The history of ground water modeling during 1960-1980 to a large extent is reflected in the career of Thomas A. Prickett (1935-2007). In the early 1960s, Prickett was a leader in the development and application of electric analog models. These models were phased out in the 1970s in favor of numerical solutions solved using digital computers. Prickett quickly adapted. With C.G. Lonnquist, he developed PLASM, the Prickett-Lonnquist Aquifer Simulation Model, which was published in 1975 as ISWS (Illinois State Water Survey) Bulletin 55. Bulletin 55 was extremely important in making numerical models accessible to ground water practitioners. Prickett also developed one of the first solute transport codes (ISWS Bulletin 65).

The types of flow and solute transport models that Prickett pioneered are standard tools today. Analytical solutions also remain important including development of improved solutions for old problems and solutions for new problems such as the hydrology of carbon sequestration in the subsurface. Geostatistical analysis, multiphase flow, and inverse solutions were focus areas in the late 20^th century. Geostatistical analysis has not gained widespread acceptance by practitioners. Inverse models are slowly entering into practice and will be essential tools for modelers in the 21^st century. Current and future challenges include modeling multiphase flow and interdisciplinary problems in areas such as ecohydrology and geomicrobiology.