gional counterparts. Administrative Services, Personnel, and Procurement and Contracts provide operational support to Geological Survey field units through the regional management offices. Information Systems Mission earth-science information. By means of microcomputers, 27 Geological Survey public contact points (in 20 cities located in 16 States and the District of Columbia) now have available earth-science information data bases to aid users of Geological Survey data and products. One of these information data bases provides data reference input from various State Governments and organizations. The Survey has established a telecommunications service within the bureau to link programs in different Divisions through a nationwide communications network called GEONET. In addition, the Division is designing local area networks to integrate a wide range of computing devices. The Information Systems Division provides guidance, technical support, and automated data processing (ADP) services to other Geological Survey Divisions, the Department of the Interior, and other Government agencies. The Division also supports planning and policy development Organization and provides program coordination and review for Geological Survey information systems and ADP technology. To meet these objectives, the Division: • Develops information systems policy. Develops long-range information resource management plans. • Administers data bases. • Designs, implements, and manages telecommunications networks. • Conducts research in computer science. • Guides the acquisition of ADP resources. • Provides computer support services, conducts user assistance training, and consults on computer sciences. The Division is assisting the bureau in establishing a system to improve access to The Information Systems Division has its headquarters office in Reston, Va. Service centers in Reston and in Menlo Park, Calif., Denver, Colo., and Flagstaff, Ariz., provide assistance to users. The Assistant Director for Information Systems chairs the Information Systems Council, which is composed of representatives from each Division and each field region. The council recommends policies, coordinates computer science research and technology, and provides guidelines for major computer systems and information management programs for the Geological Survey. SIGNIFICANT ACCOMPLISHMENTS OF RESEARCH PROGRAMS: 1986 SELENIUM IN AGRICULTURAL DRAINAGE The San Joaquin Valley is a vital natural resource in which over $5 billion worth of agricultural commodities are produced annually from more than 5 million acres of irrigated farm land. The valley is also the site of several State and Federal waterfowl management areas that are key stopping points for migratory waterfowl along the Pacific flyway. Several of these waterfowl management areas presently depend on agricultural wastewater for all or part of their water supply. Potential adverse effects of agricultural wastewater on waterfowl have recently been realized at Kesterson Reservoir, a 1,200-acre series of shallow impoundments that was jointly managed by the U.S. Bureau of Reclamation as an agricultural drainage-water storage facility and by the U.S. Fish and Wildlife Service as a national wildlife refuge. Subsurface agricultural drainage water began flowing to Kesterson Reservoir in 1978 and ceased in 1985, under a State regulatory order. Since 1982, a high incidence of mortality and birth defects among waterfowl using the refuge has been linked to the presence of high concentrations of the trace element selenium in the drainage water. The U.S. Geological Survey found that concentrations of dissolved selenium in drainage waters flowing into the canal that supplies water to Kesterson Reservoir ranged from 140 to 1,400 micrograms per liter (parts per million). The drainage water came from farm drainage systems consisting of buried grids of perforated pipe that are designed to lower the water table by removing shallow ground water and thus keep excessive moisture from the crop root zone. Subsurface drainage systems have already been installed in about 85,000 acres of agricultural land in the western San Joaquin Valley, and as much as 200,000 additional acres of farm land in the western valley area are affected by shallow water The U.S. Geological Survey, in coopera- • Where does the selenium come from? What factors cause selenium to be re- How does selenium get into shallow • What is the areal distribution of selenium • Is selenium contaminating water-supply • How much selenium is reaching the San Although the studies designed to address these questions are still in their early stages, there have been some important early findings about the distribution of selenium in soil, ground water, and the San Joaquin River. Considered together, early data from all these studies suggest a conceptual model of the processes affecting the distribution of selenium. This model forms the basis of our continuing studies. Distribution of Selenium A first step in understanding the nature and scope of the selenium problem is to explanation of this pattern that can then be tested. assess the present-day distribution of Conceptual Model selenium in soil and ground water. The accompanying map shows the areal distribution of selenium in the soil, in shallow ground water, and in regional aquifers of the western San Joaquin Valley. The highest concentrations of selenium in the entire San Joaquin Valley are in soils and shallow ground water located on the western side of the valley in the alluvial fan areas of Panoche and Cantua Creeks, which drain the Diablo Range. Concentrations generally are low in the deeper regional aquifers commonly used for water supply. The highest selenium concentrations in soil occur between the coalescing fans of Panoche and Cantua Creeks near the contact between the alluvial fans and dipping sedimentary rocks at the western edge of the valley. The highest concentrations of selenium in shallow ground water were observed downgradient from high-selenium soils, where evaporation of shallow ground water greatly increased its selenium concentration. Depth Distribution in Comparing the distribution of selenium in shallow ground water with that in deeper underlying ground water shows that selenium generally decreases with depth. But how fast, at what depth, and why? Initial data from two sites (P1 and P4, fig. 1) point to some possible answers to these questions. The data suggest that the shallowest ground water along this section has selenium concentrations in the 1- to 50-microgramsper-liter range. Selenium concentrations in water more than about 200 feet below the water table are mostly less than detectable. In between, in the range of 20 to 200 feet below the water table, there appears to be a selenium-rich zone that probably narrows in thickness from P4 to P1. In addition, data from a detailed field-study site located south of the P1-P4 section (but in a setting similar to that midway between P1 and P4) show a similar depth distribution. Since data are so sparse at this stage in our studies, the challenge is to develop a reasonable On the basis of the areal distribution data for soils and water shown on the maps, the data from multiple-depth sampling wells, and detailed data from individual fields, a working conceptual model that attempts to explain the distribution of selenium at the regional scale has been developed. This model, although preliminary and unverified, provides a unified framework for continuing studies that will undoubtedly result in changes and expansions to the model. Under natural conditions, the highest selenium concentrations probably occurred in the uppermost part of the aquifer, with no fresher water above. Concentrations were likely highest at low elevations where the natural flow system (fig. 1) brought ground water near the land surface, where it was evaporated. Concentrations were likely low to moderately high in areas where the water table was more than several feet below the land surface. Initial irrigation of soils as early as 1900 probably leached most of the readily soluble selenium during the first decade or more of irrigation. The result appears to have been the formation of a zone of ground water overlying what was the natural surface of the aquifer before irrigation began and in which selenium concentrations are higher than normal. Continuing irrigation in recent decades has added progressively fresher water to the top of the aquifer as the amount of readily soluble selenium in the soil was depleted. Thus, this fresher water apparently has displaced the higher selenium water downward. This pattern is clearest where the water table has always been too far below the land surface for evaporation to occur. The pattern is least clear where the water table is close to the land surface, where continued evaporation of ground water has occurred and thus affected selenium concentrations. The low concentrations of selenium in the deep parts of the aquifer system may be related to a combination of the climatic conditions under which those aquifer materials and the water in them were deposited and the chemically reducing conditions in part of the aquifer that greatly reduce the solubility of selenium. Past climates in the area have been more humid (and the evaporation potential less) and would not have favored development of high selenium concentrations. Water and aquifer materials in the uppermost part of the aquifer have been most affected by the present-day arid climate and are characterized by chemically oxidizing conditions that favor high selenium solubility. Low selenium concentrations in some ground water near the trough of the valley (near P1) are probably due to the ground water's origin in eastern valley geologic materials that are naturally low in selenium. Thus, the highest selenium concentrations appear to have resulted from a combination of the leaching of selenium from saline soils by irrigation water and the subsequent evaporation of ground water. Greatly increased ground-water recharge brought about by irrigation and the installation of subsurface drains have combined to bring selenium-rich water to the land surface. Economical solutions to the agricultural drainage problem in the western valley may, in the future, be based on controlling the ground-water system so that the seleniumrich water is not brought to the surface. |