There are three methods for disposing of treated wastewater effluent: surface water discharge, subsurface discharge, and land application for beneficial use.
Federal, state, and local regulations prohibit the disposal of untreated wastewater into storm drains or surface waters. In some cases, a permitted facility may discharge treated wastewater into surface waters. DEQ’s Idaho Pollutant Discharge Elimination System (IPDES) Program sets requirements and issues permits for this type of discharge, including specifying pretreatment requirements and limits on what can be discharged to ensure that the discharge does not harm water quality or public health.
Subsurface discharge occurs on-site where wastewater is treated by discharging septic tank effluent underground where it leaches through a drainfield.
Treated wastewater can also be applied to land for irrigation. The small amount of pollutants remaining in the wastewater after treatment is absorbed by the crop or are assimilated into the soil structure. Depending on the contaminants, the water may require pretreatment before discharge to meet water quality standards. DEQ issues permits for facilities treating wastewater and sludge through this method.
The reuse of recycled water is regulated by the “Recycled Water Rules” (IDAPA 58.01.17). Recycled water is water that has been treated to be safe for its intended beneficial use and has a reuse permit from DEQ.
These rules contain requirements based on the source (either municipal or industrial wastewater) and intended use of the recycled water. Municipal or industrial reuse permits specify standard conditions common to all facilities as well as site-specific conditions as necessary to address the particular quality of recycled water. The most common form of water reuse for both municipal and industrial facilities is the irrigation of agricultural crops. Reuse permits are issued for terms of five to ten years.
For facilities seeking a new reuse permit or renewing an existing permit, the process begins with a pre-application meeting with DEQ.
For facilities with an existing reuse permit, it is recommended that a pre-application meeting be requested by the permittee one year before their permit’s expiration date.
After the pre-application meeting, the facility must submit an application package. The contents of the application package will be discussed in the pre-application meeting, but generally includes sufficient documentation to develop a comprehensive understanding of the proposed site, treatment method, recycled water uses, and any other details that may be requested by DEQ.
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Municipal recycled water is wastewater collected from homes and/or businesses and treated at a wastewater treatment facility. Municipal reuse permits classify recycled water as one of five classes (Class A, B, C, D, or E). Each class of recycled water has specific treatment requirements and allowable uses. Class A is the highest quality and has more allowable uses, but requires additional operating and monitoring requirements. Lower quality municipal recycled water has fewer allowable uses and includes buffer zones and other restrictions.
Industrial wastewater is discharged from industrial processes, the characteristics of which can be variable and may change with production rates and schedules. Industrial recycled water is permitted with consideration of its source, treatment, and use. Many of Idaho’s industrial reuse facilities are associated with food processing (e.g., potatoes, sugar beets, onions, dairy products, meat processors).