The following table discusses several site conditions that need to be considered prior to determining whether a particular location is suitable for a permeable hard-scape. Site Considerations Site Condition Feasible Notes Steep Slopes No Steep pavement surface slopes may cause shifting of the pavement surface and base materials. In general, slopes greater than 5% do not make good candidates for permeable hard-scapes. External Drainage Yes The area of pavement or rooftop draining onto (“run-on”) should be no more than 2 times the area of permeable hard-scape. * High Water Table No The bottom of the permeable hard-scape installation (i.e., the bottom of the excavated area) must be at least 2 ft. above the seasonal high water table. Poor Soil Condition Yes Soil conditions do not typically constrain the use of permeable hard-scape although they do determine whether an underdrain is needed. This practice is best if the soil has good drainage. Floodplain No Permeable hard-scape should not be constructed within the 100-year floodplain Adjacent Structures Yes To avoid the risk of seepage, permeable hard-scapes should not be connected to structures so that water cannot seep into basements or damage foundations. Utilities Yes/No Interference with underground utilities should be avoided whenever possible. Approval from the applicable utility company or agency is required if utility lines will run below or immediately adjacent to a permeable hard-scape. *Only paved or stable impervious surfaces should be allowed to drain onto (“run-on”) pervious hard-scape. Turf, mulch, and other non-paved areas contribute large amounts of sediment to the pervious hard-scape which can increase the likelihood of clogging and the need for vacuum maintenance. Look at the existing surface, if it is covered in organic material (from overhead trees or similar) it may not be a good candidate for a permeable hard-scape. How do I install (or use) my permeable hard-scape? Due to the increased complexity of permeable hard-scapes and the need for some specialty equipment it is strongly recommended that homeowners work with a trained
Frederick County Sustainability Office Green Homes Challenge , Green Leader x x Monocacy and Catoctin Watershed Alliance x City of Gaithersburg RainScapes Rewards ; x x x City of Rockville RainScapes Rewards x x x Montgomery County DEP RainScapes Rewards x x x Anacostia Watershed Society x National Capital Region Watershed Stewards Academy x x Prince George’s County DER x x Howard County Government Clean Water Howard x x Howard County Watershed Stewards Academy x x Midshore RiverKeeper Conservancy x Chester River Association Corsica River Conservancy x x
Sassafras River Association x Anne Arundel Watershed Stewards Academy x x Anne Arundel County WERS x x South River Federation x x Severn River Association x x West Rhode RiverKeeper x RainScaping Campaign x University of Maryland SeaGrant Extension Watershed Restoration Specialists x x University of Maryland Extension Bay-Wise Certification Program x Bay-wise Master Gardeners Bay-wise Yard Visits x x Local Watershed Groups x DISTRICT OF COLUMBIA National Capital Region Watershed Stewards Academy x x District DDOE RiverSmart Homes x x PENNSYLVANIA Conewago Creek Watershed Conewago Creek Initiative x x