Remediation

Chromium in the periodic table.

There are mainly three types of methods to remediate hexavalent chromium in ground water and drinking water: 1) reduction of toxicity, 2) removal technologies and 3) containment technologies.

Reduction of toxicity of hexavalent chromium involves methods using chemicals, microbes and plants. Some removal technologies include transporting contaminated soil offsite to a landfill, using ion exchange resins to reduce chromium(VI) concentrations to less than detectable limit and granular activated carbon (GAC) filter. Containment technologies can be employed with the use of physical barriers such as grouts, slurries or sheet piling.

But ground water is not the only place hexavalent chromium can be found. Since it is an element that cannot be destroyed, it has to either be physically removed by excavating soil or pumping and treating groundwater or transformed to the less toxic trivalent form and stabilized within the subsurface environment by forming insoluble and immobile trivalent hydroxide precipitates and iron and sulfide complex co-precipitates. Luckily, this transformation can be performed using many of the same injectable chemicals that are used at chlorinated sites for in-situ chemical reduction (ISCR) and enhanced reductive dechlorination (ERD).

The chemical reaction between hexavalent chromium and ZVI reduces the concentration levels of hexavalent chromium and creates a less toxic daughter product, or transformed version of the contaminant, called trivalent chromium. Trivalent chromium further reacts with other minerals in the subsurface to create less water-soluble compounds. The result is that the remaining chromium is less toxic, less soluble and less mobile in the environment. The resulting trivalent chromium impacted soil can remain in place without removal and with less concern of further migration of any remaining contamination.  (How Do You Remediate Hexavalent Chromium Cr(VI)? (enviroforensics.com)