ARCHIVED REPORTS_XR0008535 - Laserfiche WebLink

Home Browse Search

n f Site Background Information Eckert Cold Storage,Manteca,CA Page 6 of 8 review of the MW-5 and MW-8 data, it appeared that the samples might have been switched and mislabeled in the field or at the laboratory. Therefore, monitoring wells MW-5 and MW-8 were re- sampled on January 10, 2005. The data from the re-sampling indicated that there was no field or laboratory mistake and that the groundwater contaminant conditions in the location of the wells had changed. Water levels were collected from all eight of the sites monitoring wells. The average groundwater elevation was approximately 4.32 feet hi her on December 30, 2004 than the previous sampling event conducted on September 7, 2004. The groundwater gradient estimated with a three-point construction using wells MW-3, MW-4, and MW-6 was approximately 0.003 ft/ft towards the north-northwest. Historically,the groundwater gradient is variable,but generally to the northwest. Condor conducted the first quarter 2005 groundwater monitoring event at the site on March 9, 2005. Because of the change in site groundwater conditions indicated by the fourth quarter 2004 monitoring described above, Condor recommended the sampling of MW-5 on a quarterly basis in addition to regularly scheduled quarterly monitoring of MW4 and MW-8. Harlin Knoll of the SJCEHD agreed but indicated that MW-1 should also be sampled to update contaminant concentrations in the site source area. Groundwater samples, therefore, were collected and submitted for laboratory analyses from monitoring wells MW-1, MW-4, MW-5, and MW-8. No separate phase petroleum was noted in the wells, but petroleum sheen and a moderate petroleum odor were noted in the groundwater inspection sample recovered from MW-8.' The groundwater samples collected from the four monitoring wells were analyzed for BTEX, TPH-G, and selected gasoline oxygenates/additives including MTBE. Laboratory analytical results of the sample collected from MW-1 . during the March 9, 2005 monitoring event indicated that contaminant concentrations were generally an order of magnitude less than for historic monitoring results. The MW-4 sample results were generally consistent with historic laboratory analytical results. Prior to the December 2004 monitoring event, historic laboratory analytical results of groundwater samples collected from MW-5 indicated generally very low contaminant concentrations. Laboratory analytical results of samples collected from MW-5 in December 2004, January 2005, and March 2005 indicated higher contaminant concentrations (but with a decreasing trend in contaminant concentrations). Conversely, prior to the December 2004 monitoring event, historic laboratory analytical results of groundwater samples collected from MW-8 indicated generally elevated contaminant concentrations. Laboratory analytical results of samples collected from MW-8 in December 2004, January 2005, and March 2005 indicated lower contaminant concentrations relative to the historic results. Water levels were collected from all eight of the site monitoring wells on March 9, 2005. The average groundwater elevation was approximately 2.25 feet higher than the previous sampling event conducted on December 30, 2004. The groundwater gradient estimated with a three-point construction using wells MW-3, MW-4, and MW-6 was approximately 0.0033 ft/ft towards the northwest. Historically, -the groundwater gradient had been variable, but generally to the northwest, so the groundwater gradient direction on March 9, 2005 was generally consistent with historic groundwater gradient directions. Condor conducted the second quarter 2005 groundwater monitoring event at the site on July 8, 2005. Monitoring wells MW-5 and MW-8 were sampled during the second quarter. As mentioned above, Condor had recommended quarterly monitoring of MW-5 along with MW-4 and MW-8 in the First Quarter Groundwater Monitoring Report. After reviewing Condor's recommendation, Mr. Harlin Knoll of the SJCEHD verbally requested quarterly monitoring of MW-5 and MW-8 provided that Site • monitoring wells MW-1 and MW4 are sampled on annual basis in the fourth quarter(December).