Concrete underslab return duct flooding

Help! I'm property chairman of a small church. One of our buildings has a brick lined return air duct under the 1st floor concrete slab that is flooding. I pumped out a foot of standing water from this under slab duct last weekend. I spoke to a few old timers, who remember pumping this duct out many years ago. Obviously they never checked on the flooding again, until I noted the problem while replacing some very old and very dirty metal mesh filters on this system - I was washing off the coils, when I noted that the concrete under slab duct was flooded with a foot of water. I have placed a sump pump in the duct, but can only pump down to 1/8 inch, since there is no sump pit. There is also a lot of mud that has settled out on the floor of the duct, that I attempted to wash loose and pump out, but I can only see a small portion of this 100 foot long duct. There is no sign of any mold or other critters growing, and the water was pretty clear before I stirred it up with the pump. I suspect this water is seeping in between the concrete floor slab and the brick lined duct. This HVAC system is run mainly on the weekends for church school and AA meetings, etc. Question: what can I do to clean this water up and prevent it from reoccurring?
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Larryboy wrote:

Fix or install drain tile around the building. Make sure the ground is sloped away from the building so that rain water drains away from the building. Find the source of the water and redirect it.
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Make sure the drain from the baptistry goes into the storm or sanitary sewer, not the HVAC duct.
See if you can get Moses to part the waters in the duct. Would that be a "Mini-Mo" to fit in there?
Hold a prayer meeting.
But first, do the gutters and grading thing like he said. And keep the sump pump handy.
--

Christopher A. Young
You can\'t shout down a troll.
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Try prayer.
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wrote:

A jack hammer will remove a substantial part of a slab in no time at all.
It will also let you cut a hole for a sump pump. I would choose a position approximately half way in the run to put the sump pump and hole.
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Thanks for everyone's good advice. I have looked around the perimeter of the building and found that someone in the past had attempted to put in a cheap french drain system on one side of the building, but it is sitting partially above ground now and obviously is no longer effective. Looks like it's time for a shovel brigade party, new pipe and a lot of gravel. The other side of the building was relandscaped last year, so I didn't go poking about there yet - I need to notify some ladies in the church before I go digging in the new shrub bed. Regarding the last suggestion posted - I can't access the middle of the duct to dig a sump pit, because this underslab concrete duct runs directly beneath the long central hallway - perhaps a large indoor fountain/baptismal font would cover it up? I've left the sump pump in the duct return access for now and will pump out the water as needed. We've had a wet summer, so that has made matters worse. Thanks again!
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