PHLT 8034 Week 4 Uranium Well Pathway Analysis Example

From Granite to the Kitchen Tap: A Source-Pathway-Receptor Analysis of Uranium in Private Wells for a Composite Rural Township, With Every Link Graded

Student Name

Walden University

PHLT 8034: Environmental Health

Instructor Name

Month Day, Year

From Granite to the Kitchen Tap: A Source-Pathway-Receptor Analysis of Uranium in Private Wells for a Composite Rural Township, With Every Link Graded

Purpose and Frame

This paper traces naturally occurring uranium from bedrock to the people who drink well water in a composite rural township of about 3,000 residents, almost all of whom rely on private domestic wells. It follows the source-pathway-receptor model literally, one section per link, and ends each section with an evidence grade: established, meaning documented for this kind of setting by direct measurement; probable, meaning supported by regional evidence and known mechanisms but not confirmed locally; or assumed, meaning plausible but resting on no evidence specific to the township. The paper invents no concentrations. Its purpose is to show which links are secure and which one most needs evidence before anyone can say whether a given household is exposed.

Source: Uranium in the Bedrock

The township sits on granitic bedrock with pegmatite veins, rock types that commonly carry more uranium than average crustal rock. Uranium in these minerals is largely locked in place while conditions underground are oxygen-poor. It becomes mobile when oxygen-rich water moves through fractures and converts it to a soluble form, and dissolved bicarbonate then holds it in solution as stable complexes. National sampling has linked uranium in groundwater to these geochemical conditions, and to nitrate from agriculture, which can promote oxidation and release (Nolan & Weber, 2015).

The grade for the source is probable. The rock type is known from state geological maps, and the mechanism is well understood, but the uranium content of the township's particular bedrock has not been measured. Granites vary widely, and some carry little.

Pathway, First Stage: Into the Aquifer

Domestic wells in the township draw from fractured bedrock rather than from sand and gravel. Water moves along fractures, and its contact time with uranium-bearing minerals depends on how connected those fractures are and how fast water travels. Two features raise the likelihood of dissolved uranium: long contact with granite and the presence of oxidizing, bicarbonate-rich water, especially where fertilizer use adds nitrate. Federal surveys of principal aquifers found uranium among the naturally occurring constituents most often exceeding human health benchmarks in untreated groundwater, with granitic and crystalline-rock aquifers prominent among them (DeSimone et al., 2014).

The grade for this stage is probable. Regional evidence and mechanism support it, but the township's aquifer chemistry, including its bicarbonate and nitrate levels, is unknown.

Pathway, Second Stage: From Aquifer to Tap

This is the link that matters most and the one least known. Each well intercepts different fractures, so uranium in neighboring wells can differ greatly even where the regional aquifer carries it. Unlike a public water system, which must meet a federal limit for uranium and test for it (National Primary Drinking Water Regulations; Radionuclides; Final Rule, 65 Fed. Reg. 76708, 2000), a private well falls under no testing requirement. In the composite township, no program tests private wells, and uranium is not on the standard bacteria-and-nitrate panel that local laboratories offer at home sales. The uranium content of any given household's tap water is therefore unknown until that household requests a specific test. Water softeners and sediment filters common in the township do not reliably remove uranium; only certain treatment systems, such as reverse osmosis or anion exchange, are designed to.

The grade for the aquifer-to-tap link is assumed. Regional surveys show that some wells in similar geology carry uranium, but they cannot say which wells, and letting a regional finding stand in for an individual tap would overstate what is known.

Receptor: Who Uses the Water, and How

Once water reaches the tap, household use determines intake. Drinking water is the main route, since uranium is absorbed through the gut; absorption is low, roughly one or two percent of what is swallowed, but continuous over years. Cooking adds intake when water is absorbed into food, as with rice, pasta and soups. Infant formula mixed with tap water matters because infants drink more water relative to body weight than adults do. Bathing and showering contribute little, because uranium is not volatile and is poorly absorbed through skin.

Two populations deserve note. Infants fed formula made with well water take in more per kilogram than anyone else in the household. Long-term residents accumulate the longest exposure. The principal concern from uranium in drinking water is chemical damage to the kidney rather than radiation, and a study of Finnish well users found associations between uranium intake and markers of altered kidney tubule function (Kurttio et al., 2002). A review of the wider literature reached similar conclusions while noting that private well users and some tribal communities carry a disproportionate share of exposure (Corlin et al., 2016).

The grade for the receptor link is established for the routes of use and probable for the effect. Household water use and gut absorption are well documented. The kidney effects are supported by consistent studies, but how they translate to the levels a township well might carry cannot be judged without measured concentrations.

The Chain Graded

The weakest link is the step from aquifer to tap. Everything upstream makes uranium in some wells likely, and everything downstream makes intake certain if uranium is there, but no evidence connects the two for any particular household. That gap is also the cheapest to close: a uranium test at a certified laboratory would move the link from assumed to established, or remove the chain entirely, for that home.

Table 1

Evidence Grades for Each Link in the Uranium Pathway

Note. Grades apply to the composite township and are the author's judgment against the definitions stated in the opening section.

References

Corlin, L., Rock, T., Cordova, J., Woodin, M., Durant, J. L., Gute, D. M., Ingram, J., & Brugge, D. (2016). Health effects and environmental justice concerns of exposure to uranium in drinking water. Current Environmental Health Reports, 3(4), 434-442. https://doi.org/10.1007/s40572-016-0114-z

DeSimone, L. A., McMahon, P. B., & Rosen, M. R. (2014). The quality of our Nation's waters: Water quality in principal aquifers of the United States, 1991-2010 (Circular 1360). U.S. Geological Survey. https://doi.org/10.3133/cir1360

Kurttio, P., Auvinen, A., Salonen, L., Saha, H., Pekkanen, J., Makelainen, I., Vaisanen, S. B., Penttila, I. M., & Komulainen, H. (2002). Renal effects of uranium in drinking water. Environmental Health Perspectives, 110(4), 337-342. https://doi.org/10.1289/ehp.02110337

National Primary Drinking Water Regulations; Radionuclides; Final Rule, 65 Fed. Reg. 76708 (2000).

Nolan, J., & Weber, K. A. (2015). Natural uranium contamination in major U.S. aquifers linked to nitrate. Environmental Science & Technology Letters, 2(8), 215-220. https://doi.org/10.1021/acs.estlett.5b00174