Water Resources of Colorado

Effects of Surface Applications of Biosolids on Soil, Crops, Ground Water, and Streambed Sediment near Deer Trail, Colorado, 1999-2003

By Tracy J.B. Yager, David B. Smith, and James G. Crock

Errata Sheet

Available from the U.S. Geological Survey, Branch of Information Services, Box 25286, Denver Federal Center, Denver, CO 80225, USGS Scientific Investigations Report 2004-5289, 93 p., 19 figs.

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The citation for this report, in USGS format, is as follows:
Yager, Tracy J.B., Smith, David B., and Crock, James G., 2004, Effects of surface applications of biosolids on soil, crops, ground water, and streambed sediment near Deer Trail, Colorado, 1999-2003: U.S. Geological Survey Scientific Investigations Report 2004-5289, 93 p.


The U.S. Geological Survey, in cooperation with Metro Wastewater Reclamation District and North Kiowa Bijou Groundwater Management District, studied natural geochemical effects and the effects of biosolids applications to the Metro Wastewater Reclamation District properties near Deer Trail, Colorado, during 1999 through 2003 because of public concern about potential contamination of soil, crops, ground water, and surface water from biosolids applications. Parameters analyzed for each monitoring component included arsenic, cadmium, copper, lead, mercury, molybdenum, nickel, selenium, and zinc (the nine trace elements regulated by Colorado for biosolids), gross alpha and gross beta radioactivity, and plutonium, as well as other parameters.

Concentrations of the nine regulated trace elements in biosolids were relatively uniform and did not exceed applicable regulatory standards. All plutonium concentrations in biosolids were below the minimum detectable level and were near zero. The most soluble elements in biosolids were arsenic, molybdenum, nickel, phosphorus, and selenium. Elevated concentrations of bismuth, mercury, phosphorus, and silver would be the most likely inorganic biosolids signature to indicate that soil or streambed sediment has been affected by biosolids. Molybdenum and tungsten, and to a lesser degree antimony, cadmium, cobalt, copper, mercury, nickel, phosphorus, and selenium, would be the most likely inorganic "biosolids signature" to indicate ground water or surface water has been affected by biosolids.

Soil data indicate that biosolids have had no measurable effect on the concentration of the constituents monitored. Arsenic concentrations in soil of both Arapahoe and Elbert County monitoring sites (like soil from all parts of Colorado) exceed the Colorado soil remediation objectives and soil cleanup standards, which were determined by back-calculating a soil concentration equivalent to a one-in-a-million cumulative cancer risk. Lead concentrations in soil slightly exceed the U.S. Environmental Protection Agency toxicity-derived ecological soil-screening levels for avian wildlife. Plutonium concentration in the soil was near zero.

Wheat-grain data were insufficient to determine any measurable effects from biosolids. Comparison with similar data from other parts of North America where biosolids were not applied indicates similar concentrations. However, the Deer Trail study area had higher nickel concentrations in wheat from both the biosolids-applied fields and the control fields. Plutonium content of the wheat was near zero.

Ground-water levels generally declined at most wells during 1999 through 2003. Ground-water quality did not correlate with ground-water levels. Vertical ground-water gradients during 1999 through 2003 indicate that bedrock ground-water resources downgradient from the biosolids-applied areas are not likely to be contaminated by biosolids applications unless the gradients change as a result of pumping.

Ground-water quality throughout the study area varied over time at each site and from site to site at the same time, but plutonium concentrations in the ground water always were near zero. Inorganic concentrations at well D6 were relatively high compared to other ground-water sites studied. Ground-water pH and concentrations of fluoride, nitrite, aluminum, arsenic, barium, chromium, cobalt, copper, lead, mercury, nickel, silver, zinc, and plutonium in the ground water of the study area met Colorado standards. Concentrations of chloride, sulfate, nitrate, boron, iron, manganese, and selenium exceeded Colorado ground-water standards at one or more wells. Nitrate concentrations at well D6 significantly (alpha = 0.05) exceeded the Colorado regulatory standard. Concentrations of arsenic, cadmium, chromium, lead, mercury, nickel, and zinc in ground water had no significant (alpha = 0.05) upward trends. During 1999-2003, concentrations of nitrate, copper, molybdenum, and selenium had significant (alpha = 0.05) upward trends at one or more wells. The upward trend in nitrate concentration (well D6) could be caused, in part, by biosolids applications. Concentrations of biosolids-signature elements in the ground water indicate that ground water at wells D6, D25, DTX1, and possibly DTX2 and D17 are more likely affected by biosolids applications than ground water at the other monitoring wells of the study area. However, these results are not conclusive because of natural contributions from geochemical sources and likely old apparent ground-water ages at wells D6, D17, and D25. Additional age dating of the ground water could further indicate whether biosolids could have affected ground-water concentrations in the study area.

Few paired streambed-sediment samples could be collected during 1999 through 2003 because runoff was infrequent in the designated biosolids-applied and control basins; relatively less sediment usually was deposited in the biosolids-applied basin than in the control basin. No appropriate sediment regulatory standards are available for these sediment data, but trace-element concentrations are consistent with concentrations in uncontaminated soil. Plutonium concentrations were near zero. Concentrations of ammonia plus organic nitrogen, organic carbon, copper, lead, mercury, and silver were significantly (alpha < 0.10) greater in sediment of the biosolids-applied basin than that of the control basin. Of the biosolids-signature elements, only copper, mercury, and silver concentrations were significantly (alpha < 0.10) higher in sediment samples from the biosolids-applied basin than in sediment samples from the control basin, although no samples were analyzed for bismuth and only about one-half the sample pairs were analyzed for silver and uranium. Natural geochemical differences between the two basins could account for apparent differences in trace-element composition between the two basins.

A signature based not on inorganic- or radioactive-constituent concentrations is needed to help differentiate the effects of biosolids from the effects of natural geochemistry on all the monitoring components. Some other property or chemical presence, such as pharmaceutical or other anthropogenic organic compounds, that is not possibly characteristic of natural soil, rock, ground water, surface water, or sediment of the area is needed to determine if biosolids could possibly have affected concentrations in the study area.

Table of Contents



Purpose and Scope


Description of Study Area

Topographic Features



Land Use


Objectives of Monitoring Biosolids

Approach for Monitoring Biosolids

Composition of Biosolids

Trace Elements

Radioactivity and Plutonium

Composition of Water Leachates from Biosolids


Objectives of Monitoring Soil

Approach for Monitoring Soil

Effects of Biosolids on Soil

Natural Geochemical Variability of Soil near Deer Trail, Colorado

Comparison with Established Soil Standards and Screening Levels

Biosolids Signature

Water Leachates from Soil


Objectives of Monitoring Crops

Approach for Monitoring Crops

Effects of Biosolids on Crops

Ground Water

Objectives of Monitoring Ground Water

Approach for Monitoring Ground Water


Water Levels


Effects of Biosolids on Ground Water

Summary of Water Quality

Comparison with Regulatory Standards

Trends in Concentration

Biosolids Signature

Streambed Sediment

Objectives of Monitoring Streambed Sediment

Approach for Monitoring Streambed Sediment

Effects of Biosolids on Streambed Sediment

Conparison with Regulatory Standards or Guidelines

Comparison of Sites

Biosolids Signature

Summary and Conclusions

Literature Cited

Supplemental Information

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