Application of Municipal Biosolids to Dry-Land Wheat 

Fields – A Monitoring Program near Deer Trail, Colorado 

(USA) 

A presentation for an international conference: “The Future of Agriculture: 

Science, Stewardship, and Sustainability”, 

August 7–9, 2006, Sacramento, CA 

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

Open-File Report 2006–1286 

U.S. Department of the Interior 

U.S. Geological Survey 
U.S. Department of the Interior 

DIRK KEMPTHORNE, Secretary 

U.S. Geological Survey 

P. Patrick Leahy, Acting Director 

U.S. Geological Survey, Reston, Virginia 2006 

For product and ordering information: 

World Wide Web: http://www.usgs.gov/pubprod 

Telephone: 1-888-ASK-USGS 

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its natural and living resources, natural hazards, and the environment: 

World Wide Web: http://www.usgs.gov 

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Suggested citation: 

Crock, J.G., Smith, D.B., and Yager, T.J.B., 2006, Application of Municipal Biosolids to Dry-Land Wheat fields 

– A Monitoring Program near Deer Trail, Colorado (USA): U.S. Geological Survey Open-File Report 2006-

1286. 

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endorsement by the U.S. Government. 

Although this report is in the public domain, permission must be secured from the individual 

copyright owners to reproduce any copyrighted material contained within this report. 

ii
Contents 

Abstract................................................................................................................................................................................1 

Introduction .........................................................................................................................................................................2 

Methology ............................................................................................................................................................................3 

Biosolids ...........................................................................................................................................................................4 

Soil.....................................................................................................................................................................................4 

Crops .................................................................................................................................................................................5 

Discussion and Results .....................................................................................................................................................6 

Biosolids ...........................................................................................................................................................................6 

Soil.....................................................................................................................................................................................7 

Crops .................................................................................................................................................................................7 

Acknowledgements ...........................................................................................................................................................8 

References Cited ................................................................................................................................................................8 

Slides From Presentation ................................................................................................................................................11 

iii
Application of Municipal Biosolids to Dry-Land 

Wheat Fields – A Monitoring Program near Deer Trail, 

Colorado (USA)

A presentation for an international conference: “The Future of 

Agriculture: Science, Stewardship, and Sustainability”, August 7–9, 2006, 

Sacramento, CA 

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

Abstract 

Since late 1993, Metro Wastewater Reclamation District of Denver (Metro District), a large 

wastewater treatment plant in Denver, Colorado, has applied Grade I, Class B biosolids to about 

52,000 acres of non-irrigated farmland and rangeland near Deer Trail, Colorado. In cooperation 

with the Metro District in 1993, the U.S. Geological Survey (USGS) began monitoring ground 

water at part of this site. In 1999, the USGS began a more comprehensive study of the entire site to 

address stakeholder concerns about the chemical effects of biosolids applications. This more 

comprehensive monitoring program has recently been extended through 2010. Monitoring 

components of the more comprehensive study included biosolids collected at the wastewater 

treatment plant, soil, crops, dust, alluvial and bedrock ground water, and stream bed sediment. 

Streams at the site are dry most of the year, so samples of stream bed sediment deposited after rain 

were used to indicate surface-water effects. This presentation will only address biosolids, soil, and 

crops. More information about these and the other monitoring components are presented in the 

literature (e.g., Yager and others, 2004a, b, c, d) and at the USGS Web site for the Deer Trail area 

studies at http://co.water.usgs.gov/projects/CO406/CO406.html. Priority parameters identified by 

the stakeholders for all monitoring components, included the total concentrations of nine trace 

elements (arsenic, cadmium, copper, lead, mercury, molybdenum, nickel, selenium, and zinc), 

plutonium isotopes, and gross alpha and beta activity, regulated by Colorado for biosolids to be 

used as an agricultural soil amendment. Nitrogen and chromium also were priority parameters for 

ground water and sediment components. 

In general, the objective of each component of the study was to determine whether 

concentrations of priority parameters (1) were higher than regulatory limits, (2) were increasing 

with time, or (3) were significantly higher in biosolids-applied areas than in a similar farmed area 

where biosolids were not applied. Where sufficient samples could be collected, statistical methods 

were used to evaluate effects. Rigorous quality assurance was included in all aspects of the study. 

The roles of hydrology and geology also were considered in the design, data collection, and 

interpretation phases of the study. 

Study results indicate that the chemistry of the biosolids from the Denver plant was 

consistent during 1999-2005, and total concentrations of regulated trace elements were consistently 

lower than the regulatory limits. Plutonium isotopes were not detected in the biosolids. Leach tests 

1
using deionized water to simulate natural precipitation indicate arsenic, molybdenum, and nickel 

were the most soluble priority parameters in the biosolids. 

Study results show no significant difference in concentrations of priority parameters 

between biosolids-applied soils and unamended soils where no biosolids were applied. However, 

biosolids were applied only twice during 1999-2003. The next soil sampling is not scheduled until 

2010. To date concentrations of most of the priority parameters were not much greater in the 

biosolids than in natural soil from the sites. Therefore, many more biosolids applications would 

need to occur before biosolids effects on the soil priority constituents can be quantified. Leach 

tests using deionized water to simulate precipitation indicate that molybdenum and selenium were 

the priority parameters that were most soluble in both biosolids-applied soil and natural or 

unamended soil. 

 Study results do not indicate significant differences in concentrations of priority parameters 

between crops grown in biosolids-applied areas and crops grown where no biosolids were applied. 

However, crops were grown only twice during 1999-2003, so only two crop samples could be 

collected. The wheat-grain elemental data collected during 1999-2003 for both biosolids-applied 

areas and unamended areas are similar to literature values for wheat grain from other areas. Wheat 

samples have been collected from the Arapahoe County site for 2006 with results still pending. 

Data from this study were used to compile an inorganic-chemical biosolids signature that 

can be contrasted with the geochemical signature for this site. The biosolids signature and an 

understanding of the geology and hydrology of the site can be used to separate biosolids effects 

from geochemical effects. 

Introduction 

Since 1993, the Metro Wastewater Reclamation District of Denver (Metro District) has 

been applying biosolids from the Denver metropolitan area to their property near Deer Trail, 

Colorado, as an agricultural soil amendment. The biosolids are applied to non-irrigated farmland 

according to agronomic loading rates. More information about the sewage-treatment process that 

results in the Metro District biosolids can be found at http://www.metrowastewater.com. The 

biosolids-application areas, dates of application, and application rates provided by the Metro 

District for their properties near Deer Trail for 1999 through 2003 are detailed in Stevens and 

others (2003), and Yager and others (2004a, b, c). As more information becomes posted, it will be 

available at the USGS project web page at http://co.water.usgs.gov/projects/CO406/CO406.html.

In 1999, the Metro District property, known as the METROGRO Farm, encompassed about 

81 mi2 (52,000 acres) of farmland in Arapahoe and Elbert Counties, Colorado. The Metro District 

property and surrounding private property are herein referred to as “the study area.” Soils in the 

study area generally are sandy or loamy on flood plains and stream terraces, clayey to loamy on 

gently sloping to rolling uplands, and sandy and shaley on steeper uplands (Larsen and others, 

1966; Larsen and Brown, 1971). Surface water consists of ponds (usually man-made 

impoundments) and intermittent and ephemeral streams; streams rarely flow except after heavy 

rain. Ground water is present in alluvial and bedrock aquifers (Yager and Arnold, 2003). The study 

area generally was vegetated during 1999 through 2006 except where the land surface was rock or 

where farm fields were freshly tilled. Crops and semi-arid prairie vegetation dominated the 

landscape. Tree canopy was sparse and consisted of primarily deciduous varieties such as 

cottonwood trees along stream beds. Topographic features of the study area include flood plains, 

terraces with incised channels, valleys with incised channels, rounded hills, and cliffs. In general, 

the geology of the study area consists of interbedded shale, siltstone, and sandstone, which may be 

overlain by clay, windblown silt and sand, or alluvial sand and gravel (Yager and Arnold, 2003). 

2
The climate in the study area is semiarid. On average less than 20 inches of precipitation usually is 

received each year. Most of the precipitation occurs as rainfall, mainly as thunderstorms, in May or 

early June and in late summer (usually July through August). Land use in the study area 

historically was rangeland, cropland, and pasture (U.S. Geological Survey, 1980). Abandoned 

homesteads and other buildings were present on the Metro District property, along with associated 

outbuildings, animal pens, and shallow windmill-pumped wells (Yager and Arnold, 2003). No one 

lived on the Metro District property 1999 through the present (2006); however, rural residences 

were nearby. About one-half of the Metro District property is farmed; the rest is rangeland with 

some pasture. Land use within the rest of the study area during 1993 through the present (2006) 

mostly was rangeland or pasture with some cropland. Farmland in the study area was not irrigated. 

Biosolids were applied to the land surface of the Metro District property as an agricultural soil 

amendment, and the primary crop was wheat. Cattle and sheep were the primary domestic animals 

grazing this area. Wildlife observed in the study area included pronghorn antelope, deer, coyotes, 

herons, hawks, owls, rodents, and turtles. 

Public concern about applications of biosolids to farmland increased after the Metro District 

agreed to accept treated ground water from the Lowry Landfill Superfund site in Denver. The U.S. 

Geological Survey (USGS), in cooperation with the Metro District and (in 1999) the North Kiowa 

Bijou Ground water Management District, studied natural geochemical conditions and the effects 

of biosolids applications to the Metro District properties near Deer Trail, Colorado, during 1999 

through present (2006). The study addressed the concerns about biosolids applications and other 

farming-related effects on the environment. The objectives of this USGS study were to: (1) 

evaluate the combined effects of biosolids applications, land use, and natural processes on soil, 

crops, the bedrock aquifer, alluvial aquifers, and stream bed sediments by comparing chemical data 

to regulatory standards, data from a site where biosolids are not applied (a control site), or earlier 

data from the same site (trends); (2) monitor biosolids for trace elements and radioactivity and 

compare trace-element concentrations and radioactivity with regulatory standards; and (3) 

characterize the hydrology of the study area. This presentation provides the 1999-2005 findings of 

this study for biosolids, soil, and crops. A complete discussion of findings (up to the end of 2003) 

for these matrices and the other study area objectives is detailed in Yager and others (2004d). 

Methodology 

In this study, biosolids, soil, crops, ground water, and stream bed sediment were separate 

monitoring components. Only the first three monitoring components are discussed in this 

presentation. Priority parameters were identified by stakeholders and were slightly different for 

each monitoring component. Priority parameters (arsenic, cadmium, copper, lead, mercury, 

molybdenum, nickel, selenium, and zinc), gross alpha and gross beta radioactivity, and plutonium 

isotopes, for each monitoring component included the nine trace elements regulated by Colorado 

for biosolids. Other constituents and parameters were also analyzed for each monitoring 

component. Consult Taggart (2002) for a complete list of all the elements determined by the 

analytical methods. 

Biosolids 

Biosolids are solid organic matter recovered from a sewage-treatment process that meets 

State and Federal regulatory criteria for beneficial use, such as for a soil amendment. The 

regulations state that land-applied biosolids must meet or exceed Table 1 Ceiling Concentration 

Limits and Class B pathogen criteria (Grade II, Class B criteria in the Colorado regulations until 

2003) (Colorado Department of Public Health and Environment, 1998; U.S. Environmental 

3
Protection Agency, 1993). Table 3 and Grade I requirements are stricter than Table 1 and Grade II 

requirements. The Metro District applies Table 3 (Grade I) Class B biosolids to their properties 

near Deer Trail. The biosolids-application areas, dates of application, and application rates 

provided by the Metro District for their properties near Deer Trail are detailed in Stevens and others 

(2003), and Yager and others (2004a, b, c). 

In 1999, the USGS began monitoring Metro District biosolids for concentrations of trace 

elements and radioactivity, as well as other selected parameters. The priority parameters identified 

by the stakeholders for biosolids were the nine regulated trace elements (arsenic, cadmium, copper, 

lead, mercury, molybdenum, nickel, selenium, and zinc), plutonium isotopes, and gross alpha and 

gross beta radioactivity. From January 1999 through June 2000 and from May 2003 through 

September 2003, biosolids samples were collected quarterly. From August 2000 through April 

2003 and October 2003 through present (2006), biosolids samples were collected monthly. 

Biosolids samples were collected directly from the Metro District facility’s processing line in 

Denver, rather than from individual trucks or fields near Deer Trail to ensure a more representative 

sample. Each biosolids sample was a 24-hour composite of 12 subsamples collected about every 2 

hours by Metro District personnel at the Metro District facility. The subsamples were collected 

from the conveyor belt that transfers the biosolids into the transport trucks. The samples were 

prepared and analyzed at the chemical laboratories of the USGS, Geologic Discipline, Denver. The 

biosolids material was air dried and then ground to less than 150 μm prior to chemical analysis. 

Complete details on the analytical methods and the quality-assurance protocols used are described 

by Stevens and others (2003), Taggart (2002), and Yager and others (2004a, b, c). The 

concentrations in the samples were compared to applicable Colorado standards for biosolids 

(Colorado Department of Public Health and Environment, 1998). 

Preliminary leach experiments of selected biosolids samples were done to determine if there 

was substantial reactivity and mobilization of elements upon contact of the biosolids with water. 

The experiment methodology was a modification of the Field Leach Test of Hageman and Briggs 

(2000). 

Soil 

In August 1999, the USGS began monitoring soils on two sites, one site on Metro District 

property in Arapahoe County and one site on Metro District property in Elbert County. The sites 

were monitored for priority parameters consisting of (1) nine trace elements for which biosolids are 

regulated (Colorado Department of Public Health and Environment, 1998): arsenic, cadmium, 

copper, lead, mercury, molybdenum, nickel, selenium, and zinc; and (2) plutonium isotopes, and 

gross alpha and gross beta activity. Soil samples were collected once in 1999 before the 

application of biosolids to the monitoring sites. Soil monitoring continued through two cycles of 

biosolids application and crop harvest; soil sampling was done within a few months after each 

harvest. Fields that received biosolids applications were monitored in addition to fields that 

received no biosolids, which represented reference conditions for comparison. Each of the two soilmonitoring sites consisted of three 20-acre (933 ft x 933 ft) fields separated by 100-ft buffer zones. 

Biosolids were applied on the center 20-acre field at each site after the initial soil sampling and 

again after each harvest. The other two 20-acre fields at each site never had biosolids applied and 

were used as control fields to determine the natural variability of soil composition for the duration 

of the study. All three 20-acre fields at each site were farmed in a similar way as the rest of the 

Metro District property and had crops planted and harvested. 

The sampling protocol was designed to provide data to determine how the application of 

biosolids affects soil chemistry within the top 12 inches (30 cm) of the surface; if there is a short4
term or long-term buildup or enhancement of metals or radioactivity in the top 12 inches of soil 

caused by the application of biosolids; and if a buildup occurs, is it within acceptable limits for soil 

quality as established by Federal and State agencies. A standard soil auger was used to collect 

subsamples in each field to a depth of 12 inches according to a systematic grid pattern. During 

each sampling event, 30 subsamples were collected for each of the 20-acre fields. After air drying, 

disaggregating, sieving to less than 2 mm, and grinding to less than 150 μm, splits of the 

subsamples were composited into one sample that represented the entire field for chemical analysis. 

Complete details on site selection, dates of sample collection, sample collection protocols, 

analytical methods, and quality assurance protocols are described by Stevens and others (2003) and 

Yager and others (2004a, b, c). 

Preliminary leach experiments of selected soil samples were done to determine if there was 

substantial mobilization of elements upon contact of the soils with water. The experiment 

methodology was a modification of the Field Leach Test of Hageman and Briggs (2000). 

Crops 

In the summer of 2000, monitoring of crops grown on the two soil-monitoring sites began. 

One of these sites is on Metro District property in Arapahoe County and one site is on Metro 

District property in Elbert County. Samples were collected from the control and biosolidsapplication fields. The crop samples were analyzed for the above listed nine trace elements for 

which biosolids are regulated in Colorado (Colorado Department of Public Health and 

Environment, 1998). Selected samples also were analyzed for plutonium and gross alpha and gross 

beta radioactivity. The study was carried out over two crop harvests, 2000 and 2002. The sampling 

protocol was designed to determine the average chemical composition of the grain in each of the 

six 20-acre fields. A variety of hard red winter wheat was planted at each site. In 2000, wheat plant 

samples were collected prior to crop maturity, and then mature wheat grain samples were collected 

about 1 month later just before harvest. In addition, millet grain was collected on the Arapahoe 

County site where it had been planted in the western part of the site after failure of the wheat crop. 

In 2002, wheat grain in the Arapahoe County fields was collected after harvest, and wheat grain in 

the Elbert County fields was collected during harvest. Complete details regarding dates of 

collection, sample collection protocols, sample preparation, and analytical methods for 1999-2003 

are provided in Yager and others (2004a, c). Wheat samples also were collected from the Arapahoe 

County monitoring fields in 2006, and results are pending. 

Discussion and Results 

Biosolids 

Biosolids exceeding the standards for trace elements could adversely affect the quality of 

soil on which the biosolids are applied and could alter Metro District plans for the application of 

biosolids in Arapahoe and Elbert Counties. The composition of biosolids was monitored to provide 

an independently determined data set against which the Metro District chemical analyses and the 

regulatory standards for biosolids can be compared. The data will also constitute a chemical 

baseline against which any future change in the concentration of constituents analyzed for in this 

study may be recognized, measured, and compared. The data set will also establish a “geochemical 

signature” for biosolids that will potentially enable scientists to recognize when biosolids have 

impacted soils or stream sediments. 

5
The concentration of all nine trace elements remained relatively consistent throughout the 

study. Arsenic showed the most variability with its high and low concentration differing by a 

factor of 6. The other eight elements varied by a factor of 3 or less. It is readily apparent from 

inspection of the data that all trace-element concentrations were less than the maximum allowable 

concentrations established for Table 3 (Grade I) biosolids. (Note that molybdenum does not have a 

maximum allowable concentration established for Table 3 biosolids. The value used is that for 

Table 1 biosolids.) 

Measurements for each of these parameters exhibit a relatively high uncertainty as shown 

by the “error bars” or “+/- standard deviation/range” associated with each of the data. There is no 

regulatory value established for gross beta radioactivity. Until 2003, there was a Colorado 

regulatory limit for gross alpha radioactivity. However, this regulation was revised, effective June 

30, 2003, to delete the previous regulation that generally restricted land application of biosolids that 

exceeded a gross alpha activity of 40 pCi/g (Colorado Department of Public Health and 

Environment, 1998). The samples collected before July 2002 have an average gross alpha activity 

of 37 pCi/g, whereas the samples collected from July 2002 through 2003 have an average of 18 

pCi/g. The uncertainty is also different, with the samples collected prior to July 2002 having an 

average uncertainty of +/- 34% while the samples collected from July 2002 through 2003 have an 

average uncertainty of +/- 12%. The samples collected from July 2002 and later were analyzed in a 

different laboratory from the samples collected prior to July 2002 (Yager and others, 2004a, b, c). 

The USGS has no basis for determining which laboratory provided the most accurate values. A 

few of the gross alpha activity values may have exceeded the old regulatory limit of 40 pCi/g, but 

with the uncertainty in the analyses, it is difficult to draw any conclusion from this data set. 

There are no published regulatory values for plutonium in biosolids. All data measured 

were always below the limit of determination (0.06 pCi/g). The radioactivity data for biosolids 

were reported in previous annual reports (Stevens and others, 2003; Yager and others, 2004a, b, c) 

in the uncensored data as received from the laboratory rather than censored by either the contract or 

calculated MDC. Relative to the censored form (data reported as less than the MDC), the 

uncensored form provides more information about the uncertainty, the very small concentrations of 

plutonium, and the gross alpha and gross beta activity. 

Chemical data for biosolids samples collected from the Metro District plant over a sevenyear period (1999–2005) show that all nine of the trace elements for which regulatory limits are 

established maintained relatively uniform concentrations and never exceeded the maximum 

allowable levels for Table 3 (Grade I) biosolids. Measurements of gross alpha radioactivity carry a 

high degree of uncertainty, but generally are below the now-outdated limit of 40 pCi/g. No 

regulatory limits have been established for plutonium, but all values are below the minimum 

detectable level. 

In addition to the nine trace elements that have regulatory standards established, USGS 

analyzed the samples for many other elements. Of the regulated elements, mercury and copper had 

the highest concentrations in biosolids compared to concentrations in soil. Of the non-regulated 

elements, silver, phosphorous, and bismuth have the highest concentrations in biosolids compared 

to soils (Yager and others, 2004a, b, c). For this reason, these five elements would be the most 

likely “geochemical signature” to indicate that soils or stream sediments have been impacted by 

biosolids. 

Soil 

Soil samples collected in 1999 prior to any application of biosolids have established 

baseline elemental information for the study area. Soil data from 2000 and 2002 indicate that two 

6
applications of biosolids have had no measurable effect on the concentration of the parameters 

monitored. Calculations indicate that about 14 applications of biosolids would be necessary to see 

a measurable change in copper concentration (Yager and others, 2004d). Arsenic concentrations in 

soil from both the control and biosolids-applied monitoring sites in both Arapahoe and Elbert 

County exceed the soil remediation objectives and soil cleanup value standards issued by the 

Colorado Department of Public Health and Environment in 1997 (Colorado Department of Public 

Health and Environment, 1997). This is a function of the manner in which the cleanup value 

standards were determined by back-calculating a soil concentration equivalent to a one-in-a-million 

cumulative cancer risk. Lead and mercury concentrations in soil from the study area did not exceed 

the soil remediation objectives and soil cleanup value standards (Colorado Department of Public 

Health and Environment, 1997). Cadmium concentrations in soil from the study area did not 

exceed the U.S. Environmental Protection Agency toxicity-derived ecological soil screening levels 

(U.S. Environmental Protection Agency, 2003b). Lead concentrations in soil from Arapahoe and 

Elbert County slightly exceed the Environmental Protection Agency toxicity-derived ecological soil 

screening levels for birds (U.S. Environmental Protection Agency, 2003a). This is true for those 

fields receiving biosolids as well as for the control fields, which never received biosolids. 

Crops 

Wheat grain was sampled on the Arapahoe County and Elbert County monitoring sites after 

the 2000 and 2002 harvests. Comparison of these data with data for winter wheat from other parts 

of North America where biosolids were not applied (Erdman and Gough, 1979; Erdman and 

Tourtelot, 1976; Gawalko and others, 2001; Severson and others, 1991) shows that wheat from the 

monitoring fields has very similar concentrations of elements in common with the other localities. 

Nickel is the exception to this statement; the monitoring fields near Deer Trail had higher nickel 

concentrations in both the biosolids-applied fields and the control fields than wheat from other parts 

of North America. 

There are no obvious differences between metal concentration of wheat grains collected in 

Arapahoe County and wheat grains collected in Elbert County. Fluctuations generally fall within 

the normal range of uncertainty associated with using a limited number of subsamples to 

chemically characterize a large population. The chemical differences between wheat collected 

from the 20-acre fields to which biosolids have been applied and wheat from the unamended 

control fields where no biosolids have been applied are minimal with three exceptions. Nickel 

concentration in the 2002 wheat grain samples from the Elbert County application field was 8.7 

mg/kg as compared to the two control fields where the 2002 nickel concentrations were 1.7 and 3.6 

mg/kg. Similarly, lead concentration in wheat grain samples from the Elbert County application 

field was 0.07 mg/kg, whereas lead concentrations in 2002 wheat samples from the two control 

fields were 0.01 and 0.03 mg/kg. The 1999-2005 study had only two crop cycles available for 

sampling. In order to draw conclusions about whether these variations are in any way related to the 

application of biosolids, data from several more crop cycles are required. For example, we see that 

selenium in the two control fields in Elbert County varies from 2.6 mg/kg to 0.36 mg/kg. If this is 

typical of the range we will likely see for the trace metals in the control fields where no biosolids 

were ever applied, then we must conclude that the differences discussed above for lead and nickel 

are nothing more than the normal variations caused, again, by the uncertainties arising from 

characterizing a large population with a limited number of subsamples. 

The radioactivity data are reported in the uncensored form as received from the laboratory 

rather than censored by either the contract or calculated MDC. Relative to the censored form (data 

7
reported as less than the MDC), the uncensored form provides more information about the 

uncertainty, the very small concentrations of plutonium, and the gross alpha and gross beta activity. 

Acknowledgements 

This study was done in cooperation with and funding from the Metro Wastewater 

Reclamation District and the North Kiowa-Bijou Ground water Management District. The authors 

also thank all private landowners for allowing access to their properties for data collection. The 

authors also wish to thank Monique Adams, Paul Lamothe, Paul Wigton, Murray Beasley, and Zoe 

Ann Brown, all with the analytical chemistry laboratories of the USGS, Denver, for their efforts in 

the preparation and analyses of the samples for this study and to LaDonna Choate and Phillip 

Hageman (both of the USGS, Denver) for their very helpful review of the slides and manuscript. 

The authors also give a special thanks to Phillip Hageman for the leach data. 

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Yager, T.J.B., Smith, D.B., Crock, J.G., and Stevens, M.R., 2004a, Biosolids, soil, crop, ground 

water, and stream bed-sediment data for a biosolids-application area near Deer Trail, Colorado, 

2000: U.S. Geological Survey Open-File Report 03-400, 90 p. 

Yager, T.J.B., Smith, D.B., and Crock, J.G., 2004b, Biosolids, soil, crop, ground water, and stream 

bed-sediment data for a biosolids-application area near Deer Trail, Colorado, 2001: U.S. 

Geological Survey Open-File Report 2004-1388, 69 p. 

Yager, T.J.B., Smith, D.B., and Crock, J.G., 2004c, Biosolids, soil, crop, ground water, and stream 

bed-sediment data for a biosolids-application area near Deer Trail, Colorado, 2002-2003: U.S. 

Geological Survey Open-File Report 2004-1404, 90 p. 

Yager, T.J.B., Smith, D.B., and Crock, J.G., 2004d, Effects of surface applications of biosolids on 

soil, crops, ground water, and stream bed sediment near Deer Trail, Colorado, 1999-2003: U.S. 

Geological Survey Scientific Investigations Report 2004-5289, 93 p. 

9
Slides from the Presentation 

10
Application of Muni

Application of Mun

Biosolids to Dry Biosolids to Dry

-Land 

Land 

Fields 

– A Monitoring P

A Monitoring P

near Deer Trail, CO 

near Deer Trail, CO 

By 

James G. Crock, David B. S

James G. Crock, David B. S

and Tracy J. B. Yager and Tracy J. B. Yager

U.S. Geological Survey (Denver

U.S. Geological Survey (Denver

Monitoring Plan Obje

Monitoring Plan Obje

Discussed in This Pres

Discussed in This Pres

 Monitor the quality of biosolids 

Monitor the quality of biosolids 

at the Metro Wastewater Recla

at the Metro Wastewater Recla

District of Denver for complianc

District of Denver for complianc

biosolids regulations and radio

biosolids regulations and radio

materials materials

 Monitor any potential buildup o

Monitor any potential buildup o

and radioactive substances in s

and radioactive substances in 

crops produced at application s

crops produced at application s
Elements/Measurements 

Elements/Measurements 

(total concentration, dry (total concentration, dry

-weigh

weigh

Arsenic Arsenic Cadmium CadmiumCopper LeadMercury Mercury Molybdenum MolybdenumNickel Selenium SeleniumZinc Plutonium (P

Plutonium (P

Gross 

α and 

β Activity Activity
Analytical Method

Analytical Method

 ICP

-MS after a 4 MS after a 4

-Acid Digestion (42 

Acid Digestion (42 

(possible biosolids indicator elemen

(possible biosolids indicator elemen

 Hydride Generation Hydride Generation

-AAS (As, Se) AAS (As, Se)

 Cold Vapor Cold Vapor-AAS or AFS (Hg) AAS or AFS (Hg) % Ash (Gravimetric) % Ash (Gravimetric) % S (Combustion % S (Combustion

-IR)

 Plutonium isotopes by Plutonium isotopes by gamma ray s

ray s

 Gross 

α and 

β by solid state scintilla

by solid state scintilla
Study 

area

2 Soil-sampling 

areas: 

(4 control fields, 2 

application fields)

24 Ground-water 

monitoring wells 

(no control sites)

2 Streambedsediment 

sampling areas (1 

control site)
Elbert County 

Field Site
Arapahoe County 

Field Site

L

L
Biosolids as delivered for 

Biosolids as delivered for 
Terra-Gator used for the applicatio
Biosolids after a
Materials Sample

Materials Sample

 Agricultural Soils: Two control site

Agricultural Soils: Two control site

site with biosolids applied for each 

site with biosolids applied for each 

counties prior to the application of 

counties prior to the application of 

(baseline). Soil is defined as the t

(baseline). Soil is defined as the t

(30 cm) material. Control sites are 

(30 cm) material. Control sites are 

down gradient to the application fie

down gradient to the application fi

 Whole wheat plants prior to grain m

Whole wheat plants prior to grain 

 Whole wheat or millet grain Whole wheat or millet grain Monthly 24 hour composite sampl

Monthly 24 hour composite sampl

biosolids at the Metro Wastewater 

biosolids at the Metro Wastewater 

District of Denver facility District of Denver facility
Soil Collection and Prep

Soil Collection and Prep

 Each field is divided into a 5 by 6 gr

Each field is divided into a 5 by 6 gr

sample locations. At each location 

sample locations. At each location 

wide by 30 cm deep is dug with a st

wide by 30 cm deep is dug with a st

hand bucket auger, placed into a dis

hand bucket auger, placed into a di

disaggregated and mixed by hand, 

disaggregated and mixed by hand, 

split is placed into a paper bag. split is placed into a paper bag.

 Soils are air dried in the laboratory (

Soils are air dried in the laboratory (

Denver) under ambient room tempe

Denver) under ambient room tempe

for 4 days. for 4 days.

 Each sub Each sub

-sample is disaggregated 

sample is disaggregated 

mechanical mortar, sieved to 2 mm 

mechanical mortar, sieved to 2 mm 

and the <2 mm material ground with 

and the <2 mm material ground with 

vertical grinder to pass an 100 mes

vertical grinder to pass an 100 mes
Soil Collection and Prep

Soil Collection and Prep

(continued) (continued)

 Each ground sub Each ground sub

-sample is mix

sample is mix

gram split from each is placed i

gram split from each is placed i

jar. This ensures equal represe

jar. This ensures equal represe

from each sub from each sub

-sample. sample.

 The 0.9 Kg composite sample i

The 0.9 Kg composite sample i

using a vertical plate grinder an

using a vertical plate grinder an

Required splits are made using 

Required splits are made using 

Splitter Splitter®.
Soil Sampling Soil Sampling
Plant Collection Plant Collection

 The 2000 plant sampling was subse

The 2000 plant sampling was subse

biosolids application to the middle p

biosolids application to the middle p

county sites. county sites.

 Whole wheat plant Whole wheat plant 

– Using a stainle

Using a stainle

pruning shears, cut the plants about 

pruning shears, cut the plants about 

the ground. Randomly collect at lea

the ground. Randomly collect at lea

within each of the fields. Plants had 

within each of the fields. Plants had 

head, but the kernels had not develo

head, but the kernels had not develo

 Whole wheat and millet grain Whole wheat and millet grain 

- Using 

Using 

steel pruning shears, cut the plants 

steel pruning shears, cut the plants 

below the seed head. Randomly co

below the seed head. Randomly co

30 sites within each of the fields. 30 sites within each of the fields.
Whole Wheat Plant Pr

Whole Wheat Plant Pr

 Dry the sample in the laborato

Dry the sample in the laborato

GD, Denver) under forced air 

GD, Denver) under forced air 

temperature. temperature.

 Grind the entire sample to <2 

Grind the entire sample to <2 

standard Wiley standard Wiley® Mill. Mix the 

Mill. Mix the 

 Use a Jones Use a Jones

® Splitter to make 

Splitter to make 

splits. splits.

 Ash an aliquot in forced air m

Ash an aliquot in forced air m

furnaces at 450 furnaces at 450

oC for the ICP C for the ICP

method. method.
Sampling 

Whole 

Wheat Plant
Whole wheat plants as sampled fro

County fields after one biosolids ap
Wheat grain 

after separation and cleaning

Whea
Grain preparation 

and storage
Sampling millet grain, 

Elbert County
Biosolids as received
Biosolids Sample Prep

Biosolids Sample Prep

 Air dry at ambient room temperature 

Air dry at ambient room temperature 

laboratory (USGS, GD, Denver) in a 

laboratory (USGS, GD, Denver) in a 

container in a regular chemical hood

container in a regular chemical hood

This may take up to 8 days. The ma

This may take up to 8 days. The ma

reduced in volume by at least reduced in volume by at least 75%. 

. 

to be very hard and difficult to grind 

to be very hard and difficult to grind 

 Jaw crush to pass 6 mm. Jaw crush to pass 6 mm. Grind to pass 150 mesh in an agate 

Grind to pass 150 mesh in an agate 

box.
1999 Metal Concentrations 

1999 Metal Concentrations 

Arapahoe County (mg/Kg) Arapahoe County (mg/Kg) 

- 

Element Element North 

-

Control Control

Middle 

–

Biosolids Applie

Biosolids Applie

As 7.0 6.6 Cd 0.18 0.28 Cu 19 17 Pb 17 21 Hg <0.02 <0.02 

Mo 0.6 0.6 Ni 13 15 Se 0.4 0.4 Zn 60 63 
Gross α and β and Pu in 19

in 19

Arapahoe County (pCi/g) Arapahoe County (pCi/g) - 

North -

Control Control

Middle –

Biosolids Biosolids 

Applied Applied

Plutonium 238 Plutonium 238 0.00+/-0.01 0.00+/-0.01 Gross Alpha Gross Alpha 16+/-12* 15+/-16 Gross Beta Gross Beta 28+/-8 27+/-8 Plutonium Plutonium 239+240 239+240 0.02+/-0.02 0.00+/-0.01 

*Analytical uncertainty as reported by the laboratoryfor Pu species is 0.06 pCi/g
1999 Metal Concentrations 

1999 Metal Concentrations 

Elbert County (mg/Kg) Elbert County (mg/Kg) 

- B

B

Element Element North 

-

Control Control

Middle 

–

Biosolids Applied Biosolids Applied

As 11.2 14.1 

Cd 0.21 0.21 

Cu 22 21 

Pb 26 36 Hg 0.03 0.04 

Mo 1.2 1.4 Ni 22 21 

Se 0.9 1.0 Zn 90 90 
Gross α and β and Pu in 

in 

Elbert County (pCi/g) Elbert County (pCi/g) - 

North -

Control Control

Middle –

Biosolids Biosolids 

Applied Applied

Plutonium 238 Plutonium 238 0.01+/-0.02 0.01+/-0.03 Gross Alpha Gross Alpha 13+/-11 17+/-12 Gross Beta Gross Beta 31+/-9 28+/-7 Plutonium Plutonium 239+240 239+240 0.00+/-0.01 0.00+/-0.0
COPPER IN SOIL,

ELBERT COUNTY MONITORING SITE

05

101520253035

1999 2000 2002

YEAR COLLECTED

CONCENTRATION, IN 

MILLIGRAMS PER KILOGRAM 
MERCURY IN SOIL,

ARAPAHOE COUNTY MONITORING SITE

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

0.045

1999 2001 2002

YEAR COLLECTED

CONCENTRATION, IN 

MILLIGRAMS PER KILOGRAM 

Note: Biosolids-applied and South-control fields plot on the same line.
2000 Metal Concentrations 

2000 Metal Concentrations 

Plant Arapahoe County (m

Plant Arapahoe County (m

Element Element North 

-

Control Control

Middle 

–

Biosolids Applied Biosolids Applied

As 0.12 0.15 

Cd 0.05 0.13 

Cu 5.4 5.8 Pb 0.17 0.30 Hg 0.006 0.005 

Mo 0.86 0.86 

Ni 0.94 1.20 

Se 0.62 0.44 

Zn 17 15 
2000 Metal Concentrations 

2000 Metal Concentrations 

Plant Elbert County (mg

Plant Elbert County (mg

Element Element North 

-

Control Control

Middle 

–

Biosolids Applied Biosolids Applied

As <0.05 <0.05 Cd 0.03 0.03 

Cu 5.5 4.0 Pb 0.06 0.04 

Hg 0.006 0.007 

Mo 1.71 1.06 

Ni 0.51 0.45 Se 1.70 0.40 Zn 21 15 
2000 Metal Concentrations 

2000 Metal Concentrations 

Grain Arapahoe County (

Grain Arapahoe County (

Element Element South 

-

Control Control

Mi

Biosolids 

Biosolids 

As <0.05 <0.

Cd 0.03 0.0Cu 5.1 6.6

Pb 0.01 0.0

Hg <0.004 <0.0Mo 0.43 0.8

Ni 0.74 1.3

Se 0.41 1.4Zn 20 20
2000 Metal Concentrations 

2000 Metal Concentrations 

Grains Elbert County (m

Grains Elbert County (m

Element Element North 

-

Control Control

Middle 

–

Biosolids Applie

Biosolids Applie

As <0.05 <0.05 Cd 0.02 0.02 

Cu 4.9 4.8 Pb <0.01 0.01 

Hg <0.004 <0.004 

Mo 0.70 0.51 

Ni 0.43 0.50 

Se 2.1 0.64 Zn 26 25 
2000 Gross 2000 Gross α and β and P

Grains Elbert County (

Grains Elbert County (

North -

Control Control

Middle –

Biosolids Biosolids 

Applied Applied

Plutonium 238 Plutonium 238 0.00+/- 0.03 0.00+/-0.01 Gross Alpha Gross Alpha 1+/-1 1+/-1 Gross Beta Gross Beta 6+/-2 6+/-2 Plutonium Plutonium 239+240 239+240

0.00+/-

0.01 0.00+/-0.00 
2000 Metal Concentrations 

2000 Metal Concentrations 

Grain, Arapahoe County (

Grain, Arapahoe County (

Element Element North 

-

Control Control

Middle 

–

Biosolids Applied Biosolids Applied

As 0.07 0.04 

Cd 0.05 0.05 

Cu 7.0 7.1 Pb 0.21 0.02 Hg <0.004 <0.004 

Mo 0.73 0.78 

Ni 6.4 6.5 Se 0.26 0.24 

Zn 22 19 
Metal Concentrations in Bioso

Metal Concentrations in Bioso

Element Element Maximum for Maximum for 

Grade I Grade I

Mar

-

99

Mar

-

01

Mar

-

02

As

CdCu

Pb

Hg

Mo

Ni

Se

Zn

41 1.9 2.3 1.1 39

1500

200

17

75 (Grade II) 75 (Grade II)

2.9

420

3.2

100

4.0

630

77

2.2

31

560

30

7.7

610

60

1.6

2729

2800

67

1.3

30

630

7.0

690

2.28.3

580
Gross α and β and Pu in Bios

in Bios

(N.D. – not determined) not determined)

Maximum for Maximum for 

Grade I Grade I

Mar-99 Jun-00 Jul-01 

Gross α, 

ppm

Gross β, 

ppm

Pu 238

Pu 

239+240 239+240

40 19+/-7 44*/-11 14+/-7 

No Set 

Standard Standard

23+/-6 23+/-6 

No Set 

Standard Standard

24+/-7

0.00+/-

0.01

No Set 

Standard Standard

0.00+/-

0.01

0.00+/-

0.01

0.00+/-

0.01

0.00+/-

0.01

0.00+/-

0.01

*Analytical uncertainty as reported by the labordetection for Pu species is 0.06 pCi/g
COPPER IN BIOSOLIDS

0

200400600800

10001200140016001800

Mar-99 Sep-99 Mar-00 Aug-00Oct-00 Dec-00 Feb-01Apr-01 Jun-01 Aug-01Oct-01 Dec-01 Feb-02Apr-02 Jun

DATE COLLECTED

 CONCENTRATION, mg/kg 

Maximum concentration allowed for Table 3 (Grade I) biosolid
MERCURY IN BIOSOLIDS

02468

101214161820

Mar-99 Sep-99 Mar-00 Aug-00Oct-00 Dec-00 Feb-01Apr-01 Jun-01 Aug-01 Oct-01 Dec-01 Feb-02Apr-02 Jun-02 A

DATE COLLECTED

CONCENTRATION, mg/kg 

Maximum concentration allowed for Table 3 (Grade I) biosoli
When do you notice pote

When do you notice pote

accumulation in soils from 

accumulation in soils from 

application? One worst cas

application? One worst ca

- Copper in Arapahoe Co

Copper in Arapahoe C

 Assume: All the Cu introduced by th

Assume: All the Cu introduced by th

in the soil of the 20 acre field and th

in the soil of the 20 acre field and th

application rate remains constant at 

application rate remains constant at 

(~ 1 yd

3/acre), every other year. , every other year.

 Measurements: Top 12 inches (30 c

Measurements: Top 12 inches (30 c

average soil density of 1.4 gm/cm average soil density of 1.4 gm/cm

3, b

, b

is 16 

± 5 ppm, average biosolids Cu 

5 ppm, average biosolids Cu 

ppm.
One worst case scenario One worst case scenario 

- C

C

Arapahoe County soils (Co

Arapahoe County soils (Co

 1.28 x 10 1.28 x 10

7 mg Cu applied to the en

mg Cu applied to the en

biosolids application biosolids application

 3.44 x 10 3.44 x 10

7 Kg soil in the top 12 inch

Kg soil in the top 12 inch

 0.37 mg Cu/Kg or 0.37 ppm Cu inc

0.37 mg Cu/Kg or 0.37 ppm Cu inc

application of biosolids or about 2% 

application of biosolids or about 2% 



±5 ppm Cu is the natural soil variab

5 ppm Cu is the natural soil variab

would equal 14 applications, or 28 

would equal 14 applications, or 28 

natural variability would not accoun

natural variability would not accoun

increase of soil Cu content increase of soil Cu content


All data are published and 

All data are published and 

Website: Website: 

http://co.water.usgs.gov/proj

http://co.water.usgs.gov/proj

CO406.html CO406.html
Interpretive and Summary R

(through 2003 results, more 
Conclusions Conclusions

 All the target metal total concentratio

All the target metal total concentratio

biosolids are consistently below the 

biosolids are consistently below the 

allowable values for Grade I biosolid

allowable values for Grade I biosolid

of Colorado and are consistent over 

of Colorado and are consistent over 

 All isotopes of plutonium were alway

All isotopes of plutonium were alway

reported limit of detection (0.06 pCi/

reported limit of detection (0.06 pCi/

 Pre

-application baseline information 

application baseline information 

fields are geochemically different fields are geochemically different 

– t

t

County field is higher in most of the 

County field is higher in most of the 

elements due to the occurrence of P

elements due to the occurrence of P

the soil parent material. the soil parent material.
Conclusions (contin

Conclusions (contin

 The method of compositing the 

The method of compositing the 

provided a representative samp

provided a representative samp

test fields. test fields.

 Vegetation samples tend to sho

Vegetation samples tend to sho

elemental patterns as the paren

elemental patterns as the paren

results, crops may prove to be 

results, crops may prove to be 

indicator of metal accumulation 

indicator of metal accumulation 

availability in the biosolids availability in the biosolids

-ame

ame
For more informat

For more informat

 Email: jcrock@usgs.gov jcrock@usgs.gov

dsmith@usgs.gov dsmith@usgs.govtjyager@usgs.gov tjyager@usgs.gov

 Website: Website: 

http://co.water.usgs.gov/pro

http://co.water.usgs.gov/pro

06/CO406.html 06/CO406.html
Thank You!!

Estes Park, CO