2023-04-07_REVISION - M2001046 - Laserfiche WebLink

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CCCf____7_)D CIVIL RES'DURCES in June of each year, and commit to submitting information in the annual report. This section was added to the "Groundwater Monitoring Plan"document and submitted with the Adequacy Review Response 3 letter dated June 23, 2021. In this letter,CR indicated that the Groundwater Quality Monitoring Plan section had been added for review even though the operator believes that there is no reasonable expectation that adverse impacts to water quality will occur due to the planned operation. Amendment 1 was approved on June 28, 2021. Regulation 41 and DRMS Technical Guidance Implementation CR performed a review of the DRMS permits approved since the Division's Groundwater Monitoring and Protection Technical Bulletin was implemented in November 2019. The review consisted of screening active 112C mine sites in Larimer, Weld, Boulder, and Adams counties by approval dates after November 2019. Seventeen (17) sites were determined to have been permitted and active since November 2019. Of these seventeen sites, only seven (7) encountered groundwater and had either slurry wall lined cells or were dry mined utilizing dewatering trenches. Only one of these sites (M-2020-007) required analytical testing as a permit condition and only baseline sampling of the neighboring wells. The remaining six (6) sites (M-2018-060, M-2019-025, M-2020-058, M-2019-028, M-2018-039, M- 2022-009) required monthly groundwater elevation monitoring but no analytical testing. There are four (4) permitted construction materials (112c) mines within one (1) mile of the site. Reviewing documents from the DRMS laserfische website, none of these sites have a requirement for groundwater quality testing or analysis even though being permitted while Regulation 41 was in place. All of these mines (M-2015-033, M-1999-006, M-2009- 018,and M-1996-052)are unlined or partially lined pits with exposed groundwater. The majority of the Nix Mine will be soil-bentonite slurry wall lined prior to exposing groundwater. The addition of the slurry wall lined cells will isolate the pit and working face from the hydrologic system. As the pit is dewatered any leakage through the slurry wall or bedrock will be into the pit. The trapped groundwater in the pit will be pumped to the permitted discharge point to surface waters, which is regulated under the Colorado Department of Public Health and Environment CDPS General Permit and under the National Pollutant Discharge Elimination System. As noted in the March 31, 2023 DiNatale letter, with the slurry walls in place and the site operating under CDPHE Discharge Permit and a Spill Prevention Control and Countermeasure plan (SPCC) among other factors, it is unlikely that the site will be a source of contamination to the groundwater table. Responses to TR-02 Adequacy 1 With that background in place, CR has the following responses to the Division's points laid out in their March 10, 2023 TR-2 Adequacy letter: 1. No slurry walls have been constructed at the site as of yet. Construction for the north slurry wall is slated to begin summer of this year(2023). 2. As noted above, RMCC chose to include the Groundwater Quality Monitoring Plan in the overall Groundwater Monitoring Plan as part of the Adequacy Review Process and the application was subsequently approved. It is unclear which federal laws the Division is referring to in their comment as sand and gravel mining is considered "high-volume, low-hazard" and is thus exempt from regulation under the Resource Conservation and Recovery Act (RCRA) and has a SPCC for compliance under the Clean Water Act (CWA). In Adequacy Response 3, RMCC did commit to submitting the baseline data with a Technical Revision. RMCC did not commit to submitting an additional Sampling and Analysis Plan as this was submitted with Adequacy Response 3 as was indicated in the response letter, It was assumed that this plan was approved along with the Application in June 2021.