Water Quality Study for proposed Poseidon Desalination Project

Transcription

1 -- Revised -- Water Quality Study for proposed Poseidon Desalination Project Board of Directors June 1, 2016

2 Background Board approved non-binding Water Reliability Term Sheet w/ Poseidon in May 2015 Term Sheet included Attachment A Water Quality Specification Approval of Term Sheet included authorization for staff to hire a consultant to review project water quality issues OCWD does not have experience with distributing drinking water Staff solicited a proposal from Trussell Technologies for a water quality study

3 Trussell Technologies Founded by Rhodes Trussell, Ph.D., P.E., BCEE Specializes in water treatment engineering, water quality, and research Strong experience with desalination integration, infrastructure corrosion, purified water stabilization, and drinking water distribution system studies Began study in October 2015, focusing on the distribution system and related infrastructure end user water quality for direct delivery customers groundwater quality from recharge and injection of desalinated water

4 Scope of Work Review Term Sheet Attachment A Water Quality Specification Assess potential for corrosion in distribution system Assess disinfectant issues (required residual and by-products) Identify potential end user impacts for direct delivery Asses potential for injection well/recharge basin fouling Predict water quality impacts under three operating scenarios Provide recommendations for any changes to Water Quality Specification to protect public health & maintain infrastructure

5 Analyzed Three Operating Scenarios Winter Operations 3 MGD to City of HB (direct) 15 MGD to OCWD Talbert Barrier (100% desal) 35 MGD desal MGD GWRS to MBI & Forebay Summer Operations 3 MGD to City of HB (direct) 36 MGD to OCWD Talbert Barrier (100% desal) 14 MGD desal MGD GWRS to MBI & Forebay 100% Desalination (during GWRS shutdown) 3 MGD to City of HB (direct) 50 MGD to all OCWD recharge/injection locations

6 Findings: Corrosion City of HB will be required to conduct Lead & Copper Rule Monitoring To be performed over first 6-12 months after introduction of new source Similar requirements for utilities receiving water from Carlsbad Desalination Plant Proper post-treatment should make desal water non-corrosive Previous studies have shown initial 1-3 month period of increased metals within distribution system prior to establishing equilibrium with new source Iron pipelines can release red water with new water sources Existing mineral scale/passivation layer can potentially dissolve away Intended stabilization with calcium carbonate should maintain scale Potential for day period of instability during transition Only 0.07% of City of HB pipelines are iron; 93% are asbestos-cement pipe (ACP) or PVC* OCWD only has a short reach of ductile iron pipeline at Talbert Barrier

7 Findings: General Water Quality Use RO modeling software to predict actual desal facility water quality Term Sheet specification for chloride will likely control plant design Water Quality Parameter Term Sheet Specification (12-mo average) Ocean Desal (Predicted) GWRS (2014)* HB Groundwater Imported MWD TDS (mg/l) Sodium (mg/l) Chloride (mg/l) Boron (mg/l)

8 Findings: Mass Loadings Relative to current 100 MGD GWRS project, the addition of 50 MGD of ocean desalinated water to the groundwater basin would contribute on mass basis: 38% more TDS 136% more sodium 396% more chloride 3% more boron *(based on model-predicted desal water quality, not term sheet specifications) Greater impact near Talbert Barrier (assumes no GWRS blending) Lesser impact for MBI + Forebay due to blend w/ GWRS water

9 Findings: Effects on plant appearance Elevated sodium, chloride, and boron can affect plants Term Sheet Specification for sodium & chloride appear protective Boron is more complicated, can cause chlorosis of leaves 2005 HortScience study in Carlsbad identified 16 common plants that would be affected by proposed desal water quality (e.g., Rose, Orange, Lemon) Recommendation: consider a similar study in HB and any other direct distribution customer service area(s) Account for local microclimate(s) and soil conditions Consider preferences of local stakeholders (e.g., garden clubs, nursery s, park managers, etc.)

10 Findings: Disinfectant Residual & By-Products Like all surface water supplies, ocean desal water requires disinfection prior to distribution as drinking water Formation of disinfection byproducts (DPBs) should not be a problem Must provide free chlorine disinfectant residual for HB direct distribution Other direct retailers may require a chloramine residual disinfectant Chloramine residual instability in ocean desal water due to elevated bromide

11 Recommended changes to Term Sheet WQ Specs Modifications to corrosion control parameters (e.g., Ca, ph, LSI, alkalinity) Set an initial range, but then dial in specific target based on observations Flexibility desired to balance corrosion control w/ injection well clogging Based on OCWD experience w/ GWRS post-treatment Variable chemical costs could be a pass through Add in specified chlorine/chloramine disinfection residual value Add bromide limit to protect chloramine residual for non-hb direct uses Reduce boron limit from 0.75 mg/l to 0.5 mg/l to protect horticulture and limit loading to groundwater basin Lower temperature limit to improve direct customer aesthetics

12 Proposed Revised WQ Specification

13 IRWD staff has communicated concerns with ocean desalination water quality Effects of desal water quality on IRWD recycled water quality Regulatory TDS limit on IRWD recycled water system Agricultural customers sensitive to chloride and boron IRWD currently enjoys excellent groundwater quality OCWD use of desal water for recharge/injection would increase chloride, and possibly TDS, of IRWD groundwater supply over long-term Increases in groundwater salinity increases to recycled water salinity IRWD currently developing projections of impacts via modeling study

14 Initial End User WQ Experiences from Carlsbad Desalination Plant Vallecitos Water District Significant area receiving 100% desal water directly No aesthetic or regulatory issues to date Just collected first set of LCR samples Some boron concerns for recycled water end users WE&RF Study led by Arcadis 8 participating agencies + Poseidon Focused on documenting WQ integration experiences Will collect data over 1 st year of integration

15 End of Presentation