A confidential client selected GZA to perform turnkey remediation of a former manufactured gas plant (MGP) where soil impacted by coal tar had contaminated groundwater at the site. The site’s location in a densely populated area necessitated additional monitoring. Compliance with the Massachusetts Contingency Plan (MCP), cost-effectiveness of the remedy implementation, and environmental impact during construction were the key client considerations.


After GZA’s site investigation, contaminant delineation, and evaluation of remedial alternatives, the selected remedy was in-situ stabilization/solidification (ISS) of the coal-tar-impacted soils from depths of approximately 3-15 feet below existing ground surface. GZA performed full-time remediation oversight and construction management for hazardous materials abatement/building demolition and implementation of ISS activities to verify compliance with specifications and regulatory and quality control requirements; maintain a perimeter air monitoring system; and coordinate construction activities and health and safety procedures with sub-contractors. GZA’s re-use of crushed building materials to limit off-site disposal and the excavation and stockpiling of surficial soil to re-use as backfill were two cost-saving measures. An analysis GZA prepared for the client using EPA’s Environmental Footprint Analysis (SEFA) methodology indicated that the ISS remedial approach reduced carbon dioxide equivalents by a factor of approximately seven in comparison with an excavation, removal, and thermal desorption remedial alternative. GZA also evaluated the feasibility of using ISS to stabilize petroleum-related light non-aqueous phase liquid (LNAPL) plumes on other properties to reach site closure.


From site investigation and evaluation of remedial alternatives to project close-out, GZA provided the broad range of environmental, engineering, and construction management services to successfully remediate the site, navigate the regulatory process, address stakeholder concerns, and moderate the client’s environmental footprint.