A new method for assessing groundwater vulnerability across Estonia has been developed by a University of Tartu doctoral student, aiming to improve land-use planning and protect the nation’s vital water resource. The research addresses limitations in existing assessment guidelines, which haven’t been updated since the 1980s, and offers a more transparent and realistic picture of groundwater protection needs.
Groundwater Vulnerability in Estonia
Groundwater is a critical resource in Estonia, supporting ecosystems, agriculture, and providing drinking water for over half the population. Protecting groundwater quality is paramount, and effective land-use planning relies on accurate vulnerability assessments.
Magdaleena Männik’s dissertation focuses on the impact of surface deposits – till, clay, sand, and gravel left by a massive glacier some 13,000 years ago – on groundwater contamination risk. According to Männik, the thickness and composition of these deposits are key determinants of groundwater protection.
“There are areas where pollution can seep into groundwater very quickly. However, if there is upward pressure from the groundwater that prevents water from moving downward, the area is very well protected from contamination,” she explained. Thick layers of clay and till offer strong natural protection, while thinner, sandier layers allow pollutants to travel more easily.
The developed method is a customized version of the internationally used DRASTIC method, utilizing a geographic information system (GIS) for rapid assessments using existing data. Männik’s adaptation addresses the specific hydrogeological conditions in Estonia, which are more complex than those assumed by the original DRASTIC model.
“In Estonia, however, hydrogeological conditions are much more complex. The main aquifers in use are often confined and groundwater vulnerability is shaped by the interaction between surface deposits and bedrock,” Männik explained. She found that areas with groundwater close to the surface can still be well-protected due to upward pressure preventing downward seepage.
Impact of Land Use and Agriculture
Groundwater vulnerability isn’t solely determined by natural factors; land use plays a significant role. Intensive agriculture, particularly the use of fertilizers, poses a substantial threat through nitrate seepage. Other pollution sources include former industrial sites, mining, and inadequate wastewater systems.
The research revealed that even naturally well-protected areas can be at high risk with intensive agricultural use, while areas with thinner surface cover but less intensive land use are less vulnerable. The most at-risk zones are those with agriculture on land with thin surface deposits.
Specific sensitive areas in Estonia include the Pandivere and Adavere–Põltsamaa regions. Conversely, the Pärnu area, with its thick layers of varved clay, and areas covered by the Lontova clays or the Narva stage confining layer, demonstrate good groundwater protection.
Cross-Border Application and Regulations
Estonia’s Water Act employs preventive measures based on groundwater vulnerability levels, including stricter fertilizer regulations in vulnerable areas, sanitary protection zones around drinking water sources, and water permit requirements.
Recognizing that groundwater transcends national borders, Männik tested the method’s effectiveness in a cross-border region between Estonia and Latvia. “Geological conditions don’t change at the state border — both Estonia and Latvia have similar systems where the confined aquifers used primarily for drinking water are covered by surface deposits that largely determine groundwater vulnerability,” she explained.
The customized DRASTIC method provides a unified framework for assessing groundwater vulnerability in both countries, facilitating coordinated water management planning. Harmonized mapping is informing decisions about monitoring, protection, and cross-border cooperation. Estonia and Latvia have increased joint projects to improve groundwater assessment, monitoring, and sustainable resource use.
Magdaleena Männik defended her doctoral thesis, “Groundwater vulnerability assessment in confined aquifers: modifying the DRASTIC method for aquifers covered by Quaternary deposits” at the University of Tartu on November 21.
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