Analysis of the Gasoline Spill at East Patchoque, New York
James W. Weaver, Joseph E. Haas, John T. Wilson
Accepted for the Proceedings of the American Society of Civil Engineers
Conference on Non-aqueous Phase Liquids in the Subsurface Environment:
Assessment and Remediation
November 12-14, 1996
Washington, D.C.
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Analysis of the Gasoline Spill at
East Patchogue, New York
James W. Weaver1 Joseph E. Haas2 John T. Wilson3
Abstract
Gasoline containing methyl tert-butyl ether (MTBE) was released from a service
station in East Patchogue, Long Island, New York. The resulting plume of contami-
nated ground water was over 1800 m (6000 feet) long, and resulted in the closing of
private water supply wells. Data from a three-dimensional monitoring network were
used to estimate the mass and position of the center of mass of benzene, toluene, eth-
ylbenzene, xylenes and MTBE contaminant plumes. The monitoring network was
sampled on three occasions so temporal information on the evolution of the plume
was available. By estimating the moments of the contaminant distributions for each
of the sample rounds, the loss of mass of each contaminant was estimated, as was
the rate of migration of the center of mass. An estimate of the volume of gasoline
released was made from plausible estimates of the gasoline composition.
Introduction
Over 300,000 releases from leaking underground storage tanks have been re-
ported to state regulatory authorities (USEPA, 1995). Depending on a number of
factors, chemicals which compose fuels may form contaminant plumes in the ground
water. Field and laboratory investigations have established that the most important
of these (benzene, toluene, ethyl benzene and the xylenes [BTEX]) are degradable
under most conditions (see e.g., Rifai et al., 1995). Oxygenated additives that are
1 National Risk Management Research Laboratory, United States Environmental
Protection Agency, Ada, Oklahoma 74820
2 Division of Spills Management, New York State Department of Environmental
Conservation, Stony Brook, New York 11790
3 National Risk Management Research Laboratory, United States Environmental
Protection Agency, Ada, Oklahoma 74820
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used as octane enhancers and as mandated by the Clean Air Act have also found their
way into subsurface water supplies (Squillace et al., 1995). The purpose of this pa-
per is to describe a gasoline release that occurred in East Patchogue, New York and
to use chemical data collected from the aquifer to estimate the mass and location
of center of mass of each constituent, the gasoline release volume, and the ground
water flow velocity. A companion paper describes simulation modeling of the site
(Weaver, 1996b).
Background
Published studies of groundwater flow on Long Island indicate that a regional
ground water divide lies along the length of the island and to the north of the ge-
ographic centerline (Eckhardt and Stackelberg, 1995). South of the divide, flow is
generally toward the Atlantic Ocean. Buxton and Modica (1993) estimate that the
hydraulic conductivity of the upper glacial aquifer is on the order of 8.1 x 10~2 cm/sec
(230 ft/day) in the outwash section near the southern shore, with estimated ground
water velocites of 3.5 x 10~4 cm/sec (1 ft/day) or greater.
Table 1 lists the density, p, solubility, S, organic carbon partition coefficient Koc,
fuel/water partition coefficient, K0, and the mass fraction in gasoline, x, of MTBE
and the BTEX compounds. Koc values were taken from Mercer and Cohen, (1990)
and US EPA (1990). The fuel/water partition coefficient and mass fraction data were
measured by Cline et al. (1991) on 31 samples of gasoline from Florida. The range
reported covers the variation in measured mass fractions in samples from other parts
of the continent and from lists of typical gasoline compositions (see e.g., Cline et al.,
1991, Corapcioglu and Baehr, 1987).
The usage of methyl tert-butyl ether, MTBE, began on Long Island in the late
1970s, after EPA approved its usage as an octane enhancer. Initial usage of MTBE
on Long Island was likely in the range of 5% by volume. Oxygenated additives were
mandated to reduce carbon monoxide emmissions in 39 cities, including New York
City and Long Island, by the 1990 admendments to the Clean Air Act. State of New
York regulations have required use of fuel with oxygen content between 2.7% and
2.9% in the winter months since 1992 (State of New York, 1995). The most com-
monly used oxygenated additive is MTBE, which provides the required oxygen con-
tent at about 15% MTBE by volume.
The subsurface behavior of MTBE is notable for two reasons. First, MTBE is
highly water soluble. As a measure of the solubility, the fuel/water partition coeffi-
cient for MTBE is about 23 times lower than that for benzene and 280 times lower
than those for m- or p-xylene (Table 1). The release of MTBE from gasoline, there-
fore, is expected to be much more rapid than the release of BTEX.
The second notable fact about MTBE is its recalcitrance to biodegradation. Mi-
crocosm studies conducted with three soils showed no degradation of MTBE over a
250 day study period under anaerobic conditions (Yeh and Novak, 1994). Degrada-
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Chemical
density
solubility
Koc(a)
KoW
x(c~>
g/mL
mg/L
L/kg
% (mass)
MTBE
0.74
48000
11.2
15.5
benzene
0.88
1750
83 (65)
350
1.73 (0.7-3.8)
toluene
0.87
535
300 (257)
1250
9.51 (4.5-21.0)
ethyl benzene
0.87
152
1100 (676)
4500
1.61 (0.7-2.8)
m-xylene
0.86
130
982 (691)
4350
(d)
p-xylene
0.86
196
870 (691)
4350
(d)
o-xylene
0.88
175
830 (691)
3630
2.33 (1.1-3.7)
Organic carbon partition coefficient reported by Mercer and Cohen (1990), the second value (in
parenthesis) from US EPA (1990).
W Fuel/water partition coefficient reported by Cline et al. (1991).
Mass fraction of chemical in gasoline reported by Cline et al. (1991).
'''' m- and p-xylene were not differentiated they composed 5.95% with range of 3.7% to 14.5%.
Table 1: Chemical parameter values
tion was induced under anaerobic conditions with the addition of nutrients, a hydro-
gen source and molybdate in an organic-poor soil. In organic rich soils degradation
of MTBE could not be induced. Horan and Brown (1995) concluded MTBE degra-
dation might occur at a very low rate, however, under aerobic conditions. In a con-
trolled field study, gasoline with 10% MTBE, and an 85% methanol/15%) gasoline
blend were released in the same aquifer (Hubbard et al., 1994). MTBE was found to
be recalcitrant to degradataion, while methanol and BTEX were degraded. Further,
the MTBE had no measurable effect on the degradation of the other compounds.
Site History
Subsurface contamination was detected at E. Patchogue, New York when water
from a residential well on Hagerman Avenue became undrinkable. The site inves-
tigation began at the well and expanded through the drilling of monitoring wells in
the up-gradient and down-gradient directions (Figure 1). The purpose of the drilling
was to delineate the extent of contamination and locate the suspected source. Ulti-
mately, the source was traced back to an abandoned service station approximately
1200 m (4000 ft) up-gradient from the Hagerman Avenue residence. Soil borings
in the area of the service station confirmed the presence of hydrocarbon contamina-
tion. The service station's tanks are believed to have been removed in 1988, which
is the latest date that gasoline could have been released. In 1994 and 1995, the con-
taminant plume was mapped from samples taken from 26 multilevel samplers and
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Figure 1: Hagerman Avenue Site Plan.
22 monitoring wells. Water samples from three sample rounds were analyzed for
BTEX and MTBE. Total organic carbon contents were determined on 11 clean core
samples.
Moments Analysis
The relatively large number of monitoring wells and multilevel samplers gener-
ated a three-dimensional data set, which were analyzed by calculating the moments
of each concentration distribution. The moments, are defined by
Mtjk = jjjxty3zknC(x1y1z)dxdydz (1)
where x, y, and : are the moment arms, n is the porosity, C(x,y,z) is the concentra-
tion. These moments can be used to estimate the mass of the contaminant distribu-
tion, given by the zeroth moment, M000. Likewise the first moments can be used to
determine the center of mass of the distribution:
Mwo Mow M001
X° ~ M000 ^c ~ M000 Z° ~ M000 ^
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where xc, yc, and are the x, y, and : coordinates of the center of mass of the dis-
tribution.
The challenge in applying equation 1 to field data is in evaluating the integrals.
The SITE-3D program developed by US EPA for visualization of site data (Weaver,
1996a) was used to generate the moment estimates by dividing the contaminant plume
into a set of nearest-neighbor polygons. The polygons represent zones of influence
of each well. In essence, the polygons replace the explicit interpolation schemes
between sampling locations that have been used in other analyses (Freyberg, 1986
among others).
For most of the plume, the wells cross the entire width of the plume. In some lo-
cations, however, monitor wells with high contaminant concentrations are located on
the edge of the sampling network (MW-12, MW-30, MW-38, MW-39). Therefore
some of the contaminant mass is not included in the estimates given below. Because
the MTBE is located down-gradient of MW-30, MW-38, and MW-39, its mass esti-
mates were not greatly impacted.
Table 2 shows the mass estimates and the distance of the center of mass of the
contaminant distribution from the contaminant source, dcom. The data in sample
round one were taken as the wells were installed from July 1994 to March 1995.
The average date of the first sample round, weighted by number of samples taken, is
December 16, 1994. Data from sample round two were taken from April 11, 1995
to April 20, 1995 and those from sample round three were taken from October 10,
1995 to October 24, 1995. Since the samples in round one were taken over a long
time period, contaminants sampled up-gradient may have been transported to down-
gradient receptor wells before they were sampled. The order of sampling, however,
proceeded up-gradient from the discovery point (MW-1) to the suspected source,
followed by the wells down-gradient from MW-1.
Each of the chemicals listed in Table 2 has some tendency for sorption. Since the
chemical data come from water samples, the sorbed mass must be estimated. Chem-
icals sorb in proportion to the fraction of organic carbon in the aquifer material, foc,
and the chemical's organic carbon partition coefficient, Koc. Sorption was assumed
to follow the linear equilibrium isotherm as given by
where Cxs is the sorbed concentration of contaminant x expressed per unit mass of
aquifer solids, and Cxw is dissolved concentration of chemical x. The sorbed mass
of contaminants was estimated from
Results
(3)
Mxs = —KocfocMxw
(4)
n
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Chemical
Sample Round One
Sample Round Two
Sample Round Three
Mxw (<*
) Mxs (fc) d,
(c)
com
MXw
Mxs
dcom
MXw
MXs dCom
kg
kg
m
kg
kg
m
kg
kg m
MTBE
268
24
1387
386
34
1557
229
20 1583
B
241
156(122)
991
117
76 (59)
1004
58
38(29) 1061
T
108
253(217)
230
65
152 (130)
298
60
141 (120) 306
E
29
249(153)
347
24
206(127)
347
21
180(111) 326
X
149
1041(804)
222
95
663(513)
277
92
643 (497) 272
M,ril is the mass dissolved in ground water.
1''' Mxs is the mass sorbed to the aquifer solids, estimated from the I. The porosity and solids
density were assumed to equal 0.30 and 2.65 g/cm3, respectively, giving a bulk den-
sity of 1.86 g/cm3. The Koc values were taken from Table 1. Table 2 lists estimated
sorbed masses for each chemical.
The estimated mass of benzene, toluene, ethyl-benzene and the xylenes decreased
between each sample round. Each of these compounds is expected to undergo biodegra-
dation in the aquifer, but each continued to dissolve into the aquifer through from
October 1995. The latter fact is established by the persistence of BTEX concentra-
tions near the source. The mass of MTBE, however, appeared to increase between
the first two sample rounds; then decreased between the second and third sample
rounds. The distribution of MTBE was such that in all sample rounds, no MTBE was
found between the source and a point approximately 600 m (2000 ft) down-gradient
(Figure 2). Thus it appears that the MTBE was almost entirely leached from the
gasoline near the source.
The average concentrations over the entire plume are given in Table 3. These
concentrations were calculated from the pore volume estimates and measured con-
centrations at all points in the sampling network where concentrations were above
the detection limit.
Estimation of the Mass of Gasoline Released
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E. Patchogue, NY: Sample Round 2
MTBE (ppb)
-120.00 1 i i i i | i i i i | i i i i | i i i i | i i i i | i i i i | i i i i | i i i i | i i i i | i i i i | i i i i | i i i i | i i i i | i i i i
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000
Distance (ft)
Figure 2: Distribution of MTBE in sample round two
The mass of contaminants in the aquifer can be used to place bounds on the vol-
ume of gasoline released. The estimated mass of MTBE in the aquifer is 292 kg
for sample round one and 420 kg for sample round two. Since the gasoline must
have been released before the Clean Air Act mandates, MTBE was assumed to com-
prise 5% by volume of the gasoline. The corresponding volume of gasoline for these
estimated masses would be 7.89 m3 (2080 gallons) and 11.35 m3 (2999 gallons).
Because of the apparent complete leaching of MTBE from the gasoline, this esti-
mate would represent the entire volume of MTBE enhanced gasoline released to the
aquifer.
The BTEX data suggest the volumes of gasoline listed in Table 4, assuming that
the density of the gasoline was 0.72 g/cm3. In the absence of specific knowledge
concerning the composition of the released gasoline, the estimates developed by Cline
et al., (1991) (see Table 1) were used in estimating the gasoline volumes in Table 4.
Unlike MTBE each of the BTEX chemicals persists in gasoline at the source (Fig-
ure 3). More of the benzene orginally contained in the gasoline, however, would be
in the aquifer than any of the other BTEX compounds because of benzene's lower
fuel/water partition coefficient. A greater fraction of each of T, E and X remain in
the gasoline because of their higher affinities for the gasoline phase (expressed in Ta-
ble 1 by their lower water solubilities and higher fuel/water partition coefficients).
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Chemical Sample Round One Sample Round Two Sample Round Three
Concentration Concentration Concentration
mg/L mg/L mg/L
MTBE 421 789 806
benzene 749 275 148
toluene 419 225 293
ethyl benzene 153 134 223
xylenes 746 558 516
Table 3: Concentrations averaged over the entire contaminant plume
The benzene-based gasoline volume estimate is the minimum estimate for these rea-
sons. To contrast with the Cline et al., (1991) average benzene mass fraction of 1.7%,
the often-used estimate of 1% by mass gives an estimated gasoline volume of 55.1
m3 (14600 gallons) for a benzene mass of 397 kg and 50.4 m3 (13300 gallons) for a
benzene mass of 363 kg.
E. Patchogue, NY: Sample Round 2
Benzene (ppb)
S
G
>
-120.00 "| I I I I | I I I I | I I I I | I I I I | I I I I | I I I I | I I I I | I I I I | I I I I | I I I I | I I I I | I I I I | I I I I | I I I I
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000
Distance (ft)
Figure 3: Distribution of benzene in sample round two
Estimation of the Average Rate of Advance of the Contaminant Plumes
The average rate of advance of the contaminant plumes are related to the ground
8 Weaver et al.
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Chemical Sample Round One Gasoline Volume Estimates (gal)
mass mass fraction from Cline et al., 1991
kg low middle high
benzene
(a)
397
20807
8567
3832
(b)
363
19025
7834
3505
toluene
(a)
361
2943
1393
631
(b)
325
2650
1255
568
ethyl benzene
(a)
278
14624
6335
3643
(b)
182
9539
4148
2385
xylenes
(a)
1190
9096
5273
2399
(b)
953
7284
4223
1921
Mass estimate using Koc of Mercer and Cohen (1990)
O Mass estimate using Koc ofUSEPA (1990)
Table 4: Gasoline volume estimates from BTEX mass estimates
water velocity and can be estimated from the position of the center of mass of the dis-
tributions during each sample round. These moment-based estimates include con-
centration changes, presumably caused by transport, from all sample locations, and
thus average fast and slow moving portions of the plume. Generally, in sample round
one the data were collected from the down-gradient wells first, followed by those
nearer the source. Thus 101 days passed between the average sample date for sample
round one and sample round two. The wells near the Hagerman Avenue residence,
however, were sampled 216 days before the sampling for sample round two. Sam-
ple rounds two and three were separated by 186 days. Based upon these durations,
average rates of advance of the contaminant plumes are given in Table 5.
Because of the long duration of sample round one, the most reliable of the results
are those for sample round two to three. The aquifer properties and gradients are pre-
sumed to vary with space, so the velocities may depend on position. For example,
the gradient is lower at the down-gradient end of the plume, which may have caused
the MTBE plume to move slower between sample rounds two and three than did
the benzene plume, because the center of mass benzene plume was approximately
500 m up gradient from the MTBE center of mass (Table 2). The increase in aver-
age MTBE concentration from sample rounds one to three supports this contention
as mass could be accumulating down-gradient, causing the average concentration to
increase (Table 3). Also, as shown in Figures 2 and 3, the vertical thickness of the
plume increases down-gradient. The velocity of the center of mass should decrease
in the thicker part of the plume by mass balance, because the mass of contaminants
fills a larger volume. The average MTBE concentration would be expected to de-
crease, which it does not (Table 3), however. The centers of mass of both the ethyl
benzene and xylenes plumes retreated from sample round two to sample round three.
This suggests that the rate of input of mass of these compounds to the aquifer is less
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than the rate of their loss.
Chemical
Rate of Advance (m/d)
Sample Rounds
One to Two Two to Three
101d 216d 186d
MTBE 1.68 0.79
benzene 0.13 0.06
toluene 0.67 0.31
0.14
0.30
0.04
-0.11
-0.02
ethyl benzene 0 0
xylenes 0.56 0.27
Table 5: Average rate of advance of the contaminant plumes
Conclusions
The extensive monitoring network at the Hagerman Ave site allows determina-
tion of the mass and moments of the contaminant distributions. The accuracy of the
mass estimates depends upon the sampling network, duration of sample events, and
the accuracy of the procedure used for forming the estimates. Each of these intro-
duces uncertainty into the estimates presented in this paper.
The mass of each of the BTEX compounds appears to decrease over the three
sample rounds, indicating a net loss of mass in the aquifer. MTBE data do not show
a clear trend. The mass of each contaminant in the aquifer can be used to give an es-
timate of the volume of the gasoline release. The mass of MTBE in the aquifer rep-
resents approximately 11.35 m3 (2999 gallons) of MTBE-enhanced gasoline. Since
MTBE was not used regularly before 1992, this gasoline volume estimate is likely
to be low. From sample round one, the mass of benzene gives a maximum lower
bound estimate of approximately 50 m3 (13200 gallons), if the benzene composed 1
% by mass of the gasoline. Since the released gasoline composition is unknown,
this estimate can be considered a tentative estimate of the gasoline volume. The
masses of the other BTEX compounds gave lower gasoline volume estimates which
are thereby consistent with the estimate from the benzene. The rates of advance of
the contaminant plumes can give estimates of the ground water velocity. From sam-
ple rounds two and three, MTBE advanced 0.14 m/d (0.5 ft/d) which gives a plausi-
ble velocity for the down-gradient portion of the site.
The mass of the release influences all activities at a contaminated site. Because
the release or releases which occurred at Hagerman Avenue occurred at unknown
times and intervals, much about the contamination at the site remains unknown. By
studying the data from the gasoline release, estimates of important quantities have
been developed. Although, the values are not completely certain, they represent
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plausible estimates for the site.
Disclaimer
The information in this document has been funded wholly or in part by the United States En-
vironmental Protection Agency. It has been subjected to Agency review and approved for
publication. Mention of trade names or commercial products does not constitute endorse-
ment or recommendation for use. The authors express their thanks to Sarah Hendrickson
and Julia Mead of the United States Environmental Protection Agency's Environmental Re-
search Apprenticeship Program, Charles Sosik of Environmental Assessment and Remedi-
ation of Patchogue, New York, and three anonymous ASCE reviewers.
References
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