HYDROCHEMICAL BEHAVIOR OF TWO DIFFERENT ARTIFICIAL FLUIDS IN A COASTAL SEDIMENTARY BASIN DURING SINGLE-WELL ("PUSH-PULL") TESTS
The aim of the project was the density dependent hydrochemical characterization of the aquifer by single-well push-pull tests. The push-pull method was already used as partitioning test to quantify organic pollutants in relatively shallow depths of about 10 to 20 metres.
As a first step the tests were conducted in the shallowest well (100 m deep). A later adaptation on a 1,100 m deep borehole is planned. As density dependent transport processes are important in coastal areas (due to the saltwater-freshwater interface) the push-pull test was conducted twice. For determination of different aquifer and fluid behaviour depending on the density of groundwater at first a mixture of groundwater, uranine, and various salts (“saltwater”) was injected and afterwards re-pumped. After a certain time distilled water + uranine (“freshwater”) was injected and re-pumped.
The measured breakthrough curves of the several anions and cations during the pumping back phase were analysed during both tests. Various redox, sorption/desorption, and solution/precipitation reactions could be observed. Some during the “saltwater” test ‘irreversible’ sorbed ions (= less than 100% recovery during pull phase) could be re-mobilized during the “freshwater” test. Even some ions were detected during the pull phases, which were neither input during push phases nor detected previous in natural groundwater. These ions were either desorbed or new produced during the tests.
The results of these combined tests deliver the typical transport behaviour of a various range of ions within the aquifer of the investigated Sarabetsu Formation and furthermore suggest a highly sensitive hydrochemical response of the aquifer-groundwater system on pumping-injection activities. The findings of the test are both, part of a better understanding of the groundwater system of Horonobe and the further development of the push-pull method.