ENVIRONMEN'TMsJ'ROTECTION A
OFFICE OF i;\HMI< KMKNT
REPORT ON
EFFECTS OF WASTE DISCHARGES
WATER QUALITY OF THE SOUTH PLATTE RIVER
DENVER METROPOLITAN AREA
NATIONAL FIELD INVESTIGATIONS CENTER-DENVER
AND
REGION VIII
DENVER, COLORADO
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ENVIRONMENTAL PROJECTION AGENCY
OFFICE OF ENFORCEMENT
Report On
Effects of Waste Discharges
On
Water Quality of the South Platte River
Denver Metropolitan Area
DRAFT FOR REVIEW ONLY
National Field Investigations Center-Denver
and
Region VIII
Denver, Colorado
February 1972
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TABLE OF CONTENTS
Page
LIST OF TABLES ii
LIST OF FIGURES ill
INTRODUCTION 1
WASTE SOURCE EVALUATIONS 3
Denver Northside Wastewater Treatment Plant 3
General 3
Wastewater Treatment Facilities 3
Discussion of In-Plant Survey and Findings 5
Metropolitan Denver Sewage Disposal Plant 9
General 13
Wastewater Treatment Facilities 13
Discussion of In-Plant Survey and Findings 15
STREAM SURVEYS 25
General 29
Findings of November Bacteriological Survey 32
Findings of the December Survey 34
WATER QUALITY IMPROVEMENT MEASURES 39
CONCLUSIONS 43
RECOMMENDATIONS 46
REFERENCES 48
APPENDICES
A SAMPLING PROCEDURES A-l
B DATA ON METROPOLITAN DENVER SEWAGE TREATMENT PLANT
AND NORTH DENVER WASTEWATER TREATMENT PLANT .... B-l
C REPORT BY ENVIRONMENTAL PROTECTION AGENCY, REGION
VII, KANSAS CITY, MISSOURI, "FEDERAL ASSISTANCE
PROJECT METROPOLITAN DENVER SEWAGE DISPOSAL DISTRICT
NO. 1, OCTOBER 1969 - FEBRUARY 1970" C-l
D COLORADO WATER QUALITY STANDARDS D-l
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LIST OF TABLES
Table
Number Description Page
1 SUMMARY OF ANALYTICAL RESULTS AND FIELD MEASURE-
MENTS FOR THE DENVER NORTHSIDE WASTEWATER TREATMENT
PLANT 7
2 MONTHLY AVERAGES OF BIOCHEMICAL OXYGEN DEMAND AND
SUSPENDED SOLIDS REMOVALS AT THE NORTH DENVER
WASTEWATER TREATMENT PLANT FOR DENVER 8
3 WASTE TREATMENT FLOWS AND COSTS AT SELECTED SATELLITE
PLANTS 11
A OTHER WASTEWATER TREATMENT FACILITIES IN THE
METROPOLITAN DENVER AREA 12
5 SUMMARY OF ORGANIC AND NUTRIENT DATA FOR NORTHSIDE
AND METRO PLANTS, August 1-9, 1971 16
6 SUMMARY OF HEAVY METALS DATA FOR METRO AND NORTHSIDE
PLANTS, August 1-9, 1971 17
7 BACTERIOLOGICAL AND CHLORINE RESIDUAL DATA,
METROPOLITAN DENVER SEWAGE DISPOSAL PLANT 18
8 REMOVAL EFFICIENCIES FOR DENVER METRO AND DENVER
NORTHSIDE FACILITIES 20
9 BI-WEEKLY AVERAGES OF BIOCHEMICAL OXYGEN DEMAND AND
SUSPENDED SOLIDS REMOVALS AT THE METROPOLITAN DENVER
SEWAGE DISPOSAL PLANT 22
10 SUMMARY OF ANALYTICAL RESULTS AND FIELD MEASUREMENTS
FOR THE SOUTH PLATTE RIVER, 19th Street to 88th Avenue,
August 30-September 2, 1971 30
11 RESULTS OF BACTERIAL ANALYSES-SOUTH PLATTE RIVER
STREAM SURVEY, November 17-21, 1971 33
12 SUMMARY OF ANALYTICAL RESULTS AND FIELD MEASUREMENTS
FOR THE SOUTH PLATTE RIVER, 19th Street to 88th
Avenue, December 13-17, 1971 36-37
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LIST OF FIGURES
Figure
Number Description Page
1 MUNICIPAL WASTEWATER TREATMENT FACILITIES -
METROPOLITAN DENVER AREA 2
2 FLOW DIAGRAM - NORTH DENVER WASTEWATER TREATMENT
PLANT 4
3 FLOW DIAGRAM - METROPOLITAN DENVER SEWAGE
TREATMENT PLANT 14
4 SOUTH PLATTE RIVER FROM 19TH STREET TO 88TH
AVENUE 28
5 DISSOLVED OXYGEN PROFILE FOR THE SOUTH PLATTE
RIVER DOWNSTREAM FROM DENVER METRO EFFLUENT 41
iii
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INTRODUCTION
Water quality investigations were conducted in the South Flatte
River Basin during August-December, 1971. Studies included an evaluation
of the waste treatment practices at the Metropolitan Denver Sewage Disposal
Plant (Metro), the North Denver Wastewater Treatment Plant (Denver North-
side), and other satellite plants [Figure 1]. Subsequently, stream
surveys were conducted on the South Platte River to determine the impact
of waste loads on water quality. The primary objectives of the survey
were to:
1. Determine if established State and Federal water quality
standards were being met.
2. Ascertain if adequate treatment were 'provided in accordance
with established treatment requirements.
3. Determine the extent of water quality improvement in the
South Platte River Basin since the 1966 Enforcement
Conference .
4. Recommend water quality improvement measures.
The in-plant survey was conducted at Metro during August 1-9, 1971,
to measure the operation efficiency and waste loads discharged. Effluent
from the Denver Northside Plant constitutes the major portion of flows
received at Metro.
This report will discuss the results of the in-plant evaluations
and the subsequent stream surveys in relation to the aforementioned
objectives.
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KULGCR
—ccu53i"Z5
I. SOUTH ADAMS SANITATION OISTIICT
. KETIOPOLITAN DENVER SEWAfiE DISPOSAL PLANT
. NORTH DENVER WASTCWATER TREATMENT PLANT
. SOUTH LAKEWOOD SANITATION DISTRICT
. EN6LEWOOD SANITATION DISTRICT
UTTLfTON SANITATION DISTRICT
. IAKER SANITATION DISTRICT
. AIVADA
. CLEAR CREEK VALLEY SANITATION DISTRICT
10. WHEATRIDEE
11. SOLDEN • COORS
12. AURORA SINITtTIQN DISTRICT
U. flUlAitl DIM HtLO
14. GLENDALE SANITATION DISTRICT
15 FITZSIMONS HOSPITAL
Figure 1. Municipal Wastrualer Treatment Facilities Metropolitan Denver Area
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WASTE SOURCE EVALUATIONS
NORTH DENVER WASTEWATER TREATMENT PLANT
General
The North Denver plant is a primary wastewater treatment facility
with a design capacity of 120 million gallons per day (mgd). The plant
was constructed in 1936, with additional clarifiers being constructed
In 1946 and 1965. Effluent and digested sludge from this facility are
piped separately to the Metro plant for additional treatment.
This plant is staffed with a superintendent, an operations foreman,
and 30 operators. Some of these operators have Class "C" and "D"
Operator's Licenses.* A laboratory staff of eight chemists monitors
treatment efficiency within the plant. Samples from approximately 80
Industrial wastewaters discharged to the Northside plant are analyzed,
and the results are used as a basis for determining customer charges.
Wastewater samples collected by the Denver County Health Department
are also analyzed in this laboratory.
Wastewater Treatment Facilities
The operation of the Northside plant has changed since it was
2
evaluated during the South Flatte River Basin Project Studies ; the
effluent now is pumped to the Metro plant for further treatment instead
of being chlorinated and discharged to the South Platte River. [The
flow diagram for this facility is shown in Figure 2.] The Northside
flow constitutes about 75 percent of the total flow to Metro.
* The State of Colorado has a Volunteer Certification Program for
Wastewater Treatment Operators, Class "A" being the highest and
a Class "D" the lowest level of certification. There are no
operators with Class "A" or Class I!B" certification at Northside.
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INFLUENT
GRIT
REMOVAL
PREAERATION
GREASE
FLOTATION
AND
REMOVAL
GREASE TO
RENDERING
COMPANY
SECONDARY
DIGESTION
PRIMARY
DIGESTION
EFFLU NT TO
METRO
DIGESTED
SLUDGE TO
METRO
LEGEND
STATION DESCRIPTION
E DENVER NORTHSIDE INFLUENT
G DENVER NORTHSIDE PRIMARY
[SAMPLED AT DENVEI METRO PLANT)
Figure 2. Flow Diagram North Denver Waslewaler Treatment Plant.
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The principal components of the system are as follows:
1. Preliminary treatment - bar screens, grit chambers (5),
pre-aeration basins (3), grease flotation and removal.
2. Primary clarifiers (8) - 150 feet in diameter and 14
feet deep with skimming arm to remove floating materials.
3. Digesters (heated) - 6 primary, 2 secondary; each 85
feet in diameter and 30 feet deep.
As indicated above, sludge is pumped to the Metro plant for further
treatment (i.e., secondary digestion). Denver Northside plant officials
claim that a volatile solids reduction of 65 percent is obtained in the
digestion process.
Discussion of In-Plant Survey and Findings
The North Denver wastewater treatment plant was evaluated August
1-9, 1971. Influent samples were collected upstream from the point of
supernatant return [Figure 2-Station £]. Effluent samples from the
Northside plant were collected where they enter the Metro plant [Figures
2 and 3-Station G]. All wastewater samples were analyzed at the DFI-DC
laboratory for BOD, COD, TOC, and solids (total, suspended, volatile
suspended, and settleable). Nutrients were determined for the influent
samples only. Influent samples were also analyzed for selected heavy
metals to ascertain if concentrations were at levels which could affect
biological processes.
According to plant officials, 130 industries discharge wastewater
to the North Denver plant (estimated at 8-10 percent of the total flow),
which was designed for peak flows of 120 mgd; if exceeded, the excess
is by-passed to the South Platte River. Although no by-passing was
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observed at the plant during the survey, an interceptor carrying
wastewater to the Denver Northside plant was observed to be overflowing
to the South Platte River at Franklin Street. Although the total
flow by-passed could not be ascertained, it was evident from the
sludge bank in the river that the interceptor had been overflowing
for a prolonged period. Another raw sewage discharge was observed
at 47th Avenue. An official of the City and County of Denver stated
that the latter by-pass results from overloading of the Broadway
sewer. The amount of by-passed flow was not available from the
official. A contract has been let to install additional interceptor
capacity by June 1972.
Analyses of influent and effluent data for this plant indicate
BOD and suspended solids removal ranges of -11 to 58 percent and 6 to
96 percent, respectively*[Table 1]. A review of plant records for the
period January 1-June 30, 1971, shows that monthly removal efficiencies
averaged between 22 and 36 percent for BOD, and between 39 and 60 per-
cent for suspended solids liable 2]. Concentrations of heavy metals
were low and would not affect biological treatment processes. Plant
officials do not know the source of these heavy metals.
* The negative BOD removal is attributed to carryover of solids from
the primary clarifiar-.
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TABLE 1
SUMMARY OF ANALYTICAL RESULTS AND FIELD MEASUREMENTS FOR THE
DENVER NORTHSIDE WASTEWATER TREATMENT PLANT
August 1-9, 1971
Parameter Measured
Flow (MGD)-
Value
Influent Effluent
76.7-92.5
Percent
Reduction (Range)
•v«v
pH (Units)
Temperature (°C)
Conductivity (umhos)
Biochemical Oxygen Demand (BOD)(mg/1)
Suspended Solids (mg/1)
Volatile Suspended Solids (mg/1)
Settleable Solids (mg/1)
Chemical Oxygen Demand (COD)(mg/1)
7.2-8.8
18-24
1000-1500
180-430
320-1240
240-1200
3.5-5.0
590-1800
105-310
30-300
30-160
0.2-0.7
160-270
UD-'-sa
6-96
67-96
86-90
73-85
J/ Flow measured at Metro plant. Northside effluent samples collected at Metro (Station G-Figure 3).
Flow recording equipment at Denver Northside not considered accurate.
2/ Numbers in parentheses are negative numbers.
Water Quality Investigations
in the South Platte River Basin
1971 - DFI-DC
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TABLE 2
MONTHLY AVERAGES OF BIOCHEMICAL OXYGEN DEMAND AND
SUSPENDED SOLIDS REMOVALS AT THE j/
NORTH DENVER WASTEWATER TREATMENT PLANT FOR 1971-
21
Month"
January
February
March
April
May
June
Percent
BOD Removal
35
36
25
23
32
22
Percent Suspended
Solids Removal
60
55
44
39
53
60
_!/ Efficiencies calculated on the basis of data provided by Northside officials.
2f Supernatant was returned upstream of the pre-aeration chambers
January-April and returned upstream of the bar screens May-June
[Figure 2].
Water Quality Investigations
in the South Platte River Basin
1971 - DFI-DC
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METROPOLITAN DENVER SEWAGE DISPOSAL PLANT
General
The Metro plant is a secondary treatment facility that began opera-
tion in May 1966. It has a primary and secondary design capacity of 27
and 117 mgd, respectively. The design BOD load is 166,350 Ibs/day. The
estimated population served by- this plant is 870,000.
The operating staff includes 9 shift supervisors (5 with Class "A"
certification) and 40 operators (most have Class "C" and "D" certifica-
tions) . In addition, the laboratory has 12 employees (chemists, micro-
biologists, and technicians) to collect and analyze in-plant and stream
samples.
Primary treated effluent from the Denver Northside plant comprises
about 75 percent of the average daily flow received. Raw municipal wastes
are received from the Sand Creek and Clear Creek interceptors. Industrial
wastes of less than 1 percent of the total flow are received directly
from the Packaging Corporation of America.
A portion of waste flows, from three satellite treatment facilities
(Arvada, Wheatridge, and Baker Sanitation District) is diverted to Metro
also. [Figure 1] The average waste flows treated and the average waste
flows diverted at each of these plants during the evaluation period are
shown in Table 3. Cost of treatment for these satellite plants and for
Clear Creek Valley Sanitation District is also shown. During in-plant
evaluations, Baker Sanitation District and Wheatridge were not meeting
the State requirement of 80 percent BOD removal.
District members are charged according to the amount of BOD, suspended
solids, and flow received by the Metre plcnt. These charsss, accord ir.~ to
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TABLE 3
WASTE TREATMENT FLOWS AND COSTS AT SELECTED PLANTS
Map"
Key
7
9
Name of Plant
Baker Sanitation
District.
Clear Creek
River Mile
305.5/3.0
305.5/7.0
Design
Capacity
mgd
1.0
2.2
2/
Flotf-
Ob served
mgd
0.9
!.«*>
Flow
Diverted
to Denver
mgd
0.8
H ^
None
Cost of . .
Treatment-*-
$/mil gal
63
185
Metro
Cost of jj/
Treating—
$/mil gal
6/
155-
123-192^-
Sanitation District.
8 Arvada
10 Wheatridge
305.5/6.2/0.3 1.2
305.5/7.5 1.75
1.09
2.2
3.5
o.o/'
102
168
8/
173-
123-192^-
I/ See Figure 1 for location.
2/ Treated flow observed during plant evaluation.
^/ Receives waste from Sigman Meat Company.
k_l Based on design flows and annual operation cost figures provided by plant officials.
_5/ Metro officials estimate the charge to customers for each million gallons delivered as $112/nil gal* The exact
charge is based on $53/mil gal flow, $46/ton BOD, and $40/ton suspended solids.
£/ Based on annual cost figures of $45,000 provided by plant officials and assuming 0.8->nigd diverted to Metro.
]_l Based on influent BOD and suspended solids concentrations of 200-350.
JJ/ Based on annual cost figures of $221,000 provided by plant officials and assuming 3.5 -mgd diverted to Denver.
9/ Plant officials indicate that flow is diverted to Metro approximately 10 minutes twice a day (between 0800-0900
ar.d 1500-1600) to facilitate cleaning of headworks.
1Q/ Presently are not connected to Metro facility. Plant located in near proximity to Clear Creek Interceptor.
Water Quality Investigations
in the South Platte River Basin
1971 - DFI-DC
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11
plant officials, are $46.43/ton BOD, $40.23/ton suspended solids, and
$53.13/mil gal. This combined cost amounts to approximately $112/mil gal
delivered. The cost per family is about $15/year. Officials of the four
treatment plants contend they can treat wastewaters at a cost less than
at Metro. Some of these plants attempt to treat flow in excess of design
capacity to avoid sending the excess wastewater to Metro. Based on in-
fluent BOD and suspended solids concentrations, treatment costs for Wheatridge
and Clear Creek Sanitation District are similar to the Metro treatment
cost rate.
The estimated operation and maintenance costs at the Arvada and the
Baker plants were provided for 1971 [Table 3]. It appears wastewater can
be treated at these plants at much less cost than at Metro. The cost of
expanding these plants to take all incoming flows would increase the treat-
ment cost. For example, the cost of a trickling filter plant (primary
treatment and sludge digester included) of 1.0 mgd is estimated at about
$500,000. At an interest rate of 7 percent and with a 20-year life ex-
pectancy, the annual cost of construction is estimated at $47,000. If
the community receives a 30 percent Federal grant, the annual cost would
be about $33,000. At design flow, the cost to treat 1 mgd varies from ^
$90 without a grant to $130 with a grant. When labor, chemical, and other '
costs are added, the cost per million gallons treated is comparable to that
of the Metro plant cost.
In addition to these four plants, nine plants operate independently
of the Metro system [Table 4 and Figure 1]. The South Lakewood Sanitation
District, for example, operates as a contact stabilization plant located
at 700 Depew Street, Lakc'.;cod, Colorado. Effluent frons this plant is
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TABLE 4
OTHER WASTEWATER TREATMENT FACILITIES IN THE METROPOLITAN DENVER AREA
Map-
Key
I/
Name
Flow Observed
During
Evaluation (mgd)
Receiving Stream River Mile
Remarks
12 Aurora Sanitation District
2/
Sand Creek
306.8/5.5/1.15 Discharges sludge to
Metro.
13 Buckley Air Field
5 Englewood Sanitation District
15 Fitzsimons General Hospital
14 Glendale Sanitation District
11 Golden - Coors
6 Littleton Sanitation District
1 Souch Adams Sanitation District
4 South Lakewood Sanitation District
_!/ Sec Figure 1 for location.
21 Not avaluated.
Water Quality Investigations
in the South Platte River Basin
1971 - JVI-DC
1.25
3.0 Coors
2.0 Golden
2.3
1.85
1.2
Sand Creek
South Platte
River
Toll Gate Creek
Tributary to
Sand Creek
Cherry Creek
Clear Creek
306.8/11.9
319.7
305.5/15.5
South Platte River 323.5
South Platte River 301.2
South Platte River 314.1/2.1W
Additional treat-
ment facilities
under construction.
Treated wastewater
is used for irri-
gation on the hospital
grounds, excess is dis-
charged to Sand Creek.
Interceptor has been
constructed to deliver
Coors Porcelain Plant
and Golden wastes to
Metro.
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13
discharged to the South Platte River. The facility is designed for
1.2 mgd, but presently receives 1.8 mgd. The plant is being expanded
to increase capacity to 1.8 mgd with the assistance of an EPA construc-
tion grant.
The total waste being treated by the aforementioned plants is less
than 15 mgd, which would represent about 12 percent of the flow now
treated by Metro. Of the five plants evaluated [Table 5], none were
meeting the State requirement of 80 percent BOD removal. The planned
expansion at Metro should include provisions for the collection and
treatment of the wastewaters presently treated at the small plants and
schedules should be developed to phase out these small plants. No grant
should be provided to these plants for further construction unless it
can be shown that such an expansion will provide for the continued pro-
tection and enhancement of the South Platte River.
Wastewater Treatment Facilities
The principal components for this treatment facility are as follows
[the flow diagram for the Metro plant is presented in Figure 3]:
1. Preliminary treatment - bar screens, grit chambers, grease
flotation and removal.
2. Primary clarifiers (4) - each 106 feet in diameter with an
8-foot, 9-inch side water depth. Each clarifier has a
skimmer to remove floating solids.
3. Activated sludge units - 12 aeration basins each consisting
of 3 tanks 210 feet long, 30 feet wide, and 15 feet deep.
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CLEAR CREEK
INTERCEPTOR
EFFLUENT FROM
NORTHSIDE PLANT
PACKAGING '
B
CORPORATION I
CrCIIICMT 1 _ I
BAR
SCREENS
GRIT
REMOVAL
/^~*\ G
/ PRIMARY \
SAND CREEK
INTERCEPTOR
SOOTH 1"
PL1TTE ,
RIVER -» •'
i
CHLORINE
CONTACT
CHAMBER
POMP
TO BORLINGTON
DITCH
STATION
A
B
C
D
F
G
H
1
J
H
LEGEND
DESCRIPTION
CLEAR CREEK RAW INFLUENT
PACKAGING CORPORATION EFFLUENT
SAND CREEK RAW INFLUENT
COMBINED RAW INFLUENT TO METRO
METRO PRIMARY EFFLUENT
DENVER NORTHSIDE PRIMARY EFFLUENT
INFLUENT TO SECONDARY UNITS
INFLUENT TO C12 CONTACT CHAMBER
METRO FINAL EFFLUENT
Figure 3.-Flow Diagram Metropolitan Denver Sewage Treatment Plant
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15
4. Secondary clarifiers (12) - each 130 feet in diameter with
a side water depth of 10 feet. There are no skimmers on
these units.
5. Chlorine contact chambers (3) - each 240 feet long, 30 feet
wide, and 15 feet deep.
6. Sludge digesters and furnaces.
The activated sludge units and secondary clarifiers are divided into
four separate systems by piping, pumps, and control buildings. Each of
these systems, consisting of three aeration basins and three clarifiers,
functionsas a separate secondary plant. In effect, there are four sec-
ondary treatment facilities at Metro which are operated separately. No
attempt was made to determine the efficiency of each of these "plants"
during this survey. However, composite samples were collected at the
influent channel to the four plants and at the combined effluent channel
before and after chlorination.
Discussion of In-Plant Survey and Findings
The Metro plant was evaluated August 1-9, 1971. All samples were
analyzed at the DFI-DC laboratory for BOD, TOG, COD, and solids (total,
suspended, volatile suspended, and settleable)-. Samples from selected
stations were also analyzed for nutrients and heavy metals [Tables 5, 6,
B-l, B-2, and B-3*]. Bacteriological samples were collected periodically
from the final effluent [Table 7]. Field measurements of the Metro
effluent showed: pH, 7.0-7.8; temperature, 19.0°-23.0°C; and conduc-
tivity, 875-1,200 ^mhos/cm.
Daily, during the survey, large amounts of suspended solids were
observed passing over cue rinai ciarifier weirs during periods of peak
* Tables B-l, B-2, and B-3 are located in Appendix B.
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TABLE 5
SUMMARY 0? ORGANIC AND NUTRIENT DATA FOR NORTHSIDE AND METRO PLANTS'
August 1-9, 1971
Station Description
A Clear Creek Raw Influent
B Packaging Corporation
Affluent
C Sand Creek Raw Influent
E 1'enver Northside Influent
G ):enver Northslde Prlnary
Uf fluent
I Influent to C^ Contact
Chamber
J Final Effluent from
Metro
Flow
med
IS. 9
0.4
10.3
86.7
86.7
116.3
116.3
BOD
rng/1
187
398
211
295
175
41
31
Susp.
Solids
me/1
334
344
349
680
120
98
123
Vol.
Susp.
Solids
nut/1
283
287
305
620
80
100
117
I/
Settl. Total (KJ)
Solids COD NH-i N NOj+NOj P
mg/1 mK/1 rag/1 ng/1 mR/1 mg/1
5.3 475 18 27
1030 1.4 5.8
6.2 695 19 30
5.9 1250 17 25
1.0 230
0.9 213
1.7 160 15 20
0.04 10.5
2.2 0.9
0.11 13.0
0.08 9.4
-
-
0.73 7.1
I/ Values listed are averages.
2j KJeldahl nitrogen.
Water Quality Investigations
In the South Platte River Basin
1971 - DFI-DC
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TABLE 6
SUMMARY OF HEAVY METALS DATA FOR METRO AND NORTHSIDE PLANTS
August 1-9, 1971
Station
A
B
C
E
G
I
J
Description
Clear Creek Raw
Influent
Packaging Cor-
poration Effluent
Sand Creek Raw
Influent
Denver Northside
Influent
Denver Northside
Primary Effluent
Influent to Cl_
Contact Chamber
Final Effluent
from Metro
Flow
MGD
18.9
0.4
10.3
86.7
86.7
116.3
116.3
Cadmium
mg/1
Average
< 0.03
0.02
0.02
< 0.14
< 0.02
-
< 0.02
Chromium
mg/1
Average
< 0.04
0.15
0.30
0.10
0.08
-
0.06
Copper
mg/1
Average
0.08
0.13
0.31
0.22
0.16
-
0.10
Lead
mg/1
Average
0.11
1.05
0.09
0.17
< 0.06
-
< 0.04
Zinc
mg/1
Average
0.18
3.14
0.29
1.01
0.28
—
0.20
Mercury
Hg/1
Average
< 0.30
< 0.57
0.55
0.58
0.53
-
0.50
< = Less Than
WaLer Quality Investigations
in the South Platte River Basin
1971 - DFI-DC
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18
TABLE 7
BACTERIOLOGICAL AND CHLORINE RESIDUAL DATA
METROPOLITAN DENVER SEWAGE DISPOSAL PLANT
Date/Time
August 2
August 3
August 4
August 5
August 6
Sampled
0400
0600
.1000
1200
1400
0200
0400
0600
1000
1200
1400
0000
0200
0400
0600
1600
1800
2000
1200
1400
1700
0000
0200
0400
0600
0800
1000
1200
Chlorine
Residual
mg/1
0.01
0.01
• 0.40
—
—
0.06
0.04
0.04
0.01
—
0.06
0.06
0.08
0.08
0.08
—
—
0.08
0.64
0.32
0.28
0.03
0.03
0.03
0.01
0.02
0.16
0.21
Coliform Count/100 ml
Total
86,000
550,000
37,000
14,000,000
9,800,000
860,000
170,000
660,000
7,300,000
540,000
370,000
410,000
210,000
72,000
380,000
31,000
36,000
19,000
9,200
26,000
29,000
17,000
330,000
200,000 -
21,000
27,000
48,000
6,600
Fecal
1,100
13,000
390
430,000
72,000
74,000
20,000
37,000
96,000
30,000
6,600
90,000
18,000
7,800
17,000
< 2,000
< 2,000
< 4,000
230
450 -
540
1,600
16,000
3,200
2,800
270
880
720
Water Quality Investigations
in the South Platte River Basin
1971 - DFI-DC
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19
flow. This solids carry-over resulted from the scouring velocities
which prevail during peak flows.
Large accumulations of floating material were observed daily in
all treatment, units. Solids were observed in the final effluent also.
The solids discharged could be reduced by the addition of skimmers on
the final clarifier.
Removal efficiencies observed at the Northside and Metro facilities
[Table 8] show that BOD removal at the Northside plant ranged from -11
to 58 percent.* If the Metro plant is considered alone (i.e., without
the BOD removal afforded by Denver Northside), the BOD removal efficien-
cies ranged from 42 to 86 and 39 to 94 percent before and after chlori-
nation, respectively. The BOD removal efficiency was below State stan-
dards 33 percent of the time. If the Northside plant is considered as
part of the overall Metro system, the range of BOD efficiencies increases
to 66 to 91 percent before chlorination and to 63 to 96 percent after
chlorination. The daily BOD removal efficiency was below State standards
20 percent of the time. Metro was designed for a BOD load of 166,350
Ibs/day. During the survey period, the influent BOD varied from 92,000
to 279,000 Ibs/day with an average of 182,000 Ibs/day. Influent BOD
loads were less than the design load during the weekend only.
Solids concentrations increase through the chlorine contact chamber.
Solids accumulate in the chamber and scour during peak flows periods. The
combined chlorine residual in the effluent varied from 0.01-G.64 mg/1,
significantly lower than the level (1 mg/1 after 15 minutes detention)
3
specified by the Colorado Department of Health. Fecal coliform concen-
trations in the effluent ranged from 230-430,000/100 ml, indicating
* The negative BOD removal was due to sludge blanket losses from the
secondary clarifiers.
-------
TABLE 8
I/
REMOVAL EFFICIENCIES FOR DENVER METRO AND DENVER NORTHSIDE FACILITIES"
Degree of
Treatment for
Norths ide
Metro before Clj
Mei.ro after Cl-
Meirro plus Northside
BOD
Range
%
UD-'-SS
42-86
39-94
66-91
Susp. Solids
Range
%
6-95
UD-'-SS
2/
(16)~ -78
27-97
Vol. Susp. Solids
Range
%
66-95
(36)- -BO
(36)~ -66
32-96
Settleable Solids
Range
%
11-81
89-91
(50)~ -91
92-98
before Cl_
Metro plus Northside
.ifter C10
63-96
39-95
31-95
54-96
_!/ Overall efficiencies were calculated by summing the load into and out of the plant.
2J Numbers in parentheses are negative numbers. These negative values are due to sludge blanket
losses from clarifiers.
Water Quality Investigations
in the South Platte River Basin
1971 - DFI-DC
-------
21
inadequate disinfection [Table 7]. According to plant officials, about
1 ton/day of chlorine is used (2 mg/1 dosage rate at design flow). The
Colorado State Criteria recommends a minimum dosage rate of 8 mg/1 for
activated sludge plant effluents.
Concentrations of heavy metals discharged in the final effluent
were insignificant. The mercury concentrations discharged, for example,
ranged from 0.2 to 1.0 yg/1 (0.18 to 0.87 Ibs/day), with an average of
0.5 yg/1 (0.48 Ibs/day). The majority of the mercury received by Metro
is contained in the North Denver plant effluent. Officials of the North
Denver plant do not know the source(s) of this mercury.
The nutrient data show that only a small amount of nitrification
takes place during treatment. Total phosphorus was reduced approximately
28 percent. The total nitrogen and phosphate loads discharged to the
South Platte River averaged 34,700 and 6,900 Ibs/day, respectively.
Bi-weekly operational data for the period May 30 - December 31, 1971
[Table 9] were obtained from Metro officials. The data for the period
July 25, 1971, through August 7, 1971, show average BOD and suspended
solids removals of about 84 and 1 percent, respectively. Plant officials
indicated that during this 2-week period, the sludge furnaces were shut
down and the digesters were loaded to capacity. Sludge that had built
up in the final clarifiers was scoured from these clarifiers during peak-
flow periods.
During twelve of the sixteen bi-weekly periods [Table 9], the plant
was operating below the minimum 80 percent BOD removal requirement speci-
fied in the Colorado State Water Quality Standards. These standards also
require chat adequate disiniieccion be provided.
-------
22
TABLE 9
BI-WEEKLY AVERAGES OF BIOCHEMICAL OXYGEN DEMAND AND SUSPENDED SOLIDS
REMOVALS AT THE METROPOLITAN DENVER SEWAGE DISPOSAL PLANT-'
1971
Bi-Weekly Period
May 30- June 12
June 13- June 26
June 27-July 10
July 11- July 24
July 25-August 7
August 8-August 21
August 22-September 4
September 5- September 18
September 19-October 2
October 3-October 16
October 17-October 30
October 31-November 13
November 14-November 27
November 28-December 11
December 12-December 25
December 26-December 31
Percent
BOD Removal
86.1
75.5
79.1
77.8
83.8
76.3
64.5
75.7
79.6
80.8
75.9
74.5
73.7
75.8
81.3
68.0
Percent Suspended
Solids Removal
60.2
38.3
53.7
48.3
0.8
1.8
24.9
31.0
47.0
47.5
39.0
37.3
48.3
41.6
63.1
36.0
j./ Data provided by Metro officials.
Water Quality Investigations
in the South Platte River Basin
1971 - DFI-DC
-------
23
Operation of Che Northside plant has a marked influence on the opera-
tion and performance of the Metro plant. Since all wastes from Northside
are discharged to Metro and constitute the majority of the flow received,
failure to remove grease, for example, at the Northside plant can cause
operational difficulties at Metro. Operations of both plants need to be
under the control of a single agency in order that the combined operations
can be controlled to produce the best, final effluent quality.
During the survey, Metro personnel were observed cleaning an in-
secticide tank. The wash water containing the insecticide was flowing
to a storm drain that discharges to the South Platte River. Plant
officials indicated this practice would be discontinued. The effluent
from the storm drain appeared black and had the odor of burnt carbon.
Further investigation revealed that effluent from two ash disposal ponds
(ashes from sludge furnaces) was discharged to the drain. This practice
has been discontinued because the sludge furnaces are no longer in use.
An in-plant study was conducted by EPA investigators from Region VIII
and DFI-Cincinnati Center, during the period October 1969-February 1970,
in order to evaluate plant operations and provide technical assistance.
Weirs on the final clarifier are inadequately placed [Appendix C], allowing
"scouring" velocities to be obtained. Moreover, it was determined that
clarification capacity of the final clarifier was not adequate. Also there
is no reserve capacity of clarifiers; i.e., if a clarifier is out of service,
solids are not effectively removed and are discharged in the effluent.
There is no method of measuring the flow to each clarifier, thus it is
difficult to obtain a balance. Surface skimmers were also recommended.
-------
24
During the October-February study, the investigators found deficiencies
in the aeration basins — detention time is not sufficient, i.e., it is
always less than four hours. Further, there is difficulty in balancing
the flow to the basin. Two of the twelve aeration basins were being used
for grease removal, an operation that should have been accomplished in
the primary units. This practice has been discontinued and during the
recent survey, four aeration basins (one in each area) were being used as
aerobic digesters.
-------
25
STREAM SURVEYS
General
In August 1964, December 1964 through March 1965, September and
October 1965 surveys of the South Platte River were conducted by the
South Flatte River Basin Project. Stream flows at the 19th Street
station averaged 140, 50,-380, and 305 cfs, respectively, during these
periods. The average dissolved oxygen values during these surveys
ranged from 6 to greater than 10 mg/1 at 19th Street; from 1.5 to
3 mg/1 at York Street; and from about 0.2 to 4.0 mg/1 in the vicinity
of 88th Avenue. Bacterial densities were high at all three stations,
exceeding 1 million total and fecal coliform organisms/100 ml at York
Street and 88th Avenue. The average BOD concentrations ranged from
10-20 mg/1 at 19th Street; from 50-170 mg/1 at York Street; and from
45 to greater than 100 mg/1 in the vicinity of 88th Avenue .
As a result of the above studies, it was recommended to the
Second Session of the South Platte River Basin Conference that the
5
following water quality objectives be established :
1. In the main stream of the South Platte River, from the
City of Littleton to the point of discharge of the Metro
Denver sewage treatment plant, the dissolved oxygen con-
tent be maintained at not less than 5 mg/1; a five-day
biochemical oxygen demand level not be allowed to exceed
10 mg/1; and the total and fecal coliform level not be
allowed to exceed 2,400 and 500 bacteria per 100 ml,
respectively.
-------
26
2. In the main stream of the South Platte River, from just
downstream of the Metro discharge to just upstream of the
Brighton Great Western Sugar Company discharge, that the
dissolved oxygen content be maintained at not less than
4 mg/1; the five-day BOD level not be allowed to exceed
20 mg/1; and the total and fecal coliform levels not be
allowed to exceed 5,000 and 1,000 bacteria per 100 ml,
respectively.
The Colorado Water Pollution Control Commission, pursuant to the
6
Federal Water Pollution Control Act, as amended , classified the South
Platte River and established water quality standards [Appendix D] for
the following reaches:
South Platte River from Exposition Avenue (RM 321.9)
to York Street (RM 313.4) -
B2 - Warm Water Fishery
C - Industrial Water Supply
DI - Irrigation Water Supply
South Platte River from York Street (RM 313.4) to
Colorado-Nebraska State Line (RM 83.7) -
C - Industrial Water Supply
DI - Irrigation Water Supply
Sand Creek throughout its length -
Basic Standards applicable to all waters of
the State apply.
Clear Creek from point of diversion of Farmers Highline
Canal (RM 311,1/16.8) to confluence with South Platte
River (RM 311.1) -
C - Industrial Water Supply
DI - Irrigation Water Supply
-------
27
The discharge from the Metro plant enters the South Flatte River
downstream from the Burlington Ditch. Facilities are available to
pump the effluent to Burlington Ditch if, at the point of diversion,
there is sufficient flow in the river to satisfy water rights. At the
time of the 1964-65 studies, the Metro plant was under construction.
The major source of pollution in the Denver area was Northside (RM 314.4),
which discharged wastes upstream of the Burlington Ditch diversion.
Subsequently, the Northside plant discharged all wastes to Metro (RM 312.2),
thus moving the discharge downstream from the diversion. There is pre-
sently a controversy over the ownership of the Metro effluent. The
Fanners Reservoir and Irrigation Company, et al, have filed suit against
the Metropolitan Sewage Disposal District No. 1, contending that it has
interfered with their lawfully decreed rights as appropriators of water
from the South Platte River. The trial court entered "final judgement"
against the District on August 30, 1968, which decision the District appealed
to the Colorado Supreme Court. A decision is pending.
During the period August 30 to September 2, 1971, a water quality
survey was conducted by DFI-DC on the South Platte River from Waterton
to Platteville, Colorado. A bacteriological survey was conducted during
November 17-21, 1971, to determine quality of the South Platte River
upstream of and downstream from the Metro discharge (19th Street-RM 317.3,
Colorado 224-RM 310.9) and to evaluate the Burlington Ditch. Sampling
was conducted at selected stations to determine whether or not Salmonella
were present. Another stream survey was conducted in the same reach
during December 13-17, 1971, to determine chemical quality [Figure 4].
-------
-N-
l E 6 E N D
1. SPR AT 19th St
2. SPR AT NORTH DENVER STP CROSSOVER
3. SPR AT YORK St
4. BURLINGTON DITCH AT YORK St
5. SAND CREEK NEAR MOUTH
6. SPR AT 1-270
7. SPR AT COLO 224
8. CLEAR CREEK AT YORK St
9. SPR AT 88th AYE
10. DENVER METRO EFFLUENT
NOT TO SCALE
Figure 4. South Plalle Kiver from I9lh Si to 88th Ave
-------
29
The total Metro effluent was discharged to the South Platte River
during the in-plant survey and during the three stream surveys and
comprised about 30 to 35 percent, 65 to 95 percent, and 95 percent
of the flow in the South Platte River, respectively, at the point of
discharge. Flow conditions in the South Platte River were above
normal from August 30 to September 2. Survey findings are discussed
below.
Findings of August-September Survey
The August survey showed that the South Platte River at 19th Street
(RM 317.3) was degraded [Table 10]. The benthos at this station were
dominated by pollution-tolerant forms such as sludgewortns and midges.
Raw municipal wastes are occasionally by-passed to the South Platte
River in that reach from Denver Northside (314.4) downstream to York
Street (313.4). Water samples collected at York Street were severely
contaminated by fecal matter. The number of fecal coliform bacteria
was greater than 13,000/100 ml (log mean value); concentrations of
total coliform exceeded 100,000/100 ml. The levels of organic matter
and suspended solids also were high in this reach. The dissolved oxygen
levels at this station ranged from 5.7 to 7.4 mg/1.
The Metro plant (RM 312.2) treats most of the domestic wastes of
the Denver area and is one of the most significant pollution sources in
the South Platte River Basin. Wastewaters discharged during the survey
period contained about 60 mg/1 BOD (62,000 Ibs/day), and 85 mg/1 sus-
pended solids (88,000 Ibs/day) [Table 10]. Total coliform bacteria
levels during the in-plant survey ranged from 6,600 to 14,000,000 per
100 ml, 230 to 430,000 per 100 ml of which were fecal coliforcs [Table 7]
-------
TABLE 10
SUMMARY OF ANALYTICAL RESULTS AND FIELD MEASUREMENTS FOR THE SOUTH PLATTE RIVER
19th Street to 88th Avenue
August 30-September 2, 1971
Station
SPR at 19th
St. (RM 317.3)
SPR at York
St. (RM 313.2)
Denver Macro
Effluent-
(RM 312.2)
Sand Creek
at Mouth
(RM 312.1/0.1)
Clear Creek
at York Street
(RM 311.1/0.3)
SPR at 88th
Date
8/30-9/2/71
8/30-9/2/71
8/30-9/2/71
8/30/9/2/71
8/30-9/2/71
8/30-9/2/71
Flow
CFS
Avg.
413
210^'
192
100T
21
700-
Temp.
°C
Range
17-24
17-22
17-21
16-21
18-22
pH
S.U.
Range
7
7
7
7
7
.2-8.3
.4-8.1
.5-8.0
.3-8.4
.3-7.6
Cond.
umhos/cm
Range
375-600
360-580
420-600
470-600
600-800
DO
mg/1
Range Avg .
6.0-7.6 7
5.7-7.4 6
6.4-7.3 6
4.8-8.7 6
3.3-5.7 4
.0
.9
.8
.7
.5
BOD5
mg/1
Average
6
7
56
8
4
29
Total Solids
mg/1
Average
405
543
570
383
690
Susp. Solids
mg/1
Average
< 80
260
85
203
< 30
233
Avenue.
(RM 308.8)
I/ Estimated flow.
2J Flow taken at gage located downstream of York Street near Sand Creek.
J}/ Da fa provided by Denver Metro personnel.
Water Quality Investigations
in the South Platte River Basin
1971 - DFI-DC
-------
31
During the August survey, the flow in Sand Creek (KM 312.1/0.1)
was comprised primarily of overflow from the Burlington Ditch. The
creek swelled of sewage and was gray in color because Burlington Ditch
carried by-passed raw municipal sewage. Log mean concentrations of
total and fecal coliform bacteria were greater than 110,000 and 8.800/
100 ml, respectively. Sand Creek transported large amounts of organic
matter, and this resulted in a BOD as high as 9 mg/1. Benthic inverte-
brates, dominated by pollution-tolerant sludgeworms, inhabited the
creek bottom in dense populations (1,494/square foot). The diversity
of organisms was limited to six kinds, most of which were pollution
tolerant or facultative forms.
The South Platte River became severely polluted downstream from
these waste sources. At river mile 311.5 (upstream of Clear Creek),
the odor of sewage was strong, and the water was gray, turbid, and
covered with soap suds. The river bed was covered with organic sludge.
The benthos community was reduced to seven kinds and consisted mostly
of pollution-tolerant sludgeworms and snails.
Clear Creek intersects the South Flatte River at river mile 311.1.
Pollutants carried by this creek contributed to the degradation of
quality of the South Platte River waters.
The pollutants discharged to the South Platte River from the sewage
treatment facilities and from polluted Sand Creek and Clear Creek,
settled to the river bottom forming sludge beds that were evident
from Clear Creek downstream - approximately 23 river miles. Throughout
this river reach, water quality was degraded severely. The densities
-------
32
of coliform bacteria were equivalent to those of many sewers; fecal
coliforms numbered more than 7,900/100 ml and total coliforms numbered
more than 320,000/100 ml.
At 88th Avenue (RM 308.8), the number of benthic invertebrates
increased to 732/square foot with a variety of only eight kinds. Ninety-
two percent of these organisms were pollution-tolerant sludgewonns.
Findings of November Bacteriological Survey
Bacteriological data [Table 11], for the November survey, showed
that the standards for a warm water fishery (B») were being met at the
19th Street Station with a log mean coliform density of 490/100 ml and
with no more than 10 percent of the samples exceeding 2,000/100 ml.
Bacterial quality remained within the standards until York Street,
where the log mean density increased to 790/100 ml; however, more
than 10 percent of the samples exceeded 2,000/100 ml. From York Street
downstream, there are no bacterialstandards for the South Flatte River*.
Salmonella tests were conducted in the South Platte River at York
Street (RM 313.2), just downstream from the Denver Metro effluent
(RM 312.15) and in the Burlington Ditch at York Street to determine
if enteric pathogenic bacteria were present. The results at all three
stations were positive. Particular serotypes isolated were Salmonella
anatum (Burlington Ditch) and Salmonella senftenberg (South Platte River
* The Colorado Water Pollution Control Commission adopted bacterial
water quality standards for the South FlaLte River, downstream frcni
York Street to the Colorado-Nebraska state line, in September 1971,
by classifying this reach of river suitable for a potable water
supply (Class 'A'). The DFI-DC conducted a survey in November,
to determine if the bacterial standards were being violated.
However, the State Attorney General advised the Commission that
any change in stream classification required a public hearing.
The Commission subsequently removed the "A" classification.
-------
TABLE 11
RESULTS OF BACTERIAL ANALYSES-SOUTH PLATTE RIVER STREAM SURVEY
November 17-21, 1971
Map~
Key
I/
Total Coliform
Count/100 ml
Station
Fecal Coliform % of
Count/100 ml Sample
Fecal Strep.
Count/100 ml
Range
Log Mean Range Log Mean -2000/100 ml Range Log Mean
1 South Platte River 3,800->90,000 >11,000
at 19th St. bridge
2 South Platte River 3,000-440,000 15,000
at Denver Northside
plant
2/
3 South Platte River" 5,000-270,000 21,000
at York St.
21
4 Burlington Ditch- 3,200-210,000 16,000
at York St.
6 South Platte River 7,000-6,200,000 340,000
at 1-270 Bridge
7 South Platte River 7,100-5,400,000 200,000
at Colorado 224
8 Clear Creek at York 600-190,000
St.
10 Denver Metro
effluent-^'
9,200-14,000,000
_!/ See Figure 4 for location.
2_l Isolated salmonella at this station.
^/ Data from in-plant survey August 1-9, 1971.
Water Quality Investigations
in the South Platte River Basin
1971 - OFI-DC
170-4,000
310-2,600
490
620
61-10,000 790
410-6,500
850
70-70,000 >7,000
160->60,000 >3,300
7,100 <10-5,300 <190
230-430,000
10
10
20
20
70
60
20
160-27,000 1,600
330-39,000 2,100
360-87,000 3,800
570-77,000 3,500
150-160,000 14,000
980-98,000 8,200
220-190,000 1,800
-------
34
stations). The presence of these pathogenic bacteria, in attendance
with fecal conforms, proves that the water is contaminated by raw or
inadequately treated sewage.
The effects of the Metro effluent, however, are very evident.
Log mean fecal coliform densities exceeded 7,000 downstream from Metro
at the 1-270 bridge (KM 312.0). Concentrations exceeding 3,300 (log
mean) were observed at Colorado 224 (EM 310.9).
Clear Creek at York Street does not have a bacterial standard.
The fecal coliform concentration (log mean) was low (<190/100 ml);
however, more than 20 percent of the samples exceeded 2,000/100 ml.
Survey results showed some improvement in the bacterial quality
of the South Platte River downstream from 19th Street since the 1964-65
studies. Total and fecal coliform concentrations were markedly lower
in November than those observed in 1964-65. Downstream from York Street,
the log mean total and fecal coliform concentrations remained in excess
of the levels recommended by the South Platte River Basin Project as
water quality objectives (i.e., 5,000 total and 1,000 fecal/100 ml).
Adequate disinfection of the Metro discharge and elimination of raw
sewage by-passes would improve the bacterial quality of the river down-
stream from 19th Street.
Findings of the December Survey
Flows in the South Platte River during December were about one-
fourth of those observed during August. Water samples were collected
at selected stations from 19th Street downstream to Colorado Highway
224 and analyzed for BOD, solids (total and suspended), and dissolved
-------
35
oxygen [Table 12]. The average BOD concentration at the background
station (19th Street) was 18 mg/1. The level decreased to 14 mg/1
at Denver Northside. At York Street the average concentration was
9 mg/1, about 50 percent less than the BOD measured in the Burlington
Ditch at York Street. A factor that could account for this difference
is that the flow of the South Platte River at York Street was primarily
made up of seepage because the entire river was being diverted to the
Burlington Ditch. Consequently, it was essentially a new river at
York Street.
Downstream from Metro (1-270) the BOD level increased to an average
of 44 mg/1 - about 500 percent higher than the average observed at York
Street. At this station, the river was mostly Metro effluent, which
contained an average BOD concentration of 44 mg/1.
The BOD level at the next downstream station (Colorado 224) re-
mained at 40 mg/1. This station is downstream from the confluence of
Clear Creek, which had an average BOD concentration of 15 mg/1 and an
average flow of 54 cfs.
During the survey, the DO levels were well above the established
standard (3.0 mg/1) at all stations, with concentrations ranging from
69 to 94 percent of saturation upstream of the Metro discharge and 55
to 85 percent downstream at 1-270 and Colorado 224.
In summary, the survey results indicated an improvement in the
South Platte River quality downstream from Denver Northside compared
to the 1964-65 studies. Obvious improvements include better BOD and
DO values as a result of the elimination of the Northside primary
effluent. However, the BOD load discharged by the Metre plant still
-------
TABLE 12
SUMMARY OF ANALYTICAL RESULTS AND FIELD MEASUREMENTS FOR THE SOUTH PLATTE RIVER
19th Street to ,88th Avenue
December 13-17, 1971
Station
SPR at 39th
St. (RM 317.3)
SPR at Denver
Date
12/13-17/71
12/13-17/71
Flow
CFS
Avg.
107
I/
135~
Temp.
°C
Range
3-6
3-6
PH
S.U.
Range
7.6-7.9
7.4-7.9
Cond . DO
Umhos/cm mg/1
Range Range Avg.
775-875 8.5-10.0 9.4
825-1000 7.8-9.8 8.9
BODc
mg/1
Average
18
14
Total Solids
mg/1
Average
675
750
Susp. Solids
mg/1
Average
40
30
Northslde plant
(RM 314.5)
SPR at York
St. (RM 313.2)
Burlington
Ditch at
York St.
Denver Metro
effluent
(RM 312.2)
SPR at 1-270
bridge
(RM 312.0)
12/13-17/71
12/13-17/71
12/13-17/71
12/13-17/71
l/
2~
2/
142^
153
I/
160-
3-5
3-5
15-15
7.7-7.8
7.5-7.8
7.1-7.4
750-1000 7.8-9.4 8.7
850-1000 7.7-9.6 8.8
1000-1100 6.0-6.4 6.1
9
14
44
44
755
725
890
30
40
95
I/ Estinated flow.
2J Flow taken at gage located downstream of York Street near Sand Creek.
Water Quality Investigations
in the ::outh Platte River Basin
1971 - IJKI-DC
ON
-------
TABLE 12 (Continued)
SUMMARY OF ANALYTICAL RESULTS AND FIELD MEASUREMENTS FOR THE SOUTH PLATTE RIVER
19th Street to 88th Avenue
December 13-17, 1971
Station
Date
Flow
CFS
Avg.
Temp.
°C
Range
PH
S.U.
Range
Cond.
umhos/cm
Range
DO
mg/1
Range
Avg.
BOD5
mg/I
Average
Total Solids
mg/1
Average
Susp. Solids
mg/1
Average
Clear Creek 12/13-17/71
at York St.
(RM 311.]/0.3).
SPR at Colo. 12/13-17/71
224 (70tl. Ave.)
(RM 310.9)
at 88th 12/13-17/71
Ave. (RM 308.8)
I/ Estimated flow.
54
220~
I/
0.3-2
7.7-8.0 825-1000 9.2-10.5 9.8
8-9 7.3-7.6 950-1050 7.4-8.0 7.8
200~ 3-12 7.4-7.7 775-1100 6.7-7.3 7.0
15
40
820
45
70
Water Quality Investigations
in the South Platte River Basin
1971 - DKl-DC
CO
-------
38
results in BOD levels in the South Platte River more than twice the
limits recommended (i.e., 20 mg/1) as a water quality objective in
the South Platte River Basin Project report.
The quality of Clear Creek has also improved over that observed
in 1964-65, and during the December survey, the BOD level (11-20 mg/1)
was within the limits recommended.
-------
39
WATER QUALITY IMPROVEMENT MEASURES
Water quality conditions could be improved by diverting the Metro
effluent to the Burlington Ditch and allowing normally diverted South
Flatte River flows to continue downstream. The Farmers Reservoir and
Irrigation Company, which owns Burlington Ditch, has water rights of
377 cfs from the South Platte River. From May to September, the majority
of the diverted water is used directly for irrigation, with any excess
being stored in Barr Lake, a 35,000 acre feet reservoir, located north-
east of Denver [Figure 4]. Three other reservoirs, Horsecreek (17,000
acre feet), Prospect (7,660 acre feet), and Lord (1,000 acre feet), also
receive South Platte River water, generally from October to April. A
flow of 130 cfs would be sufficient to fill these reservoirs. Based
on projected Metro flows, 25-100 cfs would still have to be discharged
to the river.
A study done on Barr Lake in 1964-65 concluded that the lake was
a large wastewater stabilization lagoon. The BOD, Total N, and Total
PO^ concentrations in the water entering Barr Lake ranged from 55-150;
12-37; and 11-21 mg/1, respectively. This study recommended that the
'Metro plant provide 90 percent BOD removal, which would be equivalent
to about 20 mg/1.
During the irrigation season water demands would require flows
in excess of the Metro effluent to be diverted from the South Platte
River. Direct use of the MeLro effluent un crops should have no detri-
mental effect, if adequate disinfection is provided.
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40
The dissolved oxygen concentration in the South Platte River has
been evaluated on the basis of continual discharge of Metro effluent
to the river and low flow conditions. The seven-day, ten-year low
flow at 19th Street is 20 cfs which, assuming no diversion, would
make the low flow just upstream of the Metro effluent approximately
25 cfs. Waste loads from .Metro were predicated on 30 mg/1 BOD (August
data) and 3 mg/1 DO. The BOD loading to the river is 29,100 Ibs/day
with a residual stream BOD of an additional 810 Ibs/day (includes BOD
loading from Sand Creek and Clear Creek). Calculations were made at
25°C. The minimum DO which would occur is approximately 0.5 mg/1 which
is below the approved water quality standard of 3 mg/1 [Figure 5].
The same procedures were utilized to determine the expected low
DO value with the Metro effluent containing 10 mg/1 BOD. All other
factors remained the same. The minimum DO which would occur is approxi-
mately 3.5 mg/1 [Figure 5].
Based on the above calculations, the effluent must not contain
more than 10 mg/1 BOD to prevent violation of water quality standards
(DO of 3 mg/1). This will require the Metro wastewater treatment
facility to provide at least 95 percent BOD reduction.
In summary, the Metro plant must provide: (1) a minimum BOD
removal of 90 percent when all effluent is pumped to Burlington Ditch,
(2) a minimum BOD removal of 95 percent of all the effluent is dis-
charged to the South Platte River assuming a low flow in the river of
20 cfs at 19th Street, and (3) minimum BOD removals between 90-95
percent when a portion of the effluent is being discharged to the
river.
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7-
6-
» 5.
C9
4-
CO
CO
2-
1-
Saturation at 25°c
Proposed Dissolved Oxygen Standard
Present Dissolved Oxygen Standard
LEGEND
Profile for present Metro effluent
(BOD Concentration of 30mg/l)
Profile of Metro effluent for
.BOD Concentration of 10mg/l
• i • I I i i i i i i
0 0.2 0.4 0-6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
TIME-days
FIGUl.: - DISSOLVED OXYGEN PROFILE FOR SOUTH PLATTE RIVER DOWNSTREAM OF DENVER METRO
EFFLUENT.
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42
Improvements in the water quality of the South Platte River can
be achieved by the elimination of occasional raw sewage discharges.
The water quality standards of the South Platte River downstream
from York Street should be upgraded to encourage continued water
quality enhancement. As DO concentrations observed at sampling
stations were 5 mg/1 or more, a warm water fishery (B2) classification
is feasible if adequate flow is maintained in the river (25 cfs).
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43
CONCLUSIONS
1. The Metro plant is overloaded hydraulically and organically.
The plant is designed for 117 mgd. Peak flows of 180 mil gal
were recorded during the survey. Average BOD loading of 182,000
Ibs/day was 110 percent of the design loading.
2. Adequate treatment was not being provided by the Metro plant
for BOD and suspended solids removal. Moreover, adequate
disinfection was not provided, as shown by the low chlorine
residuals and the high bacteria concentrations in the effluent.
The chlorine dosage rates were about 2 mg/1, whereas the
criteria of the Colorado Health Department recommend 8 mg/1
minimum for an activated sludge effluent.
3. Scouring velocities occurred in the final clarifiers at the
Metro plant during peak flows due to the hydraulic overload
and to the inadequate placement of the weirs. The lack of
skimmers on the final clarifiers resulted in floating solids
being discharged into the receiving waters.
4. The Metro and Northside plants are under different management
making effective operation difficult. The Northside plant
effluent constitutes the major input to Metro and operational
difficulties at Northside affect Metro significantly.
5. Small treatment plants in the metropolitan area treat flows
that are about 12 percent of the present flow treated at Metro.
Of nine plants evaluated, seven were not meeting the State
requirement of 80 percent BOD removal. These plants could be
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44
phased out and the entire flow diverted to Metro. The cost
of expansion at these plants is about 50 percent greater per
mgd design capacity than expansion of the Metro plant.
6. Sludge handling capacity at Metro continues to be a problem;
its inadequacy affects plant performance in producing
a satisfactory effluent.
7. Mercury discharges vary from 0.2 to 0.9 Ibs/day. The majority
of the mercury comes from the Denver Northside wastewater
treatment facility but plant officials do not know its source(s).
8. Minor changes in NH_ and the sum of NO- and NO- occur during
treatment. Total phosphorus is reduced approximately 28 percent.
The total nitrogen and phosphate loads discharged to the South
Platte River during the survey averaged 34,700 and 6,900 Ibs/day,
respectively.
9. Metro personnel were observed washing an insecticide tank.
The wash water entered the South Platte River through a storm
drain. This practice has been discontinued.
10. Raw sewage discharges were observed at 47th Avenue and Franklin
Street.
11. Since the studies conducted by the South Platte River Basin
Project in 1964-65, there has been some improvement of water
quality conditions in the South Platte River. Lowering of BOD
and coliform concentrations and the increase in DO levels is
.due mainly to the elimination of the Denver Northside primary
effluent.
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45
12. Violation of the bacterial standard occurred in the South
Platte River at York Street. Salmonella were isolated in
the South Flatte River and Burlington Ditch, indicating
fecal contamination in the River.
13. The South Flatte River quality could be enhanced by the ex-
pansion of the Metro plant and improvement in plant operation.
Pumping Metro effluent to Burlington Ditch would supplement
these improvement measures by allowing normally diverted river
water to continue downstream from York Street.
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46
RECOMMENDATIONS
It is recommended that:
1. The planned expansion at Metro include a capacity for waste-
waters now being treated by small plants. A time schedule
be developed to phase out these small plants when the expansion
at Metro is completed.
2. The expansion provide for an effluent which contains no more
than 10 mg/1 BOD.
3. The effluent be pumped to the Burlington Ditch to supplement
irrigation and storage demands.
4. The final clarifiers be equipped with skimming devices and
additional weirs be placed on these clarifiers to diminish
the generation of scouring velocities.
5. The chlorine feed rate be increased to provide adequate dis-
infection on a continuous basis and to maintain a combined
chlorine residual of 1 mg/1 after 15 minutes detention in
accordance with Colorado Health Department criteria.
6. Adequate sludge treatment and disposal be -provided in con-
junction with the plant expansion.
7. The Northside and Metro plants be placed under the same manage-
ment so that the combined operations can be effectively con-
trolled; and the offer of a construction grant be predicated
on the development of a single agency responsible for operations
in both plants.
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47
8. Immediate steps be taken by the City and County of Denver
to eliminate all raw sewage discharges to the South Flatte
River in the metropolitan area.
9. Flow augmentation be practiced to insure a minimum of 25 cfs
of water in the South Platte River from just upstream of
Littleton to the Colorado-Nebraska state line.
10. Consideration be given to upgrading the water quality standards
of the South Flatte River downstream from York Street to in-
clude potable water supply and warm water fishery classifications;
thus, encouraging water quality enhancement.
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48
REFERENCES
[1] Report to the Second Session of the Conference in the Matter of
Pollution of the South Platte River Basin, United States Department
of Health, Education, and Welfare, Federal Water Pollution Control
Administration, South Platte River Basin Project, April 27, 1966.
[2] PR-3, Municipal Waste Report, Metropolitan Denver Area, South
Platte River Basin, United States Department of Health, Education,
and Welfare, Public Health Service, Division of Water Supply and
Pollution Control, South Platte River Basin Project, Denver,
Colorado, December 1965.
[3] Criteria Used in the Review of Wastewater Treatment Facilities,
Colorado Department of Health, Denver, Colorado, 1969.
[4] Modern Sewage Treatment Plants, How Much Do They Cost, United
States Department of Health, Education, and Welfare, Public Health
Service, Publication No. 1229, U. S. Government Printing Office,
Washington, D. C., 1964.
[5] Conference in the Matter of Pollution of the South Platte River
Basin in the State of Colorado, Proceedings, Second Session,
Denver, Colorado, Reconvened, November 10, 1966, U. S. Department
of the Interior, Federal Water Pollution Control Administration.
[6] Federal Water Pollution Control Act, Public Law 84-660, U. S.
Department of the Interior, Federal Water Pollution Control
Adminis trat ion.
[7] Barr Lake and Its Odor Relationships, R. 0. Sylvester, United
States Department of Health, Education, and Welfare, Public Health
Service, Division of Water Supply and Pollution Control, Region
VIII, Denver, Colorado, December 1965.
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APPENDIX A
SAMPLING PROCEDURES
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A-l
Appendix A
SAMPLING PROCEDURES
Influent samples of the Denver Northside plant and the Denver Metro
plant were collected upstream of the point of supernatant return every
half hour. Denver Northside influent samples were collected using
automatic samplers. All other samples were collected manually within
the Metro plant area. All samples were flow composited, according to
instantaneous flow readings obtained near the point of collection, and
were iced during the entire 24-hour period. Field measurements of pH,
temperature, and conductivity were made at selected stations. The
composite samples were delivered to the DFI-DC laboratory and analyzed
for BOD, total and suspended solids, volatile suspended solids, settle-
able solids, total organic carbon (TOG), chemical oxygen demand (COD),
nitrogen series, total phosphorus, and selected heavy metals.
Samples of the final effluent from the Denver Metro facility
were analyzed for total and fecal coliform. These bacterial samples
were iced and delivered to the DFI-DC mobile bacterial laboratory for
analyses. At the time of collection, field measurements and chlorine
residual was measured.
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APPENDIX B
DATA ON
METROPOLITAN DENVER SEWAGE TREATMENT PLANT
AND
NORTH DENVER WASTEWATER TREATMENT PLANT
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APPENDIX B
TABLE B-l
SUMMARY OF ORGANIC DATA ON METROPOLITAN DENVER AND NORTH DENVER WASTEWATER TREATMENT PLANTS
August 1-9, 1971
I/
Station'" Description
A Clear Creek Raw Influent
B Packaging Corporation
Effluent
C Sand Creek Raw Influent
D Combined Raw Influent to
Metro
E Denver Northside Influent
F Primary EfEluent from
Flow BOD
MGD mg/1
17.3-21.2 140-250
0.4-0.6 280-480
9.5-11.0 140-290
27.2-32.6 190-250
76.7-92.5 180-430
27.2-32.6 120-160
Total Susp.
Solids Solids
mg/1 mg/1
930-1300 210-480
1120-2130 220-480
890-1200 240-440
1120-1640 300-620
920-1440 320-1240
980-1060 60-180
Vol.
Susp. Settl.
Solids Solids
mg/1 mg/1
180-440 3.5-7.0
150-400 19-100
(est)
180-420 5-8
160-540 5-9
240-1200 3.5-10
60-140 Trace-1
COD TOC
mg/1 mg/1
320-700 64-150
890-1200 80-320
350-1560 66-190
480-870 66-360
590-1800 84-340
250-290 31-120
Metro
Denver Northside Primary 76.7-92.5 80-310 620-820 <20-300 <20-160 0.2-7 160-270 31-54
Effluent
H
Influent to Secondary
Units
103.9-124.0 75-210 780-890 50-140 40-130 0.1-0.5 200-270 33-80
Influent to C12 Contact 103.9-124.0 25-95 690-790 20-240 <20-200 Trace-5 100-410 15-69
Chamber
Final Effluent from Metro 103.9-124.0 10-100 660-830 30-240 30-240 Trace-7 80-790 18-70
\J For location see Figures 2 and 3.
Water Quality Investigations
in the South Platte River Basin
1971 - DFI-DC
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APPENDIX B
TABLE B-2
SUMMARY OF HEAVY METAL DATA ON METROPOLITAN DENVER AND NORTH DENVER WASTEWATER TREATMENT PLANTS
August 1-9, 1971
Station-
Description
Cadmium
me/1
Chromium Copper
mg/1 me/1
Lead
mg/1
Zinc
mg/1
Mercury
Jig/1
A
B
C
E
J
Clear Creek Raw Influent
Packaging Corporation
Effluent
Sand Creek Raw Influent
Denver Northside Influent
Final Effluent from
Metro
<0.02-0.05 <0.02-0.07 0.05-0.10 0.05-0.20 0.17-0.21 <0.2-0.6
<0.02-<0.02 0.03-0.37 0.07-0.26 0.29-2.3 0.26-6.1 <0.02-1.0
<0.02-<0.02 0.09-0.A3 0.13-0.58 0.06-0.14 0.13-0.43 0.02-1.2
<0.02-0.04 0.03-0.26 0.16-0.23 0.09-0.22 0.69-1.9 0.2-1.-3
<0.02-<0.02 0.03-0.11 0.04-0.24 0.03-0.10 0.06-0.49 0.2-1
_!/ For location see Figures 2 and 3.
Water Quality Investigations
in the South Platte River Basin
1971 - DFI-DC
7
ro
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APPENDIX B
TABLE B-3
SUMMARY OF NUTRIENT DATA ON METROPOLITAN DENVER AND NORTH DENVER WASTEWATER TREATMENT PLANTS
August 1-9, 1971
Station"
A
B
C
E
J
Description
Clear Creek Raw Influent
Packaging Corporation Effluent
Sand Creek Raw Influent
Denver Northside Influent
Final Effluent from Metro
NH3 as N
mg/1
16-21
0.1-3.9
17-22
12-20
11-18
Total N as N
mg/1
23-31
A. 3-8
25-37
21-29
15-34
N02 + N03 as N
mg/1
0.02-0.07
0.7-3.5
0.01-0.61
0.01-0.23
0.2-1.7
Total P
mg/1
9.6-13
0.4-2.8
11-14
7.5-12
4.8-13
_!/ For location see Figures 2 and 3.
Water Quality Investigations
in the South Platte River Basin
1971 - DFI-DC
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APPENDIX C
Report By
Environmental Protection Agency
Region VII, Kansas City, Missouri
"Federal Assistance Project
Metropolitan Denver Sewage
Disposal District No. 1
October 1969 - February 1970"*
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FEDERAL ASSISTANCE PROJECT
METROPOLITAN DENVER SEWAGE
DISPOSAL DISTRICT NO. 1
OCTOBER 1969 - FEBRUARY 1970
By
Bob A. Hegg
And
John R. Burgeson
ENVIRONMENTAL PROTECTION AGENCY
WATER QUALITY OFFICE - REGION VII
911 WALNUT, KANSAS CITY, MO. 64106
MARCH 1971
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The Superintendent of Documents
classification number is:
EP 2.2: D43
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TABLE OF CONTENTS
PAGE NO.
I. Introduction *
II. Purpose and Scope 2
III. Description of Plant and Area 3
IV. Summary of Assistance Project 5
A. Control Testing - Procedures and Results 5
B. Performance Evaluation - Procedures and Results 6
C. Data Analysis - Procedures and Results 9
D. Control of Areas - Procedures and Results 11
E. Control of Sludge Characteristics - Procedures and Results. ... 12
V. Data Analysis 15
A, Analysis of Sludge Production 15
B. Analysis of Secondary Clarifiers 21
VI. Summary and Conclusions 29
VII. Recommendations 32
VIII. Appendices 33
Appendix A - A Resolution: "Concerning the Federal Government's
Responsibilities in Constructing and Operating Sewage
Disposal Facilities" 34
Appendix B - References 36
Appendix C - Determination of Substrate Removal Rate (q) and
Net Growth Rate (l/ec) 38
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LIST OF TABLES
TABLE NO. TITLE PAGE NO.
1 A Summary of Various Parameters Associated with the Selected
"Steady State" Periods 17
2 Calculated Values of ec and qgoDs - Selected Periods of
Operation - Areas #2 and #3 19
3 Average Settled Sludge Volumes for "Steady State" Periods 22
4 Zone Settling Rates (Vs) and Equivalent Surface Overflow
Rates (Or) for "Steady State" Periods 25
5 Waste Sludge Flow Required to Remove an Equivalent Amount of
Solids with Varying Underflow Concentrations 28
11
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LIST OF FIGURES
FIGURE NO. TITLE PAGE NO.
1
2
3
4
5
6
Influent BODs Loadings and Seven Day Moving Average, Effluent
Weekly Average Percentage Reduction of BODs and TSS
Waste Sludge Concentration in mg/1 vs Time
Net Growth Rate (l/8c) vs Substrate Removal Rate (o,R0nc)
Determination of Zone Settling Rate (Vs) - Height of Sludge
4
8
10
14
20
Interface vs Time - Area #3 Period: 2/9 - 2/16/70 Average
9:00 A.H 24
iii
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I. INTRODUCTION
The Metropolitan Denver Sewage Disposal District #1 (Metro Denver) plant was designed mainly as a
secondary treatment facility (activated sludge) to treat wastes from the cities and sanitary districts
1n the Metropolitan Denver Area. The plant is administered by a Board of Directors who represent the
various communities and districts that are served by the facility. The largest source of flow to the
plant is the primary effluent from the City and County of Denver's North Side Sewage Treatment Plant.
The Metro Denver plant began operation in 1966 and since that time has continually experienced
difficulties. Odor problems, insufficient sludge handling facilities, air pollution from sludge
incineration; unavailability of land for sludge disposal sites, management, labor, and maintenance
problems are the more significant of the difficulties that the plant has encountered. These problems
have served to further increase the public's awareness of the Metro Denver plant.
In an effort to resolve this situation, the Board of Directors of the Metro Denver plant passed a
resolution (see Appendix A) entitled "Concerning the Federal Government's Responsibilities in Con-
structing and Operating Sewage Disposal Facilities." In the resolution, Metro Denver petitioned the
Congress of the United States and the appropriate Federal agencies to make available to the district
a speci-al team of scientists and engineers to serve as a task force to inspect the district's acti-
vated sludge treatment plant and make appropriate recommendations. As a result of this resolution, a
three-man team from what was then the Federal Water Quality Administration was assigned to the Metro
Denver treatment facility from October 1969 through February 1970. The project officer was
Mr. Alfred West from the National Field Investigation Center (NFIC) in Cincinnati. He was assisted
by Mr. Joseph Joslin and Mr. Bob Hegg of the Kansas City Regional Office.
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II. PURPOSE AND SCOPE
The most significant problem areas at the Metro Denver plant, leading to the request for assis-
tance, were the sludge handling and sludge disposal problems. The major sludge handling problem was
processing the volume and type of waste activated sludge generated by the secondary treatment process
employed at the plant. The sludge disposal problem occurred because of the plant's Inability to
incinerate all of the sludge that was processed. It was decided at the on-set of the Federal Assis-
tance Project to concentrate efforts on the sludge handling problem by attempting to effect the mass
and characteristics of the sludge produced by the secondary treatment process.
Operational changes in the secondary treatment process, training in conducting various control
tests and data evaluation were the major tasks performed during the assistance project. These
functions were coupled with various operational recoirmendations for both short term and long term
plant operation and control.
This report documents the findings of the Federal team. Also presented are the results of
additional analyses of the data conducted after the conclusion of the project.
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III. DESCRIPTION OF PLANT AND AREA
The Metro Denver activated sludge plant is located north of Denver in Commerce City, Colorado.
The effluent from the plant is discharged to the South Platte River, an interstate stream. The State
Water Quality Standards require a minimum of 80% removal of five-day 20°C BOD by the Metro Denver
plant before discharge to the South Platte River. Since the plant began operation in 1966, it has
generally achieved this required eighty percent reduction.
The Metro Denver plant is comprised of primary and secondary sewage treatment facilities and
includes sludge processing facilities. A flow schematic is presented in Figure 1.
The primary treatment facilities were designed to treat an average flow of 27 million gallons per
day (MGD) and a maximum flow of 50 MGD. These facilities consist of an inlet structure, bar screens,
grit and grease removal units, sedimentation basins and a grec.se and scum incinerator.
The secondary treatment facilities were designed to treat an average flow of 117 MGD with a
maximum flow of 234 MGD. The design (6005) load is 166,350 pounds per day or an average influent
concentration of 170 mg/1 BOD5. The secondary treatment facilities consist of aeration basins, the
blower building, sedimentation basins and chlorine contact chambers.
The sludge processing facilities were designed to treat 37,400 pounds per day of raw primary
sludge and 131,000 pounds per day of secondary sludge from the Metro Denver plant; and 92,700 pounds
per day of digested primary sludge from the Denver North Side plant. These facilities consist of the
waste activated sludge concentrators, sludge holding tanks and the sludge processing building which
housed the vacuum filters and incinerators.
Pertinent design information about types and sizes of equipment is discussed, as necessary, in
the following sections.
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r sn
ARE/H,
FEDERAL ASSISTANCE PROJECT
METROPOLITAN DENVER SEWAGE TREATMENT PLANT
OCTOBER 1969 - FEBRUARY 1970
PLANT FLOW SCHEMATIC
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IV. SUMMARY OF ASSISTANCE PROJECT
The major emphasis during the Federal Assistance Project was aimed at the biological (secondary)
portion of the Metro Denver plant. As shown in Figure 1, the secondary portion is comprised of
twelve aeration basins each of two million gallon capacity and twelve 1.16 million gallon final
clarifiers. These twenty-four structures were equally divided into four separate areas by piping,
pumps and other control devices. Throughout the project these four areas demonstrated characteris-
tics of four different plants possibly due to undetected loading differences, flow characteristics,
etc. For this reason, operational control of each of the areas was different and was based on the
individual characteristics exhibited. Because excessive grease was contained in the influent to the
Metro Denver plant, aeration basins No. 1 and No. 2 (located in Areas SI and 82) were used as grease
flotation units. This required that Areas #1 and #2 be operated using only two aeration basins in
combination with their respective three clarifiers. Areas #3 and #4 were operated using all three
aeration basins and three clarifiers in each area.
A. Control Testing Procedures and Results
The initial phase of the project involved instigating process control testing, as outlined by
West (1), to monitor process performance. The basic control tests are the centrifuge test, the
settleometer test, blanket depth measurements, turbidity measurements and dissolved oxygen concen-
tration determinations. The main function of each of these procedures is:
1. Centrifuge tests were conducted on the effluent from the aeration basins and on the return
sludge drawn from the final clarifiers. This test indicates the relative concentrations (by
percent volume) of solids needed for determining the solids distribution in the activated
sludge process. The results from the centrifuge test can also be used for other determina-
tions. For example, the secondary clarifiers at the Metro plant are the "vacuum" type with
twelve draw-off tubes in each clarifier. By using the centrifuge to determine the suspended
solids concentrations, the height of each draw-off tube can be adjusted so that a uniform
concentration of sludge can be drawn from the clarifier bottom.
A relationship between percent solids by centrifuge and by weight (milligrams per liter) of
total and volatile suspended solids (TSS & VSS) was obtained by comparing the results of a
centrifuge test and a suspended solids analysis made on the same grab samples. This compari-
son was made on a daily basis throughout most of the project.
2. Settleometer testing was conducted on the effluent from the aeration basins to determine the
settling rate and characteristics of the sludge. Visual observations of the sludge settling
characteristics indicated the relative removals, flocculation properties, etc. of the sludges
from the four areas. Analysis of the settleometer data coupled with centrifuge aata also
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allowed a determination of the dewatering or concentrating ability of the various mixed
liquors. Settleometer data were normally collected four times per day at 5:00 A.M., 9:00
A.M., 1:00 P.M. and 9:00 P.M. During the last portion of the project, settleometer tests
were run every two hours. Readings of the settled sludge volume (SSV),'as indicated from the
settleometer, were taken every five minutes for the first one-half hour and every ten minutes
for the second one-half hour.
3. Blanket depth determinations (depth of sludge interface from surface) were taken on each of
the final clarifiers to aid in determining the solids distribution and solids mass in the
final clarifiers. During the last portion of the project, blanket readings were taken every
two hours, twenty-four hours per day.
4. Turbidity measurements were taken on samples of settled and skimned effluent from the final
clarifiers and were used to indicate the relative effectiveness of the activated sludge
process in producing a clarified effluent. The samples were settled and skimmed before
turbidity measurements were made so that clarifier limitations could be eliminated from the
analysis and only the relative effectiveness of the biological system could be judged.
5. Dissolved oxygen measurements were taken to assure that an adequate oxygen supply was avail-
able to support the process.
Plant operators were trained during the project to make the above control tests and to analyze
id interpret the obtained data. Process control adjustments could then be made on a routine basis.
In addition to conducting the control tests, the operators were required to take readings of various
low meters and to collect grab and composite samples so that the plant performance could be
monitored.
u. Performance Evaluation-Procedures and Results
The Metro plant laboratory conducted various analyses on the collected samples to provide addi-
ional data for the project. Influent and effluent samples for the secondary treatment portion of
*-he plant were composited and determinations were made for BOD5 and TSS. In addition to overall
lant influent and effluent samples, influent and effluent samples were collected and composited on
each of the individual areas. Figure 2 illustrates the loading in pounds of BOD5 applied to the
econdary treatment (activated sludge) portion of the Metro Denver plant, as well as the seven day
moving average of the overall plant effluent concentrations of BODg and TSS.
The seven day moving average BOD5 and TSS effluent concentrations are depicted on the lower por-
tion of Figure 2. The BOD5 in the effluent is closely.related to the TSS concentration. This
•elationship emphasizes the effect of the difficulties encountered with final clarifiers at the Metro
Denver plant. Without exception, each peak on the graph can be correlated with "bulking" problems in
6,
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one or more of the areas. A portion of the "bulking" problem was due to a poor-settling sludge
caused by process Imbalance. However, many times an apparent good-settling sludge in settleometer
testing was hydraulically "flushed" over the effluent weirs.
It is believed that the peaks or poor effluent quality depicted in Figure 2, prior to and during
the initial phases of the Federal project, were caused by the above-average flow and BODj loadings
(See upper portion of Figure 2) that were received at the plant during the month of October 1969.
The large peaks of effluent TSS and BODr experienced in the latter part of November and in December
were caused by a loss of process balance in Areas #1, #2 and #4. The exact reasons for these changes
are not known. However, it may have been the type of loading being used, temperature effects, meter
problems, etc. When Areas #2 and #4 were subsequently converUd so that all the sewage was applied
at the head of each aeration basin on December 12, 1969, the trend in the effluent concentrations of
BODg and TSS decreased. Area #1 was converted to this type of loading on January 5, 1970.
The peaks depicted in the month of January were caused by loss of control of Area #3. Excessive
wasting of sludge and the breakdown of a clarifier were the main causes of this failure.
The peaks in February were caused by "bulking" problems in Areas #1 and #4. Area #1 was bulking
because an attempt was made to rapidly build up solids while Area #4 was bulking because excessive
solids had accumulated due to inaccurate-flow meters on the waste sludge stream.
The effluent quality toward the end of the project (excluding the peaks in late February) was
definitely on an improving trend. The only other period of corresponding quality was experienced
during the first part of November 1969.
The effluent quality depicted in Figure 2 represents a composite of all of the areas and, there-
fore, the performance of the individual areas is not reflected directly. Areas #1 and #4 generally
had the poorest quality effluents, while areas 82 and #3 gave the most consistent high quality
effluents. The reasons for this may have been undetected differences in loading, the effects of
different operational modes or undetected difficulties with flow meters.
Also shown in Figure 2 is the loading to the secondary process in pounds of BOD^ per day. The
dotted line represents the design average day loading (166,350 Ibs. BODg per day) which was exceeded
on various days of all weeks during the project. The average loading for the entire period of study
was 161,560 pounds BOD5 per day.' However, two aeration basins were not in service as activated
sludge basins but rather as grease removal units. Thus, the aeration capacity to handle the design
load was reduced.
The BODjj load was high during the month of October because of the effects of runoff from early
snows that had occurred in the Denver area. There is no apparent explanation for the higher load-
ings in the middle of Jar.uary end e:-pec:;ny the psz'f. Icai cr- -January 1C., 1970.
Another trend that is not as apparent is the relationship between loading and effluent quality.
-------
C9
00 £1
" .a
»«
«- 3
320-
280
240
200<
1£0
120-
80-
90'
• 80<
i 70'
60'
SO'
40'
30-
20'
10 ,J
FIGURE 2
FEDERAL ASSISTANCE PROJECT
METROPOLITAN DENVER SEWER TREATMENT PLANT
OCTOBER-1969 to FEBRUARY-1970
INFLUENT BODS LOADINGS AND
7 DAY MOVING AVERAGE, EFFLUENT BODS
ANDTSS CONCENTRATIONS
VS
TIME
/ ^'\ 7 DAY MOVING £AVG.TSS
/ ^....^
•
AVERAGE DAY DESIGN
LBS
DAV
Xrx/ V
i .-i i ^nt'iYnifi i ivni'm i-rn'rhfrnrn m m f m n n itrnn'ir
i i ( i rr
tiivrttm-i'h-irhwiTf'trfiffti'i
. i nnaui am-
TIME IN DAYS
-------
The low loading in December is reflected by a consistent high quality effluent during the first one-
half of the month. The consistent steady loading during the last half of January and the month of
February is reflected by consistently improving effluent BODg and TSS concentrations. The higher
loadings in October and in January demonstrate the adverse effect of decreasing effluent quality.
Figure 3 Illustrates the percentage reduction (weekly average) of BOD,- and TSS achieved by the
Metro Denver plant. The percentage removal of BOD5 is a better indicator than effluent BOD5 concen-
trations of the benefits of process control. This fact is shown by the gradual increase in percen-
tage removal throughout the project. The percentage removal of TSS declined during the initial phase
of the project and then increased rapidly in December to a somewhat stable percentage reduction
during the final phases of the project.
The increasing trend in percentage BODg reduction in conjunction with the fluctuating effluent
BODg concentrations can be explained by the variations in the incoming BODg load. An increasing
BODg load was accompanied by increased effluent concentrations and thus a relatively constant rela-
tionship as far as percentage removal.
The average reduction of BODg for the entire period was 85% and for TSS it was 60%. These are
reductions by the secondary treatment portion of the plant only and do not include the reductions of
BODg and TSS that were achieved by primary treatment. Therefore, the reduction of BODg for the pri-
mary and secondary processes averaged greater than for the secondary treatment process only and
adequately met the 80% minimum reduction of BOD5 required by Colorado's Water Quality Standards.
C. Data Analysis - Procedures and Results
Large volumes of data were obtained from the numerous control tests that were conducted and the
various monitoring or performance determinations that were made. These data were analyzed, dai ly to
determine trends which were indicative of process performance and from these various trends process
control decisions were made. (i.e. increase or decrease return sludge flow, increase or decrease
wasting flow rate, etc.) Metro Denver plant personnel were trained in analyzing the data and
deriving the various trend relationships. Training was also provided in interpreting the various
trend curves so that control adjustments could be made.
A large number of relationships were established to determine the best parameter or combination
of parameters to use for controlling the activated sludge "process. At the conclusion of the project
many of these relationships were abandoned and only those that appeared most beneficial were recom-
mended for continual use.
A summary of the more pertinent analyses performed are presented below.
The relationship between the settled sludge volume (settleometer readings) and time was plotted
to indicate the trends in settlcability of the sludge. Also established was the trena outlining cne
-------
90-
80-
70-
60-
z
o
50-
u>
cc
40-
30-
20>
10-
/\A
NX \
FIGURE 3
FEDERAL ASSISTANCE PROJECT
METROPOLITAN DENVER SEWAGE TREATMENT PLANT
OCTOBER - 1969 to FEBRUARY - 1970
WEEKLY AVERAGE PEPCENTAGE REDUCTION OF BOD s
AND TSS ( SECONDARY ONLY )
VS
TIME
_ , _ _ _ . __ _ _ w ___ _ ___ . _ ........
'.'I £H OF 9 JO I 10 "6 I 10 111 0 20llO 17 III jlll Ifllil i7'n 14l •! I IllSlll lillj 2]ll! J»I I S ll II I I 19 I I 26
1/16 • 2/23
TIME IN WEEKS I96» - 1970
-------
ability of the sludge to concentrate or dewater. Many of the relationships were based on data from
the daily control test values. Sludge blanket depths were determined as many as twelve times per
twenty-four hour period as well1 as aeration tank concentrations, return sludge concentrations and
flow measurements. These values were averaged on a daily basis and such parameters as sludge age,
total sludge mass in the system, clarifier overflow rates, sludge detention time in the clarifier,
mass of sludge returned per gallon of sewage, etc. were calculated. Additional trends developed
were effluent quality versus time as described by BODg and TSS concentrations.
All of the above-outlined analyses, as well as others, were conducted on each of the areas.
D. Control of Areas - Procedures and Results
Prior to this project, Metro Denver plant personnel were operating the secondary treatment
facilities as one large unit. All four areas were using a two aeration basin, three clarifier com-
bination and were step loading the sewage to the aeration basins. Sewage could be Introduced at four
gates along the aeration basin: Gate A at the head end of the tank, Gate B approximately one-fourth
of the length from the head of the basin, Gate C approximately one-half the length from the head of
the basin and Gate D approximately two-thirds of the length of the tank from the head of the basin.
Metro Denver personnel were loading one-half of the sewage at Gate B and one-half at Gate C. Return
sludge was introduced at Gate A.
A short summary of the major operational changes made in each area will be described below. The
majority of the operational changes were made to determine the operational mode which would allow
maximum removal of TSS and BODg and would improve the sludge characteristics to facilitate sludge
handling.
1. Area #1 was operated using two aeration basins and three clarifiers throughout the project,
except for a short time (one week) when one of the final clarifiers was inoperable. Only two
aeration basins were used since the third aeration basin was required to remove the excessive
grease received at the plant. This area was operated using step loading (one-half flow at
Gate B and one-half at Gate C) from the start of the project until January 5, 1970, when
loading was converted to introducing all the flow at the head of each aeration basin (Gate
A). This loading procedure was used until the end of the project. All the return activated
sludge was introduced at Gate A.
2. Area #2 was operated in a manner similar to Area #1. However, Area #2 was converted to
loading all sewage at Gate A on December 12, 1969. Performance in Area 82 was generally
superior to that of Area #1 throughout the project. Although the meters didn't indicate a
difference, it appeared as though Area #2 was receiving less flow than Area #1. It was
attempted to equalize the flow to all of the areas throughout the project. However, this was
11
-------
difficult to achieve because of the plant's hydraulics and, therefore, equal splitting of the
flow to each of the four areas was not successful.
3. Area #3 was converted to a three aeration basin, three clarifier basin operation within a
week after the project started. All sewage was loaded Into the aeration basins at Gate A, as
well as return sludge. Area #3 provided the best overall performance during the project, as
measured by effluent BOD5 and TSS concentrations.
4. Area #4 was converted to a three aeration basin, three clarifier basin operation within a
week after the project started. However, a variety of methods of introducing loads was tried
on Area #4. Initially all return sludge was introduced at Gate A and the loading of one-half
the sewage flow to Gate B and Gate C was maintained. However, this was changed to loading all
the sewage at Gate D on November 12, 1969. (Contact stabilization) This loading was main-
tained until December 12, 1969 when all sewage was introduced at Gate A. Area #4, at times,
showed excellent reductions but the area was generally sporadic in its performance because of
difficulties In retaining the sludge in the final clarifiers.
The major operational changes above were affected by a variety of operational problems. Unreli-
able meter readings on the waste sludge flow, uneven flow distribution to the various areas, mechani-
cal failure of three clarifiers during the project, and a continual problem with solids "flushing" out
of the final clarifiers are but a few of the operational problems that added to the complexity of the
project.
E. Control of Sludge Characteristics - Procedures and Results
The two major problems encountered at Metro Denver were the "flushing" of solids that occurred
out of the final clarifiers and the sludge processing and handling problem. Since the initial
emphasis was to work in the secondary treatment portion of the plant, improving removal efficiencies
and effluent quality became primary considerations in operating the facility. However, a high
quality effluent representing increased removals of BOD5 and TSS also is associated with increased
sludge production, which served to magnify the sludge processing and handling problems. To compensate
for the increased sludge production accompanying the increased treatment efficiencies an attempt was
made to develop a sludge that would concentrate or dewater better than previous sludges. The end
result would be a lesser volume but increased mass of sludge being removed from the system.
At Metro Denver, the waste activated sludge is further concentrated by the use of chemical
coagulants in air flotation units. Therefore, it was also attempted to develop a sludge more amenable
to chemical coagulation.
Figure 4 illustrates the concentration of sludge wasted from the secondary treatment process. No
daca on the waste sludge total suspended solids concentration are available for the early phases of
12
-------
the project. Consequently, no comparison Is made of the overall changes in waste sludge concentra-
tions for the entire project period. The trends developed for the period of record are shown In
Figure 4. A decrease In waste sludge concentration was Initially noted paralleling the operational
difficulties encountered with Areas #1, #2 and #4 In December (See IV-D above). Later In the project
(January and February) the waste sludge concentration Increased steadily to a weekly average of
approximately 7,000 mg/1, representing a substantial Increase over the low weekly average of 4,500
mg/1 experienced during the last week of December. Figure 4 indicates that one of the goals in con-
trolling sludge characteristics, that cf Increased waste sludge concentration, was achieved. However,
the benefits derived from increasing the waste sludge concentration were partially overshadowed by the
increased sludge production resulting from increased removal efficiencies of BOD-.
13
-------
7.
8
« 6
z
o
Jr
<
ee
»-
z >
Ul
u
z
o
u
Ul
o
• DAILY CONCENTRATION
O WEEKLY AVC. CONCENTRATION
., J M
FIGURE 4
FEDERAL ASSISTANCE PROJECT
METROPOLITAN DENVER SEWAGE TREATMENT PLANT
OCTOBER-1969 (o FEBRUARY - 1970
WASTE SLUDGE CONCENTRATION IN MG /L «s TIME
L^,^ffl.tfj.B,.v^foi.n
"»»»•.'"-*^3fl___ Ilia.-^M . IIMICI-»»
10EC.
1 KB. •
-------
V. DATA ANALYSIS
The objective of the assistance project was to operate the activated sludge process so that the
waste sludge characteristics could be controlled, thereby alleviating at least a portion of the
sludge handling problems. While trying to achieve this goal a large amount of data were collected.
At the conclusion of tne project portions of these data were analyzed to further evaluate the major
problems encountered at the Metro Denver plant, namely the sludge handling problem associated with
sludge produced in the activated sludge process and the problem of solids loss from the final
clarifiers.
Certain portions of the data obtained during the project were selected so that smaller and more
workable portions could be investigated. It was decided to evaluate only Areas #2 and #3, since
these two areas covered most of the operational modes investigated and demonstrated the best
response to operational controls. Area #2 was operated with both step loading and conventional
loading and with two aeration basins in combination with the three clarifiers. Area #3 was operated
with three aeration basins in combination with the three final clarifiers. Both Areas #2 and #3
gave the most consistently good quality effluents and responded favorably to operational controls.
A. Analysis of Sludge Production
The sludge handling problems at the Metro Denver plant were affected by the amount of sludge
produced in the secondary unit. To evaluate the sludge production per pound of 6005 removed, an
application of the kinetic model which has been used and frequently outlined in the literature to
describe biological treatment systems was used. Papers by Lawrence and McCarty (2), Jenkins and
Garrison (3), Pearson (4) and McKinney (5) are a few that have discussed and presented the kinetic
model. The assumptions made In relating the data collected during the project to the analysis made
using the kinetic model are outlined in a sample calculation presented in Appendix C.
Since the kinetic model has been well documented in the literature, the following equations will
be used without a formal presentation of their theoretical basis.
Basic Kinetic Equations
q = F(Sp ~ sl) = Substrate removal rate Equation 1
X,V
v - K
-------
WHERE:
q • substrate removal rate, pounds of substrate removed per pounds of cells
In the system per day
SQ = Influent substrate concentration
Sj = effluent substrate concentration
F » Influent flow rate
X1 = MLSS or MLVSS concentration
V = volume of aeration plus secondary sedimentation basins
v = specific growth rate, pounds of cells produced per pounds of cells in
the system per day
Y • yield coefficient, pounds of cells produced per pounds of substrate
removed
Kd = endogenous decay coefficient, pounds of cells lost per pounds of cells
in system per day
X? • effluent TSS or VSS concentration
W • waste sludge flow
Xr • return sludge and waste sludge TSS or VSS concentration
e = mean cell residence time (sludge age), days = pounds of cells in system
per pounds of cells lost from system per day
To derive a kinetic description of a particular waste source requires the development of a
series of steady state conditions. In other words, the rate of change of substrate removal with
time 1s assumed to be zero. Although steady state is never achieved in a large dynamic activated
sludge plant such as Metro Denver's, certain periods of operation approach this condition. For
Areas 02 and #3 time periods were selected based on uniformity of aeration basin solids concentra-
tion and of sludge settling and concentration characteristics. The uniformity of these characteris-
tics best described a period of "steady state." Table 1 summarizes briefly the periods selected and
the average of selected parameters for each period.
The reciprocal of the mean cell residence time (ec) is the net growth rate. Equation 5, above,
outlines the relationship between the net growth rate (1/e.) and the substrate removal rate q.
These values are related by the yield coefficient (Y) and the endogenous respiration coefficient
(Kj). For normal domestic wastes, values for Y and Kd have been determined. Heukelekian, Oxford
and Manganelli (6) have presented values of Y = 0.5 milligrams volatile suspended solids produced
per milligram of waste (BOD,-) removed and values of K. = -0.055 as being representative, while
Middlebrooks and- Corlir:i (7) have presented values cf Y = 0.67 milligrams volatile tcspen-^d solids
16
-------
TABLE 1
FEDERAL ASSISTANCE PROJECT
METROPOLITAN DENVER SEWAGE TREATMENT PLANT
OCTOBER 1969 - FEBRUARY 1970
A Sumnary Of Various Parameters Associated
With The Selected "Steady State" Periods
Parameter-Average For Period
Influent Flow - MGD
Return Sludge Flow - MGD
Waste Sludge Flow - MGD
Aeration Tank Concentration (ATC)
X Volume Concentration by Centrifuge
Return Sludge Concentration (RSC)
% Volume Concentration by Centrifuge
Ratio TSS/ATC *
Ratio VSS/TSS *
Influent (To Secondary) 6005
Concentration - mg/1
Effluent BOD5 Concentration - mg/1
Effluent TSS Concentration - mg/1
AREA n
1/5/70
to
1/11/70
25.62
13.85
.611
2.96
8.27
706
0.804
197
45
68
1/29/70
to
2/12/70
27.78
11.50
.262
4.46
14.89
585
0.811
197
24
36
AREA #3
12/15/69
to
1/5/70
29.64
14.41
.593
3.71
12.00
616
0.840
188
21
40
1/10/70
to
1/13/70
29.85
11.77
.490
1.36
4.61
817
0.846
194
36
44
1/20/70
to
1/25/70
26.30
23.00
.458
5.44
13.19
482
0.793
199
37
79
2/9/70
to
2/16/70
29.47
13.01
.445
3.92
14.05
684
0.782
207
13
26
* The relationship between % volume concentration by centrifuge and TSS and VSS was established
by comparing results conducted on grab samples - normally daily grab samples.
17
-------
produced per milligram of waste (BODg) removed and values of Kd = -0.048.
The value of Y (slope) and Kd (Intercept) can be graphically determined by determining the value
of ec (Equation 4) and q (Equation 1) and plotting 1/e versus q. Values of the removal rate (q)
and the mean cell residence time (ec) were calculated using the Metro Denver data for the selected
"steady state" periods. (See Appendix C for example calculations) These data are presented in
Table 2. Values derived for ec indicate a relatively low cell residence time. Normal residence
times for conventional activated sludge are five to fifteen days, with a mean of ten days [See
Jenkins (3)]. When considering 6C and normal values obtained for Y and q during the period, K^
values were not within the recognized range (i.e. -.05, -.06), which could reflect a lack of aera-
tion capacity, complete mixing, etc.
The values of qBQD and l/ec determined from the project data have been plotted in Figure 5.
Also plotted is the line representing the relationship between l/ec and q for a typical domestic
sewage using an average of the values presented in the literature (6) (7). (Y = 0.60 Kj = -0.052)
The majority of the points determined using the Metro Denver data are located above the line drawn
for a typical domestic sewage. This indicates that the characteristics of the waste received at the
Metro Denver plant are such that they may deviate to a degree from that expected of a typical domes-
tic waste. Again, whether waste characteristic, dissolved oxygen maintenance, deviation from com-
plete mixing, etc. were responsible for the variation cannot be definitely determined. An attempt
to determine the degree of this deviation is also illustrated on Figure 5. It is recognized that
the plotted points demonstrate a considerable amount of scatter, however, a line was drawn through
the centroid of these points to estimate a yield coefficient (Y). The intercept (Kd) of the esti-
mated line was assumed to be zero to minimize any increase in slope. Since Kj must be negative, a
value of K(j other than zero will produce a line of a greater slope if the line is constructed
through the centroid. It is stressed that this line is only an attempt to estimate a yield factor
for the Metro Denver waste, although the scatter of the points may not warrant its location on the
graph or even its construction. The estimated line has a slope slightly greater than that normally
expected. However, the variation between the two slopes is not great enough to warrant a conclusion
that the sludge production at Metro Denver is greater than that of typical domestic sewage.
Figure 5 also shows that those points representing values from Area #2 are generally lower or
closer to the "typical" line than those of Area #3. The reason for this fact is not apparent.
However, Area #2 was using only two aeration basins while Area #3 was using three.
The average influent 8005 to the secondary process was 161,560 pounds 8005 per day for the
entire project. The average effluent BOD5 load for the same period was 23,700 pounds BOD5 per day.
This represents a daily average reduction of 137,900 pounds of 8005, or about 86 percent removal.
If the yield coefficient (Y) for typical domestic sewage is applied (Y = 0.60), the amount of excess
18
-------
TABLE 2
FEDERAL ASSISTANCE PROJECT
METROPOLITAN DENVER SEWAGE TREATMENT PLANT
OCTOBER 1969 - FEBRUARY 1970
Calculated Values of ec and qBQD.
Selected Periods of Operation
Areas #2 and #3
AREA #2
Day
Mon
Tues
Wed
Thurs
Fr1
Sat
Sun
Thurs
Frl
Sat
Sun
Mon
Tues
Wed
Thurs
Frl
Sat
Sun
Mon
Tues
Wed
Date
1/05/70
1/06/70
1/07/70
1/08/70
1/09/70
1/10/70
1/11/70
1/29/70
1/30/70
1/31/70
2/01/70
2/02/70
2/03/70
2/04/70
2/05/70
2/06/70
2/07/70
2/08/70
2/09/70
2/10/70
2/11/70
iBODs
Ib/lb
0.412
0.495
0.373
0.344
0.424
0.352
0.275
0.365
0.404
0.341
0.259
0.402
0.457
0.449
0.360
0.343
0.351
0.242
0.454
0.377
0.372
6C
Days
2.533
2.160
2.510
4.263
2.736
3.128
3.947
6.514
6.250
6.714
6.750
6.706
7.586
5.409
5.261
5.311
5.273
4.818
4.952
5.561
6.053
l/ec
Days-1
0.395
0.463
0.400
0.235
0.365
0.320
0.253
0.154
0.160
0.149
0.148
0.149
0.132
0.185
0.190
0.188
0.190
0.208
0.202
0.180
0.165
AREA #3
Day
Mon
Tues
Wed
Thurs
Frl
Sat
Sun
Mon
Tues
Wed
Thurs
Frl
Sat
Sun
Mon
Tues
Wed
Thurs
Frl
Sat
Sun
Mon
Sat
Sun
Mon
Tues
Tues
Wed
Thurs
Frl
Sat
Sun
Mon
Tues
Wed
Thurs
Fri
Sat
Sun
Mon
Date
12/15/69
12/16/69
12/17/69
12/18/69
12/19/69
12/20/69
12/21/69
12/22/69
12/23/69
12/24/69
12/25/69
12/26/69
12/27/69
12/28/69
12/29/69
12/30/69
12/31/69
1/01/70
1/02/70
1/03/70
1/04/70
1/05/70
1/10/70
1/11/70
1/12/70
1/13/70
1/20/70
1/21/70
1/22/-70
1/23/70
1/24/70
1/25/70
2/09 HO
2/10/70
2/11/70
2/12/70
2/13/70
2/14/70
2/15/70
2/16/70
qsoos
Ib/lb
0.592
0.483
0.606
0.629
0.492
0.299
0.217
0.408
0.407
0.323
0.271
0.351
0.276
0.220
0.304
0.252
0.285
0.187
0.312
0.276
0.305
0.443
0.956
0.658
0.902
0.512
0.366
0.325
0.207
0.290
0.224
O.i66
0.348
0.330
0.339
0.354
0.307
0.354
0.302
0.458
«c
Days
1.72
2.03
2.29
2.59
3.38
3.78
3.50
2.94
3.53
3.84
4.75
3.88
3.44
3.51
11.42
3.17
2.59
3.66
3.40
2.31
2.84
2.27
2.02
4.94
5.62
6.22
6.66
5.09
2.98
7.55
2.97
2.36
2.70
3.68
3.75
4.38
4.75
4.29
4.24
4.88
l/ec
Days-1
0.581
0.493
0.437
0.386
0.296
0.265
0.286
0.340
0.283
0.260
0.211
0.258
0.290
0.285
0.088
0.315
0.387
0.273
0.294
0.433
0.352
0.441
0.495
0.202
0.178
0.161
0.150
0.196
0.336
0.132
0.338
0.424
0.370
0.272
0.267
0.228
0.211
0-233
0.236
0.205
19
-------
0.9'
0.8 >
0.7-
0.6.
0.5*
cxi
CO
— i 0.4«
0.3.
0.2°
0.1*
•*
FIGURE 5
FEDERAL ASSISTANCE PROJECT
METROPOLITAN DENVER SEWAGE TREATMENT PLANT
OCTOBER 1969 TO FEBRUARY 1970
NET GROWTH RATE (%e)
vs
SUBSTRATE REMOVAL RATE (qBOD5)
• AREA - 3
O AREA - 2
0.1 0.2
0.3
0.4
0.7
0.5 0.6
SUBSTRATE REMOVAL RATE QB005
Q& 0.9 1.0 1.1
Ib. BOD5 REMOVED PER DAY
1.2
1.3
1.4
1.5
Ib. VSS IN SYSTEM
-------
sludge produced In the secondary would have been 82.800 pounds per day. To maintain a specific cell
residence time (sludge age), this amount of sludge should have been wasted. If the estimated yield
coefficient Y • 0.72 (See Figure 5) 1s used, 99,300 pounds per day would have been produced and
would have had to be wasted. These values are dally average values and do not represent the peaks
In loading and sludge production that occur. Both values are less than the 131,000 pounds per day
which was the design basis for the Metro Plant secondary sludge handling facilities. Although this
design loading was not exceeded on an average basis, problems did occur with the sludge handling
facilities (I.e. concentrators and Incinerators).
B. Analysis of Secondary Clarlflers
Eckenfelder and O'Connor (8) have stated that the size of secondary clarlflers In biological
systems Is related to three design factors. These factors are: (1) The permissible retention of the
settled sludge in the basin as dictated by its biological properties, (2) The area required for
clarification over the operating mixed liquor suspended solids range, and (3) The area and volume
requirements to produce by thickening an underflow of a desired concentration.
At Metro Denver sludge retention in the final clarlflers should be minimized; possibly to one
hour or less. The value of the sludge detention time, SDT, in the final clarlflers was determined
during the project on a daily average basis and normally was easily controlled by adjusting the
return sludge pumping rates. This fact Implies that the volume of the clarlfiers and the return
sludge pumping capacity was generally satisfactory to allow rapid removal of the sludge.
The clarification and thickening capacities for a secondary clarlfier can be estimated from
batch settling tests. A great number of batch settling tests were conducted during the project, and
these results were used to evaluate the clarification and thickening capacities of the Metro Denver
plant.
The limitation of this type of analysis Is in the determination of a representative batch
settling test. The previously selected "steady state" periods for Areas #2 and #3 were selected for
analysis. These periods were initially selected based on uniformity of sludge settling and sludge
concentration characteristics, as well as uniformity of solids concentration. In addition, these
periods were generally the best periods of control and operation and therefore were representative
of sludge settling characteristics that were experienced during the project.
During most of the project four batch settling tests were conducted on a daily basis at 5:00 A.M.,
9:00 A.M., 1:00 P.M. and 9:00 P.M. Values for settled sludge volume for each hourly test were
averaged for the various "steady state" periods. These values are presented in Table 3. Table 1
gives the associated average parameters and average flow values for these same periods. The period
January 10, 1970 to January 13, 1970 for Area *3 was omitted from this analysis because cf the lew
mixed liquor solids concentration and resulting rapid settling.
21
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TABLE 3
FEDERAL ASSISTANCE PROJECT
METROPOLITAN DENVER SEWAGE TREATMENT PLANT
OCTOBER 1969 - FEBRUARY 1970
Average Settled Sludge Volumes For
"Steady State" Periods
Area and "Steady
State" Period
«
January 5, 1970
to
January 11, 1970
#2
January 29, 1970
to
February 12, 1970
#3
December 15. 1969
to
January 5. 1970
#3
January 20, 1970
to
January 25, 1970
#3
February 9, 1970
to
February 16, 1970
Settling
Time (Mln)
5
10
20
30
60
5
10
20
30
60
5
10
20
30
60
5
10
20
30
60
5
10
20
30
60
Average Settled Sludge Volumes for
"Steady State" Period - cc/1
5:00 A.M.
496
346
261
224
171
666
489
403
343
276
805
660
510
431
320
922
870
742
642
480
541
413
334
294
238
9:00 A.M.
523
383
279
239
184
737
545
433
376
301
855
725
585
495
360
953
914
828
717
542
604
476
382
335
264
1:00 P.M.
424
286
211
179
144
453
332
261
228
184
650
521
408
347
260
903
752
582
482
367
470
368
294
259
207
9:00 P.M.
517
332
246
213
161
617
452
362
320
249
677
523
401
348
265
936
829
598
489
381
539
421
337
308
237
22
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The clarification capacity required 1n a clarifler can be estimated from the Initial rate at
which the solids liquid Interface subsides as outlined by Eckenfelder (8), Rich (9) and Smith and
Loveless (10). The zone settling rate (Vs) can be calculated by determining the slope of the Initial
straight line portion of the sludge settling curve. This settling rate can then be expressed as the
equivalent surface overflow rate since solids will be lost In the plant effluent If the settling rate
Is exceeded by the clarifler overflow rate.
0_ • V. x 7.5 gallons per cubic foot x 24 hours per day
r s Equation 6
» Vs x 180
WHERE:
Or = Equivalent Surface Overflow Rate (gal/sq ft/day)
V$ = Zone Settling Rate (ft/hr)
Curves were drawn from each set of average settled sludge volume values for the selected periods.
The slope of the Initial straight line portion of the curve was determined and thus the zone settling
rate (V$) was established. An example determination of V$ is shown In Figure 6. The values of the
zone settling rates (V$), as well as the associated equivalent overflow rates (Or), are shown in
Table 4.
The zone settling rate (V$) varied throughout the "average" day for the selected periods. This
Is to be expected since the zone settling rate is a function of the Initial MLSS concentration and of
the loading rate. I.e. pounds of BOD per pounds of MLSS. [Smith and Loveless (10)]. Flow variations
throughout the day caused the MLSS and the loading rates to fluctuate, causing the observed varia-
tions In the values of Vs. No attempt was made to distinguish between the portion of the change In
Vs due to changing load and that due to change of Initial MLSS concentration or in response to any
possible variances in growth rates. In addition, as mentioned earlier, cell residence time seldom
exceeded five to six days. Associated effects on settleability were also not separable.
It is shown 1n Table 4 that the maximum zone settling rate normally occurred at the 1:00 P.M.
test. However, It was observed that this was also the time of the day when most of the solids
flushing occurred. Table 4 shows the calculated overflow rates based on the daily average flow for
each area during the periods. Each area at Metro Denver had three 130 foot diameter secondary
clarifiers which gave a total surface overflow area of 39,900 square feet. Generally the 1:00 P.M.
equivalent surface overflow rates exceeded the average clarifler overflow rates for the periods
Investigated. However, this is based on maximum zone settling rates compared with average clarifler
overflow rates. If the maximum flow is assumed to occur at 1:00 P.M. and the design ratio of
I"averagehday1?atete a 2 CSee Henningson, Durham and Richardson (11)] is applied to the clarifler
overflow rates, then in every case the equivalent surface overflow rate derived from Vs values at
23
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10 «
FIGURE 6
FEDERAL ASSISTANCE PROJECT
METROPOLITAN DENVER SEWAGE TREATMENT PLANT
OCTOBER. 1969 - FEBRUARY. 1970
DETERMINATION OF ZONE SETTLING RATE ( Vs )
HEIGHT OF SLUDGE INTERFACE vi TIME
AREA #3 PERIOD: 1/V- 2/16/70 AVG.9:OOAM
SFTTLING TIME - ( MINUTES )
24
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TABLE 4
FEDERAL ASSISTANCE PROJECT
METROPOLITAN DENVER SEWAGE TREATMENT PLANT
OCTOBER 1969 - FEBRUARY 1970
Zone Settling Rates (Vs) And Equivalent Surface
Overflow Rates (Qr) For "Steady State" Periods
Area and "Steady
State" Period
#2
January 5, 1970
to
January 11 , 1970
fz
January 29, 1970
to
February 12, 1970
#3
December 15, 1969
to
January 5, 1970
#3
January 20, 1970
to
January 25, 1970
#3
February 9, 1970
to
February 16, 1970
Zone Settling Rates (Vs)
- ft/hr and Equivalent Surface Overflow Rates (Or) -
gpsfd for "Steady State" Periods *
5:00 A.M.
3.43
620
1.72
310
1.13
204
<1
<180
3.00
544
9:00 A.M.
6.80
595
1.45
262
0.88
159
<1
<180
2.70
488
1:00 P.M.
3.30
1,225
4.93
890
2.72
490
<1
<180
6.00
1,080
9:00 P.M.
3.83
690
3.03
546
2.53
456
<1
<180
3.24
585
Daily Average
Overflow Rate
For "Period"
gpsfd
644
698
744
660
740
i
* Vs values are given on top and Or values on bottom.
25
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1:00 P.M. 1s exceeded by the clarlfler overflow rate and flushing of solids could be expected to
occur. Additionally, a portion of this flushing may be attributable to the normal high return sludge
pumping rates that were utilized in the operational controls.
This problem was further aggravated by locating the effluent weirs for the 130 foot diameter
clarlflers at the outer edge of the clariflers. This allowed localized high upflow velocities to
occur 1n the final clarifiers. These localized high velocity currents could have been avoided if
weir placement had been such that more of the surface area in the final clarifiers was developed to
provide a more uniform upflow velocity. However, even if the additional weirs were located to
develop more of the surface area of the final clarifiers, the data shown in Table 4 indicates that
problems with flushing of solids still could occur.
Therefore, either more surface area must be provided or the settling characteristics must be
altered such that the zone settling rate is increased (i.e. a faster settling sludge). The zone
settling rate is dependent upon the initial MLSS concentration and the loading rate (which directly
affect the sludge flocculation characteristics). [See Eckenfelder (8) and Smith and Loveless (10)]
These factors are dependent upon the influent flow rate, which is highly variable and therefore makes
a positive control of the zone settling rate difficult to achieve. For ease of operation it appears
that more effective surface area, which is better developed by weir placement, is required at Metro
Denver to provide adequate clarification capacity.
The thickening capacity required 1n a final clarifier can also be estimated from a batch settling
test (8) (9). The average 1:00 P.M. settling test (See Table 3) was selected for analysis since this
time was assumed to coincide with normal daily peak flows which are approximated by twice the average
daily flow (11). The most rapid 1:00 P.M. zone settling rate (See Table 4) was selected to determine
a desired thickening capacity since the value determined would represent a minimum thickening area
required, (i.e. any settling rate with a lesser value would require more thickening area.) The peak
zone settling rate for Area #2 at 1:00 P.M. was 4.93 feet per hour and for Area #3 it was 6.00 feet
per hour. (See Table 4)
Rich (9) outlines an equation for determining the thickening area required:
A = ^ Equation 7
£ o
WHERE:
A = cross section required to obtain a layer of a desired concentration
-- ft*
q = flow rate of the mixed liquor entering the final clarifier ~ ft3/sec.
26
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Z'0 = initial height of the interface in the settling column - feet (The
settleometers used at Metro Denver for the batch settling tests had a
0.5 feet depth.)
T = settling time required to attain a desired underflow concentration -
sec. [This value is obtained from a graphical analysis of a cludge
settling curve as outlined by Eckenfelder (8) and Rich (9).]
To complete the analysis of thickening capacity a desired underflow concentration must be
selected. At Metro Denver the design values for underflow concentration expected ranged between
5,000 to 15,000 mg/1. Therefore, a desired underflow concentration of 10,000 mg/1 was selected.
The settling time (Tu) required to obtain a 10,000 mg/1 underflow concentration for Area #2 for
the selected period January 29 to February 12, 1970 (Vs = 4.93) was determined by a graphical
analysis of the sludge settling curve. This value was used with the average flow for the period to
determine by Equation 7 the area required for thickening. For average flows 42,500 ft2 would be
required for thickening while for peak flows 85,450 ft2 would be required. A similar analysis con-
ducted on Area #3 for the selected period (February 9 to February 16, 1970) showed required areas of
114,000 ft2 and 57,000 ft2 at peak and average flow rates respectively.
The available surface area in Areas #2 and #3 is 39,900 ft2. This is not adequate to provide the
thickening area required to achieve a 10,000 mg/1 underflow concentration with the type of sludge
obtained during the project. The above analysis also indicates the implications of limited thicken-
ing capacity on sludge handling problems. Without sufficient thickening capacity a more dilute waste
sludge flow concentration is realized. The effect of the dilute concentrations is shown by the
relative differences in total sludge volumes to waste 100,000 Ibs. of solids as summarized in Table
5.
The preceding materials were developed to compare actual performance results with the batch
settling data. Most importantly, Rich (9) describes the numerous departures of actual sedimentation
basin performance from that of ideal basins. "The net effect of all the factors that contribute
toward reducing the efficiency of sedimentation in an actual basin is to decrease the clarification
rate and to increase the detention time over that derived from a batch analysis. For the sedimenta-
tion of flocculent particles from dilute suspensions the overflow rate generally will be decreased by
a factor of 1.25 to 1.75 and the detention time wM! be increased by a factor of 1.50 to 2.00. In
scaling-up thickening operations, a factor of 1.0 to 2.0 is applied to the area required for clarifi-
cation (hindered settling) and a factor of 1.0 to 1.5 to that required for thickening."
Results of the Metro Denver settleability testing should be judged in this light and with the
reported values of loading, residence times, etc. obtained during the period.
27
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TABLE 5
FEDERAL ASSISTANCE PROJECT
METROPOLITAN DENVER SEWAGE TREATMENT PLANT
OCTOBER 1969 - FEBRUARY 1970
Waste Sludge Flow Required To Remove
An Equivalent Amount Of Solids With
Varying Underflow Concentrations
Underflow Concentrations — mg/1
Waste Volume to Remove
100,000 Lbs. of Solids - Gal.
5,000
2,400,000
10,000
1.200,000
15,000
800,000
28
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VI. SUMMARY AND CONCLUSIONS
One of the objectives of the project was to instigate additional process control testing for the
secondary treatment (activated sludge) portion of the Metro Denver plant. Plant personnel were
trained to conduct process control tests on a routine basis, to evaluate and graph various selected
parameters, and to interpret these data so that adequate daily operational changes could be made.
The full beneficial effect of these process controls was not realized because of various problems
encountered with plant operation, as outlined below:
1. Adjustment of flow to each aeration basin was difficult because each basin was fed by a gate
opening from a common channel. Balancing the hydraulic effects of ten gates to achieve equal
flow to each of the four areas required a great deal o* attention. After the gates were
adjusted, determination of actual flow to each aeration basin was questionable because of
occurrences of unreliable instrument readings.
2. Two of the twelve aeration basins provided in the secondary portion of the plant were used as
grease flotation units to remove grease from the influent waste stream and were thus unavail-
able for use as a portion of the activated sludge process. This becomes important since the
average loading to the secondary during this investigation was 161,560 pounds of B005 per day,
which is approaching the design loading of 166,350 pounds of BOD. per day.
3. The rate of wasting sludge was difficult to control on a continuous basis because the meters
and control instruments frequently gave erroneous readings. Several times it was discovered
that actual flow and meter readings differed by as much as 100 percent. This definitely
effected the ability to establish a process balance.
4. No reserve capacity was available for final clarification. When a clarifier broke down
(three clarifiers broke down during the project) solids were carried over in the plant
effluent, the effluent quality was degraded, and the process balance in the affected area was
impaired.
Other difficulties encountered were the sludge production in the secondary treatment process and
the flushing of solids from the final clarifiers into the effluent.
The initial emphasis in dealing with the problems at Metro was to control the secondary treatment
portion of the plant. Therefore, removal efficiencies and effluent quality became important consider-
ations in operating the facility. Unfortunately, a high quality affluent representing increased
removals of BOD5 and TSS is associated with increased sludge production, which served to antagonize
the sludge processing and handling problem. To compensate for the increased sludge production that
accompanied the slightly increased removals achieved during the project and to relieve the existing
sludge problem, an atterot was roade to develop a sludge that would concentrate or dewater better tlv.n
29
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previously. This would have allowed a lesser volume of a more dense sludge to be wasted. Average
concentrations of 6,900 to 7,000 mg/1 were obtained in the waste sludge flow toward the end of the
project. However, the benefits derived from increasing the waste sludge concentration were not
realized because of the increased removal efficiencies and the resulting increase in the amount of
sludge produced.
Although slightly greater BOD and suspended solids removal efficiencies were realized through
operational controls, little was accomplished to alleviate the sludge handling problems at the plant.
It is hoped that the increased removal efficiencies will be maintained and the sludge handling proce-
dures modified to alleviate these difficulties. An investigation of the sludge production character-
istics at the Metro plant to compare them with presently available sludge handling facilities was
made.
A kinetic model was applied to the collected data to determine the microbiological character of
the waste stream. At Metro Denver the results of this analysis indicate that the characteristics of
the waste received at the Metro Denver plant do not deviate significantly from those expected from a
typical domestic waste. An attempt was made to determine the amount of sludge production and to com-
pare these results with the sludge handling capacities at the plant. The results indicate that the
design sludge handling capacity (131,000 pounds per day of secondary sludge) could be exceeded during
peak loading periods. It is important when sludge handling procedures or facilities are modified at
Metro Denver that the sludge production during peak loading periods be considered in the design
criteria.
The second major operating difficulty evaluated was the flushing of solids that occurred from the
final clarifiers. Representative zone settling rates were determined for the sludge at Metro Denver
based on the numerous batch settling test data obtained. From this analysis it was determined that
the clarification capacity of the final clarifiers at the Metro Denver plant was not adequate for
the selected periods of investigation. The type of sludge developed proved to have a zone settling
rate (Vs) that was too slow to be held in the final clarifiers. A portion of the flushing problem
was also attributed to the large diameter (130 feet) final clarifiers which had effluent weirs
located at or near the outer periphery. This weir placement allowed excessive velocity currents to
develop further aggravating the solids "flushing" problem. This problem can be alleviated by a
different wsir placement arrangement that allows a more uniform use of the surface area on the final
clarifiers. (i.e. another launder of weirs located nearer the center of the tank.)
It was also determined that the thickening area requirements of the final clarifiers were not
adequate to obtain a 10,000 mg/1 underflow concentration with the type of sludge developed during the
project.
Two alternatives can be used to change the effects of the slow zone settling rates of the sludge.
30
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The first Is to increase the clarifier surface area to reduce overflow rates to less than the settling
velocity established by the zone settling rate. This would provide additional thickening area at the
same time. The second approach would be to Increase the zone settling rate of the sludge at the Metro
Denver plant. The zone settling rate is a function of the MLSS concentration and the loading rate.
Because of the constantly changing load (flow) and its effect on the MLSS concentration, it is a con-
tinuous problem to maintain a proper process balance and achieve a desired zone settling rate.
31
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VII. RECOMMENDATIONS
The following recommendations are made:
1. It is recommended that control testing established during the Federal Assistance Project be
continued.
2. An effort should be made at the Metro Denver plant to assure the accuracy of all mete red
values in order to adequately use control testing procedures.
3. It is recommended that Metro Denver be considered for demonstrating various comparisons.
Because of the unique arrangement of facilities at the Metro plant, four areas with an iden-
tical influent waste are available.for evaluation. This arrangement is ideal for conducting
comparisons of various types of equipment (i.e. provide various types of aeration equipment,
evaluate effects of different skimmer arrangements on final clarifiers, evaluate different
weir placement patterns on final clarifiers, etc.).
4. The Metro Denver plant should be operated to achieve the maximum possible reduction of waste
pollutants. To operate and achieve these high removal efficiencies, modifications to the
sludge handling procedures or facilities must be made. Any modification of the Metro Denver
sludge handling facilities should take into account the sludge production characteristics at
the Metro Denver plant which are apparently similar to those of typical domestic sewage and
the clarification-thickening capacity requirements of the secondary clarifiers.
5. Properly located additional weirs are recommended on the secondary clarifiers to develop a
more uniform distribution of flow over the surface area provided in the relatively large
diameter final clarifiers. Surface skimmers are also recommended.
6. Additional clarifier surface area with proper weir placement is recommended or the sludge
settling characteristics must be altered by operational control in order to assure that
solids will not be flushed into the final effluent. Additionally, increased area would
appear to improve sludge thickening, thereby reducing waste sludge volumes. More reliable
control would also be obtained by increased clarifier surface area.
32
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VIII. APPENDICES
Appendix A - A Resolution: "Concerning the Federal Government's Responsibilities In
Constructing and Operating Sewage Disposal Facilities."
Appendix B - References
Appendix C - Determination of Substrate Removal Rate (q) and Net Growth Rate (l/ec)
83
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APPENDIX A
A RESOLUTION ADOPTED BY METROPOLITAN
DENVER SEWAGE DISPOSAL DISTRICT NO. TS
BOARD OF DIRECTORS
ENTITLED
"Concerning the Federal Government's
Responsibilities in Constructing and
Operating Sewage Disposal Facilities"
July 11, 1969
-------
A RESOLUTION
(CONCERNING THE FEDERAL GOVERNMENT'S RESPONSIBILITIES IN
CONSTRUCTING AND OPERATING SEWAGE DISPOSAL'FACILITIES)
WHEREAS, the federal government has enacted water pollution control legislation which makes it
Incumbent upon states to establish stream quality limits, or to be subjected to stream quality stan-
dards as dictated by the federal government itself, and
WHEREAS, the water pollution legislation adopted by the State of Colorado is not consistent but
rather relates to stream classification, based upon an evaluation of each stream's individual
characteristics, and
WHEREAS, the evaluation process for stream classification relates to a multitude of factors
other than the consideration of protection to health and the abatement of nuisance, and
WHEREAS, sewage treatment to the extent of providing for the development of streams and adjacent
properties into recreational areas does require an additional capital investment for treatment
facilities, as well as substantially increasing operating and maintenance expenses thereof, and
WHEREAS, the arid and semi-arid regions of the western United States have additional burdens for
capital investments and operational and maintenance expenses, due to the lack of dilution water to
the same degree as do the other regions of the United States, and
WHEREAS, the high degree of sewage treatment required to effect water pollution control does
generate additions to solid wastes to be disposed of in the form of sludge, and
WHEREAS, cities, counties and independent sanitation districts in the Metropolitan Denver area
recognized in the early 1960's their financial inability as separate political subdivisions to meet
the strict standards being forced upon them by the national Congress and the State Legislature, and
WHEREAS, these independent political subdivisions banded together and created the Metropolitan
Denver Sanitation District No. 1, prevailing upon the Colorado General Assembly to adopt Colorado
Revised Statute 89-15-5 giving them authority so to do, and
WHEREAS, property owning electorate, demonstrating their concern over the pollution threat to
the health and welfare of the total comnunity, by a vote of 25,099 to 2,756, agreed to mortgage
their property so that bonds in the amount of $32.5 million could be issued for the construction of
a modern primary and secondary sewage treatment plant at the confluence of Clear and Sand Creeks
with the Platte River, and
WHEREAS, this plant has been constructed following review and approval of engineering and con-
struction plans by all required federal, state and regional agencies with these bond moneys, supple-
mented by some federal but no state funds, to take care of residential, commercial and industrial
34
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wastes with each participating political subdivision, by means of billings to users within their
subdivisions, paying their proportionate shares of all operating costs, and
WHEREAS, this multi-mi 11 ion-dollar plant does bring effluent dumped into the Platte River up to
water pollution control standards it does not dispose of the solid wastes..resulting from such treat-
ment for a variety of reasons not the least of which is the fact that our technology has developed a
multitude of consumer goods, paper products, garbage disposal systems-and detergents, handle human
waste, and
WHEREAS, resident property owners of Metropolitan Denver recognized their responsibilities to
take the initiative and act to abate practices which contributed to the pollution of Clear Creek,
Bear Creek, Sand Creek and other watercourses that flowed into the Platte River as well as the
Platte River itself, and
WHEREAS, residents and taxpayers of the various political subdivisions that are now participating
in this metropolitan effort to eliminate a pollution problem are being taxed the maximum they can
afford to pay for sewage disposal and do not have the financial capability to pay imminent additional
operating and maintenance costs or to effect the engineering, design and capital construction
necessary to increase the efficiency of this plant so as to halt continuing pollution of our
environment;
NOW, THEREFORE, be it resolved, that the Board of Directors of the Metropolitan Denver Sanitation
District No. 1 hereby does petition the Congress of the United States and the appropriate federal
agencies to:
1. Conduct and finance extensive research to discover new techniques of handling the variety of
waste products now being dumped into the sanitary sewers of America and being carried to
traditional plants that do not have the capabilities of handling them.
2. Make available to this district a special team of scientists and engineers assembled from
appropriate federal departments to serve as a task force to inspect the District's sewage
disposal plant and make appropriate recommendations.
3. Appropriate sufficient funds so that these recommendations can be implemented, since the
Federal government has set up the standards the District is required to meet.
4. Recognize that antipollution standards adopted by the Congress and enforced by federal and
state as well as local government agencies are placing unprecedented and unbearable financial
responsibilities on local governments and their constituents, thus making it mandatory that
the Federal government assist local communities in meeting costs involved not only in con-
structing adequate sewage facilities but of operating them as well.
35
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APPENDIX B
REFERENCES
-------
1. WEST, A. W.
Case Histories: Improved Activated Sludge Plant Performance by Operations Control -
Proceedings 8th Annual Environmental and Water Resources Engineering Conference.
Vanderbilt University. 1969.
2. LAWRENCE. A. W. and McCARTY, P. L.
"Unified Basis for Biological Treatment Design and Operation." Journal of the Sanitary
Engineering Division, ASCE, Volume 96, No. SA 3, Proc. Paper 7365, 1970, pp. 757-778.
3. JENKINS, D. and GARRISON, W. E.
"Control of Activated Sludge by Mean Cell Residence Time," Journal Water Pollution Control
Federation. Volume 40, No. 11, Part 1, 1968, pp. 1905-1919.
4. PEARSON, E. A.
Kinetics of Biological Treatment. Paper presented at: Special Lecture Series -
Advances in Mater Quality Improvement, University of Texas, Austin. 1966.
5. McKINNEY. R. E.
"Mathematics of Complete-Mixing Activated Sludge." Journal of the Sanitary Engineering
Division. ASCE, Volume 88, No. SA 3. Proc. Paper 4362. 1965, pp. 45-61.
6. HEUKELEKIAN, H., OXFORD. H. E. and MANGENELLI, R.
"Factors Affecting the Quantity of Sludge Production in the Activated Sludge Process."
Sewage and Industrial Wastes, Volume 23, No. 8, 1951, pp. 945-958.
7. MIDDLEBROOKS. E. J. and GARLAND, C. F.
"Kinetics of Model and Field Extended-Aeration Wastewater Treatment Units," Journal Water
Pollution Control Federation. Volume 40, No. 4, 1968, pp. 586-612.
8. ECKENFELDER, W. W. and O'CONNOR, D. J.
Biological Waste Treatment, Pergamon Press, New York. 1961.
9. RICH, L. G.
Unit Operations of Sanitary Engineering, John Wiley and Sons, Incorporated, Publishers,
New York, London. 1961.
10. SMITH and LOVELESS
Notes on Activated Sludge, Lenexa. 1969.
11. HENNINGSON, DURHAM and RICHARDSON
Consulting Engineers Report. Metropolitan Denver Sewage Disposal District No. 1 - Metro
Plant Expansion Study, Part 1 - Immediate Requirements. 1969.
36
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12. WEST, A. W.
Listing of Abbreviations Used to Describe Activated Sludge Systems. Lecture Presentation
to Consulting Engineers and Plant Operators Concerning Control Testing for Activated
Sludge Plants Sponsored by Water Pollution Control Division, Colorado Department of
Public Health. 1970.
37
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APPENDIX C
DETERMINATION OF SUBSTRATE REMOVAL
RATE (q) AND NET GROWTH RATE (1/6C)
-------
It is the purpose of this appendix to present a sample calculation of the determinations made of
the substrate removal rate (q) and the net growth rate (l/ec). Throughout the sample calculation the
assumptions made in relating the data collected and analyzed during the assistance project to the
analysis made using the kinetic model will be stated. Data obtained for Area #3 on December 15, 1969,
will be used for the presentation of the sample calculation.
A. Determination of the Substrate Removal Rate (q)
q • F*So " S1} [See Jenkins (3)]
1. Determination of F(S0 - S^
WHERE:
SQ = influent substrate concentration - For Metro Denver a BODg value based on a
composite sample was used to represent SQ (12/15/69 for Area #3, S - 198 mg/1).
S. = effluent substrate concentration - For Metro Denver a BOD. value based on a
composite sample was used to represent S. (12/15/69 for Area #3, S. = 16 mg/1).
F = influent flow rate (12/15/69 for Area #3, F = 34.8 MGD) - This value was obtained
from flow meters at the Metro Denver plant.
THEREFORE:
F = 34.8 MGD SQ = 198 mg/1 S] = 16 mg/1
34.8 (198-16) (8.33 Ibs/gal) = 52.760 Ibs. BODg removed/day
2. Determination of VX,
WHERE:
V = volume of aeration plus secondary sedimentation basins
X = MLSS or MLVSS concentration
NOTE:
VX1 is a number representing the total pounds of cells in the system. Normally in
determining this value mixed liquor suspended solids concentrations by weight are used
(Xj). Instead of MLSS concentrations, sludge concentrations were obtained on a percent
volume basis by using the centrifuge. During most of the project, however, daily rela-
tionships between percent concentration of sludge by volume and concentration by weight
were determined on the basis of a grab sample. These comparisons varied from 1% =
500 mg/1 TSS to 1% = 1,000 mg/1 TSS. However, during "steady state" conditions, the
relationship between spin concentrations and mg/1 remained fairly constant. Therefore,
the average of the relationship between spin concentrations and mg/1 for each "steady
state" period selected was determined and used to convert the spin concentration to
38
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mg/1 of total suspended solids. The relationship between total suspended solids (TSS)
and volatile suspended solids (VSS) was also obtained from the analysis of daily grab
samples. The average ratio of VSS/TSS for each "steady state" period was determined.
For December 15, 1969, and the associated "steady state" period the average relationship
between volume or spin concentrations and mg/1 was 1% = 616 mg/1 TSS for Area S3 and the
average VSS/TSS ratio was 0.840. Another refinement was also used in obtaining VX1,
which will be outlined below.
APPROACH:
A value comparable to VX1 called-total sludge units (TSU) was determined using the Metro
Denver data. Total sludge units are equivalent to the summation of the aerator sludge
units (ASU) and the clarifier sludge units (CSU). A sludge unit is defined as one
gallon'of sludge at 100% concentration, based on sludge concentrations obtained by cen-
trifuge testing. One of the differences between TSU and VX1 lies in the fact that a
modification is made in determining the clarifier sludge units.
a. Determination of Clarifier Sludge Units (CSU)
Final Clarifier
CONC = RSC
WHERE: [West's Symbols (12)]
CUD = clarifier water depth (mean depth if bottom is sloped) - At Metro Denver the
mean depth was 11.7 feet.
DOB = depth of sludge blanket - At Metro Denver blanket depth determinations were made
every two hours on each of the three clarifiers in the respective areas. These
values were averaged on a daily basis to obtain DOB (12/15/69 for Area #3, DOB =
9.7 feet).
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BIT = sludge blanket thickness - This value is equivalent to CWD - DOB (11.7 - 9.7 =
2.0 feet (BLT) for Area #3 on 12/15/69).
ATC » aeration tank concentration - This is the concentration of sludge by percent
volume in the aeration basin. This value was obtained by centrifuging samples of
the effluent from the aeration basins. A daily average of ATC values was obtained
for use in calculations. (12/15/69 for Area #3, ATC = 2.75%)
RSC » return sludge concentration - This is the concentration of sludge by percent
volume drawn off the bottom of the secondary clarifiers. This value was obtained
by centrifuging samples taken from the return sludge wet well. A daily average of
RSC values was obtained for use in calculations. (12/15/69 for Area #3, RSC =
11.252}
CMC = clarifier mean sludge concentration - This value is obtained by the equation
ATC + RSC^ jhis equation assumes a sludge concentration at the top of the blanket
equal to ATC and that at the bottom equal to RSC and a uniform distribution of
concentration. (2.75 + 11.25 = 7iOZ (Q^C) for Area #3 on 12/15/69)
OTHER FACTORS:
CVG = clarifier volume in gallons per clarifier multiplied by the number of clarifiers in
operation. At Metro Denver the volume of each clarifier was 1.165 million gallons
and three clarifiers were in operation. (1.165 x 3 = 3.495 MG (CVG) for Area #3
on 12/15/69)
CSP = clarifier sludge percentage or the portion of the clarifier occupied by sludge
which is determined by the ratio of ikl ( 2i° = 0.171 (CSP) for Area #3 on
CWD 11.7
12/15/69).
From the above the clarifier sludge units can be determined by the equation: CSU =
CMC x CSP x CVG.
A modification was made in the equation for this analysis in that the CMC was multiplied
by the factor representing the conversion between percent concentration by volume and mg/1
(616 mg/1 TSS = 1% for Area #3 for 12/15/69 and the related "steady state" period).
Therefore the modified clarifier sludge mass can be determined by CSU (modified) =
CMC x 616 x CSP x CVG x 8.33 Ibs/gal.
C •= 7.0 x 616 x 0.171 x 3.495 x 8.33
• 21.550 IDS, of total suspended solids or sludge in clarifier
b. Determination of Aerator Sludge Units (ASU)
ASU = AVG x ATC
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WHERE:
AVG = aeration basin volume in gallons per aeration basin times' the number of basins
in service. At Metro Denver the volume of each aeration basin was 2.0 MG and
three basins were in operation in Area #3 (2.0.-X 3.0 = 6 MG (AVG) for Area S3
on 12/15/69).
ATC = 2.75% for Area 13 on 12/15/69 (See a. above").
From the above the aeration basin sludge units can be determined. However, the per-
centage sludge concentration by volume must again be converted to mg/1 (616 mg/1 TSS =
IX for Area #3 for 12/15/69 and the related "steady state" period).
Therefore the modified aeration basin sludge mass can be determined by:
ASU (modified) = AVG x ATC x 616 x 8.33 Ibs/gal.
= 6 x 2.75 x 616 x 8.33
= 84.670 Ibs. of total suspended solids or sludge in aeration basin
c. Determination of TSU
Using the modifications outlined above the value of TSU is assumed to be equivalent
to the value VXr
THEREFORE:
TSU (modified) = VX] = ASU (modified) + CSU (modified)
= 21,550 (From a. above) + 84,670 (From b. above)
= 106,220 Ibs. of total suspended solids or sludge in system
NOTE:
The value of TSU, as determined above, was obtained on a TSS basis. Normally in
determining a substrate removal rate (q) a VSS basis is used. (VSS/TSS = 0.840 for
Area #3 for 12/15/69 and the related "steady state" period)
THEREFORE:
TSU (modified) x VSS/TSS = VX1 in Ibs. of VSS
= 106,220 x 0.840
= 89.220 Ibs. of volatile suspended solids in system
3. Example Determination of q
For Area #3 on 12/15/69:
F(S0 - S]) = 52,760 Ibs. BOD5 removed/day (1. above)
VX = 89,220 Ibs. of volatile suspended solids in system (2. above)
41
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q = 52.760
H 89,220
= 0.592 lb. of 6005 removed per day
Ib. of VSS in system
[q for conventional activated sludge normally has a value of 0.2 to 0.5, see Jenkins (3)]
B. Determination of the Net Growth Rate l/ec
l/ec » FX2 * wxr [See Jenkins (3)]
1. Determination of VX]
VX, or Its assumed equivalent was determined in Part A-2 above. This was determined for
Area #3 for the date of 12/15/69.
VX. =» 106.220 Ibs. of total suspended solids in system (A-2 above)
NOTE:
In the determination of 1/9C it is not necessary to convert from a TSS basis to a VSS
basis since both the numerator (FXg + WXr) and denominator (VX]} in the calculation can be
determined on a total suspended solids basis. Therefore, VX] on a total suspended solids
basis Is given above and WXr and FXg will be calculated on a total suspended solids basis
below.
2. Determination of WXr
WXp represents the mass of sludge wasted from the system per day.
WHERE:
W = waste sludge flow rate (12/15/69 for Area #3, W = 0.89 MGD) - This value was
obtained from, flow meters at the Metro Denver plant.
Xr = return sludge TSS or VSS concentration - This value was not determined at Metro
Denver on mg/1 basis but rather the return sludge concentration (RSC) was deter-
mined as a percent volume using the centrifuge. This value (RSC) can be related
to Xp using the relationship established between mg/1 and percent concentration by
volume based on daily grab samples. (616 mg/1 TSS = 1% for Area #3 and the
related "steady state" period) For Area #3 the daily average RSC concentration on
12/15/69 was 11.25%.
Xr = 11.25 x 616 = 6.930 mg/1
THEREFORE:
WXr = 0.89 x 6,930 x 8.33 Ibs/gal. = 51.310 Ibs. wasted per dav
42
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3. Determination of FX2
FX£ represents the cells lost from the system per day in the plant effluent.
WHERE:
X- = effluent TSS or VSS concentration - At Metro Denver the effluent ISS concentra-
tion was determined for each area based on the analysis of a composite sample
(12/15/69 for Area 13 effluent TSS = 36 mg/1).
F = influent flow rate (F = 33.9 MGD for Area #3 on 12/15/69).
THEREFORE:
FX2 = 33.9 x 36 x 8.33 Ibs/gal.
= 10.180 Ibs. of total suspended solids lost in the effluent per day
4. Example Determination of Net Growth Rate (l/ec)
FX? + WXr
1/ec ' -n^
For Area #3 on 12/15/69:
FX2 = 10,180 Ibs/day (3. above}
WXr = 51,310 Ibs/day (2. above)
VX] = 106,220 Ibs. (1. above)
THEREFORE:
I/a - 10.180*51.310
' c 106,220
= • 61.490
106,220
= 0.581 Ibs. TSS wasted or lost per day
• Ibs. TSS in__sy_s.t;enfi
The reciprocal of l/oc is equal to f»c or the mean cell residence time (sludge age). For
Area #3 on December 15, 1969. BC = 1.72 days.
Similar calculations were rnade for the other days included in the selected "steady state"
periods for Areas #2 and #3. The results of these analyses are presented in Table 2 in text.
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APPENDIX
COLORADO WATER QUALITY STANDARDS
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D-l
Appendix D
COLORADO WATER QUALITY STANDARDS
Waters of the state, the quality of which exceeds the limits set in these
standards, will be maintained at existing quality unless and until it can
be demonstrated to the State that a change in quality is justified to
provide necessary economic or social development. In that case, the best
practicable degree of waste treatment to protect the current classification
of such waters will be required. The appropriate Federal authority will be
provided with information, from time to time, required to discharge his
responsibilities under the Federal Water Pollution Control Act, as amended.
I. BASIC STANDARDS APPLICABLE TO ALL WATERS OF THE STATE;
A. All wastes capable of treatment or control prior to discharge
into any waters of the state, shall receive secondary treatment
with disinfection or its industrial waste equivalent, as deter-
mined by the State Water Pollution Control Commission. Lesser
degrees of treatment or control may be permitted only where it
can be demonstrated that the standards applicable to the classified
use of the water can be attained. Greater degrees of treatment
or control will be required where it can be demonstrated that it
is necessary to comply with the standards applicable to the
classified use of the water.
B. Free from substances attributable to municipal, domestic, or
industrial wastes, or other controllable sources that will either
settle to form unsightly, putrescent, or odorous bottom deposits,
or will interfere with the classified use of the water.
C. Free from unsightly floating debris, oil, grease, scum, and other
floating material attributable to municipal, domestic, or .
industrial wastes, or other controllable source.
D. Free from materials attributable to municipal, domestic or indus-
trial wastes, or other controllable sources that will produce
objectionable odor, color, taste, or turbidity in the water, or
objectionable aquatic life which may result in eutrophication or
other conditions that interfere with the classified use of the
water.
E. Free from high temperatures, biocides, toxic, or other deleterious
substances attributable to municipal, domestic, or industrial
wastes, or otlier controllable sources in levels, concentrations,
or combinations sufficient to be harmful to human or animal life.
F. Radioactive materials attributable to municipal, industrial or
other controllable sources will be minimum concentrations that
are physically and economically feasible to achieve. In no case
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D-2
shall such materials in the stream exceed the limits established
in the current edition of the U. S. Public Health Service Drinking
Water Standards or the limits approved by the Federal Radiation
Council, or, in the absence of any limits specified by the U. S.
Public Health Service or the Federal Radiation Council, 1/30 of
the 168-hour-week values for other radio-active substances speci-
fied in the National Bureau of Standards Handbook 69.
II. SPECIFIC STANDARDS ESTABLISHED BY THE STATE OF COLORADO;
CLASS A - The following standards shall apply to water withdrawn
for treatment as a potable supply:
a. Bacteria; Wastes or substances from controllable sources shall
not be discharged into these waters in amounts which will cause
the number of organisms of the fecal coliform group, as deter-
mined by either multiple tube fermentation or membrane filter
techniques, to exceed a log mean of 1000 per 100 milliliters or
exceed 2000 per 100 milliliters in more than 10 percent of the
samples collected in any 30-day period.
b. Dissolved Oxygen; Dissolved oxygen shall not be less than 4
milligrams per liter.
c. pH; The pH shall be maintained between 6.0 and 9.0.
d. Taste and Odor; Free from materials attributable to municipal,
domestic, or industrial wastes, or other controllable sources
that will produce taste or odor in the water.
e. Dissolved Solids; Total dissolved solids, annual volume weighted
average, should be less than 500 milligrams per liter.
f. Selected Chemical Constituents; The following substances shall
not be present in such amounts as to exceed the specified concen-
trations in a potable water supply according to the mandatory
requirements of the latest edition of the U. S. Public Health
Service Drinking Water Standards:
Substance Concentration - me/1
Arsenic 0.05
Barium 1.00
Cadmium 0.01
Chromium (Hexavalent) 0.05
Cyanide 0.20
Lead 0.05
Selenium 0.01
Silver 0.05
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D-3
CLASS B-2 - The following standards shall apply to waters classified
for fish and wildlife (Warm Water Fishery):
a. Bacteria: Wastes or substances from controllable sources shall
net be discharged into these waters in amounts which will cause
the number of organisms of the fecal coliform group, as deter-
mined by either multiple tube fermentation or membrane filter
techniques, to exceed a log mean of 1000 per 100 milliliters or
exceed 2000 per 100 milliliters in more than 10 percent of the
samples collected in any 30-day period.
b. Dissolved Oxygen; In warm water fisheries, dissolved oxygen
content shall in no case go below 5 milligrams per liter.
c. pH: The pH shall be maintained between 6.5 and 8.5. No control-
lable pH change will be permitted which will interfere with fish
and aquatic life.
d. Turbidity: No turbidity shall exist in concentrations that will
impair natural and developed fisheries.
e. Temperature; In warm water fisheries the temperatures shall not
exceed 90°F. No controllable temperature change will be permitted
which will interfere with spawning and other aspects of fish life.
Limits on temperature change have not been established due to
lack of historical temperature data and lack of conclusive tempera-
ture change criteria for the aquatic biota of waters of the state.
These factual data are being collected, however, to serve as a
basis for setting limits. In the meantime, an abrupt change in
temperature must be avoided and the normal pattern of diurnal and
seasonal changes must be preserved. The maximum allowable tempera-
ture increase due to waste discharges in streams will be 58F.
f. Toxic Material; Free from biocides, toxic, or other deleterious
substances attributable to municipal, domestic, or industrial
wastes, or other controllable sources in levels, concentrations,
or combinations sufficient to be harmful to aquatic life.
g. Other Material; Free from materials attributable to municipal,
domestic, or industrial wastes, or other controllable sources
that will produce off-flavor in the flesh of fish.
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D-4
CLASS C - The following standards shall apply to waters classified
for industrial uses:
a. Dissolved Oxygen: Dissolved oxygen content shall not go below
3 milligrams per liter.
b. pH; The pH shall be maintained between 5.0 and 9.0.
c. Turbidity; No turbidity shall exist in concentrations that will
interfere with established levels of treatment.
d. Temperature; The temperature shall not exceed 90°F.
CLASS D-l - The following standards shall apply to waters classified
for irrigation:
a. Total Dissolved Solids (Salt) Concentration; A time-weighted
monthly mean at a monitoring station which exceeds the time-
weighted monthly mean for a base period established by the
Commission by more than two standard deviations shall be subject
to review by the Commission.
b. Sodium Adsorption Ratio; A time-weighted monthly mean at a
monitoring station which exceeds the time-weighted monthly mean
for a base period established by the Commission by more than two
standard deviations shall be subject to review by the Commission.
c. Toxic Material; Free from biocides, toxic, or other deleterious
substances attributable to municipal, domestic, industrial wastes,
or other controllable sources in concentrations or combinations
which are harmful to crop life.
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