Ok this is what i know about this not much mind you. but have seen this done on purpose this old guy that i know has his washing machine drain directly through the middle of his veggie garden similar to what you have he uses a "French drain" in the center about 6 inches wide filled with rocks. he also dumps his egg shells and coffee grounds on top of the french drain his squash and tomatoes look very health but i do not know how healthy it would be to eat it. as looks can be deceiving.

You can do an immediate repair with hydraulic cement. A longer-term repair might involve the use of foam. Some kind of plumber!

Old galvanized pipes have a finite lifespan. If you repair this leak, you have a good chance of it developing another leak in another location. The only good solution is a complete pipe replacement. The major expense of a pipe replacement will involve the digging of the trench from the meter to the house. This is an area where a DIYer can save some money. Have the utilities companies come out and mark the location of the pipe and any other utilities going to the home. Then you can choose a route parallel to the current pipe but just far enough away from it that you aren't disturbing it. You can rent a trencher (Maybe $200) and hand dig the larger access points at the meter and house. Then you can call a plumber to lay the pipe and make the connections. If you are not physically capable of doing this, then do you have any family or friends that would be? Church group? Scout troop? There are usually community resources that can help you to figure out what you can do here. The worst thing you can do is to ignore the leak.

Harvey - a complete repipe will be required to go to hot water heat for a couple of reasons - steam and hot water operate under different pressures, possible leaks from the old pipes/radiators, etc. Hot water systems can be either one pipe or two pipe. No matter what you decide to do, you'll need to hire a very experienced HVAC designer/contractor especially with your needs to separately bill your tenants. There are lots of ways to go with your system - multiple boilers, multiple zones, and on and on. Make sure whoever bids the work does a Manual J heatloss for your property. Hang around the site listed below to get up to speed on what Qs to ask the contractors and what options you have. Good Luck Here is a link that might be useful: Steam - Hot water radiant heat