ARCHIVED REPORTS_SITE CONCEPTUAL MODEL 2009

Home Browse Search

amec— SITE CONCEPTUAL MODEL — JANUARY 2009 UPDATE Former Nestle Facility and Surrounding Area Ripon, California 1.0 INTRODUCTION Predecessor companies of Nestle USA, Inc. (Nestle) manufactured dairy, coffee and tea products between the 1930's and 1995 at 230 Industrial Avenue, in the City of Ripon, California, which is located in southern San Joaquin County (the Site and surrounding Study Area are identified in Figure 1). Chlorinated volatile organic compounds (VOCs), primarily trichloroethene (TCE) and its less-chlorinated degradation products, were detected in groundwater samples from two onsite industrial water supply wells and two offsite municipal supply wells in 1986 (RUST, 1994a). Because TCE had historically been used in the manufacturing operations, TCE and other VOCs became the major constituents of concern (COCs) in groundwater beneath the Site and offsite. These CDCs have been the subject of characterization, monitoring and remediation over the past two decades, under oversight by the California Regional Water Quality Control Board, Central Valley Region (Water Board). Nestle installed and/or monitored 124 groundwater monitoring wells in the Study Area and conducted several phases of soil and groundwater remediation among other response actions. The existing monitoring well network covers an area greater than 2 square miles, lying mostly within the City of Ripon, and includes 10 monitoring wells south of the Stanislaus River, in Stanislaus County. VOCs have been detected in monitoring wells installed at depths of approximately 40 feet below ground surface (bgs) to greater than 200 feet bgs, with the majority of detections in groundwater samples from wells located hydraulically upgradient (south and east) and cross-gradient (west) of the Site (within the Study Area shown in Figure 1). Because the spatial distribution of CDCs is not consistent with the typical "one source, one plume" conceptual model that is commonly applied to environmental sites, Nestle expanded and updated the Site Conceptual Model (SCM) to address the origin, fate, and transport of COCs in groundwater over the past fifty years or more, with the overall intention of strengthening the technical basis for decisions made by the project team with respect to managing the Site in the near future. AMEC Geomatrix Inc. (AMEC) revised the SCM (the last revision was in 2006; ECM, 2006) at Nestle's request, and joined Environmental Cost Management, Inc. (ECM), and other representatives of Nestle in an October 1, 2008, meeting with Water Board staff at their offices in Rancho Cordova, California, to communicate the major components, findings, and implications from the SCM revision. Water Board staff requested that this most recent revision of the SCM be available as a hard copy report. This AMEC Geomatrix, Inc. I:\Doc_Safe\9000s\9837.005\4000 REGULATORY\SCM_01.30.09\1_text\SCM Report Final.doc 1