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Crealogtcal Technics 14c Page 5 GW Monitoring Report Ted Peters-AST Project No 7012 March 5,2003 3.0 FINDINGS AND DISCUSSION ' The results of the groundwater sample analyses show the following • Groundwater samples from three of the five AST monitoring wells (MW-4, MW-6 and MW-7) reveal the presence of TPH-G or gasoline constituents Well MW-5 probably ' contains TPH-G but the detection limits are elevated due to the presence of high levels of TPH-D • Well MW-5 contained TPH-D at 57,600 µg11, which is lower then the previous ' monitoring event • A sheen of product was noted in MW-5 for this event This well has contained free product during previous events ' • Well MW-8 contain trace BTEX constituents at concentrations just above the laboratory reporting limits This is the first time since the well's installation in March 2001 that it has contained detectable contamination Well MW-8 is cross gradient to the former ' AST location and down gradient from the former UST location • Oxidation-Reduction Potential (ORP) and Dissolved Oxygen (DO) measurements (Table 3) suggest that all of the AST wells are in the core of the contamination plume or ' are immediately down gradient of the plume Negative ORP values and low DO values indicate that the wells are within the halo of reaction depleted water caused by biodegradation of the contaminants For the January 2003 event, all five wells had negative ORP values MW-6 is upgradient of the primary contamination sources (diesel ASTs) and MW-8 is perpendicular to gradient • Figure 4 illustrates TPH-G concentrations in groundwater in the vicinity of the former ASTs The highest level of TPH-G detected is in well MW-4, which is different from ' past events, which showed that MW-7 on the northwest side of the parcel had the highest concentrations Well MW-5 has previously contained the highest levels of TPH- G but contained free product sheen for this event ' • Additional monitoring is necessary to determine if the detection in MW-7 represents a detached plume from the former UST area or if it is sourced from a different release The concentrations continue to attenuate since its installation in March 2001 ' • Figure 5 illustrates TPH-D concentrations in groundwater in the vicinity of the former ASTs Well MW-5 contained free product sheen GTI's previous GeoProbe investigation revealed that the diesel contamination is limited to the area of former ASTs ' and associated dispensers 4.0 CONCLUSIONS & RECOMMENDATIONS Conclusions 1 Groundwater flow is predominantly to the northwest for both the AST and UST sites on ' this property GTI believes that previous southwesterly directions noted in the AST area are anomalous based on the presence of free product in MW-5 and/or the spatial onentation of the wells ' 2 TPH-G, TPH-D or volatile organic compounds are present in all five groundwater monitoring wells 3 The TPH-G concentrations exhibit a decreasing trend in the downgradient well MW_7 Figure 6 Well MW-7 TPH-G & Benzene versus Elevation illustrates this situation