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Mr.M. Scott Mansholt-CEMC
<br /> Third Quarter 2005 Groundwater Monitoring and Sampling Report October 25,2005
<br /> Vernalis Pump Station,Vernalis,CA Page 4 of 6
<br /> TPHc were detected in borings ASB-1,ASB-2, and ASB-4 at a maximum concentration of
<br /> 17,000 mg/kg. TPHc were not detected in any other borings. Low concentrations of BTEX and
<br /> PAHs were sporadically detected in several soil samples. Geomatrix collected grab groundwater
<br /> samples from soil borings ASB-1,ASB-5 through ASB-8,ASB-10,ASB-11, and ASB-12. TPHd
<br /> were detected in grab groundwater samples collected from borings ASB-1,ASB-5,ASB-6,
<br /> ASB-7, and ASB-11, at a maximum concentration of 2,900 gg/L.
<br /> Based on the previous soil and groundwater investigations,petroleum-affected soil and
<br /> groundwater has been delineated vertically to a maximum depth of approximately 80 feet bgs.
<br /> The RWQCB approved the delineation results in their letter dated March 19,2004. However,the
<br /> lateral extent of affected soil and groundwater has not been delineated at the site. Furthermore,
<br /> soil and groundwater appears to be affected down gradient and off site and additional delineation
<br /> was requested in the east-northeast direction by the RWQCB in a letter dated July 9, 2004.
<br /> Groundwater beneath the site has been encountered between approximately 31 to 37 feet bgs.
<br /> Based on the data from previous reports, groundwater flow direction beneath the site varies
<br /> northeast to east.
<br /> PETROLEUM DISTRIBUTION IN GROUNDWATER
<br /> Groundwater samples have been analyzed one of the four recommended events. Based on this
<br /> initial quarterly sampling, SPO has not been observed in the wells. Dissolved-phase crude oil is
<br /> indicated by TPHd analyses. TPHd has only been detected in one well,MW-7 at 240 gg/L. No
<br /> TPHg or BTEX have been detected in the groundwater from the site wells. Sporadic and low
<br /> levels of PAHs have been detected in groundwater from MW-7 and MW-6, down gradient from
<br /> the former OVP.
<br /> GROUNDWATER MONITORING AND SAMPLING
<br /> MONITORING
<br /> On July 19, 2005,depth to water(DTW)was measured in wells MW-2,MW-3,MW-4,MW-5,
<br /> MW-6, and MW-7 using a hydrocarbon/water interface probe. DTW in these wells ranged from
<br /> 34.24 feet below top of casing(btoc) in MW-6 to 38.09 feet btoc in MW-4 and MW-5. The
<br /> approximate groundwater flow direction beneath the site is to the southeast at a calculated
<br /> gradient of approximately 0.001 feet/foot(ft/ft). A DTW measurement was not collected from
<br /> well MW-1 due to the presence of SPO. Cumulative DTW measurements,groundwater
<br /> elevations, and product thickness are presented in Table 1. A map showing the potentiometric
<br /> surface is presented on Figure 3. Field data sheets are included in Attachment A.
<br /> SAMPLING
<br /> Following DTW measurements,wells MW-2 through MW-7 were purged dry with a vacuum
<br /> truck on July 17, 2005. The purpose of purging was removal of sediment in order to create a
<br /> deeper water column from which to sample. On July 19, 2005, an additional four casing volumes
<br /> of groundwater were purged from wells MW-5,MW-6, and MW-7 using a disposable
<br /> polyethylene bailer. For wells MW-5,MW-6, and MW-7,pH, specific conductance, dissolved
<br /> oxygen,turbidity, and temperature water-quality parameters were recorded. After water-quality
<br /> parameters stabilized(i.e., a minimum of three consecutive readings with values within 10
<br /> percent for each parameter), groundwater samples were collected. Due to the low water levels,
<br /> no water-quality parameters were recorded for wells MW-2,MW-3, and MW-4. Field data
<br /> sheets are included as Attachment A.
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