Designing Ozone Disinfection with and without Filtration

Robert N. Jarnis, John F. Willis, Stephen Martin, Jae R. Kim, and Tiffany Tran Camp Dresser & McKee, Inc., One Cambridge Place, 50 Hampshire Street, Cambridge, Massachusetts 02139, USA Massachusetts Water Resources Authority

Abstract

Ozone has been designed to achieve primary disinfection for the 405-mgd Walnut Hill Water Treatment Plant (WTP). The design was completed for two separate and distinct treatment options; Ozone Option and Filtration Option. The Ozone Option required a 2-log Cryptosporidium inactivation, while the Filtration Option required only a 1-log Cryptosporidium inactivation. The design approach to accommodate both options is presented.

The paper will benefit both design professionals and water utility staff who are evaluating the potential role of ozonation within their utilities.

Background

The Massachusetts Water Resources Authority (MWRA) is an independent public authority created in 1985 and shares responsibility with the Metropolitan District Commission (MDC) for the water supply system for the Greater Boston Area. MDC retains responsibility for managing supply sources, while MWRA has responsibility

for development and operations of infrastructure used to treat and convey drinking water to the user communities. The water supply system serves 46 communities, including 1.9 million people and 30,000 businesses. The average day demand is approximately 250 million gallons (mgd) per day.

The overall MDC/MWRA water supply system is shown in Figure 1. The MDC/MWRA water supply system contains two major water supply reservoirs and three major watersheds; Quabbin Reservoir and watershed, Ware River watershed, and the Wachusett Reservoir and watershed.

The Quabbin Reservoir is a 37.7 square-mile reservoir with a 187 square-mile watershed. The reservoir serves the three Chicopee Valley communities directly. It also serves the Greater Boston service area via transfers to the Wachusett Reservoir. Transfers of up to 550 mgd are made and the total transfers constitute more than half of the average annual inflow into the Wachusett Reservoir.

The Ware River watershed is 96.3 square miles. The MDC/MWRA can divert Ware River flow in excess of 85 mgd from October 15 through June 15 each year. Diversion can be directly to either the Quabbin or Wachusett Reservoir. The practice is to divert to the Quabbin to allow additional hydraulic residence time in that larger reservoir prior to use.

The Wachusett Reservoir is 6.2 square miles with a 117 square-mile watershed. The Wachusett Reservoir is the terminal reservoir. All water for transmission and treatment for the Greater Boston service area passes through the Wachusett Reservoir.

The Walnut Hill Water Treatment Plant Project (WHWTP) will provide treatment to the Quabbin/Wachusett Reservoir supplies serving the Greater Boston Area while at the same time allowing the new and existing transmission, storage and distribution networks to function as an integrated system. The WHWTP is a key part of MWRA/MDC Integrated Drinking Water Quality Improvement Program.

The MWRA/MDC Integrated Water Quality Improvement Program is a comprehensive plan to improve all components of the drinking water system from source to tap in a logical sequence, beginning with those that provide the greatest public health and water quality benefits. Key components are watershed protection, new MetroWest Water Supply Tunnel (MWWST), covered storage, distribution system improvements, and phased water treatment improvements.

A key component of the MWRA/MDC Integrated Water Quality Improvement Program is the phased water treatment plant improvements. The MWRA has initiated and implemented several important water treatment changes in the existing system to ensure attainment of Safe Drinking Water Act (SDWA) treatment and water quality goals. Projects included the following:

§ Replacing chloramination with free chlorine as primary disinfectant, followed by ammonia/chlorine addition for secondary residual disinfectant maintenance;

§ Beginning operation of the Interim Corrosion Control Facility in June 1996 to increase both pH and alkalinity in the treated water for Lead/Copper Rule compliance.

§ New Walnut Hill Water Treatment Plant (WHWTP). The cost to complete the MWRA/MDC Integrated Water Quality Improvement Program is estimated to be $1,473 million as summarized in Table I.

Table I MCD/MWRA Integrated Water Quality Improvement Program Program Component

Estimated Construction Cost, $ million

Watershed Protection

$8.9

Covered Storage

$176

MetroWest Supply Tunnel

$621

Distribution System

$457

Phased Treatment

$210

The objectives of the Walnut Hill WTP Project are to provide phased water treatment improvements including a staged construction approach that would allow a delay in the final selection of treatment process, to provide cost-effective construction, and provide a fully automated facility that will minimize additional staffing requirements. The phased water treatment approach required the design development of three separate treatment alternatives: Chlorine Option (chlorine primary disinfection with corrosion control and chloramination); Ozone Option (ozone primary disinfection with corrosion control and chloramination), and Filtration Option (DAF, ozone for primary disinfection, filtration and corrosion control and chloramination).

The project required that the design of the three treatment alternatives be completed as separate construction contract documents. All three treatment alternatives were carried

through the 60 percent design phase. The ozone and filtration option designs were completed to the bid-ready stage and finalized for bidding.

The design took a dual-track approach in that both the Filtration Option design and the Ozone Option design proceeded concurrently. The Filtration Option design included rapid mixing, coagulation, dissolved air flotation (DAF), ozonation for primary disinfection, post-treatment for fluoride addition and alkalinity/pH adjustment for corrosion control, and approximately 50 million gallons of on-site, finished water storage. The Ozone Option included ozonation for primary disinfection, post treatment and on-site storage. There were many facilities, such as the post treatment and storage tank that are common to both options.

The design was segmented into several submittals for review; 30%, 60%, 90% and final design packages. Review was by the MWRA, including engineering, construction and operations groups, as well as by a separate consultant review team of Metcalf & Eddy, Inc. and I.C.F. Kaiser, Inc. The filtration design preceded the ozone design, as an example, the 30% Filtration Option design was completed and submitted, then the 30% Ozone Option design was started. This approach offered two advantages. By completing the Filtration Option design first, it was ensured that the Ozone Option design could be readily expanded to include future filtration facilities. Secondly, appropriate review comments on the Filtration Option submittal could be incorporated into the Ozone Option design thereby minimizing repeat reviews.

The design also incorporated a modular design approach. The modular design approach would allow initial construction of the Ozone Option facilities followed by a staged construction of the filtration facilities.

The MWRA employed the conventional design-bid-construct project delivery approach. This approach had been successful on the MWRA's Boston Harbor Project to provide secondary wastewater treatment and in meeting both schedule and budget. The conventional project delivery approach also provided time to better evaluate and select the final treatment process while still maintaining progress by completing all required design work.

The construction would be done in a series of construction packages rather than a single, large construction package. This allowed those facilities common to both the Filtration and Ozone Options to be designed and construction before the final treatment decision was made. The multiple construction packages also allowed for more competitive bidding with the general earthwork and concrete storage tank bid separately from the treatment building work. The general scope of the seven construction packages and estimated construction cost are as follows:

WHCP-1 Cosgrove and Wachusett Intakes. This project will upgrade the existing raw water intakes that provide water to the new Walnut Hill WTP, including replacement of older piping, additional flow rate controls and remote operation. WHCP-1 is common to both the Filtration and Ozone Options. This project is currently under construction and has an estimated construction cost of approximately $11 million.

WHCP-2 Wachusett Aqueduct Repair. This project will repair the 100 plus year-old Wachusett Aqueduct with a reinforced concrete liner (shotcrete). WHCP-2 is common to both the Filtration and Ozone Options. The project will allow reactivation of this aqueduct for use during WHCP-4 construction and as a backup raw water transmission aqueduct. The construction work is scheduled to begin in late year 2000, and is estimate to cost approximately $15 million.

WHCP-3 Site Work and Storage Tank. This was the first construction package bid. This package includes the primary access road to the Walnut Hill WTP site (including a bridge over the existing open aqueduct), secondary access road, general site excavation and earthwork, and large diameter (10 and 12-feet in diameter) buried pipelines. WHCP-3 is common to both the Filtration and Ozone Options. This project is approximately half complete and has an estimated construction cost of approximately $63 million.

WHCP-4 Treatment Facilities. This construction package was established for the treatment facilities at Walnut Hill, and would incorporate either the Filtration or Ozone Option. This construction package also included remote control of the existing transmission system of tunnels and aqueducts. The Ozone Option is currently being bid, with a construction start in November 2000. The estimated construction cost is approximately $110 million.

There are several other smaller construction packages to provide final site work on the site after WHCP-4 is done and construction package to modify an existing facility to a maintenance facility for the Walnut Hill WTP. The total estimated construction cost of all the construction packages required to complete the Walnut Hill WTP is approximately $210 million.

The project was established for staged construction. Common facilities, as included in WHCP-3, could be constructed while the design of the treatment option was finalized. Either the Ozone Option or the Filtration Option could then be constructed. Should the Ozone Option be constructed, a subsequent, future construction stage could allow the filtration processes of DAF and filtration to be constructed while maintaining the ozonation facilities in operation.

The staged construction for the Ozone and Filtration Options is presented graphically in Figure 2: Site Overflow Plan.

The design of each option was completed. The MWRA believed that the Ozone Option was sufficient to meet public health and that a filtration waiver should be granted. The United States Environmental Protection Agency (USEPA) believed that filtration was required. The decision as to which treatment option will be constructed went to trial as the USEPA has sued the MWRA to enforce the Filtration Option. The court decision was reached in May 2000 and the court ruled that the Ozone Option would meet the drinking water needs of the MWRA service area and that filtration, at this time, would not be required.

Ozone Process Design

The objective of the ozonation process, for both treatment options is to provide primary disinfection. At the time of the project initiation, the United States Environmental Protection Agency (USEPA) regulatory requirements were established to provide disinfection for Giardia and viruses. The Authority, however, was uncomfortable with proceeding with such a large project without some consideration for disinfection of Cryptosporidium. It was established that Cryptosporidium disinfection would be an objective of the project. A total Cryptosporidium logremoval target of 3 logs was established for the Ozone Option. A Cryptosporidium log-removal target of 4 logs was established for the Filtration Option. The Cryptosporidium log removal credits for various components of the project and for both the Ozone and Filtration Option were established as presented in Table II:

Table II Log Cryptosporidium Removed Project Component

Ozone Option

Filtration Option

Watershed Protection

1.0

1.0

Primary Disinfection

2.0

1.0

Filtration

--

2.0

Total

3.0

4.0

The Ozone Option requires greater primary disinfection inactivation (2 log inactivation) than the filtration option (1 log inactivation). The ozone system for the Ozone Option, therefore, is larger than the ozone system for the Filtration Option.

At the time of the initial design, the best assessment of CT required to meet various levels of Cryptosporidium inactivation was the research work by Dr. Gordon Finch (Finch, G.R., E.K. Black and L. Gyurek, 1994. Ozone Disinfection of Giardia and Cryptosproidium. American Water Works Research Foundation). During the design, however, the MWRA participated in an American Water Works Association Research Foundation project that evaluated ozone inactivation for specific waters including the MWRA Wachusett Reservoir (Draft Technical Memorandum - "Inactivation of Cryptosporidium Under Site Specific Conditions, Montgomery Watson, November 14, 1997). The research results indicated greater CT requirements to effect a given level of inactivation than indicated by the earlier Finch research. The MWRA has adopted the AWWARF CT values for the project. The CT values extrapolated from experimental results and adopted for the project are presented in Table III.

Table III CT Requirements (mg/L-min.) Temperature (degrees C)

Filtration Option Ozone Option (1 log inactivation) (2 log inactivation)

1

10.5

21

2

10

20

3

9.1*

18*

4

8.5

17

5

8

16

6

7.5

15

7

7

14

8

6.5

13

9

6

12

10

6

12

13

5

10

14

5

10

15

4.5

9

* Actual experimental results Design Details

The Basic Design Data for the Filtration Option Ozone System is presented in Table IV. The Basic Design Data for the Ozone Option Ozone System is presented in Table

V. A discussion of design details is presented. A presentation of the Filtration Option is presented first, followed by the changes to that design for the Ozone Option.

Plant Flow

Table IV Ozone System Design Criteria - Filtration Option Average Maximum (mgd) 270 405 (cfs) 418 627

Ozone Ozone Contact Basins No. of units Effective volume, ea. (cf) Dimensions, ea. (w x l x w.d.) (ft.) Detention time, ea. (min.) Total detention time (min.) Ozone Dose mg/l (max.) mg/l (ave.) lbs/day (max.) lbs/day (ave.) Ozone Generators No. of units Capacity, ea. (lbs/day @ 10%) Ozone Destruction Units No. of units Capacity, ea. (scfm) Blower hp Cooling Water Pumps No. of units Capacity, ea. (gpm) Pump hp Motor type Liquid Oxygen Tanks No. of units Capacity, ea. (gal.) Ambient Vaporizers No. of units Capacity, ea. (Scfm) Gas Trim Heaters No. of units Capacity, ea. (scfh) Sodium Bisulfite Dose (mg/l) Daily Use (lbs.)

4 176,000 74 x118.5 x 24 7.0 28.1

4 176,000 742 x 118.5 x 24 4.7 18.7

1.2 1.0 2,700 2,250

1.5 1.25 5,070 4,220

4 2,253

4 2,253

6 160 5

6 160 5

4 320 7.5 CS

4 320 7.5 CS

3 20,000

3 20,000

3 32,000

3 32,000

2 27,750

2 27,750

0.5 1,126

0.5 1,689

Plant Flow

Table V Ozone System Design Criteria - Ozone Option Average (mgd) 270 (cfs) 418

Ozone Ozone Contact Basins No. of units Dimensions, ea. (w x l x w.d.) (ft.) Effective volume, ea. (cf) Detention time, ea. (min.) Total detention time (min.) Additional Ozone Contact Time Connecting pipe volume, tot. (cf) Connecting pipe det. time (min.) Storage tank contactor no. Storage tank contactor volume, ea. (cf) Storage tank contactor det. time, ea. (min) Total storage tank cont. det. time (min) Total Ozone Detention Time (min.) Ozone Dose mg/l (max.) mg/l (ave.) lbs/day (max.) lbs/day (ave.) Ozone Generators No. of units Capacity, ea. (lbs/day @ 10%) Ozone Destruction Units No. of units Capacity, ea. (scfm) Blower hp Cooling Water Pumps No. of units Capacity, ea. (gpm) Pump hp Motor Type Liquid Oxygen Tanks No. of units Capacity, ea. (gal.) Ambient Vaporizers No. of units Capacity, ea. (scfh) Gas Trim Heaters No. of units Capacity, ea. (scfh) Sodium Bisulfite Dose (mg/l) Daily Use (lbs.)

Maximum 405 627

4 74 x 118.5 x 24 176,000 7.0 28.1

4 742 x 118.5 x 24 176,000 4.7 18.7

80,800 3.2 2 361,800 14.4 28.8 60.1

80,800 2.2 2 361,800 9.6 19.2 40.1

1.75 1.50 3,940 3,380

2.5 1.75 8,445 5,910

4 2,225

4 3,380

6 320 10

6 320 10

4 540 15 CS

4 540 15 CS

3 24,000

3 24,000

6 27,000

6 27,000

2 47,000

2 47,000

0.5 1,126

0.5 1,689

Filtration Option

Ozone Generating Capacity. Four medium frequency, horizontal tube, oxygen-fed generators were selected. Three generators would provide the ozone production capacity over the varying production requirements due to varying water quality (demand and decay), changing water temperature, variable CT requirement and seasonal changes in water demand. A fourth generator would serve as a standby unit.

Oxygen feed gas was selected as it has consistently demonstrated to provide the least present worth cost. An evaluation of percent ozone gas for ozone confirmed that a 10% ozone concentration provided the most economical system. Each generator would have the capacity to produce 2250 pounds/day at 10% ozone concentration from oxygen. Further, each generator would be capable of producing 110% of its rated capacity at 10% concentration, and 160% of rated capacity at 5% ozone concentration. The generator would be capable of controlled and automatic operation over a 10 to 1 turn down ratio.

Each ozone generator and its respective Power Supply Unit (PSU) would be water cooled with water drawn from the ozone influent channels.

Ozone Contactors

The contactors were designed to achieve a 96-98% transfer efficiency and an hydraulic efficiency, as defined by the ratio of T10 /T of 0.7, where T10 is the hydraulic residence time of 10% of the flow and T is the total residence time as calculated from volume and flow rate. Full scale testing of previous designs has demonstrated successful performance. The successful contactor design was used as the design basis and then confirmed using Computation Fluid Dynamic (CFD) evaluation. The CFD analysis was performed by Hazen & Sawyer, P.C.

There are no provisions for foam control or removal. Foam, algae and other floatable material will be removed in the upstream DAF process.

Monitoring

It is important to include accurate ozone residual monitoring to ensure both disinfection performance (monitoring to ensure that CT required is, in fact, being met), and to allow process optimization. Process optimization can be achieved through the

use of integrated disinfection design framework. Both objectives require monitoring of ozone residual at several places. There are three places where ozone residual is measured. Samples for ozone residual flow by gravity through the ozone residual analyzers, are then collected in a closed system, and returned to the ozone effluent channel. Several sample locations are available at each ozone residual analyzer. Analyzers are located at the contactor sidewalls within the contactor galleries.

There are four contactors. The contactors are over-under baffled flow for the initial ozone injection. There are two ozone injection chambers and three ozone contact chambers each between the injection chambers. The initial injection chamber is counter-current flow and is the prime injection chamber. It is unlikely that the subsequent injection chamber will be required. Ozone is introduced through fine bubble ceramic diffusers mounted on the contactor bottom. Providing the flexibility to add ozone at a second injection chamber was thought necessary to account for temporary water quality changes with regard to ozone demand or decay. After the initial ozone injection and dissolution over-under baffles, the bulk of the contactor volume is serpentine flow to provide the additional contact time.

The flow split into the operating contactors is hydraulic control by maintaining a constant headloss across the inlet sluice gates. This will be accomplished by modulating the inlet sluice gates to maintain a constant water level in all operating contactors. Because the headloss through the inlet sluice gates is considerably greater than the headloss down the inlet channel. The modulation required is considered to be minor.

The split of ozonated feed gas to the operating contactors and split between application points within each contactor will be based on maintaining the correct ozone residuals. The correct residual will be established during plant startup and initial operation as discussed in Monitoring below.

The filters will be operated in a biological mode to reduce distribution system biological growths. Following filtration, there is a free chlorine disinfection step to inactive any pathogens that may be included in the biological material sloughing from the biological filters. Free chlorination occurs in a two small (approximately 1.0 MG each), separated sections of the 50 MG storage tanks.

Ozone Option

The design for the Filtration Option required several revisions to meet the requirements of the Ozone Option. Revisions were required to address two issues; a greater Ozone Option CT requirement, and a raw water feed water quality different

than the DAF-treated water of the Filtration Option. Further, it was a project requirement to keep the ozone contactors and ozone building design established for the Filtration Option the same for the Ozone Option. Because there was no space, the Filtration Option ozone contactors could not be enlarged for the Ozone Option to achieve the greater CT value. There was no space because the site area needed to be reserved for the DAF facility and filters should it become necessary to add these facilities to the Ozone Option in the future. It was believed that the Filtration Option Ozone Building could accommodate larger generating systems of the Ozone Option without increase in the building size. This would allow the majority of the Filtration Option Ozone Building design to remain intact for the Ozone Option.

To provide the required increased CT of the Ozone Option, and to account for slightly greater ozone demands and faster ozone decay associated with the raw water, as well as to meet the constraint imposed by the fixed ozone contactor size, it was decided to increase both ozone generating capacity and ozone contact time. The challenging part of this task was to increase contact time.

To increase contact time, we took advantage of the post-filtration chlorine contact time within the Storage Tank. This area would not be needed under the Ozone Option. By using this area, and expanding it somewhat, an additional 14.4 minutes and 9.6 minutes of hydraulic retention time at the average and maximum design flow rates respectively. This additional ozone contact time, when coupled with the time available from the contact tanks and the retention time in the piping from those contact tanks to the Storage Tank provide 60 minutes total retention time at average design flow and 40 minutes retention time at maximum design flow. The hydraulic efficiency of the Ozone Contact Tanks and the additional ozone contact area in the Storage Tank was established as a T10 /T value of 0.7. The pipeline between the time tanks was considered as plug flow with a T10 /T value of 1.0. This resulted in a substantial increase in contact time, allowing for a smaller increase in ozone generating capacity to meet the increased Ozone Option CT requirements.

To provide the additional ozone contact area within the storage tank, both concrete and stainless steel mesh baffles were employed. In that portion of the tankage that would serve as a contact area in either option (chlorine contact for the Filtration Option or ozone contact for the Ozone Option), concrete baffles were designed. These baffles are being constructed as part of WHCP-3 along with the storage tank construction. One additional baffled area only needed for the Ozone Option, and which could be added as part of the later WHCP-4 Construction Package, stainless steel mesh was selected as the baffle material.

The increase in ozone production capacity for the four generators was from a unit capacity of 2250 lbs/day to 3380 lbs/day generators. The total installed ozone production capacity of the three operating generators is 10,140 lbs/day.

The Filtration Ozone Building can accommodate the larger ozone generators of the Ozone Option only. Minor building changes were required for larger electrical switchgear, LOX storage capacity, destruct units, and cooling water pumps. The LOX System was also slightly larger, including LOX storage tanks, ambient vaporizers and gas trim heaters.

There were modifications required in the yard piping, Post Treatment Building and Chemical Building for the Ozone Option. Because the ozone contactor hydraulics grade line needed to be elevated to accommodate future filters, the hydraulic grade line control, using butterfly valves, from the contactors to the Post Treatment Building inlet were also required. The Sodium Bisulfite chemical feed system for quenching ozone residual changed the application point from the ozone contactors to the effluent from the additional ozone contactors. The application points for chlorine and aqua ammonia added to produce the chloramine residual for a secondary disinfectant were changed. Lastly, material for hatches in the Post Treatment Building that were exposed to ozonated water were changed from aluminum to 316 S.S. Also, ambient air ozone monitors and an off-gas destruct units were added to the Post Treatment Building.

Because of the concern regarding potential foaming during ozonation of the raw water, foam collection and removal facilities have been added to the Ozone Option.

Planned Redundant Facilities

There are numerous redundant facilities associated with the ozone system for both the Filtration and Ozone Options, which include:

§ Three liquid oxygen tanks will be provided. The total installed volume under each option is adequate to handle the average oxygen consumption rate estimated under each option.

§ Three ambient air vaporizers will be provided in the Filtration option. One vaporizer will be able to handle the maximum oxygen demand condition estimated for this option. Six ambient air vaporizers will be provided in the Ozone Option. Two vaporizers will be able to handle the maximum oxygen demand condition.

§ Two gas trim heaters will be provided in both the Filtration and Ozone Options. One heater will be able to handle the maximum oxygen demand condition estimated for each option.

§ Two supplemental air compressors will be provided in both the Filtration and Ozone Options. One compressor will be able to handle the maximum supplemental air demand condition estimated for each option.

§ Two supplemental air dryers will be provided in both the Filtration and Ozone Options. One dryer will be able to handle the maximum supplemental air demand condition estimated for each option.

§ Four ozone generators with associated power supply units will be provided in both the Filtration and Ozone Options. Three generators will be able to handle the maximum ozone demand condition estimated for each option.

§ Four cooling water pumps will be provided in both the Filtration and Ozone Options. Three pumps will be able to handle the maximum cooling water condition estimated for each option.

§ Six off-gas ozone destruction units will be provided in both the Filtration and Ozone Options. Four units will be able to handle the maximum ozone demand condition estimated for each option.

§ Two sodium bisulfite storage tanks will be provided in both the Filtration and Ozone Options. The total installed volume is adequate to handle the average bisulfite demand condition estimated for each option.

§ Six sodium bisulfite metering pumps will be provided in both the Filtration and Ozone Options. Four pumps will be able to handle the maximum bisulfite demand condition estimated for each option.

§ Each ozone generator's power supply unit is fed 13.8 KV electrical service by separate double-ended switchgear. All other ozone equipment is fed 480 V electrical service from two double-ended motor control centers which are fed by double-ended switchgear. All switchgear is backed up by on-site enginegenerators.

Construction Cost

The Ozone Option is currently being bid, therefore only engineer’s cost estimates are available. The cost estimates for both the Filtration and Ozone Options are summarized in Table VI.

Table VI Comparison of Estimate Ozone System Construction Costs Filtration Option

Ozone Option

Ozone System Equipment

$5.09 million

$7.45 million

Ozone Building and Contactors

31.55 million

31.55 million

Storage Tank Ozone-related Equipment

--

1.8 million

Total Treatment Option

$36.6 million

$40.8 million

Summary

The design of the Walnut Hill WTP Project was able to progress to meet Consent Order schedules, while allowing time to make the final treatment process alternative selection. By using modular design and staged construction, both the Ozone and Filtration Options were completed. The design of the Ozone system for the Filtration Option was readily and easily modified to meet the greater CT values of the Ozone Option, with minor revisions. Key revisions included increased ozone capacity and increased ozone contact time.

The project is proceeding as the Ozone Option. Construction of common facilities is ongoing, while construction of the Ozone treatment facilities is scheduled to start at the end of 2000, and be completed by mid 2004.