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Mr.M. Scott Mansholt—CEMC
<br /> Second Quarter 2006 Groundwater Monitoring and Sampling Report July 11,2006
<br /> Vernalis Pump Station Page 3 of 5
<br /> Technical Approach to Site Evaluation and Decision-Making for the Historical Pipeline Portfolio
<br /> (HPP)(herein referred to as the CTA), diesel products are not associated with the HPP sites and
<br /> typically are not present at these sites.3 However,WQOs are applied to"diesel-range
<br /> hydrocarbons" (extractable TPH, C10—C25) found in HPP site groundwater samples because no
<br /> WQOs are established for crude oil/Bunker C fuel oil, and historical data indicates that diesel-
<br /> range hydrocarbons are often detected at sites affected by crude oil/Bunker C fuel oil. Per the
<br /> CTA,groundwater samples are quantified against a diesel standard so that the comparison to the
<br /> WQOs is as direct as possible.
<br /> Based on the previous soil and groundwater investigations,petroleum-affected soil and
<br /> groundwater have 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. Based on the
<br /> 2005 site investigation, it appears that affected soil is laterally delineated north-northwest,north-
<br /> northeast, south-southwest, and south-southeast of the former boiler house and pump house, and
<br /> affected groundwater is delineated northwest and west of the former pump house and boiler
<br /> house. Groundwater monitoring wells MW-5,MW-6, and MW-7 were installed during the May
<br /> 2005 investigation. A report of this investigation is in preparation. A sheen of separate-phase oil
<br /> (SPO)was observed in well MW-1. TPH as diesel-range organics(TPHd)have been consistently
<br /> detected in one well,MW-7, at concentrations ranging from 240 to 710 micrograms per liter
<br /> (µg/L). No TPH as gasoline-range organics(TPHg)or benzene,toluene, ethylbenzene, and total
<br /> xylenes (BTEX)have been detected in the groundwater from the site wells. Low levels of
<br /> polynuclear aromatic hydrocarbons(PAHs)have been detected in groundwater from MW-2,
<br /> MW-3,MW-5,MW-6,and MW-7.
<br /> GROUNDWATER MONITORING AND SAMPLING
<br /> MONITORING
<br /> On May 4,2006, 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 was not measured in MW-1
<br /> because of the presence of a petroleum-absorbing(oleophilic) sock. DTW in these wells ranged
<br /> from 35.17 feet below top of casing(btoc) in MW-6 to 38.92 feet bloc in MW-4. The
<br /> approximate groundwater flow direction beneath the site is to the northeast at a calculated
<br /> gradient of approximately 0.001 ft/ft. Cumulative DTW measurements, groundwater elevations,
<br /> and SPO thickness measurements are presented in Table 1. A map showing the potentiometric
<br /> surface is presented on Figure 3. Field data sheets are included as Attachment A.
<br /> SAMPLING
<br /> Groundwater samples were collected from wells MW-5 through MW-7 on May 4,2006. Wells
<br /> MW-5,MW-6, and MW-7 were purged of approximately three casing volume of groundwater
<br /> using a low-flow submersible pump. Wells MW-2,MW-3, and MW-4 were not sampled because
<br /> the water volume in the wells was insufficient for sample collection. During purging of the wells,
<br /> pH, specific conductance, dissolved oxygen,turbidity, and temperature water-quality parameters
<br /> were recorded. After water-quality parameters stabilized(i.e., a minimum of three consecutive
<br /> readings with values within 10 percent for each parameter), groundwater samples were collected
<br /> using the low-flow submersible pump using new polyethylene tubing through which groundwater
<br /> was extracted. The samples were placed into laboratory-provided bottles that were labeled,
<br /> sealed, and placed immediately into an ice-cooled container for delivery to Lancaster
<br /> 3. Geomatrix Consultants,Inc.,2005. Technical Approach to Site Evaluation and Decision-Making,Historical
<br /> Pipeline Portfolio,Central Valley Region. February.
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