Time-Critical Removal Action (TCRA) Action Memorandum for Site 1121, and Zero Valent Zinc (ZVZ) Injection Pilot Studies at 12 Area Site 13 and for 1,2,3-TCP in 22/23 Area Groundwater, Marine Corps Base (MCB) Camp Pendleton, CA.

This task order was originally scoped to perform a TCRA Action Memorandum for IR Site 1121, however, the task order was modified to install additional nested monitoring wells to aid in the evaluation of the ZVZ injection Pilot Studies. GCE conducted Pilot Studies at 12 Area Site 13 and 22/23 Area Groundwater, which was intended to evaluate the effectiveness of using ZVZ to achieve in-situ remediation of persistent 1,2,3-Trichloropropane (1,2,3-TCP) in groundwater. The ZVZ injection Pilot Study represents an innovative technology which promises to lead to long term savings for 1,2,3-TCP sites. Preliminary results indicated that ZVZ degrades 1,2,3-TCP more rapidly than other reductants (e.g., zero-valent iron) and appears to give complete dichlorination to propanes and propenes, which decreases the time required to remediate the site. Pilot Study Reports were prepared for both sites.

GCE was originally scoped to perform a TCRA Action Memorandum for Site 1121 in accordance with the Naval Facilities Engineering Command Southwest (NAVFAC SW) template for Action Memorandums and in accordance with Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) guidance. However, the scope of the task order was modified to install additional nested monitoring wells to aid in the evaluation of the zero valent zinc (ZVZ) injection Pilot Studies at Area 12 Site 13 and Area 22/23.

The intent of the Pilot Study was to evaluate the effectiveness of using ZVZ to achieve in-situ remediation of persistent 1,2,3-Trichloropropane (1,2,3-TCP) in groundwater. The project encompasses two unique sites, 12 Area Site 13 and 22/23 Area at MCB Camp Pendleton, CA, with similar contaminant issues. At 12 Area Site 13, Underground Storage Tank (UST) 13 was a 1,500-gallon concrete tank used to store diesel fuel for heating and was associated with Building 1283. The groundwater underlying the 22 and 23 Areas was impacted by trichloroethene (TCE), cis-1,2-dichloroethene (cis-1,2-DCE), 1,1-dichloroethene (1,1-DCE), 1,4-dioxane, 1,2,3-TCP, and vinyl chloride. The ZVZ injection Pilot Study represents an innovative technology which promises to lead to long term savings for 1,2,3-TCP sites. Preliminary results indicated that ZVZ degrades 1,2,3-TCP more rapidly than other reductants (e.g., zero-valent iron) and appears to give complete dichlorination to propanes and propenes that decreases the time required to remediate the site.

UST 13 was reportedly removed from the site sometime prior to 1994. 12 Area Site 13 is slated to be developed into surface parking for the new communications center being constructed to the immediate north. Fuel-related contamination is most likely associated with the former UST 13. The source of the chlorinated solvents detected at the site is unknown. Although phase-separated hydrocarbons were observed in two groundwater monitoring well during the Remedial Investigation, no significant residual soil contamination was detected. Groundwater monitoring has been conducted periodically from 1995 to 2015. In June 2015, 1,2,3-TCP was detected in two monitoring wells at the highest observed concentration of 0.18 micrograms per liter (μg/L) and 0.011 μg/L. Both concentrations exceed the California maximum contaminant level (MCL) for 1,2,3-TCP of 0.005 μg/L, which was effective on 1 October 2017. At 12 Area Site 13, the ZVZ injections were completed in the vicinity of groundwater monitoring wells where 1,2,3-TCP has historically been detected in groundwater.

At the 22 and 23 Areas, 1,2,3-TCP has been reported at concentrations exceeding the California MCL in monitoring wells located at the site. The remedial strategy for 22/23 Area Groundwater consists of land use controls and long-term monitoring to prevent COC exposure to human receptors, installation of a new water production well located a greater distance from the site, and in-situ treatment of identified COC source areas. To support implementation of the in-situ treatment program described in the ROD, a limited ZVZ injection program was implemented in 2014 to evaluate the efficacy of ZVZ injection technology. The primary goal of the 22/23 Area Groundwater in-situ remedial strategy is to expand the 2014 pilot study area to address the larger impact of the 1,2,3-TCP source area present at the site. For 22/23 Area groundwater, the ZVZ injections were completed in a permeable reactive barrier configuration downgradient of wells with 1,2,3-TCP concentrations above 1 μg/L. The injections were designed to degrade 1,2,3-TCP as it migrates from the potential source area, reducing 1,2,3-TCP mass flux to the downgradient plume.

Both ZVZ injection programs were completed using the jet injection method. As part of the injection program, performance monitoring well networks were installed at both areas. The networks include monitoring locations installed upgradient, within, and downgradient of the ZVZ injection areas.