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�,� .,T^'�'%�., .�.� ' -.'� -+a.3' ..a?.+ ''� 7� : � <br /> -ti � <br /> r <br /> � <br /> .- - � .��':^k ;P :�- �:" s�+atn`«vrv,�.»8'y. ��..- �'���.$-.:� s,3-..a _ � i2.. .`•� r"-:ye.,^r,���i-y�7"w,.-.y„''"L" .s: �s?"^�' ,i"' �`^"".:,,>,"�_ <br /> �,: a�:r E;t...i� _�„-.. �. ,;r,„ , �,��; r ,.�..,�� ��e �, �a:��F�� ��m �-" .�,4.,�.�:. �a�`t" �,�,Kww..,,,:,,k�;� �. �, '%�'' w .�'iw�•i <br /> ' � .5'k d' �'V J'- ..L '... v �,�wYe[ ".IaE..� ,<'f'� `vb��3 t��. F.ks�W.,{R! "E'• <br /> t p <br /> -.v. _.,- -q .Y..F „ •� '^w.. i _;-' . � .,, f�`y� :y.1w -.L: — -r h:.i�-- iI^� t��i�.f— <br /> d <br /> A' <br /> J <br /> Ms, Linda Turkalle <br /> March 6. 1992 <br /> - -, Page 2 <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 />