PURPOSE: This rule establishes maximum contaminant levels and monitoring requirements for turbidity.

1. (1) The maximum contaminant levels (MCLs) for turbidity, applicable to all public water systems which use surface or ground water under the direct influence of surface water are as follows:

   1. (A) Equal to or less than 0.5 turbidity units in at least ninety-five percent (95%) of the measurements taken each month; and
   2. (B) Five (5) turbidity units in any one (1) confirmed measurement.
2. (2) The frequency of sampling shall be as set forth in 10 CSR 60-4.080(3).
3. (3) If the result of a single turbidity measurement exceeds the MCL established in subsection (1)(A), the measurement must be confirmed by resampling, preferably within one
4. (1) hour. The resample result must replace the original sample result for determining compliance with section (1) of this rule.
5. (4) If any confirmed sample result exceeds five (5) turbidity units, the supplier of water must notify the department by the end of the next business day and give notice as required by 10 CSR 60-8.010.
6. (5) The department, on a case-by-case basis, may allow a system to operate at an MCL for turbidity of 1.0 turbidity units in at least ninety-five percent (95%) of the measurements taken each month if the following criteria are met: the total percent removal and inactivation of Giardia lamblia is ninety-nine and nine-tenths percent (99.9%), required treatment is provided, the treatment facilities are properly operated, none of the treatment units are malfunctioning due to mechanical failure or incorrect construction, the system is in compliance with all of the disinfection requirements of 10 CSR 60-4.055, the treatment facilities are providing ninety-nine percent (99%) Giardia cyst removal and the system cannot meet the turbidity MCL of 0.5 turbidity units due to raw water quality, iron, manganese or similar compelling factors. The request to operate at the higher turbidity MCL must be made in writing and be accompanied by an engineering report which includes the results of full scale particle or Giardia cyst removal studies, operational test data, water analyses results, a report of the sanitary survey of the treatment facilities and any other information that the department may require to assure that the criteria of this rule are met. Approval of the engineering report is the approval to operate at the higher turbidity MCL.

AUTHORITY: section 640.100, RSMo (1994).* Original rule filed May 4, 1979, effective Sept. 14, 1979. Amended: Filed April 14, 1981, effective Oct. 11, 1981. Amended: Filed July 12, 1991, effective Feb. 6, 1992. Amended: Filed Feb. 1, 1996, effective Oct. 30, 1996. *Original authority 1939, amended 1978, 1981, 1982, 1988, 1989, 1992, 1993, 1995.