2021-07-21_PERMIT FILE - C1981019 ‎(5)‎

• Permit No: C1981019
• IBM Index Class Name: Permit File
• Doc Date: 7/21/2021
• Doc Name: Point of Compliance Well Investigation Report
• Section_Exhibit Name: Exhibit 07 Item19 Point of Compliance Well Investigation Report
• Media Type: D
• Archive: No

Point of Compliance Well Investigation

AECOM
2

1.2 Previous Studies
To address Stipulation 7, Colowyo previously completed a review of existing groundwater quality
data for the Mine (Peterson Hydrologic, LLC 2015). The objectives of this review were as
follows:
• Characterize the shallow groundwater systems in Wilson Creek, Taylor Creek, and Good
Spring Creek drainages in the vicinity of the Mine;
• Determine whether there is evidence that mining- and reclamation-related activities have
had detrimental impacts to water quality in the groundwater systems in these drainages;
• Determine the likelihood that impacts to these groundwater systems may occur in the future
as a result of the mining- and reclamation-related activities at Colowyo Mine; and
• Provide recommendations regarding the need for groundwater points of compliance.
The Petersen Hydrologic report concluded that groundwater points of compliance were not
required due to several factors including exceedances of water quality standards in upgradient
areas, lack of domestic and agricultural wells in the downgradient alluvial valleys, limited
potential for vertical groundwater migration, low recharge to the alluvium, mitigation through
post-mining reclamation, and lack of significant impacts to sampled groundwater in the alluvial
valleys.
An expanded Points of Compliance Evaluation Report was subsequently prepared by AECOM
(2018). The AECOM report included further analysis of hydrologic data collected both prior to
and after the 2015 Peterson Hydrologic report. The study also evaluated specific
considerations for establishing points of compliance as contained in the Rules and Regulations
of the Colorado Mined Land Reclamation Board for Coal Mining (1980 et seq.), Rule
4.05.13(1)(b). Based on the data analyzed and AECOM’s interpretation of the rule, it was
concluded that groundwater points of compliance were not needed for Colowyo Mine. This
conclusion was reached considering the degraded water quality in alluvial groundwater
upgradient from the Mine; the lack of water supply wells downgradient of the Mine in the alluvial
valleys; the success of reclamation at the Mine and lack of increasing trends in constituent
concentrations since 2006; and the low risk of lateral and vertical migration of alluvial
groundwater into the surrounding bedrock.
The Division responded on November 6, 2018 with an adequacy review of the AECOM report
but did not agree to remove the permit stipulation requiring point of compliance wells. In March
2019, AECOM assisted the Mine in preparing a response letter discussing key details of the
Points of Compliance Evaluation report. After submittal of this response letter, the Division
reiterated their stance that compliance wells were needed. In a letter dated April 2, 2019, the
Division requested that Colowyo provide updated text and maps as necessary including point of
compliance well locations to satisfy Rule 4.05.13.
1.3 2019-2021 Groundwater Investigation Approach and Objectives
Colowyo already has three downgradient monitoring wells at the Mine: Gossard Well in the
Wilson Creek drainage, MT-95-02 in the Taylor Creek drainage, and NGSW in the Good Spring
Creek drainage (Figure 1). However, these wells are known to contain elevated concentrations
of some monitored constituents, and therefore may not be suitable as permanent point of
compliance wells. Rule 4.05.13(1)(b) also states that “points of compliance shall be monitoring
locations in addition to any other monitoring points required by the Division”, implying that
separate point of compliance wells are needed to meet the intent of the Rule. Colowyo thus