WATER NEWS & PROJECTS
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How do I learn more about my drinking water?
Why did City of San Luis Obispo customers receive a public notification concerning TTHM’s ?
Water sample results for the 2
nd quarter of 2015 showed TTHM’s at levels of 82.1 parts per billion (ppb) as calculated in the locational running annual average (average of the four most recent quarters of sampling results) at the sample site on Johnson Avenue and Southwood Drive. This is above the standard or maximum contaminant level (MCL) of 80 ppb. All public water systems are required by state and federal law to notify users of any exceedance of any water quality standard and any other noncompliance events affecting their water system. The purpose of the notice is to keep consumers informed about water quality. When routine monitoring indicated that TTHM levels were above regulatory standards, the City was required to issue a Tier 2 notice and notified their customers as soon as practical, but no later than 30 days after learning of the violation. Had this been a more severe Tier 1 violation, involving an immediate risk to public health such as a waterborne illness, customers would have been notified immediately within 24 hours with more specific details.
What are the health risks of TTHM’s?
The information below is based on best available health studies. Studies of populations that have been exposed to TTHM’s suggest a possible connection between long-term TTHM exposure and certain types of cancer (bladder, colon, and rectal), developmental (e.g. fetal growth) and reproductive effects (e.g. miscarriages, stillbirths). Cancer risks generally accrue over lifetimes and very long periods of exposure. These risks are normally expressed as lifetime risks as a result of averaging daily exposure levels (associated with the lifetime daily average of ingesting 2 liters drinking water/day) over a lifetime of 70 years. More research is being conducted to better understand the potential risks between TTHM exposures and these diseases. It is important that people be aware of these potential health effects from TTHM exposure.
How did the EPA determine drinking water regulations for disinfection by-products (TTHM’s)?
In 1974, Congress passed the Safe Drinking Water Act. This law requires EPA to determine the level of contaminants in drinking water at which no adverse health effects are likely to occur. These non-enforceable health goals, based solely on possible health risks and exposure over a lifetime, with an adequate margin of safety, are called maximum contaminant level goals (MCLG). Contaminants are any physical, chemical, biological or radiological substances or matter in water. EPA sets MCLG’s based on the best available science to prevent potential health problems. Based on the MCLG, EPA sets an enforceable regulation called a maximum contaminant level (MCL). MCL’s are set as close to the health goals as possible, considering cost, benefits and the ability of public water systems to detect and remove contaminants using suitable treatment technologies.
What are Total Trihalomethanes (TTHM’s)?
TTHM’s are a group of substances known as disinfection by-products. They form when chlorine used for disinfection reacts with naturally occurring organic material in surface and ground waters. TTHM’s are formed based on the amount of time chlorine is allowed to react with available organic matter in the water. The highest levels of TTHM’s typically occur in the water distribution system where water age is the greatest. All water systems that use chlorine to disinfect the water are required by federal and state law to sample for disinfection by-products on a regular basis at several specifically identified locations in the water distribution system.