Talk to Sully Mathis at Thicket Excavations, which is found between Concord and USAF Satellite Station Olivia. He'll ask you to go into the water next to the encampment and repair three broken pipes. You'll know where they are based on the bubbles coming out of the pipes. This isn't clean water, so be sure to have clothing with decent radiation protection.
When that's done, report to Sully. Be ready with your weapons as a few Softshell Mirelurk will come out of nowhere. They're only slightly more troublesome than your average Raider, and you can make short work of them with some well-placed melee or shotgun attacks. Talk to Sully one more time to complete the mission.