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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
Printed with Soy/Canola Ink on paper that
contains at least 50% recycled fiber
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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National Center for Environmental Publications and Information (NCEPI) at 513-891-6685, or send a mail request to NCEPI, 11029
Kenwood Road, Building 5, Cincinnati, OH 45242. Please refer to the document number on the cover of the issue if available.
Ground Water Currents welcomes readers’ comments and contributions. Address correspondence to:
Managing Editor, Ground Water Currents (OS-110W), U.S. Environmental Protection Agency,
401 M Street S.W., Washington. DC 20460.
United States BULK RATE
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Cincinnati, OH 45242 Permit No. G-35
Official Business
Penalty for Private Use $300
EPA/542/N-92/006
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