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tic <br /> 44 <br /> .13336 East Highway 88 <br /> Lockeford, San Joaquin County 18 December 1998 <br /> Soil contamination is defined laterally to approximately 20 feet bgs in the vicinity of the former gasoline <br /> USTs by borings B 1 through B76. From 20 feet to groundwater, the lateral extent of soil contamination <br /> is not defined and the vertical definition is poor. Soil samples collected from boring B7;showed <br /> elevated concentrations of TPHg (to 45 feet bgs), and BTEX constituents (to 60 feet hg'). Based on ` <br /> residual contaminant mass calculations provided by GeoSoIv, approximately 67,812-kilogram- s' (4,400- <br /> gallons) n <br /> of TPHg and 895-kilograms (58-gallons) of benzene are estimated to remain in the soil below <br /> the site. <br /> Based on the Mr. Goldman's assertions and the TCLP results, leaching of contaminants to groundwater <br /> through another.migratory pathway or through vapor phase migration is likely. However, if the <br /> groundwater sampling results represent cross--contamination due to`sampling error, the analyticZiesults <br /> are riot sufficientto-meet`ouf,13 February 1998'regtiest."" <br /> Water supply wells identified in the vicinity of this site include: The Lockeford-,Water Tower well kat' <br /> Church Street and North_Tf 1ly Road, approximately 600 feet north-northeast of the site;. the Lockeford <br /> School weld approximately 700 feet southeast of the site; and:three additionalwells u'p to.2,500 feet 4 <br /> south and southwest of the site. No information regarding well completion details,was available'or s <br /> provided for the'two" Lockeford wells, but these'nearby supply wells should.be analyzed forAconstituents <br /> ofconcern. .�x .` .v _,. t.. . .� <br /> The TPHg and BTEX constituents found in the groundwater sample warrant an investigation to <br /> determine the lateral and vertical extent of groundwater contamination and potential impact on nearby <br /> production wells: 'The groundwater investigation should include drilling three soil borings t6` <br /> groundwater; collecting-discrete soil samples from the`capillary fringe and saturated zone in each <br /> borehole; and installing monitoring wells to determine the hydraulic gradient, groundwater flow '�'' •' <br /> direction, and groundwater,quality. Soil and. groundwater analyses must include TPHg;BTEX; <br /> r. .. ; <br /> 1,2-DCA and the fuel oxygenates (TBA,MTBE, DIPE, ETBE, and TAME).a The oxygenate analysis is <br /> necessary,because tertiary-Butyl Alcohol (TBA) was detected at 96 µg/Kg in the soil'sample collected <br /> from boring B7 at 50 feet bgs. <br /> With new soil and groundwater data, a fate and transport model may be appropriate to demonstrate that <br /> the residual contaminant mass`wili O'Cadversely imp act.gFoundwater qualify However;until'tl is is -" F <br /> determined, quarterly.groundwater sampling must continue. <br /> u s <br /> Summary� ,.�1.r.�+�. ,i:,.r w:;:_ . '; �' ' ". _� '` u , �, : � ., .*� " y,-- � • �,.. <br /> .4 V• <br /> Based on elevated concentrations of TPHg, benzene and toluene in the groundwater sample;`and the y <br /> large mass of contaminated soil, I am requesting three soil borings be drilled to groundwater, soil r <br /> samples collected from the capillary fringe and saturated-zone, soil borings be converted to monitoring <br /> wells,and groundwater'samples collected to evaluate chemical and hydrogeologic conditions below the " <br /> site. Soil contamination is confirmed between'10 and 60.feet b_s and groundwater is present and <br /> impacted'at approximately 100 feet bgs: "• ` "� _ _ �;. y • <br /> MRL/mrf c:/markfile/san joaquin/13336me2.doc" "' t" "w - !*�,• r x'C'�a•�3' <br />