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Work Plan for Additional Subsurface Assessment,Former Unocal#012
<br /> October 12,2000 �-
<br /> PREVIOUS ENVIRONMENTAL ACTIVITIES
<br /> A limited subsurface investigation was conducted by L. M. Swift for Wells Fargo :and is detailed in a.
<br /> Phase I Report dated March 29, 1994. The investigation included an underground electronic survey of the
<br /> parking lot to determine if any abandoned USTs existed beneath the site, and exploratory borings to
<br /> collect soil and groundwater samples. The underground survey detected no large metal anomalies, and
<br /> concluded that there were no USTs beneath the site. However, hydrocarbon-impacted groundwater was
<br /> detected in the northern portion of the site.
<br /> In May 1995, nine exploratory,soil borings were drilled And three groundwater.monitoring wells (U-1
<br /> through U=3) were installed-by Pacific Environmental Group, Inc. (PEG)at the.subject site. Exploratory
<br /> test pits were dug and two abandoned USTs were encountered'at the northern property boundary, beneath
<br /> the.1 Vh Street sidewalk. In.November 1996,the two abandoned 550-gallon USTs were removed. A third
<br /> UST that was encountered during the removal activities was abandoned in place by grout injection. One
<br /> groundwater monitoring well (U-4)was installed in December 1996'in the location of the removed USTs
<br /> to evaluate soil and groundwater conditions.
<br /> A On October 7, 1998, PEG drilled and installed two groundwater monitoring wells (U-5 and U-6) and one
<br /> soil. boring (13-4). Soil, samples collected from,the borings had detectable concentrations of total
<br /> petroleum hydrocarbons as gasoline (TPHg) (220 parts per million (ppm) at 11. feet bgs in U-6) and total
<br /> petroleum hydrocarbons as diesel (TPHd),(21.5 ppm at 10 feet bgs in B-4 and 12.3 ppm at 11 feet bgs.in
<br /> U-6). Benzene, methyl tert-butyl ether (MtBE), lead, or volatile organic compounds (VOCs) were not
<br /> detected in the soil samples. Grab groundwater samples had concentrations of TPHg (968 parts. per
<br /> billion (ppb) in U=6) and TPHd (115 ppb in B-4 and 312 ppb in U-6). Benzene, MtBE, or lead were not
<br /> detected in the groundwater samples. �. .
<br /> One soil boring.B-5 was advanced at the.northwest corner of I'Vh Street and Central Avenue on January
<br /> 12, 2000 by GR. A soil sample collected from the boring at 7•feet below ground surface (bgs) had a
<br /> detectable 'concentration of TPHd at 2.21 ppm. TPHg or benzene, toluene, ethylbenzene, and xylenes
<br /> (BTEX) werenot detected in the soil sample. A grab groundwater sample from the boring had 66,700
<br /> ppb of TPHg, 29.6 ppb of TPHd, and 36.2 ppb of benzene. Oxygenates were not detected is the soil or
<br /> grab groundwater samples.
<br /> Groundwater monitoring and sampling has been conducted quarterly since June 2, 1995, in.wells U-1,
<br /> U-2, and U-3, since March 3,.1997, in well U-4; and since October 22, 1998, in well U-5 and U-6. In a
<br /> recent event on.June 19,•2.000, concentrations of TPHg (210 ppb in U-4), TPHd (50 ppb in U-2), and
<br /> benzene (9.5 ppb in U-4) were present. Also, the halogenated volatile organic compounds (HVOCs)
<br /> cis-l,2-dichloroethene (1.1 ppb in U-1 and 1.3 ppb in U-6), tetrechloroethene (ranging from 1.5 through
<br /> 7.1 ppb in all wells), and trichloroethene (1:3 ppb in U -I) were,detected. Depth to -water during this
<br /> -monitoring event.ranged from 9.53 to 10.52 feet.bgs and groundwater flow direction was to the north-
<br /> northwest,which is consistent with available historical data.
<br /> Phase I Environmental Site Assessment
<br /> A Phase I Environmental Site Assessment report dated December.16, 1994, was prepared by Enviros Inc.
<br /> (Enviros) for Unocal.. The text.of this report without the appendices is included in Appendix A.' The
<br /> 2400013.04 2
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