Towards a Baltic Sea Region Strategy in Critical ... - Helsinki.fi

CRITICAL INFRASTRUCTURE PROTECTION IN THE BALTIC SEA REGION
of these areas is done by Regional Environment Centres and the high quality maps
of the groundwater areas are the basis for protection.
Concerning groundwater protection, the most important are class I areas and
especially groundwater works and the catchments around them. The studied Hanko
aquifer is locally a very important groundwater area and belongs to class I. Also
the groundwater areas that are potential for new groundwater works are significant
for protection. In the Hanko aquifer the most important area for protection is the
area of the Hopearanta water works. Searching for new water resources to supply
Hanko could be done by drilling new producing wells in a deeper location and
further from the coast. The shallow groundwater aquifer is thickest in NW-SE
trend from the Lindnäsudden area (Figure 6). Toward the mainland, the thickness
of the sand and gravel deposit is up to 58 m and the groundwater depth range
between less than 3 and 12 m below the surface. Sufficient information of
sedimentation pattern of the sand and gravel formations of the groundwater aquifer
would support the best location for the new wells and optimize the groundwater
supply in the long term.
The use of artificially recharged groundwater is increasing in many parts of
Finland. However, the artificial recharge could be very difficult for the Hanko
area, due to the lack of close water resources. This would cause a high investment
for the Hanko Town.
Crystalline bedrock forms the basement of the younger deposits and is
distributed throughout the Hanko peninsula. The depth of bedrock varies from
30m below sea level to the surface level. Groundwater in the bedrock is
accumulated along the fracture zones. The drilling operations to explore these
groundwater resources are certainly more expensive than the shallow groundwater.
Drilled bedrock groundwater wells in coastal areas also face the potential risk of
the saltwater intrusion or relict salt water from the former Littorina Sea.
A plan concerning groundwater protection in Hanko was prepared in 1997
and was updated in 2005 (Harju 1997; Maa ja Vesi 2005). The plan was extensive
and consists of a description of groundwater conditions, groundwater resources,
potential risk functions and proposal for actions, groundwater quality, groundwater
monitoring, and recommendations in restrictions of land use, provisions for crisis
and actions in emergency. It is aimed as a base plan and regular procedure for a
groundwater protection practice.
To protect shallow groundwater aquifers along the coastline, groundwater
monitoring is needed and this should be done for both of groundwater quantity and
quality. The monitoring of groundwater levels in shoreline areas, especially in the
area nearby the main water work also requires information on the sea level. As the
shallow groundwater in Hanko area is vulnerable to the intrusion of seawater, a
routine monitoring will minimize the risk, e.g. chloride is an indicator of the
intrusion of seawater. Monitoring will keep the groundwater quality situation in
general updated. The remediation of groundwater is enormous and expensive
work, so it is better to know the situation before the contamination reaches the
water works’ wells. Moreover, the monitoring will provide basic information of
the groundwater condition and the groundwater budget balance between use,
discharge and recharge and also on pumping control. In Hanko the monitoring of
groundwater levels in observation wells around the water works is carried out, but
the water quality in these wells is not monitored.
210 NORDREGIO REPORT 2007:5