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Table 1.---Annual daily pumpage from the Prairie du Chien -Jordan aquifer, 1970-7 9 (Pumpage in million gallons) Year _ 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 Pumpnge 148.3 145.2 144.5 158.2 160.4 153.2 1.59.9 156.6 152.3 148.5 Water -level trends in the Prairie du.Chien-Jordan aquifer also are appar- ent in the hydrographs of wells. However, depending on the proximity of an observation well to pumping centers and on the nature of the pumping, the characteristics of these hydrographs differ considerably. Figure 3A is a hydrograph of well 031N22W23CBCO2 in the Prairie du Chien -Jordan aquifer in southern Anoka County (location shown in pl. lE) where little or no water is pumped from the aquifer. The hydrograph shows that the water level rose slightly from 1971 through early 1976, due to climatic conditions, although the rise is hardly distinguishable from the seasonal change of 2 to 3 ft.'Ibe water level fell sharply about 3 feet in mid-1976 because of drought and rose slightly from 1977-80 as normal climatic conditions prevailed. Winter and Pfannkuch (1976) report that the Prairie du Chien -Jordan aquifer is in good hydraulic connection with se),eral lakes in the area. In addition, the levels of some of these lakes are controlled. These two factors help explain why the water level in the well has been so stable during the period of record. Several downward spikes in the lvdrograph during 1976-77 provide the only evidence of pumping. This pumping, apparently from standby supply wells in the area, affected the water level in the observation well for very short periods. Figure3B is a hydrograph of well 117N23W118BD01 in the Prairie du Chien Jordan aquifer in worst -central Hennepin County (location shown in pl. 1E). The well is at the western edge of the area west of Minneapolis where water levels declined during 1971-80 (see pl. 1E) because of municipal pumpage. 7t* hydro - graph sti ws relatively stable water levels during fall, winter, and spring of each year, but sharp declines due to increased summer pumping. It also shows that average water levels declined steadily between 1971 and 1980, acc:umulatinq a net decline of 6 to 7 ft. Water levels in the Prairie du Chien -Jordan aquifer fluctuate �*�asonally in much of the Twin Cities area, primarily in response to increased pumping during summer. Horn (1983, table 8 and fig. 16) determined that the seasonal component of ground -water pumpage varied among water -use categories and that total summer pumpage from all aquifers was significantly lar(,--�r tha.i winter pun.pege. For example, in 1978, a year with normal amounts of precipitation, August p Apage was about 2.5 times greater than February pumpage. In 1976, a very "Ay year, July pumpRge was about 3 times greater than January pumpage. The effects of seasonal pumpage are indicated in the water -level change maps on plate 1D and 1F, which show the difference in water levels between January --March and August 1971, and `)etween January -February and August 1990, V1