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Shallow Groundwater Contaminants Within Established Limits


In previous posts I have reported on impaired surface waters, the nature of surface water contaminants, and contamination of groundwater from hazardous waste sites. In this post I will focus on the purity of Missouri’s shallow ground water resources.

Shallow groundwater is the source of drinking water for many people in Missouri. Virtually all self-supplied water comes from shallow sources. In addition, many communities, even large ones such as St. Joseph, Independence, Columbia, and St. Charles, source their drinking water from shallow alluvial wells near rivers. Some shallow water sources are unconfined – that is, they are not surrounded by impermeable rock formations. Thus, contaminants can potentially seep into the water sources if they have the chance.

The most widespread source of potential contamination is farming. The USDA indicates that about 28,900,000 acres  (65%) of Missouri land is in farms. Slater & Ferrand estimated that in 2000 about 2 million pounds of fertilizer and pesticide were consumed in Missouri, and USDA data suggest that national consumption did not changed substantially between 2000 and 2010. Thus, it is probably safe to assume that around 2 million pounds of fertilizer are applied to about 29 million acres of Missouri land each year.

Concerns arose that fertilizers and pesticides could seep into groundwater supplies. Ironically, a well is itself a hole in the ground, and if it is not sealed properly, it could provide a path for contamination to seep into the groundwater at the very point where it would be pulled into the water supply by the well pump.



In 2006, the Missouri Department of Natural Resources and Department of Agriculture cooperated to study whether this problem was occurring in Missouri. They identified 76 counties at the highest risk because of the nature of the groundwater and overlying geology. They then collected 351 samples from 190 different wells, and checked for the presence of four common herbicides: Atrazine, Alachlor, Metachlor, and Simazine. For each the EPA has established Maximum Concentration Levels (MCL) beyond which its presence in water supplies is hazardous. The collection sites are shown in the map at right.

None of the chemicals were found in any of the wells at levels above the EPA MCL. The chemicals were found at detectable levels below the EPA MCL in only four wells (out of 190). In each case, the source of the chemical could be traced to farming activities nearby. In the remaining wells, the four chemicals were not detected.

For the 2010-2012 period, the DNR has monitored contaminants in unconsolidated aquifers along the Mississippi, Missouri, Grand, and Nodaway Rivers. The Water Quality Report (Section 305(b) Report), 2012 reports the findings for seven randomly selected water supply wells: Elsberry, Independence, Lagrange, Mattland, Missouri American Brunswick, Missouri American St. Joseph, and Mound City. The data are presented in the table at right. The table shows 31 chemicals/characteristics that affect water quality. Aquifer DataEvery chemical is tested at at least one of the water supply wells, but none were tested at all of them. No water supply well reported data for every chemical, while one well reported data for only two chemicals, and two wells reported data for only one chemical. In fact, of the 217 cells in the table, only 50 contain data (I’ve marked them pink), the remainder are marked “Not Reported.”

EPA has not established MCLs for only some of the chemicals. For those it has, some of the MCLs are simple concentrations that can be easily compared to the values reported in the table. I have added those as a 9th column to the table. None of the values reported in the table exceed their MCL in the 9th column. In saying this, however, it is important to bear in mind that data was reported for less than 1/4 of the cells in the table, and I added MCLs for only some of the chemicals.


Missouri Water Quality Report (Section 305(b) Report), 2012, Water Quality Program, Missouri Department of Natural Resources, http://www.dnr.mo.gov/env/wpp/waterquality/305b/index.html.

For fertilizers and Pesticides consumed in Missouri:  Slater, Joseph, & Farrand, Todd. (2001). Fertilizer Use in Southern Missouri. FAPRI-UMC Report #14-01. http://www.fapri.missouri.edu/outreach/publications/2001/FAPRI_UMC_Report_14_01.pdf.

For changes in U.S. consumption of fertilizer: Fertilizer Use, USDA Economic Research Service, http://www.ers.usda.gov/data-products/fertilizer-use-and-price.aspx#.UUcv9RlLq_5.

For Missouri land in farms: State Agriculture Overview, Missouri. USDA, http://www.nass.usda.gov/Statistics_by_State/Missouri/index.asp.

For MCLs of drinking water contaminants: Drinking Water Contaminants, EPA, http://water.epa.gov/drink/contaminants/index.cfm#3.

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