Whitefish Bay could end up paying between $71.1 million to $93.5 million for repairs to village sewer systems, depending upon the approach village officials decide upon at future meetings.
The village received more than 1,000 reports of basement backups during the intense rains of July 2010, either from stormwater unable to enter the storm sewer system or excessive clear water in the sanitary sewer system, which created basement backups.
Given the scale of upgrading the aging infrastructure that led to the flooding, Village Engineer Dan Naze said the village is at the beginning of a trail that not many communities have traveled down.
"Other than some isolated communities like Ann Arbor and some others, at least in this area, this type of project really hasn't been done yet," he said. "I don't know of anybody who has done any kind of significant large-scale lateral repair or foundation disconnect programs. It really hasn't happened yet."
Engineer Randy Videkovich, of Donohue and Associates, presented the consultant's final stormwater and sanitary sewer study report to the Village Board Monday night. Here is a breakdown of the consultants' recommendations and the costs associated with them:
Rain is designed to flow into storm sewers, which under the plan, will be replaced to varying degrees. Trustees will have to decide between three tiers of proposed storm sewer system improvements:
- $22 million: No ponding on streets during a 3.8-inch, 24-hour rainfall event (a rainfall event that has a 10 percent probability of occurring in any given year).
- $23 million: No basement or first floor stormwater flooding using available street storage from a 5.8-inch, 24-hour rainfall event (a rainfall event that has a 1 percent probability of occurring in any given year).
- $36 million: No basement or first floor stormwater flooding using available street storage from an 8.4-inch, 24-hour rainfall event (the July 22, 2010 rainfall event, a storm with a 0.2 percent probability of occurring in any given year).
The Village Board's Private Property Inflow and Infiltration (PPII) Committee is investigating a potential stormwater utility to fund these improvements. In addition to larger pipes, the committee recently recommended $300,000 worth of engineering work toward a stormwater retention basin in . The village is waiting to hear whether it received a $4 million grant for the $5 million project.
Sanitary sewer systems, which handle wastewater, are easily overloaded during heavy rainstorms, causing basement backups and overflows into stormwater sewer pipes. The excess rainwater or groundwater that does not belong in sanitary sewer pipes is also known as "clear water."
The consultants said clear water could be reduced by installing larger sanitary sewer pipes, but the village is restricted from sending more than 18 million gallons of water to the interceptor sewer system. Larger pipes can be used to store the water, however.
When a resident asked whether the village should consider bypassing into Lake Michigan, village officials said that would violate its permit, and in most areas, would be impossible, given the way the system is configured.
Clear water can also be reduced by disconnecting foundation drains and putting in sump pumps, which is up to the homeowner.
The Village Board's PPII Committee will be tasked with recommending one of three tiers of protection for the sanitary sewer system.
- $57.5 million: By not reducing any clear water, the village would have to create 10 million gallons of storage underneath the street. The cost of treating the wastewater is estimated at $20 million over 20 years.
- $54.5 million: This option calls for eliminating 20 percent of clear water by eliminating more than 400 downspouts and 1,000 foundation drains from the sanitary sewer system. It would leave 7.5 million gallons, and a 20-year wastewater treatment cost of $16 million.
- $49.1 million: The level of protection recommended by Donohue, this option calls for reducing 40 percent of clear water. This option would disconnect more than 400 downspouts and 2,000 foundation drains from the sanitary sewer system. This option would leave 5 million in clear water left to be treated, and a 20-year wastewater treatment cost of $12 million.
Clear water can also be reduced by replacing and lining sanitary sewer in the street, which the village has been doing, and by homeowners replacing and lining service laterals to their homes.
“The village has been making improvements in the public right of way, but it is what's between the public right of way and the building that needs to be addressed,” Videkovich said.
The sanitary sewer calculations were based on the 25-year level of protection instead of the 100-year level of protection calculated in the stormwater analysis because it has a higher probability of occurring. Videkovich said a 100-year level of protection would triple the cost of the sanitary sewer estimates, risk property damage and push the conventions of sewer management.
"It becomes a question of physically whether you can even fit it in the street," Videkovich said.
Also, by getting overly-aggressive on the sanitary sewer end, the village risks a burden on the storm sewers, said Assistant Village Engineer Aaron Jahncke.
"All that water from the foundation disconnects ends up on the street," Jahncke said. "If you have a leaky sanitary sewer system – manholes, laterals, mains – that water will infiltrate and find its way into the sanitary sewer system and also cause backups, so you don't want to pump all that water onto the street."
But which piece should go first and what should be prioritized? Consultants recommend the PPII Committee initiate a pilot sanitary sewer study in the far southeastern portion of the village, which presents the most challenges due to terrain, home construction, drainage and overland flow coming from Shorewood. The study would likely cost between $50,000 and $100,000.
"Which of the two - (replacing) laterals or (disconnecting) foundation drains - is more effective? I think that's exactly the reason why it's important to do a pilot project, because then we can do larger scale inspections of laterals: what their condition is, what we can expect over bigger areas, do one or the other or both and monitor what those results are so we can monitor what gets us the bigger bang for our buck," Naze said.
It is too early to calculate how much each homeowner would pay, or how the costs would be distributed between tax bills, sewer utility, water utility and possibly a stormwater utility. The price tag could also be higher than anticipated, due to additional work that may be needed. Additionally, the cost estimates were based on residents replacing their private stormwater laterals.
"Putting together a long-term plan doesn't necessarily mean replacing this pipe or that pipe," Naze said. "We also have a lot of areas in the village that involve old water mains. It's going to involve some street reconstruction or other improvements that are involved with that. In some areas, we are looking at increasing the size of pipes. You can do that in a lot of areas, but we have to determine, with the hydraulic analysis that we have, whether we can physically fit pipes as big as recommended. Some places have narrower streets or there's a lot of existing utilities. To do that, we may have to move the utilities, which is going to make the costs greater. There's a lot of variables that are going to go into creating a long-term plan and how much that's going to cost."
The PPII Committee will recommend an approach to improving the sanitary sewer system, and trustees will decide a storm sewer approach. Those projects will be prioritized and linked to a long-term infrastructure plan. Village Manager Patrick DeGrave said trustees will take up the sewer discussion, either on Nov. 21 or Dec. 5.