Adeq Studies Removal Of Mtbe From Water Supply


With the discovery of a gas additive in two production wells in Payson, the town water department and the Arizona Department of Environmental Quality, are examining different strategies to remove the contaminant before it gets into the drinking water.

According to Water Quality Specialist, Karen Probert, this was the first time Methyl Tertiary Butyl Ether (MTBE) has been detected in production wells and in the water supply after treatment.

"We test water samples twice a month and January was the first time that we had detected MTBE," Probert said.

According to Probert, levels detected in the wells were 10-12 parts per billion (ppb) but after going through the treatment system, levels dropped to .7 ppb.

"The fact that it was still detected, even at a low level, has made us look at what more we can do to optimize our water treatment facility," she said.

MTBE has been used in U.S. gasoline since 1979 to replace lead as an octane enhancer. It has been used at higher concentrations since 1992 in an effort to fulfill requirements of the Clean Air Act.

As an oxygenate, MTBE helps gasoline burn more completely, reducing tail pipe emissions that pollute the air.

While the Clean Air Act required the use of oxygenated gas in areas with high levels of air pollution, it did not specifically require the use of MTBE, as gasoline refiners can choose from other oxygenates.

Two programs

The Clean Air Act has two programs for reducing air pollution by the use of oxygenate additives. One is the Winter Oxyfuel Program designed for cities that have elevated levels of carbon monoxide during cold months, such as Phoenix.

The second program is for areas with the worst year-round smog problems, like Los Angeles. The Year-round Reformulated Gas Program requires the use of reformulated gasoline that is blended to have fewer polluting compounds than conventional gasoline.

Currently, about 30 percent of the country's gasoline is reformulated, of which, about 87 percent contains MTBE. Refiners have chosen MTBE, according to the Environmental Protection Agency for "economic reasons and its blending characteristics."

Yet, in an effort to reduce air pollution, some groundwater supplies have been contaminated with a chemical, the health effects of which are not fully understood.

According to the EPA, MTBE has opportunities to get into groundwater wherever gasoline is stored, transferred or transported.

Before federal legislation required all gasoline stations to have dual-sided underground tanks, leaking tanks were a common occurrence.

Despite the fact that many tanks were replaced throughout the 1990s, the contaminants continue to be discovered in the groundwater, as in the case of Payson.

The EPA is now making an effort with states to increase compliance with underground storage tank regulations through technical assistance, inspections, and enforcement.

Unlike some contaminants such as solvents, MTBE does not cling to the soil very well and migrates faster and farther, making it more likely to contaminate groundwater.

Removing MTBE

Conventional methods of treating contamination, such as carbon filtration, are not very effective in removing MTBE. Other technologies have been successful in removing MTBE from private wells.

Soil vapor extraction is one such method in which air is vacuumed through the soil to vaporize the contaminant. MTBE vapors are extracted, treated and disposed of to prevent further contamination.

A process called air stripping is another way of cleaning up MTBE. The contaminated water is passed through a column filled with packing material while upward-flowing air removes the chemicals from the water.

While these technologies have had some success, MTBE does not easily go from the water to a vapor phase. Remediation can be a long and costly process.

Although levels of MTBE found in Payson's drinking water were well below the EPA's advisory level of 20-40 ppb, even the EPA says that available data is not adequate to estimate potential health risks of MTBE at low exposure levels in drinking water. This is part the reason there is no national standard for MTBE yet.

Taking charge

Certain states, such as California, have acted much more aggressively on the issue of MTBE.

In 1996, testing done in Santa Monica revealed MTBE in high concentrations in two wells that produced more than half of the city's water. Both wells had to be shut down immediately. The city began purchasing replacement water and both the EPA and the Los Angeles Regional Water Quality Control Board began a clean-up operation.

March 26, 1999, California Gov. Gray Davis issued an executive order for a rapid phase-down and eventual phase-out of MTBE in gasoline.

In a letter to former EPA Administrator, Carol Browner, Davis stated, "California's ground and surface water resources are seriously at risk because of discharges of gasoline that has been oxygenated with MTBE. Over 60 percent of the reservoirs tested have detectable levels of MTBE, and many public drinking water sources in areas like Santa Monica, Santa Clara, Sacramento and South Lake Tahoe have been shut down because of MTBE contamination."

The University of California began an extensive research study focusing on the environmental and health effects of MTBE.

The study (which will be examined in-depth in Part 2 of this Roundup article in Friday's paper) found that among other things, "there is no significant additional air quality benefit to the use of oxygenates such as MTBE in reformulated gas, relative to the alternative non-oxygenated formulations."

While Payson's production wells have had relatively low levels of MTBE, ADEQ's monitoring wells near the south Beeline Highway have detected consistently higher levels of MTBE. Whether the contaminant will eventually flow into the production wells is one reason why treatment options are being considered.

"We are looking at using a different type of carbon in our filtering system," Probert said. "By altering the size of the carbon particles, we may be able to filter more of the MTBE, but also extend the life of the filter itself."

Fiscal concerns also arise as budget cutbacks limit water treatment options. ADEQ Hydrologist David Haag described the possibility of adding an air stripper to reduce MTBE, but Probert said it would be very expensive to operate because it would require a lot of electricity.

The chemical MTBE is a continuing concern for the country's water resources. In part 2, the findings of an extensive research study by the University of California will be explored. This document was influential in California's decision to phase-out the use of MTBE in gasoline refining.

Will Arizona follow California's lead in using gas that is MTBE-free?

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