Laserfiche WebLink
The city's manhole covers have an average pick hole size of 1.5 inches in diameter. In <br />reading the results of the Neenah study, one can conclude a significant amount of inflow <br />is entering the system through these holes, especially when you consider that there are <br />two holes in many of the city's covers. An average rainfall with some minor ponding on <br />the cover could contribute as many as 2.32 gallons per minute of inflow per pick hole as <br />shown in Appendix E, Test No. 2. Taking a conservative number of 700 to represent the <br />number of pick holes in the system we could have as many as 1,624 gallons of inflow per <br />minute flowing into our system through these covers; not to mention the dirt and <br />sediment draining in and foreign objects forced into the holes by kids and pranksters. <br />The amount of water flowing into each manhole differs based on where it lies. If it is in <br />the curb line, there could be significantly more water entering during runoff periods as <br />well. <br />Another part of the Neenah study was to investigate the amount of inflow through the <br />seemingly invisible gap between the cover and the casting bearing surface. After <br />speaking with representatives from Neenah and Ess Brothers, it has been concluded that <br />this possibility of inflow is basically a non - factor due to the fact that the city's castings <br />have machined bearing surfaces. Keeping these surfaces clean creates a virtually airtight <br />seal. Even if gaskets were included on some of the covers, staff would have to keep both <br />the gasket and the bearing surface totally clean. The gasketed covers also cost an extra <br />$16 per cover. <br />I spoke with David Mesler of Neenah and discussed our situation with him. We settled <br />on a manhole cover with concealed pick holes weighing about 122 pounds. He gave me <br />a verbal price quote of $107 per cover for the specified cover. The freight charges would <br />be waved if we ordered 200 or more covers. Freight charges would be approximately $2 <br />per cover for quantities under 200. <br />I then contacted Trent Ess from Ess Brothers & Sons Inc. They are located in Loretto, <br />MN. He faxed me a specification sheet for a concealed pick hole cover and I determined <br />that we have some of those covers in the city already. They are very easy to remove and <br />replace. They weigh approximately 170 pounds. That is still much lighter than many of <br />our existing covers and yet they will have enough weight so they will not rattle if they are <br />being run over by cars. The added weight may also help make a good seal between the <br />cover and the casting. <br />He quoted me three prices in a fax that I have included in this memo. The price for 200 <br />or more covers is $77.50. That is $30 cheaper for what I consider to be a superior cover <br />to the Neenah cover. He also stated that any order of more than 100 covers would have <br />no shipping charges. He would deliver them to the shop at no charge. For quantities <br />fewer than 100 we could pick them up at no charge or he would deliver them for about <br />$62. <br />In surveying the city's manhole covers, public works has found that at least 200 covers <br />are in locations that could contribute inflows reaching the levels of those found in Neenah <br />2 <br />