MIRANT DELTA, LLC - DRAFT 

Mirant Proposed BDCP Covered Activities 

Goal: 

To generate electric power at the Delta Plants to meet the demands of the California and 

Western electric grid. 

Brief Covered Activity Description: 

Mirant's Covered Activities are those activities associated with the generation of power at 

its Pittsburg and Contra Costa Power Plants (together the Delta Plants). These activities can be 

divided into three categories: (1) current power generation activities and water intake and 

discharge flows associated with those activities; (2) recurrent maintenance activities required to 

ensure continued operation of those existing facilities; and (3) potential future unit replacement 

projects at both plants, which would be anticipated to have much lower associated intake and 

discharge flows than the existing power generation facilities. The Pittsburg Power Plant is 

located on the southern shore of Suisun Bay near Pittsburg, California (Figure X-1), and the 

Contra Costa Power Plant is located 12 miles upstream on the southern bank of San Joaquin 

River near Antioch, California (Figure X-2) [Figures to be inserted]. 

Initially the Mirant activities to be covered by the BDCP are continued operation of the 

Delta Plants, which are dependent on the withdrawal of cooling water for non-consumptive oncethrough cooling purposes. Thus the primary goal for Mirant's initial Covered Activities will be 

to maintain existing levels of operation and associated water flows, but Mirant expects that its 

Covered Activities will evolve over the next few years as the BDCP process continues. 

Additionally, Mirant's operations are constrained by its Clean Water Act National Pollution 

Discharge Elimination System (NPDES) permits and specifically by Clean Water Act section 

316(b) of the federal Clean Water Act. Mirant's operations are also constrained by regulatory 

requirements imposed by federal and state energy agencies. These independent regulatory 

constraints may alter Mirant's Covered Activities for the purposes of the BDCP in both the shortterm and long-term. 

Longer-term Covered Activities may include the replacement of existing power 

generation units, and Mirant anticipates that any new units would not utilize once-through 

cooling technology. Accordingly, the impacts to covered species associated with longer-term 

water intake and discharge activities are expected to be much less than those associated with the 

initial Covered Activities. 

Expanded Covered Activity Description:

• Existing Plants Operation 

Mirant's Delta Plants have a total generating capacity of 2,090 gross megawatts (1,985 

net megawatts). Mirant's generating units burn natural gas and are designed to be cooled by 

water from the San Joaquin-Sacramento River Delta. Cooling water is drawn into the plants 

through 9.5 mm (3/8 inch) screens, pumped to condensers, used to cool spent steam and then 

discharged immediately back into the San Joaquin-Sacramento Delta. Source waters for the 

Delta Plants' cooling water systems are characteristic of this part of the Bay-Delta that separates 

the upstream, freshwater Delta from the downstream, saltwater bays. 

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MIRANT DELTA, LLC - DRAFT 

o Pittsburg Power Plant

The Pittsburg Power Plant (PPP) consists of seven natural gas-fired generating units, four 

of which have been retired. PPP Units 5&6 were built in 1960 and 1961, respectively, and 

generate a total of 660 gMW of power. PPP Unit 7 was built in 1972 and generates 740 gMW. 

Cooling water for the PPP is withdrawn from Suisun Bay through two adjacent shoreline intake 

structures. Units 5&6, both once-through cooled units, are each serviced by two variable 

frequency circulating water pumps (CWP) that withdraw water from the Units 5&6 intake 

structure. Each pump has a maximum design flow of 115.6 million gallons per day (MGD)(354.7 

acre-feet(AF)/day) or 231.1 MGD (709.1 AF/day) per unit (Table X-1). The approach water 

velocity in front of the bar racks can range from 0.5 to around 0.2 feet per second depending on 

how much electric generation is needed and the number of the variable frequency pumps in 

operation. Unit 7, which is equipped with two mechanical-draft cooling towers and a large 

cooling water canal, withdraws make-up water through the Units 1-7 intake structure. Unit 7’s 

closed-cycle system uses up to 44 MGD (135 AF/day) of make-up water. 

In addition to the Units 5-7 cooling water intake requirements, the PPP withdraws water 

from the Units 1-4 intake structure for station water supplies, for intermittent intake screen 

washing, and for fire suppression purposes. At maximum operation, these additional uses 

account for approximately 43.6 MGD (133.8 AF/day). The total current design flow for all PPP 

operations is approximately 565.2 MGD (1,734 AF/day)(Table X-1). 

Table X-1. Total PPP design maximum flows by subsystem 

Flow (GPM) Flow (MGD) Flow (AF/Day) 

Circulating Water Pumps 

 Unit 5 

 Unit 6 

 Subtotal

160,500 

160,500 

321,000

231.1 

231.1 

462.2

709.1 

709.1 

1,018.2

Continuous Pumps 

 Unit 7 Make-up Water Pump 

 Station Service Pumps(1) 

 Jockey Pump (Fire Suppression) 

 Subtotal 

30,300 

27,000 

 20 

57,320

43.6 

38.9 

 0.03 

82.5

133.8 

119.4 

0.1 

253.3

Intermittent Pumps 

 Units 1-4 Screenwash Pumps (2)

 Units 5&6 Screenwash Pumps (3)

 Fire Suppression-Main Pump (4)

 Fire Suppression-Auxiliary Pump (4) 

 Subtotal

 

 6,750 

 5,400 

 2,000 

 0 

14,150

 9.7 

 7.8 

 2.9 

 0 

20.4

29.8 

23.9 

8.9 

0 

62.6

TOTAL 392,470 GPM 565.2 (MGD) 1,734 (AF/Day)

1. Since the retirement of Units 1-4 in 2004, one of the six station service pumps operates 24 hours per day 

(6.5 MGD). 

2. Since the retirement of Units 1-4 in 2004, two of the three screenwash pumps are still operated about 

1 hour/week for maintenance (0.04 MGD). 

3. Design flows for pumps are reported. Two of the three pumps typically operate for a total of 90 minutes 

per day (3.9 MGD). 

4. The fire suppression pumps are always available for emergency situations. The normal operating flows 

are based on testing each pump up to one hour per week to assure pump reliability and occasionally to 

flush the header system. Flows are calculated assuming the main pump is used for 25% of the year. 

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MIRANT DELTA, LLC - DRAFT 

o Contra Costa Power Plant

The Contra Costa Power Plant (CCPP) consists of seven natural gas-fired generating 

units, five of which have been retired. Units 6&7 were built in 1964 and generate a total of 690 

gross megawatts (gMW) of power. Units 6&7 are equipped with once through cooling which 

utilizes water withdrawn from the San Joaquin River. Units 6&7 are each serviced by two 

variable frequency circulating water pumps (CWP) that each have a maximum design flow of 

152,800 gpm, or 220 MGD (675 AF/day) (Table 2-1). The total design flow for both Unit 6 and 

Unit 7 is approximately 305,600 gpm, or 440 MGD (1,350 AF/day). The approach water 

velocity in front of the bar racks can range from 0.6 to around 0.2 feet per second depending on 

much electric generation is needed and the number of the variable frequency pumps in operation. 

In addition to the Unit 6 and Unit 7 cooling water intake requirements, the CCPP utilizes 

water for station water supplies, for intermittent intake screen washing, and for fire suppression 

purposes. At maximum operation, these additional uses account for approximately 22 MGD 

(67.5 AF/day). The total current design flow for all CCPP operations is approximately 

462 MGD (1,418 AF/day) (Table X-2). 

Table X-2. Total CCPP design maximum flows by subsystem 

Flow (GPM) Flow (MGD) Flow (AF/Day) 

Circulating Water Pumps 

Unit 6 152,800 220 675 

Unit 7 152,800 220 675 

Subtotal 305,600 440 1,350 

Continuous Pumps 

Station Service Pumps 12,000 17.3 53 

Jockey Pump (Fire Suppression) 20 0.03 0.1 

Subtotal 12,020 17.309 53.1 

Intermittent Pumps 

Units 6&7 Screenwash Pumps (1) 5,400 3.9 11.9 

Fire Suppression (Main Pump) (2) 2,000 0.7 2.1 

Subtotal 7,400 4.6 14.1 

TOTAL 325,020 GPM 462 MGD 1,418 AF/Day 

(1) Assumes that all three screenwash pumps operate for two hours every four hours per day. 

(2) The fire suppression pumps are always available for emergency situations. The normal operating flows are 

based on testing each pump up to one hour per week to assure pump reliability and to occasionally flush the 

header system. Flows are calculated assuming the main pump is used for 25% of the year. 

o Variable Frequency Drive (VFD) Circulating Water Pump Operations 

The circulating water pumps at CCPP Units 6&7 and PPP Units 5-6 are mixed flow 

vertical centrifugal pumps equipped with A-C induction motor drives. The drives have been 

modified to utilize VFD controls, as well as to operate at full rated speed. The VFD controls 

provide a means to vary drive speed by varying frequency. For a centrifugal pump, flow is 

proportional to pump speed. Therefore as frequency and drive/pump speed are reduced, pump 

flow is also reduced proportionally (i.e., 50% pump speed => 50% pump flow). 

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MIRANT DELTA, LLC - DRAFT 

When operating in VFD mode, the circulating water pump speed/flow is typically at its 

minimum level when the unit is at minimum load. The minimum circulating water pump 

speed/flow is limited by both the pump and motor design and the system head requirements. For 

PPP Units 5&6 and CCPP Units 6&7 minimum flow is 50% of design and minimum load is 

~25–45 MW. As unit load increases, pump speed and flow are increased in accordance with unit 

conditions. Maximum circulating water speed/flow, 95–100% of design, is typically reached at 

~90–145 MW for PPP Units 5&6 and CCPP Units 6&7. River water temperature, tide, 

condenser vacuum, steam flow, etc., all have an effect on circulating water flow requirements. 

o Current Actual Operational Cooling Water Flows 

Actual flow rates at the Delta Plant have steadily decreased in recent years to be 

consistently substantially below all maximum permitted flow limits. Capacity utilization rates 

(the ratio between the annual net generation of power and the total net capability of the facility to 

generate power) at the Plants have steadily declined over the last five years, and intake flows 

have correspondingly decreased. For example, the combined 2006 total flow for CCPP Units 6 

& 7 and PPP Units 5 & 6 of 40,753 MG (0.13 million AF) was 83% lower than the comparable 

figure in 2002. See Table X-3. While the California Independent System Operator (CAISO) 

requires that the Delta Plants be available at any time during the year, the Delta Plants are 

primarily used during California’s peak energy demand periods, particularly in the crucial 

summer months. The Plants’ water intake spiked in 2001 when California’s unprecedented 

energy crisis required almost continual operation to meet electrical demand. Despite this unique 

circumstance, the overall use of cooling water during the last 20 years shows that water intake 

has been steadily decreasing, but has been sharply reduced in the last few years. See Figure X-3. 

Table X-3. Electrical capacity utilization and cooling water flows for CCPP and PPP from 2002 to 

2006. 

Plant/Year Capacity Utilization 

(MWh/(MW Capacity * hours of 

generation) 

Combined Annual 

Cooling Water Flows

(MG/yr) 

Combined Annual 

Cooling Water Flows 

(million AF/yr) 

CCPP Unit 6 Unit 7 Units 6&7 Units 6&7 

2002 28.7 37.4 117,099 0.36 

2003 1.9 16.4 46,740 0.14 

2004 4.1 21.7 60,926 0.19 

2005 1.2 10.1 29,875 0.09 

2006 0.8 3.9 15,641 0.05 

PPP Unit 5 Unit 6 Unit 7 Units 5&6 Units 5&6 

2002 19.9 24.5 43.2 120,340 0.37 

2003 27.1 7.1 17.2 80,876 0.25 

2004 24.0 20.8 9.5 74,991 0.23 

2005 12.5 7.3 1.8 34,710 0.10 

2006 7.7 5.3 1.4 25,112 0.08 

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MIRANT DELTA, LLC - DRAFT 

5 

0

500

1,000

1,500

2,000

2,500

19861987

19881989

1990

1991

19921993199419951996

19971998

1999

20002001

2002

2003

2004

20052006

Million Gallons per Day

Actual Daily Average Intake Permitted Intake

Figure X-3. Average daily flows (MGD) of the CCPP and PPP from 1986 through 2006. 

o Discharge Flows (including Stormwater)

In addition to once-through cooling flows, Mirant discharges process wastewater and 

stormwater (quantity and quality of discharges are subject to permits issued by the State Water 

Resources Control Board and San Francisco and Central Valley Regional Water Quality Control 

Boards). 

• Recurrent Plant Maintenance and Modification Activities and Monitoring Activities 

o Maintenance Dredging, Equipment Maintenance and Modifications, and Levee 

and Flood Control Maintenance 

Maintenance and modification activities includes those routine activities that maintain the 

capacity and operational features of the existing power generation facilities at the Delta Plants 

described above. These activities include periodic maintenance dredging in front of and in the 

plant cooling water intake structures to remove naturally occurring accumulated sediments to 

ensure that the approach velocity of cooling water entering the intake structure remains relatively 

uniform across the intake screen and as close to design levels as possible and to prevent undue 

damage to the facility from sediment in the cooling water and the related abrasion and wear of 

power plant equipment, such as condenser tubes and circulating water pumps. Dredging is also 

sometimes required around the docks and in the discharge outfalls to remove the sediment build 

so that these structures can function and operate as designed. These activities also include 
MIRANT DELTA, LLC - DRAFT 

recurrent equipment maintenance and modifications (such as shoreline and pier maintenance, 

maintenance and repair of all improvements, infrastructure, roads, electrical facilities, 

underground linear facilities, vegetation management, etc.), as well as modifications to existing 

facilities and infrastructure as needed to ensure continued power generation; levee maintenance 

(such as placement of riprap for shoreline protection and erosion control) as needed to protect 

the power generation facilities; and flood control maintenance (such as maintenance of Willow 

Creek at the PPP) as needed. 

o Aquatic Studies & Covered Species Monitoring 

Mirant is conducting, and will recurrently conduct, aquatic and covered species studies 

and monitoring, specifically involving data collection in the vicinity of the plants, in front of the 

intake and outfall structures, and within the cooling water system. 

• Planned & Prospective Unit Replacement Projects 

Future power generation projects at the Delta Plants would involve the construction of 

new units and associated infrastructure. New units would likely require some use of river water 

(e.g. for station water supplies or cooling tower make-up water), but Mirant anticipates that any 

new units would not utilize once-through cooling technology and would therefore require only a 

small fraction of the water required by existing PPP Units 5-6 and CCPP Units 6-7. 

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