Pilot Testing for Hexavalent Chromium Removal

Transcription

1 Pilot Testing for Hexavalent Chromium Removal Prepared for Cadiz, Inc October 2016

2 Contents Section Page Acronyms and Abbreviations... vi Executive Summary What is the Cadiz Water Project? How Widespread is Hexavalent Chromium in Water? How is Chromium Removed from Drinking Water? How does the RCF process work? Is there much experience with the RCF Process? What is the treatment technology being investigated at Cadiz? What does the Treatment System Cost for Hexavalent Chromium and Arsenic Removal? Cadiz Water Project Introduction and Background Conceptual Project Overview Groundwater Quality Hexavalent Chromium and Arsenic in Groundwater Introduction Hexavalent Chromium Occurrence Hexavalent Chromium Water Quality Regulations Federal Regulations California Regulations Treatment Alternatives for Hexavalent Chromium In Situ Treatment Ex-Situ Treatment Arsenic Occurrence Arsenic Removal Treatment Alternatives Conventional Filtration for Arsenic Removal Potential for Simultaneous removal of Hexavalent Chromium and Arsenic Proposed Treatment System for Pilot Testing Water Treatment Residuals Pilot Testing methods and Materials Groundwater Quality ATEC Pilot Equipment Pilot Testing Results ATEC Testing Objectives and Findings ATEC Testing Scenario ATEC Testing Scenario ATEC Testing Scenario ATEC Testing Scenario ATEC Overall Testing Results Arsenic and Chromium Removal Iron Removal Filter Run Lengths ATEC Backwash Water Results CH2M III

3 CONTENTS Section Conceptual Design of Facilities Summary Treatment System Options Water Delivery Options Water Quality Standards Conceptual Design Using ATEC System ATEC System Operation and Design Criteria Backwash Waste Flow Handling Cost Estimates Costs for ATEC Systems Treatment Cost per Acre Foot References Page Tables Table 1-1. Pilot Testing Treatment Results for ATEC Treatment System Table 2-1. Summary of General Water Quality Parameters from Cadiz Wells Table 2-2. Preliminary Water Treatment Target Constituents Table 3-1. Treatment Alternatives for Hexavalent Chromium Table 3-2. Comparison of Arsenic Removal Technologies Table 3-3. Surveyed Systems ATEC Iron and Manganese Facilities Table 3-4. Comparison of Pilot Removal Efficiency and Full Scale Removal Efficiency in Manganese Dioxide Media Filters Table 3-5. Project Construction Components for Surveyed ATEC Water Treatment Systems Table 3-6. Capital Costs of ATEC Water Treatment Surveyed Systems, Escalated to 2016 Dollars Table 3-7. Annual Operations and Maintenance Costs Report for ATEC Systems, in 2016 dollars Table 4-1. Physical Characteristics of Filter Tanks and Media Table 4-2. Pipe Configurations for Varying Contact Times Table 5-1. Pilot Testing Treatment Results for ATEC Treatment System Table 6-1. Maximum Design Flow Rates Table 6-2. Estimated Backwash Waste Volumes, mgd Table 6-3. Dry Weight Solids Produced Per Year Table 7-1. CAPEX Estimates for ATEC System for 10-month Operating Period Table 7-2. CAPEX Estimates for ATEC System for 11-month Operating Period Table 7-3.OPEX Comparison for Treatment Systems Table 7-4: Cadiz Treatment Costs Per Acre-Foot Figures Figure 1-1. Hexavalent Chromium Removal with Reduction/Coagulation/Filtration (RCF) Process Figure 1-2. Hexavalent and Total Chromium Concentrations from 2005 through 2012 after Microfiltration Figure 1-3. ATEC Pilot Filter Schematic Figure 2-1. Google Earth Image Showing Conceptual Location of Water Treatment, Ag Wells, High Wells and Transmission Route to the Colorado River Aqueduct Figure 3-1. Hexavalent Chromium Removal with Reduction/Coagulation/Filtration Process CH2M IV

4 Section CONTENTS Figure 3-2. Hexavalent and Total Chromium Concentrations from 2005 through 2012 after Microfiltration Figure 3-3. Influence of Coagulant Dose, Arsenic Type and ph on Arsenic Removal Figure 4-1. ATEC Pilot Filter Schematic Figure 4-2. ATEC Pilot Filters within the Trailer Figure 4-3. Pipe Line Reactor Segments Figure 4-4. Venturi Eductor and Bypass Pipe Figure 4-5. A 47 mm Diameter Filter Shows the PrecipitatedIiron Collected from a Prefilter Ssample during the Pilot Test at Cadiz, 8/25/ Figure 5-1. ATEC Pilot Testing August 25, 2015 Time Series Figure 5-2. ATEC Pilot Testing Hexavalent Chromium and Arsenic Removal at Various Ferrous Chloride Doses, August 25, Figure 5-3. ATEC Pilot Testing August 27, 2015, Time Series Figure 5-4. ATEC Pilot Testing September 9, 2015, Time Series Figure 5-5. ATEC Average Hexavalent Chromium Removal at Varied Contact Times Figure 5-6. ATEC Run 1, November 19, 2015, Time Series Figure 5-7. ATEC Run 2, November 19 to 20, 2015, Time Series Figure 5-8. ATEC Hexavalent Chromium and Arsenic Removal at Various Ferrous Chloride Doses, November 19 to 20, Figure 5-9. Hexavalent Chromium and Arsenic Removal at Various Ferrous Chloride Doses Figure Run 1, November 19, 2015 Iron Removal Figure September 9, 2015 Iron Removal Figure August 25, 2015 Iron Removal Figure August 27, 2015 Iron Removal Figure September 10, 2015 Iron Removal Figure Run 2, November 19, 2015 Iron Removal Figure 5-16 Floating Decant with Plate Settlers, used for backwash clarification Page CH2M V

5 Acronyms and Abbreviations µg/l AF AFY As ATEC ARZC CH2M Cr Cr +6 CRA Fe GMMMP gpm gpm/sf MAF mgd mg Fe 2+ mg/l mg O 2 Mn MET psi RCF slpm TCLP WET micrograms per liter acre feet acre feet per year arsenic ATEC Water Treatment Systems Arizona and California Railroad CH2M Engineers, Inc. chromium hexavalent chromium Colorado River Aqueduct iron groundwater management, monitoring and mitigation plan gallons per minute gallons per minute per square foot million acre feet million gallons per day milligrams of ferrous iron milligrams per liter milligrams of oxygen manganese Metropolitan Water District of Southern California pounds per square inch reduction, coagulation, filtration standard liters per minute toxicity contaminant leachate potential waste extraction test CH2M VI

6 SECTION 1 Executive Summary The State of California has developed a maximum contaminant level (MCL) for hexavalent chromium, also referred to as chromate or Chrome (VI) in drinking water at 10 micrograms per liter (µg/l) or parts per billion. Cadiz s groundwater contains hexavalent chromium above the new MCL. A significant amount of research and demonstration testing has been conducted on Hexavalent chromium treatment approaches, leading to the establishment of the best available technologies (listed in the California MCL), including ion exchange; reduction, coagulation, filtration (RCF); and reverse osmosis. Cadiz conducted pilot testing on two water treatment technologies that use the RCF treatment process and selected the ATEC Water Treatment Systems Inc., system, which is described in this report. 1.1 What is the Cadiz Water Project? The Project area is located in the eastern Mojave Desert of San Bernardino County, California approximately 200 miles east of Los Angeles, 60 miles southwest of Needles, and 40 miles northeast of Twentynine Palms. Cadiz owns 34,000 acres of land in Cadiz Valley situated over a large, naturally recharging basin. The Cadiz Valley Water Conservation, Recovery, and Storage Project (Water Project) includes property that would allow for both the beneficial use of the groundwater and storage of imported surface water in the groundwater basin. Initially 25,000 to 75,000 acre-feet per year is proposed to be piped from the Cadiz Water Project well fields approximately 40 miles to the south to the Metropolitan Water District of Southern California (MET) Colorado River Aqueduct. This supply will augment the supply of a number of water agencies in MET s service area. 1.2 How Widespread is Hexavalent Chromium in Water? Hexavalent chromium can be present in water naturally and as a result of human contamination. Chromium is the 21 st most common element in the earth s crust. The occurrence of hexavalent chromium in drinking water is largely unknown, but some recent studies suggest naturally occurring hexavalent chromium may be fairly widespread. The State of California found approximately 1/3 of 7,000 water sources sampled between 1997 and 2009 had detectable concentrations of hexavalent chromium. A Water Research Foundation project (Frey et al, 2004) found more than 400 drinking water sources in the United States in 2004 and found an average concentration of 1.1 µg/l and a median concentration of 0.2 µg/l. Chromium in groundwater averages approximately 13 to 14 µg/l at Cadiz and is naturally occurring. 1.3 How is Chromium Removed from Drinking Water? Hexavalent chromium can be removed from water using a handful of proven treatment techniques including; anion exchange (both strong-base and weak-base), membrane filtration by nanofiltration and reverse osmosis, reduction followed by coagulation and filtration, and adsorption can remove hexavalent chromium from drinking water. For the Cadiz wellfield, we focused on Reduction Coagulation Filtration (referred to as the RCF process) because of the potential for cost effectively treating a largescale supply. Weak based ion exchange would require periodic replacement of the resin and strong based ion exchange would require periodic regeneration with sodium chloride or other regenerant, which would be very difficult to dispose in the remote Mojave Desert location. CH2M 1-1

7 SECTION 1 EXECUTIVE SUMMARY 1.4 How does the RCF process work? The RCF process uses ferrous chloride or ferrous sulfate to reduce hexavalent chromium to trivalent chromium. Trivalent chromium may be present in water as hydrated chromium oxide (Cr(OH) 3). After reducing the chromium, an oxidant is used to oxidize the iron in the water. The iron and the trivalent chromium are precipitated after the oxidation step. The iron and the trivalent chromium precipitates are then removed by filtration. The reduction reaction takes place very quickly and can be made more efficient by mixing. Only a small amount of iron are needed to reduce hexavalent chromium; however, most of the RCF treatment systems use additional iron salts to ensure reducing conditions are favorable. 1.5 Is there much experience with the RCF Process? Since 2005, CH2M HILL designed, constructed and has been operating a hexavalent chromium removal facility in California using the RCF process (Figure 1-1) that works by first reducing hexavalent chromium to trivalent chromium by dosing ferrous chloride into the water. After a few minutes of reaction time, the water is aerated to precipitate the iron and the reduced trivalent chromium is sent to a clarifier and then filtered using a microfilter membrane to remove solids. Since oxygen precipitates iron quickly, but is slow to oxidize chromium, the process successfully reduces and removes hexavalent and trivalent chromium below 10 µg/l as shown in Figure 1-2. Other filters including gravity and pressure media filters can also be used to remove the precipitated iron and trivalent chromium. FERROUS CHLORIDE MIXER AERATION TANKS CLARIFIER MICRO FILTRATION Figure 1-1. Hexavalent Chromium Removal with Reduction/Coagulation/Filtration (RCF) Process (this process schematic shows a membrane filter; however, media filters are also used in the RCF process) CH2M 1-2

8 SECTION 1 EXECUTIVE SUMMARY Cr(VI) Cr(T) Cr(VI) Limit Cr(T) Limit CR, MG/L Treatment Goal for this Confidential Client Site is 8 ug/l Aug-05 Apr-06 Jan-07 Oct-07 Jul-08 Apr-09 Jan-10 Oct-10 Jul-11 Mar-12 Dec-12 Note: Non-detect values plotted at reporting limits Figure 1-2. Confidential Client Hexavalent and Total Chromium Concentrations from 2005 through 2012 after Microfiltration, demonstrates a long Operational Track Record with Reduction, Coagulation and Filtration In addition, the City of Glendale CA, the Water Research Foundation and the USEPA investigated a number of treatment technologies for hexavalent chromium removal, including the RCF process. In one Tailored Collaboration Study between the City of Glendale and the Water Research Foundation (WRF Project: Microfiltration in the RCF Process for hexavalent Chromium Removal from Drinking Water, 2015) the results showed that a dose of 2 mg/l of iron was needed to effectively reduce the hexavalent chromium. The results also showed that oxidation with air alone resulted in some membrane fouling, which was mitigated with clean-in-place procedures. Capital cost and O&M costs were developed for hexavalent chromium treatment systems in this study and they ranged from $524 to $2,474 per acrefoot of water treated. In another Tailored Collaboration study between the City of Glendale, California Water Service Company, the State of California and Water Research Foundation (WRF Project: Assessment of Ion Exchange, Adsorptive Media, and RCF for Cr(VI) Removal, 2015), the results indicated the RCF process needed several minutes for reduction and that re-oxidation was not always optimal with aeration. 1.6 What is the treatment technology being investigated at Cadiz? In the testing at the Cadiz site, the technology that is used is a simplified version of RCF. The treatment system uses process equipment supplied by ATEC Water Treatment Systems (ATEC). The treatment system uses a pipeline reactor with ferrous chloride injection. The ATEC technology tested is a pressure filtration system that has been used extensively in the US for iron, manganese and arsenic removal since There are several hundred ATEC filter installations on groundwater treatment facilities, including many in California. The ATEC system used a pipeline contactor for both the reduction reaction as well as the oxidation reaction, as shown in Figure 1-3. CH2M 1-3

9 SECTION 1 EXECUTIVE SUMMARY Figure 1-3. ATEC Pilot Filter Schematic Table 1-1 lists the average treatment results across all scenarios tested using the ATEC system. Note that these numbers include samples taken after breakthrough and immediately following filter backwash. The system was able to meet the Cadiz treatment goals for hexavalent chromium and total chromium, which are significantly lower than the regulatory limits. For all the treated water pilot testing results, 68.2% of the total chromium tests and 93.2% of the hexavalent chromium tests were below the treatment goal of 2 µg/l. Arsenic was already below the regulatory level of 10 µg/l, but some reduction in arsenic was also achieved to a level below the established treatment goal. For all of the treated water arsenic tests collected during pilot testing, 70.5% were below the treatment goal of 3 µg/l for arsenic.. Iron and manganese were also both at levels below the treatment goals and regulatory standards, however, some manganese levels actually increased from the raw water to the finished water. It is believed that the source of the manganese was from new media in the filter, which is a manganese dioxide ore. As the proposed treatment system typically is used for removal of iron and manganese, the observed levels from this pilot testing are not expected to occur and will be substantially lower in the full-scale system. Raw water iron shown in Table 1-1 is actually from the filter influent, after ferrous chloride was added. The finished water iron levels were also slightly above the treatment goal on average. There are two reasons for this; first the chemical feed dosing of ferrous chloride was at times very high, and second, the pilot operators used the effluent iron as a signal for the end of a filter run, often letting it exceed the treatment goal. The filter system selected for this pilot test, is actually used widely for iron and manganese removal in groundwater systems, and it is believed that the treated water levels will be significantly lower in a full-scale system. CH2M 1-4

10 SECTION 1 EXECUTIVE SUMMARY Table 1-1. Pilot Testing Treatment Results for ATEC Treatment System Operating Conditions Parameter Flow Loading Rate Differential Pressure Average Value 4.6 gpm a 5.9 gpm/sf a 2 3 psi Water Quality Results Parameter Raw Water Treated Water Percent Removal Treatment Goal Regulatory Standard Hexavalent chromium µg/l 0.99 µg/l 95% 2 µg/l 10 µg/l Total chromium µg/l 1.60 µg/l 91% 2 µg/l 50 µg/l Arsenic 7.15 µg/l 1.84 µg/l 79% 3 µg/l 10 µg/l Iron 3,623 µg /L 180 µg /L 95% 150 µg/l 300 µg/l Manganese <2 µg /L 5.3 µg /L None 25 µg/l 50 µg/l a Values represent average conditions; variations were experienced during backwash events. Raw water iron is the filter inlet concentration µg/l = micrograms per liter gpm/sf = gallons per minute per square foot psi = pounds per square inch 1.7 What does the Treatment System Cost for Hexavalent Chromium and Arsenic Removal? Based on the capacity of the system installed and the operating scenarios, the costs for treatment are estimated to range between $26 and $54/AF. The full range is shown in Table 1-2 and is based on the Construction and operating costs presented in Section 7 of this report. Table 1-2. Cost Estimates for Cadiz Water Treatment Option Acre-Feet Delivered Per Year 50,000 50,000 50,000 50,000 75,000 75,000 Operating Period 10 Months 10 Months 11 Months 11 Months 11 Months 11 Months Amount of Treatment Full Partial Bypass Full Partial Bypass Full Partial Bypass Construction Cost $23,900,000 $12,200,000 $21,800,000 $11,000,000 $32,000,000 $16,300,000 Annual O&M $810,000 $560,000 $770,000 $530,000 $1,000,000 $650,000 Cost Per Acre- Foot* $54.56 $30.78 $50.39 $28.25 $47.57 $26.11 * Cost per Acre-Foot based on a discount rate of 5% and a 20 Year Bond Repayment. Costs do not include design or other nonconstruction costs or disposal of solids. These costs are significantly lower than other estimates of hexavalent chromium treatment, primarily because of the lower capital and O&M costs achieved through using the pipeline reactors for reduction CH2M 1-5

11 SECTION 1 EXECUTIVE SUMMARY and oxidation, and by using a pressure filtration system that does not require a clearwell or re-pumping. Backwashing with the system is simplified the system supplies backwash water internally and does not require a backwash supply tank, backwash pumps or air scour. CH2M 1-6

12 SECTION 2 Cadiz Water Project 2.1 Introduction and Background Cadiz Inc., (Cadiz) is a private corporation that owns approximately 34,000 mostly contiguous acres in the Cadiz and Fenner Valleys (Cadiz Property), which are located in the Mojave Desert portion of eastern San Bernardino County, California. Cadiz Inc., in collaboration with other water providers participating in the Project (Project Participants), have collaboratively developed the Cadiz Valley Water Conservation, Recovery, and Storage Project (Water Project) to implement a comprehensive, long-term groundwater management program for the closed groundwater basin underlying its property that would allow for both the beneficial use of the groundwater and storage of imported surface water in the groundwater basin. Underlying the Cadiz and Fenner Valleys and the adjacent Bristol Valley is a vast groundwater basin that holds an estimated 17 to 34 million acre-feet (MAF) of fresh groundwater. The Project area, which would be sited on Cadiz Property, is located at the confluence of the Fenner, Orange Blossom Wash, Bristol and Cadiz Watersheds (Watersheds), which span over 2,700 square miles. Within this closed basin system, groundwater percolates and migrates downward from the higher elevations in the Watersheds and eventually flows to Bristol and Cadiz Dry Lakes. The Dry Lakes represent the low point in the closed watershed basin, meaning that all surface and groundwater within the surrounding Watersheds eventually flows down gradient to these Dry Lake areas and not beyond. Once the fresh groundwater reaches the Dry Lake areas, it evaporates, first mixing with the highly saline groundwater zone under the Dry Lakes and getting trapped in the salt sink, no longer fresh, suitable, or available to support freshwater beneficial uses. The portion that evaporates is lost from the groundwater basin and is therefore also unable to support beneficial uses. 2.2 Conceptual Project Overview The proposed Project includes two distinct but related components: A Groundwater Conservation and Recovery Component An Imported Water Storage Component, It is projected that an average annual delivery of up to 50,000 acre-feet (AF) of groundwater would be pumped from the basin over a 50-year period for delivery to Project Participants in accordance with agreements with Cadiz Inc., and the Cadiz Groundwater Management, Monitoring and Mitigation Plan (GMMMP). The GMMMP has been developed to guide the long-term groundwater management of the basin for the Project. The level of groundwater pumping proposed under the Groundwater Conservation and Recovery Component is designed specifically to extract and conserve groundwater that would otherwise migrate to the Dry Lakes, enter the brine zone, and evaporate. The facilities proposed for this component of the Project include a wellfield, manifold (piping) system, a 43-mile conveyance pipeline, monitoring features, other appurtenances and fire suppression mechanisms. The wellfield and manifold (piping) system would be constructed on Cadiz Property to carry pumped groundwater to the conveyance pipeline, which would be constructed along the Arizona and California Railroad (ARZC) Right of Way and tie into the Colorado River Aqueduct (CRA), which would distribute water to Project Participants via the Metropolitan Water District of Southern California (MET). A power conveyance system would be installed that would convey energy to the wellfield from CH2M 2-1

13 SECTION 2 CADIZ WATER PROJECT natural gas engines or from electricity from the grid. In addition, to meet ARZC s fire suppression and operational water needs, fire hydrants would be installed along the conveyance pipeline at strategic locations along the railroad tracks (e.g., at bridge trestles). Withdrawal of water for this Project component would be limited to a maximum of 75,000 AFY of water in any given year and a total of 50,000 AFY on average over the 50-year term of the Project. MET owns and operates the CRA and it is anticipated that water treatment will be required on the Cadiz groundwater prior to entering the aqueduct. It is anticipated that the treatment facilities would be located in between the two proposed well fields that would be developed as part of the Cadiz water project as shown on Figure 2-1. Figure 2-1. Google Earth Image Showing Conceptual Location of Water Treatment, Ag Wells, High Wells and Transmission Route to the Colorado River Aqueduct. 2.3 Groundwater Quality Table 2-1 summarizes water quality parameters for groundwater sampled from the alluvium, and carbonate units in Fenner Gap and from the Colorado River just below Parker Dam. Parker Dam holds Lake Havasu on the Colorado River from which MET pumps water into the CRA. Thus, the Parker Dam water sample results are considered to represent CRA water quality. None of the parameters in Table 2-1 have primary maximum contaminant levels (MCLs). The secondary MCLs listed in Table 2-1 are aesthetic based water quality parameters that water purveyors should achieve at the point of distribution. There was extensive water quality testing conducted for the Cadiz groundwater wells, but a discussion of the overall water quality was not part of this pilot testing project. These parameters were provided to give a general sense of the water quality. As shown in Table 2-1, both the CRA water and the Cadiz groundwater currently meet the drinking water standards before treatment. For the Groundwater Conservation and Recovery Component of the Project, groundwater would be pumped from the alluvial and carbonate units in the Fenner Gap area into the water conveyance pipeline from the wellfield to the CRA, where the water would be added to the CRA water and then sent on to the water purveyors. The percentage of Cadiz water relative to CRA CH2M 2-2

14 SECTION 2 CADIZ WATER PROJECT water may range from approximately two to 15 percent 1. Based on this overall evaluation, the potential impact would be considered less than significant. Table 2-1. Summary of Selected General Water Quality Parameters from Cadiz Wells Parameter CA Secondary MCL 3 CADIZ Wellfield Representative Average 1 Colorado River Aqueduct Average 4 Total Dissolved Solids, mg/l 500-1, Conductivity, us/cm ph, S.U. None Calcium, mg/l None Magnesium, mg/l None Chloride mg/l Sulfate, mg/l Sodium, mg/l None Potassium, mg/l None Total Alkalinity, mg/l as CaCO3 None Total Organic Carbon, mg/l None Representative Average is weighted based on the Capacity of the wells. 2 - Potential Treatment Technique above 2 mg/l based on DBP Levels 3 - California Secondary MCLs are recommended and Upper Limit are from 17 CCR Metropolitan Water District of Southern California 2014 Annual Report However, the groundwater does have some naturally occurring, elevated concentrations of hexavalent chromium, as well as the presence of low levels of arsenic, iron and manganese in some wells. These constituents are the preliminary water treatment constituents. The average Cadiz wellfield concentrations are shown in Table 2-2. The regulatory limits for the parameters are also listed in Table 2-2. There are primary standards for chromium, chromium-6, and arsenic. Primary standards are established to protect public health. Secondary, non-health based standards for iron and manganese are also listed in Table 2-2. Cadiz has set a treatment goal of 2 µg/l for total and hexavalent chromium. 2 µg/l is similar to the treatment goal that was established in testing completed by MET in 2015 to achieve at least 90% removal in the finished water using RCF treatment (Sun Liang and Shannon M. Macieko, 2015). Cadiz has set a treatment goal of 3 µg/l for Arsenic, which is comparable to the levels in CRA water. Goals for iron and manganese were set at the current secondary standards or 300 and 50 µg/l respectively. Table 2-2. Preliminary Water Treatment Target Constituents Parameter California Primary or Secondary MCL Federal Standard Cadiz Wellfield Average Concentrations Cadiz Treatment Goal Chromium, Total (includes both chromium-6 and chromium-3) 50 µg/l 100 µg/l 13.4 µg/l 2 µg/l Chromium-6 10 µg/l None 12.9 µg/l 2 µg/l 1 This range is based on a range of CRA flows of between 500,000 and 1.1 MAF and Cadiz flows of 25,000 to 75,000 AFY. CH2M 2-3

15 SECTION 3 HEXAVALENT CHROMIUM AND ARSENIC IN GROUNDWATER Arsenic 10 µg/l 10 µg/l 6.9 µg/l 3 µg/l Iron 300 µg/l (secondary) 300 µg/l (secondary) 1.6 mg/l 150 µg/l Manganese 50 µg/l (secondary) 50 µg/l (secondary) 15.4 µg /L 25 µg/ Hexavalent Chromium and Arsenic in Groundwater 3.1 Introduction Hexavalent chromium can be removed from water using a handful of proven treatment techniques depending on the level present in the source water, removal goals, other water quality parameters, competing treatment objectives, and treatment waste disposal options. Anion exchange (both strongbase and weak-base), membrane filtration by nanofiltration and reverse osmosis, reduction followed by coagulation and precipitation, and adsorption can remove hexavalent chromium from drinking water. Research conducted by a collaboration of southern California drinking water utilities Water Research Foundation, 2016), EPA, and the Water Research Foundation found that weak-base anion exchange and reduction-coagulation-filtration could remove hexavalent chromium to below 5 ppb for the utilities particular groundwater source. Other California utilities participating in additional studies found that strong-base anion exchange was a viable treatment for their particular water sources, particularly if residuals disposal options were readily available. For the Cadiz wellfield, we focused on Reduction Coagulation Filtration (RCF) because of the potential for cost effectively treating a large-scale supply potentially with a treatment capacity of 80 mgd. Weak based ion exchange would require periodic replacement of the resin and strong based ion exchange would require periodic regeneration with sodium chloride or other regenerant, which would be very difficult to dispose in the remote Mojave Desert location. 3.2 Hexavalent Chromium Occurrence Hexavalent chromium is an oxidized form of chromium that can exist as chromium (VI) oxide, chromic acid, chromate or dichromate in groundwater. Hexavalent chromium can exist in natural groundwaters or in waters that have been affected by local industrial activity. In natural groundwaters, hexavalent chromium is thought to be oxidized by manganese dioxide containing minerals from naturally occurring chromium (III)-bearing minerals. The presence of hexavalent chromium is dependent on the ph and oxidation conditions of the groundwater. Chromium is a metal found in natural deposits of ores containing other elements, mostly as chrome-iron ore. It is also widely present in soil and plants. Under most conditions, natural chromium in the environment occurs as Chromium(III), or trivalent chromium. Under oxidizing conditions, alkaline ph range, presence of manganese dioxide and minerals containing chromium, part of it may occur as hexavalent chromium dissolved in groundwater. Recent sampling of drinking water sources throughout California suggests that hexavalent chromium may occur naturally in groundwater at many locations. Naturally occurring hexavalent chromium may be associated with serpentinite-containing rock or chromium containing geologic formations. Chromium has two main oxidation states: trivalent chromium (Cr(III), chromium-3, Cr+3), and hexavalent chromium (Cr(VI), chromium-6, Cr+6). As a general rule, hexavalent chromium is expected to predominate in highly oxygenated drinking water or when strong oxidants such as chlorine or even moderately strong oxidants like chloramine are present in water. At low Cr concentrations in typical CH2M 3-4

16 SECTION 3 HEXAVALENT CHROMIUM AND ARSENIC IN GROUNDWATER drinking water conditions, hexavalent chromium is present as monovalent HCrO4 below ph 6.5 and divalent CrO4 2 between ph 6.5 to 10. At very low or no oxygen levels, Cr(III) is the dominant species, which will be in cationic (Cr +3, CrOH +2, or Cr(OH) 2 + ) or neutral (Cr(OH) 30 ) form depending on the ph. Cr(III) tends to be extremely insoluble (< 20 μg/l) between ph 7 and ph 10, with minimum solubility at ph 8 of about 1 μg/l. 3.3 Hexavalent Chromium Water Quality Regulations Federal Regulations There is no federal standard for hexavalent chromium. There is a national primary drinking water regulation that established the maximum contaminant level (MCL) for total chromium of 0.1 mg/l or 100 µg/l, which was promulgated in In 2010, the USEPA initiated a reassessment of the health risks associated with hexavalent chromium and total chromium. That assessment is still underway California Regulations In 1999, as part of the process of reviewing MCLs in response to public health goals (PHGs), the California Department of Public Health's (CDPH's) precursor, the California Department of Health Services (CDHS), identified the total chromium MCL (see below) as one for review. (CDPH s Drinking Water Program is now the State Water Resources Control Board s Division of Drinking Water.) In July 2011 OEHHA established a Public Health Goal (PHG) for chromium-6 of 0.02 μg/l. The PHG represents a de minimis lifetime cancer risk from exposure to chromium-6 in drinking water, based on studies in laboratory animals. OEHHA also prepared a PHG fact sheet. The availability of the chromium-6 PHG enabled CDPH to proceed with setting a primary drinking water standard. In August 2013 CDPH proposed an MCL for chromium-6 of milligram per liter (equivalent to 10 μg/l) and announced the availability of the proposed MCL for public comment. On April 15, 2014, CDPH submitted the hexavalent chromium MCL regulations package to the Office of Administrative Law (OAL) for its review for compliance with the Administrative Procedure Act. On May 28, OAL approved the regulations, which were effective on July 1, Treatment Alternatives for Hexavalent Chromium In Situ Treatment Hexavalent chromium is readily and rapidly reduced to the somewhat insoluble, low-toxicity trivalent form, which precipitates out of solution. Most in-situ treatment technologies rely on creating geochemically reducing conditions in an aquifer to remove hexavalent chromium from groundwater. Reducing conditions can be achieved through injection of organic substrates such as ethanol or lactate, or by injecting inorganic reductants such as calcium polysulfide (also effective on vadose zone soils when flushed) and zero valent iron. Because hexavalent chromium is often co-located with chlorinated solvents related to metal-plating operations, it is not uncommon to treat both contaminants with biologically induced reductive chemistry. Localized geochemically reduced zones in aerobic aquifers can also reduce hexavalent chromium and cause it to precipitate. In-situ remediation of hexavalent chromium most often is designed to form chromium hydroxide (Cr(OH) 3 ) which has a low solubility in water and can often be immobilized in the aquifer matrix. Methods to remediate hexavalent chromium in the groundwater matrix include: Sulfur reduction methods CH2M 3-5

17 SECTION 3 HEXAVALENT CHROMIUM AND ARSENIC IN GROUNDWATER Calcium polysulfide reduction Sodium dithionate reduction of ferrous iron Aerobic microbial reduction Anaerobic microbial reduction Ex-Situ Treatment Hexavalent chromium is found more often in groundwaters than in surface waters. It can be removed using a handful of proven treatment techniques depending on the level present in the source water, removal goals, other water quality parameters, competing treatment objectives, and treatment waste disposal options. Current treatment options for hexavalent chromium in drinking water are shown in Table 3-1. In development of the hexavalent chromium MCL, the state of California identified Reduction/Coagulation/Filtration and Ion Exchange as Best Available Treatment (BAT). Table 3-1. Treatment Alternatives for Hexavalent Chromium Treatment Process Benefits Drawbacks BAT: Reduction/Coagulation/ Filtration BAT: Anion Exchange with Weak Base Anion (WBA) Resins BAT: Anion Exchange with Strong Base Anion (SBA) resins Uses readily available technologies General familiarity with process High removal capacity in some resins Well understood technology and process Residuals handling Control of Reduction step important for removal Resin disposal ph dependent Varies among manufacturers Not well understood Brine disposal Loss of capacity after multiple regenerations Granular Activated Carbon Some Effectiveness at very low ph ph adjustment required may not work well for very low concentrations Reverse Osmosis Very effective High costs, High energy use Brine disposal Reduction/Microfiltration Should be effective Little installed capacity Reject water disposal Nanofiltration Very effective High costs, High energy use Brine disposal Electrodialysis Very effective High costs, High energy use Brine disposal Zero-Valent Iron Adsorption Should be effective Little installed capacity Biological Reduction/Filtration Reduction occurs with IRB and SRB Little installed capacity BAT Listed as best available treatment by California Water Boards for Hexavalent Chromium Removal Reducing hexavalent chromium to trivalent chromium is relatively easy to accomplish. It involves providing a source of electrons (reductant) so that hexavalent chromium can be reduced to trivalent chromium. Potential reductants include stannous chloride, sulfide, sulfite, and ferrous iron compounds. Ferrous iron coagulants are among the most effective reductants for treating hexavalent chromium in CH2M 3-6

18 SECTION 3 HEXAVALENT CHROMIUM AND ARSENIC IN GROUNDWATER drinking water. The hexavalent chromium reduction reactions involving ferrous iron is shown in Equation 1. Equation 1: 3 Fe(OH)2 + CrO H2O => 3 Fe(OH)3 + Cr(OH)3 + 2 OH - Since 2005, CH2M HILL designed, constructed and has been operating a hexavalent chromium removal facility in California using a Reduction-Coagulation-Filtration process (Figure 3-1) that works by first reducing hexavalent chromium to trivalent chromium by dosing ferrous chloride into the water. After a few minutes of reaction time, the water is aerated to precipitate the iron and the reduced trivalent chromium is sent to a clarifier and filter (in this case a microfiltration membrane is used for the filter) to remove solids. Because oxygen precipitates iron quickly, but is slow to oxidize chromium, the process successfully reduces and removes hexavalent and trivalent chromium below 10 µg/l as shown in Figure 3-2. Media FERROUS CHLORIDE MIXER AERATION TANKS CLARIFIER MICRO FILTRATION Figure 3-1. Hexavalent Chromium Removal with Reduction/Coagulation/Filtration Process Cr(VI) Cr(T) Cr(VI) Limit Cr(T) Limit CR, MG/L The Treated Water Goal for this Confidential Client was 8 µg/l Aug-05 Apr-06 Jan-07 Oct-07 Jul-08 Apr-09 Jan-10 Oct-10 Jul-11 Mar-12 Dec-12 Note: Non-detect values plotted at reporting limits Figure 3-2. This treated water Hexavalent and Total Chromium Concentrations from 2005 through 2012 after Microfiltration for a Confidential Client Demonstrates a Long Operational knowledge based for Reduction, Coagulation and Filtration. In addition to reduction/coagulation/filtration, other techniques including high pressure membranes, weak base anion (WBA) resin ion exchange and strong base anion (SBA) resin ion exchange are also CH2M 3-7

19 SECTION 3 HEXAVALENT CHROMIUM AND ARSENIC IN GROUNDWATER effective. WBA resin ion exchange treatment consists of polymeric resin that must be utilized near ph 6 for effective hexavalent chromium removal, so ph readjustment is often necessary. One benefit of this treatment is that the resin can often run for very long periods without requiring regeneration, so it can be used as a disposable media. SBA resin ion exchange is also able to remove hexavalent chromium from water but requires regeneration with salt and brine disposal. Other processes are developing or have little installed capacity for hexavalent chromium removal. 3.5 Arsenic Occurrence Arsenic is found in surface and groundwater as a result of natural processes such as weathering of minerals and microbial activities. Major anthropogenic sources include mining, particularly smelting, and pesticide manufacture and use. A variety of industries also use arsenic compounds in their production processes. Generally, naturally occurring arsenic concentrations below 1 mg/l are most common but higher concentrations occur in some geologic environments. Inorganic forms of arsenic are most common, although organic arsenic compounds associated with microbial activity and pesticide manufacture do occur. Significant concentrations of organic arsenic are generally not found in groundwater used for drinking water supply. Aqueous, inorganic arsenic can exist in four valence states, As +5, As +3, As, As -3. Only As +5 (also referred to as As(V) or arsenate) and As +3 (referred to as As(III) or arsenite) are relevant for drinking water treatment. Speciation is dependent on ph and redox conditions. Oxidizing environments tend to produce arsenate forms while arsenite is produced in acidic reducing environments. Distribution diagrams for As(III) and As(V) as a function of ph indicate that arsenite is present largely as the undissociated acid, H 3AsO 3, below a ph of 9. As(V) is present largely as HAsO 4 2- at ph values above 7; H 2AsO - 4 predominates below Arsenic Removal Treatment Alternatives Since the arsenic MCL was lowered in 2001, there has been considerable research activity and implementation of full-scale treatment systems for arsenic removal. Several technologies are capable of removing arsenic to low levels. These include conventional and newer technologies including: coagulation, iron and manganese oxidation with precipitation and filtration, lime softening, activated alumina, oxide coated media, ion exchange, membrane filtration, and electrodialysis reversal. Adsorption onto media containing granular ferric hydroxide, titanium and aluminum has also been used effectively. Source water quality, operational characteristics and cost are all factors important to successful application. Each of these removal processes has advantages and disadvantages as shown in Table 3-2. Table 3-2. Comparison of Arsenic Removal Technologies Technology Benefits Drawbacks Reverse Osmosis Membrane Filtration Removal of As(III) and As(V) Inorganic, microbial, and organic removal also achieved. Low recovery and flux rates are typical Pretreatment and post treatment required Nano-Filtration Membranes Removal of As(V) Microbial and organic removal also achieved Removal of calcium and magnesium may be achieved Sensitivity to water quality Low recovery and flux rates are typical Pretreatment and post treatment required May not be effective for As(III) CH2M 3-8

20 SECTION 3 HEXAVALENT CHROMIUM AND ARSENIC IN GROUNDWATER Technology Benefits Drawbacks Ultra-Filtration Membranes Higher flux and recovery rates than RO or Nano-Filtration membranes Microbial removal achieved Waste Stream to can often be sent to WWTP Removal of particulate As only unless pretreatment with a coagulant is needed for removal Preoxidation and ph adjustment may be needed. Coagulation/Micro-Filtration Membranes Highest flux and recovery rates of membrane processes Some microbial removal achieved Waste Stream to can often be sent to WWTP Pretreatment with a coagulant is needed for removal Preoxidation and ph adjustment may be needed. Activated Alumina Less sensitive to water quality than ion exchange Longer run times than ion exchange ph adjustment often needed Aluminum levels may increase in finished water Hazardous chemicals needed for regeneration Residuals handling is difficult with concentrated high ph liquid stream Ion Exchange (Anion Exchange) Works better at higher ph levels than activated alumina Nitrate removal can also be achieved Sulfate levels may reduce run times Higher arsenic levels may leach from resin near end of run Requires regeneration and handling of concentrated brine solution Iron Based Sorbents Arsenic in backwash water is usually very low Relatively easy disposal of solids Some adsorbents have a fairly high sorption capacity Titanium Based Sorbents Arsenic in backwash water is usually very low Relatively easy disposal of solids Some adsorbents have a fairly high sorption capacity Works over wide range of ph Periodic media replacement required Cost and length of media use before replacement is needed is dependent on water quality Capacity decreases with increasing ph Periodic media replacement required Cost and length of media use before replacement is needed is dependent on water quality Conventional Filtration for Arsenic Removal Conventional filtration can be used to remove arsenic. Its effectiveness depends on the arsenic species, the type and dose of coagulant used and the ph of coagulation. Key process considerations for arsenic removal include: Arsenic has a high affinity for co-precipitation with iron, and to a lesser degree with aluminum. Removal is nearly always better for As(V) compared to As(III) It is relatively easy to convert As(III) to As(V) with free chlorine. Removal declines as ph increases, and is limited above ph 8.5 Ferric chloride and ferric sulfate generally remove arsenic at lower doses than alum Silica may interfere with coagulation around ph 7.5 Once co-precipitated, arsenic does not tend to leach from solids after drying. CH2M 3-9

21 SECTION 3 HEXAVALENT CHROMIUM AND ARSENIC IN GROUNDWATER Coagulation can be improved by carefully controlling ph, pre-oxidizing water prior to coagulation, and adding the proper amount of coagulant. A free chlorine residual of 1.0 mg/l is sufficient to oxidize As(III) to As(V) in 30 to 60 seconds for most waters within a ph range of 6 to 9. The disadvantages of conventional filtration are the relatively high capital cost, the relatively high O&M cost and the large amount of solids that must be disposed. Conventional filtration, which is similar to the RCF process can be used to remove arsenic. Its effectiveness depends on the arsenic species, the type and dose of coagulant used and the ph of coagulation. As shown in Figure 3-3, arsenic has a high affinity for iron coagulants. Removal is better at lower coagulant doses for As(V) than for As(III) at low ph. When ph is raised above 7.5 the removal decreases. Coagulation can be improved by carefully controlling ph oxidation, arsenic III to arsenic V and adding additional coagulant. The disadvantages of this technology are the relatively high capital cost, the relatively high O&M cost and the large amount of solids that must be disposed. Figure 3-3. Influence of Coagulant Dose, Arsenic Type and ph on Arsenic Removal Several studies have shown the arsenic removal capabilities of manganese oxides. Phommavong (1992) concluded that KMnO 4 oxidation of As(III) in conjunction with manganese dioxide filtration could reduce arsenic by 61% 98%. The removal mechanism was not determined, although adsorption to the oxide media surface was suspected. Competition between arsenic and manganese for surface sites was also a factor suspected of affecting treatment performance. The Department of Saskatchewan Environment and Public Safety has developed an unpublished report documenting up to 95% arsenic removal from several full-scale manganese greensand plants. Subramamian, et al. (1995) found that manganese dioxide could effectively reduce As(III) if Fe(II) is present in the raw water at an iron/arsenic ratio of at least twenty and raw water As(III) concentration is below 200 µg/l Potential for Simultaneous removal of Hexavalent Chromium and Arsenic While treating for hexavalent chromium removal with ferrous chloride or ferrous sulfate, it is possible to see some arsenic removal. For optimized arsenic removal, we would normally want to pre-oxidize the arsenic prior to adding an iron based coagulant. However, in a Water Research Foundation Study (Simultaneous Oxidation and Removal of As(III) and As(V) by Electrocoagulation Filtration, 2011), Lakshamanan, Clifford and Samanta found that ferrous iron was formed in the electrocoagulation cell and that after oxidizing it to ferric iron, arsenic removal could occur. The oxidation used in this study is CH2M 3-10

22 SECTION 3 HEXAVALENT CHROMIUM AND ARSENIC IN GROUNDWATER with air, therefore it is likely that the arsenic will remain in the As(III) form prior to filtration, but some removal should be realized Proposed Treatment System for Pilot Testing The treatment system that CH2M proposed for pilot testing is a simplified version of Reduction Coagulation Filtration. The reduction from hexavalent chromium to trivalent chromium occurs in a pipeline, rather than a mixing tank. Similarly, the oxidation of iron occurs in a pipeline rather than in a mixing vessel or reactor tank. The reasons to use a pipeline for the reduction and oxidation reactions are two-fold. First, Cadiz already must construct a pipeline to transfer the water from the wells to the treatment plant site, which reduces the treatment infrastructure costs considerably, and second, by using a pipeline reactor, the pumped water can be maintained under pressure, which eliminates the need for re-pumping and storage. For the removal of trivalent chromium and iron, CH2M proposed using pressure filters with manganese dioxide media based on ATEC s system. ATEC has a long history of successful cost-effective operations for treatment of iron, manganese and arsenic in groundwater and their manufacturing facility is based in California. RCF treatment based on ATEC system was also recently successfully tested for hexavalent chromium removal at California Water Service Company s Las Lomas and Oak Hills facilities using a manganese dioxide pilot system, which was completed by Corona Environmental Consulting in April The system tested was similar to the proposed treatment system for Cadiz, however, they used chlorine to oxidize the iron rather than air. They found that reduction of hexavalent chromium occurred in as little as one minute and once reduced was effectively removed by the manganese dioxide media. California Water Service Company has been successfully operating the Las Lomas facility for over a year (personal communication Bill Ketchum 2016). Manganese dioxide media has been used extensively for iron, manganese and arsenic removal since 1996 in California, the U.S, and Canada by ATEC Water Treatment Systems. Table 3-3 shows a summary of ATEC facilities that have been pilot tested, designed, constructed between 1997 and 2003, and are in full-scale operation in Oregon, Washington and California. These systems participated in a survey of fullscale operations, water quality and treatment costs. Well capacities in the survey ranged from 31 to 4,500 gpm. Loading rates of the adsorption facilities range from 8.0 gpm/sq. ft. to 15 gpm/sq.ft. Table 3-3. Surveyed Systems ATEC Iron and Manganese Facilities Location Well Capacity gpm (m 3 /hr) Facility Installed year Vessels No dia. Loading Rate gpm/sq ft (m/hr) Raw Water Iron Conc. mg/l Raw Water Manganese Conc. mg/l Jefferson County PUD, WA (8) (26) Garden Farms, CA 1 45 (12) (37) Klickitat County PUD, WA NW 100 (27) (27) Skagit County PUD, WA A1 100 (27) (33) Ames Lake, WA (34) (26) Skagit County, WA CG1 150 (40) (31) Cedar Shores, WA 1 96 (26) (20) Glacier Vista, WA 1 64 (17) (23) The Dalles, OR DC 350 (94) (28) Clark Public Utilities, WA FBP 200 (54) (28) CH2M 3-11

23 SECTION 3 HEXAVALENT CHROMIUM AND ARSENIC IN GROUNDWATER Location Well Capacity gpm (m 3 /hr) Facility Installed year Vessels No dia. Loading Rate gpm/sq ft (m/hr) Raw Water Iron Conc. mg/l Raw Water Manganese Conc. mg/l Kitsap County PUD, WA K2 400 (107) (27) Kitsap County PUD, WA E5 250 (67) (59) Rainier View Water Co., Country Park, WA (67) (28) Cape George, WA (38) (13) Halsey, OR (94) (28) Rainier View Water Co., Artondale, WA (63) (28) Kitsap County PUD, WA K1 200 (54) (26) Clark Public Utilities, WA (107) (39) Fullerton, CA 12A 500 (134) (26) Clark Public Utilities 21 1,025 (275) (26) Battle Ground, WA 7/8 2,000 (537) (34) Sherwood, OR (Tualatin Valley Water District) (148) (28) Utility A* 8 1,200 (322) (31) Southern California Water Co. Century 500 (134) (26) Southern California Water Co. Juan 850 (228) (29) Spanaway Water Company, WA 4 1,200 (322) (31) Lakewood Water District, WA S1 800 (215) (27) Lakewood Water District, WA Q1 1,200 (322) (31) City of Lacey, WA 7 1,700 (456) (25) City of Batavia, IL 6,7,8 4,500 (1,208) (23) *This utility requested its name not be used in this paper Table 3-4 shows the removal efficiencies obtained in pilot testing compared to full-scale operation. Removal efficiencies for iron are typically somewhat less than for manganese however, both are typically above 90%. Table 3-4. Comparison of Pilot Removal Efficiency and Full Scale Removal Efficiency in Manganese Dioxide Media Filters Pilot Testing Removal (%) Full-Scale Removal (%) Location Well Iron Mang. n Iron Mang. n Jefferson County, WA >99 5 Garden Farms, CA >99 >99 4 CH2M 3-12

24 SECTION 3 HEXAVALENT CHROMIUM AND ARSENIC IN GROUNDWATER Pilot Testing Removal (%) Full-Scale Removal (%) Klickitat County PUD, WA NW Skagit County PUD, WA A >99 >99 3 Ames Lake, WA to >99 34 to 99 8 Skagit County PUD, WA CG >99 >99 3 Cedar Shores, WA >99 >99 2 Glacier Vista, WA >99 >99 2 The Dalles, OR DC >99 >99 4 Clark Public Utilities, WA FBP >99 >99 21 Kitsap County PUD, WA K >99 >99 4 Kitsap County PUD, WA E >99 >99 4 Rainier View Water Co., Country Park, WA 2 > >99 >99 7 Cape George, WA >99 5 Halsey, OR >99 >99 3 Rainier View Water Company, Artondale, WA >99 >99 5 Kitsap County PUD WA K >99 >99 3 Clark Public Utilities, WA Fullerton, CA 12A >99 >99 6 Clark Public Utilities, WA >99 >99 4 Battle Ground, WA 7/ to >99 86 to > Sherwood, OR (Tualatin Valley Water District) >99 >99 4 Utility A >99 >99 6 Southern California Water Co. Century >99 >99 24 Southern California Water Co. Juan >99 >99 8 Spanaway Water Company, WA >99 2 Lakewood Water District, WA S >99 13 Lakewood Water District, WA Q City of Lacey, WA City of Batavia, IL 6,7, Multiple tanks, mani-folded together at the top and bottom, are used in the design of the ATEC filters to provide an-internally-supplied source of treated backwash water, eliminating the need for a backwash pump or an external source of supply. This is an important cost saving feature, because backwashing CH2M 3-13

25 SECTION 3 HEXAVALENT CHROMIUM AND ARSENIC IN GROUNDWATER requires between 26 and 30 gpm/sq ft to fluidize the bed and adequately scrub the iron and manganese from the filter media. Table 3-5 shows the design components that were included in each of the full-scale projects for these facilities. All facilities included iron and manganese removal equipment, some were retrofitted into existing buildings (Ret), and some required construction of additions (Add) or new buildings (New). Some projects included installation of well pumps; new motor control centers, SCADA systems and chemical feed systems. Backwash disposal was accomplished either by infiltration (Inf), treatment and disposal to stormwater systems (Tre), recycling (Rec), or in the sanitary sewer (San). Table 3-5. Project Construction Components for Surveyed ATEC Water Treatment Systems Location Fe/Mn Building Chem Feed MCC/PLC Backwash SCADA Pump Jefferson County PUD, WA Ret Inf Garden Farms, CA New Inf Klickitat County PUD, WA New Inf Skagit County PUD, WA Ret Tre Ames Lake, WA Ret Inf Skagit County PUD, WA Ret Tre Cedar Shores, WA Ret Inf Glacier Vista, WA Ret Inf The Dalles, OR New Inf Clark Public Utilities, WA New Inf Kitsap County PUD, WA New Tre Kitsap County PUD, WA New Tre Rainier View Water Co., Country Park Well, WA New Inf Cape George, WA New Inf Halsey, OR New San Rainier View Water Company, Artondale, WA New Inf Kitsap County PUD, WA New Inf Clark Public Utilities, WA New Rec Fullerton, CA Pad Rec Clark Public Utilities, WA New Inf Battle Ground, WA New Inf Sherwood, OR (Tualatin Valley Water District) Ret San Utility A New Inf Southern California Water Co. Century Pad Tre CH2M 3-14

26 SECTION 3 HEXAVALENT CHROMIUM AND ARSENIC IN GROUNDWATER Location Fe/Mn Building Chem Feed MCC/PLC Backwash SCADA Pump Southern California Water Co. - Juan Pad Tre Spanaway Water Company, WA New Inf Lakewood Water District, WA S1 New Tre Lakewood Water District, WA Q1 New Inf City of Lacey, WA Pad Inf City of Batavia, IL New Inf Table 3-6 shows capital costs for each facility updated to 2016 dollars using ENR Construction Cost Index 20 Cities Average. Capital costs are broken down by treatment equipment cost, and total project cost. Treatment costs include vessels, media, manifolds, backwash controller, backwash flowmeter and pressure relief valve. Total project costs include equipment costs; chemical feed costs, design, administration, permitting, and construction of project components shown in Table 3-5. Table 3-6. Capital Costs of ATEC Water Treatment Surveyed Systems, Escalated to 2016 Dollars Location Capacity, gpm Year Constructed Equipment Cost 2016$ Total Project Cost 2016 $ Jefferson County PUD, WA $16,000 $24,000 Garden Farms, CA $26,000 $41,000 Klickitat County PUD, WA Skagit County PUD, WA $28,000 $50,000 Ames Lake, WA $31,000 $54,000 Skagit County PUD, WA $35,000 $76,000 Cedar Shores, WA $27,000 $45,000 Glacier Vista, WA $27,000 $51,000 The Dalles, OR $59,000 $67,000 Clark Public Utilities, WA $54,000 $144,000 Kitsap County PUD, WA $61,000 $286,000 Kitsap County PUD, WA $42,000 $254,000 Rainier View Water Company, Country Park Well, WA $50,000 $96,000 Cape George, WA $62,000 $242,000 Halsey, OR $64,000 $72,000 Rainier View Water Company, Artondale, WA $50,000 $135,000 Kitsap County PUD, WA $57,000 $344,000 Clark Public Utilities, WA $55,000 $142,000 Fullerton, CA $203,000 $479,000 CH2M 3-15

27 SECTION 3 HEXAVALENT CHROMIUM AND ARSENIC IN GROUNDWATER Location Capacity, gpm Year Constructed Equipment Cost 2016$ Total Project Cost 2016 $ Clark Public Utilities, WA 1, $160,000 $429,000 Battle Ground, WA 2, $96,000 $1,366,000 Sherwood, OR (Tualatin Valley Water District) $81,000 $134,000 Utility A 1, $176,000 $624,000 Southern California Water Co. Century* $292,000 $1,095,000 Southern California Water Co. - Juan, CA* $257,000 $930,000 Spanaway Water Company, WA 1, $176,000 $732,000 Lakewood Water District, WA S $127,000 $585,000 Lakewood Water District, WA Q1 1, $158,000 $686,000 City of Lacey, WA 1, $260,000 $1,023,000 City of Batavia, IL 4, $966,000 $3,493,000 Table 3-7 shows operations and maintenance costs for each facility, escalated to 2016 dollars. Electrical costs are limited to filter and controller costs, building heating and ventilation, and other associated electrical costs. Electrical costs do not include well pumping, except to for headloss through the treatment equipment. Chemical costs are limited to chlorine feed costs. Monitoring costs for systems using field-monitoring equipment are amortized over a 5-year life of the equipment. Labor costs are based on actual visits reported by utility personnel for iron and manganese monitoring, or maintenance. Backwash disposal cost is not provided for the one system discharging to sanitary sewer since no monthly or flow fees are charged to the utility. Table 3-7. Annual Operations and Maintenance Costs Report for ATEC Systems, in 2016 dollars Location Electrical Chemical Labor Monitoring Total Jefferson County PUD, WA $800 $200 $3,200 $1,500 $5,700 Garden Farms, CA $1,300 $300 $6,100 $1,500 $9,200 Klickitat County PUD, WA $500 $800 $6,100 $1,500 $8,900 Skagit County PUD, WA $500 $800 $6,100 $1,500 $8,900 Ames Lake, WA $1,000 $300 $3,200 $200 $4,700 Skagit County PUD, WA $200 $1,100 $3,100 $1,500 $5,900 Cedar Shores, WA $100 $2,600 $3,100 $500 $6,300 Glacier Vista, WA $100 $2,600 $3,100 $500 $6,300 The Dalles, OR $300 $1,000 $3,000 $1,200 $5,500 Clark Public Utilities, WA $1,300 $3,600 $3,300 $1,500 $9,700 Kitsap County PUD, WA $1,400 $6,600 $6,000 $1,400 $15,400 Kitsap County PUD, WA $1,000 $4,600 $6,000 $1,400 $13,000 CH2M 3-16

28 SECTION 3 HEXAVALENT CHROMIUM AND ARSENIC IN GROUNDWATER Location Electrical Chemical Labor Monitoring Total Rainier View Water Company, Country Park Well, WA $600 $2,700 $3,200 $600 $7,100 Cape George, WA $300 $300 $6,100 $1,100 $7,800 Halsey, OR $400 $2,500 $3,200 $1,800 $7,900 Rainier View Water Company, Artondale, WA $600 $2,700 $3,200 $1,500 $8,000 Kitsap County PUD, WA $400 $3,000 $6,000 $1,300 $10,700 Clark Public Utilities, WA $1,300 $3,600 $3,300 $1,500 $9,700 Fullerton, CA $100 $3,300 $6,000 $6,900 $16,300 Clark Public Utilities, WA $3,600 $6,400 $6,500 $1,500 $18,000 Battle Ground, WA $3,100 $8,300 $18,000 $5,200 $34,600 Sherwood, OR (Tualatin Valley Water District) $200 $3,900 $3,100 $1,500 $8,700 Utility A $7,700 $3,600 $6,100 $1,500 $18,900 Southern California Water Co. Century* $2,400 $3,100 $24,800 $13,400 $43,700 Southern California Water Co., Juan, CA* $2,700 $3,400 $24,800 $13,400 $44,300 Spanaway Water Company, WA $7,700 $3,900 $6,100 $1,500 $19,200 Lakewood Water District, WA $1,000 $3,500 $3,000 $1,300 $8,800 Lakewood Water District, WA $1,400 $3,800 $3,000 $1,300 $9,500 City of Lacey, WA $3,500 $19,500 $34,500 $7,900 $65,400 City of Batavia, IL $20,500 $10,400 $32,600 $6,000 $69,500 The survey demonstrates that the ATEC Water Treatment Systems provides an efficient cost-effective alternative for removing dissolved iron and manganese from groundwater supplies. Removal in pilot testing has been repeated in full-scale monitoring. Capital and annual O&M are reduced by the simplified design and smaller footprint of the equipment compared to conventional RCF systems that are typically described in the literature Water Treatment Residuals The types of residuals that are generated from the treatment processes are different for each type of treatment. In general, reduction/coagulation/filtration produces an iron sludge that can be dewatered and landfilled. Where sanitary sewers are available discharge limits for total chromium are normally 10 mg/l. The landfilled sludge cannot leach more than 5 mg/l of chromium in the Toxic Contaminant Leachate Potential (TCLP) test or the Waste Extraction Test (WET) in California. Cadiz is in an unusual position, in that it requires significant amounts of irrigation water year round. It may be possible that the reduced chromium in the filter backwash water, blended with additional with additional irrigation water would be suitable for crop irrigation. A mass balance is provided in the results section of this project report. CH2M 3-17

29 SECTION 3 HEXAVALENT CHROMIUM AND ARSENIC IN GROUNDWATER CH2M 3-18

30 SECTION 4 Pilot Testing methods and Materials Groundwater Quality Pilot testing was conducted with a vendor supplied system; ATEC Water Treatment System s Manganese Dioxide pressure filters. Initial testing was conducted to assess the applicability of the technology to Cadiz groundwater. Subsequent pilot tests were conducted to assess efficacy of the treatment process for a range of operating conditions as described below. 4.1 ATEC Pilot Equipment A schematic drawing of the pilot test equipment used in this study is shown on Figure 4-1. The pilot system consisted of the following: Ferrous chloride injection followed by 6-inch-diameter contact pipe from 6-foot to 25-foot-long Air eduction through a venturi eductor followed by an 8-foot-long, 6-inch-diameter contact pipe Four 6-inch-diameter cylindrical filters each containing approximately 0.6 cubic foot of ATEC 741 (Tradename) manganese dioxide media Figure 4-1. ATEC Pilot Filter Schematic Figure 4-2 shows a photograph of the Pilot Filters inside the ATEC Trailer. Figure 4-3 shows the reactor pipe segments. Figure 4-4 shows a photograph of the eductor and bypass pipe. CH2M 4-1

31 SECTION 4 PILOT TESTING METHODS AND MATERIALS GROUNDWATER QUALITY Figure 4-2. ATEC Pilot Filters within the Trailer Figure 4-3. Pipe Line Reactor Segments CH2M 4-2

32 SECTION 4 PILOT TESTING METHODS AND MATERIALS GROUNDWATER QUALITY Figure 4-4. Venturi Eductor and Bypass Pipe The ATEC pilot filter consisted of four 6-inch filter columns connected by common manifolds for influent, effluent, and backwash water. Each filter was controlled by a three-way ball valve. The system was set up to closely represent a full-scale filter system in terms of media depth, flow rates in terms of gallons per minute (gpm) per square foot (gpm/sf) of filter area, and backwash characteristics. During backwash of the pilot filters, the effluent valve and eductor bypass valve are adjusted to reduce headloss and increase flow to the backwashing filter. The filters stay on line during backwashing in full-scale systems. Source water was metered using a totalizing flow meter. Pressure was measured on the influent and effluent manifold to determine headloss. Manganese dioxide granules (pyrolusite) were used as filter media. The media has been certified through NSF Standard 61 as being suitable for drinking water applications. Details on the filtration tanks and media are presented in Table 4-1. Table 4-1. Physical Characteristics of Filter Tanks and Media Pilot Filters Sidewall Height Overall Height Diameter 60 inches 72 inches 6 inches Filter Surface Area (each) 0.20 (feet 2 ) Total Filter Surface Area 0.79 (feet 2 ) Underdrain Media Support Source Water Connections Recommended Maximum Working Pressure Stainless steel wedgewire, 0.01-inch slots ¾-inch minus crushed granite, 4-inch ¾-inch standard hose 75 psi CH2M 4-3

33 SECTION 4 PILOT TESTING METHODS AND MATERIALS GROUNDWATER QUALITY Filter Media Depth in Filters 42 Inches Volume in Filters (total) 2.75 feet 3 Approximate Weight in Filters 352 pounds Weight 125 pounds/feet 3 Physical Size Chemical Dosing Equipment 20 to 40 US mesh Prominent Concept 100 Solution metering Pumps (capacity vary) mg/l = milligrams per liter psi = pounds per square inch Ferrous chloride was added to the well water using a stock solution of ferrous chloride diluted to 1,700 mg/l and dosed using a peristaltic feed pump. The concentration of the diluted ferrous chloride stock solution was determined through field measurements, and the feed pump flow-rate was controlled to maintain the desired dose at the raw water injection point. Sections of 6-inch PVC contact pipe were connected with mechanical joints for simple modification of the contact pipe length. The lengths for the tested contact times are presented in Table 4-2. Table 4-2. Pipe Configurations for Varying Contact Times Ferrous Chloride Contact Time (minutes) Required Pipe Length (feet) Air injection was achieved using a ½-inch Model 0484 Mazzei Injector and a 1-inch ball valve to control the bypass water flowrate. Maximum air injection was reached by closing the eductor bypass valve fully and pushing 100 percent of the flow through the ½-inch eductor and increasing the pressure differential. Pressure differential across the eductor was maintained between 10 and 25 psi by adjusting the bypass valve position. Based on stoichiometry, 0.14 milligram of oxygen (mg O 2) are required per milligram of ferrous iron (mg Fe 2+ ) present in the water for oxidation. Dissolved oxygen was measured periodically during the pilot testing from November 19 to 20. The air flow was not measured, but an estimated 1 to 2 standard liters per minute (slpm) of air was injected according to the Mazzei product data. Sufficient oxidation was verified by passing the water through a filter and measuring the dissolved iron. No iron was measured in the filtrate showing that full oxidation had occurred. A visual representation of the iron precipitated on the filter is included in Figure 4-5. Additional testing could be conducted during a longterm pilot test to help optimize the air injector flow for a full-scale facility. CH2M 4-4

34 SECTION 4 PILOT TESTING METHODS AND MATERIALS GROUNDWATER QUALITY Figure 4-5. A 47 mm Diameter Filter Shows the PrecipitatedIiron Collected from a Prefilter Ssample during the Pilot Test at Cadiz, 8/25/2015 Measurements of total iron concentrations were taken using a Hach DR/2000 Spectrophotometer (Hach Company, Loveland, CO). Flow was continuously monitored using a Seametrics flow meter. Grab samples were analyzed in the lab to measure hexavalent chromium, total chromium, arsenic, iron, and manganese for the raw water, filter influent, and treated filter effluent (treated or finished water). Total suspended solids were measured in addition to these constituents for the filter backwash waste. CH2M 4-5

35 SECTION 5 Pilot Testing Results 5.1 ATEC Testing Objectives and Findings CH2M conducted the pilot testing together with ATEC Systems, Inc. (ATEC). MWH, specifically, Mr. James Borchardt, provided recommendations for comprehensively testing the efficacy of the treatment process across a range of operating conditions. The tests were conducted from August 24 to 27, 2015, from September 9 to 10, 2015, and from November 19 to 20, 2015 using raw water supplied from Cadiz Ranch Well No. 21N. The following summarizes the objectives for each phase of pilot testing: Scenario 1 (August 25, 2015): Test different ferrous chloride doses to select optimal dose. Ferrous chloride is needed to reduce the hexavalent chromium, but excess iron in the water will shorten the filter run times. Scenario 2 (August 27 and September 9, 2015): Test selected ferrous chloride dose until breakthrough. Samples are collected throughout the filter run to confirm consistent performance throughout the run. Scenario 3 (September 10, 2015): Test ferrous chloride contact times of 2, 4, 6, and 8 minutes. This scenario evaluates the length of the pipeline reactor required to reduce the hexavalent chromium. Scenario 4 (November 19 to 20, 2015): Test selected design criteria for a complete 8 12-hour filter run. In this scenario, an extended run would be developed to demonstrate the run time. An extended run time minimizes backwash frequency and waste volumes. New filter media was installed before the initial pilot testing and was backwashed at the end of each filter run. Iron samples were collected approximately every 30 minutes, while raw, pre-filter, and finished water samples for total chromium, hexavalent chromium, and arsenic were collected approximately every hour. Samples were also collected of the backwash waste ATEC Testing Scenario 1 Ferrous chloride is used to reduce the hexavalent chromium, but excess iron in the water will shorten the run time. An optimal dose is the minimal amount of ferrous chloride that will provide complete reduction of hexavalent chromium. Ferrous chloride doses of 0.80 to 6.3 mg/l, equivalent to 0.35 to 2.8 mg/l as ferrous iron, were tested during Scenario 1. The dosing was initially low and was gradually increased over the day to allow the system to stabilize at each dose for 30 to 60 minutes. A time series of the results is shown in Figure 5-1. The point of filter breakthrough (shown as a red dashed line where the total iron in the treated water, labeled as FeTot-TW, is greater than 0.15 mg/l) is included for reference. Removal of hexavalent chromium was excellent at ferrous iron doses above 1.4 mg/l, as shown in Figure 5-2. For ferrous iron doses between 1.4 and 3 mg/l, removal averaged 97.4 percent. Removal of arsenic was excellent across all ferrous chloride doses, as shown in Figure 5-2. Ferrous iron doses below 1 mg/l showed better than expected removal of arsenic from the source water. In fact, arsenic removal remained steady across all ferrous chloride doses. CH2M 5-1

36 SECTION 5 PILOT TESTING RESULTS Fe (mg/l), Cr-6 and As (µg/l) :00 AM 10:00 AM 11:00 AM 12:00 PM 1:00 PM 2:00 PM 3:00 PM Cr6-RW Cr6-TW FeTot-PF FeTot-TW AsTot-RW AsTot-TW Figure 5-1. ATEC Pilot Testing August 25, 2015 Time Series Hexavalent Chromium Removal Arsenic Removal 100% 90% Removal Achieves Treatment Goal of 2 ug/l 80% % Removal 60% 40% Ferrous Chloride Dose as Fe-Tot (mg/l) Figure 5-2. ATEC Pilot Testing Hexavalent Chromium and Arsenic Removal at Various Ferrous Chloride Doses, August 25, ATEC Testing Scenario 2 This scenario was used to demonstrate consistent removal through a full filter run. A ferrous chloride dose of 6.8 mg/l, equivalent to 3 mg/l as ferrous iron, was chosen for filter breakthrough performance testing. The results of the filter breakthrough testing are shown in the time series plots in Figures 5-3 and 5-4. The total iron concentration in the treated water (FeTot-TW) acts as a surrogate for filter breakthrough. The red dashed line separates the normal filter operation (less than 0.15 mg/l) from filter breakthrough (more than 0.15 mg/l) conditions. The lab results showed efficient removal of hexavalent chromium (Cr6-TW) and arsenic (AsTot-TW) at all stages of the filter run, even past significant iron breakthrough of the filter. At breakthrough, the CH2M 5-2

37 SECTION 5 PILOT TESTING RESULTS average chromium-6 concentration is 0.18 micrograms per liter (µg/l) and arsenic concentration is 1.7 µg/l. Note that the filter run time and time until breakthrough were linked to the ferrous chloride dose used during that run. Higher ferrous chloride doses caused increased solids loading onto the filters which resulted in shorter run times. Fe (mg/l), Cr-6 and As (µg/l) Cr6-RW Cr6-TW FeTot-PF FeTot-TW AsTot-RW AsTot-TW :00 AM 10:00 AM 11:00 AM 12:00 PM 1:00 PM Figure 5-3. ATEC Pilot Testing August 27, 2015, Time Series Fe (mg/l), Cr-6 and As (µg/l) Cr6-RW Cr6-TW FeTot-PF FeTot-TW AsTot-RW AsTot-TW :00 AM 10:00 AM 11:00 AM 12:00 PM 1:00 PM 2:00 PM 3:00 PM 4:00 PM Figure 5-4. ATEC Pilot Testing September 9, 2015, Time Series CH2M 5-3

38 SECTION 5 PILOT TESTING RESULTS ATEC Testing Scenario 3 Identifying the optimal contact time helps in designing the length of the pipeline contactor needed for the full-scale facility. Ferrous chloride contact times of 2, 4, 6, and 8 minutes were tested at a ferrous chloride dose of 6.8 mg/l and compared to one another with respect to efficiency of chromium reduction and subsequent removal efficiency. Figure 5-5 contains the average removal efficiency for each contact time, representative of two samples per contact time. All four tested contact times provided efficient hexavalent chromium removal without a clear trend. Shorter contact times could be tested in the future to determine the minimum time required to achieve substantial chromium reduction. 100% % Removal of Hexavalent Chromium 98% 96% 94% 92% 90% Contact Time (min) Figure 5-5. ATEC Average Hexavalent Chromium Removal at Varied Contact Times ATEC Testing Scenario 4 Two extended filter runs were performed to demonstrate proper performance throughout the filter run, and to document the filter run length and operating conditions such as headloss during the filter run. A ferrous chloride dose of 3.4 mg/l, equivalent to 1.5 mg/l as ferrous iron, was chosen due to results from testing Scenarios 1 and 2. The results of the filter breakthrough testing are shown in the time-series plots in Figures 5-6 and 5-7. Similar to Scenario 2, the red dashed line separates the normal filter operation (less than 0.15 mg/l) from filter breakthrough (more than 0.15 mg/l) conditions. Note that Run 2 had several variations in the ferrous chloride dose due to inconsistencies in the equipment and site conditions. Removal of hexavalent chromium was excellent at all stages of the filter run, with a treated water range of 0.3 to 2.9 µg/l. Note that the 2.9 µg/l is an outlier due to a drop in the ferrous chloride dose. Removal averaged 93.9 percent as shown in Figure 5-8. Arsenic removal was consistent through all stages of the filter run, with a treated water range of 1.6 to 2.7 µg/l. CH2M 5-4

39 SECTION 5 PILOT TESTING RESULTS Fe (mg/l), Cr-6 and As (µg/l) Cr6-RW Cr6-TW FeTot-PF FeTot-TW AsTot-RW AsTot-TW Figure 5-6. ATEC Run 1, November 19, 2015, Time Series Fe-Tot (mg/l), Cr-6 and As-Tot (µg/l) Cr6-RW Cr6-TW FeTot-PF FeTot-TW AsTot-RW AsTot-TW 0.01 Figure 5-7. ATEC Run 2, November 19 to 20, 2015, Time Series CH2M 5-5

40 SECTION 5 PILOT TESTING RESULTS 100% Hexavalent Chromium Removal Arsenic Removal 90% % Removal 80% 70% 60% Ferrous Chloride Dose as Fe-Tot (mg/l) Figure 5-8. ATEC Hexavalent Chromium and Arsenic Removal at Various Ferrous Chloride Doses, November 19 to 20, ATEC Overall Testing Results A summary of the testing results is presented in Table 5-1. All of the pilot testing operating data, raw water quality and finished water quality are shown in Table 5-2. Raw water quality and finished water quality results are all from Eurofins Eaton Laboratory, Monrovia CA. Table 5-1 lists the average treatment results across all scenarios tested using the ATEC system. Note that these numbers include samples taken after breakthrough and immediately following filter backwash. The system was able to meet the Cadiz treatment goals for hexavalent chromium and total chromium, which are significantly lower than the regulatory limits. For all the treated water pilot testing results, 68.2% of the total chromium tests and 93.2% of the hexavalent chromium tests were below the treatment goal of 2 µg/l. Arsenic was already below the regulatory level of 10 µg/l, but some reduction in arsenic was also achieved to a level below the established treatment goal. For all of the treated water arsenic tests collected during pilot testing, 70.5% were below the treatment goal of 3 µg/l for arsenic.. Iron and manganese were also both at levels below the treatment goals and regulatory standards, however, some manganese levels actually increased from the raw water to the finished water. It is believed that the source of the manganese was from new media in the filter, which is a manganese dioxide ore. As the proposed treatment system typically is used for removal of iron and manganese, the observed levels from this pilot testing are not expected to occur and will be substantially lower in the full-scale system. Raw water iron shown in Table 1-1 is actually from the filter influent, after ferrous chloride was added. The finished water iron levels were also slightly above the treatment goal on average. There are two reasons for this; first the chemical feed dosing of ferrous chloride was at times very high, and second, the pilot operators used the effluent iron as a signal for the end of a filter run, often letting it exceed the treatment goal. The filter system selected for this pilot test, is actually used widely for iron and manganese removal in groundwater systems, and it is believed that the treated water levels will be significantly lower in a full-scale system. CH2M 5-6

41 SECTION 5 PILOT TESTING RESULTS Table 5-1. Pilot Testing Treatment Results for ATEC Treatment System Operating Conditions Parameter Flow Loading Rate Differential Pressure Average Value 4.6 gpm a 5.9 gpm/sf a 2 3 psi Water Quality Results Parameter Raw Water Treated Water Percent Removal Treatment Goal Regulatory Standard Hexavalent chromium µg/l 0.99 µg/l 95% 2 µg/l 10 µg/l Total chromium µg/l 1.60 µg/l 91% 2 µg/l 50 µg/l Arsenic 7.15 µg/l 1.84 µg/l 79% 3 µg/l 10 µg/l Iron 3,623 µg /L 180 µg /L 95% 150 µg/l 300 µg/l Manganese <2 µg /L 5.3 µg /L None 25 µg/l 50 µg/l a Values represent average conditions; variations were experienced during backwash events. Raw water iron is the filter inlet concentration µg/l = micrograms per liter The system operated at filter loading rates from 5.09 gpm/sf to 8.28 gpm/sf and averaged 5.9 gpm/sf. The average flowrate was approximately 5.1 gpm, and differential pressure was between 2-3 psi across all filter runs. Pre-filtered water iron concentrations (from ferrous chloride dosing) averaged approximately 3.62 mg/l and varied according to the scenario being tested Arsenic and Chromium Removal Laboratory data was used for calculating results. Where a result was less than the detection limit, the detection limit was used for the result. Raw water arsenic concentrations were between 6.58 and 14.5 µg/l, with an average of 7.2 µg/l. Finished water arsenic was reduced to concentrations ranging from <1 µg/l to 4.6 µg/l, with an average of 1.7 µg/l. Average arsenic removal was 79 percent. The maximum arsenic concentration in the treated water was higher than expected because of a sudden rise in raw water arsenic concentration to 14.5 mg/l at 17:15 on September 9. This resulted in a spike in the treated water concentration of 4.60 µg/l which was still below the California standard of 10 µg/l. It is unknown what caused this change of water quality, but the raw water levels were reduced to normal levels the next day. Raw water hexavalent chromium concentrations were 18.6 to 20.0 µg/l, with an average of 18.9 µg/l. Finished water hexavalent chromium was reduced to between 0.05 and 9.69 µg/l, with an average of 0.99 µg/l. Removal of hexavalent chromium averaged 95 percent throughout the pilot test. The maximum value of 9.69 µg/l was higher than expected because of a drop in the ferrous chloride dose to 0.35 mg/l as total iron at 10:30 am on August 25. This caused insufficient reduction of the hexavalent chromium to chromium III. Note that at this low coagulant dose condition, the hexavalent chrome concentration was still below the California standard of 10 µg/l. Total chromium levels were also reduced below the treatment goal of 2 µg/l and averaged1.6 µg/l with an average removal of 91% CH2M 5-7

42 SECTION 5 PILOT TESTING RESULTS Table 5-2. ATEC Pilot Testing Results from Cadiz Well 21N Operating Results Raw Water Quality Finished Water Quality Scenario Date Time Flow Loading Fe-Tot, PF Comments As Cr Mn Fe Cr+6 (Diss) As Cr Mn Fe Cr+6 (Diss) gpm gpm/sf mg/l µg/l µg/l µg/l mg/l µg/l µg/l µg/l µg/l mg/l µg/l 1 8/25/2015 9: Testing performed to determine solution percent 1 8/25/2015 9: <2 < <1 <1 3.8 < /25/ : <2 < < < /25/ : <2 < < < /25/ : <2 < < /25/ : <2 < < /25/ : /25/ : <2 < /25/ : <2 < /25/ : <2 < /25/ : <2 < /25/ : <2 < Backwash 8/27/2015 8:20 2 8/27/2015 9: <2 < <2 < /27/2015 9: <1 < /27/ : <1 <1 < /27/ : <1 <1 < CH2M 5-8

43 SECTION 5 PILOT TESTING RESULTS Operating Results Raw Water Quality Finished Water Quality Scenario Date Time Flow Loading Fe-Tot, PF Comments As Cr Mn Fe Cr+6 (Diss) As Cr Mn Fe Cr+6 (Diss) gpm gpm/sf mg/l µg/l µg/l µg/l mg/l µg/l µg/l µg/l µg/l mg/l µg/l 2 8/27/ : <1 <1 < /27/ : /27/ : < Backwash 8/27/ :30 Issues with new diesel generator 2 9/9/2015 9: Testing performed to determine solution percent 2 9/9/ : <1 <2 < /9/ : /9/ : <2 < <1 < /9/ : /9/ : Target FeCl2 dose achieved <2 < <1 < /9/ : <1 < /9/ : Generator ran out of fuel <2 < <1 < /9/ : <1 < Backwash 9/9/ :25 2 9/9/ : /9/ : /9/ : <2 < a 0.06 CH2M 5-9

44 SECTION 5 PILOT TESTING RESULTS Operating Results Raw Water Quality Finished Water Quality Scenario Date Time Flow Loading Fe-Tot, PF Comments As Cr Mn Fe Cr+6 (Diss) As Cr Mn Fe Cr+6 (Diss) gpm gpm/sf mg/l µg/l µg/l µg/l mg/l µg/l µg/l µg/l µg/l mg/l µg/l Backwash 9/10/2015 9:05 3 9/10/ : < /10/ : <2 < < /10/ : <2 < <1 < /10/ : <2 < <1 < /10/ : <2 < <1 < /10/ : < <1 < /10/ : <2 < <1 < /10/ : <2 < <1 < Backwash 11/19/2015 7: /19/2015 8: Testing performed to determine stock solution % 4 11/19/2015 9: /19/2015 9: /19/ : /19/ : /19/ : /19/ : /19/ : /19/ : CH2M 5-10

45 SECTION 5 PILOT TESTING RESULTS Operating Results Raw Water Quality Finished Water Quality Scenario Date Time Flow Loading Fe-Tot, PF Comments As Cr Mn Fe Cr+6 (Diss) As Cr Mn Fe Cr+6 (Diss) 4 11/19/ : /19/ : gpm gpm/sf mg/l µg/l µg/l µg/l mg/l µg/l µg/l µg/l µg/l mg/l µg/l 4 11/19/ : /19/ : /19/ : /19/ : /19/ : Backwash 11/19/ : /19/ : b 6.33 b /19/ : /20/2015 0: /20/2015 1: /20/2015 2: b 3.14 b < /20/2015 3: /20/2015 4: /20/2015 5: /20/2015 5: As = arsenic Cr = chromium Mn = manganese Cr+6 = hexavalent chromium a Note that 3-TW7 was sampled following the backwash and shows that the backwash was incomplete b Concentration represents the average value from two samples taken simultaneously CH2M 5-11

46 SECTION 5 PILOT TESTING RESULTS Raw water total chromium averaged 19.6 µg/l, and finished water total chromium was reduced to concentrations ranging from non-detect to 9 µg/l, with an average of 2.05 µg/l. The California standard for total chromium is 50 µg/l. Removal of total chromium averaged 89.5 percent. Small amounts of manganese (less than the secondary standard of 50 µg/l) were found in the finished water samples on several occasions. Table 5-3 contains mass balance calculations for manganese accumulation on the filter media on those dates when backwash water was also tested. According to these calculations, the filter media is the main source, as the ferrous chloride solution accounts for only 4 to 17 percent of the manganese measured in the backwash water. The new manganese dioxide media was apparently insufficiently washed after installation, resulting in some additional manganese fines in the backwash water. Testing conducted in November with previously used media resulted in treated water manganese levels of less than 3.5 µg/l. Table 5-3. Mass Balance of Manganese Backwash Water and Contribution from Ferrous Chloride Date Time Elapsed min Segment min Flow gpm Mn-Tot µg/l Accum Mn- Tot (ug) Notes 8/27/2015 8: Begin Filter Run 8/27/2015 9: /27/ : /27/ : /27/ : /27/ : a /27/ : a 10.0a 5216 End Filter Run Sum = µg Mn-Tot Expected Manganese concentration in a 5 min BW at 5 gpm= 1610 µg/l Mn-Tot (calc) Mn-Tot Concentration in Backwash from Ferrous Chloride Solution = 336 µg/l Mn-Tot (calc) Mn-Tot Measured in Backwash = µg/l Mn-Tot (measured) a Values extrapolated from data; not measured directly Table 5-4 shows the percent removal during each laboratory sampling event over the pilot testing period. Table 5-4. Percent Removal of Arsenic, Total Chromium and Hexavalent Chromium during Testing Date Time Arsenic Removal Total Chromium Removal Hexavalent Chromium Removal 8/25/2015 9: % a 94.8% a 97.0% 8/25/ : % a 89.3% 90.1% 8/25/ : % a 53.4% 49.8% 8/25/ : % a 69.5% 75.7% 8/25/ : % a 93.9% 95.0% 8/25/ : % 93.5% 97.3% 8/25/ : % 93.3% 97.9% 8/25/ : % 92.1% 98.3% CH2M 5-12

47 SECTION 5 PILOT TESTING RESULTS Date Time Arsenic Removal Total Chromium Removal Hexavalent Chromium Removal 8/25/ : % 92.4% 96.6% 8/25/ : % 92.4% 98.6% 8/25/ : % 93.6% 98.7% 8/27/2015 9: % 94.8% a 8/27/ : % 8/27/ : % 94.8% a 99.2% 9/9/ : % 94.5% a 95.3% 9/9/ : % 94.4% a 9/9/ : % 94.4% a 99.1% 9/9/ : % 94.3% a 99.2% 9/9/ : % 94.3% a 99.3% 9/9/ : % 94.2% a 98.9% 9/9/ : % 89.3% 99.7% 9/10/ : % 95.1% 99.7% 9/10/ : % 93.4% 99.7% 9/10/ : % 94.4% a 97.2% 9/10/ : % 94.3% a 99.4% 9/10/ : % 94.4% a 97.5% 9/10/ : % 94.5% a 99.2% 9/10/ : % 94.4% a 98.6% 9/10/ : % 94.3% a 99.4% 11/19/ : % 82.8% 93.8% 11/19/ : % 81.8% 11/19/ : % 11/19/ : % 69.1% 85.2% 11/20/2015 1: % 11/20/2015 2: % 84.8% a To calculate the removal percentage, non-detect lab results were replaced with the detection limit value. Actual removal percentages may be higher. Hexavalent chromium and arsenic removal data is shown at various ferrous chloride doses in Figure 5-9. Removal was consistently above 90% at iron doses above 1 mg/l. Arsenic removal was generally steady across all ferrous chloride doses, though there is a wide range of removal percentages at each dose. Based on these pilot testing results, it is concluded that the treatment system is effective at removing both arsenic and hexavalent chromium simultaneously. CH2M 5-13

48 SECTION 5 PILOT TESTING RESULTS Hexavalent Chromium Removal Arsenic Removal 100% 90% 90% Removal Achieves Treatment Goal of 2 ug/l for Hexavalent Chromium % Removal 80% 70% 60% 50% 40% Ferrous Chloride Dose as Fe-Tot (mg/l) Iron Removal Figure 5-9. Hexavalent Chromium and Arsenic Removal at Various Ferrous Chloride Doses This section analyzes the ability of the ATEC pressure filters to remove iron that was added in the coagulant chemical. A plot of the iron removal for the five days of pilot testing is shown in Figures 5-10, 5-11, 5-12, 5-13, 5-14, and The ferrous chloride dose is measured as total iron to compare to the finished water total iron concentration. Finished water iron concentrations ranged from non-detectable to 0.59 mg/l and averaged 0.17 mg/l, resulting in an average removal of 94 percent. High iron concentrations were measured throughout the pilot study because of the following factors: (1) the pilot plan called for testing of a wide range of ferrous chloride doses, resulting in a higher loading of iron than would normally be experienced; (2) the pilot plan called for testing past filter breakthrough, so filters were allowed to continue running past their recommended filter volume; (3) iron was being released from the lower regions of the filter that had not been sufficiently backwashed, which is evidenced by the slow decrease in iron concentration on September 10 as the filters cleared themselves of residual iron. Despite the high iron loading rates and breakthrough conditions at various times throughout the pilot study, the ATEC treatment system still meet treatment objectives for arsenic and hexavalent chromium removal as previously shown CH2M

49 SECTION 5 PILOT TESTING RESULTS Figure August 25, 2015 Iron Removal Figure August 27, 2015 Iron Removal Figure September 9, 2015 Iron Removal Figure September 10, 2015 Iron Removal Figure Run 1, November 19, 2015 Iron Removal 5.3 Filter Run Lengths Figure Run 2, November 19, 2015 Iron Removal The filter run lengths achieved were limited by operational and water quality constraints. In the pilot testing unit filter run volumes of 3,700 and 5100 gal/sq ft were achieved in the November 19 th and 20 th test runs. Little or no headloss build up was noted during the filter runs. It is expected that there is a balance between ferrous chloride dose and filter run length. The lack of headloss buildup during all of the filter runs indicates that a filter aid polymer could potentially be effective at extending filter runs. At other locations using ATEC filters with raw water iron concentrations exceeding 1 mg/l, longer filter runs are often seen, as shown in Table 5-4. Unit filter run volumes of greater than 5,000 gal/sq foot should be easily achievable and 10,000 gal/sq foot could potentially be reached, with additional testing or operational optimization of a full-scale system. For conceptual design, discussed in Section 6, a conservative assumption of f 6 hours filter runs has been used. CH2M 5-15

50 SECTION 5 PILOT TESTING RESULTS Table 5-4. Full-Scale Systems with Iron Concentrations above 1 mg/l and Filter Run Lengths Location Well Capacity gpm (m 3 /hr) Loading Rate gpm/sq ft (m/hr) Raw Water Iron Conc. mg/l Backwash Frequency Hours of Run Time Unit Filter Run Volume gal/sq ft Jefferson County PUD, WA (8) 9.9 (26) Battle Ground, WA 8-Jul 2,000 (537) 13.3 (34) City of Batavia, IL 6,7,8 4,500 (1,208) 8.96 (23) ATEC Backwash Water Results Backwash water is characterized in Table 5-5. Each filter vessel was backwashed for five minutes at a loading rate of 28 gpm/sf (equal to 5.5 gpm for a 6 column). The sample water was grab samples collected during at various times during the backwash cycle. Table 5-5. ATEC Backwash Water Characterization Sample ID Date Time As-Tot µg/l Cr-Tot µg/l Mn-Tot µg/l Fe-Tot mg/l 2-BW1-A 27-Aug 8: BW1-B 27-Aug 8: BW1-C 27-Aug 8: BW2 27-Aug 13: BW1 9-Sep 15: Cr6 µg/l TSS mg/l Arsenic concentrations ranged from 132 to 226 µg/l, with an average value of 159 µg/l. Chromium concentrations ranged from 470 to 830 µg/l, with an average value of 722 µg/l. Iron concentrations ranged from 180 to 320 mg/l, with an average value of 262 mg/l. The fluctuation in these numbers could be a result of the variability of dosing on August 25 and 27. Manganese concentrations ranged from 2,900 to 9,540 µg/l. It is hypothesized that as the filter media was rinsed, the accumulation of manganese from the manganese dioxide granules lessened, as evidenced by the reduction in Mn-Tot concentration from August 27 to September 9, Hexavalent chromium concentrations ranged from to 20.0 µg/l. The high values may occur as total chromium is oxidized after the backwash waste was removed from the filter media and exposed to the air. Total suspended solids concentrations ranged from 72 to 824 mg/l, with an average value of 520 mg/l. Because of high loading of metals and solids in the backwash, it is recommended that the backwash water be sent to settling ponds with floating decant (As shown in Figure 5-16) and then either recycled to the front of the water treatment plant or blended with additional well water for irrigation of the Cadiz farm operation. Table 5-6 shows recommended metals water quality for irrigation, as well as potential dilution ratio with native groundwater to achieve the recommended levels CH2M

51 SECTION 5 PILOT TESTING RESULTS Figure 5-16 Floating Decant with Plate Settlers, used for backwash clarification. Table 5-6 would be used if the backwash water was to be used without settling as part of the irrigation water. However, because the dilution ratios are fairly high for iron and manganese, it is more likely that water would be settled in a backwash holding pond prior to using the clarified water for irrigation supply. Table 5-6. Recommended Irrigation Levels and Dilution Factors for Backwash Water Parameter Units Irrigation Limits Average Backwash Concentration Dilution Ratio with Additional Irrigation Water Needed Arsenic mg/l Chromium mg/l Iron mg/l Manganese mg/l Source: Ayers, R.S. and D.W. Westcot Water Quality for Agriculture (FAO 29). FAO Irrigation and Drainage Paper 29 rev. 1. Food and Agriculture Organization of the United Nations, Rome, Italy. CH2M 5-17