EPA-600/2-78-018
February 1978
Environmental Protection Technology Series
SEWAGE SLUDGE ENTRENCHMENT SYSTEM
FOR USE BY SMALL MUNICIPALITIES
'Jf, >Kl •»
Municipal Environmental Research Laboratory
Office of Research and Development
*,*?«%*?> v . * _ r , , ,
U.S. Environmental Protection Agency
Jfcfilncinnat^Ohio 45268"
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are: :
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies j
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports ;
This report has been assigned to the ENVIRONMENTAL PROTECTION TECH-
NOLOGY series. This series describes research performed to develop and dem-
onstrate instrumentation, equipment, and methodology to repair or prevent en-
vironmental degradation from point and non-point sources of pollution. This work
provides the new or improved technology required for the control and treatment
of pollution sources to meet environmental quality standards.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA--600/2-78-018
February 1978
SEWAGE SLUDGE ENTRENCHMENT SYSTEM
FOR USE BY SMALL MUNICIPALITIES
by :
J. M. Walker, L. Ely, P. Hundemann, N. Frankos and A. Kaminski
Biological Waste Management and Soil Nitrogen Laboratory
•Agricultural Research Service
Beltsville, Maryland 20705
Interagency Agreement No. EPA-IAG-D4-0510
Project Officer
K. Dotson i
Wastewater Research Division
Municipal Environmental Research Laboratory
Cincinnati, Ohio 45268
This study was conducted
in cooperation with
U.S. Department of Agriculture
Beltsville, Maryland 20705
MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT ;
U.S. ENVIRONMENTAL PROTECTION AGENCY '
CINCINNATI, OHIO 45268
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DISCLAIMER
This report has been reviewed by the Municipal Environmental Research
Laboratory, U.S. Environmental Protection Agency, and approved for publica-
tion. Approval does not signify that the contents necessarily reflect the
views and policies of the U.S. Environmental Protection Agency. Mention of
trade names or commercial products does not constitute endorsement or recom-
mendation for use by either the U.S. Department of Agriculture or the U.S.
Environmental Protection Agency.
11
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FOREWORD ;
The Environmental Protection Agency was created because of increasing
public and government concern about the dangers of pollution to the health
and welfare of the American people. Noxious air, foul water, and spoiled
land are tragic testimony to the deterioration of our natural environment..
The complexity of that environment and the interplay between its components
require a concentrated and integrated attack on the problem.
Research and development is that necessary first step in problem solu-
tion and it involves defining the problem, measuring its impact, and search-
ing for solutions. The Municipal Environmental Research Laboratory develops
new and improved technology and systems for the prevention, treatment, and
management of wastewater and solid and hazardous waste pollutant discharges
from municipal and community sources, for the preservation and treatment of
public drinking water supplies, and to minimize the adverse economic, social,
health, and aesthetic effects of pollution. This publication is one of the
products of that research; a most vital communications link between the
researcher and the user community.
Development of safe economical methods of disposing of sludges produced
by small wastewater treatment plants is an important environmental need.
This report describes a method of incorporating sludge below the surface soil
with conventional agricultural or light construction equipment.
Francis T. Mayo
Director
Municipal Environmental Research
Laboratory
111
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ABSTRACT
An economical method was developed and is described by which smaller
municipalities can entrench dewatered sewage sludge (15-25% solids). By this
method, 3 to 48 tons of freshly dewatered sewage sludge per day can be
entrenched without problems of odor or surface water runoff. Equipment and
personnel include a tractor/loader/backhoe, dump or concrete mixer trucks,
and machine operators and truck drivers. Trenches are dug 60 cm wide x 60
cm deep x 60 cm apart (2x2x2 ft). The actual incorporation time for 12
tons of dewatered sludge at the entrenchment site is one hour. The estimated
hired cost of sludge incorporation, including equipment, personnel and
hauling 32 km (20 miles) each way, and drainage, monitoring and final land
cultivation is less than $15.00 per dewatered ton. This estimate does not
include land cost.
Sites, having previously been entrenched with sludge, can be retrenched
with sludge when previously entrenched sludge has dewatered sufficiently.
Minimal time after initial entrenchment is 2 years.
Liming sludge prior to dewatering and entrenchment is recommended to
reduce the potential for metals moving through soils and becoming more avail-
able to plants. Trenching is not appropriate in some prime agricultural land
because of the subsoil brought to the surface and the relatively large
amount of heavy metals being applied. Entrenchment is most appropriate when
sludges cannot otherwise be land spread because, in comparison to lower-rate
surface application procedures, entrenchment is a resource-wasteful practice
with potential for pollution of groundwater by nitrate nitrogen leaching.
The Agricultural Research Service has conducted this research demonstra-
tion study in cooperation with the Environmental Protection Agency during
FY 1975 under Interagency Agreement No. EPA-IAG-D4-0510.
xv
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CONTENTS
5
Foreword .j ...;... 111
'i
Abstract iv
Figures .] vi
Tables .; viii
:i
Acknowledgements .; ix
!J
1. Introduction . . .| 1
i
2. Conclusions ; 2
3. Recommendations • . 4
•!
4. Sludges, Sites and Equipment j 5
5. Sludge Entrenchment J 24
In an unsludged site 24
In a previously sludge entrenched area . . . .| 32
Sludge handling and trench filling . 32
Soil conditions, weather and site drainage . J 40
Seeding . J 46
6. Environmental Risk, Its Management and SuggestedjMonitoring . . 52
Introduction . . .- , 52
Environmental risks of trenching and their management .... 52
Nitrogen . • • • 52
Heavy metals .! 53
Pathogens . . .! 54
Organics i ....... 54
Monitoring j 54
7. Costs ] 57
Sludge hauling and entrenchment , 57
Drainage > 63
Land 1 ....... 63
Monitoring ,1 ....... 63
Total . 63
References . . . » • 70
v
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FIGURES
Number
1. Location and details of plots receiving different sludges
in different soil types.
A. Aerial photo overview of entire plot area showing in-
dividual plot locations VI to XI 8
B. Schematic of previously entrenched area showing old ;
plots I to V and their relationship to new entrench-
ment plots VI, VIII, IX and X. 9
C. Details of plot VI showing sludge placement in loamy-
sand 12
D. Details of plot VII showing sludge placement in fine
loamy sand (clay near surface) with drainage 14
E. Details of plot VIII showing sludge placement in fine
loamy sand (clay near surface) 16.
F. Details of plot IXa and IXb showing sludge placement
in areas (old area la and Ib) previously entrenched
(May 1973) with digested low-lime sludge j. . . 18
G. Details of plot X showing sludge placement in paral- i
lei and perpendicular in an area (old area Illb)
previously entrenched (May 1973) with raw high-lime
sludge '...;.. ... 19
H. Details of plot XI showing sludge placement in poor-
ly drained fine loamy sand (clay layer near surface). .... 21
2. Schematic showing details of sludge entrenchment proce- ,
dure 25
3. Sludge entrenchment
A. Obtaining sludge from (9.2 m3) dump truck with TLB. ..;... 26
B. Transporting sludge from truck to trench with TLB. ...... 27
C. Filling trench segment A-l with sludge using TLB. ...... 28
D. Beginning to dig trench segment A-2 beside sludge- ',
filled trench segment A-l with TLB. . . . '.. . . 29
E. Continuing digging trench segment,A-2 and covering
sludge-filled trench segment with spoil soil A-l
using TLB . . . . 30
VI
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FIGURES, continued
Number
F. Covering sludge-filled trench segment A-n with spoil
soil from trench segment A-l using TLB •. 31
4. Sludge entrenchment in an area entrenched with sludge
2.5 years earlier. • '
A. Digging trench 60 cm wide x 60 cm deep at right
angles to previously entrenched sludge 36
B. Exposed previously entrenched sludge. . . ; . . 37
5. Sludge hauling and discharge into trenches from con-
crete mixer truck. ;
A. Preparation for sludge discharge into open trench. 38
B. Sludge discharge into open trench 39
6. Sludge hauling and unloading with TLB from 1.5 m3 |
dump truck.
A. Using a TLB with bucket too large for dump bed. 41
B. Using a TLB with smaller bucket, permitting direct
unloading and minimum spillage > . 42
7. Sludge entrenchment in a snow storm. j
A. Unloading 9.2 m3 dump truck with TLB . L ....... 43
B. Filling trench with sludge using TLB. 44
8. Peristalic-type pump (Challenge 900) being used for
pumping dewatered sludge through a hose from tank (
truck to trenches at Maryland Environmental Service
entrenchment site 45
9. . Drainage of clay soil with high water table. !
A. Digging trench for preliminary drainage. ........... 47
B. Water draining out of trench ' 48
C. Installation of fiberglas-covered slotted flex-
ible 10 cm-diameter plastic drain tile, prior to
covering with soil 49
D. Fiberglas wrapping over flexible slotted plastic
drain tile by Advanced Drainage Systems CADS). . 50
vn
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TABLES
Number Page
1. Sludge Properties 6
2. Soils and Water Table in Plot Areas ...... 22
3. Equipment 23
4. Sludge Incorporation 34
5. Applications of Fertilizer, Lime and Grass Seed 51
6. Suggested Monitoring for Sludge Entrenchment ....... 56
7. Actual Times Required for Sludge Hauling and Entrenchment . . '. . . 58
8. Estimated Sludge Entrenchment Costs - Rental (1975). .„..;.. 59
9. Estimated Sludge Entrenchment Costs - Purchase and
Self-Operation (1975). . . . t 61
10. Estimated Sludge Entrenchment Costs - Totals for
Purchase and Self-Operation vs Rental (1975) 64
11. Estimated Drainage Costs (1975). 65
12. Land Finishing Costs (1975) . 66
13. Estimated Monitoring (Analytical) Costs (1975)....... 67
14. Costs for Analytical Determinations (1975) 68
15. Estimated Total Entrenchment Costs including Site Preparation,
Hauling, Trenching, Revegetation and Monitoring (1975)....... 69
Vlll
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ACKNOWLEDGMENTS
We gratefully acknowledge the considerable efforts of the many individ-
uals and organizations who have contributed significantly to this project.
In particular, we acknowledge the help and assistance of the U.S. Environ-
mental Protection Agency's Municipal Environmental Research Laboratory in
Cincinnati and Mr. Ken Dotson of that Laboratory, the assistance of the
District of Columbia in preparing and providing sludge and lending equipment
and the assistance of the Maryland Environmental Service in transporting
sludge to our entrenchment site. !
Cooperating scientists and support personnel in ARS who have also
contributed to this work include R. L. Chaney, J. B. Munns, H. Wagner and
L. J. Sikora. Technicians employed by the Maryland Environmental Service who
also have contributed to this work have been T. L. Lathan, M. C. White and
E. Levesque. ,
xx
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SECTION 1
INTRODUCTION i
!
Entrenchment is a feasible.method'for simultaneously disposing of
dewatered sewage sludge (15-25% solids) and improving marginal land for
plant growth (7, 8). Trenching is an appropriate system to use when surface
application of sludge at fertilizer rates is not feasible, e.g., with metal-
polluted, malodorous or undigested sewage sludge, when sufficient land and
an alternative like composting is not available or during inclement weather.
The trenching system was originally developed for use by large municipal-
ities. The procedure involved use of large equipment, considerable site
preparation and extensive monitoring. Its major constraint apparently was
the possible contamination of surface and underground water with nitrate
nitrogen. ; .
'I
The Agricultural Research Service (ARS) and the U. S>. Environmental
Protection Agency (EPA) jointly initiated a research demonstration study to
develop a trenching system for use by small municipalities (4,000-100,000
population yielding 3 to 48 dewatered tons of sludge per day). The close
cooperation of the Maryland Environmental Service and of the District of
Columbia was also inherent in this work. These two groups have been using
large-scale trenching as a means of sewage sludge disposal, and they are
maintaining a continuing interest in studies on this procedure. The goal
for this trenching system was that it be clean, safe, efficient, operable
under essentially all weather conditions and of reasonable cost. For gen-
eral applicability, a trenching system must work with different sludge
types, soil textures, soil drainage conditions and should utilize readily
available equipment. j
The cooperative research between ARS and EPA was performed under Inter-
agency Agreement No. EPA-IAG-D4-0510. i
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SECTION 2
CONCLUSIONS
Sewage sludge entrenchment is an economical method by which small
municipalities can dispose of their solid residues from wastewater treat-
ment. A method is described for entrenching 3 to 48 tons per day of freshly
dewatered sludge (15-25% solids) without problems of odor, surface water
runoff or ground and surface water pollution. Trenches are dug 60 em wide
x 60 cm deep x 60 cm apart and entrenched sludge is covered with soil to an
average depth of 30 cm using a tractor/loader/backhoe. Sludges were hauled
successfully in dump trucks (1.5 to 9.2 m3 capacity) or in concrete mixer
trucks (8.4 m3 capacity) and easily transferred to trenches by the tractor/
loader/backhoe or directly, respectively.
Costs were estimated for trenching sludge based upon actual experiences
during the Beltsville pilot study. Costs for trenching 12 to 48 dewatered
tons of sludge per day, assuming a 32 km haul distance each way, were esti-
mated to be under $15.00 per dewatered ton (not including land costs) wheth-
er hauling and entrenchment was accomplished on a rental or purchase-self-
operation basis. About 50% of the $15.00 cost was estimated to be for
hauling and about 10% for draining the area where necessary, monitoring,
leveling and reseeding after entrenchment. Estimated costs for a 3 ton per
day operation were considerably higher because times were figured on an
estimated minimum unit basis, rather than on the much shorter times actually
required for the operations. If arrangements could be made for use of
equipment and personnel more nearly based upon the actual operation time,
costs for a 3 dewatered tons of sludge per day operation would also be .about
$15.00 per dewatered ton.
Sites, having previously been entrenched with sludge, can be retrenched
with sludge when previously entrenched sludge has dewatered sufficiently.
Minimal time after initial entrenchment is 2 years.
Entrenchment of raw and anaerobically digested sewage sludge was done
successfully under all summer a.nd winter weather conditions encountered in
Beltsville by careful selection, of soil types, drainage where necessary
(needed only under special high water table conditions) and use of proper
equipment. Temporary storage of sludge when raining or snowing would be a
desirable backup.
Anaerobic digestion of these solid residues is not necessary for en-
trenchment, but an addition of lime, handling promptly in a fresh state
and other suitable conditioning and handling is desirable to prevent poss-
ible odor problems during hauling and handling prior to covering with soil.
-------
Liming sludge in soil prior to dewatering and entrenchment also helps keep
heavy metals more immobilized and less available to plants.
Monitoring of a sludge entrenchment site should be the minimum necessary
to detect potential harmful effects in the environment. Monitoring data
should be readily available and acted upon when it warns that additional
steps are needed to minimize environmental degredation. A simplified monitor-
ing program is recommended. |
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SECTION 3 ; , •
RECOMMENDATIONS
Entrenchment of sewage sludge is recommended for use when surface
application is not feasible, e.g., with metal-polluted, malodorous or
undigested sewage sludge, when sufficient land or an alternative like
composting is not available or during inclement weather.
Entrenchment of sludge in prime agricultural land should be avoided
because the surface soil becomes buried during the process by an approximate
30 cm layer of a subsoil-surface soil mixture.
Liming of sludges just prior to dewatering and entrenchment is recom-
mended to reduce the potential for problems with odor, to reduce levels of
pathogens and to reduce the potential for heavy metals moving through the
soil and becoming more available to plants.
Various studies since 1971 all tend to indicate the feasibility of
trenching as an appropriate method for sludge disposal. Nonetheless, con-
siderable reduction in costs could be realized as a result of additional
studies on the fate, with time after entrenchment, of sludge-borne nitrogen,
heavy metals and virus. If the potential hazards from these sludge compo-
nents were shown to be less of a problem than they are now considered, less
monitoring, liming and backup would likely be required and sludge entrench-
ment rates could perhaps be increased.
It is recommended, therefore, that the above studies be continued which
were anticipated when this procedural study was conducted. Variables were
included during entrenchment for this purpose. Both digested and undigested
sludges were placed in trenches with and without lime added at time of
dewatering at various heights above the groundwater table. (Digestion and
liming affect pathogen survival, metal availability and movement, and the
form and amount of nitrogen; and closeness of the entrenched.sludge to the
groundwater table directly affects rate of sludge decomposition and thereby
indirectly affects the fates of sludge-borne nitrogen, metals and pathogens.)
Some sludges were seeded with virus, prior to dewatering, so that their fate
could be followed Ct° be reported elsewhere).
While trace organics (possibly present in entrenched sludges) are not be-
lieved to pose a hazard, there have been no studies specifically on their
fate, and we recommend that such studies be conducted.
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SECTION 4
SLUDGES, SITES AND EQUIPMENT
SLUDGES
Raw and anaerobically digested sludges were chosen for the trenching
study as described in Table 1. These sludges were representative of types
that small municipalities might entrench. The dewatered sludges were a
combination of primary and waste-activated sludges obtained from the Blue
Plains Wastewater Treatment Plant which serves the Metropolitan Washington,
D.C. area. Lime (CaO) was also added to some of the dige«;ted and undigested
(raw) sludges. The sludges were all dewatered. Previous work indicated
that sludges with less than about 10-12% solids were too fluid for proper
entrenchment (8). Sludges with somewhat greater solids content may also be
too fluid, depending upon the topography. ;j
j
SITES j
i
Six different areas were chosen for the entrenchment stTadies (Figure
1A-H). These areas contained soils that would require different handling
during sludge entrenchment. Two of the areas also contained previously
entrenched sludges. Determinations were made of the ease of handling the
entrenchment procedure in some of the different soil types under different
weather conditions and with different equipment. Characteristics of the
soils in the different areas are given in Table 2. Recommended consider-
ations for selecting a sludge entrenchment site can be obtained from the
Soil Conservation Service and the literature (2-4, 6-8). j
I
,[
EQUIPMENT j
I
Ordinary readily available equipment was used in the research demon-
stration studies. The tractor/loader/backhoe (TLB) machines and a number of
different trucks used are listed in Table 3. The experiences, using these
machines, are described in a later section. 1
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SECTION 5
SLUDGE ENTRENCHMENT
IN AN UNSLUDGED SITE ;
A technique for sludge entrenchment was devised and tested by which an
ordinary tractor/loader/backhoe (TLB) could be used to dig narrowly spaced
ditches. The procedure is as follows:
(1) Dig a straight trench with a TLB 60 cm wide x 60 cm deep x about
4.5 meters long (the extension of the backhoe) and pile the spoil
soil along one side as shown diagramatic'ally in Figure 2, trench
segment A, number 1.
(2) Obtain sludge from truck (Figure 3A and 3B) and 'fill trench A-l
(Figure 2) with sludge (Figure 3C).
(3) Dig a new straight trench (A-2, Figure 2) parallel to the previous
trench 60 cm to its side and pile the spoil soil uniformly along
over the sludge in the previously filled trench (shown pictorially
in Figure 3D and 3E).
(4) Fill trench A-2 with sludge.
(5) Continue digging, filling with sludge and covering with soil,
trenches A-3 through A-n, for the desired width of the area to be
* entrenched. In this manner the narrow 60 cm spacing between
trenches can be maintained. Trench A-n may be covered with spoil
soil left over from digging trench A-l or from elsewhere as de-
sired (Figure 3F).
(6) Dig a new straight trench, either B-l or B-n (Figure 2) as an
extension of either A-l or A-n. If B-n were dug first, then paral-
lel trenches would be dug in the order B-n, B-3, B-2, B-l. Assum-
ing B-l were dug first, then the order would be B-l, B-2, B-3,
B-n.
(7) Dig and fill trench B-l with sludge.
(8) Dig a new straight trench, B-2, 60 cm to the side and parallel to
trench B-l, piling the spoil soil uniformly along over the sludge-
filled trench B-l. Trench B-2 is an extension of A-2.
24
-------
Figure 2. Schematic showing details of sludge entrenchment procedure. Order
of digging and filling: Dig "A-l", excavated soil (spoil) is
stored to side "a"; fill "A-l" with sludge, dig "A-2" and cover
"A-l" with excavated spoil "b"; fill A-2 with sludge; last sludge
filled trench in segment A can be filled with excavated spoil from
trench A-l if desired, "e". Repeat process for segments B and
then C. i
25
-------
,
Figure 3. Sludge entrenchment.
A. Obtaining sludge from (9.2 m3) dump truck with TLB.
26
-------
Figure 3. Sludge entrenchment.
B. Transporting sludges from truck to trench with TLB.
21
-------
Figure 3. Sludge entrenchment.
C. Filling trench segment A-l (Figure 2) with slude using TLB.
28
-------
Figure 3. Sludge entrenchment. - ]
D. Beginning to dig trench segment' A-2 (Figure 2) beside
sludge-filled trench segment A-l (Figure 2) with TLB.
29
-------
Figure 3.
E.
Sludge entrenchment.
Continuing digging trench segment A-2 (Pigu^6 2) and covering
sludge-filled trench segment with spoil soil A-l (Figure 2),
using TLB.
30
-------
Figure 3.
F.
Sludge entrenchment.
Covering sludge-filled trench segment A-n (Figure 2) with
spoil soil from trench segment A-l (Figure 2) using TLB.
31
-------
(9) Continue digging, filling with sludge and covering with soil
through trench B-n for the desired width of the area to be en-
trenched .
(10) The length of the area to be entrenched will be achieved by
extending trenches 1, 2, 3, ...n in the A, B, C, direction.
As an alternative procedure, one long trench could be dug the entire
length of the area to be entrenched. This'procedure, unfortunately, would
not permit narrow spacing between trenches because the tires of the TLB
would sink into the freshly filled sludge trench. Hence, a lesser total
amount of sludge could be entrenched per given land area, and, with the
increased spacing between trenches, crop cover would show a zebra-striped
growth response (8).
IN A PREVIOUSLY SLUDGE-ENTRENCHED AREA
Dewatered sludge was also entrenched in areas containing previously en-
trenched sludges. In one test (Figure IF, Plot IXb) sludge was entrenched
at right angles to the previously entrenched digested sludge (Figure;4A and
4B). Some of the previously entrenched sludge was unearthed during the
process. This procedure was performed about two and one-half years after
the first sludge was entrenched. The sludge was still moist, but not malo-
dorous in this test area where the water table was about 90 cm below the
soil surface. No technical difficulties were encountered. This procedure,
however, caused greater mixing of sludge with the soil and probably will
cause faster breakdown of the sludge and release of nitrate-nitrogen which
could potentially pollute ground and/or surface water.
In a second test (Figure IF, Plot IXa), digested sludge was incorporated
in new trenches that were dug both parallel and between trenches of previous-
ly (3 years earlier) entrenched digested sludge. Somewhat less sludge was
brought to the surface when trenches were dug parallel rather than perpendi-
cular. No real technical difficulties were encountered except that it was
not possible to dig exactly between trenches of old sludge.
In a third test (Figure 1G), raw-limed sludge (limed to pH 11.5 at the
time of dewatering) was incorporated in new trenches that were dug both
parallel and between trenches of previously (3 years earlier) entrenched
raw-limed sludge. The water table was periodically as close as 120 cm below
the soil surface in this area. Some of the previously entrenched sludge was
unearthed with the spoil during the process. Maiodor was not a problem and
there were no technical problems with trenching in the raw sludge area.
SLUDGE HANDLING AND TRENCH FILLING i
Sludge was hauled in the different vehicles indicated in Tables 3 and 4.
In one procedure, sludges were unloaded directly from dump truck bodies with
the loader on the TLB and then-placed in the trenches. In this manner, very
little sludge was spilled onto the soil surface (Figure 3A, 3B, and 3C). In
another procedure, sludge was directly discharged from concrete mixer,, trucks
via chutes into the trenches (Figure 5A and 5B). This procedure caused even
32
-------
less spillage on the soil surface. In the ranges of sludge solids contents
experienced (given in the keys to Figure 1 A-H), all types of sludges could
be loaded and unloaded adequately with the different types of equipment
tested. Observations concerning each method of hauling and placing sludges
are given in Tables 3 and 4, Figure 1A-H, and in the following narrative.
\
The loader bucket on the Case 580B TLB was too wide to fit into the body
of the smallest 1.5 m3 dump truck. Hence, sludge had to be dumped and
scraped into the bucket to minimize spillage (Figure 6A).. This procedure was
time consuming and not particularly satisfactory. Direct unloading was
nicely achieved with the smaller bucket on the Case 580 TLB from the small
truck (Figure 6B), and with either TLB from the 9.2m3 dump trucks (Figure 3A
and 3B). Direct unloading was possible even in a snow storm (Figure 7A and
7B). Directly unloading sludge with a TLB was advantageous because it
avoided soil surface and possibly surface water contamination with sludge,
odor and slippery surfaces from spilled sludge, and difficulties of gathering
the jelly-like sludge into front-end loader buckets from dumped piles. The
TLB's were quite maneuverable even on wet terrain. About one hour was
required at the site to dig trenches, unload 7.7 m3 of sludge from a dump
truck, and fill and cover trenches with a TLB. i
While dump trucks were very easy to fill at the treatment plant, liquid
dripped from the bodies onto the highway during transit, A modification to
dump trucks by a hauler for the Maryland Environmental Service suitably con-
tained tailgate leakage. This modification consisted of a gasket, compres-
sion levers reinforcing the locking lugs and a trough along under the tail-
gate. Odor was not a problem but could have been, particularly in summer
months. ,
Two types of concrete mixer trucks were also used to haul sludge. These
trucks hauled sludge without spillage or malodor and could be maneuvered in
good weather to discharge sludge directly into the trenches. The horizontal-
type concrete mixer truck had to be level or positioned such that the dis-
charge chute was tilted downhill to properly discharge the sludge. This
required some additional maneuvering and restriction on:operations. A very
clean operation was possible with the concrete mixer trucks. The Rex more
vertical-type mixer was more satisfactory. The trailer;mounted extended body
mixer lacked sufficient mobility at the entrenchment site and was used only
in one trial. Overall operations took about the same length of time using
dump or concrete mixer trucks. !
In wet weather in soils incapable of bearing much traffic, sludge can be
pumped into trenches via peristaltic-type pumps such as the concrete pumps
being used to pump sludge in Figure 8. The Maryland Environmental Service
has successfully used this type of machine to pump sludges through two hun-
dred feet of flexible and rigid tubing (10 cm in diameter) into trenches at
large-scale sludge entrenchment operations being performed under contract for
the District of Columbia. Other less complicated pumps have been used for
this purpose in more recent entrenchment operations of the Maryland Environ-
mental Service. These types of machines, however, would add to the cost of
the operation and may not be feasible for smaller municipalities. Temporary
storage of sludge during wet weather would be a desirable backup. Several
33
-------
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Figure 4. Sludge entrenchment in an area entrenched with sludge 2.5 years
earlier.
A. Digging trench 60 cm wide x 60 cm deep at right angles to
previously entrenched sludge. \
36
-------
Figure 4. Sludge entrenchment in an area entrenched with sludge 2.5 years
earlier. j
B. Exposed previously entrenched sludge.
37
-------
Figure 5. Sludge hauling and discharge into trenches from concrete mixer
truck. :
A. Preparation for sludge discharge into open trench.
38
-------
Figure 5. Sludge hauling and discharge into trenches from concrete mixer
truck. ]
B. Sludge discharge into open trench. i
39
-------
Figure 6. Sludge hauling and unloading with TLB from 1.5 in3 dump truck.
A. Using a TLB with bucket too large for dump bed.
40
-------
-.. «SV'1r y +
— _, . & **''***
t* -*4t.5i,^*».r*V
*
Figure 6. Sludge hauling and unloading with TLB from 1.5 m3 dump trucks.
B. Using a TLB with smaller bucket, permitting direct unloading
and minimum spillage. I
41
/I
-------
Figure 7. Sludge entrenchment in a snow storm.
A. Unloading 9.2 m3 dump truck with TLB.
42
-------
Figure 7. Sludge entrenchment in a snow storm.
B. Filling trench with sludge using TLB.
43
-------
Figure 8. Peristaltic-type pump (Challenge 900) being used for pumping
dewatered sludge through a hose from tank truck to trenches
at Maryland Environmental Service entrenchment site.
44
-------
other methods of improving the ability to trench sludge in wet soil conditions
are described in the next section.
SOIL CONDITIONS, WEATHER AND SITE DRAINAGE |
|
Sludge could be entrenched in the sandy area throughout most seasons and
weather conditipns. Most of the sandy area was entrenched with sludge in
February and March, often on days following heavy rains. Sludge was even
entrenched in the sandy soil during a snow storm and general maneuverability
of the trucks and the TLB was possible. j
i •
On the other hand, maneuvering was difficult on a cljay soil with a high
water table. Only the TLB could be used on this soil during the winter.
Hence, the clay area was drained in a preliminary fashion with open trenches
running through the plots as shown in Figure 9A. After some of the water had
drained out (Figure 9B), tile drains were installed perpendicular to the
direction of the open ditches as shown in Figure 9C. This change in direc-
tion was made to provide for collection and carrying away of water perpen-
dicular to the direction of its normal subsurface flow, A flexible plastic
10 cm drain line was installed. This corrugated slotted line was fabricated
with a fiberglas mesh cover which permitted its installation in the clay soil
without a gravel envelope (Figure 9D). This covered drainage tile was ob-
tained from Advanced Drainage Systems. The average .depth of the tile was
approximately 1 meter below the soil surface. The tile has functioned well
in carrying off excess water. The area became drier after drainage lines
were installed during the winter, both because of the drainage system and
because of increased evaporation during the spring. Tile installation was
completed in early February. Sludge was entrenched in the' area without diffi-
culty by the end of May. j
'!
This experience shows the importance of picking site;s with different
soil properties for use during different weather conditions and seasons. If
only heavy wet soils with high water tables are available, then installation
of tile drainage systems will probably be necessary. Tile drainage may also
be necessary in high water table sandy soils. Provision for overland flow of
the drainage water over grassed areas and impoundment and/or irrigation of
the drainage water may be necessary to reduce nitrogen levels prior to its
discharge into surface drainage streams. In most situations, however, tile
drainage is not desirable or necessary. Advice on drainage of soils and
impoundment of drainage water can be obtained from the Soil Conservation
Service located in each county and state. j
i
Beltsville, in the metropolitan Washington, D.C. area, has a moderate
climate. The average annual precipitation is 105 cm including 57 cm of snow.
Snows generally are .not persistent. January is the coldest month and July
the warmest. The respective mean monthly temperatures are 1°C and 25°C.
There is an average of 194 frost-free days each year. ;
i
In colder climates, soils should be covered if they ;are likely to become
frozen to appreciable depths. If the treatment facility is in a very cold
climate, sludges possibly could be lagooned or stockpiled for entrenchment
later in the spring, provided surface runoff and infiltration are controlled.
45
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SEEDING
The test areas, entrenched with sludge between December 1974 and May
1975, were leveled and cultivated with a tractor-mounted rotovator in early
June. Rotovating of the different test areas was followed by application pf
fertilizer and lime. Finally, the different test areas were seeded by hand
with Kentucky-31 tall fescue grass seed. The applied rates of lime, ferti-
lizer and seed are given in Table 5.
Recommendations for seed, fertilizer and lime requirements for your
particular soil and area may be obtained from your local Office of the
Cooperative Extension Service, Soil Conservation Service or State Agricul-
tural University.
46
-------
Figure 9. Drainage of clay soil with high water table.
A. Digging trench for preliminary drainage.
47
-------
Figure 9. Drainage of clay soil with high water table,
B. Water draining out of trench.
48
-------
Figure 9. Drainage of clay soil with high water table, i
C, Installation o£ fiberglas-covered slotted flexible 10 cm-diameter
plastic drain tile, prior to covering with soil.
49
-------
,ss*>'jidBaaSr «*,-~~- -»>». -•*•$?«*•^ ??
Figure 9. Drainage of clay soil with high water table.
D. Fiberglas wrapping over flexible slotted plastic drain tile by
Advanced Drainage Systems (ADS).
50
-------
TABLE 5. APPLICATIONS OF FERTILIZER, LIME AND GRASS SEED
Material
! Application rate
I Kg/ha
10-10-10* fertilizer
Dolomite lime
Kentucky 31-tall fescue
: 1100
i 4400 (to pH 6)
i
165
*Equivalent to 110, 48 and 91 kg/ha N, P and K on an elemental basis.
51
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SECTION 6
ENVIRONMENTAL RISK, ITS MANAGEMENT AND SUGGESTED MONITORING
INTRODUCTION \
Monitoring of a sludge entrenchment site should be the minimum necessary
to detect potential harmful effects in the environment. Monitoring data
should be available and acted upon when it shows that additional steps must
be taken to minimize environmental degradation.
Monitoring is discussed for sites receiving sludges from municipalities
at rates from 3 to 48 dewatered, filter-cake tons (15-25% solids) per day in
this report. This monitoring is sludge and site specific, resulting in a
specific local environmental risk.
ENVIRONMENTAL RISKS OF TRENCHING AND THEIR MANAGEMENT
Potential environmentally harmful materials in sludge include nitrogen,
heavy metals, pathogens and certain organic compounds. Potential risks are
greater when larger amounts of sludge are entrenched on the same land area.
Nitrogen
The most probable environmental risk from entrenching dewatered sludge
is possible pollution of groundwater with nitrogen. It is difficult to
predict the extent of this nitrogen risk. The large amount of immobile
organic nitrogen in entrenched sludge can undergo many fates. Under aerobic
conditions, microorganisms transform the organic nitrogen into the inorganic
forms of ammonium, nitrite and nitrate. Some of these mineralized forms of
nitrogen can move into groundwater via water infiltrating through the soil.
They also.can be temporarily absorbed by the soil cation exchange complex or
taken up by crops (100 to 300 kg/ha/yr). Finally, nitrogen can be denitri-
fied (transformed microbially from nitrate to nitrogen gas) and lost harm-
lessly into the atmosphere under anaerobic conditions and with a suitable
carbon source.
Entrenchment of sludge promotes anaerobic conditions, essentially pre-
vents water percolation through the sludge for at least a year or longer,
slows nitrogen mineralization, promotes denitrification and contains and
allows microbial destruction of malodorous materials and pathogens (8).
52
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In an earlier study (8), sludge was placed in trenches 60 cm wide x 60
cm deep x 60 cm edge spacing which added over 300 dry tons of sludge per
hectare (over 1500 dewatered, filter-cake tons per hectare). Dewatered undi-
gested sludges in this study contained about 3% nitrogen.i This amounted to
20,000 total kilograms of organic nitrogen being added per hectare, which is
about 100 times more nitrogen than is needed by a grass crop during one year.
If the .sludge were mixed throughly with soil instead of being entrenched, 20
to 50% of the nitrogen could be released into the soil in mobile form. The
studies (8) showed that release and movement of nitrogen from entrenched
sludge into grqundwater was minimal during the first two years after entrench-
ment. The sludge, however, did become more aerobic during that period and
some increased nitrogen movement through the soil was observed. In subsequent
studies of this and of large-scale areas trenched by the Maryland Environmen-
tal Service,, movements of excessive amounts of nitrogen have not yet been
detected (Unpublished, personal communication, Larry Sikora, USDA, ARS,
Beltsville, MD). j
If excessive amounts of nitrogen are mineralized and begin to move to
groundwater, mineralization and movement can be reduced by promoting anaero-
bic conditions. This can be accomplished by increasing the soil water
content. In a field with the water table at considerable depth, the soil
water content can be increased by installing an asphalt barrier in the soil
uniformly under the entrenched sludge with a special machine at an estimated
cost of between $700 to $1000 per acre (1,5). In a tile-drained entrenched
field (shallow water table), drains could be plugged to increase the soil
water content. If plugging was not desired, drainage water with excessively
high nitrogen content could be impounded and/or irrigated' onto a cropped
field. A third procedure would be to pump out excessively contaminated
groundwater from we.lls and. irrigate onto cropped land. j
I
'!
Heavy Metals j
I
A second potential problem is movement of heavy metals through soil from
entrenched sludge to groundwater. However, this risk is not thought to be
very great with most sludges in most soils. Additions of! lime (CaO) to
sludges prior to .dewatering, to induce pH's of 10 to 11, have been recom--
mended (8) to maintain pH's of sludges near neutral, thereby minimizing
chances for metal movement. j - ,
ij
.i
In the studies previously mentioned (8), metals did not move out of en-
trenched sludges into soils as long as pH's remained near neutral^. In
entrenched unlimed sludges, in which the pH became acid, 'slight metal move-
ment was observed. The sludges became acidic as nitratesi and sulfates
formed. Formations of these compounds were accelerated by increasingly
aerobic conditions in the sludge and more rapid microbialj sludge decompos-
ition. It was not possible to tell in the studies how effective the lime
additions were in neutralizing acid formation in entrenched sludge during
rapid aerobic decomposition. Such studies are a continuing part of sludge •
entrenchment research at Beltsville. j
53
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Pathogens
Pathogens in entrenched sludges are not thought to pose a hazard. The
pollution indicators - fecal coliforms and pathogenic salmonella bacteria -
were not detected more than a few cm into soils outside of entrenched sludges
any time during a two-year period following entrenchment (8). Furthermore,
concentrations of these organisms dropped to nearly non-detectible levels
during this two-year period., Total coliform bacteria, measured in the same
study, were detected in soil no more than 30 cm outside the entrenched sludge.
In a recent study, the model polio virus (bacteriophage F-2) was seeded
into sludge at a treatment plant prior to dewatering. The seeded sludge was
then entrenched. The virus was not detected moving from entrenched sludge
into surrounding soil. The F-2 virus decreased in numbers within the en-
trenched sludge from 107 plaque-forming units per gram to non-detectible
levels within one month after entrenchment (Unpublished, personal communi-
cation, Wylie Burge, USDA, ARS, Beltsville, MD). Virus studies are contin-
uing at Beltsville. There will be an attempt to follow the fate of endoge-
nous enteroviruses In entrenched sludge.
Organics
The fate of chlorinated hydrocarbons, PCB's and other similar organics
has not been studied in entrenched sludges. In studies on specific organic
compounds, some movement of trace organics through soils has been observed,
particularly of water soluble trace organic compounds. Furthermore, polar
trace organics in the form of acids can be absorbed by plants (Personal
communication, Ralph Nash, USDA, ARS, Beltsville, MD.). During the process
of dewatering, most of these more soluble trace organics should move out of
the sludge into the liquid filtrate. Therefore, it is not believed that the
less soluble, nonpolar trace organics, probably remaining in the sludge after
dewatering, would move appreciably through soil from entrenched sludge under
normal circumstances; and little uptake by plants would be expected. None-
theless, the fate of trace organics in entrenched sludges needs study.
MONITORING
The specific monitoring requirements will depend upon the risks previ-
ously discussed and be up to the applicable federal, state and local author-
ities and statutes. Minimal monitoring is suggested for small entrenchment
sites, providing sound entrenchment procedures are followed.
The sludge should be adequately characterized at the treatment plant
(Table 6) so that potential for future environmental risk can be determined.
There also will be some requirements for monitoring ground and surface water
at the entrenchment site. Monitoring suggestions are given in Table 6.
Assistance in determining where monitoring wells should be located, with
crops to be grown, with drainage, etc., can be obtained through the local
County Cooperative Extension Service, Soil Conservation Service, Health
Department and/or State Geological Survey. :
54
-------
Proper use of the recommended entrenchment procedures a.nd maintenance
of grass in waterways should minimize problems with surfa.ce water contamin-
ation and need for its monitoring. If crops are grown that will enter the
human food chain, and if the sludge metal levels are high, it may be neces-
sary to monitor the crops (Table 6) at harvest to determine their safety.
55
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TABLE 6. SUGGESTED MONITORING FOR SLUDGE ENTRENCHMENT
Component
Determination
Frequency
sludge
sludge
groundwater
groundwater
total £ volatile solids;
total, NHi* and N03-N, P,
K, Cl, soluble salts, lime,
Zn, Cu, Cd, Pb, Hg, Ni
pH
and N03-N, Zn, Cl,
total and fecal coliforms
and N03-N, *C1
tile drainage NH^ and NOs-N, total and
fecal coliforms
surface water NHi+ and NOs-N, P, total
and fecal coliforms
crops
Cd, Pb, Hg, Ni
twice yearly of one represent-
ative composited weekly sample
daily -or weekly
one or two background from sev-
eral strategically located wells
once every three to six; months
during and for five years after
entrenchment i
unnecessary if provision for
impoundment or crop irrigation
unnecessary if sludge is proper-
ly entrenched
$
probably necessary at harvest if
metals high in sludge and if
crops will enter human food chain
*If a significant ^increase of these ions is detected over time, they can be
analyzed more frequently and/or for more components. Appropriate methods
should be utilized to prevent water degradation.
56
-------
SECTION 7
COSTS
SLUDGE HAULING AND ENTRENCHMENT j
Costs were estimated for entrenchment in 1975 based upon actual experi-
ences during the Beltsville pilot studies. The costs are estimated for
hauling and entrenchment of 3, 12 and 48 dewatered tons of sludge per day,
both on a rental and an ownership-self-operation basis. Assuming a hauling
distance of 32 km each way between the treatment plant and the sludge en-
trenchment site, the loading and two-way travel took less than three hours
for dump and concrete mixer trucks and the unloading at the site took less
than one hour. Reasonable working times at the entrenchment site for all
operations of the TLB, including trenching, unloading the!dump truck and
covering the sludge with soil were one-half hour per small truck (up to 3.8
m3 in size) and one hour per large truck (up to 9.2 m3 in,size) (Table 7).
Estimated rental costs for entrenchment are given in Table 8. These
estimates were based upon the minimum fraction of a day it was possible to
rent the equipment rather than upon actual working times. For any given haul
distance, cost savings can obviously accrue, particularly,for 3 to 12 ton per
day operations, as a result of any procedure that increases the effective
utilization of the trenching machine and reduces truck transport, e.g.,
stockpiling sludge for several days at the treatment plant before hauling to
the site. Considerable savings could also occur if a TLB were available both
for entrenchment and for other municipal operations, thereby enabling cost-
sharing. A third possibility for a small daily operation would be to use the
same operator for the TLB and the dump truck. j
There also would be a cost for supervision at the site. This cost would
probably be minimal. Such site supervision for the smaller operations (3 to
12 dewatered tons of sludge per day) would probably amount to no more than a
weekly visit after an initial orientation given to the TLB operator. For a
48 ton per day operation, however, it may be desirable to have an additional
person on the site to guide trench spacing and filling and truck unloading
operations of the TLB operator. This individual could also collect any
necessary samples for monitoring. If this individual earned $4.00 per hour
per eight-hour day, this would add less than $1.00 per ton of dewatered
sludge entrenched to the cost for a 48 ton-per-day operation.
Estimated entrenchment costs, assuming equipment ownership and self-
operation by the wastewater treatment authority, are given in Table 9. These
costs are estimated for hauling 32 km each way and entrenchment of 3, 12 and
48 tons of dewatered sludge per day, five days per week over a 3-year period.
|
57
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It is cheaper to rent equipment for small operations if all costs, based
upon purchase of the equipment and self-operation, must be borne by the
wastewater treatment facility for sludge entrenchment only (Table 10). If
costs can be shared with other phases of wastewater treatment or other
municipal functions, equipment ownership becomes more attractive.
DRAINAGE !
Drainage was necessary in only one of the half-dozen test sites due to
a high water table. The actual time and costs for installing drainage of the
0.24 hectare test plot-with a TLB and inexperienced labor are given in Table
11. The total cost .was $484 for the 0.24 hectare plot ($2j,000/hectare or
$800/acre). In some states drainage can be installed by professional special-
ists who use laser-guided trenching machines. Their charge for installing
perforated plastic drainage tile in a 16 hectare field (40 acres) would be
$750/hectare ($300/acre). These charges include land survey and engineering,
labor, materials and equipment. Drainage costs may vary, /therefore, between
$750 and $2,000/hectare ($300 to $800/acre). The drainage icosts per dewa-
tered ton of entrenched sludge are between $0.30 and $0.80 figuring entrench-
ing of 2,500 dewatered tons of sludge per hectare (if drainage is necessary).
LAND j
No costs for land rental or purchase are included. Hand can be farmed
within a few weeks after sludge entrenchment. Estimated ciosts for cultivat-
ing, fertilizing, liming and seeding are given in Table 12. These estimated
revegetation costs for equipment rental, labor and materials amount to less
than $0.50 per dewatered ton of sludge assuming entrenchment of 2,500 tons of
dewatered sludge per hectare..
MONITORING j
I
The total estimated analytical costs for sludge, groiihdwater and surface
water monitoring were not over $0.55 per ton of dewatered :sludge (Table 13).
These cost estimates were based upon equipment purchase arid self-operation
for pH analysis and contract analyses by some university cjr service labor-
atory for the other analyses (Table 14).
I
TOTAL j
j
Costs for entrenching 12 to 48 dewatered tons of sludge per day with 32
km haul distance each way were estimated to be under $15 per ton and not too
different whether on a rental or purchase-self-operation basis (Table 10 and
15). These costs would obviously have to be figured by each municipality.
Estimated costs for a 3 ton-per-day operation are considerably higher because
allowances were made for minimum rental times and times of employment. If
arrangements could be made for use of equipment and personnel more nearly
based upon the actual operation time required, 3 to 48 dewatered tons of
sludge per day could be hauled 32 km each way and entrenched for less than
$15.00 per dewatered ton. j
63
-------
TABLE 10. ESTIMATED SLUDGE ENTRENCHMENT COSTS - TOTALS FOR
PURCHASE AND SELF-OPERATION vs RENTAL*(1975)
Dollars/dewatered ton
Size of
operation,
dewatered
tons/day
3
12
48
Rental
43.00
11. SO-
IL 50
Low**
Purchase-
Self -operate .
40.00
13.50
9.00
Rental
60.00
15.50
11.50
High**
Purchase-
Self-operate
66.00
19.50
9.00
* Totals from Tables 8 and 9.
** Low and high estimates for rentals based on shorter and longer rental
periods and for purchase-self-operation -based upon shorter and longer
labor periods.
64
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TABLE 12. LAND FINISHING COSTS (1975)
Costed Items
LABOR § EQUIPMENT
Tractor § operator
Other labor
Total
MATERIALS
10-10-10 fertilizer
Ground dolomitic
limestone
Kentucky 31 tall fescue
Total
Process Unit cost Time reqr.
$/hr hours*
Rotovating 20.00 4
spreading 6
fertilizer £
lime and
working in
hand seeding 5.00 4
Total amt $/bag** No. bags
reqr, (kg)
450 3.10 23
1800 0.95 80
69 35.00 3
TOTAL LABOR, EQUIPMENT $ MATERIALS, for 0.4 hectare
LAND FINISHING COSTS/dewatered ton (20% solids), assuming
2,500 tons sludge/hectare
Total Cost
$
80
120
20
$220
77.50
' 76.00
105.00
$258.50
$478.50
$ 0.50
* For all test plots spread out in 40 hectare area, about 0.4 hectare total
area cultivated in our trials, about 450 total tons of dewatered sludge
was entrenched.
** Single bag rate.
66
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67
-------
TABLE 14. COSTS FOR ANALYTICAL DETERMINATIONS (1975)
Material
Dewatered
sludge
Ground and
surface water
Analysis
pH
Other*
N03
Cl
Zn
Total and
fecal coliform
Per sample
$
1.00
100.00
1.00
1.00
1.00
1.00
5.00
Capital/yr/2yrs
$
200.00
* Other - Volatile solids, N, P, K, Zn, Cd, Cu, Pb, Hg, Ni, soluble salts,
Cl, lime.
68
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REFERENCES
1. Erickson, A. E., C. M. Hansen, and A. M. Smucker. The influence of sub-
surface asphalt barriers on the water properties and the productivity of
sand soils. Transactions 9th Inter. Congr. Soil Sci. 1:331-337, 1968.
2. Land Containment in Montgomery County: Site Evaluation Report for Mary-
land Environmental Service by Resources Management Associates, Glen
Burnie, Maryland, July 1975.
3. Land Containment Sites for Undigested Sewage Sludge. Report for Maryland
Environmental Service by Whitman, Requardt and Associates, Baltimore,
Maryland, June 1972.
4. Land Containment Sites for Undigested Sewage Sludge: Montgomery and
Prince George's Counties. Report for Maryland Environmental Service by
Resources Management Associates, Glen Burnie, Maryland, June 1975.
5. Productive Soil from Sand. Amoco Moisture Barrier Company, 910 S. Mich-
igan Avenue, Chicago, Illinois 60605, 1971.
6. Sludge Utilization Project - Operations Plan and Procedures. Report for
Maryland Environmental Service by Whitman, Requardt and Associatesj
Baltimore, Maryland, August 1972.
7. Walker, J. M. Trench Incorporation of Sewage Sludge. Proceedings of the
National Conference on Municipal Sludge Management, Pittsburgh, Pennsyl-
vania, June 11-13, 1974. pp. 139-149.
8. Walker, J. M., W. D. Burge, R. L. Chaney, E. Epstein, and J. D. Menzies.
Trench Incorporation of Sewage Sludge in Marginal Agricultural.Land.
EPA-600/2-75-034. September 1975.
HUS. GOVERNMENT PRINTING OFFICE:1978 260-880/31 1-3
70
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
REPORT NO.
EPA-600/2-78-018
3. RECIPIENT'S ACCESSIOI*NO.
4. TITLE AND SUBTITLE
SEWAGE SLUDGE ENTRENCHMENT SYSTEM FOR USE BY
SMALL MUNICIPALITIES
5. REPORT DATE
February 1978 (Issuing Date)
6. PERFORMING ORGANIZATION CODE
. AUTHOR(S)
J. M. Walker, L. Ely, P. Hundemann, N. Frankos, and
A. Kaminski
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
U. S. Department of Agriculture, Agricultural Research
Service, Biological Waste'Management and Soil Nitrogen
Laboratory, Beltsville, Maryland 20705
10. PROGRAM ELEMENT NO.
1BC611,C611B,SOS#1, Task COS
11. CONTRACT/GRANT NO.
EPA-IA.G-D4-0510
12. SPONSORING AGENCY NAME AND ADDRESS
Municipal Environmental Research Laboratory--Gin.,OH
Office of Research and Development
U. S. Environmental Protection Agency
Cincinnati, Ohio 45268
13. TYPE OF REPORT AND PERIOD COVERED
Interim, 6/74 to 6/75J
14. SPONSORING AGENCY CODE
EPA/600/14
15. SUPPLEMENTARY NOTES
Project Officer: K. Dotspn (513) 684-7661
16. ABSTRACT '
A method of disposing of dewatered sewage sludge by entrenching it into soil was
developed for small communities. Readily available and relatively inexpensive equip-
ment was used. Included were a tractor equipped with a loader and backhoe, and dump
truck or concrete mixer truck. A tractor operator and a truck driver were required.
Trenches, dug with the backhoe, were 60 cm wide, 60 cm deep, and 60 cm apart. The
time required to entrench 12 tons of dewatered. sludge was one hour. The estimated
cost of sludge incorporation was less than $15.00 per ton of dewatered sludge. Cost
items included equipment, personnel, hauling (64 km round trip), land, drainage moni-
toring, and cultivation. Reuse of a previously trenched site ^indicated that about 2
years is the minimum satisfactory time lapse between the first and second entrench-
ment. !
Trenching of limed sludge cake can be done without odor pr surface water runoff
problems. Trenching is most appropriate on low quality land v/here surface applica-
tion is not feasible. !i
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDEDTERMS
c. COSATI Field/Group
Sludge disposal
Land reclamation
Trenching
Salmonella
Lime
Metals
Limed sludge
Digested sludge
13B
18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (ThisReport)
Unclassified
21. NO. OF PAGES
81
20. SECURITY CLASS (Thispage)
Unclassified i
22. PRICE
EPA Form 2220-1 (9-73)
71
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