STAT 498

The closure of the Tacoma ASARCO copper smelter, continued

Part 1 of this case contains background material.

The distant study

In the previous writeup for this case, we looked at data from a southern British Columbia monitoring network, indicating a possible reduction in SO

deposition in the year following the closure. However, there was no direct way to ascribe this reduction to the smelter closure. Below are the measurements of nitrate and arsenic for this network.

Nitrate deposition in the BC network.

Arsenic deposition in the BC network.

There should be no relation between the smelter closure and nitrate deposition, since the smelter was no source of nitrate. On the other hand, the smelter was by far the leading source of arsenic, and the substantial decrease in the arsenic deposition in southern BC is an indication of long range transport of pollutants from the Tacoma smelter having been a factor in BC air pollution.

The local study

The study by Vong et al. (1988) used a sampling network consisting of 38 sites located in grassy areas away from overhanging objects, local combustion sources, automobile traffic, and windblown dust. The location of the sites is shown on the map below.
Site map

Rainwater sampling sites for the Tacoma smelter study.

Each rain event sampled was pre-selected according to meteorological criteria, specifying winter rains from cyclonic frontal systems with SSW winds, no convergence, and relatively uniform precipitation over the extent of the network. If a morning forecast (based on 950-500 mb weather maps, NOAA's aloft soundings at Quillayute on the Washington coast, satellite imagery, and local weather observations) predicted these conditions, the samplers were deployed at noon. During February and March of 1985 and 1986, 14 events were sampled (7 before and 7 after closure). Of these, 10 events (5 before and 5 after closure) were meteorologically consistent with the forecast criteria, with 24 hr precipitation accumulations of 0.35 to 1.0 cm.

The 38 sampling sites were organized into spatially homogeneous classes based on the known wind direction and the location of major SO emission sources. There were 6 sites upwind of the smelter with hight quality data (Class 1 in the map above), 8 sites immediately downwind of the smelter (Class 2), and 11 sites downwind of both the smelter and South Seattle. Several other sites were east of the smelter and/or near local point sources (Classes 4 and 5).

The data

The data are available here.
There should be 4 columns, namely: SO4, year(1 or 2), group(1=control, 2=Vashon,3=Seattle), and storm (1-8 year 1, 9-16 year 2).

The task

Assess the local effect of the smelter closure. In particular, produce a graphic depiction of the effect of the smelter closure, taking into account the variability of the data.

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