Groundwater quality in selected Stream Valley aquifers, western United States

Background The stream-valley aquifers sampled for this study underlie an area of about 9,600 square miles, in the sedimentary deposits of the Ohio and Allegheny River drainages and parts of a few large tributaries. The study area includes parts of Pennsylvania, West Virginia, Ohio, Kentucky, Indiana, and Illinois. About 2.8 million people live in the area overlying these aquifers and about 200 million gallons of water per day were withdrawn for public supply in these states from stream-valley aquifers in 2000 (Sargent and others, 2008; Kingsbury and others, 2021). Most of the area overlying the aquifer is undeveloped (60 percent). Agricultural land use makes up about 27 percent and urban land use makes up about 13 percent of the study area. Major cities in the study area include Pittsburgh, Pennsylvania; Cincinnati, Ohio; Louisville, Kentucky; and Evansville, Indiana. The stream-valley aquifers are within the Holocene-age sand and gravel deposited as alluvium along the valleys of major streams. Some of these sediments are reworked glacial deposits that were eroded and transported downstream, and they are associated with rivers such as the Allegheny and Ohio Rivers that have their headwaters in glaciated areas (Trapp and Horn, 1997). The stream-valley aquifers are associated with the sand and gravel deposits in the valleys of the stream or river that typically is hydraulically connected to the aquifers (Trapp and Horn, 1997). Groundwater in the stream-valley aquifers commonly is under water-table conditions, or unconfined conditions, but confined conditions are in places where clay or silt make up local confining units ( Lloyd and Lyke, 1995 ). Recharge to the aquifer is from infiltration of precipitation and drainage of surface water from the streams and rivers adjacent to these aquifers (Lloyd and Lyke, 1995; Trapp and Horn, 1997). The rivers throughout much of the study area are regulated by lock and dam systems that may affect the movement of surface water into the aquifer ( Maharjan