2018-02-20_PERMIT FILE - M2017036

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To:Jared Ebert Date: February 27,2018 Page 2 • Nearly every gravel pit on the Poudre River has exposed the Pierre Shale and there are not wide-spread water quality issues associated these activities • Constituent mobility requires two principal components: — Source chemistry — Water movement • LRM commits to monitoring and managing its water to limit the potential for water quality issues While the Pierre Shale is documented to have source constituents available, it is also well documented that it is highly impermeable. On site, the Pierre Shale drilled dry, meaning there is no water present. Thus, the only mechanism to move source constituents from the Pierre into contact water is through molecular diffusion,which is a slow process. Recently, LRM collected samples of the Pierre Shale at the contact with the alluvium and subjected the samples to the synthetic precipitation leach procedure (SPLP) testing. One of 5 samples resulted in detectable selenium. Three groundwater quality samples were taken from monitoring wells MW-06, MW-13, and MW-02. MW-06 showed detectable levels of selenium below the drinking water standard. The sample from MW-06 contained sedimentation (i.e., the well has not completely developed), thus it is most likely that the detected selenium was part of the solid matrix. LRM will sample MW-06 again and filter the sample to corroborate this supposition. These data corroborate the potential for the Pierre Shale to contain selenium, and on the whole, show that ground water quality is not significantly impacted by the Pierre Shale. LRM's water management activities keep the groundwater system outside of the mining area in tact with respect to water contacting the Pierre Shale. Inside the mining area, no water that is in direct contact with the shale is proposed to leave the site. Thus, no water quality issues are anticipated. Regardless, LRM commits to monitoring its water quality in the water management pond and respond accordingly should discharges be an issue. Comment 39b The groundwater quality data provided and proposed groundwater quality monitoring program are insufficient. The applicant will need to submit a groundwater quality monitoring plan and data sufficient to demonstrate that the site will be in compliance with CDPHE Water Quality Control Commission (WQCC) Regulation 41 - Basic Standards for Groundwater during the life of the mine and during reclamation. In accordance with Rule 3.1.7(7)(b), the submitted plan should be revised to include at least: Response to DRMS Adequacy Review 3 comments T E L E S T O