2021-08-17_REVISION - M1977342 (4)

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TR-34 to Permit M-1977-342 Environmental Protection Plan 8. GROUNDWATER Groundwater at hard rock mine sites is regulated through the DRMS under authority of Senate Bill 89-181. Henderson has prepared and submitted a GWMP,Technical Revision 16(TR-16)to the DRMS which outlines practices and procedures to protect groundwater quality pursuant to Rule 3.1.7. The GWMP establishes permit conditions, including numeric protection levels (NPLs) for groundwater and is an important component of this EPP. The following section provide a general summary of the water bodies, site geology and site hydrogeology in and around the mine and mill sites as it relates to groundwater. More detailed information and related references have been developed and submitted as a part of Henderson's Reclamation Permit, as revised and amended, including the GWMP. 8.1. Water Maps Figures 1 and 2 depict major surface water bodies within the vicinity of the Mine and Mill. 8.2. Site Geology 8.2.1. Mine Bedrock in the vicinity of the Henderson Mine surface facilities is shallow, generally less than 30 feet, and is composed primarily of Precambrian Silver Plume Granite and Tertiary-age stock and dike granitic intrusions. Bedrock in the vicinity of the Henderson Mine property is, in places, hydrothermally altered and mineralized, and therefore, has the potential to naturally generate acidic conditions when contacted by meteoric water. Shallow colluvial and glacial deposits consisting of poorly sorted and unconsolidated sand, gravel, and cobbles, overlie the bedrock surface in drainage areas, such as near the West Fork of Clear Creek. Colluvial sediments east of the mine facilities is approximately 20 to 25 feet thick and consists of boulders, cobbles, gravels and sands with varying amounts of clay. Granite bedrock underlies the sediments (Ajax/Clear Creek Associates, 2013). 8.2.2. Mill The Henderson Mill and TSF are located in the Ute Creek Basin of the Williams Fork River drainage basin.The Ute Creek Basin is bounded on the west by the Vasquez Mountain Range and bounded on the north, south and east by northwest trending Williams Fork Mountains. The Ute Creek Basin basement rocks consist of weathered and unweathered Precambrian gneiss and schist of the Idaho Springs Formation and Silver Plume Granite. In some areas of the basin, the Miocene- aged Troublesome Formation consists mostly of unconsolidated and semi-consolidated lensed clays, silts, sands, gravels and volcanic ash grading to consolidated siltstone, sandstone, conglomerate and claystone derived from the weathering of the Williams Fork Mountain Range. Pleistocene-aged glacial end-moraines, lake sediments and outwash material encroach on the Ute Creek Basin and overlie the Troublesome Formation. End-moraines are a conglomeration of boulders, cobbles, gravels, sands, silts and clays. Glacial lake sediments cover low flat sections while glacial outwash was deposited in braided stream beds. Glacial outwash consists of gravels, cobbles and sands. The Troublesome Formation is generally blanketed by a 2 to 10-foot thick layer of recent slopewash and residual soils. Alluvial material generally lies within the present stream valleys. Climax Molybdenum Company August,2021 Henderson Operations Page 30 of 45