Systems Planning

Sanitary Sewer Improvements Preliminary Engineering Project

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Purpose   Public engagement   S​chedule   Fieldwork   Documents

Public meeting



The City maintains a sanitary sewer system with about 360 miles of sanitary sewer pipes. More than two-thirds of these pipes were built in the 1960s or earlier.

Together with other wet weather projects such as the Stormwater Model Calibration and Analysis, Water and Wastewater System Capital Cost Recovery Study, Upper Malletts Drainage Study, Village Oaks-Chaucer Court Drainage Study, Sanitary Sewer Wet Weather Evaluation Project, the City is taking a comprehensive and strategic approach to managing our sanitary sewer and storm water infrastructure.

Recent projects that performed analysis and modeling of the sewer did identify five potential areas in the system where a problem may be limiting capacity during wet weather events. (These are not the same as the five original FDD target areas.) Consultants on the project are using a range of techniques to attempt to determine the problems and potential impacts.

Engineers will also evaluate a sixth area within the system that is not a capacity problem, but an opportunity to improve the operation of the sanitary sewer by maximizing the amount of flow through the south interceptor to reduce the flow that must be pumped to the treatment plant.

These project areas are significantly less than what the City staff was expecting based on past studies. An action plan was prepared for each area, which led to the Sanitary Sewer Improvements Preliminary Engineering Project.

The Sanitary Sewer Improvements Preliminary Engineering Project is nearly complete. The project team has collected and analyzed data, modeled the issues and engaged the public in specific neighborhoods to discuss potential solutions.


During the Sanitary Sewer Wet Weather Evaluation project, five potential capacity issues and one operations improvement opportunity were identified in the downstream sanitary collector interceptors. These are the areas that have been identified as having wet weather capacity issues potentially due to excess inflow and infiltration (I/I), pipe capacity, and/or unusual hydraulic losses.

The goal of the Sanitary Sewer Improvements Preliminary Engineering Project was to find the cause of these potential capacity issues and to determine the best solution for each area, based on community values, cost and effectiveness.

The final determination includes recommendations for several construction projects to remedy capacity issues. Those projects will be prioritized as part of the City's Capital Improvement Plan (CIP) process and will become future capital improvement projects.

The project areas are:

Project Area A – Huron West Park Trunkline.

In this area, the project team collected flow data, and updated the City's sanitary sewer model with refined data. During the analysis, the team found that one portion of the system was functioning adequately, while another section, the east-west line, needs additional capacity. Engineers recommended that the City upsize the capacity by building a relief sewer.

Project Area B – High Level Trunkline (near 1st Street including Liberty Washington Trunkline)

Project Area C – High Level Trunkline (near State/Hoover)

Metering performed as part of the SSWWEP project showed surcharging in Areas B and C. However, given the flows and size of pipe, these areas should have adequate capacity. Field crews examined pipes and manholes for blockages that could be causing the hydraulic anomalies, but found nothing. As a next step, 12 flow meters were installed in the area to locate the anomaly. Engineers await a rain event large enough to trigger the surcharging to further attempt to isolate the cause of the issue. 

Project Area D – Pittsfield Valley

Metering from the SSWWEP project showed overloaded pipes in this neighborhood. Field crews performed additional flow metering, reviewed CCTV footage of sewer pipe inspection, inspected manholes and conducted smoke testing. Residents participated in a survey, to share their experiences with basement sanitary backups.

Analyzing the data, the project team found high footing drain flows overwhelming several pipes on the eastern side of the neighborhood, as well as a few on the northwest side. Modeling showed that the other areas of the neighborhood had adequate capacity to handle design flows recommended by the SSWWP Citizens Advisory Committee: 25 year event frequency, plus 10% additional flow for growth and/or climate change.

The project team held two neighborhood meetings with residents to discuss the findings and improvement options, which were installing a relief sewer or disconnecting footing drains. Participants opted for relief sewers to replace pipes with insufficient capacity. This improvement will be programmed as part of the City's Capital Improvement Plan.

Project Area D – Expansion

The SSIPE project was expanded to include additional neighborhoods north of Packard Road and west of Platt Road. Field crews performed additional flow metering and smoke testing, reviewed CCTV footage of sewer pipe inspection, and inspected manholes. Residents also participated in a survey about basement backups. Engineers are analyzing the field data and survey information to determine the cause and extent of issues in this area.  

Residents are encouraged to attend the December 5 meeting to learn more about the findings in this area and options to improve the sanitary sewer function.

Project Area E – Winsted Lateral (Glen Leven Area)

Modeling in the SSWEP project found that a 1500ft stretch of pipe was overloaded and surcharging three feet during large rain events. Field crews performed basement surveys in this area to determine whether the surcharging impacted homes. Engineers found sufficient clearance for the recommended design event (a 25-year return interval storm event + 10% additional flow.) As the surcharging is not impacting homes, improvements are not needed in this area.

Project Area F – Glen/Fuller Diversion Structure

In this project area, engineering consultants are evaluating the hydraulic performance and will make recommendations to improve the operation of the sanitary sewer by maximizing the amount of flow through the south interceptor to reduce the flow that must be pumped to the treatment plant. Analysis is ongoing. 

Sanitary Sewer Improvements Preliminary Engineering Project map.jpg

Public engagement

At various points, the project team met with neighbors in some of these project areas to talk about the objectives of the project, learn about residents' experiences and evaluate the potential impacts of various solutions.

In certain neighborhoods, residents were surveyed about their experiences with the sanitary sewer system. This information was used in conjunction with data from fieldwork to determine the condition of the sanitary sewer system in specific areas. At neighborhood meetings, residents reviewed the project and weighed in on potential solutions.

Project schedule

February 2016 

Project Kickoff

February – September 2016

Collect Data 

  • Flow metering
  • Manhole inspections
  • Television inspection (CCTV) of sewer mains
  • Wet weather observation
  • Basement surveys
  • Smoke testing

July – October 2016

Analyze Data

September – December 2016

Update Sanitary Sewer Model

December 2016 – March 2017

Perform Preliminary Engineering Design

September 2016 – May 2017

Neighborhood Public Meeting

Capital Improvement Programming for Construction

June 2017 – Dec 2017

Collect Data – Expanded to additional neighborhoods in Area D

  • Resident Survey
  • Manhole inspections
  • Smoke testing
  • Neighborhood Public Meeting – late Fall 


Throughout the project, crews collected and analyzed additional information from the specific location to determine what improvements were required.

Below is a table showing some of the fieldwork performed in the project areas:

SSIPE Fieldwork chart.jpg

Here is more information about the different types of fieldwork being performed:

Flow metering: A flow meter is a device used to measure the flow rate or quantity of a gas or liquid moving through a pipe. Trained field technicians will install 20 flow meters into the sanitary sewer pipes to measure the volume of flow at specific locations.

Manhole inspections: Deteriorating manholes can allow excessive amounts of stormwater to enter the sanitary sewer system. Technicians will inspect and evaluate the conditions of manholes in Project Areas D and E. They will also check for obstructions, which could impact the system performance in those areas.

Smoke Testing: Smoke testing is a method for finding points of inflow and infiltration in the sanitary sewer system. Field crews blow a mist through the sewer system pipes. The mist has the appearance of smoke and is non-toxic, non-staining and is not a fire hazard. The vapor travels throughout the system, identifying problems in all connected lines, such as leaks, connected downspouts or roof drains.

Wet Weather Observation: In some of the areas with suspected hydraulic issues, field crews will mobilize during large rainstorms to measure the sewer levels at several manholes. This could happen during the day or at night, as it's dependent on capturing readings during wet weather conditions.

Basement Surveys: In four project areas where computerized models of the sanitary sewer system show potential for surcharging (when the sewer becomes overloaded from infiltration of stormwater or footing drain flows), field technicians will be performing basement elevation surveys in homes adjacent to the surcharged pipe area, to determine whether any houses are impacted


December 5, 2017

November 30, 2016

June 16, 2016 public meeting​

Troy Baughman, P.E.
Senior Project Engineer
301 E. H​uron St., 4th Floor
P.O. Box 8647
Ann Arbor, MI 48107​
734.794.6430 x​​43798