Gross Alpha Radioactivity in San Fernando Valley Drinking Water: EPA's 15 pCi/L Standard and What the Data Shows

Gross alpha radioactivity is a regulated contaminant in public drinking water across the United States, including utilities serving the San Fernando Valley and Santa Clarita. The EPA Maximum Contaminant Level for gross alpha is 15 picocuries per liter (pCi/L), set under the Safe Drinking Water Act Radionuclides Rule. Southern California groundwater naturally contains uranium, radium-226, and radium-228 at low levels, released by the granitic and sedimentary geology of the transverse ranges and the alluvial fan deposits underlying the SFV basin. LADWP and SCV Water test for gross alpha, combined radium, uranium, and gross beta annually and publish results in their Consumer Confidence Reports. Most SFV distribution zones meet the MCL with margin, but homeowners drawing from groundwater-blended supply who have concerns about cumulative radionuclide exposure, or who want to reduce exposure below the regulatory limit, can install a point-of-use reverse osmosis system certified under NSF/ANSI 58 for radium reduction. This article explains what the numbers mean, where to find your utility's data, and what treatment actually works.

What Is Gross Alpha Radioactivity in Drinking Water?

Gross alpha is not a single contaminant. It is a measurement of total alpha-particle radiation emitted by all radionuclides in a water sample, expressed in picocuries per liter. A picocurie is one-trillionth of a curie, a unit of radioactive decay rate. A reading of 1 pCi/L means approximately 0.037 radioactive disintegrations per second per liter of water. The regulatory basis for the gross alpha MCL is the cumulative cancer risk from ingesting alpha-emitting radionuclides over a lifetime, which is why the standard covers the total rather than requiring separate monitoring of every individual alpha emitter.

In Southern California groundwater, the radionuclides most commonly driving gross alpha readings are uranium (which emits alpha particles during decay), radium-226 (an alpha emitter, part of the uranium-238 decay chain), and occasionally polonium-210 (alpha emitter, part of the lead-210 chain). Thorium isotopes contribute smaller amounts. These isotopes are geogenic, meaning they originate in the geology of the watershed and aquifer system rather than from human activity. The granitic basement rocks of the San Gabriel Mountains and the sedimentary deposits of the Transverse Ranges naturally release uranium and thorium as groundwater moves through them, with daughter isotopes including radium and polonium accumulating in pore water over decades.

The EPA's technical basis for the radionuclides rule is documented in the EPA radionuclides in drinking water guidance. The rule applies to community water systems, meaning public utilities. Private well owners are not covered by the rule but face the same groundwater, and testing a private well for gross alpha is advisable in areas with naturally elevated radioactivity in the underlying geology.

EPA's Radionuclide Rule: The Four Limits That Matter

The 2000 Radionuclides Rule established four separate MCLs that apply to public water systems. They are not interchangeable: each covers a different set of radionuclides and a different measurement method. Understanding which limit applies to which reading is necessary to interpret a CCR correctly.

Source: EPA National Primary Drinking Water Regulations and EPA radionuclides in drinking water.

One technical note that matters for reading CCR data: the gross alpha MCL of 15 pCi/L explicitly excludes uranium from the measurement. Before the 2000 rule, uranium's alpha contribution was counted in gross alpha. Under the current rule, gross alpha is measured after uranium removal. If your CCR shows a gross alpha result, it does not include uranium's alpha contribution. The uranium standard (30 µg/L) is reported separately. Both need to be checked against their respective limits independently.

Radionuclides in Southern California Groundwater: The Geological Background

Southern California sits at the intersection of three geological provinces: the granitic Peninsular Ranges and San Gabriel Mountains (which form the eastern and northern walls of the SFV), the folded and faulted Transverse Ranges, and the alluvial basin fill of the LA Basin and SFV floor. Uranium and thorium are trace constituents of granitic rock. As groundwater moves through fractured granite in recharge zones and then through alluvial sediment derived from erosion of those same mountains, it picks up dissolved uranium and radium. The process is slow and naturally occurring, not a result of industrial activity.

The USGS has studied radionuclide concentrations in Southern California groundwater as part of its National Water Quality Assessment (NAWQA) program and periodic basin-scale assessments. USGS water-quality publications document that gross alpha and uranium concentrations vary significantly across the SFV basin depending on the proportion of groundwater versus surface water in the local supply blend, the depth of the wells, and the specific geology of the recharge zone. USGS data products and reports for California groundwater are accessible through the USGS California groundwater monitoring page.

Uranium concentrations in California groundwater at and above the 30 µg/L federal MCL have been documented in several Central Valley basins. The SFV basin generally shows lower uranium concentrations because imported water dilutes local groundwater before it reaches the distribution system. But localized zones, particularly near the Tujunga and North Hollywood wellfields and in the Verdugo Basin supplying portions of Burbank and Glendale, have historically required blending management to stay comfortably below the MCL. The SWRCB maintains a database of historical compliance data for California water systems, searchable through the Safe Drinking Water Information System.

How LADWP and SCV Water Test and Report Radionuclides

Every community water system subject to the Radionuclides Rule must sample for gross alpha, combined radium (Ra-226 and Ra-228), and uranium at each groundwater entry point into the distribution system. The sampling frequency is set by the state primacy agency (in California, the SWRCB Division of Drinking Water) based on historical results. Systems with consistent results well below the MCL may qualify for reduced monitoring, typically once every three years for individual wells. Systems with results closer to the MCL sample more frequently.

LADWP reports radionuclide results in its annual Consumer Confidence Report, available at the LADWP water quality page. The CCR format lists detected range, highest detected level, and the MCL for each parameter. LADWP draws from three source types: Owens Valley aqueduct (relatively low in radionuclides because it is primarily snowmelt from the Sierra Nevada), MWD imported water (also relatively low), and SFV groundwater from the North Hollywood, Tujunga, and Jensen wellfields. The blend ratio shifts seasonally. The groundwater component is the primary contributor to any radionuclide detections in the delivered supply.

SCV Water (serving Santa Clarita) publishes its CCR at yourscvwater.com/water-quality. SCV Water's supply also blends imported MWD supply with local Santa Clarita Valley groundwater from the Saugus and Alluvial formations. Radionuclide results appear as a separate line item in the CCR table. Historical compliance records for both LADWP and SCV Water are searchable in the SWRCB SDWIS database. LADWP's California Public Water System ID (PWSID) is CA1910067; SCV Water's is CA2910024.

Reading the CCR correctly: look for "gross alpha" as a row label in the inorganic or radionuclides section. The reported value is typically the highest detected level or the range. Compare it to the 15 pCi/L MCL. Then find "combined radium" (or "Ra-226 + Ra-228") and compare to 5 pCi/L. Then find "uranium" and compare to 30 micrograms per liter. If all three are below their respective MCLs, the utility is in compliance. A reading below the MCL does not mean zero radioactivity; it means the detected level is below the threshold the EPA and California have set as protective of public health at the population level.

What Radionuclide Exposure Actually Means at SFV Tap Water Levels

Understanding the health context requires separating regulatory compliance from personal risk decisions. The 15 pCi/L gross alpha MCL was set to limit lifetime cancer risk from ingested alpha-emitting radionuclides to a level the EPA considers acceptable across the population. The EPA's risk target for the MCL corresponds to approximately 4 excess cancer cases per 10,000 people exposed at the limit for a lifetime, which is within the range the EPA typically uses for regulated drinking water contaminants. The underlying methodology is in the EPA radionuclides guidance.

Tap water at levels well below the MCL, which is where most SFV and Santa Clarita addresses fall on both LADWP and SCV Water supply, carries correspondingly lower risk. Alpha particles from ingested radionuclides affect the gastrointestinal tract and organs where radionuclides are deposited. Radium, because of its chemical similarity to calcium, deposits preferentially in bone. Uranium at the MCL (30 µg/L) is primarily a kidney toxin rather than a radiation concern at that concentration. The gross beta and photon emitter standard (4 mrem/year) applies mainly to cesium-137 and strontium-90 from past atmospheric nuclear weapons testing; ambient levels in California surface water have declined substantially since the 1960s.

The practical takeaway: if your CCR shows gross alpha at 2 to 5 pCi/L (a common range for SFV groundwater-blended supply), combined radium below 1 pCi/L, and uranium below 10 µg/L, you are well within the regulatory limits. Families who want to reduce exposure further below the MCL, including those with specific health sensitivities or who apply a precautionary standard at the kitchen tap, can do so effectively with certified point-of-use treatment.

Household Treatment That Actually Removes Radionuclides

The EPA lists the following household treatment technologies as effective for radionuclide removal, consistent with the broader treatment guidance at the EPA National Primary Drinking Water Regulations page.

Reverse osmosis (NSF/ANSI 58). Point-of-use RO is the most commonly used and versatile treatment for radionuclides at the kitchen tap. An RO membrane with a pore size of approximately 0.0001 microns physically excludes dissolved ions, including uranium (as uranyl ion), radium (as Ra2+), and other dissolved radionuclide species. Products certified under NSF/ANSI 58 for radium and uranium reduction reliably achieve greater than 90% reduction of both at typical SFV tap water concentrations. Certified product listings are searchable through the NSF consumer resources page for drinking water treatment units. When selecting a system, verify that "radium" or "uranium" appears explicitly in the certification scope, not just "total dissolved solids."

Ion exchange (cation). Radium behaves chemically like calcium and magnesium, which means it is removed by a cation exchange softener in the same way hardness is removed. A salt-based water softener will reduce radium in water passing through it. However, standard softeners are not NSF/ANSI 58 certified for radium reduction as a primary claim, and the softening process regenerates the resin with brine, concentrating the radium in the waste brine stream that must be disposed of appropriately. In municipal service areas, brine is discharged to the sanitary sewer where it is handled by the wastewater treatment plant. For uranium, cation exchange is less effective because uranium at pH above 6 often exists as anionic uranyl carbonate complexes, which repel the cation resin. Anion exchange specifically designed for uranium removal is available but rarely used in residential applications.

Distillation. Countertop distillers effectively remove radionuclides by boiling water and condensing the steam, leaving ionic radionuclides behind in the boiling chamber. The process is effective but slow (roughly 1 gallon per cycle) and energy-intensive. For most SFV households, under-sink RO is more practical for drinking and cooking water.

What does not work. Standard activated carbon filters (pitcher filters, countertop carbon blocks, refrigerator filters) do not remove radionuclides to any significant degree. They target organic compounds, chlorine, and chloramine. A filter certified only for taste and odor is not treating radionuclides. If radionuclide reduction is the goal, verify the specific NSF certification category.

Our reverse osmosis service page covers the under-sink systems we install across the Valley, all of which use membranes from manufacturers that carry NSF/ANSI 58 certification. Our water testing service includes consultation on what certified treatment matches your address and incoming water characteristics.

Private Wells and Radionuclides in the SFV Fringe

Most residential addresses in North Hollywood, Sherman Oaks, Burbank, Studio City, and the core Valley cities are on municipal supply, either LADWP or Burbank/Glendale utilities. But the foothill fringe of the service area, including portions of Chatsworth, West Hills, Sunland, Tujunga, and Sylmar, includes rural and semi-rural parcels on private wells. Private wells are not subject to the Radionuclides Rule because the rule applies only to community water systems. But the geology does not change at the property line.

Private wells in areas underlain by granitic recharge zones, or drawing from shallow alluvial aquifers near the mountain front, can carry gross alpha and uranium levels similar to or higher than public groundwater sources in the same area, because those wells do not benefit from the dilution blending that utilities perform. The California Department of Water Resources recommends testing private wells for radionuclides at least once, and more frequently if the well is near a recharge zone with naturally elevated radioactivity. Testing should be done through a state-certified lab; results are returned in pCi/L for gross alpha and combined radium, and in µg/L for uranium. If gross alpha exceeds 5 pCi/L or uranium exceeds 10 µg/L on a private well, installing an NSF/ANSI 58 certified point-of-use RO at the kitchen tap is a straightforward and effective response.

CTR-Harvest Preview: What Homeowners Actually Search on This Topic

The questions we hear most often on in-home consultations about radionuclides in SFV water are practical rather than regulatory. They cluster around three concerns: Is my water safe? How do I find my utility's actual data? And if I want a lower level at my tap, what do I install? The regulatory table above and the treatment section above address all three directly. The FAQ section below addresses the specific phrasing homeowners use when searching for answers.

Is gross alpha radioactivity in SFV tap water dangerous?

At the levels typical of SFV and Santa Clarita utility supply, which are below the 15 pCi/L EPA MCL, gross alpha in tap water represents a low cumulative risk by the EPA's own risk calculation. The MCL was set so that a person drinking water at exactly the limit for a lifetime would face approximately 4 additional cancer cases per 10,000 people by the EPA's methodology, as described in the EPA radionuclides guidance. Utility supply well below the MCL corresponds to proportionally lower risk. Families who want to reduce exposure further at the kitchen tap can do so with a point-of-use RO system certified under NSF/ANSI 58 for radium and uranium reduction.

Where do I find my utility's gross alpha data?

Your utility's annual Consumer Confidence Report is the primary source. LADWP publishes its CCR at the LADWP water quality page; SCV Water (Santa Clarita) publishes at yourscvwater.com/water-quality. Look for the radionuclides section of the CCR table, where gross alpha, combined radium, and uranium will each appear as separate line items with detected levels and the MCL. Historical compliance data for any California water system, including all SFV utilities, is also searchable through the SWRCB's Safe Drinking Water Information System. LADWP's California PWSID is CA1910067; SCV Water's is CA2910024. The SWRCB system lets you look up each utility's compliance history by contaminant and year.

What is the difference between gross alpha and combined radium?

Gross alpha measures the total alpha radioactivity in a water sample from all sources (excluding uranium and radon under the current rule). Combined radium (Ra-226 plus Ra-228) is a specific subset of the alpha emitters: the two regulated radium isotopes. A utility can meet the gross alpha MCL (15 pCi/L) and still need to check separately against the combined radium MCL (5 pCi/L), because combined radium is independently regulated at a lower limit. In practice, a system with combined radium above 5 pCi/L would typically also show elevated gross alpha, but they are separate measurements against separate MCLs. Always check both rows in your utility's CCR. Sources: EPA National Primary Drinking Water Regulations table.

Does a water softener remove radionuclides from drinking water?

A salt-based water softener will reduce radium in water passing through it, because radium is chemically similar to calcium and is captured by the cation exchange resin that also removes hardness. However, standard softeners are not NSF/ANSI 58 certified specifically for radium reduction, and the effectiveness varies with resin type and incoming water chemistry. Softeners do not effectively remove uranium when it is present as anionic uranyl carbonate complexes (common above pH 6). If the goal is verified radionuclide reduction at the kitchen drinking tap, an under-sink RO certified under NSF/ANSI 58 with explicit radium and uranium reduction in its certification scope is the more reliable and verifiable option. The two systems work independently and can be used together. See our RO service page for the certified systems we install.

Do carbon filters or pitcher filters remove radionuclides?

No. Standard activated carbon filters, pitcher-style filters, and refrigerator filters target organic compounds, chlorine, chloramine, and some VOCs. They do not remove dissolved ionic contaminants including radium, uranium, or other radionuclides to any significant degree. A filter certified only for taste and odor or chlorine reduction provides no meaningful radionuclide treatment. If radionuclide reduction is your goal, verify the specific NSF/ANSI 58 certification categories of any product you consider. The NSF certification search tool at nsf.org lets you filter by contaminant category including radium and uranium to find certified products.

How does radon in water relate to gross alpha?

Radon is a naturally occurring radioactive gas and an alpha emitter, but it is excluded from the gross alpha MCL under the current EPA Radionuclides Rule. Radon in water is addressed separately through a proposed EPA rule that has not been finalized as a federal regulation (the proposed MCL was 300 pCi/L for community water systems). In California, radon in water is primarily a concern for private well owners in granitic rock formations, where radon gas dissolves into groundwater under pressure and then volatilizes when the water is used indoors, contributing to indoor air radon levels. For public utility supply in the SFV, radon is not reported in CCRs as a regulated contaminant because the proposed rule has not been finalized. Homeowners with private wells in granitic zones who are concerned about radon in water can request radon testing from a certified lab. See the EPA radionuclides in drinking water page for the current status of radon regulation.

Last updated: August 8, 2026. Regulatory thresholds are current as of that date. MCLs and health guidance are subject to revision; verify current radionuclide standards at the EPA radionuclides in drinking water page and the EPA National Primary Drinking Water Regulations. For utility-specific radionuclide data, consult your utility's most recently published Consumer Confidence Report or the SWRCB SDWIS database.

Related reading: Nitrate in SFV Drinking Water · Arsenic in SFV Drinking Water · Chromium-6 in SFV Water · PFAS in SFV and Santa Clarita · Lead in SFV Water · TCE, PCE, and 1,4-Dioxane in SFV Groundwater · SFV Utility Water Quality Comparison · CA Water Quality Rules 2026 · How Whole-House Filtration Works · What 2,000 SFV Installs Taught Us · Reverse Osmosis · Water Testing · Whole-House Filtration · SFV Water Quality Overview · Service Areas · FAQ · Contact