Case Studies: Successful and Unsuccessful Redevelopment of Contaminated Sites - Urban Watersheds: Geology, Contamination, and Sustainable Development - page 469

>10,000

Proposed high resolution
aquifer profiling locations 0 150 m

1,000

Vertical exaggeration
is 10 times

Site Three distinct contaminant plumes

100

10

1

FIGURE 14.7
(See color insert.) Three-dimensional view of DNAPL VOC contaminant plumes.

than 305 m (1000 ft) downgradient from any suspected source, it confirmed the
degradation rate was extremely slow. Therefore, natural attenuation alone will
likely not be effective.
• Not all contaminant sources have been identified, removed, and abated. Several
potential upgradient sources have been identified, but, until they have been
fully investigated and removed, groundwater remediation cannot be effectively
implemented.
• Remedial technologies will be effective at reducing contaminant mass but will not
achieve timely and cost-effective restoration. One goal would be to reduce con-
taminant mass sufficiently so there is no detectable deterioration when the con-
taminant plumes reach surface water.

The lessons learned from this case study include

• Geologic maps are essential to all remediation efforts. In areas where there are
synergistic effects between vulnerable geology and chemicals with high contami-
nant risk factors, geologic maps can help with the determination of contaminant
extents.
• Low points within and near buildings such as concrete sumps, pits, trenches, and
floor drains are potential sources of contamination.
• The fate and migration of DNAPL VOCs in a vulnerable geologic environment can
present difficult challenges for remediation efforts.
• Because of surface and groundwater interaction, different geographic scales of
analysis—e.g., the site scale and watershed scale—must be considered to achieve
an accurate depiction of the contamination risks.
• Geologic forensic techniques and 3D mapping such as high-resolution aquifer
profiling can help provide a complete and comprehensive evaluation of the site
history, potential source evaluation, and knowledge of contaminant fate and
transport.
• Three-dimensional maps depict the extent of contamination in an easy-to-under-
stand and communicable format.