AWWA ACE54517

The Cambrian-Ordovician bedrock aquifer system underlies 161,000 square miles of the upper midwestern United States. The aquifer is widely used for municipal water supply and well yields are typically 750 to 1,500 gallons per minute. The water quality of this aquifer is generally very hard and fresh to slightly brackish throughout most of its extent. The majority of the aquifer is confined by the Maquoketa shale and where confined, often exceeds the maximum contaminant level (MCL) for combined radium, gross alpha, and/or radon. In some areas the water may also exceed the fluoride, barium, arsenic, total dissolved solids, iron, and sulfate drinking water standards. Due to water quality issues and overuse of the aquifer, many utilities have abandoned their bedrock well supply for other sources of shallow groundwater or surface water supplies. Many utilities maintain the bedrock wells, however, for emergency or standby supply. The Oak Creek Water and Sewer Utility (OCWSU) of Oak Creek, Wisconsin is one such utility. OCWSU serves a growing suburban community south of Milwaukee, Wisconsin. Prior to 1976, OCWSU supplied its customers with potable water using groundwater supplied from deep wells penetrating the Cambrian-Ordovician Sandstone Aquifer. In 1976, they began using a 6-million gallon-per-day Lake Michigan water treatment plant and placed their three Sandstone Aquifer wells on emergency standby status. Due to suburban growth, the OCWSU has embarked on an expensive expansion program that includes two phases of water treatment plant expansion to meet projected demands over the next 20 years. In 1997, OCWSU began to consider converting their standby wells to Aquifer Storage and Recovery (ASR) wells as a potential alternative to the second phase of water treatment plant expansion. If feasible, ASR would result in a 50 percent annual cost saving over construction and operation of an expanded water treatment plant. However, like many other wells in the Cambrian-Ordovician aquifer, the standby wells produce water that exceeds the primary drinking water standard for combined radium, as well as several other secondary standards. In 1998, the OCWSU received tailored collaboration funding from the AWWA Research Foundation (Project 2539) to conduct a demonstration test program to determine the feasibility of using ASR within the Cambrian-Ordovician aquifer in Wisconsin and its affect on combined radium present in the native groundwater. Four storage and recovery cycles were performed over a 12-month period to determine the influence of the native groundwater quality and aquifer mineralogy on stored water quality. Samples of the recharged and recovered water were collected and analyzed for radium, radon, gross alpha, trihalomethanes, and other inorganic parameters. One hundred percent of the water was recovered with radium activity levels below drinking water standards from the first full-scale test cycle. Other utilities that currently exceed the combined radium standard can now consider ASR as a possible cost-effective alternative to constructing treatment facilities. Includes figures.

Product Details

Edition:

Vol. - No.

Published:

06/01/2001

Number of Pages:

7

File Size:

1 file , 330 KB