Geoscience Reference
In-Depth Information
groundwater. However, it should be noted that pharmaceutical residues were found
in the groundwater under the landfill 13 years after disposal of PhACs ceased.
The fate of PPCPs during groundwater recharge was investigated by Drewes
et al. (
2003
) at two facilities in the southwestern United States. These facilities
employed surface spreading basins characterized by different soil-subsurface
conditions and treatment management schemes. The bulk organic and PPCP
concentrations in the treated effluent and in groundwater monitoring well samples
are presented in Table
17.7
. Only organic iodine, carbamazepine, and primidone
were found in groundwater after tertiary treatment of the effluent, despite the fact
that the effluent comprises a larger number of PPCPs. After subsequent travel of up
to eight years, organic iodine, carbamazepine, and primidone were still present in
the groundwater, with their concentration decreasing by about 30 %.
Studies of the presence of organic micropollutants in groundwater provide
further evidence of irreversibility of the contamination process. Samples of water
were collected in 1985 and 2005 from the same monitoring wells located along a
plume of groundwater contaminated by 60 years of continuous disposal of a
wastewater treatment plant (Barber et al.
1988
,
2009
). Fifteen percent of more than
200 analyzed organic wastewater contaminants were detected, including the
antibiotic sulfamethoxazole (SX), the nonionic surfactant degradation product
4-nonylohenol (NP), the solvent tetrachloroethene (PCE), and the disinfectant
1,4-dichlorobenzene (DCB). The 2005 groundwater sampling confirmed the
presence of the contaminants PCE, DCB, and NP that were reported in the original
1985 sampling. For example, the concentrations of NP determined in 2005 were
relatively unchanged from the results determined 20 years earlier. Changes in the
distribution of PCE, DCB, and NP after 20 years are due to the transport and
redistribution of these contaminants in the groundwater profile. Using boron as a
transport tracer, Barber et al. (
2009
) defined two oxic zones in the aquifer: (1) a
downgradient transition zone at the interface between the contamination plume
and the uncontaminated groundwater, and (2) a contaminated zone located beneath
the infiltration beds which were not loaded for 10 years. The pattern of SX
transport was nearly coincident with that of boron, while the NP transport pattern
demonstrated retardation.
Petroleum hydrocarbons reach the vadose zone and groundwater mainly as a
result of leaching from gas stations, by accidental release on land surface, and by
seawater migration to coastal shorelines. Groundwater chemistry may be altered
by the partial dissolution of petroleum products into the water phase; subsequent
groundwater flow may affect the quality of an entire aquifer. The more water-
soluble components of petroleum hydrocarbons, such as benzene and the low
molecular weight alkylbenzene, are often found in groundwater downgradient
from a pollutant source. The fraction of petroleum hydrocarbons that are insoluble
with water, called non-aqueous phase liquids (NAPLs), may be also affect
groundwater chemistry, by slow volatilization and dissolution, when adsorbed on
soluble organics or polyelectrolytes, or as microdroplets incorporated in the water
phase.
