ARCHIVED REPORTS_XR0003864 - Laserfiche WebLink

Home Browse Search

I ':iC6bgual Techflas Inc Page 6 ' Groundwater Monitoring Report Project No 770 2 0 March 16,2006 ' very consistent, but now appear to be fluctuating again The cause for the recent high spikes is unclear, possibly due to low water level in the well and associated poor recharge to the well during purging and sampling This may account for the August 19, 2004 and December 9, 2005 spike in diesel concentrations, but not the June 13, 2005 spike Purging and sampling logs suggest that sample quality may be compromised due to low water level in the well The plot in Figure 6 suggests that a previously direct relationship between groundwater elevation and contaminant concentrations has reversed since June 2002 Well MW-5 continues to contain the highest concentrations of detected contaminants (see Figure 8) It is not down gradient of the former UST location and the reason for this anomaly ' is not known, but could be related to soil structure that is oriented to the west MW-4 ' Well MW-4 lies adjacent to the former UST field Figure 7-MW-4 TPH-D vs Groundwater Elevation suggests that a predominantly inverse relationship exists between groundwater elevation and contaminant concentrations In this figure the sudden increase in diesel ' concentrations for August 2004 coincides with the same phenomenon observed in MW-5 The cause is unknown at this time, but the diesel concentrations have decreased since that event - 10 MW-105 TPH-D was not detected in MW-105 for the third consecutive event Detection of TPH-D in a the last two quarters of year 2004 indicated that the contamination has moved vertically downward in an oblique angle to the northwest from the source In Figure 9—MW-5 & MW- 1.05 TPH-D versus Groundwater Elevation, well MW-5 contaminant concentrations had previously exhibited a weak correlation with changes in the water table Well MW-105, screened below the water table, exhibits a typical on/off trend (alternating between detecting ' diesel at —100 µg/l to ND<50 µg/1), thus suggesting that the vertical extent of the diesel plume is near the depth interval of MW-105 1 Figure 10 illustrates the distribution of diesel in the deeper wells TPH-D was not detected in the deep wells so an iso-concentration diagram was not developed ' GTI makes the following recommendations • Maintain the quarterly monitoring schedule • In response to the comments from SJCEHD on the initial site conceptual model report, ' we recommend that additional site characterization work be performed and interim remedial action pian be implemented Eleven CPT borings were advanced at the site on October 28 — November 3, 2005 A site characterization report and updated Site ' Conceptual Model are being developed based on the data gleaned from this effort 1