Newlands Cross Upgrade EIS - European Investment Bank

South Dublin County Council N7 Newlands Cross Upgrade
Environmental Impact Statement
Arup Consulting Engineers
6.3.3 Hydrology
Sweeney, 1991 15 , and the OSI map were consulted for the location of any watercourses
(current or historic) in the vicinity of the development. There are no significant streams
indicated within the immediate area.
The Grand Canal is located 1.5 km to the north of the site and some small tributaries of the
Camac River can be found in the vicinity of the site.
Refer to Chapter 14 Surface Water and Drainage for further hydrological information.
6.3.4 Hydrogeology
Hydrogeology is the study of groundwater, including its origin, occurrence, movement, and
quality.
The overburden in the area consists principally of glacial till (brown and black boulder clays)
of low permeability and would not be considered a significant aquifer.
As noted in Section 6.3.1.2, the area is underlain by limestone and shales. The aquifer
potential of limestone rock varies depending primarily on the fracture state of the rock mass.
The greater the degree of fracturing of the rock, the more conduits there are for the water to
flow through, and this can in turn lead to solution weathering further increasing permeability
and aquifer potential. The aquifer potential of limestone can also be affected by dolomitisation
in which calcium minerals are replaced by magnesium minerals which can increase the
porosity by bedrock.
The areas underlain by Calp bedrock which consist mainly of low permeability are composed
of fine-grained, argillaceous limestones and shales. It is a variable unit that contains
occasional more permeable strata, which are present due to faulting, uplift, erosion and
possible karstification. The GSI National Draft Bedrock Aquifer Map describes the bedrock
aquifer as a locally important bedrock aquifer, which is moderately productive only in local
zones.
The GSI National Draft Gravel Aquifer Map illustrates that there is no sand or gravel aquifer
in the area.
Aquifer vulnerability depends primarily on the type and thickness of overburden covering the
aquifer. The aquifer can be said to be more vulnerable in areas where there is low overburden
thickness, as the risk of contamination from spillages reaching the aquifer increases.
Conversely, the aquifer vulnerability decreases significantly in areas where there are greater
depths of overburden. According to the GSI aquifer vulnerability map much of the area is
likely to be of moderate vulnerability. There are also areas of extreme vulnerability due to
rock near to the surface or rock with karst features.
Site specific ground investigation shows shallow rock in the area of the Junction, in places at a
depth of less than 1m. In these situations a bedrock aquifer is classed as extremely vulnerable.
GSI well records were consulted for the locations of wells in the area. Two records were
found for wells in Belgard Quarry. There are no source protection areas delineated by the GSI.
December 2007 Page 98