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GROUND WATER HYDROLOGY Piezometer depths and locations were chosen to obtain an appreciation of natural ground water conditions in a variety of water-bearing units to evaluate the degree of connection between the abandoned and Oooded underground mine workings and to permit a sampling of representative ground waters for chemical analysis. Most installations were located along the western mining limit, thereby allowing long term monitoring of the ground water Bow system and the effects of the proposed mining activities. Methods A total of 46 sealed piezometers were installed at 22 sites throughout the permit area in order to monitor and evaluate ground water Bow and chemistry. Depths and locations of all piezometers are summarized in Table 1 and shown on Figure 1. Each Piezometer consists o[ a one-inch ID PVC pipe installed in 4 3/4 inch diameter drillhole. The lowest 10 feet of the PVC pipe was slotted and a cap placed on the bottom. A warse sand pack oC approximately 10 to 15 feet in length was placed around the Piezometer tip and a seal of bentonite pellets placed on top of the pack. Between one and three individual piezometers were installed in each drillhole depending upon the depth and stability oC the hole. The hole was backBlled with cuttings and grout to the surface and a 6 inch steel casing was installed at the surface over the PVC pipes for protection. Between one and three holes were drilled for each Piezometer nest. Piezometers installed in old underground mine workings could not be sand packed, but were sealed above the workings with a mud basket and bentonite pellets. During visits to each station, water level measurements were made using aSoil-Test Indicating Depth Meter with a conductance bridge. Levels were recorded from the top of the well casing and reported as such. Water quality samples were collected during the biannual field trips. Samples were obtained with a hand bailer, grabbing at least three casings of water prior to sample collection. Measurements for temperature, pH and conductivity were made in the field utilizing an Orion Research Mode1399A portable pH meter and Hach Model 16300 portable conductivity meter. All other parameters were collected in precharged bottles and submitted to Chemlech Laboratory in Salt Lake Cily for analyses. Methods of analysis were consistent with EPA standard testing procedures. Results Results of the monitoring period are contained in Appendix 1 (water levels) and Appendix 2 (water quality). The permit area is located on the eastern rim of the Raton Basin. General movement of water in the permit area is eastward. Because of geologic conditions, the permit area has been divided into three hydrogeologic sectors as shown on Flgure 1. These hydrogeologic sectors are divided by major geologic features which influence the local movement of ground water. Sector 1 is bounded by a dike along the southern property boundary and Maitland Arroyo on the north. Sector ll is bounded by Maitland Arroyo on the south and a fault on the north. Sector III is bounded by a fault on the south and Gordon Arroyo on the north and contains the disturbed area associated with the existing pit. These dikes and faults act as low permeability barriers and tend to align the direction of ground water Bow in each of the sectors to the eastern boundary of the permit area. The monitoring wells located within each sector are listed below. Those marked with an asterick (•) were monitored monthly during the first six months of the year and those marked with two astericks (••) were monitored quarterly for the second six months of the year.