The Stibnite mining area was intermittently mined for most of the 20th

Question

The Stibnite mining area was intermittently mined for most of the 20th century, and decades after mining ceased, water quality in the area continues to be impaired. Concentrations of dissolved arsenic and antimony generally increased from upstream to downstream in the East Fork of South Fork of the Salmon River. Based on the majority of arsenic and antimony occurring in the dissolved phase, and inverse relationships with streamflow at most sites, the primary route of arsenic and antimony to surface waters is likely from groundwater. Mercury, in contrast, was directly related to streamflow and was associated with particulates, suggesting erosion of surface materials to be the primary route to surface waters.

Based on the information in the passage, select the statement describing a likely Source of arsenic in the East Fork of the South Fork of the Salmon River and the statement describing a a likely Source of mercury in the East Fork of the South Fork of the Salmon River. Make only two selections, one in each column.

pudu · Answer

" Based on the majority of arsenic and antimony occurring in the dissolved phase, and inverse relationships with streamflow at most sites, the primary route of arsenic and antimony to surface waters is likely from groundwater". It indicates that water is get contaminated due to thr presence of ground water. The highest possibility for this is at the source . Headwater chemical infiltration satisfy it. Headwater indicates the source.

Mercury is due to surface erosion. that will satisfy only downstream sedimentary deposit.

Mercury is due to surface erosion. that will satisfy only downstream sedimentary deposit.

Tukkebaaz · Answer

The Stibnite mining area was intermittently mined for most of the 20th century, and decades after mining ceased, water quality in the area continues to be impaired.  Concentrations of dissolved arsenic and antimony generally increased from upstream to downstream  in the East Fork of South Fork of the Salmon River. Based on the  majority of arsenic  and antimony occurring in the  dissolved phase, and inverse relationships with streamflow  at most sites, the primary route of arsenic and antimony to surface waters is likely from groundwater.  Mercury, in contrast, was directly related to streamflow  and was associated with particulates,  suggesting erosion of surface materials to be the primary route to surface waters .

Based on the information in the passage, select the statement describing a likely Source of arsenic in the East Fork of the South Fork of the Salmon River and the statement describing a a likely Source of mercury in the East Fork of the South Fork of the Salmon River. Make only two selections, one in each column.

So based on what we see (key info in bold, ignoring rest of the fluff):
 Arsenic -  largely found upstream/ at the source and is very dissolvable   (C)  
 Mercury -  flows downstream and occurs via surface runnoffs   (A)

SKJapan · Answer

The Stibnite mining area was intermittently mined for most of the 20th century, and decades after mining ceased, water quality in the area continues to be impaired. Concentrations of  dissolved arsenic and antimony  generally  increased from upstream to downstream  in the East Fork of South Fork of the Salmon River. Based on the majority of arsenic and antimony occurring in the dissolved phase, and  inverse relationships with streamflow  at most sites, the primary route of arsenic and antimony to surface waters is likely from groundwater.  Mercury , in contrast, was  directly related to streamflow  and was associated with particulates, suggesting  erosion of surface materials  to be the primary route to surface waters.

From the bold parts we can conclude the following.

1. Dissolved concentration of arsenic and antimony increase from upstream (mouth of the river) to downstream.
So source upstream near river mouth. This pollutant gets more and more dissolved as river flows.

2. Inverse relationships with streamflow for arsenic and antimony :
Faster the flow -> Less dissolution -> Less arsenic concentration

3. For mercury directly related to streamflow :
Faster the flow more erosion -> More mercury concentration

4. Mercury erosion from surface (sediments)

The source of Arsenic likely be near upstream. 
 Headwater chemical infiltration (C)

The source of Mercury likely be downstream. 
 Downstream sedimentary erosion(A)

These two options explain streamflow and other characteristics.

leepcoast · Answer

I don't understand source of arsenic. Why chemical infiltration? other options also seem reasonable

chetan2u · Answer

The question has been archived and good quality questions have already been added to the GMAT Club tests. You can discard this.

The Stibnite mining area was intermittently mined for most of the 20th

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Source of arsenic	Source of mercury
		Downstream sedimentary erosion
		Upstream mining activities
		Headwater chemical infiltration
		Downstream mineral dissolution
		Upstream particulate contamination