03_-_SBIWTP_Infrastructure_Improvement_Design_Report_woE_07312015.pdf

Final Design Report for South Bay International Wastewater Treatment Plant

Infrastructure Improvements San Diego, California

Prepared for:

United States International Boundary and Water Commission

IBM14T0013

Prepared by:

July 31, 2015

Final Design Report SBIWTP Infrastructure Improvements

USIBWC SBIWTP IBM14T0013 ii July 31, 2015

Table of Contents

1.0 INTRODUCTION.......................................................................................................... 1-1

1.1 Background .......................................................................................................... 1-1

1.2 Scope of Work ..................................................................................................... 1-1

1.3 Purpose of Report ................................................................................................ 1-2

1.4 Design Summary .................................................................................................. 1-2

1.4.1 Equalization Tank .................................................................................... 1-2

1.4.2 Secondary Sedimentation Tank ............................................................... 1-3

1.4.3 RAS/WAS Pump Station Improvements ................................................. 1-4

1.4.4 Hydraulics ................................................................................................ 1-5

1.4.5 Geotechnical Investigation Summary ...................................................... 1-6

1.4.6 General Civil Issues ................................................................................. 1-7

1.4.7 Structural Design Issues ........................................................................... 1-7

1.4.8 Electrical/Instrumentation/SCADA Considerations ................................ 1-8

1.4.9 Basis of Design ........................................................................................ 1-9

1.4.10 Opinion of Probable Construction Costs (OPC) ...................................... 1-9

1.4.11 Design Schedule ....................................................................................... 1-9

1.4.12 Final Design Drawings ............................................................................ 1-9

1.5 Abbreviations ..................................................................................................... 1-10

2.0 EXISTING TREATMENT PLANT PROCESS DESCRIPTION ............................ 2-1

3.0 EQUALIZATION TANK ............................................................................................. 3-1

3.1 Background .......................................................................................................... 3-1

3.2 Equalization Tank Capacity ................................................................................. 3-1

3.3 Flow Diversion to Equalization Tank .................................................................. 3-3

3.3.1 Alternative No. 1 – Flow Diversion Over Overflow Weir ...................... 3-3

3.3.2 Alternative No. 2 – Flow Diversion through Bypass Metering

Structure ................................................................................................... 3-4

3.4 Equalization Tank Configuration and Operation Strategy ................................... 3-4

3.5 Equalization Basin Site Layout and Yard Piping ................................................ 3-6

4.0 SECONDARY SEDIMENTATION TANK ................................................................ 4-1

4.1 Background .......................................................................................................... 4-1

4.2 Existing SST Equipment Description .................................................................. 4-1

4.3 Proposed SST Sizing............................................................................................ 4-2

4.4 Site Layout Evaluations ....................................................................................... 4-2

4.5 Design Summary .................................................................................................. 4-3

4.6 SST Operation Strategy ....................................................................................... 4-4

5.0 RAS/WAS PUMP STATION IMPROVEMENTS ..................................................... 5-1

5.1 Background .......................................................................................................... 5-1

5.2 Existing Pump Station Deficiencies ..................................................................... 5-2

5.3 Existing RAS/WAS Pump Station Improvement Options ................................... 5-2

5.3.1 Pump Station Capacity ............................................................................. 5-3

USIBWC SBIWTP IBM14T0013 iii July 31, 2015

5.3.2 Dry-Pit Centrifugal Pumps ...................................................................... 5-3

5.3.3 Replace Existing Pumps with In-Kind Pumps ......................................... 5-4

5.3.4 Replace Existing Pumps with Non-Clog Submersible Pumps ................ 5-4

5.4 Recommendations ................................................................................................ 5-4

6.0 HYDRAULICS ............................................................................................................... 6-1

6.1 General ................................................................................................................. 6-1

6.2 Existing Hydraulic Conditions ............................................................................. 6-1

6.3 Proposed Hydraulic Profile .................................................................................. 6-1

7.0 GEOTECHNICAL INVESTIGATION SUMMARY ................................................ 7-1

8.0 GENERAL SITE CIVIL ISSUES ................................................................................ 8-1

8.1 Drainage/Earthwork/Grading Plan ....................................................................... 8-1

8.2 Roadway Improvements ...................................................................................... 8-1

8.3 Utility Relocation ................................................................................................. 8-1

8.4 Yard Piping .......................................................................................................... 8-1

9.0 STRUCTURAL DESIGN ISSUES ............................................................................... 9-1

9.1 Design Criteria ..................................................................................................... 9-1

9.2 EQ Tank Structure ............................................................................................... 9-1

9.3 SST Structure ....................................................................................................... 9-2

9.4 Junction Structures ............................................................................................... 9-3

10.0 ELECTRICAL/INSTRUMENTATION/SUPERVISORY CONTROL AND

DATA ACQUISTION (SCADA) CONSIDERATIONS........................................... 10-1

10.1 Scope .................................................................................................................. 10-1

10.2 Power Distribution Analysis .............................................................................. 10-1

10.2.1 Equalization Tank .................................................................................. 10-1

10.2.2 Secondary Sedimentation Basin ............................................................ 10-1

10.2.3 RAS/WAS Pump Station ....................................................................... 10-1

10.3 Instrumentation and Control Logic .................................................................... 10-2

10.3.1 Equalization Tanks................................................................................. 10-2

10.3.2 Secondary Sedimentation Tanks ............................................................ 10-2

11.0 BASIS OF DESIGN ..................................................................................................... 11-1

11.1 Equalization Tank .............................................................................................. 11-1

11.2 Secondary Sedimentation Basin ........................................................................ 11-2

11.3 RAS/WAS Pump Station ................................................................................... 11-3

12.0 OPINION OF PROBABLE CONSTRUCTION COSTS ......................................... 12-1

13.0 DESIGN AND CONSTRUCTION SCHEDULE ...................................................... 13-1

14.0 FINAL DESIGN DRAWINGS ................................................................................... 14-1

USIBWC SBIWTP IBM14T0013 iv July 31, 2015

Appendices

A – Detailed Scope of Work B – Equalization Tank Capacity Calculations C – System Head Curves Generated by Fairbanks Morse Company) D – Geotechnical Investigation Report – Addendum 1 E – Detailed Opinion of Probable Construction Cost Estimate F – Conceptual (Final Design) Drawings (Provided Separately) G – Proposals from Equipment Manufacturers

List of Tables

Title Page

Table 1. Opinion of Probable Construction Cost ........................................................................ 1-9 Table 2. Summary of EQ Tank Volume Calculations ................................................................ 3-2 Table 3. Summary of EQ Tank Volume Calculations for Additional Data Sets ........................ 3-2 Table 4. Proposed SST Design Criteria ...................................................................................... 4-3 Table 5. Cost Evaluation for RAS Pump Replacement Options ................................................ 5-5 Table 6. Basis of Design for EQ Tanks .................................................................................... 11-1 Table 7. Proposed SST Design Criteria .................................................................................... 11-2 Table 8. Basis of Design for RAS Pumps ................................................................................. 11-3 Table 9. Opinion of Probable Construction Costs .................................................................... 12-1

List of Figures

Title Page

Figure 1. RAS Pump System Curve, Flow Vs. TDH ............................................................... 5-3 Figure 2. Project Schedule ....................................................................................................... 13-2

USIBWC SBIWTP IBM14T0013 1-1 July 31, 2015

1.0 INTRODUCTION

1.1 Background

The South Bay International Wastewater Treatment Plant (SBIWTP) is located near the United States – Mexico border on a 100-acre site south of the City of San Diego, California. The SBIWTP is located at 2415 Dairy Mart Road, near the Interstate 5 border crossing adjacent to the Tijuana River. The United States International Boundary and Water Commission (USIBWC) owns the plant; however, Veolia Water North America (Veolia) operates and maintains the plant under a contract with the USIBWC.

The SBIWTP treats wastewater from Tijuana, Mexico and the surrounding areas. Wastewater currently flows via several pump stations and a 96-inch pipe to the plant. The SBIWTP was constructed in two major phases: Phase I and Phase II. Constructed in 1996, the Phase I project included screening, grit removal, chemically assisted primary sedimentation, chlorination, unstabilized sludge storage, lime stabilization of sludge, sludge dewatering, and dewatered sludge truck-loading facilities. The design capacity of the Phase I plant is 25 million gallons per day (MGD) with a peak capacity of 75 MGD.

The Phase II project was constructed in 2011 and upgraded the original plant by adding secondary treatment facilities. The secondary treatment facilities included aeration tanks, secondary sedimentation tanks (SSTs), dissolved air floatation (DAF) units, unstabilized sludge storage tanks (USSTs), and miscellaneous ancillary facilities. The average design capacity of the secondary treatment facilities is 25 MGD with a peak capacity of 48.75 MGD.

Since the start-up of the Phase II project, there have been several National Pollution Discharge Elimination System (NPDES) permit violations for total suspended solids (TSS) and carbonaceous biochemical oxygen demand (CBOD5). These permit violations were believed to be caused by solids washout from the SSTs. The plant generally receives flows in the range of 25 to 50 MGD; flow exceeding 50 MGD bypasses the aeration tanks and SSTs.

URS Group, Inc. (URS), in association with CDM Smith, Inc., conducted a study (2012-2014) on the SBIWTP to identify the causes of the NPDES permit violations and recommend improvements for preventing future permit violations. The recommended improvements included both treatment process operational improvements as well as infrastructure improvements. The major infrastructure improvements recommended were: 1) construction of an offline equalization tank, and 2) addition of three new SSTs.

1.2 Scope of Work

URS was authorized by the USIBWC under Task Order Number (No.) IBM14T0013 to design, assist during bidding, and provide post-design support services for the construction of an offline equalization (EQ) tank, three new SSTs, and other site civil works necessary to accommodate these new treatment units at the plant. To support the design of these treatment units, topographical survey and geotechnical investigation were conducted on the proposed site. The Scope of Work (SOW), as described in detail in Task Order No. IBM14T0013 is attached in Appendix A.

USIBWC SBIWTP IBM14T0013 1-2 July 31, 2015

During the preliminary design phase of this project, operational problems with the existing return activated sludge (RAS) pumps were brought to the attention of the URS Design Team. We reviewed the original design of these pumps and pressure test data sent by the vendor of the Fairbank Morse Pump Company. We identified design deficiencies of the existing pumps, evaluated different improvement alternatives, and recommended an alternative for implementation.

Modification 1 (MOD1) was executed on 1/5/2015 to add the design of a replacement for existing RAS pumps and the design of an equalization basin pump station. The original SOW did not include the design of an EQ basin effluent pump station since the EQ tank effluent was planned to be sent back to the existing headworks via a gravity pipe. During the FDR review meeting, it was decided by the USIWBC that the EQ tank effluent would be sent to the ASTs.

Due to hydraulic constraints, an EQ basin effluent pump station is necessary to send the EQ effluent to the ASTs.

1.3 Purpose of Report

The primary purpose of this Final Design Report (FDR) is to provide a summary of the design criteria developed for an offline EQ tank, three new SSTs, RAS pump replacements, associated site civil works, electrical, and instrumentation and controls.

A summary of geotechnical investigative field work and recommendations is provided as Appendix D.

The Opinion of Probable Construction (OPC) cost was revised in the final design phase and is provided in Appendix E. Design drawings for different disciplines (mechanical, site civil, hydraulic profiles, etc.) were created and are provided in Appendix F.

1.4 Design Summary

1.4.1 Equalization Tank

Section 3 provides the design of the proposed EQ tank. The plant diurnal data were analyzed, and the EQ tank volume was calculated. The proposed EQ tank volume was 3.25 million gallons (MG), including a 20% factor of safety. During the FDR review meeting, Veolia and USIBWC requested that additional diurnal flow data be analyzed. The URS design team calculated and recommended an EQ tank volume of 3.75 MG based on the analysis of new diurnal flow data.

The EQ tank design was revised based on the new capacity of 3.75 MG.

Two flow diversion alternatives were evaluated to divert the primary effluent to the proposed EQ tanks. These two flow diversion alternatives were: 1) flow diversion over the existing emergency overflow weir, and 2) flow diversion through the existing Bypass Metering Structure.

The flow diversion through the existing Bypass Metering Structure was recommended.

USIBWC SBIWTP IBM14T0013 1-3 July 31, 2015

A total of two identical EQ tanks are proposed to provide operational flexibility. Both EQ tanks will provide the required volume of 3.75 MG. Each EQ tank is 220 feet (ft) long, 72 ft wide, and

15.88 ft deep at the middle of the tank.

A total of three electric operated mixers are recommended for each tank. Major design criteria for the proposed EQ tanks are provided in Section 11 – Basis of Design.

The operational strategy for the EQ tanks is to receive plant influent flows in excess of a preset flow of 25 MGD to ASTs, and this stored primary effluent at the EQ tanks will be discharged back to the ASTs when the influent flows fall below the preset flow. For example, if the plant influent flow meter detects a plant flow of 40 MGD, the existing flow meter and modulating butterfly valve on the bypass line will be operated to divert 15 MGD to the EQ tanks, and the remaining 25 MGD will flow to the ASTs. If the plant influent flow falls below 25 MGD, the EQ tank effluent pump will be operated at a rate to bring the flows to the ASTs to 25 MGD.

Therefore, these EQ tanks will always provide a constant flow to the ASTs.

1.4.2 Secondary Sedimentation Tank

The design criteria for the proposed three new SSTs are provided in Section 11 – Basis of Design. Each SST will have the same length and width as the existing SSTs. Each proposed SST is 160 ft long and 20 ft wide. The depth of each proposed SST is also the same as the depth of the existing SST, which is 17.65 feet at the middle of the tank.

Similar to the existing SSTs, the proposed SSTs will have a common influent channel and a common effluent channel. The width of each channel of the proposed SSTs will be the same as the respective channel of the existing SSTs. The proposed SST structure will be placed approximately 13 ft west of the existing SST structure. The justification for this 13-ft separation is explained in Section 9 – Structural Design Issues. The respective influent and channels will be connected with pipes that will allow water flow between the existing and proposed SST structures.

Each proposed SST will be equipped with a plastic chain and flight sludge collector mechanism that will move the settled sludge to two sludge hoppers. The settled sludge from the hoppers of the new SSTs will be withdrawn and directed to the existing RAS/waste activated sludge (WAS) Wet Well by gravity. Since the plant's average and peak flows remain the same, the settled sludge volume will not be increased due to the addition of three new SSTs. Therefore, the RAS/WAS Wet Well has adequate capacity to receive the RAS from proposed SSTs.

The collected skimmings will be routed to the existing Skimming Pump Station Wet Well via the existing 18-inch skimming pipe. The existing Skimming Pump Station and Skimmings Wet Well have enough capacities to handle the increased skimmings from the proposed SSTs.

The existing two air pipes, each 8 inches in diameter and installed at the influent channel, will be extended from the existing SSTs to the proposed SSTs. New coarse bubble diffusers will be installed on the influent channel of the proposed SSTs. The existing channel blowers have adequate capacity to provide air to the new diffusers.

USIBWC SBIWTP IBM14T0013 1-4 July 31, 2015

The drain pipes for the proposed SSTs will be similar to the drain pipes of the existing SSTs. A 12-inch drain pipe header will be installed at the proposed SST Effluent Gallery. Two 10-inch individual drain pipes from each proposed SST, will be connected to the 12-inch drain header.

The proposed 12-inch drain pipe header will be connected to the existing 12-inch drain pipe header, which is located at the existing SST Effluent Gallery. Since only one SST will be drained at any given time, the existing 12-inch pipe header and drain pump are adequate for draining the existing and proposed SSTs.

The design criteria for the proposed SSTs are summarized in Section 11.0 – Basis of Design.

With the addition of three new SSTs, the total number of SSTs at the SBIWTP will be 13. Each SST could receive a peak flow of 4.16 MGD, resulting in an overflow rate of 1,300 gallons per day (gpd)/ft2. The peak flow rate of 4.16 MGD is derived from the plant's peak flow of 50 MGD divided by 12. It is assumed that one of the 13 SSTs will be out of service during the peak flow occurrence at the plant. The proposed two EQ tanks, each with a maximum capacity of 12.5 MGD, will be operated continuously. The EQ tanks will receive any flow in excess of a preset flow of 25 MGD. This preset flow could be increased by the plant operation staff as long as the diverted flows to the EQ tanks do not exceed 25 MGD. If the plant influent flows fall below the 25 MGD set point, the stored wastewater from the EQ tanks will be pumped backed to the 42-inch primary effluent line ahead of the ASTs. With the continuous operation of the proposed EQ tanks, the SST will not likely receive a flow of more than 25 MGD. Assuming one SST is out of service, the overflow rate for each of the 12 operational SSTs is 650 gpd/ft2 @ 25 MGD flow.

With all 13 tanks in service, the overflow rates for the SSTs at average and peak flows are 600 and 1,200 gpd/ft2, respectively, which are below the Ten State Standards.

1.4.3 RAS/WAS Pump Station Improvements

The existing RAS pumps have been experiencing unusual mechanical failures despite the lack of noise, vibration, and other signs of distress. A field pressure test conducted by the local vendor of Fairbank Morse Pump Company revealed that the pumps were operating far off the pump head-capacity curve. This is due to a lack of total dynamic head (TDH), which was originally selected to be higher than the TDH determined in the field test. The original TDH of each pump was selected to be 44 ft at 2,700 gpm; however, field pressure testing revealed that the TDH was less than 10 ft at the same flow. The field test would have produced even less TDH if all of the activated sludge tanks (ASTs) were operated. During the field test, only six of the existing seven ASTs were running.

The URS Design Team also developed the RAS Pump Station system curve assuming all ASTs were running. Our system head curve is similar to the system head curve developed in the field by the vendor of Fairbank Morse Pump Company. We determined that the TDH is less than 10 ft at 2,700 gpm flow.

The firm capacity of the existing RAS pumps is 19.44 MGD, representing approximately 78% of the plant's average flow of 25 MGD. Typically, design standards recommend a RAS flow minimum of 50% to 150% of average design flows. We evaluated the maximum RAS flow of 150% of the plant average flow or 37.5 MGD. This 37.5 MGD flow cannot be achieved either by the existing pumps or by existing piping. The 10-inch individual pipe that delivers the RAS

USIBWC SBIWTP IBM14T0013 1-5 July 31, 2015 flow to each AST is too small to handle a maximum RAS flow of 150% of the plant average flow. We determined that a maximum RAS flow of 86% of the plant's average flow could be handled without excessive velocity at the 10-inch individual RAS pipe to each AST. The 86% of the plant average flow is 21.5 MGD or approximately 15,000 gpm. Therefore, capacity for each of the six pumps (five duty and one standby) should be 3,000 gpm. With all six pumps running, the RAS flow will be close to 100% of average design flow if needed.

We evaluated three options to replace the existing pumps, motors, and electrical and instrumentation equipment to accommodate a lower TDH and higher flows. These alternatives were: 1) replacing the existing pumps with dry-pit mounted, horizontal screw impeller, centrifugal non-clog-pumps, 2) replacing the existing pumps with in-kind vertical pumps, and

3) replacing the existing pumps with submersible pumps. All of these options are technically sound; however, the third option has the lowest capital cost. Therefore, we recommend that the existing pumps be replaced with submersible pumps. Three existing variable frequency drives (VFDs) and new electrical and instrumentation equipment will be required for the new submersible pumps.

1.4.4 Hydraulics

The water surface elevations (WSEs) from the grit chamber to the primary sedimentation tank (PST) effluent channel are unaffected by the proposed modifications in this project.

The WSEs from the Primary Effluent Bypass Structure (PEBS) to the ASTs are affected by the addition of the proposed EQ tanks. Once the EQ tanks become operational, the existing SBIWTP peak flow of 48.75 MGD would be split between the EQ tanks and ASTs. The existing ASTs would receive a peak flow of approximately 25 MGD, and the EQ tanks would receive the remaining 25 MGD flow. Therefore, the proposed hydraulic profiles from the PEBS to ASTs, presented on Sheets GC-0002 and GC-0003, are based on a peak flow of 25 MGD plus a recycle flow of 2.5 MGD. The recycle flow of 2.5 MGD is assumed to be 10% of the plant's average flow. The calculation is also based on the assumption that one of the seven ASTs will be out of service.

The proposed maximum WSE at the PEBS is 56.38 ft at 25 MGD and is approximately 1 foot lower than the WSE developed by the prior design engineers.

The proposed WSE at the ASTs of 56.09 ft is based on a flow of 49 MGD. The 49 MGD is the summation of forward flow (25 MGD), RAS flow (21.5 MGD), and recycle flow (2.5 MGD).

The recycle flow is assumed to be 10% of the plant's average flow of 25 MGD, and it includes mainly supernatant from belt presses. The RAS flow of approximately 21.5 MGD is based on the assumption that all five proposed RAS pumps will be running at full speed. The capacity of each proposed RAS pump is approximately 4.32 MGD (3,000 gpm).

The hydraulic profile presented on Sheet GC-0004 is for the proposed EQ tanks. It is assumed that both tanks will be operational when they receive a peak flow of 25 MGD. The 25 MGD flow will be split equally (12.5 MGD each) between the two EQ tanks.

USIBWC SBIWTP IBM14T0013 1-6 July 31, 2015

The WSEs at the SST effluent weirs and SST influent channel are not dependent on the upstream or downstream hydraulic conditions. The upstream hydraulic conditions, i.e., at the ASTs, are set by the weir elevations at the AST effluent channel. The downstream hydraulic conditions, i.e., at the SST effluent channel, are set by the Effluent Distribution Structure (EDS). The proposed WSEs for the SSTs are shown on Sheet GC-003. Our calculation is based on the assumption that one of the 13 (three proposed and 10 existing) SSTs will be out of service. As shown on Sheet GC-003, the proposed WSEs at various locations of the SST structure are lower than the existing WSEs. The primary reason for the lower WSEs at the SST structure is that flow to each SST would be less. The lesser flow to each SST is due to the addition of three new SSTs.

1.4.5 Geotechnical Investigation Summary

URS completed a field investigation program that advanced four geotechnical borings to depths ranging between 22 and 46 ft below ground surface (bgs). Two borings were advanced at the location of the proposed EQ basin and two borings at the location of the proposed SSTs.

URS (as its predecessor Woodward Clyde Consultants [WCC]) performed a geotechnical investigation for the original treatment plant. That report identified a liquefaction potential at the site and recommended mitigation alternatives. Deep dynamic compaction (DDC) was considered the preferred alternative by the USIBWC. Based on discussions with the USIBWC and a review of the partial information provided to us, DDC has been performed within the entire site of the SBIWTP. Further, based on a review of the topographic information prior to the original treatment plant construction and the current data, the site grades have been raised by placing and compacting 20 to 25 ft of fill.

The geotechnical borings encountered fill to depths of about 10 to 25 ft bgs underlying alluvium.

Groundwater was encountered in one boring at a depth of about 28 ft bgs. Previous explorations located in the vicinity of the proposed improvements encountered groundwater at typical depths of 10 to 15 ft bgs.

Analysis was completed to evaluate liquefaction potential at the locations of the proposed improvements. The results of the analyses indicate no potential for liquefaction at the EQ Basin site. It is estimated that up to 2 inches of liquefaction-induced settlement may occur in the area of the new SSTs; this estimate is based on an anomalous blow count observed in the current exploration, which was located in the area previously improved by DDC based on available information. In our opinion, such an occurrence of loose soil is likely to be localized to an area that the DDC did not fully impact. Further, the bottom of the tanks and the associated channels and galleries will be located deeper than this localized zone. Hence, the potential for liquefaction to impact the proposed improvements should be low.

Based on the conditions encountered in our previous and current investigations, the site subsurface conditions should not pose any geotechnical constraints for the proposed improvements. A final geotechnical report that summarizes our findings, discussions, conclusions, and recommendations is presented in Appendix D.

USIBWC SBIWTP IBM14T0013 1-7 July 31, 2015

1.4.6 General Civil Issues

The project site grading is proposed to accommodate the new EQ tanks and SSTs. The surface drainage will be directed away from all foundations, slabs, pavements, and top of slopes at a 0.5% minimum slope. Ponded water at the top of slope and sheet flow over the 2:1 slopes will not be allowed. Stormwater will sheet flow in the southwesterly direction to the adjacent earthen flood channel.

The access road (asphalt concrete [AC]) west of the existing SST structure will require realignment to accommodate the three new SSTs that will be constructed immediately adjacent to the existing SSTs. This in turn will require the realignment of the adjacent Border Patrol Road (dirt) and the fencing between the two roads. These respective roads will be constructed at a width of 16 to 26 ft. The asphalt access road is being designed to accommodate emergency fire truck turning movements. Vertical alignment of the roads will hold longitudinal slopes of 2% to 5%. Roadway design will maintain a minimum 1.5% cross slope toward the downhill side of the roadway. The proposed asphalt access road will be 4-inch AC over 10-inch aggregate base material. The realigned Border Patrol Road will be composed of compacted dirt.

No utility relocation is anticipated in the vicinity of the proposed SST or EQ structure based upon reference plans received and the field survey conducted on October 13, 2014.

Major yard piping improvements are being designed on the north and south sides of the proposed EQ tanks. The influent north yard piping will connect the existing Bypass Junction Structure (BJS) to the proposed EQ tanks. The 24-inch force main from the EQ tank effluent pumps will be connected to the existing blind flange (old PERC line) on the 72-inch primary effluent pipe.

A 2-inch drain pipe will be installed connecting the proposed EQ Tank Wet Well and Tank Drain Junction Structure No. 4. The alignment of the proposed yard pipe improvements is shown on the Final Design Civil Plans. The size and material of the piping are provided in Section 11 – Basis of Design.

1.4.7 Structural Design Issues

Three new SSTs will be added in close proximity to the existing SSTs. The existing SST structure was originally designed to allow for its future expansion. However, the new SST structure will not be built directly against the existing SST structure. Doing so would rigidly connect the new and existing structures, which could be detrimental to the integrity of the system as a whole. Construction procedures for the new SST structure could damage the existing SST structure; furthermore, working loads could lead to differential settlement across the structure if soil under the new SST were to consolidate at a different rate than the soil under the existing SST. It was determined that the optimum location for the new SST would be approximately 13 ft west of the existing SST. This separation between the new and existing SST will lessen disturbances in the soil that could adversely affect the existing SST, and it will also provide ample room for constructing the east side walls of the new SST structure. Furthermore, this separation allows the west end of the existing effluent channel to remain unaffected by new construction, thus allowing it to remain operational as is. The existing emergency access ladder and ramps on the west end of the existing SST will be removed; a new stair and access ramps will be provided for the new SST structure.

USIBWC SBIWTP IBM14T0013 1-8 July 31, 2015

The new Equalization Tank (EQ Tank) structure consists of an influent channel and two equalization tanks cast monolithically. The EQ Tanks discharge their contents to a Wet Well located on its south side. No major construction challenges have been identified for the construction of the new EQ Tanks and Wet Well as they are located beyond the influence of any adjacent existing structure.

Upstream from the new EQ Tank is the Bypass Junction Structure (BJS); the two will be connected through a new 48-inch-diameter pipe. Downstream from the Wet Well is the Tank Drain Junction Structure No. 4 (TDJS4); the two will be connected through a new 2-inch force main from the sump pump in the Wet Well. Both the BJS and TDJS4 will have to be structurally modified to accept the new proposed piping.

Wastewater can be corrosive and damaging to steel and concrete; therefore, appropriate measures must be taken to protect the structural integrity of the SSTs and EQ Tanks.

Furthermore, all exposed metal must either be stainless steel or aluminum.

1.4.8 Electrical/Instrumentation/SCADA Considerations

The slide gate actuator on the proposed EQ tank effluent pipes will be powered by a distribution panel fed from the Motor Control Center (MCC) in the DAF building. The MCC in the DAF building has available spare positions for the proposed 480-volt (V) panel which will feed the gate actuators as well as six new mixer drives and two EQ tank effluent pumps. The 480V panel will also feed a transformer to drop voltage down to 120V for instrumentation equipment, lighting, and receptacles.

The valves and drives required for the proposed SST area will be powered from the MCC in the SST1 building. There are available spare positions on the MCC to accommodate the proposed three sludge collector drives and 480V distribution panel. The 480V distribution panel will provide power for the secondary skimmers and non-potable water valves for the SSTs. The 480V panel will also feed a transformer to drop voltage down to 120V for instrumentation equipment, lighting and receptacles.

The existing RAS/WAS pump power is sufficient for the proposed new pumps. Wire sizes and routing are adjusted to be in compliance with new pump equipment and existing VFDs will be re-used for the new pumps.

The existing local control panel (LCP)-DAF panel has sufficient available input/output (I/O) space to allow for the additional required instrumentation and controls in the EQ tank area. New I/O modules will be added to the LCP to accommodate the instrumentation required for the EQ tanks.

The LCP-SST1 panel has sufficient available I/O space to allow for the additional required instrumentation and controls in the proposed SST area. Two new I/O modules will be added to the LCP to accommodate the instrumentation required for the three new SSTs.

USIBWC SBIWTP IBM14T0013 1-9 July 31, 2015

1.4.9 Basis of Design

Section 11 summarizes the design criteria for the proposed EQ tanks/pump station, three SSTs, and RAS/WAS pump station improvements.

1.4.10 Opinion of Probable Construction Costs (OPC)

The OPC for the proposed EQ tanks/pump station, three SSTs, and RAS/WAS pump station modifications is summarized in Table 1. Detailed cost estimate spreadsheets are attached in Appendix E. The costs associated with the construction contract, including contractor's mobilization/ demobilization, overhead, and profit are included in the table. The electrical, instrumentation, and control cost is based on a percentage of the total construction cost. The OPC was prepared based on the concepts developed during the design phase and includes 15% for contingencies. The estimate includes non-construction costs, construction surveying, geotechnical, administrative expenses, and permits. The construction costs are based on equipment and unit costs for 2015.

Table 1. Opinion of Probable Construction Cost

Items Costs General Conditions $1,628,691 Site Work $641,911 EQ Tanks and Pump Station $7,208,515 New SSTs (3) $3,635,329 RAS/WAS Pump Station Improvements $585,000 Bypass Pumping $500,000

Electrical, Instrumentation & Control (15%) $1,789,326 Overall Project Subtotal $15,988,772

Contingency, 10% $1,598,877 Contractor's Overhead and Profit, 15% $2,398,316

TOTAL $19,985,965

1.4.11 Design Schedule

The original design schedule was prepared and distributed in the project kick-off meeting, which was held the first week of September 2014. Since the task order for this project was issued, we have completed the final design phase, topographical survey work, and geotechnical investigation. The design project schedule is provided in Section 13.

1.4.12 Final Design Drawings

A set of final design drawings is provided in Appendix F (bound separately). The drawing set includes a modified plant flow schematic, modified hydraulic profiles, an EQ tank process schematic, a proposed SST process schematic, site and yard piping plan, etc.

The OPC for the proposed EQ tanks/pump station, three SSTs, and RAS/WAS pump stationp p Q p p , , p p modifications is summarized in Table 1. Detailed cost estimate spreadsheets are attached inp Appendix E. The costs associated with the construction contract, including contractor'spp , g mobilization/ demobilization, overhead, and profit are included in the table. The electrical,, , p , instrumentation, and control cost is based on a percentage of the total construction cost. The, p g OPC was prepared based on the concepts developed during the design phase and includes 15%p p p p g g p for contingencies. The estimate includes non-construction costs, construction surveying, g , y g, geotechnical, administrative expenses, and permits. The construction costs are based ong , p equipment and unit costs for 2015.

Table 1. Opinion of Probable Construction Cost

Items Costs General Conditions $1,628,691 Site Work $641,911 EQ Tanks and Pump Station $7,208,515 New SSTs (3) $3,635,329 RAS/WAS Pump Station Improvements $585,000p Bypass Pumping $500,000g

Electrical, Instrumentation & Control (15%) $1,789,326 ( ) Overall Project Subtotal $15,988,772 j

Contingency, 10% $1,598,877 Contractor's Overhead and Profit, 15% g y $2,398,316

TOTAL $19,985,965

USIBWC SBIWTP IBM14T0013 1-10 July 31, 2015

1.5 Abbreviations

A list of the abbreviations and acronyms used in this document is provided below.

AC asphalt concrete

AISC American Institute of Steel Construction

AST activated sludge tank

ASTM American Society for Testing and Materials bgs below ground surface

BJS Bypass Junction Structure

CBOD5 carbonaceous biochemical oxygen demand

DAF Dissolved Air Flotation

DC direct current

DDC deep dynamic compaction

DI Ductile Iron

EBS Effluent Blending Structure

EDS Effluent Distribution Structure

EQ equalization

F filtrate

FDR Final Design Report ft foot/ft gpd/ft2 gallons per day per square ft gpm gallons per minute

HP horsepower

I/O input/output

LCP local control panel

MCC Motor Control Center

MG million gallons

MGD million gallons per day

No. number

NPDES National Pollutant Discharge Elimination System

NPSH net pump suction head

OPC opinion of probable construction

PD positive displacement

USIBWC SBIWTP IBM14T0013 1-11 July 31, 2015

PEBS primary effluent bypass structure

PLC programmable logic controller ppd pounds per day psi pounds per square inch

PST primary sedimentation tank

RAS return activated sludge rpm revolutions per minute

SBIWTP South Bay International Wastewater Treatment Plant

SCADA supervisory control and data acquisition scfm standard cubic ft per minute

SOR surface overflow loading rate

SOW scope of work

SSK secondary skimmings

SST secondary sedimentation tank

TDH total dynamic head

TEFC totally enclosed fan cooled

TSS total suspended solids

TWAS thickened waste activated sludge

UF underflow

URS URS Group, Inc.

USIBWC United States International Boundary and Water Commission

USST Unstabilized Sludge Storage Tanks

V volt

Veolia Veolia Water North America

VFD Variable frequency drive

VTSH vertical turbine solids-handling

WAS waste activated sludge

WCC Woodward Clyde Consultants

WEF Water Environment Federation

WSE water surface elevation

USIBWC SBIWTP IBM14T0013 2-1 July 31, 2015

2.0 EXISTING TREATMENT PLANT PROCESS DESCRIPTION

The existing plant process diagram is provided on Sheet GC-0001. The main source of raw sewage to the plant is from the existing 72-inch-diameter International Interceptor located just south of the United States – Mexico Border. A portion of the flow from this 72-inch-diameter sewer is intercepted prior to Mexico's Pump Station Number (No.) 1 in an existing junction box located immediately south of the border with Mexico. The wastewater flows by gravity through the 72-inch-diameter raw sewage pipeline toward Junction Box No. 1, which is located approximately 10 ft north of the international border near Stewart's Drain. Junction Box No. 1 contains a sluice gate over the 96-inch-diameter outlet of the box, which can be used for flow control to the plant. From Junction Box No. 1, the flow passes through Junction Box No. 2, the Headworks Junction Structure, and the Headworks Inlet Structure before reaching the influent screens. The tank drainage system also discharges into the Headworks Junction Structure through a 48-inch-diameter pipe.

The screened influent wastewater is pumped to the grit chamber from the Headworks through the metered 60-inch pipeline. There is a 60-inch bypass line around the meter vault. The primary effluent from the PSTs is conveyed to the PEBS, which allows the flow to be split between the ASTs and the Effluent Blending Structure (EBS). A motor-operated gate allows the average flow of 25 MGD and the associated peak flow of 48.75 MGD to be sent via a 72-inch gravity flow pipeline to the ASTs for secondary treatment; flows in excess of 48.75 MGD will bypass the ASTs and flow by gravity directly to the EBS through the metered 66-inch primary effluent bypass pipeline. A 66-inch primary effluent emergency bypass pipe is provided from the PEBS to the BJS. This bypass allows peak flow in excess of approximately 100 MGD to spill over an overflow weir in the PEBS, bypass the meter vault, and be conveyed to the EBS. At the EBS, effluent flows from the primary and secondary treatment processes are combined prior to being discharged to the South Bay Land Outfall/Ocean Outfall.

The secondary effluent pipeline is an 84-inch gravity flow line that delivers flow from the secondary treatment processes (ATS and SSTs) to the EBS, where it is combined with primary effluent from PSTs via the 66-inch primary effluent bypass pipe when flows exceed the secondary treatment system peak flow capacity of 48.75 MGD.

A 42-inch pipe conveys RAS from the RAS Pump Station back to the front of ASTs. The 42-inch RAS header pipe is fed by six 16-inch vertical turbine pumps at the pump station and conveys the RAS to the seven 10-inch pipes that feed the RAS diffusers at the head of each AST.

The primary sludge and primary skimmings are produced at the PSTs and are pumped via 8-inch pipes to the USST.

The SSTs generate both secondary skimmings (SSK) and WAS. SSK is pumped via a 10-inch pipe to the USSTs, and WAS is pumped via 10-inch pipe to the WAS Thickening Facilities. The WAS Thickening Facilities generate thickened waste activated sludge (TWAS) and underflow (UF). The TWAS is pumped via 6-inch pipe to the USSTs, and the UF flows by gravity via 14-inch line back to the front of the ASTs. The sludge dewatering facilities generate the dewatered sludge (cake) and belt filter press filtrate (F) and wash water (WW). The dewatered sludge is stabilized by mixing with lime, loaded in the hauling trucks in the Truck Loading Building, and

USIBWC SBIWTP IBM14T0013 2-2 July 31, 2015 disposed of at a sludge disposal site in Mexico. The filtrate and WW flow by gravity via 16-inch pipe into the plant wide tank drain system for return to the Headworks Junction Structure.

USIBWC SBIWTP IBM14T0013 3-1 July 31, 2015

3.0 EQUALIZATION TANK

3.1 Background

Flow EQ is used to overcome the operational problems caused by flow rate variations, to improve the performance of the downstream treatment processes, and to reduce the size and cost of the downstream treatment facilities.

Flow EQ simply is the dampening of flow rate variations so that a constant or nearly constant flow rate is achieved. There are two ways flow EQ is arranged in wastewater treatment plants, in-line and off-line. In the in-line arrangement, all of the flow passes through the EQ tank. In the off-line arrangement, only the flow rate above a predetermined flow rate is diverted into the EQ tank. The stored flow at the EQ tank is returned back to the wastewater treatment plant when incoming flow rate to the plant is below a predetermined flow rate.

Currently, the SBIWTP does not have a flow EQ process. Per the Compliance Study by URS, we noted daily average plant flows varied from a minimum of 14 MGD to a maximum of 43 MGD with an average of 27 MGD. The plant also experienced instantaneous peak flows of 68 MGD in the fall of 2011. Based on the results from the modeling conducted as a part of the Compliance Study, peak flows exceeding 34 MGD will cause effluent TSS washouts from the SSTs. The modeling results were expected because the activated sludge process at the plant is reported to be designed for an average flow of 25 MGD and a peak flow 48.75 MGD.

The final Compliance Study report dated April 2014 recommended that an off-line EQ basin/tank with a capacity of 3.5 million gallons (MG) be constructed. The purpose of this EQ tank is to receive and store plant primary effluent flows in excess of 25 MGD. When the incoming plant flow drops below the 25 MGD target, the stored primary effluent at the EQ tank will be sent back to the plant at a controlled rate. The addition of the proposed EQ tank will allow the plant's activated sludge process to run at a constant flow rate of 25 MGD.

In addition to dampening the flow rate variations, there is an additional benefit of adding the proposed EQ tank. The plant occasionally receives toxic waste which has potential to upset the plant's activated sludge process. Once the proposed EQ tank is constructed, the plant operation staff will have an option of diverting and holding the toxic waste to the EQ tank for an extended period of time.

3.2 Equalization Tank Capacity

The Compliance Study determined that the proposed EQ tank should have a capacity of 3.5 MG.

This capacity was derived using diurnal flows generated during the plant process modeling with the BioWin software. Since then, the actual plant diurnal flows were collected over a period of 14 days in 2013. The diurnal flow data were collected from February 13 – 26, 2013. During the preliminary design phase of this project, we analyzed data and determined the EQ tank volume for each of the 14 days. Table 2 summarizes the EQ tank volumes for all 14 days. The average of all EQ volume data is 2.61 MG. By adding a 25% safety factor with the average EQ volume, the new EQ volume will be 3.25 MG. We recommended that the design EQ volume be 3.25 MG. A detailed EQ tank volume calculation is provided in Appendix B.

USIBWC SBIWTP IBM14T0013 3-2 July 31, 2015

Table 2. Summary of EQ Tank Volume Calculations

Dates EQ Tank Volume, MG 2/13/2013 2.15 2/14/2013 2.37 2/15/2013 2.61 2/16/2013 2.78 2/17/2013 3.14 2/18/2013 2.94 2/19/2013 3.00 2/20/2013 2.59 2/21/2013 1.84 2/22/2013 1.73 2/23/2013 2.45 2/24/2013 2.96 2/25/2013 2.84 2/26/2013 3.10 Average = 2.61

During the FDR review meeting, Veolia mentioned that it desired to have an EQ basin capacity of at least 3.5 MG. It was also decided at the FDR meeting that URS would analyze additional diurnal flow data and revise the EQ volume if necessary.

We analyzed diurnal flow data sets for the entire month of February 2014 and three additional diurnal flow data and determined EQ volume for each data set. Table 3 provides a summary of EQ volumes for the additional diurnal flow data.

Table 3. Summary of EQ Tank Volume Calculations for Additional Data Sets

Dates EQ Tank Volume, MG 2/1/2014 3.54 2/2/2014 2.60 2/3/2014 1.12 2/4/2014 2.66 2/5/2014 1.56 2/6/2014 2.37 2/7/2014 1.51 2/8/2014 2.98 2/9/2014 3.25

2/10/2014 3.25 2/11/2014 4.64 2/12/2014 2.58 2/13/2014 3.52 2/14/2014 1.70 2/15/2014 2.18 2/16/2014 3.41

USIBWC SBIWTP IBM14T0013 3-3 July 31, 2015

Dates EQ Tank Volume, MG 2/17/2014 3.85 2/18/2014 2.88 2/19/2014 1.87 2/20/2014 2.02 2/21/2014 1.76 2/22/2014 2.23 2/23/2014 2.34 2/24/2014 2.25 2/25/2014 1.74 2/26/2014 2.22 2/27/2014 1.61 2/28/2014 1.04 5/29/2014 3.43 12/2/2014 4.06 12/3/2014 1.86

90th Percentile Value = 3.54

As shown in Table 3, the 90th percentile EQ tank volume is 3.54 MG. We now recommend that a minimum EQ tank volume of 3.75 MG be provided. This 3.75 MG EQ tank volume is derived by adding a factor of safety of approximately 6% to the 90th percentile EQ tank volume.

3.3 Flow Diversion to Equalization Tank

The existing PSTs have enough process and hydraulic capacity to handle a peak flow of 50 MGD.