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June 2001 On-Post Quarterly Groundwater Monitoring Report
Section 2 - Basewide Flow Direction and Gradient
A groundwater potentiometric surface map was generated from the June 2001 groundwater elevations and is shown in Figure 1. Among the cluster wells MW6, MW8, and MW9, only the water level measurements collected from Lower Glen Rose wells were used in creating the potentiometric surface map. The June 2001 potentiometric surface map shows a variety of flow directions. The general groundwater gradient to the southeast was approximately 0.007 feet/feet. Groundwater flow directions and gradients during past monitoring events are provided in Table 3 of the Introduction to the Groundwater Monitoring Program at Camp Stanley for comparison.
The overall observation from the June 2001 potentiometric surface map (Figure 1) is that the majority of CSSA wells appear to have similar water levels. The water level measurements seem to indicate that groundwater elevations were relatively uniform in the central and western portions of CSSA and were generally higher to the north and lower to the southeast. Unlike the March 2001 water levels, the June 2001 water level data did not exhibit lower groundwater elevations in the north pasture.
The groundwater elevation in Well 10, which was measured via the air-line method, was roughly 20 feet lower than the groundwater elevation in Well 9 and Well 11. The water level in Well 10 may be lower than surrounding wells because it is an active water supply well and is frequently pumped. In addition, Well 9 had been pumped on the day prior to taking the water level measurement
The groundwater elevation of 1102.92 feet MSL in Well 16 was about 2 feet higher than the water level in Well D and was slightly higher (less than 15 feet) than water levels in other nearby wells. Interpretation of the water level data was performed by including Well 16 within the 1100-foot contour, thus allowing the potentiometric surface to be drawn in a more conservative and general fashion.
As shown in Figure 1, water levels at CSSA show much variability. This variability is likely associated with three factors: 1) differences in well completion depths and formations penetrated; 2) differences in recharge rates due to increased secondary porosity associated with the Salado Creek floodplain; and 3) differences in recharge rates due to increased secondary porosity associated with the fault zone. As discussed in the Introduction to the Groundwater Monitoring Program, all of the potentiometric surface maps prepared to date for CSSA are based on water levels in wells with different completion depths. Several wells are open to multiple water-bearing zones; therefore, contour maps should be considered qualitatively.
The differences in water levels across CSSA may stem from differences in the way that various wells are completed. Wells 2, 3, 4, MW-1, and MW-2 are completed in either the Lower Glen Rose or Lower Glen Rose and upper portion of the Bexar Shale. Well 16 is open in the Lower Glen Rose, Bexar Shale and Cow Creek. Two CSSA wells, Well H located in the northwest corner of the north pasture, and Well MW4-LGR located in the eastern portion of the inner cantonment, exhibited relatively high and somewhat anomalous water levels during June 2001 as compared to surrounding wells.