Groundwater Investigations
Project Introduction
In 2005, Southern Water commissioned Scott
Wilson to carry out groundwater investigations at numerous
wastewater treatment works.
Project Background
Under the AMP4 programme, Southern Water is
carrying out a review of the treated wastewater disposal at twenty
Wastewater Treatment Works (WTW) to determine their impact on
groundwater. The Groundwater Regulations, 1998, set out “measures
to prevent the introduction into groundwater of List I substances”
(Regulation 4) and “measures to limit the introduction into
groundwater of List II substances to avoid pollution” (Regulation
5). The issue, by the Environment Agency, of permits to discharge
requires a ‘prior investigation’ of local hydrogeology and soil
conditions to assess the potential for impact on groundwater
quality.
Project Scope
A scoping study was carried out for each WTW,
which identified the extent of intrusive investigation and/or
monitoring required, followed by the preparation of borehole
designs and specifications. Investigations at the majority of sites
involved drilling three boreholes (up gradient, down gradient and
at the discharge location) to depths of between 5 m and 75 m with
installation of standpipes and water level loggers. Cores
were extracted and centrifuged to obtain pore water samples at
various depths through the unsaturated zone and saturated zone. A
year of monitoring provided monthly water quality samples and
continuous water level records.
Value Adding Project
Achievements
The findings of the investigation were used to
assess the site specific geological, and hydrogeological,
conditions and the groundwater quality up hydraulic gradient and
down hydraulic gradient from the sites, with particular reference
to List I and List II substances. Estimates of groundwater flow
beneath the sites and a numerical estimate of the effectiveness of
natural attenuation of potential contaminants, and hence the impact
of effluent discharge on groundwater, were made.
