Section 355.201  Introduction

The need for an ammonia nitrogen (as N) WQBEL is based on the reasonable potential of a discharge to cause or contribute to a violation of the applicable ammonia nitrogen water quality standard.  During the NPDES permit review process, the Agency shall conduct an analysis of the reasonable potential for ammonia to exceed or contribute to excursions above the ammonia nitrogen water quality standard that may occur in the receiving water.  This analysis shall be conducted for both acute and chronic water quality standards for periods when early life stages are absent (winter, see 35 Ill. Adm. Code 302.212(b)(2)(B)) and periods when early life stages are present (summer, see 35 Ill. Adm. Code 302.212(b)(2)(A)).  The Agency may conduct this analysis for the subchronic standard when daily effluent ammonia samples are collected.  The Agency may subdivide summer or winter periods into quarterly or monthly segments with analysis of reasonable potential corresponding to those smaller time segments in individual permit applications.

a)         The first step in the reasonable potential analysis is to calculate the Projected Effluent Quality (PEQ), as provided in Section 355.205.  The PEQ is then compared to the total ammonia nitrogen water quality standard as provided in Section 355.203.  If the PEQ is less than or equal to the total ammonia nitrogen water quality standard as provided in Section 355.203, then no reasonable potential to exceed the standard exists and no effluent limitation will be established in the permit unless otherwise warranted under subsection (c) of this Section.

b)         If the PEQ exceeds the applicable total ammonia nitrogen water quality standard as provided in Section 355.203, the analysis shall proceed to the determination of a mixing allowance as provided in Section 355.207.

c)         If the wastewater prior to treatment contains total Kjeldahl nitrogen at levels in which a reasonable potential to exceed total ammonia nitrogen water quality standards as provided in Section 355.203 exists, then the discharge of ammonia nitrogen shall be limited in the NPDES permit by an ammonia nitrogen WQBEL.  Reasonable potential to exceed water quality standards will be determined consistent with Sections 355.203 through 355.211 of this Part.  Even if there appears to be no potential to exceed the water quality standards based on the effluent quality analysis in subsection (a) or (b), an ammonia nitrogen WQBEL shall be established.

(Source:  Amended at 27 Ill. Reg. 15774, effective September 25, 2003)