8.1 Environmental Site Assessments & Site Characterization

The framework for Environmental Site Assessments (ESA) is fundamentally driven by the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) and its provision for innocent landowner defenses. To qualify for liability protection, prospective purchasers must perform "All Appropriate Inquiries" (AAI) into the previous ownership and uses of a property. The U.S. EPA recognizes the ASTM E1527-21 standard as fully compliant with the AAI rule.

Phase I Environmental Site Assessment (ESA)

A Phase I ESA is a non-intrusive investigation designed to identify environmental liabilities. Physical sampling of soil, groundwater, or air is specifically excluded from a Phase I ESA. The process consists of four primary components:

1. Records Review: Evaluates historical use of the property and surrounding area. Sources include historical aerial photographs, Sanborn fire insurance maps, city directories, topographic maps, and environmental agency databases (e.g., NPL, RCRA, state leaking underground storage tank lists).
2. Site Reconnaissance: A visual and physical observation of the property and adjoining properties to identify signs of spills, stressed vegetation, underground storage tanks (USTs), and hazardous substance storage.
3. Interviews: Conducted with current and past owners, operators, occupants, and local government officials to gather information regarding the property's environmental history.
4. Report Preparation: Synthesizes the findings and provides the environmental professional's opinion on the presence of specific conditions.

Types of Environmental Conditions

Under ASTM E1527-21, the environmental professional must classify findings into distinct categories:

• Recognized Environmental Condition (REC): The presence or likely presence of any hazardous substances or petroleum products in, on, or at a property due to a release, a likely release, or a material threat of a future release. Examples include an active leaking UST or visible chemical staining on bare soil.
• Controlled Recognized Environmental Condition (CREC): A past release that has been addressed to the satisfaction of the regulatory authority, but hazardous substances remain in place subject to implementation of required controls (e.g., institutional or engineering controls). An example is a site with residual soil contamination capped by an engineered parking lot with a deed restriction prohibiting excavation.
• Historical Recognized Environmental Condition (HREC): A past release that has been remediated to unrestricted residential use standards and has received regulatory closure (e.g., a "No Further Action" letter) without any institutional or engineering controls.
• De Minimis Condition: A condition that generally does not present a threat to human health or the environment and would not be subject to an enforcement action if brought to the attention of regulatory agencies. A minor oil drip from a parked vehicle on a concrete pad is typically considered de minimis.

Phase II Environmental Site Assessment

If a Phase I ESA identifies a REC, a Phase II ESA is often conducted to confirm the presence and extent of contamination. A Phase II ESA is intrusive and involves physical sampling and laboratory chemical analysis.

Scope of Phase II Investigations

• Soil Borings: Drilling into the subsurface to collect soil samples for visual classification and chemical analysis.
• Monitoring Well Installation: Installing wells to evaluate groundwater flow direction and collect groundwater samples. Well construction includes a screened interval, filter pack, bentonite seal, and surface grout.
• Soil Gas Sampling: Collecting vapor samples from the unsaturated zone to evaluate the potential for vapor intrusion into indoor air.
• Laboratory Chemical Analysis: Analyzing samples using EPA-approved analytical methods (e.g., GC/MS for volatile organic compounds).

Quality Assurance and Quality Control (QA/QC)

QA/QC protocols are critical in Phase II ESAs to ensure the reliability and defensibility of the analytical data.

• Trip Blanks: Vials filled with laboratory-grade distilled water that travel from the lab to the site and back without being opened. They are analyzed for VOCs to ensure cross-contamination did not occur during transport or storage.
• Equipment Blanks (Rinsate Blanks): Collected by pouring deionized water over decontaminated sampling equipment. This verifies that decontamination procedures were effective in preventing cross-contamination between sampling locations.
• Field Duplicates (Blind Duplicates): Two separate samples collected from the same location at the same time and submitted to the laboratory without indicating they are duplicates. This evaluates the precision of the sampling and analytical processes.

Conceptual Site Model (CSM)

A Conceptual Site Model (CSM) is a dynamic, written or pictorial representation of an environmental system. It serves as the foundation for site characterization and risk assessment, evolving as new data becomes available. A complete CSM must link the following four elements:

1. Contaminant Source: The origin of the contamination (e.g., a leaking drum, an unlined landfill).
2. Release Mechanism: How the contaminant enters the environment (e.g., spilling, leaking, leaching, volatilization).
3. Transport Pathway: The environmental medium through which the contaminant migrates (e.g., groundwater advection, soil vapor migration, surface water flow).
4. Potential Receptors: Human or ecological populations that could be exposed to the contaminant (e.g., residents drinking groundwater, aquatic life in a stream).

If any one of these elements is missing, the pathway is considered incomplete, and there is no risk to that specific receptor.