Complementary data quality objectives for US EPA Methods 8260 and 8265

Previous discussions in this newsletter have covered the need for high density data, as well as the tools and methods for collecting these data. We have also discussed the need for quality assurance procedures for all tools that provide data, both semi-quantitative and quantitative. This discussion contrasts the data quality objectives (DQOs) for methods we use in the field (US EPA Method 8265) with off-site analyses (US EPA Method 8260). This illustrates why the use of both methods improves the management of sampling uncertainty due to site heterogeneity, as well as the success of site remediation.

The use of on-site, real-time, and high-density data has a different purpose from samples collected for off-site analysis, and the DQOs support these project needs. Real-time data collected using Method 8265 assists project managers in addressing the effects of site heterogeneity on sample representativeness. The ability to collect and analyze large numbers of samples allows project managers to make quick, informed decisions about where additional sampling locations are needed to accurately define the source and plume. Data from samples analyzed in a certified laboratory using Method 8260 are usually required to make decisions about site remediation actions.

DQOs for samples analyzed by Method 8260 support risk assessment and remedial e actions based on the risk assessment. Although quantitative and applied in the field using a full QA/QC program, DQOs for on-site, high-density data from samples analyzed using Method 8265 support the construction of an accurate conceptual site model that can be used to select a limited number of sampling locations for off-site analysis by Method 8260.

The combination of methods is powerful, because project managers can be assured that the final conceptual site model is based on complementary types of data that accurately represent site conditions. This process significantly reduces the uncertainty in site decisions required to manage the identified risks. Site characterization is more efficient and total project costs are reduced.

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Effective Real-time Decision Making

Previous discussions here have focused on the need for high density data, tools to cost effectively collect these data and managing the large volumes of data collected to evolve the conceptual site model (CSM) in real time. As discussed in all of the previous articles, the most cost effective approaches to site characterization include using the high density data in the field, as it is produced, to make real-time decisions. The topic for today is about preparing for how those decisions will be made.

This seems very intuitive and the process at first glance seems to be straight forward. However, experience indicates effectively using real-time data to make decisions is one of the more challenging aspects of high resolution site characterization (HRSC) projects. The last article discussed the importance of managing and communicating the data in real-time. Planning in advance how to provide decision makers with easily understood data formats (maps, tables, 3D images, etc.) greatly assists effective decision making.

The most important thing to do to ensure effective real-time decision making during the field execution of a HRSC project is planning for the decisions that will need to be made. During systematic planning and work plan development - prior to field deployment - decisions anticipated to be made in the field should be identified and discussed relative to meeting project data quality objectives. These may include, for example, decisions about contaminant concentrations in soil that define the source boundary and density of data required to manage site heterogeneity. Identifying who has authority for particular decisions is a critical part of the planning process. This person can be on-site or off-site because they should have to access the real-time data.

Efficient use of field resources depends on the absolute minimum of standby time for drilling and data acquisition equipment. Having good decision rules and communicating the real-time data effectively to the decision maker ensures valuable project resources are fully utilized to meet project objectives. Experience has demonstrated the most cost effective HRSC projects are those that employ effective real-time decision making.

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Managing high density data conceptual site models in real time

Previous discussions here have focused on the need for high density data and the tools for collecting them. We have also discussed using these data to produce accurate conceptual site models (CSMs) to support remedy selection and design. It is important to manage high density data sets in real time in order to extract the information they provide to support on-site decision making and to communicate the data effectively to off-site stake holders and decision makers.

As discussed in the last newsletter, discrete soil and groundwater sampling with on-site EPA Method 8265 analysis produces 60-80 quantitative results per day. Direct sensing data collection tools discussed previously often product hundreds of semi-quantitative contaminant data points in addition to hundreds of geologic and hydrogeologic data points in a single penetration. All these systems produce very large volumes of data each day. For those who have not worked with these tools before, the shear amount of data can be overwhelming.

It is critical when planning a high density site characterization project to develop a data management and communication plan. Prior to arriving on-site, the initial CSM for the site should be constructed. This means that all previous contaminant, geologic and hydrogeologic data should be organized into tables, maps and, if desired, into three dimensional visual formats (3D). Then, when data are collected during field deployment, the CSM can be updated as needed. This happens most often on a daily basis at the end of the day to help select sampling locations for the following day.

There are a large number of programs, as well as off-site, on-line services that can be used to manage and visualize data. Using 3D visualization from the beginning of a project can be a very effective way to manage data and is an especially useful tool to communicate high density data to off-site stakeholders and decision makers. If you take the time to set up the CSM before arriving on-site, you really allow yourself to extract the maximum amount of useful information during field execution. The old adage really does apply: "A picture is worth a thousand words". 

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Cost effective, high density data collection

Successful remediation depends on accurate site characterization. Over the past decade, tools for cost effective, high density data collection have matured. These tools include contaminant detection tools and tools for collection and real-time analysis of soil and groundwater (GW). Direct sensing tools are now available that collect high density geologic and hydrogeologic data that provide important information to guide site investigation decisions as well as remedial design. Site characterization has come a long way. Now even the most complex sites can be effectively characterized in a reasonable amount of time to reduce the total project cost from planning to site closure.

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Why Collect High-Density Data?

The objective of site characterization is to provide data to support decisions about actions to be taken at the site. Most often the actions are remediation of a source area and/or groundwater plume. The amount of data required to support these decisions varies from site to site depending on contaminants of interest, local geology and hydrogeology.   Experience has shown that successful remediation requires an accurate conceptual site model (CSM) such as the one pictured above.

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