1、American Petroleum Institute DELINEATION AND CHARACTERIZATION OF THE BORDEN MTBE PLUME: AN EVALUATION OF EIGHT YEARS OF NATURAL ATTENUATION PROCESSES Health and Environfnental Sciences Department Publication Number 4668 June 1998 STD.API/PETRO PUBL LibbA-ENGL 1998 0732290 ObLL359 703 m - T - STD.API
2、/PETRO PUBL 4bb-ENGL 1778 = 0732270 0b113b0 425 W American Petroleum Institute American Pet roleum I nst it Ute Environmental, Health, and Safety Mission and Guiding Principles MISSION The members of the American Petroleum Institute are dedicated to continuous eflorts to improve the compatibility of
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10、rs who produce, handle, use, transport or dispose of similar raw materials, petroleum products and wastes. Delineation and Characterization of the Borden MTBE Plume: An Evaluation of Eight Years of Natural Attenuation Processes Health and Environmental Sciences Department API PUBLICATION NUMBER 4668
11、 PREPARED UNDER CONTRACT BY: MARIO SCHIRMER JAMES F. BARKER CHRISTINA E. HUBBARD UNIVERSITY OF WATERLOO DEPARTMENT OF EARTH SCIENCES INSTITUTE FOR GROUNDWATER RESEARCH WATERLOO, ONTARIO, N2L 3G1 CANADA JUNE 1998 American Petroleum Institute STD.API/PETRO PUBL Ybb8-ENGL 1998 W 0732290 ObLL3b2 2T8 FOR
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15、al system, or transmitted by any means, electronic, mechanical, photocopying, recording, or otherwise. without prior written permission from the publishex Contact thepublishec API Publishing Services, 1220 L Street, N.W, Wshington, D.C. 20005. Copyright Q 1998 American kmleum Institute iii STD.API/P
16、ETRO PUBL LibbA-ENGL 1998 m 0732290 OblL3b3 L3Li m ACKNOWLEDGMENTS THE FOLLOWING PEOPLE ARE RECOGNIZED FOR THEIR CONTRIBUTIONS OF TIME AND EXPERTISE DURING THIS STUDY AND IN THE PREPARATION OF THIS REPORT API STAFF CONTACT Bruce Bauman, Health and Environmental Sciences Department MEMBERS OF THE SOI
17、L AND GROUNDWATER TECHNICAL TASK FORCE Tim Buscheck, Chevron Dwayne Conrad, Texaco Bob Hockman, Amaco Dorothy Keech, Keech Associates Gene Mancini, Arco Mark Passarini, Texaco Joe Saianitro, Shell Curt Stanley, Shell The views expressed here are those of the authors. We would also like to thank Tina
18、 Hubbard for her advice and many insightful discussions about the earlier part of the experiment and the data analysis. We also would like to thank Clint Church, Jim Pankow and Paul Tratnyek of the Oregon Graduate Institute for the analyses of the samples and many helpful discussions. As always, a l
19、arge group at the University of Waterloo contributed advice, assistance and support. iv STD-API/PETRO PUBL 4bb-ENGL L 0732290 Obll3b4 O70 m ABSTRACT In 1988, a natural gradient tracer test was performed in the shallow sand aquifer at Canadian Forces Base (CFB) Borden. This study investigated the fat
20、e of a methyl-tertiary-butyl- ether (MTBE) plume introduced into the Borden aquifer in order to quantify the status of this contaminant in shallow, aerobic settings. Solutions of groundwater mixed with oxygenated gasoline were injected below the water table along with chloride (Ci-), a conservative
21、tracer. The migration of benzene, toluene, ethylbenzene, the xylenes (BTEX); MTE3E; and C1- was monitored in detail for about 16 months. The mass of BTEX compounds in the plume diminished significantly with time due to intrinsic aerobic biodegradation. MTBE, on the other hand, was not measurably att
22、enuated. In 1995, additional exploratory sampling of the C1- and MTBE plumes found both at lower concentrations. The MTBEKl- ratio was more than two orders of magnitude lower than that of the injection solution and earlier sampling events suggesting some mass loss of MTBE may have occurred. In 1995-
23、96, a comprehensive groundwater sampling program was undertaken to define the mass of MTBE still present in the aquifer. Since the plume had migrated into an unmonitored section of the Borden aquifer, numerical modeling and geostatistical methods were applied to find an optimal sampling grid. A driv
24、e-point profiling system was then used to obtain groundwater samples. In the 1995-96 sampling rounds, MTBE concentrations measured were more than an order of magnitude lower than expected based on the modeling that considered dispersion and diffusion as the only attenuation processes. A mass balance
25、 for the remaining MTBE mass in the aquifer eight years after injection was performed using the geostatistical software packages GEOSOFTTM and GMSTM. Although the possibility exists that part of the MTBE plume was missed, the extensive sampling in a well-characterized aquifer, with the location of M
26、TBE where it was anticipated, suggests otherwise. Only about 3 percent of the initial MTBE mass was found and it is hypothesized that biodegradation played an important role in the attenuation of the MTBE within the Borden aquifer. Nevertheless, additional lines of evidence of biodegradation, such a
27、s laboratory batch and column experiments, are necessary to cob this possibility. Studies are underway, but no confirming laboratory evidence has been found to date. Thus, while there is confidence that MTBE mass has been lost, biodegradation cannot yet be confirmed as the process. 1-1 STD.API/PETRO
28、 PUBL 4bbA-ENGL 1978 0732290 ObLL3b5 TO7 TABLE OF CONTENTS Section EXECUTIVE SUMMARY ES- 1 1 . INTRODUCTION 1 . 1 2 . THE MTBE FIELD EXPERIMENT AT CFB BORDEN, ONTARIO 2-1 3 . METHODS OF GROUNDWATER SAMPLING AND ANALYSIS . 3-1 4 . SAMPLING STRATEGY FOR THE 1995-96 SAMPLING ROUNDS . 4-1 5 . THE 1996 S
29、AMPLING RESULTS 5-1 5.1. MTBE . 5-1 5.1.1 MTBE Coarse Grid Sampling Results . 5-1 5.1.2 MTBE Fine Grid Sampling Results . 5-2 5.1.3 Additional MTBE Sampling Results 5-5 5.2. TERT-BUTYL ALCOHOL (TBA) AND TERT-BUTYL FORMATE (TBF) 5-5 5.3. CHLORIDE 5-6 5.4. BTEX 5-6 5.5. OXYGEN 5-7 5.6. SULFATE . 5-9 5
30、.7. AMMONIA . 5-9 6 . SUMMARY AND DISCUSSION 6-1 7 . FUTURE WORK 7-1 REFERENCES . R-1 Appendix A PRELIMINARY MODELING AND RESULTS OF THE 1995 SAMPLING ROUND A-1 Appendix B TWO-DIMENSIONAL MODELING USING RANDOM HYDRAULIC CONDUCTIVITY FIELDS . B-1 Appendix C DETERMINATION OF THE OPTIMAL, GRID SPACING
31、USING GEOSTATISTICAL METHODS . C- 1 STD.API/PETRO PUBL -IbbB-ENGL 1998 0732290 ObL13bb 7V3 2-1. 2-2. 2-3. 2-4, 2-5. 4-1. 4-2. 4-3. 4-4. 4-5. 5-1. 5-2. 5-3. 5-4. LIST OF FIGURES Novak et al., 1985), recent work has provided increasing evidence of at least limited biodegradability. Salanitro et al. (1
32、 994,1996) isolated a bacterial culture that could degrade MTBE under laboratory conditions. In addition, Borden and Co-workers found evidence of MTBE biodegradation at a field site in North Carolina combining information obtained by laboratory batch experiments and field monitoring (Borden et al.,
33、1997). As near-source concentrations of MTBE may exceed 10,000 - 20,000 pgL, reliance on dispersive attenuation processes alone may be insufficient to provide adequate protection to down-gradient receptors. As a result, the occurrence of MTBE in gasoline-impacted ES-2 STD-API/PETRO PUBL 4bbB-ENGL 17
34、98 W O732290 Ob11370 374 W groundwater may sometimes limit the use of intrinsic remediation because MTBE is more mobile and more persistent than BTEX in shallow, aerobic aquifers. Compared to BTEX, very little field information is available to provide reliable estimates of its natural attenuation, o
35、r the factors that may influence its rate of natural attenuation at specific sites. The study described in this report is intended to provide a better understanding of the behavior of MTBE in groundwater, especially the role of biodegradation. THE INITIAL, INJECTION OF MTBE In 1988 and 1989, a natur
36、al gradient tracer test was performed in the shallow, aerobic sand aquifer at Canadian Forces Base (CFB) Borden in Ontario, Canada. A key objective of that study was to evaluate the fate and transport of MTBE and BTEX compounds. About 2800 liters of groundwater, spiked with C1- (448 mgk), gasoline-d
37、erived organics (including about 19 mg/L BTEX) and MTBE (269 mgk), were injected 1.5 m below the water table. This mixture created a discrete slug of MTBE-contaminated groundwater traveling at a velocity of about 33 dyear under natural gradient conditions. Separate, adjacent dissolved plumes were al
38、so injected at that time representing releases from non-oxygenated gasoline and from a methanollgasoline mixture. The migration of the contaminants was monitored by detailed groundwater sampling using a dense network of multilevel piezometers, typically using 14 depth-points over a 2.8 - 4.2 m verti
39、cal zone. These sampling snapshots of contaminant distribution were obtained 6,42, 106,317,398, and 476 days after injection. The BTEX compounds underwent rapid aerobic biodegradation and were almost completely attenuated during the initiai 16 month period. The experiment and the fate of the monitor
40、ed compounds are discussed in detail by Hubbard et al. (1 994). Based on the total mass present, the mass ratio MTBE/CI- was about 0.59 initially and remained about the same until day 476 when it had decreased to 0.43. The MTBE/CI concentration ratios for single samples ranged from 0.33 to 1 .O for
41、the initial 476 days of the experiment. Due to the uncertainty of the field mass balance estimates, degradation of MTBE ES-3 STD-APIIPETRO PUBL 4bb8-ENGL 1798 = 0732290 ObL137L 200 could not be demonstrated and it was concluded at the time that the compound was either persistent over the 16 months o
42、f monitoring or degrading at a rate not detectable under the experimental conditions (Hubbard et al., 1994). THE MTBE PLUME EIGHT YEARS LATER No additional monitoring of the injected MTBE plume had occurred subsequent to the final round of sampling for the original study in 1989. In late 1995, in re
43、sponse to increased interest in the long-term behavior of MTBE in groundwater, a comprehensive sampling program was undertaken to locate and define the mass of MTBE still remaining in the aquifer. Three major sampling events were planned and designed with the use of both analytical and numerical flo
44、w/transport models as well as with statistical analyses. The main goal was to delineate the MTBE plume in enough detail to perform a reliable mass balance and to compare the remaining MTBE mass in the aquifer with the amount originally injected. The physical properties, hydraulics and geochemistry o
45、f the Borden aquifer have been exceptionally well characterized. The aquifer is relatively homogeneous and the statistical properties describing the hydraulic conductivity field are well defined. The aquifer lies over an extensive regional clayey and sandy silt aquitard that is approximately 8 m thi
46、ck at the field site. The mean groundwater velocity in the aquifer is about 33 dyear and the northwards flow direction fluctuates seasonally about 20 degrees. The Borden aquifer has a relatively low carbon content of 0.02 percent and thus a low sorption capacity for organic compounds. The analytical
47、 and numerical models used to characterize flow and transport predicted that by the end of 1995, the MTBE plume should have migrated 240 m beyond the injection location and about 200 m beyond the last sampling snapshot taken at 476 days. Given that the plume had traveled well beyond the 1988/89 samp
48、ling grid, no network of multilevel sampling devices was available for sampling. Rather than install a new multi-level piezometer network, the Waterloo drive-point profiler was used to collect multiple groundwater samples at various ES-4 STD=API/PETRO PUBL 4bbB-ENGL 3778 D 0732270 Ob33372 147 W dept
49、hs at a number of locations. With this direct-push system, a stainless steel sampling device is driven downward by pressure and vibration. De-ionized water is constantly injected to keep the sampling ports of the drive-point piezometer open and to avoid cross-contamination. Samples are collected at desired depths through stainless steel or Teflon tubing connected through the drive rods to a peristaltic pump. Three sampling rounds were carried out (November 1995; July/August 1996; November 1996). Samples obtained in the first sampli
