Loading...
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. -5- 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. -7- 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 -11- 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). -19- 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**' • • • • • ::\ 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. -16-