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The distribution of legacy heavy metals in industrial city soils is not well documented. Therefore, fundamental details such as the ‘background’ (i.e., non-road/non-dripline) concentration of trace metals in urban soils are uncertain. While there has been a strong focus on mapping lead contamination near roads and residences, these studies are generally not placed in the context of the urban background. In this study, ‘background’ distributions of urban relevant trace metals: arsenic, cadmium, copper, lead, and zinc were mapped based on soil samples collected throughout Pittsburgh. Distinct spatial patterns were revealed: contamination is elevated in the eastern portion of the study area, driven by dominant wind patterns and historical coking activities in low-lying areas (paleochannels), areas subject to atmospheric temperature inversions that focus air contamination. The mixing analysis revealed spatial structures in contributions of industrial activities to metal soil contamination. In particular, regions enriched in cadmium relative to zinc (i.e., Zn:Cd<317) were located near historical coking operations, and areas enriched in lead relative to zinc (Pb:Zn>1) were located in areas with historical secondary lead smelters. These results suggest a comprehensive accounting of the trace metals concentrations in background soils has important implications for the assessment of exposure risk in populations residing in historically industrial areas. Relatively sparse sampling of background conditions in urban systems can indicate patterns of legacy contamination and attribute this contamination to historical sources.

 

Synoptic sampling of streams is an inexpensive way to gain insight into the spatial distribution of dissolved constituents in the subsurface critical zone. Few spatial synoptics have focused on urban watersheds although this approach is useful in urban areas where monitoring wells are uncommon. Baseflow stream sampling was used to quantify spatial variability of water chemistry in a highly developed Piedmont watershed in suburban Baltimore, MD having no permitted point discharges. Six synoptic surveys were conducted from 2014 to 2016 after an average of 10 days of no rain, when stream discharge was composed of baseflow from groundwater. Samples collected every 50 m over 5 km were analyzed for nitrate, sulfate, chloride, fluoride, and water stable isotopes. Longitudinal spatial patterns differed across constituents for each survey, but the pattern for each constituent varied little across synoptics. Results suggest a spatially heterogeneous, three‐dimensional pattern of localized groundwater contaminant zones steadily contributing solutes to the stream network, where high concentrations result from current and legacy land use practices. By contrast, observations from 35 point piezometers indicate that sparse groundwater measurements are not a good predictor of baseflow stream chemistry in this geologic setting. Cross‐covariance analysis of stream solute concentrations with groundwater model/backward particle tracking results suggest that spatial changes in base‐flow solute concentrations are associated with urban features such as impervious surface area, fill, and leaking potable water and sanitary sewer pipes. Predicted subsurface residence times suggest that legacy solute sources drive baseflow stream chemistry in the urban critical zone.

 

The resurgence of oil and gas extraction in the Appalachian Basin has resulted in an excess of oil and gas brines in Pennsylvania, West Virginia, and Ohio. Primarily driven by unconventional development, this expansion has also impacted conventional wells and consequently, created economic pressure to develop effective and cheap disposal options. Using brine as a road treatment, directly or as a processed deicer, however, creates substantial concern that naturally occurring radioactive material in the brines can contaminate roads and road-side areas. Current decision making is based on risk exposure scenarios developed by regulatory agencies based on recreational users in rural areas and exposures to drivers during a typical commute. These scenarios are not appropriate for evaluating exposures to residential deicer users or people living near treated streets. More appropriate exposure scenarios were developed in this work and exposures predicted with these models based on laboratory measurements and literature data. Exposure scenarios currently used for regulatory assessment of brine road treatment result in predicted exposures of 0.4–0.6 mrem/year. Residential exposures predicted by the scenarios developed in this work are 4.6 mrem/year. If the maximum range of near-road soil radium concentrations observed in the region is used in this residential scenario (60 pCi/g²²⁶Ra, 50 pCi/g²²⁸Ra), residents living near these roads would be exposed to an estimated 296 mrems/year, above regulatory exposure thresholds used in nuclear facility siting assessments. These results underline the urgent need to clarify exposure risks from the use of oil and gas brines as a road treatment, particularly given the existing disparities in the distribution of road impacts across socioeconomic status.

 

Aging water infrastructure renewal in urban areas creates opportunities to systematically implement green infrastructure (GI) systems. However, historical soil contamination from gasoline lead additives, steel manufacturing by-products, and other historical industry raise the potential that novel GI drainage patterns and geochemical environments may mobilize these legacy pollutants to green infrastructure sites previously isolated from most hydrologic flows. Characterization of GI soil chemistries across GI type to build on previous observations in other cites/regions is fundamental to accurate assessments of these emerging management scenarios and the resultant risk of increased metal exposures in downstream environments. In particular, clarification of ecosystem services this metal sequestration may provide are vital to comprehensive assessment of green infrastructure function. During 2021, soil metal chemistry, specifically, As, Cr, Cu, Fe, Mn, Ni, Pb, V, and Zn was measured at a high spatial resolution in six Pittsburgh (Pennsylvania, United States) GI installations using a portable X-ray Fluorescence Spectrometer. Patterns of trace metal accumulation were identified in these installations and evaluated as a function of site age and GI connection to road systems. Trace metals including chromium, copper, manganese, and zinc all seem to be accumulating at roadside edges. Remobilization of historically contaminated soils also seems to be a potential mechanism for transporting legacy trace metal contamination, particularly lead, into GI systems. However, metals were not clearly accumulating in installations less connected to road inputs. These findings are consistent with literature reports of trace metal transport to GI systems and reconfirm that clarification of these processes is fundamental to effective stormwater planning and management. 

Total metal concentrations for Pittsburgh soil samples collected in a stratified random sample. Samples only collected from locations (1) without evidence of recent land disturbance, (2) not near roads or residences, and (3) specifically not in private yards or industrial lots. If a site was not suitable, other random locations in the general area were assessed sequentially until a suitable site was located. 

A sediment core was collected from a small urban pond in Harmar Township, Pennsylvania. Half centimeter intervals of the sediment core were digested using 6mL of 10% (vol/vol) sub-boil distilled trace metal grade nitric acid. Sediment metals were measured to better understand the history of metal contamination in the Pittsburgh region.