Remedial Action Plan Amendment, Plessey Micro Science

Remedial Action Plan Amendment, Plessey Micro Science

PRoject consists of DTSC approval of Remedial Action Plan Amendment for Plessey Micro Science (Site) prior to residential development. The Site occupies approx. one acre, within the Mora Drive Residential Project of approx. 5.15-acres. The City of Mountain View (City) approved the development of 75 three-story row houses, consisting of 61 attached and 14 detached units, each containing two to three bedrooms and garages. The City prepared an IS/MND. The City approved the MND on Jan. 5, 2016 with mitigation measures addressing air quality hazards and hazardous materials, noise, and utilities. Since the Site is within the Mora Drive Residential Project, DTSC, as the CEQA Responsible Agency, is utilizing the MND for the Remedial Action Plan Amendment CEQA analysis. DTSC approved the May 1991 Remedial Action Plan which required the removal of underground storage tanks, removal of soil impacted with volatile organic compounds (VOCs), and construction and operation fo soil vapor/groundwater treatment system. The system operated from 2002 to 2009, and was modified in 2005 to include in-situ Hydrogen Release Compound (HRC) injections as an enhanced remedy in order to speed up the cleanup. After Plessey Micro Science went out of business and shut downt he treatment systems in late 2009, DTSC took over the cleanup. DTSC has conducted semi-annual groundwater monitoring to evaluate the effectiveness of the previous injections and conducted additional injects in 2013. The remedy continues to work well as VOC concentrations continue to decrease. HRC injections have helped to expedite the cleanup, but DTSC needs to do additional injections to meet the cleanup goals. In addition, excavation of contaminated soil beneath former buildings at the Site has become feasible since they were demolished in anticipation of future development. A formal amendment to the May 1991 Remedial Action Plan is necessary to achieve a cleanup suitable for future residential land use. Cleanup actions as proposed in the Remedial Action Plan Amendment include excavation of an estimated 1,800 cubic yards of soil contaminated with metals and VOCs at depths up to 12 feet below ground surface for off-site disposal at permitted facilities, injection of chemical to enhance reductive dechlorination in groundwater at targeted areas, and establishment of a land use covenant to restrict groundwater usage and to require vapor intrusion mitigation systems for new buildings if necessary based on future data. Field activities are anticipated to be completed in four weeks.

Mountain View

Santa Clara