7 Geology and Hydrogeology
7.8. Resources - Aquifers
Consolidated
Sediments (Bedrock)
The main bedrock
aquifers identified are:
- Karstified
limestone: Ballyadams and Clogrennan formations. These formations
contain an aquifer of regional importance. A large spring
located in the south of Paulstown is the source for a regional
water supply in a part of Co Kilkenny.
- Dolomitised
limestones, Ballysteen, and Milford formations. A substantial
part of this aquifer drains in the River Nore. This aquifer
has been developed for industrial water supply in Carlow
Town and for municipal supply in Muinebheag.
- Ballysteen
Formation: can contain aquifers of regional importance (3).
- Ballymartin
Formation: only contains aquifers of minor importance (3).
- Maulin Formation:
These rocks contain only minor aquifers (3).
The different
geological formations listed above can be identified on the
Geological bedrock maps (Sheets 16 and 19). The constraints
to route selection posed by bedrock aquifers are not likely
to be as significant as sand and gravel aquifers, so they
have not been plotted on the geotechnical constraints maps.
Unconsolidated
Sediments (Sand and Gravels)
There are a number
of thick deposits, mainly of sand and gravel, which occur
in the study area, as follows:
- Mid-Kildare
gravel aquifer, designated G-1. This is a major aquifer,
which is widely used as a source of water supply in the
area. The thickness of the gravels within the study area
is between 5 m to 30 m (Reference 4).
- Along the
Burren River in East Carlow (10 m to 15 m).
- Major aquifer
along the River Barrow north and south of Carlow Town (10
m to 25 m), designated G-2.
- Major aquifer
along the River Nore north of Kilkenny City (10 m to 30
m), designated G-3.
The other gravel
aquifers identified stretching along the main rivers occurring
in the study area are considered to be minor aquifers (Reference
5).
Aquifer Vulnerability
and Protection
A draft aquifer
protection plan for County Laois has recently been prepared
by the Geological Survey of Ireland. A similar draft aquifer
protection plan for County Kilkenny is expected to be available
by September 2001. According to the Geological Survey of Ireland,
these aquifer protection plans are intended to provide guidance
to local authorities for planning permissions but do not have
statutory status.
The draft groundwater
vulnerability mapping for County Laois and for County Kilkenny
were consulted. The data available was examined to identify
any major vulnerable aquifers occurring within the study area.
Some extremely vulnerable aquifers were reported in areas
where the shallow rocks lay within 0 m to 3 m from the surface
as follows:
- A large rock
and sand/gravel aquifer extending in a broad line from Carlow
to Athy. The rock aquifer, associated with the Karstified
Clogrenan and Ballyadams Limestone Formations, was reported
to be highly vulnerable.
Where the water
table would be lowered as a result of excavation, the potential
effects on local wells should be assessed. The lowering of
the water table could reduce or eliminate the well yield.
Road drainage
as well as accidental spillages could potentially have an
impact on the quality of the local groundwater. In areas of
road crossings through zones of high aquifer vulnerability,
specific design measures for road drainage may be required
to prevent surface activity from polluting the underlying
groundwater.
|
