TRANSFORMATION DURING RECLAMATION: AN INVESTIGATION OF THE CHANGING GEOCHEMISTRY AND GEOMOBILITY OF MINE WASTE PILES AT THE TAR CREEK SUPERFUND SITE

At the Tar Creek Superfund Site in Ottawa County, Oklahoma, mine waste, colloquially known as chat, is currently being reworked as a source for aggregate material in asphalt. In order to fractionate the marketable, larger material that can be used in road construction, some of the finer grained chat with elevated levels of zinc, lead, and cadmium are transferred to an onsite repository for storage. This has resulted in the removal of layers of chat and underlying soils at varying rates and times throughout the past decade, exposing long-buried metals to the environment. We anticipate that secondary minerals are now more geomobile, causing increased transport within the watershed.

To understand public health implications of reworked mine waste piles we partnered with local activists at the Local Environmental Action Demanded (LEAD) Agency and Quapaw Nation. We investigated the concentrations and geomobility of heavy metals such as lead, zinc, and cadmium of three chat piles at different stages of reworking including a partially removed chat pile, a base of a chat pile, and soil left underneath after the chat was removed. Additionally, we consider how heavy metal geochemical transformations may be expressed differently within these matrices in response to reworking.

Samples were analyzed using pED-XRF (Spectro XEPOS-He). Initial findings indicate a greater degree of layered heterogeneity in the chat piles than has been described prior to reworking. To better understand these processes, we have characterized the concentrations of metals as a function of grain size and determined the metal inventories to illustrate how cm to m scale heterogeneity is evolving over time within mine waste piles. We ascribe this layering to a century’s worth of size fractionation and in situ mineral weathering, enhanced and revealed by reworking. Through bioaccessibility assays we evaluate the solubility of metals in simulated gastric fluid to better understand the public health implications of secondary minerals and their export of heavy metals from reworked piles.