Soil geochemistry characterization in the northern Appalachian Basin: Possible impact from coal-fired power plants and weathering of Devonian Black Shales

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This task addresses two related issues:

I. Acid rain in the northeast U.S is a well-known environmental consequence of coal combustion. However, sulfuric acid is not the only coal combustion product with the potential to impact the environment. Particulate (fly ash) emissions represent a second but as yet poorly characterized regional coal environmental pollutant. Because arsenic and other toxic trace elements such as mercury, and lead are locally enriched in coal from the Appalachian Basin, such particulates represent an environmental concern. Literature studies document that coal fly ash is enriched in arsenic and lead by one to two orders of magnitude over the feed coal. Recent collaborative studies with USGS Water Resources Discipline have shown that combustion from coal-fired power plants has contributed to elevated arsenic, lead, zinc, and mercury found in bottom sediments of Hinkle and Mile Tree Run Reservoirs in West Virginia. These reservoirs are down wind from several coal-fired power plants. We developed additional diagnostic criteria for demonstrating that these trace element enrichments in reservoir sediments are from coal combustion products. These criteria include combustion polyaromatic hydrocarbons (PAH’s), lead isotopes, and spherical (combustion) magnetite. Soil samples from the drainage basins including these two reservoirs likewise are enriched in the arsenic lead, zinc, and mercury in amounts beyond what could be supplied by local rocks. We seek to determine whether the impact of fly ash on soils is widespread.

II. During the evaluation of environmental consequences of elevated arsenic in Appalachian Basin coal, research showed a second major source of this element. Stream sediments in areas underlain by Devonian black (organic-rich) shale are markedly high in arsenic. A preliminary field study of one small area along the western portion of the Appalachian Basin in Kentucky showed considerable soil geochemical arsenic enrichment as well as enrichment in other metals. These metals are released from pyrite during chemical weathering. Arsenic, molybdenum, selenium, and vanadium are concentrated in the soil many times over the highest values on national soil geochemical maps, and chromium and lead concentrations are about equal to the highest map concentration. There is a considerable area of the central and eastern U.S. underlain by this type of shale. The question is thus, what is the impact on soil geochemistry from weathering of black shale? This necessarily involves understanding the mechanisms of weathering and soil formation in black shale areas and development of techniques that enable us to assess the impact of this natural metal flux in areas contaminated by other metal sources. Research on the impacts of coal and black shale on soil geochemistry provide us an opportunity to compare and contrast natural and anthropogenic pollution sources. In areas underlain by Devonian black shale that are also impacted by coal combustion products, we will have a unique opportunity to assess the combined impact on soil geochemistry of these two pollution sources.

The main objectives of this task are:

We will conduct a study of soils in portions of the Ohio River corridor to test the hypothesis that elevated arsenic and possibly lead, zinc, and mercury occur in soils as the result of coal combustion. The data will come largely from portions of Pennsylvania, West Virginia, and Ohio. The NRCS contracted with Pennsylvania State University to collect and analyze several pedons (a pedon is the smallest three dimensional volume of soil that can be recognized)
We will conduct local and regional studies to test the hypothesis that soils derived on Devonian shale outside our initial study area are similarly enriched in metals. Several sampling sites will include shale out-crop samples as well as soil samples to test hypotheses on mobility, transport and accumulation of metals developed in our initial study. Regional studies will be initiated that will focus on a small watershed underlain by Devonian black shale. This small watershed will be identified in a portion of Pennsylvania with outcropping Black Shale. Watershed samples will include shale, soil, stream sediments (plus lacustrine sediments, if available), and surface water. Data from these samples will be used to 1) Compare chemical weathering reactions and mobility/transport mechanisms with those identified in initial study; 2) Verify processes that accumulate metals in the soils; 3) Prepare a metal budget for the watershed, and 4) Assess the impact of metals in the soil on the ecosystem. In subsequent years, we hope to extend our Devonian black shale watershed study to include an area known to be contaminated by coal combustion products.

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