Tarnation: National Grid files plan to keep gooey tar left over from the way its predecessor used to make gas from continuing to ooze out of the site now better known for the Ho Chi Minh tank

National Grid is seeking city permission to excavate the remains of a large Dorchester tank that still holds two to three feet of coal tar nearly 90 years after it was last used to store waste from the creation of the coal gas that once lit and heated many Boston homes.

The Boston Conservation Commission on Wednesday begins a hearing on the utility's plans to mix the tar in the former 80-foot-diameter tank with a form of grout, creaing a "monolith" that would no longer ooze through the ground under Victory Road from the company's 35-acre parcel off Victory Road and the Southeast Expressway, today better known as home to the world's largest copyrighted artwork on the side of the company's LNG tank.

National Grid needs commission approval because the site is near the shoreline of Dorchester Bay. The company says that once it solidifies the tar, it will begin to plan out how to remove the tar that has oozed under and past below Victory Road.

The roughly 80-foot-diameter tank could actually date back as far as the 1880s, when one of National Grid's predecessor companies used the site, then known as Commercial Point, to heat up coal. This released a mixture of carbon monoxide and hydrogen that was then distributed through mains, similar to the way natural gas is today. Coal-gas production ended in the late 1930s as utilities switched to natural gas - basically methane. At one point, the plant generated up to 8 million cubic feet of gas a day.

In its filing, the company says that the coal-gas operation left behind "coal tar residuals, petroleum hydrocarbons, and various other contaminants" at the site. It says construction workers during a project between 2016 and 2019 rediscovered the tank when they uncovered "a partially demolished and buried steel walled tar tank" as well as a separate "historical tar disposal area" underneath an area of the site that is now home to solar panels.

The tar tank is located approximately two feet below the existing surface grade near the road at the bottom of a steep sloped area that increases in elevation to the north toward the LNG facility property. The tank is located between 1 and 10 feet below ground surface (bgs) within this sloped area, requiring pre-excavation to access the buried structure for the remedial work. Review of historical plans, geophysical surveying, and test pitting of the tank area indicates the buried tank is approximately 80 feet in diameter and extends to approximately 10 feet bgs near the base of the slope adjacent to Victory Road. The tank was constructed of riveted steel that is approximately 1/4-inch thick and contains up to two to three feet of coal tar-saturated material in the bottom of the soil and debris-filled structure. Gauging data from groundwater monitoring wells installed within Victory Road south of the tank have indicated the presence of residual coal tar liquid at depths of greater than 40 feet bgs. In order to achieve permanent Site closure, the buried tar tank and the residual coal tar in the buried structure must be addressed to eliminate the source of coal that has been detected outside of the tank along Victory Road. This Project does not include planned activities to address the deep coal tar under Victory Road, which will be addressed after completion of the planned remedial construction work.

The company's proposed work includes using a current landscaped area for staging, digging up topsoil that can be reused after the work and storing it on site, along with any trees that can be saved, on what is now the landscaped area, digging down to the bottom of the tank, pumping out any water and then doing "stabliization/solidification" of the gunk so it can no longer spread through the ground. Once done, the site would be re-covered, graded and re-seeded - with the removed trees replanted.

To solidify the tar, workers will pump "a grout mixture" into "mixing cells" at the bottom of the tank, until all of the tar "has been solidified creating a continuous monolith
of the stabilized material" that will no longer be able to ooze outside the tank.

In addition, it is anticipated that the Contractor will construct two temporary roads within the Landscaped Area – a lower access road to provide access to the former tar tank where remediation is necessary, and an upper access road leading to the Material and Equipment Staging Area.

Not to pressure the Conservation Commission or anything, but National Grid says it has to finish the work by next spring, to make way for "an essential infrastructure project at the LNG facility later that year." The company says that if it begins site preparation in September, it can get the tar solidified and the site back to what it used to look like by March or April - with grass and tree planting in May.

Complete filing (35M PDF).