Understanding 1,2,3-TCP in Hillsborough's Merrimack Water Supply: A Step-by-Step Guide

When considering water quality concerns, data from regional water systems provide valuable but limited perspectives. The measurements taken by government agencies such as the EPA reflect water characteristics of the public supply system, not the water at any specific home or well. Understanding what the detection of 1,2,3-trichloropropane (1,2,3-TCP) in Merrimack's water means—and does not mean—helps residents make informed decisions about their household water management.

1. How a Soil Fumigant Impurity from the 1950s-1980s Reached Deep Groundwater Decades Later

1,2,3-trichloropropane is a chlorinated solvent historically used as a byproduct or impurity in soil fumigants and industrial chemicals from the mid-20th century. Though no longer produced or used widely, this compound's persistence in the environment is notable. Over the decades, it can migrate downward through soils into deep groundwater aquifers, especially in areas with agricultural or industrial histories similar to Merrimack in Hillsborough County, NH. This slow movement explains why detections can appear long after cessation of use.

2. Why the Reporting Level for This Solvent Is Thousands of Times Lower than for Common Metals

The EPA's monitoring for TCP has a very low reporting threshold of 0.03 micrograms per liter (µg/L), or parts per billion (ppb), which is far more sensitive than many other contaminant tests. This low detection limit is due to the compound's potential toxicity and the need for precaution. As a result, even trace measurements below any federal enforceable level must be recorded, but they do not signal safety breaches or violations.

3. How the Constituent Enters Groundwater or the Distribution System in This Region

In Merrimack, NH, the public water supply comes from groundwater sources. The legacy presence of TCP in deep aquifers can occasionally lead to trace detections during federal monitoring cycles. Because the Merrimack Village District water system uses groundwater, any substances present in these aquifers can enter the distribution system, though rigorous treatment and testing are designed to maintain health-based standards.

4. What 'Detected', 'Median' and 'Range' Mean in the Sampling Record on This Page

EPA UCMR3 sampling from 2013 to 2015 for Merrimack’s system reported eight sample results for 1,2,3-TCP. None showed TCP detected above the reporting level of 0.03 µg/L, meaning the instrument did not measure TCP concentrations above this threshold in any sample. The terms 'detected', 'median', and 'range' reflect measured values during monitoring but do not indicate violations or health risks. A 'non-detected' result means the test found no measurable TCP above the reporting limit in those samples.

5. What the Measured Range Means Against the Relevant Federal Standard, and What It Does Not Mean

Merrimack Village District has no health-based violations related to 1,2,3-trichloropropane, consistent with EPA records showing zero breaches of maximum contaminant levels (MCLs) because no MCL for TCP currently exists. The absence of reported TCP detections above reporting limits means the system's water meets all applicable health-based federal standards. However, individual homes may have specific water profiles, so home water testing is necessary to establish actual concentrations in any specific tap or well.

For residents wishing to address the potential presence of 1,2,3-TCP in household water, specialized filtration equipment such as the C-Series 1,2,3-TCP Filter ships ready to configure and is designed specifically to address this chlorinated solvent. This technology can supplement municipal water by targeting low-level TCP to provide additional peace of mind. Testing your own household water is the crucial first step to determining the need for such treatment.

Where this information comes from

Source: EPA SDWIS public water system record. Sampled 2015-06-15. These figures describe the public water system's record, not the plumbing inside any individual building.

On record: EPA UCMR3 monitoring (2013-2015) for Merrimack Village District (NH1531010), NH: 8 results across 1 listed contaminants, 0 detections above the reporting level; nothing detected above the method reporting level