This is a “fly ash” pond where the Sewer District stores the wet slurry from their nearby incinerator. They burn off organic material from the sewage, which leaves behind a toxic slurry of heavy metals. While you can’t access the site directly, due to toxicity, you can scope it from the nearby Lunken public bike path that runs alongside and above it, as well as from the public parking lot just south of the pit. It can be a good spot in the winter because it remains open in cold weather.