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Wasteload Allocation Procedures

Iowa’s streams, rivers, lakes, and wetlands need to be protected for beneficial uses such as swimming, fishing, and livestock watering, etc. All facilities that discharge pollutants from any point source into surface waters are required to obtain an NPDES (National Pollutant Discharge Elimination System) or operation permit from IDNR. The permits require compliance with all federal standards, state rules, and state administrative code. Wasteload Allocations ensure that the effluent limits for point source discharges will be protective of the designated uses of the waterbodies.

What is a WLA?

A Wasteload 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. WLAs establish water quality based effluent limits for point source discharge facilities.

Why a WLA is needed?

A WLA serves several purposes. A WLA is needed to ensure that NPDES permit limits will be protective of the water quality standards and designated uses of the receiving waterbody. WLAs are also used to establish design targets for consulting engineers in order to design wastewater treatment plants to meet effluent limits. Water quality standards are changing from time to time as new scientific information becomes available. As a result, water quality based limits need to be updated from time to time.

How to Request for a WLA:

To request a WLA, please fill in the WLA request form and send the WLA requests electronically to katie.greenstein@dnr.iowa.gov.

WLA Request Form and Instructions
WLA Request Form and Instructions

How is a WLA calculated?

The establishment of a WLA for a particular discharge is dependent on the outfall location of the facility, stream critical low flows, the available dilution or mixing zone, water quality standards, discharge flows and background conditions of the receiving water. Default mixing zone are used to calculate WLAs. Facilities have the option to collect site-specific mixing zone data or install a diffuser to artificially increase the mixing zone. The mixing zone study procedure can be found in the Basin Plan Support Document shown below. If a dye is used in the site-specific mixing zone study, an authorization from DNR is required to use the dye if the dye has the potential to reach the Waters of the State. Please contact Katherine Greenstein at (515)725-8400 or katie.greenstein@dnr.iowa.gov for more information.

The current rule reference document that outlines WLA methodology is as follows:

Wasteload Allocation Procedure Document (February 2018)

DNR Contact:
Katie Greenstein