Enhanced Surface Water Treatment Rule

The Enhanced Surface Water Treatment Rule (ESWTR) is one of the first Rules to be developed under the 1996 Amendments to the Safe Drinking Water Act. The ESWTR was promulgated in November 1998 and applies to systems using surface water (or ground water under the direct influence of surface water) serving 10,000 or more persons. The purpose of the ESWTR is to improve control of microbial pathogens, specifically the protozoan Cryptosporidium, through improvements in filtration. The ESWTR builds upon the treatment technique requirements of the existing 1989 Surface Water Treatment Rule (SWTR) with the following additions/modifications:

There are additional requirements of the ESWTR that deal with unfiltered water systems and those using ground water under the influence of surface water. These requirements do not apply to the Providence Water system.

Maximum contaminant level goal (MCLG) of zero for Crytosporidium - The EPA has formally established an MCLG for Cryptosporidium. An MCLG is a non-enforceable health goal that applies to contaminants which may "have an adverse effect on the health of persons" and are "known to occur ... in public water systems ... at levels of public health concern".
2-Log Cryptosporidium removal requirement for systems that filter - 2-Log removal (99% removal) of Cryptosporidium organisms is now required for systems that must filter under the 1989 SWTR.
Strengthened combined filter effluent turbidity performance standard - Conventional treatment plants must operate under strengthened turbidity performance standards of the IESWTR. Plant effluent must be less than or equal to 0.3 ntu in 95% of turbidity measurements each month and at no time can a turbidity level of 1 ntu be exceeded. This represents a tightening of previous turbidity requirements in the 1989 SWTR (down from 0.5 ntu in 95 % of measurements and maximum single measurement of 5 ntu).
Individual filter turbidity monitoring provisions - Conventional treatment plants must conduct continuous monitoring of turbidity for each filter and must provide exception reports to the State on a monthly basis. Exceptions are:
1. Any filter with turbidity level > 1.0 ntu for two consecutive measurements 15 mins apart.
2. Any filter with a turbidity level > 0.5 ntu at the end of the first 4 hrs of operation, based on two consecutive measurements 15 mins apart.
3. Any system with a filter in violation of steps 1 or 2 must perform a self-assessment within 14 days and report same to State.
Disinfection profiling and benchmarking provisions - Profiling is the characterization of a system's disinfection practice over a 1 year period. A profile consists of the compilation of daily Giardia log inactivations over one year, and is based upon daily measurements of temperature, disinfectant residual, disinfectant contact time, and pH. This profile is then used to determine a baseline (benchmark) of Giardia inactivation against which any planned changes to disinfection procedures can be measured. There are three main components of the benchmark provision: applicability requirement, characterization of disinfection practice, and State review.
Sanitary Surveys - States will now be required to conduct Sanitary Surveys of large water systems at least once every 3 years (instead of once every 5 years as per the 1989 SWTR). Systems deemed to be operating under "outstanding performance" criteria may have the survey frequency reduced by the State to once every 5 years. The "outstanding performance" benchmark will be set by each State.