National Grid developed the June 2018 Remedial Action Work Plan (RAWP) which summarizes the results the results of the 2017 Limited Design Investigation (LDI) program to supplement the existing available data, provides technical details on the Site remedy, describes Best Management Practices and the air monitoring program to be implement during construction remedy, and outlines a schedule for execution. 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 apparent source materials from three areas. These source area excavations include an approximately 100 square foot area proximate to a former underground tank (UGTT-1); a wooden raceway area which includes various sized piping and two concrete structures/vaults formerly used to transfer petroleum between portions of the Site; and an approximately 750 square foot area of fill impacted with crystallized naphthalene in the northern portion of the Site.
- Installation of engineered controls (caps and fencing) to mitigate direct contact with impacted soils and prevent tracking and erosion of materials. Approximately 50% of the engineered cap will also be designed to be impermeable to mitigate further degradation of groundwater quality. Construction of these engineered caps will require significant regrading of the Site to create a relatively uniform surface sloping down from the western edges of the Site to the river. An engineered cap will not be installed within the heavily wooded and steep slopes along the southwestern and western portions of the Site due to concerns regarding destabilizing the banks and removing mature trees along portions of the Site perimeter. Access to these slopes will be restricted via the installation of additional chain link fencing which will serve as an engineered control.
- Installation of an approximately 1,300-foot long subsurface containment wall along the eastern (downgradient) edge of portions of the Site to mitigate the potential migration of NAPL impacts towards the Seekonk River. A portion of the containment wall will be installed outboard of the existing bulkhead walls within the Seekonk River to also serve as a replacement to the existing deteriorated bulkheads. The containment wall will consist of steel sheet pile walls with sealed interlock joints driven or vibrated into the ground using a crane mounted hammer.
- Post-remedial groundwater monitoring, cap and wall inspections and maintenance, and NAPL gauging and recovery.
- Environmental Land Usage Restrictions (ELURs) will be placed on the property records that outline certain use restrictions for the parcels that comprise the Site. The ELURs will include an integral Soil Management Plan (SMP) that establishes the procedures and provisions should future construction/maintenance activities at the Site require the need to disturb soils beneath the engineered caps and within the areas restricted by the engineered control fencing. The SMP serves to supplement, and will be initiated by, the RIDEM notification requirement established by the ELURs for the Site.
The complete Remedial Action Work Plan (RAWP) can be found in the Documents tab of this website.