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The Regional Aquifer-System Analysis Program The RASA Program represents a systematic effort to study a number of the Nation's most important aquifer systems, which, in aggregate, underlie much of the country and which represent an important component of the Nation's total water supply. In general, the boundaries of these studies are identified by the hydrologic extent of each system and, accordingly, transcend the political subdivisions to which investigations have often arbitrarily been limited in the past. The broad objective for each study is to assemble geologic, hydrologic, and geochemical information, to analyze and develop an understanding of the system, and to develop predictive capabilities that will contribute to the effective management of the system. The use of computer simulation is an important element of the RASA studies to develop an understanding of the natural, undisturbed hydrologic system and the changes brought about in it by human activities and to provide a means of predicting the regional effects of future pumping or other stresses. The final interpretive results of the RASA Program are presented in a series of U.S.

Groundwater , surface-water, and streambed-sediment samples were collected from domestic, irrigation, and pub Iic supply wells and streams in southeastern Missouri during 1986-87 and analyzed for pesticides, total nitrate, volatile organic compounds, and total recoverable trace elements. Laboratory analyses identified 23 pesticides, nitrate, 3 volatile organic compounds, and 9 trace elements in some of the samples. During the 2-year study 129 sites were sampled. These included 74 domestic wells, 25 irrigation wells, 25 public-supply wells, and 5 stream sites. Of these sites, 26 domestic wells, 4 irrigation wells, 4 public-supply wells, and all 5 stream sites contained water with detectable concentrations of some pesticides, some volatile organic compounds, or some trace elements (including iron and manganese). Total nitrate as nitrogen was detected in 81 of 137 domestic well samples and concentrations in 24 of those samples were equal to or greater than 10 mi 11igrams per liter.

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