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Mike Vivas <br /> 8/06/02 <br /> Page 2 <br /> comments pertained to analytical data quality objectives and on a better presentation of <br /> proposed sampling locations. <br /> General Comments <br /> The revised Workplan Addendum does not address all of the comments provided by HERD <br /> on December 13, 2001. If the comments pertaining to the laboratory data quality objectives <br /> and the performance of the human health risk assessment will be incorporated in a separate <br /> report (Task 5), then this should be stated in the revised Workplan Addendum. <br /> Specific Comments <br /> 1. The revised Addendum does not address HERD's comment to present the detailed <br /> calculations that support Dr. Byard's risk estimates. Instead, this discussion was deleted <br /> from the revised Addendum. Please clarify whether this deletion should be considered <br /> as a response to HERD's comment. <br /> 2. Section 4.2, Task 2— Indoor and Ambient Air Sampling. One of the listed considerations <br /> for possibly adjusting sample locations is the most recent wind pattern data. This <br /> addresses HERD's comments about showing the wind rose data. This information <br /> should be included in subsequent reports. <br /> Information from Magellan Environmental Inc. indicates that the modified HVAC system <br /> will be operational 24 hours a day. It is HERD's understanding, however, that the HVAC <br /> system is currently turned off at night. HERD recommends that, until the HVAC system <br /> is being operated 24 hours a day, indoor air samples should be collected to represent <br /> different conditions: <br /> 1. At the start of the work day (before the HVAC is turned on), <br /> 2. During the course of a work day (while the HVAC is operating), <br /> 3. At night while the HVAC is turned off. <br /> HERD also recommends that there should be multiple sampling events due to the <br /> potential influence of temporal factors on vapor intrusion into buildings. <br /> Conclusions and Recommendations <br /> While the revised Workplan Addendum addressed some of HERD's comments, clarification <br /> should be provided regarding the sampling approach, i.e., proposed sampling time periods, <br /> frequency. HERD recommends that, wherever feasible, soil gas samples should be <br /> collected beneath the building where indoor air samples will be collected so that predicted <br /> concentrations of indoor air could be validated by the measured indoor air concentrations. <br /> 2 <br />