is 28.54 feet. In other words, the natural variation of the September 1 average water

Staff Report & Agenda Item Details

2. is 28.54 feet. In other words, the natural variation of the September 1 average water 0012 level is over 28 feet. And this 28-foot range represents the natural variation in just the 9 years for which complete records exist. Based on historical water level patterns in past decades when pumping was greater than recent years, it is clear that the natural range in water level variation is greater than 28 feet, even though data is not available for the MZ1 network during those periods. More insight into the natural variation in water levels during the 9 years shown in Table 2. can be obtained by calculating the “standard deviation” of the 9 values for September 1 values. The “standard deviation” is a common statical measure indicating the natural spread or variation of values relative to the average. For the 9 years data is available, the standard deviation is 7.98 feet. Cockrell’s proposed metric of 7 feet to define “unreasonable impact” clearly does not account for natural variability in MZ1 in the 9 years measured. As mentioned above, the historical water level measurements in the Wells in MZ1 containing the longest historical record indicate that the aquifer was not harmed by greater pumping volumes, and that the aquifer rebounded from significantly lower water levels than those observed in the 9 years when data is available from the full network reflected in Table 2.  2018 is an arbitrary time to use in setting an index metric. Seasonal pumping conditions can vary significantly from year to year, and September is always during the irrigation season. Therefore, September measurements do not accurately reflect a consistent and seasonal aquifer condition. Figure 1 plots the average September 1 water level for each of the 9 years reflected in Table 2. As noted above, the lowest value is 171.60 feet in 2014, which is 21.69 feet below the 2018 average of 149.91. History demonstrates that the aquifer was not harmed by this greater production, and production was not hindered during 2014. However, Cockrell’s proposed metric and rule would have triggered drastic curtailments even though history shows that the water levels increased over 20 feet in the next two years. 0013 Figure 1. Plot of Average Water Level in All MZ1 Wells on September 1  The fact that such changes occurred historically, and occur under current permitting and pumping conditions, supports the conclusion that the Cockrell proposal and arbitrarily selected metric is fundamentally flawed. Summary The MPGCD’s current Rules and associated water-level thresholds for MZ1 are based on the best available data and science. They provide protection to the aquifer, wells, and historical uses of the aquifer in general, and specifically within MZ1. Cockrell’s proposed rule is based on flawed and inaccurate interpretation of the dynamics of the aquifer in MZ1. Specifically, the proposed rule: 0014 E T P MICHAEL R. THORNHILL GEOLOGY 858  does not account for observed historical data and detailed associated evaluations by the MPGCD. MPGCD’s detailed studies validated the current water-level thresholds, and render unnecessary the proposed rule changes. The aquifer and Wells in MZ1 are protected.  does not allow for reasonable pumping from MZ1. Lower water levels than the proposed rule would allow have been observed in the recent past (2014) and in prior decades. The scientifically unsupported metric associated with “unreasonable impact” Cockrell proposes as necessary to protect the aquifer and Wells in MZ1 is contradicted by Cockrell’s own data, which have shown required production can be reasonably achieved at lower water levels. If you have any questions or would like to discuss, please feel free to contact me via e-mail at mthornhill@tgi-water.com or via phone at (512) 244-2172 (office) or (512) 656-1063 (cell). We appreciate the opportunity to assist you in our specialty.