Remedial Evaluation and Strategy Development
PCB-Containing LNAPL and Dissolved-Phase Groundwater Plume
for
ABC Chemicals
Ontario, Canada
Project Background
The ABC Chemicals Breslau facility is an oil re-refinery operated by various owners since the
1960s. Waste oil originating at a former lagoon that was closed in 1977 has been thoroughly
investigated and identified to be present on the shallow water table at the facility and on the
adjacent property owned by GravEx Limited. The waste oil, which occurs as separate phase
product floating on the water table, is referred to as light non-aqueous phase liquid (LNAPL).
The LNAPL extends from the facility onto the GravEx property a distance of approximately 150
meters. The LNAPL consists of viscous petroleum hydrocarbon oil that contains low
concentrations of PCBs and other chlorinated solvent compounds. The concentration of PCBs
measured in the soil ranges from <0.01 to 21.4 parts per million (ppm), while the oil itself has a
PCBs content ranging from 75 to 340 ppm.
The GravEx property is hydraulically downgradient of the site with respect to the direction of
groundwater flow. GravEx operates and dewaters a large open-pit aggregate (gravel) mine about
300 meters downgradient from the LNAPL. The gravel pit extends nearly to the edge of the
Great River located about 700 meters from the LNAPL. Two inactive municipal water supply
wells are located in the floodplain of the river, between the aggregate mine and the river. The
wells have not been in use by the municipality since about 1993 but will be reactivated in 2007.
The wells are designed for induced infiltration of river water and are estimated to withdraw 80
percent river water and 20 percent groundwater. The mine-pit dewatering rate is roughly
equivalent to the extraction rate of the two municipal wells at about 2 million cubic meters per
year. Mine dewatering has lowered the water table in the vicinity of the pit about 8 meters, and
about 2 meters in the vicinity of the LNAPL compared to pre-mining water levels. Elsewhere in
the vicinity, land use is agricultural.
The shallow groundwater system at the site consists of upper and lower sandy aquifers
approximately five and 15 meters thick separated by a less permeable clay till aquitard about 10
meters in thickness. A downward vertical gradient exists between the two aquifers. The upper
aquifer pinches out just downgradient of the LNAPL. The municipal wells near the river are
installed in the lower aquifer. Dissolved constituents in groundwater associated with the LNAPL
are observed primarily in the upper aquifer and occur at low concentrations in a “halo” of
relatively limited extent near the LNAPL but that diminishes rapidly a short distance away.
Dissolved constituents in the lower aquifer are less prevalent, occur sporadically and at lower
concentrations, and similarly do not exceed MOE criteria beyond a distance of about 80 meters
from the LNAPL based on the most recent data. Nearer the river, no contaminants were detected
in four Regional Municipality of Waterloo sentry wells located between the gravel pits and
inactive municipal wells sampled in April and September 2001.
Although recoverable free product occurs in the source zone on the ABC Chemical property, the
current overall condition of the LNAPL is one of a static plume. Visual comparison of historical
contaminant plume maps indicates that the extent of the LNAPL has not changed significantly in
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eleven years. The LNAPL is effectively contained by its limited mobility due to high viscosity in
the source zone, near residual saturation levels at the distal end, geologic control associated with
a trough is an underlying aquitard, and a seep collection system operated by ABC Chemicals at
the toe of the plume since 1992.
Scope of Work
There is no direct pathway between the residual LNAPL and the inactive water wells near the
Great River. However, the municipality is not convinced that their municipal wells are risk free
from potential future impacts associated with the migration of dissolved phase constituents in
groundwater. The municipality has requested that the Ontario Ministry of Environment require
ABC Chemicals to remove the LNAPL and all residual saturated soils by excavation. In
preparation for responding to MOE comments ABC Chemicals is interested in pursuing one of
the following approaches.
1. Prepare and cost different excavation and treatment options for the LNAPL and provide
ABC Chemicals a recommendation on the least expensive approach should MOE require
LNAPL removal. These are excavation and treatment options only. Do not include any
in-situ treatment options (e.g., steam injection) or partial product recovery options (e.g.
product pumping or biodegradation). Include excavation and offsite disposal (landfilling)
[if appropriate], excavation and offsite treatment, and excavation and onsite treatment.
List key assumptions.
2. Prepare and cost a contingency approach for preventing a potential dissolved phase
plume from reaching the municipal wells by evaluating and discussing several
alternatives. Since this is the municipality’s key concern, a solid plan to mitigate any
potential impact to the wells from dissolved constituents may convince them to back
away from the costly LNAPL excavation. This is to be focused on the potential
migration of constituents dissolved in groundwater, not the LNAPL. Possible options
may include for example, pump-and-treat, slurry walls, air sparge curtain, in-situ
chemical oxidation, etc.
3. Prepare an evaluation of the potential fate and transport of the dissolved phase
constituents from the vicinity of the plume to the area of the municipal wells. The idea
here is, if results are favorable, to convince the municipality that concerns over impacts to
the municipal wells are unwarranted based on the hydrogeologic setting, groundwater
flow, well characteristics, and fate and transport properties of constituents. Consider
potential migration of constituents though the aquitard and the effects if the water table
elevation changes after mine dewatering ends.
Additional site data will be provided to facilitate the above evaluations.
Contacts
All inquiries and documentation should be directed to either the Brian Martinek at Cameron-Cole
303-938-5530 (bmartinek@cameron-cole.com).
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