2021-02-01_REPORT - C1982057 - Laserfiche WebLink

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Analytical results from the groundwater monitoring conducted in 2020 are provided in Appendix B. Table B.1 provides a comparison of the DCAL-02 samples to the Dry Creek Alluvial GWPOC water quality standards established in TR-63. Table B.2 includes the analytical results for the remaining monitoring wells however a comparison to water quality standards is not made as these wells are not GWPOC's. The groundwater quality at Dry Creek Alluvial Well DCAL-02 met all applicable water quality standards. Results of a Mann-Kendall statistical trend analysis also indicate that total dissolved solids (TDS) concentration at DCAL-02 remain stable at the 95% confidence interval. Predictions for the expected TDS increases to be observed at various monitoring wells were made in the Probable Hydrologic Consequences (PHC, Tab 17) section of the SIN Permit Application Package (PAP). The following table outlines these predictions along with this year's observed value. Well Predicted TDS (mg/L) This Years TDS (mg/L) WHAL7-2 1299 1070 WOV14 4385 3830 WOV17 4295 4700* WOV25 - 1720 WW14 2630 4530* W W 17 3002 648 WW25 - 404 Note *Indicates value above prediction In 2020, the TDS at two of the seven wells exceeded the predicted TDS value. Its important to acknowledge that the TDS predictions were intended to demonstrate the magnitude of potential average increases in the postmining groundwater adjacent to the mine pits and were not intended to be compared to a singular well. This is illustrated through the application of the predicted Wadge Overburden TDS value (4295 mg/L) to WOV17. The 4295 mg/L value was calculated by multiplying the predicted 5.5% increase in TDS for this area to the pre-mine TDS average (4072 mg/L) measured at several Wadge Overburden Wells. However, the pre-mine average TDS at WOV17 was 8043 mg/L, which was already Page 8 of 17