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Austin Road Landfill Section 1 Contaminant Plume Characterization Report Introduction at a later date,MW-14. No VOCs were detected in the groundwater sampled from these wells at the time of installation. Subsequent monitoring of the well network conducted in 1996 indicated the presence of VOC contamination in wells MW-13 and MW-14. Based on this data,confirmed over several rounds of sampling,the CVRWQCB directed the City to implement a program to modify the corrective action system to achieve remediation objectives of containing the spread of the VOC plume. In correspondence dated March 7,1997,the CVRWQCB required the City to submit an amended report of waste discharge(AROWD) to bring the landfill into compliance with Section 2550.100)of the Article 5 regulations. This was to be accomplished through a field investigation to delineate the vertical and horizontal extent of contamination and to evaluate the effectiveness of the existing pump-and-treat system. CDM was selected by the City to conduct the program required by the CVRWQCB. An Investigation Work Plan,dated September,1997,detailing the scope of the field program was approved by the CVRWQCB in October 1997. The field program was initiated at the end of 1997 and concluded in July 1998. This report documents the activities and findings of the field program. 1.3 Program Objectives The objectives of the plume delineation investigation,as established in the approved Work Plan,are listed below: (i) Define the current nature and horizontal and vertical extent of the VOC contaminant plume at the ARL. (ii) Determine the effectiveness of the existing corrective action system in achieving program goals. (iii) Estimate the rate and direction of contaminant plume movement in the aquifer. (iv) Prepare an Engineering Feasibility Study(EFS) documenting the evaluation of alternatives to modify the existing groundwater remediation system. Objectives(i)through(iii)are addressed with the submittal of this report. The EFS will be conducted after regulatory review has been completed of the Contaminant Plume Characterization Report. 1 .4 Report Organization This report documents the field procedures,methodologies,and results of CDM's groundwater contaminant plume investigation at the Austin Road Landfill. The report is structured into six sections,including this introduction,as described below. Section 2.0 Investigation Methods Section 2 presents the methodologies and procedures in performing the groundwater investigation and plume characterization. A description of the techniques used to construct boreholes and ® CDM Camp Dresser&McKee CS 01 1-2 W:WSPORTSISTOCKTOMARLPLUMESMECt.WPO ®7 5 9 -- City of Stockton 190855-0006