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This article summarizes the results from a survey of polycyclic aromatic hydrocarbon (PAH) and metal concentrations measured in surface and subsurface soil samples that were collected from background locations throughout Manhattan, New York, between August 2005 and May 2006. The 95th percentile total 16 US EPA Priority Pollutant PAH concentrations in surface and subsurface soils were 24.8 and 53.1 mg/kg, respectively. Diagnostic PAH source ratios for surface and subsurface soils are presented, which provide plausible bounds for where these ratios would and would not be able to confidently differentiate background soils from soil samples that are impacted by PAH contamination. The 95th percentile concentrations for lead in surface and subsurface soils were 891 and 2,540 mg/kg, respectively, and the 95th percentile concentrations for mercury in surface and subsurface soils were 1.9 and 2.7 mg/kg, respectively. A not-unexpected finding of the study was that most surface soils and all subsurface soils contained a relatively high fraction of anthropogenic carbon, in addition to the presence of historic fill materials such as glass, brick, coal, and slag from more than 400 years of human activity on Manhattan Island. The concentration ranges for PAHs and metals measured in these background soil samples, coupled with the visual observations of historic fill materials in nearly all soil samples, emphasize that soils in Manhattan are altogether different from rural soils and thus warrant a different framework for site management decisions than rural soils. [ABSTRACT FROM PUBLISHER]

Metals concentrations in groundwater samples often exceed screening criteria, yet it is not always clear if the elevated concentrations represent contamination or have a natural source. This article presents a methodology for distinguishing naturally occurring metals from contamination. The methodology is based on well-established geochemical processes, including trace element adsorption on suspended particulates and reductive dissolution. Four cases of the applied methodology are provided. Results of these geochemical evaluations have been used to identify potentially contaminated samples and to remove naturally occurring metals from further investigation or remediation. The methodology relies on commonly available data; background data are not necessarily required. [ABSTRACT FROM AUTHOR]

The objective of this article is to establish baseline concentrations of Ba, Cr, Cu, Ni, Pb, Sr, V, and Zn (aqua regia-extractable) in natural surface soils of the Torrelles Municipal District and to investigate the relationships between these elements and soil properties and between the element concentrations themselves. Upper baseline concentrations of these elements were (mg kg -1): Ba 272.6, Cr 40.8, Cu 31.0, Ni 29.9, Pb 68.1, Sr 83.0, V 49.7, and Zn 132.7; most corresponded with the values reported in the literature. Correlation analysis showed that total Fe and Al have the strongest relationships with trace elements. [ABSTRACT FROM AUTHOR]

The levels of dioxins in house dusts are frequently associated with household exposures to emissions from incinerators, industrial stacks, and other sources. Although the U.S. EPA has studied air, soil, and water dioxin concentrations in locations considered as “unpolluted” background, comparable information for house dusts has been limited to studies outside the United States. The present study reports house dust dioxin concentrations for selected homes in Columbia, Marion County, Mississippi, an area believed to be suitable for “unpolluted” dust background data. Results indicate an average TEQ for 14 samples of 20.3 ppt, range: 1.30–53.7ppt based on WHO 1998 TEF values; or 25.2 ppt, range 2.30–63.6 ppt based on the older 1989 I-TEF values. [ABSTRACT FROM AUTHOR]

Polycyclic aromatic hydrocarbons (PAHs) in the environment have origins in various natural and anthropogenic sources. Pyrogenic tars (e.g., coal tar) are rich in PAHs, which are therefore typical constituents of concern at former manufactured gas plant (MGP) sites. Delineating the extent of PAHs in sediments is a common component of many former MGP remedial investigations. Because of the compositional similarity of weathered/degraded coal tar residues to combustion-related PAHs that comprise typical urban background, it can be difficult to determine the local PAH background contribution in sediments near MGP sites. This article presents an investigation of Mill Race Creek, a freshwater creek that flows adjacent to the Oneonta, New York former MGP. From the delineation sampling, elevated PAH concentrations were measured in “background” areas upstream of any suspected MGP releases. PAH fingerprinting revealed three primary PAH sources in creek sediments: low molecular weight (LMW), 2- and 3-ring PAHs from background petroleum sources; high molecular weight (HMW), 4- to 6-ring PAHs from site-related sources; and HMW PAHs from background sources. The results of this investigation demonstrated that site-related PAH residues were primarily localized in the subsurface of a few sediment deposits adjacent to the former MGP. Sediments containing site-related PAHs were generally buried underneath a surficial (6 in) layer of sediments with total priority pollutant PAH concentrations (55.0 48.8 mg/kg) that were almost entirely attributable to local background sources. In the context of a remedial investigation, contributions from uncontrolled background PAHs may limit the practicable feasibility of some remedial options. [ABSTRACT FROM AUTHOR]

Making defensible risk-based decisions is a complex process that incorporates risk assessment into a risk management framework. Many site investigations require additional study, negotiations and/or actions for arsenic detected in soil samples, in many cases where no process related sources are identified and no other chemicals of concern are identified. Regulatory agencies develop guidance to standardize approaches to risk-based site investigations that focus on achieving "safe" concentrations. For arsenic, the action level is frequently in the "gray region", a U.S. Environmental Protection Agency (USEPA) term associated with a region of high uncertainty for risk management decisions in the "decision performance curve" associated with the data quality objective (DQO) process. Recognizing the conservative nature of the risk-based screening value for arsenic, approaches to enforce this level (or proof of comparability to natural background) may have numerous consequences including ineffective use of resources, stigmas on properties or actions at industrial or hazardous sites that are inconsistent with their regional setting. Florida has developed regulations and guidance on investigation of brownfield sites and has supported a study by the University of Florida (UF) to evaluate natural background concentrations in Florida soils. This paper discusses the sources of uncertainty near the soil cleanup target levels (SCTLs) in the Florida decision-making framework. [ABSTRACT FROM AUTHOR]

Knowledge of arsenic background concentrations in urban soils is important for making remediation decisions. The soil cleanup target level (SCTL) for arsenic in Florida lies within the range of arsenic background concentrations. The residential SCTL is also near the practical quantification limits using analytical procedures. Currently no standard protocols are available for determining arsenic background concentrations in urban soils, apart from site-specific cases. Therefore, a pilot study was conducted to develop and employ appropriate protocols to determine arsenic distribution in urban soils. This involved: site selection (e.g. size and sampling frame), sample collection (e.g. sampling technique), and statistical considerations (e.g. design). Factors such as ease of sample collection and maintaining anonymity of private properties were also considered as they influence the successful implementation of the study. Forty surface soil samples each were collected from five categories in three land use classes (residential-yard and right-of-way, commercial and public land-parks and public building), digested using EPA method 3051a and analysed using graphite furnace atomic absorption spectrometry. Experiences from the pilot study (e.g. complications during sample selection, digestion, data censoring etc.) were used in the development of the final protocol to be used in determining the distribution of arsenic in urban areas. [ABSTRACT FROM AUTHOR]