PB86-176542
FIELD INVESTIGATION AND EVALUATION OF LAND
TREATING TANNERY SLUDGES
University of Cincinnati
Cincinnati, OH
Mar 86
U.S. DEPARTMENT OF COMMERCE
National Technical Information Service
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EPA/600/2-86/033
March 1986
FIELD INVESTIGATION AND EVALUATION OF
LAND TREATING TANNERY SLUDGES
by
Robert M. Lollar
and
Waldo E. Kallenberger
Tanners' Council of America
Cincinnati, Ohio 45221-0014
Contract No. 68-03-2976
Project Officer
Don A. Clark
Processes and Systems Research Division
Robert S. Kerr Environmental Research Laboratory
Ada, Oklahoma 74820
ROBERT S. KER.P ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
ADA, OKLAHOMA 74820
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing!
1. REPORT NO.
EPA/600/2-86/033
3. RECIPIENT'S ACCESSION NO.
6 176542/AS
4. TITLE AND SUBTITLE
FIELD INVESTIGATION AND EVALUATION OF LAND
TREATING TANNERY SLUDGES
5. REPORT DATE
March 1986
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO.
Robert M. Lollar and Waldo E. Kallenberger
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Tanners' Council of America
Research Laboratory
University of Cincinnati
Cincinnati, Ohio 45221-0014
10. PROGRAM ELEMENT NO.
CBWD1A
11. CONTRACT/GRANT NO.
Contract #68-03-2976
12. SPONSORING AGENCY NAME AND ADDRESS
Robert S. Kerr Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Ada, Oklahoma 74820
13. TYPE OF REPORT AND PERIOD COVERED
Final (Aug. 1980 - Aug. 1985)
14. SPONSORING AGENCY CODE
EPA/600/15
15. SUPPLEMENTARY NOTES
16. ABSTRACT
Land treatment of wastewater sludges from tannery processes has been
investigated during a five-year field plot study. The experimental design
included eight field test plots receiving selected applications of three'types
of tannery sludges over a three-year period.
The five-year study included analyses of sludge, soil core, plant-tissue,
and soil pore and runoff water samples to evaluate the feasibility of land
treatment of tannery sludges. The data generated indicated that land treatment
is potentially an environmentally acceptable technology for management of
wastewater sludges from trivalent chromium tanneries; however, waste application
rates must be carefully controlled.
The applied trivalent chromium appeared to remain primarily in the topsoil
without any detectable oxidation to hexavalent chromium. Transport of trace
quantities of chromium in soil runoff water appeared to be associated with move-
ment of soil particles. Application levels of tannery sludges containing hair-
burn wastes will be limited by the mineralization rate of the proteinaceous
nitrogen and the crop inorganic nitrogen requirements. Elevated salt concen-
trations of the hair-burn sludges also will require specific consideration.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group
18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (Tins Report/
UNCLASSIFIED
21. NO. Or PAGES
123
20. SECURITY CLASS (This page I
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (R«v. 4-77) PREVIOUS EDITION is OBSOLETE
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DISCLAIMER
Although the research described in this document has
been funded wholly or in part by the United States Environ-
mental Protection Agency through contract No. 68-03-2976 to
the Tanners' Council of America, it has not been subjected
to Agency review and therefore does not necessarily reflect
the views of the Agency and no official endorsement should
be inferred.
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FOREWOPD
EPA is charged by Congress to protect the Nation's land,
air and water systems. Under a mandate of national environ-
mental laws focused on air and water quality, solid waste
management and the control of toxic substances, pesticides,
noise and radiation, the Agency strives to formulate and
implement actions which lead to a compatible balance between
human activities and the ability of natural systems to support
and nurture life.
The Robert S. Kerr Environmental Research Laboratory is
the Agency's center of expertise for investigation of the soil
and subsurface environment. Personnel at the Laboratory are
responsible for management of research programs to: (a) deter-
mine the fate, transport and transformation rates of pollutants
in the soil, the unsaturated zone and the saturated zones of
the subsurface environment; (b) define the processes to be
used in characterizing the soil and subsurface environment as
a receptor of pollutants; (c) develop techniques for predicting
the effect of pollutants on ground water, soil and indigenous
organisms; and (d) define and demonstrate the applicability
and limitations of using natural processes, indigenous to the
soil and subsurface environment, for the protection of this
resource.
There is currently a lack of readily available information
relative to design, operation and closure of land treatment
sites for tannery chromium-containing solid wastes. This report
is intended to provide an assessment of potential adverse impacts
of land treatment of tannery wastes, to estimate the accumulation,
degradation and migration of soil contaminants and to provide
data for optimization of design, operation and closure of land
treatment sites where tannery chromium-containing solid wastes
are applied.
Clinton W. Hall
Director
Robert S. Kerr Environmental
Research Laboratory
111
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ABSTRACT
Land treatment of wastewater sludges from tannery proces-
ses has been investigated during a five-year field plot study.
The experimental design included eight field test plots
receiving selected applications of three types of tannery
sludges over a three-year period.
1. Two 0.2 hectare plots received beamhouse (hair-burn)
sludge at two different sludge application rates (110 mt/ha
and 220 mt/ha sludge). The 110 mt/ha sludge loading rate was
selected to provide the assumed optimum loading of protein-
aceous nitrogen.
2. Two total chromium loading rates (2240 kg/ha and
4480 kg/ha total chromium) were applied to two 0.2 hectare
plots that received trivalent chromium-containing (chrome)
sludge and to two 0.2 hectare plots that received mixed
tannery (hair-burn and chrome) sludge.
3-. A single 0.1 hectare plot received a triple total
chromium loading (6720 kg/ha) of the mixed sludge, and a
single 0.2 hectare control plot received no sludge addition.
The five-year study included analyses of sludge, soil
core, plant tissue, and soil pore and runoff water samples to
evaluate the feasibility of land treatment of tannery sludqes.
The data generated indicated that land treatment is potentially
an environmentally acceptable technology for management of
iv
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wastewater sludges from trivalent chromium tanneries; however
waste application rates must be carefully controlled.
The applied trivalent chromium appeared to. remain pri-
marily in the topsoil without any detectable oxidation to
hexavalent chromium. Transport of trace quantities of
chromium in soil runoff water appeared to be associated with
movement of soil particles. Application levels of tannery
sludges containing hair-burn wastes will be limited by the
mineralization rate of the proteinaceous nitrogen and the
crop inorganic nitrogen requirements. Elevated salt concen-
trations of the hair-burn sludges also will reauire specific
consideration.
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TABLE OF CONTENTS
Page
Foreword iii
Abstract iv
Figures ; ix
Tables x
Acknowledgments xii
1. Introduction 1
2. Conclusions 5
3. Recommendations 7
4. Project Methodology 9
Experimental Plan 9
Geology of Test Site 10
Design and Construction of Test Plots
at Site 14
Operation and Maintenance of Site 16
Closure of Site 18
5. Sludge, Soil and Plant Sampling and
Analytical Data 21
Sampling Procedures 21
Sample Preparation 26
Composition of Sludges 28
Chromium and Other Metal Loadings 30
Incremental and Total Nitrogen
Applications 35
Soil Characteristics 39
Plant Tissue Analyses 49
6. Hydrology 54
Site Characteristics 54
Sampling Procedures 56
Analytical Procedures 59
Water Budget Monitoring 59
Moisture Flux Computations 70
Preceding page blank
vn
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TABLE OF CONTENTS
(Continued)
Page
Water Quality Monitoring 74
Chromium Flux 88
Hydrological Conclusions 94
7. Feasibility Analysis 96
Environmental Constraints on Land
Treatment of Tannery Wastewater
Sludges 96
Site Closure 99
8. References ..... 107
vin
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FIGURES
Number Page
1 Site Layout (Map) 15
2 Salinity and Sodium Adsorption Ratio
Boundary 43
3 Geologic Cross-Section of Field Site .... 55
4 Map of Field Site with Contours and
Location of 1983 Monitoring Equipment. . . 57
5 Summary Graphs of Precipitation, Runoff,
and Matric Suction at Monitoring
Cluster M-3c for (a) 1983 Season and
(b) 1984 Season 63
6 Locations of Monitoring Clusters on M-3. . . 67
7 Characteristic Soil Moisture Curves for
Several Plots 68
8 Computed Cumulative Moisture Budget for
Monitoring Clusters in Plot M-3 for
1983 Season 72
9 Computed Cumulative Moisture Budget for
Monitoring Clusters in Plot M-3 for
1984 Season 73
10 Schematic Diagram of Typical Monitoring
Cluster in Plot M-3 86
11 Total Chromium Concentrations in Soil
Water at Three Locations in Plot M-3. . . 87
12 Profiles of Measured Chromium Concentra-
tions with Soil Depth 89
13 Cumulative Chromium Flux at Two Locations
in Plot M-3 (Dec. 18, 1982) 92
14 Cumulative Chromium Lost from Soil Water
at Two Locations in Plot M-3 (Dec. 18,
1982) 93
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TABLES
[Number Page
1 Statistical Analysis of Baseline Charac-
terization of Soils at the Experimental
Site. . 13
2 Soil, Sludge, and Plant Sampling and
Analysis Guide 22
3 Test Plot Soil Sampling Schedule 24
4 Analytical Procedures for Sludges
and Soils 27
5 Summary of Five Sludge Analyses Covering
Years 1980 through 1984 29
6 Total Concentration of Heavy Metals
Typically Found in Soils 31
7 Application Rates of Salz Tannery Sludges
to Seven Test Plots 32
8 Incremental and Total Chromium Added to
Seven Test Plots 34
9 Pb, Zn, Cu, and Ni Loadings on Seven
Test Plots Compared to Recommended
EPA Heavy Metal Maximums. '. . 36
10 Incremental and Total Nitrogen Applied
to Seven Test Plots 37
11 Incremental and Total Available Nitrogen
Applied to Seven Test Plots 38
12 Average and Standard Deviations for Soil
Total Chromium Analyses 40
13 Soil TOC and TKN (%) for Eight Santa Cruz
Plots During the Years 1980-1984 42
14 Sodium Adsorption Ratios (SAR) and Electro-
conductivity (EC) for Eight Santa Cruz
Plots During the Years 1980-1984 44
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TABLES
(Continued)
Number Page
15 pH and Electroconductiyity (EC) for Eight
Santa Cruz Plots during the Years 1980-
1985 47
16 Lead and Total Chromium for Eight Santa
Cruz Plots from 1980 to 1984 48
17 Prevailing Grasses at Santa Cruz Site ... 50
18 Nitrogen and Chromium Concentrations of
Ribgut Grass (Bromus diandrus Roth.)
on Four Sampling Dates 52
19 Analysis and Preservation of Constituents
of Water. 60
20 Moisture Budget Summary 75
21 AOC on Soil Water Samples (Nitrates and
Chromium) 77
22 .Surface Water and Groundwater Baseline
Data. 80
23 Typical Soil Water Analyses, Dec. 19,
1982 84
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ACKNOWLEDGMENTS
This field investigation was a multi-disciplinary
study; we thank a talented group of investigators for
their professional efforts and for cooperative assistance
throughout the five year period. Salz Leathers was re-
sponsible for the site identification, its construction
and operation. Mr. Gerald Weber of Weber and Associates
was the geologic consultant. Mr. Jerome E. Earls and
Mr. Stuart E. Miller, Jr., Salz Leathers, Inc., were the
project's field site coordinators whose activities were
especially valuable in project management.
SCS Engineers assisted in designing the land treatment
site layout and was responsible for determining sludge
loading rates, and conducting sludge, soil and plant moni-
toring. Dr. Hang-Tan Phung, Dr. Lam V. Ho, Mr. Kenneth V.
LaConde and Mr. David E. Ross provided excellent profes-
sional contributions and counsel to the project. The
efforts of Mr. LaConde in writing sections of this report,
particularly Section 5, are especially appreciated.
University of California at Santa Cruz assisted in site
design and monitoring of soil and ground waters. Water
budget monitoring and moisture flux computations were con-
ducted by this group. Dr. Shirley Dreiss, Ms. Linda D.
Anderson and Ms. Carol Creasey contributed valuable hydro-
logical information to the project. The effort of Dr. Dreiss
xn
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in writing sections of this report, particularly Section 6,
is especially appreciated.
The counsel of Mr. Carlton C. Wiles, MERL Solid and
Hazardous Waste Research Division in Cincinnati, OH, and
later of Mr. Don A. Clark, Subsurface Processes Branch at
R.S. Kerr Environmental Research Laboratory at Ada, OK, as
project officer was very valuable and they are thanked for
their patient, professional counsel. Tanners' Council of
America (now Leather Industries of America) and Salz
Leathers provided industry cost-sharing support; the
support of their staffs in Santa Cruz, CA, Washington, D.C.,
and at the University of Cincinnati is acknowledged with
our thanks.
xin
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SECTION 1
INTRODUCTION
The primary objective of this project was to character-
ize the major technical and environmental aspects which are
associated with utilization of land treatment technology
.for disposal of tannery wastewater sludges. Tanneries in
the United States primarily utilize trivalent chromium
coordination compounds in the conversion of skin and hide
substance into leather. Conrad, et al. (1) estimated that
the total process solid wastes generated annually by all
U.S. tanneries was 65,000 metric tons on the dry basis
weight (based upon 1974 production data). They reported
that approximately 87 percent of the 20 million equivalent
hides tanned in this country in 1974 were processed using
chromium tannages. They also estimated that wastewater
screenings and sludge account for about 60 percent of the
tannery solid waste.
Conrad, et al. estimated that about 27,000 metric tons
(dry basis) of tannery wastewater sludges from chromium
tannery processes were generated annually in 1974. Since
U.S. leather production declined from 20 million eouivalent
hides in 1974 to 17 million in 1984, total current genera-
tion of chromium-containing wastewater sludges is estimated
to be approximately 25,000 metric tons (dry basis) annually.
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.Alther (2) investigated soils and grasses on two German
farms with similar soils. One farm used only manure and
chemical fertilizers. The second farm had used for twenty
years only tannery wastewater treatment sludges containing
chromium. Although the chromium had accumulated in the
meadow soils on the second farm, no differences could be
detected in the yield and kinds of grasses. The chromium
in the plant tissue had also not increased.
Wickliff, et al. (3) conducted greenhouse investigations
of the application of trivalent chromium-containing tannery
wastewater sludges to two soils. The two soils were Semiah-
moo muck and an Amity silty clay loam soil; the crops were
tall fescue, hybrid sweet corn and bush beans. These workers
concluded that "tannery sludge may be applied to agricultural
land as a fertilizer amendment without adversely affecting
soil chemical properties. The amount and frequency of appli-
cation should be determined by: total and available N; total
salt content; total and available chromium; and soil organic
matter."
Tannery solid wastes containing chromium have for many
years been applied to agricultural soils since they contain
proteinaceous, slow release nitrogen. Berkowitz et al. (4)
conducted a one year experiment at a field site which had
received chromium-containing leather buffing dust sludge
during the past twenty years. Although there was a twenty-fold
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increase in the soil chromium content (equal to 1400 kg/ha)
from one application of the sludge to a virgin portion of the
site, no significant increase was found in the chromium content
of the above-ground whole corn plant. Further monitoring at
the site was recommended to identify any development of
potential problems.
Although there have been several practical examples of
land treatment of trivalent chromium-containing solid wastes
from tannery sources similar to those just mentioned, there
has not been a definitive field study which would provide
data on the design, operation and closure of tannery land
treatment sites. The five-year field project had three
specific objectives:
1. To assess potential adverse impacts of land
treatment on various environmental sectors.
2. To estimate the accumulation, degradation and
migration of soil contaminants.
3. To provide data for the optimization of site
design, operation and closure.
Since the project had such a diverse scope, four organi-
zations participated in the study. The participating organiza-
tions and their primary responsibilities were:
1. The Tanners' Council of America (now Leather
Industries of America) served as the managerial
contractor through its Washington, D.C. executive
offices and its research laboratory at the
University of Cincinnati.
3
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2. Salz Leathers, a chromium leather tannery in
Santa Cruz, CA, served as a subcontractor to
supply the wastewater sludges and to install,
operate, and close the field site in Santa
Cruz County. They retained a consulting geolo-
gist, Weber and Associates, to identify the
specific site and to determine its geology
and supervise site construction.
3. "SCS Engineers, Long Beach, CA, served as a sub-
contractor to assist in the site engineering
design and to conduct soil and plant monitoring
analyses.
4. The University of California at Santa Cruz,
Department of Earth Sciences, served as a sub-
contractor to conduct site hydrology studies
emphasizing surface and subsurface water
monitoring, especially for chromium and
nitrates.
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SECTION 2
CONCLUSIONS
Land treatment provides a potentially environmentally
acceptable technology for management of tannery wastewater
sludges from trivalent chromium tannery processes if sludge
application rates are carefully controlled. The utilization
of land treatment technology for management of these sludges
must include the following considerations:
1. Chromium tannery wastewater sludges are character-
ized by a significant organic Kjeldahl nitrogen content (2 to
4.5 percent) which primarily results from the oroteinaceous
materials in the animal hides which are converted into
leather in the tannery. Therefore, land treatment of these
sludges should be guided by the mineralization rates of the
proteinaceous nitrogen and by the inorganic nitrogen demands
of the plants grown on the treatment site.
2. Chromium tannery wastewater sludges are character-
ized by significant salt contents (4 percent sodium on a
dry basis from unhairing wastewater sludges and 2.7 percent
from the chromium-containing wastewater sludges). Land
application of these sludges may result in poor grass germi-
nation and weed intrusion; therefore, careful attention
should be paid to these possible salt effects, especially
when the unhairing wastewater sludges are to be applied.
3. Trivalent chromium in tannery wastewater sludges
remains primarily in the topsoil after land treatment;
5
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however, there may be some limited transport of chromium in
soil pore and runoff water. The transport in runoff water is
assumed to be associated with soil particle movement.
4. Hexavalent chromium.was not detected during this
five-year field study; therefore, it is assumed that applied
trivalent chromium will not oxidize to the hexavalent form
in this soil environment.
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SECTION 3
RECOMMENDATIONS
This five-year field plot study was the first in-depth
field investigation of the land treatment of chromium
tannery wastewater sludges. The study results disclosed
certain areas in which the project efforts could have been
improved by additional prior information. The following
recommendations are made for further study which would
facilitate future utilization of land treatment technology
for management of tannery wastewater sludges:
1. Improved sludge and soil sampling protocols which
recognize the high analytical.heterogeneity of the substrates
should be developed.
2. Inter-laboratory analyses of sludge and soil samples
by EPA Method 3050, SW846, Test Methods for Evaluating
Solid Wastes, 1982, showed satisfactory agreement for total
chromium and calcium. Future work involving tannery waste
sould restrict sludge and soil analysis to FPA Method 3050,
SW846.
3. Improved agricultural practices to attain more
uniform sludge incorporation into the topsoil and to secure
grass or other crop growth are needed. The effect of the
high sodium content of the hair-burn sludge on the weed
intrusion into the test plots also requires further consid-
eration.
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4. Proteinaceous nitrogen mineralization rates for
wastewater sludges from chromium leather tanneries were not
found in the literature. Combined laboratory and field
studies directed toward these mineralization rate determi-
nations are recommended.
5. Chromium transfer from the toosoil appeared to be
limited; the chromium which was transported in soil water
runoff appeared to be associated primarily with movement of
soil particles. Further field studies are recommended to
determine the ultimate form in the topsoil of the added
chromium. Dehydration of trivalent chromic hydroxide forms
very insoluble trivalent chromic oxide. Soil physical
chemical studies to provide data on the physical form of
the chromium in the topsoil would be desirable to establish
the upper permissible limit for trivalent chromium addition
to topsoils.
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SECTION 4
PROJECT METHODOLOGY
EXPERIMENTAL PLAN
Wastewater sludge was generated at the Salz tannery at
an overall level of approximately 50 wet metric tons (at 25
to 30 percent solids) per day, or 15,000 wet metric tons per
year. The sludge currently is transferred to a specially
designed municipal landfill site, reflecting State of Cali-
fornia requirements. Tannery wastewater sludges have been
delisted under RCRA (5).
The tannery wastewater pretreatment system produced
two different pretreatment sludges:
1. The dehairing wastewater sludge which results
from the hair pulping (hair-burn) processes.
This sludge was rich in lime and proteinaceous
residues resulting from the hair destruction
process.
2. The tanning process wastewater sludge generated
by Salz. This sludge was characterized especially
by its content of trivalent chromium resulting
. from the tannage of the cattlehides in their
conversion to leather.
Although these wastewater sludges were generated
separately at the Salz tannery, in many tanneries the
wastewater pretreatment sludges originate from the overall
wastewater flow. The experimental plan was designed to
evaluate the disposal of the individual sludges and their
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mixture in the ratio generated in the Salz tannery.
Each of three sludges were to be applied to individual
test plots at two different sludge levels each successive
year. Two sludge loading rates were planned, one at an
optimum nitrogen level, and the other at an excessive,
double nitrogen level.
Since there were three sludge types each applied at
two different levels, six test plots were required. In
addition, a control plot and an additional plot with still
higher loading were included. Hence, the test site included
eight experimental plots.
The total chromium loading was planned to be 2240 kg
per hectare in the plot to which the tanning process waste-
water sludge was to be applied at the lower level. The plot
to which the tanning process wastewater sludge was to be
applied at the double level would receive a total of 4480 kg
per hectare. These levels are below the FWPCA limit of 4940
kg per hectare (2000 kg per acre) for a soil with a CEC greater
than 15 meg per 100 g as calculated from cumulative irrigation
water standards for 10 year periods (Diagnosis and Improvements
of Saline and Alkali Soils, Agricultural Handbook #60, USDA,
.1954, p. 27).
GEOLOGY OF TEST SITE Site Selection
The site selection criteria were as follows:
• Relatively close (20 mi) to the Salz tannery.
• Not readily accessible to the public.
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• - Typical geology of the Santa Cruz coast.
• Mature soil with a well-developed "B" horizon.
• Shallow perched water table (controlled "worse
case" condition to facilitate ground water
monitoring).
• Owner agreeable to a long-term lease.
One of three candidate sites met all of the above criteria,
and was ultimately leased for the study. The site, about 8 ha
(20 ac) in size, was located 21 km north of the city of Santa
Cruz, California, and approximately 1.2 km from the Pacific
Ocean. It was readily accessible from Santa Cruz along paved
roads, except for a short dirt access road leading from the
county road to the site.
Site Geology and Soil Characteristics
The site was located within the Scott Creek Valley in
western Santa Cruz County, California, upon a small, almost
level marine terrace remnant lying 107 to 122 m (350 to 400 ft)
above the floor of Scott Creek. This small level area is loca-
ted within rugged and steep mountainous terrain on the western
flank of Ben Lomond Mountain. The low slopes fall off abruptly
into the deep, steep-walled (100 percent) canyons that lie
northwest, southwest, and west of the site. Similar steep
slopes are located above the site to the northeast.
The marine terrace remnant is of middle Pleistocene age,
and consists of moderately indurated sandstones, siltstones,
and conglomerates. The bedrock, Santa Cruz Mudstone, is of
11
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late Miocene to early Pliocene age, and is primarily com-
posed of well indurated fine-grained clays, silts, and silica
from the skeletal remains of microorganisms. The fine-grained
Santa Cruz Mudstone has low intergranular porosity and permea-
bility, and acts as an aquifuge or aquiclude, except in areas
of fracture porosity. There is no indication that any large
faults or fracture zones cross the test site.
The soils on the site have been mapped as part of the
Watsonville and Watsonville-Tierra complex (USDA-SCS, 1980).
The soils were typically formed on alluvial and marine terraces
in coastal Santa Cruz and San Mateo County. Both the Tierra
and Watsonville soils are very deep ( 1.5 m, or 5 ft thick)
with a thick, well-developed B horizon, and are moderately
well to somewhat poorly drained. Permeability of both soils
is very low.
Table 1 shows the chemical characteristics of the soils
prior to sludge application. The soils were slightly acidic,
and had a mean cation exchange capacity (CEC) of 17.1 to 20.3
meq/100 g. Mean value of total lead (Pb) ranged from 6.8 to
8.5 ug/g, and total chromium (Cr) from 38 to 41 ug/g. No Cr
(VI) was detected in the soil. The organic matter content of
the analyzed soil was low. Mean total organic carbon (TOO
ranged from 0.47 to 0.62 percent. Mean total Kjeldahl nitrogen
(TKN) of the natural topsoil was only 0.22 percent, and de-
creased with increasing soil depth.
12
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TABLE 1. STATISTICAL ANAIYSIS OF BASELINE CHARACTERIZATION OF SOILS
AT THE EXPERIMENTAL SITE
Soil Depth
0 - 30 cm
Range
Mean
Median
S.D.f
30 - 60 cm
Range
Mean
Median
S.O.
60 - 90 cm
Range
Mean
Median
S.O.
£H
6.48-6.85
6.62
6.58
0.16
6.56-6.92
6.71
6.67
0.16
6.00-7.09
6.51
6.48
0.51
SAR
1.66-4.17
2.50
2.09
1.13
2.55-3.54
3.15
3.25
2.45
3.05-4.62
3.75
3.67
0,78
EC
(mmho/cm)
0.21-0.32
0.25
0.24
0.05
0.10-0.19
0.14
0.14
0.04
0.10-0.21
0.17
0.18
0.05
C£C
(nteq/100 g)
16.7-26.9
20.3
18.8
4.74
15.4-22.4
18.8
18.8
2.98
16.2-18.8
17.1
16.7
1.23
TOC
...
0.29-0.69
0.53
0.56
0.17
0.59-0.68
0.62
0.61
0.04
0.43-0.49
0.47
0.48
0.03
TKN
(I) -
0.17-0.31
0.22
0.20
0.06
0.08-0.10
0.09
0:10
0.01
0.05-0.08
0.06
0.06
0.01
Total Pb
- - . . (
4.0-13
8.0
7.5
4.2
3.0-13
8.5
9.0
4.4
1.0-12
6.8
7.0
5.6
Total Cr
Ug/g)
19-50
38
42
14
29-49
38
37
10
24-49
41
45
12
• Four composite samples were taken at each soil layer.
t S.O. - Standard Deviation.
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DESIGN AND CONSTRUCTION OF TEST PLOTS AT SITE
Figure 1 shows the site layout, including fences, wells,,
berms, roadways, and drainage systems. There were a total of
eight test plots: Cl (normal rate, chrome sludge); C2 (high
rate, chrome sludge); Hi (normal rate, hair-burn sludge); H2
(high rate, hair-burn sludge); Ml (normal rate, mixed sludge);
M2 (high rate, mixed sludge); M3 (exceedingly high rate, mixed
sludge); and the control plot (no sludge). Six of the 0-.20-ha
(0.50-ac) test plots (Cl, C2, HI, H2, Ml, and M2) were located
on 5 to 10 percent slopes; the 0.20-ha (0.50-ac) control plot
was located on 5 percent slope; and the 0.10-ha (0.25-ac) plot
(M3) was located on 3 to 4 percent slope. The test plots were
surrounded by berms and ditches which diverted surface runoff
into collection boxes at the base of each test plot. A system
of 20-cm (8-in) PVC pipes connected the runoff collection boxes
with concrete sedimentation ponds, which were equipped with a
V-notch weir for discharge measurements.
Ten shallow monitoring wells and one deep well were installed
to measure ground water level fluctuations and quality. The
shallow wells, 6 to 14 m (20 to 45 ft) deep, were located down-
gradient from the test plots, and were extended through the
terrace deposits several meters into the underlying bedrock.
They were cased with slotted PVC pipe and gravel-packed the
entire depth, except for the upper 1.5 m (5 ft), which were
grout-sealed. The deep monitoring well was about 76 m (250 ft)
deep, and was located down-slope from the upper six test plots,
roughly 15 m (50 ft) south of plot Ml.
14
-------
Figure 1.
Reproduced from gr»l
best available copy, ^ps
-------
OPERATION AND MAINTENANCE OF SITE
Because of close geographical proximity to the test
site and year-round availability of technical personnel, a
Salz Leathers representative assumed the role of site manager.
Most of the activity encompassed in this role involved coordina-
tion of the sequence of events necessary to guarantee the
orderly preparation of the site and collection of relevant
test data.
Site Maintenance and Repairs
Experience at the site established the degree and nature
of effort required to assure access to, and proper maintenance
of, the test site. Annual grading of the access road was neces-
sary due to the modest erosion and heavy plant growth occurring
during the winter/spring seasons. Also, berms were cut into
the access road to prevent erosion and still allow access to
the site. Fencing and runoff systems inspection and maintenance
were also accomplished to protect the integrity of the plots.
Sludge Delivery and Application
Prior to commencement of sludge delivery to the test plots,
it was necessary to mow the heavy plant growth present in the
delivery truck access route along the entire length of the site
above the test area, as well as on the individual test plots.
After the grass was mowed, each test plot was tilled to incor-
porate the cut grasses into the soil and, thus improve equipment
traction for the subsequent spreading operation. It was found
during the first sludge application (July 1981) that the combi-
nation of modest hillside slope and wet sludge resulted in loss
16
-------
of traction for the spreading equipment. This problem was
overcome in the following sludge applications by allowing
approximately one week's drying time for the sludges on site
I
prior to spreading. This technique proved very successful for
hair sludges; however, some crusting on the surface of chrome
sludge piles was observed. This crusting resulted in some
rather large lumps of chrome sludge being spread on Plots Ml,
M2, M3, Cl, and C2 (lumps up to 12 inches in diameter). After
spreading the sludge, each test plot was tilled to incorporate
sludges into the soil to a depth of approximately six inches.
The large lumps of chrome sludge described earlier were well
broken up during this tilling operation.
Sludge application dates were:
1 - June, 1981
2 - October, 1981
3 - October, 1982
4 - October, 1983
Plots Ml, M2 and M3 were the only plots to which sludge was
applied in 1983. Plots HI, H2, Cl, and C2 had received in the
first three applications approximately the planned application
of the total tonnage of sludge (dry basis) and Cl and C2 had
received the desired maximum total chromium addition. Addi-
tional sludge was added in 1983 to Ml, M2 and M3 to assure the
planned chromium addition level to these three plots. During
this fourth sludge application rainy weather and wet soil pre-
vented tilling with a wheel tractor. A crawler with a back hoe
17
-------
and clam-shell loader was used.
Seeding
Seeding with sudan grass (276 kg/ha) supplemented with
superphospate (246 kg/ha) and potassium chloride (338 kg/ha)
was accomplished in 1981. The resultant limited grass growth
was attributed to incompatability of this grass variety with
the cool coastal area. A successful seeding procedure was
not developed and a native weed intrusion developed in the
disturbed soil of the plots, as discussed later.
Permit Application
Although the proposed study was solely research-oriented,
regulatory agencies were initially informed of the project
scope and planned activities in order to determine the need
and procedures for permitting waste disposal activities at the
site. These agencies werer the California Department of Health
Services; the Central Coast Regional Water Quality Control
Board; the Coastal Commission; and the Solid Waste Management
f
Board. Except for the Coastal Commission, which requested a
public hearing in January 1981, all of these agencies expressed
an interest in the project but did not require a permit for the
project work. These agencies received copies of the periodic
reports to the Environmental Protection Agency for their back-
ground information.
CLOSURE OF SITE
The contract statement-of-work required closure of the
site with an approved plan. Although tannery wastewater sludges
are excluded (5) from federal hazardous waste regulations since
18
-------
they contain only trivalent chromium, these sludges are
hazardous wastes under the California administrative code
based on their total chromium content. Salz wastewater
sludges customarily are transferred to a specially designed
municipal landfill site, reflecting the State of California
requirements.
Wickliff et al. (3) at the EPA Corvallis Environmental
Research Laboratory concluded that chromium tannery sludges
may be applied to agricultural lands as a fertilizer amend-
ment. However they concluded that the frequency and amount
of application should be determined by:
1. Total and available nitrogen.
2. Total salt content.
3. Total and available chromium.
4. Soil organic matter.
Chromium was the principal component of the chromium-
containing wastewater sludges which required specific emphasis
throughout the project; including site closure planning. More-
over the content of proteinaceous nitrogen in both of the tannery
wastewater sludges and their mineralization also focused our
attention upon the available nitrogen on the seven test plots.
Section 7 of this report contains the Final Site Closure Plan
which was used, based upon the guidance of the State of Cali-
fornia Regional Water Quality Board at San Luis Obispo, CA, and
the EPA Robert S. Kerr Environmental Research Laboratory at Ada,
OK.
These project plans and their initial application have
19
-------
been reported in two earlier EPA publications. Lollar (6)
described the initiation of the five year investigation in
the proceedings of the Seventh Annual Research Symposium on
Land Disposal of Hazardous Wastes. Ho, Phung and Ross (7)
presented preliminary data from the project in the Eight
Annual Research Symposium proceedings.
20
-------
SECTION 5
SLUDGE, SOIL AND PLANT SAMPLING AND ANALYTICAL DATA
Sludge, soil, and plant samples were taken from October
1980 through May 1984. Table 2 presents a schedule of sampling
dates, number of samples obtained, chemical analytical parameters,
and a list of definitions of abbreviations. The following narra-
tive discusses the details of sampling, preservation, sample
preparation, and analytical techniques.
SAMPLING PROCEDURES
Sludge Sampling
Hair-burn (H) and chrome (C) sludges.were sampled from
on-field stockpiles by randomly scooping from several locations.
Samples were placed into clean glass jars, frozen, and shipped to
the SCS Engineers Analytical Laboratory in Long Beach, California.
No preservatives were added.
Soil Sampling
Several different soil sampling techniques were used during
this study. Additionally, some of the test plots were sampled to
the exclusion of others. Table 3 presents a more detailed
explanation of soil samplings, showing which plots were sampled
and to what depth.
21
-------
TABLE 2. SOIL, SLUDGE, AND PLANT
SAMPLING AND ANALYSIS SCHEDULE
Sampling Data
October 2, 1980
November 6, 1980
November 14, 1980
December 1, 1980
February 2, 1981
April 1, 1981
June 1, 1981
July 15, 1981
September 28, 1981
October 31, 1981
December 2, 1981
February 18, 1982
Number of Samples
Soil Sludge Plant
030
12
0
0
0
24
13
0
21
0
0
0
0
0
0
0
3
0
0
0
8
8
8
0
0
0
0
8
8
Analytical Parameter
pH, EC, TOC, TKN,
NH4-N N03-N, Total Cr,
Pb, SAR, and moisture
content
pH, EC, TOC, TKN,
NH4-N, N03-N, Tptal Cr,
Pb, SAR, and moisture
content
pH, EC, CEC, TOC, TKN,
NH3-N, Total Cr, Cr(VI),
Pb, and SAR
pH, EC, TOC, TKN,
NH4-N, N03-N, T9tal Cr,
Pb, SAR, and moisture
content
TKN, Total Cr, Pb
TKN, Total Cr, Pb
TKN, Total Cr, Pb
pH, EC, TOC, TKN,
NH4-N, N03'N» Total Cr>
Pb
CEC, SAR
pH, EC, TOC, TKN, SAR,
NH4-N, N0-N» Total Ca>
Mg, Na, Cr, Pb, Cu, Ni ,
Zn, and Hg
pH, EC, TOC, TKN,
NH4-N. N03-N, Total Cr,
Cr(VI), Pb, and SAR
TKN, Total Cr
TKN, Total Cr
22
-------
TAB.LE 2 (continued)
Sampling Data
April 26, 1982
July 10, 1982
October 15, 1982
December 20, 1982
December 29, 1982
April 25, 1983
September 24, 1983*
December, 1983
May, 1984
Number
Soil SI
0
21
0
20
12
0
0
20
12
0
24
of
Samples
udge Plant
0
0
3
0
0
0
0
0
0
3
0
8
0
0
0
8
8
0
0
0
0
Analytical Parameter
TKN, Total Cr
pH, EC, TOC, TKN,
NH4-N, SAR, Total Cr,
Cr(VI), and Pb
pH, EC, TOC, TKN,
NH4-N. Wh-N, Total Ca,
Pb, SAR, Mg, Na, Cr, Pb,
Cu, Ni, Zn, Hg
Total Cr
pH, EC, TOC, TKN, N03_N
NH4-N, Cr(VI), Pb
TKN, Total Cr
TKN, Total Cr
Total Cr
pH, EC, TOC, TKN, N03_N
NH4-N, Cr(VI), Pb
pH, EC, TOC, TKN, SAR,
NH4-N, N03-N. Total Ca,
Mg, Na, Cr, Pb, Cu, Ni , Zn
pH, EC, TOC, TKN, SAR,
N°3-N, Cr(VI), Pb, Cr
* Surface 15 cm only.
23
-------
TABLE 3. TEST PLOT SOIL SAMPLING SCHEDULE
(NOVEMBER 1980 - MAY 1984)
Sampling Data
November 1980
July 1981
October 1981
July 1982
December 1982
September 1983
May 1984
Number of
Soil Samples
12
32
21
21
32
32
24
Test Plots Sampled
Control, HI, C2, M3 at 3 depths*
7 test plots at 3 depths
7 test plots at 3 depths
7 test plots at 3 depths
H2, C2, M2, M3 at 3 depths
Surface 15 cm - 7 test plots and control
7 test plots and control at 3 depths
* Depths of Sampling: 0-30 cm, 30-60 cm, 60-90 cm.
24
-------
Surface soil samples were initially taken with a
10-cm stainless steel auger. Twelve (12) separate
cores to 30 cm were mixed to form one plot composite.
Surface soil samples in 1983 and 1984 were obtain-
ed from 15 cm x 15 cm areas to a depth of 15 cm. Four
(4) such grabs were analyzed individually and were also
composited for analysis on an equal dry weight basis.
Subsurface samples were taken at 30 to 60 cm and
60 to 90 cm depths using a 2.5-cm or 10-cm stainless
steel auger. Care was taken to prevent side wall con-
tamination by removing debris and sludge particles
after the surface (0 to 30 cm) samples had been obtained,
Field soil samples were collected in commercially
available plastic bags and shipped without refrigera-
tion except for grab samples taken for the NO--N and
Cr(VI) analysis. Samples for these latter parameters
were placed in plastic bags, frozen, and shipped in
insulated containers to maintain 0°C conditions.
Plant Sampling
Clipped healthy leaves of native ribgut grass
(Bromus diandrus Roth.) were collected at multiple
spots from each test plot and placed in plastic bags.
The samples were cooled in a field ice chest and
shipped in insulated containers to maintain a temp-
erature of approximately 4 C.
25
-------
SAMPLE PREPARATION
Sludge
Sludge samples were allowed to thaw in the labora-
tory. A mixed sludge sample was then prepared by thoroughly
mixing 'on a weight basis one part hair-burn sludge with
three parts chrome sludge. This ratio represented the
quantities of hair-burn and chrome sludge generated at
Salz. The samples were dried for 16 hours at 105°C and
thoroughly ground in a high-speed mill. All analyses were
performed on the dried, milled samples.
Table 4 presents a compilation of the analytical
methods utilized throughout the study period. One notable
change, however, was made in the heavy metal digestion
procedure in mid-1982. The digestion procedure shown
in Table 4 proved to yield low results for Na, Ca, and
Mg due to the formation of an insoluble precipitate re-
moved during filtration. This method was replaced with
the EPA nitric-hydrogen peroxide method. All subsequent
sludge and soil analyses beginning with the sludge samples
of October 1982 were digested by this latter method.
Soils
Surface and subsurface samples were all handled in
the same manner. Upon receipt at the laboratory, soil
samples (except those taken for NO.,-N and Cr (VI)) were
spread on clean paper to air dry (2 to 5 days depending
on moisture content). Detritus, such as twigs and rocks,
was removed with care being taken not to remove clumps of
26
-------
TABLE 4. ANALYTICAL PROCEDURES FOR SLUDGES AND SOILS
Parameter
Moisture
PH
Procedure
Oven-dry for 24 hr at
1:1 sludge (or soil):
105°C
H00
Reference
9
9
EC
SAR
TKN
TOC
NH4-N
CEC
Cr, Cu, Ni,
Pb, Hg, Zn
Ca, Mg, Na
Cr(VI)
equilibrium, followed
by electrometric measure-
ment
Water saturation extract,
followed by Wheatstone bridge
measurement
Water saturation extract,
followed by atomic absorption
determination of Na, Ca, and
Mg by atomic absorption
Digestion and distillation,
followed by titration
(Kjeldahl method)
Dichromate oxidation, followed
by titration (Walkley-Black
method)
2N KC1 extraction, followed by
distillation and titration
2N KC1 extraction, followed by
brucine sulfate colorimetric
method
NH.-N saturation, sodium acetate
extraction, followed by titration
HN03/HC104 digestion, followed
by atomic absorption
HN03/H202 digestion, followed
by atomic absorption
KH PO. extraction, followed by
s-aipnenyl carbazide complexa-
tion and spectrophotometric
measurement
8,9
8,9
8,9
9
8,10
27
-------
sludge. The samples were ground to pass a 2-mm sieve.
Subsequent analyses were performed on the dried and
screened samples. Compositing of individual dried
samples was performed by thoroughly mixing equal weight
portions. Analyses were performed by the methodology
shown on Table 4.
Samples shipped in a frozen state for N03~N and
Cr (VI) were allowed to thaw and immediately extracted
and analyzed.
Plants
Plant tissue samples were wrapped in cheesecloth
and were copiously rinsed with deionized water. The
bundles were placed in a 70°C drying oven for 24 to 48
hours. The tissue samples were ground to a fine powder
in a high-speed mill prior to analysis.
COMPOSITION OF SLUDGES
Table 5 presents a summary of chemical analysis of
sludges applied to land during the study period. Most
constituents remained relatively constant throughout the
4-year sampling program. Only the last two sets of
analytical results for Na, Ca, and Mg were included due
to the methodology change previously discussed.
The concentrations of Crf Na, and Ca were elevated with
respect to other sludge parameters, but since Salz is a
chrome tannery, this is not surprising. Chromium concen-
trations ranging from 2.09 to 5.54 percent (dry weight
basis) are comparable to those given in similar studies
28
-------
TABLE 5. SUMMARY OF FIVE SLUDGE ANALYSES COVERING THE YEARS 1980 THROUGH 1984
Hair-Burn Sludges
Number of
Parameter Analyses Range
Moisture. X
pH
EC, mmhos/cro
SAR
TOC, X
TKN. X
N03-N. mg/kg
NH4-N, mg/kg
Metals*
Na
Ca
Mg
Cr
Cu
Hg
Ni
Pb
Zn
5
5
4
4
5
5
5
5
2
2
2
5
4
3
4
5
4
48.3-69.0
6.1-8.5
5.5-14.5
8.5-34.4
13.0-18.8
2.2-4.04
ND-15.2
77.9-7.650
35.600-45.000
94.500-142,000
2,560-3.400
28.0-675
3.5-21.0
0.0013-0.016
0.8-24.0
13.0-29.0
42. 1-400
Mean
57.9
7.5
9.9
17.8
15.8
3.55
3.130
40.300
118.300
2.980
251
9.7
0.0019
10.8
20.8
138
Median
55.9
7.9
12.5
15.6
14.4
3.78
1,125
-
-
-
168
8.2
0.0027
10.0
20.0
65.0
Chrome Sludges
Range
62.1-71.5
7.4-9.8
4.1-10.6
1.4-26.2
15.4-42.7
2.92-4.48
ND-2.2
534-4,780
25,000-29,500
51.500-151.000
10.100-11.300
20.900-55,400
26.2-68.0
0.0022-0.0031
3.1-32.0
95-320
81.5-420
Mean
66.6
8.2
8.9
16.2
29.3
3.67
2.200
27.300
101,300
10,700
42.660
50.7
0.0027
18.8
212
184
Median
68.0
7.9
10.5
18.3
27.4
3.74
934
-
-
-
46.100
60
0.0027
28
238
133
Mixed Sludges
Range
59.0-66.0
7.2-8.6
4.9-12.1
6.4-22.8
14.5-34.1
3. 18-4.06
ND-5.0
420-5,280
14,600-37.900
18.0-36.5
0.00075-0.025
2.4-26.0
60-270
66.5-250
Mean
61.8
7.9
9.3
20. 1
25.1
3.60
2.460
28.400
30.0
0.009
13.6
160
122
Heel i dn
61. 1
?.H
10. H
22.6
24.3
3.67
1 .260
29.500
36.5
0.0011
17.0
151
103
* All data expressed as mg/kg. dry weight basis.
-------
(11). Sodium and Ca salts are used extensively in the
tanning process. Slaked lime, Ca(OH)2f is the principal
dehairing agent. Na is present from soaking of previously
NaCl-brine cured hides and from the use of sodium-con-
taining chemicals in tanning, especially Na2S/NaSH in the
hair-burn operation, NaCl in hide pickling, and Na2S04 in
the tanning liquors.
Table 6 presents ranges of Cr, Cu, Hg, Ni, Pb, and
Zn typically found in soils. With the exception of ele-
vated Cr concentrations, the mean values of the other
sludge elements were within indicated typical soil
ranges. Mercury concentrations in the sludges were
less than values, indicated for typical soils.
Based on mean values presented in Table 5, organic
carbon: organic nitrogen (C/N) ratios were 4.9, 8.5, and
6.9 for hair-burn, chrome, and mixed sludges, respectively.
It is assumed that the organic N added to the soil through
incorporation of these sludges would have been mineralized;
however, the extent and rate of this mineralization was not
determined in this study.
CHROMIUM AND OTHER METAL LOADING RATES
Four (4) separate sludge applications were applied to
the test plots and are shown on Table 7. The September
1983 application was restricted to plots M1, M2, and M3.
Application rates were calculated on dry solids concen-
trations of 27.0 and 33.4 percent for hair-burn and chrome
30
-------
TABLE 6. TOTAL CONCENTRATION OF HEAVY METALS'
TYPICALLY FOUND IN SOILS
Metal
Cr
Cu
Hg
Ni
Pb
Zn
Concentration
Common
100
20
0.71*
40
10
50
(ug/g)
Range
5-3,000
2-100
0.01-4.7
10-1,000
2-200
10-300
Reference
12
12
12
12
12
12
*Mean Value,
31
-------
TABLE 7. APPLICATION RATES OF SALZ TANNERY
SLUDGES TO SEVEN TEST PLOTS*
Plot
Control
HI
H2
Cl
C2
Ml
M2
M3
May/June
Hair-burn
_
41
79
-
-
5.4
15
17
, 1981
Chrome
_
-
-
20
39
20
36
56
Oct/Nov,
Hair-burn
_
44
84
-
-
6.0
12
12
1981
Chrome
_
-
-
20
40
23
42
60
Oct/Nov,
Hai r-burn
_
18
32
-
-
5.2
10
12
1982
Chrome
_
-
-
14
27
11
23
35
Sept, 1983
Hair-burn Chrome
_ _
-
-
-
1
5.4 14
11 20
17 37
Total
_
103
195
54
106
90
169
246
* All data is mt/ha, dry weight basis, using mean solids contents of 27.0% and 33.4%, for
hair-burn and chrome sludge, respectively.
32
-------
sludges,, respectively. (The moisture concentrations of
the stockpiled hair-burn sludge shown in Table 4 differ
somewhat from the actual moisture concentrations as
measured at Salz tannery at the time when wet weights
were measured.)
The original project design called for the follow-
ing total sludge application rates:
Plot Total Sludge Application
(dry mt/ha)
HI 110
H2 220
Cl 43
C2 86
Ml 58
M2 116
M3 174
H2 was designed to receive an application rate double
that of HI; so too were C2 (Cl x 2) and M2 (Ml x 2); M3
was designed to have a threefold amount relative to Ml.
The actual total application rates shown in Table 7
came reasonably close to those planned rates for plots
HI, H2, Cl, and C2. Loadings on Ml, M2, and M3 were in
excess of those planned.
Table 8 presents incremental and total chromium
loading for each of the seven test plots. Note that
total chromium additions closely followed the projected
plan and, in fact, became the limiting factor for continued
sludge applications. This is more clearly defined in the
following section in which incremental and total nitrogen
33
-------
TABLE 8. INCREMENTAL AND TOTAL CHROMIUM
ADDED TO SEVEN TEST PLOTS (kg/ha)
Plot Application
Rate (mt/ha)
HI/103
H2/195
Cl/54
C2/106
Ml/90
M2/169
M3/246
1981
21
41
1,704
3,365
1,545
2,982
4,118
1982 1983
5
8
596
1,150
460 551
937 880
1,335 1,534
Total
26
49
2,300
4,515
2,556
4,799
6,987
Project
Plan
—
—
2,240
4,480
2,240
4,480
6,720
* Mixed (M) sludge = parts C, 1 part H,
34
-------
are discussed. Calculations for total chromium added
were based on the mean Cr values (see Table 5) of 251,
46,100, and 28,400 mg/kg for hair-burn, chrome, and
mixed sludges, respectively.
All of the chromium added was in the form of Cr
(III). Chromium (VI) was not detected at the 0.1 mg/kg
level in any of the sludge and soil samples analyzed.
In 1977, EPA adopted guidelines to determine the
cumulative amounts of Cd, Pb, Zn, Cu, and Ni that could
be applied to soils via municipal sludges. These limi-
tations were based on total metal additions to soils
needed to protect soil productivity and animal health
(13, 14).
Table 9 presents total cumulative Pb, Zn, Cu, and
Ni loadings for all seven test plots. (Note: Cadmium
concentrations were not determined; cadmium chemicals
are not used in the tannage process). EPA limitations
are included for comparison. Cation Exchange Capacity
(CEC) determinations on the HI, C2, M3, and control
plots prior to sludge amendments were all in excess of
15 meq/100 g. Based on these data, none of the heavy
metals analyzed exceeded the EPA recommended limitations,
INCREMENTAL AND TOTAL NITROGEN APPLICATIONS
Table 10 presents incremental and total nitrogen
applied to the seven test plots. Table 11 presents
incremental and total available nitrogen applied to the
35
-------
TABLE 9. Pb, Zn, Cu, AND Ni LOADINGS ON SEVEN TEST PLOTS
COMPARED TO RECOMMENDED EPA HEAVY METAL MAXIMUMS (kg/ha)
EPA
(CEC
Plot
HI
H2
Cl
C2
Ml
M2
M3
Limitations
>15)
Pb
2.1
4.1
11.4
22.5
14.4
27.2
39.4
2,240
Zn
14.2
. 26.9
9.9
19.5
11.0
20.6
30.0
1,120
Cu
1.0
1.9
2.7
5.4
2.7
5.1
7.4
560
Ni
l.-l
2.1
1.0
2.0
1.2
2.3
3.3
560
References (13), .(16).
36
-------
TABLE 10. INCREMENTAL AND TOTAL NITROGEN APPLIED
TO SEVEN TEST PLOTS (kg/ha)
Plot/Application
Rate (mt/ha) 1981
HI/103
H2/195
Cl/54
C2/106
Ml/90
M2/169
M3/246
3,020
5,790
1,470
2,900
1,980
3,820
5,190
Total Nitrogen Project
1982 1983 Loading Plan
640
1,140
510
990
590 710
1,200 1,120
1,710 1,960
3,660
6,930
1,980
3,890
3,280
6,140
8,960
4158
8316
1803
3606
2257
4514
6771
37
-------
TABLE 11. INCREMENTAL AND TOTAL AVAILABLE NITROGEN*
APPLIED TO SEVEN TEST PLOTS (kg/ha)
Plot/Application
Rate (mt/ha)
HI/103
H2/195
Cl/54
C2/106
Ml/90
M2/169
M3/246
1981
550
1,060
276
545
364
704
972
1982
341
787
237
459
291
573
801
1983
168
394
117
229
275
495
762
1984t
95
227
65
129
147
265
406
Total
1,154
2,468
695
1,362
1,077
2,037
2,941
*Available nitrogen calculated from mean sludge nitrogen values;
assumes nitrogen mineralization rates of 0.2, 0.10, 0.05, and
0.03 for first 4 years (15).
tSludge not applied in 1984, but residual from previous years
i s shown.
38
-------
same plots.
Mineralization rates for tannery sludges are not known.
For the purposes of this study, the following rates, equi-
valent to an aerobically digested municipal sewage sludge,
were used (15): first year, 20 percent mineralization of
organic N; second year, 10 percent; third year, 5 percent;
and fourth year, 3 percent. It was assumed that all
available NH.-N had been volatilized due to the long time
periods required (about 2 months) to complete stockpiling,
spreading, and incorporation.
SOIL CHARACTERISTICS
Soil samples were initially taken in November 1980,
prior to any sludge applications. Two samplings occurred
in 1981; the first, in July; the second, in October. The
October sampling was prior to the rainy field season that
hit the Santa Cruz area in 1981-1982.
As noted previously, surface samples in both 1983
and 1984 were taken to a depth of 15 cm versus the previous
samplings that were taken to the 30 cm level. The purpose
of this modification was to overcome the apparent dilu-
tion effect caused by including the entire first 30 cm
when, in fact, the zone of incorporation was only approxi-
mately the first 10 to 15 cm. Where possible, all data
for 1983 were mathematically adjusted to the 30-cm depth
for the sake of comparison.
The 1984 soil data (other than the control plot) were
39
-------
not included in any of the tables in the ensuing discussion
due to the unexplainable high variability in analytical
results. The principal reason for this high variability was
thought to be heterogeneity of the soil-waste mixture due to
poor incorporation (mixing) of applied sludge into the soil.
To illustrate soil variability, multiple soil samples
(September 1983) were analyzed for total Cr. Four (4)
randomly collected samples from each test plot were run in
duplicate. The results are shown in Table 12.
TABLE 12. AVERAGE AND STANDARD DEVIATIONS
FOR SOIL TOTAL Chromium analyses (mg/kg)
Plot/Application
Rate (mg/ha)
H1/103
H2/195
Cl/54
C2/106
M1/90
M2/169
M3/246
Average
68
150
585
1,183
1,358
1,053
2,148
Standard
Deviation
22
85
172
689
409
364
710
In most cases, the standard deviation was about 30
percent of the mean, indicating poor mixing in the zone
of incorporation and the difficulty in obtaining repre-
sentative samples.
40
-------
TOC and TKN
Table 13 presents total organic carbon (TOC) and total
Kjeldahl nitrogen (TKN) for all test plots at the three
depths sampled. Both TOC and TKN results show that
maximum concentrations were obtained in the surface
soils, and that respective concentrations diminished
with increasing .depth.
The TOC data did not show significant increases in
either the surface or lower depth soils. December 1982
concentrations appeared higher than background, but the
trend did not continue in the 1983 sampling.
Similarly, 1982 TKN data for plots H2, M2, and M3
suggested an increasing trend which was not borne out
by the 1983 data..
Sodium Adsorption Ratio (SAR) and Electroconductivity (EC)
The application of high sodium wastes may cause soil
dispersion resulting in poor soil physical conditions and
water permeability problems. The line in Figure 2 repre-
sents a generalized boundary between stable and unstable
soil physical conditions for either high sodium irriga-
tion water or the soil solution. Combinations of EC or
SAR that lie above the line are not expected to cause
dispersion or clay swelling. Those values that lie
below the line can create permeability problems (16).
Table 14 presents SAR and EC results for all plots
at the three depths sampled. In general, the data indicate
41
-------
TABLE 13. SOIL TOC AND TKN (t) FOR EIGHT SANTA CRUZ PLOTS*
DURING THE YEARS 1980*1984
Plot
HI
0-30 cm
30-60 cm
60-90 cm
H2
0-30 cm
30-60 cm
60-90 cm
Cl
0-30 cm
30-60 cm
60-90 cm
C2
0-30 cm
30-60 cm
60-90 cm
Ml
0-30 cm
30-60 on
60-90 cm
0-30 cm
30-60 cm
60-90 cm
M3
0-30 cm
30-60 on
60-90 cm
Control
0-30 cm
30-60 on
60-90 cm
November
1980
NA
NA
NA
2.7
1.0
0.3
NA
NA
NA
2.7
0.9
0.4
NA
NA
NA
NA
NA
NA
2.5
1.5
0.4
2.0
1.7
0.4
July
1981
2.1
0.6
0.3
2.0
0.9
0.4
2.6
0.8
0.3
2.4
0.8
0.4
2.5
0.7
0.2
2.8
1.8
o.a
2.6
0.8
0.5
NA
NA
NA
October
1981
2.5
1.2
0.7
2.4
1.3
0.6
2.0
0.6
0.5
2.3
1.3
0.8
2.5 '
1.1
0.5
3.0
2.4
1.0 '
2.7
1.3
0.6
NA
NA
NA
TOC
July December
1982 1982
1.8
0.7
0.4
1.8
0.7
0.4
2.9
0.7
0.4
1.7
0.8
0.3
1.9
0.7
0.2
1.7
1.5
.0.9
1.9
0.7
0.4
NA
NA
NA
NA
NA
NA
2.2
1.3
0.5
NA
NA
NA
2.7
1.4
0.5
NA
NA
NA
3.7
2.3
1.1
3.4
1.4
0.5
NA
NA
NA
September
1983T
1.5
NA
NA
1.7
NA
NA
2.2
NA
NA
2.2
NA
NA
2.2
NA
NA
1.9
NA
NA.
2.3*
NA
NA
2.1
NA
NA
1984
NI
NI
NI
NI
NI
NI
NI
NI
NI
' NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
1.2
0.4
0.1
November
1980
0.17
0.09
0.06
NA
NA
NA
NA
NA
NA
0.21
0.10
0.06
NA
NA
NA
NA
NA
NA
0.31
0.10
0.08
0.19
0.08
0.05
July
1981
0.40
0.07
0.05
0.19
0.08
0.06
0.21
0.09
0.04
0.19
0.08
0.06
0.22
0.07
0.06
0.23
0.14
0.07
0.21
0.09
0.07
NA
NA
NA
October
1981
0.29
0.12
0.14
0.28
0.13
0.09
0.19
0.09
0.07
0.26
0.11
0.13
0.24
0.11
0.08
0.27
0.20
0.10
0.28
0.15
0.08
NA
NA
NA
TKN
July December
1982 1982
O.'lZ
0.07
0.06
0.17
0.10
0.06
0.13
0.09
0.06
0.15
0.10
0.06
0.19
0.16
0.06
0.24
0.15
0.09
0.22
0.09
0.07
NA
NA
NA
NA
NA
NA
0.33
0.16
0.09
NA
NA
NA
0.29
0.12
0.07
NA
NA
NA
0.34
0.20
0.15
0.34
0.16
0.14
NA
NA
NA
September May
1983t 1984
0.24
NA
NA
0.39
NA
NA
0.19
NA
NA
0.29
NA
NA
0.24
NA
NA
0.22
NA
NA
0.29
NA
NA
0.23
NA
NA
NI
NI
NI
NI
NI
NI
NI
0.25
0.12
0.10
* All data expressed In terms of percent a1r-dr1ed soil.
t Sampling limited to top 15 cm.
NA • Not Analyzed.
NI • Not Included (see text).
42
-------
I
I
10 20 30
SODIUM ADSORPTION RATIO
40
Figure 2. Salinity and sodium adsorption ratio boundary that divides
combinations of both measures into two categories; those
which promote good permeability and those which do not.
(16).
43
-------
TABLE 14. SODIUM ADSORPTION RATIOS (SAR)
FOR EIGHT SANTA CRUZ PLOTS DURING THE YEARS 1980-1984
HI
0-30 cm
30-60 cm
60-90 cm
H2
0-30 cm
30-60 cm
60-90 cm
Cl
0-30 cm
30-60 cm
60-90 cm
C2
0-30 cm
30-60 cm
60-90 cm
Ml
0-30 cm
30-60 cm
60-90 cm
M2
0-30 cm
30-60 cm
60-90 cm
M3
0-30 cm
30-60 cm
60-90 cm
Control
0-30 cm
30-60 cm
60-90 cm
November
1980
2.1
3.4
3.1
NA
NA
NA
NA
NA
NA
4.2
2.6
4.6
NA
NA
NA
NA
NA
NA
1.7
3.1
4.2
2.1
3.5
3.1
July
1981
5.6
7.6
3.4
3.0
11.4
5.4
4.2
4.8
8.6
5.3
4.7
8.4
5.8
8.7
1.5
1.2
5.2
2.0
2.6
4.4
10.8
NA
NA
NA
October
1981
2.5
1.1
1.2
3.2
2.6
2.7
5.7
4.1
8.8
3.5
3.1
5.0
3.6
1.7
1.6
4.4
1.0
6.2
5.5
1.3
1.3
NA
NA
NA
July
1982
0.4
1,6
1.5
0.6
0.8
1.6
3.0
2.5
2.7
2.1
2.1
1.7
1.6
1.8
2.7
1.2
1.6
1.3
0.9
3.6
2.6
NA
NA
NA
December
1982
NA
NA
NA
2.1
2.1
1.9
NA
NA
NA
3.8
4.2
4.7
NA
NA
NA
1.6
3.5
2.5
1.9
1.1
2.9
NA
NA
NA
September
1983*
2.2
NA
NA
2.0
NA
NA
2.5
NA
NA
2.8
NA
NA
2.6
NA
NA
1.7
NA
NA
1.9
NA
NA
3.0
NA
NA
May
1984
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
1.5
1.7
2.2
* Sampling limited to top 15 cm.
NA = Not Analyzed.
NI = Not Included.
44
-------
TABLE 14 (continued)
ELECTROCONDUCTIVITY (EC) FOR EIGHT' SANTA CRUZ PLOTS DURING THE YEARS
1980 - 1984
EC (mmhos)
HI
0-30 cm
30-60 cm
60-90 cm
H2
0-30 cm
30-60 cm
60-90 cm
Cl
0-30 cm
30-60 cm
60-90 cm
C2
0-30 cm
30-60 cm
60-90 cm
Ml
0-30 cm
30-60 cm
60-90 cm
M2
0-30 cm
30-60 cm
60-90 cm
M3
0-30 cm
30-60 cm
60-90 cm
Control
0-30 cm
30-60 cm
60-90 cm
November
1980
0.21
0.10
1.00
NA
NA
NA
NA
NA
NA
0.22
0.13
0.20
NA
NA
NA
NA
NA
NA
0.32
0.14
0.17
0.26
0.19
0.21
July
1981
2.26
1.69
1.62
0.53
0.18
1.47
1.25
0.51
0.39
0.40
0.27
0.25
1.09
0.20
0.23
2.34
0.19
0.32
2.28
0.15
0.32
NA
NA
NA
October.
1981
2.81
2.70
1.74
5.35
1.67
0.93
1.03
0.25
0.52
1.28
0.37
0.46
3.39
0.86
0.57
3.71
1.01
0.60
5.67
1.01
0.62
NA
NA
NA
July
1982
2.03
1.53
1.20
3.26
1.24
1.39
0.22
0.13
0.15
0.38
0.17
0.18
0.37
0.23
0.33
2.34
0.61
0.40
1.92
0.62
0.60
NA
NA
NA
December
1982
NA
NA
NA
2.30
1.80
1.30
f
NA
NA
NA
0.79
0.45
0.33
NA
NA
NA
1.91
1.25
0.77
2.20
1.08
0.98
NA
NA
NA
September
1983*
1.38
NA
NA
1.52
NA
NA
0.66
NA
NA
1.25
NA
NA
0.75
NA
NA
1.00
NA
NA
1.50
NA
NA
•
NA
NA
NA
May
1984
Nl
Nl
Nl
Nl
Nl
Nl
Nl
Nl
Nl
Nl
Nl
Nl
Nl
Nl
Nl
Nl
Nl
Nl
Nl
Nl
Nl
0.33
0.24
0.42
* Sampling limited to top 15 cm.
NA = Not Analyzed.
Nl = Not Included.
45
-------
that SAR's have not reached levels associated with reduc-
tion in permeability. The SAR/EC results appear to be
within the limits for good permeability shown in Figure 2.
The apparent lower SAP values reported for the July
1982 soils are thought to be a result of the intense
leaching that occurred earlier in the year as a result
of the heavy, rainfall in the 1981-1982 winter.
Soil pH
Table 15 presents pH data for all plots at three
sampling depths. The hair-burn treated plots (H1 and H2)
show a gradual increase in acidity over the years due in
part to the mineralization of organic N and the oxidation
of sulfides to sulfates. This trend was not evident in
the chrome or mixed sludge plots. The chrome sludge was
noticeably absent of sulfides; the mixed sludge contained
only about 25 percent hair-burn sludge. Although minerali-
zation of organic N was still occurring in these plots, its
effect on pH was not as significant.
The slight change in pH of the control plot may have
been caused by the application of superphosphate, and
muriate of potash prior to planting of sudan grass in
1981. (All plots received this one-time application of
fertilizer.)
Soil Depth Profiles - Chromium and Lead
Table 16 presents total Cr and Pb data for all plots
at three sampling depths.
46
-------
TABLE 15. pH AND ELECTROCONOUCTIVI TV (EC) FOR EIGHT SANTA CRUZ PLOTS DURING THE YEARS 1980-1984
HI
0-30 cm
30-60 cm
60-90 en
H2
0-30 cm
30-60 cm
60-90 cm
Cl
0-30 cm
30-60 cm
60-90 cm
C2
0-30 cm
30-60 cm
60-90 cm
Ml
0-30 cm
30-60 cm
60-90 cm
M2
0-30 cm
30-60 cm
60-90 cm
M3
0-30 cm
30-60 cm
60-90 cm
Control
0-30 cm
30-60 cm
60-90 cm
November
1980
6.6
6.9
7.1
NA
NA
NA
NA
NA
NA
6.6
6.6
6.2
NA
NA
NA
NA
NA
NA
6.5
6.7
6.8
6.9
6.6
6.0
July
1981
7.6
6.4
6.6
7.4
6.8
6.9
7.7
6.4
5.2
7.5
6.9
6.9
6.2
6.3
6.4
6.2
5.7
6.3
6.2
6.1
6.5
NA
NA
NA
October
1981
6.2
6.2
6.2
6.2
6.1
6.5
5.8
6.2
5.7
6.0
6.6
5.8
5.8
6.1
6.5
6.0
6.4
6.2
6.4
6.4
6.6
NA
NA
NA
July
1982
5.1
5.4
6.1
4.9
5.3
5.3
6.2
5.4
4.6
6.4
6.3
6.3
6.3
6.3
5.9
5.9
6.0
6.2
5.9
6.3
6.3
NA
NA
NA
pH*
December
1982
NA
NA
NA
5.1
5.3
6.1
NA
NA
NA
6.7
6.4
5.7
NA
NA
NA
6.2
6.1
6.2
6. 7
6.3
6.5
NA
NA
NA
September
1983
5.2
NA
NA
5.1
NA
NA
6.5
NA
NA
6.6
NA
NA
6.4
NA
NA
6.6
NA
NA
7.0
NA
NA
7.3
NA
NA
May
1984
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
6.4
5.5
5.0
November
1980
0.21
0.10
1.00
NA
NA
NA
NA
NA
NA
0.22
0.13
0.20
NA
NA
NA
NA
NA
NA
0.32
0.14
0.17
0.26
0.19
0.21
July
1981
2.26
1.69
1.62
0.53
0.18
1.47
1.25
0.51
0.39
0.40
0.27
0.25
1.09
0.20
0.23
2.34
0.19
0.32
2.28
0.15
0.32
NA
NA
NA
October
1981
2.81
2.70
1.74
5.35
1.67
0.93
1.03
0.25
0.52
1.28
0.37
0.46
3.39
0.86
0.57
3.71
1.01
0.60
5.67
1.01
0.62
NA
NA
NA
July
1982
2.03
1.53
1.20
3.26
1.24
1.39
0.22
0.13
0.15
0.38
0.17
0.18
0.37
0.23
0.33
2.34
0.61
0.40
1.92
0.62
0.60
NA
NA
NA
EC
December
1982
NA
NA
NA
2.30
1.80
1.30
NA
NA
NA
0.79
0.45
0.33
NA
NA
NA
1.91
1.25
0.77
2.20
1.08
0.98
NA
NA
NA
Sept ember
19H3*
1.38
NA
NA
1.52
NA
NA
0.66
NA
NA
1.25
NA
NA
0.75
NA
NA
1.00
NA
NA
1.50
NA
NA
NA
NA
NA
May
1984
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
330
240
420
* pH performed on air-dried soils, mixed 1/1 with water.
NA - Not Analyzed.
-------
TABLE 16. LEAD AND TOTAL CHROMIUM FOR EIGHT SANTA CRUZ PLOTS FROM 1980 TO 1984*
Lead
November July October July
1980 1981 1981 ' 1982
HI
0-30 cm
30-60 cm
60-90 cm
H2
0-30 cm
30-60 cm
60-90 cm
Cl
0-30 cm
30-60 cm
60-90 cm
C2
0-30 cm
30-60 cm
60-90 cm
Ml
0-30 cm
30-60 cm
60-90 cm
VS.
0-30 cm
30-60 cm
60-90 cm
M3
0-30 cm
30-60 cm
60-90 cm
Control
0-30 cm
30-60 cm
60-90 cm
<10 <10 <10
11 <10 <10
12 6 <10
NA <10 <10
NA <10 <10
NA <10 <10
NA <10 <10
NA <10 <10
NA <10 <10
13 <10 <10
<10 33 <10
<10 12 <10
NA <10 - <10
NA <10 <10
NA <10 <10
NA 10 <10
NA <10- <10
NA <10 <10
10 <10 <10
13 <10 <10
11 <10 <10
<10 NA NA
<10 NA NA
<10 NA NA
14
15
17
28
20
16
<10
<10
15
14
<10
14
16
10
40
<10
10
10
<10
<10
22
NA
NA
NA
Chromium
December
1982
NA
NA
NA
<10
<10
<10
NA
NA
NA
<10
<10
18
NA
NA
NA
<10
<10
<10
<10
<10
<10
NA
NA
NA
September
1983t
<10
NA
NA
<10
NA
NA
<10
NA
NA
<10
NA
NA
13
NA
NA
<10
NA
NA
16
NA
NA
<10
NA
NA
May
1984
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
<10
<10
<10
November July
1980 1981
37
50
50
NA
NA
NA
NA
NA
NA
47
31
41
NA
NA
NA
NA
NA
NA
50
44
50
20
29
24
20
35
43
41
42
60
48
56
35
64
16
36
31
26
47
286
29
23
73
33
32
NA
NA
NA
October July
1981 1982
46
37
45
38
11
49
21
20
32
56
24
35
36
36
45
117
44
56
168
58
44
NA
NA
NA
60
46
48
57
55
51
171
75
25
78
63
36
65
47
43
290
122
92
171
53 '
47
NA
NA
NA
December
1982
NA
NA
NA
66
25
28
NA
NA
NA
234
91
42
NA
NA
NA
211
69
33
338
78
69
NA
NA
NA
September
1983t
31
NA
NA
40
NA
NA
295
NA
NA
840
NA
NA
765
NA
NA
540
NA
NA
1,050
NA
NA
28
NA
NA
May
1984
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
NI
28
12
* All data expressed In mg/kg, air-dried soil.
t Top 15 cm only.
NA > Not analyzed.
NI > Not.Included.
48
-------
All of the Cr applied was in the trivalent (III)
state. Chromium (VI) was not found in any of the soil
samples at the detection limit of 0.1 mg/kg. These
results are similar to those reported by others (11, 17).
The data show that Cr has concentrated primarily in the
surface 30 cm. There is some evidence (M2, July 1982;
and C2, December 1982) to suggest that some Cr has moved
to the 30- to 60-cm depth, but these data are too incon-
clusive to demonstrate this with any certainty.
The recovery of chromium in the surface soils was
generally poor. Based on total chromium application shown
in Table 8, and the September 1983 soil data, recovery
rates for plots C1, C2, M1, M2, and M3 were 51, 74, 120,
45, and 60 percent, respectively. Poor incorporation
(mixing) of the applied sludges into the soil matrix was
the probable cause for these highly variable recovery
rates.
Lead levels were generally low and were similarly
within the range shown in Table 6. Based on the analytical
data, lead is not an element of concern in these sludges.
PLANT TISSUE ANALYSIS
Prior to initial sludge applications in 1981, seven
native species were observed on the test and control plot
(Table 17). Since none of these had been studied exten-
sively, sudan grass (Sorghum Sudanese) was selected as a
49
-------
TABLE 17. PREVAILING GRASSES AT THE SANTA CRUZ SITE
Common Name
Ri bgut grass
Storksbi11
Gerani um
Fox tail barley
Wild radish
Dock
Clover
Scientific Name
Bromus diandrus Roth
Erodi um moschatum L.
Geranium sp.
Hordeum sp.
Raphamus sp.
Rumex sp.
Tri foli um sp.
50
-------
test species and applied at a rate of 33 kg/ha in the fall
of 1981. All plots were amended with 276 kg/ha super-
phosphate, and 338 kg/ha muriate of pdtash prior to
seeding.
Germination of sudan grass was poor in all plots and
necessitated a change in test species. The most prevalent
native grass, ribgut grass (Bromus diandrus Roth.), was
selected. Samples of ribgut grass -were obtained in Decem-
ber 1981, February 1982, April 1982, and June 1983.
Observations on plant growth were recorded over the
project duration. The combination of yearly tilling and
sludge applications took its toll on the native vegetation.
Growth of ribgut grass after the 1982 fall sludge applica-
tion was very sparse, with only occasional clumps of
growth, amid an abundance of native wild radish and
thistles. As time progressed, the last two species pros-
pered at the expense of the ribgut grass. Sporadic growth
was evidenced around the control plot, but not to the
extent noted at the project's beginning.
Table 18 presents the TKN and total chromium results
for ribgut grass in 1981, 1982, and 1983. Total Kjeldahl
nitrogen concentrations remained relatively constant
throughout each sampling period. The data for total
chromium suggests chromium enhancement in the M3 plot,
which received the heaviest sludge application (246 mt/ha
51
-------
TABLE 18. NITROGEN AND CHROMIUM CONCENTRATIONS OF RIBGUT GRASS
(Bromus diandrus Roth.) ON FOUR SAMPLING DATES
TKN (%)
Test Plot
Control
HI
H2
Cl
C2
Ml
M2
M3
12/2/81
4.6
6.4
6.6
5.3
5.5
5.7
5.5
6.2
2/18/82
3.5
4.5
5.4
2.8
3.8
3.8
4.9
4.5
4/26/82
1.2
1.6
1.8
1.4
1.5
1.3
1.5
1.9
1
6/83
NS
NS
1.4
NS
1.3
NS
.1.4
1.8
12/2/81
1.50
2.62
4.40
4.75
12.25
4.75
6.12
7.75
Cr (mg/kg)
2/18/82
3.64
3.87
7.14
1.38
1.09
3.68
4.26
9.48
4/26/82
3.50
4.43
5.35
3.58
4.55
3.68
4.78
8.00
6/83
NS
NS
3.93
NS
3.93
NS
2.35
4.10
NS = Not Sampled.
52
-------
mixed sludge, and 6,720 kg/ha total Cr). Only a limited
number of samples could be analyzed due to resource
limitations; therefore, the data are considered to be
inconclusive. No available literature on Cr uptake by
ribgut grass could be found to provide comparison of
data.
53
-------
SECTION 6
HYDROLOGY
SITE CHARACTERISTICS
The project site is located about 1.6 km inland
from the Pacific coast at an elevation of approximately
120 m above sea level. The site is situated on a gently
sloping marine terrace with slopes varying between 6 per-
cent on the southwest side of the area to 20 percent on
the northeast side. The root zone of native vegetation
extends to a depth of 1 to 1.5 m.
Each plot has 0.2 hectare surface area, except Plot
M-3, which is a 0.1 hectare. Surface runoff from all of
the plots is channeled by berms into buried retention
basins and released near the heads of two natural gullies.
A 3 to 16 meter-thick layer of weathered, unconsolidated
terrace deposits underlies the site (Figure 3). Beneath
the terrace deposits is the low permeability, fractured
mudstone of the Santa Cruz Formation. The water table in
the Santa Cruz mudstone fluctuates seasonally between 28
and 31 m below the ground surface. Wells in the Santa
Cruz Formation are sometimes used for water supply else-
where along the coast, although water quality and well
yields are often poor.
54
-------
500-
40O
300-
20O
i control plot
C-2 Dlot
A'
B
soa
40QJ
3oa
200
B'
Figure 3. Geologic cross-section of field site.
55
-------
The terrace deposits vary from clays to clayey sands.
Sediments beneath the southeastern portion of the site, in
the vicinity of Plot H-2, contain the greatest amount of
silt and sand. Elsewhere deposits consist of iriterlayered '
clays and sandy clays with clay contents increasing toward
the northwest and south. Sediments near Plot C-2 are the
most clay-rich and sediments near Plot M-3 are the most
variable.
Almost the entire annual rainfall at the site occurs
between October and May. In a high rainfall year, soil
moisture of the terrace deposits approaches saturation
during the rainy season. During the rest of the year,
the sediments are unsaturated and become progressively
drier from early summer to early fall.
SAMPLING PROCEDURES
Soil Water Samples
Soil water samples were collected using ceramic porous
cup samplers. The samplers were installed in clusters of
two to five samplers with three clusters in each monitored
plot for replication. (See Figure 4.) Samplers in a clus-
ter were placed at varying depths between 30 and 150 cm
below the ground surface.
The samplers were installed in 9 cm diameter boreholes,
augered to a depth of 15 cm below the desired sampling
depth. A bentonite layer was placed in the bottom of the
borehole, followed by a silica flour layer around the
56
-------
A' SITE PLAN
-1 A
EXPLANATION
f Retention basin with weir
A Recording rainguage
A Non-recording rainguage
• Tensiometers, soil water samplers,
and neutron access tube
0 Tensfometers and soil water samplers
9 Soil water samplers only
Figure 4. Map of field site showing ground surface contours and location
of 1983 hydrologic budget and water quality monitoring
equipment.
57
-------
porous cup tip. A bemtonite layer was placed above the
silica flour layer and the borehole was filled with com-
pacted soil to within 8 cm of the ground surface. The
remaining 8 cm was then filled with bentonite.
To sample the soil water, 80 centibars of suction
was applied to the samplers, and the samplers were left
sealed from atmospheric.pressure for one week. The
collected water was then removed, and no vacuum was
placed on the samplers for one week to allow natural
soil moisture gradients to re-establish.
Two samples were collected at each sampling point,
one for major cation and trace metal analyses and a second
for nitrate analyses. Sample bottles were rinsed with
soil water before collection. Sample volumes varied
between 100 and 700 ml. The samples were preserved
according to EPA guidelines (18) and stored in ice for
transport to the lab.
Surface Runoff and Seep Spring Samples
Runoff and seep spring samples were collected during
storms and preserved according to EPA guidelines (18).
Filtered and unfiltered acidified samples were collected
for major cation and trace metal analyses; unacidified,
unfiltered for alkalinity and nitrate analyses. Sample
bottles were rinsed with runoff or spring water before
collection and stored in ice for transport to the lab.
Deep Groundwater Samples
The deep well was drilled by air rotary to avoid
58
-------
contamination of the aquifer during well construction. The
well has a plastic casing and cap. Groundwater samples
were collected with a nitrogen diaphram pump to minimize
trace metal contamination during sample collection.
Because of the slow pumping rate, the well bore was not
thoroughly flushed before sampling. A two liter sample
was collected at a rate of approximately 250 ml/min, pre-
served according to EPA guidelines (18), and transported
in ice to the lab.
ANALYTICAL PROCEDURES
Procedures used to determine constituent concentra-
tions are summarized in Table 19. All techniques are
officially approved EPA procedures (18) with the exception
of the nitrate probe method. Because the nitrate probe
is sensitive to interferences from other ions in solution,
an Orion interference suppressant, Orion 930710, was added
to the water samples in a proportion of 1 part suppressant
to 1 part sample. Final results of the UCSC NO., analyses
compared well with analyses by Don Clark at Robert S.
Kerr Environmental Research Laboratory with the EPA
method. (Data presented later in table 21.)
WATER BUDGET MONITORING
The purpose of the water budget monitoring was to
estimate the quantity of water which entered the plots,
ran off as surface flow, or percolated through the soils.
59
-------
Table 19 — Analysis and Preservation of Constituents
.Constituent Preservation
Na UNO. to pll<2
refrigeration
4°C.
K UNO, to pll<2
refrigeration
4°C.
Mg HMO. to pH<2
Ca HNO3 to pil 2
refrigeration
4»C.
Cr UNO. to pH<2
Analytical Sensitivity (Concentration Detection
Instrument Methodology » .0044 Absorbance) Limit
Varion AA-6 Flame analysis
atomic spectro-
s copy 2
•
Varion AA-6 Flame analysis
atomic spectro-
scopy2
Varion AA-6 Flame analysis
atomic apectro-
scopy2
Varion AA-6 Flame analysis
atomic epectro-
Perkin-Elmer Graphite furnace
0.003 ppm 5
(0-60 ppm)
0.04 ppm .
(0-200 ppm)'
0.007 ppm 5
(0-30 ppm)
0.001 ppm _
(0-6 ppm)
0.001 ppm
0.02 ppm
0.6 ppb
0.2 ppm
3 ppro
1 ppm
0.07 ppm
0.004 ppm
0.00 ppm
0.8 ppb
Cu
NO,
refrigeration
4eC.
500 atomic spectro-
HGA 500 scopy with pyrolyti-
Prog rammer cally coated graphite
tube
UNO. to pll<2 Perkin-Elmer Graphite furnace 0.7 ppb
refrigeration 500 atomic spectro-
4°C.
HGA 500 scopy with pyrolyti-
Programmer cally coated graphite
tube
Within 24 hours Orion speci- Potentiometric
refrigeration fie ion meter equivalence
4°C. 407A
Nitrate elec-
trode model
93-07
0.7 ppb
0.06 ppm
-------
Table 19 - - (continued )
. Analytical . Sensitivity (Concentration Detection
Constituent Preservation Instrument Methodology - 0.0044 Absorbance) Limit
HCO ~ Within 24 hour* Filtration
J refrigeration with ,02N
48C. H2S04
1. Methods of Chemical Analysis for Water and Wastes, Office of Research and Development, U. S.
EPA, Cincinnati, Ohio, March, 1979.
2. Analytical Methods for Flame Spectroacopy, Varion Techron, Springvale, Australia, June, 1978.
3. Analytical Methods Using IIGA Grapliite Furnace, Perkin-Elmer, Norwalk, Conn., March, 1977.
4. Instrument Manual, nitrate ion electrode, model 93-07, Orion Research, Inc., Cambridge, Mass.,
T979.
5. Range of constituent concentration for which the instrument is optimized and to which the
sensitivity and detection limit applies.
-------
Water budget information was then combined with measured
contaminant concentrations to estimate contaminant fluxes
from the plots.
Detailed hydrologic monitoring continued for three
consecutive field seasons (1982 through 1984). Water
budget calculations used data for the later two years
(1983 and 1984) from the most heavily loaded plot (Plot
M-3). During these years, rainfall and surface runoff
were monitored continuously and soil matric suctions and
moisture contents were measured at weekly intervals.
Rainfall
Rainfall was measured between September 1982 and
June 1984 with a continuous recording raingage south-
west of Plot M-l and with a non-recording gage located
at the west corner of Plot M-3 (Figure 4). For comparison,
additional rainfall records were obtained from the Swanton
Road Fire Station, located about 1.6 km from the field site.
As illustrated in Figures 5a and 5b, the 1983 and
1984 field seasons were dramatically different hydrologically,
The 1983 season was one of unusually high rainfall. A
total of 120 cm (50 in), about twice the mean annual rain-
fall, was measured between September 1982 and August 1983.
A cumulative total of 89 cm (35 in) fell during the January
through June monitoring period. In contrast, the 1984
season had low total rainfall, about 59 cm (23 in). Most
of this occurred in November and December with only 13 cm
62
-------
19 28 ' 3 > '» 23 30
DECEMBER JANUARY
13 20 261
FEBRUARY
5 11 1* 26
MARCH
10 IT
APRIL
a It 23 291 S 12 19
MAY ' JUNE
r
Figure 5, Summary graphs of precipitation, runoff, and matric suction at
monitoring cluster M-3c for (a) 1983 season and (b) 1984 season.
63
-------
(5.2 in.) falling between January and June.
Surface Runoff
Surface runoff was controlled and measured by a
system of berms and retention ponds. The test plots
were surrounded by berms that drained into collection
boxes at the base of each test plot. The water then
flowed through eight-inch PVC pipe into buried, concrete
sedimentation ponds. To measure runoff, v-notch weirs
were constructed in each of the retention basins and
continuous recording water-level gages were placed near
two of the weirs. In 1982 and 1983, one gage was placed
below Plot M-3 and another in the basin below Plots C-l,
C-2, and M-l. Although numerous problems were encountered
with the gages, runoff from a number of storm events was
recorded during the 1982 field season and a continuous
record was collected in 1983. In 1984, measurements
were made only below Plot M-3. This was a relatively
low rainfall year, and measurable runoff occurred during
only four storms.
Surface runoff from the plots was highly variable.
For example, substantial flow occurred from Plots C-l,
C-2, and M-l during most high rainfall periods. On the
other hand, surface runoff left Plots M-2, H-l, and H-2
only during extremely intense storms. The difference in .
runoff between the different test plots is probably the
64
-------
result of variable clay contents in the soils. Soils
on the northeast side of the field area contain more
sand than soils on the northwest side. Undoubtedly,
gopher holes and lateral water movement along shallow
higher permeability layers also play a role.
Soil Water Movement
Precipitation which does not leave the plots as
surface runoff either infiltrates into the soils or
returns to the atmosphere via evapotranspiration. The
primary objective of the soil water monitoring program
was to estimate the total volume of water that moves
downward through the soils, and which might transport
contaminants from the test plots.
One method for estimating water flux beneath the
test plots is to measure changes in matric suction in
the soils with tensiometers and to interpret these
changes in terms of changes in water content. During
most of a year, the soils and terrace deposits beneath
the test plots are unsaturated. Matric suction refers
to negative pressures in the soil water, relative to the
vapor pressure, resulting from capillary and adsorptive
forces due to the soil matrix. Matric suction is a
driving force for soil water movement and also reflects
the amount of water present in the soils. In general, the
drier the soil, the higher the matric suction. As a soil
approaches saturation, the matric suction approaches zero.
65
-------
Matric suction and water content measurements were
made using replicate tensiometers and neutron access
tubes in each test plot. Plot M-3 was monitored in
most detail and only results from that plot were used
in subsequent moisture flux computations.
Data from three monitoring clusters in Plot M-3,
collected in 1983 and 1984, were used to calculate
moisture and contaminant movement (Figure 6). Each of
these clusters contained four or five tensiometers,
installed at approximately 30 cm depth intervals to a
maximum depth of 152 cm. In addition, an aluminum
neutron access tube was placed near the tensiometer
clusters. The tensiometers were read at weekly intervals.
The neutron probe was calibrated at the beginning and end
of the field season and readings were taken at bi-weekly
intervals from November through May and at weekly intervals
while the soils were drying in June and July.
The weekly moisture content data necessary for per-
colation and hydrologic budget computations were estimated
using moisture content-matric suction characteristic curves
for the field site soils. These curves were constructed
from simultaneous matric suction and moisture content
measurements. Figure 7 shows fitted curves for the
monitoring clusters in Plots M-3, H-2, and C-2.
66
-------
PLOT M-3
10m
scale
EXPLANATION
ffl Non-continuous rainguage
3 Retention basin with V-notch
o Neutron access tube
A Tensiometer cluster, 1982-83
A Tensiometer cluster, 1983-84
•""• Berm and plastic-lined drainage channel
— Fence
Figure 6. Locations of monitoring clusters on Plot M-3.
67
-------
00
0.4
0)
o>O
E 0) n «
3 i_ O.Z
"52
> w
I o.i
PLOT M-3
A
B
C
Composite
-20 -4O -80 -80
Matrlc Suction (centibars)
0.4
*
0.3
O.2
> w
I 0.1
PLOT C-2
A
B
Composite
-20
-40
-80
-80
Matrlc Suction (centibars)
0.4
o.go.3
fco
Q)O
I® 0.2
> w
PLOT H-2
0.4
0)
3
0.3
0.2
, A
————B
Composite
-20 -40 -ao -ao
Matrlc Suction (centibars)
COMPOSITE
H-
-20 -40 -60 -80
Matrlc Suction (centibars)
Figure 7. Characteristic soil moisture curves for: (a) Plot M-3, (b) Plot H-2, (c) Plot C-2,
and (d) composite curves fit to all data from each plot. Vertical bars represent'
the standard error of estimation.
-------
The characteristic soil moisture curves in Figure 7
were constructed by fitting curves of the form:
9 = 6sat a
( a + hP )
where
9 = soil moisture content.
9 .= saturated soil moisture content.
sat
h = soil matric suction.
and a, g= empirical constants
to matric suction and moisture content measurements using
non-linear least-squares regression. This equation has
been used successfully by Visser (1966), Vauclin et al.
(1979), and others. Other equations, such as those
reviewed by Hillel (1980) , could be used without signifi-
cantly altering study results. Values of 9 . were
estimated from neutron probe and gravimetric measurements
to be in the range of 0.30 to 0.40. Fitted values of a
range from 1.0 to 13., and values of grange from 0.006
to 0.20.
Although the curves cannot be clearly differentiated,
their shapes reflect the type and variability of soils near
the monitoring nests (Figure 7). Curves for clusters in
Plots H-2 and C-2 are similar indicating relatively uniform
soils, while the curves for clusters in Plot M-3 differ,
suggesting variable soils. Curves for Plots M-3 and C-2
exhibit higher moisture content values for given matric
69
-------
suctions, reflecting greater clay contents in the soils
near these plots.
In 1983, the sediment profile was close to saturation
by mid-January and, because of the frequency of storms,
remained nearly saturated until the first week of April
(Figure 5). In contrast, the sediment profile never
became completely saturated in 1984. The time intervals
between storms were periods of soil water redistribution
during which matric suctions gradually increased and
moisture content decreased. During and immediately after
significant storms, matric suctions decreased rapidly and
moisture content increased as the soil profile was re-
charged.
MOISTURE FLUX COMPUTATIONS
The rate of soil water movement through the plots was
computed as a vertical moisture flux. This flux is the
volume of water that crosses a horizontal plane of unit
area during a specified time interval. The method used
to compute the soil water flux is described in detail by
Dreiss and Anderson (19). The technique entails several
steps: 1) measurement of rainfall, soil moisture contents,
and soil matric suction as described above, 2) measurement
of K .; and 3) computation of cumulative evapotranspira-
Sclu
tion and percolation. These were performed for both the
1982-83 and 1983-84 field seasons. For both seasons,
flux computations began in the first week of January
after equipment installation and ended in May or June as
,70
-------
the tensiometers fail. As discussed by Dreiss and
Anderson (19), a sensitivity analyses was conducted
on K . because the field measurements of K , were
considered to be accurate to only an order of magnitude.
Figures 8 and 9 show computed cumulative evapotrans-
piration and percolation fluxes. Total percolation
differed greatly between the two years, ranging from
32 32
about 64 cm /cm for 1983 to approximately 9 cm /cm
for 1984. The similarity between the three monitoring
nests for each year is discussed in Reference (19).
The consistency of computed flux volumes can be
assessed by examining the total water budget for Plot M-3.
PT + AS = RT + qp + qet * e
where P_, = cum. precipitation
AS = change in moisture storage
R = cum. surface runoff
q = cum. percolation
q . = cum. evapotranspiration
and e = sum of measurement and computation errors,
This equation applies to a monitoring nest if P and R
occur uniformly over the plot. The change in storage,
AS, is found by subtracting the final volume of moisture
in the soil profile from the initial volume.
71
-------
110
10 20 i 10 20 i 10 20 |
JANUARY FEBRUARY MARCH
10 2O
APRIL
10 20 I 10 20
MAY JUNE
110
10 20 | 10 20 | 10 20 | 10 20 | 10 20
JANUARY FEBRUARY MARCH APRIL MAY
10 20
JUNE
110-
10 20 | 10 20. < 10 20
JANUARY FEBRUARY MARCH
10 20 | 10 20 | 10 20
APRIL MAY JUNE
Figure
8. Computed cumulative moisture budget for monitoring clusters in
Plot M-3 for 1983 season.
72
-------
30 ^
20-
§10
1984
NEST M-3A
-RAINFALL * iSTC=tAGS '
10 20
January
10 20
Feoruary
10 20
Marcn
10 20
Aonl
10 20
May
40
30
*e
u
•s
01
I,
20
0-1
1984
NESTM-3B
— RAINFALL +• &STCRAGE
10 20
January
10 20
Feoruary
10 20
Marcn
10 20
April
10 20
May
10 20
January
Figure 9 . Computed cumulative moisture budget for monitoring clusters in
Plot M-3 for 1984 season.
73
-------
Table 20 summarizes the moisture budget for Plot M-3.
The total error, e , varies between 11 and 20% of the
input volume, P + AS, for 1983 and between 1 and 14% for
1984. Thus computed values of cumulative evapotranspiration
and percolation appear to be reasonable estimates. Moreover,
actual errors for 1983 are probably less than the moisture
budget error because surface runoff from Plot M-3 was not
measured in 1983 and was not included in the balance.
Other possible sources of error in the balance calculations
are discussed further in Reference (19).
Of special importance to computations of the transport
of chromium from the test plot soils is the fact that cumu-
lative percolation differs by nearly an order of magnitude
between the two years. Thus, a much greater opportunity
for transport was present during 1983 than during 1984.
WATER QUALITY MONITORING
The purpose of water quality monitoring was to detect
any change in water quality in the vicinity of the field
site due to sludge applications on the test plots. In
addition, measured concentrations of Cr in soil waters
were used to compute Cr fluxes through soils beneath Plot
M-3. Water samples were collected and analyzed from sur-
face runoff, a seep spring, shallow and deep monitoring
wells, and soil water samplers. Sampling•schemes varied
between project years.
74
-------
--J
Ul
Year
MOISTURE BUDGET SUMMARY
Nest
A
1983 B
C
A
1984 B
C
Rainfall
Storage
Runoff
Qperc
Qevap
Error
(cm3/cm2)
88.8
88.8
88.8
13.2
13.2
13.2
17.5
12.0
12.3
19.8
15.1
22.8
1.17
1.17
1.17
62.2
62.9
67.8
6.23
8.32
11.9
32.8
17.9
16.3
21.9
16.8
22.4
•
3.75
2.01
0.51
Table 20. Moisture Budget Summary
-------
Monitoring began in 1981, before the first sludge
application, with baseline sampling at wells and reten-
tion basins at the site, and at springs and creeks nearby.
In subsequent years, soil waters directly below the plots
became the major emphasis of the monitoring because of the
lack of shallow, perched groundwater and because total Cr
concentrations remained at background levels everywhere
except in the soil waters. During the second (1982)
project year, soil water samples were collected at regular
intervals from all test plots and, when possible, from
shallow wells and plot runoff. In the third (1983) and
fourth (1984) years, emphasis was placed on replicate
monitoring of the most heavily loaded plots. Plots C-2,
M-2, H-2, M-l, and M-3. In the final (1985) year, water
samples were collected only from Plot M-3. These samples
yielded final baseline measurements as well as data for a
quality assurance comparison (Table 21).
All water samples were analyzed for total Cr and N0_.
In addition, samples were analyzed for major cations (Ca,
Mg, and Na) in 1982 and 1983. Samples that were collected
for Cr and major cation determinations were preserved with
HNO., in the field and all samples were transported in ice
to the lab. Nitrate analyses were performed within 24 hours
of sampling using an Orion specific ion meter. Ca, Mg, and
Na concentrations were determined by flame atomic spectro-
scopy and chromium analyses were performed using graphite
76
-------
TABLE 21
AOC on Soil Water Samples
Univ. of Calif. Santa Cruz and RSKERL Ada, OK
Sample No.
Collection Date
Nitrate*(ppm) Chromium (ppb)
SITE A
SITE B
SITE C
SITE A
SITE B
SITE C
T-8-F
C-8-F-C
C-ll-F-U
A-10-F-U
A-7-F-C
T-9-F
C-9-F-C
C-12-F-U
A-ll-F-U
A-8-F-C
T-10-F
C-10-F-C
C-13-F-U
A-12-F-U
A-9-F-C
T-8-F
C-8-F-C
C-ll-F-U
A-10-F-U
A-7-F-C
T-9-F
T-9-F-C
C-12-F-U
A-ll-F-U
A-8-F-C
T-10-F
C-10-F-C
C-13-F-U
A-12-F-U
A-9-F-C
3/10/85
3/10/85
3/10/85
3/10/85
3/10/85
3/10/85
3/10/85
3/10/85
3/10/85
3/10/85
3/10/85
3/10/85
3/10/85
3/10/85
3/10/85
3/24/85
3/24/85
3/24/85
3/24/85
3/24/85
3/24/85
3/24/85
3/24/85
3/24/85
3/24/85
3/24/85
3/24/85
3/24/85
3/24/85
3/24/85
UC EPA %RD
UC EPA
32
49
46
49
46
71
51
58
219
74
39
28
39
56
32
35
49
46
17
17
55
39
33
173
54
23
18
35
38
11
35
54
51
50
50
71
57
60
N.D.
73
44
30
43
60
31
38
54
50
18
16
58
44
33
177
61
29
20
41
44
12
9.0
9.7
10.
2.0
8.3
0.0
11.
3.4
• -
1.3
12.
6.9
9.8
6.9
3.2
8.2
9.7
8.3
5.7
6.1
5.3
12.
0.0
2.2
12.
23.
11.
16.
15.
8.7
4.8 <10
2.0 <10
3.7 <10
2.8 <10
4.1 <10
1.3 <10
3.1 <10
2.9 <10
4.1 <10
2.1 <10
1.1 <10
1.7 <10
1.5 <10
1.2 <10
1.6 <10
5.4 <10
1.8 <10
3.1 <10
2.4 <10
2.9 <10
1.5 <10
2.3 <10
2.5 <10
4.4 <10
1.6 <10
.7
-------
Table 21 (continued)
Sample No. Collection Date Chromium (ppb) *
UC EPA %RD
SITE A T-8-F 3/10/85 4.8 5.6 15.
C-8-F-C 3/10/85 2.0 1.8 11.
C-ll-F-U 3/10/85 3.7 4.4 17.
A-10-F-U 3/10/85 2.8 3.1 10.
A-7-F-C 3/10/85 4.1 5.7 33.
SITE B T-9-F 3/10/85 1.3 2.0 42.
C-9-F-C 3/10/85 3.1 3.3 6.2
C-12-F-U 3/10/85 2.9 3.7 24.
A-ll-F-U 3/10/85 4.1 5.5 29.
A-8-F-C 3/10/85 2.1 2.4 13.
SITE C T-10-F 3/10/85 . 1.1 1.3 17.
C-10-F-C 3/10/85 1.7 2.7 45.
C-13-F-U 3/10/85 1.5 1.6 6.5
A-12-F-U 3/10/85 1.2 1.6 29.
A-9-F-C 3/10/85 1.6 2.7 51.
SITE A T-8-F 3/24/85 5.4 4.7 14.
C-8-F-C 3/24/85 1.8
-------
furnace atomic absorption.
Baseline Sampling
Seven baseline surface and subsurface water samples
were collected and analyzed in March and May 1981. The
purpose of the sampling was to characterize the background
chemistry of the water in the project site vicinity before
sludge application. The sampling sites were:
1) The sediment retention box below Plot M-3;
2) The sediment retention box below Plots M-2, H-l,
and H-2;
3) The sediment retention box below Plots C-l, C-2,
and M-l;
4) The deep monitoring well;
5) A seep spring at the base of the bowl-'shaped area
adjacent and east of the control plot;
6) The cattle watering trough near the gate at Swanton
Road; and
7) Scott Creek at a point to the southwest of the gate
to the field site.
Results of the baseline monitoring are given in Table 22
In general concentrations of major cations (Ca, Mg, and Na)
were in the range of 3.5 to 30 ppm.
Shallow Monitoring Wells and Seep Spring
Ten shallow wells were installed to sample seasonally
perched water, if present, above the mudstone bedrock and
79
-------
TABLE 22.
SURFACE WATER AND GROUNDWATER BASELINE DATA
oo
o
Heavy
Loading
Sample Location Plot M-3
Date Sampled
PH
Conductivity
Temperature
HCO3 - (ppm)
NO3 - (ppm)
Fe (ppm)
Mg (ppm)
Na (ppm)
Ca (ppm)
3/25/81
6.8
(ymhos) 80
(°C) 15.0
98.2
5.0
0.8
8.0
12.5
20.5
Plots
M-2, H-l
H-2
3/25/81
6.9
60
15.5
80.3
.50
2.5
5.5
12.5
15.0
Plots
C-l, C-2,
M-l
3/25/81
7.15
65
14.0
56.2
1.96
-
-
-
-
Spring
3/25/81
6.4
45
14.0
74.9
1.07
1.5
6.0
12.0
15.0
Cattle*
Trough
3/25/81
6.6
150
16.5
8.4
2.45
1.
15.5
30.0
12.5
Deep Well
5/6/81
6.2
**
18
38.6
2.93
o:.5
8.3
• -
-
Scott Creek
5/6/81
7.4
**
14
67.8
-
0.2
3.5
• -
-
*possible salt lick contamination
**meter malfunction
-------
to provide detailed subsurface information about the geology
and hydrology of the site. The shallow wells were located
downslopi .from each test plot. They extend through the
terrace deposits and several feet into the underlying
bedrock, to total depths of about 7 to 15 m.
Most of the shallow wells remained dry throughout the
project, even though seep springs appeared in nearby
gullies during high rainfall periods. In 1982, water
appeared intermittently in several wells and was sampled.
As might be expected, the composition of the well
water was similar to that of water in the nearby seep
springs. The seep spring was developed and sampled in
1982 and 1983 until it was destroyed by cattle before the
1984 f.ield season. Water from the spring and shallow wells
generally exhibited lower NO,, Ca, and total Cr concentra-
tions than soil water directly below the heavily loaded
test plots.
Deep Monitoring Well
The deep monitoring well was installed through bedrock
of a depth of approximately 100 m. Water levels in the well
fluctuated between about 28 and 31 m below the ground surface,
The well was sampled annually or biannually in 1982, 1983
and 1984. No evidence of contamination with chromium or
nitrate from the test site was detected.
Surface Runoff
Surface runoff samples were collected during 1982 and
81
-------
1983 from the berms below the plots. Samples ha'd nitrate
concentrations ranging from 3.3 to 110 mg/liter with the
i
highest values occurring in water below Plot M-3. N03
concentrations sharply decreased during the season,
reflecting their high mobility. Ca and Mg concentrations
were greater than background in runoff from both dehairing
and mixed sludge plots, although concentrations in runoff
were generally lower than those in soil water.
Total Cr concentrations between 1 to 20 yg/liter were
measured in filtered runoff samples and concentrations
between 1 and 100 yg/liter in unfiltered, digested samples.
The higher concentrations in the digested samples suggest
that most of the Cr in surface runoff was transported as
adsorped chromium on soil particles.
The mass of Cr transported by surface water can be com-
puted by estimating the volume of sediment in the retention
basin below Plot M-3 (approximately equivalent to the average
concentration in the upper soil layer, about 2100 mg/kg (See
Table 12)). Using an average bulk density for the soil of
1.3 gm/cm , the mass transported from Plot M-3 between 1981
and 1984 is approximately 2.4 gm/m or about 0.5% of loading.
Soil Water
Soil water samples were collected at various depths in
the test plots using porous cup samplers. Water was sampled
between December and May during each project year except the
8.2
-------
first. Soil water samples were collect by first applying
a vacuum of 80 centibars to the samplers and allowing them
to collect water for 7 days. The water was then removed,
and no vacuum was placed on the samplers for the next 7
days to allow natural soil water gradients to re-establish.
The sludge application introduced high concentrations
of major cations and nitrates into underlying soil waters
(20). At the beginning of the monitoring period, concentra-
tions of Mg, Na, and Ca, in water from all of the monitored
plots were significantly higher than concentrations in water
collected from the control plot (Table 23). With the excep-
tion of Plot M-2, Cr concentrations in soil water from plots
that received chrome-sludge applications were also measurably
higher than control plot levels. All concentrations, except
Ca, decreased rapidly in January and February each year to
levels close to background by mid-March. The contaminants
were either rapidly flushed through the soils or removed
from solution by reactions with the soil.
The most detailed soil water sampling was conducted
between December 1982 and June 1983. During this period,
soil water samples were collected at two-week intervals
from three replicate soil water sampling clusters in each
of the plots receiving the greatest amount of sludge loading,
Plots C-2, M-2, H-2 and M-3 (Figure 4). Plot M-3 was
monitored most extensively and the results discussed below
focus on data from the three sampling clusters in this plot
83
-------
TABLE 23. TYPICAL SOIL WATER ANALYSES, DECEMBER 19, 1982
Location
Plot M-3
30 cm
61 cm
91 cm
122 cm
Plot M-2
61 cm
Na
(mg/1)
550
540
410
230
220
Ca
(mg/1)
540
80
120
430
530
Mg
(mg/1)
56
94
180
120
110
Total Cr
(mg/1)
43
23
14
15
<1 .0
Plot C-2
30
61
Plot H-2
61
122
Control
30
61
91
cm
cm
cm
cm
Plot
cm
cm
cm
280
120
ND*
100
ND
61
ND
160
140
ND
95
6.9
21
6.9
120
95
ND
100
ND
34
14
25
5
o
<]
*No data.
84
-------
(Figure 6). As shown schematically in Figure 10, each
cluster consisted of porous cup samplers at 30, 61, 91, and
122 cm depths, a neutron access tube to measure soil moisture,
and a group of tensiometers to monitor matric suction.
Cr concentrations in soil waters from Plot M-3 decreased
from maximum values of 35 to 45 yg/liter in December 1982
to minimum values of less than 10 yg/liter in March 1983
(Figure 11). Concentrations increased slightly in April and
May 1983 at two of the replicate monitoring clusters (M-3A
and M-3B). Although these higher concentrations late in
the season could results from the samplers drawing water
from progressively smaller pores as the soil moisture
decreases, the trend is difficult to interpret. It could
also be a figment of chemical reactions that occurred in
the porous cup samplers.
At the end of the 1982-1983 field season, the soil
water samplers were removed from the field and leached in
the lab. Between .12 and .03 mg of Cr and 83 to 623 mg of
Fe were found in leachate from individual samplers (20).
Chromium apparently co-precipitated with Fe while soils
were saturated and in a reducing chemical environment.
The reaction probably occurred sometime after the last
of the samplers was installed on January 30, 1983, because
similar amounts of Cr were leached from all the samplers
85
-------
MONITORING SOIL WATER
DEPTH SAMPLERS
NEUTRON
PROBE "REPRESENTATIVE
TENSIO- ACCESS DEPTH INTERVAL
METERS TUBE (cm) around
30 cm
60 cm
91 cm
122 cm
152 cm
-
W
^
t
J
A surrace
A*! s 45 cm
*
t
Az2 = 30 cm
y
t
Az3 = 30 cm
^
t
Az-i = 30 cm
4,
t
^25 = 30 cm
y
Figure 10. Schematic diagram of typical monitoring cluster in Plot M-3,
86
-------
40
20
M-3A
^ — -\
— — 30 cm
-- 60 cm
---- 90cm
--- 120cm
\
40
80
120
160
40
CD
3
o
"co
"o
20
M-3B
A
/ \
\ / \
40
80
120
160
40
20
- \
M-3C
\
0 40 80 120 160
Time (days after Dec 19)
Figure 11. Total chromium concentrations in soil water at M-3A,
M-3B, and M-3C. Analytical precision is approximately + 10%.
87
-------
regardless of the time of installation. Therefore measured
concentrations after this date may be less than actual
concentrations.
Figure 12 shows profiles of measured Cr concentrations
for the early part of the 1982-1983 field season, before
the soils saturated and probably before co-precipitation
in the samplers began. Concentrations in all three pro-
files, at all depths, are highest on the first date of
sampling and decrease over time. The initial Cr in the
profile apparently moved into the soil during storms in
late November and early December, 1982 after the sludge
application in October. The decrease in concentrations
at all depths indicates that the source of mobile chromium
at the ground surface during the monitoring period was
very small to zero. The Cr appears to have been intro-
duced into the soil profile by a transient source that
decreased rapidly after the sludge application and initial
storms.
A second observation that can be made from Figure 12
is that the measured Cr concentrations in the profiles are
highly variable with depth. This variability may reflect
the hetergeneity of the soil conditions or contamination
of several of the soil water samplers.
CHROMIUM FLUX
The rate of migration of Cr through the soil profile
can be estimated from the computed percolation flux and
88
-------
Dec 19
Jan 3
Jan 16 Jan 30 Feb 13
oo
10
30
£ 60
90
120
M-3A
0
20
40
30
60
90
120
M-3B
0 20 40
Total Cr (ug/o
30
60
90
120
M-3C
0
20
40
Figure 12 • Profiles of measured chromium concentrations. Analytical precision is approximately + 10%.
-------
measured Cr concentrations in 1983. Since measured concen-
trations after January 30 are probably lower than actual
concentrations because of co-precipitation in the samplers,
the computed rates of transport after this date underestimate
the actual flux. Nevertheless, relative values' are probably
correct and provide an order of magnitude estimate of flux.
The computed transport rates also depend on reliable moisture
flux estimates. Therefore, contaminant fluxes were computed
only for the relatively uniform upper 90 cm of monitoring
nests M-3A and M-3B.
k
The chromium flux, M. , defined as the mass of chromium
leaving a soil interval during a specified time interval, At,
may be approximated as the product of the measured concentra-
k
tion, c. , at sample point i during time interval k and the
k
vertical percolation flux, v. :
The cumulative chromium flux, CM., f or i time intervals is
CM. =J Wk • Atk) .
1 k=l
The mass of Cr retained in a soil interval is the difference
between the mass entering and leaving:
k k k
. RM. = M* - M^
i,
where RM. is the mass of Cr retained in soil interval i durig
time interval k. The cumulative mass, CRM., retained in
-------
interval i for £ time intervals is
1 k k
CRM. = E (RM. . At )
1 k=l X
Computed cumulative Cr fluxes, CM., at M-3B and M-3C
are shown in Figure 13- As expected, transport is greatest
during periods of high moisture flux after large storms.
For example, fluxes increase dramatically after a series
of storms between January 19 and 24, 1983.
-4 2
Approximately 6 to 8 x 10 mg/cm Cr left the upper
45 cm of soil between December 1982 and March 1983. At both
sampling nests, the flux rate decreased with depth, indicating
a net loss of Cr from solution as water flowed vertically
downward through the soils. Figure 14 shows the amounts of
Cr retained within intervals of the soil profile. At M-3C,
the amount of retention is greater in the 45-75 cm interval
than in the underlying 75-106 cm interval with about 68% of
the total mass leaving the 0-45 cm interval retained in the
two lower intervals. Nest M-3B exhibits about an equal amount
of retention in the two lower intervals and approximately 52%
of Cr from the upper layer is retained above the 106 cm depth.
In both cases, the computed amount of Cr transported past the
-4 2
106 cm depth is in the range of 2.5 to 3.0 x 10 mg/cm .
This is equivalent to a total flux over the entire quarter-
acre plot of about 3 g, less than 0.1% of the total Cr loading,
91
-------
45. cm
75 cm
106 cm
X
3
CO
CO
CO
8
6
O 4
0 20 40 60
80
100
M-3C
0 20 40 60 80 100
Time (days after Dec 18)
Figure 13 Cumulative chromium flux at M-3B and M-3C.
(December 18, 1982)
92
-------
o
T—
X
CVJ
E
o
*-.
O)
CO
°O
-------
HYDROLOGICAL CONCLUSIONS
Several conclusions can be made from field study results.
Soil Water Flux
Soil water percolation at the test site varied an order of
magnitude between years of high and low rainfall. Use of the
zero flux plane concept (Reference 19} gives reasonable esti-
mates of percolation when weekly measurements of moisture con-
tent and matric suction are used.
Chromium Mobility
Chromium exhibits very low mobility when applied to the
ground surface in tannery sludges. Less than 0.1% of the total
Cr loading was found to leave Plot M-3 in soil waters during the
1983 field season. The small amounts of Cr that leave the upper
45 cm of soil are readily removed from solution in underlying
soil layers. In addition, less than 0.5% of the Cr loading was
transported by surface runoff from Plot M-3 between 1981 and 1984,
Other Sources of Potential Contamination
Although Cr does not appear to be a potential groundwater
contaminant from the sludge applications, land treatment intro-
duces high concentrations of nitrates and major cations into soil
waters that could enter adjacent aquifers or adversely effect
vegetation.
Monitoring Uncertainty
Measured values of Cr in soil's and soil waters contain large
uncertainties. In the case of soils, these uncertainties are
introduced primarily by soil variability and insensitivity in
chemical analysis procedures. Thus analysis of the chemical com-
94
-------
position of soils alone are not adequate to detect small changes
in contaminant concentrations or to measure small flux rates.
On the other hand, estimates of contaminant flux using a neutron
probe, tensiometers, and porous cup samplers must be interpreted
with extreme care. Besides potential errors in moisture flux
computations and errors created by changes in the soil water
flow because of the vacuum at the samplers, chemical reactions
in the cups may significantly alter the composition of soil
water samples.
95
-------
SECTION 7
FEASIBILITY ANALYSIS
ENVIRONMENTAL CONSTRAINTS ON LAND TREATMENT:
TANNERY WASTEWATER SLUDGES
Greenhouse studies by Wickliff et al. (3) at the
US EPA Corvallis Environmental Research Laboratory con-
cluded that chromium "tannery wastewater sludge may be
applied to agricultural land as a fertilizer amendment
without adversely affecting soil chemical properties."
Field plot studies in this project have extended and
confirmed the constraints on surface land treatment of
trivalent chromium-containing tannery wastewater sludges.
Recognizing certain practical constraints, both the Cor-
vallis greenhouse study and this field plot study have
demonstrated that land treatment of chromium tannery
wastewater sludges is feasible.
Nitrogen
Leather meals from chromium tanned leather wastes
and also chromium tannery wastewater sludges are commer-
cially utilized as a source of proteinaceous nitrogen.
The slow mineralization of this proteinaceous nitrogen in
the soil provides available nitrogen for plant growth.
Table 11 summarizes the estimated available nitrogen
applied to the seven test plots.
96
-------
Plot M3 had an estimated, available nitrogen of
406 kg/ha in 1984 (Table 11). The soil water nitrate-
nitrogen data from this plot in March, 1985, are shown
in Table 21. These soil water levels of nitrate-nitrogen
are greater than the usual ground water levels; the
relationship between ground water and soil water levels
is unknown. Furthermore the soil water levels are two-to
seven-fold greater than the Maximum Contaminant Level for
nitrate-nitrogen in drinking water. Plot M3 was the
maximum loading plot; the estimated available nitrogen
in 1984 was three to six times the estimated available
nitrogen levels in the three minimum loading plots. Hence
these.nitrate-nitrogen data in Table 21 from plot M3
demonstrate the first constraint on the land treatment
of chromium-tannery wastewater sludges. The loading rate
for the sludge must be limited by the available nitrogen
demand of the crop grown on the treatment land. More data
are required to establish mineralization rates on tannery
sludges.
Salt Effects
Table 5 shows that the tannery wastewater sludges have
high salt contents. This is especially true for the hair-
burn sludges. The mean sodium values were 4 percent on
the dry basis for the hair-burn sludges and 2.7 percent
on the dry basis for the chromium sludges.
Table 14 presents Sodium Adsorption Ratio (SAR) and
Electroconductivity (EC) data for the eight plots. The
97
-------
SAR data have not in general reached levels associated
with poor soil physical conditions and water permeability
problems. However, the two plots receiving only the
hair-burn sludges have shown a two-unit drop in pH (Table
15).
Grass germination and growth was poor on the test
plots, especially on the hair-burn plots and the mixed
sludge plots. Intrusion of native weeds especially wild
radish and thistle occurred. It is not known whether the
weed intrusion reflected inadequate seed selection and the
effect of climatic conditions at the seeding times or the
salt content of the sludges. However, the overall project
results indicate that salt effects are a limiting factor
that must be considered in land treating the sludges,
especially the high sodium hair-burn sludge. This con-
straint must be considered in relationship to the
anticipated plant growth on the site as well as the
climatic conditions.
Chromium
Plots C1 and M1 received the lower level of trivalent
chromium addition of 2240 kg/ha. Two double level plots
(C2 and M2) and one triple level plot (M3) received the
appropriate higher levels of chromium application. The
data secured in this study indicate that the added chromium
remained primarily in the topsoil without any apparent
oxidation to hexavalent chromium.
98
-------
The data in Table 16 do not demonstrate either
significant transfer of the chromium across the root
barrier or transfer of the chromium to the grass tissue
(Table 18). Chromium recovery estimates (based on the
soil analyses in comparison to the estimated level of
chromium application) was incomplete; recovery was 74
percent from plot C2 and 60 percent from plot M3. The
available data showed limited penetration of the added
chromium below the top 30 centimeters of the soil profile.
The surface runoff data indicated that limited chromium
movement was associated with soil particle movement. In
the triple-loaded plot M3, the total chromium flux was
estimated at less than 0.1 percent of the total chromium
loading.
Overall, chromium did not appear to be associated with
environmental problems at the levels of trivalent chromium
addition used in this study. As expected, a buildup of
chromium occurred in the topsoil of all test plots. While
this study indicates land treatment of chromium containing
tannery sludges to be potentially feasible and environmentally
acceptable, the most feasible level for application could not
be established by the data generated.
SITE CLOSURE
The main objective of this five-year project was the
characterization of the technical and of the environmental
issues concerned with the utilization of land treatment
99
-------
technology for the management of tannery wastewater
sludges. Tannery operations convert proteinaceous
hide substance into leather, usually by the trivalent
chromium tanning process. Hence, the total Kjeldahl
nitrogen and the chromium contents of the wastewater
sludges were major parameters evaluated in this project.
Chromium Content of Soil
Chromium is widely distributed in the soils of the
United States. Conner and Shacklette (21) reported soil
chromium data which varied from 1 to 1500 ppm (mg/kg).
More than 3000 samples were analyzed; all soil samples
from all soil horizons contained chromium. Allaway (12)
reported common chromium levels in soils of 100 mg/kg, with
a range of 5 to 3000 mg/kg. Swaine and Mitchell (22) found
that soils derived from serpentine rock sources were
especially rich in chromium:
Horizon A 3500 ppm (mg/kg) total chromium
Horizon B 2000 ppm (mg/kg) total chromium
Horizon C 3000 ppm (mg/kg) total chromium
Shacklette, Hamilton, Boerngen and Bowles (23)
reported on 492 soil sample analyses for chromium from
B-horizon soils in the Western United States. Their data
are summarized as follows: geometric mean 38 ppm (mg/kg)
with a range of 3 to 1500 ppm (mg/kg). The background data
secured on the soils at our project site showed these total
chromium contents (Table 1 ):
100
-------
Chromium - mg/kg
Depth Mean Range of Four
0-30 cm 39 19-50
30-60 cm 38 29-49
60-90 cm 41 24-49
Thus, the soil at our project site contained chromium
equivalent to the geometric mean level found in B-horizon
soils in the Western United States.
The total added chromium levels, assuming all of the
added chromium remained in the top 15 centimeters of soil
(bulk density of 1.3) was:
Plot mg/kg Chromium
Cl 1100
Ml 1284
C2 2130
M2 2310
M3 3530
Soil samples (top 15 centimeters) were taken in September,
1983 (approximately one fifth of the total loading had not
then been applied to plots Ml, M2 and M3). These surface
soil samples were carefully composited and analyzed by
EPA/Ada, SCS and TCA laboratories. These data are
summarized as follows:
mg/kg Chromium
Plot Dry Basis
Cl
Ml
average
640
1390
range
590- 700
1240-1540
101
-------
mg/kg Chromium
Plot . Dry Basis
C2
M2
M3
average
1620
1190
2320
r
138
108
201
range
While the analytical data on the. soil samples have shown
significant sampling variation and variability reflecting
the difficulties of recovery of the chromium incorporated
in the soil matrix, the overall data clearly show a buildup
of total chromium and that the total chromium applied pri-
marily remains in the topsoil.
The soil core data below the topsoil did not indicate
a significant buildup of total chromium within the 30-90 cm
depth.
Chromium - mg/kg
Background May, 1984
30-60 cm 29-49 11- 73
60-90 cm 24-49 33-102
Combined with the topsoil data given in the previous para-
graph, however, these data do indicate the potential for
some downward migration of the applied total chromium.
Nitrogen
Soil stores of nitrogen have been reported by
Schreiner and Brown (24) to vary in the top meter of
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soil from 4500 kg/ha to 20,000 kg/ha (excluding peat).
They report a value of 18,000 kg/ha as the nitrogen
store of prairie topsoil; this is equivalent to 1380
mg/kg of soil-N (assuming bulk soil density of 1.3).
Stout and Burau (25) report a value for California
grassland of 9050 mg/kg for soil nitrogen stores. The
background total Kjeldahl nitrogen content at our field
site was found to be:
TKN - mg/kg
Depth
0-30 cm
30-60 cm
60-90 cm
Mean
2200
900
600
Ranc
1700 to
800 to
500 to
je_
3100
1000
800
The cumulative total nitrogen applied to the seven
plots (assuming application into the top 15 centimeters of
soil with a bulk density of 1.3) was:
Plot TKN - mg/kg
H1 1700
H2 3620
C1 840
M1 1250
C2 1540
M2 2450
M3 3300
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The top 15 centimeters of the plot soils were
sampled for analysis in September, 1983. These data
for total Kjeldahl nitrogen (expressed on the dry weight
basis) were:
Plot TKN - mg/kg
Control 4550
H1 4820
H2 7780
C1 3760
M1 4870
C2 5820
M2 4430
M3 5860
At that time, all sludge applications had been made to
plots H1 and H2 and to plots C1 and C2; ninety percent
of the total nitrogen loading had been applied to plots
M1, M2 and M3. The data in the above tabulations
demonstrate some increase in surface soil TKN concentra-
tions; however, this increase does not appear to be sig-
nificant in comparison to the soil nitrogen stores reported
in the literature. The increase may be important, however,
due to an increase in the potential for downward migration
of nitrate-nitrogen.
Soil water samples at a depth of 61 cm (2 ft) were
taken in plot M3 (the plot with the maximum total tonnage
of added sludge) at dual two-week intervals in March
104
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1985, from three different sites within plot M3 (Table 21).
The median of the thirty soil water nitrate-nitrogen values
was 42 ppm (mg/1) with a range from 11 to 219 mg/1.
The mineralization of the proteinaceous, Kjeldahl
nitrogen in the tannery sludges is a major source of this
level of nitrate-nitrogen in these soil water specimens.
After the final sludge addition to plot M3 in 1983, its
available nitrogen content was 406 kg/ha (Table 11, 1984
estimated value).
The high available soil nitrogen in plot M3 after
its final sludge loading as well as the resultant
mineralization of the sludge proteinaceous nitrogen
would predictably result in high soil water nitrate-
nitrogen concentrations. The median value of 42 ppm
(mg/1) is four-fold the drinking water Maximum Contaminant
Level (10 mg/1 nitrate-nitrogen).
The soil water nitrate-nitrogen data indicate that
organic nitrogen mineralization rates should be a prime
consideration when determining acceptable tannery sludge
application rates for land treatment systems.
FINAL SITE CLOSURF
Since the seven experimental plots with a total sur-
face area of 1.3 hectares do not contain soils which are
significantly atypical relative to either total chromium
or soil water nitrate-nitrogen concentrations, closure of
the site has been limited to pasturage restoration. All
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hydrology instrumentation has been removed. The land owner
permitted the fencing, wells and concrete run-off flow
dissipation devices to be left on the site.
Disturbance of the native grass cover on the test
plots during sludge application and plot cultivation
permitted excessive growth of weeds indigenous to the .
site, especially wild radish and thistle. The existing
weedy growth on the test site during summer 1985 was mowed
and the soil of the plots thoroughly cultivated. This
process aided in the creation of surface soil uniformity
and correction of the area heterogeneity of the topsoils
with regard to trivalent chromium and other inorganic salts
added to the topsoils during the sludge additions in the
1981-1983 period. This process was conducted with the
guidance of the county agricultural advisor and the land
owner.
The berm across the upper side of the test plots was
left in place and repaired where necessary to prevent plot
erosion during the heavy winter rains. The other plot areas
were left approximately in their original contours.
106
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