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' Response to DMG Comments Concerning Trapper's Groundwater Sampling Program TR-75 <br />April ]0, 1997 <br />3. Reduce Quarterly Ground Water Monitorin <br />Trapper has provided the Division annual reports concerning groundwater sampling at Trapper Mine. At least ten <br />years of information is provided on each well. The GP series wells have been monitored since 1985, the others <br />much longer. The annual reports present graphs showing seasonal fluctuation of water levels and also major water <br />quality parameters. Additional graphs, etc., would not illustrate much more information than is already available to <br />the Division in our annual reports. We feel sufficient infomlation as to graphs and discussions within the annual <br />reports is available to support the reduction in ground water monitoring requirements. Trapper will continue [o <br />conduct quarterly water level elevations on all wells. However, quality analysis will be performed on a semi- <br />annual and annual schedule. During these tests, each well will be purged prior to sampling, using a submersible <br />Pump. <br />Ground-water velocities for 1996 were calculated based on wells, GF-4, GF-5, GF-7, GMP-1 and GLUX-I. The <br />ground-water velocities varied from 0.05 to 0.3 feet per day, typically being in the 0.2 to 0.3 feet per day range. <br />The ground water, therefore, moves at a maximum of 27 feet per quarter or 54 feet every six months. This very <br />slow rate of ground-water movement shows that water-quality changes would not be expelled [o be very significant <br />each quarter. Semi-annual sampling of these wells should be adequate, due to the small rate of ground-water <br />movement. The sampling of wells each quarter would be the same as sampling two wells 27 feet apart and <br />expecting to be monitoring significant differences in those two wells in the same aquifer. <br />It is probable tlta[ semi-annual sampling could continue within the current approved time frame. However, with the <br />use of pumps to ptuge wells before sampling, it becomes necessary to get a vehicle to the sample site. During some <br />winters, it would be extremely difficult to accomplish this task due to access restrictions. Currently, in the Spring, <br />we've been sampling between mid-May and early June, if a vehicle can get to the sample site. We also sample in <br />August each yeaz. If acceptable to the Division, the semi-annual sampling is proposed for May and October if some <br />leeway is allowed for the Spring sampling due to site conditions. <br />LWH [DMG\TR75\97-04101 <br />