Hexavalent chromium (Cr(VI)) in drinking water is a significant concern for water system operators, engineers, and utility managers in California. With the state’s stringent maximum contaminant level (MCL) for Cr(VI) reinstated at 10 parts per billion (ppb) in April 2024, utilities face ongoing challenges in ensuring compliance while maintaining operational efficiency. This blog post explores the health risks of Cr(VI), the history of California’s MCL, effective groundwater treatment approaches, and ATEC Water Systems’ proven technology, with a focus on cost-effective solutions. Written for water professionals, this educational piece aims to clarify regulatory and technical considerations to help you protect your community’s water supply.
Why Hexavalent Chromium is a Concern
Hexavalent chromium, a naturally occurring compound in groundwater and a byproduct of some industrial processes, is a known carcinogen when ingested over long periods. Unlike trivalent chromium (Cr(III)), a less harmful form, Cr(VI) can increase the risk of cancers, such as stomach and lung cancer, at elevated exposure levels. The U.S. Environmental Protection Agency (EPA) regulates total chromium (Cr(VI) and Cr(III) combined) at 100 ppb, but California’s stricter 10 ppb MCL for Cr(VI) alone reflects the state’s proactive stance on public health.
In regions like California’s Central Coast, where groundwater often contains naturally occurring Cr(VI) (e.g., 13 ppb average in Watsonville, 1.9–5.1 ppb in Las Lomas), even low levels require treatment to meet the MCL. For water operators, this means balancing health protection with operational constraints, such as limited budgets, aging infrastructure, and the need for minimal service disruption. Non-compliance risks regulatory penalties and public health concerns, making effective treatment critical.
History of California’s Cr(VI) MCL
California’s journey to regulate Cr(VI) has been complex, driven by science, public advocacy, and legal challenges. Here’s a timeline of key developments:
- 2001: California’s Office of Environmental Health Hazard Assessment (OEHHA) sets a public health goal (PHG) of 0.02 ppb for Cr(VI), signaling heightened concern.
- 2014: The California Department of Public Health (now Division of Drinking Water) establishes the nation’s first Cr(VI)-specific MCL at 10 ppb, far stricter than the federal 100 ppb total chromium standard. Utilities begin investing in treatment systems.
- 2017: A court suspends the 10 ppb MCL, citing insufficient economic feasibility analysis for small systems. Utilities operate under interim guidelines, with many continuing treatment voluntarily.
- 2024: After revised economic assessments, California reinstates the 10 ppb MCL in April, requiring full compliance. This prompts renewed efforts to upgrade or install treatment systems.
The MCL’s reinstatement underscores California’s commitment to addressing Cr(VI), but it places pressure on utilities, especially in rural areas like Las Lomas or Watsonville, where groundwater is the sole water source. Operators must navigate technical and cost-related challenges to meet this standard while ensuring reliable service.
Approaches to Treating Groundwater for Chromium-6
Ion Exchange:
- Process: Resin beds exchange Cr(VI) ions for less harmful ions, removing Cr(VI) from water.
- Pros: High removal efficiency; suitable for small to medium systems.
- Cons: Generates brine waste requiring disposal; high operational costs due to resin regeneration; less effective for co-occurring contaminants like iron or manganese.
- Best For: Systems with low Cr(VI) concentrations and minimal secondary contaminants.
Reverse Osmosis:
- Process: Semi-permeable membranes filter out Cr(VI) and other impurities.
- Pros: Removes a broad range of contaminants; highly effective for Cr(VI).
- Cons: High energy use; significant water waste (reject stream); expensive installation and maintenance; complex for small systems.
- Best For: Systems needing comprehensive contaminant removal but with resources for higher costs.
Reduction-Coagulation-Filtration (RCF):
- Process: A reducing agent (e.g., ferrous chloride) converts Cr(VI) to Cr(III), followed by coagulation and filtration to remove the reduced chromium.
- Pros: Cost-effective; handles multiple contaminants (e.g., Cr(VI), iron, manganese); integrates with existing infrastructure; low maintenance.
- Cons: Requires precise chemical dosing; may need media replacement over time.
- Best For: Systems with moderate Cr(VI) levels and co-occurring contaminants, especially in budget-constrained utilities.
Adsorption:
- Process: Media like activated alumina adsorb Cr(VI) from water.
- Pros: Simple operation; effective for low Cr(VI) concentrations.
- Cons: Limited media lifespan; less efficient for high flows or complex water chemistries.
- Best For: Small systems with low Cr(VI) and minimal operational complexity.
For most utilities, RCF stands out for its balance of effectiveness and cost efficiency, particularly when retrofitting existing systems. Its ability to address multiple contaminants makes it versatile for groundwater-dependent communities.
ATEC’s RCF Approach: A Case Study in Las Lomas
ATEC Water Systems, a Cadiz Company, has established itself as a leader in Cr(VI) treatment with its Reduction-Coagulation-Filtration (RCF) technology, approved by California’s Division of Drinking Water. The Las Lomas, California, project is a prime example of ATEC’s ability to deliver reliable, cost-effective solutions for water operators.
The Las Lomas Project
Las Lomas, a rural community relying on two groundwater wells, faced Cr(VI) levels of 1.9–5.1 ppb, necessitating treatment to meet the 10 ppb MCL. ATEC retrofitted an existing iron and manganese treatment system with its RCF process, which includes:
- Ferrous Chloride Injection: Reduces Cr(VI) to Cr(III), a less harmful form.
- Chlorine Oxidation: Converts iron(II) to iron(III), which acts as a coagulant to form flocs that incorporate Cr(III).
- Manganese Dioxide Coated Media Filtration: Captures reduced chromium for removal.
Implemented in 2016, the system integrated seamlessly with existing infrastructure, avoiding service disruptions. Corona Environmental Consulting provided piloting, design optimization and regulatory coordination, ensuring compliance.
Why RCF Excels
ATEC’s RCF technology offers several advantages for water operators:
- Cost-Effectiveness: Retrofitting existing systems reduces capital investment compared to installing new infrastructure, like reverse osmosis.
- Scalability: Handles flows from 20 to 5,000 GPM, suitable for small rural systems to large utilities.
- Multi-Contaminant Removal: Addresses Cr(VI) alongside iron and manganese, streamlining operations.
- Low Maintenance: Automated controls and durable media minimize operational oversight.
- Proven Track Record: Over 500 installations nationwide, with validated performance through pilot tests and third-party reviews.
Cost-Effectiveness Considerations
For water operators and utility managers, cost-effectiveness is a critical factor. ATEC’s RCF approach minimizes expenses by:
- Leveraging Existing Infrastructure: Retrofitting, as in Las Lomas, avoids the need for entirely new systems, reducing upfront costs.
- Low Operational Costs: Automated dosing and long-lasting filtration media decrease labor and maintenance expenses compared to ion exchange or reverse osmosis.
- Waste Minimization: Unlike reverse osmosis, which produces significant reject water, RCF generates minimal waste, lowering disposal costs.
- Energy Efficiency: RCF requires less energy than membrane-based systems, reducing long-term operational budgets.
These factors make RCF preferable for systems of all sizes, and particularly appealing for small to medium systems, where budget constraints are common. The Las Lomas project shows how ATEC’s solution balances compliance with affordability, ensuring sustainable operations.
Key Takeaways for Water Operators
- Understand the MCL: California’s 10 ppb Cr(VI) MCL is among the strictest in the nation, requiring proactive treatment for even low-level contamination.
- Evaluate Treatment Options: Compare ion exchange, reverse osmosis, and RCF based on your system’s flow, contaminants, and budget.
- Prioritize Cost-Effectiveness: Technologies like ATEC’s RCF offer compliance without excessive capital or operational costs, especially through retrofitting.
- Partner with Experts: Collaborate with proven providers like ATEC and consultants like Corona Environmental to ensure regulatory alignment and system reliability.
- Focus on Community Health: Effective Cr(VI) treatment, as demonstrated in Las Lomas, protects residents and builds public trust.
Moving Forward
As California enforces its Cr(VI) MCL, water operators, engineers, and utility managers must act decisively. ATEC’s RCF technology, exemplified by the Las Lomas success, offers a blueprint for achieving compliance while optimizing costs. By choosing scalable, efficient solutions, you can safeguard your community’s water supply and meet regulatory demands.
For more information on ATEC’s chromium treatment solutions, contact us to discuss your system’s needs.
