MS 150 Statistics test six • Name:

Total Nitrogen Monthly Average Concentration (mg/L)

Part I: Basic statistics

Plant Optimization Strategy for Nitrogen Removal Town of Crewe Wastewater Treatment Facility

Recent regulatory changes in Virginia will require the majority of wastewater treatment facilities to significantly reduce the discharge of nitrogen and phosphorus in the final effluent discharge. While most facilities will require an expansive upgrade to comply with the new requirements, the Town of Crewe operating staff have been evaluating the existing treatment facility for increased reductions of nitrogen and phosphorus through operational modifications. Although the facility relies upon chemical precipitation to remove phosphorus, plant staff have made adjustments to several treatment process parameters in an attempt to reduce total nitrogen levels from the existing plant.

Plant modifications were made in the second half of 2006. Does the 2007 data show a statistically significant improvement in the reduction of nitrogen in the final effluent discharge? Bear in mind this is a "before and after" type of problem, two samples. Data originally located via Swivel.

  1. Find the difference in nitrogen levels and record your results above.
  2. __________ Determine the sample size of the difference.
  3. __________ Determine the mean difference.
  4. __________ Determine the standard deviation of the difference.
  5. __________ Calculate the standard error for the difference.
  6. __________ Determine the tcritical for the difference at an alpha α of 0.05.
  7. __________ Calculate the margin of error E for the difference.
  8. __________ Find the margin of error E.
  9. Find the 95% confidence interval for the population mean difference.
    p(______________ ≤ μ ≤ ________________) = 0.95
  10. __________ Calculate the t statistic.
  11. __________ Use the tdist function to determine the p-value.
  12. __________ Calculate the maximum confidence c that the difference is statistically significant.
  13. __________ Is the reduction in nitrogen statistically significant?
  14. __________ Do we "fail to reject the null hypothesis" or "reject the null hypothesis"?
  15. __________ Use the ttest function to find the p-value.