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April 22, 1999 • • Page S four existing wells located outside of the 0-5 yeaz panel, and the six existing wells located within the limits ofthe 0-5 year panel. A summary of the Yankee Gulch site monitoring wells included in the proposed groundwater monitoring plan is presented in Table 1. The monitoring wells are grouped together to provide four nested or co-located monitoring locations for the alluvium, Uinta Formation, A Groove, B Groove, and Dissolution Surface. This network will provide nested or co-located installations for two down-gradient, one up-gradient, and two cross-gradient locations for the first mining panel. The monitoring well layout assumes a groundwater flow direction in the Upper and Lower Aquifers of southwest to northeast. This trend is in accordance with regional groundwater data (Weeks' et al. 1974). Site-specific data from the Upper Aquifer suggests the flow direction is roughly west to east. Therefore, positions of the up-gradient and down-gradient wells, relative to groundwater flow direction, are based on an averaged flow direction ofN65°E. The monitoring well layout is shown on Figure 1. 1.2.1 Multiple-Completion Monrtoring We//s (lo be constructed) Three multiple-completion monitoring wells are proposed. The well designated 21-3 will be located down-gradient of the first-phase mine panel and will have four completion zones. Another well, designated 29-4, will be located up-gradient of the first-phase mine panel and will have three completion zones. There will not be a Dissolution Surface completion in 29-4 because it is adjacent to 29-2, which is completed at the Dissolution Surface. The third multiple-completion monitoring well, designated 21-4, will be located inside the northeast boundary of the first-phase mine panel which isdown-gradient ofthe assumed flow directions. Monitoring well 21-4 will have four completion zones, as detailed in Section 1. This layout provides for up-gradient, down-gradient, and cross-gradient groundwater monitoring, according to all published and site-specific data. The multiple-completion monitoring wells will be constructed in large-diameter boreholes to allow a grout mixture to flow freely and fully seal the borehole between the completion zones. All well construction materials (sand, bentonite, and grout) will be placed from the bottom of the borehole by the tremmie method. Each completion will be constructed of 2-inch-diameter, 'Weeks, J.B., G. H. Leavesley, F. A. Welder, and G. J. Saulnier, Jr. (1974). "Simulated Effects of Oil-Shale Development on the Hydrology of Piceance Basin, Colorado," USGS Professional Paper 908, 84 p. Agapito Associates, Inc.