Hydrogeologic Site Investigations

Section 817 Section 817.411  Hydrogeologic Site Investigations a)         Purpose.  The operator shall conduct a hydrogeologic investigation to develop hydrogeologic information for the following uses: 1)         Provide information to perform a groundwater impact assessment; and 2)         Provide information to establish a groundwater monitoring system. b)         General requirements: 1)         The investigation shall be conducted in a minimum of three phases prior to submission of any application to the Agency for a permit to develop and operate a landfill facility. 2)         The study area shall consist of the entire area occupied by the facility and any adjacent areas, if necessary for the purpose of the hydrogeological investigation set forth in subsection (a) above. 3)         All borings shall be sampled continuously at all recognizable points of geologic variation, except where non-continuous sampling can provide equivalent information, samples shall be obtained at intervals no greater than 1.52 meters (five feet) in homogeneous strata. c)         Minimum requirements for a Phase I investigation: 1)         The operator shall conduct a Phase I investigation to develop the following information: A)        Climatic aspects of the study area; B)        The regional and study area geologic setting, including a description of the geomorphology and stratigraphy of the area; C)        The regional groundwater regime including water table depths and aquifer characteristics; and D)        Information for the purpose of designing a Phase II hydrogeologic investigation. 2)         Specific requirements: A)        The regional hydrogeologic setting of the unit shall be established by using material available from all possible sources, including, but not limited to, the Illinois State Water Survey, the Illinois Geological Survey, the Agency, other State and Federal organizations, water well drilling logs, and previous investigations. B)        A minimum of one continuously sampled boring shall be drilled on the site, as close as feasible to the geographic center, to determine if the available regional hydrogeologic setting information is accurate and to characterize the site-specific hydrogeology to the extent specified by this phase of the investigation.  The boring shall extend at least 15.2 meters (50 feet) below the bottom of the uppermost aquifer or through the full depth of the confining layer below the uppermost aquifer, or to bedrock, if the bedrock is below the uppermost aquifer, whichever elevation is higher.  The locations of any additional borings required under this subsection may be chosen by the investigator, but shall be sampled continuously. d)         Minimum requirements for a Phase II hydrogeologic investigation (Phase II investigation): 1)         Information to be developed. Using the information developed in the Phase I survey, a Phase II investigation shall be conducted to collect the site-specific information listed below as needed to augment data collected during the Phase I investigation and to prepare for the Phase III investigation: A)        Structural characteristics and distribution of underlying strata, including bedrock; B)        Chemical and physical properties including, but not limited to, lithology, mineralogy,  and hydraulic characteristics of  underlying strata, including those below the uppermost aquifer; C)        Soil characteristics, including soil types, distribution, geochemical and geophysical characteristics; D)        The hydraulic conductivities of the uppermost aquifer and all strata above it; E)        The vertical extent of the uppermost aquifer; and F)         The direction and rate of groundwater flow. 2)         Specific requirements: A)        One boring shall be located as close as feasible to the topographical high point, and another shall be located as close as feasible to the topographical low point of the study area. B)        At least one boring shall be at or near each corner of the site.  Where the property is irregularly shaped, the borings shall be located near the boundary in a pattern and spacing necessary to obtain data over the entire study area. C)        Additional borings may be located at intermediate points at locations and spacings necessary to establish the continuity of the stratigraphic units. D)        Piezometers and groundwater monitoring wells shall be established to determine the direction and flow characteristics of the groundwater in all strata and extending down to the bottom of the uppermost aquifer.  Groundwater samples taken from such monitoring wells shall be used to develop preliminary information needed for establishing background concentrations in accordance with subsection (e)(1)(G) of this Section. E)        Other methods may be utilized to confirm or accumulate additional information.  Such methods may be used only as a supplement to, not in lieu of, site-specific boring information. Other methods include, but are not limited to, geophysical well logs, geophysical surveys, aerial photography, age dating, and test pits. e)         Minimum standards for a Phase III investigation: 1)         Using the information developed during the Phase I and Phase II investigations, the operator shall conduct a Phase III investigation.  This investigation shall be conducted to collect or augment the site-specific information needed to carry out the following: A)        Verification and reconciliation of the information collected in the Phase I and II investigations; B)        Characterization of potential pathways for contaminant migration; C)        Correlation of stratigraphic units between borings; D)        Continuity of petrographic features including, but not limited to, sorting, grain size distribution, cementation and hydraulic conductivity; E)        Identification of zones of potentially high hydraulic conductivity; F)         Identification of the confining layer, if present; G)        Concentrations of chemical constituents present in the groundwater and expected to appear in the leachate below the unit, down to the bottom of the uppermost aquifer, using a broad range of chemical analysis and detection procedures, such as gas chromatographic and mass spectrometric scanning. However, additional measurements and procedures shall be carried out to establish background concentrations, in accordance with Section 817.416(d), for any constituent which is listed in Section 817.106 (MALCs) or Section 817.Appendix A of this Part and which is expected to appear in the leachate; H)        Characterization of the seasonal and temporal, naturally and artificially induced, variations in groundwater quality and groundwater flow; and I)         Identification of unusual or unpredicted geologic features, including: fault zones, fractures traces, facies changes, solution channels, buried stream deposits, cross cutting structures and other geologic features that may affect the ability of the operator to monitor the groundwater or predict the impact of the disposal facility on groundwater. 2)         In addition to the specific requirements applicable to Phase I and II investigations, the operator shall collect information needed to meet the minimum standards of a Phase III investigation by using methods that may include, but are not limited to, excavation of test pits, additional borings located at intermediate points between boreholes placed during Phase I and II investigations, placement of piezometers and monitoring wells, and institution of procedures for sampling and analysis. f)         The operator may conduct the hydrogeologic investigation in any number of alternative ways provided that the necessary information is collected in a systematic sequence consisting of at least three phases that is equal to or superior to the investigation procedures of this Section.