Chlorine use for water treatment supported

Thursday, Sept. 24, 1998 | 2:13 a.m.

Chlorine used to treat the valley's drinking water creates cancer-causing chemicals, but the natural bacteria found in Southern Nevada's ground water appear to devour these chemicals, according to a U.S. Geological Survey scientist.

Scientist James Thomas who studies water and soils for the USGS office presented his findings on by-products of chlorine to members of the Nevada Water Resources Association Wednesday in Las Vegas.

The Southern Nevada Water Authority asked the USGS to study what happens to the chlorine-treated water once it's injected into the ground.

The water authority recharges ground water with 15,000 to 20,000 acre feet of Colorado River water during cold winter months when water demands are low to replenish groundwater used during peak summer months.

The bacteria in the ground water attack chemicals formed when water is treated with chlorine. Trihalomethanes (THMs) and haloacetic acids (HAAs), both chlorination by-products, form when chlorine comes in contact with organic material in the water such as dead leaves or fecal matter.

Both chemical classes have been shown to produce cancers and birth defects in animal studies. Treating drinking and waste water with chlorine, however, kills disease-causing bacteria, he said.

"The benefits of using chlorine to treat the water far outweigh the risks posed from THMs and HAAs," Thomas said. "This is good news as far as Las Vegas is concerned."

The longer the water treated with chlorine remains in the ground, the lower the levels of THMs and HAAs, he said.

Natural bacteria that need oxygen to live and those that do not both appear to remove the chemical residues, Thomas said.