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' Cieologual Tecknccs Inc Page 4 GW Momtormg Report Ted Peters-AST Project No 7012 September 19,2001 30 FINDINGS AND DISCUSSION The results of the groundwater sample analyses show the following ' • Groundwater samples from four of the five AST monitoring wells (MW-4, MW-5, MW- 6 and MW-7) reveal the presence of TPH-G or BTEX constituents • Free product was not detected in MW-5 for the event However, free product has been ' detected in MW-5 during previous events • A groundwater sample collected from MW-6 on February 17, 2000, was non-detect for all targeted compounds Previous to that event it tested positive for TPH-D, TPH-MO & TPH-K The presence of TPH-G in the well for this event indicates that individual chemicals of concern detected may be random surface infiltration, leakage from the adjacent sump, or portions of plumes originating from either the gasoline UST or/and ' the diesel ASTs During the GeoProbe investigation of August 2000, TPH-G was also found in GP-4 @ a concentration of 158 4g11, which is similar in concentration as the 146 �ig/l in MW-6 ' • Well MW-8 did not contain contaminant concentrations above the laboratory reporting limits for the second consecutive event This well is cross gradient to the former AST location and down gradient from the former UST location ' • The domestic well did not contain contaminant concentrations above the laboratory reporting limits • Oxidation-Reduction Potential (ORP) was measured (Table 3) The results suggest that several of the wells are in the core of the contamination plume or are immediately down gradient of the plume Negative ORP values indicate that the wells are within the halo of reaction depleted water caused by biodegradation of the contaminants For the August 1, 2001 event, MW-4, MW-5 and MW-7 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-7 on the northwest side of the parcel It is known that an adjacent site (SE corner of the Airport Way and Yosemite Avenue intersection) has had a gasoline groundwater impact Data from that site ' indicates a northward component of plume migration that has caused an MTBE impact to domestic wells immediately west of the Ted Peters site MTBE has not been detected at the Ted Peters site and is not a chemical of concern 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 • Figure 5 illustrates TPH-D concentrations in groundwater in the vicinity of the former ASTs Of the five wells tested, only MW-5 contained diesel contamination above the ' laboratory reporting limits GTI's previous GeoProbe investigation revealed that the diesel contamination is limited to the area of former ASTs and associated dispensers This monitoring event affirms this conclusion 4.0 CONCLUSIONS & RECOMMENDATIONS Conclusions 1 Groundwater flow is 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 1