By Steve McAdams and Nick Zaninovich
Lurking beneath the panoramic and pristine beauty of Lake Tahoe is an environmental crisis in the form of the gasoline additive MTBE. Virtually unknown in the common vernacular a decade ago, MTBE has become a household term. An acronym for methyl tert-butyl ether, MTBE has been the subject of intense environmental, legal and legislative debates regarding its impact on the environment, especially water, and South Lake Tahoe, California, has been a focal point of these debates.
Drinking water contamination
The South Tahoe Public Utility STPU provides drinking water to the city and surrounding communities from underground aquifers. Within a one-year period, the STPU was forced to shut down more than one-third of its drinking water wells due to MTBE contamination. The sources of the contamination were leaking underground storage tanks (LUSTs) used by gasoline dispensing stations.
The crisis became economic as well as environmental. As a renowned tourist destination, (the local population of 28,000 can swell to more than 100,000 thanks to visiors during the summer) South Tahoe was hard hit by the MTBE pollution. “Lake Tahoe has built a reputation as a resort community, based on a pristine lake, clean air and pure water,” said STPU spokesman Dennis Cocking. “Who wants to save up their money and go on a vacation and drink water that tastes like paint thinner?”
Taking corrective action
The STPU found itself in a crisis situation. While continuing to deliver safe drinking water to customers, the STPU developed three goals to resolve the MTBE problem. The first goal was to raise awareness. The public was encouraged to successfully demand that appropriate authorities find and stop MTBE leaks from LUSTs. The second goal was to clean up contaminated sites and impacted wells, an ongoing long-term effort. The STPU adopted a policy of zero tolerance of MTBE and now shuts down impacted wells. The third goal was to prevent future contamination. The STPU initiated a campaign to “Help Make Tahoe MTBE Free,” enlisting public support and involvement to influence local legislators to act to remove MTBE from gasoline and commerce. Not unexpected, in March, 1999, California’s then Governor, Gray Davis, directed the state’s Air Resources Board to develop regulations prohibiting MTBE use, while continuing to maintain air quality standards.
Legal redress sought and won
In alignment with its second goal to recover the cleanup costs, the STPU sued 31 companies in 1998, alleging that their defective product contaminated local drinking water aquifers. The STPU estimated the long term cleanup costs to be in the range of $30-35 million. Twenty-six companies settled for $33 million in 2001, and in April, 2002, a jury in San Francisco found that gasoline with MTBE was a defective product and that two major oil companies were aware of the chemical’s dangers but withheld the information. Litigation was concluded in August, 2002, and with all settlements to date, the STPU was awarded more than $69 million to address MTBE contamination.
With the legal settlements concluded, the STPU began the process of cleaning water and restoring wells. In 2001, the STPU commissioned an engineering study to determine the appropriate technology to clean up the contaminated Arrowhead well. At the conclusion, the STPU purchased an 800-gallon-per-minute advanced oxidation process (AOP) in July, 2001. The containerized and portable treatment system was purchased after site tests demonstrated that MTBE could be destroyed in potable water without forming undesirable byproducts such as tert-butyl alcohol (TBA) and that it could meet the District’s stringent water quality requirements. Rick Hydrick, Manager of Water Operations, stated, “We chose this treatment technology because we are confident that it can completely destroy the MTBE concentrations found at this site and will meet the District’s mission to deliver the purest possible drinking water to our customers.”
Further contamination discovered
In July, 2003, the STPU detected MTBE contamination in its Bakersfield well. Having previously tested granular activated carbon (GAC) treatment for MTBE removal, the STPU was prepared to purchase a GAC system for restoring this well. However in August 2003, the well tested positive for tertiary-butyl alcohol (TBA). That and another nearby contaminated well were shut down to avoid additional threats to the water supply quality.
Knowing TBA is much more difficult than MTBE to remove using GAC, the STPU commissioned its engineering staff to evaluate GAC versus AOP based on criteria including efficiency, reliability, complexity, constructability, site and aesthetic impacts, flow variability, portability, energy consumption and long-term (15-year) cost of ownership.
An economical choice
STPU staff concluded the two technologies were cost competitive at low levels of contamination, but at higher anticipated levels, the AOP cost of ownership was as much as 80% less than proprietary coconut-fiber GAC. Although more complex than GAC, AOP also provided guaranteed destruction versus potential breakthrough or the sudden release of accumulated compounds when using GAC. AOP is not an “accumulation technology”, thereby avoiding concerns related to hazardous waste handling, radionucleotide accumulation and biological activity. Finally, the AOP facility footprint and profile was substantially smaller than an equivalent GAC facility.
When the latter facility was completed, it included other features such as a variable-frequency well motor and multi-variable cascade controllers for energy conservation and precise control of pressure and flow. Located in a residential neighborhood and adjacent to an elementary school, the containerized AOP facility was enclosed in a residential-style facade, minimizing local visual impact and facilitating the issuance of required permits from the Tahoe Regional Planning Agency.
Following startup of the restored well, Nick Zaninovich, Senior Engineer and Project Manager, stated “We know AOP will destroy both MTBE and TBA, but it also generated no waste or byprod-ucts and used a fraction of the space required for a GAC system.”
After receiving the first-ever permits from California’s Department of Health Services (DHS) to use AOP treatment processes in potable service, the STPU began operation of systems in June, 2002, and July 2004. While cleaning up contaminated sites promises to be a task requiring years, these important first steps by the STPU are being closely followed by the local community, California DHS and other communities.
About the authors
Steve McAdams is the Vice President of Engineering and Manufacturing at Applied Process Technology, Inc., in Pleasant Hill, California. Contact him at (925) 977-1811 ext. 303. To learn more about Applied’s HiPOx advanced oxidation water treatment technology, visit www.aptwater.com