COMPREHENSIVE PERFORMANCE EVALUATION
OF THE BOZEMAN, MONTANA,
WASTEWATER TREATMENT PLANT
EPA Contract No. 68-01-7108
ERM-Southeast, inc
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COMPREHENSIVE PERFORMANCE EVALUATION
OF THE BOZEMAN, MONTANA,
WASTEWATER TREATMENT PLANT
EPA Contract No. 68-01-7108
September 1987
From
ERM-Southeast, Inc.
2629 Sandy Plains Road
Suite 201
Marietta, Georgia 30066
404/971-4671
To
Ms. Marie Perez
U.S. EPA-OMPC (WH-547)
401 M Street, SW
Washington, D.C. 20460
(202) 382-7286
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TABLE OF CONTENTS
Section Ti tie Page
LIST OF FIGURES iii
LIST OF TABLES iii
EXECUTIVE SUMMARY iv
1 BACKGROUND 1-1
1.1 Introduction 1-1
1.2 100% M/R Funding 1-1
1.3 Composite Correction Program 1-2
1.4 Purpose of Study 1-2
2 FACILITY DESCRIPTION 2-1
2.1 Background 2-1
2.2 NPDES Permit Limits 2-6
2.3 Description of the Claimed
I/A Failure 2-6
2.4 System Performance 2-8
2.4.1 Influent Wastewater Quality 2-8
2.4.2 Effluent Wastewater Quality 2-8
2.4.3 Performance of RI System
Prior to 1987 2-8
2.5 Summary 2-11
3 COMPREHENSIVE PERFORMANCE EVALUATION 3-1
3.1 Introduction 3-1
3.2 Assessment of the Quality of the
Treatment Plant Data 3-1
3.3 Major Unit Process Evaluation 3-2
3.3.1 Introduction 3-2
3.3.2 Primary Clarifiers 3-2
3.3.3 Activated Sludge System 3-5
3.3.4 Disinfection Facilities 3-5
3.3.5 Sludge Handling Facilities 3-5
3.3.6 Rapid Infiltration System 3-5
3.3.6.1 Hydraulic Capacity 3-5
3.3.6.2 Ammonia Removal 3-5
3.3.6.3 Fecal Coliform Removal 3-6
3.4 Performance Limiting Factors 3-6
3.4.1 Overview 3-6
3.4.2 "A" Factors - Fecal Coliform
Removal in RIB's 3-7
3.4.3 "B" Factors 3-8
3.4.3.1 Operator Application
of Concepts 3-8
3.4.3.2 Infiltration/Inflow (I/I) 3-8
i
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TABLE OF CONTENTS (cont'd.)
Sect ion
Title
Page
3.4.4 "C" Factors
00
1
CO
3.4.4.1
Equipment Malfunctions
3-8
3.4.4.2
Performance Monitoring
3-9
3.4.4.3
Process Flexibility
3-9
3.4.4.4
Process Accessibility
of Sampling
3-9
3.4.4.5
Industrial Loading to
Plant
3-9
3.5 Summary
3-9
REFERENCES
4-1
APPENDIX
Pathogen Removal in Rapid Infiltration
Systems
A-l
i i
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LIST OF FIGURES
Figure Title Page
2-1 Plan View of the Bozeman, MT, POTW. 2-4
2-2 Process Flow Diagram of the Bozeman, MT, POTW 2-5
3-1 Performance Potential Graph - Bozeman, MT, 3-3
Secondary Treatment Components.
3-2 Performance Potential Graph - Bozeman, MT,
Rapid Infiltration System. 3-4
LIST OF TABLES
Table Title Page
1-1 Participants in the Bozeman, Montana, CPE 1-3
2-1 Unit Process Design Data at the
Bozeman, Montana, POTW. 2-2
2-2 NPDES Permit Limits for the Bozeman, MT,
POTW (mg/L, except as noted). 2-7
2-3 Average Influent and Effluent Quality
June 1986 through August 1987. 2-9
2-4 Performance of the RI System Prior to
CPE Review Period. 2-12
i i i
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EXECUTIVE SUMMARY
On September 15 to 17, 1987, a comprehensive performance
evaluation (CPE) of the Bozeman, Montana, wastewater
treatment plant was conducted to assist state and federal
personnel in evaluating a 100% M/R grant request. During the
CPE, administrative and operating records were reviewed,
interviews with treatment plant personnel were conducted, and
an inspection of the treatment plant was performed. Using
the information collected during these procedures, an
analysis of the major unit processes and the performance
limiting factors was conducted.
Deficiencies were not found in the administrative,
maintenance, or laboratory procedures used by the treatment
plant personnel. A major unit process evaluation, however,
indicated that the rapid infiltration system is not able to
provide consistent fecal coliform removal. Other rapid
infiltration (RI) systems have reported difficulty in
removing fecal coliforms; thus, RI alone should not be
counted on for fecal coliform removal. The rapid
infiltration system does appear to have adequate ammonia
removal and hydraulic capacity.
The inability of the rapid infiltration system to
consistently provide fecal coliform removal was ranked as the
factor most limiting the treatment plant's ability to meet
its NPDES permit discharge limits. Operator Application of
Concepts and Infiltration/Inflow were rated as factors having
a major effect on performance on a periodic basis. Operator
Application of Concepts was identified as a performance
limiting factor primarily because the inspection team felt
improvement could be made in the aggressiveness with which
plant personnel attempted to solve the fecal coliform removal
problem. Infiltration/Inflow increases the flow to the plant
and could potentially cause hydraulic overloading of the
plant.
i v
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SECTION 1
BACKGROUND
1.1 Introduction
The city of Bozeman, Montana, is located in south central
Montana, approximately 50 miles north of the Montana-Wyoming
border. Bozeman has a population of approximately 21,700.
Including the outlying areas, the Bozeman treatment plant
serves an estimated population of 23,000. The treatment
plant consists of complete mix activated sludge with fine
bubble aeration, followed by rapid infiltration. Sludge is
handled by anaerobic digestion, followed by land application.
Design flow for the treatment plant is 5.78 mgd. The current
flow is 4.57 mgd.
The rapid infiltration system was designed to be used on a
seasonal basis (June through September) primarily to remove
ammonia (via nitrification) and fecal coliforms. From June
to September, flow in the receiving stream is very low.
Ammonia removal is thus needed to prevent ammonia toxicity to
the fish in the receiving stream. The Bozeman wastewater
treatment plant is also subject to effluent fecal coliform
and chlorine residual limits. When the rapid infiltration
system is not in use, a chlorination/dechlorination system is
used to disinfect the wastewater and remove any residual
chlorine. When the rapid infiltration system is in
operation, however, effluent chlorination/dechlorination is
not conducted. Nitrification in the rapid infiltration
system is a biological process and high chlorine
concentrations could potentially inhibit nitrification.
Dechlorination facilities are also not available after the
rapid infiltration system.
Fecal coliform concentrations in the effluent from the rapid
infiltration system periodically exceed discharge permit
limits. The city thus notified the Montana Department of
Health and Environmental Sciences (MDHES) and the U. S.
Environmental Protection Agency (EPA) that the rapid
infiltration system has failed to provide the desired
treatment. The city was, therefore, seeking 100%
modification/replacement (M/R) grant funding to conduct the
changes needed to bring the plant into compliance.
1.2 100% M/R Funding
The Clean Water Act as amended in 1977 (P.L. 95-217) provides
incentives to municipalities for accepting the inherent risk
of choosing innovative and/or alternative (I/A) technologies
1-1
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for treating their wastewater. To offset this risk, Section
202(a) (3) of the Act allows the EPA to pay for 100% of the
costs of modification or replacement of any of the innovative
or alternative processes which fail to meet their design
performance specifications. Before funding these 100% M/R
grants, the Agency must (1) verify that the innovative or
alternative portion of the project has caused the failures,
or (2) has significantly increased the capital or operating
and maintenance expenditures of the facility, and (3) the
failure is not attributable to negligence on the part of any
person. In addition to the above three factors, the Agency
must also determine that the facility failed within a
two-year period following the final inspection, longer than
two years, is not hydraulically or organically overloaded, or
does not lack an adequate O&M program.
1.3 Composite Correction Program
The Office of Research and Development of EPA developed the
Composite Correction Program (CCP) approach for determining
if existing POTWs can achieve compliance without major
construction. This approach is described in EPA's Handbook
No. EPA-625/6-84-008 entitled "Improving POTW Performance
Using the Composite Correction Program (CCP) Approach" (EPA,
1984). The CCP approach has two parts: the comprehensive
performance evalution (CPE) and the CCP. A CPE determines if
the major unit processes are capable of treating the existing
flows and loads; what design, operation, maintenance, and
administrative factors are limiting the performance of the
facility; and if a CCP can improve performance without major
capital expenditures. A CCP, if applicable, would implement
a program for correcting the factors identified as limiting
performance. The CPE/CCP approach is recommended by EPA as
one of the first steps in evaluating an M/R request.
1.4 Purpose of Study
At the request of the MDHES and the U. S. EPA, ERM-Southeast,
Inc. (ERM-SE) performed a CPE of the Bozeman system from
September 15-17, 1987. The results of this CPE are contained
herein. The individuals participating in various portions of
the CPE are presented in Table 1-1. Section 2 presents a
description of the Bozeman system, while the results of the
CPE are presented in Section 3. Appendix A discusses fecal
coliform removal in rapid infiltration systems.
1-2
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TABLE 1-1. Participants in the Bozeman, Montana, CPE
Name/Af filiation
Telephone Number
City of Bozeman
Mr. Jim Wysocki
Mr. Richard Holmes
Mr. Don Noyes
Mr. Don Keil
City Manager
Public Works Director
Plant Superintendent
Plant Chemist
406/586-3321
406/586-9159
406/587-3248
Bozeman Consultants
Mr. Glenn Wood
Mr. Gary Hendrix
Thomas, Dean, and Hoskins
Thomas, Dean, and Hoskins
Montana Dept. Health and Environ. Science
Mr. Craig Brawner
Project Officer for
Bozeman POTW
406/487-0277
406/761-3010
406/444-2406
U. S. Environmental Protection Agency
Ms. Marie Perez
Mr. Stan Smith
National I/A Coordinator 202/382-7286
Region VIII I/A Coordinator 303/293-1547
CPE Team
Dr. John Zirschky, P.E. ERM-Southeast, Inc.
404/971-4671
Mr. Bob A. Hegg, P.E.
CPE Technical Support
Mr. .Sherwood Reed
Mr. Glenn Taylor
Mr. Don Deemer
Process Applications, Inc. 303/223-5787
Cold Regions Res.
and Engr. Lab.
ERM-Southeast, Inc.
ERM-Southeast, Inc.
603/646-4443
404/971-4671
404/971-4671
1-3
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SECTION 2
FACILITY DESCRIPTION
2.1 Background
The basic system at Bozeman is a secondary treatment system
employing the activated sludge process, including
chlorination/dechlorination facilities. Design capacity for
the system is 5.78, with current operations at 4.57. The
rapid infiltration basins were specifically designed to
provide ammonia removal via nitrification and final effluent
polishing prior to discharge to an adjacent stream. The
basins are only generally used during the warm months of
June, July, August, and September. During this period, the
natural flow in the stream is very low and the fish
population would be sensitive to the normal ammonia
concentrations in secondary effluent discharges. During the
remainder of the year, the fish are less affected by the
wastewater ammonia because the dilution by natural background
flow is greater, so the RI basins are bypassed and the
disinfected effluent is discharged directly to the stream
(Table 2-1, Figures 2-1 and 2-2).
There are 19 RI basins in the system, most rectangular in
shape (about 250 x 450 ft), with an infiltration area of
about 2.6 acres (Figure 2-1). Only 14 of the basins are in
routine service for a total infiltration area of 41 acres.
The discharge valves to two basins (Basins 6 and 11) are
broken and thus these basins are not used. Basins 17 through
19 infiltrate very slowly and are not used. The underdrain
system may be responsible for the poor infiltration rate of
these basins. Crushed pipes during construction, air locks
in the underdrains and/or plugging of the underdrains due to
intrusion of soil after construction, or differences in soil
characteristics could be responsible for the lower
infiltration rates in basins 17-19. All of the basins are
grass covered to help sustain adequate infiltration and to
avoid sealing of the infiltration surfaces with fine silt if
bare soil had been used.
The underdrain piping is on 40-foot centers under the basins.
The minimum design depth of burial is about four feet. Some
of the pipes may be slightly less than four feet and some may
be deeper than eight feet. The depth of burial was limited
by the equipment used during construction. The underdrains
were installed using a trenching machine which cuts a narrow
trench and directly installs the plastic drain pipe. A
drainage sock was not placed around the drainage pipe. The
underdrains connect to a common header which then connects to
the discharge flume located on a drainage ditch to the
2-1
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TABLE 2-1. Unit Process Design Data
at the Bozeman, Montana, POTW.
Preliminary Treatment
Primary Clarifier
Number
Weir Overland Rate
Surface Overflow Rate
Hydraulic Detention Time
Aeration Basins
Number
Volume
Hydraulic Detention Time
BOD Loading
Aeration
Secondary Clarifiers
Number
Weir Overland Rate
Surface Overflow Rate
Hydraulic Detention Time
Volume (total)
Di s i nfeet ion
Number
Detention Time
Volume (total)
Surge Basin
Number
Volume
1-42" Mechanical Bar Screen, 1.25 clear
space.
1-42" Manual Bar Screen, 1.25" clear
space (backup).
3-Comminutor
1-18 ft by 18 ft by ? deep mechanically
scraped grit basin.
2-65 diameter by 8 ft deep
14/67 gpd/ft
871 gpdsf
2.38 hrs @ 5.78 mgd.
4-55 ft by 55 ft by 20.25 ft deep.
458,200 gallons, each
7.6 hours
25.8 lb/d/1000 cu. ft.
3-200 HP five bubble diffusion @ 19' deep
(each basin) 38.5% clean water
efficiency.
3-65 ft diameter by 12 ft deep.
9444 gpd/ft
580 gpdsf
3.71 hours @ 5.78 mdg
894,750 gallons
2-112 ft by 54 ft by 8 ft deep basins
69 minutes
277,100 gallons
1-50 ft diameter by 19 ft deep w/aeration
279,435 gallons
2-2
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TABLE 2-1. Unit Process Design Data at the
Bozeman, Montana, POTW (cont'd).
Anaerobic Digestion
Pr imary
Number
Volume
Detention Time
Secondary
Number
Volume
Sludge Dewatering
Sludge Storage
1-50 ft diameter by 28.5 ft. deep
374,517 gallons
22.2 days
1-35 ft diameter by 28.5 ft
165,522 gallons
2-Dissolved Air Flotation Units
2 ponds with total of 404,800 cu. ft.
capaci ty
2-3
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The ERM Group
FIGURE 2-1. PLAN VIEW OF THE BOZEMAN, MT POTW.
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The ERM Group
TO RAPID INFILTRATION SYSTEM ¦ EAST GALLATIN RIVER
FIGURE 2-2. PROCESS FLOW DIAGRAM OF THE BOZEMAN, MT POTW.
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receiving stream. There is no subsurface bedrock or other
natural underground barrier to vertical flow. Thus, if the
ground water table and/or percolate mound is not at a
reasonably shallow depth the underdrains would only collect a
portion of the applied effluent. The O&M manual for the
treatment plant states that the underdrain system was
designed to collect only a portion of the applied wastewater.
The natural soil profile in the RI basin area is a wind blown
loess (clayey, sandy silt) overlying a glacial till. The two
soil types became somewhat mixed during construction of the
basins. The steady-state hydraulic conductivity of the soils
was estimated about 0.78 inches per hour. This infiltration
rate represents a soil with moderate permeability and which
is near the low end of the range for soil types normally
considered for use in RI systems.
A four- to six-day cycle is normally used for basin operation
in the Bozeman system. The basins are filled to a depth of
about 30 inches in about 8 to 12 hours, with the remaining 3
to 5 days in the cycle allowed for percolation through and
drying of the infiltration surface to occur. During the
approximately 120-day operational period (June through
September) each basin experience approximately for 18 to 20
loading cycles.
2.2 NPDES Permit Limits
The Bozeman plant effluent is required to meet secondary
standards (i.e. monthly average BOD and TSS concentrations
of 30 mg/L) . Ammonia in the effluent is limited based upon
un-ionized ammonia concentration in the receiving stream and
ranges from 92 lbs/day in August to 938 lbs/day in April.
The plant has met discharge requirements for BOD and TSS
except for the first three months of 1985. Fecal3 coliform
limits are 1,414 organisms per 100 mL, with weekly peaks of
2,828/100 mL allowed. The chlorine residual limit is 0.02
mg/L (Table 2-2).
2.3 Description of the Claimed I/A Failure
The rapid infiltration system has not been able to
consistently remove fecal coliforms from the effluent
sufficiently to fully meet the effluent limits for the plant.
The city maintains that the inability of the rapid
infiltration system to remove fecal coliforms effectively has
resulted in the continual inability of the treatment plant to
meet its effluent discharge limits. The rapid infiltration
2-6
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Table 2-2. NPDES Permit Limits for Bozeman, MT,
POTW (mg/L, except as noted).
Parameter
Max. Month Max. Weekly Monitoring Sample
Average Average Frequency Type
Flow
BOD
5
TSS
CI residual
Fecal Coliforms
org/100 ml
pH, std. units
Oil and Grease
30
30
0. 02
1414*
6-9
10
45
45
0.02
2828
6-9
10
Continuous recorder
1/week composite
1/week
da ily
2/week
daily
daily
composi te
grab
grab
grab
vi sual
Ammonia
Month
Mass
Di scharge
Limi t
(lb/day)
Equ ivalent
Cone, at
Design Flow
(mg/L)
Jan
750
15.6
Feb
613
12.7
Mar
499
10.4
Apr
938
19.5
May
838
17.4
Jun
410
8.50
Jul
123
2.55
Aug
92
1.91
Sep
250
5. 19
Oct
306
6.35
Nov
438
9.09
Dec
836
17.3
* geometric mean
2-7
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system was funded was an alternative construction grants
project. Thus, the city is seeking 100% M/R funding to
finance whatever measures are needed to achieve compliance.
2.4 System Performance
2.4.1 Influent Wastewater Quality
For the period from September 1986 through August 1987, the
wastewater treatment plant treated an average of 4.57 mgd
(Table 2-3). The average influent BOD concentration was 151
mg/L (range 144 to 190 mg/L), while the average influent TSS
concentration was 123 mg/L (range 104 to 139 mg/L) . The
influent flow rate and BOD and TSS concentrations correspond
to an average loading rate of 5,760 lb/day BOD and 4,683
lb/day TSS. Influent ammonia and fecal coliform
concentration are not routinely measured.
2.4.2 Effluent Wastewater Quality
Average secondary treatment plant effluent BOD and TSS
concentrations for the period September 1986 through August
1987 , were 8.48 and 11.7 mg/L, respectively. Effluent BOD
and TSS concentration for the RI basins were 2.03 and 1.0
mg/L, respectively, while the average effluent flow rate from
the RI basins was 2.23 mgd (Table 2-3). Average effluent
concentrations for the plant for the preceding year was 4.2
mg/L. Effluent ammonia concentrations from the RI basins
averaged 0.93 mg/L. The average effluent mass discharge
during the use of the RI basins was thus 17.3 lb/day of
ammonia, well below the most stringent limits.
A comparison of the average effluent concentration (Table
2-3) versus the NPDES discharge limits for the Bozeman system
(Table 2-2) indicates only fecal coliform counts consistently
exceeds the discharge limits, and these violations only occur
during operation of the rapid infiltration system. The BOD,
TSS, and ammonia limits are consistently met throughout the
year .
2.4.3 Performance of RI System Prior to 1987
During a CPE, generally only the data for the preceeding year
is reviewed, since data collected in previous years
oftentimes does not accurately reflect the current operating
procedures. For the last year, however, the effluent applied
to the RI basins has not contained concentrations of ammonia
in excess of the permit limits. Therefore, achieving
nitrification in the RI basins has not been critical.
2-8
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TABLE 2-3.
Average Influent
and Effluent
Quali ty
June
1986 through August
1987
Influent
BOD (mg/L)
TSS (mg/L)
F1 ow
in if.
POTW
RI
Inf
. POTW
RI
Month
(MGD)
Eff.
Eff.
Eff.
Eff.
1986
Sep
4.83
144
7.03
1.56
112
6.36
0. 33
Oct
4.77
177
20.7
1.47
127
24.6
0.30
Nov
4.54
170
20.4
2.95
128
27. 6
1.13
Dec
4.43
175
21.6
2.8
120
32.6
0.7
1987
Jan
4 .40
176
7.39
_
131
7.23
_
Feb
4.52
168
4.43
-
137
6.36
-
Mar
4.36
190
2.66
-
139
9.90
-
Apr
4.30
175
5.07
-
136
8.14
-
May
4.80
153
2.52
-
117
3.37
-
Jun
4.82
180
2.56
3.27
115
4.42
3.03
Jul
4.60
153
2.39
1.02
113
3.19
0.47
Aug
4.45
149
4.97
1.13
104
6.74
1.05
Average
4 . 57
151
8.48
2.03
123
11.7
1.0
Percent
removal
(vs POTW influent)
-
94. 3
98.5
-
90. 5
99.2
Mass Load, lb/day
5756
327
37.8*
4689
44.6
18.6*
*Based upon an effluent flow rate from the RI basins of 2.23
mgd. Effluent flow is less than influent flow due to
evaporation/infiltration.
2-9
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TABLE 2-3. Average Influent and Effluent Quality
June 1986 through August 1987 (cont'd).
F. Coliform(org/100ml)
Month RI Effluent NH, (mg/L) TSS (mg/L)
Flow
Inf.
"POTW
RI
POTW
POTW
Ef f.
Ef f.
Ef f.
Eff .
(avg.)
Max.
1986
Sep
2.89
6.49
0. 51
1159
3199
Oct
-
-
9.40
1.86
1556
123000
Nov
1.60
-
13.3
2.15
-
-
Dec
1.88
-
10.3
1.92
— —
—
1987
Jan
_
_
1.36
_
_ _
Feb
-
-
1.21
-
- -
-
Mar
-
-
1.89
-
-
-
Apr
-
-
4.95
-
31
115
May
-
-
1.06
-
24
87
Jun
-
-
0.106
0.024
98
138
Jul
2.22
-
0.056
0.027
1939
7658
Aug
2.56
—
0.109
0.044
1641
3936
Average
2.23
-
4.18
0.933
921
19733
Percent removal
(vs POTW
effluent)
-
-
77.7
-
-
Mass Load
, lb/day
678
17.4
-
-
*Based upon an effluent flow rate from the RI basins of 2.23
mgd. Effluent flow is less than influent flow due to
evaporation/infiltration losses in RI system.
2-10
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In order to determine the nitrification potential of the
system, operational data from 1985 and 1986 was examined
(Table 2-4). These data indicate that the system is capable
of removing ammonia as an approximately 90 percent reduction
in ammonia occurred through the RI basin.
2. 5 Summary
This data review indicated that there was a fecal coliform
problem at the Bozeman system. The plant effluent did
consistently contain fecal coliform counts in excess of
permit limits during operation of the RI basins. The CPE
portion of the inspection was then conducted to determine the
reasons why the treatment system was not in compliance. The
CPE results are discussed in Section 3.
2-11
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Table 2-
4. Performance
o f the
RI System
Pr ior
to CPE
Review
Per iod.
F1 ow
BOD
TSS
NH -
N
Month
Inf.
Ef f.
Inf.*
Ef f.
Inf.
Ef f.
Inf.
Ef f .
1985
Jun
4.97
2.43
10.6
1.64
7.31
1.4
2.32
0.3
Jul
4.64
2.63
11.25
0.98
11.38
0.6
4.81
0.45
Aug
4.58
3.05
9.75
1.58
11.06
1.18
0.87
0.17
Sep
4.61
2.73
5.73
1.15
5.77
0.35
0.27
0.10
Oc t
1.69
0.85
14.25
1. 65
15.16
0.56
9.71
1.10
1986
Jun
5.65
3.75
7.25
2.11
7.62
1.67
2.38
0.33
Jul
5.21
3.48
6.6
1.40
5.42
0.38
7.51
0.75
Aug
4. 71
2. 72
6.0
1. 74
6.42
1.0
6. 52
0.61
Sep
4.83
2.89
7.0
1.60
6.36
0.33
6.49
0.51
Oc t
4.77
0.84
20.7
1.47
24.6
0.30
9.40
1.86
Avg.
4. 57
2.54
9. 91
1.53
10.1
0.78
5.03
6.18
Percent
Remova1
-
44.5
-
84.6
-
92.3
—
87.7
*lnfluent to RI Basins
2-12
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SECTION 3
COMPREHENSIVE PERFORMANCE EVALUATION
3.1 Introduction
The results of CPE allow an assessment of the ability of a
particular treatment plant to meet its discharge limits to be
made. Significant components of a CPE include : 1) an
evaluation of the quality of the treatment plant data, 2) a
major unit process evaluation, and 3) a performance limiting
factors analysis. The results of the Bozeman CPE are
summarized herein.
3.2 Assessment of the Quality of the Treatment Plant Data
During a CPE, several analyses are generally conducted as a
means of verifying the quality of a treatment plant's data.
Influent BOD concentrations and flow are used to calculate
the BOD loading (lb/day) to the treatment plant. Population
estimates and "rule of thumb" per capita BOD generation rates
are then used to calculate an estimated BOD loading. If the
measured and estimated BOD loadings are in approximate
agreement, the BOD data are assumed correct. If the two BOD
loadings are not in agreement and no reasonable explanation
exists (e.g., the presence of a large industry in a small
town), the BOD data may be suspect.
The population of Bozeman is approximately 23,000. Assuming
a BOD generation rate of 0.18 lb BOD/capi ta/day yields an
estimated BOD loading to the plant of 4140 pounds per day.
Treatment plant records indicate that the influent wastewater
contained 5760 lb/day. The difference between the estimated
and measured BOD loading is 1,520 lb/day, or approximately
thirty percent. A fifteen percent difference is generally
considered an acceptable balance. The average wastewater
generation rate is 200 gal/cap/day which indicates that
either the plant has a significant infiltration/inflow (I/I)
problems, or the influent flow measurement system needs to be
recalibrated. Either problem, as well as analytical error,
could be responsible for the discrepancy in the BOD loading.
A sludge accountability analysis can also be used to assess
the accuracy of the plant effluent data. For example, the
influent and effluent BOD concentrations can be used to
calculate a mass BOD removal. Suspended solids (TSS) or
sludge generation can then be estimated by converting mass
BOD removed to mass TSS generated using process specified
conversion factors presented in the CPE/CCP manual (EPA,
1983). A solids mass balance is then conducted. The
3-1
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recorded mass of sludge wasted plus the mass of solids
discharged should approximately equal the estimated mass of
solids generated. If the agreement between solids generated
and solids accounted for is good (15% tolerance) , the TSS
data are assumed to be accurate.
An attempt was made to conduct a sludge accountability
analysis without success. Inconsistencies were found in the
sludge wasting records. The mass of solids reportedly wasted
to the thickener was significantly less than that removed
from the thickener. Inaccurate flow metering may explain
this discrepancy. Due to the uncertainties associated with
the sludge wasting records, the results of a sludge
accountability analysis could not be used to verify the
treatment plant data. The inability to do a solids mass
balance, however, does further suggest problems with the
plant data quality.
The effluent ammonia data from the plant also appeared
suspect. The secondary treatment plant is achieving ammonia
removal efficiencies much better than would be expected for a
conventional secondary system. The treatment system,
however, has EPA perform an independent QA/QC check on their
laboratory procedures each quarter. The results of the
laboratory QA/QC indicate that the analytical data is
accurate even though the influent BOD data sludge
accountability analysis, and effluent ammonia concentrations
suggested otherwise.
3.3 Major Unit Process Evaluation
3.3.1 Introduction
As part of a CPE, an evaluation of the treatment performance
potential of each major unit process is conducted, and the
flow rate at which the process would function effectively is
determined. These results are then presented graphically in
a performance potential graph (Figures 3-1 and 3-2). A
discussion of factors considered in developing Figures 3-1
and 3-2 is presented below.
3.3.2 Primary Clarifiers
A surface overflow rate (SOR) of 800 gallons per day per
square foot (gpdsf) was used to evaluate the primary
clarifiers. At this SOR, the clarifiers were assigned a
performance potential of 5.3 mgd.
3-2
-------
The ERM Group.
CURRENT DESIGN
Q = 4.57 Q = 5.78
PRIMARY CLARIF1ERS
2. SOR — gpdsf
AERATION BASINS
3. HDT - Hrs.
4. ORG. LOAD - lbs/1000 ft3
5.02 AVAIL - lbs. 02/lb BOD5
FINAL CLARIF1ERS
6. SOR — gpdsf
CHLORINATION
7.HDT - MIN.
GRAVITY THICKENER
8. LOAOING RATE lbs/doy/ft2
DISSOLVED AIR FLOTATION
9. LOADING RATE lbs/doy/ft2
AEROBIC DIGESTER
10.HDT - DAYS
ANAEROBIC DIGESTER
11. HDT - DAYS
SLUDGE HOLDING PONDS
12. HDT - DAYS
ZX
' 7 7
7 7 /I
/ / /
7T
zzzz.
zz;
,/ / /
/ / /i
-7-7
7 \/ 7
/ 7 7
Z2
-7*7-
/ / / 7/
///////A
7 7/77
/ / / / ~r
7 7 /-7-7-Z
/ /
—7—7-
y-7-V
7-7-Y
'77
7 7
V 7 7
7T
7-7-7
-7-Ti
/ 7 7
7 7 7\
-7-7-
' 7 7
7 7 /\
-7—7-
-7—7-
7 /
7 7/
7 7/
7 7 *
-7—7-
7 7 7
7V
izzz:
'77
7/7
-7—7-
-7—7-
-7—r
4-° 5-° FLOW — MGD (l) 6-° 7-°
FIGURE 3-1.
PERFORMANCE POTENTIAL GRAPH - BOZEMAN, MT,
SECONDARY TREATMENT COMPONENTS.
-------
' lie ERM Group
CURRENT DESIGN
Q = 4.57 Q = 5.78
HYDRAULIC CAPACITY
AMMONIA
FECAL COLIFORM
A^>A66AA6!/xV^oo66<^^
RAPID INFILTRATION FECAL COLIFORM REMOVAL PERFORMANCE
VARIES SIGNIFICANTLY FROM SITE TO SITE. REVIEW \
OF PRESENT DATA SUGGESTS SYSTEM WILL NOT CONSISTENTLY
MEET FECAL COLIFORM LIMITS WITHOUT DILUTION OR CHLORINlATION.
0.0
\
1.0
2.0
3.0
FLOW
4.0
MGD
5.0
6.0
7.0
ASSUMPTIONS:
1. SEASONAL OPERATION, APPLICATION OF ADVANCED SECONDARY QUALITY EFFLUENT,
REPAIR NONFUNCTIONAL BASINS.
2. PAST SUCCESSFUL PERFORMANCE WITH WET/DRY RATIO OF APPROXIMATELY
0.3, INFLUENT AMMONIA CONCENTRATION OF 10 mg/L OR LESS.
FIGURE 3-2. PERFORMANCE POTENTIAL GRAPH - BOZEMAN, MT,
RAPID INFILTRATION SYSTEM.
-------
3.3.3 Activated Sludge System
Hydraulic detention time was determined to be the most
limiting design factor. Using a hydraulic detention time of
8 hours yields a performance potential of 5.45 mgd. The
secondary clarifiers were also rated based upon an SOR of 800
gpdsf of which yielded a performance potential of 6.0 mgd.
3.3.4 Disinfection Facilities
A 60-minute chlorine contact time was used to evaluate the
disinfection system. The volume of the chlorine contact time
is such that greater than 7.0 mgd can be effectively
disinfected with the present system. Dechlorination
facilities are also believed to be adequate.
3.3.5 Sludge Handling Facilities
The sludge holding ponds were determined to be the most
limiting component of the sludge handling facilities. At a
holding time of 180 days, the holding ponds were rated as
having a performance potential of 5.0 mgd.
3.3.6 Rapid Infiltration System
3.3.6.1 Hydraulic Capacity
Based upon historical records of infiltration rate of 1986
and 1987 (one measurement each year), the rapid infiltration
system appears to have adequate hydraulic capacity to treat
the design flow of 5.78 mgd. The city however should correct
the valve problems which have made two basins (Numbers 6 and
11) inoperable in order to reduce the hydraulic loading to
the remaining basins.
Three basins (Nos. 17-19) reportedly have low infiltration
rates. Possible factors for the low infiltration rate in
these three basins include an air lock in the underdrains,
blockage of the underdrains, and different soil
characteristics in these basins. Installing an air vent in
the underdrains to these basins would prevent an air lock and
allow the city to easily determine if the underdrains are
blocked.
3.3.6.2 Ammonia Removal
In 1985 and 1986, the RI system averaged approximately 90
percent ammonia removal (Table 2-4). The secondary treatment
plant has shown the capability to produce an wastewater
quality of 10 mg/L of ammonia-nitrogen. The critical month
for effluent quality for ammonia is August, during which time
3-5
-------
the treatment plant is permitted to discharge 98 pounds/day
of ammonia. At the design flow of 5.78 mgd, this mass limit
corresponds to an effluent concentration of approximately 1.9
mg/L. A significant water loss, however, occurs in the rapid
infiltration system. When the RI basins are in use, effluent
flow averages roughly 60 percent of the influent flow. The
effluent ammonia concentration during the critical month
could thus be (1.9/0.6) 3.2 mg/L. To produce an effluent
quality of 3.2 mg/L, the RI basins need only operate at 67
percent efficiency, instead of at the 90 percent efficiency
achieved in 1985 and 1986 (Table 2-4).
3.3.6.3 Fecal Coliform Removal
The RI system is not providing effective fecal coliform
removal. Based upon the literature (see Appendix A) and the
CPE team's previous experience at other RI systems, there
does not appear to be an accurate means to predict fecal
coliform removal performance. Several attempts were also
made to relate the fecal coliform removal performance to the
infiltration rate of each basin without success. Thus, there
was no means to accurately assess the fecal coliform
performance potential of the RI system.
3.4 Performance Limiting Factors
3.4.1 Overview
Seventy potential performance limiting factors were evaluated
during the course of the CPE. The 70 factors covered four
main areas: design, operation, maintenance, and
administration. Interviews, reviews of existing records,
performance data, and the results of the major unit process
evaluation were used to detemine if any of the 70 factors
were significantly affecting performance.
Once the performance limiting factors were identified, these
factors were prioritized. "A", "B", and "C" factors were
first identified, using the definitions presented below:
Rating
Class Adverse Effect of Factor on Plant Performance
A Major effect on a long-term repetitive basis
B Minimum effect on a routine basis or major effect
on a periodic basis
C Minor effect
3-6
-------
The importance of each of these factors within their rating
class was then assessed. The performance limiting factors in
order of priority are presented below:
A Factors
1. Fecal Coliform Removal in the RI System
B Factor
1. Operator Application of Concepts
2. Infiltration/Inflow (Historical)
C Factors
1. Equipment - Malfunctions
2. Performance Monitoring
3. Process Flexibility
4. Process Accessibility for Sampling
5. Industrial Loading to Plant
A brief discussion of each of these factors is presented
below.
3.4.2 "A" Factors - Fecal Coliform Removal in RIB's
Current design guidance for rapid infiltration systems (EPA,
1983) states that fecal coliform removal in RI systems is
excellent. Poor fecal coliform removal efficiencies,
however, have been experienced at several full-scale
operational systems (e.g., Waycross, Georgia). Poor fecal
coliform removal has been experienced under a variety of soil
types and site conditions and in systems with and without
underdrains. The data from the Bozeman system indicates that
the Bozeman system does not provide consistent fecal coliform
removal. Possible explanations for the poor fecal coliform
removal performance include a short travel distance to the
underdrains, the inability to dry the fine textured silt loam
soil such that pathogen die-off occurs before the next
loading cycle, and contamination of the underdrains from
non-wastewater sources (e.g., rodents). Additional studies
are recommended to further document the sources and removal
of fecal coliforms in the rapid infiltration basins such that
an effective solution can be developed.
3-7
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3.4.3 "B" Factors
3.4.3.1 Operator Application of Concepts
A number of factors combined led to the ranking of "Operator
Application of Concepts" as a performance limiting factor.
It is important to note that the operators' appitude and
abilities were felt to be very good. The CPE team, however,
felt that there was some confusion between the plant staff as
to why certain operating parameters were selected. For
example, by not operating the RI basins and using the
chlorination-dechlorination facilities, the treatment plant
would have been in compliance with its NPDES permit during
the summer of 1987. A clear explanation as to the reasons
for continued operation of the RI basins instead of using the
conventional disinfection system was not provided.
Improvement in the aggressiveness with which plant personnel
pursued special studies and operational changes to optimize
performance of the system could also be made. Finally some
common operational parameters for RI systems (e.g.,
infiltration rate) were not routinely measured and recorded.
3.4.3.2 Infiltration/Inflow (I/I)
I/I was ranked as a performance limiting factor based upon
the CPE team's past experience with the plant and the high
per capita wastewater generation rate (approx. 200
gal/person/day). As the wastewater flow approaches design
capacity, I/I could become a more significant problem.
Maximum performance and longevity of the RI basins is
enhanced by decreasing the flow through the basins. Thus,
decreasing I/I can improve system performance.
3.4.4 "C" Factors
3.4.4.1 Equipment Malfunctions
At the present time, equipment malfunctions or any of the
other C factors are not significantly limiting the
performance of the system. These factors, however, should be
addressed. Two of the basins are currently out-of-service
due to malfunctioning valves. These valves should be fixed
as soon as practical. Three basins are not being used due to
slow infiltration rates. Plant personnel believe that the
soil types are fairly uniform across the site. The CPE team
personnel generally agreed with this assessment of the soil
characteristics. The soils in basins 17-19, however, may
have had a higher clay content than soils from the other
basins. The three poor infiltrating basins are all located
on the same underdrain lines. Lack of venting for these
underdrains could have caused an air lock in the drains.
Installing vents should prevent an air lock as well as allow
3-8
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the lines to be flushed with water to determine if any of the
lines are blocked.
3.4.4.2 Performance Monitoring
Improvement could be made in the fecal coliform monitoring
procedures. Special studies should be developed to monitor
fecal coliform removal through the system to help in
developing an effective corrective measure.
3.4.4.3 Process Flexibility
Plant personnel stated that they were unable to effectively
split flow between the RI basins and the chlorine contact
basin. The system was originally designed to provide this
flexibility. Overly sensitive flow controllers could be
responsible for this lack of flexibility. Plant personnel
should more actively pursue a solution to this problem.
3.4.4.4 Process Accessibility for Sampling
At present, there is no easy means to monitor the performance
of each basin. Operational experiences at other RI systems
has shown that individual basins within a system can perform
differently. By being able to easily sample each basin,
plant personnel could develop an operating schedule which
would provide the highest quality effluent. During any
future modifications to the plant, the addition of sampling
points should be considered.
3.4.4.5 Industrial Loading to Plant
One industry periodically batch discharges a high strength
waste. The shock loading to the plant can adversely affect
performance by, for example, killing the nitrifying
microorganisms. The city should continue pursuing measures
to prevent future shock loads.
3.5 Summary
The CPE indicated that the RI basins were not capable of
achieving adequate fecal coliform removal. Before designing
corrective measures, however, additional studies should be
conducted by the city to determine more accurately, the
pathogen removal efficiency of the present facilities. With
the exception of fecal coliform removal in the RI basins, the
treatment plant appears to be capable of meeting its
performance objectives.
3-9
-------
APPENDIX A
PATHOGEN REMOVAL IN RI SYSTEMS
-------
APPENDIX A
PATHOGEN REMOVAL IN RAPID INFILTRATION SYSTEMS
Case studies and Removal Mechanisms
Pathogen removal in rapid infiltration systems, including
bacteria, virus, parasitic protozoa and helminths is
accomplished by filtration, adsorption, desiccation,
radiation, predation, and exposure to other adverse
conditions. Any protozoa and helminths are removed at the
soil surface because of their larger size. Bacteria are also
removed at the surface and in the profile by filtration, but
soil adsorption may also be important. Viruses are removed
almost entirely by adsorption. In slow rate land treatment
with application rates of a few inches per week, fecal
coliforms are typically removed by percolation through 5 feet
of soil. In contrast, the EPA Process Design Manual (1)
suggests an average fecal coliform percolate concentration of
between 10/100 mL and <200/100 mL might be expected after 15
feet of travel through unsaturated soil. These removal
mechanisms are approximately the same when either primary or
secondary effluent is applied.
The data in Table A-l suggests that, in general, rapid
infiltration systems have the capability to remove fecal
coliforms to levels well below 1000/100 mL with adequate
travel distance in the soil. In addition to the geographical
and soil differences, the systems listed in Table A-l have
quite different unit hydraulic loading rates and operational
cycles. These data suggested that fecal coliform removal is
dependent upon the following major factors:
o Soil Type and Texture: bacterial removal is
inversely proportional to the particle size of the
soil.(12) The finer the texture the better the
removal as long as there are not fissures or
channels in the soil allowing deep penetration.
o Soil Depth: the increased distance increases the
residence time to the soil and provides greater
opportunities for filtration, sedimentation, and
adsorption.
o Hydraulic Loading Rates: the unit loading rate
controls the flow rate in the soil (up to the in
situ permeability). The rate and duration of
application influence whether unsaturated flow or
temporary saturated conditions prevail in the upper
soil layers.
A-l
-------
Table A-l. Fecal Coliform Removal at Selected RI Systems.
Fecal Coliforms #/100mL Travel
Location Soil Wastewater Percolate Distance(ft)
Hemet, CA (3)3
sand
6xl04
11
7
Hollister, CA (3)
sandy loam
12.4xl06
17.1xl04
23
Lake George, NY (4)
sand
3.6xl05
72
7
Landis, NJ (5)
sand/gravel
TNTCb
16
7
Milton, WI (6)
gravel/sand
TNTC
0
40
Phoenix, AZ (7)
sand
2.4xl05
104
100
Vineland, NJ (8)
sand/gravel
TNTC
0
23
Ft. Devens, MA (9)
sand/gravel
4.2xl04
0
300
Medford, NY (10)
sand
2500
250
25
Corvallis, MT (11)
sand
1600
3
60
Reference Number
b
TNTC = too numerous to count
A-2
-------
o Loading Cycle: if the drying portion of the cycle
is too short, there may not be time for die-off of
the bacteria to occur. The next application cycle
might then desorb and flush some of the organisms
out of the soil.
o Organic and nutrient content of wastewater and
soil: there can be re-growth of fecal coliforms in
the soil in the presence of adequate moisture and
organic content. Re-growth is not likely if the
organic status of the soil is poor. Temperature,
pH, and other environmental factors can also be
s ign i f icant.
A change in the ionic composition of the water moving through
the soil accompanied by a increased rate of flow has been
shown to desorb both coliforms and bacteria from a variety of
soil types (13, 14). In these cases, movement has been
observed after sudden and intense rainfall. In a controlled
laboratory study, Lance was able to desorb viruses by
applying de-ionized water, but they were readsorbed within
the eight-foot soil column (15). Allowing the soil to dry
for five days prevented desorption with de-ionized water. It
has also been noted in other studies that removal efficiency
for bacteria increases as the soil mosture decreases (16).
Gerba has summarized movement of bacteria through soils at
ten different sources with results very similar to those
presented in Table A-l (12). The maximum observed travel
distances ranged from 3 to 1,500 feet in soils ranging from
fine loamy sands to coarse gravels. Evidence of subsurface
regrowth has been observed in Israel where chlorinated
effluent with about 2 total coliforms/100 ml has been pumped
into injection wells. Water is pumped out of the same wells
during the irrigation gSeason, and the total coliform count
ranged from 10 to 10 . Further investigation showed that
coliform re-growth was occurring in the organic mat
surrounding the well packing. Gerba also shows that virus
removal on coarse sagd is related to the hydraulic loading
rate. At^O.02 gpm/ft , a 90 percent removal was observed; at
>1 gpm/ft more than 90 percent of the virus flushed through
the system.
Bouwer described the performance of a full-scale rapid
infiltration basin system in Phoenix, Arizona (17). When
unchlorinated secondary effluent was applied to the coarse
sand basins, fecal coliform peaks (>1000/100 ml) were
observed in a well 60 feet below the basins. Chlorination
was commenced and the effluent applied to the basins averaged
3500 fecal coliforms/100 mL. The concentrations in all of
the observation wells then dropped essentially to zero. The
chlorination did not seem to affect the nitrification. The
A-3
-------
applied effluent contained 18 mg/L (mostly ammonia) while the
recovered percolate (at 60 feet) contained less than 6 mg/L
(mostly ni trate) .
Rice (18) examined pilot RI basins and soil columns receiving
primary effluent. The soil was a loamy sand and was flooded
continuously for one week followed by one to three w^eks of
drying. The applied primary effluent contained 8x10 fecal
coliforms and the percolate averaged about 50/100 mL after 8
feet of travel in the soil column.
The Medford, NY, study listed in Table A-l was conducted with
disinfected tertiary effluent. (10) The soil involved was a
coarse sand and since ground water recharge was the purpose
of the study, very high hydraulic loadings were tested (about
15 feet) per day) . The fecal coliforms in the applied
effluent averaged 2500/100 mL (range:<3-4.6x10 ). Viruses at
a concentration of <1 PFU/L were also found on six occasions
at the same depth. The hydraulic rate used in this study was
the highest found in the literature.
Application of Findings to Bozeman, MT, System
The literature discussed above indicate that even at very
high hydraulic loading rates, significant bacterial removal
is possible with sufficient travel distance in competent
soils. It seems possible that a four-foot travel distance
may be insufficient with the hydraulic loading rates in use
at Bozeman, since saturated flow is likely to prevail on a
temporary basis during at least part of the operational
cycle.
Even with a high hydraulic loading, the performance at
Bozeman is surprising given the soil characteristics. It is
possible that the soil profile is not competent above the
excavations made to install the underdrains. If this is the
case, some portion of the applied effluent may flow almost
directly to the drains. BOD and TSS data, however, do not
suggest that the soil is not competent. The relaively low
infiltration rates may also require that the basins be loaded
before the soils are dry. Thus, pathogen die-off may not
occur between loadings. Each loading may then wash out
pathogens from the previous application.
It is also possible that only some basins are perform poorly
with the other basins, in effect, providing dilution water.
An investigation of the poor performing basins should be
considered as a major focus during any further investigation
to identify any soil or construction differences as compared
to the other basins.
A-4
-------
REFERENCES
1. US EPA Process Design Manual for Land Treatment of
Municipal Effluent, EPA 625/1-81-013, US EPA CERI,
Cincinnati, OH, Oct. 1981.
2. Reed, S. C., R. W. Crites. Handbook of Land Treatment
Systems for Industrial and Municipal Wastes, Hoyes
Publications, Park Ridge, NJ, 1984.
3. Pound, C. E., R. W. Criters, J. V. Olsen. Long-Term
Effects of Land Application of Domestic Wastewater -
Hollister California, Rapid Infiltration. EPA
600/2-78-084, US EPA, Washington, DC, April 1978.
4. Aulenbach, D. B., Long-Term Recharge of Trickling Filter
Effluent into Sand, EPA 600/2-79-068, US EPA Washington,
DC, March 1979.
5. Koerner, E. T., D. A. Haws, Long-Term Effects of Land
Application of Domestic Wastewaters: Vineland, New
Jersey, Rapid Infiltration Site, EPA 600/2-79-072, March
1979.
6. Benham-Blair and Associates, Inc., Long-Term Effects of
Land Application of Domestic Wastewater: Milton,
Wisconsin,' Rapid Infiltration Site, EPA 600/2-79-145, US
EPA, Washington, DC, August 1979.
7. Bouwer, H., R. C. Rice, J. C. Lance, R. G. Gilbert.
"Rapid Infiltration Research at Flushing Meadows
Project, Arizona", Journal of the Water Pollution
Control Federation , 52(10):2457-2470, Oct. 1980.
8. Reed, S. C, R. Thomas, N. Kowal. "Long-Term Land
Treatment, Are There Health or Environmental Risks?"
Presented at 1980 Annual ASCE Annual Conference,
Seattle, WA, Oct. 1980.
9. Satterwhite, M. B., B. J. Condike, G. L. Stewart,
Treatment of Primary Sewage Effluent by Rapid
Infiltration, CRREL Rpt. 7(5-49, USA CRREL, Hanover, NH,
1976.
10. Vaughn, J. M., E. F. Landry. "The Occurrence of Human
Enteroviruses in a Long Island Groundwater Aquifer
Recharged with Tertiary Wastewater Effluents", In:
Proceedings Symposium on Land Treatment of Wastewater,
Hanover, NH, August 1978, pp 233-244.
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11. Roy F. Weston Inc. "Post Construction Evaluation of
Corvallis, Montana, Rapid Infiltration Process", US EPA
MERL, Cincinnati, OH, Nov. 1983.
12. Gerba, C. P., C. Wallis, J L. Melnick. "Fate of
Wastewater Bacteria and Viruses in Soil". Jour. ASCE
Irrigation & Drainage Division, Proc. Am. Soc. of Civil
Engrs. 101(IR3) : 157-174 , Sept. 1975.
13. Hagedorn, C., D. T. Hansen, G. H. Simonson "Survival and
Movement of Fecal Indicator Bacteria in Soil Under
Conditions of Saturated Flow" Environmental Quality,
7(1)55-59, Jan. 1978.
14. Wellings, F. M., A. I. Lewis, C. W. Mountain, I. V.
Pierce "Demonstration of Virus in Groundwater After
Effluent Discharge onto Soil" Applied Microbiology,
29(6)751-757, June 1975.
15. Lance, J. C., C. P. Gerba, J. L. Melnick. "Virus
Movement in Soil Columns Flooded with Secondary Sewage
Effluent" Applied & Environ. Microbiology.
32 (4) : 520-526, Oct. 1976.
16. Lance, J. C. "Fate of Bacteria and Viruses in Sewage
Applied to Soil", presented at ASAE Winter Meeting,
Chicago, IL, Dec. 1976.
17. Bouwer, H. , R. C. Rice. "Renovation of Wastewater at
the 23rd Avenue Rapid Infiltration Project", Jour. Water
Pollution Control Federation. 56 (1) :76 — 83, Jan. 1984 .
18. Rice, R. C., H. Bouwer. "Soil-Aquifer Treatment Using
Primary Effluent", Journal Water Pollution Control
Federation. 56(1): 84 — 88, Jan. 1984.
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