Abstract: Diversion wells implement a fluidized bed of limestone for the treatment of acid water resulting from acid mine drainage or acid precipitation. This study was undertaken to better understand the operation of diversion wells and to define the physical and chemical factors having the greatest impact on the neutralization performance of the system. The study site was located near Lick Creek, a tributary stream of Babb Creek, near the Village of Arnot in Tioga County, Pennsylvania. Investigative methods included collection and analysis of site water quality and limestone data and field study of this as well as other diversion well sites. Analysis of data led to these general conclusions: The site received surface water influenced by three primary sources 1) precipitation, 2) mine drainage baseflow, and 3) melted snow. Water mostly influenced by precipitation events and mine drainage baseflow was more acidic than water influenced by melting snow conditions. The diversion wells were generally able to treat only half or less of the total stream flow of Lick Creek and under extremely high flow conditions the treatment provided was minimal. A range of flow conditions were identified which produced the best performance for the two diversion wells. Treatment produced by the system decreased through the loading cycle and increases to a maximum value after each weekly refilling of limestone. Fine grained sediment in the stream was found to be limestone of the same general composition as the material placed within the wells. Neutralization of acid water was largely due to microscopic particles rather than the limestone sediment discharged to the stream. Additional downstream buffering due to the limestone sediment physically discharged from the vessels was not apparent. Diversion well systems are inexpensive and simple to construct. In addition, the systems were found to be highly reliable and able to effectively treat acid water resulting from mine drainage and acid precipitation. Diversion wells provide better treatment when the treatment site is located at the source of the acidity (such as a mine discharge), rather than at the receiving stream. Systems should be designed with 15 to 20 feet of hydraulic head and the site must have year-round access. Diversion well systems require weekly addition of limestone gravel to the vessels to facilitate continual treatment. A great deal of commitment is necessary to maintain a diversion well system for long periods of time. These systems are more economical and require less attention that conventional chemical treatment of acid water. However, these systems require more attention that traditional passive treatment methods for treatment of acid, including mine drainage.