Friday, May 28, 1999
Next step in clean-up of former gas station site to begin soon
By the end of this month, engineers for the Daisy family will begin drilling test wells on their Lowell Street property to collect additional data to further develop an appropriate remedial response action for contamination at the site, according to family representative Alice Daisy. Three underground storage tanks (USTs) and approximately 300 cubic yards of contaminated soil were removed from the ground last December. The soil was stockpiled at the site and removed earlier this spring.
The Daisys' licensed site professional, 21E, Inc., recently submitted to the state Department of Environmental Protection (DEP) a modified proposal for cleanup of the site based on analysis of the data obtained from the December excavation. This plan calls for installation of two monitoring wells on the eastern property line in an area downgradient from the former storage tank location. Another well couplet will be installed in the area near the former dispenser island, an area which has historically indicated impacted groundwater, according to the 21E, Inc. report. A bedrock well will also be located in front of the service station to determine groundwater flow direction and provide a location to collect groundwater. A final well is proposed for the area north of the former tank location to collect additional hydrologic information.
Following installation of the wells, the 21E, Inc. plan proposes collection of a round of groundwater samples. These samples will be analyzed for several volatile organic compounds, including methyl tertiary butyl ether (MTBE) which has previously been found at the site. Secondly, a pump test will be performed to determine the capacity of the well installed east of the former storage tanks. The 21E, Inc. plan indicates that this test may have an impact on the water level in neighboring wells due to the large amount of groundwater potentially pumped. According to 21E, Inc., groundwater removed during these tests will be transported to and disposed of at an approved off-site facility.
A remediation plan will be developed based on the data collected during the pump test. Treatment options include pumping from groundwater collection wells into a central treatment system which would be located in the former service garage. A groundwater depression system coupled with a soil vapor extraction system would also be part of the remediation plan, according to 21E, Inc.
Board of health response
The board of health has reviewed the 21E, Inc. proposal through its consultant at ENSR and has made the following comments to DEP. First, ENSR recommended further assessment be conducted to the south and west of the former storage tanks given the high concentrations of contaminants found in this area and indications of westerly groundwater flow. ENSR also suggested locating one of the monitoring wells directly underneath the former dispenser island, the location of the highest concentration of contaminants. Further, ENSR felt that the location of the pump test should not be finalized until all proposed wells are installed and sampled. Finally, ENSR questioned the proposal for a soil vapor extraction system to address the remaining elevated petroleum concentrations at the site because of the poor permeability of the soil.
Daisy added that financing for the cleanup will be provided by North Middlesex Savings Bank. The project is eligible for partial reimbursement from the state under the so-called 21J fund program.
Full reports on the Daisy site contamination and response actions are available in a large white binder at the Gleason Public Library's temporary location at 872 Westford Street.
© 1999 The Carlisle Mosquito