Geochemical Control of Arsenic, Gross Alpha, and Ra-226/Ra-228 Groundwater Impact at a Coal Combustion Plant

An electric power utility company conducts routine groundwater sampling at its facility in central gulf coast Florida (“site”) according to the facility’s industrial waste water permit. Results of this sampling have identified select areas of groundwater with elevated concentrations of arsenic (As), radium (Ra-226 and Ra-228), and gross alpha (GA).  A Plan of Study (POS) was developed as required by the State to evaluate potential sources and transport mechanisms for these constituents, site geology and hydrogeology, and potential remedial alternatives. The POS included: (i) evaluation of in-well and intra-well geochemical changes between subsequent groundwater monitoring events; (ii) evaluation of major ion chemistry and stable isotope data; (iii) performance of As, GA, and Ra 226/228 seawater leachability tests on site soils and limestone; and (iv) performance of a column soil and bedrock test to evaluate Eh changes on As solubility. 

The evaluation indicated that As, Ra-226/228, and GA have been liberated from the soil and native limestone at the site and neither the lined coal pile nor the coal combustion product ash storage/disposal area, nor other sources such as plant industrial wastewater being directed to percolation ponds, is the main source of arsenic within the groundwater monitoring wells. Rather, the constituents of concern are a result of geochemical changes in the shallow groundwater due to anthropogenic activities (e.g., compaction grouting, installation of large liners, presence of storm water features, etc.) and as a result of sea water intrusion in the vicinity of the discharge canal. Overall, the evaluation of geochemical data has allowed us to support and confirm the assertion that site processes did not cause groundwater contamination.