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Mr.M. Scott Mansholt—CEMC <br /> First Semi-Annual 2008 Groundwater Monitoring and Sampling Report April 28,2008 <br /> Vernalis Pump Station Page 3 of 6 <br /> not considered representative of the potentiometric surface at the site due to well-casing damage <br /> (bent well casing)observed during the depth-to-groundwater measurement. <br /> Calculated Groundwater Elevation: The groundwater elevation at the site ranged from 69.07 feet <br /> (MW-1)to 71.56 feet(MW-6)above mean sea level(MSL) during the 4th quarter 2007. The <br /> groundwater elevation at the site ranged from 68.04 feet(MW-1)to 71.11 feet(MW-5)above <br /> MSL during the 1 st quarter 2008. The average groundwater elevation at the site is 70.99 feet <br /> above MSL based on all groundwater elevation measurements collected to date from these wells. <br /> Approximate Groundwater Flow Direction/Gradient: East at 0.001 feet per foot(ft/ft). Wells that <br /> were found to contain SPO were not used in the groundwater flow-gradient calculations. Depth- <br /> to-groundwater measurements collected from MW-4 were not used in the groundwater flow- <br /> gradient calculations due to a bent well casing. <br /> SAMPLING <br /> Wells MW-6 and MW-7 were purged using the regulatory-accepted, low-flow minimal drawdown <br /> method following depth-to-groundwater measurements during the 4th quarter 2007 and 1St quarter 2008 <br /> events. Wells MW-2,MW-3, and MW-5 were purged using the three well casing-volume purge method <br /> due to a slow recharge rate. A low-flow submersible pump with dedicated polyethylene tubing and a <br /> 1.5 inch,4 foot-long heavy-bottom polyvinyl chloride bailer was used. Measurements of pH, specific <br /> conductance,temperature, oxygen-reduction potential,turbidity, and dissolved oxygen water-quality <br /> parameters were recorded during the purge process. Groundwater samples were collected from wells <br /> MW-2,MW-3,MW-5,MW-6 and MW-7 after water-quality parameters stabilized. Stabilization criteria <br /> are presented on field data sheets (Attachment A). Groundwater samples were collected at wells MW-2, <br /> MW-3, and MW-5 following the three well casing-volume purge and after the groundwater recharged to <br /> 80 percent of the static depth-to-groundwater level. Well MW-1 was not sampled due to the presence of <br /> SPO, and well MW-4 was not sampled due to a bent well casing. Field data sheets are included in <br /> Attachment A. <br /> Laboratory-provided bottles were used to preserve the samples. The bottles were labeled, sealed, and <br /> placed immediately into an ice-cooled container for delivery to Lancaster Laboratories, Inc. (Lancaster), <br /> under SAIC chain-of-custody protocol. Lancaster is a California-certified laboratory(ELAP#2116). <br /> GROUNDWATER ANALYTICAL RESULTS <br /> The groundwater samples from wells MW-2,MW-3,MW-5,MW-6, and MW-7 were analyzed for the <br /> following constituents: <br /> • Total petroleum hydrocarbons quantified as diesel(TPHd) (C10—C25),using U.S. Environmental <br /> Protection Agency(EPA)Method 8015B and TPHd with silica-gel preparation for samples with <br /> detectable concentrations of TPHd using EPA Method 801513; and <br /> • Polynuclear aromatic hydrocarbons(PAHs)using EPA Method 8270C with large volume <br /> injection(monitoring in October was conducted using EPA Method 8270C with selective ion <br /> monitoring). <br /> The groundwater analytical results are summarized and compared with the RWQCB Region 2 <br /> Environmental Screening Levels (ESLs) and the numerical State Water Quality Objectives(WQOs)in <br />