Department of
Environmental Quality

Once wastewater has been treated, it is "disposed" of by re-introducing it to the environment. The three main methods of disposing of treated wastewater effluent are surface water discharge, subsurface discharge, and land application for beneficial use.

Discharge to Surface Waters

Federal, state, and local regulations prohibit the disposal of untreated wastewater into storm drains or surface waters. In some cases, with a permit, a facility may discharge treated wastewater into surface waters. The National Pollutant Discharge Elimination System (NPDES) program sets requirements and issues permits for this type of discharge. NPDES permits specify pretreatment requirements and limits on what can be discharged to ensure that the discharge does not harm water quality or public health. 

In Idaho, the NPDES permit program is administered by the EPA, which means EPA is responsible for issuing and enforcing all NPDES permits in Idaho. The state's role in this process is to certify that NPDES-permitted projects comply with state water quality standards.

Subsurface Discharge

Subsurface discharge occurs on-site where wastewater is treated by discharging septic tank effluent underground where it leaches through a drainfield.

Land Application (Reuse)

In some situations, treated wastewater can be applied to land for irrigation. The small amount of pollutants remaining in the wastewater after treatment are absorbed by the crop or are assimilated into the soil structure.

Depending on the contaminants, the water may require pretreatment prior to discharge to meet water quality standards. DEQ issues permits for facilities treating wastewater and sludge through this method.