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

• Permit No: C2009087
• IBM Index Class Name: Permit File
• Doc Date: 7/9/2025
• Doc Name: Technical Memorandum
• Section_Exhibit Name: Technical Memorandum
• Media Type: D
• Archive: No

Technical Memo  Page 2 August 16, 2024
Peabody – CDPS Permit Supplement
Peabody requests that the following supplemental information be considered in the permit
renewal process as it relates to the selenium permit limit for both CO0000221 and
CO0048275.
The following table summarizes the current outfall number along with a proposed outfall
number revision, included in the draft public notice issued in June 2022; maps for the outfall
can be located in Attachments 1 – 4 of comments submitted on the draft permit, September 9,
2022. Corresponding regulatory segments and instream biomonitoring locations are also
included.
Table 1: Current and proposed revisions to the outfall number for Seneca Mine Complex and
Sage Creek Mine. The corresponding regulatory segments and instream
biomonitoring locations associated with the ongoing selenium study are also
included.
Current Outfall New Outfall
(DRAFT Permit)
Corresponding
Segment Number
(Applicable
Stream)
GEI Instream Monitoring
Location
(Corresponding Peabody
Monitoring Location)
Outfall 008 Outfall 025
COUCYA13g
(Cow Camp Creek
and Bond Creek)
G-BC-1 (SSB9A), G-BC-2,
G-BC-3 (SSB12)
Outfall 005
Outfall 006 -
COUCYA13g
(Cow Camp Creek
and Bond Creek)
G-CC-1 (SSC6),
G-CC-2 (SSC10)
Elevated selenium concentrations continue to occur during the snowmelt season associated
with climatic conditions that vary annually, which cannot be practically managed or
controlled. While the proposed numeric limits for the outfall to segment COUCYA13g
detailed in Table 1 are not yet effective, due to the proposed compliance schedule included in
the draft permit, when they do become effective, exceedances of a 30-day average selenium
limit set equal to the table value standard (TVS) of 4.6 µg/L would be demonstrated at the
outfall during higher-snowpack years.
2.Existing Dataset 2012 – Present
Since 2012, Peabody, with support from GEI Consultants, Inc. (GEI), has been conducting a
selenium study for drainages across multiple watersheds that receive discharge from the
outfall included in Table 1 and shown on Attachments 1 – 4 submitted September 9, 2022.
The study has included collection of samples to better characterize water quality, aquatic
communities, and selenium concentrations in fish and macroinvertebrate tissue as well as
sediment and periphyton, when and where available. This memo focuses on the fish tissue
collection that has been conducted as the recently finalized TSDs for implementation of the
2016 Criterion provide methods for determining reasonable potential (RP) based on selenium