7 Common Mistakes in Environmental Site Assessments (and How to Avoid Them)

Environmental site assessments (ESAs) are only as good as the people conducting them and the scope they are given. A poorly executed Phase 1 or Phase 2 ESA can miss contamination, produce undefendable data, delay transactions and expose clients to liability they thought they had covered.

After decades of collective industry experience and thousands of assessments, the same mistakes keep appearing. Here are the seven most common and how to avoid them.

1. Incomplete Historical Research

The most damaging Phase 1 ESA mistake is failing to trace the property's full use history. If the assessor only reviews records back 20 years on a property built in 1950, four decades of potentially contaminating activity go unexamined.

What Goes Wrong

• Skipping aerial photograph review because imagery is expensive or unavailable
• Not checking fire insurance maps (Sanborn maps) that show industrial uses in detail
• Relying on current owner interviews without independently verifying historical uses
• Not researching the history of adjacent properties, which can impact the subject site via groundwater migration

How to Avoid It

Require the consultant to document all historical sources reviewed and the time period covered. ASTM E1527-21 requires historical research "back to the property's first developed use, or back to 1940, whichever is earlier." Confirm the report meets this standard. If historical records are unavailable for a period, the report should document the data gap, not ignore it.

2. Insufficient Regulatory Database Search Radius

Contamination does not respect property lines. A leaking underground storage tank 500 meters away can send a groundwater plume directly under your property. If the regulatory database search does not extend far enough, these off-site sources are missed.

What Goes Wrong

• Using minimum search radii that are too small for the hydrogeological setting
• Not reviewing all relevant databases (federal, state/provincial, local)
• Dismissing nearby listed sites without evaluating groundwater flow direction

How to Avoid It

ASTM E1527-21 specifies minimum search distances for different database types (e.g., 1 mile for NPL sites, 0.5 miles for leaking USTs). But these are minimums. In areas with known groundwater contamination or high-permeability geology, the consultant should expand the search radius and evaluate whether any listed site could affect the subject property based on groundwater flow direction.

3. Cursory Site Reconnaissance

A Phase 1 site visit that consists of a quick drive around the property and a few photos does not meet the standard. Visual evidence of contamination is often subtle and requires systematic observation by an experienced assessor.

What Goes Wrong

• Not entering all buildings and inspecting mechanical rooms, basements and storage areas
• Missing evidence of underground storage tanks (fill ports, vent pipes, dispenser islands)
• Not walking the entire property perimeter, including areas with heavy vegetation
• Conducting the visit during conditions that obscure evidence (snow cover, standing water)
• Not photographing potential concerns for documentation

How to Avoid It

The site reconnaissance should be conducted by the Environmental Professional who signs the report, not delegated to a junior technician unfamiliar with what to look for. Every accessible area of the property should be inspected. If areas are inaccessible, the report must document this as a data gap.

4. Wrong Analytical Parameters in Phase 2

Testing for the wrong contaminants is the Phase 2 equivalent of looking for your keys under the streetlight because that is where the light is. The analytical program must match the property's history, not a generic checklist.

What Goes Wrong

• Testing only for petroleum hydrocarbons at a former dry cleaning site (should test for chlorinated solvents)
• Not including metals analysis at a former industrial property
• Ignoring PFAS at sites with AFFF (firefighting foam) use history
• Using screening-level methods when quantitative results are needed for regulatory comparison
• Not analyzing for breakdown products (e.g., testing for PCE but not DCE or vinyl chloride)

How to Avoid It

The Phase 2 scope should be driven by the Phase 1 findings. Every REC should have a corresponding investigation approach with analytically appropriate parameters. If the Phase 1 identified a former machine shop, the Phase 2 should test for metals, cutting oils and degreasing solvents. Review the proposed scope before fieldwork begins and question any parameter gaps.

5. Poor Sample Location Selection

Drilling boreholes in the wrong locations produces data about the wrong places. If boreholes are placed 20 meters from the former tank location, the results tell you nothing about whether the tank leaked.

What Goes Wrong

• Placing boreholes based on access convenience rather than suspected contamination locations
• Not collecting samples downgradient of potential sources (misses groundwater plumes)
• Too few boreholes to characterize the area of concern
• Not installing background wells upgradient for comparison
• Screening at the wrong depth interval (contamination may be deeper than sampled)

How to Avoid It

Sample locations should target the specific areas identified as RECs in the Phase 1. Boreholes should be placed at, immediately adjacent to and downgradient of suspected source areas. At least one upgradient background location should be included for comparison. The sampling depth should extend below the water table to assess groundwater conditions.

6. Ignoring Data Quality

Laboratory results are meaningless if the samples were not collected, preserved, transported and analyzed according to standard methods. Data quality failures invalidate results and require expensive re-sampling.

What Goes Wrong

• Using wrong sample containers or missing chemical preservatives
• Exceeding hold times between collection and analysis
• Incomplete chain of custody documentation
• Not collecting required QA/QC samples (trip blanks, field duplicates, equipment blanks)
• Not reviewing laboratory QA/QC reports for qualified or rejected results
• Using non-accredited laboratories

How to Avoid It

Require the consultant to follow a documented sampling and analysis plan (SAP) that specifies containers, preservatives, hold times, QA/QC requirements and laboratory accreditation. Review the data validation summary in the Phase 2 report. If QA/QC issues are flagged, understand whether they affect the usability of the data.

7. Vague or Non-Committal Conclusions

The purpose of an ESA is to provide clear information for decision-making. Reports that hedge with language like "contamination may or may not be present" or "further investigation could be warranted" fail their primary purpose.

What Goes Wrong

• Conclusions that restate findings without providing interpretation
• Excessive use of qualifying language that avoids definitive statements
• Not clearly stating whether RECs were identified (Phase 1) or whether contamination exceeds applicable standards (Phase 2)
• Recommendations that are overly conservative to protect the consultant rather than serve the client

How to Avoid It

Before engaging a consultant, review a sample report. The conclusions section should clearly state: what was found, whether it represents a concern, what the recommended next steps are and why. A well-written ESA gives the reader enough information to make an informed decision without needing the consultant to interpret their own report.

The Cost of Getting It Wrong

Every one of these mistakes has a cost. Missed contamination discovered during construction can add $200,000+ to project costs and months to the schedule. Undefendable data requires re-investigation at the client's expense. Incomplete assessments expose buyers to liabilities they thought they had assessed.

The difference between a thorough ESA and a check-the-box ESA is not the price - it is the experience and diligence of the consultant performing it. The cheapest assessment is rarely the most cost-effective one.

Related Reading

• Phase 1 ESA: Cost and Process
• Phase 2 ESA: Process and Cost
• Environmental Due Diligence Guide