In September 1999, the Michigan Department of Environmental Quality issued the City an Administration Consent Order (ACO) to address wet weather sanitary sewer overflows. The ACO required the City to eliminate all emergency overflows at the City's wastewater treatment plant (WWTP) associated with weather events up to those generated by 25 year-24 hour storm event.
A 43.5 MG open earthen storage basin along with a 52 MGD pump station was designed, and is currently near completion, to address the ACO requirements. The new basin was constructed on a site adjacent to the WWTP with known low levels of soil contamination, which led to additional constraints during design and construction as follows:
Earth balancing was critical because only the first 6" of soil was permitted to be excavated, yet the interior of the Basin had to be graded to allow complete drainage. Fill also had to be controlled to maximize the volume available for storage.
A Health and Safety Plan was prepared to protect both construction personnel and the public while work was performed at the site.
Dust had to be controlled and minimized.
Allowances were included in the contract for handling and disposal of any contaminated materials (Type I or II), none of which were encountered during construction.
Approximately 185,000 cubic yards of suitable clay were required to construct the Basin embankments and liner system. The City's landfill site was used as a borrow source after testing confirmed the materials there met the requirements for the clay liner. The clay was required to be capable of compaction to achieve a permeability of no greater than 1 x 10-7 cm/sec.
are benefits resulting from implementation of the 43.5 MG
- Allowed the City to comply with their ACO issued by
- Emergency bypasses to the Tittabawassee River of partially-treated
sewage generated by the City's collection system will
no longer occur during wet weather events up to the 25-year
storm. This will be a significant benefit to the environment
by reducing the pollutant load to the River.
- The GCL liner system also substantially reduces the
infiltration of rainwater into the soil below the basin,
reducing the impact of any existing contamination on the
- Using the City's landfill as a borrow area for clay
has begun the initial development of a landfill cell for
Type II refuse.
- The Storage Basin was built on property which was not
suitable for other construction, thereby saving prime
developable City property from being used for the large