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Home My WebLink AboutDWQ-2024-005195STATEMENT OF BASIS GROUND WATER DISCHARGE PERMIT NO. UGW270001 MATERION NATURAL RESOURCES TAILINGS POND January 2024 PURPOSE The purpose of this statement of basis is to describe the Materion Natural Resources(Materion, formerly Brush Resources) tailings pond facility and changes made to the permit as part of the permit renewal process. DESCRIPTION OF FACILITY AND BACKGROUND INFORMATION The Materion beryllium mill is located approximately ten miles north of Delta, in Millard County, Utah. The plant was constructed in 1968 and began operation in 1969. The plant extracts beryllium from bertrandite ore mined at Materion’smine located about fifty-five miles to the west, and from high-grade beryl ores imported from throughout the world. The facility also reprocesses beryllium hydroxide precipitate from Materion’srefinery in Elmore, Ohio. The beryllium concentrate produces a moist precipitate, which is packaged in drums and shipped to Materion’s refinery in Ohio. All plant wastewater and tailings are currently disposed of in a 220-acre tailings storage facility(TSF1) at the plant site. TSF1 has received all of the wastewater and tailings from the mill facility since 1969. Subsurface investigations conducted by Materion discovered that a seepage mound had developed in previously unsaturated sediments beneath the tailings pond. The original ground water discharge permit required the permittee to modify the tailings pond to reduce the seepage rate and to take measures to protect groundwater from potential contamination. As the result of studies, a discharge minimization technology (DMT) was approved for the existing facility and incorporated into the permit as performance criteria. To comply with permit requirements during previous permit terms, Materion has completed slime sealing ofTSF1, installed an additional 20 monitoring wells to better define the seepage mound footprint, installed 34 and continues to maintain 31 seepage mound recovery wells, and acquired all the land overlying the current seepage mound footprint and its projected lateral extent. DMT instituted by Materion during previous permit terms to reduce seepage mound volume will continue through the current permit term. Materion will begin operation of a 100-acre tailings pond expansion (TSF2) in 2024. To comply with permit requirements during the 2019-2024 permit term, Materion presented a water balance in the Seepage Mound Stabilization Report submitted along with the TSF2 Detailed Design Report to the Division of Water Quality (DWQ) in 2021. The result of the water balance was sizing and operation parameters of the TSF1 enhanced evaporation system given the size and operation parameters of TSF2. Adherence to these parameters should minimize the wetted area and depth of pooling in TSF1 thus reducing infiltration and eventually the volume of the seepage mound. SITE HYDROGEOLOGY The mill site is located in the SevierBasin of the Basin and RangePhysiographicProvince. This province includes the isolated deserts, valleys, and salt flats of western Utah. The SevierBasin was formed as a result of faulting during late Miocene time, and was then filled with unconsolidated deposits of eolian, fluvial, and lacustrine origin. Recharge to the valley-fill sediments is primarily infiltration of snow melt, surface runoff, and direct precipitation. Ground water recharge to the area is predominantly from the North Tintic and TinticMountains to the northeast. Ground water discharge is principally through evapotranspiration, interbasin flow, and ground water pumpage by wells. The subsurface stratigraphy of the site is comprised of shallow sediments underlain by two permeable aquifers. All three zones are separated by laterally extensive clay layers that act as aquicludes. Shallow sediments are stratified units comprised of gravels, sands, and silts that are considered highly permeable but are not saturated by naturally occurring recharge processes. Seepage from TSF1 has led to saturation of vadose zone sediments from the surface to the top of the first clay aquiclude. The aerial extent of this seepage mound is documented by extensive monitoring well control and is currently contained on land owned by Materion. Saturated sediments represent a multiple aquifer system and are zoned into two coarse-grained, permeable aquifers: an upper confined aquifer, and a lower confined aquifer. The upper artesian aquifer consists primarily of silty, fine to medium coarse sand and sandy gravel, with some local silty fine sand layers. Based on water level measurements, an upward hydraulic gradient exists in this aquifer. Wells completed in the upper artesian aquifer are monitored by compliance wells as one componentof the compliance monitoring program for the site. The lower confined aquifer is used as a water supply source for the general area. GROUND WATER CLASSIFICATION The ground water classification of the upper artesian aquifer under the tailings pond is Class IA Pristine ground water to Class II Drinking Water Quality ground water with an average total dissolved solids (TDS) of approximately 465mg/l. Class IA quality ground water is found in upgradient monitoring wells MW-31 (408 ± 41 mg/L) and NSW (334 ± 80 mg/L) and downgradient wells DH-55 (499 ± 115 mg/L) and DH-56 (497 ± 27 mg/L).Upgradient well DH14 (535 ± 569 mg/L) and downgradient monitoring well DH-57 (526 ± 24 mg/L) contain Class II Drinking Water Quality ground water.The average upgradient TDS concentration is 414 ± 303mg/L while the average downgradient TDSconcentration is 508 ± 70 mg/L. Background water quality is based on historical data prior to original permit issuance and subsequent compliance data collected as a permit requirement from the monitoring wells screened in the upper artesian aquifer. These wells are listed in Table 1 of this Statement of Basis. Materion has also conducted numerous hydrogeologic investigations of aquifer conditions and water quality. BASIS FOR SPECIFIC PERMIT CONDITIONSThe intent of the discharge minimization technologyis to stabilize the extent and ultimately reduce the volume of the unsaturated zone seepage mound by dewatering portions of the mound. Materion will pump the maximum amount of water possible from the seepage mound extraction pumping system. The focus of the mound stabilization is to pump from the highest producing recovery wells with secondary effort employed on locations that have limited production and a higher propensity for monitoring well and pump repairs.If it is determined that the seepage mound recovery system extraction rate is insufficient to keep up with TSF1 seepage, and mound volume increases by more than 10%, a minimum extraction rate may again be invoked as a DMT requirement by DWQ. Final containment and dissipation of the seepage mound is addressed in the currently approved Closure Plan prepared by Materion as well as in the water balance presented in the TSF2 Detailed Design Report.