If the soil is shallow, it may not provide enough of a deal to bedrock below that may be fractured. There are a few options to addressing leaks like lining the basin with clay, rubber liner, or hitting everything with SoilFloc. Rubber liners are pricey as heck, but simply don't leak. Clay requires having a good source available that is either on-site or nearby, and is applied with heavy equipment. SoilFloc is a polymer-based sealant, and may work in your circumstance, though I would recommend reaching out to TJ on this forum to have a chat to see what your options are.