Stanley Feenstra

Transport of a dissolved-phase plume from a residual solvent source in a sand aquifer

Abstract The occurrence of groundwater contamination by chlorinated solvents is widespread throughout the industrialised world. Because these solvents have a density greater than water, the sources of contaminant groundwater plumes in many cases are expected to be pools and zones of residual solvent that are located below the water table. A tracer experiment designed to provide a simplified simulation of the above scenario has been conducted at the University of Waterloo Borden field site. A homogeneous block of sand containing residual solvent at 5% residual saturation of the pore space was emplaced 1 m below the water table. This source zone measured 1.5 × 1 × 0.5 m and contained a mixture of chloroform (TCM), trichloroethylene (TCE), perchloroethylene (PCE) and gypsum powder to provide sulfate as a conservative inorganic tracer. Subsequent groundwater flow through the source zone created a continuous plume of dissolved solutes down-gradient. The plume was monitored by a three-dimensional array of over 2300 sampling points and after 15 months extended 60 m from the source. This paper presents an overview of the experiment, with field results of source dissolution and dissolved-phase plume transport. The field results were selected to give an indication of the complexity of the observed field data. Some preliminary modeling of the data to estimate the approximate magnitude of dispersion parameters and comparison of these values with other tracer tests is presented.

Lyne and McLachlan (1949): Influence of the First Publication on Groundwater Contamination by Trichloroethene

The historical context and influence of the worlds first published case of trichloroethene (TCE) contamination of groundwater by Lyne and McLachlan (1949) in The Analyst is established. Archive data and literature review, local reconnaissance, and consultation with relevant professionals were undertaken. Lyne and McLachlan were public analysts, officials authorized to provide certified (chemical) analysis, responsible for several United Kingdom (U.K.) local authority jurisdictions. They chiefly provided chemical analysis to support health risk assessments, particularly for foodstuffs. Their 1940s TCE-contaminated groundwater work appears isolated with no evidence of further related work by them. The influence of the publication was highly limited i.e., it was insignificant in contributing to the development of the general recognition of the solvents-in-groundwater problem. Although widely cited in 1950 to 1951 abstract listings, it was (until recently) only cited subsequently in a 1957 German-language Austrian journal and in a 1961 United States (U.S.) Federal Housing Administration report. The publication was essentially lost until the mid-1990s, when it began to be cited in U.S. legal cases. Overviews of development in awareness of the TCE-contamination in groundwater around the 1970s at local, national (U.K.) and international levels indicates that Lyne and McLachlan did not trigger any general recognition of this problem in the scientific, engineering, or regulatory communities over the previous 30 years. The publication appears unknown in the U.K. until after 2000, and it is quite possible that Lyne and McLachlan themselves never truly appreciated the potential prescience of their early work on this now notorious groundwater contaminant.

Heterogeneous carbonaceous matter in sedimentary rock lithocomponents causes significant trichloroethylene (TCE) sorption in a low organic carbon content aquifer/aquitard system.

This study evaluated the effects of heterogeneous thermally altered carbonaceous matter (CM) on trichloroethylene (TCE) sorption for a low fraction organic carbon content (foc) alluvial sedimentary aquifer and aquitard system (foc=0.046-0.105%). The equilibrium TCE sorption isotherms were highly nonlinear with Freundlich exponents of 0.46-0.58. Kerogen+black carbon was the dominant CM fraction extracted from the sediments and accounted for >60% and 99% of the total in the sands and silt, respectively. Organic petrological examination determined that the kerogen included abundant amorphous organic matter (bituminite), likely of marine origin. The dark calcareous siltstone exhibited the greatest TCE sorption among aquifer lithocomponents and accounted for most sorption in the aquifer. The results suggest that the source of the thermally altered CM, which causes nonlinear sorption, was derived from parent Paleozoic marine carbonate rocks that outcrop throughout much of New York State. A synthetic aquifer-aquitard unit system (10% aquitard) was used to illustrate the effect of the observed nonlinear sorption on mass storage potential at equilibrium. The calculation showed that >80% of TCE mass contained in the aquifer was sorbed on the aquifer sediment at aqueous concentration <1000 μgL(-1). These results show that sorption is likely a significant contributor to the persistence of a TCE groundwater plume in the aquifer studied. It is implied that sorption may similarly contribute to TCE persistence in other glacial alluvial aquifers with similar geologic characteristics, i.e., comprised of sedimentary rock lithocomponents that contain thermally altered CM.

Use of Logarithmic-Scale Correlation Plots to Represent Contaminant Ratios for Evaluation of Subsurface Environmental Data

Contaminant concentration ratios are used commonly to distinguish between different sources of contamination and to evaluate contaminant attenuation in groundwater, soil air, soil, and sediment. Logarithmic-scale correlation (log-log) plots provide special capabilities in representing contaminant ratios. Log-log plots can reflect the ranges in concentrations over many orders of magnitude, the magnitude and ranges of concentration ratios, and whether ratios are constant or change with declining concentration. Declines in contaminant concentrations due to dilution and dispersion processes will not change contaminant ratios, and such data should plot along isoratio lines. If contaminant concentrations are reduced also by other attenuation processes such as sorption or biodegradation that affect one of the contaminants to a greater degree than the other, the ratio will change and the data will deviate from the isoratio line trends. Examples are given to illustrate the use of log-log plots in the interpretation of chemical data from sites of groundwater, soil air, and sediment contamination.

Groundwater Pollution: The Emerging Role of Environmental Forensics

In recent years, subsurface forensics has emerged as a definable subject area in the field of contaminant hydrogeology or groundwater pollution. For the purpose of this chapter, a definition modified from Morrison and Murphy1 will be employed. Subsurface forensics will refer to: ‘the systematic and ...