ARCHIVED REPORTS_SECOND 2008 SEMI-ANNUAL GROUNDWATER MONITORING AND SAMPLING REPORT

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' M. Scott Mansholt—CEMC Second Semi-Annual 2008 Groundwater Monitoring and Sampling Report September 26,2008 Vernalis Pump Station Page 3 of 7 ' groundwater at the site is 36.59 feet btoc based'on depth-to-groundwater measurements collected to date from wells MW-1 through MW-7. Depth-to-groundwater measurements collected from MW-4 during the third quarter 2008 event are not considered representative of the potentiometric ' surface at the site because of a damaged casing. • Calculated Groundwater Elevation: The groundwater elevation at the site ranged from ' 70.09 feet(MW-7)to 70.28 feet(MW-6) above Mean Sea Level (MSL)during the second quarter of 2008. The groundwater elevation at the site ranged from 67.72 feet(MW-1)to 70.93 feet (MW-5) above MSL during the third quarter of 2008. The average groundwater elevation at the ' site is 70.93 feet above MSL based on all groundwater elevation measurements collected to date from wells MW-1 through MW-7. • Approximate Groundwater Flow Direction/Gradient: East at 0.001 feet per foot(ft/ft). Wells ' MW-1 and MW-4 were not used in the groundwater flow-gradient calculations due to the presence of SPO and a damaged casing, respectively. SAMPLING Wells MW-6 and MW-7 were purged during the second quarter 2008 sampling event using the regulatory-accepted,low-flow minimal drawdown method. A low-flow submersible pump with dedicated polyethylene tubing and a 1.5-inch,4 foot-long,heavy-bottom polyvinyl chloride bailer were used to purge and sample the wells. Groundwater samples were collected after water-quality parameters (pH, ' specific conductance,temperature, oxygen-reduction potential,turbidity, and dissolved oxygen) stabilized. During the third quarter 2008 sampling event, wells MW-2, MW-3, and MW-5 were purged using the three well-casing volume purge method due to a slow recharge rate, and wells MW-6 and MW-7 were purged using the low-flow minimal drawdown method. Groundwater samples were collected from wells MW-2,MW-3, MW-5,MW-6, and MW-7 after water-quality parameters stabilized and the wells recharged to at least 80 percent. Well MW-1 was not sampled due to the presence of sheen on the water, and well MW-4 was not sampled due to a damaged casing. Field data sheets are included as Attachment A. ' Laboratory-provided bottles were used to preserve the samples. The bottles were labeled, sealed, and placed immediately into an ice-cooled container for delivery to Lancaster Laboratories, Inc. (Lancaster), ' under SAIC chain-of-custody protocol. Lancaster is a California-certified laboratory(ELAP#2116). The groundwater samples from wells MW-2,MW-3,MW-5,MW-6, and MW-7 were analyzed for the following constituents: • Total petroleum hydrocarbons quantified as diesel(TPHd; CIO—C25),using U.S. Environmental Protection Agency (EPA)Method 801513, and TPHd with silica-gel preparation for samples with ' detectable concentrations of TPHd using EPA Method 801513; • During the second quarter sampling of MW-6 and MW-7, the samples were also analyzed for ' polynuclear aromatic hydrocarbons (PAHs)using EPA Method SW-846 8270C with selective ion monitoring.