EPA Reactivates Erosivity Calculator
Source The California State Water Resources Control Board
The California State Water Resources Control Board (SWRCB) announced it will no longer accept manual calculations for determining rainfall erosivity (R-value) as part of the construction storm water permitting process (SWRCB Memo). Instead the U.S. Environmental Protection Agency’s (EPA) online rainfall erosivity calculator must be used. For existing construction storm water projects it already calculated their risk level and has a Waste Discharge Identification (WDID) number or Erosivity Waiver ID number, dischargers do not need to re-caclulate using the EPA’s online calculator.
The R-value is part of the required calculations that a construction storm water discharger must do as part of the California SWRCB’s Construction General Permit (CGP). In 2012 and 2013, the EPA’s online calculator was unavailable while the EPA made updates and changes. During that time, the SWRCB instructed discharges to calculate the R-value manually for its construction storm water projects. The EPA’s erosivity calculator was re-activated in August 2014.
However, the updated rainfall erosivity calculator has not been without controversy since its release. Many construction storm water professionals and dischargers report that R-values are significantly different than manually calculated R-values and R-values calculated using the old erosivity calculator.
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Source: The California State Water Resources Control Board
