1. Interpreting Median and Range from Area Well Samples
USGS groundwater sampling in St. Louis County's aquifer 111ALVM shows arsenic was detected in all four samples taken from two wells at depths between 25 and 80 feet on November 7, 2013. The median arsenic concentration was 3.35 micrograms per liter (µg/L), with values ranging from 2.5 to 4.2 µg/L. These figures represent measurements observed in the area, not a test result for any individual household well.
2. Comparing Measured Arsenic to Federal Thresholds
None of the samples exceeded the federal arsenic limit established for drinking water. While arsenic was detected in every sample, these concentrations fall below levels defined by federal standards. Detection indicates the presence of arsenic, not necessarily a safety concern or a compliance violation. It means instruments measured arsenic at low levels in this aquifer area.
3. What You Should Record Before Seeking Treatment Options
For an accurate assessment of arsenic in your household water, you need a certified laboratory test specific to your well. Keep a detailed report of your water source type, well depth if available, and any prior water quality results. This information is essential prior to considering treatment solutions, as arsenic levels can vary even within nearby areas of the same aquifer.
4. Differences Between Public System Records and Private Well Testing
Public water system records represent average regional data and compliance monitoring, but they do not reveal individual household water quality. Private wells require independent sampling to establish their specific arsenic content. The USGS sampling referenced here covers only a limited set of wells in the aquifer and timeframe.
5. Influence of Well Depth and Water Source Types on Arsenic Expectations
Variation in arsenic concentration often depends on well depth and water source characteristics. The USGS samples were from wells 25 to 80 feet deep; arsenic levels may differ in shallower or deeper wells. Knowing your well’s depth and source type helps anticipate potential arsenic presence and guides testing priorities.
6. Seasonal and Multi-Year Variation in Arsenic Occurrence
The USGS data reflects a single sampling date in 2013. Arsenic concentrations can fluctuate over time due to environmental factors. Regular testing over multiple seasons or years is advisable to understand trends and identify any changes that could affect treatment needs.
Conclusion: What Area Data Does Not Establish
Area-wide USGS arsenic measurements provide useful context but do not determine your household water’s arsenic status. Detection in regional aquifers does not mean your well water is unsafe or exceeds limits. Only certified testing of your own water can establish your arsenic levels. For addressing arsenic after existing equipment failure, the Pentair Arsenic Filter ships ready to configure and is designed specifically to reduce arsenic effectively when matched to your water conditions.
Where this information comes from
Source: USGS groundwater sampling. Sampled 2013-11-07. These figures describe groundwater sampled in this area. They are not a test of any individual private well - only a test of that well can establish its own water.
On record: U.S. Geological Survey sampling of Arsenic in the 111ALVM aquifer (St. Louis County): 4 results from 2 wells, median 3.35 ug/L, range 2.5-4.2 ug/L; none above any federal threshold
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