Single-Well "Push-Pull" Partitioning Tracer Test for NAPL Detection in the Subsurface

详细信息    查看全文

• 作者：Jonathan D. Istok ; Jennifer A. Field ; Martin H. Schroth ; Brian M. Davis ; and Varadarajan Dwarakanath
• 刊名：Environmental Science & Technology
• 出版年：2002
• 出版时间：June 15, 2002
• 年：2002
• 卷：36
• 期：12
• 页码：2708 - 2716
• 全文大小：159K
• 年卷期：v.36,no.12(June 15, 2002)
• ISSN：1520-5851

文摘

Previous environmental applications of partitioning tracertests to detect and quantify nonaqueous phase liquid(NAPL) contamination in the subsurface have been limitedto well-to-well tests. However, theory and numericalmodeling suggests that single-well injection-extraction("push-pull") partitioning tracer tests can also potentiallydetect and quantify NAPL contamination. In this type oftest, retardation factors for injected partitioning tracers areestimated from the increase in apparent dispersionobserved in extraction-phase breakthrough curves in thepresence of NAPL. A series of laboratory push-pull testswas conducted in physical aquifer models (PAMs)packed with natural aquifer sediment prepared with andwithout the presence of trichloroethene (TCE) NAPL. Fieldtests were conducted in an aquifer contaminated withpetroleum hydrocarbon NAPL. Injected test solutionscontained a suite of partitioning and conservative(nonpartitioning) alcohol tracers. Laboratory push-pullpartitioning tracer tests were able to detect and quantifysorption of partitioning tracers to aquifer sediment (in theabsence of NAPL) and to detect NAPL when it waspresent. NAPL saturations computed from estimatedretardation factors bracketed those computed from knownvolumes of emplaced NAPL in the sediment pack. However,numerical modeling with assumed homogeneous NAPLdistribution and linear equilibrium partitioning of tracersbetween aqueous and NAPL phases was unable to reproduceall features of observed breakthrough curves. Excavationof the sediment pack after all tests indicated that a portionof the emplaced NAPL had sunk to the bottom of thePAM invalidating the modeling assumption of homogeneousNAPL distribution. Moreover, the apparent dispersion inextraction-phase breakthrough curves decreased when theinjection-extraction pumping rate was decreased,suggesting that mass transfer limitations existed duringlaboratory tests. Field push-pull partitioning tracer testswere able to detect NAPL in a portion of the aquifer knownto contain NAPL; computed NAPL saturations werecomparble to those obtained from sediment coring andthe results of a partitioning interwell tracer test conductedin the same location. This study clearly demonstratesthat the single-well partitioning tracer test can detect NAPLunder both laboratory and field conditions. However,additional research is needed to verify the ability of thetest to quantify NAPL saturations.