icon fb icon tw icon insta icon wp
After the Flush - Auburn Hills' Sewer System
 

small wastewater treatment Web

Sewage is something we rarely talk about. The wastewater from our toilets, showers and washing machines leaves our homes through drains that lead to a network of sewer pipes where someone else takes care of it. Sewage collection and treatment is a complex public service. It costs roughly twice as much to provide sewer service as water service because the treatment process is more expensive and there are more solids to dispose of.

It comes as a surprise to many that most US cities did not start treating their wastewater until the 1940s. Real progress came with the Clean Water Act in 1972 that required a higher level of pollutant removal in the treatment process and created a grant program to help upgrade wastewater treatment plants and sewer systems. The vast majority of plants today discharge a cleaner effluent, or treated wastewater, as a result of treatment process improvements or expansions made with those grant funds.

In southeast Michigan, approximately three million residents and thousands of businesses send wastewater down their drains each day to a network of sewer pipes that lead to the Detroit Wastewater Treatment Plant (WWTP). During the most active day in 2010, the plant treated 1.68 billion gallons of wastewater helping to keep 77 communities operating smoothly. The collection and treatment of wastewater is a coordinated effort between suburban communities, the counties and the City of Detroit. Wastewater is collected in 28,500 miles of sewer pipe leading to three major interceptor pipes that transport flows directly into the plant.

Detroit has one of the largest WWTPs in the US. Physical, chemical and biological treatment methods are used to remove solids and pollutants. On average, it takes about 8 hours to complete the treatment process and meet permit requirements.

How the weather impacts sewer service

While flushing toilets and heavy rain storms are not related, they both impact our sewer system. Combined sewers that transport both storm water and sewage in one pipe make up 30% of the sewer system land area (or 26 of the 77 communities) that sends flows to the Detroit WWTP. These older sewers were constructed when land was less developed. During rain storms, combined sewers collect the storm water that runs off our streets and houses in addition to sewage flows, receiving up to three times the volume of flow that is normally transported on a dry day. This places a burden on the collection and treatment system, forcing equipment to operate at higher capacities.

Many conventional sanitary sewers in the remaining 70% of the service area also receive more flow during storms from footing drains that are connected to the sanitary sewer. Up until the 1970s, footing drains on homes were connected to the sanitary sewer rather than to a sump in the basement. Like combined sewers, these sewers can become overloaded during storms.

As sewer volume increases during storms, the need to balance flows within the system becomes critical to avoid overloading the treatment plant, to avert sewer backups in homes, and to prevent untreated combined sewer overflows (CSO) and sanitary sewer overflows (SSO) from being discharged. Storage basins and CSO retention treatment basins (RTBs) have been constructed to address this. These basins operate during storms to capture the additional storm water flows and the treatment plant ramps up to maximum capacity.

Flowing through multiple facilities to reach its final destination

Sewer service is provided through a series of pipes owned by the homeowner, city or township, the County and the Detroit Water and Sewerage Department (DWSD). Communities purchase a portion of the transport capacity in an interceptor owned by the County. Some older communities that border the City of Detroit discharge their flows directly into Detroit sewers. Macomb, Oakland and Wayne Counties operate and maintain the large interceptor sewers that connect into Detroit’s interceptors leading to the WWTP as well as pump stations, storage basins and RTBs. The Counties have contracts with DWSD to send the suburban flows to the WWTP.

Wastewater collection and treatment is a continuous operation without holidays. DWSD staff operates the plant 24 hours a day, every day of the year. Three shifts of workers rotate through the plant each day to keep up with demand. Operators and chemists monitor the treatment process and make adjustments as needed. When rain or snow arrives, dedicated staff is needed to operate RTBs.

Suburban communities and the Counties have significant amounts of infrastructure to operate and maintain as part of the region’s sewer system. For example, the Oakland County Water Resources Commissioner’s Office operates and maintains 263 miles of large interceptors, four RTBs, two storage basins and 137 municipal pump stations.  The City of Auburn Hills operates and maintains 220 miles of sewer and 3 pump stations in the local sewer system.

The final section of the sewer system includes pipes leading to homes on private property and footing drains around the home. Homeowners are responsible for maintaining these pipes that are estimated to represent half of the pipe length in the system.

Aging infrastructure and regulations impact budgets

Sewers are among our oldest pipes. Continued investment is needed to keep the system working smoothly and to address remaining capacity needs for storm water flows. Since 1990, communities in southeast Michigan have invested $2.4 billion in CSO control projects. During 2010, these facilities prevented 6.4 billion gallons of CSO from reaching our waterways.

Sewers, WWTPs and many initial CSO projects received federal grants and low interest state funding to reduce costs charged to rate payers. However, low interest loans have replaced grant programs requiring local communities to pay for improvements through rates. This has forced many communities to reevaluate the affordability of projects with overall benefits gained.

The value of sewer service

Sewage is transported away from homes and businesses as a not-for-profit service. Sewer service costs about twice as much as drinking water. Together, water and sewer service are still one of the smallest utility bills we pay each month. This number could continue to rise as additional infrastructure to address CSOs, SSOs and more stringent regulations are funded primarily through rates. Pollution from wastewater and storm water must continue to be minimized through projects that balance environmental benefits and costs to ratepayers.

 

Monthly Utility Expenses for Three Detroit Metropolitan Area Households

 

Utility

2-person household

3-person household

4-person household

Phone

30%

27%

28%

Cable/Internet

24%

27%

20%

Electric

10%

15%

22%

Gas

18%

19%

16%

Water/Sewer

15%

9%

12%

Trash

3%

2%

2%

Total expense

$504.21

$606.38

$618.03