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Chevron Pipeline Easement Environmental Assessment Report November 21,2001 Page 12 5.0 DISCUSSION OF RESULTS Condor observed the excavation of 13 trenches and the advancement of 185 soil borings in the vicinity of Byron Road between the Alameda County line and Wicklund Road for the purpose of investigating the possible presence of petroleum hydrocarbon contamination in the soil and groundwater. No soil contamination was observed in the 13 trenches. Visual soil contamination in the form of gray green to dark brown staining of the soil was observed in 20 soil borings. Visual contamination was initially detected at depths from 4.0 feet to 18.5 feet. Contamination was detected at a maximum depth of 46.5 feet. Petroleum hydrocarbons were detected in soil samples from 18 of these 20 borings. Petroleum hydrocarbons were detected in an additional three soil samples that had no visible soil contamination. PNAs were detected in 17 of the 18 soil samples contaminated with petroleum hydrocarbons that were analyzed for PNAs. A soil sample collected from soil boring GP152 at a depth of 6.5 feet contained the greatest concentration of PNAs in soil. Unfiltered groundwater samples were collected from 10 of the soil borings in which contaminated soil was observed and from the five soil borings in the alfalfa field southeast of the intersection of Mountain - House Parkway and Byron Road. Seven of the groundwater samples collected from the soil borings with visible contamination and one groundwater sample from a soil boring in the alfalfa field were selected for laboratory analysis. The other groundwater samples were not analyzed because of their proximity to - the samples selected for analysis. Petroleum hydrocarbons were detected in the seven groundwater samples collected from soil borings with contaminated soil. No petroleum hydrocarbons were detected at or above the laboratory practical quantitation limits in the groundwater sample collected from the - _ alfalfa field. PNAs were detected in all groundwater samples contaminated with petroleum hydrocarbons. Benzo (k) fluoranthene, dibenzo (a,h) anthracene, and indeno (1,2,3-cd) pyrene were not detected at or above the laboratory practical quantitation limit in any of the groundwater samples. The remaining PNAs were detected in at least one groundwater sample contaminated with petroleum hydrocarbons. Soil and groundwater contamination by petroleum hydrocarbons in the vicinity of the historical Chevron crude oil pipeline in the areas investigated by Condor between the Alameda County line and Wicklund Road is intermittent along the alignment. Excavations below four feet in the right-of-way along the south side of Byron Road may encounter petroleum product in the soil, particularly in the locations where this investigation detected contamination. The contaminated soil is usually easy to visually identify by the gray green to dark brown stain and by the petroleum hydrocarbon odor that accompanies the staining. The presence of free product in some of the groundwater samples suggests floating product may be present in the aquifer at those sample locations. Dewatering along the south side of Byron Road will likely result in removing water containing petroleum hydrocarbons in solution, as floating product, and/or adsorbed to suspended sediment. 6.0 LIMITATIONS The stated purpose of this investigation was to determine if petroleum hydrocarbon contamination was in -- the soil, and subsequently to evaluate the potential impact on construction activities of detected petroleum hydrocarbons in the soil and groundwater. No other use of the results of this investigation is intended. Condor developed the interpretations and conclusions presented herein in accordance with generally accepted principles and practice. Conclusions presented in this report are professional opinions based on limited information obtained at the time of our site visits. Condor has endeavored to determine i«1 CONDOR