Groundwater quality, monitoring, and response
Wis. Stat. § 295.645
in effect(1) Definitions. In this section:
(a) “Alternative concentration limit” means the concentration of a substance in groundwater established by the department to replace a groundwater quality standard when the department grants an exemption.
(b) “Statistically significantly different” means an amount of change determined by the use of statistical tests for measuring significance at the 95 percent confidence level.
(2) Design management zone.
(a) Notwithstanding the rule-making authority in s. 160.21 (2) and except as provided under par. (b), for the purposes of ch. 160, the horizontal distance to the boundary of the design management zone for a mining operation is 1,200 feet from the limits of the engineered structures of the mining waste site, including any wastewater and sludge storage or treatment lagoons, the edge of the mine, and the adjacent mine mill and ferrous mineral processing facilities or at the boundary of the property owned or leased by the applicant or on which the applicant holds an easement, whichever distance is less.
(b) When issuing or modifying a mining permit or issuing or reissuing any other approval, the department may reduce the design management zone by a horizontal distance of not more than 600 feet. The department may not reduce the design management zone unless the department determines that preventive action limits and enforcement standards or alternative concentration limits will be met at the boundary of the reduced design management zone. The department shall consider the following factors in determining whether to reduce the design management zone:
1. Nature, thickness, and permeability of unconsolidated materials, including topography.
2. Nature and permeability of bedrock.
3. Groundwater depth, flow direction, and velocity.
4. Waste volume, type, and characteristics.
5. Contaminant mobility.
6. Distances to the property boundary and surface waters.
7. Engineering design of the facility.
8. Life span of the facility.
9. Present and anticipated uses of land and groundwater.
10. Potential abatement options if an enforcement standard is exceeded.
(c) Notwithstanding the rule-making authority in s. 160.21 (2), for the purposes of ch. 160, the vertical distance to the boundary of the design management zone for a mining site, including any mining waste site, extends no deeper than 1,000 feet into the Precambrian bedrock or than the final depth of the mining excavation, whichever is greater.
(d) An operator shall monitor groundwater quality at locations approved by the department along the boundary of the design management zone and within the design management zone.
(3) Point of standards application.
(a) Any point at which groundwater is monitored is a point of standards application to determine whether a preventive action limit or an alternative concentration limit to a preventive action limit has been attained or exceeded for an activity regulated under a mining permit or another approval related to the mining operation. Any of the following is a point of standards application to determine whether an enforcement standard or an alternative concentration limit to an enforcement standard has been attained or exceeded for an activity regulated under a mining permit or another approval related to the mining operation:
1. Any point of present groundwater use.
2. Any point beyond the boundary of the property on which the activity is conducted, subject to par. (b).
3. Any point that is within the boundary of the property on which the activity is conducted but is beyond the design management zone, subject to par. (b).
(b) No point at a depth of greater than 1,000 feet into the Precambrian bedrock or than the final depth of the mining excavation, whichever is greater, is a point of standards application under this subsection.
(c) Section 160.21 (2) does not apply to an activity regulated under this subchapter.
(4) Change in groundwater quality. If the analysis of samples collected through monitoring indicates that the quality of groundwater is statistically significantly different from either baseline water quality or background water quality and the evaluation of the data shows a reasonable probability that without intervention groundwater quality standards or alternative concentration limits will be attained or exceeded, the operator shall do all of the following:
(a) Notify the department within 10 days after the operator receives the results of the analysis of the samples.
(b) Determine, if possible, the cause of the difference in water quality, such as a spill, a design failure, or an improper operational procedure.
(c) Determine the extent of groundwater contamination or the potential for groundwater contamination.
(d) Implement the applicable portions of the approved contingency plan.
(5) Response concerning preventive action limits. In accordance with s. NR 140.24 (1) to (5), Wis. Adm. Code, the department shall evaluate the range of responses proposed by the operator when a preventive action limit or an alternative concentration limit to a preventive action limit is attained or exceeded and the analysis of samples indicates that the quality of groundwater is statistically significantly different from either baseline water quality or background water quality at a point of standards application. In designating the appropriate response, the department shall evaluate the operator’s proposed range of responses, including any alternate responses to those identified in s. NR 140.24, Wis. Adm. Code. For any alternate responses, the department shall consider the technical and economic feasibility of alternate responses, the practicality of stopping the further release of the substance, and the risks and benefits of continued mining operations. The department shall designate the appropriate response, except that, notwithstanding s. 160.21 (3) and the rule-making authority under s. 160.21 (1), the department may not prohibit a practice or activity or require closure and abandonment of a mining waste site, including any wastewater and sludge storage or treatment lagoon, unless it has followed the procedures in s. 295.78 and satisfies the requirements of s. 160.23 (4) and (6). The department may determine that no response is necessary and that an exemption is not required when the requirements of s. NR 140.24 (5) (a) or (b), Wis. Adm. Code are met.
(6) Response concerning enforcement standards.
(a) In accordance with s. NR 140.26 (1) and (2), Wis. Adm. Code, the department shall evaluate the range of responses proposed by the operator based on the responses listed in Table 6 of s. NR 140.26, Wis. Adm. Code, when an enforcement standard or an alternative concentration limit to an enforcement standard is attained or exceeded and the analysis of samples indicates that the quality of groundwater is statistically significantly different from either baseline water quality or background water quality at a point of standards application. In designating the appropriate response, the department shall evaluate the operator’s proposed range of responses against those identified in Table 6 of s. NR 140.26, Wis. Adm. Code. The department shall designate the appropriate response, except that, notwithstanding ss. 160.21 (3) and 160.25 (1) (a) and the rule-making authority under s. 160.21 (1), the department may not prohibit a practice or activity or require closure and abandonment of a mining waste site, including any wastewater and sludge storage or treatment lagoon, unless it has followed the procedures in s. 295.78 and all of the following apply:
1. The department bases its decision upon reliable test data.
2. The department determines, to a reasonable certainty, by the greater weight of the credible evidence, that no other remedial action would prevent the violation of the enforcement standard at the point of standards application.
3. The department establishes the basis for the boundary and duration of the prohibition.
4. The department ensures that any prohibition imposed is reasonably related in time and scope to maintaining compliance with the enforcement standard at the point of standards application.
5. If the substance involved is naturally occurring, unless the substance involved is carcinogenic, teratogenic, or mutagenic in humans, the department considers the existence of the background concentration of the substance in evaluating response options to the noncompliance with the enforcement standard or alternative concentration limit for that substance and determines that the proposed prohibition will result in the protection of or substantial improvement in groundwater quality notwithstanding the background concentrations of the substance.
(b) The department may only require a remedial action to be taken if the remedial action is reasonably related in time and scope to the substance, activity, or practice that caused the enforcement standard or alternative concentration limit to an enforcement standard to be attained or exceeded and the quality of groundwater to be statistically significantly different from either baseline water quality or background water quality at the point of standards application.
(c) If nitrates or any substance of welfare concern attains or exceeds an enforcement standard and if the analysis of samples indicates that the quality of groundwater is statistically significantly different from either baseline or background water quality, then the department shall evaluate whether the enforcement standard was attained or exceeded in whole or in part due to high background water quality concentrations of the substance and whether the additional concentrations represent a public welfare concern before it designates the appropriate response and, notwithstanding ss. 160.21 (3) and 160.25 (1) (a) and the rule-making authority under s. 160.21 (1), the department may not prohibit a practice or activity or require closure and abandonment of a mining waste site, including any wastewater and sludge storage or treatment lagoon, unless it has followed the procedures in s. 295.78 and par. (a) 1. to 4. apply.
(d) If compliance with an enforcement standard is achieved at a point of standards application, then sub. (5) applies.
(6m) Mandatory intervention boundary for mining waste site and mine.
(a) Except as provided under par. (am), the horizontal distance to the mandatory intervention boundary for a mining waste site is 300 feet from the outer waste boundary or the outer edge of the excavation, unless the boundary of the design management zone is within 600 feet of the outer waste boundary or the outer edge of the excavation, in which case the mandatory intervention boundary is one-half the distance from the outer waste boundary or the outer edge of the excavation to the boundary of the design management zone.
(am) The department may reduce the mandatory intervention boundary under par. (a) by a horizontal distance of up to 150 feet if the department determines that the reduction is necessary to adequately identify and respond to potential groundwater quality issues.
(b) An operator shall monitor groundwater quality at locations approved by the department along the mandatory intervention boundary, except for any portion of the mandatory intervention boundary that is within another mandatory intervention boundary, and within the mandatory intervention boundary. When approving locations for monitoring, the department shall ensure that duplicative monitoring is not required within overlapping mandatory intervention boundaries.
(c)
1. Notwithstanding sub. (5), if a preventive action limit or an enforcement standard has been exceeded beyond the mandatory intervention boundary, the department shall require a response in accordance with s. NR 140.24, Wis. Adm. Code, except that s. NR 140.24 (5), Wis. Adm. Code, does not apply.
2. If sampling results indicate that an enforcement standard or a preventive action limit has been exceeded within, but not beyond, the mandatory intervention boundary and a comparison of sampling results to the results of modeling indicates that the sampling results are consistent with the design and expected performance of the mining waste site, the operator may recommend a no response action, and the department may approve a no response action if that is authorized under s. NR 140.24 (5), Wis. Adm. Code.
(7) Environmental analysis not required. An action under sub. (5) or (6) with respect to a specific site does not constitute a major state action under s. 1.11 (2).
(8) Exemptions to groundwater quality standards. When issuing or modifying a mining permit or issuing or reissuing any other approval, the department may grant an exemption from a groundwater quality standard and establish an alternative concentration limit to a groundwater quality standard.
(9) Applicability of other law. Chapter NR 140, Wis. Adm. Code, applies to mining operations and mining sites, including mining waste sites, only to the extent that it does not conflict with this section.
Source: WI Statutes (Official Site)URL: https://docs.legis.wisconsin.gov/document/statutes/295.645Fetched: 10/7/2026