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� � � � � � � � � � � � � � L � � � March 2006 7 053-2442 In order to document temporal trends in VOC concentrations in groundwater, we propose to conduct quarterly groundwater monitoring at the site for a period of one year. The iirst monitoring event would be conducted immediately after the monitoring we11s are installed and developed, and subsequent monitoring events wi11 be conducted approximately every three months for a period of one year. One additional water sample wi11 be collected from the sump in the basement of the service center during the iirst groundwater monitoring event. 2.4.1 Water Levels Water 1evels wi11 he measured in each of the monitoring we11s immediately prior to collecting groundwater samples. The water 1evels will he measured to the nearest 0.01 foot relative to the marked measuring point on the top of the PVC casing, using a decontaminated electronic water 1eve1 meter. 2.4.2 Groundwater Sample Collection Procedures Groundwater samples will be collected from each of the six monitoring we11s on a quarterly basis. A11 we11s wi11 he purged and sampled using 1ow flow purging and sampling procedures. We11s wi11 be sampled starting with those suspected to have the lowest 1evels of VOC concentrations and finishing with the we11s suspected to contain the highest VOC concentrations. The we11s will be purged at a rate of 0.2 to 0.5 liters per minute, and the water 1eve1 wi11 be monitoring during the purging process using an electronic water 1eve1 meter. The pump intake wi11 be placed at the center of the we11 screen and the pumping rate will be maintained unless significant water 1eve1 drawdown is measured, in which case the pumping rate wi11 be reduced to maintain minimal drawdown. During the purging process iield parameters including temperature, pH, conductivity, and dissolved oxygen, will be monitored using a Horiba (or similar) water quality meter and flow-through ce11. Purging wi11 continue until �ie1d parameters stabilize over a minimum of three consecutive readings measured in the flow-through ce11 at approximately 5-minute intervals. Stabilization wi11 be considered complete when at least one discharge tubing volume has been purged and the three consecutive readings agree within the following criteria: i01 standard units for pH; and � 10% for temperature, conductivity and dissolved oXygen. Once the parameters stabilize, groundwater samples for 'lrOCs wi11 be collected directly into the sample containers. Dissolved metals samples wi11 be collected by passing the sample water directly through a 0.45 micron filter prior to �illing the sample container. Sample bottles wi11 be filled, preserved as necessary, and placed in coolers packed with bagged ice. The sample coolers will be shipped under chain-of-custody via overnight delivery to the analytical laboratory. 2.4.3 Decontamination Procedures Non-dedicated pumps wi11 be decontaminated in the field prior to sampling each we11. Decontamination fluids wi11 he passed through the pump by operating the pump in a vessel filled with the fluids. The external pump housing and wiring will also be rinsed with decontamination solutions. Pump decontaminationprocedures wi11 include the following steps: � F1ush the pump with potable water;