Monitoring phosphorus is challenging because it involves measuring very low concentrations down to 0.01 milligram per liter (mg/L) or even lower. Even such very low concentrations of phosphorus can have a dramatic impact on water, such as the Chesapeake Bay.
Over past several years, spikes in phosphorus and nitrogen have forced the Cape Charles wastewater plant out of compliance—the Department of Environmental Quality has levied heavy fines in response.
To stay in front of potential problems, the town has begun on-site testing for nutrient levels.
Below is a chart of the on-site testing results, which seems to indicate that the town is still struggling to calibrate the tests. The blue line graphs the results of the on-site tests, and the gold line is the (official) results from the DEQ lab.