Emerald Bay pollution study inconclusive, says its researcher
August 23, 2005
The scientist who gathered pollution data at Emerald Bay considers the study inconclusive and said he recommended no regulation of boating due to his findings.
“There’s not enough data to suggest there’s a problem with PAH in Lake Tahoe except with some of the marinas,” said Glenn Miller, professor at the University of Nevada, Reno. “We didn’t see anything that compelled us to recommend management of boating at Tahoe solely because of PAH.”
PAH is polyaromatic hydrocarbons, a byproduct of fuel combustion.
The Tahoe Regional Planning Agency is relying on Miller’s studies, more than 3 years old and conducted before a two-stroke engine ban took effect, to justify a proposed motorboat ban on Emerald Bay one day a weekend during summer months.
Miller said PAHs were barely detectable in Emerald Bay, so instruments had to be fine tuned to rule out any contamination.
“There’s always a little bit of this everywhere,” said Miller. “This is a product of combustion, so there’s some in the air. You’ve got to develop your lab so that you have ultra-clean techniques.”
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He said PAHs also come from road runoff, but the types of PAH detected at Emerald Bay are commonly associated with boat traffic.
Over the course of a year, two detections of 5 nanograms per liter of PAH were found in Emerald Bay; one on Aug. 13, 2001 and one on Sept. 4, 2001. None were detected on Aug. 29, 2001, according to a UNR graph entitled “Total PAHs found in UNR 2003 study.” No tests were taken in December, January or February.
Five nanograms per liter is 5 parts per trillion. It barely crosses the limits of detectability, Miller said.
“When you start seeing things in the 50-100 nanogram per liter range, that’s when you start seeing toxicity,” Miller said.
Higher PAH detections were found during that year at Camp Richardson, Incline, Ski Run, Zephyr Cove and Tahoe Keys.
PAHs in large enough numbers are carcinogens and mutagens. However, the amounts detected in Emerald Bay are not large enough to affect aquatic life or humans, according to scientists at Lahontan Regional Water Quality Control Board.
PAHs dissipate within 24 hours to 7 days.
United States Geological Survey studies have shown increased PAHs detections in runoff from coal-tar sealant, a petroleum product used to surface roads.
The TRPA has said it can’t explain why the pollutants are also being found at Ski Run Marina, which is open water. A large pipe allows runoff directly from roads into the lake at Ski Run Boulevard.
PAH detections at Tahoe Keys were highest during November and March, according to the data, when boats are typically no longer active in the water.
July 2002 is the most current data available. TRPA long-term planner Coleen Shade said she believed studies were done in 2003, but that data was not made available to the Tribune as of press time.
After the TRPA ban on two-stroke motors took effect in October 2001, no PAHs were detected through the end of the study in July 2002. And no phototoxic PAHs were detected at all during the whole year.
Miller explained fuel-injected two-stroke engines – currently allowed on Lake Tahoe – produce the same amounts of PAH as the carburated two-strokes that were banned. The big difference in the two engines was how much raw fuel was deposited in the water.
Carburated two-stroke engines release 30 percent of their fuel unburnt into the water. There has been an 80 percent decrease in unburnt fuel found on Lake Tahoe since the ban took place.