Background

On May 8, 2012, PG&E submitted to the California Regional Water Quality Control Board, Lahontan Region (Water Board) the Work Plan for Installation of Upper Aquifer Monitoring Wells to the west of Mountain View Road. Following were the three primary objectives of the proposed work scope:

• Evaluate groundwater gradients in the Western Area, particularly in the vicinity of the Lockhart Fault.
• Collect groundwater samples for laboratory analyses for Cr(VI) and Cr(T).
• Initiate the installation of wells to be used to support the Work Plan for Evaluation of Background Chromium in the Groundwater of the Upper Aquifer in the Hinkley Valley (February 2012 Background Study Work Plan.

With verbal concurrence from the Water Board, the scope of work proposed in the work plan was initiated in August 2012, and monitoring well installation, groundwater sampling, and laboratory analysis of chromium samples has been completed. On November 19, 2012, PG&E submitted to the Water Board the Preliminary Reporting of Geology and Hydrology for Investigations in the Western Area, which presented the geologic and hydrologic data collected from the newly installed wells; the chromium data was not yet available when the report was submitted.