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Pilkington North America, Inc. - 2- 10 September 2015 1) Selection of several down-gradient grab groundwater sampling points. 2) Implement a temporary high vacuum DPE groundwater remediation system instead of j ongoing LNAPL skimming procedures to address the free-phase petroleum and petroleum impacted soil. 3) Modifications to the proposed Work Plan recovery well installations. In place of installing larger diameter recovery wells for ongoing LNAPL skimming, the recovery wells are proposed for use as part of a temporary high vacuum(vacuum pump capable of producing 25 to 27 inches of mercury) DPE groundwater remediation system. The DPE groundwater remediation system is anticipated to operate for three months to remove free-phase hydrocarbons and known soil plume from the vadose, capillary fringe and upper saturated zones. 4) Installation of two soil pilot borings for implementation of additional remediation wells. 5) Complete weekly maintenance and usage operation of remediation equipment. 6) Submit semi-annual monitoring reports and quarterly remediation summary reports. Regional Water Board Comments: 1. The Work Plan proposed to investigate the deeper target zone by extending vertical sampling at two of fourteen locations 20 to 60 feet bgs (after first groundwater, typically 10-15 ft bgs) and collect continuous core samples at up-gradient and cross-gradient locations to determine subsurface geology and grab groundwater at both shallow and deep sampling points. Regional Water Board requested specification of when vertical sampling of the deep zone will occur. The WP Addendum proposes to extend vertical sampling to three of fourteen locations up to 40 ft bgs. The-WP Addendum states that the deep zone is presumed deeper than 30 ft bgs and not anticipated to extend past 40 ft bgs, however, no information is provided to support this presumption. Regional Water Board wants to ensure adequate vertical delineation to define potential migration of release to deep strata. Please discuss rational for reducing the vertical extent of deep zone investigation from 60 ft bgs to 40 ft bgs. 2. The WP Addendum includes a recommendation for installation of the soil borings after completion of the soil and groundwater remediation in order to finalize the plume delineation and provide field verification of the soil and groundwater remediation. Regional Water Board staff do not concur with this recommendation due to the need to delineate the PCE plume to fill in site conceptual model data gaps prior to implementation of the soil and groundwater remediation system. Evaluating the borings before remediation system startup provides the project baseline PCE concentrations prior to remediation activities that allow for quantification of remediation system removal efficiency and other important.operating parameters. Confirmation sampling will be needed following remediation activities as part of site closure request evaluation process.