Tosa Engineers Discount Big 'F' from DNR on 2010 Sewer Overflows

Wauwatosa’s engineers told the Board of Public Works that the low marks the city received from the state’s Department of Natural Resources (DNR) for its 2010 sanitary sewer overflows were the result of a nearly unique 500-year rainfall that summer.

“That’s what hurt us,” City Engineer William Wehrley told the board Monday morning.

Nine inches of rain fell on the Milwaukee area July 22, according to the Metropolitan Milwaukee Sewerage District (MMSD) website – just a week after another 5-plus inches hit the area.

The DNR gave the city an A for financial management of its sewer systems that year, but a triple-weighted F for the performance of its “collection systems” in the agency’s Compliance Maintenance Annual Report (CMAR) – yielding an overall barely-passing D (1.0) average for 2010.

Asked how they expected to do this year, municipal engineer Michael Maki said, “If we get the same amount of rain, we’ll get the same grade.”

Wauwatosa’s automated pump stations divert sanitary sewage to storm sewers whenever rains are heavy enough to force water into the cracks and leaks of the city's aging sanitary sewage lines, he explained in an interview after the meeting. Without the pumps' diversion, the rainwater's influx into the sewer lines would push the sewage back through the lateral lines that link homes and businesses to the system and into building basements.

Untreated Wauwatosa sewage diverted into its storm sewers winds up in local waterways that eventually flow into Lake Michigan, bypassing its normal sewer-line route through MMSD's sewage-treatment system.

“The pumps are intended to reduce the frequency and severity of basement backups,” Maki added, and were designed to handle the more typical five-year level storm.

Basement backups were particularly severe that year, Wehrley noted, especially in older neighborhoods with houses built before 1954, when the state passed new rules requiring basement sump pumps.

Wehrley and Maki both said they expected neighboring communities had similar results that year.

Brookfield and West Allis municipal engineers actually reported A grades from the DNR, but they don’t fault their Wauwatosa counterparts for their system’s performance.

“We were lucky,” said West Allis Assistant City Engineer Joseph Burtch in a telephone interview Tuesday. “The worst of it hit to the north and south of us.”

Brookfield Public Works Director Tom Grisa agreed. While his community earned nine A's from the DNR for operating its own wastewater treatment plant, he noted that Wauwatosa sends all its sewage to the MMSD for treatment before it's dumped into Lake Michigan.

“So did Wauwatosa get failing grades because they’re incompetent? Are they running their system poorly?” he asked rhetorically. “I don’t think so.”

Grisa, who served as Wauwatosa assistant city engineer from 1993 to 1999, also thinks the DNR should change the way it measures sewer systems’ performance to overflow per sewer-mile instead of per square mile. He noted that denser communities put more pressure on each sewer-mile than more spread-out communities.

This week's rainfall, particularly the 2.12 inches that fell Tuesday, set off alarms in three of the city's seven automated pumping stations, according to Public Works Director William Porter. Two of the pumps automatically began diverting sewage into the storm-sewer system, he said, while Public Works Department staff operate the other pumping station manually.

Three homeonwers reported basement backups during or after Tuesday's storm, but, "None of them involved problems with the city's sewers," Porter said in a telephone interview Thursday, "There were problems with the homeowner's lateral-line connections to the sanitary sewers."