Chapter 1
Conducting Groundwater Quality Investigations

1.1 Introduction

The volume is intended as a primer to address groundwater contamination often caused by legacy pollution or unintentional releases of chemicals to the subsurface. When groundwater has been adversely impacted, a variety of sciences, strategies, technologies and actions are needed to assess human and ecological risks from the contamination. The first step in assessing impacts requires a body of good practices that are recognized by industry on the whole and is referred to as the environmental site assessment.

Environmental site assessment practices are also commonly referred to as environmental audits. The practices for conducting an environmental site assessment began evolving in the United States in the 1970s. Throughout the 1980s environmental site assessment practices evolved further with the promulgation of the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) and the Resource Conservation and Recovery Act (RCRA), which required commercial facilities to identify, report and remediate recognized environmental conditions. Throughout the 1990s environmental site assessment practices were enhanced with more precise tools that aided in site characterization and quantification of recognized environmental conditions. Over the years additional analytical tools have evolved to aid environmental site assessment practices.

The goal of an environmental site assessment is to identify recognized environmental conditions. The term recognized environmental conditions means "the presence or likely presence of any hazardous substances or petroleum products on a property under conditions that indicate an existing release, a past release, or a material threat of a release of any hazardous substances or petroleum products into structures on the property or into the ground, groundwater, or surface water of the property."1

1.2 Evolution of Site Assessments

The control of hazardous substances and the prevention of the entry of these substances into the environment is the objective of several acts of U.S. Congress. Rules regulating various aspects of hazardous waste can be attributed to the Toxic Substances Control Act (TSCA); the Clean Water Act (CWA); the Clean Air Act (CAA); the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA); the Safe Drinking Water Act (SDWA); the Resource Conservation and Recovery Act (RCRA); and the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA). RCRA and CERCLA are the two that are most often associated with environmental site assessments.

RCRA was passed to control industrial and municipal solid wastes, including sludges, slurries, etc. The act also called for a tracking system to document the generation, transport, and disposal/storage of solid wastes. The discovery of a large number of uncontrolled and abandoned hazardous waste sites, such as at Love Canal, New York, prompted a much greater emphasis on the hazardous nature of the wastes. In the 1980s the regulations and resources of RCRA were primarily devoted to the control of hazardous wastes, with a lesser emphasis on nonhazardous solid wastes.

In 1980, legislation aimed at providing federal money for the cleanup of inactive waste disposal sites was enacted. The Comprehensive Environmental Response, Compensation and Liability Act (CERCLA), often called the "Superfund Act", provides regulatory agencies with the authority to deal with inactive sites, funds to deal with hazardous waste emergencies and a means to assign the liability of cleanup to the responsible parties. It also provides monies (Superfund) to pay for the mitigation of hazards from abandoned sites when no responsible party can be found or when the responsible party refuses to take action. In addition, it empowers the government to seek compensation from responsible parties to recover funds used in mitigation actions.

Section 105 of the CERCLA requires that the National Contingency Plan (NCP), developed under the Clean Water Act, be revised to include procedures and standards for responding to releases of oil and hazardous substances. The revised plan reflected and effectuated the responsibilities and powers created by the act.

Subpart F of the NCP, Hazardous Substance Response, establishes a seven-phase approach for determining the appropriate extent of a response authorized by CERCLA "when any hazardous substance is released or there is a substantial threat of such a release into the environment, or there is a release or substantial threat of a release of any pollutant or contaminant which may present an imminent and substantial danger to the public health or welfare"2. Each phase sets specific criteria to establish the need for further action. The phases are:

1. Phase I - Discovery and Notification
2. Phase II - Preliminary Assessment
3. Phase III - Immediate Removal
4. Phase IV - Evaluation and Determination of Appropriate Response - Planned Removal and Remedial Action
5. Phase V - Planned Removal
6. Phase VI - Remedial Action
7. Phase VII - Documentation and Cost Recovery

This phased approach is the basis for implementation of all CERCLA-authorized Hazardous Substance Responses with which industry is obligated to comply.

The practice of conducting environmental site assessments began in the 1970s in the United States. These practices evolved over time, which is why it is important to place them within a historical context. As early as the 1970s specific property purchasers in the United States undertook studies resembling current Phase I ESAs, to assess risks of ownership of commercial properties which had a high degree of risk from prior toxic chemical use or disposal. Many times these studies were preparatory to understanding the nature of cleanup costs if the property was being considered for redevelopment or change of land use.

The evolution of best practices in conducting site assessments was driven by an expanding knowledge base on the fate and transport of harmful chemicals. Until the early 1960s, the question of whether or not groundwater was significantly affected by organic wastes was generally addressed by observing the subsurface breakdown of sewage and similar matter. There was a general belief that the easiest way to eliminate contamination was through the natural processes of separation, filtration, dilution, oxidation and chemical reaction. Soils were believed to serve the purpose of filtration, aid in chemical reaction by adsorbing some chemicals, while groundwater was generally believed to be an infinite medium, thereby diluting any harmful chemicals. Not until the mid-1960s did organic contaminants begin to receive attention.

Some properties are associated with groundwater contamination that can be characterized as being comprised of Dense Non-Aqueous Phase Liquids (DNAPLs). DNAPLs are characterized by their lack of noticeable taste or odor and their higher density relative to water. These properties render them difficult to detect and monitor. In contrast, petroleum spills float atop the water table and are usually volatile with distinctive tastes and odors. The rare discovery of DNAPL contamination before the development and ready availability of analytical techniques allowing the measurement of organic contaminants on the ppm to ppt level is not surprising.

Although appropriate analytical methods actively existed and were relied on by industry since the mid-1950s, there was no drive to investigate groundwater for the presence of chlorinated solvents. Analytical chemists instead concentrated efforts on alkyl benzene sulphonate (ABS) detergents and organic pesticides such as DDT and aldrin. The surreptitious nature of DNAPLs led them to be disregarded as groundwater contaminants until much later. Dissolved plumes caused by DNAPLs were not discovered until the 1970s. DNAPL (the free phase, not dissolved phase) was not discovered until the mid-1980s. This was partially because monitoring wells was not understood, as it is now, to be a poor method to detect DNAPL (i.e., it has rarely been reported in wells).

The discovery of DNAPLs was prompted by legislation introduced during the previous decade: Safe Drinking Water Act (1974), Resource Conservation and Recovery Act (RCRA, 1976) and the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA, 1980). These legislations required sampling of municipal wells specifically for chlorinated solvents, which were discovered in some drinking water systems. Unlike some other contaminants, such as methyl tert-butyl ether (MTBE), chlorinated solvents have high taste and odor thresholds, meaning that people don't taste or smell the compounds in water until there is a relatively high concentration. Chlorinated solvents have taste thresholds around several hundred µg/L (i.e., ppb) whereas MTBE is nearly two orders of magnitude lower. Furthermore, taste thresholds are highly dependent on the individual.

The 1980s ushered in a vast cache of knowledge supported by reports and peer reviewed publications concerning groundwater investigations and DNAPLs. During this time period the evolution of vapor intrusion pathway (VIP) science also took place.

VIP refers to the migration of vapors from the soil zone into structures. The pathway starts from the groundwater to soil gas pathway. The origins of VIP may be traced back to the 1930s when petroleum exploration by soil gas analysis for...