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Lorenci~o Cam~vn Mirte -Groundwater rechnical Reyort <br />• <br />Calculation of the transmissivity for the alluvium is performed utilizing the formula T = Kb, <br />where T is transmissivity, K is the hydraulic conductivity, and b is the aquifer thickness (Fetter, <br />1980). Utilizing the mean hydraulic conductivity for all alluvial wells within the permit area, and <br />an aquifer thickness of 7 feet (Lorencito wells, saturated thickness), the transmissivity can be <br />derived as: <br />T=K6 <br />T = (29.52 ft/day) (7 ft) <br />T = 206.6 ft'/day or 1545 g/d/ft <br />This value is within the range characteristic of a sand aquifer (Heath, 1983), and reflects that this <br />is within an acceptable range for the materials encountered onsite. <br />The seepage velocity of the water through the alluvium can also be calculated from the hydraulic <br />conductivity, the gradient (dh/dl, I from the potentiometric surface map), and the effective porosity <br />rte. This relationship is v~ = Ki/rte. Therefore: <br />v~ _ (29.52 ft/day) (0.016 ft/ft)/10 <br />v, = 4.72 ft/day or 1724 ft/yr <br />• Potential pumping rates from wells in the alluvium can also be calculated using the formula <br />Q=Ts/1500, where Q is the flow rate, T is the transmissivity, s is the available drawdown, and <br />1500 is a constant incorporating conversion for g/d/ft to gpm. The 1500 constant is for . <br />unconfined aquifers, such as alluvium, 2000 is utilized for confined aquifers. Therefore: <br />Q = (1545 g/d/ft) [7 ft (for saturated thickness)]/1500 <br />Q = 7.2 gpm (for mean hydraulic conductivity data) <br />This would compare favorably to the experience of field personnel with bailing some of the wells. <br />A number of the wells at the site do not produce this volume of water during bailing. This <br />transmissivity indicates a fair to poor potential for domestic supply. <br />Overburden <br />The overburden in the Lorencito Canyon Permit area is located in higher elevations, above the <br />Ciruela Coal seam. The total estimated thickness of the overburden is up to 500 feet. The top of <br />this unit consists of the Poison Canyon Formation, which outcrops in the southern portions of the <br />site (Figttre GW-1). The Poison Canyon Formation was investigated by Howard (1982), and is <br />described as a medium grain sandstone, conglomerate and occasional interbedded mudstone. <br />Within the Raton Basin, the Poison Canyon may have unconfined aquifer conditions within the <br />sandstones. This is explained by the good porosity of the sandstone and the atmospheric contact <br />• <br />Groundwa¢r.J751Dctember 9, 1996 36 <br />