Section 611.956  Individual Filter Turbidity Requirements

a)         Applicability.  A Subpart B system supplier that serves fewer than 10,000 persons and utilizing conventional filtration or direct filtration must conduct continuous monitoring of turbidity for each individual filter in a supplier's system.  The following requirements apply to continuous turbidity monitoring:

1)         Monitoring must be conducted using an approved method in Section 611.531;

2)         Calibration of turbidimeters must be conducted using procedures specified by the manufacturer;

3)         Results of turbidity monitoring must be recorded at least every 15 minutes;

4)         Monthly reporting must be completed according to Section 611.957(a); and

5)         Records must be maintained according to Section 611.957(b).

b)         Failure of Turbidity Monitoring Equipment.  If there is a failure in the continuous turbidity monitoring equipment, the supplier must conduct grab sampling every four hours in lieu of continuous monitoring until the turbidimeter is back on-line.  The supplier has 14 days to resume continuous monitoring before a violation is incurred.

c)         Special Requirements for Systems with Two or Fewer Filters.  If a supplier's system only consists of two or fewer filters, the supplier may conduct continuous monitoring of combined filter effluent turbidity in lieu of individual filter effluent turbidity monitoring.  Continuous monitoring must meet the same requirements set forth in subsections (a)(1) through (a)(4) and (b).

d)         Follow-Up Action.  Follow-up action is required according to the following requirements:

1)         If the turbidity of an individual filter (or the turbidity of combined filter effluent (CFE) for a system with two filters that monitor CFE in lieu of individual filters) exceeds 1.0 NTU in two consecutive recordings 15 minutes apart, the supplier must report to the Agency by the 10^th of the following month and include the filter numbers, corresponding dates, turbidity values that exceeded 1.0 NTU, and the cause (if known) for the exceedances.

2)         If a supplier was required to report to the Agency for three months in a row and turbidity exceeded 1.0 NTU in two consecutive recordings 15 minutes apart at the same filter (or CFE for systems with two filters that monitor CFE in lieu of individual filters), the supplier must conduct a self-assessment of the filters within 14 days after the day on which the filter exceeded 1.0 NTU in two consecutive measurements for the third straight month, unless a CPE, as specified in subsection (d)(3), was required.  A supplier that has a system with two filters that monitor CFE in lieu of individual filters must conduct a self-assessment on both filters.  The self-assessment must consist of at least the following components:  assessment of filter performance, development of a filter profile, identification and prioritization of factors limiting filter performance, assessment of the applicability of corrections, and preparation of a filter self-assessment report. 

3)         If a supplier was required to report to the Agency for two months in a row and turbidity exceeded 2.0 NTU in two consecutive recordings 15 minutes apart at the same filter (or CFE for systems with two filters that monitor CFE in lieu of individual filters), the supplier must arrange to have a comprehensive performance evaluation (CPE) conducted by the Agency or a third party approved by the Agency not later than 60 days following the day the filter exceeded 2.0 NTU in two consecutive measurements for the second straight month.  If a CPE has been completed by the Agency or a third party approved by the Agency within the 12 prior months or the system and Agency are jointly participating in an ongoing comprehensive technical assistance (CTA) project at the system, a new CPE is not required.  If conducted, a CPE must be completed and submitted to the Agency no later than 120 days following the day the filter exceeded 2.0 NTU in two consecutive measurements for the second straight month.

e)         Special Individual Filter Monitoring for a Lime-Softening System.  If a supplier's system utilizes lime softening, the supplier may apply to the Agency for alternative turbidity exceedance levels for the levels specified in subsection (d).  The supplier must be able to demonstrate to the Agency that higher turbidity levels are due to lime carryover only, and not due to degraded filter performance.

BOARD NOTE:  Derived from 40 CFR 141.560 through 141.564.

(Source:  Amended at 44 Ill. Reg. 6996, effective April 17, 2020)