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

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• Rule 2.' Pr'mirr Alluvium Stream laid deposits alluvium in the Lorencito Canyon Permit area aze found in three main areas. To the north, the Purgatoire River alluvium borders the site, Lorencito Canyon alluvium bisects the property from north to south in the east, and Cow Canyon alluvia] and colluvial deposits bisect the property north to south in the west (Map 2.04.7-2). Alluvium in the Purgatoire River valley was investigated by Powell, with a transect of borings being performed near the mouth of Lorencito Canyon. The borings revealed an average depth of 12 feet for the alluvium, and a depth to water of two to three feet. Alluvium is also found in Lorencito Canyon ranging in thickness from 12 feet in the north to 22 feet in the south. Unconsolidated deposits in Cow Canyon ranges from almost non-existent up to 10 feet thick. Within the side canyons, alluvium does occur in areas demonstrating slight topographic relief. Recharge to the alluvium is principally via precipitation, infiltration of runoff, or from losing streams. Precipitation in all areas of the site is directed into the various canyons and routed along these Canyons either toward Cow Canyon or Lorencito Canyon. During this process, some of the water is infiltrated either into the small azeas of alluvium encountered in the drainages, or into the main alluvial bodies. Evidence of loss from streams is apparent in Lorencito, Cow, and Alamosa Canyons, where streams are intermittent and recharge to the alluvium occurs in the areas where streamflow is reduced or non-existent. • Discharge from the alluvium is principally through undertlow and losses to streams. In Lorencito Canyon several of the stream reaches above the Purgatoire alluvium aze losing; however, near the mouth of Lorencito Canyon, Lorencito is apparently a gaining stream. This would coincide with a decrease in alluvial thickness as apparent in LC-1. Additionally, a monthly reach mapping and monitoring events at the LC-1 site have consistently shown flow. In the area between LC-2 and slightly above Jeff Canyon, the stream reaches are generally dry and indicate and area of stream loss to the alluvium. The area between the proposed box cut and LC-2 is apparently a gaining area, and the area from the Box Cut to Alamosa Canyon losing. Areas above Alamosa appear to be gaining. Within Cow Canyon, the stream appeazs to be losing almost through the entire canyon. This may be in part to the high number of retention structures (ponds) located in this drainage (Map 2.04.7- 1). Ponds limit runoff through storage and subsequently decrease recharge downstream along the channel. This may result in a groundwater deficit within the canyon. Some intermittent flow is evident near the mouth of this canyon. Groundwater in the alluvium at the site is characterized as being under unconfined, water table conditions. The water table gradient in the Lorencito Canyon alluvium is to the north with the gradient from the respective side canyons from up canyon down toward Lorencito. Gradient averages 0.027 ft/ft in the alluvium. A potentiometric surface map of Lorencito Canyon is • PERMR 015\Dezmher i0, 1996 2.04-1 1