2010-07-13_HYDROLOGY - C2009087 - Laserfiche WebLink

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e.(? _ ?. Peabody Peabody Energy Colorado Coal Resources, LLC Mr. Tom Kaldenbach Environmental Protection Specialist Colorado Division of Reclamation, Mining and Safety 1313 Sherman Street, Room 215 Denver, Colorado 80203 701 Market Street St. Louis, Missouri 63101-1826 314-342-3400 Julg ?05NI V`® JU1- ? ? 2010 ?, OWWO(I °t od SA* 06119 RE: Water Age Report for COV23 and Implications for Additional Bedrock Monitoring Wells, Peabody Sage Creek Mine Dear Mr. Kaldenbach: Please find enclosed the report entitled "Water Age Report, Monitor Well COV23, Peabody Sage Creek Mine, Sand Wash Basin, Colorado". The report presents analytical results for isotopes of hydrogen (tritium), carbon (carbon 14) and chlorine (chlorine 36) that were obtained from water samples collected from the Yampa River and monitoring well COV23 at the Peabody Sage Creek Mine (PSCM). The concentration of the isotopes that were analyzed provides a measurement of the minimum apparent age of the water sampled. The chlorine 36 isotope concentration measured in monitoring well COV23 provided in the report show groundwater in the Wadge Overburden at this location within the PSCM coal reserves was ancient water at least 1,150,000 years old. The report also presents calculations of groundwater system parameters based on the measured chlorine 36 isotope concentration. The calculation of hydraulic conductivity based on the age dating is four to five orders of magnitude less than the measured hydraulic conductivity determined for well COV23 (0.1 ft/day - constant head aquifer test). The calculations of both travel distance and hydraulic conductivity strongly indicate that groundwater in the deeper portions of the Wadge overburden, Wadge Coal, and Wadge underburden within the PSCM permit area is not hydraulically connected to sources of recharge for these units further up- gradient. The calculated hydraulic conductivity based on the chlorine 36 concentration, which is unreasonable and 4 to 5 times less than the measured value, indicates the presence of a hydraulic boundary between the outcrops of the Williams Fork Formation and deeper units. Recall PSCM installed three down-gradient bedrock wells (CWU23 - Wadge Underburden, CW23 - Wadge Coal, and COV23 - Wadge Overburden) in the vicinity of exploration hole ccu23 back in November 2008 for collecting baseline data. This location was selected because a review of updated geologic information for the original proposed location (ccu25) in the far northwest portion of the PSCM coal reserves indicated the depth to the Wadge Coal was much greater than anticipated, and monitoring well designs and materials purchased were insufficient as they were based on much shallower conditions. The Division approved moving the location for the three down-gradient wells to the ccu23 location since these wells would provide adequate baseline data for the first five years of mining, with the caveat that any future plans to mine these reserves further to the northwest would require PSCM to install additional down-gradient monitoring wells for collecting baseline data from these more distant reserves. PSCM is now involved in permitting activities to secure the rights to mine the Federal coal further to the northwest within the permit area under an LBA application with the BLM. As part