10.114 Pollution Control The U.S. Environmental Protection Agency limit on the allowable discharge of suspended solids into rivers and streams is 60 milligrams per litre (mg/L) per day. A study of water samples selected from the discharge at a phosphate mine shows that over a long period, the mean daily discharge of suspended solids is 48 mg/L, but day-to-day discharge readings are variable. Inspectors measured the discharge rates of suspended solids for n = 20 days and found s = 39 (mg/L). Find a 90% confidence interval for o. Interpret your results.