Treatment of a Chromate-impacted Water-bearing Unit in Ogallala Sediments, Southern Lea County, New Mexico

Tischer, Steven P.

ARCADIS, Midland, TX

A natural gas processing facility located in Southern Lea County, New Mexico had a historic release associated with cooling tower water that has produced a large chromate groundwater plume.  The saturated zone hydrogeology is complex and located within the Tertiary Ogallala Formation.  In the former release area there are three distinct hydrologic units that exhibit limited vertical connectivity.  As the chromate groundwater plume migrates eastward the units thin, ultimately join and then the flow regime is dominated by the configuration of the relict erosion surface of the underlying bedrock that is comprised of the Triassic Chinle Formation.  An in situ remediation program based on injection of a carbohydrate-mixture is being implemented at the site.  In the former source area three distinct pilot programs are underway in each of the identified hydrologic units.  At the distal end of the plume, an array of injection wells has been installed for groundwater plume cut off.  Key elements in the injection program include hydrodynamics under batch and continuous injection and the life span of the injection reagents.  The varying size of the chromate plume has recently be measured to be approximately 4,400 feet (1,341 meters) in length and to have a width of 1,400 feet (427 meters). Given the size of the plume and viable conventional surface based chromate treatment the application of an in situ solution offers site closure at significantly lower costs and less time.