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
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.
This document also is available in pdf format:
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
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
Objectives of Monitoring Biosolids
Approach for Monitoring Biosolids
Composition of Biosolids
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
Water Leachates from Soil
Objectives of Monitoring Crops
Approach for Monitoring Crops
Effects of Biosolids on Crops
Objectives of Monitoring Ground Water
Approach for Monitoring Ground Water
Effects of Biosolids on Ground Water
Summary of Water Quality
Comparison with Regulatory Standards
Trends in Concentration
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
Summary and Conclusions