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HomeMy WebLinkAbout0.8.19 Natural Hazards4.08.05 (7) (e)(iv) NATRUAL HAZARDS (iv) 'I'he proposed method in which provision will be made for any potential natural hazards in the area such as avalanche areas, landslide areas, flood plain areas, and unstable soils, and the extent and mitigation of such hazard(s); (A. 97-109) GEOLOGIC REVIEW — HP Geotechnical, Inc., HP Geotech Supplemental Letter — Radiation Potential U.S.D.A SOILDESIGNATIONMAP SOIL INTERPRETATION TABLE 55 tech HEPWORTH -PAWLAK GEOTECHNICAL Hepworth-Pawlak Geotechnical, Inc. 5020 County Road 154 Glenwood Springs, Colorado 81601 Phone: 970-945-7988 Fax: 970-945-8454 email: hpgeo@hpgeotech.com GEOLOGIC REVIEW OF THE RESERVE AT ELK MEADOWS 2006 CONCEPTUAL DEVELOPMENT PLAN COUNTY ROAD 117 GARFIELD COUNTY, COLORADO JOB NO. 105 325 MAY 26, 2006 PREPARED FOR: RESERVE AT ELK MEADOWS, LLC ATTN: WILL HUMPHREY 920 SOUTH WAUKEGAN ROAD LAKE FOREST, ILLINOIS 60045 Parker 303-841-7119 • Colorado Springs 719-633-5562 • Silverthome 970-468-1989 TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY - 1 - PROPOSED DEVELOPMENT - 1 - PREVIOUS STUDIES - 2 - SITE CONDITIONS - 2 - PROJECT SITE GEOLOGY - 3 - FORMATION ROCK - 3 - SURFICIAL SOIL DEPOSITS - 4 - LANDSLIDES - 5 - GEOLOGIC SITE ASSESSMENT - 5 - ROCKFALL -6- DEBRIS FLOWS - 7 - SINKHOLES - 7 - REGIONAL GROUND DEFORMATION - 8 - TERRACE ESCARPMENT STABILITY - 9 - CONSTRUCTION RELATED SLOPE INSTABILITY - 9 - EARTHQUAKE CONSIDERATIONS - 9 - LMTATIONS - 10 - REFERENCES - 11 - FIGURE 1- WESTERN COLORADO EVAPORITE REGION FIGURE 2 - PROJECT SITE GEOLOGY MAP FIGURE 3 -REGIONAL GEOLOGIC CROSS SECTION 1 FIGURE 4 - POTENTIAL ROCKFALL AREAS FIGURE 5 - POTENTIAL DEBRIS FLOW AREAS FIGURE 6 - GEOLOGICALLY YOUNG FAULTS AND LARGER HISTORIC EARTHQUAKES PURPOSE AND SCOPE OF STUDY This report presents the findings of a geologic review of the 2006 conceptual development plan for the Reserve at Elk Meadows, County Road 117, Garfield County, Colorado. The project site is located about four miles south of Glenwood Springs, see Figure 1. The study was conducted to evaluate the geologic conditions in the project area and to assess if the geology could present potential constraints and risks to the 2006 conceptual development plan. The study was done according to our November 14, 2005 proposal to Reserve at Elk Meadows, LLC. This review is based on a field observation made in April, 2005 for our preliminary geologic site assessment (Hepworth-Pawlak Geotechnical, 2005a) and during follow-up field observations in November, 2005. In addition, we have reviewed published regional geology studies and looked at aerial photographs of the area and our previous work in the area. This report summarizes our findings and presents our conclusions and recommendations. PROPOSED DEVELOPMENT The 2006 conceptual development plan indicates that three residential areas, the East Meadow, the South Meadow and the Upper Meadow will be developed on the 500 acre Bershenyi and Martino Ranches, see Figure 2. Seventy-two single family residential lots are proposed in the East Meadow area, sixty-two residential lots are proposed in the South Meadow area and fifty-five residential lots are proposed in the Upper Meadow area. The lots typically cover about 0.3 acres. Other development facilities will include a street system, public parking areas, recreational trails and a pond in the South Meadow area. The development will have a central water distribution system. The sewer system is proposed to be connected to the City of Glenwood Springs municipal system. Job No. 105 325 GccPtech PREVIOUS STUDIES In the spring and summer of 2005, Hepworth-Pawlak Geotechnical (2005a) conducted a preliminary geologic site assessment for the Bershenyi and Martino Ranches for the Reserve at Elk Meadows, LLC. The area covered by the previous study was considerably larger than the area being considered for the currently proposed development. Much of the previous information from our 2005 geologic study has been used in this review but the previous report should be referred to for details on the regional geology that do not pertain to the 2006 conceptual development plan covered by this review. In the fall of 2005, Hepworth-Pawlak Geotechnical (2005b) performed a rockfall risk assessment for several lots in the South Meadow area that are in a potential rockfall hazard area. The rockfall risk assessment was updated in the spring of 2006 (Hepworth-Pawlak Geotechnical, 2006) for the current development plan. SITE CONDITIONS The proposed 2006 development area is located on the western side of the Roaring Fork River valley near the confluence of Fourmile Creek and the river about four miles south of the Glenwood Springs city center. The general topography in the project area is shown by the contour lines on Figure 2. The East Meadow area is on a nearly level glacial outwash terrace that stands about 280 feet above the Roaring Fork River and between about 50 and 120 feet above Fourmile Creek. Slopes on the terrace surface where the lots are proposed do not exceed about 6 percent. -The river terrace escarpment to the east is steep with an average slope of about 70 percent. The South Meadow area is located on the Founnile Creek valley floor and on the floor of a small tributary valley to the main valley. Slopes in this area are moderate, typically less than 10 percent and do not exceed about 25 percent. The moderately sloping valley floors where the lots are proposed abruptly transition to steep hillsides that typically have a slope of about 40 percent. The Upper Meadow area is a strongly sloping upland bench that stands about 400 feet above the East Meadow terrace surface. Slopes on the bench are between about 15 and 30 percent. Job No. 105 325 Ge -tech Fourmile Creek, a moderate sized tributary of the Roaring Fork River, flows along the southeast side of the proposed development area. The creek is a perennial stream that has surface flow throughout the year. Other streams in the development area are ephemeral and only have surface flow following periods of intense rainfall or snowpack melt. Most of the proposed development areas are flood irrigated hay meadows. Vegetation outside the irrigated areas is usually sage, oak and other brush with scattered juniper trees. Cottonwood trees are common along Fourmile Creek. Rural residential developments are located along Fourmile Creek to the south and a new residential subdivision is located on the terrace to the north of the East Meadow area. PROJECT SITE GEOLOGY The main geologic features at the project site are shown 011 Figure 2 and a regional geologic cross section is presented on Figure 3. The proposed development area is located on the Grand Hogback monocline where the formation rock strikes to the northwest and dips steeply to the east at about 45 degrees. The rock is covered by a variety of surficial soil deposits many of which are related to glacial and interglacial climatic cycles during the Pleistocene_ The project site is in the western Colorado evaporite region where the Grand Hogback monocline defines the western boundary of the region, see Figurel. The monocline developed during the Lararnide orogeny about 40 to 80 million years ago. The western Colorado evaporite region is an area of shallow evaporite where post-Laramide evaporite tectonics has resulted in two regional collapse centers (Kirkham and Others 2002). The project site is in the central part of the Carbondale Collapse center. FORMATION ROCK Formation rock below most the proposed development area includes the Permian- and Pennsylvanian -age Maroon Formation (PPm) and the Pennsylvanian -age Eagle Valley Formation (Pe) and Eagle Valley Evaporite (Pee). The Maroon is mainly red beds of sandstone, conglomerate, siltstone, mudstone and shale with minor beds of gray Job No. 105 325 Gtech -4 - limestone. It is a relatively strong rock unit and forms hogback ridges. The Eagle Valley Formation is present below the easternmost lots in the East Meadow area and underlies the steep terrace escarpment to the east, see Figure 3. The Eagle Valley Formation is an interbedded, reddish brown, gray, reddish gray and tan siltstone, shale, sandstone, gypsum, and carbonate rocks that represent the transition between the clastic rocks in the overlying Maroon Formation and the underlying evaporite in the Eagle Valley Evaporite. The Eagle Valley Evaporite is probably present at depths between about 500 and 3,500 feet in the proposed development area where it forms the Roaring Fork diapir and associated core of the Cattle Creek evaporite anticline. Eagle Valley Evaporite is a sequence of evaporite including gypsum, anhydrite and halite interbedded with light colored mudstone, fine-grained sandstone, thin carbonate beds and black shale. The evaporite in both the Eagle Valley Formation and Eagle Valley Evaporite is soluble and is susceptible to the formation of subsurface solution voids and related sinkholes where these rocks are near the ground surface. Evidence of sinkholes was not observed in the field in the East Meadow area, but sinkholes are locally present in the Roaring Fork River valley in the project vicinity. SURFICIAL SOIL DEPOSITS In the Upper Meadow area, it is expected that relatively thin colluvium over the Maroon Formation will be present at most of the building sites. Exploratory borings will be needed to evaluate the thickness and specific nature of the colluvium at specific development facilities sites. The colluvium is likely between 5 to 15 feet deep and should typically consist of rocks from gravel- to boulder -size in a sandy clay and sandy silt matrix. In the South Meadow area, it is expected that relatively thin colluvium over the Maroon Formation will be present at building sites near the hillside valley floor transition. Relatively deep stream alluvium (Qa7) and alluvial fans (Qf) are expected on the valley floors in the proposed building area. Exploratory borings will be needed to evaluate the thickness and specific nature of these surficial soils at specific development facility sites. The soils are likely between 5 to 40 feet deep and should typically consist of rocks from Job No. 105 325 Gtech -5- gavel- to boulder -size in a sandy clay and sandy silt matrix. The alluvial fans in the South Meadow area are geologically young and were deposited in post -glacial time during about the past 15,000 years. They are still potential sites of infrequent debris flows and floods triggered by unusually intense thunderstorms. The stream alluvium is considerably older and was probably deposited during a pre -Bull Lake glaciation and is older than about 620,000 years. In the East Meadow area the stream alluvium (Qa7) is expected to be about 40 feet deep and the underlying glacial outwash (Qtbp) may be as thick as 60 feet in the eastern part of the area near the terrace escarpment. These surficial soil deposits overlie the Maroon Formation and Eagle Valley Formation. Exploratory borings will be needed to evaluate the thickness and specific nature of these surficial soils at specific development facility sites. The stream alluvium should typically consist of rocks from gravel- to boulder -size in a sandy clay and sandy silt matrix. The glacial outwash should typically consist of rounded gravel, cobbles and boulders in a relatively clean to silty sand matrix. Both the stream alluvium (Qa7) and the underlying glacial outwash (Qtbp) were probably deposited during a pre -Bull Lake glaciation and are older than about 620,000 years. LANDSLIDES Landslides are not present in the three proposed development areas but are present in the vicinity (Hepworth-Pawlak Geotechnical, 2005a). Several shallow debris avalanches in colluvium occurred in the spring of 1995 on the steep terrace escarpment to the east of the East Meadow area. At the most, these debris avalanches are less than 4 feet deep. The • winter and spring of 1995 were unusually wet, and natural precipitation likely contributed to the 1995 avalanches. Infiltration of irrigation water over the years may also have contributed to the debris avalanches. - GEOLOGIC SITE ASSESSMENT Geologic conditions in the proposed 2006 conceptual development areas shown on Figure 2 should not present major constraints or unusually high risks to the proposed Job No. 105 325 -6 - development that cannot be mitigated. Possible mitigation concepts should be considered in the development plan. Geologic conditions that should be considered in future project planning and design are discussed below. ROCKFALL Potential rockfall areas that could affect the proposed development are shown on Figure 4. The rockfall paths and runouts shown are discussed in detail in our previous rockfall risk assessments (Hepworth-Pawlak Geotechnical, 2005b and 2006). The rockfall zones were based, in part, on the Colorado Rockfall Simulation Program (CRSP version 4.0). Past rockfall blocks observed in the field in the runout areas were Dakota Sandstone 'blocks of estimated weights between about 2 to 90 tons with an average weight of about 28 tons. Rockfall appears to be infrequent but is still an active geologic process and could result in significant damage to residential buildings and also presents a safety risk to people in the buildings. Without long-term observations it is not possible to develop statistical recurrence times for rockfall at the project site. Proposed Lots 52 and 53 in the South Meadow area are located in the potential rockfall runout where the CRSP modeling indicates that rockfall will slow down and stop. Mitigation options in this area would be: (1) avoid the rockfall area by the elimination of lots in the potential rockfall areas, or (2) construct a rockfall catching structure up slope of the facilities to be protected. The size of the structure will depend on its location and the level of risk acceptable to the developer and regulatory agencies. A larger structure will be needed if it is located in the upper part of the runout and a smaller structure can be used in the lower part of the runout. If avoidance is use, we recommend that buildings or other important facilities not be located within 100 feet of the runout Limits shown on Figure 4. The location of the mitigation structure shown on Figure 4 was analyzed in our previous rockfall risk assessment (Hepworth-Pawlak Geotechnical, 2006) and is a feasible location for the current development plan. Job No. 105 325 GeTtech 7 DEBRIS FLOWS Potential debris flow and flood areas that could affect the proposed development are shown on Figure 5. Historic debris flows and floods in the Glenwood Springs area are infrequent but have been triggered by intense thunderstorms with statistical recurrence times of less than 100 years (Mears, 1977). Although infrequent, if occupied buildings or other important facilities are located in the debris deposition areas or in the upslope hillside channels, there is a potential for facility damage and possibly a safety risk to the building occupants. Proposed Lots 52 and 53 in the South Meadow area are located in the potential debris flow and flood deposition areas near the lower parts of the alluvial fans and these two lots are also in a potential rockfall runout as discussed above. The back parts of Lots 28 through 33 are crossed by a relatively large potential debris flow and flood channel with a relatively large upslope drainage basin. Small debris flow channels with small upslope drainage basins cross through Lots 3, 4, 5 and 7 in the Upper Meadow area. It should be feasible to incorporate debris flow and flood mitigation into the rockfall mitigation on Lots 52 and 53. Further studies may show that channel improvements and deflection structures are needed to protect buildings on Lots 28 through 33. Grading for the streets, over -lot grading and channel stabilization should be a feasible mitigation for the small debris flow and flood channels that cross through Lots 3, 4, 5 and 7 in the Upper Meadow area. The grading plan design for the development should consider the potential debris flow and flood impacts. SINKHOLES Geologically young sinkholes are present in the western Colorado evaporite region mostly in areas where the Eagle Valley Formation and Eagle Valley Evaporite are shallow, see Figure 1. In this region sinkholes have collapsed at the ground surface with little or no warning during historic times. This indicates that infrequent sinkhole formation is still an active geologic process. The eastern part of the East Meadow area is Job No. 105 325 Gtech -8 - likely underlain by shallow evaporite in the Eagle Valley Formation and may be subject to sinkhole development, see Figure 3. The likelihood that sinkholes will development during a reasonable exposure time for the proposed development is considered to be low. This inference is based on the large extent of sinkhole prone areas in the region in comparison to the small number of sinkholes that have developed in historic times. Because of the complex nature of the evaporite related sinkholes, it will not be possible to avoid all sinkhole risk in the eastern part of the East Meadow area but the risk can be reduced by building site specific studies. The potential for shallow subsurface voids in this area should be evaluated:by subsurface exploration at the proposed building sites. If conditions indicative of sinkhole related problems are encountered, an alternative building site should be considered or the feasibility of mitigation evaluated. Mitigation measures could include: (1) stabilization by grouting, (2) stabilization by excavation and backfilling, (3) a deep foundation system, (4) structural bridging, or (5) a mat foundation system. Prospective lot owners should be advised of the sinkhole risk, since early detection of building distress and timely remedial actions are important in reducing the cost of building repair and for life safety concerns should an undetected sinkhole start to develop after construction. REGIONAL GROUND DEFORMATION The project site is in the central part of the Carbondale evaporite collapse center where regional ground deformations have been associated with evaporite solution and flow in the geologic past, see Figure 1. Evaporite deformation in the Carbondale collapse center started about 10 million years ago and accelerated about 3 million years ago, but it is uncertain if the regional deformation is still active or if deformation has stopped. If regional evaporite deformation is still active, it appears to be taking place at very slow rates and over broad areas with little risk of abrupt differential ground displacement except along evaporite related faults which are not known to be present in the 2006 conceptual development area. The risk of evaporite related ground deformation problems at the project site appears to be low and the risk, in our opinion, does not justify mitigation. Job No. 105 325 Ctech 9 TERRACE ESCARPMENT STABILITY Except for the small debris avalanches that occurred in the spring of 1995 on the terrace escarpment to the east of the eastern Meadow area, the terrace escarpment has had a stable geologic history with respect to slope instability during at least the past 620,000 years and it seams unlikely that large scale escarpment instability that could affect the eastern part of the East Meadow will occur during a reasonable exposure time for the development. However, it is recommended that this geologic inference be further evaluated by a geotechnical stability analysis based on subsurface exploration and numerical slope stability modeling. CONSTRUCTION RELATED SLOPE INSTABILITY The 2006 conceptual development plan has avoided locating project facilities in potential higher risk slope stability class areas presented in our previous geologic site assessment report (Hepworth-Pawlak Geotechnical, 2005a). We do not expect problems with construction related slope instability if the street and over -lot grading are properly engineered. A geotechnical engineer should develop grading design criteria based on the proposed grading and site specific subsurface exploration and laboratory testing. EARTHQUAKE CONSIDERATIONS Historic earthquakes within 150 miles of the project site have been moderately strong with magnitudes less than M 5.5 and maximum Modified Mercalli Intensities less than VII, see Figure 6. Historic ground shaking at the project site does not appear to have exceeded Modified Mercalli Intensity VI (Kirkham and Rogers, 1985). Modified Mercalli Intensity VI ground shaking should be expected during a reasonable exposure time for the proposed development, but the probability of stronger ground shaking is low. Intensity VI ground shaking is felt by most people and causes general alarm, but results in negligible damage to structures of good design and construction. The residences should be designed to withstand moderately strong ground shaking with little or no damage and not to collapse under stronger ground shaking. The U. S. Geological Survey 2002 Job No. 105 325 Gtech - 10 - National Seismic Hazard Map indicates that a peak ground acceleration of 0.06g has a 10% exceedence probability for a 50 year exposure time at the project site (Frankel and Others, 2002). This corresponds to a statistical recurrence time of 475 years. The region is in the 1997 Uniform Building Code, Seismic Risk Zone 1. Based on our current understanding of the earthquake potential in this part of Colorado we see no reason to increase the previously accepted seismic risk zone for the region. LIMITATIONS This study was conducted according to generally accepted engineering geology principles and practices in this area, at this time. We make no warranty either express or implied. The conclusions and recommendations submitted in this report are based on our field observations and our experience in the area. This report has been prepared exclusively for our client and is an evaluation of the potential influence of the geology on the 2006 conceptual development plan. The information is suitable for planning and preliminary design. We are not responsible for technical interpretations by others of our information. Development specific geologic and geotechnical engineering studies should be performed as project planning and development proceeds. Respectfully submitted, HEPWORTH - PAWLAK GEOTECHNICAL, INC. ,e):9 Rall'F `ack Engineering Geologist And by: Steven L. Pawlak, RGM/ksw cc: Chris Pates Sopris Engineering cy Nichol Applied Ecological Services — Attn: Jill Enz Land Design Partnership — Attn: Ron Liston Job No. 105 325 d:x'Stech -11 - REFERENCES Frankel, A. D. and Others, 2002, Documentation for the 2002 Update of the National Seismic Hazard Maps: U. S. Geological Survey Open File Report 02-420. Hepworth-Pawlak Geotechnical, 2005a, Preliminary Geologic Site Assessment, The Reserve at Elk Meadows, County Road 117, Garfield County, Colorado: Prepared for Reserve at Elk Meadows, LLC, Lake Forest, Illinois (Job No. 105 325, August 30, 2005). Hepworth-Pawlak Geotechnical, 2005b, Rockfall Risk Assessment, The Reserve at Elk Meadows, County Road 117, Garfield County, Colorado: Prepared for Reserve at Elk Meadows, LLC, Lake Forest, Illinois (Job No. 105 325, December 9, 2005). Hepworth-Pawlak Geotechnical, 2006, Rochfall Risk Assessment, The Reserve at Elk Meadows, County Road 117, Garfield County, Colorado: Prepared for Reserve at Elk Meadows, LLC, Lake Forest, Illinois (Job No. 105 325, May 26, 2006). Kirkham, R. M. and Rogers, W. P., 1985, Colorado Earthquake Data and Interpretations 1867 to 1985: Colorado Geological Survey Bulletin 46. Kirkham, R. M. and Others, 1996, Geology Map of the Cattle Creek Quadrangle, Garfield County, Colorado: Colorado Geological Survey Open File 96-1. Kirkham R. M. and Others, 1997, Geology Map of the Glenwood Springs, Quadrangle, Garfield County, Colorado: Colorado Geological Survey Map Series 31. Kirkham R. M. and Others, 2002, Evaporite Tectonism in the Lower Roaring Fork River Valley, West -Central Colorado, in Kirkham R M., Scott, R. B. and Judkins, T. W. eds., Late Cenozoic Evaporite Tectonism and Volcanism in West -Central Colorado: Geological Society of America Special Paper 366, Boulder, Colorado. . Kirkham, R. M. and Scott, R. B., 2002, Introduction to Late Cenozoic Evaporite tectonism and Volcanism in West -Central, Colorado, in Kirkham R. M., Scott; R. B. and Judkins, T. W. eds., Late Cenozoic Evaporite Tectonism and Volcanism in West -Central Colorado: Geological Society of America Special Paper 366, Boulder, Colorado. Mears, A. I., 1977, Debris -Flow Hazard Analysis and Mitigation - An Example from Glenwood Springs, Colorado: Colorado Geological Survey Information Series 8. Tweto, O. and Others, 1978, Geology Map of the Leadville 1° X 2° Quadrangle, Northwestern Colorado: U.S. Geological Survey Map I-999. Widmann B.. L. and Others, 1998, Preliminary Quaternary Fault and Fold Map and Data Base of Colorado: Colorado Geological Survey Open File Report 98-8. Job No. 105 325 0 Cn w CT x 0 a m04 m O 1 Z n Western Colorado Evaporite Region m CD Explanation: Shallow Evaporite in Eagle Valley Formation and Eagle Valley Evaporite. Eagle Collapse Center (960 sq. mi.) Glenwood Springs 1 i 10 Miles References: Tweto and Others (1978) Kirkham and Scott (2002) Basin Carbondale Collapse Center (460 sq. mi.) f Qtp4 Qtpb Qa7 PPin Explanation: of Qat Qa2 Qf Qls 1 Q1s2 Qtp4 Qtpb Man -Placed Fill Young Stream Alluvium: Channel and low terrace alluvium along Roaring Fork River and Four Mile Creek. Old Stream Alluvium: Older Fourmile Creek alluvium, 2 - youngest, 7- oldest. Alluvial Fans Recent Landslides Old Landslides Oldest Pinedale Outwash Terrace: Pre -Bull Lake Outwash Terrace TPsc PIPm [Pe !Pee 30 Chinle and State Bridge Formations Maroon Formation Eagle Valley Formation Eagle Valley Evaporite Contact: Approxlmate boundary of map units. Strike and Dip: Strike and dip of bedding in degrees. Notes: 1. Shallow colluvium typically covers the formation rock but is not shown on this map. 2. See Figure 2 for cross section. Modified from Kirkham and Others (1997). 0 700 ft. ! J Scale: 1 in. = 700 ft. Contour Interval: 40 ft. March 2006 �lF-IptThe Reserve at Elk Meadows Conceptual Plan 105 325 �@Cil Figure 2 Project Site Geology Map HEPWORTH•PAWLAK GEOTECHNICAL 0 G.) N 071 6 uoQoag ssOJ9 31601099 EBuoi6eH CD CD rn CD CD 0) m CD 0) a 0 1 rn m co C0) (West) 9000 8000 - 7000 - c m w 6000 - 5000 - 4000 - 3000 Sunlight Mesa Q1s2 Regional Cross Section 1 Grand Hogback Monocline Proposed Development Area Cattle Creek Anticline 8 Roaring Fork River Qtpb (East) 9000 8000 - 7000 PPm Pe 0 1000 2000 3000 4000 Explanation: Qa1 Young Stream Alluvium: Channel and low terrace alluvium along Roaring Fork River and Four Mile Creek. Qa2 Old Stream Alluvium: Older Fourmile Creek alluvium, 2 - youngest, 7- oldest. Q1s2 Old Landslides Qtp4 Oldest Pinedale Outwash Terrace Qtpb Pre -Bull Lake Outwash Terrace Tb Miocene Basalt Flows 5000 Km Kfm Kd Jm Je TaPsc PIPm Pe Pee 6000 7000 Horizontal Distance (8.) 8000 Mancos Shale Frontier Sandstone and Mowry Shale Dakota Sandstone Morrison Formation Entrada Sandstone Chinle and State Bridge Formations Maroon Formation Eagle Valley Formation Eagle Valley Evaporite 9000 10000 Pee Roaring _Fork iapsr 11000 12000 6000 -5000 -4000 3000 13000 Scale 1 in. = 1500 ft. Horizontal = Vertical Contact: Approximate boundary of map units. Faults: Flexural -slip, bedding plane faults associated with evaporite tectonics Note: See Figure 1 for cross section location. Explanation: P R Rockfall Paths: Areas down slope of outcrops that are potential paths for rockfall. Rockfall Runout: Lower part of potential rockfall paths where CRSP indicates rockfalls will slow down and stop. Contact: Approximate boundary of map units. Note: Refer to Hepworth-Pawlak Geotechnical (2005b) for detailed rockfall risk assessment report. 0 700 ft. Scale: 1 in. = 700 ft. Contour Interval: 40 ft. March 2006 105 325 Ge&ech HEPWORTH•PAWLAK GEOTECHNICAL The Reserve at Elk Meadows Conceptual Plan Potential Rockfall Areas IFigure 4 1' ' r� 105 325 Explanation: Debris Flow Paths: Potential debris flow and flood paths in shallow hillside channels above alluvial fans. D Debris Deposition Areas: Potential debris deposition areas on alluvial fans and in confined channels cut below the alluvial fans. Contact: Approximate boundary of map units. Gtech HEPWORTH•PAWLAK GEOTECHNICAL f The Reserve at Elk Meadows Conceptual Plan Potential Debris Flow Areas Scale: 1 in. = 700 ft. Contour Interval: 40 ft. March 2006 Moab UT. UT. AZ. 150 miles Y. WY. CO. Lily Park 1871 VI Rangely Rio Blanco (Explosion) 5 MM 5.7 (Explosdan) 969 ❑ M 5& Rifle Colorado Axial Basin 0 Steamboat Springs Walden ❑ °N. M���ont iss M 6.2 VII Kremmling Meeker Grand Junction Plateau Glenwood Spdngs • 0 Eagle 0 NB. CO. Rocky 1962Mtn. T to 86 VI to VII M 3.2 to M .9 open Delta° Q56b 0 Salida • 067 Montrose ❑ 420 4__ 960 manon Ridge punnison 5.5 Sp, Great C.O. NM. Explanation: Post -Glacial Faults: Fault younger than about 15,000 years. Larger Historic Earthquakes: Earthquakes with maximum intensity greater than VI or magnitude greater than M 5.0 from 1867 to present. Nuclear Explosion: Large underground nuclear explosion for natural gas reservoir enhancement. Dulce 1966 M 5.1 VII Chama M Local, surface wave or body wave magnitude VI Modified Mercalli intensity References: Widmann and Others (1998) U. S. Geological Survey Earthquake Catalogs 0 Plains °Trinidad ° Raton 50 mi. Scale: 1 in. = 50 mi. March 2006 105 325 Gtech HEPWORTH-PAWLAK GEOTECHNICAL The Reserve at Elk Meadows Conceptual Plan Geologically Young Faults and Larger Historic Earthquakes Figure 6 Gtech HEPWORTH - PAWLAK GEOTECHNICAL August 28, 2006 Reserve at Elk Meadows, LLC Attn: Will Humphrey 920 South Waukegan Road Lake Forest, Illinois 60045 Hepworth-Pawlak Geotechnical, Inc. 5020 County Road 154 Glenwood Springs, Colorado 81601 Phone: 970-945-7988 Fax: 970-945-8454 email: hpgeo@hpgeotech.com Job No. 105 325 Subject: Radiation Potential, The Reserve at Elk Meadows, County Road 117, Garfield County, Colorado Dear Mr. Humphrey: As requested, we are providing our opinions of the radiation potential at the subject property to be included in our Geologic Review of The Reserve at Elk Meadows 2006 Conceptual Development Plan report dated May 26, 2006, Job No. 105 325. RADIATION POTENTIAL The project site is not located on geologic deposits that would be expected to have high concentration of radioactive minerals. However, there is a potential that radon gas could be present in the area. It is difficult to assess future radon gas concentrations in buildings before the buildings are constructed. Testing for radon gas levels could be done when the residences and other occupied structures have been completed. New buildings are often designed with provisions for ventilation of lower enclosed areas should post construction testing show unacceptable radon gas concentration. If you have any questions or need further assistance, please let us know. Sincerely, HEPWORTH - PAWLAK GEOTECHNICAL, INC. Steven L. Pawlak, P.E. "X; 15222 :* f• SLP/vad `t, J�•:SsioNAl ;'•�4 -DF �q��> cc: Sopris Engineering — A usley Land Design Partnership — Attn: Ron Liston Parker 303-841-7119 • Colorado Springs 719-633-5562 • Silverthome 970-468-1989 o . Iitftjtobro. 64.-to - s •s 114, 19 Roaring Threemil Creek GRAPHIC SCALE OPRIS ERCINECRINC, LW. ( Par ran ) 1moa-800Pl. 1• 3—Ah 2[41 DAT GARFIELD COUNTY RESERVE AT ELK MEADOWS U.S.D.A, SOIL CONSERVATION SERVICE SOIL DESIGNATION MAP DES. YEW DR CJB OK YTN DArzsAl FILE NO. ,86016.01 SxsET OF SOIL SURVEY OF ASPEN -GYPSUM AREA, COLORAL J, PARTS OF EAGLE, GARFIELD, AND PITKIN COUNTIES, RIFLE AREA, COLORADO, PARTS OF GARFIELD AND MESA COUNTIES Elk Meadows 296404 2971300 29spa 2941100 300.000 3OG960 3011E00 3021770 303500 0 0 0 ns o4r. Ce; �le�a; V-.1% Gar1iEl _`. nom. s1 _ t.Sr rte.-��r • Lsi -'. r tet.- . _ -- �•� C'. i r •. l S. t Y�S:C' LL_T. _ ,yryf7��., 0 29200 299700 x0060 300970 301€00 302700 Feet 0 1,0002,000 4,000 6,000 8,000 USDA Natural Resources irk Conservation Service Meters 0 350 700 1,400 Web Soil Survey 1.1 National Cooperative Soil Survey 9/6/2006 Page 1 of 5 SOIL SURVEY OF ASPEN -GYPSUM AREA, COLOr<ADO, PARTS OF EAGLE, GARFIELD, AND PITKIN COUN 11ES; RIFLE AREA, COLORADO, PARTS OF GARFIELD AND MESA COUNTIES Elk Meadows MAP LEGEND Soil Map Units O Cities Detailed Counties Detailed States Interstate Highways Roads +-1 Rails 1.11 Water Hydrography Oceans AYAYAYAY Escarpment, bedrock vnvnvn\n Escarpment, non -bedrock USDA Natural Resources Conservation Service Gulley minimum Levee Slope W Blowout ® Borrow Flt Of Clay Spot • Depression, closed Eroded Spot X Gravel Pit Gravelly Spot ti Gulley A Lava Flow A Landfill 44 Marsh or Swamp Q l•:'•iscel'reoLis Viate• Ni Rock Outcrop + Saline Spot Sandy Spot 3' Slide or Slip , Sinkhole O Sodic Spot it Spoil Area o Stony Spot Cd bevy Stu; y SIA ® Perennial Water * Wet Spot MAP INFORMATION Source of Map: Natural Resources Conservation Service Web Soil Survey URL: http://websoilsurvey.nres.usda.gov Coordinate System: UTM Zone 13 Soil Survey Area: Aspen -Gypsum Area, Colorado, Parts of Eagle, Garfield, and Pitkin Counties Spatial Version of Data: 1 Soil Map Compilation Scale: 1:24000 Soil Survey Area: Rifle Area, Colorado, Parts of Garfield and Mesa Counties Spatial Version of Data: 1 Soil Map Compilation Scale: 1:24000 Map comprised of aerial images photographed on these dates 1993 The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident Web Soil Survey 1.1 9/6/2006 National Cooperative Soil Survey Page 2 of 5 Soil Survey of Aspen -Gypsum Area, Colorado, Parts of Eagle, Garfield, and Pitkin Counties, Rifle Area, Colorado, Parts of Garfield and Mesa Counties Elk Meadows Map Unit Legend Summary Aspen -Gypsum Area, Colorado, Parts of Eagle, Garfield, and Pitkin Counties Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI 6 Almy Ioam, 1 to 12 percent slopes 1 1 4.1 1.4 8 Ansel -Anvil( association, 12 to 25 383.5 4.7 percent slopes 12 Arle-Ansari-Rock outcrop complex, 12 319.2 3.9 to 50 percent slopes 13 Atencio-Azeltine complex, 3 to 6 36.7 0.5 percent slopes 18 Cochetopa-Antrobus association, 12 to 166.4 2.I 25 percent slopes 19 Cochetopa-Antrobus association, 25 to 65.5 0.8 50 percent slopes 25 Cushool-Rentsac complex, 15 to 65 1.6 i}.0 percent slopes 28 Dahlquist-Southace complex, 25 to 50 45.4 percent slopes 0.6 33 Earsman-Rock outcrop complex, 12 to 208.6 2.6 65 percent slopes 35 Empedrado loam, 6 to 12 percent 6.4 0.1 slopes 37 Ewe loam, 15 to 50 percent slopes 88.0 1.1 42 Fluvaquents, 0 to 10 percent slopes 25.8 0.3 49 Uoslin fine sandy loam. 3 to 6 percent 88.1 slopes 50 Goslin fine sandy loam, 6 to 25 percent 35.6 slopes 0.4 55 Gypsum land-Gypsiorthids complex, 0.7 0.0 12 to 65 percent slopes 64 Jerry loam, 25 to 65 percent slopes 122.7 1.5 66 Jerry-Millerlake loams, 6 to 25 percent 29.6 slopes 0.4 94 Showalter-Morval complex, 5 to 15 21.2 0.3 percent slopes 95 Showalter-Morval complex, 15 to 25 249.9 3.1 percent slopes 98 Southace cobbly sandy loam, 12 to 25 52.6 0.6 percent slopes 109 Uracca, moist-Mergel complex, 12 to 17.2 0.2 25 percent slopes, extremely 120 Water 32.0 0.4 USDA Natural Resources NUMMI Conservation Service Web Soil Survey 1.1 9/6/2006 National Cooperative Soil Survey Page 3 of 5 Soil Survey of Aspen -Gypsum Area, Colorado, Parts of Eagle, Garfield, and Pitkin Counties, Rifle Area, Colorado, Parts of Garfield and Mesa Counties Elle Meadows Aspen -Gypsum Area, Colorado, Parts of Eagle, Garfield, and Pitkin Counties Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI Rifle Area, Colorado, Parts of Garfield and Mesa Counties Map Unit Map Unit Name Symbol Acres in AOI Percent of AOI 2 Arle-Ansari-Rock outcrop complex, 12 1,357.3 I6.7 to 65 percent slopes 5 Ascalon fine sandy loam, 1 to 6 percent 28.0 0.3 slopes 6 Ascalon rine sandy loam, 6 to 12 236.4 2.9 percent slopes 7 Ascalon -Pena complex, 6 to 25 percent 33.0 0.4 slopes 8 Atencio-Azeltine complex, 1 to 3 637.4 7.9 percent slopes 9 Badland 24.4 0.3 1I Begay sandy loam, 6 to 12 percent 89.7 1.1 slopes 12 Bucklon-Inchau loams, 25 to 50 percent 125.0 slopes 1.5 17 Cochetopa loam, 9 to 50 percent slopes 415.0 5.1 18 Cochetopa-Jerry complex, 12 to 25 147.7 1.8 percent slopes 19 Cochetopa-Jerry complex, 25 to 50 1,036.0 12.8 percent slopes 21 Cushman-Lazear stony loams, 15 to 65 54.1 percent slopes 0.7 23 Detra fine sandy loam, 12 to 25 percent 253.7 slopes 3.1 25 Etoe loam, 15 to 50 percent slopes 28.1 0.3 34 lldefonso stony loam, 25 to 45 percent 84.3 1.0 slopes 39 Jerry loam, 12 to 50 percent slopes 125.2 1.5 42 Lamphier loam, 15 to 50 percent slopes 175.8 2.2 45 Morval-Tridell complex, 6 to 25 percent 4.7 slopes 0.1 64 'Panna silty clay loam, 25 to 45 percent 360.6 slopes 4.4 USDA Natural Resources Conserratiou Service Web Soil Survey 1.1 9/6/2006 National Cooperative Soil Survey Page 4 of 5 Soil Survey of Aspen -Gypsum Area, Colorado, Parts of Eagle, Garfield, and Pitkin Counties; Rifle Area, Colorado, Parts of Garfield and Mesa Counties Elk Meadows Rifle Area, Colorado, Parts of Garfield and Mesa Counties Map Unit Map Unit Name Symbol Acres in AOI Percent of AOI 65 Torzifiuvents, nearly level 30.4 0:4 67 Torriorthents-Rock outcrop complex, 587.5 7.2 steep 71 Villa Grove-Zoltay loams, 15 to 30 75.3 percent slopes 0.9 73 Water 88.5 1.1 USDA Natural Resources Web Soil Survey 1.1 9/6/2006 010011 Conservation Service National Cooperative Soil Survey Page 5 of 5