U.S. EPA Contaminated Site Cleanup Information (CLU-IN)

U.S. Environmental Protection Agency
U.S. EPA Technology Innovation and Field Services Division

Dense Nonaqueous Phase Liquids (DNAPLs)

Detection and Site Characterization



An Analytical Quantification of Mass Fluxes and Natural Attenuation Rate Constants at a Former Gasworks Site
Bockelmann, A., T. Ptak, and G. Teutsch, Centre for Applied Geosciences, Univ. of Tubingen, Germany. Journal of Contaminant Hydrology, Vol 53 No 3-4, p 429-453, 2001

A new integral groundwater investigation approach has been used to quantify natural attenuation rates at field scale. In this approach, pumping wells positioned along two control planes were operated at distances of 140 and 280 m downstream of a contaminant source zone at a former gasworks site polluted with BTEX and PAH compounds. First-order natural attenuation rate constants could be estimated based on the quantified changes in total contaminant mass fluxes between the control planes, ranging from 1.4e-02 to 1.3e-01/day for BTEX and 3.7e-04 to 3.1e-02/day for PAHs. An increase in dissolved iron mass flux and a reduction in sulfate mass flux between the two control planes indicated microbial degradation activity at the site, and an analysis of the concentration-time series measured at the control planes also allowed semi-quantitative delineation of the aquifer regions most likely to be contaminated by BTEX and PAHs.

Benefits of Partial DNAPL Source Removal: Measuring Contaminant Flux Change
Annable, M.D. (Univ. of Florida), K. Hatfield, J. Cho, M.C. Brooks, A.L. Wood, C.G. Enfield, C. Holbert, and K. Gorder. The Fifth International Conference on Remediation of Chlorinated and Recalcitrant Compounds, (Monterey, CA; May 2006): Book of Abstracts. Battelle Press, Columbus, OH. Poster presentation, 2006

At Hill AFB, two innovative methods for measuring water and contaminant mass flux at a DNAPL site were evaluated after the implementation of surfactant flushing. Ten monitoring wells on approximately 10-ft centers were placed downgradient from the DNAPL source zone. In one technique, a transect of passive flux meters (PFMs) was used to measure TCE mass flux passing through the PFMs before and after the surfactant flood. The meters indicated a reduction in TCE flux of approximately 90%. With the other technique--the integral pumping test method--water was subsequently extracted from the same series of wells, and contaminant concentration/time series was measured in each pumping well effluent. These methods were also compared to mass flux calculated using water quality data from the transect of fully screened wells. The three independent measurement techniques provided comparable results, showing significant contaminant mass flux reduction following remediation.

Adobe PDF LogoChanges in Contaminant Mass Discharge from DNAPL Source Mass Depletion: Evaluation at Two Field Sites
M.C. Brooks, A.L. Wood, M.D. Annable, K. Hatfield, J. Cho, C. Holbert, P.S.C. Rao, C.G. Enfield, K. Lynch, and R.E. Smith.
Journal of Contaminant Hydrology, Vol 102 Nos 1-2, p 140-153, 2008

Changes in contaminant fluxes resulting from aggressive remediation of DNAPL source zones were investigated at Hill AFB, Utah (surfactant flooding), and at Ft. Lewis Military Reservation, Washington (resistive heating). Passive flux meters (PFMs) and a variation of the integral pumping test (IPT) were used to measure fluxes in 10 wells installed along a transect downgradient of the TCE source zone and perpendicular to the mean groundwater flow direction. Contaminant flux measurements made using both PFM and IPT approaches at the 2 sites indicate that TCE mass depletion (>60%) in the source zone through aggressive treatment resulted in substantial (>90%) reduction in TCE mass discharge at the source control plane. Use of either PFM or IPT tests to characterize DNAPL source zone can provide critical data needed for more efficient targeting of aggressive treatment to achieve the desired reduction in source strength.

A Direct Passive Method for Measuring Water and Contaminant Fluxes in Porous Media
Hatfield, K., M. Annable, Jaehyun Cho (Univ. of Florida, Gainesville); P.S.C. Rao (Purdue Univ., West Lafayette, IN); Harald Klammler (Graz Univ. of Technology, Austria). Journal of Contaminant Hydrology, Vol 75 Nos 3-4, p 155-181, Dec 2004

This paper introduces a new direct method for measuring water and contaminant fluxes in porous media. The method uses a passive flux meter (PFM), which is essentially a self-contained permeable unit properly sized to fit tightly in a screened well or boring. The meter is designed to accommodate a mixed medium of hydrophobic and/or hydrophilic permeable sorbents, which retain dissolved organic/inorganic contaminants present in the groundwater flowing passively through the meter. The contaminant mass intercepted and retained on the sorbent is used to quantify cumulative contaminant mass flux. The sorptive matrix is also impregnated with known amounts of one or more water-soluble 'resident tracers.' These tracers are displaced from the sorbent at rates proportional to the groundwater flux; hence, in the current meter design, the resident tracers are used to quantify cumulative groundwater flux. Theory is presented and quantitative tools are developed to interpret the water flux from tracers possessing linear and nonlinear elution profiles. The same theory is extended to derive functional relationships useful for quantifying cumulative contaminant mass flux. The passive flux meter was tested in multiple box-aquifer experiments with 2,4-dimethyl-3-pentanol (DMP) used as a surrogate groundwater contaminant.

Flux-Based Assessment at a Manufacturing Site Contaminated with Trichloroethylene
Basu, N.B., P.S.C. Rao, and I.C. Poyer (Purdue Univ., West Lafayette, IN); M.D. Annable and K. Hatfield (Univ. of Florida, Gainesville). Journal of Contaminant Hydrology, Vol 86 Nos 1-2, p 105-127, 30 June 2006

Groundwater and contaminant fluxes were measured with the passive flux meter (PFM) technique in wells along a longitudinal transect passing approximately through the centerline of a trichloroethene (TCE) plume at a former manufacturing plant. Two distinct zones of hydraulic conductivity were identified from the measured groundwater fluxes that would significantly affect any remediation technology used at the site. The flux-averaged TCE concentrations estimated from the PFM results compared well with existing groundwater monitoring data. At least 800 kg of TCE was estimated to be present in the source zone. The TCE mass discharge across the source control plane was used to estimate the source strength (365 g/day), while mass discharges across multiple downgradient control planes were used to estimate the plume-averaged TCE degradation rate constant (0.52/year). The mass discharge approach provides a more robust and representative estimate than the centerline approach; the latter uses only data from wells along the plume centerline while the former uses all wells in the plume.

A New Approach to Measuring the Direction of Horizontal Groundwater Flow
Klammler, Harald; Kirk Hatfield; Michael Annable, University of Florida, Gainesville. Eos. Trans. AGU, 84(46), Fall Meet. Suppl., Abstract H21D-0857, 2003

A Passive Flux Meter (PFM) has been developed to simultaneously measure the magnitudes of ground water and contaminant fluxes in porous media. The PFM consists of permeable sorptive media in the shape of a homogeneous cylinder that is inserted into a borehole and that exactly fits the diameter of the well screen. The PFM, which initially contains a known amount of a resident tracer, thus intercepts ground water and contaminant flow, causing the partial elution of the resident tracer from the PFM and the sorption of contaminants onto the PFM. Quantitative analysis of the PFM for the amount of resident tracer remaining on the PFM media and the amount of contaminant sorbed onto the PFM after exposure to ground water and contaminant flow allows for the determination of the magnitudes of ground water and contaminant fluxes. This paper presents two modified configurations of the PFM and compares their capability for measuring the horizontal flow direction simultaneously to the magnitudes of ground water and contaminant fluxes.

Passive Fluxmeters: Application as a Characterization/Monitoring Tool for Monitored Natural Attenuation of Chlorinated Solvents
Vangelas, K., B.B. Looney, K. Hatfield, M.D. Annable, J. Cho, and M.R. Millings. Report No: WSRC-STI-2006-00315, 47 pp, Dec 2006

Contaminant mass flux is generally defined as the mass of contaminant passing through a unit area per unit time, while the integrated mass flux or contaminant mass discharge is the spatial integration of the contaminant flux over a control plane. This report presents results of a research project in which passive fluxmeters (PFMs) were used to measure changes of chlorinated ethene fluxes along the axis of a ground-water contaminant plume. A PFM is a down-hole device that operates passively to provide direct, in situ, cumulative measures of both local water and dissolved contaminant fluxes. A transect of PFMs provides information that, when spatially integrated, generates estimates of contaminant mass discharge. Multiple PFM transects located downgradient from a source area can be used to estimate spatial changes in contaminant mass discharge, which are needed to calculate contaminant mass balances and characterize the intensity of natural attenuation.

Quantification of Mass Fluxes and Natural Attenuation Rates at an Industrial Site with a Limited Monitoring Network: a Case Study
Bockelmann, Alexander, Daniela Zamfirescu, Thomas Ptak (Univ. of Tubingen, Tubingen, Germany), Peter Grathwohl, and Georg Teutsch. Journal of Contaminant Hydrology, Vol 60 Nos 1-2, p 97-121, Jan 2003

The number of available monitoring wells at a contaminated site may be limited by economic or geological considerations, making it more difficult to perform a reliable field investigation and to quantify primary lines of evidence for natural attenuation, like the documentation of a decrease of contaminant mass flux in flow direction. This study reports the results of a groundwater investigation at a former manufactured gas plant in southwest Germany. Due to difficult drilling conditions (coarse glaciofluvial gravel deposits and an anthropogenic fill above the aquifer), only 12 monitoring wells were available for the investigation and localization of the contaminant plume. Based on the sparse set of monitoring wells, field-scale mass fluxes and first-order natural attenuation rate constants of the BTEX constituents and low-molecular-weight PAHs were estimated using a different point scale and a new integral investigation method. Even at a heterogeneous site with a sparse monitoring network, point-scale investigation methods can provide reliable information on field-scale natural attenuation rates, if a dependable flow model or tracer test data is available. Lacking this information, only the integral investigation method presented can yield adequate results for the quantification of contaminant mass fluxes under sparse monitoring conditions.

Adobe PDF LogoUse and Measurement of Mass Flux and Mass Discharge
Interstate Technology & Regulatory Council (ITRC), Integrated DNAPL Site Strategy Team.
MASSFLUX-1, 154 pp, 2010

Mass discharge and flux estimates are used to quantify source or plume strength at a given time and location. This report summarizes the concepts underlying mass discharge and flux and their potential applications, and provides case studies (Appendix A) of the uses of these metrics. The text is written for readers having a general understanding of hydrogeology, the movement of chemicals (particularly DNAPL chemicals) in porous media, remediation technologies, and the overall remedial process.

Adobe PDF LogoValidation of Methods to Measure Mass Flux of a Groundwater Contaminant
Yoon, Hyouk, Master's thesis, Air Force Inst. of Technology, Wright-Patterson Air Force Base. AFIT/GES/ENV/06M-08, NTIS: ADA445057, 62 pp, Mar 2006

Flux measurements obtained using two methods were compared with known mass fluxes in a meso-scale three-dimensional artificial aquifer. One method, the tandem recirculating well (TRW) method, was applied using two different techniques. One technique is simple and inexpensive, only requiring measurement of heads, while the second technique requires conducting a tracer test. The second method, the integrated pump test (IPT), requires use of one or more pumping and observation wells in various configurations. The results of the experiments in the artificial aquifer show that the most expensive technique, the TRW method using tracers, provides the most accurate results (within 15%). The TRW method that relies on head measurements is very inaccurate, so the technique appears not to be viable for flux measurement. The IPT method, although not as accurate as the TRW method using the tracer technique, does produce relatively accurate results (within 60%). IPT method inaccuracies appear to be due to the fact that the method assumptions were not well-approximated in the artificial aquifer. While measured fluxes consistently underestimated the actual flux by at least 36% and as much as 60%, it appears that errors may be reduced when potential violations of method assumptions are taken into account.

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