MIRBCA FAQ: Groundwater Protection Pathway

The groundwater protection pathway is complete for current use when there are water supply wells that are potentially impacted from the confirmed release.  This is true for sites in municipal areas, for rural areas, and areas where groundwater is not in an aquifer.  A well survey is necessary to determine if there are any wells in the area.  Any potentially impacted well must be evaluated.  The level of effort in conducting the well survey is site-specific and depends on the likelihood of impacted water supply wells being present.

The groundwater protection pathway is complete for future use at most sites, regardless of whether it is complete for current use, whether the area is on municipal water, or whether the area properties are required by an ordinance to connect to municipal water.  With limited exceptions, the pathway is complete for future use if groundwater is in an aquifer.  Refer to MIRBCA Forms 13(2) and 13(3) and MIRBCA Appendix B for conditions to conclude that the groundwater protection pathway is not complete for future use.  In Tier 1, the future use risk is evaluated by assuming that exposure would occur from a future well installed at any point in the affected aquifer onsite and on impacted offsite properties.  In Tier 2, the future risk is evaluated at the source area and points of compliance based on a site-specific point of exposure.

A restrictive covenant or other institutional control can be used for future use to i) restrict a property’s land use to nonresidential to allow for comparison with nonresidential RBTLs for future use, or ii) eliminate the future exposure in an area.  If the future risk is unacceptable, the future risk must be addressed by either reducing the concentrations or by eliminating the pathway.  The future risk is unacceptable in a Tier 1 evaluation when the recent maximum groundwater concentrations on a property are above Tier 1 RBSLs.  The future risk is unacceptable in a Tier 2 evaluation when the recent average concentrations at specific points are above Tier 2 SSTLs.  The difference between a Tier 1 and Tier 2 evaluation is that a Tier 1 evaluation assumes that a future well could be installed at any point in the affected aquifer, and therefore risk is evaluated by the maximum concentration on each impacted property.  In Tier 2, however, a site-specific point of exposure is determined for future use.  The risk is evaluated by comparing representative concentrations at locations that would contribute to the future risk (e.g., source area, points of compliance located between the source area and the point of exposure).  If the representative concentrations in the source area and points of compliance are below SSTLs for these locations, then the future risk (at the point of exposure) is acceptable and a restrictive covenant or other alternative mechanism is not needed, even though concentrations may be above Tier 1 RBSLs.  If representative concentrations exceed applicable Tier 2 SSTLs, this indicates that the future risk is not acceptable and additional evaluation or corrective action is necessary.

Determining a future use point of exposure (POE) for the groundwater protection exposure pathway is discussed in MIRBCA Section 5.4.  In Scenario 1, there are no current or reasonable future water supply wells within 300 feet of the site property boundary.  The POE in Scenario 1 is 300 feet downgradient from the edge of the source area.  In Scenario 2, there are no current or reasonable future water supply wells on the site property, but there is either a current or reasonable future water supply well within 300 feet of the site property boundary.  The POE in Scenario 2 is at the nearest downgradient property boundary, excluding rights-of-way or restricted areas.  In Scenario 3, there is a current water supply well or a reasonable future well on the site property.  The POE for Scenario 3 is any point in the affected property onsite and on all impacted offsite properties.  The applicable RBTLs at the POE for Tier 1 and Tier 2 are given in Table 13 of the MIRBCA guidance document.  Tier 2 SSTLs for the source area and points of compliance must be calculated for each site.

In a Tier 2 evaluation, a point of exposure for future use is determined based on site-specific information.  The future risk is evaluated based on exposure occurring at the POE and not at other locations.  Although a site-specific POE is established for future use, this point is usually not directly evaluated.  Certain locations, including the source area and points of compliance located between the source and the POE, are selected as points where future risk will be evaluated.  These points are located along the transport pathway and are used to predict the concentrations at the POE and thus evaluate future risk at the POE.  Concentrations at other locations are not considered because these locations are not along the transport pathway, and therefore concentrations at these locations are not useful in evaluating future risk.

Regardless of the presence of an ordinance, the groundwater protection pathway must be evaluated for current and future use.  A well survey must be conducted to determine existing water supply wells.  If there are potentially impacted wells, the groundwater protection pathway is complete for current use and the wells must be evaluated to determine if the current risk is acceptable.  In a Tier 1 evaluation, it is assumed that a future well could be installed at any point in the affected aquifer, regardless of an existing ordinance.  A restrictive covenant or an alternative mechanism, including a groundwater use ordinance, can be used to eliminate the pathway for future use.  This is usually implemented in a Tier 1 evaluation.  In a Tier 2 evaluation, a site-specific location for a future well is established.  This site-specific point is based on multiple lines of evidence, one of which could be the presence of an ordinance.  In a Tier 2 evaluation, representative concentrations that exceed SSTLs at the source area or points of compliance indicate that the future risk is not acceptable and additional evaluation or corrective actions are necessary.

When relying on an ordinance as an alternative mechanism to eliminate the groundwater protection pathway for future use, the ordinance must comply with Section 10a of Part 213, including but not limited to: the ordinance must include a requirement for the local unit of government to notify EGLE within 30 days of any change to the ordinance; the ordinance must be recorded on properties affected by the ordinance or recorded as an instrument that affects multiple properties.  Other requirements to ensure that the ordinance is reliable, enforceable, and protective include a purpose statement that the ordinance is prohibiting groundwater use to prevent exposure to environmental contamination, a reference to the existing release, and an identified restricted area that is connected to the release.  Refer to EGLE’s Institutional Controls Technical Assistance and Program Support (TAPS) team for assistance. 

The groundwater protection pathway is considered complete for future use when groundwater is in an aquifer.  Regardless of the presence of municipal water, the groundwater protection pathway must be evaluated for current and future use.  A well survey must be conducted to determine existing water supply wells.  If there are potentially impacted wells, the groundwater protection pathway is complete for current use and the wells must be evaluated to determine if the current risk is acceptable.  In a Tier 1 evaluation, it is assumed that a future well could be installed at any point in the affected aquifer, regardless of an existing municipal water system.  A restrictive covenant or an alternative mechanism can be used to eliminate the pathway for future use.  This is usually implemented in a Tier 1 evaluation.  In a Tier 2 evaluation, a site-specific location for a future well is established.  This site-specific point is based on multiple lines of evidence, one of which could be the presence of a municipal water system.  In a Tier 2 evaluation, representative concentrations that exceed SSTLs at the source area or points of compliance indicate that the future risk is not acceptable and additional evaluation or corrective actions are necessary.

The risk for both current use and future use must be at acceptable levels.  A well survey must be conducted to identify any water supply wells.  Any potentially impacted wells must be evaluated to determine if the risk for current use is acceptable.  Assuming that current risk is acceptable, there are several options to evaluate and address future risk.  If the results of a Tier 1 evaluation determine that the future risk is unacceptable, options to address it include: i) monitoring or remediation until the representative concentrations meets applicable Tier 1 RBSLs, ii) eliminating the pathway for future use by restricting the applicable area with either a restrictive covenant or alternative mechanism (health department alternative mechanism, relying on an ordinance as an alternative mechanism, etc.), or iii) conducting a Tier 2 or 3 evaluation.