1. Introduction
This guidance document explains statistical techniques to evaluate and optimize groundwater monitoring for environmental projects. The primary audience for this guidance is environmental practitioners who have technical and project management experience, but who may not have specific expertise in statistics. Public and tribal stakeholders reviewing environmental reports will also find this guidance helpful. Other good sources of information about statistics include the United States Environmental Protection Agency’s (USEPA's) March 2009 Statistical Analysis of Groundwater Monitoring Data at RCRA Facilities (known as the Unified Guidance), Statistical Methods for Groundwater Monitoring (Gibbons, Bhaumik, and Aryal 2009), and several ASTM International (ASTM) publications on statistical methods for environmental monitoring (ASTM 2010a, 2010b, and 2012), as well as a wide variety of tools and software packages for performing statistical calculations and evaluations. Even with these resources, however, practitioners may still feel challenged when reviewing or implementing statistics. This guidance document provides an overview of the Unified Guidance and other resources and shows how to apply statistics specifically to analytical results from groundwater sampling in order to make better decisions in environmental projects.
1.1 Purpose
The purposes of this document and associated Internet-based training include the following:
- provide greater clarity to the planning, implementation, and communication of groundwater statistical methods and results
- provide information about available statistical tools and software in a useful format
- help practitioners to review and use statistical methods to improve the quality of their decisions
- help practitioners to identify the specific tasks within a project life cycle that benefit from statistical approaches
- provide better understanding of the statistical concepts that may be used for systematic planning such as USEPA's seven-step Data Quality Objective (DQO) Process (USEPA 2006a)
1.2 Scope and Limitations
This document offers practical tips for using information that is already published in other resources such as USEPA’s Unified Guidance. This document is not a stand-alone tutorial on statistics, but instead addresses the practical applications, challenges, and misapplications associated with the use of groundwater statistics. The study questions, methods, and software packages are not all-inclusive and others may be appropriate. Concepts presented in this document apply to groundwater projects in many regulatory programs such as those under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), the Resource Conservation and Recovery Act (RCRA), voluntary cleanup, and underground storage tank (UST) programs. The document is organized around life cycle stages of typical environmental projects including release detection, site characterization, remediation, monitoring, and closure. The guidance presented here will help users to ask the right questions about data and identify appropriate statistical methods to answer these questions.
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This document does not address issues associated with hydrogeology, sampling methodology, Conceptual Site Model development, and analytical data quality. For example, it does not provide guidance on well installation, sampling, or hydrogeological interpretation. The default assumption, unless otherwise stated, is that data are representative, valid, and usable. In practice, statistical approaches such as tests for outliers and
Additionally, this document does not provide guidance on geostatistical analysesAn analysis using a branch of statistics that focuses on the analysis of spatial or spatiotemporal data, such as groundwater data. One example of a geostatistical technique is kriging, which is an interpolation method that is based on a statistical model of spatiotemporal correlation (Gilbert 1987). or software, with the exception of some tools included in Appendix D that offer spatial analysis for optimizing well placement, redundancy, and sampling frequency.
In order to simplify discussions in this document, certain terms have been used to standardize various concepts. Some of terms may have different meanings for different regulatory agencies; their use here is not intended to undermine or change a particular regulatory meaning. Examples include “chemical” or “contaminant,” which are used depending on the context, and “criterionGeneral term used in this document to identify a groundwater concentration that is relevant to a project; used instead of designations such as Groundwater Protection Standard, clean-up standard, or clean-up level.,” which is used instead of terms such as “Groundwater Protection Standard (GWPS),” “cleanup standard,” or “cleanup level.”
1.3 Background
The guidance presented here condenses and simplifies a selection of important methods from the Unified Guidance. The Unified Guidance was developed for the statistical analysis of groundwater data at RCRAResource Conservation and Recovery Act facilities, but the statistical tests and graphical methods it describes are broadly applicable for a variety of other environmental programs.
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The Unified Guidance is consistent with strategies for systematic planning and conceptual site model (CSM)A living collection of information about a site which considers factors such as environmental and land use plans, site-specific chemical and geologic conditions, and the regulatory environment (ITRC 2007b). concepts and was developed to help evaluate groundwater monitoring data for regulatory compliance. The statistical analyses described in the Unified Guidance and this document require acceptable data. A series of USEPA quality management guidance documents that provide information on data quality are also available:
- Guidance on Systematic Planning Using the Data Quality Objectives Process, QA/G-4 (USEPA 2006a)
- Guidance on Choosing a Sampling Design for Environmental Data Collection, QA/G-5S (USEPA 2002a)
- Data Quality Assessment: A Reviewer's Guide, QA/G-9R (USEPA 2006b)
- Data Quality Assessment: Statistical Methods for Practitioners, QA/G-9S (USEPA 2006c)
- Guidance on Environmental Data Verification and Data Validation, QA/G-8 (USEPA 2008b)
Additionally, the information in this ITRC guidance document and others may assist with evaluation of soil contamination, remedial system optimization, and meeting goals of green and sustainable remediation. The ITRC guidance document Incremental Sampling Methodology (ITRC 2012) addresses soil sampling approaches designed to ensure representative, reproducible, and defensible data. ITRC's Improving Environmental Site Remediation Through Performance-Based Environmental Management (ITRC 2007b) and related documents address how to use remedial process optimization to systematically evaluate and manage uncertainty associated with the remediation process. Recommendations in these documents include the use of statistical tools such as the Monitoring and Remediation Optimization System (MAROS) software and the Geostatistical Temporal/Spatial (GTS) optimization algorithm to optimize monitoring networks. These software tools and others are described in Appendix D of this document. In addition, ITRC's Green and Sustainable Remediation: A Practical Framework (2011a) and related documents provide a framework to achieve green and sustainable goals with better site management decisions. Finally, additional information can be found in the Department of Energy's Scientific Opportunities for Monitoring at Environmental Remediation Sites: Integrated Systems Based Approaches to Monitoring (Bunn et al. 2012).
1.4 Document Audience
Based on the groundwater statistics survey (Appendix E), the target audience for this guidance is a project manager (in industry, government, or consulting) who must review or use statistical calculations to generate a report or demonstrate compliance for a groundwater-monitoring project. This individual typically has technical experience in one or more disciplines related to site compliance or cleanup but does not have specific expertise in statistics. This individual may not have access to in-house statistical expertise, but still must make recommendations or decisions based on statistics. This document guides the project manager in using appropriate statistical methods to address common project objectives and recognizing common misapplications of statistics. A typical application might include evaluating whether a groundwater remedy is functioning effectively or whether there is a downward trend which supports a natural attenuation remedy selection.
1.5 Project Life Cycle Stages
Groundwater statistical methods can apply throughout the life cycle of environmental cleanup projects, including monitoring of active remediation systems. The terminology and regulatory framework for the stages of the project within its life cycle, however, often vary under different regulatory programs. For clarity, this document organizes the discussion of site management around five main technical tasks:
- Section 4.2: Release Detection
- Section 4.3: Site Characterization
- Section 4.4: Remediation
- Section 4.5: Monitoring
- Section 4.6: Closure
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These tasks correlate with the activities described in various regulatory programs (such as RCRAResource Conservation and Recovery Act, CERCLAComprehensive Environmental Response, Compensation, and Liability Act, State Voluntary Cleanup, and USTunderground storage tank Site Cleanup). Although individual projects may vary in their progression through these stages, groundwater statistical tests can support decision making regardless of how the project is defined. Figure 1-1 summarizes the correlations between the terms used in this guidance document and the terms used in several regulatory programs.
Figure 1-1. Correlation of regulatory terms.
Source: Adapted from ITRC RRM IBT slide 2011.
1.6 Study Questions
Each of the project life cycle stages listed above progress through development and refinement of the CSMconceptual site model. This guidance explores some of the commonly identified problem statements that guide decision making throughout environmental projects and poses a list of typical study questions that are intended to connect life-cycle-based issues of concern with relevant statistical methods.
Ten common study questions were selected:
- Study Question 1: What are the backgroundNatural or baseline groundwater quality at a site that can be characterized by upgradient, historical, or sometimes cross-gradient water quality (Unified Guidance). concentrations?
- Study Question 2: Are concentrations greater than background concentrations?
- Study Question 3: Are concentrations above or below a criterion?
- Study Question 4: When will contaminant concentrations reach a criterion?
- Study Question 5: Is there a trend in contaminant concentrations?
- Study Question 6: Is there seasonality in the concentrations?
- Study Question 7: What are the contaminant attenuation rates in wells?
- Study Question 8: How do contaminant concentrations change with distance from the source area?
- Study Question 9: Is the sampling frequency appropriate (temporal optimization)?
- Study Question 10: Is the spatial coverage of the monitoring network appropriate (spatial optimization)?
Study questions are discussed in more detail in Appendix C. Life cycle stages and related study questions are discussed in Section 4. Statistical methods are presented in Section 5.
Publication Date: December 2013