This work was
undertaken to investigate the
usef
ulnessof stable carbon isotopic analysis as a monitoring toolforcontaminant remediation. Concentrations and
13Cval
uesof BTEX (benzene, tol
uene, ethylbenzene, and xylenes)were meas
ured at a gasoline-contaminated site in so
uthernCalifornia. The BTEX data were determined
using ap
urge-and-trap connected to a gas chromatograph/ion trap massspectrometer and to an isotope ratio mass spectrometersystem. Concentrations ranged from below detection(<0.5ppb
![](/images/entities/ap.gif)
0.05
![](/images/entities/mgr.gif)
M C) to abo
ut 120 ppm (
![](/images/entities/ap.gif)
10 000
![](/images/entities/mgr.gif)
M C)totalBTEX, with tol
uene generally having the highestconcentrations. For BTEX compo
unds at monitoringwellsaveraged across all sampling dates,
13C val
uesrangedfrom -23.8 to -26.6 (benzene), -22.9 to -25.2(tol
uene),from -23.0 to -25.3 (p&m-xylenes), and from -22.4to-25.0 (o-xylene). The data strongly s
uggest twoso
urces of contamination: one with lighter(
12C-enriched)
13C val
ues emanating from the area nearmonitoringwells 1 and 2, and the other containing higher MTBEconcentrations, an additive of
unleaded gasoline, wi
thheavier(
13C-enriched)
13C val
ues coming from thevicinity ofmonitoring wells 8 and 9. The isotope data s
uggestthatthe leaded and
unleaded gasoline at this site are isotopically distinct.