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Cumulative Hydrologic Impact Assessment

What is a Cumulative Hydrologic Impact Assessment (CHIA)?

A Cumulative Hydrologic Impact Assessment (CHIA) determines whether the mining operation has been designed to prevent material damage to the hydrologic balance outside the permit area.

  • 30 CFR 780.21(g) requires OSMRE to complete a CHIA.
  • 30 CFR 780.21(g)(2) states "an application for permit revision shall be reviewed by the regulatory authority to determine whether a new or updated CHIA shall be required."
Image of a coal mine in West Virginia; in the foreground there is a water body at the base of a mine.

A CHIA assesses the probable hydrologic consequences (PHC) of the proposed operation and all anticipated coal mining upon surface and groundwater systems in the cumulative impact area (CIA). The PHC is prepared by the applicant as required by 30 CFR § 780.21(f), and approved by the regulatory authority. The hydrologic reclamation plan required by the rules at 30 CFR § 780.21(h) recognizes that disturbances to the hydrologic balance within the permit and adjacent area should be minimized, material damage outside the permit area should be prevented, applicable Federal, Tribal, and State water quality laws should be met, and the rights of present water users protected.

Additionally, 30 CFR § 816.42 states “discharges of water from areas disturbed by surface mining activities shall be made in compliance with all applicable State and Federal water quality laws and regulations and with the effluent limitations for coal mining promulgated by the US Environmental Protection Agency set forth in 40 CFR part 434.”

The 2016 Kayenta Mine Complex CHIA assesses that

  1. the hydrologic monitoring program is adequate for OSMRE’s CHIA,
  2. assesses if impacts within the permit area have been minimized, and
  3. that the operation and reclamation plans are designed to prevent material damage outside the permit area.

This 2016 Kayenta Mine Complex CHIA supersedes the previous Black Mesa Kayenta Mine Complex CHIA’s (OSMRE, 2011), (OSMRE, 2008), (OSMRE, 1989).

View the entire document here: 2016 Kayenta Mine Complex CHIA

  • Chapter 1 - Introduction
  • Chapter 2 - Cumulative Impact Area
  • Chapter 3 - Water Resources Uses and Designations
  • Chapter 4 - Baseline Hydrologic Conditions
  • Chapter 5 - Hydrologic Impact Assessments
  • Chapter 6 - Works Cited
  • Appendices

 

As the regulatory authority for the Navajo Transitional Energy Company (NTEC), a Navajo Nation owned Limited Liability Company (LLC), the Office of Surface Mining Reclamation and Enforcement (OSMRE) is required by 30 Code of Federal Regulations (CFR) § 780.21(g) to complete a cumulative hydrologic impact assessment (CHIA). The CHIA assesses whether the mining operation has been designed to prevent material damage to the hydrologic balance outside the permit area. Federal regulation 30 CFR § 780.21(g) states “an application for permit revision shall be reviewed by the regulatory authority to determine whether a new or updated CHIA shall be required.”

Several administrative activities have prompted the need for a CHIA update.  On September 30, 2025, NTEC submitted an application for a new permit area to be added to the Navajo Mine.  The new permit area is known as the No Name Permit Area (OSMRE Permit No. NM-0043A). The total mining and mining-related disturbance within the 11,526 acre permit area will be approximately 9,041 acres in Area 4 South and Area 5 of the Navajo Mine Lease Area.

An initial CHIA was prepared in 1984, and amended in 1989. The CHIA was significantly updated in 2012 and then again in 2015. This 2026 CHIA updates and supersedes the 2015 Navajo Mine Cumulative Hydrologic Impact Assessment (CHIA) to address a new permit component within the larger Navajo Mine complex, the No Name permit area.

This 2026 CHIA continues to evaluate all mining activities in the lease area, which are currently the Navajo Mine Permit Area, the Pinabete Permit Area, and the No Name Permit Area (collectively, the Navajo Mine). This 2026 update integrates (1) the 2015 CHIA framework and record; (2) updated applicant technical materials for the No Name permit area, including updated PHC documentation and supporting modeling; and (3) updated baseline and monitoring information available through 2025 (including groundwater and surface water quality summaries and related QA/QC documentation).

The finding that the mining operation is designed to prevent material damage to the hydrologic balance outside the permit area is supported by the following chapters. The CHIA is organized as follows:

  • Chapter 1 describes the regulatory environment and general background of the assessment area.
  • Chapter 2
    • Assesses the cumulative impact potential with historical and active coal mines.
    • Delineates the surface water CIA.
    • Delineates the groundwater CIA.
  • Chapter 3 identifies water resource uses and water use designations within the CIAs.
  • Chapter 4 provides a description of baseline surface- and groundwater quantity and quality within the CIAs.
  • Chapter 5 contains an impact assessment of the mining operation on surface- and groundwater quantity and quality, and includes a determination of:
    • The minimization of impacts within the permit/lease area; and,
    • The adequacy of the monitoring program to assess potential impacts.
  • Chapter 6 Analyzes potential changes with respect to material damage designations and presents the CHIA findings statement.

View the entire document here: 2026 Navajo Mine Complex CHIA

OSMRE is the regulatory authority for Peabody Western Coal Company (PWCC) surface coal mining and reclamation operations at the Kayenta Complex. A revision to PWCC's permit application package was submitted to OSMRE in September, 2010, and OSMRE subsequently determined the CHIA should be updated.

This most current update to the CHIA (2011) replaces the 2008 updated CHIA and the original CHIA written in 1989.

View the entire document here: 2014 John Henry No.1 Mine CHIA

  • Chapter 1 - Introduction
  • Chapter 2 - Water Resource Uses and Applicable Water Quality Criteria
  • Chapter 3 - Characterization of Baseline Hydrologic Conditions
  • Chapter 4 - Hydrologic Impact Assessment
  • Chapter 5 - Material Damage Criteria
  • Chapter 6 - Works Cited
  • Appendices