Marshall STP Wastewater Treatment Plant, Marshall, Illinois

Marshall STP is a municipal wastewater treatment facility located in Marshall, Clark County, Illinois, along US 40. It serves a population of around 4,165 people, classifying it as a small to medium agglomeration under US EPA guidelines. As a US facility, Marshall STP operates under the Clean Water Act and is subject to National Pollutant Discharge Elimination System (NPDES) permitting, which sets effluent limits to protect water quality. Plants of this scale typically employ secondary treatment to meet regulatory standards. The plant's treated effluent is discharged into local streams that drain into the Wabash River, a major tributary of the Ohio River. This watershed supports diverse aquatic life and provides water resources for communities downstream. The plant plays a key role in maintaining water quality in the region.

Marshall STP discharges into the Wabash River basin, which flows into the Ohio River and ultimately the Mississippi River. The Wabash River supports a variety of fish and wildlife, including several species of freshwater mussels. The plant's operations help protect downstream ecosystems from nutrient pollution and pathogens.