Combined Sewer Overflow in Mishawaka, IndianaM. Azzarello, H. Briceño, R. Jansen, N. Logishetty, D. Manhard, A. SohnUniversity of Illinois Urbana-ChampaignAugust 2013

TABLE OF CONTENTS1. Introduction........................................................................................................................................................3

1.1 Combined Storm Sewers - Background.......................................................................................................3

1.2 Current Situation in Mishawaka, Indiana....................................................................................................3

2. Evaluation of Alternatives...................................................................................................................................6

2.1 High-Rate Clarification................................................................................................................................6

2.2 Sewer Separation........................................................................................................................................8

2.3 In-Line Storage............................................................................................................................................8

3. Economic analysis.............................................................................................................................................10

3.1 High-Rate Clarification..............................................................................................................................10

3.2 Sewer Separation......................................................................................................................................10

3.3 In-Line Storage..........................................................................................................................................11

4. Recommendations............................................................................................................................................13

Works Cited...............................................................................................................................................................14

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1. INTRODUCTIONThe city of Mishawaka, home to 500,000 people, is located in northern Indiana near the Michigan border. The St. Joseph River stretches 206 miles from its start in Southern Michigan through the heart of Mishawaka city and finally discharges into Lake Michigan. The St. Joseph River is known for fishery and for a variety of outdoor adventure sports. However, like many other cities in the USA, the city is experiencing combined sewer overflow (CSO) issues. There are currently 23 CSO source points in the city, and they discharge 49 million gallons per year (MGPY) into the river. Because the St. Joseph River is such a valuable local resource, and because it discharges into Lake Michigan, it is of tremendous environmental importance that the city of Mishawaka manages its CSO output.

1.1 COMBINED STORM SEWERS - BACKGROUNDIn the early 1900s, storm sewers were constructed to aid in the removing of excess storm water, including rain and melting snow. The sewers worked through gravity and discharged at the nearest stream. The advent of indoor plumbing resulted in many property owners connecting their sewage lines to the storm sewers, and hence came the name “combined storm sewers.” As treatment plants were constructed, the combined sewers were routed to them instead. However, during wet weather events, the excess precipitation causes the sewers to overflow into nearby waterways. This results in contamination of public waterways with suspended solids, pathogenic microorganisms, toxic pollutants, and oxygen-demanding organic compounds. These contaminants pose serious risk to human health and balanced ecosystems. This is the reason the EPA, in the 1972 Clean Water Act, clearly outlined a National Pollution Discharge Elimination System (NPDES). The NPDES called for a complete elimination of CSOs through a long-term strategy. There are currently 750 communities in the USA that have CSO problems, and are trying to solve them.

1.2 CURRENT SITUATION IN MISHAWAKA , INDIANAMishawaka has expressed concern and made significant strides in addressing its CSO problem. Originally the city discharged a total CSO of 314 MGPY into the St. Josephs River. Nonetheless through an investment of $90 million they have been able to reduce this rate to 49 MGPY. A great number of the total 23 CSO source points left are close to Merrifield Park, located in northern Mishawaka adjacent to the St. Joseph River. Mishawaka is a 17 sq. mile town located on the Northern region of the state of Indiana. It currently hosts a population of 48,200 individuals and there is an approximate of 24,000 housing units. Mishawaka is one of 700 USA

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towns that face the problem of combined sewer overflows (CSOs). Combined sewer overflows occur in a combined sewer system during wet weather conditions when the wastewater treatment plant is not able to receive both the storm water and the sewer wastewater, and the excess water must be discharged to a nearby water body.

In the case of Mishawaka, the excess water is discharged to the St. Joseph River. The river makes its way to the east and it finally discharges into Lake Michigan. Mishawaka currently has a CSO of 49 million gallons per year (MGPY). This may seem small compared to the 18.7 billion gallons per year of CSO volume that Lake Michigan receives, but it is in fact a considerable quantity of water and can have a significant effect on the composition of large bodies of water, particularly at the point of discharge, where it is most concentrated. Additionally, the CSO discharge into the St. Joseph River has proven to be a health risk to the many residents and tourists that frequent the river to participate in recreational activities, prompting the city to post warnings near the outfalls in an effort to protect patrons of the river.

FIGURE 1. CSO NOTICE IN MISHAWAKA (MAY 9, 2013).

There are 23 CSO points in the city of Mishawaka. According to the local authorities, a 2.37” design storm is used as the worst-case scenario. This storm is a 1hr-25 year return period storm, and it produces 2.9MG of CSO. Fourteen CSO points in the Merrifield park area, pictured in Fig. 2, are a threat to the health of not only people of Mishawaka, but also of all those who

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depend on the Michigan Lake in any way. The 14 CSO source points must be eliminated through the best fit alternative.

FIGURE 2A. MAP OF CSOS OF MISHAWAKA.

FIGURE 2B. MAP OF CSOS OF MISHAWAKA. CSOS ARE DENOTED BY CIRCLES; ARROWS POINT IN DIRECTION OF FLOW.

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2. EVALUATION OF ALTERNATIVESFive potential methods of bettering the CSO issue in Mishawaka were considered, as follows: in-line storage, high rate clarification treatment, sewer separation, off-line storage, and expansion of the local wastewater treatment plant (WWTP). Off-line storage, also referred to as an off-line retention basin (RB), was eliminated due to the relatively infrequent need for storage of wet weather flows, which could create a risk of septicity in the tank. The option to expand the WWTP capacity was also eliminated, due to high cost and insufficient space available. Thus, our team evaluated three alternatives: (1) high-rate clarification, (2) sewer separation, and (3) in-line storage: reservoir basin. Table 1 indicates the volume of water observed at each CSO location, with the total volume of a 2.37” storm reaching 2.9 MG, which is the quantity of water we selected for our design.

TABLE 1. VOLUME OBSERVED AT EACH CSO GIVEN A 2.37" DESIGN STORM.

CSO # MG9 1.111

11 0.23812 0.164

12A 0.07913 0.08814 0.07115 0.85416 0.00018 0.23919 0.00020 0.02221 0.00022 0.00223 0.000

23A 0.00124 0.000

TOTAL 2.9

2.1 HIGH-RATE CLARIFICATIONIn systems using high rate clarification (HRC) as treatment, a system is traditionally installed at every CSO discharge point and is in operation during wet weather conditions only. In our project, a sand filtration mechanism was chosen. It essentially works as a small wastewater

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treatment plant. The mechanism involves a process of coagulation, flocculation, filtration, and chemical treatment. The system works, nonetheless some drawbacks have to be considered, namely the cost of O&M, the cost of operation at low flow rates, and the limited amount of documented research regarding the use of high clarification systems.

One potential solution to Mishawaka’s CSO problem is the use of high rate clarification technology. This is a relatively new technology, having been introduced roughly 20 ago, which allows for water to be purified external to a treatment plant quickly and efficiently. Often times during peak flows or large storm events there are is a large amount of water that cannot be easily treated by an average municipality. Although engineers try to prepare for events like this, sometimes a little extra help is needed. High rate clarification provides a way to quickly treat water (in the case of Mishawaka, water leaving a CSO) and is often employed when building an additional water treatment plan is not feasible. A company called Krueger has found success in implementing a high rate clarification system called Actiflo (pictured in Fig. 3) into many communities. Actiflo and other high rate clarifiers work using technique called ballasted flocculation. This process uses a sand ballast chemical treatment to speed up the flocculation and sedimentation process. The small footprint and the quick treatment provided by the system make it ideal for situations like the one in Mishawaka, making it a viable option.

FIGURE 3. DIAGRAM OF ACTIFLO HIGH-RATE CLARIFICATION SYSTEM.

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High-rate clarification is attractive as a wet-weather treatment train because capital costs are relatively low and because operational costs are incurred only during peak-flow events.

2.2 SEWER SEPARATIONSewer separation refers to the complete separation of sewer flow and storm flow through the addition of a new pipe system. The city map of Mishawaka was used to calculate the amount of pipe needed for this design. 130 miles of pipe were found and pipes ranging from 12-96 inches, made of concrete, were used for the solution design. Also, excavation/installation costs were taken into account, and are described in the Economic Analysis. Through an examination of the West sewer system of the city, 90 storm pipes would be installed, with a layout similar to the current system. The storm water would be routed through the new pipes and discharged at the river. Approximately 190 km of storm sewer pipe would be needed. Pipes will be ordered from an authorized sales representative or distributor. The provider will most likely be in the field guiding the contractor to due the work. OSHA federal regulations must be followed. The alignment will be established by a field survey, and a trench will be excavated on line.

Nonetheless, some issues with sewer separation are that storm water can easily route surface pollutants to the river. The future could bring tougher regulations to storm water discharges, and this could make this option not viable in the long term. Reinforced Concrete Pipe (RCP) is limited by wall thickness requirements, pH, sulfate levels, and minimum bury depth. Polyvinyl Chloride pipe (PVC) is generally limited by size, ultraviolet degradation, flotation, pipe stiffness, and minimum cover depth. Aluminized Steel Pipe (ASP) is generally limited by pH, soil resistivity, flotation, corrosive agents, abrasive flows, and minimum cover.

2.3 IN-LINE STORAGEThe in-line storage design solution was an underground basin that is constructed out of non-corrosive steel. It has the benefit that it produces no odor problems, since it is underground, and that the stored contaminated water is treated in the original waste water treatment plant once the wet weather terminates. This system only has minor drawbacks, namely the permanent use of pump systems to move water into the wastewater treatment plant and the availability of land at low elevation regions, to avoid the structural and geotechnical difficulties that are encountered in deep underground designs. It was determined that a deep tunnel underground storage system would be excessive both in volume and cost for the needs of Mishawaka, as the CSO volume is relatively small. Thus we turned our attention to aboveground and underground retention basins.

With an underground system, odor control requires less control, but cost of installation and maintenance would increase, while the opposite issues are seen with an aboveground system.

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The design storm indicates a necessary storage volume of approximately 3 million (2.87 million exactly) gallons. To minimize the risk of failure due to excessive loading, we used a factor of safety of approximately 1.4 and designed the storage tank with a volume of 4 million gallons and determined that there would be space available directly east of the Mishawaka wastewater plant. After considering the footprint and the volume required for the basin, we settled on dimensions of 200 ft x 140 ft x 20 ft, which would easily fit onto our plot of land.

Our plan would direct all of our CSO runoff into this storage tank during large storms when CSO points would be active. Once the storm ended and the wastewater plant was functioning at a normal rate, the tank would be emptied to be treated by the plant. Overall, it would provide for 15 of our CSO points to be completely eliminated.

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3.ECONOMIC ANALYSISThese calculations take into account the cost of installation, as well as operations and maintenance over the life of the system, which was designated as 20 years. The cost of installing a high-rate clarification system was prohibitive, unfortunately, and greatly exceeded the cost of an underground reservoir system. Complete sewer separation proved to be the most costly option of the three we considered; however, it is anticipated to have the longest-lasting effect.

3.1 HIGH-RATE CLARIFICATIONHigh-rate clarification costs were calculated based on a similar installation project performed by CH2M Hill, and adjusted according to the magnitude of the Mishawaka project. These calculations are shown in Table 2.

TABLE 2. CALCULATIONS FOR INSTALLATION OF A HIGH RATE CLARIFICATION SYSTEM AT CSO OUTFALL 009.

Operation & maintenance (20y) $28,995,620.00 Cost of initial system $240,294.19 Total capital cost $3,430,400.00 Total cost $32,666,314.19

3.2 SEWER SEPARATIONA layout of a potential sewer system was created, using appropriate pipe diameters. Costs were calculated with the lengths and pipe diameters projected, and are listed in Table 3B.

TABLE 3A. CALCULATIONS FOR PIPE NEEDED IN COMPLETE SEWER SEPARATION.

Diameter Price Miles Total(inches) per 8ft of RCP Cost

18 77.03 30 $1,525,19421 96.15 20 $1,269,18024 118.65 15 $1,174,63530 175.05 15 $1,732,99536 248.93 12 $1,971,52642 343.43 10 $2,266,63848 418.05 10 $2,759,13054 570.16 5 $1,881,52860 691.04 4 $1,824,34666 832.16 3 $1,647,67772 1024 3 $2,027,520

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84 1479.6 2 $1,953,07296 1913.84 1 $1,263,134

130 $23,296,574

TABLE 3B. COST CALCULATIONS FOR COMPLETE SEWER SEPARATION.

Quantity Unit Unit Price Total PriceRemove Asphalt 152533 SY 14 $2,135,467Excavation (CY) 305067 CY 20 $6,101,333

Manholes 1525 EA 5,000 $7,626,667Rubber Gasket 1232692 LF 20 $24,653,840Field Adaptors 195 EA 2000 $390,000

Backfill & compact 305067 CY 40 $12,202,667Paving 152533 SY 90 $13,728,000

$66,837,973

Total Cost $90,134,547.64

3.3 IN-LINE STORAGEUltimately we used Acacia Park, Michigan as a model for our implementation costs. In 1999 this community installed 4 million gallon underground retention basin for its multiple CSO points. The tank was installed near the community’s wastewater plant which was located downstream of the CSO points (just like Mishawaka’s plant is). Overall, this blueprint was ideal to what we were trying to accomplish with our problem as almost all characteristics of this community were very similar to Mishawaka.

Doing more research into the Acacia Park basin, as mentioned in the Alternatives Analysis section, we found that the total cost would be approximately 10.8 million with an operation and maintenance cost of $207,000 per year. Because of the plant and tank being downstream of the CSO points, no pumping system was installed to move the water to the plant, only gravity was utilized. The basin was complete with a dewatering and decanting system, with 4 pumps (two 2800 gpm and two 3000 gpm) pumps installed for these processes.

Installing a system in Mishawaka similar to the one in Acacia Park, would be very useful in solving our CSO problem with a rough cost of 10.8 million dollars. Including operation and

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maintenance for a system with a 20-year life, the present-worth cost totals approximately $14,940,000.

FIGURE 4. MISHAWAKA WWTP WITH POTENTIAL LAND FOR STORAGE SYSTEM BOXED IN RED.

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4.RECOMMENDATIONSAfter the three alternatives were designed and their cost taken into account, we decided to opt for the lowest present cost solution for the city of Mishawaka. The design solution was #2 combined with #3: the reservoir basin and a partial separation system, which will work to safely route all excess water flow into the reservoir basin.

The reservoir basin will function to minimize excess flow, while avoiding the steep initial costs associated with sewer separation. At the same time, we felt it was important to begin sewer separation to help the city of Mishawaka proceed with the goal of complete sewer separation, which we feel should be the ultimate goal, and to avoid future need for reservoir expansions. Since all three options are possible to effectively implement in the city of Mishawaka, we opted for the lowest present cost, while also choosing to look forward with the ultimate goal of complete sewer separation, which would be obtained outside of this project. With a reservoir cost of $15M and a partial sewer separation cost of $25M over the lifespan of the project, we would anticipate a total cost of $40 million for the entire project, including capital cost and operation and maintenance.

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WORKS CITED1. "ACTIFLO®." Veolia Water Solutions & Technologies. N.p., n.d. Web. March 2013.2. B urns & Donnel Engineering Company, Inc. Urban Drainage and Flood Control District -

Araphoe County. Eaglewood, 1998.3. City of Mishawaka. Mishawaka City. 2012. March 2013 <http://mishawaka.in.gov/csonews>.4. Department of Public Works. Standard Prices for Cost Estimating. Rockville, 2010.5. EPRI Municipal Water and Wastewater Program. High-Rate Clarification for the Treatment of

Wet Weather Flows. Palo Alto: EPRI, n.d.6. GRUNDFOS. Design of Stormwater Tanks. Poul Due Jensens: GRUNDFOS A/S, n.d.7. Hubbel, Roth & Clark, Inc. Retention Basin Evaluation for the Acacia Parc CSO RTB.

Technical. Oakland County CSO Abatement Program. Bloomfield Hills, 2000.8. Indiana Department of Environmental Management. Indiana's Municipal Separate Storm Sewer

System (MS4). Indianapolis, 2003.9. Lyandres, Olga. "Reducing Combines Sewer Overflows in the Great Lakes." 2012.10. Pacific Northwest Precast Concrete Association. "Reinforced Concrete Pipe." n.d.11. U.S Department of Commerce. State & County Quick Facts. January 2013. March 2013

<http://quickfacts.census.gov/qfd/states/18/1849932.html>.12. Veolia Water. ACTIFLO - The Ultimate Clarifier. Saint-Maurice, n.d.13. "Wastewater Technology." Home. N.p., n.d. Web. March 2013.

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