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Regulatory Communication Meeting

Treatability Study for Area of Concern 65

F41624-00-D-8024/Delivery Order 0058

Parsons 740999.02000

Attendees:

*Minutes prepared by Brian Vanderglas, Parsons.

Agenda for Regulatory Communication Meeting

The meeting opened and a PowerPoint presentation was used to present the status and planned activities at the AOC-65 site.  A copy of the PowerPoint presentation was distributed at the meeting.  The agenda for the meeting is attached to these minutes.  These meeting minutes are organized in the order discussed.

AOC-65 Background

The meeting began with an introduction of the CSSA/Parsons project team.  A brief summary of the background of AOC-65 was presented.  An overview of the planned remedial activities for the AOC-65 unit was discussed.  The planned approach will include: geophysical surveys to identify subsurface features that may be controlling the distribution and migration of VOCs in the area; installation of a subslab ventilation system to remove VOCs in the fill material beneath Building 90; excavation of impacted soils west of Building 90 along a drainline and drainage ditch; and installation and testing of a soil vapor extraction system (SVE) to address VOCs in the unsaturated portion of the fractured limestone bedrock.

Geophysical Test Results and Future Geophysical Testing Needs

The presentation included a summary of the results from the geophysical surveys completed to date and examples of the survey results.  The geophysical surveys are being conducted to identify subsurface features such as faults, fractures and karst dissolution cavities that may be influencing contaminant migration.  A total of 14 survey lines have been completed and three different geophysical methods have been used.  Electrical resistivity imaging (ERI) was determined to be the method that has produced the most useful results. 

The locations of numerous subsurface anomalies have been identified in the ERI data and preliminary evaluations of potential orientation of features have been made.  Of primary interest is the indication that a fault may be present trending northeast to southwest and crossing the Building 90 area near the suspected source location.  Comparison of the projected alignment of this fault to VOC concentrations in off-post wells suggests that this feature may be serving as a primary migration pathway for the dissolved constituents.  In order for the planned remedial activities for AOC-65 to be successful, an accurate determination of the location and orientation of this fault, as well as similar features in the area, is needed.  Identification of these subsurface migration pathways is also crucial for the design and installation of the groundwater-monitoring network currently authorized by CSSA through a separate task order (TO0042).

To support the resistivity data and provide data to greater depth intervals, CSSA plans to conduct shallow, high-resolution, 2-D seismic reflection surveys in the areas of suspected anomalies indicated by the ERI data.  Additional geophysical surveys using ERI, seismic, and other methods, are planned in areas south and east of Building 90 and west of Ralph Fair Road.  The geophysical surveys are currently scheduled to be completed by the end of June 2002.  Well placement for the treatability study (vapor extraction wells and piezometers) will be modified, as necessary, pending results of future geophysical testing.

No objections were raised regarding the preliminary results of the geophysical surveys or the plans for future surveys.  The USEPA concurred with the integrated approach utilizing geophysical methods to identify the potential migration pathways.  This approach will help to maximize the effectiveness of the SVE system proposed for AOC-65 and also provide guidance for the groundwater-monitoring program.

AOC-65 Removal Actions Inside and Around Building 90

The proposed removal actions were presented for discussion.  The removal actions will include the installation and testing of a subslab ventilation system designed to remove VOC from beneath Building 90.  Soil borings will be performed inside the building to quantify the levels of VOCs present and to identify areas requiring remediation.  Vapor extraction wells will be installed in the fill material to beneath the building to remove the VOCs.  The subslab ventilation system will be tested to determine the effectiveness of the system for removing the VOCs present.  If the ventilation system is determined to be an ineffective approach for removing VOCs from under Building 90 in a timely manner, limited excavation and removal of impacted fill material will be conducted. 

The removal actions west of Building 90 will be conducted to remove soils impacted with VOCs from releases along the drainline and drainage ditch near the suspected source area.  Soil borings will be conducted to quantify the levels of VOCs present and determine locations requiring excavation.  The excavated soils will be sent to an off-post facility for disposal.  Soil samples will be collected from the excavations for possible use in supporting closure of the AOC-65 area for soil media. 

TNRCC or EPA raised no objections to the proposed removal actions on the plan to evaluate the effectiveness of subslab ventilation before initiating any excavation activities from beneath the building.  Both agencies agreed in the event the subslab system is not effective at removing the VOCs, then excavation of soils beneath the building should be implemented immediately.  TNRCC indicated approval that CSSA was attempting to demonstrate progress at removing VOCs from around Building 90 in advance of the next scheduled public meeting in October 2002.

AOC-65 Treatability Study

The proposed activities for the AOC-65 SVE treatability study were presented for discussion, which include installing and testing a SVE system and conducting a groundwater recharge study.  The purpose of the SVE treatability test is to assess the distribution of VOCs in the unsaturated portion of the fractured limestone unit and to evaluate the effectiveness of a SVE system at removing VOCs from this unsaturated zone.  The purpose of the groundwater recharge study is to evaluate the rate and extent of groundwater recharge in the area and to assess the effects of this recharge on the migration of VOCs and impacts of groundwater fluctuations on the effectiveness of the SVE system.

The proposed SVE system will consist of the installation of six vapor extraction wells (VEWs) and six multi-depth vapor monitoring points (VMPs) in and around the suspected source area at Building 90.  The VEWs and VMPs will be placed at locations of faults, fractures and karst features identified in the geophysical results.  The six VEWs will be constructed to monitor specific depth intervals in the upper 150 feet of the fractured limestone.  Each of the VMPs will be constructed with four small-diameter vapor monitoring units set to monitor four separate depth intervals in the upper 100 feet of the limestone unit.  A vapor extraction packer test will be conducted on the corehole of the deepest piezometer installed for the groundwater recharge study.  This extraction packer test will be conducted to provide guidance for the appropriate screen depths for the VEWs and VMPs. 

The VEWs will be connected to a manifold system leading to the SVE blower that will be located along the west side of Building 90.  A standard exemption will be prepared for the air discharge from the SVE blower systems and the existing air permit for Building 90 will need to be re-evaluated. 

Once the SVE system is installed, operational and performance tests will be conducted on the system.  The tests will be conducted to: assess the location and mass of VOCs in the subsurface; determine the radius of influence of the VEWs; evaluate interconnectivity of the subsurface fractures, and faults; evaluate the effectiveness of the SVE system; and, to establish operational parameters to optimize system performance.  In addition, a soil gas tracer test may be conducted by the University of Texas at San Antonio (UTSA) to assess retardation rates, travel times, and flush times for VOCs in the fractured limestone.

The proposed groundwater recharge study will include the installation of a weather station and groundwater piezometers to evaluate the rate and movement of groundwater recharge in the unsaturated limestone material.  The weather station will include a rain gauge and data logger to monitor the rate of rainfall in the area.  Six piezometers will be installed in the AOC-65 area along fractures and faults identified in the geophysical results.  Each piezometer will be constructed to monitor a specific 25-foot depth interval between the depths of 10 to 150 feet.  Pressure transducers, or other water level measurement devices, will be installed in the piezometers and connected to the weather-station data logger to monitor and record groundwater level fluctuations following rainfall events. 

At the start of the groundwater recharge study, groundwater samples will be collected from all piezometers and VEWs to establish a baseline of groundwater conditions.  Groundwater samples will also be collected from the piezometers at pre-determined time intervals following significant rainfall events to assess the change in concentration with time and rainfall intensity.  Also, groundwater recharge rates and sample results will be evaluated to determine the applicability of groundwater pumping or other types of containment to reduce migration of contaminated groundwater into the drinking water formations during recharge events.   

No objections were raised regarding the proposed plans for the treatability study.  The EPA and TNRCC approved of the integrated approach to the study presented, with the results of one task providing direction for subsequent tasks.  The TNRCC indicated that approval of the air permit standard exemption should be obtained prior to the startup of the SVE system.

Other Discussion Items

The proposed off-post groundwater sampling locations for the current quarterly monitoring event were presented.  CSSA presented the rationale for the selection of the newly sampled wells.  The EPA re-stated their approval of CSSA's decision to pursue identification and monitoring of groundwater concentrations and delineation of the contaminant plume to levels significantly below the 1.0 ug/L level standard generally applied by EPA due to the complex nature of the geology involved at the site, the large number of unanswered questions regarding plume size and contaminant concentration trends, and the sensitive issues associated with off-post contamination.  No objections to the proposed sampling locations were aired.

The proposed plan for handling cuttings and groundwater generated during drilling operations under this task order (TO 0058) and the monitoring well installation task order (TO0042) was discussed with TNRCC in hopes of obtaining concurrence or to discuss the options which may be available under existing regulations.  The proposed plan for managing investigation-derived wastes generated during the drilling efforts involves depositing the liquids and suspended solids in a settling pond.  The discussion focused on the implementability of a variety of options and possible compliance or implementation issues related to each option.

CSSA’s goal is to establish an effective method that is acceptable to TNRCC and EPA for managing the significant volumes of material generated during the drilling and monitoring well installation.  Due to the large volume of media generated during drilling of the deep wells, management of this material creates significant logistical complications for completing the drilling activities.  Past practices have involved utilizing 20 to 30 cubic yard roll-off boxes staged near the drilling locations to store the drilling media, and analysis of the  liquid fraction cannot be conducted for several days after it is generated due to the presence of the polymer foam additive used during the drilling process.  As a result, numerous roll-off boxes must be staged until adequate characterization of the media can be completed.  Historically, this material has been found to be below detection limits for the COCs in the soil fraction and below the MCL in the liquid fraction. 

The meeting adjourned without final resolution regarding the media management plan.  CSSA agreed to propose procedures for managing the groundwater and soil cuttings generated from drilling operations to TNRCC for further consideration and debate.  TNRCC agreed to an expedited review of any proposed management plan, since drilling is expected to begin in April 2002.