Contaminated Sites in Well Head Protection Areas: Methodology of Impact Assessment

Abstract

According to the Lithuanian legislation, protection zones of public water supply sources are divided into three strips on land: (1) “strip of strict protection”, (2) “strip for protection against microbiological pollution” and (3) “strip for protection against chemical pollution”. The strip of strict protection is the area immediately surrounding the abstraction point. It has to be of at least 5–50 m radius from the abstraction point (geometric criteria). The strip for protection against microbiological pollution is the territory surrounding the strip of strict protection. The size of the strip, depending on average annual abstraction with 15 years prediction, can be defined or calculated (computed). Application of protective measures on land use, in order to protect the resource from a qualitative and quantitative point of view, depends on natural protection level (vulnerability) of the primary aquifer. The strip for protection against chemical pollution is usually calculated or computed (taking in to account, that pollutant reached aquifer) using time criteria where potential pollutant travel time is 25 years (10,000 days). Two strips (strip 3a and strip 3b), with different protection measures applied, should be delimited. In 2010 more than 1,500 well fields (and single wells) were used to provide population with drinking water. For 650 well fields the sanitary protection strips were calculated or computed and required reports presented to Geological Survey. Totally sanitary protection zones cover about 1,300 km², which means about 2% of the territory of Lithuania. Inventory of more than 1,100 potential groundwater pollution sources, existing within sanitary protection strips, allowed assessing of possible impact to drinking water chemical composition. Assessment of possible or existing impact were carried out using indirect (no measurements) and direct (including measurements) methods. The results of this study are planned to be used for improvement of legislation regulating well head protection areas.