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1 • Page 4 Ms Margaret Lagono ' February 21, 1997 ' PetroIeum Hydrocarbon Analytical Data ' Certified laboratory reports and chain-of-custody documentation are presented in Appendix C Current TVH-G and BTEX results are presented in Table 3 Historic tabulation and graphical presentations for TVH-G and benzene are presented in Table 4 and Table 5, respectively 1 PSH were not observed in any of the monitoring wells The highest TVH-G and BTEX concentrations were detected in samples collected from monitoring wells MW-1, MW-4, ' and MW-12 Lower TVH-G and BTEX concentrations were measured in samples collected from Monitoring Wells MW-5, MW-9, MW-11, and MW-13 Petroleum concentrations were not detected in samples collected from monitoring wells MW-2 and MW-3, MW-6 through MW-8, MW-10, and the trip blank TB-01 In general, the ' detected petroleum concentrations were lower than those measured in the previous monitoring event, except for samples collected from monitoring wells MW-4 and MW- 12 As illustrated in the Table 4 and Table 5 historic graphical presentations, TVH-G and ' benzene concentrations are generally trending lower Biodegradation Assessment Data 10 Biodegradation analytical results are summarized in Table 6 A graphical presentation of results for samples collected from monitoring wells passing through the area of petroleum-impacted groundwater is shown in Table 7 and Table 8 1 The reference document for this biodegradation assessment, Protocol for Monitoring Intrinsic Bioremediation in Groundwater, indicates that natural biodegradation is 1 occurring when a directly proportional relationship is evident between petroleum concentrations and ferrous iron and alkalinity concentrations,and an inversely proportional relationship with dissolved oxygen, redox potential, nitrate, and sulfate concentrations A decrease of dissolved oxygen concentration, in a sample collected from 1 a petroleum-impacted well compared to a sample collected from a lower or non-impacted well, would indicate aerobic biodegradation An increase of ferrous iron or alkalinity, or a decrease in redox potential, nitrate, or sulfate would be an indication of anaerobic ' biodegradation Such evidence demonstrated for any one of these parameters suggests the occurrence of intrinsic biodegradation ' Benzene concentrations for samples collected from monitoring wells MW-6, MW-4, MW-1, MW-7, MW-12, and MW-8 (along profile A-A' of Figure 5) are plotted along with their respective dissolved oxygen concentrations on the graph in Table 7 A decrease in dissolved oxygen, evident in samples collected from those monitoring wells with 1 detectable concentrations of benzene, indicates that aerobic biodegradation is occurring Benzene concentrations for samples collected from the wells along profile A-A' are also 1 plotted along with the other biodegradation parameters in Table 8 Decreases in nitrate and sulfate concentrations, and negative redox potential values are evident in the • 1 E 121382112599714gtr96 doc 1