Nutrient TMDL Impacts on Water Recycling in Southern California: A Step Backwards?

In March 2003 the US EPA released its final nutrient TMDL for the Malibu Creek watershed, located in northwest Los Angeles County. The TMDL identified dry weather receiving water objectives of 1.0 mg/l total nitrogen (TN) and 0.01 mg/l total phosphorus (TP) as necessary to eliminate impairments due to excess algal growth in the watershed. To achieve these objectives, it identified permissible nutrient loads from various nutrient sources, including recycled water irrigation, which was allocated a zero permissible load. The rationale offered for this allocation was that existing recycled water permits issued to the water district already prohibit runoff from recycled water irrigation. The EPA interpreted this prohibition very broadly, to include both surface and subsurface runoff of both recycled water and recycled water borne nutrients. This interpretation of runoff prohibitions, which are ubiquitous in recycled water permits throughout southern California, raises numerous questions about the sustainability of existing recycling efforts and the advisability of new efforts in an era of forthcoming nutrient TMDLs.