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Small Systems Waste Residuals

Wastewater residuals from small-scale drinking water treatment plants have received little attention. Yet, in a national survey of consulting engineers, residual disposal was voted the second most pressing need (behind disinfection by-products). Transport, treatment, and disposal of residuals can be a significant cost to small communities. Handling of residuals may account for 50 percent of the total operating budget. Many small systems simply dispose of waste residuals on site or by using local waste treatment sites, such as landfills and sewer lines.

There are currently no EPA regulations or standards that specifically cover water treatment plant residuals. Depending on the residuals' composition and method of disposal, general regulations govern solid and liquid wastes. These general regulations are in:

  • The Safe Drinking Water Act (SDWA),
  • the Clean Water Act (CWA),
  • the Clean Air Act, and
  • the Resource Conservation and Recovery Act (RCRA).

Liquid Residuals

Liquid residuals from water treatment operations include brines, caustics, filter backwash, sedimentation, and solutions used for recharging solid media. Most liquid waste residuals made by public water systems (PWSs) are disposed on site (land) or by sanitary sewer. 

A significant source of liquid residuals is filter backwash. Filter backwash waters may cause to the waterborne disease outbreaks. Most drinking water systems use filters during treatment to catch contaminants from an incoming flow. When the filter’s pores become clogged, they need to be cleaned. One of the best ways to clean a drinking water system’s filter is to backwash it. This means reversing the flow and increasing the velocity at which water passes back through the filter. EPA Backwash Recycling Rule (FBRR) minimizes consumer exposure to microbial contaminants during cleaning and backwashing operations. This rule applies to all PWSs that:

  • use surface water or groundwater under direct influence of surface water
  • use direct or conventional filtration processes
  • recycle filter backwash water, sludge thickener supernatant, or liquids from dewatering processes

Liquid waste residuals may be disposed by direct or indirect discharge, underground injection, and land disposal. Underground injection is not a practical option because of cost.

Direct Discharge of Liquid Residuals

Direct discharge of liquid residuals to surface water can be performed by PWSs under the guidance of the CWA's National Pollutant Discharge Elimination System (NPDES). The NPDES requires that direct dischargers hold a permit and discharge only those pollutants allowed in the permit. NPDES permits generally include technology-based effluent limits for a particular industry. Currently, EPA does not have technology-based effluent limits for water treatment plants. Therefore, discharge permits are usually based on best professional judgment and water quality-based effluent limits. States conduct discharge permitting. Alaska, Idaho, Arizona, Massachusetts, and New Hampshire are not currently authorized to implement the NPDES program.

As long as a facility has a NPDES permit, liquid residuals that could otherwise be classified as hazardous waste under RCRA can be legally discharged, assuming that the discharge is in compliance with RCRA. Direct discharges to marine environments are subject to additional restrictions under the CWA.

Indirect Discharge of Liquids Residuals

PWSs can discharge liquid residuals to sewers. Indirect discharge does not require a NPDES permit, but pretreatment (treatment prior to indirect discharge) performed by the operator may be needed. EPA has developed pretreatment guidance and regulations for industrial discharges to water treatment plants. However, the small quantities of PWS waste typically do not meet the EPA criteria for requiring pretreatment.

Publicly owned treatment works (POTWs) that process 5 million gallons per day or more, or smaller plants that have "significant industrial users," are required to have a pretreatment program in place. It may be necessary for some small systems that use sanitary sewers for liquid residual disposal to coordinate with local POTWs to ensure requirement are met.

Land Disposal of Liquid Residuals

Liquid residuals are generally not disposed in landfills because of:

  • the prohibitive costs involved with transport and disposal,
  • the regulations surrounding such disposal, and
  • the availability of alternative methods.

PWS liquid residuals that are reused through land application and not classified as hazardous waste are subject to little federal regulation, but may be regulated by the state.
States generally implement and enforce the provisions defining sanitary landfills (as opposed to open dumping). These provisions include:

  • requirements that address location requirements,
  • protection of endangered species,
  • source water protection,
  • nonpoint discharge violations,
  • minimization of disease vectors,
  • protection of air quality, and
  • minimization of explosive gases.

It is possible that some PWSs may discharge liquid residuals to lagoons or evaporation ponds. In these cases, the SDWA and RCRA impose requirements for nonhazardous wastes that aim to protect wellhead and source water, surface water, and groundwater. States may have further requirements concerning nonhazardous liquid residual lagoons. Lagoons containing hazardous waste are subject to RCRA regulations covering design and operation standards.

Incineration of Liquid Residuals

Incineration processes for small systems’ liquid residuals are cost prohibitive. This would only be an option in extreme cases (e.g., disposal of acutely toxic waste). Regulations governing incineration are covered in the Clean Air Act.

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Solid Residuals

Solid residuals include sludge, schmutzdecke (a naturally occurring gelatinous layer of living biological matter in slow sand filtration units), and spent treatment media. Solid residuals are disposed on site (land application) or discarded for transport and disposal in municipal landfills. Solid residuals are subject to RCRA regulations. They may be hazardous or nonhazardous. A waste is characterized as hazardous or nonhazardous based on its:

  • ignitability,
  • corrosivity,
  • reactivity, and
  • toxicity.

In most cases, state and local regulations may also govern the treatment and disposal of solid residuals. Some PWSs may qualify as conditionally exempt small quantity generators of hazardous waste. This classification requires that the operation:

  • Must not generate > 200 pounds (100 kilograms) of hazardous waste/month
  • Maintain monthly waste generation inventories for amounts of hazardous waste/stored on site
  • Manage hazardous wastes in compliance with federal, state, and local regulations

Sludge generated by PWSs is not subject to regulation under the Biosolids Rule. The CWA Biosolids Rule protects public health and the environment from recycling of sewage sludge biosolids.

Land Disposal of Solid Residuals

PWS solid residuals are classified as hazardous or nonhazardous based on toxicity, which is the quality, relative degree, or specific degree of being toxic or poisonous. Toxicity is determined by the Toxicity Characteristic Leaching Procedure (TCLP). This procedure is a soil sample extraction chemical analysis. If contaminant levels are in excess of those listed in the RCRA Land Disposal Restrictions, the solid residual is classified as hazardous and must be disposed in a RCRA landfill. Transport and disposal costs for hazardous solid residuals will be considerably higher than costs for nonhazardous solid residuals.

Land Application of Solid Residuals

Because PWS sludge is not subject to the Biosolids Rule, on-site recycling of some solid residuals by land application may be an option.

Incineration of Solid Residuals
Incineration is most likely cost prohibitive for small systems.  It would not be an option except in extreme cases (e.g., disposal of acutely toxic waste). Regulations governing incineration are covered in the Clean Air Act.

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Technologically Enhanced Normally Occurring Radioactive Material (TENORM) Residuals

The National Primary Drinking Water Regulations (NPDWR) sets EPA standards for radionuclides in drinking water. Treating water to remove naturally occurring radioactive material (NORM) results in residuals that are classified as "technologically enhanced naturally occurring radioactive materials" or TENORM. TENORM is defined as naturally occurring materials, such as rocks, minerals, soils, and water whose radionuclide concentrations or potential for exposure to humans or the environment is enhanced as a result of human activities (e.g., water treatment).

Numerous regulations govern the disposal of waste streams containing radionuclides. There are no federal waste disposal regulations specifically for TENORM wastes. TENORM interaction is complex. States and disposal facilities can place additional restrictions on TENORM disposal. Liquid and solid residuals classified as TENORM may contain nonexempt levels of radioactive material.

Low-level radioactive waste (LLRW) landfills may be an option for disposal at a solid or hazardous waste landfill. LLRW landfills are licensed by the Nuclear Regulatory Commission (NRC) or by a state under agreement with NRC. Guidelines for disposing in an LLRW landfill are more stringent than the guidelines for disposing in standard landfills. TLLRW landfills are licensed.

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