These results show that real step drawdown test data from a pumping well plotted as adjusted drawdown versus adjusted time can be used to estimate the transmissivity of the aquifer near the well by using the slope of the lines on the plot, if the aquifer is confined. Thus the input value used for well loss coefficient may be computed from the graph. In our hypothetical case shown in Figure 4, this value is 0.2/100, which is 0.002. That is, the difference in adjusted drawdown for successive time steps is divided by the difference in discharge for the successive time steps. Therefore, C may be determined by C = (s/Q n -s/Q n-1 )/(Q n -Q n-1 ). When the drawdown data is plotted this way, each step plots as a straight on a semi-log graph, and the y-intercept for each step differs from the preceding step by (Q n -Q n-1 )C. Hypothetical pumping well adjusted time versus adjusted drawdown with well loss. The extra drawdown for the hypothetical well is shown (red) in Figure 3.įigure 4. If a term CQ 2 is added to equation 1 and C is given a hypothetical value of 0.002 (ft min 2 /gal 2 ), which is a relatively high value. Rorabaugh ( 1 953 ) applied a graphical procedure and concluded that the exponent y "may be unity at very low rates of discharge, or it may be in excess of 2." He recognized that CQ y, where y is not equal to 2, might more accurately reflect well loss, and higher precision might warrant determination of of the exponent y by trial and error or by a graphical procedure. Jacob represented "well loss" as CQ 2, where C is an empirical coefficient. The second component is termed "well loss" and represents various effects on drawdown in the well, such as turbulent flow in and near the well, clogging near the well, head loss through a well screen, and losses in an artificial sand or gravel filter in the annulus around a well screen. One component is drawdown proportional to discharge, and the second component is drawdown proportional to approximately the square of the discharge. Jacob (1947) stated that drawdown in a pumping well has two components. Some control panels can measure the pumping rate, and the start-up technician will verify those readings with the physical measurement.CONVENTIONAL WATER Well STEP TEST WITH WELL LOSS This provides a measurement of the pumping rate. The technician then makes a simple calculation to determine the volume that was pumped over the time interval. The pumps run for a specific amount of time and then a measurement is taken for how far down the water was lowered in the well. The Romtec Utilities start-up technician runs the pumps and measures how much water is pumped over a given time interval. When everything is set up correctly, the draw down test is straightforward. With a filled force main, the head pressure will be consistent for the test. This will lead to an unreliable reading from the draw down test, and it will be difficult to measure if the desired pumping rate for the pump station is reached. With an empty force main, the head conditions will be very unpredictable when the pumps operate. The draw down test is used to measure the pumping rate, and in order for this measurement to be accurate, the force main must be filled. One criterion of design is the desired pumping rate and another is the TDH or Total Dynamic Head conditions. Romtec designs pump stations based on a project specific set of design criteria. In order to complete a draw down test, the force main must be filled with water. The most obvious process is to test the pumps, but the water is also required to fill the force main if it is newly installed. Having the water available onsite is needed for two processes. This step can be as easy as tapping into a nearby fire hydrant, but in most scenarios, water is scheduled to be delivered by truck for the start-up. The first requirement for the draw down test is having water available onsite. This test is an important part of commissioning new lift stations and there are things to consider onsite to complete this test. The draw down test is conducted to measure the pumping rate in order to verify that the pumps will operate at the specified flow requirements. One of these tests is called the draw down test. The role of this technician is to start the pump station for the first time and to test the functionality of the system to make sure it functions per the system design criteria. Romtec Utilities commissions each of its pump stations with a start-up technician.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |