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A r Ir ' 1 ,� 10 December 2003 : !, N r r • ' , L '•. .�! UF' ' .! - t -1 I.'r al YYf S I.` 1 1 � '•f AGE-NC;Project No. 98 0504 1;Page 3 of 5 ' r ' 2.5. _ PREVIOUS SITE-ASSESSMENTS { I+h ^ On' 31 July 2002, three soil'p'robe boring(B3,B4.and�BS),were'advanced east andlno'rth--west`ofthe''1' former UST excavation;and northofthe,former dispenser area.Discrete.soil samples were collected at 5-foot intervals;,beginning at 10 feet bsg, to the total depth of the wells atbetween1.5 and 40 feet bsg. Irl addition;:a grab grourld,water sample"was colIecte'd from each.well at total depth. ; r TPH•=gland BTEX compounds were nondetected in soil samples collected.,MTBE'wa_s detecte&by - ' EPA'method;8260 in three soil samples at concentrations o'f 4 016:mg/kg {B3,30}; 0:008 mg/kg ; (B4-20)and 0.006 mg/kg.(B4-30),Analyticalresults of soil,samples are summarized in Appendix A:' TPH-g was detected in the.grabground water samples.from.boringB3;B4 and B5 at concentrations 1, of 240 ' 1 300 1 and 180 l,,res ectivel . BTEX com ounds were not detected, but,MTBE u�, [t p� p Y p and'1,2-DCA were detected by EPA method 8260 in each of the ground water samples at maximus i concentrations of 200µgel(B4) and 13 µg11(BS).'-The distribution;of dissolved MTBE is-depicted in Figure 4, and analytical results,from groundwater samples are summarized in.Appendix A. - . 3.0 GROUND WATER MONITORING u ' On l O December 2003,the depth to ground water in all three monitoring wells were measured from the top of each well casing to the nearest 0.01-foot utilizing a Solinst water level meter.-Ground ' - water elevation in.each'well was'calculated by subtracting themeasured depth to ground water from . the surveyed casing elevation (Table1). After,waterlevels,were measured;-8.0 gallons of water(a in nimum of 3 casing-water volumes,per well)were purged frorri monitoring wells MWl through MW3 using dedicated,'disposablep,astic bailers.' Ground water temperature, pH and conductivity were measured of regular intervals during' .purging using an Oakton^water analyzer. Field'sheets and data are'included iii Appendix.A.Purged,' ,wate was.stored on-site'in properly labeled, 55-gallon Department of .Transportation (DOT);' approved'drums. ' } COLLECTION AND ANALYSIS OF.GROUND WATER SAMPLES Ground water samples were collected from the monitoring wells using disposable polyethylene - 'these .bailers were disposed of after one use re uire no decontaminating, thereb bailers, ., p q , y minimizing cross.contamination due to_sampling devices. Each water sample'was transferred into three 40-m1 EPA-approved volatile organic analysis (VOA).vials containing 0.5 ml 18%'HCI as a • sample preservative..After collection,the samples'were labeled and placed in a chilled container for' transportation under chain:of=custody to Cal Tech.Environmental Laboratory(CTEL), a Califomia:' ` e Y. Advanced Geo Environ mental,Incl l