Jean Spooner

DETERMINING STATISTICALLY SIGNIFICANT CHANGES IN WATER POLLUTANT CONCENTRATIONS

ABSTRACT Water quality variability can be examined to estimate the magnitude of changes in water quality needed to detect significant differences over time. Adjustments can be made to reduce the estimate of variability, thereby decreasing the water quality change required for statistical significance. These adjustments include: accounting for changes in meteorologic and hydrologic conditions through covariate variables in trend analyses; changing the sampling frequency; increasing the number of years in the monitoring scheme; and use of other statistical trend analyses, such as t-tests, linear regression, and time series analyses. Water quality monitoring data was examined from the Idaho Rural Clean Water Program (RCWP) project. Generally, a 30 to 60 percent change in unadjusted geometric mean concentrations is required to document a significant change in water quality. However, adjustments that reduce the estimate of variability can be used to reduce the required concentration change to 20 to 40 percent.

BENEFIT/COST ANALYSIS OF NONPOINT SOURCE CONTROL IN THE TILLAMOOK BAY, OREGON WATERSHED

ABSTRACT Economics has come to play an increasingly important role in decisions concerning lake protection and restoration. This study of the tillamook Bay, Oregon, nonpoint source control efforts illustrates a methodology by which a benefit/cost analysis can be accomplished for evaluating cost-effectiveness of such projects. Tillamook Bay has been periodically closed to shellfishing for several years because of bacterial contamination. Implementation of agricultural best management practice on about 60 percent of the identified critical sources in the watershed has produced a statistically significant reduction in bay fecal coliform concentrations. With plans for nearly 100 percent implementation by 1989, the bay waters should again meet shellfish water quality standards thereby removing the threat of further closures. Total government costs for the cleanup effort will probably be in the range of six million dollars. This paper develops a benefit/cost analysis to determine the cost effectiveness of this ...