Kenneth D. Fossum | USGS Science

USGS2001

Statistical summary of selected physical, chemical, and toxicity characteristics and estimates of annual constituent loads in urban stormwater, Maricopa County, Arizona

Stormwater and streamflow in Maricopa County were monitored to (1) describe the physical, chemical, and toxicity characteristics of stormwater from areas having different land uses, (2) describe the physical, chemical, and toxicity characteristics of streamflow from areas that receive urban stormwater, and (3) estimate constituent loads in stormwater. Urban stormwater and streamflow had similar ranges in most constituent concentrations. The mean concentration of dissolved solids in urban stormwater was lower than in streamflow from the Salt River and Indian Bend Wash. Urban stormwater, however, had a greater chemical oxygen demand and higher concentrations of most nutrients. Mean seasonal loads and mean annual loads of 11 constituents and volumes of runoff were estimated for municipalities in the metropolitan Phoenix area, Arizona, by adjusting regional regression equations of loads. This adjustment procedure uses the original regional regression equation and additional explanatory variables that were not included in the original equation. The adjusted equations had standard errors that ranged from 161 to 196 percent. The large standard errors of the prediction result from the large variability of the constituent concentration data used in the regression analysis. Adjustment procedures produced unsatisfactory results for nine of the regressions?suspended solids, dissolved solids, total phosphorus, dissolved phosphorus, total recoverable cadmium, total recoverable copper, total recoverable lead, total recoverable zinc, and storm runoff. These equations had no consistent direction of bias and no other additional explanatory variables correlated with the observed loads. A stepwise-multiple regression or a three-variable regression (total storm rainfall, drainage area, and impervious area) and local data were used to develop local regression equations for these nine constituents. These equations had standard errors from 15 to 183 percent.

Arizona↗

USGS1998

Comparison of NPDES program findings for selected cities in the United States

The U.S. Environmental Protection Agency, under section 402 (p) of the Water Quality Act of 1987, has required municipalities with populations of more than 100,000 to obtain National Pollutant Discharge Elimination System (NPDES) permits for urban stormwater discharge. This regulation is intended to minimize pollutant loadings from urbanized areas and preserve the quality of streams that receive stormwater. To apply for a NPDES permit, a municipality must monitor the chemistry of stormwater from basins having residential, commercial, and industrial land uses, and estimate storm- and annual pollutant loads and event-mean concentrations of 12 selected properties and constituents. The properties and constituents include biochemical oxygen demand (BOD), chemical oxygen demand (COD), suspended solids, dissolved solids, total nitrogen, total ammonia plus organic nitrogen, total phosphorus, dissolved phosphorus, total recoverable cadmium, total recoverable copper, total recoverable lead, and total recoverable zinc. These estimates will be used by the municipalities to evaluate the magnitude of pollutant loadings and the ef ficiency of management strategies that are intended to reduce pollutant loads. As part of a national synthesis of the study units in the U.S. Geological Survey (USGS) NPDES program, data were compiled on concentrations of the 12 properties and constituents required for load calculations. This report presents a comparison of these data.

Fact Sheet↗

USGS1995

Selected chemical characteristics and acute toxicity of urban stormwater, streamflow, and bed material, Maricopa County, Arizona

The chemistry and toxicity of urban stormwater, streamflow, and bed material in the Phoenix, Arizona, area were characterized to determine if urban stormwater could degrade the quality of streams. Toxic phases of stormwater (oil and grease, suspended solids, dissolved metals, and dissolved organics) were identified to aid water-quality managers minimize the sources of toxicants. Acute aquatic toxicity tests were done using the water flea Ceriodaphnia dubia and fathead minnows (Pimaphales promelas), and acute sediment toxicity tests were done using the amphipod Hyalella azteca. Statistical analyses also were used to determine the effect of urbanization on the quality of water and bed material and to identify toxic constituents. Statistical analyses indicated that urban stormwater could degrade the quality of streamflow with oil and grease, pesticides, dissolved trace metals, and ammonia, and that ammonia, lead, cadmium, and zinc are released by urban activities and accumulate in bed material. Ammonia may be from fertilizers, fecal matter, and other sources. Lead probably is from vehicles that use leaded gasoline. Cadmium and zinc could be from paniculate metal in oil, brake pads, and other sources. Samples of the initial runoff from urban drainage basins appeared to be more toxic than flowweighted composite samples, and stormwater was more harmful to fathead minnows than to Ceriodaphnia dubia. Streamflow samples from the Salt River were not toxic to either species, which indicates that urban stormwater could degrade the quality of the Salt River. The enhanced mortality rate of fathead minnows exposed to urban stormwater from most urban drainage basins indicated that the toxicants were more detrimental to fish than to insects and could be present in stormwater throughout the Phoenix area. The most toxic stormwater samples were collected from the drainage basins with residential and commercial land use, and the toxicity probably was due to surfactants and (or) other constituents leached from asphalt and resealant Results of toxicity identification evaluations indicated that the toxicity of stormwater mostly was due to organic constituents; dissolved zinc and copper also appeared to contribute to stormwater toxicity. Statistical comparisons of chemical data to toxicity data indicated that organophosphate pesticides were not the toxic constituents, and the toxicity generally was due to organic constituents that were not analyzed. The most toxic bed-material samples were collected from a drainage basin with undeveloped land use. In these bed-material samples, mortality rates were significantly higher than in samples from ephemeral channels. Comparisons between the toxicity of bed-material samples from undeveloped and urban drainage basins and between urban drainage basins and ephemeral channels showed no significant difference. In urban drainage basins, bed-material samples collected from areas where stormwater accumulates appeared to be more toxic than samples collected from areas where stormwater does not accumulate. For bed-material samples from the undeveloped drainage basin, mortality rates strongly correlated with recoverable concentrations of zinc and moderately correlated with recoverable concentrations of copper. The high mortality rate probably was due to naturally occurring trace metals. For bed-material samples from urban drainage basins, mortality rates significantly correlated with recoverable concentrations of cadmium and zinc, which resulted from urban activities. The bioavailability of trace metals in bed material appeared to be controlled by the adsorption properties of organic carbon, iron, and manganese. Organochlorine pesticides were detected in most bed-material samples; however, mortality rates were poorly correlated with pesticide concentrations.

Arizona↗