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' TPHg maps were also plotted using data from March 17, 2004, June 13, 2004 and September 13, 2004, The March 17, 2004 and June 3, 2004 sampling data were obtained prior to system start- up. The September 13, 2004 sampling data was information obtained approximately 3 '/2 months after system operation start-up. Although there are not apparent reductions in the areal extent of TPHg, significant reductions of TPHg concentrations are apparent along the injection well ' corridor(Figure 23). 5.0 CONCLUSIONS ' Petroleum hydrocarbons and associated chemicals of concern (CDCs) detected in the groundwater samples collected from MW6a and MW7a indicate the hydrocarbon plume extends ' offsite in the shallow aquifer. Petroleum hydrocarbons and associated CDCs detected in groundwater samples collected from MW6b, MW6c, MW7b, MW7c, and MW10b indicate the plume extends offsite to the east in deeper groundwater, of benzene appear to be declining in MWI and EW1 and are possibly declining Concentrationspp g in MW4 due to the C-SpargeTM operation. The TPHg concentrations appeared to decrease ' significantly in MWI, MW4 and EW1. DO also increased significantly after system start-up in MWI from 0.36 mglL on June 3, 2004 to 4.72 mg/L on September 13, 2004 suggesting a further correlation. DO may have increased very slightly in MW4 and EW1. Although DO increased significantly after system start-up in MW2 from 1.39 mg/L on June 3, 2004 to 3.81 mg/L on September 13, 2004, the effects of the remediation system are unclear in ' this well. Interpretation of system effectiveness based on MTBE reduction in the Jamar wells is unclear at this time. ' 6.0 RECOMMENDATIONS ' Based on the results of the third Quarter 2004 monitoring episode, ATC makes the following recommendations: ' ■ Conduct fourth quarter groundwater monitoring and sampling of MWI through MWIOC and EW1 and analyze the samples for TPHg, BTEX, MTBE, ETBE, DIPE, TBA, TAME, 1, 2-13CA and EDB. ' ■ Conduct monthly groundwater monitoring and sampling for field parameters including DO and ORF in the on-site remediation well network (MWI through MWS, MW8 and EW1) 1 ■ Continue operation and monitoring of the C-SpargeTM system for existing parameters and begin monitoring electrical meter readings. ■ Install a system flow meter. Evaluate system flow on IW5 and install flow meters if necessary. ' s:1268231QM reports12004 3QR.doc 11 ATC Associates Inc.