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TIM #3 Meeting Minutes

Treatability Study for Area of Concern 65

F41624-00-D-8024/Task Order 0058

Parsons 740999.02000

Date:  July 1, and July 2, 2002

Time:  9:00 A.M. - 5:00 P.M.

Place:  Camp Stanley Storage Activity (CSSA)

Subject:  TIM #3 to evaluate field data and observations for field work completed to date; develop a conceptual model of groundwater/contaminant migration; assess completed vapor extraction well/vapor monitor point (VEW/VMP) locations and plan future VEW and piezometer locations; review data quality objectives (DQOs) for the Treatability Study relative to conditions encountered; and discuss treatment technologies that should be evaluated during the Treatability Study.

Attendees:

These meeting minutes are organized in the order discussed.

Geophysical Test Results and Future Geophysical Testing Needs

The meeting was opened with a presentation of the geophysical results and a summary of the geologic information assembled from the soil vapor extraction (SVE) drilling activities completed to date.  Over 10,000 linear feet of resistivity imaging surveys, 5,700 linear feet of seismic reflection surveys, and nearly 3,000 linear feet of microgravity surveys have been completed under the Task Order (TO) 0058.  Seven SVE vapor monitoring points (VMPs 1 through 7), two vapor extraction wells (VEWs 13 and 14) and two angle boreholes (A1 and A2) have been drilled during the installation of the SVE system outside building 90.  In addition, soil gas samples have been collected from the Building 90 subslab SVE system and from soil gas extraction packer test performed at VMP 4.

Results of the geophysical surveys suggest the presence of two faults trending northeast to southwest through the Area of Concern (AOC) 65/Building 90 area.  The northern-most fault is located north of Building 90 and is visible in the rock outcrop along the northern portion of the asphalt drive northwest of the Building.  The second fault is believed to trend through the area immediately south of Building 90.  The location of the second fault was based on results of the seismic survey and evaluations of geologic information from the area.  Based on geologic information, there is approximately 10 feet of offset across the northern fault and approximately 25 feet of offset across the southern fault.

Soil gas extraction packer tests were performed in the borehole for VMP-4.  Soil gas samples were collected from the 3-10, 9-16, 13-20, 26-33, 36-43, and 78-85 depth intervals.  Results of the soil gas packer tests indicates that the source material for the contamination is believed to be trapped in the upper 16 feet of subsurface material.  In the soil gas samples collected from the packer intervals at 3-10 feet and 9-16 feet, the oxygen levels were low, the carbon dioxide levels were high and degradation products (cis 1,2-dicloroethene) were present, suggesting that biodegradation of the contaminants is occurring. 

Drilling activities completed around Building 90 for the installation of the SVE vapor monitoring points have identified some of the subsurface features that affect migration of groundwater and contaminants through the area.  In most of the borings drilled for installation of the VMPs, a zone of highly weathered limestone was encountered at depths of 28 to 31 feet.  In several of the borings this zone included voids in the limestone rock material.  This zone is typically underlain by a competent limestone layer exhibiting little evidence of weathering.  Parsons believes that the competent limestone is relatively impermeable and that groundwater is moving laterally through the zone immediately above this layer, resulting in the significant weathering of this material.  This competent limestone layer is creating a perched groundwater zone when water is infiltrating and moving through the shallow material.  Other layers of weathered limestone zones were observed in the borehole video logs drilling at depths of 20 feet and shallower, but were not continuous across the site. 

A groundwater-bearing zone was identified at a depth of approximately 105 feet below land surface in angle boring A1.  This zone produced groundwater at approximately two to three gallons per minute during the coring operations.  This zone consists of a vuggy yellow fossiliferous limestone and has been encountered during drilling for the on-post monitoring wells.  This zone is generally considered to be the upper-most permeable zone and typically contains water during periods of high groundwater elevations.

Another important aspect of the site geology discovered during the drilling activities is that the number of fractures encountered in the borings typically increases towards the south.  Also, the occurrence of fractures with slickensides, evidence of movement along the fractures, increases to the south.  During drilling of monitoring well MW-6 CC north of Building 90, no significant fractures were encountered.

The increase in fracture density and occurrence of fractures with slickensides to the south is interpreted as the result of the faulting that has occurred south of Building 90.  The geologic data suggests that the fracture density in the upper 100 feet of material is increasing near the fault that trends immediately south of the building.  The high density of fractures observed in monitoring well MW-8CC may be associated with this fault south of Building 90 or possibly due to faulting further south of the monitoring well cluster.  The increase in the fracture density is expected to significantly influence the migration of groundwater and contaminants in the area.

The current conceptual model for groundwater flow at AOC-65 involves rapid infiltration and lateral flow through the shallow weathered zones.  Lateral flow occurs primarily through a highly weathered zone typically encountered between the depths of 28 and 31 feet below grade.  Groundwater in this zone is in effect “perched” upon the underlying competent limestone which has lower permeability.  Groundwater flows laterally through this weathered zone with an anticipated flow direction towards the south/southwest.  As the shallow groundwater moves south, it encounters a higher density of fractures and vertical migration increases.

A conceptual model for the migration of contaminant migration was developed during the meeting.  The model developed starts with the infiltration of water from rainfall runoff, infiltration along the nearby drainage ditch, and possible leakage from the Building 90 storm drains.  As groundwater moves through the shallow source zone, contaminants partition into the groundwater and are transported as dissolved constituents.  The dissolved contaminants are transported through lateral flow in the shallow weathered zones.  As it moves laterally, the contaminated groundwater will begin to migrate vertically through the fracture network associated with the faults north and south of the building.  Upon entering the fracture/fault network, the dissolved contaminants will continue to migrate along this complex network with some lateral migration into adjacent formations.

Future VEW and Piezometer Locations

Two VEWs (VEW-13 and VEW-14) located west of Building 90 were drilled in June 2002 and construction of VEW-13 has been completed.  Based on available data the locations and depths for five additional VEWs (VEWs 15 through 19) were selected.  The depths of the additional VEWs shall range from 13 feet to 80 feet and the locations will be to the west and south of the former vat location inside Building 90.  VEW-17 will be installed in the geophysical anamoly associated with the former utility trench west of Building 90.  With the addition of VEWs-15 through 19 the total number of VEWs was increased to seven, one more than originally planned. 

The locations for the six piezometers were selected to provide information regarding the shallow groundwater zones and the interaction of these zones with the fault zones to the north and south.  The zones of concern based on the current conceptual model were determined to be the weathered limestone layer at approximately 30 feet and the permeable zone encountered at a depth below 105 feet.  One piezometer will be installed in each of these zones west of Building 90 vat area, north of the northern fault zone, and south of the southern fault zone. 

DQOs

The task order DQOs were reviewed for agreement with the final VEW and piezometer configuration established during the meeting.  Due to heavy rainfall that prevented access to the base, the DQO discussion was conducted through a conference call to Brian Murphy and Brian Vanderglas.  The consensus was that the draft DQOs were adequate with only minor changes proposed.  The primary modification involved specifying the VOC compounds that are of concern for the AOC-65 Treatability Study and inclusion of total organic carbon as part of the groundwater analytical program.

Treatment Options

Additional treatment options that may be employed at AOC-65 were discussed.  One technology that may be useful at the site involves the addition of lactate and vegetable oil to enhance the natural degradation of the chlorinated compounds in the shallow subsurface.  The material could be added through injection wells or galleries installed near the source zone.  If proven effective at enhancing contaminant degradation, this method may represent a low cost remedial alternative for AOC-65.  To assess if the presence of hydrocarbons is contributing to the active degradation of the contaminants Parsons will include total organic carbon for the groundwater samples collected during the treatability study.  Parsons will prepare a technical evaluation paper with project summaries for current applications of enhanced biological degradation, for submittal to the regulatory agencies.  The use of lactate along with a backfill mixture of vegetable oil and bark mulch was also suggested for possible use at SWMU B-3.

Action items

Agenda for Technical Interchange/Progress Meeting #3