Comparison of Two Approaces for Determining Ground-Water Discharge and Pumpage in the Lower Arkansas River Basin Colorado 1997-98

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and end of a monitoring period. The same TFM moni- toring period was used with each PCC in 1998 for determining the TFM pumpage at each site. Quality Control of Data Data for this study were collected by CDWR personnel and transmitted to the USGS in electronic and paper files for data analysis. Several procedures were used to check the quality of the data. Quality - control checks consisted of developing a form (referred to as a field form) to be completed onsite during each site visit, making periodic site visits with CDWR personnel to observe onsite data collec- tion, reviewing field forms for completeness, and comparing electronic data to written data recorded on the field forms. Personnel from the USGS visited the sites to ensure that TFM's were installed according to the manufacturer's specifications. In addition, USGS personnel periodically visited selected sites with CDWR personnel to ensure that field techniques were being used correctly. During these visits, USGS personnel checked that (1) site information and essen- tial test information were documented on field forms, (2) multiple water -level measurements were made to confirm that the pumping water level had not changed more than 10 percent in the hour prior to making a well discharge measurement and collecting the PCC data, (3) portable flowmeter discharge measurements were done properly, (4) consistent methods were used in measuring TFM discharge, and (5) electrical power meter measurements were consistently determined. Field forms were used to document various characteristics of network wells. Site identifier, test date, and test methods used at each well during a PCC measurement also were recorded on field forms. Other data recorded on the field forms included a description of the discharge test procedures used and any type of problem during the measurement, instantaneous discharge (pumping rate), static and pumping water - level measurements, and PCC's determined for each portable flowmeter method used during a site visit. Personnel from the USGS reviewed the field forms for completeness, tabulations, and consistency with estab- lished collection procedures. About 10 percent of the electronic data were verified against copies of the orig- inal field forms, and all electronic data were scruti- nized for anomalous data. In addition to these quality - control measures, the three types of portable flowmeters used in the study were tested at the Great Plains Meter, Inc., facility in Aurora, Nebraska, before the start of the 1998 irrigation season. The accuracy of the method P portable flowmeter was checked by releasing a known volume of water three times through the test apparatus at the facility, while total elapsed time was measured to calculate an average rate of discharge. The discharge measured by the method P portable flow- meter for each timed release ranged from 99 to 101 percent of the known discharge. The accuracy of the method C portable flowmeter was checked by maintaining a constant flow of water through the test section at the facility. The method C portable flow- meter was installed in a straight length of pipe, and manometer readings were taken at two points in the cross section of the pipe. The instantaneous discharge measured by the method C portable flowmeter ranged from 103 to 104 percent of the discharge measured by a flowmeter installed in the test section at the facility. The test facility did not make any calibration adjust- ments to either the method P or the method C portable flowmeters. Because the measurements using method P and method C portable flowmeters were within 5 percent of known values, no adjustments were made to the well discharge data collected with these portable flowmeters. The accuracy of each method M portable flowmeter was checked using a one -point flow test and then calibrated using a three -point flow test. The rate of flow used during these tests ranged from about 100 gal/min for the 4 -in. flowmeter, to about 3,000 gal/min for the 10 -in. flowmeter. After calibra- tion adjustments, the flows measured by the method M portable flowmeters ranged from 98 to 102 percent of the known flows. Overview of the Statistics Used for Comparing Discharge and Pumpage A statistical procedure known as analysis of variance was used to make comparisons of well discharge and pumpage made using the TFM's and the PCC approaches. These comparisons were made by computing the differences in well discharge and pumpage between the two different approaches. The analysis of variance evaluates whether the average or mean difference in values is statistically different and 10 Comparison of Two Approaches for Determining Ground -Water Discharge and Pumpage in the Lower Arkansas River Basin, Colorado, 1997 -98