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In the fall of 2004, a sonic water level meter was used to measure water levels in a subset of wells <br />to evaluate its potential to improve the efficiency of measuring water levels in bedrock wells. The <br />sonic meter was used in combination with another water level measuring device to evaluate the <br />accuracy of the sonic meter. The sonic meter is a small portable handheld meter that requires only <br />a small opening at the top of the well and a few seconds to obtain a water level measurement. <br />The sonic meter was used to collect water levels at 26 sites. The results and a comparison to a <br />steel tape or m-scope measurement are presented in Figure Al and Table A1. As can be seen <br />from Figure A1, the water level measurements obtained from the sonic meter have a 99 percent <br />correlation to the steel tape or M-scope measurements. Table Al shows that most of the <br />measurements collected from the sonic meter are within 2 feet and 2 percent of values obtained <br />from other measurement devices over a large range in depth to water. These results indicate that <br />although the percent difference between the sonic meter and other devices measurements is small, <br />the absolute difference can be significant. It is recommended that other direct measurement <br />devices such as the steel tape or water level meter be used primarily and a sonic meter be used <br />only when necessary. <br />700 <br />600 <br />,., 500 <br />d <br />a <br />0 <br />v <br />N <br />d <br />~ 400 <br />d <br />d <br />N <br />d <br />;~ 300 <br />3 <br />0 <br />r <br />a <br />d <br />~ 200 <br />100 <br />Depth to Water (Sonic) <br />Figure Al -Comparison of Sonic Measurements and Other Device Measurements <br />SPDSS Phase 3 Task 39 TM -Final <br />09/27/2006 A-1 <br />100 200 300 400 500 600 700 <br />