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Central Valley Pinpoints Hot Spots
The Central Valley's most polluted waterways occur near the City of Stockton, according to a report just released by the Regional Water Quality Control Board. While the most ubiquitous pollutants are the insecticides diazinon and chlorpyrifos, mercury, which has accumulated in sediments throughout the Estuary, may be longer lived and harder to control.
According to the report, runoff from the 500,000 pounds of diazinon sprayed each winter on Central Valley orchards has made the Delta toxic to zooplankton at the base of the aquatic food chain. And runoff of diazinon and chlorpyrifos - ingredients in household products like Raid, Ortho and Black Leaf - have caused several backsloughs and urban creeks near Stockton and Sacramento to be designated as candidate hot spots as well.
"If we could control the offsite movement of the insecticides, they could be gone in a year," says the Regional Board's Chris Foe, "but with mercury, even if we rolled up our sleeves and starting working right now, we might see improvement in 50 years. We managed, through Placer gold and mercury mining, to create this problem over a long period of time. It's going to take a long time for nature to heal that."
Another hot spot-the San Joaquin River near the Stockton wastewater treatment plant-is less of a long-term problem but may still be difficult to solve. Although the treatment plant has attempted to comply with stringent effluent limitations, the river consistently tests low in dissolved oxygen. Modeling performed by the City, however, showed that the river would not meet dissolved oxygen standards even without the plant's discharges. In late summer, when the big pumps at Tracy are exporting large amounts of water, the San Joaquin's flow near Stockton is sometimes zero-or is even reversed, contributing to even lower oxygen levels.
Low dissolved oxygen levels are also suspect in frequent fish kills in four urban waterways in the South Delta listed as hot spots. Although the cause of the low oxygen is thought to be urban runoff, the exact chemicals depleting the oxygen are yet to be identified. Foe says most of the kills occur when the first rain of the season washes leaf litter and urban debris-as well as anything illegally dumped in storm drains-into the sloughs, which "don't flush very well themselves."
DeltaKeeper Bill Jennings, who recently found 5-Mile Slough toxic to fathead minnows, thinks most people don't realize the degree of toxicity in these waterways. "Following storms, all of the waterways in and around Stockton go toxic," he says. "Almost every bioassay we send up to Davis comes back showing acute mortality." Jennings attributes the low oxygen problem to discharges from area dairies and food-processors, some of which have repeatedly violated discharge standards, he says.
The Regional Board plans to work with stakeholders over the next six to eight months to finalize a cleanup plan for the hot spots. The Board must report its findings to the state board by December 1998 for inclusion in a California-wide hot spot plan to be turned over to the legislature.
Contact: Chris Foe (916)255-3113 or Bill Jennings (209)464-5090
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