Remediation for Town Historical Commission

SCOPE OF WORK: LSP services, assessment, and remediation at a historical building

A release of #2 fuel oil from an aboveground storage tank (AST) occurred in the basement of a building constructed circa 1715, which is under the protection of the local historical commission as a historical asset and historical artifact museum. Omni Environmental Group was retained by the Town’s insurance company to provide Licensed Site Professional (LSP) services, design and oversee a remedial program, and achieve regulatory closure under a Release Abatement Measure (RAM) and the Massachusetts Contingency Plan (MCP – 310 CMR 40.0000).

Petroleum-contaminated soil (PCS) was identified in a 12 square foot area in the basement, abutting two sides of the field stone foundation, extending up to 9 feet below floor grade. Due to the age, construction, and condition of the field stone foundation; lithology of the sandy soils; and overall historical significance of the building; we utilized a Structural Excavation Plan (SEP) to allow for remediation while maintaining the historic integrity of the building. The SEP included narrow concrete underpins performed in two vertical passes beneath affected portions of the field stone foundation; crib towers and beams supporting the wood framing of the building; and construction of a shoring system to allow for the removal of deeper impacted soils.

Through successful implementation of the SEP and remedial action, a significant mass of contaminated soil was removed from beneath the basement, to a maximum depth of 7 feet below floor grade. Although residual PCS remained at depths and could not be excavated due to concerns for worker safety and structural stability, residual PCS was limited in extent, well-defined, and determined not to represent a threat of impact to groundwater. Following remedial actions, the basement was fully restored to pre-existing conditions.

In order to evaluate the potential for residual PCS to impact indoor air via the vapor intrusion pathway, two soil gas points were installed within the footprint of the basement. Post-excavation soil gas data indicated that air-phase petroleum hydrocarbons was not present at levels exceeding the MassDEP sub-slab soil gas screening values for residential usages.

The subsequent risk characterization concluded that a condition of No Significant Risk existed and supported the submission of a RAM Completion and Permanent Solution Statement with No Conditions to MassDEP in accordance with the MCP.