The closure of the Tacoma ASARCO copper smelter

The ASARCO smelter

Until March of 1985, the main source of man-made sulfate deposition in the state of Washington was a copper smelter in Tacoma run by ASARCO. In 1983 the smelter emitted an average of 199 tons of sulphur dioxide per day, or about 1/3 of the total emissions in the state (87% of the emissions in the Puget Sound region). The second largest emitter in 1983 was the electric power generating plant in Centralia (96 tons per day), while Mt. Saint Helens, emitting 147 tons per day, was the largest natural source

Figure 1: Major emission sources in Washington and British Columbia. P=point source, A=area source. Number is average SO emission in tons per day. From Faulkner (1987)

In addition to being a major sulfur emission source, the ASARCO smelter also was a major source of atmospheric arsenic. In 1974 the smelter was reported to emit abou 300 tons/year of particulate material into the air. The stack dust was composed of approximately 30-40% As, 20-30% Pb and small amounts of other metals.

Acid rain background material

For general information and some data, see the EPA Acid Rain home page

A fairly old review paper on acid rain is also available.

British Columbia sulfate results

There is some evidence that detectable amounts of pollutants from the Puget Sound region are advected north to British Columbia. Precipitation along the South Coast BC network (see map below) is most acidic on the southern Strait of Georgia area lying in the path of low-level air flows from Puget Sound.

The South Coast BC precipitation monitoring network. From Faulkner (1987).

Data from January 1982 to April 1986 (before and after the shutdown of the Tacoma smelter) were collected by volunteers at the request from a coordinator in Vancouver, who tried to get samples for events when widespread precipitation was expected.

Some of the stations in the network (Vancouver Airport, Ladner, Cloverdale, Abbotsford and Agassiz) were previously operated by Atmospheric Environment Service.and had a slightly different protocol. In particular, the Vancouver airport site used utomatic samplers, and thus obtained many more samples, often of small precipitation amounts.

The British Columbia samples were subjected to chemical analysis at two different laboratories (using different analytic techniques). After correcting for laboratory differences, mean concentrations of the major ions (sulfate, nitrate, ammonium, sodium, chloride, and hydrogen) as well as of some trace elements (such as arsenic) before and after the smelter closure were compared using t-tests.

The figure shows that sulfate concentration decreased at most stations (excess sulfate means that the data have been corrected for the influence of sea salt). The changes are statistically significant except for the three western-most sites, for Pender Island, and for Vancouver Airport. The latter two sites had a significant increase in sulfate concentration.

The problem

How should a study be designed to assess the effect of the smelter closure on local as well as distant deposition? Some factors to consider:

• Meteorology
• Background levels
• Other sources
• Emissions signature

The report

Your group task is to produce a proposal for a study that assesses both local and distant effects of the Tacoma smelter closedown. The proposal can be at most three pages in 10 point text, and needs to address at least the factors mentioned above.