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KEY CONCEPTS 1. Key pollutants of concern have been identified

Nitrogen, phosphorus, sediment and pathogens have been identified as the most important pollutants to address with this plan. These pollutants pose risks to human health and the environment, which are outlined within this chapter in greater detail. Strategies to prevent increases in stormwater rates and volumes also need to be considered, as stormwater tile flow and runoff are the largest carriers of these pollutants to the receiving streams. Local flooding has also caused damage to private property and infrastructure.


2. Water quality monitoring data is valuable

Data collected by the Iowa Soybean Association / Agriculture's Clean Water Alliance (ISA/CWA) and the IOWATER volunteer monitoring program has been valuable to identify pollutant loads and their potential sources.


3. Nutrient levels appear higher in rural areas

Monitoring data has demonstrated that levels of nitrogen and phosphorus compounds are usually seen at higher levels in the rural areas within this watershed.


4. Bacteria levels appear higher in urban areas

Observed levels of E.coli bacteria have been much higher within the urban landscape, although levels all across the watershed were consistently above the state’s water quality standard.


5. Key sources of sediment loading

Streambank erosion, construction sites and gully erosion are projected to be the leading current sources of sediment loading to Walnut Creek. Almost 30,000 tons of sediment per year are estimated to be delivered from the Walnut Creek watershed to the Raccoon River.


6. Small footprint, big impact

Construction sites make up only 0.1% of the watershed on average each year, but contribute significantly to the overall sediment load.

HOW DO THESE CONCEPTS INFLUENCE DEVELOPMENT OF THE PLAN? To develop targeted, effective solutions, the key pollutants posing the greatest risk need to be identified. The likely sources of these pollutants need to be identified so that effective practices can be implemented to achieve the desired load reductions.


Pollutants of Concern

Key pollutants of concern within the Walnut Creek watershed have been defined by considering the following information gathered through development of this plan:

1. Review of past studies, including the Water Quality Improvement Plan for the Raccoon River (TMDL), the Raccoon River Water Quality Master Plan and Iowa’s Nutrient Reduction Strategy.


2. Review of past local and municipal watershed assessments and storm water infrastructure studies.


3. Collection of stakeholder input at WMA meetings, open houses and individual conversations.


4. An overview of the available water quality monitoring information collected from sites within the watershed.

Potential Impacts of the Identified Pollutants of Concern

This document identifies key sources of pollution and determines methods to reduce their impacts, both in this watershed and the downstream receiving waters. Reducing pollutant loads will require policy changes and implementation of practices requiring significant investment. To understand why such investments are necessary, it is important to realize the impact these pollutants have on health, the environment and local economic interests. (1) Nutrients (Nitrogen and Phosphorus) Nutrients like nitrogen and phosphorus exist in both surface and ground water under natural conditions. Their presence supports the growth of algae and aquatic plants, providing food and habitat for fish and other aquatic life within streams and lakes. Excessive algal growth can occur when the levels of these nutrients are too high. Algal blooms can block sunlight below the surface, clog fish gills, reduce habitat quality and diminish habitat. The death and decay of algae can lead to diminished oxygen levels, known as hypoxia. Oxygen levels can fall to a range where fish and other wildlife may be sickened or killed. As of 2013, there were 166 of these hypoxic “dead zones” that had been identified in and around the United States. The largest of these areas was a 5,840 square mile area (approximately 10% of the size of the entire state of Iowa) in the Gulf of Mexico, largely attributed to nutrient polluted runoff received from the Mississippi River watershed (which includes the entire state of Iowa).

Excessive algal growth can also increase growth of bacteria and other human pathogens. In some cases, algae can form toxins which can cause rashes, stomach/ liver illness, respiratory and neurological effects in humans. Direct exposure to this algae affects fish and other wildlife, with the toxic impacts being carried up the food chain if they are consumed by other animals. If toxic algae enter into the water supply stream, they can be converted into dioxins through the use of chemical disinfectants in the water treatment process. Risks to human health from dioxins include cancers, reproductive and developmental issues.

(1) Nitrate has been observed at elevated levels in stream flows within the Walnut Creek watershed. Des Moines Water Works' main intake point for surface water from the Raccoon River is located just downstream of where Walnut Creek flows into that river. Nitrates have been known to cause illness and death of human infants when at high levels.

Blue baby syndrome can affect the elderly and bottle-fed infants, with those younger than three months being most at risk. High nitrate levels in drinking water supplies can be converted by the human body into nitrite. These react with red blood cells, reducing their ability to carry enough oxygen throughout the body. The mouth, hands or feet of the affected person may appear blue. Complications can include trouble breathing, diarrhea, vomiting, lethargy, loss of consciousness and seizures. Extreme cases may be fatal.

(2)For this reason, Water Works employs a state of the art nitrate removal system, which is used when elevated levels of nitrate are detected in the source water. This system is expensive to operate and maintain, costing $7,000 per day to operate. From December 2014 to July of 2015, DMWW spent more than $1,500,000 to remove nitrate from the water. The cost of this operation is being transferred to residents and local businesses through annual water use rate increases.

Pollutant of Concern Reasons

Nitrate (Nitrogen)

• While not considered a pollutant directly, volumes and rates of stormwater runoff are observed to be well above those which would have been expected prior to agricultural and urban development. These changes to the hydrology of the watershed increase the risk of flooding, streambank erosion and act as a carrier for larger pollutant loads being delivered through and out of the watershed.

Potential Impacts of the Identified Pollutants of Concern

This document identifies key sources of pollution and determines methods to reduce their impacts, both in this watershed and the downstream receiving waters. Reducing pollutant loads will require policy changes and implementation of practices requiring significant investment. To understand why such investments are necessary, it is important to realize the impact these pollutants have on health, the environment and local economic interests.(1)

Nutrients (Nitrogen and Phosphorus) Nutrients like nitrogen and phosphorus exist in both surface and ground water under natural conditions. Their presence supports the growth of algae and aquatic plants, providing food and habitat for fish and other aquatic life within streams and lakes. Excessive algal growth can occur when the levels of these nutrients are too high. Algal blooms can block sunlight below the surface, clog fish gills, reduce habitat quality and diminish habitat. The death and decay of algae can lead to diminished oxygen levels, known as hypoxia. Oxygen levels can fall to a range where fish and other wildlife may be sickened or killed. As of 2013, there were 166 of these hypoxic “dead zones” that had been identified in and around the United States. The largest of these areas was a 5,840 square mile area (approximately 10% of the size of the entire state of Iowa) in the Gulf of Mexico, largely attributed to nutrient polluted runoff received from the Mississippi River watershed (which includes the entire state of Iowa).

Excessive algal growth can also increase growth of bacteria and other human pathogens. In some cases, algae can form toxins which can cause rashes, stomach/ liver illness, respiratory and neurological effects in humans. Direct exposure to this algae affects fish and other wildlife, with the toxic impacts being carried up the food chain if they are consumed by other animals. If toxic algae enter into the water supply stream, they can be converted into dioxins through the use of chemical disinfectants in the water treatment process. Risks to human health from dioxins include cancers, reproductive and developmental issues.

(1)Nitrate has been observed at elevated levels in stream flows within the Walnut Creek watershed. Des Moines Water Works' main intake point for surface water from the Raccoon River is located just downstream of where Walnut Creek flows into that river. Nitrates have been known to cause illness and death of human infants when at high levels.

Blue baby syndrome can affect the elderly and bottle-fed infants, with those younger than three months being most at risk. High nitrate levels in drinking water supplies can be converted by the human body into nitrite. These react with red blood cells, reducing their ability to carry enough oxygen throughout the body. The mouth, hands or feet of the affected person may appear blue. Complications can include trouble breathing, diarrhea, vomiting, lethargy, loss of consciousness and seizures. Extreme cases may be fatal.

(2)For this reason, Water Works employs a state of the art nitrate removal system, which is used when elevated levels of nitrate are detected in the source water. This system is expensive to operate and maintain, costing $7,000 per day to operate. From December 2014 to July of 2015, DMWW spent more than $1,500,000 to remove nitrate from the water. The cost of this operation is being transferred to residents and local businesses through annual water use rate increases.

Pathogens Pathogens are the most common cause for water quality impairment in the United States, with nearly 11,000 waterbodies listed as impaired for this cause in 2014. Pathogens are microscopic organisms which can cause disease in humans or animals. These include viruses, bacteria, protozoa and parasitic worms. The likely presence of pathogens is typically identified by measuring levels of fecal indicator bacteria (FIB) such as Escherichia coli (E. coli) or fecal coliform. Elevated levels of these indicator species demonstrate that conditions are favorable for pathogens at a level which could impact human health when exposures occur.

The primary concern is incidental human ingestion during recreational contact, resulting in illness. In addition, respiratory, skin, ear and eye infections are also possible. Those most at risk are the very young, those with compromised immune systems and those with no prior exposure to the pathogen. The level of exposure required to cause illness varies with each type of pathogen.

Runoff Rates and Volume Hydrology

The study of how water moves through and over the landscape. Stormwater runoff caused by rain, snowmelt and groundwater movement are the main ways that pollutants are carried from the landscape to receiving waters. As volumes of surface and subsurface runoff increase, a larger load of nutrients, pathogens and sediments are likely to be driven to the stream. Understanding the activities that increase the rates and flows of runoff can help us identify potential sources of such increases to address.

Activities that reduce the soil’s ability to soak up water (infiltration) or restrict its ability to move through the soil (percolation) lead to increases in stormwater runoff volume. Both infiltration and percolation are decreased when soils are compacted. In rural areas, compaction can occur when large equipment is driven over or through the soil during agricultural activities. Tilling, fertilizing, harvesting and tile installations are all activities which can compact soils. In urban areas, soil compaction primarily occurs by use of heavy equipment during grading and construction operations as part of land development. Installation of impervious surfaces such as roofs, driveways, parking lots and streets can virtually eliminate infiltration which increases runoff volume.

Runoff volume is also increased when native plants, trees and other vegetation are removed. Plants use water in photosynthesis, changing air and water into sugars for growth. They also distribute water to their leaves and release it back into the atmosphere using a process called transpiration. Their root structures dig deep into the soil, helping to keep it loose and porous. They provide habitat for worms, insects and burrowing animals which also increase void spaces within the soil.

As landscapes are developed, many changes also effect the speed at which runoff is funneled to streams. This decreases the time of concentration, or the longest time it takes for runoff to reach the most downstream point from the extents of a given area. In agricultural areas, many ditches and tiles were constructed to drain wetlands and low lying areas. In some areas, the alignments of larger streams were straightened. Roads were installed with ditches and culverts. In urban areas, impervious areas collect runoff and quickly funnel it into gutters and storm sewers. The pipe network very quickly routes this runoff to the nearest pond or stream.

The combination of these effects results in a system which has been significantly altered from natural conditions. By modeling a case study of a developing area, the effects of these changes can be seen. Runoff volumes in both the agricultural watershed and suburban environments are likely to be several times higher than pre- settlement conditions. The proportion of increases are highest during the smaller, most frequently occurring storms. It should be noted that this comparison is based on suburban conditions (primarily single-family with some commercial growth, with a total of 40-45% impervious cover). More intense development scenarios would be expected to generate even higher runoff volumes.

Shortened time of concentrations magnify the effects of increased runoff volume. In rural areas, peak rates of flow may be nearly 20 times higher than pre-settlement levels during the most frequently occurring storms. In the suburban environment, peak rates for these events are expected to be 20-45 times more than the natural conditions. These drastic changes demonstrate how storm events of less than three inches of rain can cause rapid rises in stream levels and flash flooding. These effects are likely most dramatic in smaller streams in urban developed areas. These quick bounces account for a significant amount of streambank erosion on an annual basis, leaving the streambanks weakened and vulnerable for more significant impacts from the more rarely occurring larger events.

Review of Existing Monitoring Data for Key Pollutants

Now that we have identified the key pollutants of concern, it is important to review the available monitoring data for these pollutants in greater detail.

Data collected by the ISA/ACWA offers the highest number of samples, typically collected every other week. Site 40 is also located just downstream of a USGS gaging station, and is less than two miles from the weather station located at the Des Moines Airport. Collectively, this information offers opportunities to understand how pollutant concentrations vary with time, streamflow and climate patterns.

IOWATER data collection does not have as many samples at each site, but has more sites distributed throughout the watershed. This data can be used in determining where higher pollutant concentrations are most likely located.

Nitrate (Nitrogen) ISA/ACWA Monitoring A total of 168 samples were collected and analyzed for nitrate from the ISA/ACWA site 40 between 1999 and 2014. At sites 70.0, 70.1 and 70.2; a total of 131 samples were collected between 2002 and 2014. Reviewing this data indicates that nitrate concentrations appear to be significantly higher in streams within the rural landscapes. (The site 70 locations were positioned in a primarily rural watershed, whereas site 40 received runoff from both urban and rural sources.) It appears that nitrate concentrations in urban runoff is lower, diluting nitrate concentrations as those flows enter the stream.

At both sites, concentrations were highest during the months of April through July, with peak levels occurring in May and June. This trend seems to follow the times after spring fertilization has occurred and when rainfall patterns are near their highest levels. It should be noted that concentration levels were noted to drop significantly in August, although average precipitation remains high during this month. Concentrations remained

Nitrate concentrations were 78% higher on average in rural areas; 49% of all samples taken at the rural ISA/ ACWA site were above the state's water quality standard.

Several IOWATER sites had average lab results for nitrate concentrations which exceeded the state standard.

Several IOWATER sites had average lab results for nitrate concentrations which exceeded the state standard.

Test kit data also indicated elevated nitrate concentrations in rural areas.

The Walnut Creek Watershed Management Authority was formed in 2014