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surface, lower the tape and record the depth to which the tape is extended, then <br />raise the tape using a hand crank and record the mark that identifies the division <br />between wet and dry chalk, and finally subtract the two measurements. <br />Pros: Can be used with very small opening in the wellhead. <br />Cons: Time-intensive process to deploy and retrieve the tape; may require <br />multiple attempts depending on initial estimate of water level; may be difficult to <br />read clearly due to well condensation; requires disinfection of tape; limited to <br />length of steel tape. (DWR's steel tape is 500 feet long.) <br />Airline <br />To obtain a water level measurement using an airline, one needs to have a <br />nitrogen tank, regulator, pressure gages and tube fittings. A tube leaving the <br />regulator is connected to the airline at the well. The airline is filled with nitrogen <br />gas and all the water is purged out of the airline. When the pressure in the airline <br />comes to equilibrium with the water level in the well, the pressure in the airline <br />is recorded. This pressure is then converted into a depth to water level using the <br />airline depth. <br />Pros: Is anon-obtrusive method to measure a water level; may be the only <br />available method to measure the water level in a given well. <br />Cons: Requires nitrogen tank, gages and fittings; requires accurate airline depth; <br />airlines may have leaks that inhibit pressure equalization; time intensive to set <br />up connections; the accuracy of the pressure gage is a limiting factor in the <br />accuracy of the water level reading (commonly limited to +/-1 psi, equivalent to <br />+/- 2.31 feet of water). <br />Pros: Process is very quick, is non-obtrusive, works for large depth range (25' to <br />1500'). <br />Cons: Obstructions in the well can cause erroneous readings; borehole <br />temperature estimates and setting the sounding depth may lead to inaccurate <br />readings. Comparisons with steel tape and M-scope measurements were made at <br />several sites during Phase 2 of Task 39; results of this comparison are shown in <br />Appendix A. <br />SPDSS Phase 3 Task 39 Technical Memarandum -Final <br />09/27/2006 <br />