Contaminant-Induced Irreversible Changes in Groundwater Chemistry - Contaminant Geochemistry - page 482

Table 17.8 Concentrations of petroleum hydrocarbons contaminants from groundwater samples
data set collected under 47 service station sites throughout California, USA (Zemo 2006 ).
Reprinted from (Zemo 2006 ). Copyright 2006 with permission of John Wiley and Sons
Maximum
(mg/L)

Minimum
(mg/L)

Average
(mg/L)

Vs. Average from Laboratory
Studies(%)

TPHg 320 1 86 -14

Benzene 15 0.012 4.9 -83

Toluene 47 0.0003 8.6 -76

Ethylbenzene 6.2 0.022 2.1 -21

Xylenes 33 0.022 9.6 -35

MTBE 310 0.180 48 -78

Table 17.9 Frequency of undissolved petroleum hydrocarbons collected from the service station
sites throughout California, USA (Zemo 2006 ). Reprinted from Zemo (2006) . Copyright 2006
with permission of John Wiley and Sons
Frequency of exceedance of concentration criteria
Minimum concentration
(%)

Average concentration
(%)

Maximum concentration
(%)

Lab 1 Sheen 2 Constituent Lab Sheen Lab Sheen

Ethylbenzene 38 81 12 20 1 0.8

Xylenes 35 86 9 19 0.4 0.4

TPHg NA 85 9 13 NA 0.6

Note NA = not applicable
1 Lab = minimum, average, and maximum concentration from laboratory partitioning studies
using fresh gasoline (see Table 17.3 ) used as criteria
2 Sheen = minimum, average, and maximum concentration from groundwater samples with
entrained sheen (see Table 17.4 ) used as criteria

Petroleum hydrocarbon contamination under downward flow: An example of a
large monitoring survey of groundwater chemistry changes due to petroleum
product leaks below service stations is given by Zemo ( 2006 ). Petroleum hydro-
carbon contamination was evaluated on the basis of groundwater monitoring data
from 47 service stations throughout California, during the years 1988 to 2002,
which were compared to laboratory solubility data. The study considered total
petroleum hydrocarbons (TPH) and associated benzene, toluene, ethylbenzene,
xylenes (BTEX), and methyl-tert-butyl-ether (MTBE) in groundwater samples
collected from an aquifer zone where both dissolved and undissolved compounds
were present. The minimum, maximum, and average petroleum hydrocarbon
concentration values at the sites are presented in Table 17.8 . Petroleum hydro-
carbon concentrations determined in the laboratory studies are generally higher
than those obtained directly from the monitored wells; this can be attributed to
in situ contaminant attenuation.
The frequency of undissolved petroleum hydrocarbons at the 47 sites was
compared to data from laboratory partitioning studies (Table 17.9 ). The frequency
of entrained undissolved gasoline and compounds in groundwater samples ranged