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JUNE 2010GROUND\ilATER MONITORING RESULTS

\Benson Town Garage

Hulett Hill RoadBenson, Vermont

' ' SMS Site # 9l-1166SMS Project Managpr: Lynda Provencher

Verterre # 95-036

Date Submittedi July. 30, 2ol0

Report Prepared for:Mr. Ronald Ryan, Superintendent

Addison-Rutland- Supervisory UnionNorth Park Place

Fair Haven, Vermont 05743-1094

Written By:

Reviewed By:

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Copyright @ 2010All rights reserved. No portion of this report may be copied without prior written permission of The Vertèrre Group

414 Roosevelt Highway, Suite 200 Colchester, Vermont 05446 ' Te|802.654.8663 ' Fax 802.654.8667

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Initial Site InvestigationCorrective Action feasibilityInvestigation

Corrçctive Action Plan

Corrective Action Summary RptMonitoring Report

D Work Scope./ Technical ReportE.,PCF Reimbursement Request

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Benson Town GarageBenson, VermontSMS Site No. 9l-l 166

I.O INTRODUCTION AND BACKGROUND

This report was prepared by The Verterre Group (Vertene) to present the findings of the groundwatersampling event at the Benson Town Garage (the SITE), located in Benson, Vermont, (SMS SITE No.9l-l166). A SITE Location Map and a SITE Plan are provided as Figures I and2, respectively.

The site is currently a town garage facility with no known underground storage tanks (USTs). Anaboveground storage tank (AST) at the site is used for diesel fuel for the Town vehicles. Previously,the property was occupied by a privately-owned vehicle service garage.

During the removal of a former underground storage tank (UST) system at the site in I99l,arelease ofpetroleum contamination was discovered, and soil and groundwater were found to be impacted.

The monitoring activities that have been conducted and presented in this report include:

o Collection of depth to water measurements used for the calculation of groundwater elevations;o Collection of groundwater samples from MW-l01 and MW-I02 for the determination of 80218

volatile organic compounds (VOCs); and,o Abandonment of monitoring wells MV/-2, MW-l04 and MW-203.

The following reporting work was also performed after the above activities were complete:

Preparation of a groundwater contour map which illustrates an interpretation of groundwaterflow underlying the SITE at the time of sampling;Preparation of a contaminant distribution plan; and,

Completion of this groundwater monitoring report.

2.0 SUMMARY OF ACTIVITIES

Vertere conducted groundwater monitoring activities at this SITE on June 9, 2010. This samplingevent included the collection of depth to groundwater data and groundwater samples from on-SITEmonitoring wells MW-101 and MW-102. In addition monitoring wells MW-2, MW-104 and MW-203were properly abandoned at this time. MW-103 had previously been destroyed.

To allow for a representative groundwater sample, each well was purged of three (3) volumes of waterwith a dedicated bailer. Purge water from the wells was discharged directly to the ground surface.

Sampling at each monitoring well was conducted with dedicated bailers.

Quality assurance/quality control (QA/QC) samples that were collected during this sampling eventincluded one (l) duplicate sample collected from MV/-l0l (labeled DUP-l) and one (1) Field Blank.All samples were submitted for VOC analysis by US EPA Method 80218. Resource Laboratorieslocated in Portsmouth, New Hampshire performed the laboratory analyses.

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Verterre Project No. 95-036

Benson Town GarageBenson, VermontSMS Site No. 9l-l166

3.0 GROUND\ilATER ANALYTICAL RESULTS

3.1 Groundwater Elevation and FIow Direction

Groundwater elevation data is presented in Table I and depicted on the Groundwater Elevation Plan

presented as Figure 3. Graphical summaries of water levels for individual monitoring wells are

presented in Appendix A.

Depth to water levels ranged from 0.98 feet to 2.49 feet below top of casing (btoc) in MW-102 and

MV/-I01, respectively. On average, the water table elevation was approximately 0.05 feet higher than

the May 2009 sampling round. The water level in MW-102 was not within the wells screen area. Nomeasurable free product was detected during this sampling round; however a petroleum sheen was

noted in well MW-101.

Groundwater contours could not be calculated with only two monitor wells however, groundwater flowdirection has historically flowed to the south.

3.2 Analytical Results

The current groundwater sampling results are summarized in Table 2, the complete analytical

laboratory report is provided as Attachment 1. Graphical trend analyses of historical data of the

monitor wells are provided in Appendix A. A Contaminants Distribution Plan is presented as Figure4.

The maximum dissolved concentration of total contaminants of concem (COCs) was reported inmonitoring well MW-l01 at 1,780 micrograms per liter (pgll). MW-l01 is located within the formerunderground storage tank (UST) cavity. COCs were not reported above their respective Method

Detection Limits (MDLs) in MW-102.

Benzene was not reported above the MDL in any sampled well; however the reporting limit in MV/-101 was raised above the VGES of 5 pgll, due to laboratory dilution.

Toluene was not reported above the MDL or the VGES of 1,000 pgll in any sampled well or the

surface water sample.

Ethylbenzene was reported above the MDL but below the VGES of 700 þg4 in MW-101 (1a0 pgll).Ethylbenzene was not reported above the MDL in any other sample well.

Total Xylenes were reported above MDL but below the VGES of 10,000 ¡rgll in MW-101 (670 pgll).Total xylenes were not reported above the MDL in any other sampled well.

Methyl-tertiary-butyl ether (MTBE) was not reported above the MDL or the VGES of 40 ¡tgll in any ofthe sampled wells.

Vertene Project No. 95-036

Benson Town Garage

Benson, VermontSMS Site No. 9l-1166

Trimethylbenzenes (135 &124) were reported above the combined VGES of 350 pgll in MW-101 at

860 pgll. Trimethylbenzenes were not reported above the MDL in any other sampled well.

NaphthalenewasreportedabovetheVGES of 20 ¡^rgllinMW-l0l (110pg/l). Naphthalenewasnotreported above the MDL in any other sampled well.

Since the last sampling round in May 2009, COC and MTBE levels fluctuated as follows:

WellLocation COCs MTBE Sheen Present

MW-l0l + nc/nd yes

MW-102 nc/nd no

+ increase nc no change nd not detected - decrease nl not located ns not sampled

3.3 QA/QC Results

The Relative Percent Difference (RPD) for total COCs in sample MW-l0l and its duplicate, DUP-1

was 6.50/o. The RPD was not calculated for MTBE since both results were less than the detection

limits. An RPD of up to 25%ois generally considered acceptable for precision.

The laboratory data was evaluated for the following parameters prior to acceptance in this report:

o conect sample ID's;o analysis date within method specified holding times;. acceptable detection limit multipliers;o acceptable matrix spikes (MS), where applicable;o acceptable MS duplicates (MSD), where applicable; and,o acceptable RPD between MS and MSD, where applicable.

The Field Blank contained no detectable levels of target anal¡es.

Based on Vertene's QA/QC evaluation, the data was found to be acceptable.

4.0 FINDINGS AND CONCLUSIONS

Based upon information and anal¡ical data collected during this scope of work, Verterre offers the

following:

o Groundwater samples were collected from MW-l0l and MW-I02 on June 9, 2010.

o Additionally, on the same date monitoring wells MW-2, MW-104 and MW-203 were properly

abandoned. MW-103 had previously been destroyed.

o MW-101 contained trimethylbenzenes and naphthalene at concentrations that exceed the VGES.

Ethylbenzene, and total xylenes were reported above the MDLs but below the VGES in MW-101.

Verterre Project No. 95-036

Benson Town Garage

Benson, VermontSMS Site No. 9l-l166

o COCs were not reported above the MDLs in MW-102.

o Groundwater flow direction at the SITE has historically flowed to the south.

o No measurable free product was detected during this sampling round; however a petroleum sheen

was noted in well MW-101.

o Concentrations of total COCs in the source area have generally remained stable since 1994 and

decreasing since April 1998.

5.0 RECOMMENDATIONS

Based on the available data, Verterre recommends continuing annual groundwater monitoringactivities. The next round of groundwater monitoring would occur in June 20ll and would involve

sampling MW-101 and MW-l02 for VOCs via US EPA Method 80218. Depth to water will also be

collected at these wells.

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Vertene Project No. 95-036