R2026-109 Resolution Authorizing Amendment to an Agreement with Intera, Inc. to Provide Professional Engineering Services to the City of Decatur for Yield Analysis of the Harristown Vulcan Reservoir, City Project 2024-02

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Council Memo Public Works Department No.2026-51 DATE: 5/18/2026 TO: Honorable Mayor Julie Moore Wolfe and City Council Members FROM: Melissa Hon, City Manager Matt Newell,Director of Public Works Robert Weil,Water Production Manager SUBJECT: Resolution Authorizing Amendment to an Agreement with Intera, Inc. to Provide Professional Engineering Services to the City of Decatur for Yield Analysis of the Harristown Vulcan Reservoir, City Project 2024-02 SUMMARY RECOMMENDATION: It is recommended that the City Council approve the attached Resolution authorizing the Mayor to sign, and the City Clerk to attest,to an amendment to a professional services agreement between the City of Decatur and Intera, Inc. to provide professional engineering services to the City for yeld analysis of the Harristown Vulcan Reservoir, for an increased fee of$4,291.33. BACKGROUND: Since the 473-acre Harristown Vulcan Reservoir property was acquired in late 2024, the Water Production Division has been actively investigating the potential yield for drought resilience and other water emergencies. An initial yield analysis, based on bathymetry of the former sand and gravel pits as well as available hydrogeological records,was positive. In September 2025, Council authorized Intera to complete a field investigation for water yield. This investigation involved drilling a test well and two monitoring wells. As the test well was pumped,the water level in the monitoring wells was measured. This provided an assessment of"hydraulic conductivity"; i.e. how quickly water flowed through the soil which would indicate how effective the water flow from the Sangamon River would recharge the pits as they are pumped down. The engineering fee was based on a single well run. Unfortunately,the initial well run did not generate enough flow to complete the measurement. Intera was authorized to have their well contractor further develop the test well and repeat the well run which required an additional day at the site along with added cost beyond what was originally anticipated. The second well run was successful, and the estimate of hydraulic conductivity was completed. The next step will be to convert this information into a conceptual plan for the reservoir and a pipeline back to the South Water Treatment Plant. This will be accomplished as part of a budgeted project to update the alternative water supplies plan. All of the reports related to the yield analysis of the Harristown Vulcan Reservoir are available online at https://decaturil.gov/554/Planning-and-Progress. SCHEDULE: The yield analysis is complete.