Maximum Setback Zones

Under section 14.3 of the Illinois Groundwater Protection Act (IGPA) counties and municipalities utilizing any community water supply well are authorized to establish a maximum setback zone, up to 1,000 feet, around their well(s). The law established minimum setback zones of either 200 or 400 feet.

Benefits of Establishing Maximum Setback Zones

• Prevention of contamination by siting restrictions up to 1000 feet
• Regulation of existing and new potential sources of contamination
• Awareness of sensitivity of the zone to contamination problems
• Exercise of local controls and authorities

Who Can Establish a Maximum Setback Zone?

Municipalities or counties served by community water supply wells are empowered to enact maximum setback zone ordinances. If the community water supply well is privately or investor owned, a municipality or county served by that well can submit an application on the behalf of the owner.

Maximum Setback Zone Eligibility

If a lateral area of influence (see figure 1), created by pumping a well under normal operating conditions, is greater than the 200/400 foot minimum setback zone, then the well is eligible for a maximum setback zone.

When is a Maximum Setback Zone in Effect?

The zone is in effect after the county or municipality adopts an ordinance for each well. The county or municipality has two years after the Agency confirmation of the technical adequacy to adopt the maximum zone ordinance.

What is the Lateral Radius of Influence?

When a well is being pumped, water in the immediate vicinity begins to flow from all directions toward the well. The reduction (drawdown) of the water level is greatest at the well and decreases with distance away from the well. The shape of the water surface around the well resembles a cone and is commonly referred to as the cone of depression. Each cone (lateral area of influence) differs in size and shape depending upon several variables including pumping rate, pumping duration and aquifer characteristics. Figure 1 illustrates this cone of depression and lateral area of influence that is produced by a pumping well under normal operating conditions. The lateral area of influence refers to the area on the surface of the water table which is affected by the cone of depression, as well as the land surface above this area. The radius of influence is the horizontal distance from the center of the well to the limit of the cone of depression. In other words, it is the distance from the well to where there is no drawdown in the aquifer's water level.

How to Apply for a Maximum Setback Zone

Interested parties can pursure a maximum setback zone by contacting the Agency and requesting the necessary rules and procedures. A workbook on how to establish a maximum setback is available upon request from the Agency. In addition, detailed procedures are covered in Appendix A through E in Part 671 Maximum Setback Zone for Community Water Supply Wells. Also the county or municipal officials who will be involved in the application process should be contacted. The following information will be required to complete the application:

• radius of influence distance
• aquifer test data
• geological logs and well construction details
• description of the pump test procedure or the estimation
• technique selected to determine the lateral area of influence
• draft ordinance
• signature of a county or municipal official

If the water supply owner does not have a copy of pump test data, copies can often be obtained from the drilling contractor or the Illinois State Water Survey. Boundaries determined by the pump test procedure are used to help shape the maximum set back zone. The Agency is required to confirm the adequacy of the determination method and a proposed ordinance prior to adoption by a county or municipality.

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