What Is a Phase I Environmental Site Assessment? A Complete Guide

If you're buying, selling, leasing, or developing property, a Phase I Environmental Site Assessment (ESA) isn’t just a box to check—it’s a smart investment in your protection. Phase I ESAs identify potential environmental issues like hazardous substances or petroleum contamination that could lead to costly cleanups or legal liabilities down the line. Beyond due diligence, a properly conducted Phase I ESA can qualify you for liability protections under federal law (CERCLA), shielding you from being held responsible for pre-existing contamination. Whether you’re a buyer wanting peace of mind, a seller aiming to boost property value, or a developer looking to avoid delays, a Phase I ESA helps you move forward with confidence.  

Below is a quick guide to help you understand Phase I Environmental Site Assessments. 

What is a Phase I Environmental Site Assessment? 

A Phase I Environmental Site Assessment (Phase I ESA) is the industry standard process for evaluating environmental conditions related to hazardous substances and petroleum products on a property. Often a Phase I ESA is conducted prior to purchase of real estate, before beginning a leasehold, or prior to refinancing or development of a property.  

What is included in a Phase I ESA? 

A Phase I ESA includes a review of regulatory databases for the subject property as well as nearby properties within up to a one mile radius; interviews with the owner, key site manager, operator, and a local or state regulatory official; a review of historical use sources such as aerial photographs, topographic maps, city directories, and Sanborn maps back to the first developed use of the property or 1945 (which ever is earlier); review any environmental files provided for the property; and the environmental professionals opinion of the potential for the presence of hazardous substances and petroleum products in on or at the property due to a release or material threat of release.     

What is the current Phase I ESA ASTM Standard 

The current ASTM Standard for a Phase I ESA is E1527-21. If the property is rural or forestland, ASTM Standard E2247-16 is a more applicable standard to use.  

Who needs a Phase I ESA? 

A Phase I ESA is typically conducted by a prospective purchaser of real estate prior to closing but can also be a helpful assessment for a seller prior to listing a property for sale, or before engaging on a leasehold.  

Why would you conduct a Phase I ESA? 

A Phase I ESA can provide property owners or lessees with three avenues of liability protection under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) with respect to the range of contaminants with CERCLA (U.S.C. §9601) and petroleum products: 

• Innocent Landowner Defense (traditional) 
• Contiguous Property Owner Protection 
• Protects from off-site migration 
• Bona Fide Prospective Purchaser 
• Protection for owner of a property with known contamination at the time of purchase 

How to qualify for limited landowner liability protection under CERCLA 

All three liability protections require a Phase I ESA prior to purchase. To qualify for limited landowner liability protection under CERCLA a prospective purchasers can follow the All Appropriate Inquiry (AAI) protocol in 40 Code of Federal Regulations Part 312. MFA’s completion of a Phase I ESA satisfies the environmental professional’s requirements under AAI and ASTM E 1527-21. 

Who can conduct a Phase I ESA? 

As required by ASTM E1527-21, a Phase I ESA must be conducted by a qualified environmental professional who possesses a specific mix of licensure, education, and relevant experience. MFA’s Phase I ESA’s are conducted by environmental professionals with well rounded experience and industry leading expertise.  

What is a Phase II Environmental Site Assessment? 

A Phase II Environmental Site Assessment (Phase II ESA) is a physical investigation of environmental conditions of potential concern on a property. Often samples are collected, such as from soil, groundwater, soil gas, air, surface water, and/or sediment. A Phase I ESA may also be conducted to investigate select feature conditions, like those of an underground storage tank.   

Maul Foster & Alongi – Environmental Site Assessment Experts  

Since our incorporation more than 20 years ago, MFA’s core business has been in the environmental site characterization and remediation industry. Our staff has conducted hundreds of Phase I and Phase II Environmental Site Assessments (ESAs) at a wide range of properties, including large tracts of forest and agricultural land, multi-unit residential properties, commercial properties, and complex industrial sites. All of MFA’s Phase I ESAs are conducted consistent with the requirements of ASTM and the All Appropriate Inquiries process. We are able to tailor the scope of work to satisfy client objectives