City of Ann Arbor SSWWEP - Citizens Advisory Committee Coordination

Comments

Jim Osborn on 30 Jan, 2014:

They most likely base it on a large rain-fall flow rate, as this is when problems occur. The sewer system has plenty of extra capacity during dry days, so it would be unfair to base it upon those days. It makes more sense to base it upon the average footing drain during a rainy day.

Can improved stormwater drainage, paid for by a developer or the county or city, also cause footing drains to not discharge water into a sanitary sewer, instead of a FDD?

Peter Houk on 30 Jan, 2014:

I think Jim is right about basing the calculation on the peak flow condition.

What I am picking up from the OHM presentations is that it's much easier to predict the flow from sources like showers and toilets than from footing drains. Flow from footing drains varies with conditions (dryness of soil, rate of rain fall, duration of rain fall).

So I can understand why city engineers might prefer to have sanitary flow from new development (toilets, showers, sinks) instead of footing drain flow from existing sources. Even if the new daily flow is greater, it will be spread out more evenly over time instead of all at once during a storm.

It would be nice to get some input form the OHM team on this one.

Robert Czachorski on 31 Jan, 2014:

I have been hesitant to comment on this thread because we have not been involved in the City's FDD program and the methods used to compute the developer offset requirements. The City really should chime in on the actual methods used. I believe that they are working on some additional information to share on how the FDD mitigation works. I can comment on the general concepts of the rainfall and flow that Jim and Peter are commenting about.

Jim is correct that the computation must consider the peak flows during wet periods, because that is the critical condition for the system performance - on dry days the system has plenty of capacity. There are other ways to mitigate stormwater from reaching the sanitary sewer, but as Craig Hupy described, the FDD seems to be the most effective for the developers. One item that could be done is rehabilitation of other stormwater sources into the sanitary, such as repairs of cracks in sanitary manhole and pipes. However, these flow sources may be smaller, and more expensive to remove on a per gpm basis than FDD. We have evaluated the flow removal effectiveness of this type of rehabilitation on many systems around the Midwest and usually found it to be fairly ineffective at removing significant flow. We suspect this is because the flow migrates to other defects or crack in the system, but this is just a theory. I think a general observation would be that scattered spot repairs to the sanitary sewer are fairly ineffective at removing significant wet weather flow, and that more comprehensive rehabilitation of all defects and wet weather sources in a focused area is more effective.

I completely concur with Peter that it is much easier to predict the sewage flow generated from sources like showers and toilets than from footing drains. Flow from footing drains vary not only with conditions (wetness of soil, rate of rainfall, duration of rainfall, etc), but also from house to house depending on the house grading, subsurface conditions, etc. I would venture to guess that these variations are the reason why the City requires mitigation of 120% of the sanitary flows from the new development, and not just 100% of the new flows.

To illustrate the variability in FDD flows, please see the attached plot of the sump pump monitoring that has been performed by CDM. They have monitored something like 70 sump pumps after FDD for many storms to directly measure the flow from a footing drain. They have measured the FDD flow and rainfall that caused that flow, and plotted these rainfall / flow pairs on the attached scatter plot. So each blue dot on the plot represents one of these rainfall / flow pairs for one FDD from one storm event. Note the tremendous scatter in the plot. Some points show that for huge amounts of rain, the FDDs are generating hardly any flow, and some points also show huge FDD flows for smaller rain. The blue line is a trend line fit to all data, and this shows a general increasing flow trend for higher rains, which makes sense, and suggests an average flow rate of 3-5 gpm for design rainfall in the 3-4 inch range. This is consistent with the original design basis for the FDD program. (and as I understand it, it was sump pump monitoring after a pilot FDD program that they used to establish these values).

The conclusion from this is that for any give FDD for any given storm, there can be a tremendous variation in the FDD flow, but when many FDDs are considered in aggregate the results converge to an average flow of about 3-5 gpm per FDD (edit: for large design storms in the 3-4 inch range). This is consistent with what we saw when we looked at the before and after flow data as well.

Hope this help!

Take care,

Robert

Frank Burdick on 31 Jan, 2014:

Robert I would like to see the results of the 70 sump pumps counters in real data, and not a scatter plot. This data would include, how often a pump ran in specifac periiod, for how long, and, the average "head" above the pump.....all leading to how much flow or actual volume did each of these pumps discharge at a given time. I also would like to see these collated by neighborhood. Is this data available?

Jim Osborn on 31 Jan, 2014:

While much too invasive and expensive to do, it would be nice if the footing flow into a sewer during a heavy rain could be measured and then only perform a FDD on those homes that are above a certain level of flow. But, to measure this beforehand would involve digging that is worse or equal to the actual FDD.

It appears that the second best method is to monitor the sewer flows of each neighborhood or group of homes during rain storms and then mitigate that group of homes, or not, either by a FDD or other solution.

This weekend I will read the study posted with Robert's excellent comment.

Frank Burdick on 31 Jan, 2014:

It appears that we now have an expert on Sump Pumps commenting on this string. I would request that one of the city approved contractors appear before "jury" so that the assertions of our new expert could be addressed in public. I have replaced my share of sump pumps with pebbles in the impeller or obstructed floats. Our new expert needs to hear from City approved experts.

In addition, a review of the 2001 SSOE report, the current Counter Data, and the layout of most clean-outs from the footing drains, would reveal the FACT that it is possible to monitor the flow of individual house footing drain discharges on a per house basis, without exterior excavations. A "builder" understands this.

The City needs to provide the "counter data" actual flows, and durations of each counter location and collate them by neighborhood. What if we find that one neighborhood has very little flow and others have excessive flow.... but the city is mandating that ALL home be penalized with the invasive pump or TAX if the mandatory pump is not installed.

Robert Czachorski on 31 Jan, 2014:

Frank - I do not know the answers to the questions about the sump pump monitoring because we are not involved in it. I would pass your question along to the City to address.

Edit: I will pass your question along to the City.

Take care

Robert

Charlie Fleetham on 31 Jan, 2014:

Frank - who are your referring to as the "new expert?" Robert or Jim? In either case, neither of them claimed to be an expert on sump pumps, so I assume you are being sarcastic. As you know, sarcasm puts a chill on the discussion and can intimidate committee members from participating. Please stop.

Jim Osborn on 31 Jan, 2014:

Where is there an "expert on Sump Pumps commenting on this string", or anything about the operation and usage of a sump pump?

What is being discussed is monitoring the footing flows from a home, per the original question, and that includes the flow from a sump pump.

Where are footing drain clean-outs located? I do not see one on my home. If there is a method of easily measuring flow from each home, then in an ideal world, a FDD would be done to those homes that have a high flow rate and no other economical method to reduce it has worked, and other solutions such as storage or increasing the sewer plant capacity and sewer line capacity cost too much.

As a city homeowner, I desire low sewer rates and low property taxes; too.

Robert Czachorski on 31 Jan, 2014:

Jim,

We are not aware of an easy or economical method of measuring the flow from a footing drain prior to FDD. I concur that if there were a method, it would be use useful in identifying the most effective homes for FDD. A few years ago we did some research at OHM on the possibility of using a temperature sensor to measure changes in the water temperature as a result of footing flow versus normal domestic sewage. We were not able to identify a reliable methodology from this research.

Take care,

Robert

Jim Osborn on 31 Jan, 2014:

Robert,

Do you have any ballpark estimate about the cost difference between a FDD that is in a home's basement Vs outside?

Outside, it is easier to dig, but you need to go much deeper, since you are starting at ground level, and it ruins landscaping.

Inside, in the basement, you already are deeper, so less digging, but the concrete must be cut and it is a faster method for water to enter the home from the footings if the sump were to fail. And, the home could lose living area depending upon where it is placed.

If landscaping is torn up, as I've heard, then this implies that digging was done outside. If so, why is the sump then placed inside? I know that some footing drains are under the basement slab while others are located outside, along the edge. Is outside digging nessary to help determing if the footing drain system is inside or outside? I need some education, since I'm not an "expert".

Frank Burdick on 31 Jan, 2014:

Homes in Lansdowne have 2 clean outs. It is at this location that the city demands to put the sump pump. (any other location in the basement cost more money to the homeowner). In many homes, this location is at the base of the stairs along the front of the house. One of these cleanouts goes to footing drain, the other goes to sanitary sewer lateral. Robert, review the FDD CAC website...they show some photos of the installation. You may be able to see the correlation of the footing drains to the lateral main.

A flow meter could be inserted in the clean out prior to the connection to the main lateral to monitor just the flow of the footing drains.

Perhaps Robert could consult with CDM, or more effectively, contact one of the City approved contractors to "pick their brain" on how to do this. We should not rely on JUST the CDM provided response. We need our independent evaluation of this. There should be the available technology to monitor this flow.

For the record, questions related to this exact issue have been on my log since NOV/ DEC 2013 and have also been sent to the silent and mysterious FDD CAC with ABSOLUTELY no acknowledgement of receipt of the questions. Hence, we can not rely on CDM.

Signed

a REAL expert

Lori Byron on 5 Feb, 2014:

Ms. Marten originally asked: When the city is saying that a developer must have 20% offset mitigation, shouldn't this be based on daily usage?

If they use 4GPM = 1 FDD, that number is the amount of water surcharging the system during a large rain event. So actually the offset mitigation is very small, as most days, the flow is very low, if at all.

Can you please clarify?

[CITY] The purpose of the DOM program is to offset the proposed flows being added by the development project to result in a zero impact to the existing sanitary system during wet weather events. The most common method of mitigation selected by developers has been FDD. The enclosed “DOM Guidelines.PDF” contains the method (as well as sample calculations) for how the number of FDDs are determined for development projects. In summary, the developer is required to mitigate the peak dry weather flow rate plus an additional 20% (i.e. 120% of the project’s peak flow rate). The additional 20% is known as the system recovery factor and the intent of this factor is to gradually gain back lost system capacity.

Joe Conen on 5 Feb, 2014:

Frank Burdick on 5 Feb, 2014:

Frank Burdick Fri, 31 Jan at 4:30pm

AGAIN

A flow meter could be inserted in the clean out prior to the connection to the main lateral to monitor just the flow of the footing drains.

Lori Byron on 5 Feb, 2014:

Mr. Conen, here are the DOM Guidelines [attached.]

Robert Czachorski on 5 Feb, 2014:

Frank – we are not aware of a technology that will accurately meter the flow at this location continuously and affordable. The pipe is too small for conventional open channel metering like we used in the sewers. We experimented a few years back with a temperature sensor without success.

It’s my understanding that the drawing you are looking at is a standard drawing to show a concept, and that each house is different, and the City works with homeowners address issues as you have described with cleans out at that location. This is just my understanding – I will ask Lori and Nick to verify and post a follow up response to this example.

Robert Czachorski on 5 Feb, 2014:

Jim – there are many factors that affect costs as you have suggested. For almost all houses the clean out junction of the footing drain and sewer service is beneath the basement inside a house. Therefore, constructing an external pump would require work inside and outside the home, which would generally be more expensive.

Frank Burdick on 5 Feb, 2014:

My house (and many others) have the 2 clean outs. As to the FDD city website, I am referring to the actual photos of the installation. You can SEE the pipe configuration.

Mr. Higgins contacted the UofM and this research revealed some flow metering devices.

Perhaps IF there was seamless communication between the concurrent studies (ie FDD CAC) and the SSWWE CAC, that we could get timely and accurate information from each other. As it stands now, the FDD CAC refuses to communicate to our CAC and has totally ignored all direct and indirect communications. All attempt by me to contact this FDD CAC via Charlie Fleetham, Nick Hutchensen, Cressen Slotta, and many others have failed. The FDD CAC must be operating under a GAG order as they will not respond. Once again, the City has chosen to transmit the perception of "hiding" something.

If the City was truely interested in WIN WIN, and collaborative solutions, the City Staff and Council would demand inter-CAC cooperation. A solution that would have been assembled by a "good" facilitator by now, would involve a meeting with reps from CDM, Perimeter or Hutzel, or other approved contractors, N. Hutchinsen, C. Slotta, R. Welton, the Plumbing Inspector, and whomever OHM would be willing to invite from our CAC...hopefully me and others. THIS would be a PRODUCTIVE meeting. I won't hold my breath.

Nick Hutchinson on 6 Feb, 2014:

Frank,

The questions that have been submitted have been answered by City or OHM staff (or are in the process of being answered). We have not sent them on to the FDD CAC specifically.

Since the FDD program was put on hold, the FDD CAC has only been meeting sporadically, and only has about 3 active members remaining on it. In addition, I believe all but one of members were not part of the original SSO task force, and therefore are not really in a position to answer many of your questions. Recent meetings have consisted of not much more than updating FDD CAC members on what was going on with the parts of the FDD program that were still active, and briefing them on what was going on with the SSWWE project and other related projects.

Finally, when we embarked on this project, part of the instruction that we were given was that this is to be a fresh look at the issue of sanitary backups and the FDD program. The FDD CAC, CDM, and City Staff that were closely involved with the project previously were not intended to be part of the process - new people, new eyes on the problem. That said, we still have had to go to CDM or staff members previously involved in the program in order to answer many of the questions that have come from the SSWWEP CAC, but that is the extent that we have felt they should be invovled at this time.

Nick

Robert Czachorski on 6 Feb, 2014:

Frank - I understand that the City's standard specifications and photos of installation show the sump pump at the clean out location - I did not mean to imply otherwise. What I am saying is that in instances where the clean out location is at the bottom of the stairs, that I believed that there is some flexibility in the location to address such concerns.

I spoke to the City's FDD PM Anne Warrow and CDM about this at the FDD CAC this morning. She indicated that their standard allowance for preparing costs estimates was for moving the sump pump location by up to 8-feet for such issues, but that this was a standard allowance, and specific variances are evaluated on a case by case basis that considers the individual circumstances of each house. The basis for the 8-feet radius for relocating the sump pump was that this is usually adequate to move the sump out of travel areas and into corners or utility areas. For the houses with the clean outs located at the bottom of the stairs, this provides enough allowance to move the sump to beneath the stairs. Would moving the sump pump location under the stairs address the issue you are describing?

If during our follow-up examination of houses with issues from the FDD survey, we find that moving the sump under the stairs is frequently insufficient or longer runs are often needed, perhaps this could be a component that the SSWWEP CAC might want to consider in their recommendations for "if FDD goes forward, what needs to change?", which is the topic of the April 17 CAC meeting.

-------------

I spoke to Bill Higgins this morning about his discussions with a UM professor friend on metering the footing drain flow prior to FDD. He indicated that his friend is a specialist at electrical sensors, and they discussed the idea of measuring the flow as a research project and technology development idea. Developing such technology would require funding and development time. It would be wonderful to see such technology researched as it *may* provide a method to measure footing flows and triage priority houses before FDD is conducted. However, the technology does not currently exist, and we are not aware of a suitable sensor available today that will accomplish this. (I used the word *may* because there are many inherent technical challenges to overcome to make an accurate, continuous, electronic, affordable measurement of such a pipe.)

------------

Regarding communications with the FDD CAC - we did discuss the communications in detail near the end of the meeting this morning with the FDD CAC. Bill Higgins made the request for improved communications. Anne Warrow and the CDM staff affirmed their commitment to answering questions about the FDD program. We discussed that we would make the identification and transmittal of these questions to Anne a little more formalized process. We will ask Lori to identify questions submitted for the Q&A log as being relevant to the FDD program, and to forward those to Ann Warrow. When answers are provided, they will be identified by who answered them (Anne Warrow, Nick or others). Would this address your concerns? Do you have any other suggestions that we should be doing?

Take care,

Robert

Robert Czachorski on 6 Feb, 2014:

Frank - please see response from CDM below regarding the sump monitoring data you requested in this thread above. I think the short answer to your question is - this data is available. Note their comments about the volume of data involved. I think it would be helpful if we focused on what you are trying to accomplish. Perhaps we could ask CDM to provide the sample data for a typical sump pump for a large storm. This would help illustrate what the data looks like and how it is analyzed. Would that suffice?

I have also attached a sample graph provided by CDM that shows the resultant flows plotted in time from one FDD for one storm. This was used at our Dec 12 CAC meeting as an example.

Please let me know what your objective us with the data request, so that we can figure out the best way to get you the data you need.

Take care,

Robert

From: "TenBroek, Mark" <TenbroekMJ@cdmsmith.com>

Subject: RE: CAC question on FDD sump monitoring

Date: January 31, 2014 at 2:03:00 PM EST

To: "Czachorski, Robert" <robert.czachorski@ohm-advisors.com>

Cc: "Charles (Charlie) Fleetham" <charlie@projectinnovations.com>, "Nick Hutchinson" <NHutchinson@a2gov.org>, "Warrow, Anne" <AWarrow@a2gov.org>, "Zawacki, Jason" <ZawackiJR@cdmsmith.com>

Bob:

For the response to the second question, we can certainly provide the pump start and stop times that are used to calculate the peak flow and total volume by event. The data includes thousands of records (in a couple of formats depending on the monitor type) that include the monitor ID and start and stop dates and times to the nearest half second.

There is also a table that contains records for each pump location. This data includes the monitor ID, address, and the measured sump pump rate. We perform multiple drawdown tests for each location to determine the site specific pumping rate. This rate accounts for the head that the pump is discharging against (elevation of pump to the high discharge point) and discharge piping (some runs are longer). Since all these pumps discharge to an elevation higher than the potential flooding in the street, we do not need to account for this depth.

The process of assembling this data is simple in theory, but difficult logistically given the large amount of data. We can certainly supply data that you might need, but I might be a little concerned about providing the addresses of each of the homes that are monitored. Let me know what is needed and we will get it transmitted. Thanks.

Joe Conen on 7 Feb, 2014:

I think a deeper dive into this data would be helpful in forming
recommendations going forward and possibly remedies going backwards. For
example, if we could get a tabulation or some other representation of the
pump run cycle frequency, we can make some inferences about the reliability
of the system and about the value or drawbacks of a DC backup system (such
as how long it could operate without AC power, whether the DC pump could
keep up with the flows, etc.)
Since the data is available, we should try to identify whether and how it
can be used to both understand the dispersion of results of FDD to date and
to inform our recommendations going forward.

Joe Conen on 7 Feb, 2014:

To clarify a little, I imagine that there is a broad range among the installed sump pumps in terms of pump run cycle frequency and flows, during storms or clear weather. I would be interested in getting information on the medians and the extremes in these data sets, and maybe examples. This kind of information might define performance requirements for a typical installation as well as potential contingencies needed when the extremes are found. I am also interested in whether local topology can be predictive of sump pump flows - do lower homes in a target area have higher flows? Has this data been evaluated in these ways to date?

We can discuss whether the data (without addresses) can be tabulated and analyzed for the monitored locations. I do not envisage needing addresses, unless a specific desire to follow up at an outlier location is desired.

Thanks

Joe

Kathy Boris on 7 Feb, 2014:

Nick and Robert—
Thank you for meeting with three CAC members (of which I was one) this past
Wed afternoon. I learned a lot at that meeting.

1) As was requested at that meeting, please provide copies of the letters
and post cards that were sent to homeowners informing them of the FDD
program, and that their neighborhood was going to be part of the FDD
program.

2) Nick—Please send the link to the GIS program showing sanitary sewer
and storm sewer pipes in Ann Arbor. The public version would be fine.

3) Also please send some information regarding Check Valves. Are they
legal in Ann Arbor? Does a homeowner need a permit to get one? What
circumstances warrant a check valve installation? As Frank Burdick
requested at last night’s meeting, please provide an updated version of the
table showing pre-FDD sanitary sewer backups and post-FDD sanitary sewer
backups by adding a column showing which houses had check valves installed,
and the date of their installation. A good diagram of a Check Valve
would also be most welcome.

Thank you in advance.

Robert Czachorski on 7 Feb, 2014:

Joe - I will pass your request on the FDD team and CDM. Very nice description of what you are looking for - thanks!

Kathy - I believe that the City should follow up on your requests. Lori - can you add these to the log for the City to follow-up on. Thanks!

Lori Byron on 21 Feb, 2014:

[CDM]

Mark TenBroek of CDM provided a file with the entire set of data for the sump pump monitors.

From his email:

"This is raw data that was requested so they [CAC members] could review independently.

This includes a spreadsheet with the time ranges a monitor was installed

at each location along with pumping rate. Some monitors were shifted

with time.

Also, no rainfall data has been included. No analysis was provided."

Please note, the attached file is very large, 52 MB.

City of Ann Arbor SSWWEP - Citizens Advisory Committee Coordination — City of Ann Arbor

4 gpm = 1 FDD

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