Ann Arbor to Study Sanitary Sewer Flow

A study of the city of Ann Arbor’s sanitary sewer flows – meant to assess the impact of a decade-long footing drain disconnection program – will be undertaken by Orchard, Hiltz & McCliment Inc. over the next year and a half to two years.

The city council authorized the $968,348 contract with OHM at its Feb. 4, 2013 meeting as part of a project budget that includes a $192,000 contingency and $85,000 to account for city staff time. The money will come from the city’s sanitary sewer capital fund.

The city of Ann Arbor’s footing drain disconnect (FDD) program was implemented in 2001, prompted by repeated incidents of raw sewage backing up in residents’ basements and the discharge of only partially treated sewage into the Huron River.

The city of Ann Arbor has separate sanitary and stormwater conveyance systems. However, during construction of new developments before 1980, footing drains – permeable pipes buried around the perimeter of a foundation, roughly at the depth of a basement floor – were frequently connected directly to the sanitary sewer pipes. Those connections were convenient to make, because the footing drains and the sanitary sewers are buried at roughly the same depth.

However, during very heavy rains, that configuration leads to a volume of stormwater flow into the sanitary sewer system that it’s not designed to handle. That can cause two problems. First, near the point where the extra water is entering the sanitary system, it can cause raw sewage to back up through the floor drains of basements. Second, farther downstream at the wastewater treatment plant, the amount of water flowing into the plant can exceed the plant’s capacity. That can result in only partially-treated wastewater being discharged into the Huron River.

It was wastewater discharges into the river that led the city to agree to an administrative consent order with the Michigan Dept. of Environmental Quality (MDEQ) to establish a way to offset the impact of new connections to the sanitary system required by new developments. That program essentially requires developers who are building projects that place additional burdens on the sanitary sewer system to pay for a number of footing drain disconnections elsewhere in the city, according to a formula.

The footing drain disconnection program was targeted initially in five neighborhoods that accounted for about half of all reported basement sewage backups. Since implementation, 2,538 footing drains have been disconnected, including nearly all of the houses in three of the five areas. In the two other areas, between 55% and 60% of footing drains have been disconnected.

In one of the remaining areas – in the Glen Leven neighborhood – overland flooding during heavy rains in the spring of  2012 resulted in basement flooding in some houses that had been included in the disconnection program. The procedure includes the installation of a sump to collect water from the footing drains – which previously fed into the sanitary system – and a pump to move the water from the sump to the storm water system.

Emphatic protest came from residents of that neighborhood, which has in recent weeks included rumblings of possible litigation. The litigation is based on the legal theory that the city’s footing drain disconnection program has proceeded without valid contracts with homeowners, and that the installation of the wells and pumps constitutes an illegal “taking.” The city council decided on Sept. 17, 2012 to suspend temporarily the footing drain disconnection program.

It’s in that context that the city is now undertaking the study to be done by OHM – to determine if the footing drain disconnect program needs to continue and if so, where the efforts should be focused.

The scope of OHM’s work includes: (1) perform flow monitoring on the sanitary sewer in the five priority areas; (2) update, calibrate, and validate the existing sanitary sewer model; (3) evaluate the effectiveness of the current FDD program; (4) provide recommendations for reducing or eliminating wet weather flow impacts; and (5) do public engagement throughout the entire project, including a citizen advisory committee, a technical oversight committee, focus groups, and the general public.

This brief was filed from the city council’s chambers on the second floor of city hall, located at 301 E. Huron. A more detailed report will follow: [link]