How To Build A Soil Treatment Facility

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1 Geological and Soil Hazards Report PDC Energy Metcalf Soil Treatment Facility OA Project No Horizon Drive, Suite 102 Grand Junction, CO TEL FAX

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3 GEOLOGIC AND SOIL HAZARDS REPORT Introduction Metcalf Property Management LLC proposes to construct a soil treatment facility to be located in Section 24, Township 7 South, Range 96 West, of the Sixth Principal Meridian, located west of the town of Battlement Mesa, east of Interstate 70, and south of the Colorado River, in Garfield County, Colorado (Fig. V-1). The proposed Soil Treatment Facility is located in the eastern part of the Piceance Basin south of the Colorado River on a terrace between Dry Creek and Monument Gulch at the western base of Battlement Mesa. The proposed location is shown on a map provided (Fig. G-1). Structural Geology The proposed project is located in the eastern part of the Piceance Basin; an irregularly-shaped elongated basin formed by tectonic forces associated with the Laramie orogeny that downwarped the earth s crust as a result of the uplift of the Colorado Rocky Mountains. Areas on all sides of the Piceance Basin have been uplifted by these same tectonic forces. The Piceance Basin is the major structural geologic feature in the region. It is bound to the east by the Grand Hogback monocline, the White River Uplift to the northeast, the Gunnison Uplift to the south, the Uncompahgre Uplift to the southwest, the Douglas Creek Arch to the westnorthwest, and the axial basin uplift to the north (Grout and Verbeek, 1992). The Grand Hogback monocline is a sinuous feature comprised of Upper Cretaceous age bedrock of the Mesaverde Group, which includes the Williams Fork Formation and the underlying Mancos Shale. The Grand Hogback forms part of the boundary between two major physiographic provinces, the Colorado Plateau and the Rocky Mountain foreland. Bedrock Geology Two bedrock units crop out, or are exposed in the Grand Valley Quadrangle, the Tertiary age (Eocene and Paleocene) Wasatch Formation and (Eocene) Green River Formation. The Wasatch Formation is at the surface or it underlies surficial deposits in most of the quadrangle. Rocks of the Green River Formation comprise the main bulk of the uplands of the Roan Plateau and Battlement Mesa, and are exposed along the steep slopes and cliffs to the east of the Grand Valley. Metcalf Property Management LLC. Olsson Associates Metcalf Soil Treatment Facility Grand Junction, CO January 2013 OA Project #

4 The Wasatch Formation is more than 6,000 feet thick, according to geophysical logs of gas wells within the basin. The Wasatch Formation consists of claystone, mudstone, and siltstone interbedded with sandstone and conglomerate. Fine-grained sediments predominate the formation and range in color from very light gray, to brown, olive gray, reddish, and tan. Claystones and mudstones are poorly to moderately indurated, and sandstones are generally discontinuous, commonly lenticular and are yellowish gray to olive gray in color. The Wasatch Formation is prone to landslides as described in the section on geologic hazards (Madole and Streufert, 2003). The Green River Formation is comprised of lithified lacustrine sediment deposited in a group of intermontane freshwater Eocene lake basins in Colorado, Utah, and Wyoming. Over 3,000 feet of interbedded sandstone, mudstone, siltstone, limestone, dolomite, and marlstone were deposited in the deep lake known as Lake Uinta in very fine annual layers called varves. The Green River Formation is comparatively resistant to erosion, and comprises many of the high cliffs and escarpments several miles to the east of the site. Surficial Geology The location for the proposed facility is located in river terrace deposits of the Holocene epoch (Fig. G-1), which overlie the Wasatch Formation. Battlement Mesa, along the east side of the quadrangle, consists primarily of the Green River Formation, with large slump blocks of basalt irregularly veneered with young Pinedale glacial drift. Alluvial and colluvial deposits consist of silt, sand, gravel, and clay are found in debris fans, stream channels, flood plains, and adjacent hill slopes along tributary valleys. Depositional processes in stream channels and on floodplains are primarily alluvial, whereas colluvial and sheet-wash processes pre-dominate on debris fans, hillslopes, and along the hillslope/valley floor boundary. An alluvial fan is a fan or cone-shaped deposit of sediment built up by streams or debris flows. Undifferentiated deposits of older gravels and alluvium underlie terraces and hill slopes 10 feet to 40 feet above small perennial and intermittent streams. The maximum thickness of these deposits is up to about 30 feet, and areas may be prone to sheet wash and rockfall. Geologic Hazards The processes of mass wasting, flooding, hydrocompaction, and piping are the principal geologic hazards in the Grand Valley Quadrangle, with mass wasting processes being the most widespread hazard. Mass wasting is defined as earth materials transported downslope primarily by gravity. Mass wasting differs from other modes of sediment transport in that the materials move as a mass rather than as individual fragments or particles borne along by a transport medium such as wind or flowing water. Water is an important component in masswasting, and commonly triggers movement, but the water is part of the moving mass rather than Metcalf Property Management LLC. Olsson Associates Metcalf Soil Treatment Facility Grand Junction, CO January 2013 OA Project #

5 the transport agent. Mass wasting may take the form of slope creep, as a slow or imperceptible and progressive downslope movement, or can be more sudden and dramatic in areas prone to slumping, debris flows, or landslides. Triggering mechanisms are most commonly the result of wetting from rain or heavy snowmelt. Most failure occurs on steep slopes and involves movement of all surficial geological materials (alluvium, colluvium, decomposed bedrock) overlying competent bedrock. Debris flows are dense mixtures of sand, silt, clay, rock debris, and lesser amounts of water and air that move as a fluid mass. Debris flows may resemble wet concrete with variable fluidity depending on the amounts of debris and water present. Most debris flows become channelized as they descend to the main valleys regardless of whether the flow was initiated at the valley heads or on the valley sides. Debris flow deposits are a major constituent of fan-shaped masses that accumulate where large gullies and tributary valleys converge. The site for the soil facility is located in an area of Garfield County that has been mapped by Garfield County for landslides or landslide potential. No major slope hazards have been identified in the immediate area. Landslides occur in areas that are vulnerable to slope failure due to a variety of reasons. Weak rocks, high relief, steep slopes, and locally abundant moisture are all contributing factors in causing landslides. Much of the Wasatch Formation consists of fine-grained materials that are weakly cemented. These materials are often overlain by indurated strata that are more resistant to weathering, both within and overlying the Wasatch Formation, resulting in different erosion rates and over steepening of slopes. The Wasatch Formation also may contain expansive clay minerals that can reduce rock strength and slope stability. Natural events, including intense rainfall, rapid snow melt, groundwater level changes, and earthquakes, in addition to human activities, may trigger landslides. Human activities which may cause failure include construction projects, the use of earth fill for construction, cutting benches into hill slopes, and use of unlined pits or septic systems that change water levels or add weight to the natural slope, increasing the shear stress. Floods are another potential hazard in the area, although they are more predictable and more frequent than landslides and debris flows. Areas subject to debris flows are also subject to flash floods. The areas that are prone to flooding are smaller as compared to the areas that are vulnerable to landslides. Mapped flood plain areas are shown along the banks of the Colorado River near the facility but do not include the facility area itself, as seen in figures F-1 and F-2. Hydrocompaction occurs in areas underlain by thick deposits of fine-grained sediments that have a low bulk density and indicate that the sediment contains a relatively high volume of void space between grains. Hydrocompacted sediments may undergo significant reduction in volume and collapse when wetted, or when additional weight is added on top of them, or by a combination of weight and wetting. Hydrocompaction is most common in relatively young, fine- Metcalf Property Management LLC. Olsson Associates Metcalf Soil Treatment Facility Grand Junction, CO January 2013 OA Project #

6 grained sediments deposited by wind, sheet flow, and in some mudflows or debris flows where entrapped air results in a high percentage of void space. The area of the project site is not considered to be at risk for hydrocompaction hazard.. According to the Colorado Geological Survey, there have been earthquakes in the eastern part of Garfield County near Glenwood Springs and New Castle, but there are no recorded earthquakes or faults shown in the vicinity of the of the soil treatment facility. Soils According to information prepared by the Natural Resources Conservation Service Soil Survey, the predominant soils in this section have been mapped as the Nihill channery loam (46), the Potts-Ildefonso complex (58), and the Arvada loam (4), with small deposits of Ildefonso stony loam (34), Torrifluvents (65), and Wann sandy loam (72). The Nihill channery loam (46) soils cover 40.8 percent of the area in which the Metcalf Soil Treatment Facility will be located as seen in figure S-1. The soil in this area occupies 1 to 6 percent slopes at elevations ranging from 5,000 to 6,500 feet above mean sea level. The Nihill channery loam is a deep and well-drained soil that forms on valley sides and alluvial fans. The capacity of the most limiting layer to transmit water is moderately high to high. Depth to water table is more than 80 inches. The parent material is alluvium derived from sandstone and shale. The Potts-Ildefonso complex (58) soils cover 27 percent of the project area, occupying 12 to 25 percent slopes at elevations ranging from 5,000 to 6,500 feet in elevation. This well-drained soil forms on valley sides, alluvial fans, and mesas. The capacity of the most limiting layer to transmit water is moderately high to high. Depth to water table is more than 80 inches. The parent material is alluvium derived from sandstone and shale. The Arvada loam (4) soils cover 21.3 percent of the project area, occupying 6 to 20 percent slopes at elevations ranging from 5,100 to 6,200 feet in elevation. This well-drained soil forms on terraces and alluvial fans. The capacity of the most limiting layer to transmit water is moderately low to moderately high. Depth to water table is more than 80 inches. The parent material is alluvium derived from sandstone and shale. Radon Radon is a naturally occurring, odorless and colorless radioactive gas that is produced by the radioactive decay of radioactive minerals present in the soils and bedrock. According to the Colorado Department of Public Health and Environment (CDPHE), Colorado has a moderate to high radon potential. Since the site is a facility that does not have buildings or an area that is occupied throughout the work day, the potential presence of radon is not expected to represent a geologic hazard or a significant worker exposure issue. Metcalf Property Management LLC. Olsson Associates Metcalf Soil Treatment Facility Grand Junction, CO January 2013 OA Project #

7 Garfield County Geographic Information System Olsson personnel have reviewed the relevant county maps prepared by Garfield County s Geographic Information System (GIS) Department that pertain to this study. According to the Flood Plain Profile the 100-year flood plain is indicated immediately along the Colorado River, and is not shown to be in the immediate vicinity of the proposed soil treatment facility. According to the Slope Hazard Map provided by Garfield County, Colorado - GIS Department website, no moderate or major slope hazard is indicated within the vicinity of the proposed soil treatment facility. According to the Surficial Geology Map provided by Garfield County, Colorado GIS Department website the hazards associated with alluvial fan, landslide, mudflow, mudflow/slide are low. Conclusions and Summary According to the information provided by Garfield County, Colorado - GIS Department pertaining to the location of the proposed soil treatment facility, the overall geologic and soil hazards appear to be low. Stormwater controls and Best Management Practices (BMPs) should take into consideration the geology and soil types present at this location. These engineering controls and practices should be used temporarily and permanently to divert stormwater away from the construction areas and to prevent additional weight which could trigger a debris flow or landslide. Pits are required to be lined by COGCC rules, but pit liners may also prevent water infiltration into unconsolidated sediments which could trigger slope failure. Pits and catchment basins should be sited and designed so as not to add weight to potentially unstable areas. William Monroe Project Geologist Olsson Associates Metcalf Property Management LLC. Olsson Associates Metcalf Soil Treatment Facility Grand Junction, CO January 2013 OA Project #

8 References Harman, Jerry B. and Murray, Donald J., 1985, Soil Survey of Rifle Area, Colorado, Parts of Garfield and Mesa Counties, Colorado: U.S. Department of Agriculture, Soil Conservation Service, in cooperation with the Colorado Agricultural Experiment Station, 149 p. two plates, and 20 map sheets. Online References Colorado Oil and Gas Conservation Commission Natural Resources Conservation Service - Soil Survey Garfield County Slope Hazards: Soil Hazards: Surficial Geology of Garfield County: Metcalf Property Management LLC. Olsson Associates Metcalf Soil Treatment Facility Grand Junction, CO January 2013 OA Project #

9 Qa Two Bent Creek Clear Creek Parachute Placer Eldora Ql Stone Quarry Soil Data provided by NRCS Soil Survey Legend Affected Parcel Geology Type Highway/Interstate Qa - Modern alluvium County Roads Ql - Landslide Deposits Two - Wasatch formation and Ohio Creek formation Feet ,000 PROJECT NO: DRAWN BY: DATE: Jenna Muhlbach 1/28/13 GEOLOGY MAP PDC ENERGY METCALF SOIL TREATMENT FACILITY GARFIELD COUNTY, COLORADO 760 HORIZON DRIVE, SUITE 102 GRAND JUNCTION, CO TEL FAX FIGURE G - 1

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11 Bent Creek Parachute Clear Creek Placer 46 4 Eldora Stone Quarry Soil Data provided by NRCS Soil Survey Legend Affected Parcel Soil Type Highway/Interstate 3 - Arvada loam, 1-6% slopes County Roads 4 - Arvada loam, 6-20% slopes 34 - Ildefonso stony loam, 6-25% slopes 46 - Nihill channery loam, 1-6% slopes 56 - Potts loam, 6-12% slopes 58 - Potts-Ildefonso complex, 12-25% slopes 65 - Torrifluvents, nearly level 72 - Wann sandy loam, 1-3% slopes 73 - Water Feet ,000 PROJECT NO: DRAWN BY: DATE: Jenna Muhlbach 1/28/13 SOILS MAP PDC ENERGY METCALF SOIL TREATMENT FACILITY GARFIELD COUNTY, COLORADO 760 HORIZON DRIVE, SUITE 102 GRAND JUNCTION, CO TEL FAX FIGURE S - 1

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13 Empire Silver Queen River Bluff 6 70 Smokey Hill Emerald Silverton Horizon Bent Creek Placer Eldora Thunderberg Mahogany Mineral Springs Tamarisk Cedar Rainbow Oro Bonanza Tamarack Ironwedge Parachute Cobre Parcel Stone Quarry Floodplain Data provided by Garfield County GIS Department Legend Affected Parcel Parcels FloodPlain Highway/Interstate Feet County Roads ,250 2,500 PROJECT NO: DRAWN BY: DATE: Jenna Muhlbach 1/9/13 FLOODPLAIN MAP PDC ENERGY METCALF SOIL TREATMENT FACILITY GARFIELD COUNTY, COLORADO 760 HORIZON DRIVE, SUITE 102 GRAND JUNCTION, CO TEL FAX FIGURE F - 1

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15 Stone Quarry Floodplain Data provided by Garfield County GIS Department Parcel Legend Affected Parcel Parcels FloodPlain Highway/Interstate Feet County Roads PROJECT NO: DRAWN BY: DATE: Jenna Muhlbach 1/9/13 FLOODPLAIN MAP PDC ENERGY METCALF SOIL TREATMENT FACILITY GARFIELD COUNTY, COLORADO 760 HORIZON DRIVE, SUITE 102 GRAND JUNCTION, CO TEL FAX FIGURE F - 2

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