Welcome to the Forum!

You can certainly use hydraulic cement to patch small areas in the vermiculite, I've done it many times. (thanks or teaching me how to spell "hydraulic" )

If this is a problem that only occurs when you have a period of heavy rain combined with spring snow melt off, it's probably 'surface water', as opposed to the level of the 'ground water' rising. If I'm correct, curtain drains would solve your problem, which would save you the trouble of installing a 'well point' and the collection network of corrugated pipe that Ben spoke of.

If you don't understand what the &&*%$ I'm talking about - feel free to ask for clarification - and if you'll give me a good idea of the topography of your yard (a couple pics would be worth a couple 1000 words), I'll do my best to help you design the curtain drain system.