Application of Transient Hydrogeological Modelling for Optimisation of Artificial Infiltration System of the Baltezers Well Field, Latvia

The steady state 3D-hydrogeological model (HM) has been developed for the Baltezers, Rembergi and Baltezers water supply complex which provides the Riga city with drinking water from groundwater resources. Because the HM plane approximation step is rather fine (55 metres), detailed investigations of groundwater flow processes and contamination migration are possible for the complex. However, transient modelling and refinement of the HM grid are necessary, to investigate the artificial infiltration system of the Baltezers well field. The system takes water from the Baltezers lake and feeds infiltration basins, in order to keep the well field siphons to perform properly when drinking water consumption is large. Fortunately, the system also prevents contamination of siphon wells by accidental toxic spills that may occur on the nearby highway and railroad. The water consumption of Riga has decreased almost threefold, since 1995. For this reason, the large capacity of the Baltezers siphons system cannot be exploited in full. Nowadays, the following contra dictionary requirements regarding this well field should be fulfilled: low price of drinking water (no artificial infiltration); igh water quality; protection of the well field against contamination; capability of sharp increase of groundwater withdrawal, to compensate possible failure of the water supply complex taking water from the Daugava river. In order to solve this optimization problem, the local transient HM has been created, on the base of the existing regional HM. The plane approximation step of local HM is 0.5 × 55=27.5 metres. Presently, HM uses variable water withdrawals and infiltration rates that can be changed every mouth. The first results are obtained and more precise requirements are formulated to obtain the needed optimal solution regarding exploitation the Baltezers well field in future