‘Groundwater’ the seminar text book from Freeze and Cheery (1979) is free in pdf now…just follow the links here. This text book is almost as old as I am and important parts of modern hydrogeology are rusty or non-existent (like hydroecology amongst other topics) but it is still lucidly written and useful. I routinely send students to read chapters so I am happy that it is now available free.
Kudos to Pearson Publishing, Alan Freeze and John Cherry and Hydrogeologists without Borders! I look forward to Groundwater2.0 which is in the works!