What has already been done to reduce CSO impacts?

Construction of two wastewater treatment plants in the 1950s eliminated Evansville's direct discharge of untreated sewage into the Ohio River and Pigeon Creek. The Ohio River Valley Water Sanitation Commission (ORSANCO) is an eight-state water pollution control agency established in 1948. ORSANCO data indicates that the Ohio River's water quality has improved considerably during that time. ORSANCO's web site, "EMPACT", states, "Ohio River pollution control on the federal, state, and local levels have done much to improve water quality in the Ohio River. Fifty years ago, the Ohio River was treated as an 'open sewer'.

People are now using the river for swimming, boating, jet-skiing, and fishing; festivals in celebration of our Ohio River heritage are held in many towns along the river ... all possible because of improved water conditions over the last few decades. " Since the 1930s, interceptor sewers were constructed which connect multiple CSOs and "intercept" wet weather flow immediately prior to it reaching the receiving stream via the CSO outfall. That "intercepted" flow is retained in the system and diverted to one of the two wastewater treatment plants. While interceptor sewers have no problem carrying the waste water to the plants during dry weather, additional water flowing into the system during wet weather often exceeds the capacity of the interceptors.

During the 1980s, the City of Evansville constructed seven large CSO control structures along Pigeon Creek. They were designed to eliminate approximately 66% of CSO bypassing at the largest outfalls to the creek, while storing and allowing treatment of the more serious short-duration1 high-intensity storms. The electronic controls of these stations were updated in 1990. The approximate total expenditure for this system was 5.7M dollars.

The City has spent millions of dollars completing treatment plant and collection systems improvements during the last decade. Collection system rehabilitation projects and the rerouting of a major eastside sub-basin have reduced volumes and eliminated several bottle-necks, thus saving treatment plant capacity for other wet weather flows. Each year funds are allocated to perform collection system rehabilitation which reduces system failures and keeps groundwater from entering joints and cracks. Continuing efforts such as these will ensure the improvement of Evansville's combined sewage network.

What is presently being done to reduce CSO impacts?

In April 2001, Emironmental Management Corporation (EMC), under the direction of the EWSU, began development of an LTCP. The LTCP will lltilize the results and recommendations of the Pigeon Creek SRCER to help establish practical and effective CSO controls for the Pigeon Creek CSO network. The same type of controls will be considered for the Ohio River CSO network. In both networks, E. coli reduction will be a targeted priority.

Extensive collection system flow monitoring has recently been performed which will allow the creation of a computerized hydraulic model of the CSS. The model is useful in simulating the CSO reduction possible by modi6cations to the collection system. It creates a cause/effect relationship between precipitation and CSO discharge quantities. It will also be used to determine what net reduction prior control projects have had upon CSO discharge frequency and volume.

The USEPA states, "Monitoring and modeling activities are central to implementation of the CSO Control Policy. Thoughtfil development and implementation of a monitoring and modeling plan will support the selection and implementation of cost-eflective CSO controls and an assessment of their improvements on receiving water quality".

Typical CSO control projects consist of separating sanitary and storm sewers, increasing primary treatment capacity at wastewater treatment plants, inflowlinfiltraton reduction efforts, in-line storage projects (similar to the seven structures mentioned earlier), off-line storage facilities, and runoff control programs. The LTCP will consider the feasibility of these and additional technology-based CSO controls for the Evansville community. Evansville's LTCP was completed during the spring of 2002.

Evansville is presently conducting bacterial (E. coli and fecal coliform) sampling along the Ohio River to establish the degree of their impact upon the Ohio River. This sampling is being conducted according to discussions held with both the IDEM and ORSANCO. Also, bacterial sampling data regularly obtained by the ORSANCO is available on their website.

Evansville's sanitary sewers and lift stations, combined sewers, and two wastewater treatment plants are managed by EMC, under the direction of the EWSU Board and its General Manager, Jim Cameron. This publidprivate partnership provides high quality wastewater services to Evansville citizens, and keeps the city compliant with state and federal regulatory requirements. EMC and the Utility Board operate in a proactive manner, allowing the Utility to adapt to emerging technologies and regulations.

Solutions to CSOs

Since 1980, the City of Evansville has invested approximately $70,000,000 in CSO control related projects which are separated by the following categories:

  • » Pigeon Creek Overflow Control Facilities
  • » Sewer Rehabilitation and Infiltration/Inflow Reduction Projects
  • » Backflow Prevention Projects
  • » Sewer Separation Projects
  • » Relief Sewer Project
  • » Long Term CSO Control Projects

Pigeon Creek Overflow Control Facilities

The Pigeon Creek Overflow Control Facilities were completed in the 1980. It involved the installation of automatically controlled, hydraulically operated sluice gates to control the discharge of the following seven CSOs along Pigeon Creek:

  • » CSO 011 (Oakhill)
  • » CSO 012 (Maryland)
  • » CSO 013 (Delaware)
  • » CSO 014 (Dresden)
  • » CSO 016 (Franklin)
  • » CSO 024 (Baker)
  • » CSO 025 (Diamond)

The figure above Figure 3.2 shows the details of a typical overflow control structure. The position of the sluice gates is set by on-site controllers to maximize storage of wet weather flows in the sewers and minimize bypassing to Pigeon Creek. The total maximum storage capacity of the sewers is estimated at 5.5 million gallons (MG). Shut-off gates were also installed in the diversion structures to prevent the flow intrusion from Pigeon Creek.

The Pigeon Creek Interceptor, which can also be utilized to store combined sewage if the 7th Avenue Lift Station pumps are throttled, has a maximum storage capacity of approximately 2.2 MG (Note: the Pigeon Creek Interceptor begins at Diversion Structure #025 and runs south toward the 7th Avenue Lift Station).

As part of the project, all brick sewers larger than 24-inch in diameter tributary to the CSO control structures were structurally rehabilitated with reinforced pneumatically applied concrete (shotcrete) to stand the internal pressures exerted by the stored wastewater. The control systems for the seven in-system storage facilities were further revised and updated in 1990.

Sewer Rehabilitation and Infiltration/Inflow Reduction Projects

The sewer rehabilitation and I/I reduction program for the City of Evansville has produced many corrective sewer projects since approximately 1980. One purpose of the program is to rehabilitate existing sewers in order to reduce I/I during wet weather events. Another purpose is to reduce infiltration during high groundwater conditions. The result of these programs is the reduction of flow to CSO outfall points.

Since 1993, several sewer rehabilitation and infiltration/inflow (I/I) reduction projects have been completed within both east and west sewer basins. These projects were in Subsystems E-1, E-2, E-3, E-5, E-7, E-8, E-9, E-10, E-11, E-12, W-2, W-4, W-5, W-6, W-7, W-8, and W-10.

There were no flow measurements before and after each sewer rehabilitation project; therefore, it is impossible to estimate the amount of I/I that was reduced as a result of each sewer rehabilitation project. However, according to the plant operation personnel, the dry weather flow to the two wastewater treatment plants may have been reduced by as much as 3 MGD.

Backflow Prevention Projects

Since 1995, Tide-Flex type backflow prevention valves have been installed in the outfalls of the following CSOs to prevent river water from backing into the sewer system:

  • » CSO 002 (Cass)
  • » CSO 004 (Adams)
  • » CSO 010 (Sycamore)
  • » CSO 011 (Oakhill)
  • » CSO 013 (Delaware)
  • » CSO 015 (7th Avenue east)
  • » CSO 024 (Read)

In addition, a metal flap gate was installed at CSO 009 (7th Avenue west).

 

Sewer Separation Projects

A Stormwater Master Plan was prepared in 1997 for the City of Evansville's Department of Public Works. The major component of this plan involved the identification, evaluation, and recommendation of projects to reduce street and basement flooding in the combined sewer areas. The proposed storm sewers also have the benefit of reducing the amount of storm water to the combined sewer system.

The Stormwater Master Plan is presently being implemented. Storm sewers have been constructed for flooding control at the following locations in the combined sewer area with a total cost of approximately $28,000,000.

  1. Fulton and Columbia
  2. North Weinbach
  3. St. Joe and Maryland

The remaining $36,000,000 in CSO related flooding projects, described in Subsection 4.5.8, are proposed to eliminate flooding problems in Evansville.

Relief Sewer Project

In an effort to reduce wet weather overflow at CSO 11 (Oakhill), the S-5 Relief Sewer Project was undertaken in 2001 near the Evansville State Hospital. It involved the construction of a 42-inch sanitary sewer from Division Street to Villa Street to redirect the sanitary flows from subsystems E-9, E-10 and E-12 to subsystem E-5. This reduces the average daily and peak hourly flows to the Weinbach Avenue diversion structure by approximately 3 MGD and 12 MGD, respectively.

The redirected wastewater eventually flows to Diversion Structure 001 just upstream of CSO 001, before continuing on to the Eastside WWTP. Surface drainage in the State Hospital area, located in subsystem E-5, was diverted to the 48" pipe that flows to the Weinbach Avenue Lift Station. Future projects to remove the State Hospital storm flow from CSO 011 (Oakhill) will be beneficial to CSO reduction efforts.

Long Term CSO Control Projects

Since 1993, Evansville has conducted a number of engineering studies to meet the CSO control requirements of its two NPDES permits and for the preparation of the CSO Long Term Control Plan (LTCP). These studies are as follows:

  • CSO Operational Plan (1993)
  • CSO Solids and Floatables Study (1996)
  • Treatment Plant Stress Testing Protocol (1996)
  • Combined Sewer System Flow Monitoring (1997)
  • Pigeon Creek Stream Reach Characterization and Evaluation Report (1999-2001)
  • CSO Sewer Survey and Flow Monitoring Program (2000-2001)
  • LTCP Survey (2000-2001)
  • LTCP Flow Monitoring ( 2001)
  • CSO Long Term Control Plan (2000-2002)

Impact of Previously Completed CSO Control Projects

The SWMM model was used to estimate the overflow amount and frequency for each CSO. The purpose of this simulation was to establish a baseline condition of the combined sewer system. The results were used to assess the effectiveness of the CSO controls previously implemented.

Westside Combined Sewer System

Table 3.2 contains the simulation results for the current and prior to CSO control conditions. The results indicate that the Pigeon Creek in-system storage facilities have reduced the CSO volume for the Westside by more than 5%. The CSO volume to Pigeon Creek decreased by 47%, while the CSO volume to the Ohio River increased by 54%. During wet weather events, the CSO outfall sluice gates close allowing the upstream interceptor to surcharge for temporary storage of flow.

The primary benefit of the Pigeon Creek in-system storage facilities is the decrease in CSO discharges to Pigeon Creek. Therefore, the water quality and aesthetics of Pigeon Creek have been improved dramatically since the construction of the seven (7) in-system storage facilities. Although this results in an increase in CSO discharge to the Ohio River, the impact on the Ohio River is relatively small since it is a much larger water body.

Another benefit of these control facilities is the capture of the first flush of pollutants. The overflow control structures were designed to store the initial storm runoff that has the highest pollutant loading, known as the "first flush". The stored wastewater is conveyed to the WWTP for treatment after the event is finished.

Eastside Combined Sewer System

As can be seen from Table 3.2, the previous CSO control efforts have resulted in a 2% CSO volume reduction in the Eastside system. This is most likely due to the overflow control structure on CSO 011 (Oakhill) and the S-5 Relief Sewer Project.

Total Combined Sewer System

Overall, the total CSO volume in the combined sewer system has decreased by 4%. The percent capture of wet weather flow has increased from 36% prior to CSO controls to 39% for the current situation. The percent capture is defined as the percent of wet weather flow collected in the combined sewer system that is eliminated or captured for treatment. The wet weather eliminated or captured for treatment is determined by the amount treated in the SWMM model, while the total wet weather volume is the total sanitary sewer and rainfall volume that enters the SWMM model.

Table 3.2

Estimated Average Annual Overflow Events and Discharge Volume

Outfall

CSO Volume (MG)

No. of CSO Events

 

Prior to CSO Control

Current Situation

Percent Reduction

Prior to CSO Control

Current Situation

Percent Reduction

 

CSO 006 ( Fulton L.S.)

0

0

0%

0

0

0%

CSO 009 ( 7th Ave West)

0

0

0%

0

0

0%

CSO 012 ( Maryland)

81

56

31%

51

41

20%

CSO 013 ( Delaware)

58

128

- %

27

37

- %

CSO 014 ( Dresden)

0

3

- %

3

19

- %

CSO 015 ( 7th Ave East)

203

701

- %

47

44

6%

CSO 016 ( Franklin)

79

55

31%

37

28

24%

CSO 018 (Oakley)

7

6

15%

26

26

0%

CSO 020 ( 9th Ave)

19

41

- %

35

43

- %

CSO 022 (St. Joe)

136

200

- %

53

53

0%

CSO 023 ( West WWTP)

0

0

0%

0

0

0%

CSO 024 (Baker)

50

40

20%

30

25

17%

CSO 025 (Diamond)

1009

324

68%

43

29

33%

West CSO Total

1642

1554

5%

 

 

2%

CSO 001 ( Kentucky)

73

88

- %

33

36

- %

CSO 002 (Cass)

38

39

- %

18

18

0%

CSO 003 ( East WWTP)

580

610

- %

44

44

0%

CSO 004 (Adams & Sunset)

49

49

- %

39

39

0%

CSO 005 (Shadywood)

6

6

0%

38

38

0%

CSO 008 (Chestnut)

84

84

0%

32

32

0%

CSO 010 (Sycamore)

67

67

0%

40

49

-%

CSO 011 (Oakhill)

94

29

69%

36

33

8%

CSO 038 (Oak)

44

44

0%

35

35

0%

East CSO Total

1035

1016

2%

 

 

0%

CSO Total

2677

2570

4%

53

53

0%

Bee Slough Total

166

182

- %

39

39

0%

Ohio River Total

1133

1747

- %

53

53

0%

Pigeon Creek Total

1378

641

53%

51

41

20%

% Capture*

36%

39%