Wastewater Monitoring

Assisting the wastewater permit program

Carefully regulating discharges to Oregon waters from municipal and industrial facilities is a major function of DEQ’s water quality program. Laboratory and Environmental Assessment Division (LEAD) monitoring staff, analysts and data managers work closely with regional staff to provide the necessary information to ensure that water quality and beneficial uses are protected. LEAD staff conduct mixing zone investigations, provide technical assistance evaluating whole effluent toxicity test results, and offer other technical review and field sampling services in support of DEQ’s implementation of the National Pollutant Discharge Elimination System (NPDES) permit program.

Mixing Zone Surveys

A mixing zone is the small area of water body where initial dilution of treated waste water occurs as it is discharged into the environment. Provided that beneficial uses of the water body such as fisheries and recreation are protected, numeric criteria for some water quality parameters may be waived in the mixing zone when authorized in a NPDES permit. LEAD staff conduct numerous mixing zone surveys each year based on regional permit priorities.

Mixing zone surveys include:

1) Delineation of the area of waste water mixing during critical flow conditions. This is often accomplished through dye studies or conductivity mapping exercises.

2) Sampling of the effluent (undiluted waste water), mixing zone, and ambient water.

3) Physical stream data collection including flow measurements, outfall characteristics, and stream channel observations. Such data are collected to be utilized by regional staff for dilution modeling.

4) A final report that includes the field activity summary, analytical data review, and environmental mapping of the surrounding area. This report aids the regional permit staff during permit review, renewal, and modeling of the discharge.

Whole Effluent Toxicity Tests

Major NPDES permits written for individual municipal or industrial facilities require monitoring for toxicity using a battery of tests. These toxicity tests, which are sometimes referred to as bioassays, use algae, invertebrate and fish species to determine the acute and chronic toxicity of the effluent. Effluent toxicity is evaluated at several concentrations that range from whole or undiluted effluent down to dilute mixtures more typical of a well mixed waste water discharge. Acute toxicity tests measure mortality over a relatively short period of time (four days or less). In conjunction, chronic toxicity tests are designed to measure sub-lethal effects such as impaired growth or reproduction over a longer period of time.

LEAD monitoring staff work with permit writers and other program staff on the interpretation of toxicity test results and development of appropriate toxicity limits in NPDES permits. LEAD is also working on the Internal Management Directive for toxicity testing. This will provide clear guidance for permit writers statewide and establish consistent requirements in permits. When coupled with proper delineation of the regulatory mixing zone, effluent toxicity limits protect aquatic life that drift or swim through the mixing zone from toxic exposures to waste waters.
LEAD staff also provides technical and sampling assistance to regional staff as requested. Currently, LEAD staff are assisting with such diverse projects as the Drinking Water Source Monitoring and Pesticide Stewardship Partnerships. In addition, as requested, staff provides technical review of data submitted for regional permitting activities.

For More Information: