DES MOINES - A public comment period will be closing June 23, 2020 for a proposed amendment that updates the current aquatic life water quality criteria with the latest scientific information on metal toxicity.
While current criteria are expressed as total recoverable metals, research has established that dissolved metals, except for aluminum, more closely approximate the bioavailable fraction of metals in the water column. These new data indicate that the dissolved portion of metals in the water column is the portion that is most easily absorbed by aquatic life, and therefore is a better measure of toxicity. In light of the new data, measuring for total recoverable metals is an overly stringent approach.
Based on this research, the Environmental Protection Commission (EPC) is proposing to convert the aquatic life water quality criteria from total recoverable metals to dissolved metals based on available conversion factors for the following metals: arsenic (III), cadmium, chromium (VI), lead, mercury, nickel, silver, and zinc. In addition, the proposed aquatic life criteria for cadmium have been recalculated from the U.S. Environmental Protection Agency (EPA)-published 2016 national criteria for Iowa waters based on the aquatic species residing in Iowa waters.
Unlike other metals, some non-dissolved forms of aluminum can be toxic to aquatic life. As a result, the EPC is proposing aluminum aquatic life water quality criteria in the form of bioavailable concentration values, which include both dissolved and some non-dissolved (colloidal) aluminum which can be toxic to aquatic life. The proposed aluminum criteria also incorporate new data which establish that aluminum bioavailability is dependent upon ambient levels of certain chemical parameters in the receiving stream, such as pH, dissolved organic carbon, and hardness. These criteria were developed using the EPA-published 2018 national criteria with associated toxicity data and site-specific water chemistry data for Iowa waters. The criteria also provide wastewater permittees the option of collecting data specific to the permittee’s own receiving stream.
Any interested person may submit written comments concerning this proposed rulemaking. Written comments in response to this rule making must be received by the Department no later than 4:30 p.m. on June 23, 2020. Comments should be directed to:
Department of Natural Resources
Wallace State Office Building
502 East Ninth Street
Des Moines, Iowa 50319
A public hearing at which persons may present their views orally or in writing will be held via conference call June 23, 2020 from 3:00 pm to 4:00 pm. Persons who wish to attend the conference call should contact Roger Bruner via email at email@example.com. A conference call number will be provided prior to the hearing. Persons who wish to make oral comments at the conference call public hearing must submit a request to Roger Bruner prior to the hearing to facilitate an orderly hearing.