The costs to run and maintain most metropolitan sewer and water utilities are largely fixed.  For example, +80% of the costs the Detroit and New York systems are fixed.  Fixed costs include: debt repayment, utilities, chemicals, salaries, benefits, etc. This means that the amount of flow or lack of flow produced by a homeowner doesn't significantly impact the cost of operating the system. I will check into the fixed cost ratio for Ann Arbor. 

The key term in the 70-90% removal rates is "wet weather flow".  This is peak flow during large, design rainfall events.  It typically rains about 150 hours out of 8,760 hours in a year in Michigan. So the vast major it of the time, the sanitary sewer system is not collecting wet weather flow. 

We often find that although the wet weather inflow and infiltration sources like footing drains dominate the peak design flow, over the course of an entire year, it is common for them to be in the 2-5% range of total sanitary flow.  So these wet weather flows are very short, intense bursts of flow that drive the performance and design conditions of a sanitary sewer system.

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If I were to peg a typical sanitary sewer system, I would say the following:

Over the course of a whole year: (numbers picked not for precision, but to get the total to add to 100%)

3% of the flow is wet weather inflow and infiltration

60% of the flow is sewage from water consumption

37% is ground water infiltration

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During peak wet weather flow: (numbers picked not for precision, but to get the total to add to 100%)

80% of the flow is wet weather inflow and infiltration

12% of the flow is sewage from water consumption

8% is ground water infiltration

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Hope this helps illustrate the flow components. It also sheds some light on the potential for water conservation measures to make a significant dent in the peak flow.  We published some information about these flow components in the flow metering report.  If anyone is interested, I would be happy to dig up some specific examples from the Ann Arbor metering. 

Take care,

Robert

Frank has raised a good point in this post.  Residents who have disconnected use much less sewer capacity than those who are still connected.  Yet both pay the same for their water and sewer bills.  

In the target areas that aren't complete, there are residents who have disconnected living next door to residents who have not disconnected.  

This is an issue of fairness that the CAC needs to address.    

Actually, this relates to one of the concepts I was thinking of when I used the phrase "incentivize" (not addressing "robust" yet). Suppose we gave the FDD homes a $100 per year credit. This could help defray operating and maintenance costs. The present value cost to offer this forever for a single FDD is about $2500 (assuming 4 per cent discount rate), for example. This is one approach (or part of an approach) to incentivize a future FDD. Also, I am in Michelle's miracle world where ideas and costs are separated to foster discussion.

Joe

Joe--interesting idea for sure. 

How did you figure the $2500 number? 

I used Excel, but $2500 is a nice case. $2500 plus 4 per cent is $2600. Minus $100 is $2500.

New year, start over.  Other numbers may be used to fine tune this, but the point was to try to develop a sense of the costs involved to offer incentives.  By the way, I believe higher discount rates, like 6 or 7 per cent are used for typical municipal pension obligations.  This would lower the "cost."

Also, this was just an example. Rather than doing this forever, ending at change in ownership might make sense.  Or an entirely different incentive could be considered.

Joe

And there are also those in older homes whose footing drains have never been connected to the sanitary sewer. 

And those newer homes that never have been connected, as well as BIG businesses...

My understanding is that ones sewer bill is based on ones water usage. Although I'm sure the city sets the rates knowing there is a certain amount of 'storm' water going to the WWTP as well.

So, are homes (and businesses) where sanitary and storm water are separate helping subsidize those scofflaws who still have combined systems??

so maybe we could recommend a surcharge for all who are still having connected footing drains.

That's what the $100 fee, (is that per month !!) people are charged now.  If they refuse to have a FDD.

But that would seem excessive, looking at Robert's figures:

3% of the flow is wet weather inflow and infiltration (except for peak wet weather flow)

So I'd vote for a 5% surcharge.  Or usually being positive is better--- and offer a 5% reduction, to those who have a FDD.  Everyone loves a bargain!

Pat is correct that what Michelle described is a basic part of the existing program.  Our existing "mandatory" program has an option for people who do not want to disconnect.    

$100 per month is excessive.  But the idea that those who put more in pay more seems reasonable to me.  Or, if you prefer, those who don't put footing drain water into the sanitary pay less.  

Can our team work through how much a more reasonable surcharge/discount should cost?  Pat has a good start in the previous post, but 5% of my sewer bill is about $13 per year.  That amount would not be incentive enough for me to get an FDD, and it would not begin to cover the costs that FDD recipients have incurred (maintenance, inconvenience, noise, risk of flooding, cost of a backup, etc.)

This is a valuable topic for us to keep discussing.  I like Pat's approach of backing up the surcharge value with a relevant computation of costs.  

  

"This is a valuable topic for us to keep discussing.  I like Pat's approach of backing up the surcharge value with a relevant computation of costs. "

 If one new FDD can stop a rain storm addition of X amount to an already over burdened system, and make room for a new hook-up that provides a revenue stream, it does seem that the homeowner should get more than just a pump that will wear out, a higher electric bill, and the possibility of a failure.

Should there be a discount built in?

I have always thought that the FDD program, even if it does a good job, and I have yet to see all of the data, is like a game of Russian roulette where most are winners and just a few are "losers"; those who got the FDD. That is the city could have a better job of implementing this program, and if carried forward, it must.

It might be that FDDs give the best bang for our hard earned dollars, and only a few neighborhoods in low lying areas need them. If so, and I am not saying that this is so at all, but if it were decided to be so, why should these few bear the brunt of the burden to benefit the many?

Should the city provide backup pumps and replacements? Even to existing FDD people? No, if all of us were made to have a FDD, but if only a few were selected, then this is different.

But back to the start, we need costing info...

When I said "all" I meant in fact, all.  There are plenty of addresses all over Ann Arbor still having footing drains connected to the sanitary sewer.  If there is going to be a surcharge it should be on all who are still connected.  Presently, I believe only those in the targeted areas are surcharged.

interesting point; why should only some homeowners be the "losers" at Russian roulette?

I think that the amount of $100 is too, much, though, and perhaps it should be double (whatever this amount is) if someone is given a chance to disconnect it and says, "no" or the opposite, a reduction if someone does have the FDD

The surcharge is for those in the target areas, that refuse to have it done.  Other areas, are not required to have it done, so penalty will be imposed on them.  

After we see the maps, there may not be any problem areas left...... as there were no flooding issues reported (per Robert's chart, only 1 and it was due to other issues--tree roots maybe).

Maybe be time to consider the city as a whole and not with target areas.

I think we will find that the 90 - 10 rule will apply here. By this I mean that most of the benefit in further FDD would come from disconnecting a small (relatively) number of homes in selected areas (speaking about basement backups).  If this is true (hopefully we will see on March 20), it does not seem to be fiscally prudent to come up with a program that intends to disconnect the whole city, and it also seems like this would impose a burden on many homeowners that is hugely disproportionate to the community benefit derived.  This means we could disconnect about 18000 more homes at an additional cost of about $180 MILLION dollars while deriving only a small fraction of that value in terms of benefit to the city. And this will be an unnecessary annoyance and burden for most of those homes.

I have seen nothing so far that remotely suggests that footing drain flow into the WWTP is likely to impact growth and development. But even if it did, it would not be right, in my view, to impose on current homeowners so that some development and growth that would profit a different private party could proceed. 

So we need to go back to the problems we are trying to solve. Basement backups and system and WWTP overflows.

I would suggest the charge versus incentive argument is non-symmetric.  The variable cost of reducing WWTP flow is probably very low. Charging their share of these variable costs to homeowners who have footing drains connected to the sanitary system is probably fair, but is a distraction from our goal, in my view. It would be too small to incentivize most people to disconnect, but it might be large enough to get some people to request a city funded disconnect in locations that would not be cost beneficial to the city ( meaning us, the folks who pay the bill).

On the flip side, if there are places where further FDDs would be helpful, the value to the city (us again) is far higher than the marginal cost of treatment at the WWTP.  And the burden to a homeowner being disconnected may be substantial. So I think we should approach those homeowners with an appreciation of the burden we want them to assume. We should provide a top quality solution and reward those homeowners with a reasonable incentive that recognizes their inconvenience during the process and the ongoing operation and maintenance costs they will be assuming.  This would cost us much more than the marginal cost of flow at the WWTP, but would cost less than the next best solution (or we would choose that solution).

In summary:

I do not support a thesis that all homes in Ann Arbor should be disconnected; this is too expensive and unnecessary.

I do not currently support the idea of charging all homeowners who are connected (even a small fee), since that would imply we wanted them to disconnect.

If we believe further disconnects are the best approach, we should reasonably compensate homeowners who disconnect based on our recommendations.

Joe

It should be fair.  If footing drain disconnects are targeted to an area, then that area should benefit in proportion.  It doesn't seem like Lansdown is particularly happy to disconnect (and all that that implies) in order to benefit Ann Arbor in general.  If each homeowner is happy to disconnect for the benefit of their own selves, as well as their neighborhood (each neighborhood having its own situation) then that's fantastic.  But it doesn't seem to be the case.

When I say charge all homes still using a connection between sanitary and sewer, it needn't be $100 as A2 has thus far charged.  Given the large number of dwellings still connected it might be $10, or $1, or less. 

If you want to charge someone $10/month, would they get the option of a city funded FDD even if they were in an area that was not challenging capacity?

Not necessarily.  But maybe.  I mean some areas challenge vehicular traffic capacity far more than others, yet that cost is spread out... 

1.  Not $10/month = $120/year which is pretty steep, given the widespread application of this scenario.  How many sewer bills are there in Ann Arbor? 

2.  And -by the way - I am not arguing for this (nor against).  I am just upending and turning inside out the way it is fee'd now.  And, now upended,  exploring it.

3.  DOM FDD's might have to be harvested from the targeted, challenged areas.  A volunteer gets a) a paid-for FDD and b) released from a fee.