Data and Site Study Selections

The data used in this study were obtained from many sources including literature, technical reports of specific sites, and database websites (e.g., OREIS, DBHYDRO, SFWMD, etc.).

Data from selected research contributors were used to confirm the model estimation capability for Hg. In order to confirm the model capability, the Hg experimental conditions obtained from the literature were set for the model. Then the model results were verified by the results from the literature. The model confirmation using the literature data was made for Hg-species, ion-exchange, and surface complexation processes.

Data from technical reports of the specific sites and related websites, including site geology, water quality data, flow characteristics, etc., were used for 2 purposes: 1) model confirmation 2) model application. The model confirmations are explained in sections 4.6 and 4.7. The model application for Hg geochemical and transport processes are documented in Chapter 6.

4.3.2 Site Selections

In this study, two test-beds, Oak Ridge Reservation (ORR) at Oak Ridge, TN, and South Florida Region, FL, were selected for the development and evaluation of Hg

geochemical processes, and also for the application in fate and transport of the enhanced model.

ORR, Oak Ridge, TN consists of three large industrial production facilities constructed as part of the World War II-era Manhattan Project: the Oak Ridge National Laboratory (formerly known as the X-10 Site), K-25 Site, and the Y-12 National Security Complex or Y-12 Plant. The accidental spill and discharge of Hg to the surroundings of Y-12 plant was reported during the Y-12 operation time, 1950-1963 (Brooks and Southworth, 2011). Studies have also shown that Hg accumulated in the soil, rock, and groundwater of the site consequentially became sources of contamination to nearby rivers and creeks, such as the East Fork Poplar Creek (EFPC) located downstream from the Y- 12 plant (Figure 5). Many cleanups have been attempted for ORR sites. Y-12 is divided into the Bear Creek Valley Watershed and the Upper East Fork Poplar Creek (UEFPC) Watershed (Figure 5). Later on as part of this study, applications of the enhanced model of this research to understand the transport of Hg were made for Bear Creek Valley and EFPC within the Y-12 complex area.

Figure 5 Oak Ridge Reservation Map (modified after www.esd.ornl.gov)

The South Florida region (Figure 6) includes the Florida aquifer and Everglades National Park (ENP). ENP is a unique wetland environment with a specific ecosystem and wildlife that has been reported to have contamination of Hg. The high Hg levels are found in wildlife and especially in aquatic animals (e.g., fish, shell, etc.). Those findings have raised the concern of many researchers to investigate the Hg behavior in attempts to control the sources and implement cleanup. The unique water environment of ENP has

water with high dissolved organic carbon (DOC) that also covers a wide range of salinity from oceanic to freshwater, which offers a special opportunity to study the Hg behavior under the effect of those main variables. The model was first tested for its capability to simulate major ions using data from the Florida aquifer. This test evaluated the model’s ability to estimate typical ions, such as Ca, Mg, Na, K and SO4, at different salinity levels

(section 4.6) or ionic strengths. An encouraging confirmation would justify using the model to calculate the Hg-species distribution of ENP water as a function of salinity. Second, the model with its enhanced thermodynamic database was used to investigate the fate and transport of Hg in ENP area as a function of DOC, peat and salinity.

Figure 6 Everglades National Park (ENP)

The two test-beds were chosen because of the high concern of Hg contamination at the sites; another reason was that because of the difference in geology, water composition, and flow characteristics between these two sites, their evaluation would

provide a better insight into the Hg behavior in a range of environmental condition. The major differences of the two sites are described below.

1. ENP surface water sediment is classified as the peat soil type, which consists up to 90% of DOC. Drexel et al. (2002), Watanabe et al. (2012) and Evans et al. (2005) showed that peat releases vast amounts of DOC in the water column, resulting in high DOC concentration in ENP’s surface water. DOC content in the peat sediment can retard the Hg from its transport while DOC in the water can form with Hg and move with the water. Thus, the DOC is one of the important factors that play an important role on fate and transport of Hg at this site. However, the studies (Hill et al., 2001; Depledge, M.H. 1999; Loar et al. 2011; Stewart et al., 2011) showed that the major sediment of ORR surface water, for example, sediment of EFPC, are sand, rock and gravel which consist of natural minerals, such as, FeO and Fe(OH)3. These minerals can complex with

Hg and retard it from its transport. The typical EFPC surface water consists of various chemical compositions (e.g. Ca, Mg, Zn, Pb) however, the concentration of DOC is negligible (Loar et al. 2011; Southworth et al. 1995 and 1999) and was not considered for this site.

2. According to contaminant transport equation or Advection- Reaction-

Dispersion (ARD) equation,

t

q

x

C

D

x

C

ν

t

C

∂

∂

−

∂

∂

+

∂

∂

=

∂

∂

-

concentration with time is a function of advection and dispersion transports and reactions. For these two selected sites, the physical parameters controlling the transport of Hg are significantly different. ENP surface water velocity (~777 m/d) and dispersion coefficient (~4660 m2/d) reported by Harvey et al.(2002 and 2005) and Leonard et al. (2006) are

very low compared to those for EFPC surface water, velocity is ~12,960 m/d and dispersion coefficient is ~77,000 m2/d (Vasquez, 2008; Loar et al., 2011). Thus, the evaluation of Hg transport of these two sites will help to better understand the Hg behavior and identify the physical parameters influenced its transport.

3. Groundwater settings and qualities of the both sites are different. Although, groundwater bedrock of the both sites mostly consist of limestone, however, the bedrock of ORR groundwater also consist of shale, kaolinite, gibbsite and Fe(OH)3.

The last three minerals have abilities to complex with Hg resulting in retardation of Hg from its transport. The retardation of Hg by limestone is not studied in this dissertation. The analysis of ORR groundwater qualities showed significantly different from those for ENP. ORR groundwater qualities at different wells showed variation in pH value (Elvado Environmental LLC, 2009 and 2011), while ENP groundwater qualities showed variation in salinity (Blanco et al., 2013; Price et al., 2003; Walton 2007). Thus, the effects of pH and salinity on Hg transformation are investigated. This helps to understand the chemical processes influenced Hg fate and transport at different water conditions.