Wilson’s Creek is a 5^th order stream that carries water from its headwaters near north Springfield through urban and agricultural land, passes through the Southwest Wastewater Treatment Plant (carrying away the effluent), eventually enters James River south of Springfield and finally ends up in Table Rock Lake. All three of these water bodies are seriously polluted with heavy phosphorus concentrations that contribute to algal blooms in the rivers and lake, potentially harming fish and other aquatic life. This study was conducted to determine if phosphorus and heavy metal concentrations in sediments are higher in Wilson’s Creek downstream from the Springfield Southwest Wastewater Treatment Plant (SWTP), and if so, whether the concentrations can be attributed to the effluent from the SWTP or to the contributions from South Creek, a tributary that enters Wilson’s Creek immediately upstream from the treatment plant. Sediment samples of restricted grain size were collected from Wilson’s Creek downstream from the treatment plant and control samples were collected from Wilson’s Creek and South Creek upstream from the treatment plant. In each stream segment, pH was monitored since a change in pH may affect the solubility of the metals and thus the amount of metals adsorbed or precipitated on the sediments. All samples were sieved and the 0.088mm to 0.0625mm (very fine sand) size fractions from the samples were used in this study. The concentrations of acid-extractable P, Zn, Cu, and Pb were determined by ICP techniques. A two-tailed t-test was performed and trend charts of the variation in concentrations along the stream were produced and used to analyze the data. Results indicated that phosphorus, copper and lead were significantly enriched in sediments downstream from the SWTP. Zinc concentrations did not vary significantly between the control and test samples collected from Wilson’s Creek. South Creek, however, did have significantly lower levels of Zinc than the downstream portion of Wilson’s Creek and was not found to contribute any of the excess measured pollutants to Wilson’s Creek. From this limited study, it appears likely that although recent enhancements to the SWTP are reported to have reduced heavy metals and phosphorus in the effluent that enters Wilson’s Creek, the sediments in the creek still show the effects of pollution.

Introduction

Wilson’s Creek is a tributary to the James River; its headwaters are in north Springfield and it flows through urban and agricultural land before joining the James, then eventually into Table Rock Lake. Its watershed area is approximately 84 square miles. As the city of Springfield and its surrounding area grows, more demands are placed on public services, including waste disposal and water treatment. Wilson’s Creek has been a depository of effluent from the Southwest Wastewater Treatment Plant in southwest Springfield since it began operation in 1959. Since 1959, the plant has undergone two major expansions and upgrades, bringing the flow capacity to 30 million gallons per day. In addition, many other point sources are permitted to discharge pre-treated wastes into the Wilson’s Creek drainage area. These include governmental and educational institutions, several industries, and some small subdivisions. One result of the increased development (and increased waste) is the eutrophication of James River and Table Rock Lake.

Location

Geographic setting

Wilson’s Creek watershed is located in southern Greene County, Missouri in the Springfield Plateau physiographic region of the Ozark Highlands (Figure 1). The watershed is part of the James River Basin, which is a sub-basin of the White River Basin, which is part of the Arkansas-White-Red drainage system. Figure 2 shows the area of this study is a two-mile stretch of Wilson’ Creek from the control sample sites north of Sunshine Street to the test sample sites just south of M Highway. Additionally, sediments from a short stretch of South Creek, a Wilson’s Creek tributary, were collected as another group of control samples.

Figure 1: Overview of study area

Figure 2: Detail of Wilson's Creek Study Area

Geologic setting

The area is dominated by limestone, shale and sandstone. Most of the bedrock surface in the Wilson’s Creek basin is formed of the Burlington-Keokuk limestone (Thomson 1986). Since it is highly affected by solution activity, the county is covered in karst features, such as sinkholes, caves, springs, and losing streams. Stretches of both Wilson’s Creek and South Creek are intermittent losing streams. The karst character of the watershed makes it vulnerable to contamination from both surface sources and leaking septic systems. Numerous fracture zones in the bedrock create pathways for preferential flow of groundwater and pollutants, or in some cases, barriers to flow.

Groundwater may flow relatively freely through and between four limestone formations before encountering the Northview formation, a shale or siltstone layer that acts as an aquitard and restricts flow and dips slightly from northeast to southwest. The Northview formation generally hinders downward flow of groundwater except where it is breached by wells or faults or fracture zones.

Below the Northview formation is the Ozark aquifer – the primary source for municipal and industrial wells in the Springfield area. It is a primarily dolomite formation that can be up to one thousand feet thick, capable of yielding flows up to 2,500 gallons per minute.

Land use

Land use in the basin is primarily agricultural (mostly pasture and some row cropping), some forested, and increased urban development (Figure 3). The only major city in the basin is Springfield, but it is the third largest city in Missouri and profoundly affects resource use in and around the watershed.

Figure 3: Land use around study area

Hydrology

In the James River basin area, the average annual precipitation in the area is 40 inches, and the average annual runoff is 12 inches.

Streams in the Wilson’s Creek basin are of the typical Ozark type with gravel substrates, clear water, and characteristic Ozark flora and fauna (Bullard 1997). There are numerous small impoundments, primarily small farm ponds. Due to the karst topography in the region and the cherty soils and poor clay materials, most ponds are leaky and streams lose substantial portions of their flow to groundwater. Both Wilson’s Creek and its tributaries, including South Creek, flow through some urban areas where the creeks have been channelized or altered. Streams have been straightened, lined with materials such as concrete and riprap, cleared of riparian vegetation and in some cases, re-routed through underground channels (Kiner and Vitello 1997).

Both Wilson’s Creek and South Creek are classified for “Livestock and Wildlife Watering” and “Protection of Warm Water Aquatic Life and Human Health-Fish Consumption” beneficial uses by the Missouri Department of Natural Resources. However, Wilson’s Creek has had health advisories listed on selected fish species. A level I advisory is issued for a species or area if contaminant levels are high enough that consumption of the fish species should be limited. A level III advisory is issued if the fish species should not be eaten due to contaminant concentration above levels of concern. Both level I and level III advisories were issued in 1991 due to chlordane contamination in Wilson’s Creek. Both advisories were lifted by 1995. From 1980 to 1997, five fish kills on Wilson’s Creek and four fish kills on South Creek were investigated. In all but 3 of the cases, the cause was untreated sewage (Missouri Department of Conservation Fish Kill Summary 1997).

In addition to the above-mentioned chlordane and sewage problems, the state has identified other surface water concerns within the basin. These include wastewater discharges from other point and non-point sources, agricultural runoff, spills or leaks of materials, landfills, biocides, storm water runoff/flooding, solid wastes, destruction or deterioration of riparian zones, and high volume of water use.

History of emission sources

Within the Wilson’s Creek drainage basin there are many sources of possible contamination, both point- and non-point sources.

Point sources

The Southwest Wastewater Treatment Plant (SWTP) is located at the confluence of Wilson’s Creek and South Creek in southwest Springfield. Originally built in 1959, the plant has undergone two major enhancements and upgrades to bring its continual flow capacity to 42.5 million gallons per day and a short-period flow of 65 million gallons per day. Currently, the average daily flow is approximately 39 million gallons per day. (City of Springfield 2000). Approximately 70,000 pounds of pollutants are removed from the wastewater per day are removed before it is discharged. The plant discharges its effluent into Wilson’s Creek.

Biosolids removed from the wastewater are disposed of in two ways: sludge thickening and dispersal as fertilizer on fields and/or dewatering and mixing with an amendment such as woodchips or sawdust then composting for 25 days. Compost can be stored until is can be used on fields.

Water is tested continuously (approximately 5000 samples per month) to ensure that the plant meets all Federal and State standards. Typical effluent water quality from the STWP is summarized below in Table 1:

Table 1: Typical effluent water quality from the SWTP

*Waste Component*	*Concentration*
Biochemical Oxygen Demand	< 2 mg/L
Total Suspended Solids	< 2 mg/L
Ammonia Nitrogen	< 0.1 mg/L
Dissolved Oxygen	> 20 mg/L
Fecal Coliform	< 10 colonies per 100 mL
Passes Whole Effluent Toxicity Test
pH	7.10 std. Units
Copper	15 ug/L
Chromium	< 10 ug/L
Zinc	40 ug/L
Cadmium	< 5 ug/L
Lead	< 20 ug/L
Nickel	< 10 ug/L
Mercury	< 0.2 ug/L
Silver	< 5 ug/L
Arsenic	< 20 ug/L
Cyanide	< 10 ug/L
Total Toxic Organics	Below detection limits

City of Springfield (2000)

In the past, copper has been the most limiting factor for Springfield’s Biosolids. However, copper loading “has recently been greatly reduced due to much lower emissions from one large local industry” (Bullard 1997).

Other point sources within the basin are residential areas including subdivisions such as Prairie View Heights and Village Addition, mobile home parks, and apartment complexes. Also contributing significant amounts of pollution are industries and businesses such as Burlington Northern railroad, Southwest Regional Stockyards, Paul Mueller Company, Dayco Products, and others. Government and educational institutions such as the Springfield Medical Center (US Department of Justice) and the Springfield Southwest Power Plant contribute as well.

Non-point sources

Non-point sources in the basin could contribute as much as 70% of the nutrient pollution within the basin (City Utilities 2001). Runoff from dairy cattle operations, poultry and turkey farms, sedimentation, sludge application, coal pile runoff, volatile organics, and seepage from septic systems are all probable contributors. Storm water overflow continues to be a problem for the city of Springfield.

Hypothesis

If the Southwest Wastewater Treatment Plant were a significant source of heavy metal and nutrient contamination in Wilson’s Creek, we would expect to find higher concentrations of these pollutants in the sediments downstream from the plant than in either Wilson’s Creek or South Creek upstream from the plant.

Methods

Choice of sediment size and collection of samples

According to a study by Mantei, Ernst and Zhou (1993), sediment size and sieving technique affect the concentration of metals that are adsorbed to and can be extracted from the sediments. They found that “homogeneity of metals in the very fine sand size sediments appears to be relatively high” and that the “sediment size used for chemical analysis should be obtained through sieving at the collection site.” They further cautioned that the sediments should not be crushed or sieved in the laboratory because this could result in false metal quantities for the elements. The collection and preparation techniques used in this study followed the recommendations given in the Mantei, Ernst, and Zhou paper.

Twenty-one samples were collected from the two study streams. Four South Creek sediment samples were collected as control samples upstream from the SWTP along the South Creek Greenway south of Battlefield Road. Three control samples from Wilson’s Creek were collected upstream from the SWTP north of Sunshine Street. Fourteen test samples from Wilson’s Creek were collected downstream from the SWTP beginning at the confluence of South Creek and Wilson’s Creek and ending just south of M Highway. Samples were collected from near the bank with water depths of approximately 10-20 cm and sediment depths of approximately surface to 20 cm. The samples were collected within a five-day period of dry weather. Samples were wet-sieved at the collection site to a grain size of 0.088mm to 0.0625mm and placed in plastic sample bottles.

Lab preparation of samples

The sediments were transferred to 150 mL glass beakers and rinsed with double-deionized water until all visible organic matter and suspended particles were removed. The samples were then dried in an oven for 24 hours. Each sample was gently stirred with a glass rod until all visible clumps were disaggregated.

Each sample was massed on an electronic balance and a 1.000-gram portion was removed for testing. The sample was placed in a clean plastic centrifuge tube and 20mL of 3M HNO3 was added. Sample bottles and contents were placed in a water bath and agitated for 24 hours. The samples were centrifuged and the supernatant decanted into clean plastic sample bottles.

ICP setup and chemical analysis

Three standard solutions for each of the metals (2, 5, and 10 ppm), phosphorus (20, 50, and 100 ppm) and a blank sample of HNO3 for ICP analysis were prepared.

An ICP spectrophotometer was programmed and calibrated using the previously prepared standards for each of the elements to be analyzed. The concentrations of each element in each of the test and control samples were determined by standard ICP procedures. A printout of the results was produced for analysis.

Tables and trend charts

Results of the ICP testing were entered into Microsoft Excel and Quattro Pro spreadsheets for further analysis. Microsoft Excel was used to produce a concise table of results (Table 2) and trend charts for each of the element concentrations and pH of surface water (Figure 4).

Statistical analysis

Quattro Pro spreadsheet software was used for statistical analysis because the t-test function gave more comprehensive results. Three t-tests were run for each element in order to determine if the differences between sample groups were statistically significant. Results from the t-tests can be found in Table 3.

Results and discussion

Samples numbered 1-4 were collected from South Creek along the South Creek Greenway area south of Battlefield Road in southwest Springfield. These samples were collected as controls to determine if an apparent increase in metal or phosphorus concentration could be attributed to the SWTP or if South Creek, since it runs primarily through urban areas and joins Wilson’s Creek at the SWTP, might be contributing some of the contamination. Samples 5-7 were collected from Wilson’s Creek just north of Sunshine Street in west Springfield as controls to determine background levels of metals and phosphorus in the creek before any effluent enters from the SWTP. Samples 8-21 were collected adjacent to and south of the SWTP, beginning at the confluence of Wilson’s Creek and South Creek and continuing downstream from the SWTP to just south of Highway M. The metal concentrations for each of the samples and the pH values for each of the streams can be found in Table 2.

Table 3 shows the levels of significance determined by t-tests on each combination of samples groups and the associated metal and phosphorus concentrations. It appears that the SWTP is contributing (or has contributed) significant amounts of phosphorus, lead and copper to Wilson’s Creek. Although the pH of the streams did vary upstream and downstream from the SWTP, the pH was lower (more acid) downstream from the treatment plant and thus would lead us to expect the levels of metal precipitation to be lowered. If the difference in pH has any effect at all, it would result in the concentrations of metals to actually be higher than reported. South Creek samples had mean concentrations of all pollutants that were lower than the mean concentrations of Wilson’s Creek control samples as well as the samples collected downstream from the SWTP.

Trend charts were produced (Figure 4) to graphically represent the concentrations of metals and phosphorus at each site, as well as the pH measured in that stretch of stream. It shows the increase in concentrations of each of the metals and phosphorus beginning at or near the SWTP discharge pipe (immediately after sample site 8). Additionally, the metals tend to track each other to some extent. This may indicate a common source, indiscriminate precipitation of all metals on the sediments present in the specific location, or some other process happening in the local “microenvironment.”

Table 2