Jet Grout Silo Pad Demolition

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. In addition, the WM contractor completed the disassembly and load out / demobilization of the temporary enclosure structure (tent) and the associated air handling system (two remaining of the four TIGG units). The WM contractor continued the removal of the jet grouting working asphalt platforms from the site.

General maintenance and security activities also continued at the Site. Contractor demobilization of construction equipment and materials commenced. 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 11, 2012 through June 17, 2012, six 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. Since site intrusive work has been completed and as approved by NYSDEC, future CAMP operations will only measure PM10 and the total volatile organic compound (TVOC) measurements were suspended on June 3, 2012. On June 15, 2012, a PM10 exceedance was measured for one 15-minute time interval during which a corrective action was implemented for the Site Wide Cap remedial action (i.e., subgrade preparation task).

For the week of June 18, 2012 through June 22, 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 demolition of the former jet grout plant silo reinforced concrete pad, with off-site transport and disposal at an NGRID approved and permitted material recycling facility. The WM contractor will commence the final Site Wide Cap subgrade preparation operations at the northern part of the Site. Six fixed base CAMP units will be in operation to measure PM10. Dust suppression activities will be conducted, as necessary. The contractor will perform general maintenance activities and housekeeping at the Site, as necessary.