ABSTRACT
Selenium concentrations in groundwater underlying agricultural areas of the western San Joaquin Valley, California, result from the complex interactions among irrigated agricultural practices and physical and chemical processes. Although irrigated agriculture in the western valley began in the late 1800s, most of the area remained unirrigated until the 1930s and 1940s. The total acreage of land irrigated with pumped groundwater increased more than threefold in 1924 and continued to increase through 1955 [1]. Surface water imported from northern California replaced groundwater for irrigation from the early 1950s to the late 1960s and further increased the amount of irrigated acreage.
