Containment berms on their own are not always enough to prevent winter runoff because they only control surface flow, not seepage or leaks that occur below the soil line. During winter, frozen or saturated ground may allow water movement beneath or around a berm, especially if the soil shifts during freeze–thaw cycles. Heavy snowmelt or rain-on-snow events can also overwhelm a berm if the volume of water rises too quickly.
Even when the berm appears intact, nutrients can escape through small cracks or porous soil in an unlined system. While berms help slow and direct runoff, they are most effective when used alongside liners or other containment measures that block both surface and subsurface pathways for nutrient loss.
