AbstractsEarth & Environmental Science

An integrated study of hydraulic anisotropy and its impact on saltwater intrusion in an inland aquifer

by Jialiang Cai

Institution: Freie Universität Berlin
Department: FB Geowissenschaften
Degree: PhD
Year: 2014
Record ID: 1101997
Full text PDF: http://edocs.fu-berlin.de/diss/receive/FUDISS_thesis_000000097891


The two-dimensional hydraulic anisotropy (a), defined as the ratio of horizontal to vertical hydraulic conductivity (Kh/Kv), is a standard parameter of hydrogeological characterization, However, a is not routinely determined and correspondingly its value is often empirically set to 10 in the numerical modeling studies for solving anisotropic problems in sediments, owing to the fact that one of the challenging tasks hydrogeologists face today is the high-resolution characterization of directional hydraulic conductivity (DHC) in sediments. Therefore, an integrated laboratory method, called modified constant-head permeameter test (MCHPT), was established for the efficient determination and verification of consistent DHC values in fine-to-medium sandy sediments, based on a new methodological framework that includes a precise and standardized procedure for preparing the experimental setup. As known, detailed information on a can provide an important fundament for modeling transport phenomena in sediments, e.g. saltwater intrusion. Saltwater intrusion is a widespread problem of continuing great practical interest in many coastal and inland aquifers all over the world, which is considered a special category of contamination to make groundwater unsuitable for human, industry and irrigation uses. There is an increasingly significant effect of salinization in most abstraction wells with a great depth of ~ 50 m below the surface in an inland aquifer at the Beelitzhof waterworks in southwestern Berlin (Germany) and a very thin film of saline groundwater (centimeter scale) has been observed in fine-to-medium sandy sediments on the top of the Rupelian clay at the site, thus, it could be assumed that Elsterian glacial channels would be in the close vicinity of the site, which results in saltwater upconing owing to pressure release by pumping a large amount of groundwater in drinking-water-production wells. Consequently, the impact of a on the intensity of saltwater intrusion due to pumping at the site was demonstrated based on the precise quantification of an a value of 2.3 using MCHPT in comparison with the empirical value of 10, by developing a conceptual model representative of the field situation and implementing it in a numerical density-dependent groundwater flow and solute transport model. During the aforementioned modeling study, it has been found to be not yet able to be proven at the site whether there are hydraulic windows in the clay caused by glacial erosion or not. Therefore, two hypotheses about geological conditions in an inland aquifer leading to pathways for upwelling deep saline groundwater due to pumping, were raised as to: (1) there are windows in the clay, where their locations are uncertain; and (2) there are no windows in the clay, but the clay is partially thinned out but not completely removed by glacial erosion, so salt can merely come through the clay upwards by diffusion and eventually accumulate on its top. These hypotheses were tested to demonstrate the impact of the lateral distance between…