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Environmental Investigation and Remediation of a Hazardous Waste Site

Part 6 - Risk Assessment, Feasibility Study and Engineered Remediation

Samir G. Khoury, Ph.D., P.G.


Course Outline

This course, Part 6: Risk Assessment, Feasibility Study and Engineered Remediation, briefly reviews the key points of the previous courses in the sequence (Parts 1 through 5), and presents the results of the risk assessment and feasibility study. This phase of work started with the performance of a risk assessment to determine if an emergency situation exists that would require immediate attention, and the development of a set of corrective action objectives to guide the engineering feasibility study.

The engineering feasibility study starts by evaluating the "No Action" alternative. This assessment is required by the Environmental Protection Agency (EPA), and includes addressing what may happen if nothing is done at the site. The "No Action" alternative is considered the baseline against which the other remediation options are compared.

The following step considered the nature and extent of existing institutional control measures to assess their adequacy to protect humans from inadvertently contacting the waste, or the plume of contaminants. Institutional controls also include ensuring that records of the site contents, spatial distribution of trenches and boundaries of the waste disposal area exist in several state and federal government repositories. These steps are taken to ensure that no one "forgets" that there is hazardous and radioactive waste buried in this area.
 
The next stage involved the identification of a universe of appropriate engineering options for the remediation of the waste disposal area and the down-gradient plume of contaminated groundwater. The technical and regulatory feasibility of the proposed options are first evaluated to determine their relative effectiveness in mitigating existing conditions. Then, based on an assessment of overall appropriateness and cost effectiveness, a preferred engineered option is selected for inclusion in the Corrective Action Plan that is submitted for regulatory review and approval prior to implementation. The process is somewhat more complex because engineering alternatives are considered both individually and in combination and by the inclusion of auxiliary measures that could enhance the overall performance of the selected engineered remediation option.

Following regulatory review and approval, the proposed measures are cleared for implementation. The final design drawings are then prepared and construction can proceed in accordance with the established specifications. Following completion of the construction, effectiveness of the engineered remediation measures is ascertained and documented through the results of the ongoing monitoring program. The monitoring program is usually continued for a period of at least five years following the implementation of the corrective measures to ascertain that the contaminant levels have dropped to below the applicable regulatory limits.

This course series ends with the presentation of graphs from four down-gradient monitoring wells documenting the steady decrease in the concentration of the marker contaminant chloroform. These graphs show a clear decrease in the concentration of the marker contaminant in the monitoring wells over the monitoring period of five years. These graphical results attest to the efficacy of the remedial measures that were implemented at the site.

This course includes a multiple choice quiz at the end, which is designed to enhance the understanding of the course materials.

Learning Objective

At the end of Part 6, the student should understand how the data collected during the various parts of the investigation program are used to support an assessment of the health related risks posed by the site and the approach to developing viable engineering remedial alternatives to improve existing conditions. The student should recognize the important distinction between identifying levels of contamination and identifying a risk to human health. Since it is usually not economically or practically feasible to return all contaminated soil and water to a pristine state, a specific methodology is used to evaluate the risk and make remediation decisions based on that evaluation.

Using the contaminants identified at this site as an example, the students should be able to learn and understand how to:

Through this process, the student should also become familiar with the numerous types of remedial technologies available for both source control and plume remediation and the advantages and disadvantages of each. As part of this course, the student should also become aware that every site has its own unique problems and potential solutions, and there is no "one size fits all" approach to dealing with the remediation of old hazardous and radioactive waste disposal sites.

Intended Audience

This series of courses is intended for environmental engineers, environmental scientists, geotechnical engineers, civil engineers, engineering geologists, environmental geologists, hydrologists and other individuals who are interested to learn how environmental investigations are conducted.

Benefit to Attendees

Students who take this series of courses will learn how environmental problems are investigated; feasibility studies conducted and engineered remediation implemented. These steps are taken to prevent the spread and migration of contaminants to the accessible environment, thus protecting the health and safety of the population and stopping the otherwise inevitable and continual degradation of the environment.

Course Introduction

A research institute (“Institute”) operated a small (0.65 acre) hazardous chemical and radioactive waste burial facility on its campus for about 20 years, starting in the mid 1960s. All waste buried at the site resulted from the use of radioactive elements and chemicals in research experiments. Waste brought to the disposal site was in both solid and liquid form, and the liquids were in various types and sizes of containers. The waste was placed into narrow trenches dug into the soil at the burial site. The trenches were about 8 to 12 feet deep. Once waste reached about 4 feet from the surface, dirt was used to fill the trench to grade.

When the site was decommissioned and no longer used, it was fenced, posted and locked. Minimal grounds maintenance was done until the State Radiation Protection Agency (RPA) notified the Institute that they were to keep the fence clear of vegetation and the area within the fence mowed and free of trees. The following photo shows the disposal area after the site was decommissioned and the grounds maintenance started:

figure 1

Figure 1: Decommissioned waste disposal site at the Institute

Yearly testing of soil, surface water and vegetation by the State RPA following decommissioning of the site showed no evidence of significant radioactive contamination outside the burial area. In the late 1980s the State RPA recommended that the Institute install a series of monitoring wells to allow sampling and testing of the groundwater. In response, and under the guidance of the State Groundwater Protection Agency (GPA), the Institute installed five monitoring wells around the waste disposal site. The location of the five wells is shown on the following figure.

figure 2

Figure 2: Location of Initial Monitoring Wells Surrounding the Waste Disposal Site

About a month after installation, the State RPA collected groundwater samples from the five monitoring wells for radiological analysis. A year later, an additional groundwater sample was collected from Well No.3 for radiological and organic chemical analysis. The radiological analyses indicated that some of the groundwater samples in the immediate surroundings of the restricted area had elevated Tritium activities. It also appeared that organic chemical contamination might be present in the groundwater in the vicinity of the waste disposal area. Discovery of both chemical and radiological contamination outside the burial area prompted the State RPA to require the Institute to design and implement an extensive investigation program. The Institute issued an RFP to environmental and engineering firms for a technical services consultant (“Consultant”). The winning bidder reviewed existing information within the Institute’s files and developed an estimate of the inventory of the waste disposed of at the site and evaluated existing soil, vegetation, groundwater and surface water test results. The Consultant issued a Preliminary Site Condition Report summarizing the results of these initial studies. The State RPA and other State Regulatory Agencies then requested additional soil, groundwater and surface water sampling, including the installation of additional groundwater monitoring wells, in order to determine the size, extent, and characteristics of the contaminant plume, and characterize the geology and hydrology of the area.

Because the disposal site contained hazardous chemicals and radioactive isotopes, no additional field investigations could be started until a project-specific Health and Safety Plan was developed. A project-specific Quality Assurance Plan was also created, and the technical requirements were developed as part of the Sampling and Testing Plan. A set of Project Procedures was written to guide the field sampling and analysis programs that incorporated the requirements of each of the project plans. The relationship of the various plans, procedures and the field and laboratory activities is shown on the following flowchart.

figure 3

Figure 3: Relationship of the Various Project Plans, Procedures and Activities

Field investigations were divided into two phases. The Phase 1 work provided insights with respect to:

One of the recommendations of the Phase 1 studies was to initiate the Phase 2 field investigation program, including additional work in the up-gradient direction as well as the down-gradient direction. This approach was taken to verify the extent and configuration of the area considered up-gradient and therefore free of contamination, and to determine the extent and nature of contamination down-gradient of the waste disposal area.

The Phase 2 field investigations included the implementation of the following activities at the Site:

The collected data were evaluated, integrated and interpreted to arrive at the recommendation to perform a public health risk assessment, prepare an engineering feasibility study, recommend a remedial action plan, obtain the necessary regulatory approvals and implement the remedial measures to control the contamination and improve existing conditions.

Course Content

The course content is in the following PDF file:

Environmental Investigation and Remediation of a Hazardous Waste Site: Part 6 - Risk Assessment, Feasibility Study and Engineered Remediation

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Course Summary

All of the information collected at the Institute's waste disposal site: including the history of burial of chemical and radioactive waste and the geology, hydrology and geochemisty of the subsurface soils and groundwater was used to determine:

  1. If an emergency situation existed at the site, and
  2. The extent to which remediation of the waste disposal area and the down-gradient plume were necessary.

These issues were addressed by performing an assessment of the risk posed by the waste disposal site to human health and the natural environment. Following these assessments, a set of corrective action objectives were developed and used to guide the performance of an engineering Feasibility Study to identify the optimal corrective measures that could be implemented to effectively isolate the waste disposal area from its surrounding environment. Once a corrective action plan was developed, it was submitted to the State Regulatory Agencies for review and approval.

Following the guidance and recommendations provided by the State Regulatory Agencies a qualified design engineering firm prepared the construction drawings and applicable specifications for execution by a qualified constructor under the Quality Assurance supervision of the Consultant. The constructed features of the remedial measure that was implemented are presented on maps and cross-sections at the end of this course (Part 6). The efficacy of the remedial measure is documented by a series of graphs that illustrate the gradual decrease of the contamination over time in the down-gradient monitoring wells. Finally, the Consultant anticipates that over a longer period of time the levels of contamination will eventually come down even further, to possibly below the detection limit of the analytical methods used to analyze the samples.   

Quiz

Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.

Take a Quiz

DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDH Center or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered architect and/or professional engineer/surveyor. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.