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Use and Measurement of Mass Flux and Mass Discharge

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1 Introduction
2. Concept and Theory of Mass Flux and Mass Discharge
2.1 Basic Concepts
2.2 Calculating Mass Flux and Mass Discharge
2.3 Approaches to Mass Flux Estimation
2.4 Factors that Affect Mass Flux
2.5 Managing Uncertainties
3. Applications for Mass Flux and Mass Discharge
3.1 Site Characterization and Conceptual Site Model
3.2 Potential Impact and Exposure Evaluation
3.3 Remedy Selection and Design
3.4 Performance Monitoring and Optimization
3.5 Compliance Monitoring
3.6 Site Prioritization
3.7 Conceptual Examples for Using Mass Flux and Mass Discharge
3.8 Regulatory Considerations
4. Measuring Mass Flux and Mass Discharge
4.1 Transect Methods
4.2 Well Capture/Pumping Test Methods
4.3 Passive Flux Meters
4.4 Transects Based on Isocontours
4.5 Solute Transport Models
4.6 Key Considerations Using Models to Obtain Mass Flux
4.7 General Comparison of Five Mass Flux Measurement Methods
4.8 Managing Uncertainty
5. Key Findings
6. Research Needs
Appendices
Appendix A: Mass Flux Case Study List
Appendix B: Overview of Comparison Studies with Passive Flux Meters
Appendix C: Team Contacts
Appendix D: Glossary
Appendix E: Acronyms and Symbols
Appendix F: References
Acknowledgements
Special Acknowledgements
Acknowledgements
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Use and Measurement of Mass Flux and Mass Discharge
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Appendix A: Mass Flux Case Study List

Case study ID Reference Site Constituents Use Mass flux/discharge measurement method Benefits of mass flux/mass discharge estimates Method used to estimate specific discharge
1 Annable et al. 2005 CFB Borden, Ontario PCE and TCE Site characterization—Evaluated depth-specific mass flux and specific discharge using PFM. Pumping well, passive flux meter (PFM) Not applicable (n/a) n/a
    MtBE Site characterization—Evaluated depth-specific mass flux and specific discharge using transect method (TM) with PFM and TM with multilevel sampling (MLS) wells and identified increasing mass discharge with distance from initial source due to transient conditions. TM, PFM n/a n/a
2 Barbaro and Neupane 2006 Dover AFB, Delaware VOCs Site characterization—Used Md values calculated from two transects to evaluate natural attenuation along the flow path. TM Detailed three-dimensional plume delineation improved conceptual site model (CSM) and provided more reliable determination of plume attenuation rate between two transects. Used a uniform specific discharge across both transects based on relatively uniform head distribution, lithology, and aquifer thickness in the vicinity of the two transects.
3 RTDF 1998 Dover AFB, Delaware Total chlorinated organics Site characterization—Used multiple transects to evaluate the degree to which natural attenuation was occurring downgradient of a source zone. Indirect— synthetic transect from contours n/a n/a
Case study ID   Reference   Site   Constituents   Use Mass flux/discharge measurement method   Benefits of mass flux/mass discharge estimates   Method used to estimate specific discharge
4 Basu et al. 2006 Former electronic parts manufac- turing plant, midwestern United States TCE Site characterization and evaluation of remediation alternatives— Measured mass flux and mass discharge to characterize (a) site hydrogeology, (b) source strength, (c) vertical delineation of specific discharge and contaminant flux at well locations, and (d) degradation rates. Isoconcentration contours and depth-specific Darcy flux were used to estimate mass discharge at three transects transverse to groundwater flow for the purpose of calculating a biodegradation rate. Depth- integrated mass flux was calculated at various locations along a cross section parallel to groundwater flow. PFM and isoconcentration contour transects Depth-discrete flux monitoring indicates that the zone of higher permeability and lower concentrations needs to be considered as a target zone for remediation because it represents a relatively large portion of the source strength, which shows that focusing remediation only in the zone of high concentrations may be “suboptimal.” Detailed contaminant flux vertical profiles revealed valuable information about the upgradient source distribution that could not be determined using conventional monitoring well data. High- resolution profiles of specific discharge versus depth determined using the PFM provide valuable information about variability in hydraulic conductivity that may affect the distribution of injected solutions during remediation. PFM was used to quantify specific discharge at approximately 0.3 m intervals. The average specific discharge determined using the PFM for shallow, intermediate, and deep zones were compared to specific discharge estimates based on average single-well response tests for monitoring wells completed in corresponding horizons.
5 Basu et al. 2009 Former manufac- turing site, Australia TCE Site characterization—Used Md values to compare mass discharge from source zone to Md in plume about 175 m downgradient to evaluate potential for natural attenuation of TCE. Determined that higher Md in plume relative to smaller source zone Md is because of declining source concentrations and six-year travel time between the source and plume control plane transects. Transects using PFMs Flux-based site management approach in heterogeneous aquifer resulted in improved CSM, which will lead to improved effectiveness of site remediation measures. Mass flux and specific discharge measurements were used to demonstrate that residual DNAPL mass was present in low- permeability zones and that source treatment was unwarranted. PFMs were used to quantify specific discharge at approximately 0.3 m intervals over different periods of time to allow for assessment of seasonal fluctuations.
Case study ID   Reference   Site   Constituents   Use Mass flux/discharge measurement method   Benefits of mass flux/mass discharge estimates   Method used to estimate specific discharge
6 Bauer et al. 2004 Linz, Austria PCE, TCE Risk prioritization based on regional characterization of relative strengths of multiple source zones at different sites—Used the integral pumping test (IPT) method to evaluate mass discharge at three transects. Purpose was to quantify the relative strength of multiple source zones contributing to a dissolved plume. Two to five pumping wells were used on each transect. Water generated during pumping tests was disposed to the sewer system without treatment. Source zones between transects were identified as being stronger than upgradient sources. IPT Basin-wide mass discharge analysis determined which source zones should be targeted for further characterization and remediation and identified which portions of the aquifer could be excluded from further investigation and remediation. n/a
7 Beckett, Stanley, and Walsh 2005 Fuel release site, Morro Bay, California MtBE Mass discharge framework used to evaluate potential threat of MtBE plume to nearby water supply wells. n/a n/a n/a
8 Bockelmann, Ptak, and Teutsch 2001 Former manufac- turing site near Stuttgart, Germany BTEX, polycyclic aromatic hydrocarbons (PAHs) Site characterization—Evaluated natural attenuation between two transects situated at distances of 140 and 280 m downgradient of the source zone. Mass discharges at each transect were used to estimate first-order biodegradation rates. Each transect included four pumping wells, and the average travel time between the two transects under static conditions is 70 days. IPT based on wells along transects Mass discharge estimated using the IPTs facilitated the estimation of natural attenuation rates in a highly heterogeneous aquifer with a curvilinear flow path. Changes in mass discharge of electron acceptors and metabolic by- products between transects was also evaluated to provide additional lines of evidence for biodegradation. n/a
Case study ID Reference Site Constituents USE Mass flux/discharge measurement method Benefits of mass flux/mass discharge estimates Method used to estimate specific discharge
9 Bockelmann et al. 2003 Former
manufac-
turing site
near
Stuttgart,
Germany
BTEX, PAH Site characterization—Compared the
mass discharge across two transects
using two approaches: (a)
integrating mass flux estimated at
each well based on point-source
concentrations and (b) IPT method.
Also estimated plume attenuation
rates for BTEX and PAH species
between three transects using three
methods: (a) conventional
concentration vs. distance
attenuation estimates along the flow
path, which was determined based
on a natural gradient tracer test; (b)
mass discharge at each transect
based on integrated mass flux; and
(c) mass discharge based on IPTs.
Transects are 30, 140, and 280 m
downgradient of the source zone.
Each transect incorporated four
monitoring wells with approximate
spacing of 30–40 m between.
Investigators determined that mass
discharge estimates using
monitoring well concentrations and
well spacing of 30–40 m at this site
resulted in significantly different
discharge estimates than the IPT
method (up to 159% difference).
TM Evaluated uncertainty when using
large spacing between wells along
transect for estimating mass flux.
n/a
Case study ID   Reference   Site   Constituents   Use Mass flux/discharge measurement method   Benefits of mass flux/mass discharge estimates   Method used to estimate specific discharge
10 Borden et al. 1997 Sampson County, North Carolina MtBE, BTEX Site characterization—Installed four transects up to 177 m downgradient of the source zone to delineate vertical and horizontal contamination and to facilitate estimation of biodegradation rates along the flow path. Five to six clusters of monitoring wells were installed along each transect. At each location, typically three wells were installed at different elevations, each having a 1.5 m screen length. The well screen length was selected to facilitate a flux-averaged evaluation over 1.5 m. The use of mass discharge to estimate biodegradation rates reduced uncertainty by eliminating the effect of vertical and transverse dispersion and mitigating the effect of nonideal well placement. Temporal variations in mass discharge were also evaluated over a two-year period. TM Using mass discharge to estimate plume attenuation rates between transects overcame previous limitations in estimating a biodegradation rate along the nonlinear flow path. Used medium-resolution vertical sampling with flux-averaged concentrations in 1.5 m well screens to estimate mass discharge and plume attenuation at each transect. Further vertical delineation was not required for this study. n/a
11 Brooks et al. 2008 Hill AFB, Utah TCE and cis- 1,2-DCE Remediation performance monitoring—Compared the mass discharge at a transect approximately 10–15 m downgradient of the source zone before and after remediation to assess performance efficiency. Multiple methods were used for mass discharge estimates to reduce uncertainty. Ten monitoring wells situated on the transect with approximate spacing of 3 m. PFM, modified integral pump test (MIPT), TM Demonstrated that source treatment resulted in a significant reduction in mass discharge from the source. Multiple methods were used to estimate mass discharge to reduce the uncertainty of the remediation performance assessment. High- resolution mass flux delineation indicates a potential reduction in source zone permeability due to stimulated biodegradation that occurred as a result of source treatment. PFM and IPT
Case study ID   Reference   Site   Constituents   Use Mass flux/discharge measurement method   Benefits of mass flux/mass discharge estimates   Method used to estimate specific discharge
12 Brooks et al. 2008 Fort Lewis, Washington TCE and cis- 1,2-DCE Remediation performance monitoring—Compared the mass discharge at a transect approximately 6 m downgradient of the source zone before and after remediation to assess performance efficiency. Multiple methods were used for mass discharge estimates to reduce uncertainty. Ten monitoring wells situated on the transect with approximate spacing of 5 m. PFM, MIPT, TM Demonstrated that source treatment resulted in a significant reduction in mass discharge from the source. Multiple methods were used to estimate mass discharge the reduce the uncertainty of the remediation performance assessment. High- resolution mass flux delineation indicates a potential reduction in source zone permeability due to stimulated biodegradation that occurred as a result of source treatment. PFM and IPT
13 Brusseau et al. 2007 Tucson Internation- al Airport area, Arizona TCE Remediation performance monitoring—Used mass removal data from an operating pump-and- treat system to confirm the presence of NAPL in the source zone and evaluated the transient relationship between mass flux reduction and source mass depletion. n/a Mass removed by the pump-and- treat system over 19 years was reported to be higher than the initial estimate of dissolved-phase mass, suggesting that NAPL is present in the source zone. Partitioning interwell tracer testing to measure source mass indicates that a 90% reduction in mass flux occurred with only a 50% reduction in source mass. This detailed characterization helps to improve the effectiveness of site management decisions. n/a
14 Burton et al. 2002 Beach Point, Maryland Chlorinated solvents and heavy metals Risk assessment—Evaluated potential risks associated with discharge of chlorinated solvents and heavy metals from the Beach Point surficial aquifer to Bush River, a tributary of Chesapeake Bay. n/a Groundwater discharge was used to evaluate dilution in the surface water body and the applicability of a Maryland “regulatory mixing zone,” i.e., a localized discharge zone in which local water quality standards may be exceeded. n/a
15 Buscheck, Nijhawan, and O’Reilly 2003 Gas station, Tahoe City, California MtBE Mass discharge used to evaluate potential impact to downgradient river. n/a n/a n/a
Case study ID   Reference   Site   Constituents   Use Mass flux/discharge measurement method   Benefits of mass flux/mass discharge estimates   Method used to estimate specific discharge
16 Buscheck, Nijhawan, and O’Reilly 2003 Fuel terminal, San Jose, California MtBE Mass flux measured to select optimal rate of dissolved oxygen addition to PRB with diffusive emitters. n/a n/a n/a
17 Buscheck, Nijhawan, and O’Reilly 2003 Unnamed site MtBE Mass discharge measured at three transects to evaluate natural attenuation of plume. n/a n/a n/a
18 Buscheck, Nijhawan, and O’Reilly 2003 10 fuel release sites in California MtBE Mass discharge values used to prioritize remediation. Shows sites with high Md values are not necessarily the sites with the highest concentrations. n/a n/a n/a
Case study ID Reference Site Constituents Use Mass flux/discharge measurement method Benefits of mass flux/mass discharge estimates Method used to estimate specific discharge
19 USEPA 2009 Well 12A
Superfund
Site,
Tacoma,
Washington
Chlorinated
solvents
Remedial action objectives and
remediation performance monitoring
—Based on computer modeling
results, it was determined that a
future reduction in mass discharge
from the source zone of 90% would
be sufficient to meet MCLs at the
compliance wells, allowing for a
future transition from active source
remediation to MNA in the plume.
Based on this work, an RAO
developed for the site is a 90%
reduction in mass discharge from the
source zone. A transect of
monitoring wells will be used to
evaluate changes to mass discharge
during active remediation and to
assess changes in mass flux at other
wells closer to the source zone. The
compliance transect includes six
horizontal locations with
approximate spacing of 400 ft
between locations, and each location
includes two to three nested wells.
The distribution of mass flux
changes over time will be used to
optimize the active remediation of
the source zone. The PFM will be
used to assess mass flux in
monitoring wells.
TM using PFM Use of a mass discharge reduction
as an interim remediation goal
provides a single metric for
evaluating the integrated effect of
source treatment and is directly
related to the source strength that
affects plume response to
remediation. A mass discharge
reduction goal can also be readily
compared to the range of mass
discharge reductions documented
as being achievable for various
technologies under site-specific
conditions.
PFM
Case study ID   Reference   Site   Constituents   Use Mass flux/discharge measurement method   Benefits of mass flux/mass discharge estimates   Method used to estimate specific discharge
20 Chapman and Parker 2005 Industrial site, Connecticut TCE Site characterization and remediation performance monitoring—Measured the mass discharge across a transect of MLS wells to evaluate the distribution of mass in the plume and assess the influence of source zone isolation conducted six years earlier. TM High-resolution vertical sampling resulted in an important refinement to the CSM because the zone of concentrated source strength in the aquifer is thinner than what was apparent based on conventional monitoring well data. A mass balance demonstrated that 3,000 kg of TCE was stored in the aquitard over a distance of 280 m downgradient from the source. Based on a conservative comparison to mass discharge across the plume transect after the DNAPL source had been isolated, the authors determined that it would take longer than 80 years for TCE mass stored in the aquitard to be removed. The measured mass discharge at the transect was also used in a mass balance to demonstrate that substantial mass depletion had occurred in the source zone due to natural dissolution over four decades prior to source zone isolation. Specific discharge was applied as a uniform value along the transect because the variability of K in the mildly heterogeneous aquifer was much smaller than the variability in TCE concentrations.
Case study ID   Reference   Site   Constituents   Use Mass flux/discharge measurement method   Benefits of mass flux/mass discharge estimates   Method used to estimate specific discharge
21 Chapman et al. 2007 Industrial site, Connecticut TCE, cis-1,2- DCE Site characterization—Evaluated processes contributing to natural attenuation of chlorinated solvents across three transects situated between the DNAPL source zone and a river. The three transects were located 280–700 m downgradient from the source zone. The mass discharge investigation was conducted to facilitate the characterization of processes causing the natural attenuation of TCE and by-products along the groundwater flow path and to support a detailed mass balance assessment. TM A detailed mass discharge assessment significantly improved the CSM for contaminant transport pathways and the relative quantitative contribution of multiple attenuation processes. The mass balance included quantitative prediction of the relative mass discharged to local drainage streams versus the mass discharged from groundwater to a downgradient river. The mass balance also included quantification of mass loss through volatilization in local surface-water ponds. Specific discharge was applied uniformly across all three transects.
22 Chapman et al. 1997 Former gasoline station, Ontario BTEX Remediation performance monitoring—Three transects were installed using MLS wells along each transect. The purpose of the transects was to evaluate the reduction in BTEX mass flux downgradient of a treatment zone consisting of passive wells containing oxygen-releasing compound between the first and second transect. Several monitoring events were conducted to evaluate changes to source mass discharge and treatment efficiency in the biobarrier over time. TM Mass discharge estimated at transects 2 and 3 was used to evaluate the degree to which natural attenuation was occurring downgradient of the biobarrier. The mass discharge calculations indicated that other organic and inorganic species represented significant sinks of oxygen which reduced the efficiency of BTEX treatment. Specific discharge was applied as a uniform value along both transects. “Given the relatively small variation in flow velocity observed and the number of other unknowns, the assumption of a uniform velocity field is justified for these first- approximation estimates. The assumption of a uniform velocity field is not expected to significantly bias the conclusions drawn from these mass flux estimates, since the conclusions are based on differences between Fences 1 and 2.”
23 Einarson et al. 2005 MtBE release site, Calistoga, California MtBE Mass discharge calculations suggest release from one site responsible for chemical impacts detected in supply well. n/a n/a n/a
Case study ID   Reference   Site   Constituents   Use Mass flux/discharge measurement method   Benefits of mass flux/mass discharge estimates   Method used to estimate specific discharge
24 Einarson and MacKay 2001 Port Hueneme, California MtBE Transect of MLS wells. TM n/a n/a
25 Einarson and MacKay 2001 Site 1, Alameda Naval Air Station cis-1,2-DCE Transect of MLS wells. TM n/a n/a
26 Einarson and MacKay 2001 Unnamed MtBE Transect of MLS wells. TM n/a n/a
27 Einarson and MacKay 2001 Vandenberg AFB, California MtBE Transect of MLS wells. TM n/a n/a
28 Guilbeault, Parker, and Cherry 2005 Florida TCE Site characterization—Measured the mass discharge across a transect downgradient of a source zone. TM High-resolution sampling improved the CMS with respect to hot-spot locations. Three distinct local high-concentration zones were identified with concentrations ranging 4%–15% of solubility. Approximately 60% of the source mass discharge was in <5% of the transect area, and 80% of the mass discharge was in <10% of the transect area. Specific discharge was applied as a uniform value along the transect because the variability of K in the mildly heterogeneous aquifer was much smaller than the variability in concentrations.
29 Parker et al. 2008 Florida TCE Remediation performance monitoring—Estimated the change in mass discharge across a transect due to the implementation of a hydraulic control remedy downgradient of the source zone. The estimate of mass discharge change due to the source zone containment system was based on temporal changes in groundwater concentrations at multilevel wells along the transect, assuming that there was no change in groundwater specific discharge across the transect. TM The estimated mass discharge occurring in the plume after the source zone had been hydraulically isolated was used to demonstrate that the mass stored in a thin clay layer is much higher than the mass discharge rate. This comparison was used to illustrate that back-diffusion from a thin clay represents a long-term process likely to sustain concentrations in the plume above MCLs. n/a
Case study ID   Reference   Site   Constituents   Use Mass flux/discharge measurement method   Benefits of mass flux/mass discharge estimates   Method used to estimate specific discharge
30 Guilbeault, Parker, and Cherry 2005 Ontario PCE Site characterization—Measured the mass discharge from the source zone across a transect. TM High-resolution sampling improved the CSM with respect to hot-spot locations. Four distinct local high-concentration zones were identified with concentrations as high as 16% of solubility. Approximately 60% of the source mass discharge was in <5% of the transect area, and 80% of the mass discharge was in <10% of the transect area. Specific discharge was applied as a uniform value along the transect because the variability of K in the mildly heterogeneous aquifer was much smaller than the variability in concentrations.
31 Guilbeault, Parker, and Cherry 2005 New Hampshire PCE Site characterization—Measured the mass discharge from the source zone across a transect. TM High-resolution sampling improved the CSM with respect to hot-spot locations. Fifteen distinct local high-concentration zones were identified with concentrations 1%–62% of solubility. Approximately 60% of the source mass discharge was in <5% of the transect area, and 80% of the mass discharge was in <10% of the transect area. Used two specific discharge zones: one above and one below a clay layer. The hydraulic conductivity of the clay layer is orders of magnitude less than the sand layers, so the clay layer was ignored in the mass flux and mass discharge calculations, and the thickness of the clay was subtracted in the areal elements where it was present.
32 D’Affonseca et al. 2008 Coal tar site near Hamburg, Germany Naphthalene Site characterization—Used a transect with three well clusters over a total width of 60 m, with three vertical well screens at each cluster location. Also used the IPT with one extraction well having a capture zone width of 15 m. The purpose was to evaluate DNAPL architecture in the source zone. Two- and three- dimensional modeling of multicomponent DNAPL depletion was conducted, and simulated mass discharge was compared to estimated values based on field data. TM, IPT Vertical delineation of mass flux confirmed that one portion of the source zone was contributing a majority of the discharge making up the total source strength. Modeling illustrated that the mass flux of naphthalene has likely reached its peak and will begin to decline over time. Field and model data were used to evaluate the potential benefits and limitations of partial mass removal on downgradient mass discharge trends. Specific discharge was applied uniformly across the transect.
Case study ID   Reference   Site   Constituents   Use Mass flux/discharge measurement method   Benefits of mass flux/mass discharge estimates   Method used to estimate specific discharge
33 DiFillippo and Brusseau 2008 Several sites, North America Various Remediation performance assessment—Evaluated the relationship between mass discharge reduction and source mass depletion for 21 remediation projects. Various n/a n/a
34 Ellis, Mackat, and Rivett 2007 River Tame, U.K. Inorganic parameters Regional characterization— Estimated mass discharge of various inorganic parameters from the Birmingham Aquifer to River Tame. n/a Provided a quantitative comparison of the degree of base flow loading to the river relative to contributions from other sources of surface water. n/a
35 Ford, Wilklin, and Hernandez 2006 Superfund site, Massachu- setts Arsenic Site characterization—Used arsenic mass flux calculations to compare the relative contribution of groundwater discharge and sediment dissolution/desorption to arsenic in surface water. Synoptic sampling n/a n/a
36 Goltz et al. 2009 Test site, New Zealand Bromide and nitrate Measurement method validation— Used an artificial aquifer with dimensions of 9.5 × 4.7 × 2.6 m to validate TCW methods and to compare to the MIPT method. TCW, MIPT n/a n/a
37 Imbrigiotta et al. 1997 Picatinny Arsenal, New Jersey TCE Conducted a detailed mass balance to assess relative contributions of various processes representing gains and losses for plume mass. The mass discharge to a brook downgradient from the source zone was included in the mass balance assessment. Hand calculations n/a n/a
38 Johnson, Truex, and Clement 2006 Unidenti- fied site Unknown Remedial design—Demonstrated an example application where RT3D was used to estimate the plume mass discharge corresponding to different remedial alternatives. Modeled n/a n/a
Case study ID   Reference   Site   Constituents   Use Mass flux/discharge measurement method   Benefits of mass flux/mass discharge estimates   Method used to estimate specific discharge
39 Kao and Wang 2001 Gasoline spill site, Garysburg, North Carolina BTEX Site characterization—Used mass discharge estimates from three transects at distances of 8, 48, and 88 m downgradient of the source zone to estimate natural biodegradation rates. TM Plume attenuation rates were estimated based on declines in mass discharge between transects, independent of transverse horizontal and vertical dispersivity estimates. Specific discharge was applied uniformly across all transects.
40 Landmeyer et al. 2001 Gasoline station near Beaufort, South Carolina MtBE Site characterization—Used mass discharge estimates across three transects adjacent to a creek receiving groundwater discharge. Results showed that MtBE was undergoing extensive biodegradation in a small oxic zone caused by mixing of groundwater and surface water adjacent to the creek. TM n/a n/a
41 Pitz 1999 South Puget Sound, Washington Nitrate Site characterization—Estimated nitrate mass loading to South Puget Sound by groundwater discharge. Recharge zone method Nitrate mass discharge estimates facilitate tracking of annual changes in nutrient loading to South Puget Sound. n/a
42 Ricker 2008 Former wood treating site, Louisiana Naphthalene Site characterization—Estimated temporal changes to dissolved plume mass and the potential for downgradient migration of the plume center of mass, as part of a plume stability evaluation. n/a Analysis of plume stability based on individual well trends can be challenging when some wells show a decreasing trend and other wells show an increasing or stable trend. This study demonstrated the application of plume dissolved mass and the center of mass location over time to demonstrate that the naphthalene plume is shrinking over time. n/a
43 Semprini et al. 1995; Weaver Wilson, and Kampbell 1997 St. Joseph, Michigan Total ethenes Site characterization—Used multiple transects to evaluate natural attenuation rates along the groundwater flow path. TM Estimated natural attenuation rates based on mass discharge are independent of dispersivity estimates and less susceptible to transient fluctuations in groundwater flow direction and uncertainty in the location of the plume centerline. Not specified
Case study ID   Reference   Site   Constituents   Use Mass flux/discharge measurement method   Benefits of mass flux/mass discharge estimates   Method used to estimate specific discharge
44 Thomson, Hood, and Farquhar 2007 CFB Borden, Ontario TCE, PCE Remediation performance assessment—Used a transect of MLS wells to compare pre- and post-treatment mass flux distribution and mass discharge. TM n/a n/a
45 Thomson, Hood, and Farquhar 2007 Coal tar creosote source, Borden, Ontario PAHs, BTEX Remediation performance assessment—Conducted a mass balance to evaluate efficiency of permanganate injections and evaluated changes to mass discharge associated with source treatment. n/a A detailed mass balance involving permanganate and contaminated species was critical to evaluating the efficiency of remedial injections. Temporal fluctuations in mass discharge and plume mass provided valuable information regarding the effectiveness of source treatment and the corresponding influence on downgradient plume response. n/a
46 Thuma, Kremesec, and Kolhatkar 2001 Long Island MtBE Site characterization—Calculated mass flux across several transects downgradient from the source zone using monitoring well concentration data and compared these data to calculations from a solute transport model to validate the model calibration. TM, solute transport model Mass flux data were used to demonstrate natural attenuation due to biodegradation was occurring along the groundwater flow path. Using mass discharge as a model calibration target provides an important metric that may help to improve the representativeness of the calibrated model. n/a
47 Kingston 2008 (Table 5.5) Thermal Treatment Site 1 Total VOCs Remediation performance assessment. TM n/a n/a
48 Kingston 2008 (Table 5.5) Thermal Treatment Site 2 Total VOCs Remediation performance assessment. TM n/a n/a
49 Kingston 2008 (Table 5.5) Thermal Treatment Site 3 Total VOCs Remediation performance assessment. TM n/a n/a
50 Kingston 2008 (Table 5.5) Thermal Treatment Site 4 Total VOCs Remediation performance assessment. TM n/a n/a
Case study ID   Reference   Site   Constituents   Use Mass flux/discharge measurement method   Benefits of mass flux/mass discharge estimates   Method used to estimate specific discharge
51 Kingston 2008 (Table 5.5) Thermal Treatment Site 5 Total VOCs Remediation performance assessment. TM n/a n/a
52 Kingston 2008 (Table 5.5) Thermal Treatment Site 6 Total VOCs Remediation performance assessment. TM n/a n/a
53 Kingston 2008 (Table 5.5) Thermal Treatment Site 7 Total VOCs Remediation performance assessment. TM n/a n/a
54 Kingston 2008 (Table 5.5) Thermal Treatment Site 9 Total VOCs Remediation performance assessment. TM n/a n/a
55 Kingston 2008 (Table 5.5) Thermal Treatment Site 11 Total VOCs Remediation performance assessment. TM n/a n/a
56 Kingston 2008 (Table 5.5) Thermal Treatment Site 12 Total VOCs Remediation performance assessment. TM n/a n/a
57 Kingston 2008 (Table 5.5) Thermal Treatment Site 14 Total VOCs Remediation performance assessment. TM n/a n/a
58 Kingston 2008 (Table 5.5) Thermal Treatment Site 15 Total VOCs Remediation performance assessment. TM n/a n/a
59 Kingston 2008 (Table 5.5) Thermal Treatment Site 16 Total VOCs Remediation performance assessment. TM n/a n/a
60 Kingston 2008 (Table 5.5) Thermal Treatment Site 18 Total VOCs Remediation performance assessment. TM n/a n/a
Case study ID   Reference   Site   Constituents   Use Mass flux/discharge measurement method   Benefits of mass flux/mass discharge estimates   Method used to estimate specific discharge
61 Troldborg et al. 2008 Naerum Supply Well Field, Denmark   Risk prioritization and forensic evaluation—A model decision support tool is applied to evaluate the site(s) causing contamination at a water supply well field. Estimated source mass discharge from multiple sites are input to a regional groundwater model to evaluate the relative risks and contribution to pollution at the water supply wells. Groundwater flow and transport models Prioritization of site cleanup is based on a quantitative assessment of relative risks to the downgradient receptors for multiple sites. This method also identified the sites most likely to be contributing to pollution at the water supply wells. n/a

Table A-2. Mass flux/discharge methods and configuration

Case study ID     Reference   Sample collection device for mass flux estimation   Method used to estimate specific discharge # transects perpen- dicular to ground- water flow   Width of transect(s) (m) # transects parallel to ground- water flow Horizontal spacing along transects   # vertical wells on transects Vertical well screen lengths (m) Vertical interval between screens (m)
2 Barbaro and Neupane 2006 Direct-push rig used to vibrate drill rods to deepest sampling depth (12– 15 m bgs). Stainless steel well screen was then exposed to aquifer. Samples extracted with peristaltic pump using Teflon tubing. Then drill rod with exposed screen was pulled up to next sampling depth. Stability of drill string indicated that borehole collapsed below sampling depth, which “minimized cross contamination.” Used a uniform specific discharge across both transects based on relatively uniform head distribution, lithology, and aquifer thickness in the vicinity of the two transects. 7 130–380 Not applicable (n/a) 40–45 m 3–4 1.2 2.4
Case study ID     Reference   Sample collection device for mass flux estimation   Method used to estimate specific discharge # transects perpen- dicular to ground- water flow   Width of transect(s) (m) # transects parallel to ground- water flow Horizontal spacing along transects   # vertical wells on transects Vertical well screen lengths (m) Vertical interval between screens (m)
5 Basu et al. 2009 Longitudinal transect along plume centerline: PFMs installed in wells for time-integrated mass flux measurements for periods of 6 and 72 days. Source and plume transects perpendicular to flow: PFMs installed in wells for time-integrated mass flux measurement over 20 days. PFMs also deployed in a two-screen well nest during three flux sampling periods described above to measure seasonal variability in groundwater flux distribution. PFMs were used to quantify specific discharge at approximately 0.3 m intervals over different periods of time to allow for assessment of seasonal fluctuations. 2 13–40 1 Source transect: 3–6 m spacing, plume transect: 15–21 m spacing Total of 2– 3 screens in each well nest over two aquifers separated by a 1–2- m-thick clay confining unit 2–6 2–5
9 Bockelmann et al. 2003 Groundwater samples from permanent wells Not specified 3 n/a n/a 30–39 1 n/a n/a
10 Borden et al. 1997 Groundwater samples from permanent wells Not specified 4 n/a n/a 10–16 3 1.5 m well screens to provide flux- averaged concentra- tions across screen, for purpose of estimating mass discharge at the transect 0–1 m on cross section parallel to ground- water flow
Case study ID     Reference   Sample collection device for mass flux estimation   Method used to estimate specific discharge # transects perpen- dicular to ground- water flow   Width of transect(s) (m) # transects parallel to ground- water flow Horizontal spacing along transects   # vertical wells on transects Vertical well screen lengths (m) Vertical interval between screens (m)
11 Brooks et al. 2008 PFM sorbent was silver- impregnated granular activated carbon. PFMs were constructed to match the saturated thickness in each well, and multiple PFMs (1.5 m long) were deployed as needed in wells to cover well screen intervals longer than 1.5 m. Each PFM sock was divided into 25-cm- long segments separated using Norprene rubber washers to prevent vertical water flow in the PFM and section the device upon retrieval. PFM, IPT 1 n/a n/a 3 1 3-m-long screens completed across the entire saturated thickness of the aquifer n/a
12 Brooks et al. 2008 PFM, IPT 1 n/a 10 6.1 1 7.5 n/a
19 USEPA 2009 Passive flux meters PFM 1 500 n/a 100 2 n/a n/a
20 Chapman and Parker 2005 “Groundwater samples were collected using a peristaltic pump and dedicated sampling tubes. After purging at least two tubing volumes, the pump was shut off (maintaining the vacuum at surface), the sample tube withdrawn from the multilevel point, the pump reversed or suction released, and groundwater in the sample tube pumped or drained into a 25-mL VOA vial……………….. ” Specific discharge was applied as a uniform value along the transect because the variability of K in the mildly heterogeneous aquifer was much smaller than the variability in TCE concentrations. 1 485 n/a Average: 24 m, minimum: 7 m, maximum: 47 m 4–8 0.10–0.15 0.3–1
Case study ID     Reference   Sample collection device for mass flux estimation   Method used to estimate specific discharge # transects perpen- dicular to ground- water flow   Width of transect(s) (m) # transects parallel to ground- water flow Horizontal spacing along transects   # vertical wells on transects Vertical well screen lengths (m) Vertical interval between screens (m)
21 Chapman et al. 2007   Specific discharge 3 485–590 n/a Average MLSs: 4– MLSs: MLSs:
  was applied uniformly       spacing on 8, 0.10–0.15, 0.3–1,
    across all three       transects Waterloo Waterloo Waterloo
    transects.       ranged profiler: profiler: profiler:
            from 24 m varied, depth- 0.15–0.6,
            upgradient piezo- discrete, piezo-
            to 41 m meters: 3– piezometers: meters: 3–
            down- 5 0.10–0.15 4 screens
            gradient     over 3 m
                  thickness
                  or 3–5
                  screens
                  over 2 m
                  thickness
Case study ID     Reference   Sample collection device for mass flux estimation   Method used to estimate specific discharge # transects perpen- dicular to ground- water flow   Width of transect(s) (m) # transects parallel to ground- water flow Horizontal spacing along transects   # vertical wells on transects Vertical well screen lengths (m) Vertical interval between screens (m)
22 Chapman et al. 1997 Groundwater samples from permanent wells Specific discharge was applied as a uniform value along both transects. “Given the relatively small variation in flow velocity observed and the number of other unknowns, the assumption of a uniform velocity field is justified for these first-approximation estimates. The assumption of a uniform velocity field is not expected to significantly bias the conclusions drawn from these mass flux estimates, since the conclusions are based on differences between Fences 1 and 2.” 3 2 n/a 0.3 6 n/a 0.15
28 Guilbeault, Parker, and Cherry 2005 Waterloo profiler (temporary) and permanent multilevel wells Specific discharge was applied as a uniform value along the transect because the variability of K in the mildly heterogeneous aquifer was much smaller than the variability in concentrations. 1 40 n/a Average of 3 m Average of 25 vertical samples per profile location Depth- discrete Varies, minimum spacing of 0.15
Case study ID     Reference   Sample collection device for mass flux estimation   Method used to estimate specific discharge # transects perpen- dicular to ground- water flow   Width of transect(s) (m) # transects parallel to ground- water flow Horizontal spacing along transects   # vertical wells on transects Vertical well screen lengths (m) Vertical interval between screens (m)
30 Guilbeault, Parker, and Cherry 2005 Waterloo profiler (temporary) and permanent multilevel wells Specific discharge was applied as a uniform value along the transect because the variability of K in the mildly heterogeneous aquifer was much smaller than the variability in concentrations. 1 72 n/a Average of 5 m Average of 10 vertical samples per profile location Depth- discrete Varies, minimum spacing of 0.15 m
31 Guilbeault, Parker, and Cherry 2005 Waterloo profiler (temporary) Used two specific discharge zones: one above and one below a clay layer. The hydraulic conductivity of the clay layer is orders of magnitude less than the sand layers, so the clay layer was ignored in the mass flux and mass discharge calculations, and the thickness of the clay was subtracted in the areal elements where it was present. 1 27 n/a Average of 2 m Average of 12 vertical samples per profile location Depth- discrete Varies, minimum spacing of 0.15 m
32 D’Affonseca et al. 2008 Groundwater samples from permanent wells Specific discharge was applied uniformly across the transect. 1 60 n/a 30 3 3.7 9
39 Kao and Wang 2001 Groundwater samples from permanent wells Specific discharge was applied uniformly across all transects. 3 32 n/a 8 4 0.6 1.2
Case study ID     Reference   Sample collection device for mass flux estimation   Method used to estimate specific discharge # transects perpen- dicular to ground- water flow   Width of transect(s) (m) # transects parallel to ground- water flow Horizontal spacing along transects   # vertical wells on transects Vertical well screen lengths (m) Vertical interval between screens (m)
43 Semprini et al. 1995; Weaver, Wilson, and Kampbell 1997 Auger with 5 ft well screen, collected samples at continuous 5 ft intervals Not specified 4 115–200 1 19–50 Various 1.5 0 (contin- uous 5 ft sample intervals using a slotted auger)

Table A-3. Mass flux/discharge estimates pre- and post-treatment

Case study ID   Constituents   Treatment process   Pretreatment mass discharge (kg/y) Post-treatment mass discharge (kg/y)   % reduction pre vs. post
41 Nitrate   Nitrate: 160,000–190,000 Not applicable (n/a) n/a
8 BTEX, PAH Natural attenuation between transects due to Chloride: 38,832 Chloride: 37,588 Chloride: 3%
    biodegradation. Pre- and post-treatment represent Total BTEX: 0.7 Total BTEX: 0.04 Total BTEX: 94%
    mass discharge values from transects at distances Total PAH: 12 Total PAH: 5 Total PAH: 58%
    of approximately 140 m (pretreatment) and 280 m NO3: 88 NO3: 274 NO3: –211%
    (post-treatment) downgradient from the source Mn(II): 254 Mn(II): 161 Mn(II): 37%
    zone. Fe(II): 770 Fe(II): 1,142 Fe(II): –48%
      SO4: 79,351 SO4: 77,468 SO4: 2%
51 Total VOCs Thermal treatment. 680 82 88%
37 TCE Natural attenuation via biodegradation and Gains: n/a n/a
    volatilization. Desorption: 550    
      Infiltration: <1    
      DNAPL dissolution: unknown    
      Losses:    
      Biodegradation: 360    
      Discharge to surface water: 50    
      Volatilization: 50    
      Dispersion: <1    
      Sorption: <1    
Case study ID   Constituents   Treatment process   Pretreatment mass discharge (kg/y) Post-treatment mass discharge (kg/y)   % reduction pre vs. post
20 TCE A sheet pile enclosure was installed around the DNAPL source zone. Mass discharge was estimated across the transect at a distance of 280 m downgradient from the source zone six years after source isolation. The investigators estimated that the mass discharge prior to source zone isolation was 10 times higher than the post-isolation mass discharge, based on the observed magnitude of changes in TCE concentrations in monitoring wells over this time period. 360 (estimated) 36 (measured) 90% (Complete restoration was not obtained due to back- diffusion from the silt aquitard to the aqueous plume outside the isolated source zone.)
43 Total ethenes Natural attenuation via biodegradation. Pre- and post-treatment mass discharge values represent calculations for transects situated 130 and 855 m downgradient of the source zone (i.e., separation distance of 745 m over which natural attenuation was evaluated). TCE: 120 DCE: 130 Vinyl chloride: 17 Ethene: 7.6 Total ethenes: 280 Methane: 66 Chloride: 1,500 TCE: 0.95 DCE: 10 Vinyl chloride: 1.7 Ethene: 0.16 Total ethenes: 13 Methane: 47 Chloride: 5,300 TCE: 99.2% DCE: 92% Vinyl chloride: 90% Ethene: 98% Total ethenes: 95% Methane: 29% Chloride: –250%
12 TCE Thermal treatment and multiphase extraction. PFM: 240 MIPT: 170 TM: 220 Average: 210 PFM: 0.84 MIPT: 0.55 TM: 0.69 Average: 0.69 PFM: 99.6% MIPT: 99.7% TM: 99.7% Average: 99.7%
4 TCE Natural attenuation between transects due to reductive dechlorination. Pre- and post-treatment represent mass discharge values from transects at distances of approximately. 0 m (pretreatment) and 31 m (post-treatment) downgradient from the source zone. MW8-99 (x = 0): 201 MW2-98 (x = 12m): 133 MW-13I (x = 31m): 100 50% over 31 m downgradient from source zone
32 Naphthalene n/a 176 n/a n/a
3 Total chlorinated organics n/a 100 n/a n/a
12 cis-1,2-DCE Thermal treatment and multiphase extraction. PFM: 49 MIPT: 82 TM: 92 Average: 74 PFM: 1.4 MIPT: 0 TM: 0 Average: 0.47 PFM: 97% MIPT: 100% TM: 100% Average: 99.4%
Case study ID   Constituents   Treatment process   Pretreatment mass discharge (kg/y) Post-treatment mass discharge (kg/y)   % reduction pre vs. post
46 MtBE Natural attenuation via biodegradation. Pre- and post-treatment mass discharge values represent the calculated flux at transects situated approximately 1000 and 4400 feet downgradient of the source zone. 91 4 95.6%
48 Total VOCs Thermal treatment. 60 4.9/21 65%/92%
24 MtBE n/a 55 n/a n/a
47 Total VOCs Thermal treatment. 52 0.19 99.63%
49 Total VOCs Thermal treatment. 49 0.13 99.73%
28 TCE n/a 31–45 n/a n/a
21 TCE, cis-1,2- DCE Natural attenuation in via biodegradation and discharge to the on-site pond and drainage creeks where dilution and volatilization occurred. Mass discharge values represent Transects 1 and 3, separated by a distance of 420 m and a travel time of several years. TCE: 36 cis-1,2-DCE: 0.84 TCE: 0.07 cis-1,2-DCE: 0.11 TCE: 99.80% cis-1,2-DCE: 86.96%
50 Total VOCs Thermal treatment. 32 2.1 93%
11 TCE Surfactant-enhanced aquifer restoration (SEAR). PFM: 28 MIPT: 28 TM: 28 Average: 28 PFM: 2.2 MIPT: 1.4 TM: 2.6 Average: 2.1 PFM: 92% MIPT: 95% TM: 91% Average: 93%
39 BTEX Natural attenuation via biodegradation. Mass discharge values for pre- and post-treatment represent transects at distances of 8 and 88 m downgradient of the source zone. Benzene: 11 Toluene: 5.2 Ethylbenzene: 1.5 m- and p-xylene: 1.9 o-xylene: 1.7 1,2,4-trimethylbenzene (TMB): 1.1 Total BTEX: 22.3 Benzene: 1.6 Toluene: 0.064 Ethylbenzene: 0.29 m- and p-xylene: 0.16 o-xylene: 0.080 1,2,4-TMB: 0.56 Total BTEX: 2.8 Benzene: 85% Toluene: 98.8% Ethylbenzene: 81% m- and p-xylene: 92% o-xylene: 95% 1,2,4-TMB: 48% Total BTEX: 88%
30 PCE n/a 20.5 n/a n/a
31 PCE n/a 15 n/a n/a
25 cis-1,2-DCE n/a 11 n/a n/a
53 Total VOCs Thermal treatment. 9.4 0.027 99.71%
59 Total VOCs Thermal treatment, 9.3 0.017 99.82%
6 PCE, TCE n/a PCE: 8.2 TCE: 0.82 n/a n/a
52 Total VOCs Thermal treatment. 4.6 0.073 98.41%
27 MtBE n/a 0.44–2.5 n/a n/a
Case study ID   Constituents   Treatment process   Pretreatment mass discharge (kg/y) Post-treatment mass discharge (kg/y)   % reduction pre vs. post
5 TCE n/a Source: 1.1 Plume (x = 175 m): 2.1 n/a n/a
54 Total VOCs Thermal treatment. 1.7 0.6 65%
26 MtBE n/a 1.5 n/a n/a
11 cis-1,2-DCE SEAR DCE below level of quantification PFM: 1.1 MIPT: 0.73 TM: 1.4 Average: 1.1 n/a
60 Total VOCs Thermal treatment. 1.3 2.8 –115%
58 Total VOCs Thermal treatment. 1.2 0.054 96%
2 VOCs Natural attenuation between transects (possibly oxidation of cis-DCE under iron-reducing conditions). Pre- and post-treatment represent mass discharge values from transects at 91 m (pretreatment) and 335 m (post-treatment) downgradient from the source zone. PCE: 0.19 TCE: 0.35 cis-DCE: 0.20 PCE: 0.20 TCE: 0.38 cis-DCE: 0.07 PCE: n/a TCE: n/a cis-DCE: 65%
44 TCE, PCE In situ chemical oxidation with potassium permanganate recycling for 485 days followed by 180 days of enhanced flushing in the source zone via groundwater extraction. TCE: 0.31 PCE: 0.32 TCE: 0.0026 PCE: 0.036 TCE: 99.2% PCE: 89%
40 MtBE Natural attenuation via biodegradation. Mass discharge values for pre- and post-treatment represent transects separated by less than 6.5 m adjacent to the creek. 0.51 0.019 96%
55 Total VOCs Thermal treatment. 0.40 0.03 93%
57 Total VOCs Thermal treatment. 0.097 0.061 37%
56 Total VOCs Thermal treatment. 0.019 1.80 × 10–7 100.00%
29 TCE n/a n/a n/a 90%–99% (Complete restoration was not obtained due to back- diffusion from the silt and clay lenses to the aqueous plume outside the contained source zone.)
Case study ID   Constituents   Treatment process   Pretreatment mass discharge (kg/y) Post-treatment mass discharge (kg/y)   % reduction pre vs. post
10 MtBE, BTEX Natural attenuation via biodegradation and volatilization. Mass discharge reduction efficiency volatilization. Mass discharge reduction efficiency represent the difference in mass discharge between the source zone and a transect located 88 m downgradient of the source zone. n/a n/a Toluene: >99%
Ethylbenzene: >99%
m- and p-xylene: >99%
o-xylene: 89%
Benzene: 87%
MtBE: 74%

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Use and Measurement of Mass Flux and Mass Discharge

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