Hennepin Ash Pond 2 Dam is an earth dam located in Putnam County, Illinois. It carries a Significant hazard potential classification.
Dam profile
NID height · 52 ft52 ft tall and 3,200 ft long, taller than 93% of U.S. dams with a recorded height. Height is drawn to scale against a ten-story building, about 100 ft; the profile is a generic embankment section and the water level is illustrative.
About Hennepin Ash Pond 2 Dam
Hennepin Ash Pond 2 Dam is a dam in Putnam, Illinois. The dam is owned by Dynegy Midwest Generation, LLC (public utility). It impounds the Illinois R near Hennepin.
The dam stands 52 feet tall and stretches 3,200 feet across, creates a reservoir covering 5 acres, has a maximum storage capacity of 60 acre-feet, and collects water from a drainage area of 0 square miles.
This dam has a significant hazard potential classification, meaning that a failure could cause significant economic damage — flooding roads, bridges, or property downstream — but is not expected to result in loss of life. The most recent inspection on record was 09/10/2025.
At 52 feet, this dam is taller than 93% of dams nationwide.
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Location
| State | Illinois |
| County | Putnam |
| Nearest City | Hennepin |
| River/Stream | Illinois R |
| Coordinates | 41.30471, -89.30751 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 52 ft |
| Dam Height | 52 ft |
| Dam Length | 3,200 ft |
Storage & Hydraulics
| NID Storage | 60 acre-ft |
| Max Storage | 60 acre-ft |
| Normal Storage | 25 acre-ft |
| Surface Area | 5 acres |
| Drainage Area | 0 sq mi |
| Max Discharge | 48 cfs |
| Spillway Type | Uncontrolled |
Ownership & Safety
| Purpose | Other |
| Owner | Dynegy Midwest Generation, LLC |
| Owner Type | Public Utility |
| Hazard Classification | Significant |
| Condition Assessment | Not assessed |
| Last Inspection | 09/10/2025 |
| Emergency Action Plan | No |
Identifiers
| NID ID | IL50663 |
| Federal ID | IL50663 |
| More Info | State Dam Safety Program |