by Joe McDonald, AWWA Small Systems Engineer

Q. A caller from a small surface water supply in Arkansas recently asked: "How can we be sure we are doing everything possible to prevent potential contamination from pathogenic organisms in our water system? Will the requirements of the Stage 1 Disinfectants and Disinfection By-products Rule (D/DBPR) make it more difficult for systems serving fewer than 10,000 people to minimize microbial risk? We haven't had a positive bacteriological sample in more than five years and have never had any indication of waterborne disease in our community. However, we are concerned that some of our customers with weakened immune systems could still be at risk.

 A. To be effective, any program to protect the community from waterborne pathogens must address source water protection, treatment, distribution system water quality, and public information. Eradicating microbial risk is made more complicated by the potential of disinfection by-product formation, the growing population of individuals with compromised immune systems, and the deterioration of raw water quality. The Stage1 D/DBPR and the Interim Enhanced Surface Water Treatment Rule (IESWTR) were promulgated together recently to improve control of pathogens while minimizing the formation of DBPs (See the RegTalk column in the March 1999 issue of Opflow).

Source Water Protection

The first step in protecting a community's water supply is the development of a watershed or wellhead protection program. Eliminating pathogens before they reach the water source will go a long way toward simplifying treatment. Contamination risk evaluation could influence treatment technology decisions and guide emergency preparedness plans that need to be in place. Anything that you do to improve the quality of your water source will pay dividends in more effective treatment at the plant. Reducing pathogens in the watershed can eliminate DBPs in the distribution system. Note that surface water systems that don't filter must take an even stricter approach to watershed control than those that have the extra barrier of filtration.

 Treatment

 Treatment has become more complicated with the increased concern for balancing the threat of microbial contamination and the potential development of DBPs. The Stage 1 D/DBPR and IESTWR represent The US Environmental Protection Agency's response to this difficult balancing act. The purpose of the Stage 1 D/DBPR is to improve public health protection by reducing exposure to DBPs, some of which have been shown to cause cancer. This rule applies to all sizes of community and nontransient noncommunity systems that add a disinfectant to the drinking water during any part of the treatment process.

 At the same time that Stage 1 D/DBPR is addressing disinfection byproducts, the IESWTR is intended to improve control of microbial contaminants, particularly Cryptosporidium, and to prevent increases in microbial risk that might otherwise occur when systems implement the Stage 1 D/DBPR. The IESWTR, however, applies only to systems serving more than 10,000 people; USEPA is working on the Long-Term 1 ESWTR, which will extend most IESWTR requirements to smaller systems. The LT1ESWTR and the Grundwater Rule, which will establish criteria for determining which groundwater systems must disinfect, are to be promulgated by November 2000.

 Twenty years ago Cryptosporidium was for the most part an academic consideration and rarely came up among operators. Now the threat of viable Cryptosporidium oocysts passing through treatment and into the distribution system, has completely redefined effective microbial treatment. Plant optimization and a multiple barrier approach to treatment has been the response for most conventional treatment plants. The Stage 1 D/DBP and IESWTR specifically calls for 2-log (99 percent) removal of crypto for systems that filter and watershed control programs for unfiltered systems. The intended public health benefits are increased protection from pathogens through improved filtration, reduced likelihood of endemic illness from crypto, and a reduced likelihood of outbreaks of cryptosporidiosis.

 Distribution System

 After establishing an effective watershed protection program and satisfying all the requirements of the Stage1 D/DBPR and IESWTR, pathogens can still find their way to the consumer's tap through a compromised distribution system. Results from AWWA Research Foundation's study, Pathogens In Model Distribution System Biofilms, demonstrate that pathogens can survive in the distribution system under certain conditions. Some organisms persist for prolonged periods of time in biofilms, even in the presence of low levels of disinfectants. The findings suggest that utilities should follow a sustained disinfection program after main breaks and other disruptions to ensure that few organisms are capable of attaching to biofilms and that any organisms released over time are adequately disinfected. AWWA Standard C651 provides specific procedures for disinfecting existing water mains after repair.

 Public Information

 Consumers deserve effective and timely communication in the event of a breach of water quality - particularly those consumers whose health may be affected. Consumers at risk have a lower tolerance for microbial infections, and they must be educated about the risks from microbials and DBPs so they can chose the options that best suit their individual needs. Customers should also be alerted to potential problems caused by the treatment processes, such as chloramination. Systems that chloraminate should alert consumers that chloramines present at the point of use will affect dialysis patients and aquatic species in aquariams.

 Conclusion

 Providing protection against pathogens begins at the source and continues all the way to the tap. The more effective the source water protection program, the less complicated the treatment phase. The IESWTR and Stage 1 D/DBPR are written to guide utilities in balancing microbial protection and DBP formation. Distribution system water quality cannot be overlooked if water quality is to be the best it can be. Flushing, line disinfection after main breaks, and maintaining an adequate chlorine residual are recommended to ensure quality to the tap.

 Finally, establishing effective lines of communication is a critical part of ensuring that the best interests of all segments of the community are protected.