Industrial wastes have been silently leaching into soil, air and water for decades. The two that might cause the most harm also are the most persistent in the environment: methyl tertiary butyl ether (MTBE) and perchlorate. Those chemicals have been linked to health problems in humans and are suspected carcinogens; moreover, both of those water-soluble contaminants are proving difficult to remove from water.

The U.S. Environmental Protection Agency (EPA) has yet to establish a maximum contaminant level (MCL) for either MTBE or perchlorate, although it promises to review the standards within the next few years. In the meantime, states such as California, which has found high concentrations of MTBE and perchlorate in its groundwater, are setting their own limits.

Environmental groups and local agencies estimate it will cost millions or even billions of dollars to rid the country's public drinking water supplies of each contaminant. Cities and counties only have a couple of options to secure clean water: drilling new wells, importing drinking water or remediating their contaminated drinking water.

Who foots the bill — government or industry — still is being debated, but local governments often are the ones determining how best to clean up the mess safely, quickly and economically. The problem most local leaders face is choosing the appropriate technology. The first step in that process is understanding the contaminants and the various remedies available.

Houdini of pollutants

MTBE is a synthetic chemical that is added to gasoline to make it burn cleaner. Although it was first used in the late 1970s as a lead-substitute octane-enhancer, major oil companies began using MTBE heavily in the 1990s as an inexpensive, federally mandated fuel oxygenate to comply with the EPA's Clean Air Act and Federal Reformulated Gasoline program.

Often called the “Houdini of pollutants,” MTBE dissolves quickly into soil, air and water, making it difficult to detect and expensive to remove. The contaminant can leak from a number of sources, including underground storage tanks; accidental fuel spills; automobile and tanker accidents; motorized recreational vehicles on lakes and drinking water reservoirs; spills and drips from refueling automobiles, lawnmowers, tractors and other machines; and pipelines and above-ground storage tanks.

Although MTBE supplements gasoline in only 16 states, it has been detected in water supplies in 49 states. As many as 55 percent of large, urban water systems have detected some level of MTBE in their water supplies, according to the U.S. Geological Survey's July 2003 Water Quality Assessment. Three years earlier, only 15 percent of drinking water sites tested in the Northeast were found to contain MTBE. Conservative estimates place the contaminant in about 500 public drinking water wells and in about 45,000 private wells across the U.S.

At about 20 parts per billion (ppb) to 40 ppb, MTBE-tainted water tastes bitter and smells foul. Ingesting MTBE-contaminated water over an extended period causes the human liver to convert the additive into formaldehyde and tertiary butyl alcohol, which the human body has a hard time eliminating. Released into the air, MTBE forms tertiary butyl formate, which adversely affects the human respiratory system. MTBE also is a suspected human carcinogen.

Researchers currently are investigating ways to remove MTBE from soil, air and water. While some headway has been made in cleaning up the soil, removing the contaminant from drinking water is proving more challenging. Its chemical structure and methanol roots make MTBE very mobile, less degradable and more soluble in water than other gasoline compounds (see “Cleanup options” p. 25).

To fight MTBE, Colorado, Connecticut, Maine, Michigan, Minnesota, New York and South Dakota are considering legislation that would outlaw using the substance in their gasoline supplies. As of press time, California's proposed ban on using MTBE in gasoline is scheduled to take effect on Jan. 1, 2004.

Although EPA classifies MTBE as an unregulated contaminant, the agency continues to study possible adverse health effects from the gasoline additive. However, Congress is debating H.R. 6, an energy bill that would, with few exceptions, excuse producers of MTBE-laden gasoline from paying remediation costs. That means the local, state, and, possibly, federal governments could end up footing the cleanup bill, which is estimated to be more than $29 billion.

“The nation's mayors are very concerned with the tremendous financial burden that will be placed on local governments to clean up drinking water supplies that have been contaminated by MTBE,” says James Garner, president of the Washington, D.C.-based U.S. Conference of Mayors. “Passage of this provision will put the costs of pollution cleanup on local taxpayers rather than on the polluters. If enacted, this has the potential to be the largest unfunded mandate passed down from Congress to local governments.”

Last year, several states, cities, water utilities and landowners filed MTBE contamination lawsuits. For example, New Hampshire is suing 22 major oil companies for their possible roles in contaminating some of the state's water supply. The suit holds the companies responsible for paying investigative and cleanup costs, as well as punitive damages. In another case, a California public utility district won a $69 million settlement against several major MTBE manufacturers and local refineries for possibly polluting the public drinking water supply with MTBE.

As the controversy continues, some in Congress are advocating the use of corn-based ethanol instead of MTBE as a fuel oxygenate. Ethanol opponents argue, however, that alternative would significantly increase gasoline prices and use more energy to produce it than it provides.

The costs of remediation*

Technology	Contaminant removed	Estimated cost
Atmospheric air stripping	MTBE	$75 to $125
Biological treatment with anoxic and aerobic microbial reactors	MTBE	$65 to $150
Granular activated carbon	MTBE Perchlorate	$80 to $150
Ion exchange	Perchlorate	$100 to $350 (regenerable or non-regenerable)
Fluidized bed reactor	Perchlorate	$75 to $125
Reverse-osmosis membranes	Perchlorate	Costs depend on total dissolved solids of water (generally $200 to $500)
*Estimated costs per acre-foot for technologies used to remove MTBE and perchlorate from groundwater. Approximations depend on influent total dissolved solids, contaminant concentration and pH. One acre-foot is 326,000 gallons of water or enough to supply a family of four with enough water for two years.

Weapons of waste

The second commonly used substance leaking into drinking water is perchlorate salt, which has been used for many years to provide smokeless fireworks or munitions (potassium perchlorate), control thyroid activity (sodium perchlorate) and oxidize rocket fuels for enhanced combustion (ammonium perchlorate). Still used in numerous national defense weapon systems, perchlorate also is used in road flares; air bag inflators; nuclear reactors and electronic tubes; lubricating oils; tanning and finishing leather; fabrics and dyes; electroplating, aluminum refining, and rubber manufacture; paint and enamel production; and certain imported Chilean fertilizers.

In the last decade, perchlorate has been detected in soil and water near U.S. military bases and defense industry sites, aerospace manufacturing and testing facilities, and former contaminant disposal sites. Perchlorate-contaminated water has been discovered in 38 states.

Nineteen major perchlorate contamination sites exist in California alone, and 37 other states also have reported the contaminant in their well water. The EPA estimates 900 pounds of perchlorate leak into the Colorado River daily. Even if the flow could be immediately stopped, it would take decades to rid the river entirely of the contaminant. Experts predict it will cost anywhere from $1.5 to $4 billion to clean up perchlorate nationwide over the next few decades.

Perchlorate's chemical structure makes it very water-soluble, meaning it can travel far and wide in groundwater, surface water and well water. The largest recorded plume to date extends 30,000 square miles in western Texas.

Federal toxicologists confirm perchlorate ingested over long periods of time and in sizeable amounts may cause developmental or thyroid problems. Preliminary studies indicate the contaminant also may be a potential carcinogen. Testing also has indicated that plants like lettuce and tomatoes absorb and store perchlorate, putting some food at risk.

The EPA classifies perchlorate as an “unregulated contaminant” and has not set its MCL but plans to do so by 2006. Two years ago, the EPA indicated it would reduce its reference dose levels (RfD), allowing 1 ppb of perchlorate in drinking water. Some states, California for instance, followed suit, reducing the perchlorate method detection limit to 4 ppb. California's Office of Environmental Health Hazard Assessment recommends a public health goal of 2 to 6 ppb.

Toxicology studies for both the Department of Defense and the EPA still differ greatly in their assessment of the RfD. In the meantime, the EPA has established a recommended concentration in drinking water of 4 to 18 ppb for perchlorate, based on the original RfDs.

States where perchlorate has been found in the groundwater are generally adopting 4 ppb as a standard of treatment for potable water. California requires water utilities to notify water customers when perchlorate exceeds 4 ppb.

Only getting worse

With MTBE and perchlorate continuing to creep into public drinking water supplies, more communities are expected to discover the potentially carcinogenic fuel additive in their groundwater. Contamination sources are sometimes difficult to trace, leaving affected cities and counties to pay for its cleanup without the help of the responsible parties.

Perchlorate contamination also is becoming more prevalent as new testing shows concentrations of the substance in many more municipal wells than originally anticipated. Cleanup will continue for decades, but the health ramifications could extend into generations.

While removing perchlorate and MTBE from water can prove challenging, various remediation technologies and services are available. Local communities must often fend for themselves. Although Washington will set MCLs for both contaminants in the near future, temporary-action limits are in place that can help utilities determine an appropriate response when contamination is detected.

Timothy Peschman is senior business development manager for USFilter Remediation Services in Roseville, Minn.

Cleanup options

MTBE	Several technologies, such as granular activated carbon (GAC) filtration, biological treatment using anoxic and/or aerobic microbial reactors and atmospheric air stripping, can remediate MTBE polluted groundwater that meets the National Pollutant Discharge Elimination System (NPDES) permitted release and have been approved for potable applications.
	MTBE's high water solubility and polar properties make it difficult to remove from water by adsorption. Carbonaceous adsorbents like GAC can be very effective, provided they possess a high total surface area. The majority of the adsorbents' pore volume also must be in the high-energy micropore region.
	Carbonaceous adsorbents also may remove other organic compounds typically found in gasoline. Selectivity for lower molecular weight compounds, side-by-side performance and third-party testing are all important criteria in selecting the proper carbonaceous media.
	Biological treatment may use anoxic/aerobic microbial reactors to oxidize or mineralize MTBE. The reactors may be either outside the contaminated aquifer (ex-situ) or within the contaminated aquifer (in-situ). Various forms of the anoxic/aerobic biological process continue to be tested for MTBE removal effectiveness. Certain states, however, oppose using those biological processes to produce potable water.
	Atmospheric air stripping is an effective technology for remediating MTBE-contaminated waters. It must be paired with a vapor phase removal or destruction technology to eliminate the MTBE from both the water and air, as the treatment method requires using a high air-to-water ratio (typically greater than 150:1) which moves the MTBE from the water and into the air. Local air permitting requirements should be consulted before using the technology.
Perchlorate	Four treatment technologies can be used to remediate perchlorate-polluted groundwater: ion exchange, GAC, reverse-osmosis (RO) and bacteriological reduction of perchlorate using a process called a fluidized bed reactor (FBR).
	Ion exchange systems use once-through, “throw-away” perchlorate-selective or nitrate-selective styrene divinylbenzene resins. Acrylic anion resins are used for regenerable systems, but they require proper disposal of concentrated, perchlorate-laden brine. Newly developed non-regenerable perchlorate selective ion exchange resins have significantly reduced the treatment costs for perchlorate contamination.
	Activated carbons, tailored with an organic cation, also remove perchlorate. While the application of that technology to remove perchlorate still requires development, it may be cost-competitive with other approaches — especially in applications that require the simultaneous removal of both perchlorate and organic contaminants.
	Membrane filtration, using either RO or nanofiltration, significantly removes perchlorate. Nanofiltration membrane removal is generally based on the membrane surface charge and depends on the influent water's Ph. Removal by RO depends on the influent total dissolved solids content and the system's operating pressure. For either of those technologies, the perchlorate is concentrated in a waste stream that must be disposed of properly.
	Bacteriological reduction of perchlorate using FBR also is well-proven and accepted for potable water treatment by the California Department of Health Services. The process uses indigenous bacteria's ability to generate enzymes that can dechlorinate the perchlorate anion.