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

Plume Architecture

Abstracts of Journal Articles

Accurate Assessment of Natural Attenuation using Depth Discrete Multi-Level Monitoring: Evidence at Three Chlorinated Solvent Sites
Guilbeault, M.A. (Univ. of Waterloo, Waterloo, Ontario, Canada); B.L. Parker; J.A. Cherry. 2001 International Containment & Remediation Technology Conference & Exhibition, 10-13 June 2001, Orlando, Florida. Conference Program Abstracts. Florida State Univ., Tallahassee. p 120, 2001

Releases of PCE and TCE decades ago at three industrial sites in Florida, New Hampshire, and Ontario formed suspended DNAPL source zones and dissolved phase plumes within sandy aquifers. Detailed multi-level monitoring of ground-water concentrations along transects orthogonal to flow was performed at all three sites to examine natural attenuation processes. The Waterloo Profiler and permanently installed multi-level bundle samplers were driven by an Enviro-Core direct-push rig at more than 70 locations and used at a vertical spacing as close as 15 cm to determine peak concentrations within the source areas and downgradient dissolved phase plumes, where conventional monitoring wells had underestimated peak concentrations and even the location of the plume. Continuous cores used to determine stratigraphy and concentration profiles showed that the maximum concentration peaks along vertical profiles were extremely sharp and varied a maximum of 4.5 orders of magnitude over a vertical interval as small as 30 cm. The high resolution sampling showed that 90% of the mass discharge occurs within less than 20% of the transect cross-sectional area at each site. All three sites showed strong attenuation of peak concentrations from solubility to less than 15% (Ontario), 10% (New Hampshire), and 1% (Florida) of solubility within 10 m, 5 m, and 30 m, respectively. Dispersion was the dominant attenuation mechanism at all three sites and degradation accounted for considerable attenuation at the Florida site.

Detailed Vertical and Lateral Delineation of Redox Zones in Contaminant Plumes Using Redox-Sensitive Tapes (RST)
Blum, P. (Eberhard-Karls Univ. Tuebingen, Germany); F.D. Oeste (gM-Ingenieurbuero, Kirchhain, Germany); R. Melzer (URS Deutschland GmbH, Hannover, Germany); P. Martus (URS Canada Inc., Vancouver, BC). Eos, Transactions of the AGU, Vol 87 No 52, Abstract B53B-0345, 2006

Innovative redox-sensitive tape (RST) has been developed for a detailed vertical and lateral delineation of redox zones in contaminated aquifers. The tape consists of a synthetic textile 2 cm wide and coated with reactive manganese dioxide minerals. RST is submerged into existing monitoring wells for approximately one month, which is sufficient time to allow for a reaction of the mineral coating with ground water. RST can be used to investigate four different redox zones in contaminated aquifers: Mn(II)-oxidizing, Mn(IV)-reducing, Fe(III)-reducing, and sulfate-reducing. Two RST case studies are presented. RST investigations on a coal tar-contaminated site allowed for a precise lateral and vertical delineation of the contaminant plume via the existing monitoring well network. RST investigations on a BTEX-contaminated site showed good correlation of RST data with hydrochemical data in sampled wells. Repeated application of RST facilitated an assessment of the plume dynamics. RSTs have the potential to become an integral part of a data acquisition strategy for monitored natural attenuation.

Investigation of NA Processes at Reactive Fringes: Sampling Bias Introduced by High Resolution Multi-Level Monitoring
Piepenbrink, M. (Univ. of Tuebingen, Tuebingen, Germany); T. Ptak (Univ. of Goettingen, Goettingen, Germany); P. Grathwohl (Univ. of Tuebingen). Eos Trans. AGU, Vol 86 No 52, Fall Meet. Suppl., Abstract B31A-0966, 2005

High-resolution multi-level sampling (MLS) in the order of decimeters or less is an essential prerequisite for the investigation of natural attenuation processes at the reactive fringes at field scale. In contrast to engineered remediation techniques that usually address high contaminant concentration levels close to the source zone, monitored natural attenuation (MNA) relies heavily on the accuracy of the low concentration levels (down to the legal limits) measured in the plume. These data are often strongly biased due to the monitoring equipment. This paper presents results from ongoing controlled laboratory material tests and research on high-resolution MLS at six field sites. The focus was on a optimized site-specific hydraulic design and contaminant/MLS-material interaction. The most acceptable solutions (MLS resolution on the order of 0.1m) were found using sampling tubes with a small inner diameter (3-4 mm), which resulted in a small stagnant water volume prior to sampling, but was still not problematic with respect to the flow induced hydraulic losses within the tube. The authors present two major conclusions of the study to date. (1) Due to sorptive losses in dedicated, pristine tubing material, MLS systems tend to underestimate the contaminant concentrations, which leads to an overestimation of the NA potential. To avoid this false negative concentration bias, the most inert tubing material should be used. (2) Due to leaching of plasticizers (e.g., phthlates) out of the pristine tubing material, MLS systems tend to overestimate TOC sum parameters. To avoid this false positive concentration, only polymers with no or low plasticizer content should be used.

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