Influence of fissuring and karstification of the carbonate aquifer unsaturated zone on its vulnerability to contamination (Cracow Upper Jurassic Region, Poland)

Abstract

The carbonate fissure–karstic aquifer of Upper Jurassic age is the main aquifer in the Cracow Upper Jurassic Region (CUJR). The aquifer is recharged directly or indirectly by Quaternary or Quaternary–Cretaceous overburden of varying permeability, which predominates diffused recharge. Concentrated recharge occurs locally and has a diverse nature. Field studies carried out in 20 quarries show moderate permeability of the unsaturated zone of carbonate massif. Karst funnels are filled with rubble and clay material and dominate filled fissures with an opening b < 10 mm. The average surface fissure porosity of massive with chalky limestones and bedded limestones reach 0.12 and 0.45 %, respectively, while fissure permeability coefficient is, respectively, kS 6.60 × 10−5 and 1.27 × 10−3 m/s. The average karstification in quarries was determined as nk = 2.5 %. Tracer studies, carried out in an unconfined carbonate Zakrzowek horst in Cracow (Krakow), document vertical migration of infiltrating water through the systems with different hydraulic resistance, with a flow rate from 8.1 × 10−6 to 4.9 × 10−5 m/s and the lateral migration velocity between communicated caves from 6.94 × 10−6 to 1.06 × 10−4 m/s. The significant presence of poorly permeable overburden and moderate fissuring and karstification of rock in the unsaturated zone of CUJR are reflected in the assessment of the Upper Jurassic aquifer vulnerability to contamination, performed by a modified DRASTIC method. In the area of unconfined karst, occupying 55 % of the area, vulnerability to contamination is high, while as much as 45 % of the area is characterized by medium and low vulnerability.