DERIVING A GENERAL USE WATER QUALITY STANDARD FOR SULFATE

EPA does not recommend a national water quality standard for sulfate; therefore, the State of Illinois has adopted its own standards for specific designated uses of waters. USEPA and IEPA identified a conflict between a 3,500 mg/L daily maximum specific for waters receiving coal mine discharges and a 500 mg/L standard for waters designated as general use, for what, on paper, is the same designated use of receiving waters. The elimination of the 3,500 mg/L daily maximum sulfate standard specific to waters receiving coal mining discharge was proposed, resulting in the application of the general use sulfate standard of 500 mg/L to all surface waters. IEPA determined the 500 mg/L standard was overly stringent as a General Use standard protective of aquatic organisms and cause for a significant economic burden to the coal industry. IEPA and the Illinois Coal Association (ICA) initiated an effort to develop an alternative general use sulfate standard. ADVENT-ENVIRON's contribution included an unsuccessful attempt at re-deriving water quality criteria using the traditional approach and an evaluation existing aquatic field data to determine ecosystem health versus sulfate concentrations relationships that verify biological sulfate tolerance.A review of toxicity data indicated a concentration of 2,000-mg/L sulfate would be protective of resident aquatic organisms. We also reviewed water-quality based biological survey data from within the coal mining regions of Illinois to field-verify that 2,000 mg/L sulfate was protective of resident sulfate-sensitive aquatic organisms. The statewide application of a proposed General Use standard of 2,000 mg/L sulfate is currently being reviewed by IEPA.