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'~1 <br />' SHEPHERD MII,LER, INC. <br />Environmental and Engineering Consultants <br />TECHNICAL MEMORANDUM <br /> DATE: May 5, 2000 <br /> TO: Bill Lyle, BMG <br /> <br /> FROM: Jim B. Finley <br />_ ~ . ,. _. <br />' SUBJECT: San Luis CUSUM <br />COPY: Ron Zumwalt, BMRI <br />' This technical memorandum presents the results of the CUSUM-Shewhart analysis conducted for <br />the TR-026 performance water quality monitoring program. Basic conditions et~ployed in the <br />analysis consisted of the method as described in TR-026 (Section 6) with the follo~ing additional <br />conditions: <br />• The baseline period used for calculating the mean and standazd deviat~on for use in <br />determining the value of the upper 95% threshold limit was extended tolinclude water <br />quality data collected through July 1999. <br />• In the calculation of the CUSUM statistics, h was set equal to 5, k was set equal to 1, and <br />' the Shewhart control limit was set to a value of 4.5. <br />• For the purposes of calculating control statistics and plotting the water quality data, there <br />' was no outlier analysis conducted. <br />The interpretation of the results shown in the control charts (Figures 1 through 3) should be <br />' considered in the context of the basic hydrologic and geochemical functioning of tl~e groundwater <br />system in the vicinity of the West Pit. Groundwater flow directions in the vicinity o~ the backfilled <br />West Pit have been modified as a result of the lowering of the groundwater level irl the backfilled <br />' West Pit. Therefore, the hydrologic and geochemical conditions in the backfilled hest Pit and in <br />the Rito Seco alluvial aquifer do not represent steady-state conditions, which is a b~sic premise of <br />' the application of water quality assessments using CUSUM-Shewhart control jcharts. As a <br />consequence of the current dynamic status of the overall groundwater system, there will be <br />' 3801 Automation Way, Suite 100, Fort Collins, Colorado 80525 I' <br />' Telephone (970) 223-9600 /FAX (970) 223-7171 i <br />