Fernando Cadena has moved his research to Picacho Avenue where a former gasoline station's underground gasoline tank ruptured and leaked, contaminating the nearby groundwater about 20 years ago. Cadena's research, funded with about $100,000 from the Waste-management Education and Research Consortium and a private oil company consortium, offers a new and potentially inexpensive "pump and treat" method of cleaning groundwater.
A typical gasoline tank holds about 10,000 gallons, but it's not known how many gallons leaked at the study site. Cadena said the spill flow is substantial, stretching many feet from the source and 20 to 30 feet below the surface.
"This problem of leaking underground storage tanks is endemic nationwide, but we have a bigger problem in the Southwest because 90 percent of our communities get water supplies from the ground," Cadena said.
There are 5,800 underground storage tanks in New Mexico, according to Tony Moreland, a geologist with the New Mexico Environment Department. Of those, 916 are leaking. Within Do¤a Ana County, there are 420 underground storage tanks, and 97 of those leak, he said.
Len Murray, an environmental specialist with the New Mexico Environment Department's Las Cruces district office, said that all leaking tanks are a potential threat to groundwater and hence, drinking water. Several New Mexico communities, including Tatum and Hobbs, have lost municipal drinking water supplies to petroleum-based pollutants flowing from leaking underground tanks, Murray said.
Last year, Murray led efforts to permanently close 125 underground tanks including some that were not leaking throughout southwestern New Mexico. Leaking underground storage tanks are responsible for about 45 percent of all known cases of groundwater contamination, according to a February 1993 department report.
In August 1995, Cadena and graduate student Jim Roberts treated about 1,000 gallons of polluted water below Las Cruces' old downtown station. The first step in Cadena's project was to establish a well to pump the polluted water to the surface. The water then was filtered through a 55-gallon drum lined with organically treated zeolite, a mineral used in Kitty Litter that acts as a pollutant filter to remove hazardous benzene, toluene and xylene found in gasoline and diesel fuels.
"This process removes a good 80 percent of the pollutants," Cadena said. "Then, the same water goes to a reservoir to remove any remaining pollutants."
Current water cleanup technologies, absorption and air stripping, require passing polluted water through an absorbent such as charcoal to filter the pollutants, or blowing air through the water and stripping off the pollutants. Neither technology completely eliminates the pollutants, Cadena said. With absorption, the filter eventually becomes saturated and must be regenerated or disposed. With air stripping the pollutants become airborne.
Cadena's technique, a hybrid of the two, incorporates both absorption and air stripping. In Cadena's process, the filter can be recycled and is not burned. When the filter becomes clogged, a hair dryer-like device heats and destroys the pollutants. Thus, the filter is reused indefinitely, he said.
After the "pump and treat" process, the water is treated again with the air stripping technique. By the end of the process, the water meets federal drinking water standards, Cadena said. Cadena has received support through the WRRI for several projects. His most recent project on removing arsenic from wastewaters is described in WRRI technical report #293.