US EPA launches new drinking water standards
The US EPA is to introduce two new drinking water standards aimed at improving protection against water-borne pathogens and reducing exposure to potentially toxic chemicals formed when disinfectants are used to purify drinking water.
The Interim Enhanced Surface Water Treatment Rule (IESWTR) and Stage 1 Disinfectant and Disinfection Byproduct Rule (DDBR1) are the first of a set of rules under the Safe Drinking Water Act (SDWA) Amendments, signed by President Clinton in August 1996.
The rules will for the first time force public water systems to directly address Cryptosporidium. while lessening the health risk posed to the public by disinfection byproducts (DBPs).
Disinfectants used to treat microbial pathogens, such as Cryptosporidium in drinking water, can react with materials in the water to form byproducts which may pose health risks.
In 1993, Cryptosporidium caused 400,000 people in Milwaukee to experience intestinal illness. More than 4,000 were hospitalised, and at least 50 deaths have been attributed to the disease. There have also been cryptosporidiosis outbreaks in Nevada, Oregon, and Georgia over the past several years.
Many DBPs have been shown to cause cancer and reproductive and developmental effects in laboratory animals. More than 200 million people consume water that has been disinfected.
The Surface Water Treatment Rule (SWTR) is the current regulation covering microbial contaminants: promulgated in 1989, it applies to all public water systems using surface water sources or groundwater sources under the direct influence of surface water.
The SWTR establishes maximum contaminant level goals (MCLGs) for viruses, bacteria and Giardia. It also includes treatment technique requirements for filtered and unfiltered systems that are specifically designed to protect against the adverse health effects of exposure to these microbial pathogens. The Total Coliform Rule, revised in 1989, applies to all public water systems and establishes a maximum contaminant level (MCL) for total coliforms.
For DBPs, the US EPA set an interim maximum contaminant level (MCL) for total trihalomethanes of 0.10 mg/l in 1989. This applies to any community water system serving at least 10,000 people that adds a disinfectant to the drinking water during any part of the treatment process.
The EPA finalised the IESWTR and DDBR1 in November 1998, as required by the 1996 Amendments to the SDWA.
The IESWTR applies to systems using surface water, or ground water under the direct influence of surface water that serve 10,000 or more persons. The rule also includes provisions for states to conduct sanitary surveys for surface water systems regardless of system size.
The rule’s modifications to the SWTR include:
the introduction of a MCLG of zero for Crypto
a 2-log Crypto removal requirement for filter systems
systems using groundwater under the direct influence of surface water are now subject to the new rules dealing with Crypto
inclusion of Crypto in the watershed control requirements for unfiltered public water systems
requirements for covers on new finished water reservoirs
sanitary surveys, conducted by states, for all surface water systems regardless of size
Stricter turbidity performance criteria and mandatory individual filter monitoring measures also contained in the rule are intended to improve treatment reliability and to minimize Crypto levels in drinking water.
The rule also includes disinfection benchmark provisions to assure continued levels of microbial protection while facilities take the necessary steps to comply with new DBP standards.
The DDBR1 applies to community water systems and non-transient non-community systems, including those serving fewer than 10,000 people, that add a disinfectant to the drinking water during treatment.
The DDBR1 includes the following provisions:
maximum residual disinfectant level goals (MRDLGs) for chlorine (4 mg/L), chloramines (4 mg/L), and chlorine dioxide (0.8 mg/L);
MCLGs for four trihalomethanes (chloroform (zero), bromodichloromethane (zero), dibromochloromethane (0.06 mg/L), and bromoform (zero)), two haloacetic acids (dichloroacetic acid (zero) and trichloroacetic acid (0.3 mg/L)), bromate (zero), and chlorite (0.8 mg/L);
MRDLs for three disinfectants (chlorine (4.0 mg/L), chloramines (4.0 mg/L), and chlorine dioxide (0.8 mg/L));
MCLs for total trihalomethanes – a sum of the four listed above (0.080 mg/L), haloacetic acids (HAA5) (0.060 mg/L)- a sum of the two listed above plus monochloroacetic acid and mono- and dibromoacetic acids), and two inorganic disinfection byproducts (chlorite (1.0 mg/L)) and bromate (0.010 mg/L)); and
a treatment technique for removal of DBP precursor material.
The EPA has also announced its intention to introduce a number of future M-DBP rules.
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