Fertilizing naturally occurring bacteria seems to be cleaning an underground dry cleaning fluid spill by the Kenai River in Soldotna faster than expected.
Concentrations of the fluid -- tetracholorethylene, also called PCE -- have fallen dramatically since the fertilizer was injected at River Terrace RV Park in October, said Rich Sundet, project manager for the Alaska Department of Environmental Conservation. But while there has been an increase in a byproduct from the early stages of degradation -- dichloroethene -- there has been no spike in byproducts from the later stages, he said.
That has some observers worried.
Fairbanks hydrologist Michael Lilly told the Kenai River Special Management Area Advisory Board in February that at two sites near Fairbanks, the natural degradation of similar chlorinated solvents stopped at the dichloroethene stage.
Whether the degradation at River Terrace finally produces nontoxic end products may depend on the chemistry of the groundwater and soil, he said. Contacted later, University of Alaska Fairbanks microbiology professor Joan Braddock said changes in the availability of oxygen had big effects at the Fairbanks sites.
"You'd get totally different microbes acting," she said. "You'd get completely different degradation pathways."
At another site, she said, fertilizer completely inhibited degradation of a diesel spill because the soil was too dry.
"That was new information," said Lance Trasky, regional supervisor for the Alaska Division of Habitat and Restoration. "We weren't aware that PCE could proceed to some step like vinyl chloride or others and just stop there. Some of the products are only slightly less toxic than PCE, and, in the case of vinyl chloride, it may be more so. I don't think DEC had a good answer for that."
Lilly said it is crucial to characterize a site beforehand to predict the effects of treatment.
"Are you going to wind up creating something that's going to get to the river and is a worse problem?" he asked. "At the meeting, I was asking these guys, 'Do you know what you're getting?' And they didn't -- or they didn't feel confident enough to answer."
On its Web site, HRC manufacturer Regenesis Bioremediation Products Inc. says HRC releases lactic acid, stimulating growth of naturally occurring bacteria that produce dissolved hydrogen. The hydrogen stimulates bacteria that strip the chlorine from spilled solvents.
Sundet said HRC will simply enhance natural degradation already occurring at River Terrace.
"We did pilot studies. We took samples of soil and groundwater and sent them to the lab to monitor chemical properties. Everything came back saying there was a high probability that HRC would enhance the natural attenuation at this site," he said.
DEC also has installed monitoring wells to track the effects of treatment.
"Of all the break-down products, vinyl chloride is the only one that is more toxic than the original PCE," Sundet said. "We don't want to see a huge spike of vinyl chloride, but we're monitoring. Right now, the level of vinyl chloride isn't extremely high."
If vinyl chloride does accumulate, it likely could be treated by aerating the soil, he said. Regenesis says HCR has never been shown to stimulate a significant or permanent buildup of vinyl chloride, but if it ever does, vinyl chloride degrades rapidly in the presence of oxygen.
DEC and River Terrace owners Gary and Judith Hinkle disagreed for years on how to assess and clean the spill in the area of a former dry cleaner at the site. In August 1997, the Hinkles signed an agreement by which the federal Environmental Protection Agency would oversee emergency cleanup of the most contaminated soil, while DEC would assess groundwater contamination, determine how thoroughly the site should be cleaned, and oversee long-term cleanup and monitoring.
The Hinkles excavated and treated the most contaminated soil. DEC hired a contractor to assess groundwater contamination. It found high levels of PCE in several monitoring wells and evidence that contamination is reaching the Kenai River. A 1999 court order gave DEC full control of the long-term cleanup.
DEC hired Oasis/Bristol JV to conduct more studies and design a cleanup plan. Oasis found two plumes of contamination -- one migrating from the former dry cleaner through the excavated area toward the Kenai River, and one migrating from the former dry cleaner to the Sterling Highway, where Sundet believes contamination follows a storm drain to the river.
Sundet said there still could be contaminated soil under the former dry cleaner, but attempts to bore under the building and check have failed. DEC concluded it would be too expensive to excavate all of the contaminated soil, he said. Instead, it plans to treat contaminated groundwater before it leaves the Hinkles' property. That could take from five to 15 years, he said.
In September, the Hinkles signed a settlement ending litigation with the state and agreeing to pay the state $1.6 million over time, plus interest, to cover costs from the spill. Sundet said the Hinkles already have paid $300,000. The state holds a lien on their property as security.
In October, Oasis installed 56 injection wells and injected the first dose of HRC. By January, PCE levels had declined sharply in groundwater downstream from the injection wells. Sundet said PCE levels also declined sharply in one well upstream of the injection wells, suggesting HRC may be diffusing back toward the former dry cleaner.
Levels of dichloroethene were rising, but levels of vinyl chloride, the next step in the degradation path, remained low. Continued degradation should produce ethene, which contains no chlorine, and eventually carbon dioxide and water. However, Max Schwenne, a principal with Oasis, said the microbes strongly prefer PCE to its breakdown products and may not attack dichloroethene until the PCE is gone.
This spring, Sundet said, DEC plans to install up to 50 more injection wells to increase coverage and reduce the treatment time. DEC probably will inject HRC biannually for three years, then continue monitoring, he said.
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