Report Cover   Table of Contents   Sec. 1   Sec. 2   Sec. 3   Sec. 4   Sec. 5   Sec. 6   Sec. 7   Sec. 8

Download the Report PDF (874 KB) ("Right-click", then "Save as..." to your desktop)
View Report Appendices

SECTION 1

INTRODUCTION

1.1 PROJECT DESCRIPTION AND LOCATION

On 22 January 2002, Parsons Engineering Science, Inc. (Parsons) was awarded delivery order DK01 under United States Department of the Army, Corps of Engineers (USACE) Contract Number F44650-99-D-0005. The scope of this delivery order is to provide services, technical labor-hours, and materials to support Remedial Process Optimization (RPO) evaluations and demonstrate the effectiveness of Passive Diffusion Bag Samplers (PDBSs) for sampling volatile organic compounds (VOCs) in existing groundwater monitoring programs at selected Base Realignment and Closure (BRAC) installations administered by the Air Force Real Property Agency (AFRPA). The former Technology Transfer Division of the Air Force Center for Environmental Excellence (AFCEE/ERT) initiated the PDBS demonstration to introduce this technology to multiple Department of Defense (DoD) installations and to improve the cost effectiveness of groundwater monitoring programs for VOCs.

This report describes the activities and results of a field demonstration of six different diffusion and grab groundwater sampling devices at the former McClellan Air Force Base (McClellan), located in Sacramento, California. Analytical results from these samplers are compared to ‘baseline’ analytical results from samples collected using conventional (low-flow and three-casing-volume purge) techniques for all analytes. As described at the beginning of Section 6, conventional techniques represent baseline data only in the sense that they are the commonly-used sampling methods that are generally accepted by the regulatory community. They do not necessarily represent the correct answer (only a different answer). The activities described in this report were performed in accordance with the Final Work Plan for the Demonstration of Passive Groundwater Sampling Devices at Former McClellan AFB, California (Work Plan) (Parsons, 2004a). The geology and hydrogeology of McClellan are briefly described in the Work Plan (Appendix E).

This demonstration project included an assessment of diffusion and grab samplers (i.e., no-purge samplers) for collection of groundwater samples to be analyzed for VOCs, metals, and selected contaminants listed as California emergent chemicals (California Regional Water Quality Control Board [CRWQCB], 2003), including 1,4 dioxane and hexavalent chromium. The six sampling devices demonstrated were classified as either diffusion or grab samplers depending on the predominant operative mechanism of the sampling device. The group designated as diffusion samplers was comprised of the PDBS, a rigid porous polyethylene sampler (RPPS), a polysulfone membrane sampler (PsMS), and a regenerated cellulose sampler (RCS). The group designated as grab samplers included the Snap Sampler™ manufactured by ProHydro, Inc. and the HydraSleeve® manufactured by GeoInsight. It should be noted that the membrane pore size of the RPPS and PsMS may be sufficiently large to permit some limited advection of water molecules through the sampler wall. However, diffusion is believed to be the dominant mechanism for transport of dissolved constituents into these samplers. All of the diffusion and grab samplers tested at McClellan are “no-purge” sampling devices in that they are intended to be used to collect groundwater samples without prior purging of the well.

The diffusion and grab sampling devices tested are relatively new approaches to groundwater sampling that eliminate the need for well purging. Typically, a capsule (e.g., diffusive membrane or self-sealing “grab” container) is deployed at a specified position within the screened interval of a well. Depending on the type of sampler, the capsule may either be filled with purified water and sealed at the surface prior to deployment (e.g., PDBS, RPPS, PsMS, RCS), or it is deployed empty and filled with groundwater and sealed upon retrieval (e.g., Snap Sampler™ and HydraSleeve®). With the PDBS, RPPS, PsMS, and RCS, the constituents in the groundwater enter the sealed sampler through the process of diffusion, and the water quality inside the sampler reaches equilibrium with groundwater quality in the surrounding well. The sampler is subsequently retrieved from the well, and the water in the sampler is transferred to a sample container and submitted for laboratory analysis. The grab samplers are empty when deployed and, following an equilibration period, they are either closed remotely to trap ambient groundwater (Snap Sampler™) or they are filled and sealed during the retrieval process (HydraSleeve®). Potential benefits of using diffusion or grab sampling methods include reduced sampling costs and reduced generation of investigation-derived waste (i.e., purge water).

1.2 TECHNOLOGY BACKGROUND

To date, the primary application of diffusion samplers has been to sample for VOCs in groundwater using PDBSs. The PDBS technology has been validated through various studies (Vroblesky and Hyde, 1997; Parsons, 1999, 2003b and 2004b; Church, 2000; Hare, 2000; McClellan AFB, 2000; Vroblesky et al., 2000; Vroblesky and Peters, 2000; Vroblesky and Petkewich, 2000), and a guidance document for their use has been developed (Vroblesky, 2001). The Interstate Technology and Regulatory Council (ITRC) has formed a workgroup to expand on the PDBS guidance document and to address technical and regulatory implementation issues as they arise.

Use of the PDBS method can provide significant long-term cost savings compared to conventional sampling methods. However, LTM programs at many sites include sampling and analysis for non-volatile parameters (e.g., metals, semi-volatile organic compounds [SVOCs] inorganic anions and cations, dissolved gases, and other geochemical parameters) that cannot be targeted using PDBSs. In addition, although studies performed to date have indicated that the PDBS method is capable of accurately monitoring concentrations of VOCs dissolved in groundwater in most instances, this method is not suitable for all VOCs. For example, methyl tert-butyl ether (MTBE) does not efficiently pass through the wall of the PDBS, and therefore this method cannot be used to sample for this compound. As a result of these limitations, development and testing of other no-purge samplers that can be used for a wider variety of analytes is desirable to take advantage of the cost effectiveness of this approach, while at the same time meeting sampling objectives for non-volatile analytes.

1.3 OBJECTIVES

The overall objective of this demonstration is to evaluate and demonstrate the use of selected diffusion and grab sampling technologies that potentially represent useful and cost-effective alternatives to conventional groundwater sampling approaches (e.g., three volume purge/sample and low-flow purge/sample) for analytes other than VOCs. Specifically, technologies that potentially can be used to sample for non-volatile constituents such as metals, anions, and 1,4 dioxane are evaluated. Expansion of the suite of accepted no-purge sampling methods could be useful in augmenting or possibly substituting for the PDBS method in certain applications. In addition, the comparative sampler demonstration at McClellan has the following specific objectives:

• Compare analytical results obtained using each sampling method with analytical results for the same constituents obtained via each of the other sampling methods;
• Evaluate how each diffusion and grab sampler reflects any observed chemical stratification in wells included in the demonstration;
• Identify variables that could explain observed differences in the sampling results obtained using the various sampling methods; and
• Compare the approximate costs of the various sampling methods (including conventional methods).
  
  

1.4 SCOPE

The sampling demonstration at McClellan required three field mobilizations to the site as described in Section 3.1.1.

The samplers selected for this demonstration monitor chemical conditions in a well. Conventional sampling methods (e.g., purge and sample) disrupt well and aquifer equilibrium for an unknown period of time. Therefore, for this demonstration an effort was made to target only those wells that were not scheduled to be sampled during the regular April-May 2004 basewide LTM conventional sampling event. In the event that a well was selected for use in this demonstration that also was sampled with conventional methods during the LTM event, a minimum time lag of at least one month between the LTM and no-purge sampling demonstration events was used as a well selection criterion. A total of 20 wells at McClellan were included in this demonstration project. Parsons coordinated with both McClellan and the base LTM contractor (URS Corporation [URS]) to determine which wells should be included in the demonstration.

1.5 SCOPING GUIDELINES

The following general scoping guidelines were developed for this comparative sampler evaluation:

• Sampling devices selected for field testing will be suitable for at least a sub-group of the analytes of interest, and will yield sufficient sample volume to enable testing for the analytes of interest.
• Sampling devices selected for field testing can be deployed at multiple depths within a single well to evaluate vertical stratification of analytes, and each sampler cluster (consisting of multiple types of samplers) can be deployed at a similar depth. This will allow comparison of sampling results from less-depth-discrete methods (i.e., 3-volume purge and low-flow purge) with results from more depthdiscrete methods. This topic is of interest in part because the degree to which lowflow purge provides a depth-discrete sample is not well-defined.
• Time lag between sample collection using different methods will be minimized to avoid bias of the comparative evaluation by temporal fluctuations in groundwater quality.
• Analyte reporting limits specified in the McClellan Quality Assurance Project Plan (QAPP) (URS, 2003) will be met to the extent feasible given sample volume limitations and the capabilities of the selected analytical laboratory.
• One or more ‘baseline’ sampling methods will be included to provide data against which the results of the alternative passive diffusion samplers (PDSs) and grab samplers can be compared.
• Standard operating procedures (SOPs) will be used that minimize loss or transformation of the analytes of interest during the sample collection, handling, shipping, and analysis process, and that ensure the representativeness of the sample to the greatest degree possible.
• Sufficient data will be collected to allow use of appropriate qualitative and quantitative data analysis methods (e.g., graphs, tables, statistical tests) in order to compare results obtained using the various sampling devices/approaches and determine which alternative samplers can be used in place of the current, conventional sampling methods and therefore warrant further evaluation.
  
  

1.6 DOCUMENT ORGANIZATION

This report is organized into eight sections, including this introduction, and six appendices. Section 2 is a brief summary description of the sampling technologies used in this demonstration. Section 3 is a description of field activities and the laboratory analytical approach. Section 4 is a presentation and discussion of analytical results. A cost analysis is presented in Section 5. Conclusions and recommendations are presented in Sections 6 and 7, respectively. References cited in this report are presented in Section 8. Appendix A is a Data Quality Assessment Report. Well-specific plots depicting vertical stratification of various target compounds are included as Appendix B.

Appendix C includes results of tests for normality performed on the data sets. Appendix D contains X-Y scatter plots comparing the results of each sampling device/method to each of the other devices/methods. Appendix E is a compact disk containing an electronic version of the analytical data in various formats as well as an electronic version of the Work Plan (Parsons, 2004a). Field notes are contained in Appendix F.

Report Cover   Table of Contents   Sec. 1   Sec. 2   Sec. 3   Sec. 4   Sec. 5   Sec. 6   Sec. 7   Sec. 8