Geotechnical Investigation of Land in the Municipality of Descalvado (SP, Brazil) for Selection of Suitable Areas for Residuary Water Treatment Lagoons
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Journal of Geography and Regional Planning Vol. 3(8), pp. 200-207, August 2010 Available online at http://www.academicjournals.org/JGRP ISSN 2070-1845 ©2010 Academic Journals Full Length Research Paper Geotechnical investigation of land in the municipality of Descalvado (SP, Brazil) for selection of suitable areas for residuary water treatment lagoons Reinaldo Lorandi*, Cássia de Ávila Ribeiro Junqueira, Lorraine Silva Lara, Gabriel Vendrúscolo Freitas, Sirleno Alves Pereira and Marco Antonio Albano Moreira Department of Civil Engineering, Federal University of São Carlos -UFSCar., Rodovia Washington Luís (SP-310), Km 235, São Carlos, Zip code 13565-905 - Post office box 676, SP, Brazil. Accepted 10 July, 2010 Selecting suitable areas for the location of effluent treatment lagoons requires detailed analysis procedures of various attributes of the physical environment, in order to avoid environmental degradation, hence protecting it against the possible impacts that may result from the implementation of such lagoons. To indicate potentially suitable areas for the location of residuary water stabilization lagoons, a map was drawn up on a scale of 1:50,000, based on the cross-referencing of representative cartographic documents describing the attributes of the physical environment (textural classification, declivity, common toxicity criteria (CTC), permeability, surface drainage, lithology, clay mineralogy, depth of the saturated zone, and depth of the rock substrate) in the municipality of Descalvado (SP, Brazil). The AHP technique of multi-criteria analysis was used herein, with paired analysis of the attributes, enabling the information of the physical environment to be treated in order to obtain a result that is more compatible with the real conditions found in the surroundings. The final result was the identification of the following classes of suitability, 1% of urban areas and highways; 27% of forbidden areas; 13% of favorable areas; 11% of moderate areas; 47% of severe areas; and 1% of restrictive areas. Key words: Residuary waters, territorial planning, geoprocessing, treatment lagoons. INTRODUCTION According to Marques and Zuquette (2004), selecting suggestion to mitigate these problems is to internally suitable areas for effluent treatment lagoons needs waterproof the lagoon by applying layers of clay, asphalt- detailed analysis procedures of the socioeconomic and based paint, geosynthetics or other procedures. The physical environmental characteristics, as for instance, suitability analysis to implement these ponds through taking into account the various features and elements of geotechnical characteristics is crucial because it takes the land and its interactions with the effluent disposal site. into account the intrinsic characteristics of these lagoons The decomposition of organic matter in the anaerobic for the economic and environmental viability. process generates gases. Thus it is recommended that For adequate construction of a wastewater disposal residences should be built at considerable distance away lagoon, the ideal soil should have a distribution of about from these lagoons in order not to be affected by the bad 30 to 35% between the amount of sand and clay smell generated through volatization. Determining the materials to achieve, a balance between infiltration and ideal distance will be accomplished by analyzing the surface drainage. The propensity is for the water to prevailing wind direction. accumulate in the micropores, prevalent in most clayey The risk of groundwater contamination by percolation soils. (infiltration) is also critical in this system, thus the Installing a wastewater treatment system is imperative for the city of Descalvado, as it flows 1461 kg BOD/daily into the Rio Bonito, given that this river has no treatment of any type.This study evaluates the potentially suitable *Corresponding author. E-mail: [email protected]. Tel: 55-16- sites to install wastewater lagoons in Descalvado, SP, 3351-9656. Fax: 55-16-3351-8262. Brazil (Figure 1), using thematic maps, which will be Lorandi et al. 201 Figure 1. Location of Descalvado. standardized for the application of fuzzy logic and Santa Rita do Passa-Quatro Formation (Tertiary), weighted AHP techniques, hence generating a physical consisting of sand without any kind of sediment structure, land suitability map based on the current environmental shows at the base a line of pebbles or gravel; conditions. Pirassununga Formation (Tertiary), consists of unconsolidated sandy sediments, non-laminated and unstructured, vertically homogeneous; and recent Study area characterization deposits (Quaternary) that occur in the alluvial plains, consisting of sands, clays and gravels. The study area is in Descalvado (SP, Brazil), located in As for groundwater, the Descalvado municipality is the State of São Paulo’s east-central region, at located on the Guarani sediment aquifer system. approximately 756 km². According to results published by São Paulo (1997), According to Mendonça and Danni–Oliveira (2007), the among the region’s aquifer systems, the Botucatu- climates in the region are the macrotype wet-dry tropical Pirambóia system is the one that shows the highest rates climate; subtype tropical climate of Central Brazil without of vulnerability due to its sandy formation, with a low clay drought; characterized by rainfall in all months of the content and homogeneous nature. year, with higher pluviometric concentrations in summer According to Moreira et al. (2008), besides the and a reduction in winter. In the summer, temperatures Botucatu-Pirambóia system, the following aquifer units are high and in winter they are low. The geology of the occur in the municipality of Descalvado: Undifferentiated studied area, according to São Paulo (1984a, 1984b, cenozoic coverage (alluvial sediments); Itaqueri 1986) and Ferreira (2005), are: Corumbataí Formation Formation, showing higher levels of vulnerability and (Upper Permian), consisting of argillites, shales and Corumbataí Formation, characterized as an aquitard, a siltites; Pirambóia Formation (Triassic), consisting of low permeability geological unit, which slows but does not poorly selected sandstones and pebble lines; Botucatu prevent the flow of water from adjacent aquifers or to Formation (Juro-Cretaceous), consisting of well selected adjacent aquifers. fine to medium sands, highly silified, with no clayey In accordance with the geomorphological division of the matrix; Serra Geral Formation (Juro-Cretaceous), State of São Paulo, proposed by Ross and Moroz (1997), composed of basalts, with intercalations of sand layers; the study area is located in the Morphostructural unit Itaqueri Formation (Cretaceous/Tertiary), lithologically called the Paraná sedimentary basin, partially comprising made up of alternating members of sandstones with and two morphostructural units: West Plateau Paulista without clayey cement, shale and ferriferous clusters; (morphological unit “São Carlos residual plateau” where 202 J. Geogr. Reg. Plann. denuded relief forms are prevalent; it is modeled, Establishing criteria to identify wastewater disposal areas basically, by convex and tabular hill tops, prevailing The selection of suitable areas for wastewater disposal involves altitudes ranging from 600 - 900 m and slopes ranging deciding from several possible alternatives based on the defined from 2 - 20% in most of the area, exceeding 30% in the criteria. The decision theory states that a criterion is a measurable relief sectors most studied and the Paulista peripheral basis for a decision, which may be a factor or a restriction. depression (morphological unit “Depression of Moji- The decision norm is the procedure by which the designated Guaçu”), where denuded relief forms also predominate, criteria, factors or restrictions, are combined (Calijuri et al., 2002). but with extensive tabular hill tops, prevailing altitudes The way the data influence the suitability definition for a wastewater disposal area was studied, considering the geological and between 500 and 650 m and slopes between 5 and 10%. geotechnical parameters directly involved in the selection of sites For unconsolidated materials, two groups of such were for this purpose. As a result, some data were classified in scores mapped in the study area: Residual and reshaped according to their suitability for the desired use. materials. According to Zuquette (1987), the unconso- lidated residual materials include various levels of Scaled criteria (factors) saprolites, contemporary and old residuals, in other words, they correspond to the material from the altered Slope rocks, without having undergone any transport, while the Low slopes favor the operational setting up of the wastewater reshaped materials are unsaturated transported lagoons, facilitating the soil movement , causing less impact to the materials, often clayey and with a high concentration of drainage system. According to Zuquette and Gandolfi (2004), the organic matter. most appropriate slopes for setting up wastewater ponds, are in the range 0 to 30%. METHODOLOGY Unconsolidated material Deciding the best area for waste water ponds involves analyzing all of the inherent aspects of the process and their inter-relationships, For this component of the physical environment, the thin soils that -5 including the types and variability of attributes involved. The method have a permeability coefficient in the range of (K20 < 10 cm/s or -6 adopted for the preparation of this map was adapted from Zuquete 10 cm/s) and