As a general rule, concrete is a very good soundproofer, however, if sound is transmitted directly into the concrete,the slab will carry (transmit) that sound quite readily.
Now, if this does not alleviate all of the noise or get it to tollerable levels, you will need to construct a box or enclosure to enclose the noisy pump. You will want to line the inside of this box with a sound blocking and absorbing foam mat. You'll need to leave some space at the bottom if ventilation is a requirement for the pool pump.
This same proceedure can be used to soundproof a gas emergency generator or even a camping generator, to keep from bothering your fellow campers thus making your campsite much more tollerable.
You can find tons of information on soundproofing a generator when you go to www.soundproofing.org There is a wealth of knowledge on that website, and a great staff willing to help you with all of your soundproofing needs.