9b Chromate Removal Plant Part 2_20170726

IWC-13-14
Chromate Removal at the Hanford Site (Part 2)
James P Hanson, U.S. DOE, Richland Operations Office
Chuck Miller, CHPRC
Kristine Ivarson, North Wind, Inc.
Naomi Bland, U.S. DOE, Richland Operations Office
Dean Neshem, CHPRC
Peter Meyers, ResinTech, Inc.
Keywords: chromate, groundwater remediation, Hanford Site, hexavalent chromium, ion
exchange
ABSTRACT
It's been more than two years since the first weak base units were installed at the
Hanford Site. These units are now approaching 200,000 bed volumes throughput on
the lead vessels. All the remaining systems have been successfully converted from
strong base to weak base resin. Not a single resin replacement has been necessary to
date. This paper chronicles the modifications needed for the switch from strong base to
weak base resin and provides operating data for the various systems. Additional data
regarding the pH sensitivity and relationship between pH, flow rate and chromate
leakage is also presented.
1

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INTRODUCTION
In the two years that have passed since
the last report, the three remaining
chromate groundwater pump and treat
remediation systems at the Hanford site
have all been converted from strong base
anion resin to weak base anion resin. The
transition has been smooth and very cost
effective.
The first system to use weak base anion
resin, DX, still has the original resin in
service (startup December, 2010). The
lead beds are nearing 200,000 bed
volumes of throughput and around 6 lbs.
of chromium (as Cr) per cu. ft. The
successful performance of the weak base
resin has been duplicated at four other
groundwater pump and treat remediation
facilities at the site. These weak base
anion resin remediation systems were
placed into service to meet two goals: the
first is to protect the Columbia River from
groundwater contaminated with
hexavalent chromium, and the second, to
cleanup the groundwater to meet drinking
water standards within the aquifer.
To accomplish these goals, now that
startup operations have been completed
at these facilities, the focus has
transitioned from construction/
implementation to optimization of the
systems including extracting groundwater
from contaminant "hot spots," providing
more uniform capture along the shoreline
of the Columbia River as well as mass
2
removal from within the aquifer. These
sites along the Columbia River are unique
creating many pump and treat operational
challenges including transient river stage
effects due to upstream dams used to
control potential flooding, energy
generation, and ecologic habitat
protection. These challenges are all
considered in the operations of the pump
and treat remediation systems, and
evaluated frequently within an annual
reporting period to maximize the rate at
which chromium is removed from the
groundwater, minimizing the operating
costs associated with remediation.
To accomplish the goals above, the DOE's
decision to convert from strong base anion
resin to weak base anion resin will allow
DOE to meet its groundwater cleanup
goals in a reasonable period of time.
Specifically, the use of the SIR-700' weak
base anion resin has been a substantial
contributor to DOE's remediation
success.
OF HISTORICAL NOTE
The Hanford site, located in eastern
Washington State, was chosen in 1943 as
part of the Manhattan project for
1 1 SIR-700 is a special epoxy polyamine
granular weak base resin with a
secondary capture mechanism for
chromium. Not all weak base resins
exhibit this removal capability. To avoid
possible commercial conflicts, further
references will refer to this resin as a
"special weak base resin"

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production of plutonium for nuclear
weapons (figure 1). The site was chosen,
because it was close to the established
electrical infrastructure from the Grand
Coulee Dam, was sparsely populated,
considered stable geologically and had a
large amount of water available from the
Columbia River used in cooling the
nuclear reactors
Residents of the small communities of
White Bluffs and Hanford were given 30
days to move from their homes. The initial
reactor went from design to completion in
13 months. The B reactor was the world's
first plutonium production facility. It had a
graphite core, 2004 process tubes and
flowed 186,000 gallons per minute of
cooling water. (Hanford Story video,
2011).
Over the years, additional reactors were
built. A total of 8 single pass reactors
were constructed and operated at Hanford
between 1944 and 1971, all using the
same once through cooling and sodium
dichromate as a corrosion inhibitor.
Much of the land surrounding the Hanford
site is very porous. Leakage of
concentrated sodium dichromate from
underground piping and other accidental
spillage resulted in substantial quantities
of chromate finding its way into the soil
and gradually moving downward through
the soils into the groundwater and
impacting the Columbia River.
3
Figure 1
CHROMIUM CONTAMINATION
Hexavalent chromium on the Hanford site
is primarily found near the reactor sites. It
is estimated that a 0.75 km2 (0.29 mil had
contamination at concentrations greater
than 100 pg/L. (DOE/RL-2011-01 ) Peak
concentrations of 69,700 pg/L were
measured near the 105-D and 105-DR
reactors in 2010. An area over 8 km2 (3
sq miles) had contamination above 20
pg/L.
Control of the contaminant plumes is
accomplished using a combination of
extraction wells and injection wells, along
with periodic realignment of wells.
Contaminated groundwater is extracted
from near the Columbia River and pumped
to the ion exchange facility for treatment.
Following treatment, the water is sent to a
series of injection wells upgradient of the
plume. Injection water drives the
contaminants toward the extraction wells
to accelerate remediation.
The plume maps from 2009 to 2012
clearly show the effectiveness of the
treatment process. The chromate plume

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and concentrations have already been very significantly reduced.
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---------------
ORIGINAL EQUIPMENT DESIGN
All of the Ion exchange vessels for
chromium treatment initially employed the
following design philosophy. The systems
were modular, utilizing groups of four
vessels or "trains" rated at 100 gpm. To
expand capacity, additional trains are
added rather than changing the size of the
vessels. Each vessel holds 80 ft3 capacity
for ion exchange resin. Each of the four
vessels could assume any part of a train,
the positions being lead, lag 1, lag 2, and
polish configuration. The position of each
vessel was determined by manual valving.
Each unit could also be bypassed.
0
The original four -bed systems were
developed for strong base anion resin
used for chromate removal. The strong
base resins worked well and provided
predictable results, but had limited
throughput resulting in frequent resin
change outs. Regeneration of the strong
base anion resin was problematic,
requiring a high level of regulatory scrutiny
prior to shipping off -site, plus considerable
manpower. These costs and difficulties
were the drivers behind the switch to weak
base anion resin.
The original design concept has proven
not only to be a predictable and forgiving

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system, it also lends itself nicely to
modifications in operation and has allowed
doubling the capacity of the units by
splitting them in into two smaller units
consisting only of lead and lag vessels.
Consistency in the vessel design between
facilities allows for operational flexibility,
since the operators can switch between
facilities without extensive retraining.
With the new resin, resin change outs
have been essentially eliminated. The
chromium leakage from the lead vessel is
predictable and increases very slowly over
time. The leakage from the lag vessel is
much below the current 20 ppb regulatory
limit set by the site, and in fact is generally
down close to or below the limit of
detection (approximately 1 ppb with
current colorimetric analysis methods).
This has allowed the option of decoupling
the lag 2 and polish vessels and using
them as a second lead lag pair, essentially
doubling the size of each facility. This
modification results in large increases in
facility throughput, with almost no
additional operating cost.
THE QUESTION OF pH ADJUSTMENT
One of the activities that influences the
operating costs has been the need to
reduce the pH at the inlet of the trains to
approximately 5.5. This pH was initially
chosen because it allows the secondary
capture mechanism to occur rapidly, even
when the inlet chromium levels are
relatively high. The exceptional capacity
of the resin is due to more than simple ion
exchange. Testing showed the special
weak base resin had more than an order
5
of magnitude greater capacity than any of
the other resins tested. (Neshem, 2010)
The capture mechanism is ion exchange,
followed by reduction within the resin
matrix and covalent bonding of trivalent
chromium inside the resin matrix. This
hybrid property is both flow and pH
sensitive in that the rate, at which
chromate is reduced to trivalent chrome, is
slower at higher pH.
Early tests done with actual site water
demonstrated the pH sensitivity but
because they were static (equilibrium)
tests they did not demonstrate time related
effects.
Table 5. Results of SIR-700 pH Evaluation
Chromium
Solution
(pH)
Absorption
(mg)
Relative Capacity
5.0
57,0
1,00
5.5
44.3
0.78
6.0
43.6
0.77
6.5
24.3
0A3
7.0
17.5
0.31
8.0
11.2
0.20
It should be clearly understood that not all
weak base resin have this secondary
capture mechanism. In particular, the
styrenic macroporous type weakly basic
anion resins show capacities no higher
and in some cases lower than the original
strong base anion resins used.
ResinTech originally recommended an
operational pH of 5 to 5.5 to optimize resin
performance to achieve the greatest
longevity and increase hexavalent
chromium treatment performance of the

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weak base anion resins. Based on
performance criteria, PRC recommended
acidification and neutralization to optimize
resin performance and ensure minimal
impacts to aquifer chemistry and injection
well performance. Therefore, the DX and
HX P&T systems incorporated acidification
and neutralization processes within their
designs.
Based on the excellent special weak base
anion resin performance at DX P&T facility
(based on 1 year of operational data) and
preliminary test results at KWest P&T
facility (also operating with special weak
base anion resin), PRC recommended to
operate KX and KR-4 at lower pH and not
neutralize the effluent stream; similar to
ongoing testing at the KWest P&T system.
This recommendation was different from
specifications, design criteria, and design
as implemented at DX and HX (100-HR-3
OU) P&T. As monitoring had not been
performed at the KWest system to assess
any longer -term impacts to groundwater
and potential mobilization of other COCs
that might require additional treatment with
increased cost, additional groundwater
monitoring was recommended. At the
KWest Pump & Treat systems, additional
pH testing and associated groundwater
monitoring was implemented to assess the
potential impacts identified and
documented within PRC SGW Report.
As a result, recent monitoring has
documented a decreasing groundwater
pH trend resulting in an increase in Sr90
mobility. This outcome was expected at
this location. Decreased pH results in
increased solubility of CaCO3. Calcium
n
ion competes for Sr90 sites in the
groundwater matrix, resulting in an
increase in Sr90 mobility and higher levels
of Sr90 in the groundwater. Again, this
was an expected consequence of
reducing the pH in the aquifer.
At the KWest location, due to the low
groundwater concentrations of Sr90
(maximum of -50 pic/I a significant
distance away), the degree of mobilization
of Sr90 does not appear to be of
significant concern. In addition the Pump
& Treat system includes an active, robust,
groundwater extraction network, which
captures and recirculates any mobilized
Sr90.
Downstream Sr90 concentrations are well
below groundwater regulatory criteria. The
KWest P&T is an optimal testing location
to show impacts of pH on the groundwater
chemistry with little impacts to the aquifer
at this location at this time. However, the
results of the KWest test clearly indicate
that alteration of the groundwater
chemistry through pH adjustment may not
be compatible at locations with known
high concentrations of Sr90 due to the
increased solubility of calcium and
consequent increased mobilization of Sr90
in the groundwater.
Due to this uncertainty, DOE provided
PRC with Pump & Treat effluent limits on
pH of 6.7 for KX and KR-4 in order to
minimize potential impacts to the aquifer
and avoid risk of potential mobilization of
Sr90 and other contaminants of concern.

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The special weak basic anion resins have
been operating at the KX and KR-4 Pump
& Treat systems for more than 1 year at
feed pH of 6.7 without neutralization.
Performance has been cost effective and
treatment performance has been excellent
even at the higher than vendor
recommended operating pH range (6.7 vs.
5.0 to 5.5). PRC is continuing to maintain
the pH at —6.7 at the influent tank prior to
treatment with no downstream pH
neutralization
TESTING OF THE SPECIAL WEAK
BASE RESIN AT HIGHER pH RANGES
The special weak base resin has been
demonstrated to operate at a pH of 5.0 to
5.5 at both Hanford and at Boomsnub and
to provide greatly increased throughput
compared to strong base anion resins.
The Boomsnub facility in Vancouver, WA,
which treats groundwater contaminated
with hexavalent chromium, has deviated
from these optimal conditions. This facility
initially operated the resins within the
range recommended by the vendor, but
modified the process due to longevity and
performance achieved with the resins.
The facility no longer acidifies due to
groundwater pH being 6.0 and the
resulting effluent after treatment of 7.5 pH.
The facility achieves effluent performance
standards and discharges via a State of
Washington discharge permit.
Based on the above example, operation
with KR-4 and KX Hanford groundwater
has been tested over the past year with
7
slight acidification (to pH 6.7). This
ensures that the resins continue to remove
chromium well beyond the capacity of a
strong base resin. The exact capacity is
unknown because the resins are not yet
exhausted. KX has been in service for
approximately 1 year thus avoiding
replacement costs associated with over 50
strong base resin bed change outs (April
2011 thru April 2012). There have been
additional cost savings associated with
characterization/sampling, transportation,
and regenerations associated with the use
of strong base anion resins over the same
time frame. The testing indicates that
operation at a higher pH value around 6.7
has been a cost effective solution.
TESTING TO EXTEND THE SPECIAL
WEAK BASE RESIN LONGEVITY AND
PERFORMANCE
To attempt to extend the longevity of the
resins, PRC followed their vendor
recommendation and developed two resin
acid "conditioning" processes. The first
process consists of a "no flow" method to
increase reaction time for hexavalent
chromium reduction within the resin
granules. The second process consists of
a "soak" step where the resin is allowed to
soak in a lower pH solution, then is
returned to operation at a higher pH.
These methods have been shown to
improve longevity and re-establish lower
effluent leakage of chromium.

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The acid "conditioning" process
temporarily lowers each vessel's pH
environment to accelerate the hexavalent
chromium conversion process (reduction)
and decrease chromium leakage, thus
maintaining acceptable groundwater
discharge limits at a significantly higher
net operating pH.
At pH of 6.7, effluent hexavalent chromium
concentrations after —1 year's use from
individual lead vessels were increasing
from non detectable to 3-8 ppb
(hexavalent chromium) and sometimes up
to 10 ppb. The special weakly basic anion
resins were treating concentrations of
approximately 30 ppb.
The first method allows resins to "sit" with
"no flow" through them for a period of time
to allow the hexavalent chromium on the
resin surface to convert to trivalent
chromium. This phenomenon was
experienced at KWest P&T when the resin
trains were split to increase throughput.
Prior to splitting, the effluent
concentrations were increasing from the
effluent of the lead vessel. By taking the
resins offline (no flow through the
vessels), the resins had time for the
secondary capture mechanism to convert
available hexavalent chromium on the
surface of the resin to trivalent chromium
and for the trivalent chromium to
precipitate inside the resin granules. As a
result of non-use for a period of time, the
effluent concentration from the lead
vessels were reduced from approximately
8 ppb to the typical effluent values
encountered at start-up, which typically
were 1 ppb or less (measurement
E
obtained using a Hach Test method by
field operators with a detection limit of
approx 1 ppb).
The second method is an "acid
conditioning" method implemented early in
March, 2013. This method temporarily
decreases the pH through the vessels to
accelerate the conversion of hexavalent
chromium to trivalent chromium. Acid
conditioning re-establishes low effluent
concentrations of hexavalent chromium for
discharge to groundwater. The reduced
pH was run through treatment trains D, E,
and F at full flow (100 gpm/train or
combined flow rate of 300 gpm) and was
expected to set up an environment within
the vessels to accelerate the reduction of
hexavalent chromium to trivalent
chromium and the consequent
precipitation of trivalent chromium.
Increasing the rate at which hexavalent
chromium converts to trivalent chromium
and precipitates inside the resin matrix
decreases the concentration of total
chromium exiting each vessel, enhancing
the weak base anion resin performance.
This process is expected to increase the
allowable pH and extend the life
expectancy of each of the vessels
containing the special weak base anion
resins. Hexavalent chromium and pH are
monitored to identify when hexavalent
chromium concentrations within the first
vessel drops to near non -detect levels and
pH is monitored to determine when the
buffering capacity of the lead vessel has
occurred so that the effluent discharged to
the aquifer sees a minimal pH impact.

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This pH was reduced to between 5.0 and
5.5. The total test took approximately 2
days to implement and run. Upon
completion the influent tank was adjusted
back to pH of 6.7 and trains A, B, and C
flows were maximized to the optimal flow
(100 gpm) with flows decreased through
the other trains (D, E, and F) to 50 gpm.
During this process, sampling frequency
from each vessel was increased to daily.
Both pH and hexavalent chromium
measurements are taken to ensure that
effluent values meet discharge limits prior
to re -injection to groundwater. Increasing
flow rates from trains A, B, and C and
decreasing the flow rates of D, E, and F
minimize the effect of the pH wave
(buffering capacity of the conditioned
vessels) through dilution of the D, E, and F
trains. Trains A, B, and C were
conditioned according to the same
process outlined above upon completion
of trains D, E, and F.
As a result of pH "conditioning,"
hexavalent chromium values decreased
from the lead vessels to 1 ppb. The
resulting pH injected to groundwater was
lowered temporarily for a short duration
due to the buffering effect of the resin
which climbs back to normal effluent
operating pH range (near pH 7.0). The
process time frame for "conditioning" of all
6 KX treatment trains is approximately 15
days.
Although there appears to be a minimal
impact to the aquifer, evaluation of
potential waste site locations in proximity
to injection wells and groundwater
monitoring may be warranted. This aspect
9
is of greater concern for injection wells
associated with KR-4 P&T due to injection
well impacts on waste sites associated
with KE Reactor Area. However, these
would be short duration transient events
within the aquifer and may be noted by
PRC groundwater analysts to potentially
explain anomalous groundwater
monitoring results associated with less
mobile constituents.
Overall, the resin "conditioning" test shows
near -term success; success criteria
include re-establishing/decreasing the
hexavalent chromium vessel effluent
concentrations and minimizing effect of pH
changes to the aquifer. Continued
monitoring of vessel effluent
concentrations over a longer period of
time will provide input to assess the
applicability of the test as a means to
extend the life expectancy of the weak
base anion resins.
Based on these results, both methods,
"no -flow" and "acid conditioning" of
treatment trains may be viable methods to
extend the life of the weak base anion
resins, while operating the pH above
vendor recommended levels. Additional
monitoring will be required to fully assess
degree of performance extension, cost
effectiveness and assess impacts to
groundwater as a result of the process.
The following is a recap of the excellent
performance data from the various sites.

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The DX site was placed on line in fall
2010.
a
z
DX Site Bed volume data 2012 and 2013
DX Site Chromate Leakage pH55
Other sites now operate at pH
approximately 6.7 and there is additional
test work being done to determine if even
higher pH can be tolerated provided resin
conditioning steps are employed.
10
KW Site Chromate leakage pH 6.7
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KX Chromate
Inlet
leakage
pH = 6.7
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CLOSURE
Over the last two years, considerable
optimization of the various chromate
removal systems has been performed,
resulting in very significant performance
improvements and cost reductions. Most
of the trains have been reconfigured from
four -beds into dual -beds (lead lag). The
pH of the feed has been increased to 6.7
at most facilities without significant
deterioration in leakage or reduction in
resin longevity. The latest pH condition
steps have been able to reduce chromate
leakage from the lead vessels with very
little labor.
CH2M HILL estimates more than 600
resin changes have been avoided in the
last 2.5 years in groundwater treatment
facilities along the Columbia River, more
than $6 million in cost savings.
11