Eisenbach & Ruhnke - Phase III Remedial Investigation/Remedial Action

6.0 Phase III Remedial Investigation/Remedial Action (Phase III RI/RA) Process

6.1 Purpose

A Phase III is a combination of investigations and remediation efforts performed to fully characterize and remediate environmental contamination and liabilities previously discovered on site during the Phase-II SI process.

The objectives of the Phase III process include:

¨ Characterize the vertical and horizontal extent of soil and groundwater contamination;
¨ Assess health risks;
¨ Identify and review potential remedial action alternatives;
¨ Determine the feasibility of implementing these alternatives;
¨ Select and implement the most appropriate cleanup strategies

The standards for the Phase III process have been established by the CERCLA, and the National Oil and Hazard Substance Contingency Plan (NCP). The process has been developed for superfund sites and is designed to identify, evaluate, and select cost effective remedial action alternatives that adequately protect human health and the environment. Not all components of this process apply to all sites, but the general framework this evaluation process can be applied to each site to evaluate potential impact to public health, to assist in identifying applicable remedial action alternatives and in setting appropriate cleanup levels. The following sections provide and overview of the process.

6.2 Site Characterization

The objective of a site characterization is to fully define the horizontal and vertical extents of the soil and groundwater contamination, and gather on the physical properties of the site, including soil characteristics, groundwater conditions and surface water influences. This data is then used to develop remediation alternatives.

A work plan should be developed to characterize the site. The work plan can be agreed upon by all parties and include all quality control programs and specific standards to be used for characterization. The work plan should also provide details on collection, analysis, and review of soil, water and air.

6.3 Exposure Assessment and Selection of Remedial Action

Remediation of sites are typically designed to reducing the human exposure of contaminants to within an acceptable risk levels. The exposure evaluation is based on a contaminant being present at a certain level on site and migrating to a population where exposure to this population may occur. The remediation is then developed to reduce or control the exposures to allowable levels. Once a remedial action is complete, post remediation sampling and monitoring will continue to ensure the remediation was successful.

6.3.1 Public Health Evaluation Process

The health evaluation process begins with the identification of indicator chemicals (chemicals identified to be of greatest concern) at the site where a known release has occurred. Potential exposure pathways for these chemicals are identified by determining release sources and release media. Potential human exposure points are identified and characterized. Release sources are reevaluated within the context of potential human exposures to identify environmental transport methods and pathways (exposure routes and pathways). An evaluation of sensitive receptors (human populations) is also included in this phase of the exposure assessment.

Chemical releases are then quantified to estimate exposure point concentrations and to predict how these chemicals will react in, move through the environment, and expose human populations. Estimated exposure concentrations are calculated and compared to existing requirements and standards.

6.3.2 Indicator Chemicals

Indicator chemicals are chemicals identified on site to present the highest public health risk. These chemicals are considered the greatest public health risk because they represent the most toxic, mobile, and persistent and are those known to be present in the greatest amounts. A list of these indicator chemicals are developed per site and used in the public health assessment process.

6.3.3 Fate/Transport Evaluation

Receptors such as residential neighborhoods, onsite workers, and employees are first identified. The potential pathways for these populations to be exposed are determined, including ingestion of soil, inhalation of dust particulates, dermal (skin) contact, etc. The evaluation estimates the baseline environmental concentrations of indicator chemicals so that the duration of human exposure in the absence of remedial action can be determined. The evaluation estimates how and when exposures to human health will occur from the known hazardous waste on site.

6.3.4 Toxicology Assessment

Human intake of indicator chemicals are calculated from exposure point concentrations. The intake amounts at exposure points can be estimated or determined by actual sampling at the exposure point. The intake amounts are then used with toxicity data to perform a toxicology assessment. Toxicology assessments determine the increased health related risks associated with the exposure.

6.3.5 Remedial Action Alternatives Analysis

The analysis of each remediation alternative is an evaluation of how effective each alternative is on controlling the source of contamination, how migration is to be prevented, and how effective the alternative is in reducing exposures.

6.3.6 Remedial Action

Remediation selected for a site may be as simple as capping the contaminated soil on the site with a clean layer of soil and developing a vegetative growth (grass) cover. Other remediation alternatives may consist of a complete removal of the source contamination with a groundwater and vapor recovery system.

6.3.7 Closure, Post-Closure, and Certifications

Depending of the selected remediation method, closure and post closure sampling may be needed. For example, if remediation consists of capping a site with clean soil then no closure or post closure sample may need to be completed. Once the remediation is completed, the leading government agency directing the remediation would issue a certification letter, or a no-further-action letter indicating the remediation was complete.

If the remediation consisted of an ongoing groundwater and vapor recovery system then sampling may be required to demonstrate the groundwater had been cleaned to standards, and sampling may need to continue after closure to ensure contamination does not recur.

Each remediation strategy will be structured specifically for each site with closure sampling and monitoring requirements determined by the lead agency.