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define ground -water flow in the K xmt Simon -Hinckley aquifer. The configura- tion of the cone of depression may be much more complex than depicted in this report. More observation points (wells) are needed to delineate this possible complexity and to determine the mutual interference of pumping centers. This is important because the effects on water levels of each pumping center may spread far out into the aquifer. Water -.Level data for the Mount Simon -Hinckley aquifer will become increasingly important if ground -water users in the Twin Cities area develop additional water supplies from this aquifer to avoid localized contamination of the Prairie du Chien -Jordan aquifer. Another problem is insufficient water -level measurements at 6- to 8-week intervals, particularly in wells open to the Mount Simon -Hinckley aquifer. Although the measurement of a large number of wells twice in a year every 5 years may be adequate to define long-term water -level trends, this approach is inadequate for measurinc, seasonal changes. Seasonal water -level changes are large in the Twin Cities are% as water levels decline rapidly in response to summer pumping. Consequently, the extreme seasonal water levels can easily be missed by one-time summer measurements. The potential problems associated with seasonal water -level changes and the accompanying reorientation of flow patterns may be much greater than those associated with long-term changes. The present water -level -data collection program is designed for analyzing long-term trends; significantly more observation wells are needed in which water levels are measured at least monthly, as well as more wells equipped with continuous water -level recorders. Monthly pumpage data are currently (1982) available for over 60 percent (Horn, 1983, table 8 ) of the approximately 950 wells in the Prairie du Chien - Jordan aquifer and 150 wells in the Mount Simon -Hinckley aquifer for which pumpage data have been compiled However, in 1982 there were only 6 obeerva- tion wells in the Mount Simon -Hinckley aquifer and 32 in the Prairie du Chien - Jordan aquifer in which water -level measurements were made at least bimonthly. The water -level network must be d-rr_3er in order to adequately define the rela- tionship between seasonal pumpage and water levels. i�