Standard Active Last Updated: Jan 14, 2019
ASTM D6235-18

Standard Practice for Expedited Site Characterization of Vadose Zone and Groundwater Contamination at Hazardous Waste Contaminated Sites

Significance and Use

4.1 The ESC Process—This practice describes a process for characterizing hazardous waste contaminated sites8, that provides cost-effective, timely, high-quality information derived primarily from judgement-based sampling and measurements by an integrated, multidisciplinary project team during a limited number of field mobilizations. (See Appendix X1 for additional background on the ESC process, its distinction from traditional site characterization, and its relationship to other approaches to site characterization and Appendix X5 and X6 for illustrative examples of the ESC process.)

4.2 Determining Appropriateness of ESC—The ESC process should be initiated when an ESC client, regulatory authority, and stakeholders determine that contaminants at a site present a potential threat to human health or the environment and the ESC process will identify vadose zone, groundwater, and other contaminant migration pathways in a timely and cost-effective manner, especially when decisions concerning remedial or other action must be made as rapidly as possible. Situations where the process may be applicable are as follows:

4.2.1 ESA—Sites where environmental site assessments (ESAs) conducted by using Practice E1527, Practice E1528, and Guide E1903 identify levels of contamination requiring further, more intensive characterization of the geologic and hydrologic system of contaminant migration pathways. Section X1.5.3 discusses the relationship between ESAs and the ESC process.

4.2.2 Petroleum Release Sites—Large petroleum release sites, such as refineries. The user should review both this practice and Guide E1912 to evaluate whether the ESC or ASC process is more appropriate for such sites.

4.2.3 Subsurface Radioactivity—Sites or facilities with subsurface contamination by radioactivity.

4.2.4 Other Subsurface Contamination—Other sites or facilities where contaminant migration in the vadose zone and groundwater is a matter of concern and heterogeneity of the vadose zone and groundwater system or potential complex behavior of contaminants requires use of the ESC process.

4.3 Defining Objectives and Data Quality Requirements—The ESC process requires project objectives and data quality requirements that will provide the ESC client, regulatory authority, and stakeholders with the necessary information to analyze risk or apply regulatory standards-based cleanup in order to choose a course of action. Once these have been defined, the ESC process relies on the expert judgement of the core technical team, operating within the framework of an approved dynamic work plan, as the primary means for selecting the type and location of measurements and samples throughout the ESC process. An ESC project focuses on collecting only the information required to meet the project objectives and ceases characterization as soon as the objectives are met.

Note 4: This practice uses the term “data quality requirements” to refer to the level of data accuracy and precision needed to meet the intended use for the data. The U.S. EPA Data Quality Objectives (DQO) process is one way to accomplish this. The ESC process applies the concept of quality control and data quality requirements to geologic and hydrologic data as well as chemical data, but within a general framework of judgement-based rather than statistical sampling methods. Section X1.4.4 discusses the DQO process in more detail along with the role of judgement-based and statistically based sampling methods in the ESC process. Practice D5792 provides guidance on development of DQOs for generation of environmental data related to waste management.

4.4 Use of ESC Process for Risk Analysis and Remedial Action: 

4.4.1 Characterizing Contaminant Migration Pathways—Normally an ESC project will characterize the contaminant migration pathways (and sources if not already known) before any detailed risk analysis involving exposure to environmental receptors is performed, because environmental receptors are not known until the migration pathways are known. Risk analysis expertise will normally be required as an input into defining project objectives and data quality requirements (see 4.3); such expertise is involved as appropriate during field data collection phases of an ESC project. Identification of contaminant sources and environmental receptors for risk analysis is straightforward at most sites and does not, per se, require the ESC process. The ESC process focuses on characterizing vadose zone and groundwater contaminant migration pathways and determining the distribution, concentration, and fate of contaminants along these migration pathways, because these factors are more difficult to identify than sources and environmental receptors.

4.4.2 Considering Remedial Action and Alternatives—The ESC process is designed to avoid a presumption that remedial action is required (that is, an engineered solution rather than no further action or ongoing monitoring). In any ESC project, remediation engineering expertise is incorporated into the process at the earliest point at which a need for remedial action is identified. (See 13.3.) Guide D5745 provides guidance for developing and implementing short-term measures or early actions for site remediation.

4.5 Flexibility Within ESC—Modification of procedures described in this practice may be appropriate if required to satisfy project objectives or regulatory requirements, or for other reasons. The ESC process is flexible enough to accommodate a variety of different technical approaches to obtaining environmental data. However, for an investigation to qualify as an ESC project, as formalized by ASTM, modifications should not eliminate any of the essential features of the ESC process listed in Table 1. Alternative site characterization approaches that use some, but not all, of the essential elements described in Table 1 may be appropriate for a site, but these approaches would not qualify as an ESC project as defined in this practice.

Note 5: Users may prefer to use or develop alternative terminology for different aspects of the ESC process, depending on the regulatory context in which it is applied. However, precise or approximate equivalencies to steps or functions in the ESC process should be clearly identified.

4.6 Use of ESC in Conjunction with Other Methods—This practice can be used in conjunction with Guide D5730 for identification of potentially applicable ASTM standards and major non-ASTM guidance. In karst and fractured rock hydrogeologic settings, this practice can be used in conjunction with Guide D5717.


1.1 Applicability of the ESC Process—This practice covers a process for expedited site characterization (ESC) of hazardous waste contaminated sites2 to identify vadose zone, groundwater and other relevant contaminant migration pathways and determine the distribution, concentration, and fate of contaminants for the purpose of providing an ESC client, regulatory authority, and stakeholders with the necessary information to choose a course of action.3 Generally, the process is applicable to larger-scale projects or contaminated sites where the ESC process can be reasonably expected to reduce the time and cost of site characterization compared to alternative approaches. The ESC process has been applied successfully at a variety of sites (see Table X1.1). It typically achieves significant cost and schedule savings compared to traditional site characterization (see X1.2 and X1.3),4 although it should be recognized that in-depth site characterization of hazardous waste contaminated sites may require a more elaborate process than ESC.

1.2 Features of the ESC Process—The ESC process operates within the framework of existing regulatory programs. It focuses on collecting only the information required to meet characterization objectives and on ensuring that characterization ceases as soon as the objectives are met. Central to the ESC process is the use of judgement-based sampling and measurement to characterize vadose zone and groundwater contamination in a limited number of field mobilizations by an integrated multidisciplinary team, led by a technical leader and operating within the framework of a dynamic work plan that gives him or her the flexibility of responsibility to select the type and location of measurements needed to optimize data collection activities. Table 1 identifies other essential features of the ESC process, and Fig. 1 presents a flow diagram for the entire ESC process.

FIG. 1 Overview of the Expedited Site Characterization Process

Overview of the Expedited Site Characterization ProcessOverview of the Expedited Site Characterization Process

1.3 Investigation Methods—The process described in this practice is based on good scientific practice but is not tied to any particular regulatory program, site investigation method or technique, chemical analysis method, statistical analysis method, risk analysis method, or computer modeling code. Appropriate investigation techniques in an ESC project are highly site specific and are selected and modified based upon the professional judgement of the core technical team (in particular the technical team leader). Whenever feasible, noninvasive and minimally invasive methods are used, as discussed in Appendix X2. Appropriate chemical analysis methods are equally site specific. Analyses may be conducted in the field or laboratory, depending on data quality requirements, required turnaround time, and costs.

1.4 Sites Generally Not Appropriate for the ESC Process—Generally, the ESC process is not applicable to: small petroleum release sites, real estate property transactions that require no more than a Phase I ESA, sites where contamination is limited to the near surface or there is no basis for suspecting that contaminant movement through the vadose zone and groundwater is a matter of concern, sites where the cost of remedial action is likely to be less than the cost of site characterization, or sites where existing statutes or regulations prohibit the use of essential features of the ESC process.5

1.5 Other Potentially Applicable ASTM Standards for Site Characterization—Guide E1912 addresses accelerated site characterization (ASC) for petroleum release sites, and Guide E1739 addresses use of the risk-based corrective action (RBCA) process at petroleum release sites. Section X1.5.1 describes the ASC process, and X1.5.2 discusses the relationship between ESC and the RBCA process. Practices E1527 and E1528 and Guide E1903 address real estate property transactions, and X1.5.3 discusses the relationship between the ESC process and investigations for real estate property transactions. Classification D5746 addresses environmental conditions of property area types for Department of Defense installations, and Practice D6008 provides guidance on conducting environmental baseline surveys to determine certain elements of the environmental condition of federal real property.

1.6 The values stated in both inch-pound and SI units are to be regarded separately as the standard. The values given in parentheses are for information only.

1.7 All references in this standard to the “engineer” must be understood as referring to a qualified professional (such as an engineer, soil scientist or geologist) who has the appropriate experience and, if required by local regulations, certification.

1.8 This practice offers an organized collection of information or a series of options and does not recommend a specific course of action. This document cannot replace education or experience and should be used in conjunction with professional judgment. Not all aspects of this practice may be applicable in all circumstances. This ASTM standard is not intended to represent or replace the standard of care by which the adequacy of a given professional service must be judged, nor should this document be applied without consideration of a project's many unique aspects. The word “Standard” in the title of this document means only that the document has been approved through the ASTM consensus process.

1.9 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.10 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

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Book of Standards Volume: 04.09
Developed by Subcommittee: D18.01
Pages: 50
DOI: 10.1520/D6235-18
ICS Code: 13.030.99