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Evaluation of Water Level Measurement Methods <br />Steel Tape <br />To obtain a water level measurement using a steel tape, one needs to remove <br />tlne top cap of a well, disinfect the portion of the tape being lowered into the <br />well, chalk up the end portion of the tape expected to come in contact with tlne <br />water surface, lower the tape and record the depth to wlnicln the tape is <br />extended, then raise the tape using a Hand crank and record tlne mark that <br />identifies the division between wet and dry chalk, and finally subtract the two <br />measurements. <br />Pros: Can be used with very small opening in the welllnead. <br />Cons: Time-intensive process to deploy and retrieve the tape; may require <br />multiple attempts depending on initial estimate of water level; maybe difficult <br />to read clearly due to well condensation; requires disinfection of tape; linnited <br />to length of steel tape. (DWP's steel tape is 500 feet long). <br />Airline <br />To obtain a water level measurement usinng an airline, one needs to leave a <br />nitrogen tank, regulator, pressure gages and tube fittings. A tube leaving the <br />regulator is corunected to tlne airline at flee well. The airlune is filled with <br />nitrogen gas and all the water is purged out of the airline. When flee pressure in <br />the airline comes to equilibrium with the water level iln the well, the pressure lln <br />the airline is recorded. This pressure is then converted into a depth to water <br />level using flee airline depth. <br />Pros: Method is non-obtrusive; may be the only available method to measure <br />flee water level in a given well. <br />Cons: Requires nitrogen tank, gages and fittings; requires accurate airline <br />depth; airlilnes may have leaks that inhibit pressure equalization; time intensive <br />to set up connections; the accuracy of the pressure gage is a limiting factor in <br />the accuracy of the water level reading (commonly limited to +/-1 psi, <br />equivalent to +/- 2.31 feet of water). <br />Sonic Meter <br />To obtain a water level measurement using a sonic meter one needs to measure <br />or estivate the borehole temperature and input this into flee meter, create a seal <br />around flee surface of well to facilitate a good signal response, select flee <br />sounding depth range depending on expected water level depth, and iinitiate <br />sonic instrument readung. <br />Pros: Process is very quick, is non-obtrusive, and works for large depth range <br />(25' to 1500'). <br />SPDSS Phase 4 Task 39 TM -Final <br />0/20/2008 A-1 <br />