Anadromous Napa River fish species must find their way up the river from the ocean to reproduce.

The historic large population of coho salmon has vanished.  While the chinook salmon are hanging on with a small relict population, the steelhead trout are listed as endangered and their numbers are dropping. 

False Assurances Threaten the Napa River

As our neighbors in Napa county work to protect the Napa River watershed with ballot Measure C in an effort to limit the negative effects of agricultural development in the headwaters, Vallejo residents are fighting a development project that would damage the lower stretch of the fragile riparian system.  Vallejo councilmember Verder-Aliga has publicly stated that she’s been assured by an expert that a proposed mill to grind blast furnace slag from the steel industry at the mouth of the Napa River would pose no risk to the aquatic environment.  She did not indicate how exactly her friend came to a conclusion that has been repeatedly and consistently contradicted in the scientific literature.  A charitable explanation might posit that it’s just a matter of not keeping up with current research.  It’s more than an academic question since the councilmember will soon vote on an appeal of the planning commission’s decision to deny the project permits.

The Orcem component of the proposed Vallejo Marine Terminal project would haul in slag from Asia to offload with clamshell buckets at reconstructed docking facilities for storage in huge open piles.  The environmental analysis reveals the project would release more than sixteen tons of fugitive dust each year at the many transfer points before milling the slag to a fine powder and mixing into cement products.   The environmental report also shows that holding the dust releases to that level requires spraying down the slag piles and roadways with more than three millions gallons of drinking water each year.  An image from a parent company site in Europe shows the ground covered in a layer of slag, and ‘leachate’ water percolating through the open piles and seeping out from the bottom.

Parent company Ecocem slag cement plant in the Netherlands

Water percolating through slag enters the ground and travels through the soil to nearby bodies of water.

USSteel Safety Data Sheet: "Very Toxic to aquatic life with long lasting effects."

It is well recognized in the scientific literature that leachate from steel industry open slag piles presents a significant environmental hazard for nearby bodies of water.  The abstract for a 2009 article in the science journal Water Science Technology begins with the following sentence as a statement of fact:  “High pH (> 12) leachates are an environmental problem associated with drainage from lime-rich industrial residues such as steel slags, lime spoil and coal combustion residues.”  A more recent 2015 study published in the journal Environmental Monitoring and Assessment summarizes the results of a comprehensive long term study of the impacts to nearby streams from steel industry slag mounds.  It gives the lie to any false assurances about how safe a slag mill would be for the sensitive aquatic environment at the entrance to the Napa River system.

In a paper titled “Long-term evolution of highly alkaline steel slag drainage waters,” the researchers summarize a 36-year dataset that monitored the chemical properties of two watercourses where the water leaching into the soil under slag piles was making its way underground into nearby streams.  The introduction begins with a review of previous published reports of the effect of open slag storage on nearby bodies of water.  Along with extreme alkalinity the studies show a consistent major enrichment of a range of trace elements. These include some elements that environmental regulators might not normally look at as part of ambient water quality monitoring such as vanadium, lithium and molybdenum.  Elevated concentrations of aqueous calcium, fluoride and chromium are also consistently reported.

In addition to the extreme alkalinity and mobility of trace element contaminants, “... steel slag waters are also characterized by vigorous rates of precipitation of secondary carbonate minerals which can smother the stream beds,” according to the cited published research.  One study finds "diminished diversity of invertebrate and fish populations in a stream a
ffected by steel slag leachate from a riparian slag disposal area.”  A 2014 investigation showed “total invertebrate abundance and diversity to be negatively correlated with pH, with an impoverished benthic fauna around source areas.”

Ecocem France - Slag covers the ground waiting for rainfall or dust control sprinking systems to leach into the soil and eventually into the adjacent waters of the harbor

The long term study adds another disturbing element by revealing how long it takes for the environment to recover once contaminated: “Declines in calcium and alkalinity have been modest over the monitoring period and not accompanied by significant declines in water pH.  If the monotonic trends of decline in alkalinity and calcium continue in the largest of the receiving streams, it will be in the region of 50–80 years before calcite precipitation would be expected to be close to baseline levels, where ecological impacts would be negligible.”  That’s a long. long time to get back to normal.  Is this the kind of legacy we want to leave future generations?


Councilmember Verder-Aliga owes the community a much better explanation than ‘I’ve been told by an expert’ for her cavalier dismissal of the entirely predictable negative environmental consequences that would flow from this project.  The scientists who have monitored this issue for decades in the real world are the true experts, and they do not at all agree with her friend’s safety assessment.  We have a lot of work ahead to bring the Napa River system back to a state of health, and the VMT/Orcem project represents a giant step in the wrong direction.

A polluting slag mill along with future industrial tenants at this critical waterfront location would further degrade sensitive habitat for threatened native marine species and negatively impact water quality at the gateway to the Napa River system.