Frank Burdick’s Log Number: 24, 27

Submitted by: Burdick’s Log, email from resident

Category (1,2,3): 1

Status: Closed

Estimated date to address: N/A

A. Note that the percentages typically mentioned are 70% to 90%. In addition to the flow monitoring analysis presented during October CAC meeting, and curb line monitoring data from previous question, see response below for multiple measurements conducted. The final results of the flow monitoring and engineering analysis will be presented to the CAC at the December 12 meeting and to the public at the January 16 meeting, as well.

 

This question was posed to CDM (who did the 2001 study), and their response is pasted below. The key take away is that they were estimates – very soon we will have the actual values computed.

 

Tables 6 & 7 and Figures 6-8 in the Duluth paper “Was it Worth the Price” that was presented to the “Best Practices” sub-group has some good study results. We also provided the sub-group with the Auburn Hills report. These studies both show fairly significant flow removal rates from FDD. There is not much dispute in the industry that FDD can be very effective at removing flows. 

 

The key questions for Ann Arbor is how much did their FDD program remove, and then given that knowledge, the current state of the system, and the desire of the public, what is the best way to move forward from here? Those items will be our focus for the next several months of the study. The first piece (how much flow was removed) will be ready very soon, and tabulated using multiple techniques and multiple measurements.  The second piece (where to go from here) will be performed over the winter and spring. All options are on the table and will be explored, and the City has made it clear that they hope and expect that the CAC will make a recommendation.

 

Message from Mark TenBroek, CDM dated 11-7-13:

 

The SSO report presented an estimate that 70%-90% of the observed I/I during wet weather was likely from connected footing drains in the study areas.  This estimate was largely based on the following data sources:

 

·      Direct Storm Measurements – CDM Smith identified 20 house leads in Ann Arbor during the SSO project that discharged directly to manholes.  During two rain events, 14 of these locations in 4 of the study areas were measured using a bucket and stopwatch method while flow metering was concurrently taking place in sanitary sewers.  A comparison of these measurements led to the conclusion that 70% to 90% of the I/I flows were sourced from connected footing drains.

·      Pilot FDD Monitoring – Pilot FDD work was performed after the flow metering was completed to establish the range of expected flows generated by disconnected footing drains.  These monitored sump pump flows were consistent with the directly monitored house leads, which estimated peak flows in the range of 3-5 gpm/home for large storm events. 

·      Peer Community Observations – Footing drain disconnection work had been performed in West Lafayette Indiana, Canton Township, and Auburn Hills prior to the Ann Arbor SSO study.  These peer communities had observed reductions in I/I after the disconnection of these footing drain sources, but the percentage of I/I flow from these sources had not been quantified at the time of the SSO study. 

 

After the SSO project was completed, additional data was collected as the FDD program proceeded to develop additional evidence of the source of I/I that was observed in the sanitary sewers, as described below:   

 

·      Southeast Michigan Sump Pump Monitoring – After the SSO project was completed, CDM Smith deployed a number of sump monitors in homes around SE Michigan that were of a similar vintage as the Ann Arbor homes, but where sump pumps had been installed.  This was done as part of the DWSD Wastewater Master plan. The monitored sump pump flows were similar to that observed in the pilot FDD installations in Ann Arbor.

·      Continuing Ann Arbor FDD Sump Pump Monitoring – CDM Smith installed a large number of sump pump monitors that were moved to new sump pumps as the FDD work was performed in Ann Arbor.  This data collection was performed from 2001 until present.  The results of that work show that while the peak footing drain flows are variable for individual homes, the average of the peak flows generated by footing drains was typically in the range of 3-5 gpm/home during large storm events.