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Wasteload Analysis for Developing Permit Limits


A waste load allocation (WLA) is the portion of a receiving water’s assimilative capacity that is allocated to one of its existing or future point sources of pollution. DWQ conducts a waste load analysis to calculate the maximum amount of a pollutant that a waterbody can receive and still meet water quality standards. Computer models are used extensively for water quality management and determining water quality based effluent limits (WQBEL) for discharge permits. The models predict the water quality in a water body in response to changes in seasons, pollutant loading, and various waste load allocation strategies.

General guidelines have been developed for how DWQ conducts waste loads.

Mathematical Modeling—QUAL2kw

DWQ has adopted the QUAL2Kw model for the determination of UPDES permit limits for nutrient related discharges to dissolved oxygen sensitive rivers and streams. Other models and tools are used to evaluate the discharge of conventional and toxic pollutants to rivers and streams, as well as discharges to lakes and reservoirs

Model Overview/Abstract

QUAL2Kw is a water quality model that simulates nutrient and oxygen dynamics in rivers and streams. It is applicable to rivers that are vertically well mixed and for periods with steady flow. QUAL2Kw is widely used for Total Maximum Daily Load studies of rivers for evaluation of temperature and eutrophication, including nutrients, dissolved oxygen, and pH. QUAL2Kw is based on the QUAL2K model and is maintained and distributed by the Washington State Department of Ecology.

Site Specific Data Collection

DWQ intends to collect site specific data to support model build and calibration. Due to limited resources, this will not be possible in all cases. Sites will be prioritized based on the magnitude of the discharge and the sensitivity of the receiving water. Standard operating procedures have been developed for the data collection to support QUAL2Kw modeling.

Facilities can submit site-specific information on both the receiving waterbody and the discharge characteristics for consideration. Wastewater treatment facilities are encouraged to plan ahead when considering any data gathering effort. Many of these efforts require seasonal data particularly collected during low stream flow conditions.

Model Calibration

DWQ staff, in collaboration with researchers at Utah State University, have developed standard operating procedures for model build and calibration.

Model Application to Waste load Analysis

Once the models are built and calibrated, they are used by DWQ staff for determining discharge permit limits. The results of the waste load analysis are included as an addendum to the Statement of Basis for the UPDES permit. All supporting data and models used in the determination of permit limits are available for review by the permittee and other interested parties.

Training Materials

A four hour workshop, Applying QUAL2Kw Model to Waste loads for UPDES Permits, was conducted on December 4, 2012. Below are PDF copies of the presentations.

Additional Information

If you need additional information and/or assistance in determining UPDES water quality based permit limits in the state of Utah, please contact:

Ben Holcomb (bholcomb@utah.gov)
Utah Division of Water Quality
(385) 271-4484

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