Publications

Multivariate correlations between the concentrations of selected herbicides and herbicide derivatives in outflows from selected reservoirs in the Midwestern United States for April 1992 through September 1993 were investigated using principal component analysis (PCA) and multivariate curve resolution (MCR). Two independent sources for alachlor ethanesulfonic acid, one major source...

No abstract available.

A new approach is presented to condition geostatistical simulation of high‐permeability zones in fractured rock to hydraulic‐connection data. A simulated‐annealing algorithm generates three‐dimensional (3‐D) realizations conditioned to borehole data, inferred hydraulic connections between packer‐isolated borehole intervals, and an indicator (fracture zone or background‐K bedrock)...

A comparative assessment of two reactive-transport models, PHREEQC and HYDROGEOCHEM (HGC), was done to determine the suitability of each for simulating the movement of acidic contamination in alluvium. For simulations that accounted for aqueous complexation, precipitation and dissolution, the breakthrough and rinseout curves generated by each model were similar. The differences in...

No abstract available.

Extensive research has been conducted regarding the occurrence of herbicides in the hydrologic system, their fate, and their effects on human health and the environment. Few studies, however, have considered herbicide transformation products (degradates). In this study of Iowa ground water, herbicide degradates were frequently detected. In fact, herbicide degradates were eight of the 10...

The effect of simultaneous competitive speciation of dissolved rare earth elements (REEs) in acidic waters (pH 3.3 to 5.2) has been evaluated by applying the PHREEQE code to the speciation of water analyses from Spain, Brazil, USA, and Canada. The main ions that might affect REE are Al3+, F-, SO42-, and PO43-. Fluoride, normally a significant complexer of REEs, is strongly associated...

Sulfur hexafluoride (SF6) is primarily of anthropogenic origin but also occurs naturally. The troposphere concentration of SF6 has increased from a steady state value of 0.054±0.009 to more than 4 parts per trillion volume during the past 40 years. An analytical procedure was developed for measuring concentrations of SF6 to less than 0.01 fmol/L in water. Groundwater can be dated with...

The biodegradation potential of two drinking water disinfection byproducts was investigated using aquifer materials obtained from approximately 100 and 200 meters below land surface in an aerobic aquifer system undergoing aquifer storage recovery of treated surface water. No significant biodegradation of a model trihalomethane compound, chloroform, was observed in aquifer microcosms...

Extended tailing of tracer breakthrough is often observed in pulse injection tracer tests conducted in fractured geologic media. This behavior has been attributed to diffusive exchange of tracer between mobile fluids traveling through channels in fractures and relatively stagnant fluid between fluid channels, along fracture walls, or within the bulk matrix. We present a field example...

Under methanogenic conditions, microbial degradation of [1,2-14C]vinyl chloride (VC) resulted in significant (14 ± 3% maximum recovery) but transient recovery of radioactivity as 14C-acetate. Subsequently, 14C-acetate was degraded to 14CH4 and 14CO2 (18 ± 2% and 54 ± 3% final recoveries, respectively). In contrast, under 2-bromoethanesulfonic acid (BES) amended conditions, 14C-acetate...

The crystallization of calcium carbonate minerals plays an integral role in the water chemistry of terrestrial ecosystems. Humic substances, which are ubiquitous in natural waters, have been shown to reduce or inhibit calcite crystal growth in experiments. The purpose of this study is to quantify and understand the kinetic effects of hydrophobic organic acids isolated from the Florida...