JOHN HIMMELREICH & ASSOCIATES

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1 JOHN HIMMELREICH & ASSOCIATES Phone and FAX (719) , 1010 So. Sierra Madre Street Colorado Springs, Colorado April 6, 2012 JRW Family Limited Partnership th Street, Suite 3000 Denver, Colorado Attention: James Walker Subject: Preliminary Geologic Evaluation of Pine Canyon Ranch Property Douglas County, Colorado JHA Project No Dear Mr. Walker: This report presents the results of a Preliminary Geologic Evaluation conducted for the Pine Canyon Ranch property in Douglas County, Colorado. The evaluation was planned to provide general geologic and geologic hazards information for master planning of the property. We understand that the property is proposed to be annexed into the Town of Castle Rock, and is planned for mixed use development. This report summarizes the results of a brief geologic reconnaissance, a review of published and unpublished mapping and reports, review of aerial photographs, and our opinions regarding the potential influence of geologic hazards may have on planning and development of the site. This study was designed to provide a basis from which more detailed geotechnical (geologic and engineering) studies can be performed. No subsurface explorations were part of the scope of this study. The evaluation did not include evaluation of possible risks related to environmental contamination, wetlands, or evaluation of wildfire hazards. Detailed hydrologic, geologic, and subsurface investigations are recommended to verify the geologic mapping and to provide mitigation design parameters. Planning considerations for the geologic hazards recognized are discussed in the report. The data was developed for the project as described. Information disclosed by additional hydrologic, geologic, or subsurface investigations or changes in the proposed development could influence our conclusions and recommendations. We should be contacted to review the contents of this report if changes are made. SITE CONDITIONS The site is situated in portions of Sections 34, 35 and 36 Township 7 South, Range 67 West, and Section 1, Township 8 South, Range 67 West, in Douglas County, Colorado (see Figure 1) and contains about 500 acres. The site is bisected by Interstate 25 and East Plum Creek flows through the extreme westerly part of the site. The portion of the site east of Interstate 25 consists mainly of east-west trending ridges separated and Copyright 2012 by JOHN HIMMELREICH & ASSOCIATES

2 dissected by swales and drainages. Topographically, most of this part of the site slopes westerly at grades between about 5 to 50 percent (see Fig. 2). The steeper slopes are located in the east-central portion. Several small, unnamed drainages originate here and drain westerly to East Plum Creek. The easterly portion consists of easterly sloping ground with grades of between about 6 to 12 percent, and drains to tributaries of McMurdo Gulch. The western portion of this area is dominated by open grasslands, cactus and yucca with scattered brush and scrub oak. Ponderosa pine and thick to sparse scrub oak cover the majority of the eastern portion of the site. Short stretches of some of the drainages contain riparian vegetation (willows). The extreme eastern portion of this easterly part of the site is dominated by grassland. The portion of the site west of Interstate 25 consists mostly of gently sloping ground that drains westerly to East Plum Creek. Vegetation consists mostly of grasses, with some scattered trees and brush mostly adjacent to the drainages. The area in and adjacent to East Plum Creek contains wetlands, trees and other riparian vegetation. SITE GEOLOGY Geologically, the site lies in the Denver Basin. Sedimentary rocks underlying the site consist of the Dawson Formation. Outcrops on the site indicate the Dawson Formation consists of brown to buff sandstone, siltstone and claystone. Some sandstone layers are moderately to highly cemented. Bedding dips are gentle to the northeast at the site. See References 15 and 19 for more detailed descriptions of the various units of the Dawson Formation. Figure 2 shows the mapped geologic units on the site. During recent geologic time, erosion and deposition processes have been serving to alter the terrain. These have eroded and covered the bedrock at the base of the slopes with younger surficial deposits. Alluvium and colluvium have also been deposited in and along the drainageways. The lower portions of the site have been covered by a variable thickness of a mixture of sand, gravel, silt and clay consisting of older and recent alluvial and colluvial deposits. The surficial deposits were derived mostly from the sedimentary Dawson Formation and consist of predominately clayey to silty sands, and sandy clays. The alluvial/colluvial deposits in the drainages may contain organic layers. The portion of the site west of Interstate 25 is dominated by mixed alluvial and colluvial deposits that overlie several levels of alluvial terraces associated with East Plum Creek. Some of the alluvial terraces are coarser (contain gravel and cobbles) and contain less clay and silt. Well logs for two wells in the west portion of the site indicate the terrace deposits range from 40 to 62 feet deep. GROUNDWATER A few seasonally wet areas were observed in the drainages during our site reconnaissance. These are shown on Figure 2. Seasonal seepage/shallow groundwater is likely in and adjacent to all the drainages on site. Perched groundwater also is present beneath the alluvial terraces on the west side of Interstate 25 and East Plum Creek is a continuously flowing stream. The groundwater level (in the alluvial terrace deposits) reported on the well log for Permit No was 25 feet below the ground surface. Ground water is also contained in the bedrock aquifer(s) below the site. One bedrock well is located in the west portion of the site (Permit No ), and one well in the east portion of the site (Permit No ). See Figure 2 for the location of these wells. Copyright 2012 by JOHN HIMMELREICH & ASSOCIATES 2

3 GEOLOGIC HAZARDS Several geologic processes will affect the planning and ultimate development of the site. The geologic hazards mapped on site are shown on Figure 2. The primary factors that will affect the planning phase are the presence of steep slopes and the flood plain of East Plum Creek and its tributaries. The geologic hazards mapping by the Colorado Geological Survey in 1978 (Reference 13) shows hazards on the site to include various mass wasting phenomena; however, my experience, the site reconnaissance, and analysis of aerial photographs show the site is not subject to these phenomena (debris flows, rockfall, rock slide, debris avalanche deposits) that are found in steeper regions in the area and region (References 8, 9 and 11). Slope Stability Special attention will be needed in the steeper slope areas (those in excess of 25%) during the planning and development of the subdivision. Alterations in the drainage or alterations of steep slopes and other factors can adversely affect the stability of slope conditions, especially on potentially unstable slopes. These steeper slope areas should be considered as potentially unstable and can be subject to creep (slow down slope movement of the upper few to several feet of soil). Parts of the slope mass could be destabilized if support is removed, the materials become saturated, and/or the slope is loaded either naturally or by fill placement. Detailed analysis of the steeper slopes (where construction is planned) and design of roadways on the steeper slopes should be performed prior to construction. Proposed building sites should be located outside of the potentially unstable slope areas. Flooding and Erosion Flooding and erosion hazards exist on site. Since the east portion of the site is located at the top of the drainage basins, flooding hazards are considered to be relatively minor but are important to consider. Water flooding appears to be generally confined to the drainages and these areas should be avoided for development, or channelization or other structures should be constructed to mitigate flood hazards. This is also the case for the drainages (except for East Plum Creek) in the western portion of the site. A FEMA flood plain has been mapped for East Plum Creek (Reference 22). The approximate limits of this flood plain are shown on Figure 2. The soils on the site are considered susceptible to water erosion. Care should be taken during planning and development of the project to protect the site from erosion during the construction process and on a permanent basis after development. Erosion control plans should be developed according to local, State and Federal guidelines for storm water control during and after construction. Eroded sediment should be mitigated by the use of sediment control structures and erosion control measures. Ground Subsidence Because of the mode and nature of deposition, it is not uncommon for colluvial deposits to be hydrocompactive (prone to settlement upon moisture increases). This possibility should be evaluated during subsurface investigations for the sites. Mitigation usually involves proper foundation design and/or ground preparation prior to construction. Copyright 2012 by JOHN HIMMELREICH & ASSOCIATES 3

4 Expansive Soils Expansive overburden soils or bedrock are likely to be encountered on the site. Our experience indicates that the hazard presented by the occurrence of expansive materials is significantly reduced when a thick cover of non-expansive soils occur between improvements and the expansive soils. This may be the case in portions of the site where granular deposits exist. Mitigation techniques for expansive soils are reasonably well developed along the Front Range of Colorado and are normally handled during the individual investigations for proposed structures. Additional investigations should take this possibility into account. Seismicity This area like most of central Colorado is subject to a degree of seismic risk. The Colorado Geological Survey considers this area of Colorado to be in Seismic Risk Zone 2 (Reference 4). The closest mapped faults are located several miles to the west along the base of the Front Range. Radioactivity There is not believed to be any unusual hazard from naturally occurring sources of radioactivity on this site; however all rocks contain small amounts of radioactive materials. The principal hazard produced by deposits of the type which underlie the site is usually associated with radon gas, build-ups of which can be mitigated by providing increased ventilation of basements and crawlspaces, venting of perimeter foundation drains, and sealing of joints. Groundwater and Seepage Seasonal seepage/shallow groundwater is likely in, and adjacent to, the drainages on site. This should be taken into account during construction if roadways or utilities cross these areas or if structures are placed in these areas. The occurrence of shallow groundwater may also increase due to development and irrigation in the area. The need for subsurface drainage systems should be assessed as part of the more detailed subsurface investigations for the site and structures. The lower terraces adjacent to East Plum Creek also are likely to possess a shallow groundwater table. Shallow Bedrock Areas of shallow bedrock are likely to be encountered on the site during grading and utility construction. Some of the sandstone beds are cemented. Generation of oversized material may occur from grading and utility excavations. Blasting may be required if highly cemented bedrock is encountered. Excavation factors should be evaluated during geotechnical studies of the site when plans are finalized. Copyright 2012 by JOHN HIMMELREICH & ASSOCIATES 4

5 PLANNING AND DEVELOPMENT CONSIDERATIONS The presence of steep slope areas is the factor that will most affect planning of the project. Drainage and the potential for flooding are also important factors to consider. The other geologic hazards will need to be evaluated in the later phases of design and construction. Site Grading Cuts and fills in steep slope areas should be investigated to analyze stability. Generally, cut and fill slopes should not be steeper than 3:1 (horizontal to vertical). If steeper graded slopes are planned, they should be analyzed for stability or adequately retained. It should be emphasized that some risk is associated with development and subsequent construction on steep slopes. The degree of risk for potential future movement of slopes can be reduced by avoiding or minimizing the number of structures located on these features, restricting the amount of landscape irrigation, maintaining positive surface drainage, by reducing the amount of cutting and filling which occurs on the slopes, and by installation of mitigation features. If development on the steeper slopes is planned, a detailed subsurface investigation and stability analysis should be performed to define subsurface conditions, geometry of the slope subsurface, and potential mitigation that might be feasible. LIMITATIONS This investigation included preliminary level geologic mapping to provide a general picture of geologic hazards. Subsurface conditions will be variable across the site. We did not evaluate environmental related conditions or wildfire hazards as part of this investigation. No subsurface explorations were performed. This report provides preliminary geological and geological hazard opinions. Additional investigations should be performed to confirm geologic mapping and develop specific details for more detailed planning, mitigation design, grading, construction of roadways, utilities, retaining walls, foundations, floors, basements, and pavements. We should be provided with the opportunity to review development plans as they are formulated to confirm that the geotechnical factors have been taken in to consideration. The opinions presented in this report were developed from the review of aerial photographs, topographic and geologic maps, site reconnaissance, research of published and unpublished information, and our experience. Should additional surface or subsurface data become available, the conclusions and recommendations contained in this report shall not be considered valid unless the data are reviewed and the conclusions of this report are modified or approved in writing by our firm. Copyright 2012 by JOHN HIMMELREICH & ASSOCIATES 5

6 This report was prepared using methods and procedures consistent with other professionals practicing geology in this area at this time. No other warranty, express or implied, is made. If we can be of further service in discussing the contents of this report or in the analysis of the influence of geologic hazards on the planning of the development, please call. Respectfully, JOHN HIMMELREICH & ASSOCIATES John W. Himmelreich, Jr., P.G. Copyright 2012 by JOHN HIMMELREICH & ASSOCIATES 6

7 PARTIAL LIST OF REFERENCES 1. Trimble, D.E., and Machette, M.N., 1979; Geologic Map of the Greater Denver Area, Front Range Urban Corridor, Colorado; U.S. Geological Survey, Miscellaneous Investigation Series, Map I-856- H. 2. Trimble, D.E., and Machette, M.N., 1979; Geologic Map of the Colorado Springs-Castle Rock Area, Front Range Urban Corridor, Colorado; U.S. Geological Survey, Miscellaneous Investigation Series, Map I-857-F. 3. Nelson-Moore, J.L., et al; 1978, Radioactive Mineral Occurrences of Colorado and Bibliography; Colorado Geological Survey, Bulletin Kirkham, R.M., and Rogers, W.P.; 1981, Earthquake Potential in Colorado; Colorado Geological Survey, Bulletin Johnson, E. J. and Himmelreich, J. W., Jr., July 1998; Geologic Hazards Avoidance or Mitigation: A Comprehensive Guide to State Statutes, Land Use Issues, and Professional Practice in Colorado. Colorado Geological Survey Information Series Rogers, W. P., et.al, 1974; Guidelines and Criteria for Identification and Land-Use Controls of Geologic Hazard and Mineral Resource Areas, Colorado Geological Survey, Special Publication Himmelreich, J. W., Jr. and Essigmann, M. F., November 1986; Engineering Geology Study, Union Village, Castle Rock, Colorado. Geotechnical Consultants, Inc. Job No Himmelreich, J. W., Jr. and Bowden, W. L., 1993; Reconnaissance Engineering Geology Map, Greenland Ranch, Douglas County, Colorado. CTL/Thompson, Inc. Job No. CS Himmelreich, J. W., Jr., April 2001; Preliminary Geologic Hazards Investigation, Spruce Mountain Ranch, Douglas County, Colorado. John Himmelreich & Associates Project No Himmelreich, J. W., Jr., October 2001; Reconnaissance Geologic Hazards Evaluation, Pine Canyon Ranch, Douglas County, Colorado. John Himmelreich & Associates Project No Himmelreich, J. W., Jr., November 2003; Debris Flow Hazard Evaluation, Portion of Dawson Butte Ranch, Douglas County, Colorado. John Himmelreich & Associates Project No Hansen, W. R., 1973; Effects of the May 5-6, 1973 Storm in the Greater Denver Area, Colorado. U. S. Geological Survey Circular Soule, J. M., 1978; Geologic Hazards in Douglas County, Colorado. Colorado Geological Survey Open-File Report OF Thorson, J. P. and Himmelreich, J. W., Jr., 2003; Geologic Map of the Greenland Quadrangle, Douglas and El Paso Counties, Colorado. Colorado Geological Survey Open-File Report Copyright 2012 by JOHN HIMMELREICH & ASSOCIATES 7

8 15. Thorson, J. P., 2005; Geologic Map of the Castle Rock North Quadrangle, Douglas County, Colorado. Colorado Geological Survey Open-File Report Thorson, J. P., 2004; Geologic Map of the Castle Rock South Quadrangle, Douglas County, Colorado. Colorado Geological Survey Open-File Report Morgan, M. L., McHarge, J. L. and Barkmann, P. E., 2005; Geologic Map of the Sedalia Quadrangle, Douglas County, Colorado. Colorado Geological Survey Open-File Report Morgan, M. L., Temple, Jay, Grizzell, M. T. and Barkmann, P. E., 2004; Geologic Map of the Dawson Butte Quadrangle, Douglas County, Colorado. Colorado Geological Survey Open-File Report Thorson, J. P., with contributions by B. H. Archuleta, P. Barkmann, B. Berg, A. Busacca, C. J. Carroll, M. Dechesne, M. T. Grizzell, J. W. Himmelreich, Jr., J. W. Keller, N. R. Lindsay, R. F. Madole, D. Martin, J. L. McHarge, D. Mendel, M. L. Morgan, E. Route, P. D. Rowley, R. Sacerdoti, K. Sicard, C. S. Siddoway, A. Stevenson, and J. Temple, 2011; Geology of Upper Cretaceous, Paleocene and Eocene Strata in the Southwestern Denver Basin, Colorado. Colorado Geological Survey. 20. Aerial Photographs, various years. 21. Colorado Division of Water Resources, on-line water well permit files. 22. Federal Emergency Management Agency, Flood Insurance Rate Map (FIRM), September 2005, Panel Number 0188F. 23. Natural Resources Conservation Service, 2012; Web Soil Survey Soils Data. Copyright 2012 by JOHN HIMMELREICH & ASSOCIATES 8

9 LEGEND FOR FIGURE 2 PRELIMINARY GEOLOGIC AND HAZARDS MAP GEOLOGIC UNITS DA Disturbed areas adjacent to roads and railroads Qa Channel and flood plain alluvium Qac Alluvium and colluvium in swales and drainages Qt Alluvial terrace deposits. Numbers indicate lowest (1) to highest (3) Qcao Thicker deposits of colluvium and older alluvium Td Dawson Formation HAZARD UNITS sw Seasonally wet. Drainages, swales, and low terraces subject to minor flooding and permanent or seasonal shallow ground water pfp Physiographic flood plain and mapped FEMA flood plain hc Deposits may be subject to hydrocompaction NOTES: 1. All geologic units may contain expansive soils or bedrock 2. Slopes steeper than 25% are considered to be potentially unstable Copyright 2012 by JOHN HIMMELREICH & ASSOCIATES 9

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