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respectively. The water -level changes depicted in these maps may not repre- sent the total seasonal change for the year, because they were calculated from two sets of one-time measurements rather than continuous measurements. In 1980, for example, hfdrographs of wells influenced by pumping (see figs. 39 sari 3C) indicate that water levels recorded in July in the primary pumping center were as much as 10 ft lower than in August. However, the maps are still very useful for analyzing seasonal water -level changes on a regional basis. Plate 1D shows that during 1971 water levels declined more than 10 ft in much of east -central Hennepin County and southwestern Ramsey County and that there were two r ijor centers of water -level decline. . One was in the Edina -St. Louis Park area in Hennepin County where municipal pumping caused water levels to decline as much as 50 ft. the other extended along the Mississippi River from St. Paul to Mi.meapolis where withdrawals for air conditioning in commercial buildings caused water levels to decline as much as 70 ft. Water levels also declined significantly in a relatively small area south of the Mississippi River near West St. Paul. Water levels declined less during 1980 than caring 1971 and the area where water -level declines exceeded 10 ft was smaller (pl. 1F), despite the fact that the summer of 1980 was dryer than the summer of 1971. Maximum water -level declines were about 40 ft in the Edina -St. Louis Park area and about 50 ft in Minneapolis. Comparison of maps D and F of plate 1 suggests that the seasonal component of pumpage for the prAirie du Chien--.7ordan aquifer decrea: d between 1971 and 1980. This decrease it related to use of water from the Mount Simon - Hinckley aquifer and is discussed further in a later section of this report. Changes in water level from winter to summer are well doom., -rated in the hyirograph of well 117N21W1FCCA01 in the Prairie du Chien -Jordan aquifer (fig. 3C) at St. Louis Park in east -central Hennepin County (pl. l-) and 1F). Seasonal water -level fluctuations in this well are due c.rimarily to Dumping from municipal wells. From 1971 to 1980, the seasonal water -level changes ranged from about 10 to 30 f"t. In 1976, the seasonal change was the ;ximum for the period and the sumnwr low -water -level period was longer than ttat of other years, reflecting the extremely dry conditions and heavy pumping of that year. In contrast, the hydrograph shows a much smaller seasonal change in 1977 and water levels in late 1977 and early 1978. The hydrograph segment. of 1980 is similar to that of 1971. The net change in water level over the 10-year period was small. Figure 3D is a hydrograph of well 028W2WO6ABDO2 in the Prairie du Chien - Jordan aquifer (location shown on pl. 1E) in downtown St. Paul (pl. 1D and 1F) where water levels in the aquifer are strongly influenced by pumping for air conditioning in commercial buildings. The seasonal water -level changes are so large (as much as 70 ft) because pumpage for commercial buildings during August is commonly more than 10 times that during February (Horn, 1983, fig. 16). The magnitude of seasonal change (averaging aboat 60 ft) did not vary significantly over t.3ie period 1971-80, indicating that seasonal pumpage for air conditioning of commercial buildings imar the well was :miform over the period. The hydro -- graph shows that the average water level rose between 1971 and 1980, probably because of a decrease in total .industrial pumpage in the area (Horn, 1993, fig. 10). This rise in water levels is also indicated an plate 1E. 12