The Big River is a tributary of the Meramec River . Running 145 miles, it drains an area of 955 square miles in east-central Missouri, roughly 14% of the state. Its course runs through Missouri’s Old Lead Belt, a region in and around St. Francis County. For more than a century, Missouri was the leading lead producer in the world, and more than 8.5 million tons of lead were produced from the Old Lead Belt before production tailed off in the 1950s and 1960s.
Though mining activities have ended in the Big River Basin, the area is still affected. Six large piles of mine waste remain on the land surface. Together they consist of some 2,800 acres. Figure 1 shows the drainage area of the Big River and the Old Lead Belt mining district. The black dots represent towns, while the red dots show the locations of the six piles of mine waste.
Historically, wind blew dust from these piles into the air, and precipitation washed it into streams, both of which collected into the Big River, which flows near the piles. Because it was (and is) impossible to extract all of the heavy metals from these mine wastes, the dust blown into the river contained heavy metals that posed a threat to human and animal health.
Between 2008 and 2012, the EPA attempted to reclaim the piles by capping them to prevent further erosion. In 2015, the U.S. Geological Survey (USGS) conducted a study of heavy metals in the Big River to assess the results of the capping operation. They studied 4 heavy metals known to have significant toxic effects on humans and animals: barium, cadmium, lead, and zinc. These 4 metals can get into river water in two ways. They can dissolve into the water, like sugar dissolves into your tea. Or, particles containing the metals can get washed into the river. Larger particles (sand-sized and larger) get moved into the river during heavy precipitation, but once the current calms, they sink to the bottom. There, they either tumble downstream along the bottom, or they rest until the next stormflow picks them up again. Fine particles (silt-sized or smaller) eventually settle to the bottom, also. However, they are kept suspended in the water by the current for a longer period of time. Thus, they can travel downstream farther, and they also have a greater chance of coming into contact with humans and animals.
The USGS studied the 4 metals at two locations between October 2011 and September 2013. The upstream location was at Gauge 07017610, just north of Bonne Terre. The downstream location was Gauge 07018500, at Byrnesville, about 68 miles from the upstream location, a few miles above the Big River’s confluence with the Meramec River. The locations are shown as black triangles on Figure 1.
The study developed a lot of information about the Big River at these two locations. I will focus on only a few of the major conclusions.
- Some heavy metals, but very little, were getting into the Big River by getting dissolved in the water. Most of the heavy metals in the river were in suspended sediments.
- The concentration of suspended sediments in the Big River was much higher after precipitation, much lower during dry periods. (This is hardly surprising. Anybody who knows rivers knows that precipitation causes erosion, which muddies the water. The water then clears gradually during dry weather as the suspended sediments settle to the bottom.)
During stormflow events, the concentration of cadmium, lead, and zinc were all significantly higher than the Toxic Effect Threshold, the concentration at which significant toxic effects are expected to occur. Figure 2 shows the results for each metal. Blue columns represent the amount of metal present in small sediments, green columns the amount in larger sediments. The yellow dotted line represents the level below which effects are not expected. The orange dotted line represents the level above which effects become more common. The red dotted line represents the level above which toxic effects are expected.
- Concentrations of cadmium, lead, and zinc were all higher at the upstream location than the downstream location, suggesting that the amount of these metals in the streambed decreased from upstream to downstream. One possible reason would be that their source lay upstream, possibly in the Old Lead Belt.
- No Toxic Effect Threshold was reported for barium. Barium was present in all stormflow events. It was significantly higher at the downstream location than the upstream, suggesting that a significant source of barium enters the Big River between the two locations. Two possibilities would be Mineral Fork Creek and Mill Creek, which flow through a barite (barium sulfate) mining district in Washington County.
- Fine particles accounted for the larger fraction of the heavy metal load, suggesting that the metals may be slow to clear from the water after precipitation.
- Lead and zinc concentrations at the upstream site were lower than those found in a study at Desloge in the early 1990s. Barium and cadmium concentrations at the upstream site were similar to those from the Desloge study. Care needs to be used in considering these comparisons. The locations were different, and the hydrological conditions were different. Both probably affected results.
- The amount of metal carried in the river water was not trivial. Modeling suggested that during the sampled events of 2013, the river carried 69.6 tons of barium, 0.34 tons of cadmium, 68.7 tons of lead, and 32.3 tons of zinc.
- Capping the mine waste piles did not eliminate the metals from the Big River. One reason may be that metals continue to leach from the piles, despite capping. Another might be that they originate from sources other than the piles. And a third may be that the metal sediments may already be deposited in the streambed. They rest there until storms cause the river to rise and the current to increase, at which point they get picked up and carried by the water.
In considering this study, it is important not to imagine it to be an evaluation of the general water quality of the Big River. The findings reviewed above concern heavy metals carried by the water during stormwater events. There were only a few of these in each year studied. The Missouri Department of Conservation seems to be of two minds about the overall water quality of the Big River: the Department’s website declares the river to “generally have good water quality.” At the same time, however, the Department “classifies the lower 93 miles of Big River as not suitable for aquatic life protection and fishing or livestock and wildlife watering. (Missouri Department of Conservation 2013). This 93-mile stretch would include the entire area in this study, and in fact, the entire area below the Old Lead Belt.
The results of this study seem to indicate that, whatever the quality of the water may be during dry periods, during periods of stormflow, it carries relatively high concentrations of these four heavy metals. The concentrations for all 3 that have established Toxic Effect Thresholds are well above the level at which effects are expected to occur. Capping operations may have decreased the load of the 4 metals carried by the river, but the observed decrease could have come from other factors not related to the capping.
Barr, M. 2015. Surface-Water Quality and Suspended-Sediment Quantity and Quality Within the Big River Basin, Southeastern Missouiri, 2011-13: U.S. Geological Survey Scientific Investigations Report 2015-5171, http://dx.doi.org/10.3133/sir20155171.
Menau, Kevin. 1997. Big River: Inventory and Assessment for Big River Watershed. Missouri Department of Conservation. http://mdc.mo.gov/your-property/greener-communities/missouri-watershed-inventory-and-assessment/big-river.
Missouri Department of Conservation. 2013. Water Quality, Big River. Accessed online 4/26/2016 at http://mdc.mo.gov/your-property/greener-communities/missouri-watershed-inventory-and-assessment/big-river/water-qualit.