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---------------- 10 Evaluation of Natural Attenuation: 7SOO West Eleventh Street, Tracy, C.4. Page 14 not close to the bottom of the well) and approximately 2-3 gallons of water were pumped through the system before a water sample was carefully introduced into the glass testing container. Great care was taken when introducing the water to prevent entrainment of air into the sample. After sampling a well, the line filter was discarded, the peristaltic pump lines were thoroughly decontaminated and a new filter was installed before proceeding to test water for ferrous oxide in the next well. When the 1,10 phenanthroline reagent was added to the samples, the color of the water became orange only in the cases of the samples from Monitoring Well MW-7 and MWFP-l. In the sample from all other wells, the sample water remained clear. These results are documented.in Table 5 and further discussed in Section 7.0. 4.1.2 Dissolved Oxygen and Redox Potential Dissolved oxygen and redox potential was measured in the field by use of a YSI Model 556 Multiprobe System equipped with an in-line flow chamber. Groundwater was pumped from each well by the peristaltic pump and the system was i purged of entrained air in the same manner as was the case for the ferrous oxide tests discussed above. The results of the measurements are presented in Table 5 and discussed in Section 7.0. 4.1.3 Temperature, Conductivity and pH r.:.I Temperature, conductivity and pH of the groundwater were also measured using the YSI Model 556 Multiprobe System. The values of these parameters were recorded at the same time as the measurements of dissolved oxygen and redox potential. The results of the measurements are presented in Table 5 and discussed in Section 7.0. .1 4.2 Sampling and Laboratory Analyses for Natural Attenuation Parameters The peristaltic pump system (without filtration) was also used to recover samples for laboratory analyses for natural attenuation parameters. The slow discharge rate of the peristaltic pump permitted the aliquots of groundwater to be introduced into the glassware without entrainment of air. The glassware was provided by the laboratory and, where necessary, contained the appropriate pre-dispensed preservatives. -� After the caps had been placed on the glassware, the sample vials and bottles were then tightly closed, labeled for identification, entered into chain-of-custody control and packed j` on chemical ice for transport, on the same day that they were recovered, to Severn Trent Laboratories' (STL) laboratory in Pleasanton, California for analysis. E Each groundwater sample recovered was analyzed at the laboratory for the following suite of analytes. f sic