The Bush administration proposed Monday to allow sewage treatment plants to release partially treated sewage into waterways when utilities are inundated with wastewater during heavy rainstorms or snowmelts.
The change would be the latest in a series of apparent rollbacks of environmental regulations by the administration, a record Democrats hope to capitalize on during the presidential election next year.
The Environmental Protection Agency said the proposal would help local utilities prevent the accidental overflows of raw sewage into waterways that sometimes occur when treatment plants are overloaded.
"We are working with these facilities to prevent backups of sewage in homes and the environment while requiring all discharges to meet Clean Water Act permit limits," said G. Tracy Mehan, assistant EPA administrator for water.
But environmental groups said the proposal would violate the Clean Water Act and allow more viruses and parasites into drinking and swimming water.
"More Americans would get sick from waterborne illnesses because of this indefensible and illegal policy change," said Nancy Stoner, director of the clean water program at the Natural Resources Defense Council, a national environmental group.
Wastewater agencies said the proposal would merely authorize treatment plants to continue doing what many of them have done for years.
"Blending has always been an accepted practice," said Adam Krantz, a spokesman for the Assn. of Metropolitan Sewerage Agencies. The agency estimates that 20% to 50% of treatment facilities sometimes blend treated and partially treated water and then release it into waterways, enabling them to handle large amounts of wastewater.
Neither Krantz's group nor the EPA had data on how much blending occurs and how much might occur under the new rule.
The proposal would allow plants to divert some wastewater from biological treatment, where tiny microbes eat pollutants. Before the diverted water is blended with the treated water, it would be disinfected and solids would be filtered out.
Some regions allow blending, and others forbid it unless there is no other feasible alternative, according to James Hanlon, director of the EPA's Office of Wastewater Management.
If the new policy is adopted, some states, including California, could maintain tougher regulations. But 25 states prohibit environmental regulations that exceed federal standards.
Tom Howard, deputy director of the California State Water Resources Control Board, said the proposal would have little consequence in California, where most sewage plants were designed to handle surges of wastewater. The state's requirements would also protect water quality.
"You can't just bypass treatment and dump sewage into waterways," Howard said.
The EPA stressed that all the water released into waterways would meet requirements for various pollutants. But there are no standards governing illness-causing protozoa.
Hanlon said that as wastewater agencies have improved their sewer pipes in recent years, more water is reaching treatment facilities instead of seeping into the ground. The water sometimes exceeds the capacity for treating it.
Hanlon said the EPA had no information to indicate whether the proposed policy would increase illnesses, as environmentalists charged. However, he said the proposed policy would encourage permitting agencies to consider putting additional limits on blending if the water is released into waterways that are used for recreation downstream.
Some drinking water experts said they hoped the policy would improve drinking water by letting local governments spend less on sewage treatment and more on water treatment.
Times staff writer Miguel Bustillo in Los Angeles contributed to this report.