When transportation improvements move forward in Northern Illinois, environmental due diligence moves with them. In 2025, A3 Environmental supported four separate Illinois Department of Transportation (IDOT) Preliminary Site Investigation (PSI) assignments across the Greater Chicagoland area, serving as subconsultant to Arcadis. Each project required strict adherence to IDOT Bureau of Design and Environment procedures, disciplined field execution, and defensible documentation.
For general business stakeholders, IDOT work can feel procedural and opaque. In reality, a well-executed Preliminary Site Investigation is about one thing: generating reliable subsurface data so infrastructure decisions can proceed without regulatory surprises. Across Zion, University Park, Chicago, and Winnetka, A3E delivered focused, schedule-driven field programs tailored to corridor-specific conditions in 2025.
IDOT Preliminary Site Investigation Scope and Field Execution in Chicagoland
The 2025 IDOT assignments spanned four transportation corridors in the Greater Chicagoland area:
• IL-173 (Rosecrans Road) in Zion
• IL-50 (Cicero Avenue) in University Park
• I-290 at Loomis Street in Chicago
• I-294 at Willow Road in Winnetka
While each Preliminary Site Investigation followed an approved work plan, the scale and intensity of field activities varied considerably.
Work Order 1A in Zion involved advancing five soil borings to a maximum depth of 10 feet below ground surface. Eight soil samples were collected in accordance with IDOT sampling protocols and Illinois EPA analytical requirements. The objective was targeted: evaluate potential subsurface impacts within a defined project corridor and provide Arcadis with defensible data for the final submission.
Work Order 2A in University Park required a significantly larger program. Forty-two soil borings were advanced to approximately 9 feet below ground surface, and more than seventy soil samples were collected. This multi-day mobilization within an active roadway corridor demonstrated the logistical demands often associated with IDOT projects. High-density sampling, strict chain-of-custody procedures, and real-time coordination with drillers were essential to maintaining schedule.
Work Order 3A at I-290 and Loomis Street in Chicago required seven borings advanced to depths of up to 15 feet below ground surface. Operating within a dense urban interstate environment introduces constraints not present in suburban corridors. Traffic control, right-of-way limitations, and safety coordination must align with IDOT standards at every step.
Work Order 4A along I-294 at Willow Road involved twenty-six borings and more than one hundred soil samples. Even when maximum depths remain relatively shallow, the density of sampling can reflect a comprehensive approach to corridor characterization under IDOT requirements.
Across all four assignments, groundwater was evaluated as part of the investigation planning process. In each case, groundwater was not encountered within the explored interval or did not warrant monitoring well installation under the approved scope. That determination, while straightforward in writing, requires disciplined observation and documentation in the field.
Process and Methodology: Meeting IDOT BDE Standards
An IDOT Preliminary Site Investigation is not simply a drilling exercise. It is a regulated process governed by Bureau of Design and Environment procedures and supported by Illinois Environmental Protection Agency analytical standards.
Before mobilization, A3E prepared site-specific Health and Safety Plans and reviewed project drawings to confirm boring locations within the IDOT right-of-way and, where necessary, within roadway limits. Boring locations were staked in the field to ensure alignment with the approved PSI work plan. Drilling subcontractors were coordinated and supervised throughout execution.
During field activities, environmental scientists logged soil classifications, documented lithologic changes, and screened samples as required. Soil samples were collected at prescribed intervals and depths consistent with IDOT protocols. Each sample was labeled, preserved, and transferred under strict chain-of-custody procedures to maintain data integrity.
For general business stakeholders, the phrase “chain-of-custody” may sound administrative. In IDOT work, it is foundational. Every sample must be traceable from the moment it leaves the borehole to the moment analytical results are issued. Data defensibility depends on it.
Laboratory analyses were performed in accordance with Illinois EPA requirements. The resulting data packages were reviewed for completeness and transmitted to Arcadis for incorporation into the final PSI reports. A3E’s role was confined to field investigation and data generation; Arcadis, as Prime Consultant, prepared and submitted the final documentation to IDOT.
The consistency across all four 2025 assignments reflects an important reality: IDOT compliance is procedural, but execution is practical. Plans must be followed precisely, but field conditions still demand professional judgment.
Business Impact and Risk Management Value in 2025
For general business audiences, the question is simple: why does an IDOT Preliminary Site Investigation matter?
In 2025, transportation improvements across Chicagoland continued to intersect with legacy land uses—former commercial operations, historic fill, and corridor-adjacent properties with varying environmental histories. An IDOT PSI provides the data necessary to determine whether recognized environmental conditions are present and whether additional assessment or remediation may be required.
Without a properly executed IDOT investigation, project teams risk schedule delays, cost overruns, or regulatory findings late in the design process. With defensible subsurface data in hand, decision-makers can:
• Confirm that no further action is required
• Delineate impacted areas early
• Refine design to avoid contaminated zones
• Budget appropriately for remediation if necessary
Across the four 2025 assignments, A3E delivered field programs that stayed within defined mobilization windows and complied with IDOT standards. From a business perspective, that translates into predictability. When environmental fieldwork is executed efficiently and correctly the first time, downstream design and construction phases proceed with fewer surprises.
The scale differences between five borings in Zion and more than forty borings in University Park illustrate another key point: IDOT projects are not one-size-fits-all. The scope is calibrated to corridor risk, historic use, and design objectives. A competent field team must adapt to each scenario without compromising documentation quality.
Local Considerations in the Greater Chicagoland Area
Performing an IDOT Preliminary Site Investigation in the Greater Chicagoland area requires understanding more than the written work plan. Local soil conditions, historic industrial corridors, and transportation density all influence field execution.
Northern Illinois soils can range from cohesive clays to granular fill materials placed during decades of roadway expansion. Urban interchanges, such as I-290 in Chicago, introduce tight access constraints and heightened safety considerations. Suburban corridors like IL-173 in Zion or I-294 near Winnetka may offer more staging flexibility but still require careful coordination within the IDOT right-of-way.
Seasonal timing also matters. Spring and summer field programs in 2025 required coordination around traffic volumes, weather conditions, and drilling subcontractor availability. Even when groundwater is not encountered, soil moisture and site drainage influence sampling conditions and equipment access.
Chicagoland infrastructure corridors are layered environments. Beneath modern pavement can lie decades of historic fill, utility crossings, and prior improvements. A thorough PSI must account for those realities, even when the final conclusion is that no additional action is required.
Conclusion: Delivering IDOT PSI Programs with Discipline and Clarity
Across four separate assignments in 2025, A3E Environmental supported Arcadis in executing IDOT Preliminary Site Investigation field programs throughout the Greater Chicagoland area. From limited-scope five-boring efforts to high-density, multi-day drilling campaigns, each project required adherence to IDOT Bureau of Design and Environment standards and disciplined field documentation.
For general business stakeholders, the value of an Preliminary Site Investigation lies in risk reduction. Accurate subsurface data informs design decisions, supports regulatory compliance, and keeps transportation improvements moving forward without avoidable environmental setbacks.
If your organization is planning infrastructure improvements in Northern Illinois and requires support navigating IDOT environmental requirements, A3E provides technically rigorous, schedule-focused field investigation services designed to deliver defensible results.
Contact A3E Environmental to discuss your upcoming IDOT or PSI project and how a properly executed Preliminary Site Investigation can protect both timeline and budget.
