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-s- �a ;.� `s ��;€:r. c `w-- ,��'���'y�z=�5,4�:.:- :r..� � •°..� sr..�, �"�--� - - ;� �- -''a�.x` �-- -�{ �-�Y ;.,.:ts3�.��,-{.� ., ' <br /> 3. k', 5:�{.,sx :' �+..•' A '"^ t :"..s. ... ".'.s .r"<r. . :r Ssat" c^,--«,.. v N 3" �ri,4�as - a..'.�.aii'ryt�y.•r �, :t',vs:.s .-7.7tu r "ia fm s <br /> _.n - ^ ' <br /> SEEMt".a <br /> �.fi °a * ,.>ap,; �r��s�t � .� sr �°� �€ ,�` -�s' 4✓ _t� ��' r'`�'�" �� '°��`f;., �� ;�}-rR� '�,.�, a 4 a <br /> as <br /> i <br /> . Y <br /> Quarterly Monitoring, first Quarter 1991 \lay 23, 1991 <br /> Dormer Unocal Station 2859, Stockton, California A(._JS 38012-7 <br /> the soil underlying the tank cavity (Applied GcoSystems, April 23, 1988. Report No. <br /> 38012-1), In June 1988,we installed 3 ground-water monitoring wells MW-1 through NI W-3 <br /> i (Applied GeoSystems, July 25, 088, Report No. 38012-2). Results indicated a further <br /> investigation of ground water downgradient was warranted. Therefore, in August 1939, two <br /> groundwater wells were installed offsite to delineate dissolved hydrocarbons (Applied <br /> (jeoSystems. December 12. 1990, Report No. 38012-5). <br /> In response to the detection of hydrocarbons in soil and ground water,Applied GcoSystems <br /> began periodic monitoring of the ground water in June 1988, Results of previous <br /> 1 monitoring events indicated that dissolved hydrQcarbons were detected in water samples <br /> collected from the five wells. the highest concentrations of hydrocarbons were detected in i <br /> well h1W-2. <br /> Applied GcoSystems evaluated the dircctiost of groundwater flow to be northeast from June: <br /> 1 1988 to May 1990 (before the wells were dry). The average gradient was 0.002. The <br /> j direction of ground water now for May 30, 1990 was to the northeast as shown on Plate P-2. <br /> ! j <br /> Ground- Vater Samulingj <br /> An Applied GeoSymems geologist was onsite February 25, 1991, to collect groundwater <br /> samples from wells MW-4 and MW-5 for subjective analysis of dissolved hydrocarbons using j <br /> procedures summarized in an attachment to this report. 'I3te geologist noted no subjective <br /> i <br /> evidence of hydrocarbons in the two wells. Cumulative results of subjective analyses are I <br /> I presented in Table 1• <br /> The geologist purged wells MW-4 and MW-5 and collected water samples for laboratory I <br /> analyses. A Chain of Cus'.ody Record was initiated in the field and accompanied the i <br /> samples to the laboratory. A copy of that record is attached. The methods of groundwater <br /> sampling are discussed in an attachment to this report. The purge water was stored onsite <br /> in properly labeled 17-E steel drums pending the results of laboratory analyses. At Unocal's <br /> request, drummed water was subsequently removed by Armour Petroleum of Fairfield, <br /> California, the week of March IS. 1991, and disposed of. <br /> I <br /> i�borataty Anaivses <br /> . i <br /> The water samples were submitted for analyses of total petroleum hydrocarbons as gasoline <br /> (TP14g)using modified Environmental Protection Agency(EPA)Method 8015 and benzene, 4 <br /> toluene. ethylbertzene, and total xylene isomers (BTEX) using EPA Method 602, f <br /> laboratory analyses were performed at Applied Analytical Environmental laboratories in <br /> f <br /> f <br /> 2 <br /> 5 <br /> F <br /> F <br /> `�- AppO1ed 6990SySAWns <br />