401 KAR 8:150 Disinfection and filtration. 

401 KAR 8:160 Enhanced filtration and disinfection.

A surface water or groundwater under the direct influence of a surface water system shall sample combined filtered water every four hours of operation and report the results in the monthly operating report (MOR). For conventional filtration or direct filtration serving fewer than 10,000 people, the level shall be less than or equal to 0.5 nephelometric turbidity unit (NTU) in at least 95 percent of the measurements taken each month, and the level shall not exceed five NTUs. For conventional or direct filtration serving at least 10,000 people, the level shall be less than or equal to 0.3 NTU in at least 95 percent of the measurements taken each month, and the level shall not exceed one NTU.  For other filtration, regardless of population served, the level shall be less than or equal to one NTU in at least 95 percent of the measurements taken each month, and the level shall not exceed five NTUs.  A system serving at least 10,000 people shall conduct continuous monitoring for each individual filter and record the results every 15 minutes.  If there is a failure in the continuous monitoring equipment, the system shall conduct grab sampling every four hours and the repairs shall be completed in five working days. Otherwise, the system shall be in violation. 

The system shall report the following information, if applicable, in the MOR: (1) if a filter exceeds 1.0 NTU in two consecutive recordings and there are no obvious reasons, the system shall produce a filter profile within seven days; (2) if a filter exceeds 0.5 NTU in two consecutive recordings at the end of the first four hours of operation and there are no obvious reasons, the system shall produce a filter profile within seven days; (3) if a filter exceeds 1.0 NTU in two consecutive recordings in three consecutive months, the system shall produce a filter assessment within 14 days; (4) if a filter exceeds 2.0 NTUs in two consecutive recordings in two consecutive months, the system shall arrange a comprehensive performance evaluation within 30 days.

Technical information from EPA regarding turbidity.