PROJECT PHASE SUBMITTAL TYPE (check one) (check one) ¨ Site Investigation ¨ Work Scope ¨ Corrective Action Feasibility Investigation x Technical Report ¨ Corrective Action Plan ¨ PCF Reimbursement Request ¨ Corrective Action Summary Report ¨ General Correspondence x Operations & Monitoring Report MAY 2015 GROUNDWATER MONITORING REPORT FORMER EXIT 8 MOBIL / IRVING OIL CORP. PROPERTY #72619 ROUTE 131 / I-91 ASCUTNEY, VERMONT SMS #98-2524 Prepared for: Irving Oil 1 Germain Street, Brunswick Square, 7th Floor Saint John, NB Canada E2L 4V1 Contact: Erin Norton Tel: (506) 202-3269 email: [email protected] Prepared by: GeoInsight, Inc. 186 Granite Street, 3rd Floor, Suite A Manchester, New Hampshire 03101 Contact: Darrin L. Santos, P.G. Tel: (603) 314-0820 email: [email protected] September 2, 2015 GeoInsight Project 5650-000 File: 5650/CAP-CVR September 2, 2015 GeoInsight Project 5650-000 Gerold Noyes, P.E. Sites Management Section Vermont Department of Environmental Conservation 1 National Life Drive – Davis 1 Montpelier, VT 05626-3704 RE: May 2015 Groundwater Monitoring Report Former Exit 8 Mobil / Irving Oil Corp. Property #72619 – SMS #98-2524 Route 131 / I-91 Ascutney, Vermont Dear Mr. Noyes: At the request of Irving Oil Corporation, GeoInsight, Inc. (GeoInsight) prepared this report summarizing the May 2015 groundwater monitoring event performed at the Former Exit 8 Mobil / Irving Oil Corp. Property (#72619) located at Route 131 / I-91 in Ascutney, Vermont. A site locus map is presented as Figure 1 and a site plan is presented as Figure 2. The scope of work and associated costs for these activities were presented in a Work Plan Budget Sheet dated February 19, 2009, which was approved by the Vermont Department of Environmental Conservation (VTDEC) in a letter dated February 25, 2009, and amended by the VTDEC in a letter dated August 10, 2010. The monitoring program was changed from annual to biennial sampling in a VTDEC letter dated October 12, 2011 (the last monitoring event was performed in May 2013). GROUNDWATER MONITORING Sampling and Analysis GeoInsight performed a groundwater monitoring event at the site on May 21, 2015. During the event, groundwater elevations were gauged from seven monitoring wells (MW99-2, MW99-3, MW99-6, MW99-4, MW99-7, MW00-8, MW00-11 HA-1, HA-2, and HA-3). Groundw ater elevations were measured using an electronic water level meter. Groundwater gauging data is summarized in Table 1. Groundwater samples were collected from wells MW99-2, MW99-3, MW99-6, MW99-7, and HA-2 using new dedicated, disposable polyethylene bailers. Prior to sample collection, at least three times the volume of water in the wells was purged using the bailers or the wells were GeoInsight, Inc. GeoInsight, Inc. GeoInsight, Inc. 186 Granite Street, 3rd Floor, Suite A One Monarch Drive, Suite 201 200 Court Street, 2nd Floor Manchester, NH 03101-2643 Littleton, MA 01460-1440 Middletown, CT 06457-3341 Tel (603) 314-0820 Tel (978) 679-1600 Tel (860) 894-1022 Fax (603) 314-0821 Fax (978) 679-1601 Fax (860) 894-1023 www.geoinsightinc.com ® purged dry. After a short stabilization period (approximately 30 minutes), groundwater samples were collected from the monitoring wells for analyses of volatile organic compounds (VOCs). The groundwater samples were analyzed by United States Environmental Protection Agency (USEPA) Method 8260B, but were reported using the VTDEC USEPA Method 8021 list of selected petroleum constituents. Table 2 provides a current and historical summary of ground water VOC data for the site. The laboratory analytical report for the May 2015 monitoring event is presented in Attachment A. An updated discussion of groundwater impacts at the site is provided in the Updated Conceptual Model section of this report. Quality Assurance/Quality Control GeoInsight included a trip blank sample during the May 2015 monitoring event to evaluate sampling quality assurance and quality control. GeoInsight also reviewed the surrogate recovery data reported by the laboratory for the May 2015 monitoring event, which were within the acceptable limits listed by the laboratory in the analytical reports. VOCs were not detected above the laboratory reporting limits in the trip blank sample submitted for the May 2015 monitoring event. The trip blank sample was comprised of a laboratory-prepared VOC vial containing deionized water, which accompanied the sample containers in a cooler from delivery from the laboratory through sample receipt by the laboratory. UPDATED CONCEPTUAL MODEL Groundwater Elevations and Flow Direction Using the groundwater elevation data collected in May 2015, GeoInsight plotted groundwater elevation contours, which are presented on Figure 3. The observed groundwater flow pattern for May 2015 indicated groundwater flow was generally directed to the east and northeast, toward Route 131 and the stream located northeast of the site. This groundwater flow pattern was generally consistent with historical observations. Groundwater elevations for on-site wells MW99-2, MW99-3, MW99-6, and MW99-7 were generally consistent with the lower elevations on record (the groundwater elevations in wells HA-1, HA-2, and HA-3, which are immediately adjacent to the stream northeast of the site, do not fluctuate as significantly). Constituent Concentrations and Dissolved-Phase Plume During the May 2015 monitoring event, VOCs were detected at concentrations exceeding the Vermont Primary Groundwater Enforcement Standards (VPGESs) in the groundwater sample collected from wells MW99-3 and MW99-6 only. The only other groundwater sample to show detections of VOCs above laboratory reporting limits was the sample collected from monitoring well MW99-7, with 3 micrograms per liter (µg/L) of toluene, 57 µg/L of xylenes, and 14 µg/L of naphthalene. VOCs were not detected above laboratory reporting limits in samples collected in the remaining on-site and off-site monitoring wells. During May 2013 (last event prior to 2015), VOCs were detected at concentrations above VPGESs at on-site well MW99-3. September 2, 2015 GeoInsight Project 5650-000 Page 2 ® Bas ed upon the recent and historical data (Table 2), VOC concentrations are highest at mon itoring well MW99-3 (7,321 µg/L total detected VOCs in 2013; total detected VOCs 32,707 µg/L in 2015). VOCs detected at monitoring well MW-99-6, while variable during recent moni toring events, have also exhibited relatively high total VOC concentrations recently. Conc entrations of benzene, methyl tertiary butyl ether (MTBE), and naphthalene detected in ground water samples during May 2015 were plotted on Figure 4 along with inferred dissolved plume iso-contours. The iso-contours from the May 2013 monitoring event are also plotted on Figure 4 for comparison. As the figure illustrates, the dissolved plume extends from the vicinity of the plume center of mass located near well MW99-3, downgradient toward off-site monitoring well HA-2, consistent with expected migration pathways based upon historical groundwater flow patterns. Charts illustrating benzene and MTBE concentrations in select wells are presented in Attachment B. The data plotted on the chart for well MW99-3 (in the plume center of mass) exhibit a moderate trend of exponential decay over the monitoring history, as indicated by regression coefficient (R2) values of 0.66 and 0.68, respectively, for the exponential curves fitted to benzene and MTBE data. The MTBE data plotted for on-site well MW99-6 and off-site monitoring well HA-2 also exhibit moderate exponential decay trends (Attachment B). CONCLUSIONS AND RECOMMENDATIONS VOC concentrations increased between the May 2013 and May 2015 sampling events primarily in the groundwater collected from well MW99-3. There was an also a slight increase in VOC concentrations detected in groundwater collected rom well MW99-6. It is too early to conclude if these higher concentrations represent the migrating of the plume or short-term conditions (possibly resulting from high groundwater elevations). Historically, benzene and MTBE concentrations exhibit decreasing trends at well MW99-3 and the leading edge of the dissolved plume near the stream downgradient of the site appears to be contracting. Based upon the increases noted in 2015, GeoInsight recommends groundwater monitoring be increased to an annual basis for 2016 only to evaluate recent variable VOC trends. September 2, 2015 GeoInsight Project 5650-000 Page 3 ® If you have questions regarding the contents of this letter report, please contact us at (603) 314-0820. Sincerely, GEOINSIGHT, INC. Darrin L. Santos, P.G. Brian D. Kisiel, P.G. Senior Geologist President Attachments cc: Erin Norton, Irving Oil Corporation George Lamb P:\5650 Irving Oil Ascutney VT\May 2013\5650May2013Rpt.doc September 2, 2015 GeoInsight Project 5650-000 Page 4 ® FIGURES Site GeoInsight Practical in Nature GeoInsight Practical in Nature GeoInsight Practical in Nature GeoInsight Practical in Nature ® TABLES TABLE 1 SUMMARY OF GROUND WATER ELEVATIONS FORMER EXIT 8 MOBIL / IRVING OIL CORP. PROPERTY #72619 ROUTE 131 / I-91 ASCUTNEY, VERMONT SMS #98-2524 Well Depth Top of Well I.D. FT-BGS Casing Elevation MW99-1 25 498.99 MW99-2 30 497.57 MW99-3 30 495.35 MW99-4 33 497.77 MW99-5 30.5 497.96 MW99-6 30.5 492.29 MW99-7 30 489.81 MW00-8 35 498.24 MW00-9 35 496.22 MW00-10 35 497.69 MW00-11 53 498.03 HA-1 7 466.88 HA-2 7 465.42 HA-3 7 466.92 Well I.D. 5/28/1999 6/23/1999 7/22/1999 9/1/1999 10/14/1999 11/11/1999 12/9/1999 1/13/2000 2/3/2000 3/28/2000 MW99-1 DRY DRY DRY DRY DRY DRY - - - - MW99-2 469.60 468.85 468.42 468.17 468.13 468.23 468.47 468.78 468.78 470.63 MW99-3 468.82 467.99 467.69 466.69 467.01 467.31 467.44 467.73 467.83 470.95 MW99-4 469.09 468.81 468.13 467.26 467.72 467.88 468.17 468.52 468.47 470.31 MW99-5 468.88 - 469.49 469.95 469.87 472.43 Monitoring wells MW99-5, 6, and 7 installed MW99-6 464.25 - 464.91 465.26 465.26 - October 6, 1999.