Further Research/Information Needed   More research needs to be done on effectiveness and application issues. Some questions that remain to be answered are:     -Whether porous paving remains effective over time, especially with resurfacing or snow removal.     -Whether porous pavements can still remove pollutants after subfreezing weather and snow removal.     -The costs of different maintenance and rehabilitation options to restore porosity.     -The exact effects of porous pavement on groundwater contamination.