Total maximum daily loads and waste load allocations for Las Vegas Bay: Rationale and calulations

In September 1987 the Nevada Division of Environmental Protection revised Water Quality Standards for Las Vegas Wash (LVW) and Lake Mead. Standards were set for chlorophyll-a and unionized ammonia in Las Vegas Bay (LVB) (NDEP 1987). The 1986 and 1987 LVB data showed non-achievement of both the chlorophyll-a and unionized ammonia standard which triggered an analysis of total phosphorus and total ammonia Total Maximum Daily Loads and Waste Load Allocations which are presented in this report. This report is separated into three sections: 1. 1987 Las Vegas Bay Water Quality Conditions and Seasonal Periodicity. 2. Concentration Estimates at Northshore Road to Meet Water Quality Standards in Las Vegas Bay. 3. Total Maximum Daily Loads at North Shore Road and Waste Load Allocations. Blue-green algae were present in 1987 but did not build to bloom levels observed in 1986. Mean summer chlorophyll-a at station 3 was 53.2 ug/1 which is considerably higher than the standard of 30 ug/1 (4 year mean). From April 9 through August 3 unionized ammonia was never below the .04 mg/1 chronic toxicity standard at station 2. The acute unionized ammonia standard (.45 mg/1) was not exceeded. The standards were not achieved from April through September but were met from October through March. Over the period of record examined (1977-1987) the density of LVW has decreased significantly in comparison to LVB. At present, there are months when LVW enters LVB as a neutrally buoyant or buoyant jet