Standards & Requirements
What Is ASTM E1527-21? The Phase 1 ESA Standard Explained
ASTM E1527-21 is the standard that defines what a Phase 1 Environmental Site Assessment must include to satisfy federal law. Approved November 1, 2021 by ASTM International, it replaced E1527-13 and — per the EPA's All Appropriate Inquiries rule (40 CFR Part 312) — remains the accepted practice for AAI compliance in commercial real estate transactions across the United States.
Updated April 2026 · 8 min read
Why ASTM E1527-21 exists: CERCLA liability protection
Under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), a property owner can be held responsible for cleaning up contamination even if they did not cause it. The law provides four defenses — called Landowner Liability Protections (LLPs) — for parties who perform adequate environmental due diligence before acquiring a property (CERCLA § 101(35); 40 CFR Part 312):
Innocent Landowner Defense
Available to buyers who had no knowledge of contamination at the time of purchase and conducted All Appropriate Inquiries.
Contiguous Property Owner Defense
Protects owners whose property became contaminated by migration from an adjacent site, provided they performed AAI.
Bona Fide Prospective Purchaser (BFPP) Defense
Available to buyers who knowingly acquire contaminated property, provided they performed AAI and take required care post-acquisition.
Government Involuntary Acquisition Defense
Available to government entities that acquire a contaminated property involuntarily — for example, through tax delinquency, bankruptcy proceedings, or eminent domain — provided they did not cause or contribute to the contamination (CERCLA § 101(35)(A)(ii)).
To qualify for any of these defenses, the buyer must complete All Appropriate Inquiries (AAI) — the due diligence standard defined in EPA's rule at 40 CFR Part 312. The EPA has confirmed that a Phase 1 ESA conducted in accordance with ASTM E1527-21 satisfies the AAI requirement.
The four required components
ASTM E1527-21 (Section 7) organizes the Phase 1 ESA into four primary components. All four must be completed for the assessment to be considered AAI-compliant under 40 CFR Part 312.
Review of historical records (aerial photographs, fire insurance maps, city directories, topographic maps), regulatory databases, and physical setting sources to identify past uses and known environmental conditions.
A physical inspection of the subject property and, where accessible, adjoining properties by the Environmental Professional to observe conditions that may indicate RECs.
Interviews with current and past owners, operators, and occupants of the subject property, as well as key local government officials as deemed necessary.
A report documenting all findings, opinions, and conclusions signed and dated by the Environmental Professional who conducted or supervised the assessment.
Phase 1 does not include sampling
Section 7.4 of ASTM E1527-21 explicitly states that the standard does not include collection of samples of soil, groundwater, or building materials. Sampling is the domain of Phase 2. A Phase 1 ESA that includes sampling is outside the scope of E1527-21 (though a firm may propose it as a separate add-on service).
Timing requirements: the 180-day and 1-year rules
For a Phase 1 ESA to satisfy AAI under CERCLA, the standard imposes two timing constraints on when key work must be completed relative to the date of property acquisition:
| Requirement | Time limit |
|---|---|
| Site interviews, visual site inspection, reviews of government records, and searches for recorded environmental cleanup liens (per 40 CFR § 312.20(b)) | Within 180 days before acquisition |
| Remaining components (historical records review, physical setting sources review, written report) | Within 1 year before acquisition |
| Full report update required if | Any component exceeds 1 year |
In practice, this means a Phase 1 ordered more than a year before a closing date must be updated or re-performed. Firms typically note this in the report and can provide an update letter for a fraction of the original cost if conditions have not materially changed.
Key definitions in ASTM E1527-21
ASTM E1527-21 (Section 3) defines several terms that appear in every Phase 1 report. Understanding these terms is essential for reading the conclusions section.
The presence or likely presence of hazardous substances or petroleum products in, on, or at a property due to a release to the environment, under conditions that indicate a release to the environment, or under conditions that pose a material threat of a release to the environment. A REC does not include de minimis conditions. (ASTM E1527-21, Section 3; 40 CFR § 312.10(b))
A past release of hazardous substances or petroleum products that has been addressed to the satisfaction of the applicable regulatory authority, with no requirement for further action, and which the EP believes is unlikely to be subject to further regulatory action. (ASTM E1527-21, Section 3)
A REC resulting from a past release that has been addressed to the satisfaction of the applicable regulatory authority with the application of institutional or engineering controls, with ongoing obligations — such as deed restrictions or monitoring requirements — still in effect. (ASTM E1527-21, Section 3)
A condition that generally does not present a material risk of harm to public health or the environment and that generally would not be subject to enforcement action if brought to the attention of the appropriate governmental agency. (ASTM E1527-21, Section 3)
A lack of or inability to obtain information required by the standard, despite good faith efforts by the EP. (ASTM E1527-21, Section 3)
A data gap that the EP believes could affect the ability to identify RECs. Significant data gaps must be documented and explained in the report. (ASTM E1527-21, Section 3)
Who can conduct an ASTM E1527-21 Phase 1 ESA?
ASTM E1527-21 requires that the assessment be conducted or supervised by an Environmental Professional (EP), as defined in 40 CFR § 312.10(b). An EP must meet at least one of four qualification paths:
Path 1 — Licensed engineer or geologist
Licensed Professional Engineer (PE) or Professional Geologist (PG) with at least 3 years of relevant full-time experience.
Path 2 — Government-licensed or certified environmental professional
Licensed or certified by a federal, state, tribal, or territorial government body to perform environmental inquiries as defined in 40 CFR § 312.21, with at least 3 years of relevant full-time experience (40 CFR § 312.10(b)(2)).
Path 3 — Science or engineering degree
A bachelor's or higher degree in science, engineering, or a related field from an accredited institution, with at least 5 years of relevant full-time experience.
Path 4 — 10 years of experience
Ten or more years of relevant full-time work experience, for individuals who entered the field before formal credentialing was widespread.
The EP must sign and date the report and include a statement of their qualifications. An assessment signed by someone who does not meet EP qualifications does not satisfy AAI under CERCLA, regardless of how thorough the work appears.
What ASTM E1527-21 does not cover
The standard explicitly excludes the following from the scope of a Phase 1 ESA (Section 1.2 of the standard):
These items can be addressed separately by the firm as non-scope considerations (NSCs) or add-on services, but they are not part of the standard Phase 1 ESA scope. PFAS is addressed in an informational appendix of E1527-21 as an emerging contaminant requiring special consideration, but it is not formally within scope — the standard notes the evolving regulatory landscape for PFAS.
What changed from E1527-13 to E1527-21?
Per ASTM's published comparison of E1527-13 and E1527-21, the 2021 revision retained the same four-component structure. The key changes were:
E1527-21 explicitly includes vapor migration — the movement of contaminant vapors through soil into a building or the atmosphere — within the definition of migration under the REC definition. E1527-13 was less explicit on this point, creating inconsistency in practice.
The 2021 standard requires more specificity when characterizing a condition as a CREC (with ongoing institutional or engineering controls) or HREC (addressed to regulatory satisfaction). The EP must explain the basis for each characterization.
The Brownfields Utilization, Investment, and Local Development (BUILD) Act of 2018 modified certain CERCLA liability provisions. E1527-21 incorporates these changes to ensure AAI compliance aligns with current law.
An informational appendix was added to address PFAS (per- and polyfluoroalkyl substances) as emerging contaminants. The appendix notes that PFAS are not within standard Phase 1 scope but provides guidance for EPs on how to handle PFAS indicators when encountered during research.
Practical implications for buyers and lenders
Several points from the standard have direct practical consequences for commercial real estate transactions:
- Standard specification. Commercial real estate contracts and lender requirements commonly specify ASTM E1527-21 by name rather than simply "Phase 1 ESA," because firms occasionally conduct assessments under older standards or internal protocols that do not satisfy AAI.
- EP qualification verification. Every compliant Phase 1 ESA report includes a qualifications statement from the signing EP demonstrating that they meet one of the four paths under 40 CFR § 312.10(b). Lenders and counsel routinely review this statement.
- Timing relative to closing. Under 40 CFR § 312.20(b), key AAI components — including the site visit — must be completed within 180 days of property acquisition. Assessments completed more than 180 days before a closing date require an update to remain AAI-compliant.
- Conclusion language. The EP's standard conclusion statement uses defined terms. "No RECs identified" means no recognized environmental conditions were found under the standard's definitions — it does not constitute a certification that a property is free of contamination.
This article is based on ASTM E1527-21 (Standard Practice for Environmental Site Assessments: Phase I Environmental Site Assessment Process, approved November 1, 2021) and the EPA's All Appropriate Inquiries rule (40 CFR Part 312). Content is provided for informational purposes only and does not constitute legal or environmental advice. Consult a licensed Environmental Professional for guidance specific to your transaction or property.
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