ARCHIVED REPORTS_XR0008137 - Laserfiche WebLink

Home Browse Search

normal precipitation, respectively This pattern is not expected to change as a result of changes in water uses or available surface water supplies in the foreseeable future Figure 8 illustrates the pattern described above This figure displays a hydrograph of measurements of depth to static water level in CWS well 21-01, which is located 4500 feet to the northeast of the maintenance shop, for the period from January 1970 to June 1994 This well is screened from 200 to 400 feet bgs within the deeper aquifer system According to personnel of the San Joaquin County Flood Control and Water Conservation District, the increasing water levels in the 1980's through 1986 are the result of a series of years of greater than normal precipitation In 1983, 31 37 inches of precipitation were recorded at the Stockton Fire Station This was twice the annual average and an all time maximum for that station Thus the water levels measured in well 21-01 during the mid to late 1980's were abnormally high, culminating in 1986 and 1987 in water levels representing a maximum over the period of record for this well Water levels measured su ed m JHK monitoring well MW 2, screened from 31 to 51 feet bgs within the shallow aquifer system are also included in the hydrograph in Figure 8 The earliest water level available for this well was measured on July 24, 1987, at 34 8 feet bgs Water levels in this well, and the other two JHK monitoring wells subsequently fell sharply, until by January 41, 1989 the depth to water in MW-2 was 48 95 feet bgs, and the other two wells were dry During this same period, water levels in the deeper groundwater system, shown by the trend of the hydrograph for well number 21-01, were also falling steeply Due to the declining water levels, the JHK monitoring wells were abandoned, and four new wells installed by Dames & Moore as described in Section 3 3 1 above Water levels were first measured in these wells in August 1990 Water levels in one of these wells, DMW-1, screened from 63 to 78 feet bgs, are shown in the hydrograph in Figure 8 The four water level measurements made between August 1990 and July 1991 show a continuing downward trend without indication of a seasonal cycle The last measurement shows a net water level rise between July 1991 and May 1994, probably reflecting the higher than normal precipitation in 1993 Typically water levels in shallow groundwater systems follow the water levels in the deeper system with the same period but reduced amplitude The hydrographs shown in Figure 8 are consistent with this pattern Thus water levels in the shallow groundwater system at the site can be expected to be following the same declining trend as water levels in the deeper groundwater system From this it follows that the measurements in the JHK wells in 1987 represented abnormally high groundwater levels in the shallow system which are unlikely to be repeated in the foreseeable future SAC116 07 7 AUGUST 1994 DAi, Es &z MOOAB