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t ;tali BI.M1•1 Stone Cabin 3t) Seismic Surroey f:mironmcntal Assessment Page 2 of 17 <br />The gently noriheasl-dipping surfaces of the plateau wdhin the Protect Area are dissected by southwest to <br />northeast trending canyons (Figure 1-1 ), Exposed m the Protect Area's canyons are the upper and middle <br />members of the Green River Formation (Weiss et al 1990). Rocks of the lower Colton Formation are exposed <br />only In the easternmost portion of the Project Area in the lower reach of Jack Creek Canyon. These canyons <br />begin rn the highlands near the Roan Cliffs and become Increasingly deeper toward Nine Mde Creek Canyon to <br />Ilia northeast and the Green River's Desolation Canyon to the earl. <br />Slopes ~n ttte canyons mostly range from 40 to 50 percent; however, both less steep and even steeper slopes <br />occur in the canyons throughout the Project Area. In localized situations slopes reach Hoar vertical along the edge <br />of Qte plateau surface and in the bottoms where stream action has rut vertical walls and cleared the colluwum <br />and Fallen rocks Ro<;k fall ~s the main form of mass wast~n~ in the Project Area's canyons. Only one landslide has <br />been mapped in the Protect Area (Harty 1991); the slide 'is locatedin a canyon t~i6iiiary To Jack Creek Canyon in <br />Section 18. T13S, R16E The mostly consolidated rocks of the Green River Formation are mostly sl.:ible whrn <br />exposed and this stabitily lends to the perseverance of clifts in the Project Area. Rock falls are caused mostl~by_ <br />forces of erosion in the form of freezelthaw actions and c~rawty as the rocks slough-off slowly over time <br />Od and gas production in the Protect Area comes from several anticlinal geologic structures that have been <br />successfully drilled for gas (Weiss al, al 1990) The major unds in this area are Prickly Pear, ,lack Canyon, Paters <br />Point, and Nrne h9de Production from the Paters Point-Stone Cabin gas unit produce primanly gas and, u, the <br />past. some oil from the Green River and Colton formations al a depths of 2,800 to 4,300 feet (UGAP 1991, UGS <br />and UEES 1996, and Weiss et al. 1990). There are curcentty 19 wells capable of producing natural qas in the <br />Project Area (Frgure 1-4). <br />A deposit of bilummous or asphaltic sandstones, sometimes call tar sands, defined as the Sunnysrde Deposit. <br />underlies much of the western part of the Project Area (UGS and UEES 7996) The bituminous zone composing <br />This Ceposlt Is included in the middle and lower members of the Green Rver Formation and the upper portion of <br />the Colton Formation The Sunnysrde Deposit is the largest tar sand deposd in this region Tho deposd's outcrop <br />is exposed along the western side of Ute Roan Cliffs. There are also reported exposures of extensions of this <br />deposd rn Cottonwood. Jacks, and Nme Mile Canyons <br />Exposures below the Roan Cliffs were mined for paving material up to the Tate 19a0's. Covington and Young <br />(1985) suggested that nearly 300 mdtion barrels of petroleum are recoverable in the area. In the t970's and early <br />1980's, tests of in•situ extraction methods Involving the injection of hot water or steam to extract liquid petroleum <br />from the tar sands were not commercially successful. <br />3.2.1.2 Environmental Consequences <br />3.2.1.2.1 Alternative A • Proposed Action <br />i'he dnlliny of sttol holes to receive the exploswes placed al depths of 50 or 60 feet as part of the Proposed <br />Action would create a potential path for surface water to flow into the dolled hole and to potentiany accumulate <br />where the water could possibly Ireeze Bunny pouods of freezing temperatures or possibly produce saturated <br />conddions in subsurface geologic, materials and subsequent rock movement, especially if holes were located <br />close to cliff or escarpment edges. However, potential effects o1 water accumulating tit open shot holes would not <br />tikety occur as the holes are immediately packed wdh explosive following dolling followed by the hole bmng <br />backtilled with cuttings up to within about three foot of Rte surface where at plug is inserted urio the hole to seal <br />the hole. Above the plug, additional cuttings and sod are added to the hole to complete the backfill to the surface. <br />Tho back till and the plug would likely preclude any intillration of water, and backhlting to the surface would <br />prevent water wllec--ling and being channeled into the hole Therefore. any impacts to rocks penetrated by the <br />drdhng of shot holes by the channelization of water into the holes would be prevented <br />The detonation of the explosive shots at depths of 50 and 60 feel for buggy drill and heti-portable doll holes, <br />respectively, would inmally result in peak particle velocities or vibrations greater than 0.75 inches per second al <br />the point of detonation and would diminish with distance. peefkpart;cle vo!ordies al the base of standing <br />_ _ _.. <br />structures and rock art should not exceed a 0.75 inches per second threshold cntenon reported by the BLM u, <br />Hai dbook 3150, Illustration 10 Resource Proleclion Offsets forCultural Resource Structures and Other Facddies. <br />1_.----_ _ _ ---- - - - -- _ _ _ _ <br />BLM's recommended safe distances from buried shots to cultural resource structures and other facilities aro about <br />284 and 199 feel for 20 pounds of explosive at a depth of 60 feat for buggy drilled source points and tU pounds of <br />explosve at 50 feet for heir-portable dolled source points, respectively. <br />5 $r?Illlh <br />hty,: w,cw,ut.him.~!uw'.,tunrrrhin'I ,\ rhaplrr?a.hhn <br />