Permeable Resin-Bound Surfacing in Baltimore, MD

Baltimore's fee, the 45% treatment credit and the MDE redevelopment rule

The Department of Public Works (DPW) bills the stormwater remediation fee on impervious area. Single-family homes fall into three tiers, and other properties pay by the equivalent residential unit with a one-unit minimum. The fee regulations then treat permeable pavement in a specific way: pavement associated with a treatment practice is still defined as impervious surface, and the practice is rewarded through a credit once DPW approves an application.

That treatment credit tops out at 45% for treating all of a property's impervious area, scaled by the share treated, measured as the area for which the practice treats 1 inch of runoff. The BMP type must be MDE-approved, approvals run three years, and owners sign an inspection and maintenance agreement. Single-family owners reach the same ceiling through the Other Residential BMPs path, which requires DPW technical review.

On the development side, Maryland requires Environmental Site Design to the maximum extent practicable. Many Baltimore projects fall under the Maryland Stormwater Design Manual redevelopment policy, which applies to commercial, industrial, institutional and multifamily sites where existing imperviousness exceeds 40%, and asks projects to cut existing impervious area within the limit of disturbance by at least 50%, treat at least 50% of it with ESD, or combine the two. Permeable pavement counts toward treatment through a reduced curve number, though the manual says these surfaces are not considered permeable surfaces for other programs.

Fall line soils, harbor fill and old industrial ground

Baltimore straddles the fall line. Northwest neighborhoods sit on Piedmont rock and silty saprolite, while the harbor side, from Canton to Locust Point and Curtis Bay, is Coastal Plain sediment under centuries of port and industrial fill. MDE's permeable pavement criteria rule out Hydrologic Soil Group D soils and compacted fill, require field-verified soils before final design, and call for an infiltration rate of at least 0.52 inches per hour on applications over 10,000 square feet.

A large lot near the water may therefore need a geotechnical program before anyone discusses surfacing, and contaminated fill may call for a lined section draining through an underdrain. The reservoir bottom must sit at least four feet above the seasonal high water table, which matters in low ground around the Inner Harbor, the Middle Branch and the lower Jones Falls. MDE also keeps permeable pavement off hotspots with heavy hydrocarbon or metals loads, which rules out some industrial yards.

Winters bring regular freeze-thaw, and MDE requires that the 10-year, 24-hour storm never backs water up into the pavement. Have the engineer size the overflow path to a stable outfall from the start.

Baltimore sites where a permeable resin-bound section makes sense

• Rowhome rear yards and alley-side parking pads in Federal Hill, Hampden and Charles Village, where owners can pursue a treatment credit through DPW technical review.
• Church, school and nonprofit lots, where large paved areas drive the fee and a treatment practice can earn credit three years at a time.
• Mixed-use redevelopment in Remington, Station North, Harbor Point and Port Covington, where the 50% redevelopment target has to fit inside tight footprints.
• Courtyards and promenades at hospitals, universities and apartment buildings, where a drain-through stone finish can share space with treatment volume.

Rowhome basements often sit tight to the lot line, and MDE calls for permeable pavement to be downgradient of buildings with a ten-foot setback, so small rear-yard sections need careful layout or a liner.

From DPW plan review to a credit application

Development projects go to Baltimore City DPW for stormwater review, which under the MDE process covers concept, site development and final plans. Existing properties apply separately for the treatment credit with documentation of the practice and the impervious area it treats. In both cases raise the surface material early: MDE's guidance describes three basic permeable pavement types, porous asphalt, pervious concrete and permeable interlocking concrete pavers, so expect the reviewer to ask for data and a maintenance plan for a resin-bound course.

Resin Rock supplies the system rather than installing it: UV-stable binder, natural stone blends, trims and the Rock Crete permeable sub-base, with technical data sheets for your submittal. We train and approve installers and can usually match a Baltimore project with one within 24 hours through find an installer. If you just want to renew a worn rowhome slab with no stormwater goal, our Baltimore concrete resurfacing page is the better fit.