Lake County's Financial and Administrative Committee approved a $1,294,769.65 change order Oct. 9 for intersection improvements at Winchester Road and Illinois Route 83 after contractors discovered larger-than-expected peat deposits beneath the project area.

County Engineer Shane Schneider told the committee the contractor found additional unsuitable soil on the south leg of Illinois 83 while the work was about three-quarters complete. "The contractor has discovered there's additional unsuitable soil. So it's basically a peat bog," Schneider said, adding that the design-phase borings had underestimated the limits of the peat. The change order will remove the soil and install additional aggregate grouted piers to stabilize the area.

The project involves a state highway and is governed by a cost-share agreement with the Illinois Department of Transportation. Schneider said the county learned the previous afternoon that the state would provide an additional $1,000,000 to help cover the overage. The committee approved a joint resolution appropriating a supplemental $921,000 of quarter-percent sales tax transportation funds and the change order by motion from Member Clark, seconded by Member Vlitzak; the item passed unanimously.

Schneider said the county will review its geotechnical examination procedures and consultant methodology after the project, noting the design followed IDOT standards for soil borings. "We are reviewing with the consultant their approach and methodology for determining these," he said, adding the county would adopt any warranted procedural changes.

Committee members asked whether the peat required environmental mitigation. Schneider said the county had not tried to determine the full extent of the wet areas beyond the project footprint and that the work is a stabilization measure to support the roadway, not an environmental remediation project.

The county will continue to assess lessons learned and consider whether to broaden geotechnical parameters in future designs to better detect conditions like the discovered peat bog.