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<br /> <br />c> a prediction that impacts to irrigated crops in the <br />Trout Creek alluvial valley floor adjacent to the <br />permit area may occur if Trout Creek surface water <br />specific conductivity exceeds 1.0 mmhos/cm (page 21 of <br />Findings). <br />Page 2.5-95 of the approved permit application contains an equation <br />which was apparently used to derive TDS numbers from electrical <br />conductivity measurements. Page 4.6-142a contains a second <br />equation which was apparently used to derive those same numbers <br />after November 1990. It is not clear whether the TDS numbers in <br />Edna's AHR are analytical results, are derived from the equation on <br />page 2.5-95 or are derived from the equation on page 4.6-142a. <br />Furthermore, it is not clear whether reported data has been <br />corrected to 25 degrees Celsius or not. <br />In order to resolve the concerns above, the applicant should: <br />a) clarify whether conductivity readings are corrected for <br />temperature, <br />b) clarify how TDS numbers for both surface and alluvial <br />well water samples were derived, and <br />c> explain how TDS values may exceed conductivity values <br />or remove the equation on page 4.6-142a of the permit <br />and correct any calculated TDS values which have been <br />derived using that equation. <br />The hydrologic monitoring program at the mine site has experienced <br />problems in recent years related to equipment failure, flooding and <br />beaver activity. As a result, conductivity measurements of surface <br />and ground water samples have been erratic and of questionable <br />value, and surface flow measurements have been consistently <br />collected at only one site on Trout Creek. In order to meet the <br />requirements of Rule 2.05.6(3)(b>(iv) and to ensure that adequate <br />data is collected to make the required demonstrations regarding <br />protection of the hydrologic balance, the Division requires that <br />the applicant: <br />a) incorporate at least one flow monitoring station on <br />Trout Creek downstream from station TR-a into the <br />hydrologic monitoring plan, <br />b) add a laboratory analysis for TDS to the list of <br />parameters to be evaluated for surface and ground water <br />samples, at least until such time that it can be <br />demonstrated to the Division that reliable conductivity <br />measurements can be obtained and a consistent <br />relationship to TDS values established, and <br />c) modify the hydrologic monitoring plan to include a <br />laboratory analysis of specific conductivity whenever <br />problems are encountered with field equipment or commit <br />to collecting samples a second time is field <br />measurements are suspect the first time. <br />-23- <br />