10 Soil and GW Mag Superfund Site Cleanup Article_20170726

SUPERFUND SITE CLEANUP OF CHROMATE CONTAMINATED
GROUNDWATER
By Dick Chmielewski, Published in Soil & Groundwater Magazine, December 1999/ January 2000
The Boomsnub site in the state of Washington was
listed as a Superfund site in 1995. the site consists
of two parcels of land, previously containing two
unrelated businesses, which contributed separately
to soil and groundwater contamination. The
Boomsnub Metal Plating facility operated on about
0.5 acres, from 1967 to 1994. This facility was
responsible for releases of chromium contaminated
wastes which resulted in contaminated soil and
groundwater by hexivalent chrome.
Across the street from the Boomsnub site, on
approximately four acres, is an active compressed
gas production facility. Various organic releases at
this location have resulted in volatile organic
compounds (VOCs) contamination of both soil and
groundwater. Migration of the groundwater has
resulted in a merged plume containing both
chromium and VOCs. Both locations have been
combined as one site for purposes of environmental
investigation and remediation.
For the chrome contamination, ion exchange was
selected as the cleanup technology. A standard
weak base anion resin was selected to remove the
dissolved hexivalent chromate, which is an anion.
The state installed an anion exchange system in
1992 to handle groundwater contaminated by
chromate. Also at this time, the building housing
the plating business was demolished and removed
from the site along with 6,000 tons of contaminated
soil.
Under normal range of pH (1-10), and at low
concentrations, chromium is present in groundwater
as either monovalent, HCr207, or divalent chromate,
Cr04. The monovalent form predominates in acidic
water while the divalent form predominates at
neutral pH and above. At the Boomsnub site,
divalent chromate is the major species present.
2 R OH + Cr04 2 ------> R2Cr04 + 2 OH- (1)
R2Cr04 +2 NaOH -----4 2 R OH + 2 Na+ + r04 2 (2)
The initial ion exchange process for chromate
removal used a macroporous tertiary amine weak
base anion resin. This system, sized to treat the 50
gpm flow rate, while effective, was found to be
costly to operate due to limited resin capacity and
expensive regeneration. Equations 1 and 2 show the
ion -exchange and regeneration reactions for the
chromate ion — WBA resin system.
As can be seen by equation 1, which represents the
service cycle, the resin readily removes chromate
from the contaminated ground water. This requires
two exchange sites for each chromate ion. A weak
base anion resin was selected for its relatively high
capacity and reasonable selectivity for chromate.
Equation 2 represents the regeneration cycle in
which the hydroxyl ion deprotonates the amine to
form water, releasing the chromate from the resin as
a sodium salt.
One concern with regenerating ion exchange resins
in this type of application is that the spent
regeneration solution contains high concentrations
of the heavy metals, in this case chromium.
Care must be taken to handle and dispose of this
waste stream in an environmentally acceptable way.
Commercial regeneration facilities licensed to
regenerate such resin are available, but the price for
such service is expensive as can be seen below in
the economic evaluation.
The initial Weak Base (WB) anion exchange system
consisted of a single vessel containing 25°CF of
resin and was operated at a flow rate of 50 gpm as
shown in Figure 1. Typical feed concentrations for
chrome were 2-6 ppm as chrome. The maximum
contaminant limit (MCL) for chrome in drinking
water has been established by the EPA as 100 ppb.
The loading obtained with this system was about 2
lb Cr/CF of resin. This corresponded to a treated
volume of 2.5 Million gallons. Regeneration

frequency was therefore on the order of 30 — 40
days.
Chrome Selective Resin
The initial 50 gpm system was operated for about
two years, when it was proposed that a specialty,
chromium selective resin be evaluated for this
project. The chrome slective resin is a specialty
anion resin with a proprietary functional group,
which is very selective for chromate. The capacity
of the specialty resin for chromate is more than
three times that of the standard weak base anion
resin. This means that the instead of having a
capacity of 2.5 million gallons to exhaustion, the
same volume of the chrome selective resin can treat
approximately 7.5 million gallons before capacity is
achieved.
Run lengths are increased from 30 — 40 days to
more than 90 days. Although the chrome selective
resin is more expensive than a standard weak base
anion resin, the significantly higher capacity allows
the system to operate in a one-time use or throw-
away mode. That is, the resin is used once and
Feed 50 gpm
2-6 ppm chrome
25 CF
WeakBase
Anion Resin
< 10 ppb chrome
disposed of along with soil removed from the site,
to a secured, approved landfill for hazardous waste.
Figure 1. Initial 50 gpm system
This avoids the expense of regenerating a resin
containing a heavy metal such as chrome. The cost
to perform this regeneration are high since the
chrome -rich stream produced in the regeneration
needs to be treated in an environmentally acceptable
way. The chrome is bound to the solid resin beads
and cannot be leached out with water, thereby
immobilizing the chrome when placed in a secured
landfill.
As can be seen from Table 1, the economics shows
that the one -use operation of the chrome selective
resin is about 15 % less than using a standard weak
base anion resin with regeneration. Also note that
the capacity of the standard weak base anion resin is
too low to consider one time use. It would be about
50 % more expensive to use the standard weak base
resin on a one time use basis than to regenerate this
resin.
The chrome selective resin was recommended and
initial testing was very encouraging. On the basis of
these tests a new larger system was designed and
built.
Three Bed System
A new three -bed system was designed to treat a
flow rate of 100 gpm, as shown in Figure 2. Each
bed contains 50°CF of chrome selective resin. The
three -bed system, which was built in 1994, operates
as follows: The first bed is the working bed. This
bed does the initial removal of chromate. The
effluent quality from the first bed is monitored and
when the bed is no longer removing chrome, it is
removed from service.
The second bed is the polishing bed. This bed
begins to remove chrome when the first bed
becomes exhausted.
The third bed is the guard bed. When the first bed
Feed 50 gpm
2-6 ppm chrome
SIR-700 SIR-700 SIR-700
< 10 ppb
chrome
Working Bed Polishing Bed Guard Bed
is removed from service, the second bed becomes

the working bed and the guard bed becomes the
polisher.
Figure 2. three bed system
After removing the resin from the first bed and
installing new resin, it is returned to service as the
new guard bed.
In this way the beds and the resin are cycled through
the plant to achieve extremely high capacity for
chrome removal. This system has been in
successful operation for five years. The system is
very effective in removing chrome from the
contaminated groundwater. The treated water from
this system is discharged to the City of Vancouver
POTW.
Future Plans
In August of 1999, the EPA issued a proposed plan
to upgrade the existing treatment system. The EPA
evaluated seven alternatives for improving the
cleanup of the Boomsnub site. The preferred and
recommended alternative is to continue to use the
ion -exchange technology with the highly selective
chrome resin and to increase the treatment capacity
of the system to 200 gpm. This proposal will
involve drilling more wells to remove contaminated
groundwater at a faster rate to insure that the
contaminant plume does not spread beyond the
existing boundaries and to improve treatment in
areas of highest concentration.
The treatment system can be easily upgraded by
installing three new tanks and the associated piping.
The two systems with three tanks each can be
operated in parallel. It is anticipated that this system
will be installed within a year.
Specialty ion exchange resins for removal of heavy
metals has shown to be an economical treatment
technique for control of chromate contamination at
the Boomsnub Superfund site. This technology
would be equally effective for other heavy metals
including mercury, nickel and lead. Specialty resins
are also available for nitrate and several other
specific contaminants.
Standard WB-
Standard WB — Throw —
Specialty Resin Throw —away
Regenerated
away
Resin Cost
$780.
$37,500.
$22,500.
Re en Cost
$22,500.
-
-
Labor Cost
3,840.
$ 3,840.
$ 1,280.
Total Cost
$27,120.
$41,340.
$23,780.
Notes:
l . Standard WB resin cost based on 4 year life. 3. Labor costs based on 16 man-hours to unload and load 25 CF tank.
2. Regeneration cost based on $75/CF for chrome -laden resin. 4. Throw -away standard WB changed out 12 times per year.
5. Throw -away specialty resin changed out 4 times per year.
Table 1 - Operating Costs for 50 gpm System