Disturbing one acre or more in Johnson County triggers Iowa DNR's NPDES construction stormwater permit. Iowa City, Coralville, and North Liberty add local MS4 detention rules on top.
Construction that disturbs one acre or more, or a smaller lot inside a larger common plan, needs coverage under Iowa DNR's NPDES general permit for construction stormwater before ground is broken, backed by a Stormwater Pollution Prevention Plan. Runoff across Johnson County drains toward the Iowa River, Clear Creek, and Coralville Reservoir, so Iowa City, Coralville, and North Liberty enforce local stormwater, detention, and water-quality standards under their MS4 permits. Post-construction detention basins and rain gardens must be maintained by the property owner, and dumping anything but clean stormwater into the storm sewers is an illicit discharge.
Disturbing an acre without DNR permit coverage draws state enforcement and stop-work orders. Illicit storm-drain discharges and neglected detention basins bring local fines until corrected.
Other ordinances people look up for this city. Green dot = verified primary-source excerpt.
Johnson County, IA
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See how Johnson County's stormwater management rules stack up against other locations.
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