A PSI — a Preliminary Site Investigation — is the exact same thing as a Phase 2 ESA, only instead of the investigation being done on a single commercial property, it’s performed inside a corridor of Rights of Way (ROW). Essentially it’s a long, narrow Phase 2 ESA that seeks to confirm or deny the existence of environmental contamination along the corridor being assessed. If you’re with a financial lending institution looking for a “Preliminary ESA,” you are most likely looking for a Transaction Screen Assessment (TSA) instead — the two are frequently mistaken for one another.
Before we get too deep, it helps to read our explainer on what a Phase 2 Environmental Site Assessment is. It gives you a solid base for understanding the corridor version.
Who Needs a PSI?
First of all, nobody needs one unless a Preliminary Environmental Site Assessment (PESA) shows areas of concern. The PESA is the first step in the process, just like a Phase 1 ESA is the first step in commercial due diligence.
Governments — State Departments of Transportation, counties, and municipalities — typically purchase a PESA and subsequently the investigation that follows it. Agencies installing infrastructure like roads and water mains need to understand the environmental conditions around the area where they’ll be working. These road and pipeline projects are linear in nature and cross the Rights of Way of many other landowners.
A road widening along a state highway that passes several dry cleaners, gas stations, and industrial parks may have contaminated soil at any point along it. This investigation confirms or denies the existence of that contamination.
Why Do Governments Order One?
Agencies are interested in the contamination along the corridor for several reasons:
- Worker exposure. Construction workers potentially exposed to contamination is a health and safety risk, and precautions may be required.
- Budgeting. Contaminated soil is expensive to haul off-site. Clean Construction & Demolition Debris (CCDD) soil is cheaper to haul but must be clean. Soil can be reused on-site but must be clean, so there can be costs associated with bringing in backfill.
- Contamination travels. Contamination moves along infrastructure such as pipelines. Putting a pipeline through a contaminated area is almost certain to transmit the contamination along the pipe, spreading it to adjacent properties.
How Long Does It Take?
The time to complete the work depends on the area covered. Generally there are only small areas of concern along the corridor — the spots the PESA flagged. If the area is relatively small, expect it to take about the same time as a Phase 2 ESA: roughly 15 to 30 days.
What Does a PSI Cost?
Again, this depends on the size of the corridor being studied, but figure roughly $6,000 and up to start. The number of borings, sample depth, and laboratory analytes all drive the price. Contact A3E for a quote based on your scope.
How Long Is It Good For?
The report is typically used once and done. It’s used for budgetary purposes and in preparation for work being done in the Right of Way.
Assets Not Liabilities
Who Performs the Investigation?
The majority of these are completed by environmental consultants — municipalities typically don’t complete them internally. A3 Environmental Consultants performs this service in Illinois, Southern Wisconsin, Northwest Indiana, and Western Michigan. We are headquartered in Chicago, Illinois.
See This Work in the Field
Want to see what a real project looks like? Read our profiles: an IDOT PSI program across four Chicagoland corridors in 2025, an IDOT investigation on McConnor Parkway in Schaumburg, and a 2022 project profile.
What Else Should I Know?
- In the State of Illinois, the Department of Transportation subs the PESA process out to the Illinois State Geological Survey.
- If you’re having one performed as a government, the work is public record and can be subject to FOIA.
- Municipalities need permits to drill in state Rights of Way, the state needs permits to drill in municipal Rights of Way, and utilities need permits to drill in anyone’s right of way.
Frequently Asked Questions
Is a PSI the same as a Phase 2 ESA?
Functionally, yes — it uses the same subsurface sampling approach as a Phase 2 ESA but applies it to a linear corridor of Rights of Way instead of a single parcel.
Do I always need one after a PESA?
No. You only need the follow-up investigation when the PESA identifies a High Risk area of concern. If the assessment comes back clean, none is required.
How much does it cost?
Pricing starts at roughly $6,000 and scales with the number of soil borings, sample depths, and laboratory analytes. Contact A3E for a quote on your specific scope.
What does it test for?
It depends on what the PESA flagged, but common analytes include VOCs, SVOCs, metals (such as the RCRA metals), and occasionally elemental mercury — validated against Illinois’ Tiered Approach to Corrective Action Objectives (TACO).
Need a PSI? Let’s Talk.
If you need this investigation for an upcoming corridor or infrastructure project, give A3 Environmental Consultants a call. We can be reached at (888) 405-1742 or by email at Info@A3E.com. Learn more about our Preliminary Site Investigation services.
We Fix Gnarly Environmental Problems
Reviewed by the A3 Environmental Consultants team, headquartered in Chicago, Illinois, under the supervision of a licensed Professional Geologist (P.G.).
