SITE INFORMATION AND CORRESPONDENCE

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' hevron - M4chae4 0ltiphant G t)evr _ Mountain douse Development Site#6 SWRCB) Resolution No. 92-49, oration (SAIC) evaluated with State Water Resources control In ea conal Corp ther than natural Consistent Science Appllca Section III.A through to technologies- ortionally costly since the affected ments area alternative cleanup les. SAICs' review founddrophat methods the railroad tracks right-of-way and utility corridor eas attenuation would be ine ineffective, infeasible, an is primarily under the highway. Issues: A release of non-hazardous crude oil to soil and groundwaterImpacts consist bof moderately listed primarily of total petroleum hydrocarbons elines that cross the Site was discovered in 2001 . historical pip acts co weathered residual crude or�a SOonta� polynuclear aromatic hydrocarbons (PAHs I an as crude oil (TPHc) wh�lbenze e, and xylenes (BTEX). benzene. toluene, ethy agricultural area with some nearby Setting: Located along West Byron Road within a rural residential properties under development Source: Historical leak from OVP/TAOC crude oil pipelines} installed in the early 1900's and removed from service by the late 1960's to early 1970's Actions: Preliminary Site investigations were conducted between�001groundwaterd09. In 2001 , fourteen exploratory borings were advanced a • samples were analyzed for TPH constituents of concern. Crude oil affected soil was detected at ND to concentrations ranging from 880 milligrams per kilogram (mg/kg) to EX 29,000 mg/kg at boring depths of 12 �� 1 Seearate phase cbelow u de osurfal (SPO) was noted irti compounds were ND in all soil same p some of the 14 borings; an area of SPO at about 100 feet across and four to six feet bgs (approximate depth of the historical pipelines) was noted in two soil borings. Additional Site characterization was needed. • in March-April 2008, 29 soil borings were drilled to depths of '2 to 40 feet bgs: 78 soil samples and 20 groundwater samples, collected at depths of 4 to 40 feet bgs, were submitted for TPH analysis, TPHc detected in samples from between 4.5 and 10 feet bgs ranged from ND to 26,000 mglkg. TPHc results for samples at about 13 feet bgs and deeper ranged from 740 to 2.900 mg/kg. Analysis of deeper samples from several borings did not detect TPHc at depths ranging from 26 to 40 feet bgs, the maximum depth sampled. The vertical extent of affected soil was defined by ND results for samples from several borings at depths of 26 to 39 feet bgs. BTEX and polynuclear aromatic hydrocarbon (PAH) compounds were ND for deeper samples defining the vertical extent. Fuel fingerprint analysis determined the TPH present was consistent with residual San Joaquin Valley crude oil. The lateral extent of affected soil and groundwater was partially defined but additional characterizatior was needed. • Concentrations of TPH as diesel (TPHd) reported in groundwater were ND for most samples to 94 micrograms per liter (pg/L) and up to 150 pg/L; the highest result was one detection of 1 ,000 pg/L TPHd. BTEX compounds were ND, Low concentrations of PAHs were slightly above laboratory method detection limits and/or respective screening levels. Depth to groundwater is about 6 to 12 feet bgs. • In late 2009, SAIC conducted the additional characterization with offset borings and analysis of samples for delineation purposes. Based on S{AIC's February 2010 rePo� the recent findings were consistent With priorch,9raClerlZC�I�Q � V extent of crude oil affected soil and �res*aid the The report Concluded that the e 9 oUndwater was �afe��af] adequate and additional work was Of aff@CtEd ad�4Ua��1 as not loll andgroundwater Wasdgbl eat necessary. ed- considered