O papel dos poços verticais e horizontais na contenção hidráulica de poluentes nos aquíferos livres.

Abstract

In this dessertation, an analysis was done on the capture zones of pollutants, that pertain to vertical and horizontal wells. The horizontal well is a recent innovation that emerged in the developed countries, such as in the United States o f America and Canada, only in the past 9 or 10 years and this technique is being used in the world over due to its simplicity and efficient use in removing the pollutants, without destroying or perturbing beneath such structures as gas tanks, houses etc. This procedure had proved to be useful in the decontamination of the shallow part of the aquifer, with practical applications that could be employed in the field, should such a contamination occur. The advantage of horizontal wells is that they can have exact access to the area that is to be cleaned, however difficult the situation be, even i f the lower parts of the leaking containers/tanks are to reached. Without menace to the natural environment, it is possible to have total capture of the pollutant. The technique o f vertical wells consisting o f one or more o f these units, as per the program explained in the text o f this dissertation, was studied. The plume geometry of the contaminant, in both vertical and horizontal wells, was determined, with the object o f l i m i t i n g the contaminant spread of the plume and criteria were established to obtain the maximum efficiency as a function of percentage of flow tubes which were captured (as a ratio of tubes that are captured by the given well to the total number of tubes) in the remediation system. Turbo-Pascal Version VI computer programs used were and the resolution o f the figures so obtained was encouraging, with clarity and definition that is needed for an engineer to study and interpret the phenomenon of capture of flow tubes, using the Potential theory. For the purpose of removing the pollutants in shallow aquifers, a battery of vertical wells was employed, with one, two or up to three extraction wells, with the idea o f containing the hydraulic spread of contaminants. The physical parameters involved included the size, depth and spacing in between of the wells, apart from the permeabilities of the media (of the well and that of the formation matrix under question). Detailed analysis o f the results presented confirmed the efficiency and applicability o f this method for the region under study. The method presented here-in for determining the characteristics of capture zones in a rectangular flow domain, be it for the vertical wells or horizontal wells, proved to be very useful for purpose o f project design, location and operation of extraction systems for contaminant plumes that penetrate partially into shallow aquifers. The 2-D solutions were obtained for capture zones. The general specifications for vertical and horizontal wells were furnished in the text of this thesis and these were used all along the study. The hydraulic contaminant contention system composed of a single horizontal well showed to be more efficient than that composed of with vertical wells. However, such efficient condition would be more evident for the case o f thick aquifers, once that for horizontal well(s), one does not have such factor as the l i m i t i n g factor, for the aquifer thickness. This method is very sensible to fluctuation o f phreatic levels, as for the case o f shallow aquifer systems. A analysis undertaken for horizontal wells resulted in an increase in depth of installation, beginning from 40% of the total depth (which amounts to 0,4j ) which is not recommended. Beyond this dimensionless depth, the capture of flow tubes was however not verified, as no measurable increase was observed. In the hydraulic contention system of contaminants, the case o f the horizontal two-well system was conducted purely from an academic point of view. The general specifications used for horizontal wells were presented in the respective tables which show that the efficiency o f horizontal wells is a function o f the number of flow tubes captured. A comparison was made between capture Capture Zones for vertical and horizontal wells and this proved useful in designing field projects to contain the contamination as also to give continuity to such decontamination projects. The recommendations suggested here-in would help one to implement these concepts to structures and installations that need this technique of decontamination of pollutants, wherever they be.