Environmental Engineering Reference
In-Depth Information
The geology of the site was dominated by fluvial sediments composed of interbed-
ded sands, silts, and clays to depths greater than 15 m (50 ft) below the ground surface.
Groundwater is encountered within 1.5 m (5 ft) of the surface at most locations near the
river and less than 6 m (20 ft) at locations furthest from the river. The direction of ground-
water flow is generally west toward the river. The absence of a detailed geological map of
unconsolidated sediments for this urban region increased the difficulty of characterizing
the subsurface flow patterns.
This case study demonstrates the behavior of contaminants with low groundwa-
ter contamination risk factors. Despite its location within a geologically vulnerable
area (vulnerability rating = 67), a synergistic effect between the geologic environment
and contamination did not occur. Even though shallow groundwater was present
and the contaminants did not have far to migrate to impact a surface water body, the
relative immobility of the contaminants released prevented their migration into the
groundwater.
The remedial method selected for soil was excavation since the contamination was
accessible after demolition and did not extend to depths greater than a meter. The reme-
dial methods selected for groundwater were removal of PAH-free product and monitored
natural attenuation (MNA).
For nonfoundry areas of the site, cleanup of near-surface soil was required in the area
located along the east side where a former shooting range was located. Here, shallow soils
were impacted with lead. Other areas required a deed restriction and institutional controls
including nondisturbance of certain areas (areas previously used as landfill areas) and
maintaining a direct contact barrier such as asphalt pavement.
This case study was costly, because of the size of the site and its nearly 250 year duration
of industrial operations. The precise total cost of investigation and remediation have not
been determined because environmental work at the site is incomplete.
The lessons learned from this case study include
• Geologic maps are essential to all remediation efforts. In areas where there is high
geologic vulnerability and relatively immobile contaminants, the potential for
synergistic effects produced by their interaction can be better predicted by know-
ing the subsurface flow patterns.
• There are benefits to “front loading” the investigation by applying effective urban
investigative and geologic forensic techniques. In this case, a very thorough Phase
I ESA consisting of a comprehensive historical review set the stage for a detailed
Phase II subsurface investigation that resulted in the demolition of buildings and
provided access to the subsurface. These actions ensured the site was adequately
characterized.
• If a contaminant has a low groundwater risk factor, it suggests there will not be any
synergistic effects between it and a vulnerable geologic environment. Examples
of this are provided by the fate and migration of PAHs, PCBs, SVOCs, arsenic,
lead, cadmium, and mercury. All of these contaminants were present, but none
required groundwater remediation.
• Low areas on sites are often sources of contamination. Here the foundry portion
contained sumps, pits, trenches, tanks, and floor drains.
• Outdoor storage areas offer potential sites for contaminant release.
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