ARCHIVED REPORTS XR0006301 - Laserfiche WebLink

Home Browse Search

' Third Quarter 2002 Status Report 7 Eleven 3 Inc Store#17647 1048 West Yosemite Avenue Manteca CA October 22 2002 During drilling, groundwater was encountered at approximately 15 feet bg During the current sampling event, depth to water ranged from 14 00 to 14 78 feet bg Groundwater flow directions are generally to the northwest(ranging from north to southwest), at a gradient of about 0 002 foot per foot ' Sensitive Receptors A sensitive receptor evaluation (IT Corporation, May 2000) indicates that there are approximately 14 wells ' within a one-mile radius of the site, but few within 1,000 feet of the site The nearest public supply wells are located approximately 993 feet north (usually crossgradient) of the site Two wells are also located approximately 4,956 feet southwest(downgradient) of the site ' Groundwater Monitoring Data ' Before monitoring, the well caps were opened to allow the water in each well to stabilize to atmospheric pressure The DTW was measured to the nearest 0 01 foot from the top of the well casing using an interface probe A potentiometric surface map prepared using the quarterly groundwater elevation data is shown in Attachment 1, Figure 2 Based on the groundwater elevation data, groundwater flow was toward the north at a hydraulic gradient of approximately 0 005 foot per foot Quarterly groundwater monitoring results and historical data are summarized in Tables 1 and 1A, respectively (Attachment 2) Field data sheets are ' included in Attachment 3 ' Monitoring Well Sampling and Analytical Results Before sampling, each of the wells was purged of three volumes of water by hand bailing Dissolved oxygen (DO)concentrations were also measured prior to sampling The wells were sampled using disposable bailers Groundwater samples were placed in analysis-specific containers with analysis- specific preservative The samples were then sealed Using Teflon septum caps, labeled with the lob identification number, the sample number, date, time, and type of laboratory analysis required The samples were stored on ice and transported with a chain-of-custody record to a state-certified laboratory Groundwater samples were analyzed for BTEX and TPH-G using EPA methods 8021/modified 8015, and for the oxygenates MTBE, TBA, RIPE, ETBE, and TAME using EPA methods 8020 and 8260 Dissolved benzene and TPH-G were not detected in any of the wells Dissolved MTBE was detected in wells MW-1, MW-2, and MW-3 at 0 94 pg/L, 2 6 ug/L and 1 9 lag/L, respectively, based on results from EPA method 8260 The other oxygenates were not detected, consistent with a trend established during ' previous quarterly sampling events (Table 1A) Dissolved 1,2-DCA was not detected above 1 lag/L Dissolved EDB levels were non-detectable Quarterly analytical results are presented in Table 1 Laboratory analytical reports for the groundwater samples are included in Attachment 4 17647Q23 doc