National Grid developed the July 2011 Remedial Alternative Evaluation (RAE) which assessed several approaches to address the findings of the Site Investigation Data Report and meet the Remedial Objectives for the site. The remedial technologies were evaluated for effectiveness, short- and long-term impact on the community, technological capability, and cost, among other factors. National Grid’s proposed remedy is designed to mitigate identified potential exposure pathways and risks to human health and the environment. This proposed remedy includes the following:
- Excavation and off-site disposal of limited source material. The former tank (UGGT-1), raceway structures and an area of crystallized naphthalene encountered during the 2010 site investigation in the northern-most portion of the site would be addressed via physical removal and off-site disposal.
- A below ground containment wall (approximately 1,600 linear feet) would also be installed along the eastern (downgradient) edge of the site proximate to the Seekonk River to mitigate potential migration of NAPL impacts towards the river. Focused NAPL recovery would be performed immediately upgradient of the wall from a series of newly installed recovery wells and in other site areas where NAPLs have accumulated in monitoring wells.
- An engineered cap would be installed to mitigate potential direct exposure to impacted soils, potential erosion and tracking of impacted surface soils, and contributions to the further degradation of groundwater quality. With the exception of the northern-most portion of the site, this cap would consist of an impermeable cap comprised of up to 2 feet of clean soil underlain by a geomembrane or clay material. The cap on the northern-most portion of the site would consist of a one-foot thick permeable soil cap underlain by a geotextile. Institutional controls (an Environmental Land Use Restriction) would be applied to the site which would include restrictions on the use of the groundwater at the site, restrict use of the site, and guidelines on disturbance and maintenance of the engineered cap.
- Post-remedial groundwater monitoring, cap and wall inspections and maintenance, and NAPL gauging and recovery.
The complete Remedial Alternative Evaluation (RAE) can be found in the Documents tab of this website.