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EPA faulted on waterway pollution from sprawl

"EPA faulted on waterway pollution from sprawl"
10/15/08, By DINA CAPPIELLO, AP

Source: Directly, Department of Water Resources' California Water News online, October 16, 2008

WASHINGTON (AP) - The Environmental Protection Agency is failing to stem the pollution washing into waterways from cities and suburbs, the National Academy of Sciences reported Wednesday. The report's authors urged "radical changes" in how the federal government regulates stormwater runoff so that all waters are clean enough for fishing and swimming.

"The take-home message is the program as it has been implemented in the last 18 to 20 years has largely been a failure, said Xavier Swamikannu, one of the authors and the head of Los Angeles' stormwater program for the California Environmental Protection Agency.

Stormwater runoff is the toxic brew of oil, fertilizers and trash picked up by rain and snowmelt as the water flows over parking lots, roofs and subdivisions.

The report said responsibility for managing stormwater must shift from developers to local governments, and permits should be issued on the boundaries of a watershed, rather than state borders. Such a change probably would require a new law and take between five years to 10
years, the report said.

While urban areas cover only 3 percent of the U.S., it is estimated that their runoff is the primary source of pollution in 13 percent of rivers, 18 percent of lakes and 32 percent of estuaries.

Current law is ill-equipped to deal with the problem, the authors said.

Congress required the EPA in 1987 to start issuing permits under the Clean Water Act to industrial and construction sites. But lawmakers changed the focus on water pollution, from industrial discharges and sewage pipes to runoff, a problem that is much larger and harder to
pinpoint. The law is designed to target specific contaminants, when the problem with stormwater often is one of volume. A surge of water after a storm can cause streams to erode and fill waterways with sediment.

Benjamin H. Grumbles, the EPA's assistant administrator for water, said the findings underscored the approaches the EPA is taking. The agency requested the review in 2006, but Grumbles disagreed on Wednesday with the conclusion that the stormwater program was failing.

"We want to accelerate the progress on reducing pollution and managing stormwater. We believe sound science, pollution prevention, and watershed protection will ensure continued clean water progress," he said.

The National Academy of Sciences is a private organization chartered by Congress to advise the government of scientific matters.

Replicating Natural Runoff Through Retention and Dissipation

A simulation model for estimating retention volumes
By Randel Lemoine, Stormwater E-magazine September 2008

Natural watersheds retain and dissipate most rainwater. This water is retained on the surfaces of vegetation and in ground depressions, such as puddles, wetlands, and marshes. Natural processes such as transpiration by plants, infiltration into the soil, and evaporation dissipate this water. A natural watershed’s retention and dissipation capacity is sufficient to prevent any runoff from occurring during most rainfalls. Occasionally, when there is a heavy rainfall, a small amount of the rainwater becomes surface runoff that enters nearby creeks, rivers, and lakes.
The natural processes that retain and dissipate the rainwater are diminished when land is developed, whether for agriculture or for urban use. Land development removes vegetative cover, fills in low areas, compacts the soil, and creates impervious areas. The result is increased water runoff flowing more frequently across the land and discharging into the watershed’s rivers, streams, and lakes. This increased runoff causes downstream flooding, accelerated soil loss from erosion, unstable stream banks, and pollution of water resources.

Problems in Mitigating Increased Runoff
Detention basins temporarily hold collected runoff and slowly release the water. They are constructed in an attempt to mitigate the downstream flooding problems by limiting the peak discharge rate of the runoff. However, they do not reduce the volume of runoff discharged into the nearby creeks, rivers, and lakes. Consequently, the runoff volume discharged remains greater than when the land was in its natural condition. Therefore, detention basins fail to match the natural runoff pattern that occurred prior to the land being developed. Streambank erosion, stream channel instability, and occasionally even downstream flooding continue to be problems.
Retention basins hold a certain volume of water. There are two types of retention basins: water-quality basins and water-volume basins. Water-quality retention basins remove pollutants collected by the runoff. These basins allow the runoff to pass through after holding it long enough to give natural processes time to remove a percentage of the pollutants. They do not reduce the volume of runoff discharged. Water-volume basins capture and dissipate the runoff, thereby reducing the volume and frequency of discharges from a site. A discharge of runoff occurs only when the runoff volume exceeds the basin’s maximum retention volume. However, the actual volume available for retaining the runoff from the next rainfall depends upon the dissipation of the water held from the previous rainfall. Therefore, a key factor in determining the effectiveness of a water-volume basin is the dissipation rate.
Two commonly used methods for estimating the maximum retention volume for a water-volume retention basin are the “90% Rule” and the “Two-Year-Difference Rule.” The 90% Rule requires the capture of 90% of the runoff coming from a developed site. The Two-Year-Difference Rule requires that the maximum retention volume should be equal to the difference between the two-year runoff from the developed site and the two-year runoff from the site in a natural undeveloped condition. Neither rule addresses the necessary dissipation rate relative to the storage volume. Therefore, it is uncertain that the maximum retention volume derived by these rules will adequately address the adverse effects caused by the increased runoff coming from developed land.

An Alternative Method for Determining Retention Volume and Dissipation
An alternative to these methods is to use a simulation model. This model is set up on a Microsoft Excel spreadsheet and uses local historical precipitation data. The runoff volume for each day of the simulation is estimated using the TR-55 runoff equations (USDA 1986). The retained water volume for each day is calculated by taking the difference between the precipitation volume and the runoff volume, then subtracting the daily dissipation volume. This retained water volume is added to the precipitation of the next day, which is valid because the effect of the retained water on the next day’s runoff volume has the same effect as if it were part of the precipitation for the next day. Adding the previous day’s retained water to the precipitation provides the continuity needed for determining the appropriate combination of retention and dissipation to replicate the natural runoff.

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