Correlations between Total Solids, Total Suspended Solids, Total Volatile Suspended Solids, and Phosphate at Deer Creek Reservoir

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1 Correlations between Total Solids, Total Suspended Solids, Total Volatile Suspended Solids, and Phosphate at Deer Creek Reservoir Blake Buehler 1, Pablo Moreno 1, Gustavious P. Williams 2*, E. James Nelson 3, Oliver Obregon 1, Nicolas Gonzalez 1, and Nathan R. Swain 1 1 Graduate Research Assistant, Civil and Environmental Engineering Department, Brigham Young University, Provo, Utah (blakedonbuehler@gmail.com) 2 Associate Professor, Dept. of Civil and Environmental Engineering, Brigham Young University, Provo, UT gus.williams@byu.edu 3 Professor, Dept. of Civil and Environmental Engineering, Brigham Young University, Provo, UT jimn@byu.edu ABSTRACT Deer Creek Reservoir, located in Utah, supplies municipal and agricultural water for Utah and Salt Lake counties. During the past four decades the high levels of total phosphorus and dissolved oxygen in the water have introduced both taste and odor problems from algae growth, which have necessitated additional treatment to clean the water. In an attempt to discover why late summer algae blooms continue to persist at Deer Creek, the Brigham Young University Deer Creek Research Group collected data using several water quality laboratory tests on samples from 11 different sampling sites within the reservoir: total solids (TS), total suspended solids (TSS), total volatile suspended solids (TVSS), and phosphate. These tests were performed on samples collected during the summers of 2010 (May through October) and 2011 (April through November). Samples from Secchi depth were used for this analysis because of excessive variability introduced if samples from above and below the thermocline and at bottom layers of the reservoir were included. The purpose of this study is to determine if any correlations exists between these three measurements: solid, phosphate, and Secchi depths. We used total suspended solids as an indicator for algal mass. We suspect that phosphate is being trapped in solid material, specifically sediment, and being released into the reservoir slowly over time. Our analysis shows that solids at Deer Creek do not exhibit significant correlations with phosphate or Secchi depths. We suggest that a different approach to the phosphate problem be used that we should analyze and correlate Deer Creek phosphate with sediment oxygen demand (SOD) measurements taken using SOD chambers to correlate algae with potential phosphate release from sediments. KEYWORDS: Deer Creek, Phosphate, Solids, Water Quality INTRODUCTION Deer Creek Reservoir (Figure 1) is a major source of municipal and agricultural water for Utah and Salt Lake counties. The reservoir is located about 16 miles northeast of Provo, Utah and is central to Utah s water quality improvement effort due to its high total phosphorus and dissolved oxygen content. High levels of phosphorus and dissolved oxygen cause large algae blooms in the late summer, which introduce taste and odor problems into the water. Local water treatment facilities have used additional measures, at a high economic cost, during the past four decades to remove these problems (BOR, 2009; Psomas, 2002). 1

2 Total Solids (TS) are the sum of total suspended solids (TSS) and total dissolved solids (TDS). TS analyses are important for assessing water treatment processes such as digester efficiencies and sludge cake processing parameters. TSS is composed of two components: volatile and fixed solids. The volatile solids are organic compounds of animal or plant origin. Water treatment plant operators use the total volatile suspended solids (TVSS) to estimate the amount of organic matter in solid fraction of wastewater, activated sludge, and industrial wastes. Biological processes can treat these. The fixed solids are things such as sand, gravel, and salt (American Public Health Association, 2005; Lenhart and Lehman, 2006). The Deer Creek Research Group made over 50 sampling trips to Deer Creek Reservoir from April to October of 2010 and from May to November of Water samples were taken on each trip, Figure 1. Deer Creek Reservoir (Google Earth) and over 850 samples were collected from 11 locations. Table 1 contains a list of the Deer Creek site names, abbreviations, and coordinates. We analyzed a subset of these samples to determine if any significant correlation exists between phosphate and solids in Deer Creek. We investigated solids further to determine if they significantly contribute to the late summer algae blooms. Our working hypothesis was that if solids are correlated with algae blooms, it is reasonable to assume that phosphates are being entrapped in solid material, specifically sediments, within the reservoir. APPROACH AND DESIGN A Van Dorn horizontal sampling tube was used to collect water samples, which were stored and transported in 500 and 1000 ml Nalgene bottles. Three samples were taken at each site at the Secchi depth, just below the bottom of the thermocline, and at the bottom of reservoir. The sampling sites match those used by the Central Utah Water Conservancy District (CUWCD) reservoir operations team, which has been sampling the reservoir for over 30 years. The group ran tests weekly to develop an extensive time series of data. 4

3 TS, TSS, TVSS values were determined in a lab using the procedures from Standard Methods (2005). Phosphate values were measured using a Hach DR 5000 spectrophotometer (American Public Health Association, 2005). The comparisons examined include solids (TS, TSS, and TVSS) versus phosphate and solids versus secchi depths. Using JMP statistical software the authors created reduced and full models for each comparison to determine the percent variability (R 2 ) explained by each considered parameter. Only solids values corresponding to Secchi depths ( ) were used in the analyses because of excessive variability introduced if data from below the thermocline and bottom layers of the reservoir were included. The reduced model accounted for confounding variables (i.e., date and site location), while the full model also accounted for the solid in question (i.e., TS, TSS, or TVSS), phosphate, or Secchi depth. All tables in the Results section are based on a 95 percent confidence level and relate the R 2, p-value, and difference in R 2 between the full and reduced models. Statistical significance is defined as a parameter having a p-value below five percent (according to a 95 percent confidence level), whereas practical significance is accounted for in the difference between R 2 values. A Cook s D analysis was used to identify possible outliers, which were then eliminated manually. RESULTS Comparisons between phosphate and solids can be found in Table 2. Comparisons between solids and Secchi depths are located in Table 3. Table 1. Deer Creek Site Names, Abbreviations, and Coordinates Site Abbrv Coordinates Bridge BR N, W Daniels Creek Inflow DC N, W Mid-lake A MA N, W Mid-lake B MB N, W Near Dam ND N, W Upper-lake A UA N, W Upper-lake D UD N, W Upper-lake F UF N, W Wallsburg A WA N, W Wallsburg B WB N, W Wallsburg Inflow WI N, W Table 2: Comparisons Between Phosphates and Solids at Deer Creek Reservoir Parameter(s) R 2 P-value ΔR 2 Date (Month) and Site Full Model with TS Date (Month) and Site Full Model with TSS Date (Month) and Site Full Model with TVSS Table 3: Comparisons Between Solids and Secchi Depths at Deer Creek Reservoir Parameter(s) R 2 P-value ΔR 2 Date (Month) and Site Secchi Depth for TS Date (Month) and Site DISCUSSION OF RESULTS Secchi Depth for TSS Analysis of all TS, TSS, TVSS and Date (Month) and Site Secchi Depth for TVSS phosphate tests shows that none of the parameters are correlated at the statistically significant or practically significant level. Analysis of all TS, TSS, TVSS and Secchi depths shows that only date and site have correlations at statistical significance level and even this only in the TVSS comparison. The change in R- squared values shows that practical significance is weak for all parameters. Even if p-values are not considered, the R-squared values do not show significant correlations between parameters since all R-squared values are less than The analysis was run with a 95 percent confidence level, which may be high for this type of model. However, when the model was run at a 90 percent confidence level, the p-values remained the same. 5

4 CONCLUSION The high levels of phosphorus and dissolved oxygen at Deer Creek cause large blooms in the late summer. The approach in this study was to determine correlations between types of solids, phosphates and secchi depths for the data collected during 2010 and The statistical models developed suggest that there are not correlations at the statistical significant or practically significant level. We suggest that the BYUDCRG take a different approach to the phosphate problem by attempting to analyze and correlate Deer Creek phosphate with sediment oxygen demand (SOD) measurements taken using SOD chambers. 6

5 REFERENCES American Public Health Association, American Water Works Association, Water Environment Association. (2005). Standard methods for the examination of water and wastewater: 21st edition, Port City Press, Baltimore, Maryland. BOR. (2009). Deer Creek Dam. (Feb. 27, 2011). Lenhart, J. and Lehman, J. (2006). Measuring total volatile suspended solids in stormwater to understand the influence of organic matter on BMP performance. 1, 2011). PSOMAS. (2002). Deer Creek Reservoir drainage, TMDL study. (Mar. 10, 2011). Standard Methods for the Examination of Water and Wastewater, Method 8178, Phosphorus, Reactive (Orthophosphate),