Fugitt, Todd

Kim, Burmshik

Steele, Kenneth F.

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Journal of the Arkansas Academy of ScienceVolume 58 Article 212004Comparison of Dissolved and Acid-ExtractableMetal Concentrations in Groundwater, EasternArkansasBurmshik KimUniversity of Arkansas, FayettevilleKenneth F. SteeleUniversity of Arkansas, FayettevilleTodd FugittArkansas Soil and Water Conservation CommissionFollow this and additional works at: http://scholarworks.uark.edu/jaasPart of the Fresh Water Studies Commons, and the Water Resource Management CommonsThis article is available for use under the Creative Commons license: Attribution-NoDerivatives 4.0 International (CC BY-ND 4.0). Users are able toread, download, copy, print, distribute, search, link to the full texts of these articles, or use them for any other lawful purpose, without asking priorpermission from the publisher or the author.This General Note is brought to you for free and open access by ScholarWorks@UARK. It has been accepted for inclusion in Journal of the ArkansasAcademy of Science by an authorized editor of ScholarWorks@UARK. For more information, please contact scholar@uark.edu.Recommended CitationKim, Burmshik; Steele, Kenneth F.; and Fugitt, Todd (2004) "Comparison of Dissolved and Acid-Extractable Metal Concentrations inGroundwater, Eastern Arkansas," Journal of the Arkansas Academy of Science: Vol. 58 , Article 21.Available at: http://scholarworks.uark.edu/jaas/vol58/iss1/21117Comparison of Dissolved and Acid-Extractable Metal Concentrationsin Groundwater, Eastern ArkansasBurmshik Kim*and Kenneth F. SteeleEnvironmental Dynamics Program113 Ozark HallUniversity of ArkansasFayetteville, AR72701*Corresponding AuthorStandard Methods for the Examination of Water andWastewater (Clescerl et al., 1999) and EnvironmentalProtection Agency Analytical Methods (EPA, 1994)recommend that all water samples should be filteredthrough a 0A5/jm pore-size membrane immediately aftersample collection and acidification of the sample. Theserecommendations are needed in order to provide the"dissolved" metal concentrations, which are used for mostmonitoring projects (Lussier et al., 1999). Most domesticwater supplies and irrigation waters are not filtered prior touse; thus, the suspended solids concentrations may supplyions that are environmentally available to people, animalsand plants (Pohlmann et al., 1994). Inmany wells, the waterat depth is a reducing environment, however Fe mayprecipitate in the well as it is mixed with more oxygenatedwater. Filtration of this well water removes the precipitatedFe, resulting inunderestimation of the amount ofFe inmanyaquifers. Iron concentrations can be used to determine thelikelihood ofiron oxides clogging well screens or damagingpumps, but if the samples are filtered, the Fe concentrationin water at depth willbe underestimated and the potentialdamage also underestimated. Iron and Mn maximumconcentration levels are set for esthetic reasons— to avoidprecipitation in sinks, toilets and tubs. The potential forstaining porcelain also may be underestimated ifthe sampleis filtered (Pohlmann et al., 1994). Toxic metals, such as As,Pb, Cr are often associated with suspended solids-clays andiron oxides. Once ingested, metals from these suspendedsolids may become bioavailable.The objective of this study was to determine the effectof filtration on metal analyses of groundwater from theMississippi River Valley Alluvial aquifer (Alluvial aquifer)and the Sparta aquifer. Because of the high concentration ofFe and the importance of precipitated iron oxides, Fe wasthe focus of the study.The study site is in the Grand Prairie region of easternArkansas (part of the Mississippi River Alluvial Plain),which includes Arkansas, Lonoke, Monroe, Prairie, andPulaski counties (Fig. 1). This area is dominated byagricultural production of rice, soybeans, cotton, milo,andin recent years, aquaculture of catfish and game fishfingerlings. The Alluvialaquifer is the most intensively usedaquifer inArkansas. Inthe late 1990's, withdrawals from theTodd FugittArkansas Soil and Water Conservation Commission101 East Capitol, Suite 350Little Rock, AR 72201Alluvialaquifer were 20.1 million mVday (Czarnecki et al.,2003), with 1million mVday being withdrawn from Spartaaquifer (McKee et al., 2004). Use of Sparta aquifer hasincreased rapidly since the mid-1980s. Sands and gravels ofthe Alluvialand Sparta aquifers coarsen northward and withdepth. The gravel is mostly chert and is overlain bymedium- to fine - grained sand. Discontinuous lenses of clay, silt orsandy silt occur at many places (Cooper, 2002).Fifty-two domestic, agriculture, and monitoring wells inthe Alluvialand Sparta aquifers were investigated. The welllocations are shown in Fig. 1. The wells were sampledduring spring and summer 2002 and 2003. Allwells weresampled as near to the wellhead as possible throughavailable outlets. Most wells were in use at the time ofsample collection. Typical well depths for the alluvialaquifer range from 30 m (98 ft) to 45 m (148 ft),and wells inthe Sparta aquifer ranged from 120 m (390 ft) to 170 m (552ft) in depth. Samples for dissolved metals were filteredthrough a 0.45//m pore-size membrane immediately aftersample collection. All samples were collected in cleanpolypropylene bottles and were preserved withnitricacid toa pH of 2.0. Allsamples were stored on ice and deliveredto the Water Quality Laboratory of the University ofArkansas, Fayetteville. The sample pretreatmentmethodology followed EPA Analytical Methods Manual,Method 200.15 (EPA, 1994), for total recoverable metals ingroundwater with the exception that samples were notheated. That is the acid-extractable sample pretreatment forthis project consists of only the addition of nitric andhydrochloric acids prior to analyses. Samples were analyzedfor major and some trace metals (Ca, Mg, Na, K, Fe, Mn,Cu, Pb, and Zn) and total suspended solids. Analyticalmethods followed Standard Methods for the Examination ofWater and Wastewater (Clescerl et al., 1999) i.e. inductivelycoupled plasma (ICP) instrumental analyses method formetals. The differences between dissolved and acid-extractable concentrations were assessed by the PairedStudent-t test.Calcium, Mg,and Na concentrations are relatively high(Table 1),but similar to data for other alluvial aquifer studies(Aremu et al., 2002; Elbaz-Poulichet et al., 2002; Kresse andFazio, 2002). The geochemical environment of the aquifersis such that high Fe concentrations occur in these aquifersJournal of the Arkansas Academy of Science, Vol. 58, 2004117Journal of the Arkansas Academy of Science, Vol. 58 [2004], Art. 21Published by Arkansas Academy of Science, 2004Comparison of Dissolved and Acid-Extractable Metal Concentrations inGroundwater, Eastern Arkansas118Fig. 1. The map of research site and well locations. Note that around the wellnamed LO4, MN1, PR4, PR5 and PX, severalirrigation wells were sampled within 1-mile from the monitoring well. Around LO4 and PR4 each, six wells are sampled.Around PX, seven wells were sampled, and around MN1, six wells were collected.(Steele et al., 2003). Acid-extractable samples havesignificantly (P = 0.05) higher concentrations of Fe, Mn,Pb,and Ca than dissolved concentrations (Table 1). Sodiumdifferences were marginally significant at the P = 0.06.Magnesium, K, and Zn were not found to be significantlydifferent significant differences (P >0.05) between dissolvedand acid-extractable concentrations (Table 1).The difference between dissolved and acid-extractableconcentrations can be represented by difference ratios,calculated by R m. =L-2± 'llxlOOwhere R^f is the difference ratio, Ca e is the acid-extractableconcentration, and Cd is the dissolved concentration. HigherFe concentration leads to larger Rdff value. The Rdff for Fehad a positive relationship with total suspended solidsconcentrations, i.e., the greater the total suspended solidsconcentrations, the greater the Rdff(Fig. 2).In most cases the difference ratios are small (< 25%),but inabout 30% of samples the difference ratios were quitelarge, more than 90%. Although there are small differenceratios (< 5%) for Ca, Mg, Na, and K, statistical analysesrevealed significant differences for Ca, and Na at the 94%confidence level. The differences are interpreted to beprimarily the result of precipitation of Fe and the othertransition metals and cation exchange of Ca, Mg,Na, and Kwith clay. Reducing conditions within the well dissolvelarge quantities of Fe and other transition metals, but duringpumping, the water becomes oxygenated and large amountsof these metals are precipitated. Thus, the amount of Fe insolution at the well head is not representative of Fe withinmost of the aquifer. Filtration of the precipitated iron oxidescauses the Fe concentration of the aquifer to beunderestimated and not to be a useful predictor of ironoxide problems with well screens or pumps. Also toxiceffects of metals (e.g., Pb) may be underestimated because ofthe bioavailability of the metal from suspended solids (e.g.,Journal of the Arkansas Academy of Science, Vol. 58, 2004118Journal of the Arkansas Academy of Science, Vol. 58 [2004], Art. 21http://scholarworks.uark.edu/jaas/vol58/iss1/21Burmshik Kim,Kenneth F. Steele and Todd Fugitt119Table 1. Comparison of dissolved and acid-extractable metal concentrations, difference ratio,and statistical P value. The P valuewas calculated by the Paired Student-t test where the hypothesis was that the differences between dissolved and acid-extractablemetal concentrations were zero. R^ is difference ratio (see text), n is number of samples and SD is standard deviation.Species Acjd-extractable (mg/L) Dissolved (mg/L) p n R^Mean + SD Mean + SDCa 72.053 + 43.763 70.892 ± 41.986 0.044 28 1.611Cu 0.014 + 0.044 0.005 ± 0.004 0.120 33 65.539Fe 13.233 ± 19.400 5.336 ± 7.167 0.003 52 59.678Pb 0.010 ± 0.020 0.001 ± 0.003 0.014 33 85.127Mg 17.616 ± 10.492 17.564 ± 10.193 0.362 28 0.298Mn 0.768 ± 1.026 0.285 ± 0.383 0.001 52 62.852K 2.846 ± 1.264 2.855 ± 1.225 0.411 28 -0.339Na 41.616 ± 37.764 40.524 ± 35.378 0.060 28 2.625Zn 0.019 ± 0.048 0.018 ± 0.043 0.441 28 3.933Literature CitedAremu, D. A., J. F. Olawuyi, S. Meshitsuka, M. K.Sridhar, and P. A. Oluwande. 2002. Heavy metalClescerl, L.S., A.E. Greenberg, and A.D.Eaton. 1999.Czarnecki, J. B., B. R. Clark, and G. P. Stanton. 2003.Journal of the Arkansas Academy of Science, Vol. 58, 2004119Journal of the Arkansas Academy of Science, Vol. 58 [2004], Art. 21Published by Arkansas Academy of Science, 2004Comparison of Dissolved and Acid-Extractable Metal Concentrations in Groundwater, Eastern Arkansas120Lussicr, S. M., W. S. Boothman, S. Poucher, D.Champlin, and A.Helmstertten. 1999. Comparisonof dissolved and total metals concentrations fromacutetests with saltwater organisms. Environ. Toxicol. andChemistry, 18(5):889-898.McKee, P. W., B. R. Clark, and J. B. Czarnecki. 2004.Conjunctive-use optimization model and sustainable-yield estimation for the Sparta Aquifer of southeasternArkansas and northcentral Louisiana. U.S. GeologicalSurvey water resources investigation report 03-4231,Little Rock, AR.30 pp.Pohlmann, K.F., G. A.Icopini, R.D.McArthur,and C.G. Rosal. 1994. Evaluation of sampling and field-filtration methods for the analysis of trace metals inground water. EPA/600/SR-94/119. EPA. Las Vegas,NV,119 pp.Steele, K.F., T. M.Kresse, and R.K.Davis. 2003. Smallscale spatial variation of water quality within theMississippi River Valley Alluvial Aquifer, Arkansas,USA. Two Rivers 4th Joint International Association ofHydrologists-Canadian National Chapter, CandianGeotechnical Society Conference Proceedings (CDvolume). IAH,Winnepeg, Canada. 8 pp.Journal of the Arkansas Academy of Science, Vol. 58, 2004120Journal of the Arkansas Academy of Science, Vol. 58 [2004], Art. 21http://scholarworks.uark.edu/jaas/vol58/iss1/21

Comparison of Dissolved and Acid-Extractable Metal Concentrations in Groundwater, Eastern Arkansas

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