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M-10A Investigation Work Plan Addendum October 28, 2011 Nestl6 USA,Inc.,Ripon, Califomia 1 INTRODUCTION On behalf of Nestle USA, Inc. (Nestle), Environmental Cost Management, Inc. (ECM) has prepared this M-10A Investigation Work Plan Addendum (Work Plan)for the California Regional Water Quality Control Board-Central Valley Region (RWQCB). ECM proposes additional investigation activities to the west and northwest of previous CPT investigations at the Site and in the vicinity of the M-10 nested wells. The investigation is intended to complete the subsurface characterization, which was initiated in 2010 to characterize concentrations of trichloroethene (TCE) and associated byproducts ("constituents of concern" or "COCs") in groundwater in the vicinity of well M-10A. The 2010 investigation was triggered by an increasing trend in COC concentrations at monitoring well M-1 OA'. ECM will employ cone penetrometer test (CPT) methods to evaluate lithology at each groundwater sampling location, and collect groundwater samples using hydropunch-type sampling methods. A contract laboratory will analyze the samples for COCs, allowing ECM to assess groundwater conditions in each of the borings. 2 BACKGROUND ECM conducted an initial investigation in October 2010 to assess the cause of an increase in COC concentrations at well M-10A. The 2010 investigation was supplemented by a previous CPT investigation conducted in 20052. The investigation report was submitted to the RWQCB on November 30, 2010. The RWQCB commented on the report and requested additional investigation in a letter dated August 31, 201 13. During a meeting between Nestle, ECM, AMEC-Geomatrix, and RWQCB representatives on August 22, 2011, participants agreed that further investigation is necessary to delineate the extent of COC-affected groundwater northwest and west of the M-10 monitoring well nest. 3 INVESTIGATION OBJECTIVES AND APPROACH The objectives of this Work Plan are to further characterize the distribution of COCs to the northwest and west of the M-10 well nest by: 1) Completing the A Zone characterization; and 2) Defining potential geologic pathways for transport of TCE and its degradation products in the C Zone. ECM will focus data collection and investigation activities in the following locations: • The M-10 monitoring well nest • The M-13 monitoring well nest • The M-28 monitoring well nest • City of Ripon supply well MW-3 • Ripon Public School well RPS-1 As requested by the RWQCB 4, ECM has prepared and analyzed additional geologic cross sections along 10 transects, A-A' through J-J' (Figure 2), to assist with recommendations for the placement of additional soil borings and monitoring wells in these focus areas. Proposed boring and sampling locations are indicated on Figure 2. ECM will use the subsurface information 3