My main point was about developing countries. Eric himself noted that "the idea is to utilize mines within 300 km (186 mi) of the destination beach" and "or many of the first beaches, we will be looking to use tailings piles (waste rock) from previously dug and developed mines, as well as the infrastructure from those mines, such as rail for transport". The idea is summarized in this image [1], which shows mines and their associates beaches that the project intends to target due the proximity.

Most of those beaches are in developing countries. If nourishing the beaches with olivine has some unforeseen, negative ecological consequence, those countries might not be financially equipped to deal with the cleanup. How are those beaches going to be insured?

In the case of California, I'm not familiar with their beach nourishing process, but I assume they are using sand that is more similar in content to what was naturally present. If the beaches have been replenished for years, then we at least have some idea about the short-term effects.

1. https://projectvesta.org/wp-content/uploads/2019/04/Image-59...