Practical Skimming Well Design
Well patterns and designs have been investigated in order to compare the technical performance and costs of several possible skimming facilities. It was established that, for aquifer properties typical in Pakistan, individual skimming wells can be expected to discharge in the range of 0.1 to 0.2 cfs. It is shown that several closely spaced wells can be pumped at a higher total discharge than a single isolated well, even though the individual wells in the battery are discharging at less than capacity. This results from the fact that distributed pumping produces a smaller maximum drawdown than does a single well pumping at the same rate. The discharge obtained by pumping in battery from closely spaced wells (i.e., 10 to 15 feet apart) is approximately 60 percent greater than for a single isolated well. The increased investment for the battery of wells is more than 60 percent higher than for a single well, however. Cost estimates are contained in the report that indicate a single skimming well will cost approximately Rs. 2200. A typical private tube well costs approximately Rs. 7000 for comparison. On a per-unit discharge basis, the investment in a private tube well is about Rs. 7000 per cfs and for a skimming well about Rs. 18,000 per cfs. Operating costs for electrically powered skimming wells is estimated to be about 15 percent of the operating cost for a typical tube well. On a per acre foot of water pumped, a skimming well will provide water at about Rs. 20 per acre foot compared with a cost of about Rs. 13 per acre foot for a private tube well.