HomeMy WebLinkAbout1980-04-01; City Council; 6211; Encina Water polluction control facilityAGENDA BILL NO._A^U
c_m __ PJ_
Initial:
DATE: _ _ _____________ APRIL 1, 1980 ____ _____ C. Atty
DEPARTMENT: PUBLIC WORKS c- M9r-
SUBJECT: ENCINA WATER POLLUTION CONTROL FACILITY
PROPOSED CHANGE IN CAPACITY AND FUNCTION
STATEMENT OF/THE MATTER
The Joint Advisory Committee of the Encina Joint Powers has recommended that each member
agency agree to: (1) rerate the Encina Water Pollution Control Facility (EWPCF) from
13.75 million gallons per day (MGD) to 16.0 MGD; and (2) allow the EWPCF to operate as
a regional solids handling facility for satellite plants within the service area.
The support for both positions is found in a report entitled "Treatment Capabilities to
1983 for the Encina Water Pollution Control Facility," March, 1980, prepared by the
Encina General Manager. The recommendations made by the Encina General Manager have
been modified to the extent that the JAC recommendation would allow all agencies to
process their satellite solids through to Encina provided that they either operated
within their own capacity or made arrangements with another agency for use of "leased"
capacity. This position is consistent with the position taken by the City Council on
the Lake Calavera Hills project.
If the agencies agree, in concept, with the JAC recommendations, the JAC general counsel
will prepare the necessary documents amending the JAC agreements. These documents will
be returned to each agency for ratification by their board or council.
EXHIBIT
Encina General Manager's report, March, 1980
RECOMMENDATION
That the City Council, by minute motion, approve in concept the proposals to:
(1) rerate the EWPCF from 13.75 MGD to 16.0 MGD; and (2) allow the EWPCF to function
as a regional solids handling facility for satellite plants owned and operated by
member agencies.
Council Action:
4-1-80 Council approved in concept the proposals to rerate the EWPCF to 16.0 MGD; and
to allow the EWPCF to function as a regional solids handling facility for
satellite plants owned and operated by member agencies, subject to Council
policy as detailed in minutes.
TREATMENT CAPABILITIES TO 1983
for the
Enclna Water Pollution Control Facility
March 1980
Dennis M. Reid
TABLE OF CONTENTS
I. Conclusions and Recommendations 1
II. Introduction . 3
III. Plant Treatment Processes 4
IV. Improvements and Additions 11
V. Satellite Facilities 13
VI. Regulatory Considerations 14
VII. References 16
VIII. Appendices 17
I. Conclusions and Recomn ten dat ions
£°I1£] usions:
The recommended improvements deemed necessary for increasing the treatment
plant capacity of the Encina Water Pollution Control Facility have been made.
As this Report explains, the Facility is now capable of treating an average
daily wastewater flow of 16 MGD, as well as treating solids from 20.9 MGD
of wastewater flow. The Facility's peak wet weather flow capacity is 34.8
MGD, greater than 2 times the projected average daily flow. The total im-
provements cost for increasing the capacity of the Facility has been approx-
imately $250,000.
The odor problem has subsequently lessened with the improvements and ad-
ditional operator training and awareness. The odor problem, as evidenced
by the complaint record for the last five months, is under control. Further
minor improvements should improve this further.
Recommendations:
1. The Encina Joint Powers Joint Advisory Committee approve an increase in
each members capacity, based on their percentage of ownership, to a
total capacity of 16 MGD average daily flow (ADF).
AGENCY
City of Carlsbad
Vista S.D.
Buena S.D.
*
San Marcos C.W.D
Leucadia C.W.D.
Encinitas S.D.
2.25
2. The Encina Joint Powers Joint Advisory Committee approve Leucadia County
Water District's and Buena Sanitation District's request to have the
% OWNERSHIP
24.95
29.46
4,51
17.45
16.36
7.27
13.75 MGD ADF
CAPACITY
3.430
4.050
0.620
2.400
2.250
1.000
16 MGD ADF
CAPACITY
3.992
4.714
0.722
2.792
2.618
1.163
CAPACITY
INCREASE
0.562
0.664
0.102
0.392
0,368
0.163
solids from their respective treatment facilities treated at the Encina
Water Pollution Control Facility. Cost sharing arrangements are to be
made at a later date upon approval of cost sharing principles being pre-
pared in a report at this time.
II. Introduction
Presently, approximately 12.3 million gallons per day (MGD) of wastewater
is provided primary treatment at the Encina Water Pollution Control Facility
prior to discharge through the ocean outfall. The Encina Water Pollution
Control Facility currently has a design rating of 13.75 (MGD), The Encina
Joint Powers are currently planning under Phase III to upgrade and enlarge
the present facilities to secondary treatment with a rated capacity of 18.0
MGD. Phase III is currently under design and construction will begin in
May 1980. The expanded facilities will be completed by November 1982. Be-
cause of sewer moratoriums in effect for several years there is a need for
additional capacity in the service area at the present time. The Encina
Joint Advisory Committee (JAC) has directed that studies be made to facilitate
the handling of additional sewage flows through the present plant facilities, •
until completion of Phase III in November 1982.
This Report reviews the capabilities of the existing treatment plant processes
and anticipates the additional flows and solids derived from the service
area during the three year period. The improvements and modifications re-
commended to handle additional flows in previous reports are reviewed, along
with the modifications that have been currently made or are under construction,
The regulatory aspects of increased flows are also reviewed.
III. Plant Treatment Processes
The Encina WPCF began operation in September, 1965, providing primary treat-
ment for an original ADWT capacity of 4.50 MGD. Primary treatment capacity
has subsequently been increased during three expansion phases. Phase I en-
largement, in 1971 increased treatment capacity and improved solids handling
to 6.75 MGD by addition of a third primary sedimentation tank and a centrifuge
facility for dewatering digested sludge. The construction program for Phase
II and IIA enlargements was.completed in July of 1975, increasing capacity
to 13.75 MGD by the addition of a fourth and fifth primary sedimentation tank
and a third anaerobic digester. Table 5-2 provides a design data description ••
of major unit process in the 13.75 MGD facility. A layout of the existing
plant site is presented in Figure 5-3. while a process flow diagram is shown
in Figure 5-4.
Each plant process has been separately analyzed as to capability to handle
increased flows. Condition of the process, present operational problems,
anticipated operational problems, reliability, and required improvements
were considered.
First, a listing of each unit is presented which provides pertinent data
in summary form. This is followed by a brief narrative or discussion on each
process.
Mechanical Car Screen
Number 1
Maximum Capacity 34.8 MGD @ 5' depth
Condition Good
Stand-by Bar Rack (Hand Cleaned)
There is one mechanically cleaned bar screen and one standby hand cleaned screen.
The mechanically cleaned bar screen is capable of handling 34.8 MGD at a depth
of five feet in the channel. The hand cleaned bar screen is used as standby
EXISTING WASTEWATER SYSTEM
Table 5-2. Encina WPCF Design Data1
Item Value Item Value
Loadings
Population equivalent thousands 128
Flow, mgd
Average dry weather 13.75
Peak dry weather 21.1
Peak wet weather 3.4.8
Strength
BOD5, mg/1 257
BOD5, 1000 Ibs/day 29.5
Suspended solids, mg/1 294
Suspended solids, 1000 Ibs/day 33.7
Preliminary treatment
Mechanically cleaned bar screens
Number 1
Hand cleaned bar screen 1
Velocity through screen ADWF ft/sec 2.4
Preaeration grit removal tanks
Number . 1
Width, feet 20
Length, feet 30
Average water depth, feet 15
Detention time at ADWF, min. 7.8
Primary treatment
Sedimentation tanks
Number 5
Width, feet 20
Length, feet 160
Average water depth, feet 9
Detention time, hours
Average dry weather 1..9
Surface loading rate gal/sq.ft/day
Average dry weather 860
Solids treatment
Anaerobic digesters
Number 3
Digester 1 (primary)
Inside diameter, feet 50
Side water depth max. feet 23
Volume, 1000 cu. ft. 48.7
Digester 2 (secondary)
Inside diameter, feet 50
Cover travel,'feet 6
Side water depth max. feet 24
Max. volume, 1000 cu. ft. 50.7
Digester 3 (primary/secondary)
Inside diameter, feet 50
Cover travel, feet 8
Side water depth max. feet 26.5
Max. volume, 1000 cu. ft. 52.6
Loadings (digesters 1 and 3 as
primaries) Ibs. volatile solids/
cu.ft/day 0.146
Centrifuge
Bowl dimensions, inches
Diameter 24
Length 60
Assumed solids concentration in
feed sludge, percent 4
Digested sludge feed rate, gpm 7u
Sludge drying beds
Number 20
Dimensions
Width, feet 35
Length, feet 60
Total area, sq. ft. 42,000
Grit treatment
Grit treatment
Grit washer
Number 1
Capacity, gpm 300
Chlorine treatment
Chlorinators
Number
Capacity, Ibs/day/unit
2
1,000
Reference 1
in the event of a breakdown in the mechanically cleaned bar screen. Screen-
ings are placed in trash bins for disposal at a Class II landfill.
Grit Removal Tank
Number 1
Capacity Dependent on Detention Time
Detention @ ADWF 13.75 MGD 7.8 Minutes
Condition Good
There is one aerated grit removal tank. The detention time at 13.75 MGD is
7.8 minutes. Increasing flows decrease the detention time in the grit removal
tank, and allows more grit to pass to the sedimentation tanks. This grit
essentially makes its way to the bottom of the digesters reducing the
effective capacity by about }Q%. Cleaning of digesters on a regular schedule
eliminates this problem. The grit is presently placed in trash bins for
disposal at a Class II landfill.
Primary Sedimentation Tanks
Number 5
Flow Per Tank 2.75 MGD
Total Capacity 13.75 MGD
Detention Time 1.9 Hours
Surface Overflow Rate 860 Gal/sq.ft./Day
Condition Good
There are five primary sedimentation tanks. The average surface loading rate
is 860 gallons/sq. ft./day, at 13.75 MGD. Surface loading rates used in
evaluating capacities of primary sedimentation basins presently range from
1000-1400 gallons/sq. ft./day. After the Phase III improvements the surface
loading rate will be increased to 1125 gallons/sq. ft./day giving the primary
sedimentation tanks a capacity of 18 MGD. No improvements will be necessary to
increase the loading rate.
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Sludge Treatment
Digester 1 - Primary (Heated to 95 Degrees F. & Mixed)
Volume 52,600 Cf
Maximum Loading 0.15 #Vol. solids/cf/day
Equivalent capacity 6.9 MGD
This unit is well mixed and heated so a loading of 0.15 #v.s./cf/day and a
detention of 19 days is reasonable with careful operation.
Digester 2 - Primary (Heated to 95 Degrees F. & Mixed)
Volume 48,400 Cf.
Maximum Loading 0.15 #Vol. Solids/cf/day
Equivalent Capacity 6.35 MGD
The digester operates successfully at a loading rate of 0.15 #v.s./cf/day and a
theoretical detention time of 19 days.
Digester 3 - Secondary or Primary
Volume • 50,700 Cf
Maximum loading as Primary 0.15 £Vol. Solids/cf/day
Equivalent capacity 6.65 MGD
In order to stabilize the sludge removed from a wastewater flow in excess
of 13.75 MGD, this unit was converted from a secondary to a primary digester.
The rated capacity of Digesters 1 and 2 is 13.25 MGD. Therefore additional
capacity is available at all times and sufficient flexibility in operation
exists.
The existing heating system for this digester is adequate for the primary
mode of operation. The digester is presently u-sed for storage and standby.
The digester should operate successfully at a loading rate of 0.15#v.s/cf/day
and a theoretical detention time of 19 days.
Combined Equivalent Capacity: (Based on Average Daily Flow)
Digesters 1, 2, 3 20.90 MGD
Raw Sludge JPjjmjD s_
The two units are a special type of positive displacement pump for transporting
raw sludge from the sedimentation tank hoppers to the digesters. Each pump
is adequate to pass all sludge at increased-flows by operating approximately
12 hours per day @ 55 gpm. The second pump could be considered a standby,
although, they are actually both used on alternate days.
Sludge Circulation Pumps
Each digester is served by a separate circulation pump that must operate when
the digester is being heated. The pumps also aid in the digestion process
by facilitating the mixing of the sludge. The circulation rate for heating and
mixing is adequate for sludge generated from 20.90 MGD of average daily waste-
water flow.
Sludge Heating Boilers
Number - 2
Rating ' • 1,000,000 BTU/hr. @ 15 psig
Condition Good
Capacity Adequate
There are two identical boilers each rated at 1,000,000 BTU/hr. @ 15 psig
that are used to generate steam which is directly injected into the recir-
culated sludge flow to maintain the desired digestion temperature of 90 - 95
degrees F. Each boiler is adequate to maintain sludge temperatures in two
primary digesters receiving sludge from a flow of 13.75 MGD. Both units will
be required during the winter cold period if the plant is rerated upward.
If one of the boilers failed, it is feasible to repair the unit within a week
or two, and thus, maintain adequate heating capability.
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C ' O
Dewatering Centri fuge
Number 1
Feed Rate 75 GPM Maximum
Operation @ 13.75 MGD 11 hrs./day
Condition Bad (Requires Continual Overhaul)
Capacity Inadequate
This unit removes water from the digested or stabilized sludge so it can be
transported to final disposal. It is estimated the centrifuge will operate
11 hours/day at the 13.75 MGD flow rate. The mechanism will experience
accelerated wear from the grit carry-through and will be inadequate if flows
increase beyond 13.75 MGD. Yearly, or more frequent, overhaul is presently
required. The present capture rate of solids is less than 75% (normal oper-
ating would be 90%). The unit needs a major overhaul which would require
4 months. It would proably not be cost effective to overhaul the unit but
rather replace it with a new or another type of dewatering device. During
the overhaul, or an emergency repair, sludge can be stored in the digesters
for a short period (2 days). For a longer down time, sludge must be hauled
off site to a Class I landfill located in Otay.
Sludge Drying Beds
Number 20
Area 42,000 sq. ft.
Stand-by Service Only (To be Removed During" Phase III)
The sludge drying beds emanate foul odors when used and generate complaints
from nearby residents. The beds will be removed in May 1980 under Contract
7/9 of the Phase III Construction.
-8-
Air Blowers
Number 3
Blowers 1 & 2 350 cfm each
Blower 3 " 500 cfm
Capacity Adequate
The blowers provide air to operate the grit removal tank and are adequate
for service at an increased flow rate.
Chlorination
Chlorinators 2
Capacity Each 1,000 Ibs./day
Condition Good
Capacity Adequate
The chlorinators are used to control in-plant odors and can be used to chlorinate
plant effluent when necessary. The capacity of these units is adequate.
Flow Meter
Number 1
Maximum Capacity 30 MGD
Condition Good
Capacity Adequate (For Determining Average Daily Flows'
The propeller type flow meter is satisfactory at present. As flows increase,
the peak wet weather flow may exceed meter capacity. If occasional pegging
of the meter is considered significant, the meter head can be replaced to
accommodate peak flows.
Pipelines and Channels
Number Various Sizes and Shapes
Maximum Capacity • Approximately 34.8 MGD (Equal to About
16 MGD Average)
Condition Some good, others corroded
Capacity Critical Areas to be Modified if Bottleneck
is Observed
A review of plant hydraulics and projected peak wet weather flow indicates that
the maximum flow that could be passed through the plant is 34.8. By referring
to Table 4-12 on page 1.03 of the Phase III Project Report, it can be seen that
a peak wet weather flow in this range corresponds to an average dry weather
flow of about 16 MGD. The viability of this table has been confirmed using
present day flow data.
oSee Reference 1
^.
'
Figure 5-3
O
c
IV- IMPROVEMENTS AND ADDITIONS
Increasing the capacity of the Encina Water Pollution Control Facility
.has been discussed since the completion of Phase IIA in 1976. In April
1977, the Joint Advisory Committee (JAC) authorized the County of San Diego
to do feasibility studies for increasing the capacity of the Facility.
This culminated in a Report distributed December 1977 , which made certain
recommendations for enabling the Facility to treat 16 MGD average daily flow.
Listed below are the recommendations of that Report and the changes in the
Facility to date:
RECOMMENDATIONUNIT
1. Mechanical Bar Screen
2. Disintigrator
3. Grit Removal Tank
4. Sedimentation Tanks
5. Raw Sludge Pumps
6. Digester No. 1
7. Digester No. 2
8. Digester No. 3
9. Centrifuge
10. Centrifuge Area
11. Main Plant Piping
and Flow Channels
12. Major Plant Equipment
Replace
Abandon
No Action
Haul Grease Away
Need Sludge Meter
Install Draft Tube
Mixing System
Install Draft Tube
Mixing System
Convert to Primary
Digester and Install
Draft Tube Mixing System
Purchase Overhaul Spare
Parts to Limit Downtime
Enclose w/building and
Odor Scrubbing System
Raise Channel Walls and
Add Piping, if Needed
ACTION
Replaced under Phase HA
Abandoned
None
Haul ing Grease Away
Determined not needed if
Pumping Rate Used
Installed •
Installed
Installed
Abandoning Centrifuge
Interim Belt Press In-
stallation Under Construct
Completion set for May 1,
1980.
Not Needed
Determined, Mot Needed
Add to Spare Parts Inven- Done
tory to Reduce Down Time
See References
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As shown, all the improvements deemed necessary for increasing the waste-
water flows to 16 MGD have been made. Actual analyses regarding capability
of each unit process has been done in previous reports (See references and
Appendices 4 and 5).
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V Satellite Facilities
The Encina Joint Powers has received requests from two of its member agencies
to process solids at the Encina Water Pollution Control Facility prior to
the completion of the Phase III construction. Solids will be received from
Buena Sanitation District's 1.0 MGD Shadow Ridge Plant and Leucadia Water
District's 0.75 MGD La Costa Plant. San Marcos County Water District, which
is reactivating its 0.6 MGD Meadowlark Plant and Carlsbad which is planning
for its 0.57 MGD Lake Calvera Plant will have aerated solids digestion from
their respective facilities (Appendix 5). Unless the two agencies are planning
for dewatering facilities also, the digested sludge will be a part of the
influent solids load to Encina. Total solids projection from the four sat-
ellite plants is at most expected to be 3400 dry/pounds per day (less than
10% of the total solids flow). The total solids received by the Encina Water
Pollution Control Facility with satellite solids will be 36,000 dry/pounds
per day (See Figure 4, Appendix 5).
The total active volume of Digesters 1, 2, and 35 is 151,700 cubic feet. By
1983, the solids loading will be less than 0.15 15. VSS/ft. day and the detention
time will be 20 days. Both parameters are well within conservative operating
ranges for good high rate digestion. Prior to completion of Phase III
construction in November 1982, digester operations will be switched to a
new 105 foot diameter digester with a capacity of about 303,000 cubic feet.
(Appendix F). This will facilitate installation of heat exchangers and piping
for Digesters 1, 2, and 3.
Cost sharing of utilizing the Encina Water Pollution Control Facility as a
solids facility for the satellite plants is the subject of a report being
prepared by Brown and Caldwell. This Report will represent the first stage
in cost sharing between the agencies based on flow, and SS. The final
cost sharing after Phase III will be based on flow, BOD, and SS (Appendix 4).
-13-
VI Regulatory Consideratjonj
On May 23, 1977, the San Diego Regional Water Quality Control Board (RWQCB)
adopted Order 77-19 (NPDES CA0107395 - See Appendix 1) prescribing waste
.discharge requirements for the Encina WPCF Ocean Outfall. This order mandates
secondary treated effluent quality and establishes a timetable to accomplish
the upgrading. Order 79-46 (Appendix 2), v/as subsequently issued prescribing
primary standards that would be effective until secondary facilities have
been constructed, or January 1, 1983.
The waste discharge requirements of Order 79-46 limit the suspended solids
(SS) to a monthly average of 125 mg/1, the grease concentration to a monthly
average of 30 mg/1. There is no requirement for biochemical oxygen demand
(BOD). The present discharge requirements have been consistently met. During
the last year, SS values have averaged 92 mg/1 and the grease content has averaged
16 mg/1 (Plate 1).
The NPDES Permit sets effluent limitations (Order 79-46) for the discharge
of treated wastewater through the outfall into the Pacific Ocean. Increase
in flows beyond the 13.75 MGD design rating would be subject to the 18 MGD
flow, the 125 mg/1 Suspended Solids and 30 mg/1 grease as specified in the Permit.
On occasion foul odors have been detected beyond the boundary of the plant site.
This condition is a violation of Cease and Desist Order No. 78-33 (Appendix 3),
issued by the Regional Water Quality Control Board (RWQCB). The Encina staff
has taken corrective measures to reduce foul odors from the facility. How-
ever, without the odor scrubbing facilities planned for in Phase III, the
facility will be subject to occasional foul odors during plant upsets and
during the upcoming Phase III construction.
The Cease and Desist Order was enacted July 24, 1978, for violation of Provision
C.4 of the NPDES Permit. Provision C.4. states "Odors, vectors, and other
nuisances of sewage or sludge origin beyond the limits of the treatment plant
site are prohibited". The RWQCB has indicated that the Order will be kept
-14-
in effect until four months have elapsed without an odor complaint.
Increase in flows to the treatment facility are not a part of the Cease
and Desist Order and have no bearing on it.
28
24
20
16
MONTHLY AVERAGE OCEAN JDISCHARGE
" 1979
'Plate 1"
GREASE
Monthly Average Grease 1979 = 19.7 mg/1
-Monthly Average Grease Limit = 30 mg/1
\
\
••-1
12
Dec.'78 Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. '79
170
150
1 30
110
90
70
50
-
; - - - -
'--'• - •-'•-'-"-•" SUSPENDED SOLIDS '"••" :
• - -
.. - .. . .... - ..:....:L ;.'::::- -
- - - -
-
- — Average Suspended Solids 1979 = 92 mg/l
'y."~ '.'"''' /^— Monthly Average Sus. Solids Limit = 125 mg/1
/ ' -
-- - - - -
Ns:-:--r:--:f::::-:.:-:.-
TSr~^
.- - -— -. . .-
- - - •- - -• - -.. -- , - - --
— -- — - — -- -.-. <
^"•:/.-:.->
^"i —
— - —
:
. ,. „.
>L - '
. . .
. . .
' "
' -- - -
....
. ^f**'
• • • • •
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DEC 78 jAfl FEE MARCH APR -MAY JUNE JULY AUG SEPT OCT NOV DEC'79
VI! References
1. PROJECT REPORT - Phase III Enlargement and Upgrading of Encina Water
Pollution Control Facilities, Brown and Caldwell, February, 1975.
2. ENCINA WATER POLLUTION CONTROL FACILITY .CAPACITY STUDY, Department
of Sanitation and Flood Control, December 1977.
3. SOLIDS HANDLING STUDIES AND IMPROVEMENTS, C M Engineering Associates,
January, 1979.
4. TEN PERCENT SUPPORT, PHASE III ENLARGEMENT AND UPGRADING OF ENCINA
WATER POLLUTION CONTROL FACILITIES, Brown and Caldwell, February,
1979.
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