Total Trihalomethanes (TTHM)
Unresolved Total Trihalomethanes Rule violation cited in 2025 (total trihalomethanes (tthm)).
City · TRI 2024
San Marcos, Texas Pollution
3 TRI facilities inside the city limits and 3 public water systems serving residents. In-city TRI releases rose meaningfully year over year (+19%). Toxic releases concentrations have more than doubled since 2010.
FIPS 4865600 · population 67,143 · Hays County
Anomaly engine
Notable Signals
Pollutant pathways
San Marcos Pollutant Multi-Year Trends
Ozone 8-hour 4th-highest daily max (NAAQS 0.070 ppm (8-hour))Health riskGround-level ozone (smog) forms when vehicle and industrial emissions react in sunlight. Inflames the airways, triggers asthma attacks, and worsens heart and lung disease.
Single-vintage exposure modeling — EPA cadence is multi-year, so no trend line yet.
NO₂ annual mean (NAAQS 53 ppb (annual))Health riskA tailpipe and combustion gas. Concentrates near busy roads and industrial sites; raises risk of airway inflammation, asthma, and lower respiratory infections in children.
Single-vintage exposure modeling — EPA cadence is multi-year, so no trend line yet.
Lifetime cancer risk all pollutants (100 in a million (EPA elevated threshold))Health riskEPA-modeled added cancer cases per million residents from a lifetime of breathing local air toxics. EPA flags 100-in-a-million as elevated.
Single-vintage exposure modeling — EPA cadence is multi-year, so no trend line yet.
Formaldehyde ambient mean (0.077 µg/m³ (1-in-a-million URE))Health riskAn air toxic emitted by refineries, wood products, and combustion. EPA classifies it as a known human carcinogen — long-term inhalation raises cancer risk.
Single-vintage exposure modeling — EPA cadence is multi-year, so no trend line yet.
Benzene ambient mean (0.13 µg/m³ (1-in-a-million URE))Health riskAn air toxic from gasoline, refineries, and tobacco smoke. A known human carcinogen — chronic exposure is linked to leukemia and other blood cancers.
Single-vintage exposure modeling — EPA cadence is multi-year, so no trend line yet.
TRI air releases (5.1 fugitive + 5.2 stack)Health riskToxic chemicals reported by industrial facilities as released into the air — fugitive leaks plus smokestack emissions. Higher pounds means more inhaled exposure for nearby residents.
TRI air releases (5.1 fugitive + 5.2 stack) volumes here are too small to anchor a multi-year trend; YoY movement is still shown above.
TRI water releases (5.3)Health riskToxic chemicals reported by industrial facilities as discharged to surface waters (rivers, lakes, the ocean). Affects fishing, recreation, and downstream drinking-water intakes.
TRI water releases (5.3) volumes here are too small to anchor a multi-year trend; YoY movement is still shown above.
TRI land + off-site releasesHealth riskToxic chemicals released to land on-site or transferred off-site for disposal — landfills, deep-well injection, and similar. Risks groundwater contamination over time.
TRI land + off-site releases concentrations have fallen 30% since 2023.
Greenhouse gases (GHGRP large emitters, through 2023)Health riskGreenhouse gases reported by large industrial emitters under EPA's GHGRP, in metric tons of CO₂ equivalent. Drives climate warming and the heat-related health effects that follow.
Greenhouse gases (GHGRP large emitters, through 2023) concentrations are up 30% since 2010.
Top facilities · TRI 2024
Largest Emitters Inside The City
| Facility | Top chemical | Total releases | YoY |
|---|---|---|---|
| Epic PipingEpic Piping LLC | Xylene (mixed isomers)Health riskEye, skin, and respiratory irritant; central-nervous-system effects from chronic exposure. (EPA) | 12k lb | — |
| Collins Aerospace San MarcosRtx CORP | Nitric acidHealth riskStrong corrosive irritant to skin, eyes, and the respiratory tract. (NIOSH) | 1k lb | -90% |
| Pavestone - San Marcos Tx PlantQuikrete Holdings | LeadHealth riskNeurotoxin. Even low childhood exposure impairs cognitive development; chronic adult exposure damages kidneys and the cardiovascular system. (EPA, ATSDR) | 0 lb | -24% |
Drinking water · SDWIS
Water Systems Serving San Marcos
1 unresolved violation on the SDWIS record across utilities serving this city.
3
Utilities serving
116,522
Population served
1
Health-based · 5yr
1
Unresolved
| Water system | PWSID | Population served | Health-based · 5yr | Status |
|---|---|---|---|---|
| City Of San Marcos Municipal | TX1050001 | 72,970 | 1 | UNRESOLVED |
Showing the 1 system with recorded health-based or unresolved violations. 2 additional systems are in compliance with no recorded health-based violations in the past 5 years and are not individually tabulated.
A public water systemis the regulated entity, not the city. EPA's SDWIS definition covers anything serving 25+ people for 60+ days a year or with 15+ service connections — that includes municipal utilities (City of Stockton), water districts, mobile home parks operating their own wells, schools, and small private subdivisions. Each system is independently monitored. Some systems serve multiple cities; some cities are served by many systems.
Equity context · ACS 2018-2022 · USEPA-clone EJ disparity
Who Lives In San Marcos
San Marcos, Texas (Census place block groups): 67,143 residents. City disparity score for pm2.5 (fine particulate) sits well above the reference burden (158). Why we surface this →
27.7%
Low-income
55.1%
People of color
3.1%
Under age 5
9.4%
Over age 64
- PM2.5 (fine particulate)Health riskFine inhalable particles 2.5 micrometers or smaller. They travel deep into the lungs and into the bloodstream — linked to asthma, heart disease, stroke, and premature death.71above the national median
- OzoneHealth riskGround-level ozone (smog) inflames the airways. Even short exposures trigger asthma attacks and worsen chronic lung and heart disease.66above the national median
- Nitrogen dioxide (NO₂)Health riskA tailpipe and combustion gas. Concentrates near busy roads and industrial sites; raises risk of airway inflammation, asthma, and lower respiratory infections in children.66above the national median
- Diesel particulateHealth riskSoot from diesel engines (trucks, trains, ports, construction). EPA classifies it as a likely human carcinogen and a major driver of childhood asthma near freight corridors.46near the national median
- Toxic releases (RSEI)Health riskEPA's Risk-Screening Environmental Indicators score — weights TRI chemical releases by toxicity, where they go, and how many people are nearby. Higher means greater modeled cancer and chronic-health risk.18below the national median
- Traffic proximityHealth riskPopulation-weighted distance to high-volume roads. Living close to heavy traffic raises exposure to PM2.5, NO₂, and diesel exhaust — and the cardiovascular and asthma risks that follow.47near the national median
- Lead-paint risk (pre-1960 housing)Health riskShare of housing built before 1960, when lead-based paint was common. Dust from deteriorating paint is the leading cause of childhood lead poisoning, which permanently impairs cognitive development.47near the national median
- Superfund site proximityHealth riskPopulation-weighted distance to NPL Superfund sites — the most contaminated waste sites in the country. Nearby groundwater, soil, and air can carry industrial solvents, metals, and other long-lived contaminants.56near the national median
- RMP-facility proximityHealth riskDistance to facilities holding chemicals at quantities large enough to require an EPA Risk Management Plan (refineries, fertilizer plants, etc.). These pose acute exposure risk during accidental releases.47near the national median
- Hazardous-waste site proximityHealth riskDistance to RCRA hazardous-waste handlers (treatment, storage, disposal facilities). Indicates potential exposure to industrial chemicals in air, soil, and groundwater.50near the national median
- Underground storage tanksHealth riskDensity of underground tanks (gasoline, heating oil, industrial fluids). Leaking tanks are a leading source of benzene and other volatile organic compounds in groundwater drinking-water supplies.75above the national median
- NPDES wastewater proximityHealth riskDistance to permitted industrial wastewater dischargers. Closer proximity raises exposure to pollutants released into surface waters used for fishing, recreation, and downstream drinking-water intakes.23below the national median
- Drinking-water non-complianceHealth riskEPA score for public water systems with health-based Safe Drinking Water Act violations. Higher means more residents on systems that recently exceeded safe limits for contaminants like lead, arsenic, or nitrate.86in the highest 20% nationally
| Indicator | Disparity score | Reading |
|---|---|---|
| PM2.5 (fine particulate) | 158 | well above the reference burden |
| Ozone | 111 | moderately above the reference |
| Nitrogen dioxide (NO₂) | 140 | moderately above the reference |
| Diesel particulate | 102 | near the reference |
| Toxic releases (RSEI) | 39 | well below the reference |
| Traffic proximity | 100 | near the reference |
| Lead-paint risk (pre-1960 housing) | 61 | below the reference |
| Superfund site proximity | 0 | well below the reference |
| RMP-facility proximity | 102 | near the reference |
| Hazardous-waste site proximity | 108 | near the reference |
| Underground storage tanks | 138 | moderately above the reference |
| NPDES wastewater proximity | 27 | well below the reference |
| Drinking-water non-compliance | 57 | below the reference |
Source: Census ACS 2018-2022 (5-year) + USEPA-clone EJ blockgroup stats (raw indicators + EJ disparity mirror).
Health context
Co-Located Health Indicators
Modeled adult-prevalence estimates published by CDC PLACES, paired with this city's pollution and demographic context. Comparisons are ecological, not causal — pollution and disease prevalence covary at the area level, but the data does not attribute any individual's diagnosis to local exposure. How this section works →
Adult asthma (current)
10.5%
CDC PLACES · 2025 release · BRFSS 2022-2023
COPD prevalence
4.4%
CDC PLACES · 2025 release · BRFSS 2022-2023
Coronary heart disease
3.6%
CDC PLACES · 2025 release · BRFSS 2022-2023
Diabetes (diagnosed)
7.9%
CDC PLACES · 2025 release · BRFSS 2022-2023
Frequent mental distress
22.3%
CDC PLACES · 2025 release · BRFSS 2022-2023
PLACES uses BRFSS-modeled small-area estimates, not individual records. Crude prevalence shown above is the local rate as published; comparators are age-adjusted vs the Texas mean and the US mean — both population-weighted across counties — so geographies with different age structures stay apples-to-apples. Sources: CDC PLACES · 2025 release · BRFSS 2022-2023.
Sources.
- EPA Toxics Release Inventory · retrieved 2026-05-07.
- EPA Safe Drinking Water Information System · retrieved 2026-05-07.