Abstract
Volatile organic compound (VOC) contamination of subsurface geological material and groundwater was discovered on the Nortel Monkstown
industrial site, Belfast, Northern Ireland. The objectives of this
study were to (1) investigate the characteristics of the geological
material and its influences on contaminated groundwater flow across the
site using borehole logs and hydrological evaluations, and (2) identify
the contaminants and examine their distribution in the subsurface
geological material and groundwater using chemical analysis. This
report focuses on the eastern car park (ECP) which was a former storage
area associated with trichloroethene (TCE) degreasing operations. This
is where the greatest amount of volatile organic compounds (VOCs),
particularly TCE, were detected. The study site is on a complex deposit
of clayey glacial till with discontinuous coarser grained lenses,
mainly silts, sands and gravel, which occur at 0.45-7.82 m below ground
level (bgl). The lenses overall form an elongated formation that acts
as a small unconfined shallow aquifer. There is a continuous low
permeable stiff clayey till layer beneath the lenses that performs as
an aquitard to the groundwater. Highest concentrations of VOCs, mainly
TCE, in the geological material and groundwater are in these coarser
lenses at similar to 4.5-7 m bgl. Highest TCE measurements at 390,000
mu g L-1 for groundwater and at 39,000 mu g kg(-1) at 5.7 m for
geological material were in borehole GA19 in the coarse lens zone. It
is assumed that TCE gained entrance to the subsurface near this
borehole where the clayey till was thin to absent above coarse lenses
which provided little retardation to the vertical migration of this
dense non-aqueous phase liquid (DNAPL) into the groundwater. However,
TCE is present in low concentrations in the geological material
overlying the coarse lens zone. Additionally, VOCs appear to be
associated with poorly drained layers and in peat < 3.0 m bgl in the
ECP. Some indication of natural attenuation as VOCs degradation
products vinyl chloride (VC) and dichloromethane (DCM) also occur on
the site.
Original language | English |
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Pages (from-to) | 1117-1131 |
Number of pages | 15 |
Journal | Environmental Geology |
Volume | 52 |
Issue number | 6 |
DOIs | |
Publication status | Published - Jun 2007 |
Keywords
- trichloroethene
- glacial till
- groundwater
- volatile organic compounds
- dense non-aqueous phase liquid
- aquifer
- aquitard