Cecil B. Slaughter | USGS Science

USGS2012

Summary and evaluation of the quality of stormwater in Denver, Colorado, 2006-2010

Stormwater in the Denver area was sampled by the U.S. Geological Survey, in cooperation with the Urban Drainage and Flood Control District, in a network of 5 monitoring stations - 3 on the South Platte River and 2 on streams tributary to the South Platte River, Sand Creek, and Toll Gate Creek beginning in January 2006 and continuing through December 2010. Stormwater samples were analyzed at the U.S. Geological Survey National Water Quality Laboratory during 2006-2010 for water-quality properties such as pH, specific conductance, hardness, and residue on evaporation at 105 degrees Celsius; for constituents such as major ions (calcium, magnesium), organic carbon and nutrients, including ammonia plus organic nitrogen, ammonia, dissolved nitrite plus nitrate, total phosphorus, and orthophosphate; and for metals, including total recoverable and dissolved phases of copper, lead, manganese, and zinc. Samples collected during selected storms were also analyzed for bacteriological indicators such as Escherichia coli and fecal coliform at the Metro Wastewater Reclamation Laboratory. About 200 stormwater samples collected during storms characterize the quality of storm runoff during 2006-2010. In general, the quality of stormwater (2006-2010) has improved for many water-quality constituents, many of which had lower values and concentrations than those in stormwater collected in 2002-2005. However, the physical basis, processes, and the role of dilution that account for these changes are complex and beyond the scope of this report. The water-quality sampling results indicate few exceptions to standards except for dissolved manganese, dissolved zinc, and Escherichia coli . Stormwater collected at the South Platte River below Union Avenue station had about 10 percent acute or chronic dissolved manganese exceedances in samples; samples collected at the South Platte River at Denver station had less than 5 percent acute or chronic dissolved manganese exceedances. In contrast, samples collected at Toll Gate Creek above 6th Avenue at Aurora station, Sand Creek at mouth near Commerce City station, and the South Platte River at Henderson station, each had about 30 to 50 percent exceedances of both acute and chronic dissolved manganese standards. Of the samples collected at Sand Creek at mouth near Commerce City, 1 sample exceeded the acute standard and 4 samples exceeded the chronic standard for dissolved zinc, but no samples collected from the other sites exceeded either standard for zinc. Almost all samples of stormwater analyzed for Escherichia coli exceeded Colorado numeric standards. A numerical standard for fecal coliform is no longer applicable as of 2004. Results from the 2002-2005 study indicated that the general quality of stormwater had improved during 2002-2005 compared to 1998-2001, having fewer exceedances of Colorado standards, and showing downward trends for many water-quality values and concentrations. These trends coincided with general downward or relatively similar mean streamflows for the 2002-2005 compared to 1998-2001, which indicates that dilution may be a smaller influence on values and concentrations than other factors. For this report, downward trends were indicated for many constituents at each station during 2006-2010 compared to 2002-2005. The trends for mean streamflow for 2006-2010 compared to 2002-2005 are upward at all sites except for the South Platte River at Henderson, indicating that dilution by larger flows could be a factor in the downward concentration trends. At the South Platte River below Union Avenue station, downward trends were indicated for hardness, dissolved ammonia, dissolved orthophosphate, and dissolved copper. Upward trends at South Platte River below Union Avenue were indicated for pH. At the South Platte River at Denver station, downward trends were indicated for total ammonia plus organic nitrogen, dissolved ammonia, dissolved nitrite plus nitrate, dissolved orthophosphate, total phosphorus, dissolved organic carbon, and dissolved lead, manganese, and zinc, and total recoverable zinc. An upward trend in properties and constituents at South Platte River at Denver was indicated for pH. At Toll Gate Creek above 6th Avenue at Aurora, downward trends were indicated for residue on evaporation, total ammonia plus organic nitrogen, dissolved ammonia, dissolved orthophosphate, total phosphorus, and total recoverable copper, lead, manganese, and zinc. Upward trends in properties and constituents at Toll Gate Creek above 6th Avenue at Aurora were indicated for pH, specific conductance, and dissolved nitrite plus nitrate. At Sand Creek at mouth near Commerce City, downward trends were indicated for hardness, dissolved calcium, total ammonia plus organic nitrogen, and dissolved ammonia, orthophosphate, manganese, and zinc. An upward trend in properties and constituents at Sand Creek at mouth near Commerce City was indicated for pH. Downward trends at South Platte River at Henderson were indicated for specific conductance, hardness, dissolved magnesium, residue on evaporation, total ammonia plus organic nitrogen, dissolved ammonia, dissolved nitrite plus nitrate, dissolved orthophosphate, total phosphorus, dissolved lead and manganese, and total recoverable copper, lead, manganese, and zinc.

Colorado↗

USGS2005

Surface water-quality and water-quantity data from selected urban runoff-monitoring sites at the Rocky Mountain Arsenal, Commerce City, Colorado, water years 1988-2004

The U.S. Geological Survey has monitored the quality and quantity of streamflow at the Rocky Mountain Arsenal (RMA) northeast of Denver, Colorado, since the early 1990s in cooperation with the U.S. Army. This report, prepared in cooperation with the U.S. Fish and Wildlife Service, documents existing surface-water-quality conditions on the RMA. All RMA water-quality data for the Irondale Gulch and First Creek Basins adjacent to and on the RMA were reviewed. Where applicable, water-quality data were compared to State standards established by the Colorado Department of Public Health and Environment. At both the Havana Interceptor below 56th Avenue gaging station and the Uvalda Interceptor below 56th Avenue gaging station, all of the dissolved-oxygen concentrations met the State standard requiring at least 5.0 milligrams per liter (mg/L) of dissolved oxygen for the protection of aquatic life. In contrast, the dissolved-oxygen concentrations at the Peoria Interceptor below 56th Avenue gage commonly were less than 5.0 mg/L. Excluding one suspect concentration of 1.6 mg/L, the dissolved-oxygen concentrations for the First Creek Basin ranged from 4.2 to 12.6 mg/L. Excluding the one suspect value, three dissolved-oxygen concentrations failed to meet the State standard of 5.0 mg/L at the First Creek below Buckley Road site. At the Peoria Interceptor below 56th Avenue site, all pH values were within the range specified by the State standard (6.50-8.99). Results of seven sampling events at the Havana Interceptor below 56th Avenue gaging station indicated a pH greater than or equal to 9 (pH values of 9 or greater exceed the upper limit of the standard). No sampling events indicated a pH less than 6.50. Results from one sampling event at the Uvalda Interceptor below 56th Avenue indicated pH values outside the range specified by the State standard. The concentrations obtained for chloride, magnesium, and sodium generally were below 200 mg/L at all three Irondale Gulch monitoring stations for the entire period of record, but there were a few sampling events at each of these sites where much higher concentrations for these analytes were obtained. The median concentrations for calcium, magnesium, and sodium generally were higher at the First Creek below Buckley Road site than in the three Irondale Gulch sites, while the 90th percentile and maximum concentrations for magnesium and sodium generally were higher at the three Irondale Gulch sites than at the First Creek below Buckley Road site. The urban runoff flowing onto the RMA had low concentrations and few, if any, detections for most organic contaminants. Part of the reason for low detections of organic contaminants may be in how the samples are collected. The existing surface-water sampling program was not designed specifically to target storm runoff and therefore does not characterize water quality for all hydrologic regimes, most notably storm runoff. As a result, the existing data may not adequately represent potential contaminant transport onto the RMA. In addition, during stormwater-runoff events, the sites examined for this report frequently are subject to sharp increases in discharge, and just as quickly the discharge rapidly recedes. These types of transient flow events make water-quality sampling difficult, and none of the sites have a safe place to sample the higher flows that occur in any given year. As a result, most of the surface-water-quality samples were collected after the flow had decreased substantially from the peak flow, which may have transported much of the chemical contaminant load through the system. Thus, little is known about the water quality during the critical initial stormwater-runoff period when contaminants are most likely to be mobilized and transported through the stormwater conveyances past the locations where gaging stations are located.

Colorado↗