Detailing the Hydrogeological Parameters of the Aquifer in Karst Limestones (Zvenigirod Research Site of the Lomonosov Moscow State University)

Abstract

Aquifers in carbonate karst rocks are characterized by a known extreme heterogeneity of hydrogeological parameters both in the plan and in the section. This paper presents the results of the study of the distribution of permeability and capacity of the Podolsko-Machkovsky limestone aquifer in the scale of the first meters. On the basis of theoretical developments, supported by many years of field experimental research, it is shown that the main elements of the aquifer structure are thin permeable zones formed as a result of the karstification on the contacts of limestone layers of different lithological composition (bedrocks). The zones do not have measurable thickness and are characterized by individual transmissivities and specific capacities varying at distances of about a meter. The zones are separated by relatively low-permeability layers of unkarsted limestone. The methods of flowmetry in the static and dynamic variants, resistivimetry with details in determining the flow rate are used to identify the thin permeable zones. Layer and zone contacts are performed using electrical logging. Changes in the horizon transmissivity and the specific capacity of the zones in the cluster of 7 wells on an area of about 40 m2 with distances between adjacent wells of 3 m, was determined by cross-wells pumping tests with the recording of pressures and temperatures. All applied methods are modified to solve the presented problems. Even in such an area the neighboring wells show the difference of the aquifer conductivity almost one and a half times. Specific capacities of one thin zone vary by an order of magnitude. The asymmetry of the determined parameters at changing the roles of the experimental and observation wells has been revealed. The results allow us to take a new look at the problem of accuracy of the initial information for hydrogeological modeling — the studied area corresponds to the usual block of the model.