South Tahoe recovers MTBE-contaminated water

By Jill Foster

An 800-gallon-per minute advanced oxidation treatment system from US-based Applied Process Technology, Inc. is cleaning up methyl tertiary butyl ether (MTBE)-contaminated drinking water supplies from Lake Tahoe in the US state of California. Lake Tahoe's perfect and unspoiled beauty has drawn visitors from around the world, but the MTBE contamination jeopardised the lake's spotless reputation and the local community's economy when the gasoline additive leaked into South Lake Tahoe's pristine drinking water supplies.

Private citizens and the South Tahoe Public Utility District (District) urged authorities to identify and stop leaks from underground storage tanks (USTs) at gas stations that were the source of the contamination and lobbied to make Tahoe an "MTBE free" zone, whereby gasoline containing the additive could no longer be offered. Meanwhile, the district sued 31 oil companies and responsible parties, making legal history when a San Francisco court declared MTBE a faulty product. Parties named in the suit agreed to pay settlements totalling US$ 69 million.

The recent settlements mark the end of the district's four-year battle to recoup the cost of damages wrought by MTBE on South Lake Tahoe's water supply; however a new chapter in the region's recovery has just begun — MTBE removal from drinking water. A suspected carcinogen, MTBE degrades slowly and is highly mobile in subsurface environments. It spreads through groundwater quickly, covering greater distances than other waterborne contaminants.

Internal views of the HiPOx water treatment system installed at South Tahoe's Arrowhead #3 well. Click here to enlarge image

The district adopted a non-detect standard for drinking water because MTBE tastes and smells very unpleasant, even when present at low concentrations. District Information Officer Dennis Cocking explains, "As a resort community, Lake Tahoe has built a reputation on a pristine lake, clean air and pure water. Who wants to save up their money, go on vacation and drink water that tastes like turpentine?"

In 1998, MTBE contamination rendered approximately 2.16 million gallons of water per day unusable. More than one-third of South Tahoe's 34 drinking water wells was taken out of service. The district worked diligently to identify and implement the best treatment methods possible, tackling the problem one well at a time, starting with a well called Arrowhead No.3.

Schematic diagram of the HiPOx system. Click here to enlarge image

MTBE is not easily removed by traditional treatment methods such as carbon filtration or air stripping, so the district broadened its search for a solution beyond the scope of these standard methods. District Manager of Water Operations Rick Hydrick explained: "We wanted something that would completely destroy all traces of MTBE and would produce the purest drinking water possible."

The district purchased an 800-gallon-per-minute advanced oxidation treatment system from Applied Process Technology, Inc. (Applied) based in Pleasant Hill, California. The portable system, called HiPOx, was purchased after site tests demonstrated that HiPOx could destroy MTBE in potable water and would meet the district's stringent requirements, probably the highest water quality standards in the USA.

Terry Applebury, Applied's president and CEO, says the HiPOx technology sets a new standard for removing MTBE from drinking water. "The HiPOx system is extremely precise and robust and can completely destroy MTBE without creating by-products associated with older treatment methods." The HiPOx advanced oxidation technology mixes hydrogen peroxide and ozone to form hydroxyl radicals, an aggressive oxidant that reacts chemically with MTBE, breaking it down into harmless carbon dioxide and water. The carbon dioxide is vented off while the cleansed water is returned to the drinking water system for distribution.

The HiPOx system is the first advanced oxidation treatment system approved by California's Department of Health Services (DHS) to completely eliminate MTBE contamination in drinking water. Since the HiPOx's commissioning on 26 June 2002, the previously unusable Arrowhead well has been providing clean, MTBE-free drinking water to the South Lake Tahoe public and surrounding communities.

"The Arrowhead well is the first MTBE-contaminated well to be brought back on line. Its restoration marks an important milestone in the total recovery of South Lake Tahoe's drinking water supply," said Cocking.