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Ms. Rebecca E. Setliff Page 3 of 4 Monitoring Well Placement Ground Zero disagrees with EHD's recommendation to move the location of monitoring well cluster MW15A-C toward the west. The well location proposed in the October 31, 2001 Workplan was intended to complete the definition of the downgradient extent of groundwater contamination originating from the release at 102 S. Wilson Way. " Ground Zero is unable to understand why it would be advantageous to construct the proposed monitoring well cluster within the estimated limits of the plume. According to our interpretation of the downgradient extent of contamination (see Figures 4 and 5, Workplan for Additional Site Activities, 10/31/01) at EHD's proposed location MW 15A and MW 15B would almost certainly be contaminated. If this were to be the case, additional downgradient wells would then be required. We also do not see the benefit of constructing deep wells at this time near the locations of current wells MW 12 and MW13. Monitoring well MW13 is within the heart of the plume of contamination and this fact does not need verification with additional wells. By itself, the proposed MW 15 cluster should adequately define the downgradient limits of the plume and another downgradient monitoring point near MW12 may prove unnecessary. Mud rotary drilling necessitates a larger footprint for the drilling and mud system equipment than does hollow stem auger work. Since the obstructions (trees and overhead lines) along the south side of Market Street likely will not accommodate the equipment, we recommend moving the location of the well cluster to the east side of the building as shown on Figure 2. We recommend conducting several quarters of sampling in order to confirm analytical results prior to evaluating the need for any additional wells. If the data indicate that plume definition is incomplete, additional wells will be proposed Sample Collection and Analysis Soil samples from borings drilled with hollow stem augers will be collected and analyzed as described in the October 31, 2001 Workplan. Due to the mud rotary drilling method, we do not expect to collect undisturbed soil samples for laboratory analysis from MW15C. Stratigraphy of the boring will be determined by logging the cuttings. Well Development, Surveying and Groundwater Sampling All new monitoring wells will be developed, surveyed and sampled as described in the October 31, 2001 Workplan. Evaluation of Ozone Injection Ground Zero will research and evaluate ozone injection as a potential remedy. Although we are conceptually familiar with the method, we have no applied experience. It would be helpful if EHD would identify to us example sites located in San Joaquin County where ozone injection has been successful. We hope to review the files in order to evaluate the specifics of the technique prior to proposing and designing a pilot test. Roek\c1osure\workp1m\addendum.dm