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A 2007 toxicity report for the National Toxicology Program provided evidence that high doses of chromium 6 caused cancers of the gastrointestinal tract in rats and mice at levels higher than 5 mg/L of water, (5 ppm, or 5,000 ppb). [41] [42] Average hexavalent chromium levels in Hinkley were recorded at 1.19 ppb, with an estimated peak of 20 ppb.
The 580 ppb chromium(VI) in the groundwater in Hinkley exceeded the 100-ppb total chromium maximum contaminant level (MCL) set by the United States Environmental Protection Agency (EPA). [60] It also exceeded the California MCL of 50 ppb (as of November 2008 [update] ) for all types of chromium. [ 61 ]
Groundwater pollution (also called groundwater contamination) occurs when pollutants are released to the ground and make their way into groundwater.This type of water pollution can also occur naturally due to the presence of a minor and unwanted constituent, contaminant, or impurity in the groundwater, in which case it is more likely referred to as contamination rather than pollution.
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Erin Brockovich (née Pattee; born June 22, 1960) is an American paralegal, consumer advocate, and environmental activist who was instrumental in building a case against Pacific Gas & Electric Company (PG&E) involving groundwater contamination in Hinkley, California for attorney Ed Masry in 1993.
In 2011, the World Health Organization suggested a level of fluoride from 0.5 to 1.5 mg/L (milligrams per litre), depending on climate, local environment, and other sources of fluoride. [71] In the United States, the HHS's guideline has been set at 0.7 mg/L since 2011. [72] Bottled water typically has unknown fluoride levels. [73]
In the aquifer, groundwater flows from points of higher pressure to points of lower pressure, and the direction of groundwater flow typically has both a horizontal and a vertical component. The slope of the water table is known as the “hydraulic gradient”, which depends on the rate at which water is added to and removed from the aquifer and ...