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TOAG Review Comments on the Hydraulic Modeling and Six Project Areas

Posted by Robert Czachorski on 6 Oct, 2014
Category: No category

Folks,

On September 18, 2014, OHM presented the results from the hydraulic modeling and the six (6) project areas to the TOAG.  The results of the TOAG's review and input is summarized in the attached memo from the TOAG. The TOAG Members were generally satisfied with both the analytical approach taken by OHM and the recommended Action Plans for the six problem areas.  Below is a brief overview of the conclusions outlined in the memo:

  1. The TOAG is generally satisfied with the techniques being used to monitor flows in the system and to determine the return frequency for large wet weather events. The TOAG suggested that review and evaluation of the Glen Leven and Dartmoor areas may be warranted to explain why the post FDD wet weather flow rates remain so high. 
  2. With respect to climate change, the TOAG is generally satisfied with the analytical techniques being used to quantify climate change impacts, and believes that the study is appropriately incorporating this information into the SSWWE project analysis.
  3. The TOAG pointed out that the 25 Year Frequency Event is probably fairly conservative with regard to the whole System, since large rain events typically show significant spatial variation in rainfall volumes and intensities over an area as large as the Ann Arbor Sanitary Sewer System service area. For that reason, the total flow from the Service Area is likely to be lower than what the model predicts since some areas would be expected to receive less rainfall than others.
  4. TOAG Members questioned whether the future growth projections for the City are sufficient to accommodate redevelopment projects which might generate a substantial increase in flows. In particular, the potential for high density projects such as high rise buildings in the downtown area may need to be considered. It was noted that the Developer Offset Mitigation Program (DOMP) may provide an opportunity for offsetting such flow increases if this program is continued into the future. 
  5. With regard to design event "Scenario B" and "Scenario C" that were used to evaluate the system, TOAG Members generally agreed that the two Scenarios are appropriate for the analysis since they show how the Sanitary Sewer System is expected to perform in the future.
  6. With regard to the six (6) identified project areas, TOAG Members expressed support for conducting additional investigation of the target areas, as outlined in the action plans, before proceeding with design and construction of remedial projects. 
  7. With regard to the WWTP, it was generally agreed that the wastewater treatment plant impacts are not expected to be a significant issue, especially as compared to the surcharging problems predicted to occur in the six key areas.

Please let me know if you have any questions.

Take care,
Robert

Comments

Patricia Marten on 6 Oct, 2014:

In the TOAG report it says:
The TOAG Members expressed interest in having further discussion 
with City staff and the Consultant Team to consider the DOMP program and to weigh in on 
issues relating to continuing, modifying or eliminating the program.
But the summary says:
It was noted that the Developer Offset Mitigation Program (DOMP) may provide an opportunity for offsetting such flow increases if this program is continued into the future. 
This summary, seems to me, to provide a different "feeling" to the statement.  

Last month's meeting, also brought up the idea of eliminating the DOM, and using the 10% extra we threw in for climate change for new development instead.  I'm not ready to eliminate the DOM, and don't want to let this slide, due to lack of time, at the next meeting.

Charlie Fleetham on 7 Oct, 2014:

Our agenda includes time for a DOM discussion and it is not the last topic this time.