Researchers track water quality flowing into Lake Tahoe

INCLINE VILLAGE -- Desert Research Institute researchers Todd Mihevc and Jim Thomas took advantage of several breaks in last month's weather to visit Incline Village.

But rather than taking in the beauty of Lake Tahoe in the winter or skiing Diamond Peak, they were instead mucked about in snow, mush and mud at a culvert outlet in the downtown area, installing a sophisticated stormwater-monitoring station.

The station, and others likely to be scattered about the Tahoe Basin, are part of a program aimed at understanding how the infall of material from the basin and the air harm Tahoe's environment. The most noticeable sign is the gradual loss of the lake's famous clarity.

Fine sediment and algae-sustaining nitrogen and phosphorus compounds are thought to be among the biggest contributors to the problem.

Each station is a desk-sized box with a stubby, hour-glass-shaped flume sticking out of one side. Mihevc, an assistant hydrogeologist, said its main purpose is to analyze water during and after storms. They'll target areas between streams.

"We want to know how land use contributes to Tahoe's problems," Mihevc said recently. "Well be looking at residential areas, dense communities, undeveloped and vegetated areas, and along highways."

Mihevc said data from the station, other instruments and historical records will be used to address this land-use aspect.

Thomas, an associate research professor, says the stations automatically measure the water's sediment load, electrical conductivity and clarity, as well as its nitrogen and phosphorus content. The stations can bottle samples for later study. The flume will measure the speed and volume of the flow.

DRI and the Tahoe Research Group at the University of California, Davis, will split the lake between them for the stormwater study.

The goal of the larger program, called Total Maximum Daily Load (TMDL), is to provide the scientific underpinnings of all measures to reverse environmental harm. The stormwater study is one of 17 that will be jointly overseen by the Nevada Division of Environmental Protection and California's Lahontan Regional Water Quality Control Board.

Dave Roberts, California's lead project researcher, said the Lake Tahoe TMDL and others like it in the nation are mandated by the 1972 Clean Water Act, which requires the U.S. Environmental Protection Agency to enforce the act. He said his agency initiated its first TMDL project last summer in the Heavenly Valley Creek area.

"The act set up TMDLs as the way to address distressed water bodies, bodies that don't meet their water quality standards," Roberts said. "The need for these programs was ignored for some time, but a flurry of lawsuits (resolved) about five years ago simulated the EPA to take action."

In addition to determining what loads can be sustained by the lake without environmental harm, Roberts says the project will craft a program to reduce current loads to levels that are healthy.

Roberts said the TMDL project will play a crucial role in helping the Tahoe Regional Planning Agency meet its mandate to protect the basin.

"The results of the TMDL project will play a big role in the update of TRPA's Water Quality Threshold in the spring of 2007," Roberts said, which is part of the larger Regional Plan update.