HARWICH PORT — It took first responders many hours to control the public safety threat after a tanker truck flipped over and spilled gasoline on Sisson Road last month. But it will take cleanup crews much longer to try and reverse the environmental damage caused by the accident.
A New Hampshire environmental engineering firm has completed an immediate response action plan following the July 18 spill, outlining the cleanup and monitoring operations done so far as well as future actions. The plan calls for the excavation and cleaning of a small part of the marsh south of Route 28 and the installation of extraction wells to remove gasoline from the groundwater.
Drafted by Manchester-based Edge Environmental on Aug. 13, the plan provides an overview of the accident. At 3:49 a.m., the Delaney Fuel Transport truck hit a raised traffic island in the center of the road by the Star Market entrance and flipped over.
“The position of the tanker, the volume of gasoline still in the tanker and the loss of gasoline to the environment was a catastrophe with the potential for a larger catastrophic event,” the report reads. Crews built an impromptu berm around the tanker, but leaking gasoline still flowed along the edges of the road, entering catch basins. The fuel flowed through the stormwater pipes into a shallow swale behind 333 Route 28, which empties into a marsh that leads to Allen Harbor. Absorbent booms were placed in the swale, and as a precaution, in the adjacent marsh. An anti-pollution boom was also installed just north of the Lower County Road bridge at Allen Harbor.
The tanker was reportedly carrying 12,000 gallons of gasoline, and crews were able to pump between 8,175 and 8,500 gallons into another tanker truck. Environmental technicians recovered another 2,130 gallons of gasoline from storm drains and other locations, leaving between 1,370 and 1,695 gallons unaccounted for. Some of that fuel was caught by absorbent rolls and pads, and the rest entered the soil.
Crews sampled soil from 26 locations to judge the extent of the underground contamination, and found the highest readings in areas close to catch basins or where the berms retained gasoline. Lab results are still pending from some of the samples, and a series of monitoring wells have been installed for longer-term monitoring of the plume.
A focus of the cleanup will be the swale behind 333 Route 28, where crews saw gasoline pooling on the surface of the water shortly after the spill. Working from a property at the end of Glendoon Road, a contractor will use two track-mounted excavators, one at each side of the ditch, to dig out and remove contaminated soil. The swale is about 90 feet in length and 10 feet wide, so crews are prepared to remove as much as 67 yards of soil, enough to fill six large roll-off containers. Contaminated water will be removed from the soil, and both the soil and the liquid will be sent to hazardous waste processing facilities like ones in New Hampshire and Connecticut.
The excavation is tentatively planned to start on Sept. 2.
Crews also plan to excavate an area around a public water supply main after there were signs that gasoline had migrated into a fire hydrant. That work will be scheduled once soil and groundwater data is available from the laboratory.
If all goes according to plan, crews will also be installing larger-diameter extraction wells late this week to recover gasoline that is migrating through the sandy soil. Three wells will be installed in the sidewalk on the west side of Sisson Road, with three more along the edge of the east side of the road near Bud’s Go-Karts. Once installed, the wells will allow crews to rapidly pump out water and gasoline for testing and disposal. The mixture will be pumped into a truck and transferred into a special tank at the town DPW facility. The pumping is tentatively scheduled for Aug. 26, 28 and 30, after which time additional pumping sessions will be scheduled if needed.
During the cleanup effort, the absorbent materials in catch basins, manholes and other locations will be monitored each week and replaced if necessary.
The cleanup is being conducted under the guidance of Edge Environmental, which reports regularly to the state Department of Environmental Protection and to the Harwich Conservation Department. Harwich Conservation Agent Amy Usowski could not be reached for comment.
While the spill happened near an environmentally sensitive wetland, the public health risks are likely low. The contamination is not close to any public water supply wells, and the properties around the accident site all appear to be connected to the town water system.