nitrate levels exceeding the MCL?

  1. Nitrates are groundwater contaminants derived from fertilizer, septic tank seepage and other sewage, nitrate poisoning is particularly hazardous to infants under the age of 6 months. The Maximum Contaminant Level (MCL) is the highest level of a contaminant the government allows in drinking water. For nitrates, the MCL is 10 mg/L. The health department wants to know what proportion of wells in Madison County that have nitrate levels above the LCL. A worker has been assigned to take a simple random sample of wells in the county, measure the nitrate levels, and assess compliance. What size sample should the health department obtain if the estimate is desired to be within 2 percent with 95% confidence if :

A. There is no prior information available?

B. A study conducted two years ago showed that approximately 7% of the wells in Madison County had nitrate levels exceeding the MCL?