ASSESSMENT OF ACID LEACHATE FROM A CONFINED DISPOSAL FACILITY TO AN IMPAIRED SALT MARSH ON CHINCOTEAGUE BAY, VIRGINIA

Greenbackville and Franklin City, VA were booming Chincoteague Bay coastal communities sustained by the oyster industry in the mid-1800s to early 1900s. A myriad of human activities including overharvesting, human/agricultural waste runoff, marsh channel infilling and mosquito ditching, creation of an unnatural beach from waste oyster shell, and dredging for a marina all resulted in catastrophic oyster population decline, degradation of the salt marsh, and eventual economic collapse. These activities have legacies that continue to impact the salt marsh today. In the mid-70s, a confined disposal facility (CDF) was initially constructed to contain dredged sediments. After upgrades, the enclosed catchment now accumulates an average of ~12.2 mil gal/year of rainwater, provides habitat for the invasive reed, Phragmites australis, and modifies groundwater and surface water chemistry entering the adjoining salt marsh and bay.

For this study, we analyzed soil and groundwater samples from the marsh and CDF for pH, metals, nitrates, DO, salinity, temperature, and elemental composition via scanning electron microscope (SEM) and XRF. An initial 2014 study found low pH and elevated concentrations of Al, Mg, Zn, Fe, Mn, Cu, and Ca in soil samples. We collected twenty new water and soil samples from Summer and Fall 2021. The pH values of groundwater ranged from 7.47 to 5.27, which are below healthy salt marsh pH of 7.5. The lowest pH values were adjacent to the CDF, and demonstrates the presence of acid leachate. With SEM, we observed framboidal pyrite in the marsh sediments. This corroborates the presence of acidic and anoxic conditions. Here we present the results of SEM, XRD, XRF, Flame AA, ICP-OES, and Milestone DMA-80 analyses. Sampling will continue in Spring 2022 to evaluate seasonal variability. The USACE plans to use the CDF for the next 30 years and it will continue to impact the marsh unless there is a change in management strategy. We will discuss solutions that include regular flushing, stabilizing the eroding edge, eventual decommissioning of the CDF, and thin-layer application of dredge spoils to the salt marsh. Our analyses, along with comparison to acid mine drainage remediation in PA, will be used to inform strategies to neutralize the acid of the CDF runoff and begin to remediate the salt marsh.