1,2,3-Trichloropropane in San Fernando Valley Water: California's Unique Standard and the Aerospace Contamination History Behind It

California is the only U.S. state to set a drinking water standard specifically for 1,2,3-trichloropropane, a synthetic chlorinated compound classified as a probable human carcinogen. The California State Water Resources Control Board established a maximum contaminant level of 5 parts per trillion in December 2017, after California scientists identified the chemical as a cancer-causing agent decades earlier. In the San Fernando Valley, 1,2,3-TCP is not a legacy agricultural issue. It traces primarily to the defense and aerospace manufacturing corridor that operated across the northern Valley from the 1940s through the late twentieth century. The Burbank Operable Unit, a federal Superfund cleanup project covering parts of Burbank and North Hollywood, was the site where state water quality regulators first flagged TCP contamination in groundwater in 1999, leading directly to California's notification level and eventually its first-in-nation MCL. Los Angeles County data published by the SWRCB shows 51 public water system sources with confirmed TCP detections at concentrations above the 5 ppt MCL.

The SFV carries one of the most documented industrial groundwater contamination histories of any metropolitan basin in California. Articles elsewhere on this site cover the VOC and TCE contamination from aerospace-era operations, hexavalent chromium in SFV groundwater, and perchlorate from rocket propellant operations. 1,2,3-TCP deserves its own treatment because it triggered a regulatory first: California became the only jurisdiction in the country to set an enforceable limit for the compound, a milestone driven in part by SFV contamination data. This article assembles the publicly available SWRCB, EPA, and USGS data to give SFV homeowners a factual baseline on what the standard means and what the local exposure history looks like.

What is 1,2,3-trichloropropane and how does it differ from other VOCs in SFV groundwater?

1,2,3-trichloropropane is a synthetic chlorinated solvent that does not occur naturally in the environment. Unlike trichloroethylene (TCE) and perchloroethylene (PCE), which the SFV's VOC contamination article covers in detail, TCP was not primarily used as an industrial degreaser. In the San Joaquin Valley, it entered groundwater as an impurity in D-D soil fumigant, a pesticide product used in agriculture from the 1940s through the 1980s. In the San Fernando Valley and other Southern California industrial corridors, TCP appears at Superfund sites tied to aerospace manufacturing and defense operations.

The compound was listed on California's Proposition 65 registry of carcinogens in 1992, more than two decades before a drinking water standard took effect. The California Office of Environmental Health Hazard Assessment established a public health goal (PHG) of 0.0007 parts per trillion for TCP in August 2009, based on a lifetime cancer risk assessment. The PHG is not enforceable; it represents the concentration at which no significant health risk is anticipated over a lifetime of exposure. The enforceable MCL of 5 parts per trillion, adopted in 2017, sits substantially higher than the PHG, reflecting the limit of reliable laboratory detection technology at the time of rulemaking rather than a judgment that concentrations above 0.7 ppt are safe.

California's drinking water standard for TCP: what the numbers mean

The California State Water Resources Control Board adopted the MCL for 1,2,3-TCP in July 2017, with compliance monitoring beginning January 1, 2018. The standard applies to all community water systems and nontransient noncommunity water systems in California, the same universe of public water systems covered by all primary drinking water standards. Private well owners are not covered by the MCL; they are responsible for their own testing and treatment. The SWRCB's TCP regulatory page at waterboards.ca.gov documents the full regulatory history and current compliance monitoring requirements.

The cancer risk associated with TCP at the 5 ppt MCL has been calculated at approximately 1 in 142,857 over a lifetime of exposure, based on the state's risk assessment framework. The PHG of 0.0007 ppt corresponds to a theoretical excess cancer risk of 1 in 1,000,000. The gap between the two figures reflects a common pattern in California drinking water regulation: the PHG is set at a health-protective ideal, while the MCL is set at what is technically and economically feasible to achieve through treatment and monitoring. For a broader look at how California sets these two-tier standards for other SFV contaminants, see the arsenic PHG vs. MCL analysis and the overview of California drinking water rules in 2026.

The Burbank Operable Unit: how aerospace manufacturing introduced TCP to SFV groundwater

The San Fernando Valley's encounter with 1,2,3-TCP in its public water supply traces directly to the Burbank Operable Unit, one of three contamination zones that make up the San Fernando Valley Superfund site. The EPA established the site in 1986, documenting releases from aerospace and defense manufacturing facilities operated by Lockheed and Honeywell in the corridor running through Burbank and into North Hollywood. Those facilities used and stored chlorinated solvents and other industrial compounds over decades of operation, releasing them into the underlying alluvial aquifer.

In 1999, California water quality regulators detected 1,2,3-TCP specifically at the Burbank Operable Unit, which led the SWRCB to establish its original notification level of 5 ppt for the compound that year. It was the discovery at this SFV site that first put TCP on California's regulatory agenda. The EPA's Superfund site profile for San Fernando Valley Area 1, documented at cumulis.epa.gov, shows the Burbank Operable Unit cleanup system operates at a capacity of 9,000 gallons per minute around the clock, treating contaminated groundwater extracted from the aquifer before it reaches distribution systems. Lockheed Martin was ordered to fund the cleanup under EPA authority.

The contamination pathway in the SFV is distinct from the agricultural pathway that dominates Central Valley TCP contamination. In the San Joaquin Valley, TCP entered groundwater primarily as an impurity in D-D soil fumigant applied to farmland. In the SFV, the source is industrial: solvent storage, disposal practices, and operational releases at aerospace manufacturing and testing facilities that operated across the northern Valley from the 1940s through the 1980s. The same industrial era that introduced TCE, PCE, and 1,4-dioxane to the SFV aquifer, documented in the SFV VOC and groundwater remediation article, also introduced TCP. The perchlorate contamination from Rocketdyne and other propellant operations originates from the same era and the same corridor.

What the statewide data shows about TCP detection rates and Los Angeles County

A USGS Groundwater Ambient Monitoring and Assessment (GAMA) study, the findings of which are published at pubs.usgs.gov, sampled 1,237 wells across California and detected 1,2,3-TCP in 6.5 percent of them. Detection rates differed by well type: approximately 8 percent of domestic wells and 5 percent of public supply wells showed TCP at any concentration. The highest detection rates occurred in the San Joaquin Valley, where TCP exceeded the 5 ppt MCL in 16 percent of USGS-sampled wells and 18 percent of Division of Drinking Water monitoring wells, driven primarily by the agricultural fumigant history of that region.

Statewide, the SWRCB has documented 569 public water system sources across 30 counties with confirmed TCP detections above the 5 ppt MCL. Los Angeles County accounts for 51 of those sources, placing it third behind Kern County (110 sources) and Fresno County (64 sources). The SWRCB regulatory summary notes that Southern California's TCP detections trace primarily to industrial and defense-aerospace activity rather than the agricultural fumigant use that dominates the Central Valley pattern. The source water blending practices that LADWP uses to manage its SFV supply, described in the LADWP source water blend article, are directly relevant here: treated groundwater from the SFV basin is blended with imported aqueduct water before delivery, which dilutes contaminant concentrations from any single source.

Does LADWP monitor for TCP in finished water delivered to SFV taps?

LADWP monitors for a comprehensive suite of volatile organic compounds in its finished water and reports the results annually in its Consumer Confidence Report, available through the utility's drinking water quality page. The monitoring program covers the compounds for which California has set MCLs, including 1,2,3-TCP since compliance monitoring began in January 2018. LADWP's 2024 Drinking Water Quality Report, published in July 2025, states that the utility met all 106 regulated substance MCLs. Customers can review the full monitoring results tables through the utility's reporting infrastructure at ladwp.com.

For SFV homeowners, the practical context is that LADWP treats groundwater before blending it into the distribution system. The treatment plant and extraction well network at the North Hollywood Operable Unit is specifically designed to remove VOCs, including chlorinated solvents, before that groundwater fraction reaches the distribution network. Finished water delivered to SFV taps is a blend of treated local groundwater and imported aqueduct supply. Depending on neighborhood and season, the groundwater fraction in that blend varies, as the SFV source water blend article explains. For broader context on SFV water quality, see the SFV utility water quality comparison and the water quality overview.

What filtration reduces 1,2,3-TCP in drinking water?

Granular activated carbon (GAC) is the primary treatment technology water utilities deploy to reduce 1,2,3-TCP in source water. Cal Water, which operates in multiple California service areas with TCP-affected groundwater, built GAC treatment facilities specifically to address TCP after the MCL took effect. GAC adsorbs the compound onto the carbon surface, removing it from the water stream before it reaches the distribution system. At the point of use, reverse osmosis systems certified to NSF/ANSI 58 can reduce volatile organic compounds including 1,2,3-TCP. Activated carbon block filters certified to NSF/ANSI 53 for VOC reduction also address chlorinated compounds in this chemical class.

For SFV homeowners on LADWP supply, the utility's treatment infrastructure is the primary line of defense for TCP and other VOCs. A point-of-use reverse osmosis system at the kitchen tap provides an additional reduction layer and addresses the full spectrum of contaminants documented in LADWP monitoring: TCP alongside PFAS compounds, arsenic, disinfection byproducts, and hexavalent chromium. For homes with private wells in unincorporated SFV areas, TCP testing is the responsibility of the well owner, and a state-certified laboratory test is the only way to know what concentrations are present. The private well testing guide for the SFV covers the testing protocol in detail.

UpTown Cares installs whole-house and point-of-use filtration systems across the full SFV service area, selecting configurations based on what water testing at each home actually shows. For an overview of how these systems work for SFV water chemistry, see how whole-house filtration works for SFV water and the main whole-house water filtration guide for the Valley.

What is 1,2,3-trichloropropane (TCP) and why does it matter for San Fernando Valley water?

1,2,3-trichloropropane is a synthetic chlorinated compound classified as a probable human carcinogen by California's Proposition 65 program since 1992. In the San Fernando Valley, it entered the underlying groundwater primarily through aerospace and defense manufacturing operations that operated across the northern Valley from the 1940s through the 1980s. California is the only U.S. state that has established an enforceable drinking water limit for TCP, set at 5 parts per trillion in December 2017.

Is 1,2,3-TCP regulated in California drinking water?

Yes. The California State Water Resources Control Board adopted a maximum contaminant level (MCL) of 5 parts per trillion for 1,2,3-TCP, effective January 2018. Community water systems are required to monitor for TCP and must take corrective action if finished water exceeds the MCL. California remains the only state in the U.S. with an enforceable MCL for this compound. The federal EPA has not established a national MCL for 1,2,3-TCP as of 2026. Details are published at waterboards.ca.gov.

How many Los Angeles County water system sources have exceeded the TCP limit?

The California State Water Resources Control Board reports 51 public water system sources in Los Angeles County with confirmed 1,2,3-TCP detections above the 5 ppt MCL since compliance monitoring began in January 2018. Statewide, 569 sources across 30 counties have had MCL exceedances. Los Angeles County's detections are linked primarily to industrial and aerospace-era contamination, distinct from the agricultural fumigant history that dominates the Central Valley contamination pattern.

Where was 1,2,3-TCP first detected in Southern California?

California regulators first identified 1,2,3-TCP at the Burbank Operable Unit, part of the San Fernando Valley Area 1 Superfund site covering portions of Burbank and North Hollywood. The 1999 discovery led the California SWRCB to establish its initial notification level for the compound. The Burbank Operable Unit cleanup, ordered by the EPA in 1986, targets contamination from Lockheed and Honeywell aerospace manufacturing operations and treats up to 9,000 gallons per minute of extracted groundwater before it can reach drinking water supplies.

Does LADWP test for TCP in water delivered to San Fernando Valley taps?

Yes. LADWP monitors for 1,2,3-TCP as part of its volatile organic compound compliance monitoring program, which began in January 2018 when the California MCL took effect. Results are published annually in the utility's Consumer Confidence Report and monitoring results tables, available at ladwp.com. LADWP's 2024 Drinking Water Quality Report states that the utility met the MCL for all 106 regulated substances monitored that year, including TCP.

What filter removes 1,2,3-TCP from tap water at home?

Reverse osmosis systems certified to NSF/ANSI 58 reduce volatile organic compounds including 1,2,3-TCP at the point of use. Activated carbon block filters certified to NSF/ANSI 53 for volatile organic compound reduction also address this compound class. Granular activated carbon is the technology that California water utilities, including those affected in the San Joaquin Valley, have deployed at the treatment plant level to meet the 5 ppt MCL. For SFV homeowners on LADWP supply, utility treatment is the primary layer of protection; a point-of-use RO unit provides an additional reduction layer.

Last updated: September 1, 2026. For the most current LADWP monitoring data on 1,2,3-TCP and other volatile organic compounds, visit ladwp.com/drinking-water-quality-report. For SWRCB TCP compliance data across all California water systems, visit waterboards.ca.gov.