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date posted: December 1 2005

Lake Tahoe Report #128
Aug. 8, 2005
By Heather Segale and John Cobourn

The large spill that recently occurred in Kings Beach on the north shore of Lake Tahoe (approximately 120,000 gallons of raw sewage) was a very serious and unfortunate incident. This accident has caused economic impacts for local businesses, it has affected tourists visiting the area, and creates the possibility of health impacts.

Local health officials do not believe that there will be any long-term permanent health impacts from this incident. Fecal coliform and E.Coli are used as markers for contamination, and repeated testing has revealed only pre-spill background levels. At this point, risk is considered to be negligible.

Across the country, sewage spills frequently contaminate drinking water, make people sick, cause fish kills, and close beaches. Raw sewage flows into U.S. rivers, lakes, and coastal waters about 40,000 times a year, according to the U.S. Environmental Protection Agency (EPA). Sewer overflows contain bacteria, viruses, fecal matter, hormones, toilet paper, and other waste. In fact, between 1.8 and 3.5 million people nationwide get sick every year from swimming in waters that are contaminated with raw sewage.

It is an unavoidable fact of nature that humans produce waste. Consequently, there will always be a continuous supply of sewage requiring disposal, and accidents are always possible. One of the most beneficial water quality improvements made by the Lake Tahoe community in the late 1960s to 1970s was to export all sewage outside of the Basin. However, after this recent accident, locals may have questions about the sewer system and potential risks.

Why are sewer pipes even in or near the lake?
Design and construction of our wastewater collection systems (sanitary sewers) happened decades ago. Sewer systems were usually designed to take advantage of gravity as much as possible for economical reasons. In some places, sewer pipes have been buried on or near the lake floor to provide service to those properties and businesses that exist closest to the lake.

Could these pipes be moved away from the lake?
“Given the environmental controls necessary to construct anywhere near the lake, the construction cost of new facilities (in particular the redirection of sewage flows and change from gravity to pressure pipes), and the value of the properties needed for and affected by the construction, moving these sewer lines may be an unaffordable proposition,” says Lee Schegg, North Tahoe Public Utility District.

The U.S. Army Corps of Engineers recently estimated the cost of such a project at more than $90 million lake-wide. “Beyond the expense of moving pipelines, we might be doing more environmental damage by moving the pipelines than by leaving them,” says Dennis Cocking, South Tahoe Public Utility District. “Just to move them would be hard to justify from an economic standpoint.”

Another way to minimize future spills would be to fund public utility districts to perform all the maintenance needed to keep the system working properly. In areas where the sanitary sewers are well-constructed and maintained, it may be that they can safely stay in place until they have reached their designed life spans and need to be replaced.

What are the risks to human health?
Sewage contains disease-causing (pathogenic) bacteria, viruses and protozoa along with other parasites which can give rise to potential hazards to the health of humans, animals and plants. The health risks depend on the microbes present, duration of exposure and method of exposure. Microbes in raw sewage can enter the body via the nose, mouth, and open wounds or by inhalation of aerosols or dusts. Of course, drinking untreated water from any creek, river or lake is not recommended.

How long will this spill affect human health?
The survival of pathogens depends on a number of factors: location, type of surface contaminated, whether disinfectants are used, and environmental conditions. UV radiation reduces the survival rate of pathogens. Mild temperatures and higher humidity increase survival times. In this case, we are fortunate to have cold water and high UV exposure to reduce the survival of pathogens.
What about Tahoe’s clarity?

Residents may also be concerned about nutrient loading to the lake from this recent sewage spill. Sewage contains very high levels of nutrients – phosphorus and nitrogen. These nutrients stimulate the growth of algae. Currently, Tahoe’s algal growth is now largely controlled by the availability of phosphorus, so this spill actually represents a localized fertilization of the lake.

Typical domestic raw sewage contains between 25 and 85 mg/L nitrogen and 5 to 55 mg/L phosphorus. Therefore, the 120,000 gallons (454,250 liters) of sewage contains approximately 11 – 39 kilograms (25 – 85 pounds) of total nitrogen and 2 – 25 kilograms (5 – 55 pounds) of total phosphorus. As a comparison, dumping twenty 20-lb bags of 20-7-7 (Nitrogen-Phosphate-Potash) fertilizer directly into Lake Tahoe would contribute 80 pounds of nitrogen and 11 pounds of phosphorus.

To put this into perspective, scientists estimate that an average of 400 metric tons (440 tons) of nitrogen and 43.6 metric tons (48 tons) of phosphorus go into the lake each year. The Kings Beach sewage spill represents approximately 0.002 - 0.01 percent of the annual nitrogen load and 0.005 – 0.06 percent of the annual phosphorus load to Lake Tahoe. Also, the amount of nutrients contributed from this single sewer spill is approximately the same amount of phosphorus and half the amount of nitrogen that the small Tahoe City Constructed Wetland (next to Albertsons at the “Y”) removes from urban stormwater during a full one-year period (Heyvaert, Subalpine Stormwater Treatment with a Constructed Surface-Flow Wetland, 2004).

Due to nutrient cycling, once nutrients get into the lake, they will remain there providing food for algae for decades to come. So while the public health officials are confident that the risks to public health have passed, the nutrients will remain to cause continued water quality impacts and algal growth.

A quick local response removed a good deal of the danger created by the spill, and nature will slowly, but surely, take care of the rest.

Watch for the “Lake Tahoe Report” in the Tahoe Daily Tribune each Wednesday, and tune in to KOLO-TV News Channel 8 Tuesdays at 5 p.m. to learn more. The “Lake Tahoe Report” is a collaborative effort of the Lake Tahoe Environmental Education Coalition, University of Nevada Cooperative Extension, UC Davis Tahoe Environmental Research Center and the California State Water Resource Control Board. For more information, contact Heather Segale, UC Davis Tahoe Environmental Research Center, (530) 583-3279, or logon to www.lteec.org or www.tahoe.unr.edu.