EPA Region 9, 6 pp, 2020

The Dual Site Groundwater operable unit (OU) is shared by both the Montrose Chemical Corporation Superfund site and Del Amo Superfund site, which have both contributed contamination into one of three plumes in the OU. The OU consists of a plume primarily contaminated with chlorobenzene from the Montrose property, a plume primarily contaminated with benzene from beneath the Del Amo property, and a plume primarily contaminated with TCE from other companies north of the former Montrose property. EPA decided that achieving maximum contaminant levels was technically impracticable in a portion of the plumes, so a technical impracticality waiver zone (TI Zone) was established. Under EPA oversight, Montrose built a groundwater treatment system to prevent polluted groundwater from migrating out of the TI Zone. The system also remediates groundwater outside the TI Zone to federal and state drinking water standards. The system utilizes advanced oxidation, air stripping, granular activated carbon filters, and ultrafiltration and dissolved oxygen removal systems before reinjection into the subsurface. Since operating continuously at a low pumping rate, the system has met or exceeded all treatment standards and has removed over 7,000 lbs of contaminants. https://semspub.epa.gov/work/09/100018256.pdf See the five year review for more information: https://semspub.epa.gov/work/09/1154452.pdf