Passage I

Two artificial marshes were built to help reduce the amounts of iron and manganese in, and the acidity of, water seeping into a stream from a coal mine site (see Figure 1). Table 1 shows precipitation, in centimeters (cm); flow rate, in liters per minute (L/min); pH (acidity); and iron and manganese content, in milligrams per liter (mg/L), of inlet and outlet water over 5 days.

Water having a higher level of iron or manganese or a lower pH than the values given in Table 2 is said to be contaminated.