That's not a very big area. I would use some Hydraulic Water-Stop CementHydraulic Water-Stop Cement for this type of issue. This is designed primarily to prevent water from entering a buildingthrough basement or retaining walls. However, I have used it to stop leaks as well and it works great. It's easy to mix and sets up in about 5 minutes. Fill the cracks and then spread a generous amount around the pipe. There are many types on the market.