Jet Grouting Operation for 120 foot deep barrier wall.

National Grid’s contractor and Project Team continued to construct the composite 120-foot deep dense non-aqueous phase liquid (DNAPL) Migration Barrier Wall (i.e., jet grouted barrier). The contractor continued the Production Jet Grouted Column Barrier Wall Installation Program. Further, the contractor continued the management of jet grouting derived wastes within the Waste Management Facility (WMF). The WMF, which manages wastes (e.g., soils, cement mix and water) that are generated from jet grouting activities, is operated inside the tent with an active Vapor Management System (VMS). Jet grouting wastes were managed in accordance with NYSDEC approved procedures and wastes were disposed of off-site at a licensed and permitted disposal facility. General maintenance and security activities also continued at the Site. Attached is a representative photograph of the jet grouting operations.

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 March 26, 2012 through April 1, 2012, six fixed base CAMP units were in operation and measured total volatile organic compounds (TVOC) and particulates (PM10). Fifteen-minute averages for PM10 and TVOC data remained in the Operational Condition except for a short period of TVOC exceedance on Friday, March 30, 2012. TVOC concentrations at FAM 1 located at the northern part of the site were measured above the National Grid Site Response Limit but below the New York State Department of Environmental Conservation (NYSDEC) and the New York State Department of Health (NYSDOH) Action Limit of 25 parts per million (PPM). The elevated TVOC concentrations measured onsite were the result of jet grouting operations in the area of FAM 1. The site was placed in the Action Condition for a period of less than ten minutes until TVOC concentrations returned to levels below the National Grid Site Response Limit. The Weekly Report that summarizes the CAMP data can be found as a separate tab in the Weekly Report Archive section.

For the week of April 2, 2012 through April 6, 2012, the contractor is scheduled to continue the Jet Grouting Production Program and Quality Control (QC)/Quality Assurance (QA) Testing Program. Further, the load-out of the jet grouting derived wastes is scheduled to continue throughout the week. Dust suppression activities will be conducted, as necessary. The contractor will perform general maintenance activities and housekeeping at the Site, as necessary.