December 1992, Issue No. 2 (PDF)

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					                                    United States                       Solid Waste and                    EPA/542/N-92/006
                                    Environmental   Protection          Emergency Response                 December 1992
                                    Agency                              (OS-110W)




Innovative Measures Distinguish Natural
Bioattenuation from Dilution/Sorption
By John Wilson and D. H. Kampbell, Robert S. Kerr Environmental Research Laboratory

T he EPA’s Robert S. Kerr           ground water are 2.4, 67, and       above the water table. The         demonstration was to deter-
Environmental Research              21 mg/L, respectively.              core data and soil gas data        mine the extent to which bio-
Laboratory (RSKERL) recently              A gasoline service station    were used to estimate the          attenuation is responsible for
demonstrated natural                had been operated for many          total amount of gasoline re-       the reduction in the concen-
bioattenuation of organic           years on a corner lot where         maining in the subsurface          tration of BTEX compounds.
contaminants from a gasoline        Michigan Highway M-22               (1,200 gallons).                       The strategy was to identi-
spill in ground water at the        crosses the Platte River. The            Clusters of monitoring        fy an innocuous component
Sleeping Bear Dunes National        National Park Service acquired      wells were installed at three      of the plume that sorbs as
Lakeshore site near Honor,          the land and removed the ser-       locations in the plume of con-     strongly as the contaminants
Michigan. The results of the        vice station. On December 11,       taminated ground water -           and that should not be biode-
demonstration offer conclusive      1989, three underground stor-       at the source of the plume,        graded, at least not anaerobi-
quantitative evidence of nat-       age tanks were excavated and        at the bank of the river and       tally. The contaminant
ural bioattenuation distinct        removed. Fill and excavated         at an intermediate point.          plume contained several low
from dilution and sorption.         soil around the tanks smelled       Concentrations of contam-          molecular weight branched al-
Additionally, nitrate depletion,    of gasoline. The excavation         inants and potential electron      kanes that should not biode-
sulfate depletion and increased     was backfilled with the same        acceptors were monitored in        grade in the absence of
methane production (methano-        soil that had been removed to       the plume over time.               oxygen, and should sorb at
genesis) under anaerobic con-       prevent injuries to visitors to          Attenuation of contami-       least as strongly at the BTEX
ditions are found to be important   the open pit. The distance          nants in ground water plumes       compounds. One of the al-
indicators of natural bioattenu-    from the source of the plume to     may be due to dilution or          kanes, 2,3-dimethylpentane,
ation, which should be measured     the Platte River is only 70 feet.   sorption. Unless the contri-       was used as a tracer.
in addition to the traditional            The following strategy was    bution by dilution and sorp-            For example, in November,
measure of oxygen depletion.        used to acquire information         tion can be quantified, it is       1992, the concentrations of
      The geology of the            that would allow a quantitative     impossible to evaluate the         benzene and toluene in the
Sleeping Bear site is charac-       assessment of natural bio-          contribution of biodegrada-
teristic of many urban and          attenuation at field scale. A       tion. One of the goals of this     (SEE BIOATTENUATION, PAGE 3)
industrial sites where BTEX         soil gas survey for hydrocarbon
compounds (benzene, toluene,        vapors was used to identify
ethylbenzene and xylenes) are       those areas that still contained
found. The water table aquifer      oily phase hydrocarbons and
is in highly transmissive glacial   could act as a source of ground
sands and gravels; and, water       water contamination. Core
flow is rapid. The ground water      samples were taken in the ar-
 is cold (10 to 11 degrees           eas that showed hydrocarbon
Centigrade), hard (alkalinity        vapors in order to define the
 200 to 350 milligrams per liter     vertical extent of gasoline
 (mg/L)) and well-buffered (pH       contamination and to deter-
 6.1 to 7.6). Ambient concen-        mine the depth to which the
 trations of oxygen, nitrate and     spill penetrated moving ground
 sulfate in uncontaminated           water. Most of the spill was



                                                                                                         Recycled/Recyclable
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Surfactant Flushing of Ground Water Removes DNAPLs
By John C. Fountain, Ph.D., State University of New York at Buffalo

R    ecent research results from     the cell and five extraction
                                     wells on the other side. Ten
                                                                               The pool of DNAPLs,          volume using conventional
a field test have demonstrated                                            originally 50 centimeters         pump-and-treat methods.
that the surfactant flushing         multi-level monitoring wells         thick, was only 3 millimeters     Once the free-phase PCE is
process is capable of rapid          were also installed.                 thick at the end of the pilot.    removed by surfactant flush-
removal of dense nonaqueous                  Next, 231 liters of          Additionally, out of the 231      ing, aquifer restoration can be
phase liquids (DNAPLs) from          reagent-grade PCE were               liters of PCE injected into the   accomplished by circulating
a contaminated aquifer. The          released into the cell through a     cell, only 8 liters remained,     water, using a conventional
surfactant solution successfully     shallow injection well in the        spread between the thin layer     pump-and-treat operation.
removed perchloroethylene            center of the cell. The well         above the treatment zone, the     Results from the pilot scale
(PCE) at a rate far greater than     penetrated to a depth of about       DNAPL pool and in the probe       demonstration at Corpus
it could have been removed by        30 centimeters (well below the       holes in the aquitard.            Christi are expected in March
conventional pump-and-treat          water table). Thus, the entire             Data from the field study   1993. Preliminary data from
methods. Surfactants have the        contaminated zone was below          show that the surfactant flush-   surface cores show DNAPLs
ability to greatly increase the      the water table. Prior to            ing method circulation of 18      below detectable limits. For
solubility of organic compounds      starting surfactant flushing, all    pore volumes would require 90     more information call John
in water and thus to increase        free-phase PCE that could be         days of pumping at a standard     Fountain at 716-645-3996 at
the efficiency of pump-and-          directly recovered was pumped        rate of 500 gallons per day. By   the State University of New
treat operations. It has been        out; approximately 47 liters of      comparison, it would take         York at Buffalo.
shown that pump and treat            PCE were recovered by this           many years to clean the same
alone is not always effective for    process. When direct pumping
restoring aquifers contaminated      was no longer recovering
with organic compounds.              significant volumes of free-
      The research began just        phase PCE, water flushing was
four years ago at bench scale at     begun to flush any free-phase
the State University of New
York at Buffalo and has been
                                     PCE that could be so
                                     mobilized and to determine
                                                                          EPA Directive Updates Ground
field tested at the Canadian         the vertical and horizontal          Water Policy to Include DNAPLs
Forces Base Borden at Alliston,      variations in hydraulic
Ontario, Canada. It is believed      conductivity within the cell.        By Kenneth Lovelace, Office of Solid Waste
to be the most carefully.            Twelve liters of PCE were            and Emergency Response
controlled field test of an           recovered by water flushing.

                                                                          E PA’s Office of Solid Waste
aquifer remediation surfactant               After recovery of free-
flushing process conducted to        phase PCE by water flushing                                             waste sites to the fullest
date. The field test of surfac-       ceased, surfactant injection        and Emergency Response             extent possible while
 tant flushing was considered         began. A 2% (by weight)             (OSWER) has updated a              acknowledging at the same
 successful enough to warrant a       aqueous solution was used,          1989 ground water policy to        time that, in some situations,
pilot scale demonstration at a        composed of equal weights of        address nonaqueous phase           complete ground water
 contaminated site at Corpus          nonyl phenol ethoxylate and a       liquid (NAPL) contaminants,        restoration may be technically
 Christi, Texas.                      phosphate ester of the nonyl        including dense NAPLs              impracticable. The directive
       At the Borden field test, a    phenol ethoxylate. The sur-         (DNAPLs). The policy               builds on previous policies
 three-meter-square cell was          factant solution containing         directive promotes a               and good science to address
 built in a four-meter-thick          the PCE was then pumped             consistent ground water            special problems associated
 surficial sand aquifer by driv-      from the extraction wells into      cleanup approach for both          with NAPL contamination.
 ing sheet piling walls into the      a holding tank, through two         Superfund sites and Resource       It recognizes that DNAPLs
 underlying clay. A second            air strippers, into a second        Conservation and Recovery          may be more widespread at
 sheet piling wall was then in-       tank where additional surfac-       Act (RCRA) Corrective              hazardous waste sites than
 stalled one meter beyond the          tant can be added to bring the     Action sites. The policy           previously realized. The
 first wall for secondary con-        surfactant concentration to 2%      reinforces EPA’s commitment        presence of NAPLs, especially
  tainment. Five injection wells       if it is necessary to repeat the    to clean up ground water
  were installed on one side of        surfactant injection again.         contamination at hazardous        (SEE DIRECTIVE, PAGE 3)
Bioattenuation                     elapsed and extent of attenua-    to estimate the extent of bio-     electron acceptor demand was
                                   tion in ground water was used     attenuation of BTEX com-           slightly greater than the
(from page 1)                      to calculate bioattenuation       pounds that could be expected      theoretical supply of electrons.
                                   rate constants.                   from these processes. Typically,   Thus, other compounds in the
spill area were 253 micro-              Bioattenuation of toluene    as BTEX compounds are de-          plume, such as trimethylben-
grams per liter (µg/L) and         ranged from 16% to 47% per        graded, there is a decrease in     zenes and naphthalenes, may
31,400 µg/L, respectively.         week, ethylbenzene from 2.2%      oxygen followed by anaerobic       have also been biodegraded.
The concentration of 2,3-di-       to 7.7% per week, p-xylene        degradation supported by ni-       The ground water also
methylpentane was 23.3 µg/L in     1.7% to 6.7% per week, m-         trate and sulfate. After deple-    contained large concentra-
the spill and 1.6 µg/L at the      xylene 1.0% to 2.6% per week      tion of nitrate and sulfate,       tions of non-volatile total
river bank, 6.9% of the            and o-xylene 1.1% to 2.8%         methanogenesis occurs and          organic carbon, presumably of
original concentration in the      per week. These results are       methane concentrations in-         natural origin. Total organic
spill area. Based on the atten-    consistent with those seen in     crease as BTEX compounds           carbon was reduced from 58 mg/L
uation of 2,3-dimethylpentane,     other methanogenic aquifers       are further degraded.              in the well cluster at the spill
the expected concentrations        contaminated with petroleum             Between the spill and the    to 47 mg/L 30 feet down
of benzene and toluene due to      hydrocarbons. The rate            bank of the river, 42.6 mg/L       gradient and 21 mg/L 70 feet
dilution or sorption would be      constants for individual          BTEX compounds were con-           down gradient.
17.4 and 2,170 µg/L, respec-       compounds at sites at Bemidji,    sumed after correction for              Although benzene failed
tively; the actual concentra-      Minnesota, and Traverse City,     dilution. Methane that accu-       to degrade, benzene degrada-
tions were 23.3 and 1.69 µg/L.     Michigan, and at the Sleeping     mulated would account for          tion has been observed at two
     A pumping test was con-       Bear Dunes site do not vary       removal of 39 mg/L of BTEX,        other field sites where the
ducted to measure the hydrau-      more than an order of             nitrate reduction for 14 mg/L,     plume was longer. The failure
lic conductivity of the aquifer.   magnitude. The agreement is       sulfate reduction for 4.2 mg/L,    of benzene to degrade (after
The hydraulic gradient was         remarkable, considering the        iron reduction for 1.1 mg/L       correction for dilution) at the
monitored over time to esti-       level of uncertainty intro-       and oxygen respiration for         Sleeping Bear site is incon-
mate the direction and veloci-     duced into these field scale      0.8 mg/L BTEX removed.             sistent with these other two
ty of ground water flow.           estimates from variation in             The amount of nitrate,       field studies where benzene
Information on flow was used       ground water flow and              sulfate, oxygen and iron          was biodegraded. Because the
to predict the average time        changes in plume geometry.         reduction and methanogenesis      plume at Sleeping Bear was
elapsed since the water sam-            Oxygen consumption, ni-      was greater than would be          short (less than 100 feet) and
pled in the well clusters left     trate and sulfate reduction,      expected from the quantity of      the residence time of the
the source area of the plume.      methane production and iron        BTEX compounds removed
The information on time            solubilization were measured      from the plume. The actual         (SEE BIOATTENUATION, PAGE 4)




 Directive                         actions should be used to         larger phased approach to          requirements, which will
                                   minimize further migration of     allow coordination with later      protect human health and the
(from page 2)                      dissolved or NAPL contam-         cleanup efforts. Furthermore,      environment and that are
DNAPLs, will significantly         inants. Early response actions    because the mass proportion        appropriate for each site’s
affect the time and likelihood     should also include extraction    and spatial extent of residual     specific conditions.
of achieving ground water          of free-phase NAPLs, when-        NAPLs are usually much                  For a copy of the full di-
cleanup standards.                 ever possible. Careful ground     greater than that of free-phase    rective, contact the National
     Ground water contami-         water monitoring should be        NAPLs, new conventional            Technical Information Ser-
nation is found at more than       included in all cleanup efforts   and innovative technologies        vice at 703-487-4640 and ask
70% of Superfund National          in order to measure effective-    should be considered for           for NTIS Publication No.
Priorities List sites and almost   ness and to allow for warrant-    enhanced recovery of residual      PB92-963358, which is
50% of permitted RCRA land         ed design improvements.           NAPLs from the subsurface.         OSWER Directive 9283.1-06
disposal facilities. The direc-    Because NAPLs dissolve                  For those sites where        "Considerations in Ground
tive emphasizes the need to        slowly, they are a potential      hydrogeologic or contaminant       Water Remediation at Super-
determine the likelihood of        long term source of signifi-      characteristics may ultimately     fund Sites and RCRA
NAPL contamination - es-           cant contamination.               make long-term ground water        Facilities - Update.” The
pecially DNAPLs - early in              Accumulations of free-       cleanup targets unattainable,      directive lists the names and
the site investigation. Where      phase NAPLs, which are not        EPA reserves the right to issue    phone numbers of contacts
NAPLs are likely, the nature       removed as an early action,        technical impracticability        at EPA.
and extent of contamination        should generally be removed       waivers for National Priority
should be characterized to de-     during the final remedy, to        List sites and to modify RCRA
termine appropriate remedial       the extent practicable. The        permits or enforcement orders.
actions (both early and long       directive envisions NAPL           In such cases, EPA will
 term actions). Early remedial     remedial actions as part of a      identify alternative remedial
EPA’s Multi-Faceted Efforts to Improve Ground
Water Remediation
E PA has several efforts un- sites wherelikely. Thiscontam- study, see the September,
derway to enhance ground     ination is
                                          DNAPL
                                                      survey,
                                                                                      developing model consent de-
                                                                    1992, issue of Ground Water          cree language addressing a
water remediation. The            to be completed by March,         Currents (Document No. EPA/          technical impracticability
Robert S. Kerr Environmental      1993, will help to assess the     542/N-92/005).                       waiver process for implement-
Research Laboratory (RSKERL)      extent of this problem for the         A technical work group          ed pump-and-treat remedies
will evaluate innovative tech-    Superfund program.                within OSWER is developing           at Superfund sites.
nologies related to ground             OSWER is also support-       further guidance concerning               Look for news of the
water remediation, including      ing a National Research           waivers due to technical imprac-     availability of products from all
technologies with the potential   Council (NRC) study, “Alter-      ticability for ground water.         of these efforts in future issues
to remove nonaqueous phase        natives for Reducing Risk         Another work group, led by           of Ground Water Currents.
liquids (NAPLs) from the sub-     from Existing Ground Water        the Office of Enforcement, is
surface. The Office of Solid      Contamination”, that will as-
Waste and Emergency Re-           sess the current state-of-the-
sponse (OSWER) will work          science concerning ground
closely with RSKERL to de-
velop fact sheets and guidance
                                  water remediation and look at
                                  alternative approaches for ad-
                                                                    Bioattenuation
on site characterization, reme-   dressing ground water con-        (from page 3)
diation and performance mon-      tamination. The NRC study
itoring for sites contaminated    is scheduled for completion by
with dense nonaqueous phase       September, 1993.                  ground water was short (5 to 35           For more information, call
liquids (DNAPLs). Additionally,        Additionally, OSWER re-      weeks), there may not have been      John Wilson at EPA’s Robert
OSWER has initiated a survey      cently inventoried alternatives   adequate opportunity for anaerobic   S. Kerr Environmental Research
to determine the potential        to pump-and-treat technologies.   degradation of benzene.              Laboratory at 405-332-8800.
number of existing Superfund      For more information on that

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