1992-08-05_GENERAL DOCUMENTS - C1980005

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Specific Conductance threshold offered by Peabody (1.53 mmhos/cm) is acceptable, we can make certain conclusions regarding Seneca II's impacts, if any, on the Fish Creek AVF. Hem (USGS Professional Paper 2254, 1985) details the relationship between specific conductance and TDS concentrations revealing the following formula for natural water corrected for 25 degrees Celsius: KA=S where, K = Specific Conductance in umhos/cm A = Empirically derived value between .59 and .75 S = Dissolved solids in mg/l. The value of A approaches .75 as the water in question receives higher concentrations of sulfate. Therefore, using the above relationship we may conservatively conclude that TDS values in excess of approximately 1148 mg/l (1530 umhos/cm * .75) would cause . at least a 10% decline in Orchardgrass crop yields. The greatest TDS concentration since 1987 of 614 mg/1 measured SW-S2-13 occurred in August of 1990 when discharge from Seneca II was not reaching Fish Creek. Therefore, not only is there a considerable comfort zone between current maximum TDS levels in Fish Creek and hay crop salt tolerances (1148-614 - 534 mg/1) , but Seneca II is not contributing significantly to the higher TDS levels especially during the late summer. Mean TDS values reported over the last five years at SW-S2-13 indicate that Peabody's maximum TDS prediction of 607 mg/1 is reasonably substantiated. To further demonstrate Seneca II's lack of impact on the water quality of Fish Creek and therefore the Fish Creek AVF, the enclosed graphs depicting mean annual TDS at SW-S2-13 versus TDS levels along both Bond and Cow Camp creeks have been included. A quick scan of these graphs indicates that despite significant increases in TDS levels at both NPDES 004 and 008 since 1987 (Approximately 100% and 33% respectively) , the TDS levels in Fish Creek have remained static or have actually declined (1991 was a high precipitation year during which unusually high dilution occurred) . CONCLUSIONS AND RECOMMEND TIO S Given the limited potential for Seneca II mine discharge to reach Fish Creek, the extremely high dilution potential of Fish Creek, the enclosed graphs showing documented evidence of such assertions, the inability of impacted ground water exiting the permit area to reach Fish Creek for well over 100 years, and the great extent to which the area within the permit boundary potentially impacting Fish Creek water quality and quantity has already been disturbed, it is deduced that the Fish Creek AVF has not been and should not be either impaired or damaged by Seneca II mining activities.