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o Down slope of steep, erosion prone areas that are likely to deliver sediment. o Where fill soils are used that can become unstable when saturated. o Excessively steep slopes where water within the aggregate base layer or at the sub -grade surface cannot be controlled by detention structures and may cause erosion and structural failure, or where surface runoff velocities may preclude adequate infiltration at the pavement surface. o Where permeable pavements can not provide sufficient strength to support heavy loads at industrial facilities such as ports. o Where installation of permeable pavement would threaten the safety or reliability of pre-existing underground utilities, pre-existing underground storage tanks, or pre-existing road sub -grades. The following criteria can be cited as reasons for a finding of infeasibility without further justification (though some require professional services to make the observation): o Within an area designated as an erosion hazard, or landslide hazard. o Within 50 feet from the top of slopes that are greater than 20%. o For properties with known soil or ground water contamination (typically federal Superfund sites or state cleanup sites under the Model Toxics Control Act (MTCA)): o Within 100 feet of an area known to have deep soil contamination; o Where ground water modeling indicates infiltration will likely increase or change the direction of the migration of pollutants in the ground water; o Wherever surface soils have been found to be contaminated unless those soils are removed within 10 horizontal feet from the infiltration area; o Any area where these facilities are prohibited by an approved cleanup plan under the state Model Toxics Control Act or Federal Superfund Law, or an environmental covenant under Chapter 647nRCW o Within 100 feet of a closed or active landfill. o Within 100 feet of a drinking water well, or a spring used for drinking water supply, if the pavement is a pollution -generating surface. o Within 10 feet of a small on -site sewage disposal drainfield, including reserve areas, and grey water reuse systems. For setbacks from a "large on -site sewage disposal system", see Chapter 246-272B WAC. o Within 10 feet of any underground storage tank and connecting underground pipes, regardless of tank size. As used in these criteria, an underground storage tank means any tank used to store petroleum Volume V — Runoff Treatment BMPs — December 2014 5-19