2014-11-21_PERMIT FILE - C1996084 (23)

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Rulc 1 ~ Permilr • presented as Map 2.04.7-3. Aquifer characteristics of the alluvium were determined via slug testing. Statistical analyses of the hydraulic conductivity was conducted to determine the average hydraulic conductivity for the alluvium. The range of the data was from 0.43 to 149.8 ft/day. The mean value calculated for the data was 29.52, with a population standard deviation of 42.27. This indicates a wide variance in the data from the alluvial wells. Consideration of the individual standard error from each data set (derived during analyses) indicates that each well analysis has a fairly high degree of certainty; therefore, the alluvial properties probably vary widely within the alluvium itself. All values for the alluvium fall within ranges typical for clean fine-grained sand to coazse grain sand (Heath, 1983). Storativiry values for the alluvium cannot be calculated from the testing performed. Storativity in this case is estimated from literature sources to be 0.1 to 0.3 (Heath, 1983). Calculation of the transmissiviry for the alluvium is performed utilizing the formula T = Kb, where T is transmissiviry, K is the hydraulic conductivity, and b is the aquifer thickness (Fetter, 1980). Utilizing the mean hydraulic conductivity for all alluvial wells within the permit azea, and an aquifer thickness of 7 feet (Lorencito wells, saturated thickness), the transmissivity can be derived as: • T=Kb T = (29.52 ft/day) (7 ft) T = 206.6 ft~/day or 1545 g/d/ft This value is within the range characteristic of a sand aquifer (Heath, 1983), and reflects that this is within an acceptable range for the materials encountered onsite. The seepage velocity of the water through the alluvium can also be calculated from the hydraulic conductivity, the gradient (dh/dl, I from the potentiometric surface map), and the effective porosity rte. This relationship is vs = Ki/t><, Therefore: v, _ (29.52 ft/day) (0.016 ft/ft)/10 v, = 4.72 ft/day or 1724 ft/yr Potential pumping rates from wells in the alluvium can also be calculated using the formula Q=Ts/1500, where Q is the flow rate, T is the transmissiviry, s is the available drawdown, and 1500 is a constant incorporating conversion for g/d/ft to gpm. The 1500 constant is for unconfined aquifers, such as alluvium, 2000 is utilized for confined aquifers. Therefore: Q = (1545 g/d/ft) [7 ft (for saturated thickness)]/1500 Q = 7.2 gpm (for mean hydraulic conductivity data) • PERMIT.~l5lDexmbcr Z0. 1995 2.04-12