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Brainwork on the Drain
A new scientific model forecasts that using a dedicated drain to shunt selenium-laced waters out of the San Joaquin Valley into the Estuary would put sensitive ducks, splittail and sturgeon at grave risk. The model’s predictions, released this January (see Now in Print), provide sobering new insights into the prospects for solving the valley’s salt and selenium build-up problems via some kind of drain extension to the Bay.
"Our model is more specific to this Estuary, and it’s most vulnerable food webs, than anything ever done before," says Theresa Presser of the U.S. Geological Survey, who developed the bioaccumulation-focused model with the Survey’s Sam Luoma. "In the past we’ve only studied isolated links, or done toxicity tests, but this approach is outdated for selenium because it passes so efficiently through food. In our model, we plug in pounds of selenium and move it all the way up the food web to effects on predators."
"You can make up any drainage scenario you want and track multiple lines of effects," adds Luoma. "What’s exciting is how reliable our estimates are. We’ve skipped no steps."
U.S. EPA and Contra Costa County, which funded the research, specifically asked the Survey to model various scenarios for taking contaminated drainage "out-of-valley via a drain." Though the political prospects for a completed San Luis Drain, or some reincarnation, remain dim, the Bureau of Reclamation is under a court order to give farmers a drainage solution. The three historic reasons for building a drain were "too much salt, too much selenium and too much irrigation water" in the valley, says Presser. Rain and irrigation transport the selenium, a naturally occurring trace element in the mineral and salt-laden soils of California’s Coast Ranges and Western San Joaquin Valley. The valley’s arid climate oxidizes the weathered selenium into a highly mobile form.
The big conclusion of the modeling work, says Luoma, is that any attempt to move significant amounts of selenium out of the valley and into the Estuary would take a toll on sensitive wildlife. Researchers plugged in the kind of drainage scenarios, based on current documented loads, which would be necessary to help alleviate the area’s enormous groundwater degradation due to selenium and salt build up. "If you started draining the Western San Joaquin Valley," says Presser of their findings, "there is enough of a selenium reservoir to yield discharges of 42,000 pounds of selenium every year for at least a century."
Part of the problem is that the Bay-Delta is such an efficient ‘bio-reactor’ for selenium, she says. In other words, as selenium is passed from soil and irrigation water to clams, then to fish or birds, its effects may intensify. In the most extreme cases, effects might include the kind of birth deformities and fatalities seen in ducks at the Kesterson National Wildlife Refuge in the 1980s.
"Even when we run the model backwards, starting with low concentrations of selenium in the water, we find that concentrations necessary to protect sensitive species are less than 1 part per billion," says Presser, noting that EPA’s current water quality criteria for the protection of aquatic life is 5 ppb. Data from the new model could weigh in on several current regulatory initiatives, among them public review of draft environmental impact reports related to the continued use by local farmers and drainers of a section of the long-closed San Luis Drain called the Grasslands Bypass Channel (see Now in Print). EPA is also re-evaluating its 5 ppb national criteria for selenium at the request of U.S. Fish & Wildlife and others.
Also interesting are model predictions for selenium loads from the San Joaquin River, where CALFED and others are focusing a lot of dollars and research on restoring flows for fish. More water, of course, could bring more selenium into the Estuary from a river whose low, or sometimes even reverse flows, have historically imported little selenium downstream.
Researchers modeled load discharges from the river with concentrations capped at 0.5 ppb and 1 ppb, both optimistic scenarios given historic levels. "You don’t get rid of a huge amount of salt and selenium this way," says Luoma. "But it’s enough to basically put the same selenium loads back into the Bay that we worked so hard to get the oil refineries to take out."
Some of these issues may be tackled at a drainage summit to be held March 27 (see calendar). In the meantime, "It’s clear that solving the Western San Joaquin Valley’s problems will require a multi-component, rather than a one-drain-only, solution," says Luoma.
Contact: Theresa Presser (650)329-4512
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