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Government groundwater sampling in San Juan County for aquifer N300COPLTS reports arsenic was detected in some tested wells but remained below federal arsenic thresholds in all samples.
1. Interpreting median and range values as a homeowner
Median arsenic concentration value
The median concentration measured among wells was 4.2 micrograms per liter (ug/L), meaning half of the samples had arsenic levels above and half below this figure.
Range of detected arsenic levels
Individual wells showed a range from 1.9 ug/L to 8.6 ug/L across the sampled locations, indicating variability in arsenic presence within the area.
Sampling scope
These results come from 61 samples collected over 13 different wells between 2012 and 2025, with wells typically between 32 and 52 feet deep.
2. Clarifying terms in the sampling record
Detected arsenic explained
Arsenic detected means it was measured above laboratory reporting limits but does not imply the water is unsafe or exceeds any regulatory limit.
Median interpretation
The median is a middle value that summarizes the distribution of data points but does not predict arsenic levels at individual wells.
Range significance
The range shows the minimum and maximum detected values but does not indicate that any single well is representative of all wells or household water.
3. Comparing San Juan County with neighboring regions
Regional variability of arsenic presence
Arsenic levels can differ across areas; this aquifer's median and range reflect local groundwater quality and may vary from those in adjacent counties.
Importance of local sampling
Comparisons should account for differences in well depth, geology, and sampling methods to avoid overgeneralizing from regional data.
Avoiding assumptions
Government area-wide sampling does not establish conditions for private wells, which require individual testing for accurate water quality assessment.
4. Understanding certified laboratory arsenic testing
What testing reports show
Laboratory tests provide specific concentration results for individual water samples; these tests are required to assess personal water safety accurately.
Interpreting test figures
Reports quantify arsenic in micrograms per liter and indicate whether levels are below detection limits or at measurable concentrations.
Testing frequency recommendation
Periodic laboratory testing is recommended to monitor arsenic levels over time and confirm if treatment is necessary.
5. Effects of untreated arsenic in household water
Long-term exposure concerns
Consistent exposure to arsenic above regulatory levels may have health implications, but the San Juan County aquifer data show no federal threshold exceedances.
Symptoms are not apparent from water quality alone
Arsenic presence is not linked to taste, odor, or appearance; testing is the only way to determine arsenic content reliably.
Role of treatment options
When needed, properly selected filtration systems can reduce arsenic in household water to levels below established limits.
6. Fixtures and processes affected first by arsenic presence
Primary water use points
Water used for drinking and cooking is the most critical pathway for arsenic exposure, making treatment at the point of entry or point of use important.
Appliance considerations
Arsenic does not typically damage appliances but can influence water quality where treatment is absent.
Routine monitoring importance
Regular water testing can help detect changes in arsenic levels affecting household consumption points.
These findings are based on 61 groundwater samples from 13 wells in San Juan County aquifer N300COPLTS taken over 2012 to 2025, as documented by the U.S. Geological Survey. For additional details, consult the official government groundwater database.
If arsenic treatment is part of your household water management plan, the Pentair Arsenic Filter ships ready to configure and is designed to address arsenic presence effectively when used following your water test results.
Where this information comes from
Source: USGS groundwater sampling. Sampled 2025-09-18. 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 N300COPLTS aquifer (San Juan County): 61 results from 13 wells, median 4.2 ug/L, range 1.9-8.6 ug/L; none above any federal threshold