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i= C ® R 1709 Station #11191 Quarterly Groundwater Monitoring Report (102006) April 28, 2006 • Page 3 Groundwater samples were collected using a disposable Teflon® bailer, placed Into appropriate Environmental Protection Agency (EPA) approved containers, labeled, logged onto chain-of- custody documents, and transported on Ice to Sequoia Analytical, a California state-certified laboratory Copies of the field notes are in Attachment B GROUNDWATER SAMPLE ANALYSES The groundwater samples were submitted to Sequoia Analytical laboratory for analysis of gasoline range organics (GRO), BTEX, and fuel oxygenate MtBE by EPA Method 8260B Results are discussed below The certified laboratory analytical report and chain-of-custody documentation are presented as Attachment C GROUNDWATER SAMPLE RESULTS AND DISTRIBUTION Gasoline range organics (GRO) and methyl tert-butyl ether (MtBE) were detected above laboratory reporting limits in groundwater samples collected from site monitoring wells this quarter Both GRO and MtBE concentrations Increased In wells MW-1 and MW-4 since fourth quarter 2005 GRO levels also Increased in MW-2 MtBE levels decreased since fourth quarter 2005 in wells MW-2 and MW-3 Benzene was detected under the laboratory reporting limit at each monitoring well Other analytical concentrations were generally consistent with previous • sampling events The depths to groundwater In site monitoring wells decreased in first quarter 2006 relative to the well depths of the previous monitoring event The range of depths to groundwater In monitoring wells in fourth quarter 2005 was 52 96 to 54 80 feet below ground surface (bgs), while the range In first quarter 2006 was 49 23 to 51 30 ft bgs The Inferred direction of groundwater flow across the site ranged from east/southeast at an average hydraulic gradient of 0 015 ft/ft (Figure 3) This report Is based on data, site conditions, and other Information that are generally applicable as of the date of the report, and the conclusions and recommendations herein are therefore applicable only to that time frame Groundwater analytical results for benzene, TPHg and MtBE dissolved In groundwater are presented on Figure 4 and are summarized In Table 1 , Dissolved MtBE Distribution The constituents of concern at the site Include dissolved MtBE MtBE has historically been detected in the majority of the site wells, with the highest concentrations during the first quarter 2006 reported in wells MW-4 and MW-5 at maximum concentrations of 8,300 pg/L and 4,300 I pg/L, respectively The concentration of MtBE also Increased In well MW-1, from 45 pg/L to 3,600 pgIL In wells MW-2 and MW-3, MtBE levels have decreased since fourth quarter 2005 from 3,700 pglL to 1,500 pg/L (MW-2) and from 1,700 pglL to 900 pgIL (MW-3) Concentrations of MtBE remained below laboratory reporting limits In wells MW-6 and MW-7 • I I6P-ARC0105 BP-COP s[tes1111911ReportslQMRs111191 1QO6 QMR final doc SECOR International Incorporated