2012-08-03_PERMIT FILE - C1981012 (4)

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April 16, 2012 Page 3 impact on future construction may differ from the interpretations presented in this report. This may be due either to the inherent limitations of the investigation and evaluation methods, or to undisclosed or unforeseen variations in geologic and soil conditions. Unanticipated subsurface conditions that cannot be fully determined by field reconnaissance, drilling and sampling of bore holes and related exploration techniques, are commonly encountered and frequently require that additional expenditures be made to attain a properly constructed project. Any conditions discovered during construction that seem to conflict with the contents of AAI' report should be brought to AAI's attention promptly so that modifications to the recommendations can be made. In the event that any changes to design concepts and criteria in AAI reports are made, AAI's conclusions and recommendations shall not be considered valid until the changes are reviewed, conclusions are modified, and both are approved in writing by AAI. The conclusions contained within this report were valid as of the date performed. Changes in the condition of the site can occur with the passage of time as a result of either natural processes or human activity in the area. Changes in the state of art of geotechnical and engineering geology may affect the validity of the conclusions herein. No warranty, either express or implied, is made or intended in connection with the work performed. 2.0 SITE LOCATION, SURFACE CONDITIONS AND HAZARDS The DWDA site is located near the West Portal in the (projected) SE quarter of Section 21, Township 33 South, Range 68 West (USGS 7.5 Minute Vigil Quadrangle (see Figure 1, site map). The proposed DWDA will consist of an approximate 90 foot (ft) high impoundment area with a footprint anticipated to cover approximately 4.25 acres. 2.1 Surface Conditions The ground surface within the area of the West Portal has been disturbed due to past mining activity. More recent activity has included re- grading and re- vegetation although very little topsoil containing organic matter was encountered in areas of the borings. Vegetation was sparse and consisted primarily of grasses and an occasional shrub. Evergreen trees are present along the toe of the mountain slope to the south. The ground surface generally slopes south to north with the southern portion of the proposed DWDA butting up against the north facing mountain slope while the northern portion of the DWDA is founded within the alluvial valley of the Purgatoire River. Photographs 1 and 2 illustrate the existing site conditions at the time of the field investigation. 2.2 Geologic and Man -Made Hazards Based on our limited site investigation, no geologic hazards were identified that would significantly impact the proposed DWDA construction. However, as a result of historical mining activity, a tunnel, which served as a walkway underneath the railroad bed, will need to be excavated, collapsed and associated concrete removed. The south end of the tunnel appears as a sink hole in the large flat area to the south of the portal. The historical mine portals will need to be appropriately excavated and properly closed prior to or as part of the DWDA construction. Agapito Associates, Inc.