### MEMORANDUM

TO: Bill Swietlik, EPA

FROM: Lydia Lambert, Kristi Bubb, ERG

DATE: September 2, 2010

SUBJECT: Drinking Water Treatment Technologies that Can Reduce Metal and Selenium Concentrations Associated with Discharges from Steam Electric Power Plants (DCN SE02154)

In support of the development of revised effl uent guidelines for the steam electric power industry, EPA will conduct an environmental assessment (EA) analysis to evaluate the environmental impact of identified pollutants of concern under current (i .e., baseline) discharge practices and assess the potential environmental improvement from reductions in pollutant loads under varying regulatory option scenarios. As pa rt of this analysis, EPA may consider the potential impact steam electric discharges pose to downstream drinking wa ter treatment plants and the potential reduction in treatment costs as sociated with lower pollutant loads entering surface waters. As a preliminary assessment for the drinking water impact analysis, EPA directed

ERG to conduct a literature search to determine if drinking wate r treatment processes can reduce or eliminate metals (e.g., arsenic, mercur y, chromium, copper, and manganese) or other pollutants of concern (e.g., selenium) commonly de tected in wastewater discharges from steam electric power plants. This memorandum presents the drinking water standards for the potential pollutants of concern, common drinking water treatm ent technologies that treat heavy metals and selenium, drinking water source water monitoring programs, and potential next steps for the drinking water impact analysis.

1.0 D RINKING W ATER S TANDARDS FOR P OTENTIAL P OLLUTANTS OF C ONCERN

The nation’s drinking water is regulated unde r the Safe Water Drinking Act (SDWA) of 1974 and its 1986 and 1996 amendments. Under the SDWA, EPA is required to set enforceable national health-based drinking wate r standards to control the leve l of contaminants in drinking water and its sources (i.e., rive rs, lakes, reservoirs, springs, an d ground water wells). In addition to the primary drinking water standards, EPA has set secondary drinking water standards, which are non-enforceable guidelines for contaminants that may cause cosmetic effects (e.g., skin and tooth discoloration) or aesthetic effects (e.g., taste and odor). Drinking water treatment plants are not required by EPA to adopt these secondary standards; however, states may choose to adopt and enforce them (U.S. EPA, 2004).

Under the drinking water standards, EPA sets two types of enforceable standards for a pollutant: the Maximum Contaminant Level (MCL ) and the Treatment Technique (TT). EPA strives to set a MCL, which is the maximum amo unt of a contaminant allowed in water delivered to a public water system that can be achieved using the best available treatment technology. However, a TT is set instead of a MCL if a relia ble method that is economically and technically

feasible to measure a contaminan t at particularly low concentra tions is unavailable (U.S. EPA,Memorandum September 2, 2010 Page 2

2004). Table 1-1 presents the drinking water treatm ent standards for the potential pollutants of concern in steam electric power pl ant discharges. Drinking water treatment technologies must be designed to effectively treat these pollutant s to the following drinking water standard concentrations in the produced water from the tr eatment facility. However, the effectiveness of the treatment operations are impacted by the specia tion of the pollutant (i.e ., total or dissolved), which is dependent on the characteri stics of the plan ts’ operations.

Table 1-1. Drinking Water Treatment Standards for Potential Pollutants of Concern in Steam Electric Power Plant Discharges

Analyte Unit Drinking Water

Standard Value Type of Drinking

Water Standard Potential Health Effects from Ingestion of Water Selenium, Total mg/L 0.05 MCL  Hair or fingernail loss.

 Numbness in fingers or toes.

 Circulatory problems. Arsenic, Total mg/L 0.010 MCL  Skin damage.

 Problems with circulatory
systems.

 Increased risk of cancer. Mercury, Total

(inorganic) mg/L 0.002 MCL  Kidney damage.

Chromium, Total mg/L 0.1 MCL  Allergic dermatitis.

Copper, Total mg/L 1.3 TT (Corrosion

Control)  Short term exposure:

Gastrointestinal distress.

 Long term exposure: Liver or kidney damage. Manganese, Total mg/L 0.05 Secondary

Standard  Brownish-red discoloration

of water.

 Off-taste or odor of water.
Source: U.S. EPA, 2009.

2.0 D RINKING W ATER T REATMENT T ECHNOLOGIES

Conventional wastewater trea tment unit processes are used to remove the potential pollutants of concern from drinking water. Typi cally, these unit processes are designed to treat

to the MCL or TT levels. Conventional wastewat er treatment is a comb ination of physical, chemical, and biological processe s and operations that remove so lids, organic matter, and/or

nutrients from wastewater. Conve ntional wastewater treatment proc esses are defined in order of increasing treatment level: primar y, secondary, and tertiary (comm only referred to as advanced wastewater treatment).

Conventional treatment trains us ed to remove metals from drinking water typically begin with coagulation followed by flocculation. Afte r flocculation, drinking wa ter source water is then treated by either sedimentation or filtra tion or a combination of the two processes. Descriptions of these unit processes are as follows:

 Coagulation . A unit process that involves the addi tion of one or more chemicals (i.e., coagulants) to promote the aggregation of pa rticles in the drinking water source water.Memorandum September 2, 2010 Page 3

Chemicals commonly used for coagulation of heavy metals include inorganic metal compounds (e.g., aluminum sulfate and ferric ch loride), prehydrolyzed metal salts, and synthetic organic chemicals (MWH, 2005).

 Flocculation . A unit process that involves the mixing of chemically treated water to induce coagulation. This process causes very small suspended particles to collide and form larger heavier particles (i.e., floc) th at can settle out by gravity. The purpose of flocculation is to aggregate particles in the s ource water to a size that can be efficiently removed from suspension by sedimentation and filtration treatment systems. To optimize solids removal, organic polymers are commonl y used as flocculant aids to enhance settleability and filterability of floc particles (Viessman and Hammer, 2005).

 Sedimentation . A unit process that involves the separation of settleable solids by the force of gravity. This unit process involve s the introduction of dr inking water source water to a large inactive basin (i.e., sedimenta tion basin) for an exte nded period of time. Over time, the suspended particles settle to the bottom of the basin, separating the solids from the source water. This unit process co mmonly follows coagulation and flocculation treatment to remove flocculated impuri ties and precipitates (MWH, 2005).

 Filtration . A unit process that involves the se paration of non-settleable solids from drinking water source water by passing the liquid through a porous medium, which traps and removes the solids. The primary goal of filtration is to completely remove the targeted solids from suspension. The most common forms of filtration are granular

filtration and membrane filtr ation. The two types of me mbrane filters primarily employed by drinking water treatment faciliti es are pressure-driven microfiltration (0.1- μm sized pores) and ultrafiltration (0.01-μmsized pores), which utilize the semipermeable membrane as a mechanism for separation (MWH, 2005).

Principal advanced treatment unit operations a nd processes for removal of metals and/or selenium include the following:

 Chemical Precipitation . A unit process that is the most commonly operated treatment technology for the removal of heavy metals fr om drinking water. This unit process

involves the addition of chemicals to water to alter the physical st ate of dissolved and suspended solids and facilitate their rem oval by sedimentation. The precipitation of substances in water depends primarily on the solubility of the complexes formed in the drinking water source water, which is genera lly controlled by the pH level. Typically, metals precipitation occurs at a high pH (i .e., 9 through 9.5). For example, heavy metals found in source water typically form hydroxide and sulfide complexes, which have low solubility in water at a high pH. Therefore, the formation of insoluble complexes causes the metals to precipitate out of solution. The precipitation of heavy metals in source water is usually accomplished by the addition of chemicals, such as alum, lime or iron salts, and polyelectrol ytes (AWWA, 1999).

 Ion exchange . A unit process in which an ion in a liquid phase is exchanged with an ion in a solid phase. The solid phase (i.e., an ion exchange resin) is an insoluble material thatMemorandum September 2, 2010 Page 4

varies depending on exchange capacity, particle size, and stability. When the resin comes in contact with the liquid solution, the contam inant ion migrates out of solution to the charged functional group, being replaced by the counterion in solution. In drinking water treatment applications, ion exchange is primarily used for water softening and demineralization (e.g., removal of mineral cont ent); however, the use of ion exchange for other applications has increased due to a greater concern fo r health effects from other contaminant ions (i.e., arsenic and selenium) (MWH, 2005).

 Reverse Osmosis (RO) . A unit process that separates solutes from drinking water source water by utilizing the physical and chemical properties of the solutes for separation. During RO, a high-pressure stream is direct ed across the surface of a semi-permeable membrane opposite in direction and greater th an the osmotic pressure imposed across the membrane. Due to the pressure differential between the sides of the membrane, the flow

of the stream travels from the more concentr ated to the less concen trated side of the membrane. As water passes through the memb rane, solutes are rejected and the reject stream becomes more concentrated (MWH, 2005). Typically, the RO process is used for

the treatment of arsenic in source water.

 Distillation . A unit process that separates metal contaminants from drinking water source water through a combination of vaporization and c ondensation. During this unit process, the water is heated to its boiling point until the water vaporizes. The vaporized water is removed from its heating source, fed to a new location, and condensed to its original liquid form. Contaminants with a higher boi ling point than water will remain in their original location to yield contaminant-free s ource water in the new location. (Metcalf & Eddy, 2003).

 Electrodialysis . A unit process that separates metal ions in drinking water source water through the use of an electri cal voltage-driven membrane. This membrane process is driven by the electrical potential between tw o electrodes, which generate an electric current that passes through the source water. The electric current causes the negatively charged ions to be drawn toward the positively charged electrode and the positively charged ions to be drawn toward the nega tively charged electrode, resulting in ion removal from the source water (ASCE/AWWA, 2005).

3.0 D RINKING W ATER S OURCE W ATER M ONITORING

A database containing nation- wide drinking water source wate r monitoring data would be beneficial to the drinking water impact analysis. The data would allow ERG to identify pollutant concentrations upstream of dri nking water intake locations, in order to determine if the

concentrations have increased si gnificantly enough to impact the effectiveness of drinking water treatment processes. In an effort to locate the data, ERG conducted research on source water protection regulations an d practices. ERG determined that EPA does not require states to monitor pollutant concentrati ons in source water; however, the SDWA Amendments of 1996 require states to develop and implement s ource water assessment programs. Under these programs, states develop a source water assessment for each public water system. This assessment includes a susceptibility analysis to determine how likely a water supply is to be contaminated by identified potential sources of contamination. Alt hough the susceptibilityMemorandum September 2, 2010 Page 5

analysis does not require states to collect monitoring data of pollutant concentrations in the source water areas, EPA encourages states to undertake monitoring to accurately identify potential significant sources of contamination, whic h could be utilized for the EA analysis (U.S. EPA, 1997).

4.0 P OTENTIAL N EXT S TEPS FOR THE D RINKING W ATER I MPACT A NALYSIS

Drinking water treatment opti ons are typically designed to treat for the removal of the pollutants of concern in the steam electric indus try (i.e., arsenic and mercury); therefore, ERG would suggest the following next steps to dete rmine if steam electric power plant discharges have a significant impact on pollutant concentr ations in the source water entering the drinking water treatment facilities. Potential next steps for the drinking water impact analysis include:

 Proximity Analysis . ERG will use outfall latitude and longitude data requested in the steam electric questionnaire to determine the proximity of steam electric outfalls discharging flue gas desulfur ization (FGD) scrubber wast ewater and ash wastewater upstream from drinking wa ter intake locations.

 Review Available Source Wa ter Assessment Documentation. ERG will contact Lee Kyle

at EPA’s Office of Ground Water and Dri nking Water to determine if the data

documented in source water assessmen ts are accessible to the public.

 Hotspot Analysis . If ERG determines that the so urce water assessments are readily available to the public, ERG will conduct a hotsp ot analysis to examine waterbodies that receive FGD wastewater discharges from mu ltiple power plants to determine if the pollutant concentrations are signif icantly greater in these areas.

 Review Sampling, Monitoring, and Questionnaire Data . ERG will review data collected through the sampling episodes, long-term m onitoring, and questionnaire to calculate pollutant concentrations in FGD scrubber wa stewater and ash wast ewater discharges by accounting for dilution based on cooling wate r flows. ERG will develop a methodology to predict effluent concentrations discharged from the plant to determine if a subset of discharges exceeds MCL or TT levels at end-of-pipe.

 Estimate Source Water Concentrations . ERG will use sampling data, monitoring data, questionnaire data, and stream flow data from the NHD Plus system to estimate the potential concentration of pollutants of concern reaching downstream drinking water

intake structures.

5.0 R EFERENCES

American Society of Civil Engineers (ASCE) /American Water Works Association (AWWA).

2005. Water Treatment Plant Design (4 th ed.). New York, NY: McGraw Hill.

American Water Works Association (AWWA). 1999. Water Quality and Treatment (5 th ed.). New York, NY: McGraw Hill.Memorandum September 2, 2010 Page 6

Metcalf & Eddy. 2003. Wastewater Engineering: Treatment and Reuse (4 th ed.). New York, NY:

McGraw Hill.

MWH. 2005. Water Treatment: Principles and Design (2 nd ed.). Hoboken, NJ: John Wiley & Son, Inc.

U.S. EPA. 1997. State Source Water Assessment and Pr otection Programs: Final Guidance.

Office of Water. Washington, DC (August). Available online at: http://www.epa.gov/safewater/so urcewater/pubs/swpguidance.pdf

U.S. EPA. 2004. Drinking Water Standards & Health Effects . Office of Ground Water and Drinking Water. Washington, DC (June). Available online at: http://www.epa.gov/safewater/sd wa/pdfs/fs_30ann_standards_web.pdf

U.S. EPA. 2009. National Primary Drinking Water Regulations. Office of Ground Water and Drinking Water. Washington, DC (May). Available online at: http://www.epa.gov/safewater/consumer/pdf/mcl.pdf

Viessman, Jr., W, and Hammer, M.J. 2005. Water Supply and Pollution Control (7 th ed.). Upper Saddle River, NJ: P earson Education, Inc.