Abstract

In 1984, in Taubaté County, Brazil, was carried out a study to identify the groundwater pollution due to land disposal of chemical industrial wastewater. After the characterization of the wastes, some analytical parameters were selected for a monitoring programme: TOC, COD and Electrical Conductivity. This programme had started after a network of 39 monitoring wells were installed. Monthly the water level surface were depicted and four times a year samples from the groundwater were collected to the chemical analysis. The data were interpreted by a computer programme (SYMAP) which gave hydrochemical and isopotencial maps. The interpretation of theca maps point out a groundwater pollution due to wastewater infiltration and that limit of the pollution plume were the adjoining stream. Besides the horizontal trend pollution into the aquifer, research is necessary to verify a vertical pollution in order to evaluate the compromise degree of the aquifer.

Keywords

Industrial wastewater; land disposal; infiltration ponds; groundwater monitoring; groundwater pollution.

Introduction

The populational industrial growth have caused gradually increase of the production of wastes and-its inadequate disposition causes serious environmental problems. The soil as an alternative of disposition of wastes is being used more frequently today. This results from legal restrictions of discharge in superficial waters, favorable economic factors and the possibility of reutilízation of such wastes.

An important example is the reutílization of vinasse in Brazil, as fertilizer in sugarcane crop production (Gloria, 1975 and Copersucar, 1979).

It is necessary to poit out that the use of the soil as a receptor of efluents should be considered carefully, in order to preserve its purifying characteristcs and to assure groundwater protection. To enable this, the site must present favorable hidroqeologigal characteristcs, employing adequate technology during the implantation and manaqement of the. disposal area. The effluents must be compatible with the purification capacity of the soil system If such aspects are not followed, the consequence will be the compromising of the groundwater quality.

Rocha 1986 considers, in a general way, that São Paulo State groundwater presents naturally good chemical quality, but points out a great potential of pollution from solid wastes and chemical products. The actual situation of groundwater pollution is not well known, since little research is being done in this area.

In order to evaluate the problems caused from soil use as receptor system of residues a monitoring program of the groundwater quality was carried out in the city of Taubaté, São Paulo State, where two chemical industries apply their wastewater in infiltration ponds.

The experimental site was selected because this area have been used for a long time as a receptor soil system. Other aspects considered were the hydrogeological factors, high urbanization, the characteristics and high level production of the wastes. Another important aspect, was a social problem,where the local population were forced to abandon the utilization of shallow wells because of the bad water quality.

As a first step it was evaluated the lateral flux of pollutants in the shallow aquifer to identify the effects of the infiltration on groundwater. In the next step will be done the characterization of pollutants distribution related with the depth and the identification of the physical, chemical and related with the depth and the identification of the physical, chemical and hydrogeological phenomena involved. With such parameters it is intended to hydrgeological phenomena involved. With such parameters it is intended to propose methods to recover the aquifers that have already been contaminated

Description of the area

The experimental site is located in Taubaté County (23° 01's, 45° 36'w) in the southeast part of the State of São Paulo, Brazil. The area is in the Paraiba Valley which constitute one of the most important industrial park of the country.

The climate in most of the area is subtropical, hot with rainy summers and dry winters; annual mean temperature above 21°C and mean air humidity above 70%. The average annual rainfall varies between 1,200 mm and 2,500 mm, promoted mainly by its topographic configuration.

The Paraiba Valley is an alongated depression (approximately 300 Km in length) and narrow (25 Km in width), between "Hantiqueira" Mountain and "Mar" Mountain which may be classified as a semi-graben because of its characteristics in section (Almeida, 1976).

The depression is mainly fulfilled by terciary sediments and in specific points by quaternary sediments which belongs to Taubaté Group of Taubaté Sedimentary Basin. The sedimentary block may reach 500 m in depth (DAEE, 1977).

The Taubate Group is divided in two formations: the Tremembé Formation, constituted by shale and claystone, with intercalations of sandstones. siltstones and intraformational breccias typical of lacustrine environment and Caqapava Formation, constituted by sandstones, conglomerates and siltstones few consolidated, pelitcs intercalations with plane-parallel or lenticulars layers typical of fluvial environments.According to Hasui and Ponçano, 1978, the relations between these two formations are linked to interfingering and diastem.

Groundwater occurence

The sedimentary aquifer of Paraiba Valley (DAEE, 1977), is characterized by a great horizontal as well as a vertical granular variability. The aquifer layers are formed by coarse materials and the confining layers by fine materials. The quality of the aquifer is determined by the relation between fine and coarse sediments.

The central area of Taubaté Basin (Taubaté, Tremembé and Pindamonhangaba region) is formed by fine sediments (Shales and Claystones), occuring few intercalations of coarse material which does not constitute a good aquifer. In the region some wells were drilled exploring lenticular bodies of high permeability (coarse material) reaching flows of 20 to 30 cubic meters per hour.

The two regions located at the basin edge are considered to be better aquifers than those of the central part, because of their greater number of intercalation of coarse material. The first area includes the counties of Santa Isabel, Jacarei, São José dos Campos and Cagapava. The second includes the counties of Lorena, Guaratinguetá and Cruzeiro.

The wells drilled in these areas present flows of 100 to 250 cubic meter per hour. The water of these aquifers presents in general good quality (Rocha, 1986), and could be used for any purposes.

The site of study is located in the central part of the Taubaté Basin, where there are mainly fine sediments, with claystones and shales from Taubaté formation covered by coarser sediments, typical of fluvial origin, showing young sandstones of variable granular sizes, with lenticular clay layers and clay pellets, and also plane-parallels and lenticulars layers of conglomerates.
Both the local and regional are shallow aquifers.

Material and methods

The experimental area contain two chemical industries settled in adjoined areas, both discharging intermittently their wastewaters in infiltration ponds.

The Plastificants Taubaté S.A. (PLASBATE) Industry has been disposing its wastes since October 1972 , at a mean rate of 1C cubic meters per day. The Quimica Taubaté Industry (IQT), started to seep its wastes in 1979, with a mean rate of 5 cubic meters per aay.

The Figure 1 shows the localization of these industries and their position in the State of São Paulo.

Fig.1 Localization of the studied area in the taubaté county. The square in the
left shows the position of this county in the São Paulo State            

In this site was installed a network of 39 monitoring wells in order to observe the flux of groundwater and pollutants. They were located to a depht of 1.5 meters below the water table. After, it was carried out a topographical levelling of the wells and these data were used to elaborate isopotential maps. In a next step, started a montly rotine to measure the groundwater level and a water sampling for chemical characterization each two months.

It was done a chemical characterization of the seeped wastewaters (Table 1), and from this data was stabilished the parameters which would be monitoried in the water samples. These parameters, and oil and greases, were periodically monitored during the sampling period but in the work, are presented only variations of Total Organic Carbon (TOC), Chemical Oxigen Demand (COD) and the Electrical Conductivity (EC) which can provide a good characterization of the wastewater pollution.

Table 1 - Chemical characteristics of the wastwater
industries (average values)

The sampples collected were preserved in the field and transported to the laboratory where they were immediately analysed. The methodology adopted to this analysis follow the Standard Methods, 1980.

The interpretation analysis of the data was done by computer program. This program (SYMAP), use a value interpolation which gives the hXdrochemicai maps and the water level surface maps.

Results and discussion

From Figure 2 can be observed the direction of the local flux groundwater. The lines of flux were traced from isopotential lines, procedure which results the approximated trend of the flux due from the anisotropic mean.

Fig.2 Water-Level surface and monitoring wells at the contaminated site

Through the observed values of samples from the monitoring wells, can be observed the high degree of contamination of the aquifer. Table 2, shows the values of TOC and COD detected, which demonstrate the prodominance of organic pollution of the aquifer.

Table 2  -  Representative water quality analyses of monitoring wells

Unfortunately, it could not be identified the compounds which are responsible for the contamination because of analytical problems. However, determinations of TOC can provide valuable diagnostic evidence of the extent groundwater contamination by organic compounds (Barcelona, 1934).

The lines of same concentration of TOC (Figure 3) can be observed simultaneously with their distribution trend through out water table aquifer flux. It could be seen that although high values of TOC appeared nearby the ponds, higher concentrations could be found downstream. This could be explained by the intermittency discharges of the wastewater and the pollutants transport by the flux of groundwater, which are responsible for the high values found at the time of the sampling. By the other side, the low values of TOC observed nearby the ponds, can be explained because we were not able to get the value in the monitoring wells number 7,8,9 and 12.

Fig. 3 - Hydrochemical map of the total organic carbon
distribution in the water table aquifer

The dispersion tendency observed for COD in Figure 4 makes evident the aquifer pollution due to the wastewater infiltrations. High values of COD were found around the ponds and its dispersion tendency follows clearly the one presented by TOC. It was not observed a region with concentration higher than those found around the ponds, as show in Figure 3 for TOC. This could be explained by the nature of the organic compounds found in the wastewater. Possibly these compounds could not be precisely quantified for TOC as they were for COD analysis.

Fig. 4 - Hydrochemical map of the chemical oxigen demand
distribution in the water table aquifer

The high conductivity values (Table 2) express that there is pollution from inorganic compounds as well as organic ones. The Figure 5 shows the same dispersion tendency of the pollutants as verified before for TOC and COD. So it's confirmed the ciclic character of disposition of wastes, observing the surfaces of same concentration.

Fig.5 - Hydrochemical map of the electrical condutivity
distribution in the water table aquifer

Through analysis of Figures 3, 4 and 5, could be seen that the infiltration ponds are responsible for Iocal ground water pollution, being the adjoining stream the aquifer discharge zone.

Conclusions

From the data, can be conclued that:

- The adjoining strearr to the area of infiltration is the limit of the pollution plume.

- Soil disposal of this industrial wastewaters as an alternative to protect surface waters has caused, as verified,
  dangerous consequences not only to surface waters but also to groundwaters.

- The viability of this alternative as a system of treatment of wastewaters is believed to be possible, but in this
   particular case there is necessity of adequated management so that the assimilation capacity of the soil and
   groundwater should not be exceeded.

- It was observed a horizontal trend pollution into the aquifer. However research is necessary to verify a vertical
  pollution in order to evaluate the compromise degree of the aquifer.

References

Almeida. F.F.M. de (1976)- The system of continental rifts bordering the Santos Basin. Brazil, Anais da Academia Bras. Ciências, 48, 15-26

"Aproveitamento da vinhaça, viabilidade tècnico econõmica". (1979) COPERSUCAR, Piracicaba, 71p

Barcelona, M.J. (1984). TOC determinations in groundwater. Groundwater 22 (1). 18-24

"Controle da poluição das ãguas subterrãneas - Projeto Rio Paraiba" (1979). CETESB, São Paulo, 126 P.

"Estudos de ãguas subterrãneas" Região Administrativa 3 e Faixa Litorãnea - São Josè dos Campos" (1977). DAEE, São Paulo, vol. 1, 112 p.

Glõria, N.A. da (1975) utilização agrícola da vinhaça. Brasil Açucareiro 86 (5), 11-7

Rocha, G.A. (1986). Riscos de poluição das aguas subterráneas no Estado de São Paulo, Brasil. 2° Reunião do Comite do Programa de Prevenção e Controle de Contaminação das Åguas Subterrãneas - CEPIS - Cidade do Mexico, 30 P.

"Standard methods for the examination of water and wastewater", (1980). American Public Health Association, 15^th ed, Washington D.C., 1134 p.

Comentarios al Webmaster

[ Homepage CEPIS   ]