ARCHIVED REPORTS XR0011750 - Laserfiche WebLink

Home Browse Search

I. Report:Groundwater-quality Monitoring—January 26,2004: 7500 West Eleventh Street, Tracy, CA. Page 11 of 2.0 gg/L, which is a slight reduction from the concentration of 2.9 gg/L in the sample recovered from that well in October 2003. It is notable that the sample from Monitoring Well MW-5 in January 2004, as was also the case in October 2003, contained no concentration of diesel. Diesel was apparently present at a concentration of 68 gg/L in the sample recovered from that well on July 30. However, that sample was not treated with silica gel according to EPA Method 3630 prior to analysis. It was, therefore, taken to be a false positive for a component of fuel hydrocarbons (The San Joaquin Company Inc. 2003c); the negative results for diesel obtained from the October 2003 and January 2004 samples, which were pretreated by EPA Method 3630, confirm that conclusion. As is i.., shown on Figure 2, Monitoring Well MW-5 is located at the extreme western perimeter of the plume of affected groundwater. �.. The only analyte of concern detected in Monitoring Well MW-6 on January 26, 2004 was MTBE at a concentration of 200 gg/L, which is only slightly higher than the 130 gg/L detected in the sample recovered in October 2003. Though diesel-range petroleum hydrocarbons at concentrations of 130 gg/L, and 55 gg/L were detected in the July and October 2003 monitoring rounds, respectively, the sample recovered on January 26, 2004 from Monitoring Well MW-6 contained no measurable diesel-range hydrocarbons. Gasoline had been present in that well during the earliest monitoring rounds, but for the 12 months between July 2002 and July 2003 it had been absent. It was detected at a concentration of 130 gg/L in October 2003, but was not detected on January 26, 2004. As was the case for the sampling round conducted on October 27, 2003, the only analytes of concern detected in the sample recovered from Monitoring Well MW-10, which is *- located on the eastern perimeter of the plume, in the sample recovered on January 26, 2004 were TPHg at 88gg/L and MTBE at 90gg/L, both of which are moderate decreases compared to the concentrations in the sample recovered from that well in October 2003. L 2.4.1.3 Analytes of Concern in Secondary Groundwater Plume R As is also shown on Figure 2, a secondary plume of diesel and gasoline emanates from an area to the rear and slightly to the east of the Casa Mendoza restaurant on the 7500 West Eleventh Street property. However, in compliance with SJCEHD guidance for the current groundwater-quality monitoring program, no samples were recovered from either of the wells in the area of the secondary plume on January 26, 2004. 4 AIM 2.4.2 Groundwater Quality in the Deeper Confined Aquifers In compliance with SJCEHD guidance for the groundwater monitoring program at the 7500 West Eleventh Street site, no samples were recovered from Monitoring Wells MW- 3A, 3B and 12A, which are screened at the deeper aquifers on the 7500 West Eleventh Street site, on January 26, 2004. t �- sic