For stations extracted from the 33-mile-long RF1 reach (07010206001) from the Minnesota River (UM 844.7) to the St. Croix River (UM 811.6) where the oxygen sag zone is located, however, the "signal" of worst-case DO improvement is much sharper, with mean tenth percentile dissolved oxygen concentrations as low as 2.5 mg/L "before" and 6.0 mg/L "after" the CWA (see Figure 1-5). The RF1 reach scale results reflect the considerably stronger influence of the wastewater discharge from the St. Paul METRO facility for stations located in closer proximity to the point source input. A detailed time series of summer DO data extracted from stations located only within the oxygen sag zone of the Upper Mississippi River (UM 820-830) during "dry" years documents an even stronger "signal" of improvements in DO from < 1 mg/L in 1961 to > 6 mg/L in 1987-1989 (see Figure 12-15 in Chapter 12).
Comparison of the Change in Signal Between the Reach and Catalog Unit Scales Using the Upper White River Basin (Indiana) as an Example
Recall that the underlying objective of the second leg of the three-legged stool approach of this study was to measure the change in the response "signal" linking point source discharges with downstream water quality before and after the CWA at sequentially larger aggregations of spatial scales (reach, catalog unit, and major river basin). The theory is that, if a signal change can be detected at sequentially larger scales, this would provide evidence that the CWA's technology-based and water quality-based effluent control requirements yielded broad as well as localized benefits (that is, stream reaches both within and beyond the immediate sag curve have benefited from the CWA).
The purpose of this subsection is to provide a practical comparison of reach scale and catalog unit scale signals using worst-case DO from monitoring stations in the Upper White River Basin, the catalog unit (05120201) in which the city of Indianapolis, Indiana, and several smaller municipalities are located.
Background In the 1960s, the citizens of the city of Indianapolis depended on primary treatment. Secondary treatment was added in the 1970s, and in 1983, the city further upgraded its POTWs to advanced wastewater treatment (AWT) to achieve compliance with water quality standards for DO. Two municipal facilities, designed to treat up to 379 cfs (245 mgd), currently discharge effluent to the White River. The baseflow of the river is low; the 10-year, 7-day minimum (7Q10) flow is about 50 cfs in the channel upstream of the two POTWs. Consequently, under these low-flow conditions, In-dianapolis's wastewater effluent accounts for about 88 percent of the downstream flow.
In addition to Indianapolis, the 2,655-square-mile drainage area of the Upper White River Basin contains several smaller municipalities that also discharge municipal wastewater into the White River network. Population centers upstream from Indianapolis include Muncie, Anderson, and Noblesville. Waverly, Centerton, and Mar-tinsville are towns located downstream of the city. Land use in the basin includes agricultural uses (65 percent) and urban-industrial uses (25 percent), with other uses accounting for the remaining 10 percent (Crawford and Wangness, 1991).
Using point and nonpoint source loading estimates of BOD5 for contemporary conditions (16.3 mt/day ca. 1995) compiled for the NWPCAM (Bondelid et al., 2000), municipal loads in the basin are estimated to account for 50 percent of the total loading to basin waterways. The remaining one-half of the total BOD5 load is contributed by major and minor industrial sources (11 percent), rural runoff (24 percent), urban runoff (13 percent), and CSOs (2 percent).
In a pre-AWT (1978-1980) and post-AWT (1983-1986) study of changes in water quality of the White River following completion of the upgrade to AWT from secondary activated sludge facilities for the city of Indianapolis, Crawford and Wang-ness (1991) concluded that there were statistically significant improvements in ambient levels of DO, BOD5, and ammonia-nitrogen downstream of the upgraded municipal wastewater facilities. DO, in particular, improved by about 3 mg/L as a result of reductions in carbonaceous (BOD5) and nitrogenous (ammonia) oxygen demands. For this study, Crawford and Wangness (1991) selected monitoring stations located about 10 and 15 miles downstream of Indianapolis's outfalls to collect data within the critical oxygen sag location of "degradation" and "active decomposition" (Waverly) and the "recovery" zone (Centerton) (see Figure 3-6).
During the before-CWA period from 1961 to 1965, streamflow conditions in the Upper White River Basin were characterized as dry, with persistent drought conditions for three consecutive summers from 1963 through 1965. During these three summers, streamflow ratios ranged from 40 to 63 percent of the long-term summer mean flow (see Figure 3-4a for 1963). Similarly, during the after-CWA period of 1986-1990, the Upper White River Basin was affected by the severe drought conditions of 1988 (streamflow ratio of only 34 percent of mean summer flow) that extended over large areas of the Midwest, Northeast, and upper Midwest (see Figure 3-4b). The hydrologic conditions of the White River are particularly critical in assessing before and after changes in DO because the municipal effluent flow of the upgraded AWT facilities (after 1983) accounted for about 88 percent of the river flow downstream of Indianapolis under low-flow conditions of the White River.
Upper White River Catalog Unit Level Signal The analysis of before- and after-CWA worst-case DO data for the Upper White River catalog unit revealed that this catalog unit improved by 1.75 mg/L, from 3.80 mg/L (mean value of worst-case DO from 37 stations) before the CWA to 5.55 mg/L (mean value of worst-case DO from 14 stations) after the CWA. This level of improvement ranked it 64th out of the 246 catalog units with before and after data sets (see Appendix D). A companion examination of BOD5 revealed that worst-case (ninetieth percentile) loading in the catalog unit was reduced from 34.8 mg/L before the CWA (1961-1965) to 6.9 mg/L after the CWA (1986-1990).
The signal change detected provides evidence that:
• The signal linking point source discharges with downstream water quality inherently resides in the before- and after-CWA worst-case DO data collected at stations throughout the Upper White River catalog unit.
• The signal is strong enough to be detected using a catalog unit scale summary statistic (mean of tenth percentile worst-case DO measurements for stations within the catalog unit).
• Improved wastewater treatment by the city of Indianapolis, as well as upgrades of wastewater treatment from other small municipal facilities throughout the basin, resulted in broad water quality improvements in the Upper White River after the CWA.
Upper White River RF1 Reach Level Signals The POTW discharge/downstream water quality signal detected at the catalog unit scale is, in reality, a statistical aggregation of signals associated with all the monitored point source-influenced reaches in the Upper White River watershed. If one breaks the catalog unit down and examines the before- and after-CWA summary statistics for individual reaches, one would expect to find that the reaches in the "degradation" and "active decomposition" zones have more pronounced DO changes than reaches located outside those zones. An examination of reaches in the Upper White River catalog unit revealed this hypothesis to be true. Figure 3-34 includes the locations and before- and after-CWA bar charts for each of the seven reaches in the Upper White River that have paired worst-case DO data. Figure 3-35 presents data showing changes in worst-case (ninetieth percentile) BOD5 concentrations for the same reaches.
Key observations include the following:
• The reach with the greatest reduction of BOD5 and greatest improvement in DO was the reach located immediately downstream of Indianapolis (05120201004) in the vicinity of Waverly. DO in this reach, which ranked sixth out of 311 reaches with before- and after-CWA DO data nationwide (see Table 3-1), moved from 0.7 to 6.4 mg/L, an increase of 5.7 mg/L. In this same reach, the ninetieth percentile BOD5 concentration declined from 58.1 mg/L to 4.3 mg/L.
• Reaches located immediately upstream of Indianapolis showed little change in before- and after-CWA DO conditions (Eagle Creek 05120201032; White River 05120201007, 05120201009; and Fall Creek 05120201006). BOD5, however, decreased from 20.6 to 7.0 mg/L in reach 05120201007 and from 12.4 to 3.0 mg/L in reach 05120201009. The decline in BOD5 levels most likely reflects upgrades in municipal facilities for the small towns upstream of Indianapolis.
• Farther upstream, in the vicinity of Muncie and Anderson, greater improvements in DO were detected (along with decreasing trends in ninetieth percentile BOD5 concentrations). In reach 05120201013 (Muncie), DO in the White River improved by 4.2 mg/L, from 2.2 mg/L before the CWA to 6.4 mg/L after the act. In the compilation of 311 reaches with the greatest before and after improvements in DO, this reach ranked 24th. For the reach in the vicinity of Anderson (05120201011), located downstream of Muncie, DO improved by 2.8 mg/L, from 3.4 mg/L to 6.2 mg/L. This reach ranked 44th in the nationwide ranking of stream reaches with DO improvements (see Appendix E).
• The Lower White River catalog unit is located downstream from the Upper White River unit. Before and after station records from the most upstream reach of the basin reflect the impact of the wastewater discharges from the small towns of Centerton and Martinsville, as well as the recovery zone of the sag curve associated with the Indianapolis point source inputs. In this recovery reach of the White River (05120202031), DO improved by 1.9 mg/L, from 3.4 mg/L to 5.3 mg/L.
White River IN (05120201007)
White River IN (05120201009)
White Rhrar IN (05120201011)
Eagle Creek IN (05120201032)
White River IN (05120202031)
White River IN (05120201004)
Fall Creek IN (05120201006)
White River IN (05120201013)
Figure 3-34 Before and after changes in worst-case DO (mg/L) for RF1 reaches of the Upper White River Basin (05120201) in Indiana.
Upper White Basin IN (05120201)
10th Percentile Dissolved Oxygen (mg/L)
White River IN (05120201004)
Was this article helpful?