Upon completion of the Phase II Contamination Assessment, where contamination has been detected, a Phase III Contamination Delineation Assessment of the soil and groundwater (if applicable) contaminant plume(s) must be conducted.  A Phase III Contamination Delineation Assessment consists of the logical stepwise delineation of the contaminant plume(s) using invasive testing, such as soil vapour surveying (where applicable) and/or the installation of additional monitoring wells.

Upon completion of the Phase III Contamination Delineation Assessment, the volume of contamination media (soil and groundwater) may be calculated and costs for the Phase IV Site Remediation may be estimated.  In some instances, less stringent remediation criteria may be deemed to be appropriate to apply to a specific site or a Phase IV Site Remediation may not need to be conducted at all due to the low level of risk to human health and/or the environment.  Therefore, a Risk Assessment may be prudent to conduct on the subject site.

Risk Assessment (Optional)

The Phase III Risk Assessment or "… Site Sensitivity Assessment is a means of ranking sites for the purpose of assigning appropriate risk management criteria.  The assessment considers both the sensitivity of the potential human and environmental receptors and the likelihood of impact on those receptors for a number of possible exposure pathways associated with contaminant releases.  Experience has shown that human impact almost always dominates over other agricultural and environmental concerns; however, the latter issues may warrant consideration in certain circumstances."[1]

It is generally accepted that remedial actions for contaminated soil will not completely remove all constituents to background or ambient levels, although some regulatory agencies may require cleanup to background levels.  Instead, some residual contamination will be left in the soil either by:

1. determination of contamination boundaries for the soil being excavated; or

2. limiting the extent of soil treatment.

Specific standards for determining acceptable residual concentrations have not been established by Environment Canada because the threat of exposure from contaminated soil is highly site specific and depends on surface activities, climatic conditions, hydrogeological factors, etc.  Alberta Environment has proposed acceptable residual standards as outlined in the publications entitled "Alberta Tier I Criteria for Contaminated Soil Assessment and Remediation"[2] and "Remediation Guidelines for Petroleum Storage Tank Sites, 1994."

For many instances, the available guidelines will be appropriate to determine the required cleanup levels and site-specific remedial criteria do not need to be established.  Where a case can be made, to Alberta Environment, to demonstrate that existing criteria are too conservative for a given location, site-specific remedial criteria must be established using a risk management approach.  The complexity of the assessment can vary greatly from:

• detailed evaluations of exposure pathways to humans and/or the environment, and site-specific potentially adverse effects from the contaminants; to
• simple judgments based upon currently acceptable practices in the area.

Regardless, the following steps are usually included in the Phase III Risk Assessment:

·        Hazard Identification:  Determines the potential toxicity of the contaminants and/or     their potential negative effect on the environment and/or land use values;

·        Dose Response Assessment:  Describes the quantitative relationship between the exposure and the extent of injury and disease;

·        Exposure Assessment:  Determining human, wildlife, and/or environmental receptors that could potentially be exposed to the contaminants, considering the following pathways:

a)      direct contact;

b)      airborne;

c)      groundwater;

d)      surface water; and

e)      crop uptake.

The pathways are identified for both in-situ conditions and those conditions that may occur during remedial processes.  This includes dose response assessment for contaminant exposure:

·        Risk Characterization:  Determining the degree of potential risk to human and wildlife health, the environment and/or land use as a result of predicted exposure levels for a reasonable range of remedial criteria; and

·        Risk Management:  Selecting the most appropriate cleanup concentrations considering the potential risks, remedial feasibility and reliability, and costs.

The Phase III Risk Assessment classifies a site according to its sensitivity (high, moderate, or low) on the basis of a number of site-specific factors governing the likelihood of impact and receptor sensitivity.  Risk assessment is determined relative to the two (2) major exposure pathways, inhalation and ingestion.  Agricultural impacts and other potential environmental effects are examined as possible modifiers to the final risk assessment level.  The Risk Assessment is performed for all potential receptors, and the resultant site sensitivity ranking is based on the most critical receptors.  The soil and groundwater at a given site would be remediated to the lowest, or governing, risk management criteria indicated by the site sensitivity assessment for the principal exposure pathways.

Guidelines for inhalation and ingestion sensitivity include a determination of receptor sensitivity, the likelihood of impact, the ranking of the site (high, moderate, or low), the relationship of site sensitivity to the required level of risk management criteria, and other ecological and human considerations (effects on aquatic life, wildlife, plant life, etc.).

Figure 4.1, Exposure Pathways Considered by Site Sensitivity Assessment, outlines the exposure pathways considered from a petroleum storage tank (PST) release.

Figure 4.2, Site Sensitivity Assessment Process, outlines the methodology employed by Alberta Environment for determining the risk associated with a given site.

 

Figure 4.1
Exposure Pathways Considered by Site Sensitivity Assessment

 

 

Figure 4.2
Site Sensitivity Process

 

 

Remedial Investigation/Feasibility Study (RI/FS)

The overall objective of the Remedial Investigation / Feasibility Study (RI/FS) process is to select, from available technologies, those remedial solutions consistent with Environment Canada and Alberta Environment cleanup guidelines.  Such guidelines may be found in the following publications:

• "Canadian Environmental Quality Guidelines;"[3]

•  “National Guidelines for Decommissioning Industrial Sites;”[4]

•  “Criteria for Contaminated Soil/Sediment Cleanup;”[5];

•  “Guidelines for the Reclamation of Land in Alberta;”[6]

•  “National Classification System for Contaminated Sites;”[7]

•  “Guidance Manual on Sampling, Analysis, and Data Management for Contaminated Sites, Volume I:  Main Report;”[8]

•  “Guidance Manual on Sampling, Analysis, and Data Management for Contaminated Sites, Volume II:  Analytical Method Summaries;”[9]

•  “Alberta Tier I Criteria for Contaminated Soil Assessment and Remediation;” and

•  “Remediation Guidelines for Petroleum Storage Tank Sites.”

The general process used to attain this objective includes the following steps:

1. Development of Remedial Action Objectives (RAOs) specifying the media of interest, exposure pathways, and remediation goals for the contaminants of concern.

2. Identification of areas and volumes of contaminated media.

3. Development of general response actions that address the remedial action objectives.

4. Identification of potential remedial technologies and the initial screening of these technologies primarily on the basis of technical implementability.

5. Final screening of remaining technologies on the basis of effectiveness, implementability, and the relative cost during which representative process options and technologies are selected for the development and evaluation of remedial alternatives

Remedial Action Objectives

Environment Canada and Alberta Environment require selection of remedial actions that attain a degree of cleanup that assures protection of human health and the environment, are cost effective, and utilize permanent solutions and alternative treatment technologies or resource recovery technologies to the maximum extent practicable.

Areas and Volumes of Contaminated Media

Based on the RAOs defined during the Contamination Assessment and the Remedial Investigation at a given site, the areas and volumes of contaminated media are determined.  Analysis and evaluation of sample data for the site and the RAOs will indicate whether more than just the source areas and groundwater will require remediation.

General Response Actions

Before developing a list of potential remedial technologies and process options applicable to the remediation of source areas and groundwater, general response actions must be identified.  General response actions are classified as broad actions or remedies that meet the remedial action objectives.  The following eight (8) general response actions are typically identified for contaminated sites:

1. Institutional Controls:  Restrictions are established and implemented to control public and environmental contact with the contaminants (e.g., site access and use restrictions).

2. Containment:  Includes direct physical or chemical isolation of contaminants.

3. Removal:  Involves excavation or extraction of the contaminated media and removal from the immediate area.

4. On-Site Treatment:  Includes application of biological, chemical, physical, or thermal processes to reduce toxicity, mobility, or volume of the contaminated media.

5. Off-Site Treatment:  Similar to on-site treatment except the contaminated media are transported to an off-site facility for treatment.

6. In-Situ Treatment:  Involves in-place treatment to render the contaminated media less harmful.

7. On-Site Disposal/Discharge:  The contaminated media are disposed of or discharged on-site in such a way that their interaction with the public and the environment is reduced.

8. Off-Site Disposal/Discharge:  Involves transporting the contaminated media to an off-site disposal facility.

Initial Technology Screening

The general categories of potentially applicable remedial action technologies are further subdivided into process options.  The technologies and process options identified are subjected to a preliminary screening based primarily on their technical implementability.  The  term, process option, refers to a specific process within each general category of technology. 

During this preliminary screening step, process options and entire technology types are eliminated from further consideration primarily on their technical implementability.  In special cases, administrative feasibility, effectiveness, and cost are also used to screen technologies.  This preliminary screening is accomplished by using information from the Risk Assessment on contaminant types, concentrations, and site characteristics.  This is done to screen out technologies and process options that cannot be effectively implemented.  Specifically, technologies and process options may be rejected for one or more of the following reasons:

• would not be a practical method for the volume, or area, of contaminated media that is to be remediated;
• would not be an effective method for the remediation of all of the contaminants due to the characteristics, or concentrations of contaminants present at the site;
• would not be feasible and/or effective due to site conditions.  These include conditions such as site location and size, weather, geology, soils, hydrogeology, characteristics of the contaminated media and surrounding land uses;
• could not be effectively administered;
• could result in the creation of a new site at a different location with the associated risks and liabilities;
• has not been proven on site contaminants or media; and
• has extremely high costs relative to other equally effective technologies.

Table 4.1, General Response Actions and Associated Remedial Action Technologies for Source Areas, and Table 4.2, Potential Remedial Technologies for Source Areas, respectively illustrate the technology types and associated process options currently available in bench, pilot, and full scale for the remediation of source areas (soil).

 

Table 4.1
General Response Actions And Associated
Potential Remedial Technologies For Source Areas