Department of Health Seal

TGM for the Implementation of the Hawai'i State Contingency Plan
Section 3.0


Figure 3-1. Expanded Overview of the Site Assessment Process No Further Action (NFA) letter recommended, which may be requested from HEER Office if site data passes the EHE. Coordination with the HEER Office and Response Action Determination required if site data fail the EHE.

This Section of the Technical Guidance Manual (TGM) provides an overview of the Site Investigation element of the site assessment process (Figure 3-1; refer also to Figure 2-1 in Section 2).

The steps outlined above for implementation of a site investigation are discussed in Subsection 3.2. A site investigation is conducted in order to collect environmental data, evaluate the extent and magnitude of site contamination ("How bad is it?") and support decision-making ("What needs to be done?"). Site investigations can be carried out at different stages of the State Contingency Plan (SCP) process (refer to Subsection 2.1) in order to answer key questions, such as:

  • Has a hazardous substance release occurred at the site?
  • What is the extent and magnitude of contamination caused by the release?
  • Does the release pose an environmental hazard under current or potential future site conditions?
  • What method should be used to remediate this site?
  • Has the cleanup eliminated the environmental hazard?

The scope and detail of the site investigation will vary from site to site, depending on the questions the investigation is intended to answer and the site complexity. A systematic planning approach is recommended to ensure that the data collected during the site investigation are of the type and quality needed to meet the overall site assessment objectives. In addition, the Site Investigation and Environmental Hazard Evaluation (EHE, see Section 13) stages of the site assessment process are necessarily interlinked and iterative (refer to Figure 3-1). The EHE is continually updated as additional site investigation data are obtained. These updates are used to guide and support further site investigation as needed.

For example, detection of high levels of tetrachloroethylene in groundwater during a site investigation could suggest vapor intrusion as a potential environmental hazard (e.g., groundwater action level for vapor intrusion exceeded). This could trigger the collection of soil gas samples in the source area as well as beneath and nearby existing buildings. Under some circumstances the resulting data could trigger the need for indoor air data and/or a review of the building ventilation system. This could then lead to the need to seal floors in order to prevent the potential intrusion of vapors into the building.

Linking the Site Investigation and Environmental Hazard Evaluation stages of the process in this manner from the very beginning of the project improves the effectiveness and efficiency of the overall site assessment process. This in turn helps to expedite completion of the project, minimize disruptions in site use and delays in site redevelopment.