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s1 Geological reckmcs Inc Page 5 3`d Quai ter 2003 Groundwatei Motu toring Repoit ' Project No 507 2 16 November 13,2003 f� • Watei table well MW-10 did not contain contaminant concentrations above the ' laboratory i eporting limits for the sixth consecutive event The well has previously f contained xylene at levels Just above the laboratory reporting limit of 0 3 µg/l + Deep well MW-109 did not contain contatnmants above the laboratory reporting limits for the second consecutive event The reduction in contaminant concentrations from the first sampling event on June 1, 2001 is noted and sufficient monitoring has been pei formed to conclude that it was probably a drilling artifact or the bottom of the gioundwatei plume • Figure 4 illustiates the relationship between groundwater elevation and TPH-G ' concentiations in well MW-9 (located in the core of the plume) An inverse trend was consistent lot the first lour monitoring events, but since the March 2001 event the telationship has been piedommantly parallel • Figure 5 illustrates the relationship between groundwater elevation and TPH-G concentrations in well MW-5 (located up/cross gradient of the core of the plume) An inverse trend was consistent for the first four monitoring events, but since the March ' 2001 event the relationship has been predominantly parallel The March event recorded a return to an invetse ielationship between the two parameters • Tiend line~ added to the data in Figure 4 show that as the groundwater elevation has lowered since 1999 that the concentration of TPH-G has increased This suggests that concentiation is dncetly ielated to groundwater level at the site ' o Figuie 6 indicates an inconsistent relationship between groundwater elevation and contaminant concentiations in well MW-6 No data is included for the December 2002 event due to the well's inaccessibility ' • Figures 4, 5, & 6 illustiate that the concentrations of TPH-G increases as the water table decreases, suggesting that the plume is stable and not being degraded by natural biodegradation causes The groundwatei gradient is relatively flat and the direction of groundwater flow has varied dui ing the coui se of the investigation ' • Oxidation-Reduction Potential (ORP) was measured (Table 4) and the results suggest that all of the wells sampled are either in the core of the contamination plume or are immediately down gi adient from the plume and within the halo of reaction depleted _ ' water caused by biodegradation of the contaminants • Figure 7 is a contour ural) indicating the TPH-G concentrations on September 11, 2003 The gioundwatet plume is localized in the vicinity of the foriner UST excavation The bulls-eye pattei n to the TPH-G contour map in Figure 7 shows that the center of the plume has not moved fiom its source and suggests that contaminant migration may be occur ing pi nnai dy by diffusion with a slight influence by advection