| (i) The number and location of attenuation monitoring points shall be demonstrated to be adequate to reliably verify over time the current and future conformance with the plume management zone response objectives. The number and location of attenuation monitoring points shall depend upon a site-specific evaluation of the hydrogeologic conditions of an affected property, the fate and transport characteristics of the COCs, and the length and configuration of the plume management zone. (ii) The person shall calculate attenuation action levels for each COC at each attenuation monitoring point that cannot be exceeded in order for the critical groundwater PCLs to not be exceeded at the POE. The person shall periodically evaluate the adequacy of the attenuation action levels using any newly acquired empirical monitoring data and reestablish them as necessary to ensure the critical groundwater PCLs are not exceeded at the groundwater POE. (iii) The person shall monitor concentrations of COCs in groundwater at the attenuation monitoring points and the POE in accordance with a schedule approved by the executive director which is adequate to reliably demonstrate conformance with the applicable groundwater response objectives. If an attenuation action level is exceeded at its respective attenuation monitoring point, or a critical groundwater PCL is exceeded at the groundwater POE, then the person shall take an active response action to meet the response objectives presented in subparagraph (F) of this paragraph. The executive director may authorize the person to implement an accelerated monitoring program prior to initiating an active response action in order to verify that a response action is warranted. (E) The person is required to reduce NAPLs which contain COCs in excess of PCLs within a plume management zone to the extent practicable. In the determination of adequate NAPL reduction, the executive director may consider conformance with the following criteria and other relevant factors: (i) readily recoverable NAPLs have been recovered; (ii) the NAPLs will not generate explosive conditions as defined in §350.31(c) of this title (relating to General Requirements for Remedy Standards); (iii) the NAPLs will not discharge to the ground surface, to surface waters, to structures, or to other groundwater-bearing units; (iv) the vertical and lateral extent of NAPLs will not increase under natural conditions, or sufficient NAPLs have been recovered such that an active recovery system can be demonstrated to effectively control or contain migration of NAPLs (i.e., no increased NAPL extent); and (v) the NAPLs will not result in the critical groundwater PCLs being exceeded at the downgradient boundary of the plume management zone or in the critical PCLs for other environmental media being exceeded at the applicable POE. (F) The person shall have the continuing obligation to assess whether changes to local hydraulic gradients would increase the likelihood that COCs can migrate beyond the plume management zone at concentrations above the critical groundwater PCLs. If such changed conditions occur, the person must take any necessary corrective action to ensure that concentrations of COCs exceeding the critical groundwater PCLs do not migrate beyond the boundary of the plume management zone and report the changed condition to the executive director in a timely manner. The person may demonstrate that the hydrogeologic characteristics of a property are such that off-site activities cannot influence an on-site plume management zone and, thus, not be required to monitor changes in the hydraulic gradient. (i) A person may choose to attain the groundwater response objectives for a plume management zone at an affected property either by conducting a response action, if necessary, which makes use of removal and/or decontamination, or with use of removal and/or decontamination with controls or controls only. For both of these approaches, in situations where the PCLE zone extends beyond the limits of an institutional control and the POE to groundwater is thus located within the existing limits of the groundwater PCLE zone, a person may use monitored natural attenuation as a decontamination process provided the person shall demonstrate that the groundwater PCLE zone is not expanding and that the critical groundwater PCL will be met at the POE within a reasonable time frame given the particular circumstances of an affected property. In the situation where the groundwater PCLE zone has not reached steady-state conditions and is migrating downgradient within the plume management zone, the person must use a response action other than monitored natural attenuation, unless it can be demonstrated that the critical groundwater PCL and any other critical PCLs will not be exceeded at the respective POEs. (ii) When a person chooses to attain the groundwater response objectives for a plume management zone at an affected property by conducting a removal and/or decontamination response action, the person must comply with the requirements of this clause. (I) The person must remove and/or decontaminate the groundwater PCLE zone to the extent necessary so that the critical groundwater PCLs will not be exceeded at the POE and the attenuation action levels are not exceeded at their respective attenuation monitoring points, and so that the critical PCLs for other environmental media will not be exceeded at their applicable POEs. (II) The person shall fulfill the post-response action care obligations described in the approved RAP. (III) Provided the person adequately documents attainment of the groundwater plume management zone response objectives provided in subclause (I) of this clause, there are no financial assurance requirements. (iii) When a person chooses to attain the groundwater response objectives for a plume management zone at an affected property by conducting a response action which uses removal and/or decontamination with controls or controls only, the person must comply with the requirements of this clause. (I) The person must remove, decontaminate, and/or control the groundwater PCLE zone to the extent necessary so that the critical groundwater PCLs will not be exceeded at the POE and so that the critical PCLs for other environmental media will not be exceeded at their applicable POEs. (II) The person may use physical controls (e.g., slurry walls, sheet piling, interceptor trenches, or hydraulic control wells) which are capable of reliably containing and preventing the expansion over time of the groundwater source area. (III) For any portion of a groundwater PCLE zone within class 2 or 3 groundwater which is outside of any physical control constructed in accordance with subclause (II) of this clause, the person must reduce the concentration of COCs such that the remaining COCs will satisfy the conditions specified in clause (ii)(I) of this subparagraph. (IV) The person shall fulfill the post-response action care obligations described in the approved RAP. (V) The person shall provide financial assurance for post-response action care in accordance with subsections (l) and (m) of this section. (g) The type, method and extent of post-response action care will be defined on a site-specific basis in the approved RAP and shall be a function of the long-term effectiveness of the response action used to address the soil and/or groundwater PCLE zones or other environmental media containing COCs, the nature and design of any physical controls, the physical and chemical characteristics of the COCs, the geology and hydrogeology of the affected property, and the adjacent land use. The person shall conduct post-response action care as appropriate which includes, but is not limited to: (1) monitoring of environmental media to verify response action effectiveness over time; (2) inspection, operation, and maintenance of physical controls to ensure the effectiveness and integrity of the controls over time; and (3) any other actions after the initial completion of the response action at an affected property which are necessary to protect human health or the environment. (h) The post-response action care period begins upon approval of the RACR by the executive director. The person shall perform post-response action care for 30 years unless the person demonstrates that a shorter post-response action care period would be appropriate due to: (1) the nature of the response action; (2) the persistence, migration potential, and toxicity of the COCs; and (3) the physical characteristics and location of the affected property. (i) The post-response action care activities shall continue throughout the initial post-response action care period in response to subsection (h) of this section and during any continued post-response action care period in response to subsection (j) of this section until a demonstration is made that there is no longer a threat to human health or the environment from the presence of COCs in any environmental media or physical controls. If the person submits a demonstration which documents that post-response action care is no longer necessary then, upon Cont'd... |
