Prediction of Soil Lead Recontamination Trends with Decreasing Atmospheric Deposition

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<ul><li><p>This article was downloaded by: [Northeastern University]On: 01 November 2014, At: 20:26Publisher: Taylor &amp; FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registeredoffice: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK</p><p>Soil and Sediment Contamination: AnInternational JournalPublication details, including instructions for authors andsubscription information:</p><p>Prediction of Soil Lead RecontaminationTrends with Decreasing AtmosphericDepositionTeresa Bowers a , Peter Drivas a &amp; Rosemary Mattuck aa Gradient , Cambridge , Massachusetts , USAAccepted author version posted online: 18 Nov 2013.Publishedonline: 05 Feb 2014.</p><p>To cite this article: Teresa Bowers , Peter Drivas &amp; Rosemary Mattuck (2014) Prediction of Soil LeadRecontamination Trends with Decreasing Atmospheric Deposition, Soil and Sediment Contamination:An International Journal, 23:6, 691-702, DOI: 10.1080/15320383.2013.857294</p><p>To link to this article:</p><p>PLEASE SCROLL DOWN FOR ARTICLE</p><p>Taylor &amp; Francis makes every effort to ensure the accuracy of all the information (theContent) contained in the publications on our platform. However, Taylor &amp; Francis,our agents, and our licensors make no representations or warranties whatsoever as tothe accuracy, completeness, or suitability for any purpose of the Content. Any opinionsand views expressed in this publication are the opinions and views of the authors,and are not the views of or endorsed by Taylor &amp; Francis. The accuracy of the Contentshould not be relied upon and should be independently verified with primary sourcesof information. Taylor and Francis shall not be liable for any losses, actions, claims,proceedings, demands, costs, expenses, damages, and other liabilities whatsoever orhowsoever caused arising directly or indirectly in connection with, in relation to or arisingout of the use of the Content.</p><p>This article may be used for research, teaching, and private study purposes. Anysubstantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &amp;Conditions of access and use can be found at</p><p></p></li><li><p>Soil and Sediment Contamination, 23:691702, 2014Copyright 2013 GradientISSN: 1532-0383 print / 1549-7887 onlineDOI: 10.1080/15320383.2013.857294</p><p>Prediction of Soil Lead Recontamination Trendswith Decreasing Atmospheric Deposition</p><p>TERESA BOWERS, PETER DRIVAS,AND ROSEMARY MATTUCK</p><p>Gradient, Cambridge, Massachusetts, USA</p><p>The mathematical model of soil mixing after atmospheric surface deposition developedin Drivas et al. (2011) is expanded here and applied to a case study of soil recontamina-tion in areas near a lead smelter in Herculaneum, Missouri. Soil lead samples collectedfrom the yards of several residences in Herculaneum between 2001 and 2009 show thatrecontamination of previously remediated yards has taken place. The model is used topredict a relative soil lead recontamination trend with time, based on the remediationdate and decreasing smelter emissions over time. An average scaling factor betweenrelative and absolute soil lead levels is derived based on over 1600 data points from 24properties, using modeled air lead levels and the remediation date for each property. Thescaling factor was used to predict soil lead recontamination trends at an additional sixproperties that were remediated in the mid-1990s. The predicted soil lead concentrationvs. time curves match the time-trends in the soil data, explaining the observations thatsoil lead levels increased during the 2000s for properties remediated in 20012002, butdecreased during the same time frame for properties remediated in the 1990s. The modelcan be used to predict expected recontamination trends under differing air depositionscenarios and to extrapolate expected recontamination trends into the future.</p><p>Keywords Atmospheric deposition, mathematical modeling, soil contamination, lead</p><p>Introduction</p><p>This analysis provides an evaluation of soil lead recontamination data collected in Hercu-laneum, Missouri, using the soil mixing mathematical model developed by Drivas et al.(2011), which describes the time behavior of the soil mixing of a chemical after atmosphericdeposition onto the soil surface. The aim of the analysis presented here is to determine theextent to which the model proposed by Drivas et al. (2011) can explain observed soillead recontamination trends. The Drivas et al. (2011) model makes use of an effectivediffusion coefficient to model the combined physical, chemical, and biological processesthat result in downward mixing of atmospherically deposited chemicals in the soil column.The effective diffusion coefficient is derived from fitting the model to observations of thedistribution of lead, cesium, and dioxins in soil from several locations (Fernandez et al.,2008; Doering et al., 2006; Rosen et al., 1999; VandenBygaart et al., 1999; He and Walling,1997; Brzuzy and Hites, 1995). The model developed by Drivas et al. (2011) can be used to</p><p>Address correspondence to Teresa Bowers, Gradient, 20 University Road, Cambridge, MA02138, USA. E-mail:</p><p>Color versions of one or more of the figures in the article can be found online</p><p>691</p><p>Dow</p><p>nloa</p><p>ded </p><p>by [</p><p>Nor</p><p>thea</p><p>ster</p><p>n U</p><p>nive</p><p>rsity</p><p>] at</p><p> 20:</p><p>26 0</p><p>1 N</p><p>ovem</p><p>ber </p><p>2014</p></li><li><p>692 T. Bowers et al.</p><p>estimate chemical concentrations in soil as a result of either a one-time (i.e., instantaneous)or continuous deposition to the surface soil. The model also can be used to estimate theeffect of changing, in this case decreasing, deposition to the surface soil resulting from theserial implementation of various air pollution controls.</p><p>In Herculaneum, air lead emissions from the lead smelter result in deposition of leadfrom the air onto soil over time, resulting in a build-up of lead in soil and a measureableincrease in surface soil lead concentrations. A significant data collection effort took placebetween 2001 and 2009 for a group of properties that were remediated in 2001 or early2002. In addition, some properties that were remediated in the mid-1990s were sampledsubsequently, allowing an examination of recontamination trends from the mid-1990s tothe present. Several emission controls at the lead smelter were implemented over this timeperiod. As a result, total lead emissions from the facility have varied over this time period,and have generally decreased, with corresponding decreases in local air lead levels. Themodel presented in Drivas et al. (2011) is combined with information on lead emissionsfrom the smelter and air lead levels in the community in order to estimate, based on thelocation of each property relative to the facility, the expected trend of surface soil leadconcentrations. These expected trends are compared to measured soil lead data.</p><p>Model Development</p><p>Drivas et al. (2011) presented mathematical equations to calculate the impact on concen-trations in soil of either an instantaneous or continuous source of atmospheric surfacedeposition of a contaminant. Here we expand this analysis to calculate the impact of a con-tinuous source that, through the implementation of air pollution controls at specific points intime, results in decreasing emissions and surface deposition with time. The equations usedhere are a superposition of Eqs. (9) and (13) in Drivas et al. (2011) for the depth-averagedsoil concentration from continuous deposition and the depth-averaged soil concentrationafter a finite period of continuous deposition, respectively. These two equations for a soilconcentration averaged from the surface to a depth L are:</p><p>Cs,ave = Q tL</p><p>[(L</p><p>Deff t</p><p>)exp</p><p>( L24Deff t</p><p>)+ erf</p><p>(L</p><p>2Deff t</p><p>)</p><p>(</p><p>L2</p><p>2Deff t</p><p>)erf c</p><p>(L</p><p>2Deff t</p><p>)](1)</p><p>Cs, ave(t) = Q L2 Deff </p><p>[exp</p><p>(s2L) sL +</p><p>(1 + 1</p><p>2 s2L</p><p>) erf (sL)</p><p>exp(s2U ) sU </p><p>(1 + 1</p><p>2 s2U</p><p>) erf (sU )</p><p>](2)</p><p>with sL = L2Deff t</p><p>and sU = L2Deff (t T )</p><p>,</p><p>where:</p><p>Cs,ave = average soil concentration (g/cm3)Q = continuous surface deposition rate per unit area (g/yr-cm2)Deff = effective diffusion coefficient (cm2/yr)</p><p>Dow</p><p>nloa</p><p>ded </p><p>by [</p><p>Nor</p><p>thea</p><p>ster</p><p>n U</p><p>nive</p><p>rsity</p><p>] at</p><p> 20:</p><p>26 0</p><p>1 N</p><p>ovem</p><p>ber </p><p>2014</p></li><li><p>Soil Lead Recontamination Trends 693</p><p>L = soil depth (cm)t = time (yr)T = deposition time (yr).</p><p>Eq. (1) applies for t T (i.e., during the deposition period), and Eq. (2) applies for t &gt;T (i.e., after the deposition has ended). These equations can be superimposed to represent acase of decreasing atmospheric deposition with time. For example, lets consider the case ofan initial atmospheric deposition rate (Q0) from an industrial source that decreases by 50%after a given time period T0 (i.e., Q = 1/2 Q0 for times t &gt; T0). For the initial time periodt T0, the continuous deposition solution in Eq. (1) applies with Q = Q0. For the timeperiod t &gt; T0, continuous deposition is reduced by half and modeled with Q = 1/2 Q0 in Eq.(1). Eq. (2) with Q = 1/2 Q0 models the impact of the half of the previous deposition thatis no longer occurring after T0. The soil concentrations in Eqs. (1) and (2) are summed torepresent the changes in average soil concentration due to the reduced atmospheric surfacedeposition after t &gt; T0. Similar superposition of the solutions in Eqs. (1) and (2) can beused to model several sequential emission decreases over specified time periods.</p><p>Summary of Available Data</p><p>Soil Lead Concentrations</p><p>Soil lead concentrations are significantly elevated in this community. Many properties havebeen remediated since the early 1990s, some of them more than once. Other propertieswere acquired by the facility and have not been remediated. In addition, some owners haverefused remediation. As a result, there is no uniform soil lead pattern consistent with adeposition source at this time in the community. The amount of data available varies byproperty, as some properties have been sampled numerous times and others only rarely ornot at all. This disparity largely reflects the willingness of property owners to be includedin various sampling plans.</p><p>In this analysis, we examine 24 properties from which the U.S. EPA collected soilsamples for lead analysis on a monthly or quarterly basis beginning in 2001. This data set isreferred to below as the EPA soil lead data set. These properties were all remediated in the20012002 time frame by excavation of 12 to 24 inches of soil and replacement with cleansoil. The original goal of this sampling was to assess the extent to which recontaminationoccurred. A single composite soil sample was collected from each of four quadrants (frontright and left, back right and left) of each property included in the study. Analyses wereconducted in the field with a portable X-ray fluorescence machine (XRF). Concentrationsabove approximately 20 mg/kg were detectable. Samples were collected from a shallowdepth of approximately 0.6 cm. Not all properties have a complete data set, as someproperties were added or dropped during the course of the EPA study.</p><p>Initial sample results shortly after property remediation indicated soil lead concen-trations approximating natural background levels, in the range of 25 to 100 mg/kg. Withtime, soil lead concentrations on most properties increased, although there was significantvariability in the concentrations, likely reflecting both soil heterogeneity and analyticaluncertainty. Concentrations on some properties increased to levels above the EPAs currentsoil lead screening level of 400 mg/kg. In addition to the EPA soil lead data set, we also ex-amined data from a few properties in Herculaneum that were remediated in the mid-1990s,have not been remediated since, and have multiple soil lead sampling events. Soil samplesfrom these properties were taken from the surface to a depth of 2.5 cm. Samples were</p><p>Dow</p><p>nloa</p><p>ded </p><p>by [</p><p>Nor</p><p>thea</p><p>ster</p><p>n U</p><p>nive</p><p>rsity</p><p>] at</p><p> 20:</p><p>26 0</p><p>1 N</p><p>ovem</p><p>ber </p><p>2014</p></li><li><p>694 T. Bowers et al.</p><p>Figure 1. Map showing locations of emissions source, properties, air monitors, and air dispersionmodel lead concentration isopleths. Properties remediated in the mid-1990s include C, D, K, L, Mand T. All other properties (the EPA soil lead data set) were remediated in 2001 or 2002.</p><p>composites of either the front or back yard in the 1990s, while samples taken after 2000followed the quadrant sampling scheme described above. All analyses were by portableXRF. Soil lead concentrations on these properties, although initially low after remediation,increased in several cases to above 1000 mg/kg by several years after the remediation. Thelocations of properties in both data sets are shown in Figure 1. All soil lead data wereprovided by personal communication from the Doe Run Company.</p><p>Dow</p><p>nloa</p><p>ded </p><p>by [</p><p>Nor</p><p>thea</p><p>ster</p><p>n U</p><p>nive</p><p>rsity</p><p>] at</p><p> 20:</p><p>26 0</p><p>1 N</p><p>ovem</p><p>ber </p><p>2014</p></li><li><p>Soil Lead Recontamination Trends 695</p><p>Table 1Annual lead emissions (data provided by personal com-</p><p>munication from the Doe Run Company)</p><p>Year Annual Lead Emissions (tons)</p><p>1997 101.31998 96.21999 139.52000 139.82001 113.52002 58.82003 25.12004 26.02005 28.12006 28.42007 21.32008 19.3</p><p>Air Lead Emissions</p><p>The lead smelter has been a source of lead emissions and lead deposition to soils inHerculaneum throughout its operational history. However, emissions have varied withtime. Table 1 gives annual lead emissions reported by the Doe Run Company in AnnualEmissions Inventory Questionnaires filed with the U.S. EPA (data provided by personalcommunication from the Doe Run Company). Decreases in emissions shown in this tableare largely a result of the implementation of various emission controls that reduced bothstack and fugitive emissions, primarily implemented between mid-2001 to mid-2002 andtowards the end of 2008. Table 1 shows that annual lead emissions decreased from 2001 to2002, and decreased again in 2003, after which they remained relatively constant through2008.</p><p>Air Lead Concentrations</p><p>Air lead concentrations are measured at several high-volume TSP (total suspended par-ticulate) monitors in the community. Concentrations were always above detection limits.Table 2 summarizes annual air lead levels measured at four monitors near the facility.Annual air lead levels at these monitors showed a decrease between 2001 and 2002, andthen stayed relatively constant until apparently decreasing further in early 2009. The loca-tions of the monitors are shown in Figure 1. All air lead data were provided by personalcommunication from the Doe Run Company.</p><p>Model Application</p><p>Model Parameterization</p><p>A model of soil lead concentration as a function of soil depth and time was constructedbased on the information given in Tables 1 and 2 to describe deposition rates t...</p></li></ul>


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