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Figure 3
Set-up:
This graphic shows how median phosphorus concentrations have decreased at the sewage treatment plant (STP) and seven sites throughout the James River Basin. The green line and square symbols represent phosphorus concentrations prior to the completion of the sewage treatment plant upgrade in March 2001, while the blue line and triangle symbols show phosphorus concentrations after the upgrade. The bottom scale on the graph provides the location of the sample sites as distance (miles) from the sewage treatment plant. Phosphorus concentrations are presented in micrograms per liter, or parts per billion, on the left axis. |
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Interpretation:
Phosphorus concentrations have decreased throughout the James River Basin since the treatment plant upgrade. Decreases of 87% were measured at sites I and II, located in Wilson’s Creek just below the treatment plant and in the James River at the Delaware Access, respectively. In the James River Arm of Table Rock Lake (sites IV – VII) the reduction of phosphorus was smaller, averaging around 40% for the four lake sites. At Site IV, the most up-lake site, median phosphorus decreased from 126 micrograms per liter to 77 micrograms per liter. At the most down-lake site, Site VII, median phosphorus decreased from 15 to 10 micrograms per liter. The reduction in phosphorus was considered statistically significant for all seven sites in the basin.
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