[ggreer]

Hexavalent chromium can come from many industrial sources, including welding stainless steel. If you go to Tesla's lithium refinery in google maps[1] and follow the drainage ditch along highway 77 (to the northeast) about a half mile, you'll see a company called Tex-Isle Processing. They supply steel pipes and coating services for oil drilling.[2] It could be that one of their manufacturing processes creates hexavalent chromium.

In my opinion there isn't enough information to blame anyone for the slightly-above-drinking-water levels of hexavalent chromium. The drainage ditch goes along a highway and a rail line, so pollution could come from all kinds of places.

1. https://maps.app.goo.gl/7iNTbiPcs1sZ9CqP8

2. https://www.texisle.com/

[bloaf]

Something else to note:

The lab tested for chromium in two ways: one test (ICP) measures all chromium of any kind, and the other measures hexavalent chromium specifically. The ICP test returned a concentration that was an order of magnitude smaller than the hexavalent test (0.0003 vs 0.0104 mg/L). That is to say, the tests contradict each other (because the whole is smaller than the part).

https://www.documentcloud.org/documents/28055380-j2673-1-uds...

[xg15]

Ok, that's one of the pollutants...

But I agree, measuring at the end of the ditch was the wrong thing to do if they take issue with that specific factory (though it was the right thing to do to prove a harmful pollution exists in general)

So another measurement directly at the pipe would be in order.

[ggreer]

The measured levels of arsenic, strontium, and vanadium are below the limits for drinking water, even in California. And 4% of drinking water sources in California have higher hexavalent chromium content than the water in that ditch.[1] Besides sodium from salt, the only metal that was particularly high was lithium, at 0.0714mg/L or 71 micrograms per liter. A significant fraction of drinking water in the US has higher concentrations than that.[2]

The level of salt shouldn't affect much. Adding up the chloride and sodium content gets you 684mg/L, which is on the low end of brackish water (500-30,000mg/L). The limit for agricultural irrigation is 2,000mg/L, and photos of the pipe show plenty of grass growing around and in the water.

The phosphorous could come from fertilizers, as there's plenty of farm land in the area. That would also explain the higher ammonium levels, as both anhydrous ammonia and ammonium phosphate are common fertilizers.

The article is really about how sensitive our scientific instruments are, not how dangerous the water is. It reminds me of articles like Vice's American Honey Is Radioactive from Decades of Nuclear Bomb Testing[3], where the most radioactive honey they could find was 10 times less radioactive than a banana.

1. https://www.waterboards.ca.gov/drinking_water/certlic/drinki...

2. https://www.sciencedirect.com/science/article/abs/pii/S00489...

3. https://news.ycombinator.com/item?id=26906838