, and operational standard(s), as well as other requirements related to the frequency of monitoring, recordkeeping, and reporting. In terms of pollutant limits, the regulation established limits for three inorganic pollutants (arsenic, chromium, and nickel) for active biosolids units that do not contain a liner and leachate collection system. In addition, site-specific limits can apply in certain situations.
Local governments must follow management practices when biosolids are placed on a surface disposal site. Examples of management practices are:
(1) Threatened or Endangered Species. Biosolids cannot be placed in a surface disposal site if it is likely to adversely affect a threatened or endangered species (under Section 4 of the ESA) or its designated critical habitat.
(2) Wetlands. An active biosolids unit cannot be located in a wetland unless a permit is issued under Section 402 (NPDES permit) or Section 404 (dredge and fill permit) of the CWA). If the owner/operator of a surface disposal site suspects that all or some portion of an active biosolids unit is in a wetland, he or she should contact the local Corps of Engineers District Office to request a wetland delineation.
(3) Methane Gas Concentrations. Methane, an odorless and highly combustible gas, is generated at surface disposal sites. When biosolids are covered by soil or other material either daily or at closure, there are limits on concentrations of methane gas in air because of its explosive potential. The gas can migrate and be released into the environment. To protect site personnel and the public from risks of explosions, air must be monitored for methane gas continuously within any structure on the site and at the property line of the surface disposal site. When biosolids units are not covered, the air does not have to be monitored for methane gas.
· Incineration. Incineration of municipal biosolids is regulated under the CAA. There are national ambient air quality standards for six pollutants, including total suspended particulates. Biosolids incinerators contribute primarily to ambient particulate loadings. Pathogens and toxic organic chemicals are destroyed during biosolids incineration. However, metals, such as cadmium and lead, are not destroyed during incineration and are associated with the ash and fine particulates in the stack emissions. The emission of mercury and beryllium from sludge incinerators and drying equipment is regulated under 40 CFR 61. However, this regulation rarely causes concern, since most biosolids have low concentrations of these elements.
Incinerators constructed or significantly modified since June 11, 1973, are subject to additional regulation under the NSPS, which limit discharge of particulates. There standards apply to any incinerator that burns more than 10 percent wastewater sludge at a rate greater than 1,000 kg per day (40 CFR 60). Usually incinerators will have to use high pressure scrubbers to meet these requirements, but some incinerators have been able to meet the standard solely through strict operating practices. SIPs may require a facility to demonstrate that air quality impacts will be within acceptable limits.
· Landfilling. Landfilling is a biosolids disposal method in which sludge is deposited in a dedicated area alone or with solid waste, and buried beneath a soil cover. Landfilling is primarily a disposal method, with no attempt to recover nutrients and only occasional attempts to recover energy from the biosolids. If biosolids are placed in a municipal solid waste landfill, the local government is responsible for ensuring that the biosolids meet the provisions of 40 CFR Part 258.
Impact of Biosolids Composition on Disposal/Use Options
The composition of biosolids can limit a local governments choice of biosolids use/disposal options or make certain options more appealing. The most important constituents are organic content, nutrients, pathogens, toxic organic chemicals, and metals. Biosolids may contain varying amounts of heavy metals and inorganic ions (e.g., cadmium, cooper, lead, mercury, silver) that, at high concentrations, may be toxic to humans, animals, and plants. The metals concentrations in biosolids are among the foremost considerations in land application because of their potential to damage crops and, in the case of cadmium, to enter the human food chain. Metals may also be a concern in landfilling, if conditions are acidic and promote leaching of metals, and in incineration, if improper design or operating procedures results in the release of metals into the atmosphere.
Under the hazardous waste provisions of RCRA, municipal wastewater biosolids are neither excluded nor specifically listed as hazardous waste. However, biosolids from POTWs with highly industrialized areas may need to be evaluated for characteristics that designate hazardous waste. The test most appropriate for municipal biosolids is the toxicity characteristic leaching procedure (TCLP). If the biosolids fail the TCLP test, it must be handled as a hazardous waste according to the requirements of RCRA.
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 wastewater collection and treatment operations, such as cleaning, disinfecting, or other maintenance activities. Specifically, chlorine and sulfur dioxide are commonly used in the disinfection (chlorination/dechlorination) process. Additional chemicals are used for laboratory procedures used to analyze wastewater 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, 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.
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