What Is a Phase I ESA? A Plain-Language Guide

What Is a Phase I Environmental Site Assessment?

A Phase I Environmental Site Assessment (Phase I ESA) is a standardized investigation into the environmental condition of a property. Its purpose is to identify whether current or past activities on or near the property have resulted in - or could result in - contamination by hazardous substances or petroleum products.

A Phase I ESA does not involve any drilling, sampling, or laboratory analysis. It is entirely a records review, physical inspection, and interview process. The assessment is performed by a qualified Environmental Professional (EP) following procedures defined in ASTM E1527-21.

The practical outcome of a Phase I ESA is one of two things: either the EP finds no evidence of contamination (no Recognized Environmental Conditions identified), or the EP identifies conditions that warrant further investigation (typically a Phase II ESA with actual sampling).

Why Phase I ESAs Exist

Environmental liability in the United States is governed largely by the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), commonly known as Superfund. Under CERCLA, the current owner of a contaminated property can be held liable for cleanup costs - even if they did not cause the contamination and did not know about it when they purchased the property.

This strict liability framework means that buying a property without understanding its environmental history is a significant financial risk. A contaminated commercial property can carry cleanup costs ranging from tens of thousands to millions of dollars, and the current owner is on the hook regardless of fault.

To address this, CERCLA provides several defenses for property purchasers who conduct appropriate due diligence before acquiring a property. These are commonly called Landowner Liability Protections (LLPs) and include the innocent landowner defense, the bona fide prospective purchaser defense, and the contiguous property owner defense. To qualify for any of these protections, the purchaser must demonstrate that they conducted “All Appropriate Inquiries” (AAI) into the property’s environmental condition before the acquisition date.

A Phase I ESA conducted under ASTM E1527-21 satisfies the AAI requirement. This is why lenders and investors require them for commercial real estate transactions - without a Phase I, there is no liability protection.

The ASTM E1527-21 Standard

ASTM International publishes the standard that governs how Phase I ESAs are conducted. The current version is ASTM E1527-21, which became the required standard for AAI compliance as of February 13, 2024. The previous version (E1527-13) is no longer accepted for CERCLA liability protection purposes.

The standard is revised every eight years to reflect evolving practices. Key changes in the 2021 revision include a clarified definition of Recognized Environmental Conditions, more specific requirements for historical records research, a new flow chart for classifying environmental conditions (REC vs. HREC vs. CREC), a formal definition of “significant data gap,” and requirements for photographs and property boundary maps in the report.

ASTM E1527-21 applies to commercial real estate. A separate standard, ASTM E2247-23, exists for forestland and rural property.

What a Phase I ESA Covers

A Phase I ESA has four main components, all of which must be completed for the assessment to comply with ASTM E1527-21.

Records Review

The EP reviews federal, state, tribal, and local government records to identify known or potential environmental contamination on and near the property. This includes environmental database reports (commonly ordered from commercial database providers) that compile information from sources like EPA’s CERCLIS/SEMS list, state leaking underground storage tank databases, hazardous waste handler lists, and enforcement action records.

The EP also reviews historical records to understand how the property and surrounding area have been used over time. Under E1527-21, four historical sources must be reviewed at minimum for both the subject property and adjoining properties: aerial photographs, fire insurance (Sanborn) maps, city directories, and historical topographic maps. If any of these cannot be reviewed, the report must explain why.

Additional sources commonly reviewed include building department records, property tax files, zoning and land use records, and any available prior environmental reports.

Site Reconnaissance

The EP conducts a physical inspection of the property and observes adjoining properties from the subject property or public rights-of-way. The site visit looks for visual evidence of current or past environmental concerns - things like stained soil or pavement, stressed vegetation, abandoned drums or tanks, vent pipes (which may indicate underground storage tanks or vapor mitigation systems), and chemical storage areas.

The EP also observes the general condition of the property, identifies current uses and operations, and documents features with photographs - a requirement that E1527-21 made explicit.

Interviews

The EP interviews current and past owners, operators, and occupants of the property, as well as local government officials, to gather information about current and historical property uses, known environmental conditions, and any awareness of contamination. Under E1527-21, interviews are classified as a historical source of information rather than a standalone component.

Report

The EP compiles findings into a written report that includes descriptions of all sources reviewed, observations from the site visit, interview results, an evaluation of potential environmental conditions, and the EP’s professional opinions and conclusions. The report must identify any Recognized Environmental Conditions, Controlled Recognized Environmental Conditions, Historical Recognized Environmental Conditions, de minimis conditions, and significant data gaps.

E1527-21 requires the report to include photographs of the property and a map showing the property boundaries. The report must also include the dates each component was completed, which determines the report’s shelf life.

Key Terms

Understanding these terms is essential to reading a Phase I ESA report.

Recognized Environmental Condition (REC) - The presence or likely presence of hazardous substances or petroleum products at the property due to a release, under conditions indicative of a release, or under conditions that pose a material threat of a future release. A REC means there is a real possibility of contamination that typically warrants further investigation.

Historical Recognized Environmental Condition (HREC) - A past release that has been addressed to the satisfaction of the applicable regulatory authority and meets current unrestricted use criteria. In other words, there was contamination, it was cleaned up, and the regulatory agency closed the case with no restrictions on property use. An HREC is not a REC.

Controlled Recognized Environmental Condition (CREC) - A recognized environmental condition that has been addressed to the satisfaction of the applicable regulatory authority, but with hazardous substances or petroleum products allowed to remain in place subject to controls. This means contamination exists but is being managed through land use restrictions, engineering controls, or other measures. A CREC is a type of REC.

De Minimis Condition - A condition related to a release that generally does not present a threat to human health or the environment and would not typically be the subject of enforcement action. Small, incidental releases that do not rise to the level of a REC.

Significant Data Gap - A data gap that affects the EP’s ability to identify a recognized environmental condition. E1527-21 requires the EP to document significant data gaps and explain their impact on the assessment’s conclusions.

What a Phase I ESA Does NOT Cover

A Phase I ESA under ASTM E1527-21 is specifically designed to identify CERCLA-related hazardous substances and petroleum products. Several common environmental concerns fall outside its scope.

Non-scope considerations that are commonly added to Phase I ESAs as supplemental services (but are not required by the standard) include asbestos-containing materials, lead-based paint, radon, mold, wetlands, indoor air quality, and ecological assessments.

Emerging contaminants such as PFAS are currently non-scope under ASTM E1527-21 because they are not yet classified as CERCLA hazardous substances (though EPA rulemaking to designate certain PFAS under CERCLA is underway as of 2026). However, a prudent buyer may want to include PFAS in the scope of work, particularly for properties with a history of industrial operations, firefighting foam use, or proximity to known PFAS sources. Your EP can advise on whether expanding the scope is warranted.

Vapor intrusion - the migration of volatile chemicals from contaminated soil or groundwater into indoor air through building foundations - is addressed within the Phase I framework to the extent that the EP evaluates whether conditions indicative of vapor intrusion exist. However, a Phase I does not include vapor sampling.

State Programs May Have Additional Requirements

ASTM E1527-21 is the national standard and satisfies federal AAI requirements. However, individual states may have their own environmental due diligence requirements that go beyond what ASTM requires. If you’re working within a specific state cleanup or transfer program, the ASTM Phase I alone may not be sufficient.

A few examples of how state requirements can differ:

Ohio’s Voluntary Action Program (VAP) conducts Phase I property assessments under OAC 3745-300-06, which follows a similar framework to ASTM but uses program-specific terminology and requirements. The VAP Phase I introduces the concept of “Identified Areas” (IAs) - areas on the property potentially affected by Recognized Environmental Conditions - which are used to design the Phase II sampling program. The REC/IA distinction is specific to Ohio’s VAP and does not appear in the ASTM standard. See our Ohio VAP Program Overview for details.

New Jersey requires a separate Preliminary Assessment (PA) under NJDEP rules (N.J.A.C. 7:26E) that goes beyond the ASTM standard. A Phase I ESA alone does not satisfy New Jersey’s state-level innocent purchaser defense or ISRA (Industrial Site Recovery Act) requirements. For New Jersey transactions, a combined Phase I/PA report is often recommended.

Other states may require evaluation of emerging contaminants, additional historical research, or compliance with state-specific reporting formats. Always check with your EP about applicable state requirements before relying solely on an ASTM-compliant Phase I.

Report Shelf Life

Under ASTM E1527-21, a Phase I ESA report is valid for 180 days. The 180-day clock starts at the earliest completion date of the following components (not the report date): interviews, environmental lien searches, government records review, site reconnaissance, and the EP’s declaration.

This is a change from the prior standard and can shorten the effective shelf life in practice. If the EP ordered database reports three weeks before the site visit, the 180-day window starts from the database report date, not the date the report was finalized.

A Phase I report can be extended up to one year if the following components are updated within 180 days of the transaction: interviews, environmental lien search, government records review, site reconnaissance, and the EP declaration. The historical records research does not need to be updated for the extension.

Cost and Timeline

Phase I ESA costs vary based on property size, complexity, location, and the firm performing the work. A straightforward assessment of a small commercial property is significantly less expensive than a complex evaluation of a large industrial site with a long operational history.

Timeline is typically 2 to 4 weeks from engagement to final report. The primary variables are turnaround time for environmental database reports and government records requests, scheduling the site visit, and completing interviews with knowledgeable parties.

Factors that increase cost and timeline include large properties requiring extensive site reconnaissance, properties with long industrial histories requiring more historical research, properties in urban areas with dense surrounding land uses, and difficulty reaching past owners or operators for interviews.

What Happens If Something Is Found

If the Phase I ESA identifies one or more Recognized Environmental Conditions, the typical next step is a Phase II Environmental Site Assessment. A Phase II involves collecting actual environmental samples - soil borings, groundwater samples from monitoring wells, soil gas probes, and/or indoor air samples - to determine whether contamination is present and at what concentrations.

The Phase II results are compared against applicable regulatory standards (which vary by state) to determine whether further action is needed. If contamination is confirmed above applicable standards, the property may require remediation before or after the transaction, depending on the deal structure and the parties’ risk tolerance.

Not every REC leads to a Phase II. In some cases, the EP may recommend additional records research or a more targeted investigation of a specific concern rather than a full Phase II. The appropriate response depends on the nature of the REC and the intended use of the property.

Related Resources

• Ohio VAP Program Overview - How Ohio’s cleanup program layers additional Phase I requirements on top of ASTM
• Low-Flow Groundwater Sampling Guide - Field procedures for Phase II groundwater sampling
• PFAS Sampling Best Practices - If PFAS are added to the Phase I scope