computer files. From a synthesis of these data and geologic maps, high quality large scale hydrogeologic maps are being prepared (e.g., Kanivetsky 1989a, b; Piaget 1989). In contrast, some states keep no systematic record of well logs, although subsurface data are available in consulting reports and published literature.
Finally, little attention has been paid to development of a national or regional effort to characterize the stratigraphic column between the upper 1.5 meters, which is investigated by soil scientists, and the water table. Although research in vadose zone hydrology is expanding, most studies are highly site-specific and no regional compilation of data has been made. In places like the Southwest, the vadose zone can be hundreds to thousands of meters thick, and its properties arguably will have a large effect on whether contaminants reach the water table.
Weather and climate can have significant influence on the transport of materials from the soil surface to the water table. Water from precipitation or irrigation is the main transport agent for most pollutants that affect ground water quality. Weather and climate elements important to water quality are: (1) precipitation, including intensities and timing of precipitation events, (2) solar radiation, (3) wind speed, (4) air temperature, (5) relative humidity, (6) potential evaporation, and (7) air quality variables.
The National Weather Service (NWS) is the federal agency responsible for coordinating, collecting, maintaining, and distributing climate data. It operates a data collection network of some 8,000 weather stations producing the daily and monthly precipitation and temperature information that forms the backbone of our nation's climate database. This information was initially collected to evaluate climate in populated areas, and also used for weather prediction and flood warnings. Later, weather stations were placed in areas around airports to assist in aviation control. This arrangement has served the country well except in the less populated western third which has been sparsely covered with weather stations in mountain areas, which are natural water supply producing areas. As a result, several natural resource oriented agencies, such as the Forest Service, SCS, National Park Service, Bureau of Land Management, Bureau of Reclamation, and Bureau of Indian Affairs, and similar state government and university entities have developed climate data collection systems and databases to suit their own needs in their areas of jurisdiction. Also, agency coordination in climate data collection