ARCHIVED REPORTS_DRAFT - PHASE I REMEDIAL INVESTIGATION REPORT

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Kennedy/Jenks Consultants • ' • Several exploratory trenches were excavated in May 2005 in areas where buried pipelines were suspected based on the geophysical survey. Water, sewer, and storm drain service pipelines were exposed during these trenching activities. Two additional pipelines of unknown historic usage were exposed in the Boring B4 area. Soil associated with the backfill in one of these trenches, reportedly contained petroleum hydrocarbons. Approximate boring and trenching locations from Geocon's site characterization activities were summarized in the Addendum. Considering results of these past investigations, four general AOIs were identified within OU-5 that warranted further evaluation in the remedial investigation (note, the AOI numbering is a continuation of the sequence from the RI Work Plan for the Railyard [e.g., AOI 1 is in OU-1]): • AOI 9 — Shallow Soil. This area includes the northern portion of OU-5 where lead and arsenic were detected in shallow soil samples. • AOI 10 — Boring B4 Area. This area includes the portion of OU-5 in the vicinity of ' Boring B4 where petroleum hydrocarbons were detected in soil and groundwater samples. • AOI 11 —Vicinity of Trenches PTP5 and PTP9. This area includes the northern and eastern portions of OU-5, where two exploratory trenches were excavated and purple-colored soil and soil containing coal and asphalt fragments were variously encountered. • AOI 12 — Buried Pipeline Area. This area includes the southern portion of OU-5, where buried pipelines were identified on the station map, and the southern edge of the Boring B4 Area, where two pipelines of unknown historic usage were exposed. The approximate boundaries of each AOI are shown on Figure 2. • DRAFT Phase t Remedial Investigation Report Page 10 Former Tracy Railyard, Tracy, California g:lis-groupladminyo610510565777.18_uprr109-reportslri rpNext.doc