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Interest in low-cost direct filtration facilities and their effectiveness in treating the potable water sources of the Intermountain Region is increasing as the need for treated water supplies increase. Direct filtration is a water treatment scheme which does not include sedimentation and in some cases flocculation. Compared to conventional treatment, direct filtration has lowered capital costs, reduced space requirement, and decreased sludge quantities. Moreover, the direct filtration process may offer large reductions in coagulant dosages and costs.

Currently information comparing a direct filtration system to a conventional water treatment system in the Intermountain area is not readily available. The specific objective of the research was to compare by statistical methods the direct filtration, Utah Valley Water Purification Plant (Orem, Utah) and the conventional Little Cottonwood Metropolitan Water Treatment Plant (Salt Lake City, Utah). These treatment plants were chosen for comparison on the basis that they are the two most compatible treatment plants having the highest correlation of source water. The Little Cottonwood Plant receives approximately 65% of its source water from Deer Creek Reservoir whereas the Utah Valley Plant receives all of its source water from Deer Creek Reservoir.

The parameters, most common to both treatment facilities chosen for comparison were total daily flow, raw water turbidity, effluent pH, finished water temperature, and alum dosing concentrations. Data from August 1, 1980 through August 31, 1983 were obtained from the daily water quality and plant operation logs of the two treatment plants. Utilizing the computer, these parameters were compared statistically in several fashions.

The most beneficial results were obtained from a randomized block design analysis of variance using an F-ratio as the reference for significance. The data from each treatment plant were blocked into seasonal means and compared with a degree of significance of = 0.01.

The parameter under investigation of most importance in the comparison of the conventional and direct filtration water treatment plants is the finished water turbidity has typically been the main criterion for determining the quality of water of operating and pilot-scale direct filtration plants. The F-ratio for this parameter at the degree of significance alpha = 0.01 proved not significant. Further the mean finished water turbidities for the Utah Valley and Little Cottonwood treatment plants were well below the EPA Primary Drinking Water Regulation of a maximum contaminant level of 1 TU.

The overall statistical analysis exhibits that the Utah Valley Purification plant produces not only an acceptable quality of water but one that is also comparable in quality to that of the conventional processes of the Little Cottonwood Metropolitan Treatment Plant.