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<br /> Ms, Linda Turkalle
<br /> March 6. 1992
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<br /> n Nitas jrLrULrt s
<br /> The presence of free-phase hydrocarbons or free-hydrocarbon sheen in the monitoring wells was
<br /> recorded using; procedures described in Enclosure A. Free-phase hydrocarbon was detested in
<br /> monitoring well MW-2 (thickness 0.33-foot),and in monitoring well NIW-4(thickness 0.03 foot)on
<br /> January 28, 1992, Hydrocarbon sheen was not observed on water samples collected from the other
<br /> monitoring wells. Observations are included in Table I.
<br /> A Westinghouse pneumatically-operated product-only pump was operating alternately in monitoring r
<br /> wells MW-2 and MW-7 between January and April 1991. Hydrocarbon recovery pumps have been
<br /> operating in both wells simultaneously since May 1991. The pumps were modified in January 1992
<br /> to recover free-phase hydrocarbons and ground water(total fluids). The total amount of free-phase
<br /> hydrocarbons recovered since May 1991 is not known because the pumps have been discharging
<br /> ground water as well as product.
<br /> Ground W r am lin• and Analytical R .tilts
<br /> Ground water samples were collected from monitoring wells MW-1, NIW-3, MW-5, MW-6, hiW-7,
<br /> MW-8, MW-9, and MW-10 on January 28, 1992. Monitoring wells MW-2 and MW-4 were not
<br /> sampled due to the ire;euce of free-phase hydrocarbons,as described above. Monitoring well MW-7
<br /> was manifolded for pumping ground water, therefore, the well was not sampled. Ground water
<br /> samples were collected using procedures described in Enclosure A. Each ground water sample was
<br /> submitted for analyfis of benzene, toluene, ethylbenzene, xylenes (BTEX), and total petroleum
<br /> hydrocarbons(TPH) as gasoline, using U.S. Environmental Prntection Agency and California
<br /> Department of Health Services approved methods. The analytical laboratory results for ground water
<br /> samples collected on January 28, 1992, are summarized in Table 2. Previous results are also
<br /> provided in Table 2 for comparison. Copies of the certified laboratory reports for the January 1992
<br /> sampling event are included in Enclosure B.
<br /> Analytical test results indicate that detectable concentrations of petroleum hydrocarbon constituents
<br /> were present in each of the ground water samples collected on January 28, 1992, except for MW-6.
<br /> Concent,ations cf TPH as gasoline ranged from none detected(less than 0.13 part;per million(ppm))
<br /> in MW-6 to 200 ppm in 11W-9, and benzene concentrations ranged from none detected (less
<br /> than O.00(i3 ppm) in MW-6 ,) 25 ppm in MW-9. Concentrations of total petroleum hydrocarbons
<br /> in ground water samples show an increase from the October sampling; Nvent. A dissolved benzene
<br /> isoconcentration map prepared using the January 28, 1992,ground water sampling results is included
<br /> a: Figure 5.
<br /> Fu ure 1Vnrk
<br /> Quarterly sampling of the ground water monitoring wells will continue. The next sampling event is
<br /> scheduled for April 1992.
<br /> Installation of the ground water extraction and treatment system was completed in January 1992. The
<br /> system is pumping* total fluids from monitoring wells MW-2 and MW-7 and directing the flow
<br /> through a separation tank. Ground water from the separation tank will be directed through two
<br /> carbon adsorption canisters prior to discharge to the Stockton sanitary sewer. Sewer discharge
<br />
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