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Lorencito Canyon Mirte - Groundwnrer Techn¢a( ReDOrt <br />• <br />To present a better understanding of the aquifer physical characteristics in the permit area, slug <br />tests and field observations will be presented. Site specific slug tests were conducted in all of the <br />consolidated rock water-bearing zones and in the alluvial wells. Site specific mapping of outcrops <br />will be incorporated to determine the areas of recharge and discharge into and from the aquifers. <br />Alluvium <br />Stream laid deposits alluvium in the Lorencito Canyon Permit area are found in three main areas. <br />To the north, the Purgatoire River alluvium borders the site, Lorencito Canyon alluvium bisects <br />the property from north to south in the east, and Cow Canyon alluvial and colluvial deposits bisect <br />the property north to south in the west (Map 2.04.7-2). Alluvium in the Purgatoire River valley <br />was investigated by Powell, with a transect of borings being performed near the mouth of <br />Lorencito Canyon. The borings revealed an average depth of 12 feet for the alluvium, and a depth <br />to water of two to three feet. The cross-section of this transect is depicted as Figure GW-7. <br />Alluvium is also found in Lorencito Canyon ranging in thickness from 12 feet in the north to 22 <br />feet in the south. Unconsolidated deposits in Cow Canyon ranges from almost non-existent up to <br />10 feet thick. Within the side canyons, alluvium does occur in areas demonstrating slight <br />topographic relief. <br />Recharge to the alluvium is principally via precipitation, infiltration of runoff, or from losing <br />• streams. Precipitation in all areas of the site is directed into the various canyons and routed along <br />these Canyons either toward Cow Canyon or Lorencito Canyon. During this process, some of the <br />water is infiltrated either into the small areas of alluvium encountered m the drainages, or into the <br />main alluvial bodies. Evidence of loss from streams is apparent in Lorencito, Cow, and Alamosa <br />Canyons, where streams are intermittent and recharge to the alluvium occurs in the areas where <br />streamflow is reduced or non-existent. <br />Discharge from the alluvitun is principally through underflow and losses to streams. In Lorencito <br />Canyon several of the stream reaches above the Purgatoire alluvium are losing; however, near the <br />mouth of Lorencito Canyon, Lorencito is apparently a gaining stream. This would coincide with <br />a decrease in alluvial thickness as apparent in LC-1. Additionally, a monthly reach mapping and <br />monitoring events at the LC-I site have consistently shown flow. In the area between LC-2 and <br />slightly above Jeff Canyon, the stream reaches are generally dry and indicate and area of stream <br />loss to the alluvium. The area between the proposed box cut and LC-2 is apparently a gaining <br />area, and the area from the Box Cut to Alamosa Canyon losing. Areas above Alamosa appear to <br />be gaining. <br />Within Cow Canyon, the stream appears to be losing almost through the entire canyon. This may <br />be in part to the high number of retention structures (ponds) located in this drainage (Map <br />2.04.7-1). Ponds limit runoff through storage and subsequently decrease recharge downstream <br />along the channel. This may result in a groundwater deficit within the canyon. Some intermittent <br />• flow is evident near the mouth of this canyon. <br />Groundwamr.175\December 9, 1996 33 <br />