Chlorinated Solvent Remediation in a Dense Industrial/Residential Neighborhood with Offsite Commingling Plumes
At a Glance
From 1961 to 1983, a steel fabrication business utilized a sub-grade
vapor degreaser in a manufacturing business that was located in a dense industrial/residential
neighborhood in Newark, New Jersey. Following facility closure and building demolition in 2003,
soil and groundwater was found to be impacted with tetrachloroethene (PCE), trichloroethene
(TCE), and their degradation products. Soil, which contained concentrations of TCE and PCE
up to 4,080 mg/kg and 36 mg/kg, respectively, were not beyond the property boundary.
Groundwater delineation was complex due to TCE and PCE coming onto the site from at least
three offsite upgradient or side-gradient sources. Because of this, defining site cleanup goals
was challenging. Initial site-related concentrations of TCE and PCE in groundwater were up to
17,000 µg/L and 940 µg/L, respectively. The plume extended approximately 570 feet by 200
feet by 48 feet deep. The objective of the remedial design was to find the best solution given
the location and concentration of site-related contaminants, current and future conditions and
planned future use of the site, physical limitations and constraints in the offsite neighborhood,
the desire to minimize remediation of TCE/PCE plumes caused by other responsible parties,
and the need to control cost and protect human health and the environment.
Three areas of concern (AOCs) were defined and delineated to the extent
feasible, and a three-area remedial solution was designed and implemented. The site property
was defined as Area 1, where soil was remediated via a soil-vapor extraction (SVE) system.
Following removal of the soil source, groundwater is being remediated via monitored natural
attenuation (MNA). Since offsite upgradient impacts continue to commingle with onsite
groundwater, regulators allowed site cleanup goals to be defined by offsite upgradient
concentrations of TCE and PCE. The core of the site-related plume is currently located in Area
2, the city block located immediately downgradient of Area 1. Groundwater in this area is
inaccessible due to densely packed buildings and narrow accessways. Although no active
groundwater remediation can be conducted in Area 2, soil gas and indoor air monitoring are
performed periodically. Area 3 is the offsite dense industrial/residential neighborhood located
downgradient of Area 2, where the leading edge of the plume is emerging from beneath Area 2.
A 100 foot long by 20 to 60 feet deep biobarrier, composed of colloidal activated carbon, organic
carbon electron donor, and a dechlorinating microbial culture, was injected beneath the street
located between Areas 2 and 3. The biobarrier is intended to adsorb TCE and PCE as they
emerge from beneath Area 2, concentrating them on a high surface area medium to improve
contact with electron donors and bacteria and enhance biodegradation.
The bulk of the soil in Area 1 was effectively remediated by the
SVE system to below concentrations that were recharging groundwater. TCE/PCE groundwater
concentrations in Area 1 are now below site cleanup goals. In Area 2, ongoing receptor
monitoring has not identified impacts from the plume as it migrates underneath the
neighborhood. July 2019 groundwater data indicated that the plume was emerging from
beneath Area 2 to pass through the biobarrier, but treated groundwater had not yet reached the
downgradient performance monitoring wells. MNA is being performed downgradient of the
biobarrier in Area 3 to address TCE/PCE that pre-dates biobarrier installation. With regard to
plume commingling, defining the upgradient offsite contamination that continues to impact the
site was critical to limiting the owner’s responsibility and cost for remediation.