Sub-soil contamination due to oil spills in zones surroundingoil pipeline-pump stations and oil pipeline right-of-ways inSouthwest-Mexico

Rosario Iturbe & Carlos Flores &

Alejandrina Castro & Luis G. Torres

Received: 18 August 2006 /Accepted: 30 November 2006 / Published online: 8 February 2007# Springer Science + Business Media B.V. 2007

Abstract Oil spills due to oil pipelines is a veryfrequent problem in Mexico. Petroleos Mexicanos(PEMEX), very concerned with the environmentalagenda, has been developing inspection and correctionplans for zones around oil pipelines pumping stationsand pipeline right-of-way. These stations are located atregular intervals of kilometres along the pipelines. Inthis study, two sections of an oil pipeline and twopipeline pumping stations zones are characterized interms of the presence of Total Petroleum Hydrocarbons(TPHs) and Polycyclic Aromatic Hydrocarbons(PAHs). The study comprehends sampling of the areas,delimitation of contamination in the vertical andhorizontal extension, analysis of the sampled soilsregarding TPHs content and, in some cases, the 16PAHs considered as priority by USEPA, calculation ofareas and volumes contaminated (according to Mexicanlegislation, specifically NOM-EM-138-ECOL-2002)and, finally, a proposal for the best remediationtechniques suitable for the contamination levels andthe localization of contaminants.

Keywords PAHs . Pipelines . Pumping stations .

Soil contamination . TPHs

Introduction

Oil and oil-products transport is a crucial operation fortheir production-transformation-distribution cycle. Thereare several ways to transport petroleum hydrocarbons,including tank-cars, ships, trains, and ducts, amongothers. Pipelines are metallic pipes that connect oilproduction zones with refinery facilities or refinerieswith oil storage and distribution stations separated bylong distances. Pipelines can even connect installationsfrom one country to another with any of the previouspurposes. Mexico has a large pipeline system. The mainproducts transported by means of this net are crude(oilducts), gas (gas-ducts), petrochemical products, fuel-oil (fuel oil-pipelines), and even different productstogether, such as diesel, gasoline, and gas (polyducts).In 2000, Mexico had a pipeline net of about 28,450 kmof pipelines with mean diameters between 16 and 29 in.(Instituto Mexicano del Transporte 2000). For that year,20% of the pipelines were devoted to oil transport,while 35.6% were used for gas transportation. Most ofthe pipelines (39.8%) transported more than oneproduct (polyducts) and only 3.7% of the pipelineswere built to transport petrochemical products.

It has been reported that more than 30% of the oilpipelines in Mexico have been in operation for more

Environ Monit Assess (2007) 133:387–398DOI 10.1007/s10661-006-9593-y

R. Iturbe : C. Flores :A. Castro : L. G. Torres (*)Grupo Saneamiento de Suelos y Acuiferos: Coordinacionde Ingenieria Ambiental. Instituto de Ingeniería,Universidad Nacional Autonoma de Mexico,Apartado Postal 70-472, Coyoacan,04510 Mexico City, D.F., Mexicoe-mail: LTorresB@iingen.unam.mx

than 30 years. Oil ducts’ lifetime has been calculatedin 25–30 years (La Jornada 2001). This is a bigproblem for PEMEX, the national-industry in chargeof exploration, production, transformation, storage,and distribution of oil and oil-derivatives. There arethree main causes for oil spills in oil and oil-productspipeline systems: (1) The bad physical state ofpipelines due to their age. (2) Problems in mainte-nance operations. (3) Clandestine poaching, mainly ofrefined oil-products (i.e., gasolines). Unfortunately, inLatin America and Mexico this is a common practice.More than 80% of oil spills near oil pipelines are dueto this infamous practice. PEMEX, very concernedwith the environmental agenda, has been developinginspection and correction plans for zones around oilpipelines pumping stations and pipeline right-of-ways. These stations are located at regular intervalsof some kilometres along the ducts’ extension. Thereare big pumping stations where installations compriseseveral operation facilities, offices, sometimes storagetanks or ditches, treatment plants, etc. The mainproblems are encountered in zones far away fromcities and frequently used roads, since those pumpingstations are more exposed to vandalism and clandes-tine poaching of gasoline and other fuels.

The aim of this investigation is to show thecharacterization carried out in a zone around oil-ductpumping stations located in southwestern Mexico, nearan important refinery located at Salina Cruz, Oaxaca.The specific places to evaluate soil contamination were:(1) km 0+800, km 1+900, km 4+590, km 6+020, km 8+800, km 9+500, km 11+499. (2) Zones located southfrom diesel-storage tanks, and south from the storageditch of theMedias Aguas pumping station. (3) A zoneused for residues treatment, located in the northwest ofthe Loma Larga pumping station and south from thestorage ditch. (4) The area corresponding to Petapa,km 27+200 of the 16-in. multiproduct pipeline (closedline). All these sites were selected because thepreliminary observation of the facilities revealed thepresence or risk of hydrocarbon spills.

The study comprehends sampling of the areas,delimitation of contamination in the vertical andhorizontal extension, analysis of the sampled soilsregarding TPH and, in some cases, the 16 PAHsconsidered as priority by USEPA, calculation of areasand volumes contaminated (according to Mexicanlegislation, specifically NOM-EM-138-ECOL-2002)and, finally, a proposal for the best remediation

techniques suitable for the contamination levels and thelocalization of contaminants. This study was performedat the end of 2004, this is the reason for using the 2002-legislation regarding environmental issues.

There are few publications available on literatureregarding monitoring petroleum contaminated sites. Rifaiet al. (2000) made an excellent review regardingcharacterization and remediation considerations in mon-itoring hazardous waste sites, while other authors havemade excellent contributions, i.e., Adeniyi and Afolabi(2002), Al-Sarawi et al. (1998), Barakat et al. (2001),Rong (2001), Shriadah (1999), to mention some.

In previous works, our group has carried out sitecharacterizations at petroleum facilities, includingrefineries, oil storage and distribution stations, andmarine ports (Iturbe et al. 1998, 2003a, b, 2004c,2005, 2006a, b, c). These studies included soil andgroundwater characterizations, health risk analysis,determination of the contaminated areas and volumes,calculations of cleanup levels, and suggestions onremediation techniques suitable for some of thecontaminated sites, among other activities. This is afirst investigation related with oilduct ways andpumping stations. Three aspects should be taken intoaccount when characterizing oilduct ways and pump-ing stations (1) Oil pipelines and pumping stations area conjunction of sites, interconnected with thepipeline itself, and can be separated by tens andhundreds of kilometres, (2) Some pipeline pumpingstations are big installations including auxiliaryfacilities, but most of them are very small sites inthe middle of nowhere. (3) Although some sections ofthe pipelines and some pumping stations coincidewith small and big cities, large amounts of pipelinesections and pumping stations are located in thecountryside, in arid regions with no industrial,agricultural, or housing developments.

Materials and methods

Sampling of sites was carried out following the sug-gestions of an Environmental Audit performed at the siteby PROFEPA. It was decided to sample 11 points atSalina Cruz pipeline right-of-ways, five points at LomaLarga pumping station, five points at Medias Aguaspumping station, and two points in the area of Petapa,km 27+200 of the 16-in. polyduct. Sampling wasperformed at different depths, from 0.8 to 3 m. Sampling

388 Environ Monit Assess (2007) 133:387–398

equipment consisted basically of pneumatic systems, onesemi-portable (12 HP and variable perforation speed),and one standing equipment, Longyear model 34,mounted on a pick-up. More details regarding thesampling procedures are found in Iturbe et al. 2006b.

TPHs were analysed according to NOM-EM-138-ECOL 2002 (NOM 138 2003), using EPA 418.1-1995(USEPA 1985) method. Bulk density was evaluatedusing the pycnometer method (C-128-93-ASTM)(ASTM 1993), apparent density was assessed withthe probe method (FC 1990). For pH determination,were followed the Mexican method AS-02-NOM-021(SEMARNAT 2000) SEMARNAT-2000), and PAHsassessment was made following EPA-8310-1996.

Results and discussion

Figure 1 shows the oilduct that connects Salina Cruz(Oaxaca, Mexico) with Minatitlan (Veracruz, Mexico),and the points from which samples were taken for thiswork, Salina Cruz oilduct section, the pumpingstations of Loma Larga and Medias Aguas, and theoilduct section known as Petapa. The right squaredepicts the points for the Salina Cruz pipeline right-of-

way with TPH and total PAH concentrations at twodepths. From this point on, TPH and PAH values weredrawn either at 1 or 3 m depth, since there weredifferent sampling depths, but there are not enoughpoints to draw them at every depth. This is the reasonwhy concentrations are reported around 1 and 3 mdepths (Fig. 2).

Table 1 shows TPHs distribution for the Salina Cruzand Petapa pipelines right-of-way, Loma Larga, andMedias Aguas pumping stations. Note that points weretaken at different depths. At a first glance, it isremarkable to observe that, from the 42 samples, onlysix showed values above 2,000 mg/kg corresponding tothe maximum level approved by Mexican legislation forindustrial soils in 2002. Current legislation allows up to6,000 mg/kg for industrial soil. Regarding the SalinaCruz pipeline right-of-way, the higher value was locatedat point 6+020 2A (at 1.8 m depth), with a value of13,683, exceeding 6.8-times the acceptable value. Thenext point exceeding 2,000 mg/kg was 9+850 2A, with8,286 mg/kg at 1 m depth. This point exceeds almost4.1-times the limit. Finally, there is point 8+800 1A,again at 1.8 m depth. This point with 4,882 mg/kg is2.4-times above the limit value. Petapa samples did notreveal the presence of TPHs.

COATZACOALCOS

MINATITLÁN

GULF OFTEHUANTEPEC

GULF OFMEXICO

95˚0096˚00 30' 30'

16˚00

17˚00

30'

30'

18˚00

30'

Without scale

Petapa

Medias Aguas

Loma Larga

Salina Cruz

Fig. 1 Salina Cruz-Minatitlan oil pipeline, and localization ofSalina Cruz and Petapa oilduct ways, as well as the pumpingstations of Loma Larga (LOLA) and Medias Aguas (MEDAG).

In the right square, the sampling points for Salina Cruz pipelineright-of-way are shown with TPH and total PAH concentrationsat two depths

Environ Monit Assess (2007) 133:387–398 389

< 5000 mg/kg

5000 - 25000 mg/kg

25000 - 50000 mg/kg

50000 - 75000 mg/kg

> 75000 mg/kg

TPHs (1m depth)

TPHs (3 m depth)

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500025

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LOLA 3

LOLA 5LOLA 4

LOLA 1

LOLA 2

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T.D.R

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Sampling points

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12000

Fig. 2 Loma Largapumping station samplingpoints (a) and distributionfor TPH concentrationsshown at two depth layers,i.e., around 1 (b) and 3 m(c) depths

390 Environ Monit Assess (2007) 133:387–398

Regarding the Loma Larga pumping station, threepoints exceeded the limit values regarding TPHconcentrations, LOLA 3B, with 101,759 mg/kg(almost 51-times), LOLA 3A, with 15,566 mg/kg(7.8-times), and LOLA 4B, with 2,829 mg/kg (just1.1-times). The Medias Aguas pumping station didnot present any point with TPH concentrations abovethe Mexican limit. Figure 1 shows the Loma Largapumping station sampling points, as well as TPH’sspatial distribution in the sampled points at twodepths: around 1 and 3 m. Figure 3 shows the LomaLarga pumping station sampling points withoutspatial distributions for TPHs or PAHs since datawere scarce.

Although there are a lot of sampled points where noTPHs were found, in certain points TPH concentrationswere quite high. Averaging the TPH concentrations forthe Salina Cruz and Petapa pipeline right-of-way, andthe Loma Larga and Medias Aguas pumping stations,values are: 12,079 mg/kg for Loma Larga; 1,435 mg/kgfor Salina Cruz pipeline right-of-way, and 21 mg/kg forMedias Aguas and ND for Petapa pipeline right-of-way.

This is an indication of the urgency in remediation forthe zone of Loma Larga in first place, followed by theSalina Cruz pipeline right-of-way.

Regarding the PAHs found at different samplingpoints, Table 2 shows the values for those PAHs con-sidered by the Mexican legislation (i.e., benzo(a)pyrene, benzo(a)anthracene, benzo(b)fluoranthene,benzo(k)fluoranthene, and chrysene). Besides, thevalues for three additional PAHs (i.e., phenanthrene,dibenzo(a,h) anthracene, and indene(1,2,3c–d) pyr-ene) considered as priorities by USEPA, but not byMexican legislation) are included. The total amountsof PAHs measured for every point are included also.The concentrations of these PAHs found in 60 crudesform around the world (Kerr et al. 2001) are includedfor comparison purposes. Points correspond only tothe Salina Cruz pipelines right-of-way and LomaLarga pump station, since in Medias Aguas andPetapa, TPHs were so low, that it was decided not toperform PAHs analysis.

Figure 4 shows again the Loma Larga pumpingstation and the correspondent sampling points, as well

Table 1 TPH distribution at Salina Cruz and Petapa pipelines right-of-way, as well as Loma Larga and Medias Aguas pumpingstations as a function of localization and depth

Sample identification Depth (m) TPH (mg/kg) Sample identification Depth (m) TPH (mg/kg)

0+800 1A 1.0 ND LOLA 1A 1.0 1150+800 1B 1.7 1,711 LOLA 1B 3.0 580+800 2A 0.8 1,450 LOLA 2A 1.0 ND0+800 3A 1.0 ND LOLA 2B 3.0 ND1+900 1A 1.0 ND LOLA 3A 1.0 15,5661+900 2A 2.0 ND LOLA 3B 2.7 101,7591+900 1B 1.0 58 LOLA 4A 1.5 2731+900 2B 2.0 44 LOLA 4B 3.0 2,8294+590 1A 1.4 ND LOLA 5A 2.0 1794+590 1B 3.0 ND LOLA 5B 4.0 134+590 2A 1.0 ND MEDAG 1A 1.5 ND4+590 2B 2.5 ND MEDAG 1B 3.0 ND6+020 1A 2.0 18 MEDAG 2A 0.8 206+020 2A 1.8 13,683 MEDAG 2B 1.8 208+800 1A 1.8 4,882 MEDAG 3A 1.5 ND9+500 1A 1.5 ND MEDAG 3B 3.0 209+500 2A 1.8 110 MEDAG 4A 0.8 ND9+850 1A 1.0 ND MEDAG 5A 1.8 249+850 2A 1.0 8,286 MEDAG 5B 3.0 ND11+499 1A 1.0 24 PETAPA A 1.4 ND11+499 2A 1.0 222 PETAPA B 1.9 ND

In bold, concentrations higher than those established by Mexican legislation.

Environ Monit Assess (2007) 133:387–398 391

LOLA 3

Sampling points

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> 30 mg/kg

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4 - 6.5 mg/kg

< 10 mg/kg

PAHs (1 m depth)

LOLA 2

LOLA 1

LOLA 4

1.5 - 4 mg/kg

1 - 1.5 mg/kg

< 1 mg/kg

Fig. 3 Loma Largapumping station samplingpoints (a) and distributionfor PAH concentrationsshown at two depth layers,i.e., around 1 (b) and 3 m(c) depths

392 Environ Monit Assess (2007) 133:387–398

as a spatial distribution of the PAH measured at everysampling point, distributed at two depths: around 1and 3 m.

Table 3 shows the PAHs legislated by Mexicanlaws and the levels accepted for industrial soils whenpresent in diesel and oily products. Besides, the limitsfor the 16 priority PAHs when present in industrialsoils for the state of Arizona (USA), reported byKostecki et al. (2002) and Bournicore (1996), areincluded for comparison purposes. Arizona legislationwas chosen arbitrarily for comparison purposes, sincedifferent limit concentrations have been reported foreach state in the USA, but Arizona State has reportedallowed limits for many compounds.

It is noticeable that acenaphthylene was the onlyone of the 16 PAHs considered by USEPA that didnot appear at any of the sampling points. In

accordance to Kerr et al. (2001), this PAH is the onlyone not encountered in any of the 60 studied crudes.In opposition, PAHs that were found in 100% of theanalysed crudes were naphthalene, fluorene, chrysene,and benzo(k)fluoranthene. Another point to underlineis the fact that only seven from the 16 PAHs areconsidered carcinogenic, these PAHs correspond tothe five considered by Mexican legislation plusdibenzo (a,h) anthracene, and indene (g,h,i) perylene.

PAH concentrations were highly variable. Points 9+500 1A, 11+499 1A, and LOLA 5B did not reveal thepresence of any of the 16 PAHs. In the rest of thepoints, at least one PAH was detected at a concentra-tion higher than the detection limit. In particular,some points showed high concentrations in one ormore of the evaluated PAHs, as, for example, points6+0202 A, 9+850 1A, and LOLA 3B. Of course the

Table 2 Some PAH concentrations at Salina Cruz pipeline right-of-way and Loma Larga pumping station, all in mg/kg

Sample PAHs considered by Mexican legislation (mg/kg) Other PAHs not considered by Mexican legislation(mg/kg)

Total PAHs**(mg/kg)

BaPyr BaAnt BbFluo BkFluo Chry Phen DbAnth InPyre

0+800 1A ND ND 0.0019 0.0017 ND 0.0017 ND ND 0.00950+800 2A 0.3765 0.3704 0.3346 0.1752 0.5528 ND 0.0519 ND 1.93100+800 3A 0.0021 ND 0.0117 ND ND 0.0149 ND ND 0.15431+900 1A 0.1920 0.1655 0.1997 0.0958 0.2099 0.1688 0.0391 0.0709 1.96091+900 1B 0.1493 0.1198 0.1527 0.0754 0.1698 0.1060 0.0302 0.0770 1.37984+590 1A 0.0513 0.0630 0.0588 0.0263 0.0846 0.0736 0.0110 0.0176 0.75894+590 2A 0.0273 0.0316 0.0325 0.0148 0.0357 0.0173 0.0053 ND 0.28676+020 2A 15.2076 16.7931 16.9957 8.2544 20.3734 42.6769 1.7840a 9.5417a 217.82738+800 1A 0.1343 ND 0.1361 0.0453 0.1213 0.0304 0.0186 0.1055 0.91749+500 1A ND ND ND ND ND ND ND ND –9+850 1A 2.0450 2.5400 2.1507 1.1090 3.2745 4.8735 0.2890 1.2869 33.479611+499 1A ND ND ND ND ND ND ND ND –LOLA 1A 0.1230 0.1420 0.1460 0.0626 0.1450 0.1915 0.0215 0.0456 1.5856LOLA 1B 0.0430 0.0390 ND 0.0085 0.0256 ND ND ND 0.1322LOLA 2A 0.0069 0.0035 ND 0.0006 0.0015 ND ND ND 0.0125LOLA 2B 0.0013 ND 0.0024 ND ND 0.0025 ND ND 0.0107LOLA 3A 0.0760 0.3816 0.4910 0.1284 0.2858 1.1818 ND ND 6.9481LOLA 3B 2.3085 3.2535 3.2900 1.2400 2.1260 4.4758 0.3777 0.9735 35.5489LOLA 4A 0.0214 0.0212 0.0367 0.0153 0.0273 0.0329 0.0091 0.223 1.0092LOLA 4B 0.0050 0.0597 0.0667 0.0301 ND ND ND ND 0.2467LOLA 5A 0.0682 0.0472 0.0604 0.0303 0.0726 0.0577 0.0145 0.0299 0.6226LOLA 5B ND ND ND ND ND ND ND ND –Aver crude* 2.0 5.5 3.9 0.46 28.5 176.7 1.0 0.06 75.285

In bold, values above legislation limits in Mexico or Arizona, USA (2002). *From Kerr et al. (2001). a From Bournicore (1996), NDnon detected, under the detection limit. Code: BaPyr Benzo(a)pyrene, BaAntr Benzo(a)anthracene, Bbfluo Benzo(b)fluoranthene,Chry chrysene, Phen Phenanthrene, Dbanthra Dibenzo(a,h)anthracene, InPyre Indeno(1,2,3,c,d)pyrene.**Including other PAHs notreported in this table

Environ Monit Assess (2007) 133:387–398 393

PAH concentrations are meaningless, if not comparedwith legislation limits or values suggested by sitehealth risk analysis.

Using these values to analyse the different PAHvalues presented in Table 1, it is possible to state thefollowing. There are only three points where at leastone PAH considered by Mexican legislation is presentat an over the limit concentration. This is the case ofpoint 6+020 2A, with 15.20 mg/kg of benzo(a)pyrene, 16.79 mg/kg of benzo(a)anthracene, and16.99 mg/kg of benzo(k)fluoranthene. The threevalues are higher than those recommended byMexican legislation and this point corresponds to aTPH concentration of 13,683, and a total PAHconcentration of ca 217 mg/kg. The second point is9+850 1A, with 2.04 mg/kg of benzo(a)pyrene, and2.54 mg/kg of benzo(a)anthracene, both levels higherthan those legislated in Mexico. The point showed aTPH concentration value lower than the detectionlimit. The third point, LOLA 3B, corresponds to aTPH concentration of 101,759 mg/kg and revealedthe presence of 2.31 mg/kg of benzo(a)pyrene, higherthan the Mexican limit. It is interesting to note thatpoints 9+500 1A and LOLA 5B, where TPHconcentrations were high, did not show PAHs atconsiderable concentrations.

Considering the State of Arizona legislation limitsthe analysis of the presence of PAHs is as follows.Only one point showed values of dibenzo(a)anthra-cene (1.78 mg/kg) and indene (1,2,3,cd)pyrene(9.54 mg/kg). These values are higher than thoseconsidered as limit for the State of Arizona, accordingto Bournicore (1996). No other point, showed PAHvalues higher than those established by the State ofArizona. Phenanthrene values are shown because theywere quite high for some sampling points, but neverexceeded the Arizona State legislation. At this point itis important to mention that PAH legislation is veryvariable worldwide: for example, just for the differentstates in the USA, PAH limits are quite different.Three examples: pyrene limit lies between 6.1 and1,500 mg/kg, depending on the USA state. Phenan-threne is accepted at levels between 23 and10,000 mg/kg. Finally, fluorene is legislated at12 mg/kg for one state and 3,800 mg/kg for anotherstate (Bournicore 1996).

If the total amount of PAHs found at a single point isconsidered, point 6+020 2A showed the highestamount (217.8 mg/kg), followed by LOLA 3b, with35.5 mg/kg, and 9+850 1A, with 33.5 mg/kg. Twopoints that presented considerable TPH concentrations(8+800 1A and LOLA 4B) revealed no PAH content.

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Fig. 4 MEDAG pumping station and sampling points

394 Environ Monit Assess (2007) 133:387–398

There is always a question when characterizinghydrocarbons contaminated soil sites: Are the specificorganic compounds (i.e., PAHs, BTEX, MTBE,TAME) related with the gross fractions (TPHs,TPH-diesel fraction, TPH-gasoline fraction, heavyoils) used to characterise contaminated soils in aquick, reliable way? In other works (Iturbe et al.2003b, 2005, 2006a), we tried to find answers to thisquestion. In this work, every individual PAH wascompared with the TPH fraction concentration, inorder to find a relationship between the gross fractionand the specific compound’s concentration. Whencontrasting the PAH concentrations for every PAH inthe whole set of points where PAHs were present(Salina Cruz pipelines right-of-way and Loma Largapump station), there were no good correlations (R2<0.85) except for the case of fluorene (R2=0.9943).When doing the same correlation with PAHs at SalinaCruz pipelines right-of-way points, good correlationswere found for most of the considered PAHs,including benzo(g,h,i)perylene (0.8464), but not fordibenzo(a,h)anthracene (0.2156), and indene(1,2,3,c,d)pyrene (0.2144). In the case where comparison wascarried out for points at Loma Larga and PAHconcentrations, fair correlations were found for mostPAHs except for naphthalene (0.3852). Although wedo not have any hypothesis regarding these findings,it is important to underline the trends. Table 3, lastrow, shows the PAHs found at the 60 crudes reportedby Kerr et al. (2001). If we take a look at theindividual PAH concentrations, it is noticeable thatsome PAHs are found in crudes at low concen-trations (average values), as low as 0.06 mg/kg (i.e.,indeno(1,2,3,c,d)pyrene), while other PAHs arefound at medium concentrations (chrysene at 28.5and fluorene at 73.6 mg/kg, to mention two), and atvery high concentrations, such as 176.7 and422.9 mg/kg (for phenanthrene and naphthalene,respectively). It is important to remember that everyPAH has a different limit value, tightly related withthe carcinogenicity of the compound and it toxico-logical characteristics.. On the other hand, each oneof the 16 PAHs shows a detection frequency relativeto the analysis performed in the 60 crudes fromaround the world. For example, it has been alreadymentioned that the only PAH that has never beenfound in a crude is acenaphthylene, whereas otherPAHs are found at a low frequency (i.e., indeno(1,2,3,c,d) pyrene, in 7% of the studied crudes),

other PAHs are found with medium detectionfrequencies (dibenzo(a)anthracene at 47% and fluo-ranthene at 40%). Finally, four PAHs were found in100% of the studied crudes, i.e., naphthalene,fluorene, fluoranthene and benzo(b)fluoranthene(Kerr et al. 2001).

Some physical characteristics of the sampled soilswere determined in samples from the oilduct zone, theLoma Larga and the Medias Aguas pumping stations,i.e., pH, apparent density, bulk density, and porosity.

Table 3 PAH limits in the soil according to Mexican standardNOM-EM-138-ECOL-2002, and the suggested limits for theState of Arizona (USA)

Contaminant NOM-EM-138-ECOL-2002(mg/kg soil)

Arizona StateBournicore(1996)(mg/kg soil)

Arizona StateKostecki et al.(2002)(mg/kg soil)

Diesel:Benzo(a)pyrene 0.8 0.8 2.6Benzo(a)anthracene

8.0 4.6 26

Benzo(b)fluoranthene

8.0 NR NR

Benzo(k)fluoranthene

80.0 4.6 260

Chrysene 800.0 462 2,600Oily products:Benzo(a)pyrene 0.75 0.8 2.6Benzo(a)anthracene

7.5 4.6 26

Benzo(b)fluoranthene

7.5 NR 26

Benzo(k)fluoranthene

75.0 4.6 260

Chrysene 750.0 462 2,600Regardless the oil fraction:Chrysene 750.0 462 2,600Naphthalene NC 16,450 27,000Acenaphthylene NC 24,500 NRAcenaphthene NC 24,500 41,000Fluorene NC 16,450 27,000Anthracene NC 122,500 20,000Fluoranthene NC 16,450 27,000Pyrene NC 12,250 20,000Indene(1,2,3,cd)pyrene

NC 4.6 26

Dibenzo(a,h)anthracene

NC 0.46 26

All limits for industrial soils.

NC not considered, NR not reported.

Environ Monit Assess (2007) 133:387–398 395

All these parameters are related with aspects ofcontaminant migration in the non-saturated zone andthe biodegradation capability of the system. Table 4shows a summary for these parameters at pointscorresponding to Salina Cruz pipelines right-of-way,Loma Larga and Medias Aguas pumping stations.Regarding pH, a parameter related with the type ofsoil, it varied for the Salina Cruz pipelines right-of-way zone in the interval of 6.35–7.35, i.e., from aslightly acidic to a slightly basic soil. For Loma Largaand Medias Aguas pumping stations, only one pointwas characterised in terms of pH, resulting in valuesof 7.55 and 7.35 units for Loma larga and Mediasaguas pumping stations, respectively. The average forthe three sets of pH values is 6.96 units,corresponding to a basic type of soil, near neutrality.

Regarding bulk densities, values for Salina Cruzpipelines right-of-way were between 1.21 and1.49 g/cm3. In the case of Loma Larga and MediasAguas pumping stations, values of 1.17 and 1.13 g/cm3

were measured. As an average, an apparent density of1.26 g/cm3 was determined. Finally, porosity valueswere calculated as the difference between the real andbulk densities. Values for points near the Salina Cruzpipelines right-of-way were between 0.21 and 0.48(non-dimensional), but, in fact, just one point (4+590)showed a low porosity of 0.22, and most of the valuespresented porosities higher than 0.41 (non-dimension-al). For the Loma Larga and Medias Aguas pumpingstations, values of 0.52 and 0.52 (non-dimensional) werecalculated. The average porosity value resulted 0.44 (-).

Regarding the size of the contaminated area, it canbe said that at point 6+020, in Salina Cruz pipelineright-of-way, the affected area is about 20 m2 with a

contaminated depth of 2 m. This means a volume of40 m3. Regarding the Loma Larga pumping station,the area affected is around 264 m2, with a depth of4 m. Volume that should be cleaned is about1,056 m3, but contamination levels are not homoge-neous throughout that soil volume, yielding a total of284 m2 and about 1,096 m3.

Given the areas and volumes that need to becleaned, as well as the physical position of contam-inants, it has been considered that excavation of thecontaminated soil is feasible and the cleaning processcould consist of soil washing assisted with surfac-tants. The process can be developed fairly simpleinstallations built near the contaminated place, oreven transported to another place, where big soiltreatment plants clean huge amounts of soils comingfrom different petroleum installations.

In previous reports, our group showed the attrac-tiveness of using surfactant-enhanced soil washing forthe recovery of soils contaminated with petroleumhydrocarbons. This process can be developed in situ(Iturbe et al. 2004b) or in washing ditches (Iturbe et al.2004a), the process is based on the high capabilitiespossessed by surfactants to increase the hydrophobiccompounds solubility in water and, even, to formmicelles, which in turn will mobilize the contaminantsinto the surfactant solution, eliminating them from thesoil (Lopez et al. 2004; Torres et al. 2004).

Conclusions

After discussion of the results generated in this work,it is possible to conclude the following:

Sample identification PH Bulk density(g/cm3)

Real density(g/cm3)

Porosity(non-dimensional)

0+800 7.35 1.2149 2.2824 0.46771+900 7.26 1.2234 2.3067 0.46964+590 6.58 1.2446 1.5772 0.21086+020 6.87 1.3356 2.4210 0.44838+800 6.35 1.4925 2.5718 0.41969+500 6.40 1.2619 2.4354 0.4818LOLA 7.55 1.1735 2.4485 0.5230MEDAG 7.35 1.1358 2.3813 0.5207Average 6.96 1.2602 2.3030 0.4426

Table 4 Some physicalcharacteristics of the sam-pled soils

396 Environ Monit Assess (2007) 133:387–398

1. It is remarkable to observe that from the 42sampled points, only six of them showed valuesover 2,000 mg/kg, corresponding to the maxi-mum level approved by Mexican legislation forindustrial soils in 2002.

2. Regarding the Salina Cruz pipeline right-of-way,the highest TPH value was located at point 6+020 2A, with a value of 13,683. Petapa samplesdid not reveal presence of TPHs. Regarding theLoma Larga pumping station, three pointsexceeded the limit values regarding TPH concen-trations, LOLA 3B, with 101,759 mg/kg, LOLA3A, with 15,566 mg/kg, and LOLA 4B, with2,829 mg/kg. Medias Aguas pumping station didnot present any point with TPH concentrationsabove the Mexican limit.

3. There are only three points where at least one PAHconsidered by Mexican legislation is present at aconcentration above the limit. This is the case ofpoint 6+020 2A, with 15.20 mg/kg of benzo(a)pyrene, 16.79 mg/kg of benzo(a)anthracene, and16.99 mg/kg of benzo(k)fluoranthene. The secondpoint is 9+850 1A, with 2.04 mg/kg of benzo(a)pyrene and 2.54 mg/kg of benzo(a)anthracene,both levels are higher than those legislated inMexico. The third point, LOLA 3B, corresponds toa TPH concentration of 101,759 mg/kg andrevealed the presence of 2.31 mg/kg of benzo(a)pyrene, higher than the Mexican limit.

4. If the total amount of PAHs found at a singlepoint is considered, point 6+020 2A showed thehighest amount (217.8 mg/kg), followed byLOLA 3b, with 35.5 mg/kg, and 9+850 1A, with33.5 mg/kg.

5. When contrasting the PAH concentrations forevery PAH in the whole set of points wherePAHs were present (Salina Cruz pipelines right-of-way and Loma Larga pumping station), therewere no good correlations (R2<0.85) except forthe case of fluorene (R2=0.9943). When doingthe same correlation with PAHs at Salina Cruzpipelines right-of-way points, good correlationswere found for most of the considered PAHs,except for dibenzo(a,h)anthracene (0.2156), andindene(1,2,3,c,d)pyrene (0.2144). Comparisonbetween points at Loma Larga and PAH concen-trations yielded fair correlations for most PAHsexcept for naphthalene (0.3852).

6. In Salina Cruz pipelines right-of-way, the affectedarea is about 20 m2 with a contaminated depth of2 m. This means a volume of 40 m3. Regardingthe Loma Larga pumping station, the areaaffected is around 264 m2, with a depth of 4 m.Volume that should be cleaned is about 1,056 m3,but contamination levels are not homogeneousthrough that volume of soil, yielding a total of284 m2 and about 1,096 m3.

7. Given the areas and volumes that need to becleaned, as well as the physical position ofcontaminants, it has been considered that excava-tion of the contaminated soil is feasible and thecleaning process could consist of surfactant-assisted soil washing.

Acknowledgement The entire investigation was supported byPEMEX-Refinacion (Grant GPASO/UNAM-II-4311). Theauthors thank the participation of Jesus Flores (supervisor),Carlos Flores V, David Garibay, Daniel Flores, and Luis Acevedoin the sampling procedures. Part of the sampling procedure wascarried out by Esteban del Campo. Authors thank the participationof J. Lopez, L. Corona, and G. Casimiro (II/UNAM) in theexperimental part of this investigation or in the treatment of rawdata. The review of the initial draft of this paper by R.M. Flores(II/UNAM) is acknowledged and thanked.

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