MATHEMATICAL MODELS OF DUAL TRANSMISSIVITY AND EXAMPLES OF THEIR APPLICATION IN INTERPRETING PIEZOMETRIC TESTS CONDUCTED IN THE BEŁCHATÓW LIGNITE MINE

Piezometric tests such as the slug test or PARAMEX test usually result in observing damped oscillations or exponential movement of the water level. However, during some tests, a bi-exponential response of the water table has been recorded. Bi-exponential movement may indicate the presence of a dual-permeability medium around the piezometer screen. Such medium is composed of two subdomains, each characterized by different hydraulic properties (including transmissivity, T). The paper aims to present two mathematical models – the piecewise exponential model and the bi-exponential model – which were applied in order to interpret the results of slug test conducted in heterogeneous sediments of the Bełchatów Lignite Mine. Theoretical background, interpretation algorithms and examples of dual transmissivity estimation for several chosen piezometers are presented. All necessary calculations were performed using Paramex 4 and MATLAB software. Furthermore, the limitations of the interpretation algorithms are discussed.