PEX to galvanized underground?

Sep 3, 2018
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I have been using a cabin near Big Sur, California that was built in the 60s. The cabin has a spring-fed tank as a water source, and the building is fed by 3/4" galvanized pipe running underground for a length of ~60 ft. The 3/4" pipe has become partially exposed and rusty and recently sprung a leak where it crosses the "driveway" into the cabin property. The water into the cabin also contains a lot of rust.

I would like to replace the galv. pipe entirely with an underground run of PEX. I was planning to run the PEX through larger diameter PVC pipe to protect it, prevent potential damage from cars driving over the area, and make it easier to replace in the future. However, I'm not sure how to properly connect the PEX to the large diameter steel fittings at either end. I estimate that the pipe coming down from the hill is 3-5" OD, but I haven't dug up its junction with the 3/4" pipe yet. The large pipe also feeds a water tap for firefighters, so I don't want to mess with that.

If I connect to steel underground at either end using brass fittings, won't they corrode rapidly, especially when the ground gets wet with rain?

Should I run the PVC conduit protecting the PEX up out of the ground to keep the steel-brass connections dry?

What type of PEX is recommended? Do I need oxy barrier PEX or will A or B be fine in this application.

This area gets really hot during the summer, but rarely drops below freezing.The pipe run is underground in an area that gets full sun most of the day.

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