Wisconsin Administrative Code
Department of Natural Resources
NR 700-799 - Environmental Protection - Investigation and Remediation of Environmental Contamination
Chapter NR 726 - Case closure
Section NR 726.15 - Closure letters and continuing obligations

(a) A statement that the site will be included in the department database, and that if the property owner intends to construct or reconstruct a well, prior department approval is required, in accordance with s. NR 812.09(4) (w).

(b) A requirement that the property owner shall inform any purchaser of the property about the continuing obligations identified in the closure letter that apply to the property. The closure letter may also require the property owner to notify affected occupants of the need for specific continuing obligations.

(c) For conditions of closure that restrict site conditions, occupancy or property use from what is conditioned or identified in the final closure letter, a requirement that the property owner at the time that the condition changes shall notify the agency of the change in site condition, occupancy or land use, so that the agency can determine if further actions are necessary to maintain protection of public health, safety, or welfare or the environment.

(d) For conditions of closure that require maintenance, a requirement that the property owner operate and maintain the applicable system, cover or containment system in accordance with the operation and maintenance plan developed under ch. NR 724. The closure letter shall also include conditions regarding inspections, documentation, availability, and submittal of an inspection log, at a frequency determined by the agency.

(a) Residual groundwater contamination. If there is residual groundwater contamination at the time of case closure, the final closure letter shall include a description of the extent of groundwater contamination.

(b) Residual soil contamination. If there is residual soil contamination at the time of case closure, the final closure letter shall include a description of the extent of soil contamination, and shall state that any soil that is excavated in the future from an area that had residual soil contamination at the time of case closure shall be sampled, analyzed, handled, and disposed of as a solid waste in compliance with applicable state and federal laws.

(c) Monitoring well abandonment.

(d) Building, cover or containment structure for protection of groundwater. For sites or facilities where there is residual soil contamination beneath a building or a cover, such as concrete or asphalt pavement, a soil cover, or composite cover, or within an engineered containment structure, that exceeds residual contaminant levels based on protection of groundwater as determined under ch. NR 720, which would pose a threat to groundwater if the building, cover, or containment structure were removed, the closure letter shall include a description of the residual contamination and the location of the building, cover or containment structure, and shall require the property owner to take any steps necessary to ensure that the building, cover, or containment structure will function as intended, to protect the groundwater, as required by the applicable performance standard. The closure letter shall also require the property owner to maintain and repair or shall require the property owner to notify the agency prior to replacing the building, cover, or containment structure with a structure of similar permeability or with a cover that is protective of the new use until such time as further investigation demonstrates that the concentration of contaminants no longer exceeds residual contaminant levels that protect the groundwater, as determined under ch. NR 720.

(e) Building, soil cover, cover or containment structure for prevention of direct contact with soils. For sites or facilities where a building, or an engineering control, such as a soil cover, cover, or engineered containment structure is required to be maintained in order to prevent direct contact with contaminated soil within 4 feet of the ground surface that exceeds residual contaminant levels as determined under ch. NR 720, the closure letter shall include conditions which require the property owner to ensure that the building, soil cover, or cover such as concrete or asphalt pavement, or a composite cover, or engineered containment structure will be repaired and maintained until it is no longer needed. The closure letter shall include a description of the residual contamination and the location of the building, soil cover, cover, or engineered containment structure, and shall restrict the use of the land where the building, soil cover, cover, or engineered containment structure is located to ensure that the building, soil cover, or cover, will function as intended, to prevent direct contact, as required by the applicable performance standard. The closure letter shall also require the property owner to maintain and repair or shall require the property owner to notify the agency prior to replacing the building, soil cover, cover, or engineered containment structure with a structure of similar permeability or with a cover that is protective of the new use until such time as further investigation demonstrates that the concentration of contaminants no longer exceeds residual contaminant levels that protect human health from direct contact, as determined under ch. NR 720.

(f) Structural impediment. For sites or facilities where a building or other structural impediment at a site or facility has prevented the completion of an investigation to determine the degree and extent of residual contamination, or the completion of a remedial action, the closure letter shall include a description of the general location of the residual contamination and shall require the property owner to notify the agency and then conduct an investigation of the degree and extent of contamination at such time that the removal of structural impediments makes the formerly inaccessible contamination accessible.

(g) Industrial residual contaminant levels. For sites or facilities where industrial residual contaminant levels under ch. NR 720 have been applied for closure, the closure letter shall include a condition that restricts the use of that property to an industrial land use until non-industrial soil cleanup standards are achieved in the future through natural attenuation or additional remediation.

(h) Vapor mitigation system for sites where sub-slab levels attain or exceed the vapor risk screening level. The agency may require installation and operation of a vapor mitigation system for sites or facilities where sub-slab levels attain or exceed the vapor risk screening level. The closure letter shall include conditions which require the property owner to maintain the system until it is no longer needed. The closure letter may include conditions which require maintenance of certain structural features of existing buildings. The closure letter shall include conditions which require the immediate repair and replacement of system components that fail.

(i) Vapor mitigation system where compounds of concern are in use. The agency may require installation and operation of a vapor mitigation system for sites or facilities where the site is using the compounds of concern in their daily operations, in accordance with par. (h). The agency may require restrictions on the use or occupancy of the property to ensure that closure will be protective. The closure letter shall require notification of the agency and evaluation of the vapor intrusion pathway prior to changing use to a residential setting. The closure letter shall include a description of the type and location of the residual contamination.

Note: This would include sites or facilities where closure was based on worker exposure conditions, which then change to a different use, with different exposure assumptions.

(j) Vapor mitigation system for sites where vapor intrusion is of concern due to hydrogeologic conditions. The agency may require installation and operation of a vapor mitigation system and any other systems necessary for the proper operation of the vapor mitigation system, for sites or facilities which present a vapor risk, based on site-specific hydrogeologic circumstances. The closure letter shall identify the specific hydrogeologic conditions and a description of any other system necessary for the proper operation of the vapor mitigation system.

Note: This may include sites where contaminated groundwater enters the structure, or sites where the moisture content of soils below the slab is high or sub-slab samples are difficult to obtain, but where other conditions indicate the potential for vapor intrusion.

(k) Site-specific exposure conditions. The agency may restrict the use or occupancy of the property for sites or facilities based on specific exposure assumptions for vapor intrusion, to ensure that closure will be protective. The closure letter shall include the specific exposure assumptions on which the closure decision was based.

Note: This may include non-residential settings; sites or facilities where certain commercial or industrial exposures were applied at the time of closure, which later change to a residential setting, such as single or multiple family residences, or educational, child, or senior care facilities, where a residential exposure would apply.

(L) Potential for future exposure to vapors. For sites or facilities where residual soil or groundwater contamination from volatile compounds exists, but where no building is present, the agency may require protective measures to eliminate or control vapor intrusion into a future building. The closure letter may include conditions requiring that the agency be notified prior to any building construction, and a requirement that appropriate vapor control technologies be used in the construction of any building, unless an assessment is conducted which shows that the residual contaminant levels are protective of the new use.

Note: The potential for vapor migration into a future building is dependant on the type of building and the planned use of the building. Building control technologies may include but are not limited to passive barriers, passive venting, sub-slab depressurization, sub-membrane depressurization, sub-slab pressurization, building pressurization, and indoor air treatment.

(m) Site-specific conditions. For sites or facilities where closure is requested, and where the agency determines that there are site-specific circumstances that warrant site-specific closure conditions, the closure letter shall specify the exposure assumptions, use or occupancy restrictions, and necessary maintenance and notification of the agency if conditions change such that the exposure assumptions used no longer apply to the site, facility or property. Site-specific circumstances may include but are not limited to situations where contamination remains in media other than soil, groundwater, or vapors; or exposure and migration pathways not otherwise addressed make a continuing obligation necessary to adequately protect human health, safety, or welfare or the environment. If there is contamination remaining in media other than soil, groundwater, or vapor, the final closure letter shall also state that any sediments or other solids excavated in the future from an area that had residual contamination at the time of closure shall be sampled, analyzed, handled, and disposed of in compliance with applicable state and federal laws.