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Mr. Harlin Knolls R I O N . <br /> q <br /> San Joaquin County Environmental Health division <br /> -- q 27 June 2001 <br /> Page 2 <br /> F i <br /> samples beneath Tank #3 at' concentrations up ,to"916200 milfxgrams per kilogram <br /> (mg/kg). Groundwater samples were not-collected during this investigation. <br /> II' In December 1998, QST Environmental drilled 'soil borings 6F5-1, and:8FS-2 in the <br /> Ik vicinity of the three closed-in-place USTs.; Figure 2:;slOWs these', boring locations. <br /> Groundwater was encountered in these bor�n'gs�at approxitiately,28 feet below grade._ A <br /> groundwater sample collected from boringi-BFS-1 contained a 'TPHg concentration of <br /> 4,200 micrograms per liter (µg/l) and b&nzene, toluene;' ethylbenzene,. and xylenes <br /> (BTEX) concentrations of 220 1, 400 f 1, 340 I, and 1,500: I, `res ectivel <br /> µg/ µlb µg/ . - µlb p Y <br /> Methyl tert-butyl ether (MTBE_) was also'detected in groundwater' from boring.BFS-1 at a <br /> concentration of 0.78. µg/1. Of the gasoline-:related _compounds` :listed above, only <br /> M xylenes were detected in a groundwater sample collected from boring.BFS-2 (0.55 µg/l). <br /> In January 2000, Orion installed three groundw -1, <br /> ater monitoring wells, (MW , MW°2, <br /> ' and MW-3) in the vicinity of the former �USTs. ° The well locations are shown,. on <br /> Figure 2. One soil sample was selected and: analyzed from each boring.,09ring the <br />' drilling program. The soil sample from'MW-1., collected at a depth of 2Qyfeef below <br /> grade, contained an MTBE' concentratiori;of 99 micrograms per kilograrn (µtog). :The. <br /> soil samples analyzed from MW'-2 and MW-3 for MTBE were below detection Iimifs at <br />{ depths of 35 and 15 feet below grade, respectively. TPHg and BTEX were not detected <br /> in any of the soil boring samples. <br /> 4roundw.atenarth <br /> r samples from well MW-1 (installed. ee <br /> 1n January and May -2000, g p ,. . <br /> former source area) contained no detectable concentrations of TPHg or BTEX.. .A small. <br /> arriount of MTBE was detected in MW-1 at a concentration of 7.9 µg/1 during the first <br /> Lround of sampling-rand 4.0 µg/1' during -the second round Upgradient well MW-2 <br /> contained TPHg concentrations -of 91 ;' I during the 'first round of sampling and. <br /> c g µl� g _ . <br /> 440 pg/I from the second round; MTBE s,not detected in either round of sampling. <br /> The 'samples from cross-gradient well.MW-3 did not contain d-iatec#able'conceetrations <br /> of. TPHg, BTEX, and MTBE during both rounds of groundwater sampling. The <br /> groundwater gradient was toward the north-northeast.. <br /> In August.2000 and January 2001, groundwater, samples from well. MW-1 contained no <br /> detectable amounts of TPHg or BTEX. A small amountof MTBE was detected in MW <br /> lin event at a concentration of 7.7 and 42 µg/l, respectively. Upgradient <br /> in each sampling g vel MTBE <br /> well MW-2 contained,TPHg concentrations of 440 and 170 <br /> d ! res enot de ect ctii l January <br /> was detectedlin'August 2000 ata concentration of 8.6 µg/ <br /> k , <br /> 2001 sampling, The samples from cross-gradient well MVV-3 did not contain detectable <br /> } concentrations of TPHg, BTEX, and MTBE during any round of groundwater sampling. <br /> MX* <br /> 5:\BFS\STOCKTON\LTR\LTR010.DOC 6/27/01 <br /> ` yU <br /> direct p(I nro_.,.._r__.., <br />