By Jay F. Marks, Business WriterRegulators are investigating a hydrochloric acid spill earlier this week in an alfalfa field in Kingfisher County. The Oklahoma Corporation Commission is trying to figure out why nearly 500 barrels of acid spilled Monday at a well site near Hennessey, spokesman Matt Skinner confirmed Thursday. Producers have used acid treatment to improve well productivity for almost 120 years, according to the American Petroleum Institute, predating all other well stimulation techniques. It helps maximize initial production in new wells and restore productivity in older wells. Monday’s spill killed vegetation in the field, but a spokeswoman for the Oklahoma Department of Environmental Quality said it did not affect a water supply or body of water. The acid was contained at the well site operated by Oklahoma City-based Blake Production Co.Read more on NewsOK.com