Geology topics

K. McCarthy

Publications and source records attributed to K. McCarthy.

4 recordsLinked to original sources

USGS2008

Comparative study of transport processes of nitrogen, phosphorus, and herbicides to streams in five agricultural basins, USA

Agricultural chemical transport to surface water and the linkage to other hydrological compartments, principally ground water, was investigated at five watersheds in semiarid to humid climatic settings. Chemical transport was affected by storm water runoff, soil drainage, irrigation, and how streams were linked to shallow ground water systems. Irrigation practices and timing of chemical use greatly affected nutrient and pesticide transport in the semiarid basins. Irrigation with imported water tended to increase ground water and chemical transport, whereas the use of locally pumped irrigation water may eliminate connections between streams and ground water, resulting in lower annual loads. Drainage pathways in humid environments are important because the loads may be transported in tile drains, or through varying combinations of ground water discharge, and overland flow. In most cases, overland flow contributed the greatest loads, but a significant portion of the annual load of nitrate and some pesticide degradates can be transported under base-flow conditions. The highest basin yields for nitrate were measured in a semiarid irrigated system that used imported water and in a stream dominated by tile drainage in a humid environment. Pesticide loads, as a percent of actual use (LAPU), showed the effects of climate and geohydrologic conditions. The LAPU values in the semiarid study basin in Washington were generally low because most of the load was transported in ground water discharge to the stream. When herbicides are applied during the rainy season in a semiarid setting, such as simazine in the California basin, LAPU values are similar to those in the Midwest basins. Copyright ?? 2008 by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. All rights reserved.

Journal of Environmental Quality↗

USGS2007

Investigation of hydrophobic contaminants in an urban slough system using passive sampling - Insights from sampling rate calculations

Semipermeable membrane devices (SPMDs) were deployed in the Columbia Slough, near Portland, Oregon, on three separate occasions to measure the spatial and seasonal distribution of dissolved polycyclic aromatic hydrocarbons (PAHs) and organochlorine compounds (OCs) in the slough. Concentrations of PAHs and OCs in SPMDs showed spatial and seasonal differences among sites and indicated that unusually high flows in the spring of 2006 diluted the concentrations of many of the target contaminants. However, the same PAHs - pyrene, fluoranthene, and the alkylated homologues of phenanthrene, anthracene, and fluorene - and OCs - polychlorinated biphenyls, pentachloroanisole, chlorpyrifos, dieldrin, and the metabolites of dichlorodiphenyltrichloroethane (DDT) - predominated throughout the system during all three deployment periods. The data suggest that storm washoff may be a predominant source of PAHs in the slough but that OCs are ubiquitous, entering the slough by a variety of pathways. Comparison of SPMDs deployed on the stream bed with SPMDs deployed in the overlying water column suggests that even for the very hydrophobic compounds investigated, bed sediments may not be a predominant source in this system. Perdeuterated phenanthrene (phenanthrene-d10). spiked at a rate of 2 ??g per SPMD, was shown to be a reliable performance reference compound (PRC) under the conditions of these deployments. Post-deployment concentrations of the PRC revealed differences in sampling conditions among sites and between seasons, but indicate that for SPMDs deployed throughout the main slough channel, differences in sampling rates were small enough to make site-to-site comparisons of SPMD concentrations straightforward. ?? Springer Science+Business Media B.V. 2007.

Environmental Monitoring and Assessment↗

USGS2004

Remediation of spilled petroleum hydrocarbons by in situ landfarming at an arctic site

A simple, economical landfarming operation was implemented to treat 3600 m3 of soil at a site just northeast of Barrow, AK (latitude 71.3 ??N). Prior to landfarming, diesel-range organics (DRO) and trimethylbenzenes (TMB) were present in the soil at concentrations more than an order of magnitude greater than the established cleanup goals, and moderate levels of gasoline-range organics (GRO) and BTEX compounds were also present. The landfarming operation included application of a commercial fertilizer mix at a rate designed to approach, but not exceed, soil concentrations of 100 mg N/kg soil and 50 mg P/kg soil, and an aggressive schedule of soil tilling using heavy equipment that was readily available from a local source. The operation was designed to continue through the brief thaw season-a scheduled duration of 70 days-but was successfully completed more than 2 weeks ahead of schedule. This work demonstrates that even in extremely harsh climates, soils that are moderately contaminated with petroleum hydrocarbons can be effectively and economically remediated within reasonable time frames via landfarming. ?? 2004 Elsevier B.V. All rights reserved.

Cold Regions Science and Technology↗

USGS2004

Subsurface fate of spilled petroleum hydrocarbons in continuous permafrost

Accidental releases of approximately 2000 m3 of fuel have resulted in subsurface contamination adjacent to Imikpuk Lake, a drinking-water source near Barrow, AK. This paper presents a conceptual model of the distribution and transport of subsurface free-phase hydrocarbons at this site. The mean annual temperature in Barrow is -13 ??C, and average monthly temperatures exceed 0 ??C only during the months of June, July, and August. As a result, the region is underlain by areally continuous permafrost that extends to depths of up to 300 m and constrains subsurface hydrologic processes to a shallow zone that temporarily thaws each summer. During the 1993 and 1994 thaw seasons, the measured depth of thaw varied across the site from approximately 0.5 to 2 m. However, exploratory borings in 1995 showed that free-phase hydrocarbons were present at depths greater than 3 m, indicating that permafrost at this site is not a barrier to the vertical migration of nonaqueous-phase liquids. In 1996, a subsurface containment barrier was installed to prevent lateral movement of contaminated water to Imikpuk Lake, and a recovery trench was excavated upgradient of the barrier to facilitate removal of free-phase hydrocarbons. Free-phase hydrocarbons were recovered from the trench during 1996, 1997, and 1998. Recovery rates diminished over this time, and in 1999, no further product was recovered and the recovery operation was halted. Subsequent exploratory borings in 2001 and 2002 have revealed that some product remains in the subsurface. Data indicate that this remaining product exists in small discrete pockets or very thin layers of hydrocarbon floating on brine. These small reservoirs appear to be isolated from one another by relatively impermeable permafrost. Published by Elsevier B.V.

Cold Regions Science and Technology↗