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December 15, 1993 -4- 933-2713 <br /> Piezometer Installation <br /> A 2-inch diameter piezometer is proposed to be installed into each of the four boreholes <br /> discussed above. The piezometers will be screened across the groundwater table as <br /> determined from geophysical activities and borehole drilling. This information will be <br /> critical for calculating the groundwater flow gradient between the upstream and downstream <br /> pair of piezometers (shown as "i" in equation 1). The piezometers will also allow routine <br /> monitoring of water levels and will provide routine groundwater gradient information. <br /> In-Situ and Laboratory Testing <br /> Two methods are proposed for determining hydraulic conductivity of the Cement Creek <br /> sediments. The first involves introducing or removing a slug of water into/from each of the <br /> piezometers and monitoring the time required for the groundwater to return to pre-test <br /> elevations. This type of test is referred to as in-situ, since it provides data for the in-place <br /> materials. The second type of test proposed for this project involves measuring hydraulic <br /> conductivity in the laboratory utilizing the samples collected during borehole drilling. <br /> Laboratory testing allows for conditions to be controlled more precisely than is possible <br /> during in-situ testing. In addition, laboratory testing can more accurately determine <br /> hydraulic conductivity of very coarse-grained materials than is generally possible using the <br /> in-situ testing method described above. In combination, the in-situ testing and laboratory <br /> soils testing will provide reliable data regarding hydraulic conductivity of the Cement Creek <br /> sediments (shown as "K" in equation 1). <br /> Calculation of Conjunctive Flow <br /> After the necessary parameters have been determined, conjunctive flow can be calculated by <br /> combining the measured surface water flows with the calculated groundwater flows <br /> determined from equation 1. This will yield the total volume of water passing through <br /> Cement Creek at any given time. By calculating conjunctive flow on a regular basis, it will <br /> be possible to develop a database of total flow which can be used to determine if total flow <br /> through the creek changes as a result of tunnel plugging. It should be recognized, however, <br /> that other environmental factors such as changes in precipitation and temperature will have <br /> an effect on the volume of flow in the creek. Therefore, temperature and precipitation data <br /> must be accounted for prior to assigning impacts to tunnel plugging. It is anticipated that <br /> meteorological data for Silverton can be used for this purpose. <br /> To provide a database of conjunctive flow, it is proposed that monitoring of the piezometers <br /> and flume be conducted on a monthly basis during March through November, with bi- <br /> monthly (twice monthly) monitoring conducted during December through February. Bi- <br /> weekly monitoring is proposed during December through February to correspond to low-flow <br /> conditions. As described in previous sections of this proposal, potential impacts from the <br /> tunnel plugging will most readily be detected during low-flow conditions when groundwater <br /> discharge to the creek forms the majority of the flow in the creek and creek sediments. By <br /> measuring conditions bi-monthly during low-flow periods, it will be possible to more quickly <br /> develop a reliable database from which to draw conclusions. <br />