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average velocity multiplied by the cross - sectional area of the discharge pipe was used to compute <br />the discharge in gallons per minute. Whenever possible, discharge measurements were made at each <br />network site using all three types of portable flowmeters. <br />Comparison of Instantaneous Ground -Water Discharge Measurements <br />Instantaneous discharges measured using portable flowmeters were compared to instantaneous <br />discharges measured using TFM's. The analysis is based on 747 paired measurements taken at 105 wells <br />during a 2 -year period. A mixed analysis of variance model with both fixed and random effects was <br />applied. The overall mean difference in discharge measurements between portable flowmeters and <br />TFM's was 0.00 percent, indicating no difference on average between the two approaches for the entire <br />network of wells. More than 80 percent of the differences in the paired discharge measurements were <br />less than 10 percent. <br />Temporal Variations in Power Conversion Coefficients <br />Analysis of variations in PCC's measured during the 1998 irrigation season indicated that <br />58 percent of 104 wells had less than 10- percent change, and 86 percent of 104 wells had less than <br />20- percent change in the well PCC's. Seasonal variations in PCC's generally were not evident for the <br />measurements made during the 1998 irrigation season. Thirty -seven of the 41 wells with PCC's <br />measurements in 1997 had at least one PCC in the same range as 1998 PCC measurements. The compar- <br />ison of the 2 years of data indicate that PCC measurements were similar in 1997 and 1998. About <br />48 percent of available pre -study State - approved PCC's made during 1994 -97 were within 10 percent of <br />the 1998 site average PCC's, and about 67 percent of the pre -study State - approved PCC measurements <br />made during 1994 -97 were within 20 percent of the 1998 site average PCC's. <br />Comparison of Ground -Water Pumpage Estimates <br />Pumpage estimates computed using the PCC approach were compared to pumpage measured by <br />a TFM at network wells. PCC pumpages were computed by applying each PCC obtained during a site <br />visit in 1998 to the total 1998 electrical power consumption. The analysis was based on 553 paired <br />pumpage estimates at 103 wells. The overall mean difference in pumpage between the TFM and PCC <br />approach was 0.01 percent for the entire network of wells, indicating no significant difference on <br />average between pumpage measured by a TFM and pumpage computed by the PCC approach. About <br />80 percent of the differences in the paired pumpage estimates were less than 10 percent. <br />Sources of Discrepancy Between Pumpage Estimates <br />There are several potential sources of discrepancy between pumpage as measured by a TFM and <br />pumpage as computed by the PCC approach. One potential source is temporal variability of the PCC. <br />The analysis indicated that the year -to -year variance component was about nine times the date- within- <br />year variance component and represented a standard deviation of about 15 percent, indicating that the <br />year -to -year variability was a major component of overall variability for this PCC data set. <br />EXECUTIVE SUMMARY 3 <br />