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Polustrovo
 
Expert Conclusions on the Developed Ground Water Flow Model for Polustrovo pilot area (in the framework of Project "Integrating Geological Information in City Management to Prevent Environmental Risks").
General information.

Polustrovo site is located within the built-up area. It hosts mineral water deposits and in-dustrial companies. Along with that, an intensive intervention into the subsurface layers is going on. Due to this it is necessary to forecast processes, which, on one hand, are relevant for the pro-tection of groundwater from pollution and, on the other, adverse phenomena caused by the im-pact of high-pressure water on buildings and infrastructure both a the stage of construction and operation. Of high concern is also a problem of land and buildings flooded by groundwater.

In the studied territory the upper intermoraine aquifer lies at the depth of 5-24 m. The aq-uifer has a pressure head, which is evaluated as 3,5-30 m. It is separated from the overlying layer of vadose water by clayey deposits of Ostashkov (Luga) moraine. The moraine layer has eroded locations ("hydraulic windows"). The vadose water aquifer lies directly on the upper intermo-raine aquifer, which creates conditions for hydraulic exchanges between the aquifers. Modeling of this process was one of the tasks in the reported work. Contours of piezometric level have the absolute values of 12.5-13.0 m; in most cases its depth is up to 5 m, but in some places it is 0.5-3.5 m above the daylight surface (depending on relief marks).

Work objective

Main objective of the work is to study and forecast flooding of basements and subsurface struc-tures by the high-pressure groundwater of intermoraine aquifer; develop a complex of measures to prevent negative consequences of construction projects neighboring mineral water deposits Grazhdanskoe and Polustrovskoe; protect and preserve the groundwater of Grazhdanskoe and Polustrovskoe from pollution.

Main tasks:
- model groundwater flow in the two main aquifers: vadose and intermoraine (confined); identify the .hydraulic exchanges between the vadose water and intermoraine aquifer in the studied area;
- identify locations of most probable flooding caused by water from the high-pressure in-termoraine aquifer;
- develop and propose engineering solutions to prevent flooding.

Summary.

As a whole, the groundwater flow model has produced adequate results with an accept-able level of error. The modeled places of waterlogging coincide with the actual flooded territo-ries. The developed groundwater flow model can be accepted as a tool for solving the problems of Polustrovo site. Models 2 and 3 can be considered for this, because they propose options for partial or complete solution of flooding problem by introducing the network of boreholes or drainage canals.

It should be noted that the comparison of modeling results produced by the VADOSE-GIS and Groundwater Vistas software has shown their good convergence. The VADOSE-GIS software updated and adapted for the problem solution on the much more complex territory of St. Petersburg has demonstrated efficient and easy-to-use applicability, so it can serve as a reli-able instrument of hydrogeological modeling.

 

 
 
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