geological characterization and environmental implications of the placement of the morelia dump,...

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Geological Characterization and EnvironmentalImplications of the Placement of the MoreliaDump, Michoacán, Central MexicoIsabel Israde-Alcantara a , Otoniel Buenrostro Delgado b & Alejandro Carrillo Chavez ca Departamento de Geología y Mineralogía, Edif. U. Ciudad Universitaria , Institutode Investigaciones Metalúrgicas,Universidad Michoacana de San Nicolás de Hidalgo ,Morelia , Michoacán , Méxicob Instituto de Investigaciones Sobre los Recursos Naturales, Universidad Michoacanade San Nicolás de Hidalgo , Morelia , Michoacán , Méxicoc Centro de Geociencias , National Autonomous University of Mexico, CampusJuriquilla , Querétaro , MéxicoPublished online: 01 Mar 2012.

To cite this article: Isabel Israde-Alcantara , Otoniel Buenrostro Delgado & Alejandro Carrillo Chavez (2005) GeologicalCharacterization and Environmental Implications of the Placement of the Morelia Dump, Michoacán, Central Mexico,Journal of the Air & Waste Management Association, 55:6, 755-764, DOI: 10.1080/10473289.2005.10464665

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Geological Characterization and Environmental Implicationsof the Placement of the Morelia Dump, Michoacan, CentralMexico

Isabel Israde-AlcantaraDepartamento de Geologıa y Mineralogıa, Edif. U. Ciudad Universitaria, Instituto deInvestigaciones Metalurgicas, Universidad Michoacana de San Nicolas de Hidalgo, Morelia,Michoacan, Mexico

Otoniel Buenrostro DelgadoInstituto de Investigaciones Sobre los Recursos Naturales, Universidad Michoacana de SanNicolas de Hidalgo, Morelia, Michoacan, Mexico

Alejandro Carrillo ChavezCentro de Geociencias, National Autonomous University of Mexico, Campus Juriquilla,Queretaro, Mexico

ABSTRACTThe landfill of Morelia, the capital city of the state ofMichoacan in central-western Mexico, is located 12 kmwest of the city and has operated since 1997 without astructure engineered and designed to control the genera-tion in situ of biogas and leachates. A geological evalua-tion of the landfill site is presented in this paper. Theresults indicate that the site lacks ideal impermeable sub-surface strata. The subsurface strata consist of highly frac-tured basaltic lava flows (east-west fault and fracture sys-tem trend) and sand-size cineritic material with highpermeability and porosity. Geochemical analysis ofgroundwater from Morelia’s municipal aquifer shows ahigh concentration of heavy metals (Cd, Pb, As) exceed-ing the Mexican environmental regulations, along with

the presence of some organic pollutants (phenols). Anal-yses of samples of the landfill’s permanent leachate pondsshow very high concentrations of the same contami-nants. Samples were taken from the leachate pond andfrom nearby water-wells during the rainy season (summer1997) and the dry season (spring 1997, 1998, and 1999).In all cases, the concentration of contaminants registeredexceeded the standards for drinking water of the WorldHealth Organization (American Public Health Associa-tion, American Water Works Association, and Water Pol-lution Control Federation, 2000). Some metal contami-nants could be leaching directly from the landfill.

INTRODUCTIONThe Final Disposition of Solid Wastes in Mexico

Adequate management of municipal solid waste (MSW) isone of Mexico’s most critical land planning needs be-cause, as a consequence of the deficiencies in manage-ment and in ecological regulation, the final disposition ofthese wastes is in open-air dumpsites, which have becomeone of Mexico’s most imperative environmental prob-lems needing to be solved. In addition, changes in con-sumption patterns and unplanned industrialization havecaused an increment in the per capita generation of MSWin the country, which is reflected in the increased quan-tities and heterogeneity of solid wastes generated by agrowing urban population.1

In Mexico, approximately 90% of the MSW producedis deposited on the land in different ways, such as inopen-air dumpsites, uncontrolled/unmanaged landfills,

IMPLICATIONSStructural, stratigraphic, and geophysical analyses togetherwith geohydrological and water analyses are of importanceto understand the potential migration of leachate fromwastes. Several dumps concentrated in the Mexican HighPlateau are located over cineritic cones. This analysis is ofrelevance in the search for solutions for solid waste man-agement plans in developing countries such as Mexico.Understanding the composition of the leachate from land-fills, the geological risk of their diffusion, and the exposurerisks this represents to the population in nearby settlementscan be of aid to solid waste management planners, policy-makers, and lawmakers involved in the improvement ofsolid waste management plans and regulation.

TECHNICAL PAPER ISSN 1047-3289 J. Air & Waste Manage. Assoc. 55:755–764

Copyright 2005 Air & Waste Management Association

Volume 55 June 2005 Journal of the Air & Waste Management Association 755

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or in a very few cases, in sanitary landfills.2 According toofficial statistics, there has been an increase in the use ofthe latter two options for the final disposition of MSW, atrend that could be an indicator of an improvement in themanagement of these wastes.2 Unfortunately, the factremains that sanitary landfills in Mexico are not managedproperly and do not meet the standards of the environ-mental regulations because there is no control of whatenters the landfills and because of inadequate covering ofthese wastes, which is basically related to the presence ofthe garbage pickers (in Spanish, “pepenadores,” derivedfrom Nahuatl, “to pick up something”) who make theirliving by collecting materials from the MSW in the zone.3

The majority of Mexico’s dumpsites and landfills arenot equipped with well-engineered technologies to en-able the control of water sources (such as rain), leading tothe production of leachates. Likewise, these dumpsites donot have control systems to confine and treat MSW,which is merely left to the action of biological purificationand of whatever retention capability may exist in theground. The growing accumulation of leachates in thesubstrata slowly saturates the filtration and retention ca-pacities of the ground, with consequent percolation of thecontaminants downward to groundwater systems.4 ThisMexican case of groundwater contamination is not iso-lated; several examples of it have occurred in developedcountries such as Finland, Sweden, and Canada.5-7 Manyof the dumpsites in Mexico are located on faulted orfractured zones or on sandy substrata8 with high perme-ability. In addition, seismic activity has not been takeninto account despite being a factor of the failure of landfillsites.9 For example, the largest MSW confinement site inMexico (Santa Catarina) is located in the country’s capitalat the edge of a lake basin, which in itself allows for a largemigration of contaminants because of the high perme-ability in these substrata and the accumulation of water asa result of the 3-month rainy period.10 This site receives�8000 tons of MSW per day, which includes industrialwastes.11

A great body of scientific work has been built regard-ing the environmental impact of landfills, and differentmodels have been developed for the field-scale predictionof the arrival to aquifers of polluted leachate coming fromthe lower boundaries of a landfill. Very few studies havebeen made in Mexico about the production of leachate inopen-air dumps and of their impact on the environmentand on public health; despite this lack of data, it is likelythat the refuse can cause air pollution because it is piledup in the open, producing harmful components that arepotentially dangerous to the environment as a result ofuncontrolled seepage. For this reason, the main objectivesof this work were (1) to analyze the composition of theleachates produced in the municipal dump of Morelia and

(2) to characterize and/or evaluate the geological layout ofthe terrain to determine the environmental impact asso-ciated with the production of leachates at the dumpsite’spresent location.

Geographical Location and Current Situation ofthe Morelia Municipal Dump

Morelia is the capital city of the state of Michoacan and islocated in western-central Mexico; it has �600,000 inhab-itants.12 The municipal dumpsite is located 15 km west ofthe city (Figure 1) and has received MSW since 1984. Thelayers of garbage are currently covering an estimated sur-face of �15,000 m2, with a depth of 25 m. The concen-tration points for the dumping of MSW have been movedwithin the dumpsite’s limits to three different areaswithin a radius of 400 m. Presently, this dumpsite receives�689 tons of MSW daily; it is therefore estimated that thedumpsite currently contains �2,413,426 m3 of MSW.13

One area of this site is designated for the dumping ofdangerous residues that come from a variety of industrialorigins, such as manufacturers of matches, bottled oil,storage batteries, resin, paints and their derivatives, andslaughter houses as well as the deposition of hospitalrefuse.14

The dumpsite has no means for trapping or contain-ing leachates, nor is there anything to trap the biogas thatis constantly undergoing spontaneous combustion,which causes frequent solid waste fires, particularly in thedry season. It has been found that the composition of theleachates produced at this site surpasses the legally per-mitted concentrations of cadmium (Cd), lead (Pb), arsenic(As), chromium (Cr), and hexavalent chromium. Theseelements filter through the foundation and percolatedownward to the groundwater systems.4 For this reason,the current situation of the municipal dump of Moreliahas taken on new interest, mainly because there is evi-dence of the vulnerability of the aquifer layer in thevicinity of the dumpsite.

Geology of the Dumpsite ZoneThe dumpsite is located on top of a natural valley formedbetween two cinereous cones (named Cerritos and CerroPelon) and a small plateau made up of basaltic lava. Theregion adjacent to the dumpsite is formed of pyroclasticdeposits from the Quinceo volcano and have been esti-mated to be 500,000 years old.15 The dumpsite’s substra-tum is made up of fractured basaltic lavas that are inter-calated with pyroclastic deposits and fall deposits ofPlioquaternary age, which are a product of the volcanoesin the region. The volcanoes, which are the source of thematerial used to cover the layers of solid waste at thedumpsite, are aligned along the length of the faults run-ning from northeast to southwest and from east to west,

Israde-Alcantara, Delgado, and Chavez

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and the faults can be observed on the surface as well as inthe subsoil.4 Flood zones are scarce because of the recentemissions from the Cerro Pelon cone, the source of thevolcanic sand and tuff extracted to cover the solid wasteson a daily basis.

Stratigraphy and Geohydrology of the DumpsiteRegion

The dumpsite is located in the western region of theCuitzeo lake basin. The stratigraphy of the area has beendetermined through deep perforations and geophysicalprospecting, and from these it can be deduced that theterrains are made up of fractured lava flows, scoria, ashes,and layers of volcanic sands that vary from coarse to fine.These sands are poorly cemented. From the geohydrologi-cal point of view, the zones favorable for recharging theaquifers are conformed of fractured lava, sand, and gravelthat supply the groundwater reservoirs of the Cerritos-LosItzicuaros region (Figure 2); in these coarse structures thegroundwater flow is most significant.16 The springs in thisregion are an important water supply for the city of Mo-relia. The main sources that contribute to the feeding ofthe aquifer system in the region of Cerritos-Los Itzicuarosare in the Quinceo and Aguila volcanoes, which are

situated to the north and south of the basin, respectively.The groundwater flow is confined to the west by nonfrac-tured lava flows, whereas basaltic fractured flows andsands are, qualitatively, aquifers with high permeability.

The static levels of the aquifer layer in the wells thatwere analyzed indicated that the flow of groundwater isfrom west to east, with two possible aquifers that are cutby horizons with low permeability. The first aquifer fluc-tuates between 45 and 60 m in depth, and the second is atan approximate depth of 180–200 m. Lavas with basic tointermediate composition constitute the nonpermeablematerials that contain the aquifer, whereas the westernboundary is made up of lacustrine clayey sediments.17

The groundwater flows naturally toward the southeasternpart of the dumpsite, and permanent ponds have beenobserved in the western part of the site, whereas towardthe west, temporary draining and small dams used aswatering holes for cattle have been observed.

The slope in the dumpsite area is of �1.2% in relationto the city of Morelia. Between the northern and westernfronts up the dumpsite, permanent leachate ponds havebeen observed with a total area of 700 m2. These poolspercolate directly downward to the aquifer system throughthe fractures in the 80-cm thick basaltic substratum,

Figure 1. Locations of the Morelia dump and of the sampling wells and springs.



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particularly during the rainy season (June through Sep-tember), a season when the leachate ponds increase involume (Figure 3).

MATERIALS AND METHODSSampling and Analyses of Groundwater,

Leachate, and LavasSampling. For 3 years, water samples were taken from thenine wells existing in the dumpsite’s surrounding area,along with samples from two springs located to the westof the dumpsite. All wells and springs are confined to asector known as E-W. Two samplings were done duringthe wet summer season and another two in the dryseason. The samples from the wells were taken directlyfrom the water flow, at least 20 min after the pump had

begun to work, and filtered. The leachate samples weretaken from the base of the heap of garbage in both therainy and dry seasons and were collected in 1-L jars thatwere previously washed with a 10% muriatic acid solution.

The samples used for determining metal concentra-tions were placed in Bayler bottles, and 50 drops of nitricacid were added. These bottles were kept refrigerated untilthe moment of analysis. The samples used for measuringnitrates were placed in glass jars and/or 0.5-L polyethyl-ene containers with a lid and a security lid, all of whichhad been washed previously, and to which 5 mL of H2SO4

was added to lower the pH to 2.We also drilled a 50-m deep well at a distance of

300 m to the south of the landfill site, obtaining contin-uous rock cores from the drilling. Samples of materials

Figure 2. Local geology of the western part of the municipality of Morelia. 1, Cuitzeo Lake; 2, alluvial deposits; 3, scoria cones and relatedpyroclastic flows; 4, andesite and basalts (Quaternary); 5, pyroclastic flows deposits (2.8 million yr); 6, andesites and basalts (Upper Miocene);7, lacustrine and fluviolacustrine deposits (Upper Miocene–Lower Pliocene); 8, ignimbrites (Middle and Upper Miocene).



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were extracted at different depths of the monitoring welland from two other sites where lava outcrops occurred todetermine the porosity and permeability of the subsoil, aswell as for the purpose of estimating the depth and typesof contaminants that could be migrating from the landfillsite toward the lower zones of the area. Once the well wasfinished, a � ray test was done to determine the porosityof the material. When bombarded with � rays, materialswith fine grain sizes respond with increases in the fre-quency of beats per second (BPS); in this case, a scale of0–50 BPS was used.

Analysis of Groundwater. Chemical analyses of metals ingroundwater were done by inductively coupled plasma(ICP)–mass spectrometry in the certified Laboratory ofGeochemistry Cooper State in Arizona, and duplicateanalyses were performed with a PQ3 (VG-Elemental) ICP-mass spectrometer in the Laboratory of Isotopic Geologyat the Geophysics Institute of the National AutonomousUniversity of Mexico (UNAM). In UNAM, the instrumen-tal conditions and general method parameters are as fol-lows. Ion lens setting and the x-y-z position of the torchwere manually optimized for maximum sensitivity (5 �

105 to 1 � 106 counts/sec) for isotope115 of In and theminimum percentage for BaO/Ba2� (below 3%), using asolution containing 10 �g/L Be, Co, In, Tb, Bi, and Ba.Under routine conditions, one element menu is used forcharacterization of the metals and metalloid to be ana-lyzed. The linear dynamic range was extended by use of asimultaneous pulse-analog dual detector. The dual modewas usually selected when high analyte concentrationranges were anticipated. When a high signal was encoun-tered (for each element between 50 and 200 �g/L), the

pulse detector tripped, and the signals were acquired inthe analog mode. The elements were determined by thecalibration curve method with five standard solutionscontaining 0 �g/mL, 1 �g/L, 10 �g/L, 100 �g/L, or 500�g/L of each element. The standard solutions were pre-pared by diluting a 1000 �g/mL certified stock solutioncontaining all elements (QSC-19, High Purity Standards)in deionized water prepared by filtration through a Milli-pore-Q system and 2% HNO3. Matrix effects were mini-mized by preparing the calibration blanks and standardsin the same matrix (2% HNO3) as the samples. HNO3 waspurified by sub-boiling-point distillation of Merck HNO3,with three replicates measured per sample.

The polychlorinated biphenyls (PCBs) and the vola-tile organic compounds were analyzed by gas chromatog-raphy (GC), and the phenols by the liquid-liquid extrac-tion method with GC (APHA) at Cooper Stade Laboratory.

Analysis of Lavas and Cores. The solid materials (rocks)and leachates from the landfill (liquid samples) weredigested with a microwave digestion system (CEM-MDS-2000). The method used for the digestions wasU.S. Environmental Protection Agency (EPA) Method SW846-3051, which allows the digestion of metals in differ-ent material (solid and liquid) for further analysis withICP-mass spectrometry.

Determination of Configuration of theSubstratum

The electric resistivity method and the georadar methodwere used to determine the presence in the subsoil ofstructural features and groundwater. Vertical electricalsounding was carried out with a Schlumberger-type

Figure 3. Stratigraphy of the subsoil and static levels and depths of the wells in the western sector of the municipality of Morelia. Source:Israde et al.5



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interelectrodic array through a geoelectrical section run-ning from northwest to southeast. The stratigraphy of thedumpsite was interpreted based on the configuration ofthe three space-resistive bodies that were registered.

In addition to the above, we used a georadar, aninstrument that can localize ancient structures in thesubsoil, such as paleochannels, faults, and fractures. Thisis a nondestructive method based on Maxwell’s equationsdescribing the behavior of electromagnetic waves in dif-ferent materials. Electrical conduction of the materials inthe subsoil is propagated by waves. The application of thisinstrument is based on the placement of electrodes con-sisting of a pair of antennas, one for transmission and onefor reception. These electrodes produce potential differ-ences that generate electromagnetic impulses that movetoward the subsoil, which sends return signals that con-figure reflection surfaces. The surfaces that are generatedby this instrument are two-dimensional and are known asradargrams.18,19

Frequencies between 10 mHz and 1 GHz were used.The above method was used to determine whether thestructures observed in the surface area were being pro-jected toward the subsoil. Although the sounding had amaximum depth of 22 m, it was possible to distinguishthe reflection surfaces associated with faults.

Analysis of the Soil, Lavas, and CoresTo determine the porosity and permeability of the subsoiland to estimate the depth and types of contaminants thatcould be percolating from the dumpsite toward the lowerzones of the area, a 50-m deep well was drilled 900 msouth of the dumpsite, and nuclei were extracted in acontinuous form. Samples of materials were extracted atdifferent depths of the monitoring well and from twoother sites with lava outcrops. Once the well was finished,a � ray test was done to determine the porosity of thematerial.

Materials with fine granulometry respond to the ac-tion of � rays with an increased frequency in BPS; in thiscase, a scale of 0–50 BPS was used.

Data AnalysisThe results of laboratory analyses of the samples were sub-mitted to statistical analyses (measurements of central ten-dency and deviation) to establish a relationship between theconcentrations of metals in the water samples and in therock substrata that could be naturally leaching metals.

RESULTSLeachate Composition and Its Effect on

Groundwater SystemsThe analyses of leachates revealed high concentrations ofthe metals Pb, Cd, Zn, Ni, Cr (both total and hexavalent),

and As, and of the organic PCBs (Table 1). Except for Zn,

the measured concentrations of the metals and the PCBs

exceeded the maximum permissible limits established by

Mexican environmental regulations.20

Configuration of the SubstratumVertical electric drilling revealed that the pyroclastic ma-

terials that are predominant in the surface also constitute

a significant part of the subsoil, interlaid with lava flows

of different thicknesses (Figure 4).

The georadar method revealed faults and fractures in

a northeast to southwest direction that are consistent

with the cartography of the surface and provide possible

conduits for infiltration toward the subsoil, more so on

the northeastern border of the dumpsite. The four geo-

electrical profiles obtained in different directions were

correlated to give the resistive profile of the subsoil, in

which strata having high resistivity were interpreted as

corresponding to hard rock, whereas the less resistive

strata were interpreted as water-saturated zones. In addi-

tion, a superficial phreatic level was detected at a depth of

4–6 m, a possible body of groundwater was observed at a

depth of 10–30, and another, more permanent body of

groundwater was detected at a depth of 60–70 m.

The isoresistivity curves obtained from the � ray elec-

tric register showed four different strata: the first of these,

at a depth of 22–27 m, could correlate with sand; the

second, at 27–37 m, could correlate with fractured igne-

ous rock; the third, at 37–47 m, could correspond to

massive rock; and the fourth, at 47–50 m, could be asso-

ciated with fractured rocks. The resistivity in the column

varied from 38 to 80 ohms. Finally, the � ray curve in this

well revealed clay layers with a thickness �1 m, assuming

that a value �15 bits/sec corresponds to compacted ma-

terials with a fine granulometry. From this information, it

was concluded that of the total length of the perforation

made, at least a 40% contained porous and permeable

materials.

Geochemical Analysis of Samples of Outcrops ofLava and the Well

The results of the geochemical analyses of the outcropped

lava and of all the materials extracted from the subsoil

showed very low concentrations of most metals analyzed

(As, Cd, Cr, and Ni), with the exception of Pb; for this

reason, the notion that the metal concentrations found in

the leachate and groundwater originated naturally from

the rocks was discarded (Table 2).

As shown in Table 2, we found high concentrations

of titanium (Ti), molybdenum (Mo), and Pb in the three

lava samples. On the other hand, Cd and As were found in



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low concentrations in the lava samples but in high con-centrations in the groundwater samples, from which itcan be inferred that the high concentrations of theselatter metals had an anthropogenic origin and that theironly source was the leachate permeating from the dump-site.

Another source of Pb in the bodies of groundwater isfrom the pottery activities in the village of Capula, located5 km from the dumpsite. A blood sample of a boy fromCapula was found to contain high concentrations of Pb.14

However, to determine the relationship between the highlevels of Pb found in the environment and in the blood ofpeople who live in the area, it will be necessary to extendthe analyses to other population strata because it has beenobserved that variables such as age, sex, socioeconomicstatus, and food intake greatly affect the level of riskassociated with these metals.20

DISCUSSIONInternationally, high concentrations of Cd and othermetals such as As, mercury (Hg), Pb, and Ti have beenreported in rivers, lakes, and bays located near miningand industrial zones,21 and in landfill leachates.22,23 Theuncontrolled infiltration of leachate into the vadose zone(unsaturated) and finally into the saturated zone (ground-water) is considered to be the most serious environmentalimpact of a dumpsite or landfill.

In Mexico, regulations for the final deposition ofindustrial wastes have been overlooked since the early1990s, these wastes being commonly deposited in munic-ipal dumpsites. Hundreds of contaminating organic sub-stances and heavy metals are found in the leachates fromdumpsites, Cd, Pb, and hexavalent Cr being amongthe most commonly found because these metals arewidely used in the cleaning products, paper, and tobacco

Table 1. Concentrations of metals and organic compounds in leachates and groundwater at the Morelia dumpsite.

As Cd

Cr

Cu Pb Ni Zn PCBsVolatileOrganics Phenols

Date ofSampling

(month/day/yr)Total Hexavalent

Leachates

1 — 0.06 — — — — 0.45 0.89 — — — 06/17/1997

2 0.302 0.462 47,731 1200 2403 1102 10,678 6389 — �0.0005 — 06/17/1997

0.045 — — — — 0.3 0.65 — — —

3 �0.1 0.1 4 — — 9 — — Presence �0.0005 — 12/12/2001

1 Capula farm 0.152 0.009 0.198 0.200 0.007 0.080 0.001 0.035 — �0.0005 0.558 06/17/1997

0.030 0.004 �0.01 �0.01 — — — — — — — 02/18/1998

1� Capula-Iratzio 1001 0.045 0.45 �0.01 — — — — — — — 02/18/1998

2 Tacícuaro 0.880 0.002 �0.01 �0.01 — — — — — — — 02/18/1998

0.075 �0.005 �0.01 — — �0.01 — — — — — 02/23/2000

Monitoring well

45 m 0.16 �0.005 — �0.1 — �0.01 — — — — — 09/14/1999

50 m 0.22 �0.005 — �0.1 — 0.17 — — — — — 09/14/1999

�0.01 �0.005 �0.01 — — �0.01 — — — — — 02/23/2000

55 m 0.25 �0.005 — �0.1 — 0.15 — — — — — 09/14/1999

60 m 0.13 �0.005 — �0.1 — 0.18 — — — — — 09/14/1999

0.032 �0.005 �0.01 — — �0.01 — — — — — 02/23/2000

3 Gasera 0.005 0.046 0.234 0.200 0.043 0.069 0.159 0.044 Presence �0.0005 0.065 06/17/1997

1506 0.024 �0.01 �0.01 — — — — — — — 02/18/1998

0.158 �0.005 �0.01 — — �0.01 — — — — — 02/23/2000

4 Maestranza — ND — — — ND — ND — — —

5 Las Garzas 0.081 0.127 0.128 0.100 0.075 0.066 0.149 0.037 Presence �0.0005 0.215 06/17/1997

�0.01 0.005 0.22 �0.1 — — — — — — — 02/18/1998

ND 0.05 — — — — ND ND — — —

�0.01 �0.005 �0.01 — — �0.01 — — — — — 02/23/2000

�0.01 �0.005 — �0.1 — 0.07 — — — — — 09/14/1999

6 El Cajón — ND — — — — ND 0.18 — — —

7 La Palma 0.063 �0.005 �0.01 — — �0.01 — — — — — 02/23/2000

8 Tanganxoan 0.117 �0.005 �0.01 — — �0.01 — — — — — 02/23/2000

9 Magisterio �0.005 0.005 �0.01 �0.005 — — — — — — — 02/18/1998

Notes: ND not done; bold indicates a very high concentration.



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industries. In Mexico, Cd was very uncommon in theenvironment throughout the past decade, but its concen-tration has increased because of its growing use as ananticorrosive cover for metals and in the manufacturingof batteries.24 Such was also the case of the leachate

from the municipal dumpsite of the city of Guadalajarain western Mexico, in which hexavalent Cr has beendetected.25

In this study, we determined that the Morelia dump-site has operated in two neighboring sites to the east andwest of the present dumpsite, with spontaneous combus-tion being registered throughout the year in some zones,along with the percolation of old leachates. Likewise,dumping zones were found to the north and to the east ofthe dumpsite. Pools of leachate have formed at the base ofthe current dumpsite, both to the west and to the north-east. The latter is a more permanent pond because nofractures have been observed at this site.

The factors that influence the production of leachatesat the Morelia dumpsite are both internal and external.The internal factors are associated to the composition anddegradation properties of the wastes, because organic andinorganic wastes are deposited together. Among the ex-ternal factors are insufficient covering of the wastes andthe use of an inadequate cover material: pyroclastic prod-ucts such as sands and pumice are used instead of clays,which would be an economical alternative. Prospectingfor clays rich in smectite has revealed in the area largedeposits of Tertiary clays with very high plasticity.4,26 Ithas been demonstrated that the laminar structure of claysgives them a large cation-exchange capacity,17 and there-fore, a large capacity for retention of metals and organicmolecules,27,28 as in the case of beydellite, which is com-mon in the area, dominantly as the sodium type.29 Theseproperties of clays are of major importance in the futureuse of clay membranes for the containment of hazardouswastes.

Another determining factor in the production ofleachates is the concentration of rainfall during themonths of June through September. During this season,the overflow of leachate from the lagoons increases. Theseleachates flow from the base of the solid waste heap andpermeate through the fractures in the subsoil. Measure-ment of the leachate production during the rainy seasonshowed an average flow of 0.62 L/sec.

The high permeability of the terrain and evaporationduring the dry season causes the leachate pools to disap-pear, which justifies the lack of a decision for adequateconfinement of the leachate by the people in charge ofmanaging the dumpsite, who claim that the evaporationoccurring during the dry season is enough to control thepolluting leachates. The geohydrological study done onthe site localized two aquifers at depths of 20 and 70 m.The latter represents a severe environmental risk factor forthe population living in proximity of the dumpsite be-cause the leachates have considerable mobility throughthe highly permeable substratum, a permeability that is

Figure 4. Local interpretation of the subsoil stratigraphy of theMorelia dump through electric resistivity drilling. SEV electrical verti-cal sounding. Source: Israde et al.5

Table 2. Metal concentrations in the lava outflows and in the

subterraneous lavas found in the dumpsite.

ElementDetectionLimit (ppb)

Concentration (ppm)

M1 M2 M3

Be 0.040 0.14 0.16 0.29

Ti 0.101 672.45 765.22 508.62

V 0.037 42.08 24.99 26.12

Cr 0.092 24.10 25.45 22.06

Mn 0.027 327.54 119.99 128.26

Co 0.010 17.68 8.91 8.57

Ni 0.053 32.95 22.96 20.19

Cu 0.072 14.05 12.62 11.39

Zn 0.043 33.30 15.34 17.14

As 0.083 0.24 0.12 0.10

Se 0.132 0.70 0.48 0.38

Mo 0.531 1.08 0.55 0.27

Cd 0.010 0.06 0.07 0.05

Sb 0.051 0.76 0.65 0.57

Pb 0.031 1.58 1.26 1.66

Note: M1, basalt lave outcrop from the dumpsite entrance; M2, andesitic-

basaltic core from the monitoring well; M3, vesicular basalt from the

monitoring well.



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the result of the terrain being composed of fractured lavaintercalated by poorly consolidated sands.

It is important to mention that high concentrationsof naturally occurring Cd, As, and Pb could be leachingfrom the volcanic materials in the substratum, but theother metals and organic pollutants are directly related toanthropogenic activities. Analysis of the lavas in thedumpsite showed high concentrations of Ti and beryl-lium (Be), which could account for the high concentra-tions in the groundwater. In the case of Cd and Pb, themeasured concentrations were very low in the lavas andhigh in the groundwater, which led us to discard thepossibility that these superficial lavas may be the source ofthe high concentrations of metals found in the ground-water. However, because the majority of the sampledwells are located along the eastern and western zones ofthe dumpsite and because no wells exist in the southernportion, it was not possible to evaluate the probable tri-dimensional behavior of the plume of pollutants.

For the above reasons, we strongly suspect that thesemetals and solvents have migrated over the last 20 yrfrom the dumpsite to the groundwater, and we believethat there are clear indications for questioning the drink-ing quality of the water in the underlying aquifers.

The vertical electrical drilling carried out allowed usto determine the entrance mechanism of the leachatestoward the subsoil, which begins with their gradual infil-tration toward the nonsaturated zone where fractures upto 80 cm in thickness are present. The leachates then flowslowly because they are retained in the porous matrix andby surface tension forces. However, once the surface ten-sion is overcame by saturation of the sands and fractureswith water, the leachates flow toward the aquifers, mixingand dispersing in patterns that depend on the subterra-neous flow according to the seasonality of the rains andon the quantity of water that infiltrates during the year.The latter factors probably account for the variability ofthe concentrations of pollutants in the groundwater thatis observed throughout the year. Such is the case of thevariable concentrations of Pb measured in the monitoringwell, which was always above the limits tolerated by thecorresponding Mexican regulation.20 Likewise, the analy-ses of the water from the wells located along the east-westboundary of the dumpsite also showed concentrations ofCd, Pb, Zn, Ni, Cr, and As that are above the qualitystandards for drinking water established internationally.30

CONCLUSIONSWith the help of geological, geophysical, stratigraphic,and cartographic evaluations, as well as of the geohydro-logical information for the Morelia dumpsite, we detectedthe existence of a system of fractures in the terrain and ahydraulic gradient toward the east. Various extraction

wells for drinking water are located in this zone, whichmakes the location of the dumpsite a severe environmen-tal risk factor, particularly for the nearby population, be-cause analyses revealed that the pollutants found in theleachates and in the groundwater surpassed the maxi-mum permitted concentrations for Cd, Pb, Zn, Ni, Cr, andAs.

Although the exact location of the source from whichthese metals originate and how they enter into thegroundwater system are not precisely known, what isunmistakable is that the porosity and permeability of thesubstrata on which the Morelia dumpsite is situated facil-itates the percolation of these pollutants to the ground-water. Because the high concentrations of heavy metalsand organic compounds observed in the dumpsiteleachate were also found in nearby wells, it has beensuggested that these pollutants may have their source inthe Morelia dumpsite; for this reason, it has been recom-mended that the dumpsite be relocated and restructuredto comply with existing regulations. The clays in theregion located to the east of the current site have a largecationic-exchange capacity and a low permeability, whichmakes them an ideal material for the confinement ofdangerous materials in sanitary landfills because theywould block the filtering of the leachate generated in thedumpsite toward the subsoil, where it could contaminatethe aquifer system. In addition, the clay traps and cap-tures heavy metals that are otherwise difficult to neutral-ize. These clays are found to the southeast of Morelia andcould function as efficient traps of the polluting mole-cules.13,15

The modeling of the groundwater flow, which is inprogress, will be an important tool in understanding thehydraulic behavior of the site, such as the advective iontransport and the possible diffusion of contaminants.

It is urgent that the management of urban solidwastes in Mexico be modernized through the implemen-tation of programs for the reuse and recycling of wastematerials as well as by putting into operation treatmentsystems with the objectives of counteracting environmen-tal impacts and of diminishing the pressure put on natu-ral resources, as well as providing needed facilities for thefinal disposition of solid wastes.

ACKNOWLEDGMENTSThis research was supported by CONACYT-SIMORELOS(Project number 980306010). The authors thank the Na-tional Commission of Water (CNA) for information re-garding the static levels of the wells of the study zone.

REFERENCES1. Buenrostro, O.; Bocco, G.; Bernache, G. Urban Solid Waste Generation

and Disposal in Mexico. A Case Study; Waste Manage. Res. 2001, 19,169-176.



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4. Israde, I.; Garduno, V. Lacustrine Record in a Volcanic Intra-Arc Set-ting: The Evolution of The Late Neogene Cuitzeo Basin System (Cen-tral Western Mexico). In Ancient and Recent Lacustrine Systems in Con-vergent Margins; Cabrera, L.; Saez, A., Eds. Paleo 3, 1999, 151 (1-3);209-227.

5. Assmuth, T.; Strandberg, T. Ground Water Contamination at FinnishLandfills; Water Air Soil Poll. 1993, 69, 179-199.

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7. Goudall, D.; Quigley, R. Pollutant Migration from Two Sanitary Land-fill Sites near Sarnia, Ontario; Can. Geotech. J. 1977. 14, 223-236.

8. Mazari, M.; Mackay, D. Potential for Groundwater Contamination inMexico City; Environ. Sci. Technol. 1993, 27, 794-802.

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11. Paz, J. Efecto del Tiradero de Basura de Santa Catarina en Pozos deAgua Potable. In Proceedings of The First National Conference of SolidWastes and Hazardous Wastes. Asociacion Mexicana de Residuos So-lidos y Peligrosos: Mexico City, 1991, pp 1–27.

12. INEGI. XII Censo General de Poblacion y Vivienda. 2000. ResultadosDefinitivos, Tabulados Basicos (XII Census of Population and Housing2000). Instituto Nacional de Estadıstica Geografıa e Informatica (IN-EGI): Aguascalientes, Mexico, 2000, p 2384.

13. Buenrostro, O.; Israde, I. La Gestion de los Residuos Solidos en laCuenca del Lago de Cuitzeo, Mexico; Rev. Int. Contam. Ambient. 2003,19, 161-169.

14. Israde, I. Evaluacion del Impacto Ambiental al Agua Subterranea del Ti-radero de Morelia y su Afectacion en las Poblaciones del Entorno. Informefinal. Proyecto No. 19980306010; Sistema de Investigacion SIMORE-LOS-CONACyT: Michoacan, Mexico, 2000, p 60.

15. Suter, M.; Lopez, M.; Quintero, L.; Carrillo, M. Quaternary Intra-ArcExtension in the Central Trans-Mexican Belt; Bulletin 6; Geological So-ciety of America: Washington, DC, 2001, p 113.

16. Bengtsson, L.; Bendz, D.; Hogland, W.; Rosquist, H.; Akensson, M.Water Balance for Landfills of Different Age; J. Hydrol. 1994, 158,203-217.

17. Carbajal, G.; Israde, I.; Serrato, J.; Reyes, J. Electron Microscopy andX-Ray Analysis of Lacustrine Clays from the Charo Canyon State ofMichoacan, Mexico; Clay Clay Miner. 1998, 46, 330-339.

18. Hudak, P.F. A New Method for Designing Configurations of NestedMonitoring Wells Near Landfills; Hydrol. J. 1998, 6, 341-348.

19. Akgun, H. Lined Waste Containment Systems: A Method for Designand Performance Evaluation; Environ. Geol. 1997, 30, 209-214.

20. Norma Oficial Mexicana NOM-127-66A1-1994 (Mexican Official Stan-dard NOM-127-66A1-1994). Salud Ambiental, Agua para Uso y Con-sumo Humano, Limites Permisibles de Calidad y Tratamiento a QueDebe Someterse el Agua Para Su Potabilizacion. Diario Oficial de laFederacion. Primera seccion: Mexico City, January 18, 1996, p 43.

21. Wong, H.; Gauthier, J.; Nriagu, O. Dispersion and Toxicity of MetalsFrom Abandoned Gold Mine Tailings at Goldenville, Nova Scotia,Canada; Sci. Total Environ. 1999, 228, 35-47.

22. Bolton K.A.; Evans. L.J. Elemental Composition and Speciation ofSome Landfill Leachates with Particular Reference to Cadmium; WaterAir Soil Poll. 1991, 60, 43-53.

23. Maxfield, L.P; Vanderbilt, S.E. Conceptual Models of GroundwaterContamination Investigations at a Solid Waste Landfill; SWANA. Pro-ceedings of Solid Waste Association of North America: Silver Spring,MD, WQI 1997, 36-39.

24. Marin, L.; Leal, R.; Rubio, R.; Prieto, E. Geochemistry of the ChiltepecSanitary Landfill, Puebla, Mexico; Geof. Int. 2001, 40, 301-307.

25. Bernache, G.; Bazdresch M.; Cuellar, J.L; Moreno, F. Basura y Metropoli;Universidad de Guadalajara: Guadalajara, Mexico, 1998, p 238.

26. Garduno V.H., Israde, I., Francalanchi, L., Carranza, O., Chiesa, S.,Corona, P., Arreygue, E. Sedimentology, Volcanism and Tectonics ofthe Southern Margin of the Lacustrine Basins of Maravatıo andCuitzeo, Michoacan, Mexico. International Association of Vulcanol-ogy, General Assembly, 1997, 25 pp.

27. Foged, N.; Baumann, J. Clay Membrane Made of Natural High Plastic-ity Clay: Leachate Migration due to Advection and Diffusion; Eng.Geol. 1999, 54, 129-137.

28. Sezer, G.A.; Turkmenoglu, A.G.; Gokturk, E.H. Mineralogical and Sorp-tion Characteristics of Ankara Clay as a Landfill Liner; Appl. Geochem.2003, 18, 711-717.

29. Israde-Alcantara, I.; Robles Camacho, J.; Domınguez, J.M. Presencia deBeidelita-Nontronita en Una Secuencia Lacustre al Sur del Lago deCuitzeo, Michoacan, Mexico. In Cuarto Congreso Nacional de Crista-lografıa, Morelia, Michoacan, 2003, p. 224.

30. American Public Health Association (APHA), American Water WorksAssociation (AWWA), Water Pollution Control Federation (WPCF).Metodos Normalizados para el Analisis de Aguas Potables y Residuales,2000. Ediciones Dıaz de Santos: Madrid, Spain, 1992, p 4237.

About the AuthorsIsabel Israde-Alcantara, Ph.D., is a researcher at the Insti-tuto de Investigaciones Metalurgicas in the UniversidadMichoacana de San Nicolas de Hidalgo. Otoniel Buenrostrois a researcher at the Instituto de Investigaciones sobre losRecursos Naturales (INIRENA) in the Universidad Mi-choacana de San Nicolas de Hidalgo. Alejandro CarrilloChavez is currently at the Instituto de Geologıa, CampusJuriquilla, UNAM. Address correspondence to: Isabel Is-rade-Alcantara, Departamento de Geologıa y Mineralogıa,Edif. U. Ciudad Universitaria, Instituto de InvestigacionesMetalurgicas, Universidad Michoacana de San Nicolas deHidalgo, Apartado Postal 888, CP. 58,000, Morelia, Mi-choacan, Mexico; phone (fax): �52-443-3265766; e-mail:[email protected].



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geological characterization and environmental implications of the placement of the morelia dump,...

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