Site wide cap after barrier installation

National Grid’s contractor and Project Team completed the construction of the composite 120-foot deep dense non-aqueous phase liquid (DNAPL) Migration Barrier Wall (i.e., jet grouted barrier) in April 2012. The Waste Management (WM) contractor continued the process of decommissioning and demobilization of construction equipment, supplies and materials associated with the on-site waste management operation. Further, the WM Contractor continued the demolition of the former jet grout plant silo reinforced concrete pad, with off-site transport and disposal at a National Grid approved and permitted material recycling facility. In addition, the WM contractor commenced the final Site-Wide Cap sub-grade preparation operations along the north central part of the Site. Attached is a photograph of the Site-Wide Cap construction activities.

General maintenance and security activities also continued at the Site. . Maintenance of the imported backfill material (i.e., clean fill) stockpile covers and soil erosion and sediment control (SESC) measures continued. Odor and dust suppression activities were conducted, as necessary. National Grid’s consulting engineers continued to monitor the site activities with the community air monitoring program (CAMP) equipment.

During the period from June 18, 2012 through June 24, 2012, one portable and five fixed base CAMP units were in operation and measured particulates (PM10). Fifteen-minute averages for PM10 data remained in the Operational Condition. The Weekly Report that summarizes the CAMP data can be found as a separate tab in the Weekly Report Archive section. On June 20, 2012, a PM10 exceedance was measured for one 15 minute time interval during which a correction action (i.e., dust suppression with water) was implemented during the Site-Wide Cap subgrade preparation activity.

For the week of June 25, 2012 through June 29, 2012, the WM Contractor will continue conducting decommissioning and demobilization of the construction equipment, supplies and materials associated with the on-site waste management operation. Further, the WM contractor is scheduled to continue the final Site-Wide Cap sub-grade preparation and Site-Wide Cap construction operations along the north central part of the Site. Dust suppression activities will be conducted, as necessary. The contractor will perform general maintenance activities and housekeeping at the Site, as necessary.