Joseph Harp Corr Inst

What it means: 2,4-Dichlorophenoxyacetic acid (2,4-D) is one of the most widely used herbicides in the world, applied to lawns, turf, pastures, and crops to control broadleaf weeds. It remains in active use in the United States. 2,4-D is water-soluble and can enter drinking water through agricultural and residential runoff and leaching into groundwater.

Health effects: Chronic exposure to 2,4-D is associated with kidney, liver, and adrenal gland damage in animal studies. IARC classifies it as possibly carcinogenic to humans (Group 2B); EPA's classification is not likely to be carcinogenic under current guidelines. Individuals with kidney or liver conditions may face greater risk from long-term exposure.

Limit: 0.07 mg/L (70 ppb)

What it means: This entry tracks violations of the Maximum Residual Disinfectant Level (MRDL) for chlorine — meaning too much disinfectant residual in the distribution system, not too little. Chlorine is added to water to kill pathogens, but excess residual can react with organic matter to form disinfection byproducts.

Health effects: Acute high-dose exposure to chlorinated water can cause eye and nose irritation, stomach discomfort, and nausea. Chronic exposure above the MRDL is primarily a concern because elevated chlorine accelerates formation of trihalomethanes and haloacetic acids, which are associated with increased cancer risk over time.

Limit: MRDL: 4.0 mg/L as an annual average

What it means: Radium-226 and Radium-228 are naturally occurring radioactive isotopes produced by the decay of uranium and thorium in bedrock. They dissolve into groundwater, particularly in deep aquifers with low oxygen and low pH. Granite bedrock and some deep sandstone and limestone aquifers present conditions where combined radium can reach detectable levels in drinking water.

Health effects: Radium is a bone-seeking radionuclide that accumulates in skeletal tissue after ingestion. Long-term exposure increases the risk of bone cancer and leukemia. There is no safe threshold for ionizing radiation — the MCL is set at a level balancing risk reduction with treatment feasibility. Children are particularly vulnerable due to higher rates of bone growth and calcium uptake.

Limit: 5 pCi/L (combined Ra-226 and Ra-228)

What it means: Uranium is a naturally occurring radioactive heavy metal found in rock and soil formations across the United States. It leaches into groundwater through weathering of uranium-bearing minerals, and is more prevalent in granite-rich and other uranium-bearing geologies. Mining and milling operations can also elevate uranium in nearby water supplies.

Health effects: Uranium poses both radiological and chemical health risks. Chronic exposure is primarily associated with kidney damage due to its chemical toxicity as a heavy metal. The radiological risk — increased cancer probability — is also present but secondary to the nephrotoxic concern at drinking water concentrations. There is no safe threshold for radiation exposure.

Limit: 0.030 mg/L (30 µg/L)

What it means: Diquat is a broad-spectrum contact herbicide used to control aquatic weeds, algae, and terrestrial vegetation. It remains in active use in the United States, applied directly to water bodies and irrigation canals. Diquat binds tightly to soil but can enter surface water directly during aquatic applications.

Health effects: Chronic exposure to diquat is associated with cataracts and kidney damage in animal studies. Acute high-level exposure causes gastrointestinal distress. EPA has not classified diquat as a human carcinogen. Individuals with kidney conditions may be at elevated risk from chronic exposure.

Limit: 0.02 mg/L (20 ppb)

What it means: Glyphosate is the most widely used herbicide in the United States, applied to crops, lawns, and roadsides. It is the active ingredient in Roundup and related products. It enters water through agricultural and urban runoff.

Health effects: Long-term exposure above the MCL is associated with kidney and reproductive damage in animal studies. EPA's current classification does not designate glyphosate as a human carcinogen, though IARC classifies it as probably carcinogenic (Group 2A). This classification remains a subject of active scientific and regulatory debate.

Limit: 0.7 mg/L (700 ppb)

What it means: Gross alpha particle activity is a screening measurement of all alpha-emitting radionuclides in water, excluding radon and uranium (which are regulated separately). If gross alpha exceeds 5 pCi/L, further analysis is required to identify specific radionuclides. Elevated gross alpha typically indicates water drawn from deep aquifers in contact with uranium- or thorium-bearing bedrock.

Health effects: Alpha-emitting radionuclides accumulate in bone and soft tissue, delivering sustained internal radiation doses that increase lifetime cancer risk. There is no established safe threshold for ionizing radiation. Individual contributors such as radium-226 and polonium-210 have their own MCLs; gross alpha serves as a cost-effective screening tool that triggers more specific radionuclide analysis when exceeded.

Limit: 15 pCi/L (excluding radon and uranium)

What it means: Gross beta particle activity is a screening measurement of beta-emitting radionuclides in water, such as strontium-90 and tritium. Monitoring is required mainly for systems the state designates as vulnerable to man-made radioactivity, for example those near nuclear facilities, and most systems test only every few years. When the screening level is exceeded the system must identify the individual radionuclides.

Health effects: Beta and photon emitters deliver a radiation dose when ingested. Long-term exposure increases the risk of cancer; strontium-90 concentrates in bone and tritium is distributed through body water. The limit is a dose-based standard rather than a concentration.

Limit: 4 millirem per year to the total body or any organ; a gross beta screening level of 50 pCi/L triggers identification of the specific radionuclides

What it means: The 2013 RTCR (effective 2016) replaced the original TCR. It triggers automatic E. coli testing whenever total coliform is found. A single E. coli-positive sample is an acute MCL violation. It also requires systems exceeding 5% total coliform-positive samples to conduct a formal assessment and correct any deficiencies, helping prevent contamination before it escalates.

Health effects: Total coliform bacteria indicate that the disinfection barrier has been breached or fecal contamination is entering the system. E. coli specifically indicates fecal contamination and the possible presence of disease-causing pathogens (norovirus, Salmonella, Shigella, Campylobacter). Illness can be severe in elderly, young children, and immunocompromised individuals.

Limit: Zero E. coli; ≤5% of monthly samples total coliform-positive