11 Miss. Code. R. 3-2.2.2 - Brownfield Site Evaluation

A. Conceptual Exposure Model (SCEM)

(1) The SCEM is a graphical representation of actual and potential Site conditions based on available data and an understanding of those Site conditions. A BASELINE and a REMEDIAL SCEM must be completed and are provided in forms prescribed by MDEQ. The BASELINE SCEM represents the risk and exposure conditions that exist prior to the implementation of remediation. The REMEDIAL SCEM represents the risk and exposure conditions that exist or are expected to exist after the implementation of remediation. Items to be identified in the SCEM include the following:

(a) chemical of concern (CoC) sources;

(b) CoC movement (migration/transport);

(c) the actual or potential exposure pathways; and

(d) the actual or potential receptor populations.

(2) Based on the results of the completed BASELINE SCEM, exposure point concentrations (EPCs) must be identified for CoC(s) with completed and potentially completed exposure pathways. EPCs are the concentrations of site-related compounds in a specific media that a human or environmental receptor will contact (Complete) or may potentially contact (Potentially Complete) through ingestion or inhalation at the point of exposure.

(3) All four elements identified in the SCEM must be complete for exposure to occur. It is important to note that the BASELINE SCEM should be developed early in the process (i.e., Brownfield Application and/or work plan stage) and identified as "draft" if additional information is pending. The BASELINE SCEM can be updated and modified as the site investigation progresses and more site-specific information becomes available. BASELINE SCEM should be identified as "final" once the Site Characterization is complete.

(4) If additional issues of concern pertaining to exposure at the site (additional pathways, media, sources, transport mechanisms, receptors, etc.) are not specifically addressed in the SCEMs, the Applicant should provide an attachment(s) to the appropriate SCEM discussing the additional issues.

(5) The BASELINE and REMEDIAL SCEM worksheets must be included as part of the Site Characterization Report and the Corrective Action Report.

(6) The procedures for completing the SCEMs follow:

(a) Identify the Primary Sources (on-site and off-site) of contamination that exist or are believed to have existed.

(b) Identify the Secondary Sources. Mark the media (soils, groundwater, sediments, or surface water) that have been impacted (Complete) or could potentially be impacted (Potentially Complete) by a release from a primary source.

(c) Identify the Transport Mechanisms by which the contaminants may move through the environment.

(d) Identify the Exposure Pathway that is the medium (soil, groundwater, air, sediments, or surface water) that a receptor will contact (Complete) or may contact (Potentially Complete).

(e) Identify the Actual (Complete) and the Future (Potentially Complete) Receptors for restricted and unrestricted land-use.

B. Criteria For Completing The SCEMs

(1) BASELINE SCEM - The following sections describe the criteria for evaluating the completeness and potential completeness of contaminant exposure for the Site. All potential exposure pathways should be evaluated for completeness, as identified in the SCEM worksheets. The Applicant should provide as much detail as possible. Indicate all sources, transport mechanisms, pathways and receptors that are complete or potentially complete. If information is not available to support a pathway as incomplete then that pathway should be considered to be potentially complete and should be identified for evaluation until such information becomes available. A description of each of the BASELINE SCEM criteria is provided in the following sections.

(a) Sources can be defined as either Primary Sources or Secondary Sources. Primary Sources are those present or past storage units (i.e., tanks, impoundments, piles), distribution systems (i.e., piping, manifolds, lines, pumps), operations (i.e., wash areas, repair bays, water treatment, blending tanks, formulation areas), waste management units (i.e., burn pits, disposal units, dumps) and other on-site and off-site sources of actual or potential contamination that have or may have leaked, leached, spilled, or otherwise been released and may have impacted the Site. Several categories of potential primary sources are included on the SCEM worksheet and can be identified by filling in the appropriate boxes on the worksheet. If the sources listed do not pertain to the Site, then use "Other". The Applicant should be as specific as possible about the source of contamination. Supporting documentation (i.e., analytical results, product storage/transmission information, tank information, etc.) of the primary source of contamination should be provided in the appropriate section(s) of the Work Plan and/or Site Characterization Report.

Secondary Sources are defined as transport media (i.e., surficial soils, subsurface soils, groundwater, sediments, or surface water) that have been impacted or potentially impacted by the primary (release) source. Identify all media that may serve as secondary sources of contamination. For the purposes of this Subchapter 2 surficial soil is defined as extending to 6 ft. below ground surface (bgs). The presence of CoCs that cannot be attributed to background should be identified as "complete," and any secondary source that is potentially affected by an on-site or off-site primary source should be identified as potentially complete." The Applicant must provide adequate documentation to demonstrate that a secondary source has not been affected in order to remove that medium from further consideration. If such documentation has not yet been gathered to support the exclusion of a secondary source, then that medium must be identified as "potentially complete" until such time as such information becomes available. The BASELINE SCEM can be updated as additional site-specific data are gathered.

(b) Transport Mechanisms are means by which the CoC release can migrate from the identified secondary sources and result in actual or potential human exposure. A variety of potential transport mechanisms are generally applicable to a site. Indicate on the BASELINE SCEM Worksheet those transport mechanisms that are applicable or potentially applicable to the site. Those transport mechanisms identified as applicable or potentially applicable should be marked "complete" or "potentially complete," respectively.

(1) Surficial Soils - If surficial soil has been identified as a secondary source, then the following transport mechanisms must be identified as "complete" or "potentially complete":

(i) Wind Erosion and Atmospheric Dispersion (For Non-Volatile Compound Only)

(ii) Volatilization and Atmospheric Dispersion (For Volatile Compounds Only)

(iii) Volatilization and Enclosed-Space Accumulation (For Volatile Compounds Only)

(iv) Leaching and Groundwater Transport

Note: The Soil Exposure Pathway must also be identified as "complete" or "potentially complete" if surficial soil has been identified as a secondary source.

(2) Subsurface Soils - If subsurface soil has been identified as a secondary source, then the following transport mechanisms must be identified as "complete" or "potentially complete":

(i) Volatilization and Enclosed-Space Accumulation (For Volatile Compounds Only)

(ii) Leaching and Groundwater Transport

(3) Groundwater - If groundwater has been identified as a secondary source, then the following transport mechanisms must be identified as "complete" or "potentially complete":

(i) Volatilization and Enclosed-Space Accumulation (For Volatile Compounds Only)

(ii) Leaching and Groundwater Transport

(4) Sediments or Surface Water - If sediment or surface water has been identified as a secondary source, then Surface Water Runoff or Surface Water Transport must be identified as "complete" or "potentially complete."

(c) Exposure Pathways are the processes by which human uptake or exposure to site-related compounds may occur. Identify all "complete" or potentially complete" exposure pathways at the Site that may provide a means for human exposure. All exposure pathways should be identified as potentially complete if supporting information for the exclusion of the pathway is not currently available.

(1) Soil - If surficial soils are affected, then direct exposure through incidental ingestion must be indicated as complete or potentially complete. Contamination in surface and subsurface soils may be available for exposure through direct contact during intrusive activities, such as construction. The future use of the site and any plans for construction should be considered when evaluating the completeness of direct contact to subsurface soils.

(2) Air - Contamination of surface soil provides the potential for human uptake or exposure through inhalation of vapor from volatile compounds and through inhalation of non-volatile compounds that have adsorbed to surface soil particulates. Contamination of subsurface soil provides the potential for human uptake or exposure through inhalation of vapor from volatile compounds (i.e., migration into basements or during intrusive activities such as construction) and through inhalation of nonvolatile compounds that have adsorbed to subsurface soil particulates during intrusive activities, such as construction. In addition, the presence of volatile compounds in groundwater at the site produces the potential for volatilization into air (i.e., migration into basements, depth to groundwater is less than six (6) feet or intrusive activities).

(3) Groundwater - Contamination of groundwater requires that the Groundwater Exposure Pathway be marked as "complete" in the BASELINE SCEM. Surface and subsurface soils capable of leaching into groundwater at levels above the Groundwater TRG require that the Groundwater Exposure Pathway be marked as "complete" in the BASELINE SCEM. The presence of CoCs in surface and subsurface soils requires that the Groundwater Exposure Pathway be marked as "potentially complete" in the BASELINE SCEM. The Applicant must provide adequate documentation to demonstrate that CoCs in surface and subsurface soils will not leach into groundwater in order to remove that medium from further consideration. If documentation has not been gathered to support the exclusion of exposure pathway, that pathway must be identified as "potentially complete." The BASELINE SCEM can be updated as additional site-specific data are gathered.

(4) Surface Water - The exposure pathways applicable to surface water are included in the SCEM Worksheet in order to protect surface water bodies that may be used for domestic or recreational purposes. The presence of site-related compounds in soils, sediments, surface water, or groundwater provides the potential for migration or discharge to either on-site or off-site surface water bodies that may be used for recreational purposes, for a potable water supply, or for livestock watering. If contaminants are present in onsite media and such a surface water body is present within 500 ft. of the Site boundary, the pathway should indicate "potentially complete." Provide documentation in the Work Plan and/or the Site Characterization Report that a water body is not associated with or affected by the Site.

(d) The identification of Potential Receptor populations at the site is an important part of the completion of the BASELINE SCEM. It is important to know as much about the current and potential future use of the site and receptor populations, as possible. The receptor populations and the planned future use of the site are integral in supporting the remedial options at the site. Any and all potential receptor populations that could be exposed to site-related compounds should be identified on the BASELINE SCEM.

(2) REMEDIAL SCEM - Once the BASELINE SCEM has been completed, remedial options (i.e., institutional controls, engineering controls, or active cleanup) for the Site that can "shut off" or eliminate exposure to contamination should be evaluated. Those complete and potentially complete exposure routes linking sources to receptor populations must be remediated using one or a combination of options. Free product must be remediated in a manner consistent with Rule 2.2.6(A)(4)(d). The REMEDIAL SCEM includes shut-off valves to graphically depict "open" or "closed" pathways between contaminated media and the receptor population. Shut-off valves are marked (shut) to indicate the remedial action that has been taken or proposed for the Site. A description of the types of remedial actions follow:

(a) Institutional Controls - The use of institutional controls (land userestrictions and agreed order with MDEQ) can serve as barriers in preventing future contact with subsurface soils and groundwater. Site land-use may be "unrestricted" or "restricted" that relates generally to residential and industrial/commercial, respectively. The potential to restrict the future use of the site (example: use of the site to a defined industrial use only, or the limitations of future construction activities, prohibiting groundwater use) can be considered in the remediation of the Site. If no restrictions for future use will be placed on the property by the Applicant, the identified remediation goals will be based on the future unrestricted (residential) use of the Site. Documentation of the institutional controls must be provided to support the proposed site remediation. A land use restriction and agreed order with MDEQ shall be used for "restricting" the Site. Institutional controls are to be used to "shut off" exposure to contamination. The Site Characterization Report and/or Corrective Action Plan must document the appropriate restrictions to be implemented. The Institutional Control Shut-off Valve on the REMEDIAL SCEM should be marked to reflect this option. An institutional control by itself cannot be used if there is further migration and/or Expansion of the contamination.

(b) Engineering Controls - The use of engineering controls can reduce or eliminate the potential for exposure to contaminants through containment. Engineering Controls may include, but are not limited to, physical or hydraulic control measures (such as groundwater recovery trenches and leachate collection systems), groundwater treatment systems, engineered caps, liner systems, slurry walls or permanent structures, but shall not include the exclusive use of security fencing. Ingestion and dermal contact of soil contamination that exists under a building may be considered "shut off" provided the institutional control restricts contamination via ingestion or dermal contact. If an engineering control is used to "shut-off" exposure to contamination, the Site Characterization Report and/or Corrective Action Plan must document the appropriate engineering control and/or institutional control to be implemented. The Engineering Control Shut-off Valve on the REMEDIAL SCEM should be marked to reflect this option. An institutional control must be coupled with the engineering control to ensure the engineering control is maintained until the site is remediated to an unrestricted level.

(c) Active Cleanup - The active cleanup (i.e., removal, treatment) of contamination to levels that are protective of human health and the environment can reduce or eliminate the potential for exposure to contaminants. If active cleanup is used to "shut off" exposure to contamination, the Site Characterization Report and/or Corrective Action Plan must document the active cleanup activities and/or institutional control to be implemented. The Active Cleanup Shut-off Valve on the REMEDIAL SCEM should be marked to reflect this option. An institutional control may be necessary, depending upon the projected length of the cleanup, particularly if groundwater has been impacted (e.g., pump and treat system has been installed and projected to continue for 30 years).

C. Site Characterization

(1) A Site Characterization must be conducted to delineate the nature and extent (vertically and horizontally) of contamination on and under the Site. Site characterization data should be collected and presented in accordance with the Quality Assurance Project Plan (QAPP) and Site Characterization Report formats. In general, the Applicant must demonstrate that the data are representative of the actual and/or potential contamination conditions at the Site. Collected data must include information describing and delineating the contaminant source area. Information pertaining to the characteristics of the CoCs, including the chemical and physical properties as well as the potential of the CoCs to migrate and transport to receptor locations through or in the affected media, must also be provided.

(2) The degree of contamination in surface and subsurface soil should be determined by performing soil boring(s) down to the depth of groundwater in the saturated zone. Surface soil is defined as the soil located at the surface and extending to a depth of six (6) feet below the ground surface. The subsurface soil depth is any depth beyond six feet. The Applicant must address ingestion, potential dermal contact, and inhalation (through volatilization and particulates) of hazardous chemicals present in the surface soil. In addition, CoCs in the surface soil may be transported off-site through precipitation runoff.

(3) The Applicant must demonstrate that groundwater is not impacted by the site-related contaminant; or that if groundwater is impacted, the impacted groundwater is confined and will remain confined within the Site. Groundwater contaminant concentrations should be determined by collecting groundwater samples.

(4) Measured data are those data collected from temporary or permanent (monitoring) wells. The Applicant should install wells, as necessary, to delineate the vertical and horizontal extent of groundwater impact and to determine flow direction and groundwater quality. Wells must be installed, developed, purged, and sampled in a manner consistent with EPA Region IV, Science and Ecological Support Division, Environmental Investigations Standard Operating Procedures and Quality Assurance Manual, May 1996, as amended, or other procedures approved by MDEQ. Measured groundwater data must be based on unfiltered groundwater samples.

(5) The site characterization data should be collected in accordance with data quality objectives (DQOs) stipulated in the QAPP. The DQOs shall, at a minimum, identify the number of field and quality control samples, quantitation limits, analytical methods, and sample collection, preservation, and handling methods. Matrix interferences shall be minimized to the extent feasible by modified sample extraction and preparation methods in accordance with EPA or MDEQ approved analytical methodologies.

(6) The data collection strategy should be based on the Site Conceptual Exposure Model (SCEM) that hypothesizes or describes how the source chemicals or CoCs are released, transported, and exposed to the receptors.

(7) The Applicant must demonstrate that the analytical laboratory data have been reviewed for compliance with the DQOs. In the Site Characterization Report, the Applicant shall data that meet DQOs.

(8) To establish background chemical concentrations, the Applicant may collect samples from locations, as approved by MDEQ, outside of the influence of known contaminated areas and regionally prevalent chemicals and must analyze these samples using the same analytical methods as the CoC analyses.

(9) To establish regionally prevalent chemical concentrations, the Applicant may collect samples from locations, as approved by MDEQ, throughout a substantial geographic region and outside the influence of known contaminated areas and must analyze these samples using the same analytical methods as the CoC analyses.

(10) Historical data approved by MDEQ may be submitted in lieu of collecting new data provided that:

(a) the Site characterization data requirements are summarized and presented in accordance with the Quality Assurance Project Plan and Site Characterization Report Formats; and

(b) the data was collected in a manner consistent with appropriate sampling protocols, as approved by MDEQ.

All detailed information must be referenced in the reports including sampling protocols. In any event, relevant previous site characterization reports should be submitted along with the application. Deviations from the required methodologies in the Quality Assurance Project Plan, Site Characterization Report, for Corrective Action Plan formats must be presented to and approved by MDEQ.

D. Site Ecological Checklist

The Ecological Checklist is used to determine if ecological receptors of concern are present and potentially impacted (See Appendix D). If such receptors are present, MDEQ will make a determination as to whether a Tier 3 assessment of ecological risk should be performed to assess the potential ecological impact. Tier 1 and Tier 2 Evaluations are applicable for Sites with no known ecological receptors of concern.

Notes

11 Miss. Code. R. 3-2.2.2

Miss. Code Ann. §§ 49-35-1, et seq., 49-2-9(1)(b), 49-17-17, 17-17-1, et seq., 49-2-1, et seq. and 49-17-1, et seq.

Amended 12/4/2023