2017-03-23_PERMIT FILE - C1981019A

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RULE 2 PERMITS crosses from the Collom Pit to the Gossard loadout, Wilson Creek is at least 20 feet deep. The banks show some undercutting and blocks of valley fill material coming off the sides. The vegetation on the land on both sides of the creek in this area is predominantly upland vegetation. The vegetation is old growth due to the size of the brush in this area. The deep valley of the creek and vegetation continues along the length of Wilson Creek to the north of the loadout and for several miles north of the loadout. Groundwater is this area is at least 20 feet below ground surface (bgs) in the shallow monitoring wells, Gossard Well and MW -95-02. The Gossard Well is located northeast of the Gossard Loadout in the field and MW -95-02 is located on the east bank of Wilson Creek, southwest of the loadout. The historical average depth to water at the Gossard Well is approximately 21 feet (2009 Annual Reclamation Report). Tetra Tech (2005) concluded that such depths to groundwater are too great to allow for agriculturally significant subirrigation. MW -95-02 had a water level of 25.1 feet bgs in November 2016. (Further information on groundwater occurrence is provided in Section 2.04.7). In September of 2015, four geotechnical holes were drilled on both sides of Wilson Creek where the crossing for the haul road leading from the Collom pit to the loadout is to be located. Groundwater was detected in these geotechnical test hole at approximately 25 feet bgs. There are no visible seeps on the sidewalls of the valley in the crossing area and both upstream and downstream of the crossing area. This new data provides additional information to the conclusion that groundwater in the area is too deep for any subirrigation. The near surface valley fill materials in the area of the Collom haul road crossing over Wilson Creek were found to be predominantly clay, based on the four geotechnical test holes. The clays do contain minor amounts of gravel, sand and silt and were gray to dark brown in color. The thickness of the clays are at least 10 feet thick and are stiff to hard. The materials present do not appear to meet the definition of alluvial material for alluvial valley floors. No evidence of flood irrigation was found for the fields surrounding the Gossard loadout. However, some limited flood irrigation was conducted in the floodplain of Wilson Creek, north of and outside the permit boundary (north of County Road 17). The ditch constructed for this irrigation is now heavily overgrown with upland vegetation. The gate for this water diversion sets several feet above the Wilson Creek channel and cannot be reached by current water flow from Wilson Creek. The area of concern surrounding the Gossard Loadout facility was bypassed for flood irrigation historically in order to apply irrigation water downstream to lands outside the current permit boundary. Irrigation diversion points, irrigation ditches, and topography are shown on Map IOB. These areas are well outside the subject drainages of Collom Gulch, Little Collom Gulch, and Jubb Creek. Thus, the same conclusions as those previously presented for the creeks in the Collom syncline area may be reached for the area of disturbance for construction of the Collom Haul Road in the vicinity of the Gossard Loadout facility (Map 25E Sheet 5 of 10): • Alluvial materials are present in the valley bottom of the Gossard Loadout complex, and the lower reaches of the Lower Wilson Creek drainage, but the materials are intermixed with significant fractions of colluvium and sheetwash from adjacent slopes and the mass wasting event experienced in 1983-1984. • Based on an average depth to groundwater of at least 20 feet, coupled with data from monitoring wells and geotechnical test holes in the Wilson Creek area drilled in 2015,subirrigation within this valley bottom is very limited in extent (outside and north of the permit area) or non-existent. Active erosion in the stream channels is causing further incision and reduced flood frequency, reducing the ability of this valley bottom to support any agricultural use other than rangeland or Collom — Rule 2, Page 131 Revision Date: 1/6/17 Revision No.: TR -109