Connor et al. (2014) – Supporting Information
Manuscript No. GW20131118-0253
Issued: 23 May 2014
Page 1 of 10
1
SUPPORTING INFORMATION
2
3
Review of Quantitative Surveys of the Length and Stability of MTBE, TBA, and Benzene
Plumes in Groundwater at UST Sites
4
5
6
7
John A. Connor1, P.E., P.G., B.C.E.E.; Roopa Kamath2, PhD, P.E.; Kenneth L. Walker3, Jr., P.E.; Thomas E.
McHugh4, PhD, D.B.A.T.
8
Data were compiled from 13 studies discussed in the main text (see Table 1).
9
2.
1.
DATA COMPILATION
PLUME LENGTHS
10
Statistical distribution parameters for estimated plume lengths are provided from the source references
11
(Table S-1), as called out in either the text or tables. In some instances, statistical parameters were
12
estimated from associated figures (e.g., histograms, cumulative probability distribution plots). In some
13
cases, the original source data were obtained from the authors and utilized to calculate the statistical
14
parameters. For example, distribution numbers for Rice et al. (1995), which were not originally reported,
15
were calculated from data provided by the authors, as reported in Newell and Connor (1998). Values
16
from Kamath et al. (2012) not reported in the original paper are from the author.
17
After compilation of the data, the weighted mean was calculated for both the 5 and 10 µg/L contour
18
limits. The median and 90th percentile statistic for each dataset was weighted by the number of samples
19
in that dataset. In other words, studies with more sites were weighted more heavily than studies with
20
fewer sites. The minimum and maximum values were taken as the minimum and maximum plume
21
lengths, respectively, reported in the literature, not a weighted mean of the minimum and maximum
22
values.
Connor et al. (2014) – Supporting Information
Manuscript No. GW20131118-0253
Issued: 23 May 2014
Page 2 of 10
15 µg/L
10 µg/L
5 µg/L
5 µg/L Aggregated
Results
10 µg/L Aggregated
Results
24
89
50
55
38
35
212
36
96
132
0
10
0
85
96
391
225
325
780
110
145
175
451
315
99
120
Maximum
88
121
120
99th
36
80
90th
40
85
75th
51
30
Median
0
25th
Reference
Happel et al. 1998
Reid et al. 1999; Reisinger et
al. 2000
Rifai and Rixey 2004; Rifai et
al. 2003; Shorr and Rifai 2002
Mace and Choi 1998
Reid et al. 1999; Reisinger et
al. 2000
Kamath et al. 2012
Wilson 2003
Rifai and Rixey 2004
Shih et al. 2004
Total number of sites
Weighted Mean (except
min/max)
Total number of sites
Weighted Mean (except
min/max)
10th
MTBE Concentration
Used to Define
Plume Length
20 µg/L
Total
Number of
Sites
Meeting
Threshold
Criteria
50
Mean
Table S-1: Statistical Plume Length Data from the Literature for MTBE, Benzene, and TBA
Minimum
23
1096
174
255
386
750
140
140
458
0
199
110
178
211
454
400
135
96
174
96
473
315
132
276
96
377
96
531
96
0
1040
96
85
135
175
360
275
375
530
-
1040
391
124
124
90
391
124
336
124
302
0
71
85
165
165
245
400
965
1650
1519
1649
1400
Connor et al. (2014) – Supporting Information
Manuscript No. GW20131118-0253
Issued: 23 May 2014
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95
34
165
23
0
165
Total
Number of
Sites
Meeting
Threshold
Criteria
Maximum
115
99th
115
90th
10th
146
219
261
325
550
831
1713
267
185
480
1400
1013
351
273
439
713
82
22
129
118
59
165
197
206
165
167
125
165
259
254
165
341
356
165
1320
34
551
1662
165
0
65
125
230
180
295
425
1320
1660
826
560
560
325
826
560
772
560
537
10
60
90
130
140
185
345
695
1715
51
75
194
145
210
366
698
700
49
95
141
240
200
338
433
108
108
108
108
108
108
108
22
108
85
130
230
190
310
420
700
700
Kamath et al. 2012
10 µg/L
Shih et al. 2004
86
Total number of sites
Weighted Mean (except
min/max)
108
0
10 µg/L Aggregated
Results
101
144
207
12 µg/L
22
133
Maximum
826
75th
78
Median
36
Mean
10
25th
212
66
108
212
99th
Reference
21
144
90th
TBA Concentration
Used to Define Plume
Length
54
42
80
100
75th
10 µg/L Aggregated
Results
8
20
104
Median
5 µg/L Aggregated
Results
271
289
66
Mean
5 µg/L
18
25th
10 µg/L
50
10th
20 µg/L
Reference
Reid et al. 1999; Reisinger et al.
2000
Rice et al. 1995
Mace and Choi 1998
Reid et al. 1999; Reisinger et al.
2000
Wilson 2003 (BTEX)
Rifai and Rixey 2004; Rifai et al.
2003; Shorr and Rifai 2002
Shih et al. 2004
Kamath et al. 2012
Total number of sites
Weighted Mean (except
min/max)
Total number of sites
Weighted Mean (except
min/max)
Minimum
Benzene
Concentration Used to
Define Plume Length
Total
Number of
Sites
Meeting
Threshold
Criteria
Minimum
25
0
630
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26
27
28
29
30
31
32
Notes:
1. Aggregated results are the weighted mean, weighted by the sample size (total number of sites meeting threshold criteria), except for the minimum and maximum
values, which are taken as the minimum and maximum values of the aggregated sample population. Aggregated results were rounded to the nearest 5 feet.
2. For TBA, values were aggregated at 10 µg/L to increase the sample population.
3. Distribution numbers for Rice et al. (1995), which were not originally reported by the author, were calculated from data provided by the authors, as reported in Newell
and Connor (1998).
4. Values from Kamath et al. (2012) not reported in the original paper are from the author.
Connor et al. (2014) – Supporting Information
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33
3.
34
Plume stability data were compiled and aggregated from five studies that considered whether MTBE,
35
benzene, and/or TBA plumes were increasing in length, stable, decreasing, no trend, exhausted/non-
36
detect, or were associated with a detached plume (Table S-2).
37
Table S-2: Plume Stability Results for MTBE, Benzene, and TBA
PLUME STABILITY
Plume Stability Condition
Number of Sites
Increasing
Stable
Decreasing
No Trend
Exhausted /Non-Detect
Plume
Detached Plume
Total Percent NonIncreasing
MTBE Plume Length Trend Distribution (%)
Reid et al. 1999;
Reisinger et al.
Kamath
Shorr and
20001
SUMMARY1,2
et al. 2012 Rifai 2002
45
41
36
122
6%
4.4%
5%
8.4%
20%
6.6%
17%
41.7%
60%
89%
73%
8.4%
12%
41.7%
-
5%
-
2%
96%
90%
92%
93%
38
Plume Stability
Condition
Number of Sites
Increasing
Stable
Decreasing
No Trend
Exhausted /Non-Detect
Plume
Detached Plume
Total Percent NonIncreasing
Rice et al.
1995
271
8.1%
42%
32.8%
-
Benzene Plume Length Trend Distribution (%)
Mace et al.
Kamath et al. Shorr and Rifai SUMMARY
1,2
1997
2012
2002
566
217
42
36
6%
3%
5%
2.8%
48%
61%
14%
61.1%
32%
26%
81%
8.3%
2%
27.8%
17.3%
-
9%
-
0%
-
12%
-
92%
97%
95%
97%
94%
39
Plume Stability Condition
Number of Sites
Increasing
Stable
Decreasing
No Trend
Exhausted /Non-Detect Plume
Detached Plume
TBA Plume Length Trend Distribution (%)
Kamath et al. 2012
34
26%
15%
53%
6%
Total Percent Non-Increasing
68%
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Manuscript No. GW20131118-0253
Issued: 23 May 2014
Page 6 of 10
40
41
42
43
44
Notes:
1. Study data reported to the same number of significant digits as in the study. Summary values are rounded to the nearest
percentage for consistency.
2. Summary values are weighted mean values of the individual studies. To ensure that the summary values sum to 100
percent, categories that were not reported were assumed to have a percentage of 0 in calculation of the summary values.
45
4.
46
Concentration trend data were compiled and aggregated from seven studies that considered whether
47
MTBE, benzene, and/or TBA concentrations were increasing, stable, decreasing, no trend,
48
exhausted/non-detect, or were associated with a detached plume (Table S-3). Since these studies
49
employed a variety of methods, mostly using various statistical techniques, there are some differences
50
in how they accounted for stable/no-trend/exhausted trends, which is why this paper focuses on the
51
non-increasing values.
52
Table S-3: Concentration Trend Results for MTBE, Benzene, and TBA
CONCENTRATION TRENDS
MTBE Concentration Trend Distribution (%) in Monitoring Wells
Tarr and Galonski 2007
During
After MTBE
MTBE Use 2
Use 2
Concentration
Trend
Mace and
Choi 1998
Stevens
et al.
20061
No. of Wells
Increasing
Stable
Decreasing
No Trend
Exhausted /NonDetect Plume
Detached Plume
Total Percent NonIncreasing
471
7%
50%
9%
10%
83
7.2%
61.4%
31.3%
78
32%
68%
-
24%
-
93%
Kamath
et al. 2012
SUMMARY3,4
78
15%
85%
-
306
4%
6%
80%
10%
10165
9%
25%
45%
10%
-
-
-
11%
-
-
-
-
-
93%
68%
85%
96%
91%
53
Concentration Trend
No. of Wells
Increasing
Stable
Decreasing
No Trend
Exhausted /Non-Detect
Plume
Total Percent
Non-Increasing
Rice et
al. 1995
Benzene Concentration Trend Distribution (%)
in Monitoring Wells
Buscheck et
Mace et
Kamath et al.
al. 19966
SUMMARY3,4
al. 1997
2012
271
7.7%
15.5%
59.4%
-
119
9%
51%
40%
227
14%
27%
47%
-
288
2%
7%
83%
8%
905
8%
14%
63%
8%
17.3%
-
11%
-
8%
92%
91%
86%
98%
92%
Connor et al. (2014) – Supporting Information
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54
55
TBA Concentration Trend
Distribution (%)in
Monitoring Wells
Concentration Trend
No. of Wells
Increasing
Stable
Decreasing
No Trend
Exhausted /Non-Detect Plume
Total Percent Non-Increasing
Kamath et al. 2012
241
14%
9%
49%
28%
86%
56
57
58
59
60
61
62
63
64
65
66
67
Notes:
1. Mann-Kendall trend test results.
2. MTBE concentration data from Tarr and Galonski (2007) were analyzed using linear regression analysis for 78 wells at 25
sites for both pre-ban data and post-ban data.
3. Study data reported to the same number of significant digits as in the study. Summary values are rounded to the nearest
percentage for consistency.
4. Summary values are weighted mean values of the individual studies. To ensure that the summary values sum to 100
percent, categories that were not reported were assumed to have a percentage of 0 in calculation of the summary values.
5. 938 unique individual wells were evaluated, but since the pre- and post-removal data from Tarr and Galonski (2007) were
considered separately, there are 1016 total data values.
6. 10 of 11 sites had insufficient data and were assigned to the increasing category by Buscheck et al. (1996).
68
In one paper, the authors (Tarr and Galonski 2007) calculated linear regression statistics on
69
concentration trends over time, and they assigned any negative slope values to a decreasing trend.
70
They did not statistically evaluate whether their linear regression trends were significant. As a
71
conservative measure, we considered any positive regression slope to indicate an increasing trend,
72
which likely overestimates the percentage of increasing wells for this dataset. Furthermore, this study
73
considered MTBE trends during the use of MTBE as a gasoline additive, as well as trends after MTBE
74
use was phased out. Although not strictly independent datasets, we considered them as independent
75
datasets for the purposes of data aggregation.
76
Stevens et al. (2006) evaluated concentration trends in four different ways, with the primary objective of
77
determining whether the MTBE ban in Connecticut in January 2004 led to decreasing MTBE
78
concentrations in observation wells. The authors compiled a dataset of 83 observation wells at 22
79
different sites. First, they combined two years of pre-MTBE ban data and two years of post-MTBE ban
80
data for each of 83 wells and compared the means of the two datasets; the statistical significance of the
Connor et al. (2014) – Supporting Information
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81
difference in means was not determined. Second, they combined the last four monitoring events for
82
each of the 83 monitoring wells in one dataset and all other MTBE sampling data in a second dataset
83
and compared the means of the two datasets; again, the statistical significance of the difference in
84
means was not determined. Third, a Mann-Kendall trend analysis at the 90th confidence level was
85
conducted for each of the 83 monitoring wells to determine trends in MTBE concentrations over time.
86
Finally, a pooled variance T-test was conducted by combining all the pre- and post-ban MTBE data for
87
each of the 22 sites at the 90th confidence level. Results of these four tests are presented in Table S-4.
88
Table S-4: Results from Stevens et al. (2006) analysis
Pre-ban vs.
Post-ban (well by
well)
Early data to last
four monitoring
events
Mann-Kendall
Trend Analysis1
83
16.9%
83.1%
---
83
7.2%
92.8%
---
83
7.2%
61.4%
31.3%
No. of wells
Increase
Decrease
No Trend
Pooled pre-ban
and post-ban
data (by site)1
22 sites
(83 wells)
4.5%
54.5%
40.9%2
89
90
91
Notes:
1. Trends determined at 90th confidence level
2. Increasing and decreasing trends that were not statistically significant were taken to have no trend.
92
For the purposes of combining data from multiple studies, we only evaluated the results of the Mann-
93
Kendall trend analysis because this method was most similar to those employed in other studies used
94
in the combined data set. Also, Stevens et al. (2006) explicitly calculated those wells with no trend with
95
this method. Given that each of the four methods led to similar percentages of increasing and non-
96
increasing trends, we believe that selecting a single statistic does not impact the final results, and we
97
avoid counting the same dataset four times had we chosen to use each method independently in our
98
combined study dataset.
99
REFERENCES
100
Buscheck, T.E., D.C. Wickland, and D.L. Kuehne. “Multiple Lines of Evidence to Demonstrate Natural
101
Attenuation of Petroleum Hydrocarbons.” 1996. In: Proceedings of the Petroleum Hydrocarbons
102
and Organic Chemicals in Ground Water, pg. 445-460. National Groundwater Association/American
103
Petroleum Institute, Houston, Texas, November 1996.
Connor et al. (2014) – Supporting Information
Manuscript No. GW20131118-0253
Issued: 23 May 2014
Page 9 of 10
104
Happel, A. M., E.H. Beckenbach, and R.U. Halden. An Evaluation of MTBE Impacts to California
105
Groundwater Resources. 1998. Lawrence Livermore National Laboratory: UCRL-AR-130897.
106
Report submitted to the California State Water Resources Control Board Underground Storage
107
Tank Program, Department of Energy Office of Fossil Fuels, and the Western States Petroleum
108
Association. 68 pgs.
109
Kamath, R., J.A. Connor, T.E. McHugh, A. Nemir, M.P. Le, and A.J. Ryan. 2012. “Use of Long-Term
110
Monitoring Data to Evaluate Benzene, MTBE, and TBA Plume Behavior in Groundwater at Retail
111
Gasoline Sites.” Journal of Environmental Engineering, Vol. 138 (4): 458-469, April 2012.
112
Mace, R. E., R.S. Fisher, D.M. Welch, and S.P. Parra. 1997. Extent, Mass, and Duration of
113
Hydrocarbon Plumes from Leaking Petroleum Storage Tank Sites in Texas. Bureau of Economic
114
Geology, University of Texas at Austin, Austin, Texas. Geologic Circular 97-1.
115
Mace, R. E. and W.J. Choi. 1998. “The size and behavior of MTBE plumes in Texas.” In: Proceedings
116
of the Petroleum Hydrocarbons and Organic Chemicals in Ground Water, pg. 1-11. Houston,
117
Texas, November 11-13, 1998.
118
Newell, C.J. and J.A. Connor. 1998. Characteristics of Dissolved Petroleum Hydrocarbon Plumes:
119
Results from Four Studies. American Petroleum Institute Soil and Groundwater Bulletin 8. American
120
Petroleum Institute, Washington, D.C. December 1998.
121
122
Reid, J.B., H.J. Reisinger, P.G. Bartholomae, J.C. Gray, and A.S. Hullman. 1999. Comparative MTBE
versus Benzene Plume Behavior. BP Oil Company Florida Facilities, February 1999.
123
Reisinger, H.J., J.B. Reid, and P.J. Bartholomae. 2000. “MTBE and Benzene Plume Behavior: A
124
Comparative Perspective.” Soil, Sediment and Groundwater Journal, MTBE Special Issue, 43-46.
125
Rice, D.W., R.D. Grose, J.C. Michaelsen, B.P. Dooher, D.H. MacQueen, S.J. Cullen, W.E. Kastenberg,
126
L.G. Everett, and M.A. Marino. 1995. California Leaking Underground Fuel Tank (LUFT) Historical
127
Case
128
Restoration Division, Lawrence Livermore National Laboratory, Livermore, California. Submitted to
Analyses.
UCRL-AR_122207,
Environmental
Protection
Department,
Environmental
Connor et al. (2014) – Supporting Information
Manuscript No. GW20131118-0253
Issued: 23 May 2014
Page 10 of 10
129
the California State Water Resources Control Board Underground Storage Tank Program and the
130
Senate Bill 1764 Leaking Underground Fuel Tank Advisory Committee, November 16, 1995.
131
Rifai, H.S., G.G. Shorr, and A. Bagga. 2003. “MTBE Behavior at Field Sites and Plume
132
Characterization.” In: Proceedings of the Petroleum Hydrocarbons and Organic Chemicals in
133
Ground Water, pg. 138-145. Costa Mesa, California, August 19-22, 2003.
134
Rifai, H.S. and W.G. Rixey, 2004. Final Report: Characterizing the Intrinsic Remediation of MTBE at
135
Field Sites. EPA Grant Number: R828598C791, Subproject 791. Retrieved online on 21 October
136
2013:
137
http://cfpub.epa.gov/ncer_abstracts/index.cfm/fuseaction/display.abstractDetail/abstract/5882/report
138
/F.
139
Shih, T., Y. Rong, T. Harmon, and M. Suffet. 2004. “Evaluation of the Impact of Fuel Hydrocarbons and
140
Oxygenates on Groundwater Resources.” Environmental Science & Technology, Vol. 38 (1), 42-48,
141
doi: 10.1021/es0304650.
142
Shorr, G.L. and H.S. Rifai. 2002. “A Closer Look at MTBE Behavior within the Subsurface.” In:
143
Proceedings of the International Petroleum Environmental Conference, Albuquerque, New Mexico,
144
October 22-25, 2002.
145
Stevens, G.J., M.J. Metcalf, and G.A. Robbins. 2006. “Evaluation of the Effects of the Connecticut Ban
146
of MTBE on Ground Water Quality.” Department of Natural Resources Management and
147
Engineering, University of Connecticut, Storrs, CT, November 22, 2006.
148
Tarr, J.M. and A.M. Galonski. 2007. “MTBE After the Ban.” In: Proceedings of the Petroleum
149
Hydrocarbons and Organic Chemicals in Ground Water, pg. 148. National Groundwater
150
Association, Houston, Texas, November 5-6, 2007.
151
Wilson, B.H. 2003. “Comparison of Plume Lengths for MTBE and BTEX at 212 South Carolina Sites.”
152
In: MBTE Remediation Handbook, edited by E.E. Moyer and P.T. Kostecki. Amherst Scientific
153
Publishers, Amherst, Massachusetts.