Arizona Department of Environmental Quality (ADEQ) has found the gasoline additive MTBE in tests of a contaminated area in Payson.
David Haag, project hydrologist with the ADEQ, gave the public the update on the tetrachlorethylene (PCE) contaminant remediation site on Tuesday evening.
While Haag's report to the public demonstrated progress in remediation of PCE in Payson's water, he also announced that another contaminant, Methyl Tertiary Butyl Ether (MTBE) was detected in TOP-4 and TOP-5 at 10-12ppb, which is below 35ppb safe standard in Arizona.
When a solvent called PCE was discovered in high quantities in two of the town's wells in 1990, the state began the lengthy project to lower contaminant levels and make the town's drinking water meet national safety standards.
PCE is classified as a "probable human carcinogen" and investigations revealed the likely source to be a dry cleaning operation that was located at 908 S. Beeline Hwy. during the late 1970s and early 1980s.
In 1993, ADEQ designated the area a Water Quality Assurance Revolving Fund Site (WQARF) which is similar to a Superfund Priority List site, but is funded by the state rather than the federal EPA.
While testing groundwater at various locations to map the contamination plume, another source of PCE contamination was discovered at a dry cleaner operating in the Bonanza Square area.
A site inspection which included soil and soil vapor sampling around the Grand Way Cleaners detected PCE and another solvent, TCE, in high concentrations. This site was later added to the WQARF Registry List.
Three groundwater monitoring wells were installed near the new "Tonto and Cherry" WQARF site.
By 1997, several monitoring wells were drilled to map the extent of the contamination of the Payson PCE site and an interim groundwater treatment system had been constructed to remove contaminants.
One year later, an expanded groundwater treatment system was added to expedite the cleanup process. Hydrologists also continued to test samples from the 33 monitoring wells.
The expanded system circulates the water through two large carbon filters which strain out PCE before the water is pumped back into the drinking supply. The filters are periodically changed out depending on the level of PCE and other contaminant concentrations that are discovered during testing.
In May of 2001, a system to extract soil vapors was approved by ADEQ. Soil Vapor Extraction (SVE), also known as soil venting, is a vacuum that is applied through wells near the source of contamination in the soil. The vapors are pulled toward the extraction wells which have a carbon filtration that absorbs contaminants before they are released into the air.
During this time, a Community Advisory Board (CAB) was formed to promote community awareness and obtain constructive community review and public comment on environmental action to accelerate the overall cleanup of the site.
CAB meetings allow Haag, ADEQ project manager, and Tina Wesoloskie, community involvement coordinator, to update the public on the remediation project and the condition of Payson's water supply.
At the most recent CAB meeting, Haag discussed the progress of the Payson PCE site. PCE levels were low enough to shut down a portion of the remediation components.
"We have been able to turn off the interim groundwater treatment system and the soil vapor extraction system has been decommissioned," Haag said.
In an effort to capture the plume, one of the towns wells, TOP-4 was shut off because pressure from extracting the water was pulling the contaminants toward the well and making it more difficult to contain the pollution.
"Production well TOP-4 has been turned back on," Haag stated. "We reconditioned that well and turned it back on."
MTBE is an additive to gasoline that replaced lead as an octane enhancer.
By increasing the oxygen content of gasoline, MTBE burns gas more completely, reducing tailpipe emissions.
The EPA has not set a national standard for MTBE, but has issued a drinking water advisory that states concentrations of MTBE in the range of 20-40ppb or below will not cause unpleasant taste or odor for most people.
EPA documents state that data is not adequate to estimate potential health risks of MTBE at low exposure levels in drinking water.
Before a federal law required that gas stations' underground tanks and their components be dual-walled, many tanks leaked, allowing gasoline to enter the groundwater. Several tanks in Payson had to be removed and stations had to convert tanks to meet the new federal standards.
In 1993 Circle K settled a 1.7 million claim in Arizona to clean up leaking underground gas tanks, one of which was a defunct mid-town Circle K near the Tonto Plaza. A 1993 Roundup article described a mound of contaminated dirt that was dumped in the Tonto Plaza parking lot off Wade Ln. when the tank was removed.
"There are a number of former gas station sites in town," Haag said, "So it may be difficult to pinpoint the source(s) of the contamination."
A feasibility study by ADEQ has been in progress for the last year. A feasibility study evaluates a site and offers different remedies, some more aggressive than others.
"The feasibility study has been delayed due to the new findings of MTBE," Haag said. "Because of the nature of that chemical, we may need to add an additional component to the system."
Haag stated that MTBE does not retard easily so a treatment method called airstripping may be needed to capture the MTBE.
"Because of the MTBE, the carbon filters, which cost between $25,000 and $30,000 may need to be changed out every eight months rather than every couple of years as they are currently.
The Tonto and Cherry WQARF site is in it's initial stages of remediation, according to Haag.
"We will be conducting our semi-annual groundwater sampling the first week in March and an initial draft of the Remedial Objective Report will be written," Haag said.
Three other production wells, not included in either WQARF site, continue to be monitored for PCE levels. The Woodland Meadows No. 2, Rodeo Grounds (Rumsey Park), and McKamey wells were found to be impacted by PCE. While these wells continue to be monitored, further remediation has not been ordered due to consistently acceptable levels of PCE.
The next CAB Meeting is scheduled for May 13. The time and location will be announced at a later date.