Friday, March 19, 1999
Clean-up expenses mount at DPW
In this season of budget overruns, it was unwelcome news to the selectmen on March 9 that clean-up of the contamination from gas leaks found at the department of public works in connection with removal of the old underground fuel storage tank will cost the town at least an additional $46,000. This brings the total cost of the project, including removal of the underground storage tank and replacement with an above-ground version and previous clean-up costs, to over $170,000.
Chris Mariano of ENSR, the company hired by the town to oversee the clean-up, related a brief history of the problem. Last fall, in the process of removing the underground fuel tank, workers encountered a strong petroleum smell. Pursuant to an immediate response action required to be filed with and approved by the state department of environmental protection, approximately 250 cubic yards of contaminated soil were excavated and monitoring wells were installed.
Early this year, a sheen indicative of gasoline appeared in one of the monitoring wells. After digging in several locations around the contaminated well, ENSR found that the concentration of contaminants was highest in the area of the old dispensing island, implying that there had been a leak in the old pump or fuel line connection. Moreover, a pipe used to drain groundwater around the DPW septic system runs close to the area of highest contamination. Contaminants entered this pipe through a perforation and were carried to the point of discharge close to the surrounding wetlands.
Clean-up of the petroleum in the soil will occur through a process known as bioremediation. Mariano explained that ENSR will periodically inject into the contaminated soil bacteria that "eat" petroleum and turn it into harmless fatty acids. Mariano anticipated that the injections would be needed monthly for at least one year.
"Are these microbes safe?" asked selectman Vivian Chaput. Mariano replied that this is the most commonly asked question about this up-and-coming process. "There are thousands of these bacteria all over us," he answered. The process will be monitored to make sure the bacteria have an appropriate nutrient level and that they are not being injected at a rate that will adversely impact the wetlands. The bacteria die when there is no more petroleum to eat.
Mariano recommended that the clean-up be started as quickly as possible both to reduce costs and to minimize the impact to the wetlands, which Mariano suggested has probably been going on for years. Of a total cost of $46,910, up to $20,000 will be needed to be transferred from this year's reserve fund for work to be performed before July 1, and the rest will be paid from next year's budget.
In addition, the perforated drainage pipe will be diverted around the contamination. This work can be done by the DPW.
Effect on neighbors
The contamination will have no effect on the water quality in neighboring wells, said Mariano. ENSR tested the well at the DPW and found no contamination. One residential neighbor also requested that his well be tested and this well was also clean. Mariano explained that the gasoline constituents found in the soil are "heavy" and do not migrate easily.
Mariano also said that the clean-up is held to the highest standards because Carlisle residents rely on wells for drinking water. This explains the high cost of clean-up, said Mariano. "In an area like Carlisle where you have to deal with high standards, the costs are tough."
Police station clean-up
It is because of the high clean-up standards that the police station remediation cannot yet be closed, said Mariano. Mariano reported that benzene levels are still bouncing around the acceptable minimum level and must remain consistently below this level before the case can be closed. Selectman Doug Stevenson suggested that bioremediation may be useful at this site too.
"In an area like Carlisle where you have to deal with high standards, the costs are tough."
© 1999 The Carlisle Mosquito