SITE INFORMATION AND CORRESPONDENCE

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FEB--18--99 THH 09:54 AM P. 09 FEB. -11' 99{THul 15; 18 UNOCAL".T NORTH RE TEL 10 94,-.w,781 P. 008 DRAFT Stockton. is about 2.000 feet to the west. Shallow groundwater at the site flows in a general easte riy direction with a gradient of about 0.002. In larttwy 1988, analyses of soil samples from five soil bvtings denied to depLlts of ZO to 30 feet indicated that a release had occurred at the site. In FebnAry 1988, three groundwater monitor wells were installed to assess site groundwste r canditiems. The initial groundwater samples from the three wells revealed an absence of gasoline consdw eats in graundwatet near the location of the two gasoline USTs, high exiru,marAtivas(99,000 pph TPH-g and 5,700 ppb benzene)in the viddnity of the easterly pump fir4 wid low concemtradam(170 ppb TPI-g and 1 ppb b )in the vicinky of the waste oil UST. Dara gained from the wet batallations also indicated that the gtoum1water was confined and that is$o and in an eastariy direcdoo. In March 1988, the two 10,000-gallon cxsaty gasolme USTs,the waste oil UST, and the dispensers and associated piping were n=oved from the site. Vtsual ingxcdm of she bottom afld side-walls of the gmofiae UST e=vation revealed that sol]was affected by a release prompting petitioner to over4=mte an estimated 850 cubic yards of sal to at feat depot of 28 to 30 feed. Soil samples cofiem!d from rite bottom and We waft of the acravation indicated TP'H-g and be==e moons reaped from 3 to 18 ppm and less than 0.05 to 1.7 ppm, respectively. In August 1989, two add'dotW g mundwater monitaor weft vmm constructed structed o$site appro)drnatdy 100 feet east and norsbewterly of the fbimer pump idand where high cOnstitue[i conceemrations had previously been de a.-O-1 in groemdwater, Analyses of groundwater samples from these wed revealed low corxmtrabom of K'P'H-g(150 and 240 ppb), *=c(1.4 and 1.9 ppb), and cthylluazerae(less than 0.5 and 8.1 ppb);be me and toIuene were got detected. In February 1992, three vapor emiction wells and two more groundwater monitor well wum installed. TwO of tht vapor extraction wells were located where the caste dy The volow of sail =rated is a prime of=me:tt4on. Pttitiaaer indkwe s its ils Sive Casale:S�mmaryr TgWt ural an aWnuated 1.104 cubic yards Of sail were eh�rasrate d while;the Conary taotrtends that o*350 cubic yards am doextrnemted to hive been ammie d. f w*c-=. in a March 12. 1991 )atter ea petitioner, the:Cooney stases iket:..,aWroXimatcly 13004400 cubic yards of contaminated swj..."vA-m ctcavated. Ba=d on etre rq)oned di1nomiam W ft=CUM000%.Wr.,fewer cstinwwd&V cwft yards. 5