Awareness of 1,4-dioxane as a contaminant associated with chlorinated volatile organic compound (CVOC) plumes has raised public and regulatory concerns over past or potential future exposure. Because 1,4-dioxane?s water solubility and low soil-partitioning result in 1,4-dioxane migration ahead of co-released CVOCs, a plume previously defined by CVOC extent required timely re-characterization at NAS Brunswick. The objective of the investigation was to use piezometers and a Headspace Solid Phase Micro-Extraction with Gas Chromatography/Mass Spectrometry (HS/SPME/GC/MS) method for rapid analysis of samples to delineate a 1,4-dioxane plume in a wetlands.
Limited wetlands access and project economics required setting proper piezometer screen intervals using hollow-stem auger (HSA) methods to intercept 1,4-dioxane during a single mobilization. The original proposed investigation plan was based on a conventional approach with long equipment down-times waiting for off-site analytical results at a costly premium for quick turnaround time. However, replacement of the conventional approach with the innovative HS/SPME/GC/MS method allowed for plume characterization using a Triad dynamic work strategy.
Using HS/SPME/GC/MS, the Henry?s Law dynamic equilibrium between gas-phase and dissolved 1,4-dioxane is disturbed by irreversible 1,4-dioxane adsorption onto the SPME fiber. Following Le Chatelier's principle, there is a net transfer of 1,4-dioxane from solution to gas-phase prior to SPME extraction, which results in higher extraction efficiencies compared to purge and trap methods.
Open communication and systematic planning with initially sceptical stakeholders allowed for objective evaluation and managing uncertainty in using such an innovative method in the field for the first-time. A Demonstration of Method Applicability (DMA) to show the utility of the HS/SPME/GC/MS method was conducted prior to and during the field program at the project site. USEPA provided performance evaluation (PE) samples for analysis and quality assurance (QA) samples were sent to an off-site Navy certified laboratory. Statistical evaluation of these PE and QA analyses was conducted, and the technique was deemed acceptable for use.
An adaptive sampling approach was followed once the HS/SPME/GC/MS real-time field characterization method was approved for use, which allowed for refinement of the conceptual site model (CSM) and a more cost-effective plume characterization within a single field mobilization.
|Site Name||Mere Brook and Merriconeag Stream Floodplain and Upper Area Investigation, Eastern Plume (OUs 2 and 5), Naval Air Station (NAS) Brunswick|
|Site Type||Aircraft Rework Facility|
|Site Regulatory ID||EPA ID#: ME8170022018/ Site ID#: 0101073|
|Project Lead Type||U.S. Navy Lead|
|Regulatory Lead Program||Base Realignment and Closure (BRAC)|
|Reuse Objective Identified||Yes|
|Proposed Reuse:||Residential and Ecological|
NAS Brunswick is an active base owned and operated by the Federal government through the Department of the Navy. In 1987, NAS Brunswick was placed on the National Priorities List (NPL) by the U.S. Environmental Protection Agency (EPA) and is currently participating in the Navy?s Installation Restoration Program. In 2005, NAS Brunswick was included in the Department of Defense (DoD) Base Re-Alignment and Closure (BRAC) list of facilities to be closed, however the base will continue to operate through 2010.
The Eastern Plume is comprised of groundwater contamination resulting from three sites; Site 4 - Acid Caustic Pit, Site 11 - Fire Training Area, and Site 13 - Defence Reuse and Marketing Office. The Eastern Plume is identified as OUs 2 and 5, and is located within the central and eastern portion of NAS Brunswick. The Eastern Plume has been attributed to past solvent disposal practices from Site 4, Site 11, and Site 13, which led to contaminants leaching into groundwater. The dissolved-phase plume associated with these disposal activities was found to consist primarily of CVOCs. The Mere Brook/ Merriconeag Stream confluence and the associated floodplains are located to the east and southeast of the Eastern Plume. The area of investigation is located in the southeast portion of the Eastern Plume.
The goal of this investigation was to address data gaps associated with previous investigative actions conducted in Mere Brook, Merriconeag Stream, and the associated floodplain areas. Specific objectives of the investigation include the following:
Four phases of work were scheduled to be completed between February through September 2007. Not all phases were conducted during the same mobilization.
Geological - Results of the soil boring program indicate geologic conditions within the Mere Brook and Merriconeag Stream confluence and floodplain areas are homogeneous with conditions observed during previous investigations conducted within the Eastern Plume. A distinct, mappable lower sand unit was evident in the lower portion of the transition zone directly above the top of clay. See cross sections in ground water flow maps. This lower sand unit is comprised of gray/brown fine to coarse sand and was observed in each of the deep monitoring well borings but was not observed in piezometer borings. On the eastern side of Mere Brook and Merriconeag Stream, current and historical indicate the continued gradual rise in elevation of the confining clay surface and top of bedrock surface provides a flow boundary which limits contaminant migration to the east of Mere Brook and Merriconeag Stream.
Hydrogeological - Groundwater flow directions indicate a predominately north to south flow direction in the northern portion of the site above the Mere Brook and Merriconeag Stream confluence and floodplain area, and a predominately west to east flow direction in the southern portion of the site. See cross sections in ground water flow maps. Site groundwater flow directions generally follow site surface water flow directions (Mere Brook flows west to east, and Merriconeag Stream flows north to south) within the area of investigation. Groundwater flow directions indicate a predominately north to south flow direction in the northern portion of the site above the Mere Brook and Merriconeag Stream confluence and floodplain area, and a predominately west to east flow direction in the southern portion of the Investigation Area. Groundwater flow directions within the Investigation Area generally follow surface water flow directions (i.e., Mere Brook west to east, and Merriconeag Stream north to south).
Groundwater Sampling - Analytical results indicate that concentrations of chemical constituents of the Eastern Plume have migrated to the south and east of the currently delineated extent of the Eastern Plume, consistent with measured groundwater contours See data maps. CVOCs (including vinyl chloride) and 1,4-dioxane were detected within the area of the Mere Brook and Merriconeag Stream confluence and floodplain wetlands areas in exceedance of Maine maximum exposure guidelines (MEGs) and EPA maximum contaminant levels (MCLs) for drinking water/residential exposure. The lower sand unit appears to be the preferential pathway for contaminant migration from the Eastern Plume into the Mere Brook and Merriconeag Stream floodplain areas. This is evident when comparing contaminant concentrations reported in the shallow and intermediate monitoring wells to concentrations in the deep monitoring wells.
Concentrations of 1,4-dioxane were not detected in any of the shallow monitoring wells, in two of the intermediate wells at 11.5 ug/l, and 198 ug/L, and in all six of the deep monitoring wells at concentrations ranging from 14.4 ug/L in to 171 ug/L. A review of the total concentrations of CVOCs in groundwater also indicates higher concentrations in most of the deeper intervals. Geological cross-sections interpreted from soil boring logs generated during the investigation illustrate the gradual rise in elevation of the three primary overburden units (upper sand unit, transition/lower sand unit, and clay layer) from north to south in the northern portion of the site, and from west to east in the southern portion of the site. See cross sections in ground water flow maps.
Of the 73 confirmatory groundwater samples collected during this investigation, 29 samples contained CVOCs and/or 1,4-dioxane at concentrations exceeding regulatory criteria. In groundwater samples collected from the upland monitoring wells surrounding the wetland areas, contaminant concentrations were significantly greater in samples collected from the deep monitoring wells screened in the lower sand unit then in samples collected from the shallow and intermediate monitoring wells screened in the upper sand and transition zones. In groundwater samples collected from the piezometers, installed at lower elevations within floodplain, contaminant concentrations were generally greater in the shallow and intermediate screened intervals (approximately two feet to 12 feet bgs) than in the deeper screened intervals.
Conclusions based on the geological, hydrogeological, and analytical data indicate that contaminants of the Eastern Plume are migrating from north to south and from west to east into the Mere Brook and Merriconeag Stream floodplain area via the lower sand unit. As the lower sand unit approaches the floodplain area, it rises in elevation following the top of clay. The lower sand unit thins and gradually pinches out. Groundwater from the lower sand unit is under artesian conditions, with a prominent upward flow gradient. The Eastern Plume contaminants are migrating upward in the vicinity of the Mere Brook and Merriconeag confluence through the sand and silty sand layers of the transition zone into the upper sand unit, eventually discharging into the floodplain area and ultimately into Mere Brook and Merriconeag Stream.
Benefits included real-time decision making based on adaptive sampling (i.e., a dynamic work strategy). The DWS produced cost and time savings by eliminating the need for fixed-laboratory rapid turn-around-time with associated surcharges, equipment and personnel stand-by, and/or multiple field mobilizations to the site.
The initial CSM for the Eastern Plume was developed in 2000 and served as an on-going summary of Stakeholder understanding and consensus of the geologic and hydrogeologic conditions of the Eastern Plume. See pre-Triad CSM slides. This document was periodically updated when new information was available on the Eastern Plume and on which the Project Stakeholders had reached consensus. The CSM was considered to be a working document to be continually updated and used as a tool by site decision makers.
Prior to this investigation, the CSM established the need for:
The CSM for the Eastern Plume was significantly revised based on the findings of the 2007 Triad investigation. The site CSM was revised in corroboration and consensus with the Project Stakeholders as the foundation for site decision-making. The revised 2007 CSM represented the fourth revision of the Eastern Plume CSM.
Field analytical uncertainty was managed through the correlative comparison of field analysis data to fixed-laboratory data. A total of seventy-three (73) (including QA/QC samples) groundwater samples were collected for laboratory analysis during this investigation. Fifty-five (55) groundwater samples were collected from piezometers and eighteen (18) groundwater samples were collected from monitoring wells. The majority of the samples were hand delivered from the site to the HS/SPME/GC/MS mobile laboratory set up within the Groundwater Extraction and Treatment System (GWETS) facility at Building 50 located at NAS Brunswick.
The results were submitted to Project Stakeholders for review and discussion regarding the selection of the piezometer screen intervals. General discussion between all stakeholders included appropriately timed review and comment rounds on the work plan, results of fieldwork efforts, and discussion of sampling strategy in preparation for the next phase of work.
The principal decision makers for the site were from the U.S. Navy, EPA Region 1, and Maine DEP. Other stakeholders included a U.S. Navy contractor (ECC). A subcontractor to ECC, Stone Environmental, Inc. provided on-site mobile laboratory HS/SPME/GC/MS services.
Data collected from one phase of investigation was used to drive the strategy for the next phase of work, as follows:
During Phase II, HS/SPME/GC/MS was used in an adaptive sampling approach, which allowed for refinement of the CSM, a more cost-effective plume characterization, and a single field mobilization. This was the first applied use at NAS Brunswick of the field analytical technology HS/SPME/GC/MS for combined CVOC and l,4-dioxane analysis. The field analytical results were submitted to Project Stakeholders for review and discussion during the mobilization to identify additional data collection needs and refine the investigation strategy.
No Decision Trees were established in the investigation planning documents. Instead, an informal decision logic process was used, as field analytical results were submitted to Project Stakeholders for review and discussion regarding the selection of the piezometer screen intervals.
The application of HS/SPME/GC/MS and other real-time measurement technologies assisted the fieldwork team at the NAS Brunswick site. Activities performed using field-based methods included:
This method, based on SW-846 EPA Method 8260B for the analyses of volatile organic compounds (VOCs), is designed to measure the concentration of VOCs in water, soil and air samples using solid phase microextraction (SPME) and a gas chromatograph (GC) equipped with a capillary column and mass spectrometer (MS).
In addition to the GC and MS, other equipment required for analysis includes the following:
An initial DMA was conducted by the mobile laboratory contractor using spiked laboratory matrixes. This DMA was performed to demonstrate baseline method performance to the project team, and specifically to verify that HS/SPME/GC/MS could extract 1,4-dioxane and CVOCs simultaneously. Other method start-up activities were also completed, such as statistical method detection limit (MDL) studies and initial calibration curves.
DMA activities continued into the main field program through the collection of QA splits for non-detect, mid-range, and high-range samples that were sent to a NELAP/Navy laboratory. Quality Assurance (QA) and Performance Evaluation (PE) samples were analyzed as part of the overall dataset. The last six samples collected from locations MB-01 and MB-02 were screened at an off-site laboratory See Data Maps.
TQRS not prepared
Project fixed laboratory data were validated by H&S Environmental using the following Validation Functional Guidelines, as modified for non-CLP methods and project-specific QAPP measurement performance criteria (MPC):
The data were assessed against the MPC listed in the approved Eastern Plume LTMP QAPP. Data validation findings were documented on method/QAPP specific data validation worksheets. On these data validation worksheets the data quality acceptance criteria were presented, analytes requiring qualification based on MPC and/or validation guidance criteria were listed, assigned qualifiers, qualifying rationale was documented, and any potential bias noted. The worksheets also presented an overall evaluation of the data generated by each method.
The HS/SPME/GC/MS mobile laboratory analyst was responsible for primary review of sample analysis data. Instrument calibrations and recoveries of all mobile laboratory QC samples were assessed relative to performance criteria established by the DMA. If instrument calibration or the recoveries of any QC sample exceeded specified tolerances, then the affected sample results were evaluated and generally the samples were re-analyzed. To further determine if analytical results were acceptable, secondary review and data verification were performed on a weekly basis by the ECC Project Chemist. Secondary reviews included comparisons of HS/SPME/GC/MS data to off-site fixed laboratory results. A QA/QC checklist was used to indicate any problems with specific analytical batches.
The QA/QC checklist further addressed any corrective action taken. All calibrations, calculations, and transcriptions were checked for accuracy, and QC sample results were evaluated against specified limits. If instrument calibration and recoveries of all QC samples were within the specified criteria, then the data reports were submitted to the Project Manager as final results with no qualifiers. If recoveries of any QC samples exceeded specified limits and re-analysis was not an option, then the samples were qualified as estimated with a ?J? qualifier (J= The analyte was positively identified; the associated numerical value is the approximate concentration of the analyte in the sample). Data were reported if significant QC issues affect the batch analyses.
Data was supplied to stakeholders consistently throughout scheduled fieldwork. During HS/SPME/GC/MS on-site analysis, data was provided to stakeholders on a near real-time basis to aid systematic planning of continued fieldwork efforts. However, the approach to data management and data transmission is unknown.
The Triad application for this project occurred during the Phase II investigation in February and March 2007. The data from this investigation guided further investigation activities that occurred through September 2007. Additional information on project schedules and milestones is presented in the ?Dynamic Work Strategies? and ?Sources of Information? fields of this Triad profile.
|Cross sections in ground water flow maps (1.5 MB)|
|Data Maps (1.2 MB)|
|Eastern portion of NAS Brunswick (3.4 MB)|
|Initial CSM slides (374 KB)|
|SPME Practice (587 KB)|
To update this profile, contact Cheryl T. Johnson at Johnson.Cheryl@epa.gov or (703) 603-9045.