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Thermoluminescent Dosimeters (TLDs) <br />• The lithology and mineralogy' of the opposing valley slopes at the Schwartzwalder Mine site are <br />quite different. The sandstone, mudstone, and clay rock types of the east-northeast valley side, <br />where the nearest feasible receptor resides, are associated with higher background gamma counts <br />than the metamorphic gneiss and schist rock types of the west-northwest side, where the licensed <br />facilities are located. This difference in lithology substantially limits the use of a TLD for <br />background subtraction at this site. To quantify this problem Cotter proposed the placement of <br />ten (10) TLDs on the east-northeast side of the valley for a period of one (1) year. This proposal <br />was approved by the CDPHE and monitoring began on April 1, 1988 and was completed in <br />1989. <br />The average annual background gamma exposure rate for the ten locations studied was measured <br />as one hundred eighty-four (184) mrem (21uR/hr). Historically, the one-hundred eighty-four <br />(184) mrem exceeded the measured gamma emission rate for both perimeter monitoring stations. <br />2008 and 2009 results are shown at four (4) locations as depicted on Figure 0-1: Control which <br />is located near Sump 4 at the old boot wash station, AS Main located near Sump 1, AS Creek <br />which is located near the old bone yard and bridge and Gate located near the property line just <br />inside the security gate. Gate location was added in the fourth (4th) quarter of 2008 and is <br />indicative of previous mining activity. The AS Creek location has shown an apparent marked <br />uptrend especially for the second (2nd) quarter of 2009. No apparent physical changes have <br />occurred at this site. Elevated readings have also been noted for radon. Additional monitoring <br />will be conducted to evaluate: this situation. <br />• Semiannual and annual averages for 2008 and 2009 are depicted in the following Tables and <br />Figures. <br /> <br />16