S.C. Code Regs. § 61-98.II

Current through Register Vol. 48, No. 07, July 26, 2024

Section 61-98.II - Site Rehabilitation Risk-Based Corrective Action Procedures

Risk-Based corrective action procedures outlined in this Section shall apply to all petroleum and petroleum product releases from underground storage tanks.

A. General Site Rehabilitation Requirements.

1. UST owners or operators shall implement site rehabilitation activities based on this regulation and on performance standards and criteria developed by the Department. Alternate approaches that accomplish the same goals as the performance standards will also be approvable. The UST owner or operator shall, upon Department approval, begin site rehabilitation activity and monitor, evaluate, and report the results of the activity in accordance with a schedule and in a format approved by the Department.

2. The current use and reasonably anticipated future use of sites shall be considered in making risk-based decisions including, but not limited to, the development of site conceptual exposure models, establishment of exposure points, and corrective actions. The reasonably anticipated future use of sites shall be determined based on factors such as: the current use of the site; zoning laws; comprehensive community master plans; population growth patterns and projections; accessibility of the site to existing infrastructure such as transportation and public utilities; site location in relation to urban, residential, commercial, industrial, agricultural, and recreational areas; Federal/State land use designation; historical or recent development patterns; and location of Wellhead Protection Areas.

3. UST owners or operators must take actions to prevent further releases, control fire and explosion hazards, and remove free product pursuant to the UST Control Regulations, R.61-92, Section280.

B. Site Priority System, Risk Evaluation, and Corrective Action for Releases of Petroleum and Petroleum Products.

1. UST releases, regardless of its time of occurrence, shall be classified using this priority system.

a. Releases are placed in Classification 1 if any one of the following conditions exists:

(1) an emergency situation;

(2) a fire or explosion hazard;

(3) vapors or free product in a structure or utility;

(4) concentrations of chemicals of concern have been detected in a potable water supply or surface water supply intake;

(5) free product exists on surface water;

(6) chemicals of concern exist in surface water.

b. Releases are placed in Classification 2a if any one of the following conditions exists:

(1) a significant near term (zero to one year) threat to human health, safety, or sensitive environmental receptors;

(2) potable supply wells or surface water supply intakes are located less than one year ground-water travel distance downgradient of the source area.

c. Releases are placed in Classification 2b if any one of the following conditions exists:

(1) free product in a monitoring well measured at greater than one foot thickness;

(2) potable supply wells or surface water supply intakes are located less than 1000 feet downgradient of the source area (where ground-water velocity data is not available).

d. Releases are placed in Classification 3a if any one of the following conditions exists:

(1) a short term (one to two years) threat to human health, safety, or sensitive environmental receptors;

(2) potable supply wells or surface water supply intakes are located greater than one year and less than two years ground-water travel distance downgradient of the source area;

(3) sensitive habitats or surface water exist less than one year ground-water travel distance downgradient of the source area and the ground water discharges to the sensitive habitat or surface water.

e. Releases are placed in Classification 3b if any one of the following conditions exists:

(1) free product in a monitoring well measured at greater than 0.01 foot thickness and less than one foot thickness;

(2) concentrations of chemicals of concern above the risk-based screening levels have been detected in a non-potable water supply well;

(3) concentrations of chemicals of concern in surface soil (less than three feet below grade) in areas that are not paved;

(4) sensitive habitats or surface water used for contact recreation are less than 500 feet downgradient of the source area (where ground-water velocity and discharge location data are not available);

(5) the site is located in a sensitive hydrogeologic setting, determined based on the presence of fractured or carbonate bedrock hydraulically connected to the impacted aquifer;

(6) ground water is encountered less than 15 feet below grade and the site geology is predominantly sand or gravel.

f. Releases are placed in Classification 4a if any one of the following conditions exists:

(1) a long term (greater than two years) threat to human health, safety, or sensitive environmental receptors;

(2) potable supply wells or surface water supply intakes are located greater than two years and less than five years ground-water travel distance downgradient of the source area;

(3) non-potable supply wells are located less than one year ground water travel distance downgradient of the source area.

g. Releases are placed in Classification 4b if any one of the following conditions exists:

(1) free product exists as a sheen in any monitoring wells;

(2) non-potable supply wells are located less than 1000 feet downgradient of the source area (where ground-water velocity data is not available);

(3) the ground water is encountered less than 15 feet and the site geology is predominantly silt or clay.

h. Releases are placed in Classification 5 if any one of the following conditions exists:

(1) there is no demonstrable threat, but additional data are needed to show that there are no unacceptable risks posed by the site;

(2) assessment data for the site indicate concentrations of chemicals of concern are above the risk-based screening levels or site-specific target levels, as appropriate, and further assessment is needed;

(3) assessment data for the site indicate concentrations of chemicals of concern are below the risk-based screening levels or site-specific target levels, as appropriate, but the samples are determined to not be representative; therefore, further assessment is needed.

i. The Department or owner or operator may re-evaluate the priority of a release upon receipt of additional information. However, the Department shall make the final decision as to priority classification.

2. The following risk-based corrective action procedures shall be used for releases from USTs upon Department approval. Risk evaluations shall be performed in accordance with this regulation and applicable Department performance standards and criteria.

a. The information necessary for a Tier 1 evaluation includes, but is not limited to, the following:

(1) A review of historical records of site activities and past releases;

(2) Quantification of the concentrations of the chemicals of concern;

(3) Parameters necessary to utilize soil leachability models, if appropriate;

(4) Location of source(s) of chemicals of concern;

(5) Location of maximum concentrations of chemicals of concern in soil and ground water:

(6) Determination of regional or site-specific hydrogeologic conditions such as depth to ground water, ground-water flow direction, hydraulic gradient, ground-water flow velocity;

(7) Determination if the chemicals of concern in the soil will leach to ground water in excess of risk-based screening levels;

(8) Location of current and reasonable future receptors;

(9) Identification of potential significant transport and exposure pathways.

(10) Determination of current and reasonably anticipated future use of the property, ground water, surface water, and sensitive habitats where the release has occurred and the surrounding property.

(11) If an exposure is identified, concentrations of chemicals of concern measured at point(s) of exposure.

b. The UST owner or operator shall use the data collected as described in

(a) to evaluate the risk presented by the release using the following Tier 1 evaluation method:

(1) Develop a site conceptual exposure model to identify all exposure pathways.

(a) Information about the facilities operations, the source of chemicals of concern, current and expected site conditions and/or land use, proximity to receptors, current and expected use of ground water, and human receptors is necessary to develop the model.

(b) Potential exposure pathways to be considered for evaluation based on the site conceptual model shall include: air inhalation, ground water ingestion, surficial soil ingestion, dermal contact, and subsurface soil leaching to ground water.

(c) A summary of all complete exposure pathways at a site shall be completed for current conditions and for reasonably anticipated future use if different from the current use.

(2) Use the site conceptual exposure model developed in (1) to identify the data required to quantify the exposure by estimating the dose for all complete pathways. In Tier 1, risk-based screening levels for dermal contact, soil ingestion, and vapor inhalation pathways are based on a Carcinogenic Risk Limit of 10⁶ and a Hazard Index of >= 1 for non-carcinogens unless a different risk level for a specific chemical of concern has been established by the Department. Risk-based screening levels for the soil leaching to ground water pathway shall be based on leaching models approved by the Department. Risk-based screening levels for ground water ingestion shall be based on maximum contaminant levels or other health based criteria for chemicals of concern without established maximum contaminant levels. For complete pathways other than the soil leaching to ground water and ground-water ingestion, risk-based screening levels shall be calculated based on the carcinogenic risk limit and the hazard quotient values stated in (2) above, published toxicity data and published reasonable maximum exposure values. The exposure factors used in the calculations shall be based on reasonable maximum exposure.

(3) Calculate the exposure for all identified complete pathways. The risk-based screening levels established by the Department for the chemicals of concern must be met at the exposure point(s). In Tier 1, the exposure point(s) and point(s) of compliance shall be located within the source area of the release or the area containing the highest concentrations of the chemicals of concern.

c. Representative concentrations of chemicals of concern in affected media are determined by the following:

(1) For ground water: the maximum concentrations of chemical of concerns obtained from last sampling event.

(2) For soil: the maximum concentrations of chemicals of concern obtained in the last sampling event for the ingestion, inhalation, and dermal contact pathway; and the average chemical of concern concentrations in the source area for the soil leaching to ground water pathway. To determine representative chemical of concern concentrations in the soil to be used in a leachability model, for each chemical of concern, the three soil samples with the highest non-zero concentration of chemicals of concern shall be averaged.

(3) For vapor: the maximum concentrations of chemicals of concern obtained in last sampling event.

d. If the concentrations of the chemical of concern at representative sample locations are below the Risk-Based Screening Levels, further assessment or cleanup may not be necessary, upon Department approval.

e. If the representative concentrations of chemical(s) of concern in the affected media are above the risk-based screening levels, the UST owner or operator shall conduct one or more of the following: interim remedial action; remedial action using the risk-based screening levels as target levels, as approved by the Department; other Department approved actions necessary to reduce risk; or further Tier evaluation. Further tier evaluation is warranted if: the site-specific target levels developed under further tier evaluation will be significantly different than the Tier 1 risk-based screening levels, the cost of remedial action to risk-based screening levels will likely be greater than further tier evaluation and subsequent remedial action, or the approach or assumptions, used to derive the current tier's goals are not appropriate for conditions at the site.

f. If a Tier 2 assessment is warranted, the UST owner or operator shall perform a Tier 2 assessment in accordance with this regulation and applicable Department criteria. Additional site assessment for a Tier 2 evaluation may include, but is not limited to: determination of site-specific hydrogeologic conditions; determination of horizontal and vertical extent of chemicals of concern relative to the Risk-Based Screening Levels, as appropriate; determination of changes in concentrations of chemicals of concern over time; determination of concentrations of chemicals of concern measured at exposure points; and, fate and transport evaluation to predict the attenuation of the chemicals of concern away from the source area.

g. The UST owner or operator shall use the data collected as described in (f) to evaluate the risk presented by the release using the following Tier 2 evaluation:

(1) Establish the exposure point. The most likely point of exposure closest to the source area shall be established as the exposure point for each complete pathway identified.

(2) For the ground-water ingestion pathway, the exposure point shall be established based on the current and reasonably anticipated future use of the ground water.

(a) If the ground water at a site is a current source of drinking water, or is reasonably anticipated to be utilized, the exposure point shall be established in the source area of the release or the area with the highest concentrations of chemicals of concern.

(b) If the ground water at a site is not currently used as a source of drinking water, or is not reasonably anticipated to be utilized, the exposure point shall be located hydraulically upgradient of the nearest receptor or the first ground water hydraulically downgradient of the site reasonably anticipated to be utilized.

(c) If the site is located within a designated Wellhead Protection Area, the exposure point(s) shall be established to prevent concentrations of chemical(s) of concern from exceeding maximum contaminant levels in the drinking water well.

(3) Establish a site-specific target level for each chemical of concern identified at the site which exceeds it's risk-based screening level. A site-specific target level shall be established for each complete pathway identified that calculates an acceptable source area concentration so that risk-based screening levels are not exceeded at the point(s) of exposure.

(a) For the ground-water exposure pathway, the reduction of chemicals of concern in the saturated zone shall be estimated using either empirical data or models approved by the Department and implemented with site-specific data. Empirical data can be used to estimate the overall concentration reduction factor of the chemicals of concern in the relevant media from the source to the exposure point. Models can also be used to estimate the fate and transport of the chemicals of concern away from the source area.

(b) For the soil leaching to ground water pathway, the site-specific target level for each chemical of concern in soil shall be calculated using leachability models approved by the Department.

(c) Site-specific target levels for the dermal contact, soil ingestion, and vapor inhalation pathways shall be based on a Carcinogenic Risk Limit of 10⁶ and a Hazard Index of >= 1 for non-carcinogens to be applied at the exposure point unless a different risk level for a specific chemical of concern has been established by the Department. Department approved less conservative exposure factors may be used in the calculations for commercial and industrial scenarios. Site-specific exposure factors or most likely or average exposure factors may be used, as appropriate.

(4) Establish the point(s) of compliance. The point(s) of compliance shall be established hydraulically downgradient of the source area and hydraulically upgradient of an exposure point. At least one point of compliance must be located directly downgradient of the source area between the source area and the exposure point for each complete pathway. A minimum of one year travel time for the chemicals of concern from the point of compliance to the exposure point shall be established where possible. Additional point(s) of compliance are necessary where complex hydrogeologic conditions exist that may control chemical of concern migration.

h. If the concentrations of the chemicals of concern are below their site-specific target levels, the UST owner or operator shall submit a corrective action plan proposing a monitoring program to verify intrinsic remediation.

i. If representative concentrations of chemical(s) of concern in the affected media are above the site-specific target levels, the UST owner or operator shall conduct one or more of the following: interim remedial action; remedial action using the site-specific target levels, as approved by the Department; other Department approved actions necessary to reduce risk; or further Tier evaluation. Further tier evaluation is warranted if: the site-specific target levels developed under further tier evaluation will be significantly different than the Tier 2 site-specific target levels; the cost of remedial action to site-specific target levels will likely be greater than further tier evaluation and subsequent remedial action; or the approach or assumptions, used to derive the current tier's goals are not appropriate for conditions at the site.

j. If further Tier evaluation is warranted, the UST owner or operator shall perform a Tier 3 assessment to collect additional appropriate site-specific data to evaluate the risk presented by the release for a Tier 3 evaluation.

k. Based on the results of the Tier 3 evaluation, the owner or operator shall perform the appropriate action as approved by the Department based on the following:

(1) If the concentrations of the chemicals of concern are below the site-specific target levels, the UST owner or operator shall develop a corrective action plan proposing a monitoring program to verify intrinsic remediation.

(2) If the concentrations of the chemicals of concern are above the site-specific target levels, the UST owner or operator shall develop a corrective action plan which shall include active cleanup which may include intrinsic remediation as a component.

3. Corrective Action.

a. The UST owner or operator shall develop and implement a Department approved corrective action plan for each release to achieve risk-based screening levels or site-specific target levels established under the risk-based corrective action procedures. The corrective action plan shall include a schedule for implementation and for achieving risk-based screening levels or site-specific target levels. The corrective action plan must be developed and implemented in accordance with R.61-92 including procedures for Department approval and public notice. Any selected corrective action alternative funded by the SUPERB Account shall be a reasonable, cost-effective response for soil and/or ground-water contamination. In evaluating the cost effectiveness of proposed action, the UST owner or operator shall take into account the total short and long-term costs of such action, including the costs of operation and maintenance for the entire period during which such activities will be required.

b. The UST owner or operator and the Department shall encourage the use of innovative treatment technologies, where appropriate.

c. The Department shall require monitoring, evaluation, and reporting of corrective actions to evaluate whether the corrective action is efficient and cost effective.

d. UST owners or operators shall implement modifications to the corrective action, as required by the Department, to increase efficiency and cost effectiveness.

e. Once the Department agrees that monitoring data supports the conclusion that: the risk-based screening levels or site-specific target levels have been met; the chemicals of concern have reached equilibrium or are not moving at a significant rate; concentrations of chemicals of concern are not increasing, no unacceptable risk to human health, safety, or the environment exists, and that concentrations of chemicals of concern will not exceed risk-based screening levels at the exposure point or receptor, the Department may issue a decision that further site rehabilitation is not necessary. These shall be conditional no further action decisions based on site-specific conditions and the current or reasonably anticipated future use of the site. The assumptions and conditions shall be outlined in writing. The Department shall maintain a registry of releases having conditional no further action decisions.

f. The Department approval of a corrective action plan or issuance of a conditional decision that further site rehabilitation is not necessary shall be considered an order of the Department enforceable pursuant to the 1976 Code Section 44-2-140. The UST owner or operator shall not undertake any actions that result in an increase in risk of exposure to the chemicals of concern including modification of the current or reasonably anticipated future use of the site without Department approval. The SUPERB Account shall not be responsible for funding further site rehabilitation as a result of an increase in risk under these conditions unless a variance to this provision is granted by the Department.

g. The Underground Storage Tank Program shall coordinate, on behalf of the owner or operator, all Department permits associated with implementation of a corrective action plan.

4. Variances. The Department may issue a variance to this Section, when, in its opinion, the UST owner or operator has demonstrated that an equivalent degree of protection will be provided to human health and the environment. Any variance granted or denied by the Department shall be in writing and shall contain a brief statement of the reasons for the approval or denial.

S.C. Code Regs. 61-98.II