Groundwater monitoring of legacy contamination in Aizkraukle

The project monitored groundwater to track the spread of historical contamination between the end of the investigation and the start of remediation. Monitoring covered 24 observation wells on two industrial sites in Aizkraukle, at Enerģētiķu iela 2 and Dzelzceļa iela 10. The aim was to measure the groundwater level, the presence and thickness of a floating oil product layer (LNAPL), and to take reliable groundwater samples from wells without LNAPL. The groundwater level was recorded in the Pļaviņas Formation aquifer, where it ranged from 0.74 m to 25.60 m below the well head, or 34.80–46.24 m in the LAS height system. Measurements were taken with an acoustic level meter (interface probe), which detects even a minimal presence of oil product on the groundwater surface. In wells with LNAPL, a standard interface probe cannot measure the layer's thickness accurately, because the product's viscosity stops it from sinking. For this, VentEko used a device of its own design: a turned steel pipe with a pointed end, weighing about 6 kg. Lowered into the LNAPL zone together with the interface probe, its weight lets it push through the product, giving an approximate layer thickness. In wells without LNAPL, groundwater samples were taken from the middle of the screened interval, following the client's technical specification. All measurements were documented, and the data give precise information on the groundwater condition, the presence of contamination and its changes over time, which is essential for planning the remediation and keeping the environment safe.