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WATER QUALITY EV ATIONS AT STATION A72 ON THE ANL RIVER USING <br /> CONTROL CHARTS <br /> CONCLUSIONS <br /> 1. Reference water quality at Station A72 should be evaluated in terms of a probability <br /> distribution of Zn concentrations classed by stream flow. <br /> 2. Ongoing data collection should be evaluated using X-chart control charts in which <br /> the control limits are set for a significance level of 0.05, given that baseline data set <br /> represents a reference population of zinc concentrations that can be described by <br /> Student's-t distribution. <br /> 3. Water-quality data (i.e., Zn) should be evaluated in terms of classes of stream flow. <br /> 4. For Low-Flow conditions (Q< 100cfs), the upper control limit for Zn should be <br /> 731 ug/l. An X-control chart for Low-Flow Conditions is presented as Figure 2, <br /> together with the spreadsheet from which the chart is calculated. <br /> 5. For Intermediate-Flow conditions (100 cfs < Q < 300 cfs), the upper control limit <br /> for Zn should be 452 ug/l. An X-control chart for Intermediate Flow Conditions is <br /> presented as Figure 3, together with the spreadsheet from which the chart is <br /> calculated. <br /> 6. For High-Flow conditions (Q > 300 cfs), the upper control limit for Zn should be <br /> 421 ug/l. An X-control chart for High Flow Conditions is presented as Figure 4, <br /> together with the spreadsheet from which the chart is calculated. <br /> 7. Attached to this memorandum is a DS/DD 3.5-inch floppy disk that contains three <br /> EXCEL spreadsheets for compiling and graphing the water-quality data at A72. <br /> The X-control charts of Figures 2 to 4 were graphed from these spreadsheets. Data <br /> from each sampling period will be entered from the laboratory analytical report into <br /> the appropriate spreadsheet, based on measured flow. The spreadsheet includes a <br /> field for the initials of a quality-control reviewer to certify that the data have been <br /> correctly entered. <br /> 8. SGC and WQCD should establish a series of contingency actions to be implemented <br /> in the event that water quality values at A72 exceed the upper control limit. <br /> Because one explanation for a single value that exceeds the upper control limit in <br /> any control-charting exercise is that the exceedance represents a gross error in <br /> measurement, the first logical step would be rapid re-analysis to confirm (or refute) <br /> the measurement. Other steps, some of which might be sequential, might include <br /> auditing the sampling and analysis process, increasing the frequency of sampling, <br /> reviewing other water-quality data with which Zn has a known covariance (from the <br /> baseline set), site reconnaissance, and upstream sampling. <br /> 9. Water quality at A72 will not have exceeded "reference water quality" due to <br /> potential releases from SGC facilities unless (a) three consecutive sampling events <br /> show Zn concentration greater than the upper control limit; and (b) contingency <br /> evaluations have eliminated all other sources of Zn on the upper Animas drainage. <br /> 10. The effects of SGC reclamation activities on the Animas drainage will be evaluated <br /> for a period of time after bulkheading of the American Tunnel. The time period for <br /> evaluation shall be the longer of two alternative periods: (a) until two (2) years <br /> following the time at which water level in the mine pool has reached 86% of its <br /> predicted equilibrium level; or (b) until five (5) years after the date of valve closure <br /> at the American Tunnel property-line plug. <br /> Geochimica, Inc. 6 ANIMAS RIVER/9-Jun-95 <br />