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CIVIL RES'SOURCES, LLC ENGINEERS & PLANNERS March 1711,2023 Colorado Division of Reclamation and Mining Safety Mr. Eric Scott 1313 Sherman Street,Room 215 Denver, CO 80203 RE: Technical Revision 5-Heit Mine(Permit M-2003-016),Weld County, Colorado Dear Mr. Scott: The City and County of Broomfield (CCOB) requests a Technical Revision (TR) to Permit M-2003-016 to allow for the cessation of groundwater level monitoring at the Site. A site location map is provided on Figure 1. Background The CCOB applied for and was granted a Succession of Operators(SO)to become the holder of the DRMS Reclamation Permit in February of 2023. On March 2°d, 2023, CCOB was informed by the Division of the requirement to report monthly groundwater levels from piezometers located in the area surrounding the Site. Civil Resources, LLC. (CR) sent personnel to monitor these wells on March 3rd, 2023. The water levels measured by CR were added to the tables submitted to the Division by Pioneer in January 2022 and are included in Attachment C. The initial monitoring plan for the Site included ten (10) piezometers, MW-1 through MW-10. These piezometers were measured monthly for eighteen (18)months starting in March 2004 to obtain baseline data prior to construction of a soil- bentonite slung wall (slurry wall)around the Site. Monitoring for baseline groundwater elevations ended in August 2005. The slurry wall construction was completed in June 2007 and eight (8) piezometers (MW-11 through MW-18) were subsequently drilled in April 2008 for the 90-day provisional leak test. Groundwater elevation monitoring of MW-11 through MW-18 began in March 2009 and continued until June 2009, at which point the slurry wall was provisionally approved by the State Engineer's Office(SEO). The slung wall was fully approved by the SEO on June 24,2009. No groundwater elevation monitoring took place at the Site from June 2009 until September 2013. In September 2013, the Division performed a routine inspection where water level monitoring was discussed and instruction given to the Site representative by the Division, after which monthly groundwater level monitoring began again on all wells exterior to the slurry wall (MW-1 through MW-11, MW-13, MW-15,and MW-17). MW-5, located between the Heit and Lupton Meadows slung walls was removed by BURNCO in 2017. Water level monitoring continued on the rest of the wells until December 2022. During the groundwater elevation monitoring performed by CR on March 3rd, it was determined that in addition to MW-5 (removed in 2017), MW-6, MW-8, and MW-11 have also been removed. Heit Pit Slurry Wall Effects on Groundwater Elevation In order to determine the effect that the Site and slurry wall had on the surrounding groundwater table the eighteen months of baseline measurements were broken out per month and a minimum and maximum value of plus or minus three (3)feet was set for each month. The three (3)foot value was determined to be the acceptable limit by the Mined Land Reclamation Board (MLRB) decision on September 24, 2003 (see Attachment B). No baseline data was collected for MW-11 through MW-17 and they were not included in this analysis. See graphs for each well compared to baseline in Attachment A. 8308 COLORADO BLVD•SUITE 200 9 FIRESTONE,CO 80504•PHONE: 303.833.1416 9 FAX: 303.833.2850