Wastewater and Stream Health in Indian Creek, Johnson County, Kansas, 2004–2013

Indian Creek basin: wastewater treatment facilities (WWTFs) and study sites. USGS (Graham and others, 2014).

Indian Creek drains one of the most urban basins in Johnson County, Kansas. Two treatment plants — the Douglas L. Smith Middle Basin and Tomahawk Creek Wastewater Treatment Facilities — discharge into it. From June 2004 to June 2013, the USGS and Johnson County Wastewater measured how that effluent, and the city around it, affect the creek.

The study

• Sites: two upstream urban sites and four downstream of the plants — five on Indian Creek and one on Tomahawk Creek, its largest tributary.
• Data: discrete and continuous water-quality records (June 2004–May 2011 and June 2011–June 2013), compared with the biological community and ecosystem function along the gradient.
• Upgrades: in summer 2010, Middle Basin's capacity rose from 18.6 to 22.4 cubic feet per second and it added biological nutrient removal. Tomahawk Creek added chemically enhanced primary treatment in 2009, which also removes phosphorus.

Cleaner effluent

Annual mean effluent nitrogen and phosphorus: A, Middle Basin concentrations; B, Tomahawk Creek concentrations; C, Middle Basin loads; D, Tomahawk Creek loads. USGS (Graham and others, 2014).

• Middle Basin: effluent total nitrogen fell 46% but stayed above its NPDES permit goal of 8.0 mg/L; the phosphorus goal of 1.5 mg/L or less was met in 2010, 2012 and 2013. Annual loads fell 42% (nitrogen) and 54% (phosphorus), though effluent volume rose 11%.
• Tomahawk Creek: effluent phosphorus fell below 1.5 mg/L, and annual phosphorus loads fell 54% despite 33% more effluent.
• Headroom: in 2010–2013 Middle Basin ran at about 75% of design capacity. Even at full capacity, its estimated maximum loads are 27–38% lower than before the upgrade.

Nutrient loads from the plants compared with total loads at State Line: A, nitrogen; B, phosphorus. Numbers are the wastewater percentage. USGS (Graham and others, 2014).

Wastewater supplied between about 30% and nearly 100% of the creek's annual nutrient load, depending on flow. Nitrogen came mostly from effluent except in the wettest year (2010); phosphorus came mostly from effluent in dry years (2006) and from other urban sources in wet ones.

Still a big effect downstream

For about 75% of the time — normal and low flows — effluent made up about 24% or more of the creek's water, and its mark was clear:

• Nutrients: concentrations downstream were 10 to 100 times those upstream, even after the upgrades. Median nitrate plus nitrite was 10 to 15 times higher (April 2012–June 2013).
• Nitrate limit: the state's 10 mg/L nitrate target for Indian Creek was exceeded only at the sites just below the plants.
• Phosphorus at State Line fell 42% after the upgrades; nitrogen did not, because only Middle Basin cut it and effluent made up more of the flow during later sampling.

How often nitrate plus nitrite exceeded each concentration at each site, April 2012–June 2013, with the Kansas nitrate endpoint. USGS (Graham and others, 2014).

The city matters too

• Construction raised turbidity; winter road salt pushed chloride past the EPA's aquatic-life criteria for weeks or months at every site, with or without wastewater.
• Streambed sediment carried wastewater's nutrients and organic wastewater compounds, and urban polyaromatic hydrocarbons.
• Habitat was suboptimal or marginal everywhere, declining downstream as urbanization added up.
• Algae of nutrient-rich water increased just below the plants and faded further on.
• Macroinvertebrates showed impairment at all sites, and the state's aquatic life support scores were nonsupporting everywhere — urban influences, not only effluent, shape these communities.

Kansas Department of Health and Environment aquatic life support scores, August 2012 and April 2013. USGS (Graham and others, 2014).

Recovery downstream

Effluent kept the creek flowing and raised nutrients, algae, primary production and respiration below the plants. These faded with distance: by Mission Farms, 9.5 kilometers downstream from Middle Basin, stream function was no longer impaired compared with the upstream 119th site.

Sources

Based on Graham JL, Foster GM, "Effects of wastewater effluent discharge on stream quality in Indian Creek, Johnson County, Kansas," U.S. Geological Survey Fact Sheet 2014–3100, prepared in cooperation with Johnson County Wastewater; a work of the United States government in the public domain. Full results are in Graham and others (2014), USGS Scientific Investigations Report 2014–5187. Figures from the fact sheet's PDF.