I have been following news on a 2600 acre sprayfield on the edge of Tallahassee, Florida. It is suspected of causing environmental problems 10 miles away in Wakulla Springs State Park and the Wakulla River. A recent 1000 Friends of Florida report (pdf) ties excessive hydrilla plant growth to nitrate from the sprayfield. The news this week is that the city, USGS and Florida DEP will be conducting dye tests to better understand how the groundwater beneath the sprayfield moves down gradient. I am reading the report. Striking is the relatively low (1.0 mg/l)nitrate-N needed to control the situation.
Image source: Tallahassee Democrat