The effects of agricultural activities on the migration of the Hinkley chromium plume, San Bernardino County, California

The hexavalent chromium (Cr VI) plume in the Hinkley Valley, located in the Mojave Desert of Southern California, has proven to have adverse effects on the local groundwater supply. The Cr VI plume is a result of the operations from Hinkley Natural Gas Compressor Station. The station began treating the gas lines with a corrosion inhibitor that contained Cr VI and discharged the corrosion inhibitor to unlined ponds and trenches after the treatment. The local Cr VI plume that is in the Hinkley Valley today is the result of the years of discharge from the Hinkley Compressor Station.;In order to protect the groundwater not affected by the plume, the boundary of the plume must be accurately delineated. This research evaluates the eastern area of the Hinkley Valley where the majority of the agricultural activities (dairy farms and alkalfa fields) occur. The hypothesis is that this agricultural activity has impacted the Cr VI plume migration to the east. The groundwater elevation data from MW-01 ranged from a maximum of 647.63 meters (m) above mean sea level (AMSL) in 2009 to a minimum of 643.12 (m) AMSL in 1993. The remaining groundwater monitoring wells showed a similar change in elevation over the sampling period. The results showed that the groundwater flow direction was primarily to the northwest with small shifts to a west northwest direction. The groundwater elevation data showed evidence of a change in groundwater gradient from 0.006 in 1989 to 0.004 in 2012. There was no evidence that the agricultural activities had any adverse effects on the groundwater flow direction.