A survey of the underground injection of steel processing waste pickle liquor (wpl) was made by Bureau of Mines engineers. Hydrochloric and sulfuric acids wpl are being injected into deep wells completed in the Cambrian age Mt. Simon Sandstone Formation in Illinois and Indiana. The Mt. Simon Formation ranges up to 1,800 feet in thickness. The average depth of wpl injection wells is 4,000 feet, and injection is mostly by gravity flow at rates as high as 4,000 barrels per day. The details of the design and operating history of a wpl well located near Gary, Indiana, are discussed. Laboratory tests showed that the Mt. Simon sandstone is sensitive to fresh water. The adsorption of iron and neutralization of acids by sandstone cores from deep wells and an outcrop were determined.