Agricultural Land-Use History in Bexar County and Its Correlation with 1,2,3-TCP Detections
The chlorinated solvent 1,2,3-trichloropropane (TCP) has origins linked to soil fumigants used primarily in agricultural applications from past decades. Bexar County's landscape, while largely urban and suburban today, includes regions where agricultural activities occurred historically. These former agricultural areas are important because TCP, a minor impurity in some soil fumigants, can persist in the environment and, over time, migrate into groundwater or surface water supplies. However, in Bexar County, the dominant water source is surface water managed by the San Antonio Water System, which has a history shaped by regional land use including agriculture but also urban development and watershed management.
Comparing California's 5 ng/L Limit with the Absence of a Federal Maximum Contaminant Level for 1,2,3-TCP
California has set a state-level advisory limit for 1,2,3-TCP at 5 nanograms per liter (ng/L), or 0.005 micrograms per liter (μg/L). This threshold aims to guide risk management without implying an enforceable standard nationally. By contrast, the United States Environmental Protection Agency (EPA) has not established a federal maximum contaminant level (MCL) for 1,2,3-trichloropropane. This means that while occurrence is monitored and reported as part of the Unregulated Contaminant Monitoring Rule (UCMR3), no federal health-based violation or enforceable limit applies. Lack of an MCL does not mean TCP levels are unsafe; it indicates that EPA continues to evaluate data to consider future regulation.
Interpreting the San Antonio Water System's Monitoring Record as a Homeowner
Between 2013 and 2015, the San Antonio Water System conducted federal occurrence monitoring for 1,2,3-TCP, analyzing 70 samples with a reporting threshold of 0.03 μg/L (parts per billion). None of these samples showed detections above that threshold. For a homeowner evaluating these findings, the median TCP concentration in these samples is effectively below the detection level, and no range of elevated values was observed. This record suggests that typical 1,2,3-TCP levels in the public water supplied to Bexar County residents were very low, within or below the sensitivities of federal monitoring equipment and well under California’s advisory level.
The Legacy of Soil Fumigant Impurities from the 1950s Through the 1980s Impacting Deep Groundwater Today
The presence of 1,2,3-trichloropropane in water sources arises mainly from impurities in soil fumigants used decades ago, primarily before stricter chemical regulations were enacted. These impurities percolated through soil layers and sometimes reached deep groundwater reservoirs. Although Bexar County’s public water relies on surface water sources, this historical contamination route explains why TCP appears sporadically in other regions’ groundwater. Understanding this legacy helps explain why regulatory agencies monitor TCP even if present concentrations remain low or undetectable in many systems.
Clarifying 'Detected,' 'Median,' and 'Range' in the EPA Sampling Record for 1,2,3-TCP
Within the EPA’s monitoring reports, 'detected' signifies that laboratory instruments found a measurable concentration above the method reporting level—in this case, 0.03 μg/L. However, detection does not equate to a safety violation or health risk; it is a quantitative measurement only. The 'median' is the midpoint value of all sample results, providing a central tendency indication but excluding nondetects. The 'range' shows the minimum to maximum values measured and helps capture variability. For Bexar County’s public system, no detected levels above reporting limits means the median and range reflect values below detection, reinforcing a low presence.
Deciding whether additional testing of household water is necessary hinges on knowing your specific water source. The regional data describe public supply quality but cannot confirm the exact composition of any individual home's water. Testing at a certified laboratory can identify personalized levels of 1,2,3-TCP or other constituents for informed decision-making.
When elevated 1,2,3-trichloropropane is found, treatment options using a Fleck 1,2,3-TCP Filter, which ships ready to configure, provide a documented method to address this chlorinated solvent effectively.
In summary, Bexar County’s public water system shows no detectable 1,2,3-TCP at levels above federal reporting thresholds according to EPA monitoring. Understanding this regional record and the nature of the contaminant supports homeowners in evaluating their water quality concerns and considering appropriate steps, including targeted laboratory testing and treatment if needed.
Where this information comes from
Source: EPA SDWIS public water system record. Sampled 2015-12-04. These figures describe the public water system's record, not the plumbing inside any individual building.
On record: EPA UCMR3 monitoring (2013-2015) for San Antonio Water System (TX0150018), TX: 70 results across 1 listed contaminants, 0 detections above the reporting level; nothing detected above the method reporting level