2025-07-09_PERMIT FILE - C2009087 (10)

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Technical Memo  Page 4 August 16, 2024 Peabody – CDPS Permit Supplement •Evaluation of selenium concentrations in water (potentially dissolved, dissolved, and total fractions) Collected on an ongoing basis instream and at outfalls by mine personnel 2.2 Summary of Selenium Study Results The limited presence of water throughout many of these drainages, especially in the upper reaches, adversely impacts the ability of these streams to support robust fish communities except for select downstream locations on Cow Camp Creek and Bond Creek. Flow conditions vary substantially throughout the year with some sites being partially or completely frozen in winter, and only intermittently wetted during snowmelt runoff and precipitation events. In addition, the overall habitat complexity, as determined by the number and type of habitat units observed, is generally low at most sites. These conditions have been well documented in past Use Attainability Analyses (UAAs) submitted during previous basin hearing cycles, including GEI 2014 and 2017, and the selenium study updates provided in 2020, 2021, 2022, and 2023 (GEI 2014, 2017, and 2020, 2021, 2022, 2023). Seasonal sampling has revealed marginal benthic macroinvertebrate populations and the absence of fish in the upper reaches of Cow Camp and Bond creeks. Fish have been present in almost all years in the lower reaches of Bond Creek Site G-BC-3, with only limited populations present in some years in the lower reaches of Cow Camp Creek. The intermittent flow and natural obstructions (e.g., plunge pools, beaver dams, wetlands, and seasonal drying) limit the ability of Cow Camp Creek to support reproducing fish populations consistently over time. Cow Camp and Bond creeks have flow durations that are restricted predominantly to the snowmelt runoff period and often exhibit no flow by mid-to-late summer. Therefore, the collection of fish tissues for analysis has focused on spring monitoring for the lower extent of each drainage. Selenium concentrations in the macroinvertebrate tissue collected is typically lower in the upper drainage and then increases downstream, fish tissue results have also followed a similar trend at the lower sample locations where populations persist, largely in response to the influx of naturally occurring selenium from underlying geology. While Creek Chub and White Sucker are both considered trophic level 3 species under the EPA’s TSDs, fish tissue results indicate that Creek Chub generally have higher selenium tissue concentrations compared to White Sucker at these sites. Creek Chub are also the more common species found within these drainages, so the larger dataset available for Creek Chub may be impacting this trend. All sites discussed in this memo located on Cow Camp and Bond creeks, even if the reach is fish-limited, show mean values by species for the comprehensive dataset below the EPA’s whole-body fish tissue criterion of 8.5 milligrams per kilogram dry weight (mg/kg dw). The dataset for egg/ovary samples is limited and should be interpreted cautiously. The 2016