Oakland County water commissioner briefs Birmingham on combined sewers, retention basins and flood drivers

At a Sept. 8 workshop of the Birmingham City Commission, Oakland County Water Resources Commissioner Jim Nash and his staff outlined how combined sewer systems and regional retention/treatment basins work, described why regulators sometimes close outflows to downstream systems during storms, and urged cities and residents to coordinate on aging pipes, stormwater changes and funding.

Why it matters: Birmingham lies inside multiple drainage districts that send combined sewage and stormwater to different county retention/treatment basins. Decisions about whether to store stormwater in local basins or convey it to regional systems affect where overflows occur, how often basements back up and who pays for capital and operating costs.

Nash said the county oversees large assets and operations for many communities. “My name’s Jim Nash. I’m the Oakland County Water Resources Commissioner,” he told commissioners as he introduced a team of engineers and legal staff. He said the county operates 433 county drains and hundreds of miles of enclosed storm drains, and manages retention/treatment basins built to capture combined storm and sanitary flow for later screening, settling and disinfection.

Oakland County staff described the historical reason for combined sewers — many streets and home drainage systems were enclosed as communities urbanized — and the regulatory response. “Back in the day the combined sewage would just run straight to the river,” said Gary Nigrove, a county manager, describing earlier uncontrolled outfalls. Under state and federal rules, discharges to surface waters require NPDES permits and oversight by EGLE (the Michigan Department of Environment, Great Lakes and Energy).

County staff explained two common responses to combined flows: (1) retention/treatment basins (RTBs) built to store and partially treat excess flow during storms, and (2) separated sanitary systems that send concentrated sewage to full secondary treatment plants. Carrie Cox of the county described how the Evergreen Farmington system operates for parts of Birmingham: during dry weather “100% of the flow in that district goes to the Evergreen Farmington system,” she said; during moderate storms most rain is stored in RTBs and later pumped to the interceptor; during very large storms communities that opted not to buy extra capacity into Evergreen Farmington close their regulators and store 100% of flow in local RTBs until levels allow discharge.

That deliberate operational tradeoff helps prevent overloading downstream systems, county staff said, but it also concentrates more overflow volume into RTBs. County staff said the Bloomfield Basin can see inflows on the order of hundreds of cubic feet per second in a storm while permitted outbound rates are much lower; county staff gave rough order‑of‑magnitude numbers in the presentation. Carrie's summary: closing regulators during peak downstream flows reduces sanitary sewer overflows in downstream communities (the county cited Southfield as previously affected) but can mean short-term higher levels locally that require storage and later release.

Cost, capacity and rates: Nash said Oakland County manages about $18,400,000,000 in assets and serves hundreds of thousands of residents through its systems, with about 156,000 residents served by county water systems and roughly 149,000 by county sewer systems (the county’s presentation listed those figures). Carrie Cox and county staff said Evergreen Farmington recently purchased 52 cubic feet per second (CFS) of additional capacity, bringing a long‑term allocation with the Great Lakes Water Authority (GLWA) from about 172 CFS to roughly 229 CFS. County staff said communities declined to buy the full upgrade because the price to add secondary treatment capacity and long conveyance mains would have been on the order of tens or hundreds of millions of dollars — staff cited a previously discussed $150,000,000 project estimate and also mentioned $135,000,000 of corrective-action projects in Evergreen Farmington to date.

Funding for past basin construction was largely federal, Nash said; he noted the Birmingham CSO tunnel project cost about $35 million at the time and had federal participation, with local ratepayers covering the remainder. Nash and staff said ongoing operations, major maintenance and future capital expenses are planned through the county’s five‑year capital plan and reflected in rates; staff stressed that about 80% of the county’s typical customer rate goes to the GLWA treatment charge and is passed through to communities.

Basement backups and local impacts: Commissioners and residents pressed county staff on basement flooding and whether closing regulators creates a “dam‑back” effect that can raise upstream levels. Commissioner Anthony Long and others raised examples of streets and basements that flooded repeatedly in past decades. County staff replied that the RTB storage is hydraulically separated from the local collection system (when a pump station/wet well disconnects hydraulically) and that regulators are monitored; they said they typically limit regulator closure to short periods and operate to avoid creating upstream backups to the extent possible. Gary Nigrove and Carrie Cox also said intense, localized storms — sometimes delivering several inches in a small area — can overwhelm neighborhood pipes even while regional systems still have capacity, because neighborhood systems were designed for far less intense events.

Residents and commissioners pressed for practical help. County staff offered to meet with property owners and city staff to investigate local bottlenecks, to share maps and monitoring data, and to host site visits to nearby retention basins; staff also said the county monitors depth and flow after larger rain events and meets quarterly with customer communities. “We’re more than happy to work with you,” Carrie Cox said, and the county offered a planned Earth Day open house at the Birmingham RTB to show how the basin works.

Local programs and pilot work: Alyssa Taube, the county’s community engagement representative, described a two‑year “RainSmart” pilot that paid rebates to homeowners for rain barrels, rain gardens and similar measures in residential areas where 63% of the drainage district is residential. Taube said the pilot is ending and county staff are seeking additional funding; she suggested the city could replicate a similar homeowner‑incentive program.

What didn’t change: County staff repeatedly noted that major hydraulic changes require careful regional planning — upsizing local pipes without coordination can move problems downstream. They also warned that proposals to “upsize everything to future‑proof” can be expensive to build and maintain and must be evaluated against projected rainfall changes and long‑term asset plans.

Next steps: The county offered to supply more detailed graphics, meet in the field with commissioners and residents, and work with city staff on specific neighborhoods. County staff said they are participating in an Army Corps of Engineers regional flooding study that runs several years and urged continued city‑county coordination.

Discussion-only outcome: the workshop produced no formal votes; commissioners asked staff to follow up and allowed county staff to return with more detailed maps and proposed next steps.

Ending: Commissioners said they would arrange follow‑up technical meetings with county staff and welcomed the county’s offer to host an RTB site visit for elected officials and residents.