Illinois Administrative Code
Title 35 - ENVIRONMENTAL PROTECTION
Part 352 - PROCEDURES FOR DETERMINING WATER QUALITY BASED PERMIT LIMITATIONS FOR NATIONAL POLLUTANT DISCHARGE ELIMINATION SYSTEM DISCHARGERS TO THE LAKE MICHIGAN BASIN
Subpart D - ASSESSMENT OF REASONABLE POTENTIAL TO EXCEED WATER QUALITY STANDARDS, CRITERIA, AND VALUES
Section 352.424 - Determination of Reasonable Potential

a) If the PEQ is less than or equal to the PEL, it will be concluded that there is no reasonable potential to exceed. Under such circumstances a permit limit for that contaminant will not be set unless otherwise justified under one or more provisions of Section 352.430.

b) If the PEQ is greater than the PEL, and the PEQ was calculated using a data set of more than 10 values, a water quality based effluent limitation (WQBEL) will be included in the permit. If the PEQ was calculated using a data set of less than or equal to 10 values, and the alternative PEQ calculated under Section 352.421(b) also exceeds the PEL, a WQBEL will be included in the permit.

c) If the PEQ was calculated using a data set of less than or equal to 10 values, and the PEQ is greater than the PEL but the alternative PEQ is less than the PEL, the Agency will either establish a WQBEL in the permit or incorporate a monitoring requirement and reopener clause to reassess potential to exceed within a specified time schedule, not to exceed one year. In determining which of these options to use in any individual application, the Agency shall consider the operational and economic impacts on the permittee and the effect, if any, deferral of a final decision would have on an ultimate compliance schedule if a permit limit were subsequently determined to be necessary.

d) The WQBEL will be set at the PEL, unless the PEL is appropriately modified to reflect credit for intake pollutants when the discharged water originates in the same water body to which it is being discharged. Consideration of intake credit will be limited to the provisions of Section 352.425.

e) The reasonable potential analysis shall be completed separately for acute and chronic aquatic life effects. When WQBELs are based on acute impacts, the limit will be expressed as a daily maximum. When the WQBEL is based on chronic effects, the limit will be expressed as a monthly average. Human health and wildlife based WQBELs will be expressed as monthly averages. If circumstances warrant, the Agency shall consider alternatives to daily and monthly limits.