Rock infiltration pits and trenches are depressions filled with rock that store runoff water until it can soak into and be purified by the underlying soil. Rock infiltration areas are placed to intercept runoff water, or diversions are created to direct water to them. They are carefully placed to avoid drainage to basements, wells, and septic systems. Rock infiltration pits and trenches are sized according to the area of hard surface that drains to them. They are effective in sandy and loamy (not clay) soils. Deer Lake homeowners have installed over thirty infiltration areas around Deer Lake. Infiltration areas are sometimes created with buried plastic cells or culverts. Many infiltration projects are not visible once the project is complete and lawn is restored.