SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

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; C,o—C25),using U.S. Environmental Protection Agency(EPA)Method 8015B,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.