United States
Environmental Protection
Agency
Solid Waste and
Emergency Response
(5102G)
EPA 542-N-99-008
December 1999
Issue No. 34
CONTENTS
Pump and Treat
Optimization
Technology Brings
Significant Cost
Savings
Pg.l
AFCEE Develops
Algorithm to Optimize
Long-Term Ground-
Water Monitoring
Networks Pg. 2
Remediation System
Evaluations Help to
Optimize Systems Pg. 3
New Case Studies on
Ground-Water Cleanup
Systems Released Pg. 4
About this Issue
This issue highlights various
approaches to system
optimization for the
characterization or
remediation of contaminated
ground water.
Pump and Treat
Optimization Technology
Brings Significant Cost
Savings
by Kathleen Yager, U.S. EPA
Technology Innovation Office,
and Robert Greenwald, HSI
GeoTrans
The U.S. EPA Technology Innovation
Office (TIO) and Office of Research
and Development (ORD) recently
teamed with HSI GeoTrans in a study
evaluating the effectiveness of an
optimization technology for pump and
treat (P&T) systems. The optimization
approach consists of using ground-water
flow models coupled with mathematical
optimization techniques to develop
improved pumping strategies. Study
results indicated mat significant savings
in annual operation and maintenance
(O&M) costs are possible from optimi-
zation-simulation analyses. Potential
cost savings at two of the three sites
evaluated in the study ranged from
$200,000 to $550,000, annually.
Nearly 700 pump and treat systems have
been selected, are under construction, or
currently operate at Superfund sites
across the county. These systems are not
only costly to construct but can be
extremely expensive to operate and
maintain for the long periods of time
commonly required for site cleanup. A
primary objective of the study was to
evaluate a technology that could improve
the efficiency of P&T systems while
significantly reducing O&M costs. EPA
also aimed to highlight the importance of
evaluating system performance on a
regular basis, and to develop guidance on
when a detailed optimization analysis
may be beneficial.
The scope of the study included selection
of three sites with existing P&T systems,
screening of the sites for optimization
potential, and application of a hydraulic
optimization code (MODMAN) at each
site. MODMAN couples a ground-water
flow model (MODFLOW) with math-
ematical optimization techniques (linear
and mixed-integer programing) to
determine the best locations and rates for
extraction and/or injection wells. A
major advantage of hydraulic optimiza-
tion is that it considers all possible
combinations of flow rates at potential
well locations, so that the best combina-
tion is identified. Three diverse sites
(located in Kentucky, Utah, and Ne-
braska) were selected for the study to
allow for demonstration of the optimiza-
tion technology under various
conditions. The sites differed in total
ground water flow rate, the number of
extraction/injection wells, the type of
aboveground treatment, and the annual
O&M cost.
Results of the study can be illustrated by
selected findings from the Kentucky site,
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(2) identifying spatially redundant wells;
and (3) projecting cost savings gained by
eliminating wells and/or reducing sam-
pling frequencies. The temporal algorithm
involves both computation of a composite
temporal variogram to determine the least
redundant overall sampling interval, and
"iterative thinning" of the sampling data at
selected wells to determine well-specific
sampling frequencies. A temporal
variogram is a one-dimensional
geostatistical measure of autocorrelation
across a range of lag times between
sampling events. The smallest lag time at
which the variogram reaches a stable
plateau or "sill" is the sampling interval at
which the same-well measurements
become essentially uncorrelated and,
therefore, non-redundant. "Iterative
thinning" involves an estimation of a
baseline trend at each well, followed by
re-estimation of the trend after random
deletion of sampling events from the
well's historical record.
The spatial algorithm is predicated on the
notion that well locations are redundant if
nearby wells offer nearly the same
statistical information about the underly-
ing plume. At MMR, a well was
considered redundant if its removal did
not significantly change a concentration
map of the plume. To identify well
redundancy, indicator kriging was used to
generate an initial plume map. Kriging
weights assigned to each well location
then were used to gauge each well's
relative contribution to this initial map.
By temporarily removing that subset of
wells with the lowest global kriging
weights and re-estimating the plume map,
it was possible to determine how many
wells could be removed without substan-
tially altering the map, leading to a list of
potentially redundant wells.
Based on application of the optimization
algorithm at MMR, close to 20 percent of
the known monitoringlocations were
tagged as spatially redundant at each site.
Furthermore, the temporal variogram
indicated that quarterly sampling could be
relaxed and replaced by annual sampling
at FS-12 and by once-per-5-quarters
sampling at Eastern Briarwood. The
overall reduction in MMR's total annual
sampling and analytical budget for these
ground water plumes was estimated to be
36 percent for Eastern Briarwood and 42
percent for FS-12.
AFCEE currently is testing the algorithm
at other Air Force sites. For additional
information, contact Philip Hunter
(AFCEE) at 210-536-5281 ore-mail
philip.hunter@hq.afcee.brooks.af.mil.
Remediation System
Evaluations Help to
Optimize Systems
by Dave Becker, U.S. Army Corps
of Engineers/Hazardous, Toxic,
and Radioactive Waste Center of
Expertise
The Remediation System Evaluation
(RSE) process can help reduce operating
costs substantially for long-term cleanups
and help identify performance problems.
Developed by the U.S. Army Corps of
Engineers (USAGE) to identify cost
savings and assure the protectiveness of
remedies, the RSE process: recommends
cost-saving changes in system operations
or technologies applied at a site, verifies a
reasonable closure strategy, and assesses
maintenance of government-owned
equipment. Besides identifying potential
cost savings, the RSE process serves as an
extension of the CERCLA 5-year review
process. The evaluation addresses
protectiveness issues such as system
performance relative to remedial action
objectives, monitoring or operational
deficiencies that may jeopardize ad-
remedy's protectiveness, and changes in
surrounding land use or risk-based/
regulatory cleanup standards.
The USAGE Hazardous, Toxic, and
Radioactive Waste Center of Expertise,
with assistance from USAGE district staff
and other agency personnel, has applied
the RSE process at three sites. The RSEs
identified potential cost savings of
$80,000 to more than $300,000 per year
in operations and maintenance at each
site. On average, each evaluation cost
slightly under $20,000 to conduct,
including associated travel for a site visit
and final report generation. The costs
that may be incurred in addressing those
issues, however, are not shown to offset
the reported cost savings.
In order to assist the USAGE district
personnel and contractors in performing
these RSEs, a suite of checklists was
developed. These checklists address the
overall system goals, subsurface perfor-
mance, above-ground treatment
effectiveness, and equipment mainte-
nance, and offer possible cost saving
alternatives. The checklists are intended
for use by experienced technical staff
when conducting RSEs on a wide variety
of long-term remedies, including pump
and treat, soil vapor extraction,
bioventing, and air sparging.
Over 250 RSE checklists are available.
Several of the checklists assist in assess-
ment of subsurface system performance,
aboveground treatment plant effective-
ness, monitoring programs, and
alternatives for treatment water discharge.
Other checklists are intended for use in
evaluating specific equipment, including
air strippers, carbon adsorption systems,
metals precipitation units, piping, pumps,
blowers, control systems, solids handling
systems, thermal treatment units, ad-
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