Cronk, G. | Groundwater Resources Association Remediation Conference: Optimization of Remediation Systems and Long-Term Monitoring, 13-14 November, Santa Ana, CA, 17 slides, 2019

Multiple in situ remediation technologies were implemented over 25 years at a large, complex groundwater site in Los Angeles County that allowed for more rapid and cost-effective remediation. Two distinct but overlapping plumes of benzene and chlorinated compounds plus 1,4-dioxane required continual implementation of new remediation technologies over time. Treatment of the two plumes has been ongoing since 1995 through a combination of pump and treat, soil vapor extraction, in situ chemical oxidation (ISCO), and monitored natural attenuation (MNA). ISCO was implemented via direct push injections of hydrogen peroxide and later with sodium persulfate and achieved nearly complete removal of benzene (<5 µg/L). Multiple injections of potassium permanganate were performed on the chlorinated plus 1,4-dioxane plume over a two-year period. Robust aerobic populations of methane-oxidizing bacteria and mono-oxygenase enzymes were confirmed to be co-metabolizing the remaining levels of TCE, 1,1-DCE, and 1,4-dioxane. An MNA strategy was implemented to achieve the final cleanup of the plume. Since 2015, the TCE, 1,1- DCE, and 1,4-dioxane in key wells have attenuated by more than 50% due to aerobic microbiological degradation. The total savings using these innovative technologies as opposed to pump-and-treat is estimated to be over $1 million. https://www.grac.org/media/files/files/47014fd6/cronk.pdf