What should be used to prevent migration of sand fines into voids in the pea gravel when both are used as backfill?

The use of filter fabric is essential in preventing the migration of sand fines into voids in the pea gravel during backfill operations. Filter fabric serves as a physical barrier that allows water to pass through while retaining finer particles like sand. This is crucial because when sand fines migrate into gravel voids, it can lead to clogging and loss of the drainage properties of the gravel, potentially compromising the integrity of the system designed to manage water flow around the underground storage tank.

Filter fabric's design allows it to maintain the separation of different soil types, ensuring that the supportive structure of the pea gravel remains intact and effective in both drainage and stability. By placing filter fabric between the sand fines and the pea gravel, it enhances the overall performance of the backfill system, ensuring that the gravel remains well-drained and that the structural integrity required for UST operations is maintained.