Charles River habitat improvements coming


by Mark Jaquith, Cambridge Chronicle

The wildlife in the Charles River might be getting a habitat upgrade soon. Mirant Kendall Cogeneration Station, the electric generating plant at 265 First Street is in the process of modifying its pollution discharge permit. The changes reflect plans to install new equipment to sell more steam from the heat used to generate power.

EPA has recently released a new draft National Pollutant Discharge Elimination System (NPDES) permit for this facility. Mirant Corp. has been operating the plant with temporary permits since at least 2006, as that permit was appealed, as was the modification issued in 2008.

Currently, the plant is allowed to discharge up to 70 million gallons per day(MGD) of heated water into the Lower Basin of the Charles River through an outfall pipe located in the sea wall just downstream from the Broad Canal. Water is taken in through two cooling intakes in the Broad Canal by six pumps, each capable of handling 13 million Gallons per day. They are allowed to discharge the water after it has been used to condense steam used to run generators. The maximum allowable temperature increase is 20 degrees, and the maximum discharge temperature is 105 degrees. This operation has a very large effect on the aquatic habitat of the lower Charles.

The changes set out in the draft permit would reduce the heat dumped into the river by up to 95 percent. The plan is to increase the amount of steam available for sale, thereby selling more of the heat produced from burning fuel oil and reducing the pollution and waste. They currently sell some steam for use in heating and cooling of local buildings to Trigen Boston Energy Corp. which in turn distributes and
resells it through a pipeline network. Mirant will be installing a back pressure steam turbine and an air cooled condenser to allow more steam for injection into the Trigen distribution system, and use less
river water for cooling. At the same time, Trigen will be building a new pipeline on the underside of the Longfellow Bridge concurrent with the planned repair and reconstruction of the bridge by the
Commonwealth. Mass. General Hospital will be the primary customer for the additional steam. Construction will be a multi year process. EPA will be issuing a compliance order with timelines for construction and operation of the new equipment.

The temperature limits for heated water discharges into the Charles won’t change, but the volume will be reduced from 70 MGD to 3.2 MGD, so the total heat load from this source will be drastically reduced.
With the reduced flow volume will come reduced speed of water from the Broad Canal. A new set of filters and screens with cleaning procedures will be added to the cooling water intake structures to reduce mortality of impinged (trapped) fish, fish eggs and larvae, and other small organisms. The current mortality of this is 100% I believe that there will also be a finer mesh to reduce entrainment (being drawn in and taken through the full length of the cooling system) as well. With
a flow of 70 MGD, greater than the natural flow of the river in a dry late summer, and sufficient to draw all the water in the Lower Basin through the plant in a few days, this has a major effect on fish populations. The current permit is structured so as to create a zone of passable habitat between the Longfellow Bridge and the Museum of Science covering half of the basin from the midpoint to the Boston
shore. The Cambridge side, by implication, being the dead zone in extreme conditions for vulnerable species at certain stages of their life cycle. It is certainly not completely dead. I have seen herring and caught my share of bass, perch,and sunfish there. The zone of passable habitat will increase to about 85 percent of the river surface in the Boston side.

What will this mean for the health of the river? It should mean an increase in survival rates of the fish species most affected by the added heat. Specifically, blueback herring, alewife, and yellow perch.
The other big plus will be that with lower temperatures, there should be fewer blooms of algae and toxic cyanobacteria.

From my reading of the draft permit, many of the other technical details will remain the same. Maximum water temperatures at outfall and in the river are the same. There will be less monitoring required,
and a predictive formula will be used to warn of the necessity of shutdowns due to excessive river temperatures. There will be a raft of exceptions most notably for repair and maintenance work, but these will be limited.

The Kendall plant is the only active remnant of the manufacturing and industrial works which dominated Kendall Square and the East Cambridge riverfront in the nineteenth and twentieth centuries. One can often get a reminder of the coal gasification which happened at this site and nearby when walking through the area. The soil in the area is severely contaminated from this and other past uses. When any digging for construction is happening the smell is quite strong.

Mirant operates eleven power plants with operations in Georgia, Maryland, Virginia, New York, Massachusetts, and California. It is in the process of merging with RRI Energy. Both companies have had their share of environmental issues, but this looks like a step in the right direction.

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