2020-02-26 CC Packet - Laserfiche WebLink

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Rain gardens have not worked very well in town due to a generally high water table. Replacement of the filtering media may have no effect on percolation. Some of the storm water ponds have been measured during winter to determine the amount of sedimentation. The ponds that have been measured have not shown any significant change in depth or storage capacity. Municipal Separate Storm Sewer System (MS4) rules indicate a pond is non-functioning if it is below 50% of design capacity. None of our measured ponds are below that level. Even when they are below 50%, the ific maintenance. Public Wo believe we should perform much, if any, maintenance on ponds until they are below 30% capacity. It is difficult to determine when city ditc need to be dredged or deepened. We did a Sewer Service. The length of the project was 140 feet and the bid was $4,912. That works out to about $35 per foot. That bid was about half of the other bid received, so the cost may not be representative for other projects. Staff has used a price of $40 per foot for estimating ditch maintenance costs. Rain gardens will likely fill great handle on how long that happens on average. Since the percolation has been very poor in the rain gardens that have been installed, it may not make sense to reconstruct gardens will not be required in the future by Rice Creek Watershed District (RCWD), so we have not budgeted to replace the existing ones. The legal standard regarding when we need to test sediment removed from these water features is when 3,000 cubic yards of material are removed. The testing is to determine if Polycyclic Aromatic Hydrocarbons (PAHs) primarily from coal tar based driveway sealers are present. It is ss that that amount annually to avoid the necessity of testing. Staff has reviewed the original spreadsheet and found a couple of errors. We are researching how we ended up with two ponds numbered 94 and 95. Re-sorting the ponds shows that we have 78 public ponds of which 6 are dry. Staff estimates a cost of $2,000 as an average to remove sediment from the inlet and outlet of each wet pond. We plan to do maintenance to each of the 72 public wet ponds during a 10 year period. That leads us to a total of $144,000 for all ponds or an average of $14,400 per year. Staff would plan to start a regular pond maintenance program in 2021.