Illinois Administrative Code › Title 35 - ENVIRONMENTAL PROTECTION › Part 310 - PRETREATMENT PROGRAMS › Subpart C - REMOVAL CREDITS › Section 310.311 - Demonstration of Consistent Removal

Current through Register Vol. 48, No. 28, July 12, 2024
The Agency must authorize a POTW to grant a removal credit
				  that does not exceed the POTW's consistent removal rate. To demonstrate
				  consistent removal, the POTW must, for each pollutant with respect to which
				  removal credit authorization is sought, collect influent and effluent data, and
				  calculate consistent removal in accordance with the following requirements. As
				  a condition of retaining removal credits authorization, the POTW's consistent
				  removal must continue to be equal or greater than the removal credit.
a) Representative Data. Seasonal. The data
				must be representative of yearly and seasonal conditions to which the POTW is
				subjected for each pollutant for which a discharge limit revision is
				proposed.
b) Representative Data.
				Quality and quantity. The data must be representative of the quality and
				quantity of normal effluent and influent flow if such data can be obtained. If
				such data are unobtainable, alternate data or information may be presented for
				approval to demonstrate consistent removal.
c) Sampling Procedures
1) Composite. The influent and effluent
				operational data must be obtained through 24-hour flow-proportional composite
				samples. Sampling may be done manually or automatically, and discretely or
				continuously. For discrete sampling, at least 12 aliquots must be composited.
				Discrete sampling may be flow-proportioned either by varying the time interval
				between each aliquot or the volume of each aliquot. All composites must be
				flow-proportional to either stream flow at time of collection of influent
				aliquot or to the total influent flow since the previous influent aliquot.
				Volatile pollutant aliquots must be combined in the laboratory immediately
				before analysis.
2) Number of
				Samples
A) Twelve samples must be taken at
				approximately equal intervals throughout the full year. Sampling must be evenly
				distributed over the days of the week so as to include non-workdays. If the
				Agency determines that this schedule will not be most representative of the
				actual operation of the POTW treatment plant, the Agency must approve an
				alternative sampling schedule.
B)
				Upon concurrence of the Agency, a POTW may utilize a historical database
				amassed during the three years immediately preceding the application if the
				data otherwise meet the requirements of this Section. For the historical
				database to be approved, it must present a statistically valid description of
				daily, weekly, and seasonal sewage treatment plant loadings and performance for
				at least one year.
3)
				Effluent sample collection need not be delayed to compensate for hydraulic
				detention time unless the POTW elects to include detention time compensation or
				unless the Agency requires detention time compensation. The Agency must require
				that each effluent sample be taken approximately one detention time later than
				the corresponding influent sample when failure to do so would result in an
				unrepresentative portrayal of actual POTW operation. The detention period must
				be based on a 24-hour average daily flow value. The average daily flow used
				must be based upon the average of the daily flows during the same month of the
				previous year.