Stannous for Hexavalent Chromium Reduction at Full-Scale

Dan Ruiz, Coachella Valley Water DistrictTarrah Henrie, Corona Environmental Consulting

CVWD Challenges

• Short compliance timeline• CEQA• Financing• Compliance cost

Compliance

• Protect consumer confidence and reduce liability• Plan A – Accelerate compliance plan decisions

based on Best Available Technologies (BAT)• Plan B – Legislative Fix

• 2014 Appropriations Trailer Bill - Governor’s staff recommendation

• SB 385 (Hueso) - ACWA sponsored bill to maintain compliance while installing BAT by earliest feasible date

• Plan C – Alternative control measure variance

Compliance TimelineEPA’s Arsenic MCL example• 2001 rule – Cost Benefit Analysis based on Activated

Alumina treatment, POU for <500 service connections• Innovative treatment developed later

• Adsorption medias and brine reduction for IX• More reliable and cost effective than AA• 5-year compliance period provided time & flexibility

California’s Cr6 MCL example• Accelerated decisions limited selection to BAT• SB 385 “Earliest feasible” provision still limited

innovation • POU not currently a long-term compliance option

California Environmental Quality Act (CEQA)

• Well sites too small for BAT treatment facilities• Mitigation for off-site impacts, some conservation

areas

• Tribal consultation (AB 52)• Management of treatment residuals• Greenhouse gas emissions (brine management)• Infrastructure impacts in jurisdictional waters• Community impacts & protest

Financing • Compliance options usually exceed pay-go capacity• Drinking Water State Revolving Fund (DWSRF)

• Long application process• Requires CEQA Plus (Federal nexus)• Multiple prerequisites (debt service coverage, secure

revenue)• TMF capacity can rule out some systems

• Bonds• Requires bond rating • Higher cost financing

• Requires rate covenants & higher debt service coverage• Consultants (bond counsel, financial advisor, underwriter)

• Noncompliance increases risk represents greater liability and results in higher financing costs

Compliance Cost• Expedited schedules increase costs

• Traditional Design-Bid-Build optimize competitive pricing but take more time

• Premium paid for compressed schedule alternatives• Design-Build • Construction Manager At Risk (CMAR)• Transfers risk to contractor and increases project cost

• Liquidated damages added to contract price

• Quality can suffer resulting in costly change orders

Compliance Cost

Treatment Option Source of Supply Study - Capital Cost Range ($Millions)

Cluster Well Treatment

Individual Well Treatment

Mid-Valley SWTP and Individual Well TreatmentEast Valley SWTP and Individual Well TreatmentPoint-of-use

Mid-Valley and East Valley SWTP and Individual Well Treatment

134 307

74 210

117 302

139 338

183 429

169 363

Game Changer?• Corona’s Stannous work showed promise• Potentially much lower treatment cost• Stopped construction contract to investigate

Stannous Chloride (SnCl2) Alternative

• Salt made of tin & chloride• Approved drinking water additive

• Solution used to protect pipes

• Antioxidant used in consumer products (including some foods and toothpaste)

• Quickly reduces Cr VI to essential Cr III

Sn

ClCl

• Summary of bench test results

• ID-8 system overview• Baseline system

conditions• Full-scale demonstration

objectives• Results

Stannous Work

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Summary of Bench Results

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• Reduction of Cr(VI) to Cr(III) is rapid (<1 min)• Re-oxidation to Cr(VI) is also rapid (majority

within the first hour) and limited• Re-oxidation is inversely correlated with stannous

dose• Re-oxidation does not appear to be impacted by

chlorine dose• Stannous doses of 0.3 mg/L-Sn and greater

achieved water quality goals independent of chlorine dose

• ID-8 System• Isolated system• Wells 3405-1, 3408-1, 3409-2, 3410-1• Hydraulic model – 10 day maximum residence time• Chlorine residual of 0.3 mg/L

Full-scale Demonstration

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1. Demonstrate full-scale efficacy of stannous application followed by chlorination to achieve the water quality goals at the compliance points

2. Inform the fate of Sn, Cr(VI), and Cr and from well head application through the distribution system

3. Confirm applied stannous dose 4. Inform stannous stock solution efficacy over

time in field storage conditions

Full-scale Demonstration Objectives

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Tin Base Preservation

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Stannous Stock Efficacy over TimeMarch 2nd, 2018

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• Achieve Cr(VI) concentrations below 10 µg/L

• Find the condition that minimizes re-oxidation of Cr(III) by chlorine

• Remain below the turbidity SMCL of 5 NTU

Water Quality Criteria for Success

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Flushing Experiment

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• Baseline flushing of hydrant in the Sky Valley subdivision• November 29th

• 10-min flush• Filtration using 0.35 µm and1 µm cartridges

Baseline Flushing Results

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Full-scale Demonstration Start-up

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• Stannous feed start-up on November 29th, 2017

• Target dose of 0.5 mg/L-Sn

• End full-scale demonstration on January 31st, 2018

Full-scale Demonstration

Results

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Total Tin

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Total Tin

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Total Sn Boxplot

24 Note: Sn Feed data include all results after Cr(VI) first reaches <10 µg/L per site, and Post-Sn Feed data include all results after Cr(VI) is > 10 µg/L per site

Cr(VI)

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Chlorine Residual

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Turbidity – With Sn Feed

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Total Cr

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Total Cr Boxplot

29Note: Sn Feed data include all results after Cr(VI) first reaches <10 µg/L per site, and

Post-Sn Feed data include all results after Cr(VI) is > 10 µg/L per site

• Not found during tank draining experiment• Not found during hydrant flushing experiment

Where Are the Sn and Cr?

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• Pipe sample collected for ICP-MS, X-ray diffraction (XRD), and Scanning Electron Microscopy (SEM) at UC Riverside

Distribution System Pipe Sample

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Interior of pipe sample Outer layer pipe scales

Pipe Scale Analysis

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1. Demonstrate full-scale efficacy of stannous application followed by chlorination to achieve the water quality goals at the compliance points

2. Inform the fate of Sn, Cr(VI), and Cr and from well head application through the distribution system

3. Confirm applied stannous dose 4. Inform stannous stock solution efficacy over

time in field storage conditions

Full-scale Demonstration Objectives

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• Three community outreach presentations• No customer complaints during the

demonstration

Community Considerations

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CVWD Staff• Steve Bigley • Dan Ruiz• Sushmitha Reddy• Steven Hernandez• Wil Gonzales• David Pena• Craig Richardson• Jesse Aguilar

Acknowledgments

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DDW Staff• Eugene Leung• Steven Williams• Manual Delgado• Kurt Souza• Paul Richter• Sean McCarthy

Corona Staff• Tarrah Henrie• Sarah Plummer• Chad Seidel

UC Riverside Staff• Haizhou Lui• John Orta

Questions and Comments

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