|
SECTION 4 FIELD ACTIVITIES AND RESULTS
<br /> and BTEX concentrations,200,000 and 26,000µg/L,respectively, were detected in CPT-3 at
<br /> 91 feet bgs.
<br /> 1,2-DCA was detected in all CPT borings except CPT-2,at depths of 70 feet bgs or greater in
<br /> (Table 4-2,Figure 4-3). The maximum concentration of 1,2-DCA was detected in CPT-4 at 75
<br /> feet bgs (2,000 µg/L). Similar to 1,2-DCA,EDB was detected in all CPT borings with the
<br /> exception of CPT-2,and a maximum concentration of 1,400µg/L(in CPT-1 at 90 feet bgs).
<br /> Oxygenates were not detected in any groundwater samples collected from the source area.
<br /> Downgradient(Borings CPT-6,-7,-8,40,41,42,43, and-15)
<br /> TPH-gas and BTEX compounds are present in groundwater at depths of 70 to 130 feet bgs in
<br /> downgradient CPT borings CPT-6,-7,and-8.The highest concentrations were found in
<br /> CPT-7 and-8 at depths of approximately 70 to 80 feet bgs. The maximum TPH-gas and
<br /> BTEX concentrations,20,000 and 5,500µg/L,respectively, were detected in CPT-7 at 76 feet
<br /> bgs. Since the freeway elevation is approximately 20 feet below the grade of the site, these
<br /> depths correspond with 90 to 100 feet bgs beneath the site. The lateral and vertical extent of
<br /> benzene is delineated on Figures 4-8 and 4-10. TPH-gas and BTEX compounds are not
<br /> found at depths greater than 130 feet bgs or in downgradient borings CPT-10,-11,-12,-13,
<br /> and-15.The lateral and vertical extent of groundwater impacted with benzene is presented
<br /> on Figures 4-8 and 4-10.
<br /> Detectable levels of 1,2-DCA in groundwater are present in all CPT borings downgradient
<br /> of the source area.The lateral and vertical extent of groundwater impacted with 1,2-DCA is
<br /> presented on Figures 4-9 and 4-11. The highest downgradient concentrations of 1,2-DCA
<br /> are from borings CPT-7,-8,and-12 at depths of 70 to 90 feet bgs.
<br /> EDB and oxygenates are not present in groundwater samples downgradient of the source
<br /> area. TBA is detected in groundwater samples collected from borings CPT-I1,-12,43,and
<br /> -15 up to 28µg/L.
<br /> Low concentrations of petroleum hydrocarbons and/or 1,2-DCA were detected in the deep
<br /> groundwater samples from borings CPT-6,-7,and-8,at depths of 140, 126,`and 130 ft bgs,
<br /> respectively.The presence of hydrocarbons at these depths was unexpected since they were
<br /> 1 collected below the thick,fine-grained/clay layer underlying the impacted zone. These
<br /> detections may be a result of cross-contamination during sampling,since hydrocarbons
<br /> were present at high concentrations in the shallower groundwater zone in these same
<br /> borings, and the sample tools passed through this impacted zone.
<br /> I
<br /> Cross gradient(CPT-9 and-14)
<br /> i
<br /> TPH-gas and BTEX compounds,EDB, 1,2-DCA,and oxygenates were not detected in cross-
<br /> gradient CPT boring CPT-9 (Table 4-2 and Figure 4-6). Low concentrations of TPH-gas (610
<br /> µ/L) and toluene (9.9µg/L)were detected in CPT-14 at 94 feet bgs.(Table 4-2 and Figure
<br /> 4-5).
<br /> {
<br /> L
<br /> S SF01CPT REPORT-].DOC/003670036 4.4
<br /> I
<br />
|