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Ground Water Quality. <br />Ground water samples were collected from 17 wells on an annual or <br />biannual basis. The parameter lists used for all wells sampled this year <br />are given on Tables 4 and ACZ Laboratory (ACZ) in Steamboat Springs, <br />Colorado has performed 4A in Appendix A. Analyses since May 31, 1983. <br />ACZ performs all analyses by EPA or equivalent methods. Samples are <br />delivered the day of collection to the lab in an iced cooler. The PSCM <br />ground water monitoring program may be found on Table 2.04.7-T9, page <br />2.04-104 (Vol. 1) of the PSCM PAP. <br />The following discussion of the analytical data collected during the <br />reporting period is arranged by strata being monitored and coincides <br />with the format (by aquifer type) in which the analytical data are <br />presented in Appendix C. The discussion of water quality will be limited <br />to a description of total dissolved solids (TDS) concentrations. A <br />separate section, Comparison of Ground Water Quality to Water Use <br />Standards, will discuss any samples that exceed water use standards. <br />Data for each well in Appendix A begin with a listing of the water <br />quality data collected during the past two years, followed by remarks <br />explaining the sampling procedure. This is followed by a plot of TDS <br />versus time for the entire period of record. The regression line on this <br />plot is generated by a method known as Locally Weighted Scatter plot <br />Smoothing (LOWESS) (Cleveland, 1979). Unless otherwise noted, a <br />smoothness factor (SF) of 1.0 (�n a scale of 0 to 1) was used, which <br />results in maximum "smoothing". <br />Alluvium. <br />Two wells are sampled in the Grassy Creek alluvium. Well 71 monitors the <br />alluvium upstream of mining at the PSCM. It displays an increasing TDS <br />trend with the peak occurring in May 2013. Well 70 monitors the alluvium <br />below Seneca II (and the PSCM) and downstream of the confluence with <br />Scotchmans Gulch. Most recently it displays an increasing TDS tr nd; <br />with the peak TDS value occurring in September 2015. <br />11 <br />