Laserfiche WebLink
0 <br />E <br />Chapter 4-Site-Specific Industrial Storm Water BMPs <br />When and Where to Use Them <br />There are two types of subsurface drains: relief drains and interceptor drains. Relief drains are <br />used to dewater an area where the water table is high. They may be placed in a gridiron, <br />herringbone, or random pattern. Interceptor drains are used to remove water where sloping soils <br />are excessively wet or subject to slippage. They are usually placed as single pipes instead of in <br />patterns. Generally, subsurface drains are suitable only in areas where the soil is deep enough for <br />proper installation. They are not recommended where they pass under heavy vehicle crossings. <br />What to Consider <br />Drains should be placed so that tree roots will not interfere with drainage pipes. The drain design <br />should be adequate to handle the volume of flow. Areas disturbed by the installation of a drain <br />should be stabilized or they, too, will be subject to erosion. The soil layer must be deep enough to <br />allow proper installation. <br />Backfill immediately after the pipe is placed. Material used for backfill should be open granular soil <br />that is highly permeable. The outlet should be stabilized and should direct sediment-laden storm <br />water runoff to a sediment trapping structure or another stabilized area. <br />Inspect subsurface drains on a regular schedule and check for evidence of pipe breaks or clogging <br />by sediment, debris, or tree roots. Remove blockage immediately, replace any broken sections, and <br />restabilize the surface. If the blockage is from tree roots, it may be necessary to relocate the drain. <br />• Check inlets and outlets for sediment or debris. Remove and dispose of these materials properly. <br />Advantages of Subsurface Drains <br />• Provide an effective method for stabilizing wet sloping soils <br />• Are an effective way to lower the water table <br />Disadvantages of Subsurface Drains <br />• May be pierced and clogged by tree roots <br />• Should not be installed under heavy vehicle crossings <br />• Cost more than surface drains because of the expenses of excavation for installation <br />0 <br />4-75