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A clear solution – Sacramento State civil
engineers help preserve a national treasure

Lake Tahoe’s Emerald Bay and Fannette Island. Photographer: Will Hart Photo courtesy of Lake Tahoe Visitors Authority

Top tourist draw Lake Tahoe is considered one of the clearest large lakes in the world, but it has been steadily losing clarity over the last 40 years. With the help of Sacramento State civil engineering professor John Johnston and Office of Water Programs research engineer Dipen Patel, the California Department of Transportation (Caltrans) has been developing award-winning technology to reverse this trend.

Since 2001, Johnston, Patel and others have been helping Caltrans carry out a program to identify, test and evaluate potential treatment methods to clean up storm water runoff.

“Runoff from highways, local roads, parking lots and even residences contains phosphorus—which causes algae growth—and small particles—which cloud the lake water,” says Johnston. “Caltrans owns and maintains 68 miles of roadway in the Tahoe Basin, and even though it is a minor part of the whole problem, Caltrans has invested heavily in this program.”

The University’s Office of Water Programs designs experiments, sets the research questions and interprets the results of the storm water and algae treatment studies for Caltrans.

“The effluent, or pollution, limits for storm water runoff into Lake Tahoe are extremely stringent—more so than for most city wastewater treatment plants,” says Johnston. “In the beginning, we didn’t have the technology to meet those requirements, especially technology that could operate on the side of the road without power or operators.”

With oversight from the Office of Water Programs staff, consulting engineering teams collected storm water samples at various locations around the lake and tested a variety of treatment systems to clean the water, which involved small-scale tests with combinations of filters and chemicals. “This was basically adaptations of drinking water treatment technologies,” says Patel.

Based on those results, Caltrans constructed and tested six full-scale pilot filters using novel filtering media. This approach to storm water treatment is unique in the nation.

“Through this research, we’ve been able to develop efficient storm water treatment techniques that others can adopt,” Patel says.

“Plus,” says Johnston, “we’re contributing to the preservation of a unique natural resource.”

Last week, the Sacramento Section of the American Society of Civil Engineers recognized their efforts in giving Caltrans the Outstanding Engineering Project of the Year Award (water environment category).

ASCE Award entries are judged by a volunteer group of civil engineers, as well as journalists covering civil engineering issues. The awards recognize contributions to the well-being of people and communities, resourcefulness in planning and solving design challenges, pioneering in use of materials and methods, and innovations in construction and impact on the physical environment.