Risk-Based Remediation

Risk-Based Remediation. A. Risk-Based Remediation Goals (1) Risk-based remediation goals (RGs) may be quantitative for chemical-specific RGs or qualitative for remedial action-specific RGs. The methodology for quantifying the chemical-specific RGs involves solving for the concentration term given a defined risk level in a deterministic or probabilistic risk assessment and shall be proposed for the principal threat chemicals or all CoCs if the principal threat chemicals cannot be identified. The chemical-specific RG may be modified upward or downward based on risk management considerations by MDEQ. A qualitative RG is established by describing the objectives for engineering controls that reduce site risk to an acceptable level. Risk-based remediation goals shall accompany the proposed remedial action(s) in the Site Characterization Report and/or the Corrective Action Plan (CAP). (2) Quantitative RG - Site-specific information that is relevant to the future use of the Site shall be used in the risk methodology. (a) The derived value shall not be higher than the soil saturation limit (Csat) for the soil or sediment RG for a CoC with a melting point less than 30 degrees Celsius. The derived value shall not be higher than the solubility limit (Csol) for the groundwater RG for groundwater. At sites where a mixture of contaminants is present (e.g., gasoline), the effective solubility limit may be used if required by MDEQ. Values for Csat and Csol may be found or derived from equations in EPA's Soil Screening Guidance: Technical Background Document (EPA/540/R-95/128), May 1996 or other reference approved by MDEQ. (b) The derived chemical-specific RG for a carcinogen for the protection of human health shall be: (1) the MCL value, (2) a value derived using the acceptable carcinogenic risk level of 1x10-6, or (3) a value defined in state/federal programs and approved by MDEQ. (c) The derived chemical-specific RG for a non-carcinogen for the protection of human health shall be: (1) the MCL value, (2) a value derived using the acceptable hazard quotient level of unity (1), or a value defined in state/federal programs and approved by MDEQ. (d) The MDEQ may consider an alternative quantitative or qualitative remediation goal (RG) for each individual contaminant, provided the Applicant can demonstrate to the satisfaction of MDEQ that the attainment of (1) a Risk Level of 10-6 for each individual carcinogenic contaminant or (2) a total hazard quotient of not more than 1 for each individual systemic toxicant is technically impracticable except with regard to a background chemical concentration or a regionally prevalent chemical. In no event, except with regard to a background chemical concentration, may either (1) the cumulative (total) site carcinogenic risk exceed 1x10-4 for carcinogenic CoCs or (2) the site hazard index (summation of hazard quotients) exceed 3 for non-carcinogenic CoCs affecting the same organ or organ system. (e) Any of the following methods may be used to derive chemical- specific quantitative RGs in soil or sediment to protect human health: (1) algorithms or methodology employed by MDEQ in deriving the TRGs in appendix A of this Subpart II; (2) algorithms or methodology employed by EPA Region III (Technical and Program Support Branch, 3HW70) to derive the Risk-Based Concentrations (RBCs); (3) algorithms or methodology employed by EPA (Office of Solid Waste and Emergency Response) to derive the SSLs using EPA's Soil Screening Guidance: Technical Background Document (EPA/540/R-95/128), May 1996; (4) algorithms or methodology employed by the American Society of Testing and Materials (ASTM) to derive the Risk-Based Screening Levels (RBSLs) (Emergency Standard Guide ES 38-94); or (5) other EPA published or peer-reviewed methodologies that have been reviewed and approved by MDEQ. Note: All input/default values must be approved by MDEQ prior to employing any of the above methodologies. (f) Fate and transport modeling and/or the use of a dilution- attenuation factor (DAF) to determine migration-to-groundwater soil RGs approved by MDEQ may be used to demonstrate that the concentrations of CoCs at the source area provide adequate protection of human health and the environment at the Site boundary, except when it appears that free product is present. (g) The acceptable level of a CoC in groundwater at the Site boundary is its groundwater RG or if the boundary is a surface water body, the water quality criteria published by MDEQ, whichever is lower. (h) Any of the following methods may be used to derive chemical-specific quantitative RGs in groundwater: (1) algorithms or methodology employed by MDEQ in deriving the TRGs in Appendix A of this Subchapter II; (2) algorithms or methodology employed by EPA Region IX (Technical Support Team, DFD-8-B) to derive the Preliminary Remediation Goals (PRGs); or (3) other EPA published or peer-reviewed methodologies that have been reviewed and approved by MDEQ. (i) The quotient method may be used to derive quantitative RGs for the protection of an ecological receptor of concern. (j) The following methods may be used to derive chemical-specific quantitative RGs in soil and sediment for protection of an ecological receptor of concern: (1) algorithms or methodology described in the Risk Assessment Handbook, Volume 2 - Environmental Evaluation (EM 200-1-4) developed by the U.S. Army Corps of Engineers; or (2) other EPA published or peer-reviewed methodologies that have been reviewed and approved by MDEQ. (3) Qualitative RG - A qualitative RG shall define objectives and describe how land- use restrictions and/or engineering controls are expected to reduce site risk to an acceptable level. The following information shall be presented: (a) complete exposure pathway that contribute to human health or environmental risk; (b) the CoC or principal threat chemical and its background concentrations; (c) physical, chemical, and fate and transport properties of the CoC or principal threat chemical (including the potential for adsorption and monitored natural attenuation); (d) presence of any man-made or natural conveyances, conduits, or transport routes from the source to the receptor location; (e) Potential engineering controls that will exclude the exposure pathway based on treatability study data and/or practical experience may also be considered. Engineering controls may include physical or hydraulic control measures, but shall not include the exclusive use of security fencing. Typical engineering controls are presented below and the Applicant may propose alternative controls for MDEQ approval. (1) groundwater recovery trenches and leachate collection systems; (2) groundwater extraction (pumpage) and treatment systems; (3) engineered caps with or without liner systems; (4) slurry walls, funnel-and-gate barrier walls, bio-polymer walls, or any modifications thereof; and (5) permanent structures such as building, driveways, and paved roads. (4) No further action at the Site shall be based on obtaining either the quantitative or qualitative RGs, or both, and/or other terms and conditions stipulated by MDEQ (i.e., Brownfield Agreement, Corrective Action Plan). The Applicant has the option to propose either type of RGs or a combination of the two for delineated areas of the Site, depending on the site-specific factors, chemical data, and risk management considerations approved by the MDEQ. The following criteria shall be met for this determination: (a) The remedial action has achieved the chemical-specific RGs based on verification sampling and analyses at the point of exposure or at the contaminated source area. The 95% UCL of the normalized verification sample data must be less that the chemical-specific RG. (b) The engineered control measures proposed by the Applicant and approved by MDEQ completed. (c) The groundwater quality at the Site boundary shall not exceed MCLs or risk-based TRGs for groundwater identified in Appendix A. The Point of Compliance is the Site Boundary. (d) Free product must be removed from the Site, unless it can be demonstrated to the satisfaction of MDEQ that removal of the free product is technically impracticable and that the contamination is confined and will remain confined within the Site boundaries. Free product is considered to exist if: (1) concentrations in soil exceed Csat for CoCs with a melting point of less than 30 degrees Celsius; (2) concentrations in groundwater exceed Csol for any CoC or the effective Csol or (3) measurable using best available technologies.