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December 23, 1999 Pngr 7 • 'Chree new alluvial monitoring wells were drilled in 1999, bringing the total to four wells _. (19-3, 21-2, 21-5, and 28-1). Three of the four existing alluvial monitoring wells (21-2, 21-5, and 28-1) will be used to monitor the water level and water quality of the Alluvial Aquifer adjacent to Piceance Creek. The fourth alluvial monitoring well is located downstream of the proposed location of the upper plant evaporation pond. It will be used to monitor for potential leakage from the pond. There are three multiple-completion monitoring wells (21-3, 21-4, and 29-4), which were installed in 1999. These multiple-completion monitoring wells provide nested or co-located monitoring locations for [he alluvium, Uinta Formation, A-Groove, B-Groove, and Dissolution Surface. The multiple-completion monitoring wells were constructed in large-diameter boreholes to allow a grout mixture to Bow freely and fully seal the borehole between the completion zones. All well construction materials (sand, bentonite, and grout) were placed from the bottom of the borehole by the tremmie method. Each completion is constructed of 2-inch-diameter, PVC or fiberglass well casing and well screen. A diagram of a typical multiple-completion monitoring • well is shown on Figure 3. Well 21-3 is located down-gradient of the first-phase mine panel and has four nested completion zones (Uinta, A Groove, B Groove, and Dissolution). Another well, designated as well 29-4, is located up-gradient of the first-phase mine panel and has three nested completion zones (Uinta, A Groove, and Dissolution Surface). A separate B-Groove completion is located adjacent to the 29-4 nest (29-4B). The third multiple-completion monitoring well, designated as well 21-4, is located inside the northeast boundary of the first-phase mine panel and is down-gradient of the assumed flow directions. Monitoring well 21-4 has three nested completion zones (A Groove, B Groove, and Dissolution Surface), and an adjacent Uinta well completion (21-4U). According to published and site-specific data, this layout provides for up- gradient, down-gradient, and cross-gradient groundwater monitoring. In addition to the three multiple-completion well locations, there are a number of single- completion wells at the Piceance Site. The majority of these wells were constructed to monitor the test mine phase and are incorporated into the 0-5 year commercial monitoring plan. Recent changes to the network of single-completion wells included re-completing 20-4 (formerly a B Groove monitoring well) as an A Groove well (now called 20-4A) and installing a new • B Groove well (20-4B) adjacent to well 20-4A. Well 29-2, which was a Dissolution Surface Agapito Associates. Inc.