City of Arlington

Excerpt from Arlington Texas Design Criteria Manual

5.10.3. Stormwater Quality Measures

A. Site Layout

While site layout will not give a specific reduction credit, conscientious site layout will reduce the impervious area, thus reducing the post-construction BMP requirements. When the predevelopment grade is steeper than five horizontal to one vertical (5:1) or the site contains natural creeks or wetlands, the site layout shall be designed to require the least modification to the existing topography and drainage. Factors to be considered are lots oriented and designed to minimize change in grade, drainage systems designed to minimize change in time of concentration, and street layouts designed to minimize extents of pavement.

B. Potential Pollutants

Potential pollutants to be treated with post construction BMPs may consist of, but are not limited to the following:

• Total suspended solids
• Increased temperature
• Oil and grease
• Floatables (trash)
• Nutrients (fertilizers)
• Bacteria
• Metals
• Pesticides
• Sediment (soils due to erosion)

C. BMP Selection

Examples of factors that shall be considered when evaluating and selecting BMPs area as follows:

• Effect of the development on runoff volumes and rates
• Potential pollutants from the development
• Drainage area to be treated by the BMP
• Effectiveness of the BMP on potential pollutants from the development
• Natural resources on the site (pre and post construction)
• Configuration of site, including changes to existing waterways.

D. Allowable Post-Construction BMPs:

The following post-construction BMPs may be used. Refer to the NCTCOG iSWM Technical Manual for Site Development Controls or other acceptable North Texas design criteria for detailed design guidance not contained in this manual.

• Bioretention Pond;
• Rain Garden;
• Enhanced Swale;
• Vegetated swale – maximum grade is 2%;
• Filter Strip – at least 20 ft wide with flow spreaders to ensure sheet flow;
• Dry Detention with Forebay (see Stormwater Storage Facility design guidance);
• Retention Pond (see Stormwater Storage Facility design guidance);
• Permeable pavers – designed with an underdrain system and engineered. Design shall address life expectancy, load bearing capacity, soil condition, and drainage
  to ensure no standing water;
• Infiltration – discharge of roof drains or impervious area to an infiltration trench, soakage trench or planter box;
• Rainwater Harvesting – holding tank for irrigation. Must show irrigation plan utilizing the holding tank;
• Floatables exclusion system – inlet inserts, trash racks, grates on curb inlets installed on private inlets, and designed to account for clogging. Must demonstrate no adverse impacts as detailed in manual if installed on a public outfall. Credit will not be given for grated surface inlets in parking lots unless installed with an inlet insert;
• Subsurface Treatment Devices – oil/water separators, centrifugal treatment devices, and other commercially available devices that are able to treat the design storm without causing structure flooding;
• Natural Area Preservation – can reduce impervious area and count towards postconstruction BMP requirements. This may include preserving, restoring, or creating natural areas and/or riparian areas.

Other post construction BMPs and innovative designs will be considered when submitted with supporting calculations and removal efficiencies in accordance with nationally or regionally recognized design criteria.

E. Easement Requirements

Refer to Section 2.2 of this manual.

F. Construction and Maintenance

The owner shall construct and maintain all post construction BMPs. Ownership and maintenance responsibility of the BMPs are transferable upon the sale of a property. For subdivisions, maintenance may be performed by an association (including home owners associations), but ownership and maintenance responsibility are transferred to each individual property within the association. The plat or separate instrument dedicating the easement shall include a statement of the owner’s responsibility for maintenance; and a Maintenance Agreement shall be filed with detailed information concerning BMP operation, maintenance responsibilities and enforcement actions to be taken if BMPs are not maintained. Standard language for Maintenance Statements and agreements can be obtained from the City.

G. Post-Construction BMP Inspection

The City will inspect the installation of Post-Construction BMPs. The Engineer must submit a letter stating that the post-construction BMPs were constructed as designed. This may be incorporated with the as-built letter for private improvements.

Per the maintenance agreement, the Owner may be required to submit an inspection form to the City on an annual basis as detailed in the maintenance agreement. The City may perform periodic inspections for the purpose of confirming the validity of the inspection reports and ensuring that the BMPs are still functioning as designed. The City may require repair or removal and replacement based on its inspection.

Links

Arlington Design Criteria Manual (PDF)

Arlington Texas Stormwater Website