ARCHIVED REPORTS_MONITORING WELL M-10 INVESTIGATION REPORT 2010

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M-10A Investigation Report November 30, 2010 Nestle USA, Inc., Ripon, California the Site, (screened in Upper Aquifere). That well may have influenced the groundwater flow direction beneath the southern portion of the Site to the west/southwest when pumping at times when the Nestle supply wells N-1 and N-3 were not pumping. Historical pumping of all of these wells and Nestle's on-site industrial wells (which comprise the single largest water production center in the Study Area between 1960 and 1980), would have resulted in a very complex and dynamic flow system within the Upper Aquifer. Additionally, wells screened across multiple zones could have acted as vertical conduits of COC movement during periods of inactivity. Due the variability of both on- site and offsite well pumping histories and limited data in the Upper Aquifer A zone between the Site and well M-10A to the northwest, ECM concluded that additional subsurface data was needed to understand the concentration variation in well M-10A and the movement of COCs in this area. 2.3 OBJECTIVES Based on this review of historical data presented in Section 2.2, ECM and AMEC Geomatrix proposed a field investigation in the vicinity of M-10A. The primary objectives for conducting this investigation were: 1) to evaluate potential explanations for the recent concentration increase in well M-10A; 2) to evaluate the potential influence of historical pumping activities on the COC concentrations in well M-10A; and 3) to delineate the extent of CDCs in the vicinity of well M-1 OA. The investigation approach will be discussed further in Section 2.4. 2.4 APPROACH ECM and AMEC Geomatrix jointly recommended use of the Cone Penetration Test (CPT) in situ technology for this investigation because it provides a continuous profile of soil type with depth as the CPT probe (also called a piezocone) is advanced through the subsurface using a truck-mounted hydraulic ram. Soil type (e.g., sand versus clay) is inferred from sensors that measure stresses on the piezocone as it is advanced through the soil column, and a computer algorithm converts these stresses to soil type. The operator receives this information in real-time and provides it to a field geologist for review and interpretation. ECM elected to use this technology in conjunction with Rockworksf software to prepare lithologic cross-sections in the field, allowing for field decisions regarding sampling depths. The driller advanced a Hydropunch° groundwater sampling device directly adjacent to each CPT borehole and collected discrete groundwater samples at each target depth. In conjunction with this real-time analysis, ECM requested expedited turn-around-times from the laboratory so the latest sampling data could be used to make informed decisions about sample locations and depths in subsequent borings. By employing these methods, ECM was able to select step-out (delineation) CPT locations in areas where targeted sample intervals would provide the most relevant information for the overall investigation. e Screen interval unknown; total well depth terminated at 115 feet bgs. f Rockworks is a licensed product of Rockware, Inc. Geologic and GIS Software. 3