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I March 2006 7 053-2442 r 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 first monitoring event would be conducted immediately after the monitoring wells are installed and developed, and subsequent monitoring events will be conducted approximately every three months for a period of one year. One additional water sample will be collected from the sump in the basement of the service center during the first groundwater monitoring event. I l 2.4.1 Water Levels L Water levels will be measured in each of the monitoring wells immediately prior to collecting groundwater samples. The water levels will be 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 level meter. l L l 2.4.2 Groundwater Sample Collection Procedures Groundwater samples will be collected from each of the six monitoring wells on a quarterly basis. All wells will be purged and sampled using low flow purging and sampling procedures. Wells will be sampled starting with those suspected to have the lowest levels of VOC concentrations and finishing with the wells suspected to contain the highest VOC concentrations. l The wells will be purged at a rate of 0.2 to 0.5 liters per minute, and the water level will be monitoring during the purging process using an electronic water level meter. The pump intake will be placed at the center of the well screen and the pumping rate will be maintained unless significant water level drawdown is measured, in which case the pumping rate will be reduced to maintain minimal draw down. I l ( During the purging process field parameters including temperature, pH, conductivity, and dissolved oxygen, will be monitored using a Horiba (or similar) water quality meter and flow-through cell. Purging will continue until field parameters stabilize over a minimum of three consecutive readings measured in the flow-through cell at approximately 5-minute intervals. Stabilization will be considered complete when at least one discharge tubing volume has been purged and the three consecutive readings agree within the following criteria: :1:0.1 standard units for pH; and:1: 10% for temperature, conductivity and dissolved oxygen. Once the parameters stabilize, groundwater samples for VOCs will be collected directly into the sample containers. Dissolved metals samples will be collected by passing the sample water directly through a 0.45 micron filter prior to filling the sample container. L I l Sample bottles will 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 L Non-dedicated pumps will be decontaminated in the field prior to sampling each well. Decontamination fluids will be 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 decontamination procedures will include the following steps: I . Flush the pump with potable water; l I