Pi-Pa-Tag Technical
Assistance Report: Review of Current Geophysical and Groundwater Studies at the
SMC Tarpon Springs Superfund Site, June 2002
Overview
The Stauffer Management Corporation (SMC) site
is a 130-acre Superfund site located along the Anclote River on the
Pasco/Pinellas county line in Tarpon Springs, Florida. During operations the
site converted phosphate ore to liquid phosphorus. After operations ended in the
early 1980’s, there was elemental phosphorus left in storage and in several
on-site ponds, as well as large amounts of industrial slag. The slag contains
low-level radioactivity (as “hot spots”) and arsenic, a human carcinogen
(cancer-causing agent). Other toxic materials include heavy metals and asbestos.
The
US Environmental Protection Agency (EPA) designated the SMC site as a
“Superfund” site. The Superfund cleanup process includes the discovery
phase, Remedial Investigation, Feasibility Study, Record of Decision, Consent
Decree, Remedial Design, and Remediation. The Remedial Investigation (RI) is a
testing stage where soil, subsurface soil, sediments, ground and surface water
are tested for pollutants. The Feasibility Study (FS) involves analysis to find
a technology allowing the site to be cleaned to National Contingency Plan (NCP;
or “Superfund”) criteria. The 9 Superfund criteria are: protection of human
health and environment; implementability; meets all laws; short-term effective;
long-term effective; cost-effective; reduces mobility, toxicity or volume; and,
state and community acceptance. For the SMC site, a Record of Decision (ROD) was
developed using a remedy of in situ stabilization of underground
elemental phosphorus, with mounding and capping of slag. In situ
stabilization uses underground mixing of cement with the toxic waste. After the
cement solidifies, the toxins are immobilized and should not move into
groundwater. Mounding and capping would involve moving the slag to form large
heaps, which are then “capped” with a mixture of clean soil. There may be
fabric layers as well. The surface is covered with clean dirt and usually
planted with a grass that will not damage the cover. Although all of the waste
is still on the site, erosion and leaching into groundwater is reduced or
prevented.
During
hearings on the Consent Decree with EPA Ombudsman Robert Martin, sponsored by
Congressman Bilirakis, public concern was expressed over the selection of the
remedy. The Florida Department of Environmental Protection (FDEP) also
questioned the safety of the remedy. The main issues were possible presence of
sinkholes under the site that may not support the mound and cap remedies; the
potential of in situ stabilization failing to immobilize elemental
phosphorus; and confusion over the Environmental Protection Agency’s public
statements that arsenic was not a carcinogen while choosing a cleanup standard
of 24 parts per million for soil. That resulted in the decision by EPA and the
potentially responsible party to withdraw the Consent Decree and perform new
tests. The new studies include:
Geophysical studies looking for sinkholes or
other underground phenomena;
Geophysical tests to locate drums or buried
objects that may interfere with the remedy;
Examining the clay layers separating the
groundwater aquifers under the site;
New groundwater studies to map flow patterns;
Examining “connections” between the two
aquifers;
Additional toxin testing in both soil and
groundwater; and, Examining the effects of tides on the area where in situ
stabilization will be used.
The
studies are expected to begin in the summer of 2002, with testing and data
analysis through early 2003.
Preparation for Site Studies
Several projects have occurred on-site during the period the geophysical
studies were in the planning stages. The shore of the Anclote River was
stabilized by placement of quarried rock (or “rip-rap”). This should reduce
shoreline erosion and help keep the water around the site cleaner.
A
number of buildings were removed as well. The “demolition project,” as it
was called, was controversial. There was, at least, the appearance that the site
was being remediated without following the Consent Decree process. However,
there always was concern that old equipment and siding might be incorporated
into the mounds during remediation, landfilling even more solid waste at the
site. Under the demolition project, the buildings were to be demolished and
removed. The PRP had contracted for asbestos testing and removal (many of the
buildings contained asbestos material). Opposition during demolition was limited
to questions on staging materials, and testing of old stored chemicals in some
of the facilities. Overall, the demolition operated smoothly, with few incidents
of spills. Air monitoring for particulate emissions was poorly done, and
improvements in the monitoring system must be in place for the final remediation
phases.
Just
prior to the onset of the geophysical studies, the site was cleared of brush
that grew during the past couple of decades. Brush removal was needed in order
to freely move the instruments along “transects”—lines laid out on the
ground for positioning of portable equipment.
The brush was reduced to chips in a shredder and hauled away for other
remediation projects. The waste left at SMC is not the type that can easily
enter and contaminate plants, so shredding and disposing was appropriate.
Geophysical Studies
Geophysical
studies examine the structure of the ground layers under the site. Beneath the
site are rock layers of limestone, gravel layers, and clay layers. The thickness
of the layers depends on the location in the site. Some of the layers--
especially the limestone and gravel layers-- are “aquifers” or
water–bearing structures.
Both
the surficial and Floridan aquifer layers under the site are near the surface.
The surficial aquifer is the topmost groundwater layer that receives rainfall.
Site contaminants are found in the surficial aquifer. The Floridan Aquifer is the drinking water aquifer for most
of the county. In some areas the two aquifers are separated by a clay layer, in
other areas the clay is very thin with no separation, or only a weak separation.
It appears likely that the aquifers are also connected to the Anclote River.
There are indicators that salt water moves freely under portions of the site
during high tides. Nearby there are known sinkholes and solution channels, so
there may be sinkholes on the 100+ acres of the site that might interfere with
the remedy. There are persistent reports of chemical drums left on the site. One
report based on a 1987 Geophysical survey has the drums in or near pond 47 near
the shore of the Anclote River. Other reports locate drums nearer to areas
around the former railroad tracks. There are also questions regarding the depth
of old ponds that received process water and off-grade product.
Elemental
phosphorus is very chemically reactive. Mostly known for exploding on contact
with air, elemental phosphorus can react with many other chemicals. At a site in
southeast Georgia a material known as caustic brine, which is also very
reactive, “ate” away the limestone where it was dumped, Originally that site
was to be cleaned up using in situ stabilization with mound and cap
technologies as well, but the plan had to be abandoned when geophysical studies
indicated waste had moved much farther than anyone thought it could. Checking to
see if the remedy was even practical at this site should have received priority
during the RI/FS process.
The
basic techniques to be used in the geophysical testing include:
Survey Grid: A precise grid will be installed on the ground
across the site to provide accurate reference bearings for the instruments.
Small flags marking the intersection lines of the survey grid should be visible
from the road around the site during the studies.
Magnetometer: The geophysical studies will map the site using
magnetometer (metal detector) technology. That
will provide a precision view of any buried metal material in addition to
providing information on the subsurface soils. Salt water can interfere with
these measurements, so the magnetometers may not work near the shore.
Microgravity: Microgravity measures small, localized changes in
the gravity field at the surface. When plotted, these measurements can reveal
underground phenomena, such as caves.
Electroconductivity:
EC instruments pass an electric current between electrodes as they are pushed
into the ground. The flow of electric current between the electrodes provides
information on the minerals between the electrodes.
Ground Penetrating Radar:
Also called “GPR” this technique draws a radar unit along the ground and
examines the patterns of radio wave reflections from rock layers.
Electromagnetics: An electrical technique used to non-invasively
map soil conductivity. This should be used over the entire site looking at soil
structure.
Multi-Frequency Electromagnetics:
A high-resolution technique that maps electrical properties in the shallow soil
subsurface. This technique will be used in the ponds area targeted for in
situ stabilization.
“Downhole” Photography:
Television cameras will be dropped down both old and new well boreholes to image
layers of rock, gravel and sandstone. That
can lead to better understanding of the layers noted in the GPR studies.
Marine Geophysics: Sonar mapping and other techniques in the
shallow water of the Anclote River around the site.
Cone Penetrometers:
Designated as “follow-up” work,
this technique pushes a sensor into the ground to get data related to layer
density. This technique will look at “anomalies” to see if a structure or
void inferred by other techniques really exists.
Groundwater
The
main objectives for the groundwater studies include tests for flow and direction
in each aquifer; examination of the amount of transfer between the aquifers;
studies on groundwater quality in the pond and process areas; studies on tides
in the aquifers; some studies of hydraulic parameters; and providing a baseline
of groundwater conditions for future monitoring. Generally, groundwater studies
taking place are less than the community and EPA would prefer. The Record of
Decision called for remedy implementation followed by groundwater monitoring as
a separate second “Operable Unit” (OU2). Performing an entire Remedial
Investigation on the groundwater would provide a wealth of data on toxin
movement in the subsurface. However, SMC argues that the sole purpose of the
current studies is to determine if the selected remedy can be performed
successfully. If not, then a different remedy would be imposed and a full OU2 RI
might not be required. Unfortunately, it is not very clear what kind of
information is really important in determining the “sufficiency” of data
requirements for specifying in situ stabilization.
In
situ
stabilization was selected since it would not expose elemental phosphorus to the
air during treatment. In situ, therefore, is considered safer than
removal or ex situ processing, which digs up material, processes it, and
returns it to the hole. Removal would also leave a hole that may fill and drain
during tide-cycles, which may not meet Superfund requirements for short-term
effectiveness.
The
basic in situ concept is to use large hollow-core augers to drill into
the soil; then cement is pumped into the hole while mixing and withdrawing the
auger. Since soil is not very compressible there is a practical limit on the
amount of cement that can be pumped into the ground using this method. At
another Superfund site high rates of groundwater influx during stabilization was
found to dilute the cement, resulting in an unsafe volume of stabilant needed
for success. EPA decided at that site that a “zone of technical impractabilty”
existed and the remedy had to be abandoned. So rate of groundwater movement in
areas requiring stabilization is one type of data needed. Saltwater can
interfere with cement setting, so the tidal fluxes in the areas are important
information. Quantitative presence of other minerals, including the waste
itself, is needed. Although the term “monolith” is often used for in situ
stabilization, rarely is the product a single solidified mass. The solid mass
can vary from the weight and consistency of oatmeal to as heavy as concrete in a
driveway. Cracks, voids, holes, bubbles, fissures, cavities, and pores—all of
these phenomena occur within the “monolith.” Water can move freely through
the larger voids, and capillary action allows water to enter even the more
highly solidified portions. In the
case of SMC, virtually all of the mass will be below the water table, so an
understanding of water movement around and through the stabilized mass is
essential. Also, at least
“guesstimates” on the amount of cement likely to be required, both the
percentage of cement, any buffers or additives, and both the depth and lateral
extents of the solidified mass would be needed information.
Since
the groundwater studies have a very narrow focus it is not clear if conclusions
regarding the lateral extent of groundwater sources can be obtained. Experience
at other Superfund sites shows that toxins in groundwater contaminate other
areas of the aquifer over time. The proposed studies emphasize the ponds, which
are known to be primary sources of contaminates. However, after this length of
time there may be secondary sources of contamination further downgradient.
Treating the ponds would not be effective in stopping groundwater contamination
for the near term if there are now secondary sources outside of the ponds.
It was unclear from the presentation at the groundwater studies “kick
off” meeting whether or not discovery of secondary sources would be targeted.
The
groundwater tidal studies seemed poorly designed. Tidal influences should follow
the contours of the shoreline. However, tidal monitoring was only planned for
the immediate vicinity of the pond area along a line parallel with the expected
flow directions. The study’s authors seem more interested in “proving”
tides are not a factor in remedy selection that they are in establishing
baselines for understanding tidal influences at the site. Overall these studies
seem weak, and discovery of subterranean voids during the geophysical studies
may lead to contradictory conclusions regarding tides. No conclusions about
storm surge or long-term effects modeling of tidal influences would be
acceptable from this study.
Earlier,
the EPA requested an independent review of existing site studies by Black and
Veatch. The newly proposed groundwater studies will not address all data gaps
identified by Black and Veatch. Of particular concern is a statement by EPA’s
consultant that “The anticipated effect of groundwater mounding during the
summer months and the subsequent steeper hydraulic gradient is to increase
groundwater flow velocity toward the Anclote River.”
It did not appear that this phenomenon would be examined in this new
groundwater study. Obviously, seasonal variations in groundwater velocity could
impact the remedy, so this effect should not be ignored.
There still needs to be a set of treatability studies before a remedy
can be designed, However, it seems unlikely that a treatability study could be
undertaken until more information is available on the subsurface structure and
chemistry.
Conclusions
Overall,
the proposed geophysical studies are very comprehensive; the groundwater studies
are not comprehensive. If the
geophysical work is executed as described they should go a long ways toward
answering concerns regarding reports of drums buried at the site, possibility of
sinkholes or other phenomena that could impact the remedy, and defining the
scope of the cleanup. The format of the geophysical studies is also very good.
The study’s authors started with an unbiased aim of determining the subsurface
structure and inclusions.
Groundwater
studies will aid in defining conditions for the treatability studies and
somewhat support the geophysical studies. However, a complete second Operable
Unit for groundwater may be necessary before the remedy is undertaken. One of
the weakest aspects of the original remedy was the presumption that waste put in
ponds would still be in the vicinity of the pond area and thus be immobilized
during the in situ treatment. At other Superfund sites decades of
groundwater waste transport has created additional contaminated sources
downgradient, so that merely treating the original area only targeted the
primary source, not secondary sources. It is possible, perhaps even likely, in
situ treatment may be needed over a much larger area than simply the
footprint of the ponds. Additional testing would be needed in that case.
Largely the groundwater studies are merely confirming earlier tests and
may add little new information.
It
is hoped that data from these new studies will answer these questions:
Is there enough information from the studies to determine if buried
drums or other contaminated objects are present?
Do these studies clarify the results of earlier geophysical studies,
such as the confusion over pond 47?
Does
saltwater reach areas requiring remediation?
Is
analysis of areas indicated for in situ stabilization sufficient to find
solid objects or voids that might interfere with underground mixing?
Does
analysis of areas designated for support of slag mounds show voids, subsidence,
or sinkholes?
Are
there old solid waste impoundments, old foundations, burial pits or buried
debris requiring treatment?
Since
EPA has previously determined that “zones of technical impractability” exist
where groundwater flow volumes exceed the ability of immobilants to solidify
waste, can groundwater influx volumes be calculated?
Are
their tidal or seasonal groundwater influences affecting either the
solidification technology or long-term stability?
What
is the overall footprint of actual areas requiring in situ stabilization,
since these may be different than the surface indications of former ponds?
Can
a model be developed for groundwater movement between aquifers, and between
aquifers and the river?
Although
the net groundwater flow is “generally” toward the river, can the flow
reverse during high tides or storm surges?
Studies
merely reaffirming that waste was placed in the former ponds would be considered
inconclusive. What is important to know is where the waste has spread, both
vertically and horizontally. The worse case scenario for the outcome of these
studies would be another set of opinions rather than conclusions based on data.
Dr. R. Kevin Pegg
Dr. Mary Starnes Saunders
