Costly Treatment Feared for Polluted Delta Water

Within the next few years, the Southern California Metropolitan Water District may have to spend $1.4 billion on new treatment facilities to purify polluted and potentially cancer-causing water from the Sacramento-San Joaquin Delta.

That gloomy news was contained in two reports from state and local water officials, prompted by concern over the safety of delta water. The delta, fed by Northern California rivers, is a major source of Southern California water.

The fact that delta water contains pollutants has long been known. But the most recent reports, along with interviews of water officials, gave the most detailed account yet of pollution in the delta, a maze of sloughs and islands east of San Francisco Bay, and of the cost of cleaning it up.

At the heart of the delta purity problem is the region’s rich agricultural harvest and the rich soil in which the crops grow. The soil, plus roots, leaves and other crop leftovers, flow into the delta from the fields and eventually find their way to Southern California through the California Water Project aqueduct.

In 1974, a Dutch researcher found that such organic material, harmless in itself, became potentially lethal when mixed with the chlorine used by water districts to purify water. When the two materials were combined in purification plants, they produced trihalomethanes, or THMs, the most common of which is chloroform. Chloroform has been classified by federal authorities as cancer causing.

The Metropolitan Water District, which relies on the delta for part of its water supply, began treating its water with another substance, chloramine. Such treatment reduced THMs to within acceptable federal Environmental Protection Agency standards. But now, water district officials say they have been told by the EPA that standards will be drastically tightened--by at least 50%--by 1991, and new treatment methods are needed.

Federal authorities, water district officials said, are becoming increasingly concerned over the mounting evidence that THMs cause cancer.

A Metropolitan Water District report estimated the costs of a new treatment method at $1.4 billion. There was no indication of how the facilities would be financed, officials said, except to increase the water rates of Southland residents, unless there is assistance from either the state or federal governments.

The money would finance the use of granular activated carbon for purification of the Metropolitan Water District water supply. In that method, carbon, in a form that looks like crushed charcoal briquettes, is exposed to gas at high temperatures. Thousands of tiny holes are made in each carbon particle. Water is forced through them, and toxic chemicals adhere to the sides of the particles.

“Chloramine solved only part of the problem and it became clear . . . that we need activated carbon to meet the lower (federal) numbers,” said Michael J. McGuire, director of water quality for the Metropolitan Water District. “We expect we will have to do something other than chloramines, something much more expensive, to comply.”

Although federal officials appear to prefer the carbon cleanup method, another way to remove such pollutants from water is by using an ozone treatment method, which the water district said would cost $244 million.

As a third alternative, the district report suggested cleaning up pollution at the source, in the delta. But they proposed methods that would likely anger Northern Californians, who fear that Southern California water importation plans are depriving the north of water and wrecking the delta as a natural resource.

One method would be to treat water with activated charcoal in the delta, the report said. Another would be to construct a channel to route the contaminated agricultural runoff away from the delta channels that feed the aqueduct. “Drain flows could be collected and piped to a location in the western delta that will not cause an impact on import users,” the report said.

Such a plan, however, would bring the polluted water close to San Francisco Bay, angering Bay Area residents.

Another suggestion was for a form of a peripheral canal around the delta to avoid agricultural runoff. Such a canal was rejected by voters overwhelmingly in 1982.

A State Department of Water Resources report shed new light on the extent of pollution in the delta, revealing 1987 findings from more than 40 water collection points, far more than included in previous studies.

Officials said the study is significant because it pinpointed, for the first time, agricultural runoff as the source of the organic materials that eventually wind up as THMs.

“Agricultural drainage from the delta continues to be high in THM formation potential,” the report said.

The report also noted that the cancer-causing potential of the drainage may be made worse when it is mixed with saltwater that edges into parts of the delta from San Francisco Bay.