Many have wondered about the structure being built near the Upper Truckee Bridge at US50 and River Drive in South Lake Tahoe. It’s tall framing from two weeks ago has become a system of steel, cement, sand and is an in-line facility for stormwater collection and treatment.
This system, called a Delaware sand filter, stands alone and requires no pond or pretreatment. There was a like filter system installed at US50 and Rufus Allen Boulevard a couple of years ago. It has been found to be effective in removing common pollutants from stormwater drain off.
The new filter system is part of the three-year long U.S. Highway 50 “Y” to Trout Creek water-quality improvement project.
Here is an explanation on the Delaware sand filer and how it works from the California Department of Transportation (Caltrans):
It consists of two trenches. Stormwater runoff flows into the first trench where it is stored. The large suspended solids settle out in the first chamber and as the water reaches a calculated height, it flows through a rectangular weir into the second trench. This trench consists of the sand filter, typically with 18 inches of sand in place with no underdrain pipe. Instead, the water flows through the sand to a mesh filter grate at the bottom of the filter. The water then leaves the system through an outfall pipe near the mesh filter grate.
The first trench is usually covered by grated steel through which the water flows. The second trench (the filter) is usually covered by steel plates. The grated steel and steel plate covers are easily removable, allowing for very easy maintenance. Also, since most of the large particulates settle out in the first trench, the sand filter does not clog as quickly, requiring less maintenance and replacement. Among the advantages of the Delaware sand filter, the system offers ease of accessibility, less maintenance, and less use of less space while still removing pollutants before water is released to the Truckee River. Such factors are of critical importance in urban areas such as South Lake Tahoe, where stormwater runoff is the biggest water quality problem. If the Delaware sand filter can be shown to meet water quality requirements, it can make a substantial contribution to solving urban stormwater runoff problems. A similar Delaware sand filter was constructed adjacent to Highway 50 and Rufus Allen Boulevard as part of a previous Highway 50 water-quality improvement project.