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' Mr.M. Scott Mansholt—CEMC
<br /> First Quarter 2007 Groundwater Monitoring and Sampling Report April 24,2007
<br /> ' Vernalis Pump Station Page 3 of 5
<br /> range hydrocarbons(extractable TPH, C,o—C25) found in groundwater samples from HPP sites because no
<br /> WQOs are established for crude oil/Bunker C fuel oil,and historical data indicates that diesel-range
<br /> ' hydrocarbons are often detected at sites affected by crude oil/Bunker C fuel oil. Per the CTA,
<br /> groundwater samples are quantified against a diesel standard so that the comparison to the WQOs is as
<br /> direct as possible.
<br /> ' Based on the previous soil and groundwater investigations,petroleum-affected soil and groundwater have
<br /> been delineated vertically to a maximum depth of approximately 80 feet bgs. The RWQCB accepted the
<br /> ' delineation results in their letter dated March 19, 2004. Based on the May 2005 site investigation, it
<br /> appears that affected soil is laterally delineated north-northwest,north-northeast,south-southwest, and
<br /> south-southeast of the former boiler house and pump house, and affected groundwater is delineated
<br /> northwest and west of the former pump house and boiler house. Groundwater monitoring wells MW-5,
<br /> ' MW-6,and MW-7 were installed during the May 2005 investigation. A report of this investigation was
<br /> prepared and submitted to the RWQCB in August 20064. A sheen of SPO has been consistently observed
<br /> in well MW-1. TPH quantified as diesel (TPHd)have been consistently detected in one well,MW-7, at
<br /> ' concentrations ranging from 52 to 710 micrograms per liter(pg/L). No TPH quantified as gasoline
<br /> (TPHg)or benzene, toluene, ethylbenzene,and total xylenes (BTEX)have been detected in the
<br /> groundwater from the site wells. Low levels of polynuclear aromatic hydrocarbons(PAHs)have been
<br /> ' detected in groundwater from MW-2,MW-3,MW-5,MW-6, and MW-7.
<br /> GROUNDWATER MONITORING AND SAMPLING
<br /> ' MONITORING
<br /> On January 24, 2007, depth to groundwater was measured in wells MW-1 through MW-7 using a
<br /> ' hydrocarbon/water interface probe. Depth to groundwater in these wells ranged from 34.19 feet below
<br /> top of casing(btoc)in MW-6 to 38.29 feet btoc in MW-1. Calculated groundwater elevations ranged
<br /> from 68.09 feet(MW-1)to 71.24 feet(MW-4)above mean sea level(MSL). The approximate
<br /> groundwater flow direction beneath the site is to the east at a calculated gradient of approximately
<br /> ' 0.001 ft/ft. Cumulative depth-to-groundwater measurements, groundwater elevations, and SPO thickness
<br /> measurements are presented in Table 1. A map showing the potentiometric surface is presented on
<br /> Figure 3. Field data sheets are included as Attachment A.
<br /> ' SAMPLING
<br /> Following depth-to-groundwater measurements,wells MW-5,MW-6, and MW-7 were purged using the
<br /> ' regulatory-accepted, low-flow minimal drawdown method. Wells MW-2,MW-3, and MW-4 were not
<br /> sampled because the water volume in the wells was insufficient for sample collection. No sample was
<br /> collected from MW-1 due to the presence of SPO in this well. A low-flow submersible pump with
<br /> ' dedicated polyethylene tubing was used. During the purge process,pH, specific conductance,
<br /> temperature, oxygen-reduction potential,turbidity, and dissolved oxygen water-quality parameters were
<br /> recorded. After water-quality parameters stabilized(stabilization criteria is presented on field data
<br /> sheets), groundwater samples were collected. The groundwater samples were decanted into laboratory-
<br /> provided bottles that were labeled, sealed, and placed immediately into an ice-cooled container for
<br /> delivery to Lancaster Laboratories, Inc. (Lancaster),under SAIC chain-of-custody protocol. Lancaster is
<br /> a California-certified laboratory(FLAP#2116).
<br /> ' GROUNDWATER ANALYTICAL RESULTS
<br /> The groundwater samples from MW-5,MW-6,MW-7, and MW-6 field duplicate were analyzed for the
<br /> ' following constituents:
<br /> ' 4. SAIC,2006. Soil and Groundwater Investigation Report, Vernalis Pump Station, Vernalis, California. August.
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