OCR Text |
Show from approximately 20% of the average annual pumping to more than 220% of the average annual pumping over a 10 year period from 1973 to 1982. South Salt Lake has the most stable groundwater demand over this 10 year period with only an approximately 67% variation of the mean pumping from the highest to the lowest demand year. Figure 3.3 shows an approximate contour map of piezometric drawdown over the study region. The drawdown in the aquifer appears to be highly concentrated in the Sandy and White City areas from approximately 20% of the average annual pumping to more than 220% of the average. Figure 3.4 shows the water supply agencies considered and their boundaries. Table 3.5 presents some summary statistics for the 1973- 82 historical pumping for each water agency considered. The total groundwater demand, energy cost, average unit cost, average background pumping lift, and average drawdown at the wells for the whole county for the 10 year period were estimated as 414,640 Acre- feet, $ 4.90663 million, $ 11.83/ Acre- feet, 114.92 feet and 30.785 feet. The demand tabulated for each agency is the total pumping by the agency over the 10 year period. The total cost reported is not the total cost of groundwater supply, but a total cost for energy use for pumping at each well, assuming a cost of 9 cents/ Kilowatt hour for electricity at each well. Based on this criterion the total cost ranges from $ 0 for South Salt Lake ( Area 4) to $ 1,597 million for Salt Lake County ( Area 1). South Salt Lake has a number of free flowing wells ( the average lift at the wells with only background pumping and recharge is - 34.63 feet), and the average drawdown ( 5.87 feet) at their wells still leads to free flowing conditions. Note that the resulting average lift after all pumping activities would be the average background lift less the average drawdown at the wells ( e. g., the average lift subsequent to pumping for South Salt Lake would be - 34.63 feet less 5.87 feet or - 28.76 feet). On the other hand Salt Lake County has the highest average annual pumping ( 8890 Acre- feet), relatively large pumping lift ( 169.75 feet with only background activity) and a larger average well drawdown ( 54.29 feet), contributing to the higher total energy cost. The unit cost is defined as the average cost per acre- foot of water pumped for each agency. It varies from 0 for South Salt Lake to $ 21.53/ Acre- foot for White City ( Area 8). WTiite City has the highest average pumping lift ( 233.69 feet with background activity only) and also has the highest average drawdown at the wells ( 66.33 feet), leading to the high unit cost. In general, higher lifts and higher pumping rates ( and hence drawdowns) combine to generate higher unit and total costs, and vice versa, as would be expected. Murray, South Salt Lake, Granger and Magna ( areas 2,4,7 and 10) exhibit very attractive pumping lifts and drawdown characteristics and seem to have a good potential for increased pumping activity. On the other hand, White City, Sandy, Salt Lake County and Holladay ( areas 8, 9,1, and 5) seem to have high unit costs for pumping which are characterized by relatively higher lifts and drawdown. 38 |