Subsurface Chemical Contamination and the
1-4 Expansion in Downtown Orlando
Challenges and Opportunities
By Michael A. Orcino, PE, Geotechnical and Environmental Consultants,
Inc
FES Florida Engineering Journal, July 2007
Have you ever wondered how “chemical contamination”
and “opportunity” go together? The answer is that
relatively new regulations have paved the road to alternative
methods of dealing with subsurface chemical contamination. Some
of these methods involve construction of impermeable surfaces
such as concrete, asphalt, plastic liners, and installation
of sheet pile walls—all familiar elements of roadway construction.
Chemical contamination of environmental media, primarily soil
and groundwater, can be problematic for any roadway improvement
project. Roadway components such as pavements, pile foundations
for bridges, and stormwater ponds must be designed and constructed
in such a fashion to prevent spreading the contamination to
unimpacted areas. Additionally, appropriate construction methods
designed to protect site workers should be employed for construction
areas that intersect contaminated soil and groundwater.
Chemical contamination issues can be critical in downtown environments,
where a virtual “toxic stew” may be present in some
areas as a result of chemical releases to the environment from
decades of high density commercial and industrial land uses.
Such chemical releases are typically comprised of petroleum
constituents, solvent compounds such as perchloroethene (a.k.a.
“drycleaner solvent”), and inorganic constituents
such as lead and arsenic. This is certainly the case for downtown
Orlando, which has exhibited commercial and industrial land
uses as early as the 1800s. For the majority of that time (until
the 1970s), there were no regulations that governed the handling,
storing, or disposing of chemical wastes. This, coupled with
the fact that chemical storage and delivery vessels were usually
constructed of steel or other materials that would readily corrode
and leak over time, resulted in numerous soil and groundwater
contaminant plumes throughout downtown Orlando.
For some roadway projects, sites containing chemically contaminated
soil and/or groundwater can be bypassed to avoid the need for
special design and construction considerations. This is not
the case for the ultimate I-4 reconstruction project through
downtown Orlando, where significant realignment of the roadway
is not economically feasible. Therefore, alternative construction
methods, engineering controls incorporated into the design of
certain roadway components, and subsurface modeling will be
used to facilitate construction through known contaminated areas.These
activities will eliminate theneed for remediation of underground
contamination prior to, or during, roadway construction, while
producing project cost savings.
Identifying the Issues
For Florida Department of Transportation (FDOT) roadway improvement
projects, the firststep in identifying potential implications
associated with chemical contamination is conducted during the
project development and environment (PD&E) study phase.
The initial phase (Level I Assessment) involves qualitative
investigation methods including public record research, interviews,
and site visits to identify current and past sources of chemical
contamination within the roadway corridor. Based on the results
of the Level I Assessment of the corridor, quantitative investigations
or Level II Assessments, are conducted at the suspect sites
to haracterize the nature and extent of chemical impacts. Level
II Assessments include collection of soil and groundwater samples
for chemical analysis, hydrogeologic studies to evaluate chemical
fate and transport mechanisms, and geophysical studies such
as ground penetrating radar (GPR) to search for contaminant
sources including but not limited to buried petroleum storage
tanks.
For the I-4 expansion project, Level I and numerous Level II
asessments have been conducted since 1998. Additionally, through
coordination with FDOT staff, a hybrid process was developed
to prioritize the most problematic sites, thereby reducing project
costs during the design phase. Thirty-six contamination sites
were identified through Level I analysis in the downtown I-4
corridor. Level II Assessments were conducted at less than 20
sites as a result of the hybrid screening process.
The majority of the suspect sites were impacted with petroleumproducts,
which are are typically very manageable during construction
with regard to costs since the contamination is generally present
near the water table surface (equal to less than 15 feet below
land surface in downtown Orlando). However, two relatively large
chlorinated solvent groundwater plumes are located beneath the
I-4 corridor that present specific design challenges for bridge-driven
pile foundations and stormwater management facilities. Unlike
typical petroleum constituents,chlorinated solvent constituents
such as perchloroethene, trichloroethene, and vinyl chloride
sink below the water table surface and are more costly to assess
and clean up in comparison to petroleum-impacted soils and groundwater.
Therefore, the use of alternative design and construction methods
is key to avoiding the significant costs and schedule delays
that would occur if remediation of the contamination was necessary
prior to construction.
Is “Clean to Clean” Necessary?
In the past, contaminated sites were rehabilitated to “clean”
levels. “Clean” typically related to naturally occurring
background levels of chemical constituents. One problem is that
some chemicals, such as arsenic, are naturally occurring in
the environment. So, in the case where a potential chemical
release of arsenic had occurred, to what level is one to “clean”
if naturally occurring background levels are present at or near
the clean-up goals? Some previous assessment and remediation
projects have run into the millions in rehabilitation dollars
quickly in a futile attempt to clean up sites below naturally
occurring levels. So, the question in those cases is what is
“clean”?
Another approach or alternative to “clean to clean”
is the use of engineering controls and/or institutional controls
to prevent or reduce exposure to chemical contamination by humans.
Engineering controls, such as impermeable barriers (pavements,
plastic liners, sheet pile walls), are designed to limit access
and exposure to contamination. Institutional controls are defined
in the Florida Statues as “the restriction on use or access
to a site to eliminate or minimize exposure to petroleum products’
chemicals of concern, drycleaning solvents, or other contaminants.
Such restrictions may include, but are not limited to, deed
restrictions, restrictive covenants, or conservation easements.”
What
this really means is that in some cases, soil and groundwater
can be left in place and controlled using physical and administrative
means without the need or expense to remediate the contamination.
This approach to contamination issues is important for the I-4
expansion project. Remediation of contamination in the areas
where roadway components such as pile foundations and stormwater
management ponds are to be constructed within the limitsof known
groundwater contaminant plumes, would be extremely costly and
slow. Therefore, engineering controls can be utilized to facilitate
construction of these facilities, while equally protecting the
environment and reducing the potential for exposure to humans.
Regulatory Involvement a Must
Due to the large scale and long timeframe of this design and
construction project,(the PD&E study, design, and construction
phases will span 2 decades), the ultimate I-4 design and the
environmental impacts related to design are constantly changing.
Further, the use of engineering controls with regard to contamination
plumes must be approved by the Florida Department of Environmental
Protection (FDEP). Consequently, multiple meetingsbetween the
roadway design engineers, environmental consultants, FDOT representatives,
and the FDEP were conducted at various stages of thedesign process
to obtain preliminary opinion and approvals regarding proposed
contaminant mitigation strategies that were being considered
as part of the roadway design.
These meetings ultimately resulted in a comprehensive understanding
of the project and potential implications related to known chemical
contamination from both the design and regulatory (FDEP) viewpoints.
Therefore, the design process could move forward with preliminary
regulatory approval for the proposed engineering controls. The
periodic meetings also created open communication lines between
designprofessionals, the FDOT, and the FDEP so that modifications
could be readily discussed as the design process continued.
Merging Engineering Design with Contamination Control –
Challenges and Environmental Benefits
Specific design challenges and solutions associated with
the project are as follows:
