legacy of manganese accumulation in water systems

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Legacy of Manganese Accumulation in Water Systems

Literature Review

Prepared by:

Phil Brandhuber, HDR Engineering

Published by: Water Research Foundation


OBJECTIVE Manganese which has accumulated in the distribution system as part of sediment or pipe

scale is referred to as “legacy manganese”. The objective of this literature review is to present a summary of current conditions within drinking water systems and industry understanding specific to legacy manganese. It should be noted that Kohl and Medlar (2006) conducted a comprehensive literature review of manganese occurrence, health effects, regulatory background, and treatment. The reader is referred to Kohl and Medlar (2006) for a more detailed literature review on numerous aspects of manganese in drinking water. The following aspects of legacy manganese in drinking water distribution systems are discussed in this document, to varying extents based on the availability of published data:

Background Health effects and regulatory requirements, Occurrence of legacy manganese Direct and indirect impacts, and Remediation and preventive strategies.

This literature review is meant to expand on several of these topics with additional data

sources focusing on legacy manganese, as well as to identify data gaps that will need to be filled through utility case studies. Ultimately, this literature review will be used to provide the project team with data and reference tools that can be used in subsequent project tasks. BACKGROUND

It is anticipated that most distribution systems contain some level of legacy manganese,

even systems that are served by surface waters with very low background manganese concentrations. For example, a drinking water utility in Washington State measured manganese levels in water flushed out of distribution system piping as part of a pilot flushing program. While the manganese level of the surface water supply entering the distribution system was 1.4 µg/L, water from one of the flushed areas exhibited 54.3 µg/L of manganese, an increase of more than 38 times the level seen entering the distribution system. This was attributed to stagnant conditions in a new, undeveloped subdivision (HDR 2008).

Kohl and Medlar (2006) studied manganese in drinking water sources, treatment and distribution system bulk water, including occurrence and treatment. The results of distribution system bulk water monitoring showed that manganese concentrations decreased as the water moved farther from the treatment plant, demonstrating that manganese was accumulating in the distribution system. The authors observed that moderate levels of manganese in finished water may cause aesthetic problems at the customer’s tap if manganese is present in the finished water over extended periods of time. In utility surveys, Kohl and Medlar (2006) found that the average level of manganese leaving the treatment plant was 22 µg/L with a 90th percentile of 50 µg/L. Even a moderate level of manganese entering the distribution system can potentially deposit large quantities of legacy manganese. For example a 2 million gallon per day flow containing 20 µg/L of manganese has the potential to deposit up to 122 lb/year of legacy manganese in the


distribution system. This legacy manganese can then be mobilized or released back into the water over short time periods at concentrations much greater than those found in the source of supply or finished water. General Manganese Chemistry

Manganese is a naturally occurring element present in soil, and water. It is essential for

the health of plants and animals. Manganese chemistry is very complex and consists of multiple oxidative states. The most important states from a drinking water perspective are Mn(II), Mn(IV), and Mn(VII). Both Mn(II) and Mn(VII) are soluble in water, while Mn(IV) is not. In fact, one method for treating manganese in drinking water is to convert soluble manganese (Mn(II)) by oxidation to insoluble manganese (Mn(IV)) and remove the insoluble Mn(IV) by filtration.

However, manganese treatment does not completely remove all manganese from the treated water, allowing some manganese to enter the distribution system. Kohl and Medlar (2006) point out that under moderate oxidation conditions, typically, solid MnO2 can form colloidal clumps which do not settle and are not easily captured onto a filter. But when using ozone as an oxidant, soluble MnO4

- can reach the distribution system if too much oxidant is added. Soluble Mn(II) can be formed and reach the distribution system as well if MnO2 is chemically reduced during treatment (Kohl and Medlar, 2006).

As presented by Schock (2007) and shown in the Mn Pourbaix diagram provided as Figure 1, relatively small changes in treated water chemistry – specifically pH and oxidation-reduction potential (ORP) – can shift the stable form of Mn(IV) (pyrolusite) to soluble Mn(II) species. These changes in water chemistry, which are discussed in the section on release mechanisms, can occur in distribution systems. For example, systems which rely on multiple sources and/or blend surface water and groundwater are likely to experience significant changes in chemistry throughout the distribution system. Alternatively, regulatory actions may result in higher manganese disposition in distribution systems. For example, under the Groundwater Rule the increased use of disinfectants by small systems may cause additional accumulation of manganese in their distribution systems.


Figure 1. Pourbaix Diagram for Mn Species

(Adapted from Schock, 2007) Accumulation Mechanisms

Sly et al. (1990) investigated manganese deposition at four points within an Australian

drinking water distribution system with dirty water problems. The research was conducted using Robbins biofilm sampling devices fitted onto mains. (A Robbins device is used to collect in situ samples of biofilm growth and is fitted with multiple sample stubs, which are removed for sample analysis.) Using this device the researchers found manganese accumulation was occurring through both chemical and biological means. They determined that chemical accumulation of manganese was caused by the oxidation of aqueous manganese in the distribution system bulk water by chlorine used to provide disinfection. They also determined that biological manganese accumulation occurred when insufficient disinfectant residual was present in the distribution system to control the growth of manganese depositing biofilm. The investigators recommended that finished water manganese be controlled to below 20 g/L and chlorine residual in the distribution system be maintained at greater than 0.2 mg/L to prevent discolored water events related to chemical or biological accumulation.

Friedman et al. (2003) described several system-specific factors that will influence sediment accumulation in the distribution system. Those factors that could generally be controlled by the utility include: pipe diameter, pipe material, finished water quality, time since last cleaning, and method of last cleaning. However, accumulation is also impacted by factors that are more difficult to control by utilities, such as routine and peak demands, occurrence of hydraulic disturbances such as flow reversals, and rapidly changing flow velocities that may suspend and transport particles. As described in Friedman et al. (2010) and others (Shock and Holm 2003, Shock 2005), inorganic contaminants can physically accumulate on the surface of or


be occluded within solid materials commonly found within drinking water distribution systems. These solid materials are referred to as substrates or “sinks,” and they include corrosion scales, precipitates, biofilm, and sediment. Figure 2 shows a conceptual representation of the heterogeneous nature of distribution system scales and sediments.

Figure 2. Conceptual Representation of Accumulated Scales and Sediments

(Source: Lytle, 2008) Accumulation rates will be dependent on water quality conditions, mineralogy,

composition properties of the contaminant substrates or sinks and hydraulic conditions. These sinks typically exist in a heterogeneous and dynamic matrix that reflects the variety of factors influencing their formation and stability. Physico-Chemical Accumulation

Manganese may be deposited within the distribution system through the physico-

chemical mechanisms of precipitation and sorption (Friedman et al. 2010). Manganese precipitates may form depending on pH, oxidation-reduction potential, and other water quality conditions. These precipitates can deposit onto interior surfaces of the distribution system piping, reservoirs, and plumbing systems. Precipitates are of particular interest to research on physical contaminant accumulation. Common precipitates, such as those involving iron, manganese, aluminum, and phosphate, have been shown to have a high affinity for concentrating regulated inorganic and radiological elements (Schock, 2005). Sorption involves the retention of manganese on (adsorption) or within (absorption) the surface of a substrate. Sorption is driven by physical, electrostatic, and/or chemical interactions. Physical Accumulation

Physical deposition occurs when particulates, such as insoluble manganese, are deposited

in the distribution system by low-velocity or stagnant water. Mechanistically, this occurs when the settling velocity of the particle in the water column exceeds the scour velocity. The particle


settles on the pipe wall rather than being swept along with the bulk water flow. Accumulated sediments are often associated with dead-end mains and storage reservoirs (USEPA 2006) and low velocity regions. Biological Accumulation

Well water piping often develops dense iron and manganese encrustations of Gallionella,

Leptothrix, Siderocapsa and other bacterial species that catalyze oxidation of dissolved iron and manganese. Extracellular microbial reactions scavenge manganese in a highly efficient manner, enabling waters containing as little as 20 µg/L manganese to deposit visible MnO2 within a few days (Dickinson et al, 1996). Manganese can also be subject to sorption onto biofilm or bacterially-mediated precipitation reactions. Sly et al. (1990) studied manganese deposition onto distribution system piping and determined that microbial deposition of manganese oxidizing microorganisms coated with manganese oxides occurred in an area with no chlorine residual. Kohl and Medlar (2006) also noted the occurrence of biochemical deposition of manganese oxides onto pipe surfaces, indicating this may occur in systems without adequate chlorine residual. Release Mechanisms

Many of the mechanisms that can contribute to manganese accumulation are reversible,

allowing manganese to be released back into the water (Friedman et al. 2010 and other references). Releases can be caused by physical, hydraulic, or chemical conditions in the distribution system. Physical or Hydraulic Release

Physical or hydraulic disturbances may be capable of dislodging sinks (i.e. corrosion

scales, chemical precipitates, biofilms and sediments) containing accumulated manganese and entraining the solids in bulk water. According to Friedman et al. (2010), examples of physical and hydraulic disturbances which may impact distribution system sinks are: increases in flow rate and velocity (due to peak demands, fire fighting activities, main breaks); flow reversals; hydraulic pressure transients (due to sudden changes in velocity, pump start/stop cycles, valve slams), valve exercising, earthwork, or construction adjacent to active system components. Lakin and Bryan (2007) reported an event in which a 10-ton vibratory roller used for road construction physically disturbed pipe scales and sediments causing over 11,000 colored water complaints. Chemical Release

Manganese that has accumulated on or within distribution system scales and sediments

may be liberated into the bulk water by dissolution or destabilization of the sink and contaminant desorption along with other accumulated inorganic contaminants (USEPA 2006). Releases that occur in the particulate phase will have different transport properties compared to releases due to dissolution in the bulk phase. As discussed in Friedman et al. (2010), pH, oxidation-reduction


potential, alkalinity, dissolved inorganic carbon (DIC), and phosphate generally govern the stability of corrosion scales. Calcium, aluminum, and sulfate are also significant to the stability of precipitates. Aluminum-based salts (e.g., aluminum sulfate hydrate; polyaluminum chlorohydrate) are often used as chemical coagulants in drinking water treatment processes. Depending on treatment efficiency and pH, aluminum may concentrate in the distribution system due to post-precipitation of coagulant residual or filter breakthrough (Snoeyink et al. 2003). Constituents such as aluminum may form films which inhibit corrosion or barriers to diffusion (AWWARF-TZW 1996; Schock 1989; Schock et al. 1995; Schock 1999; Schock et al. 1996; Snoeyink et al 2003). Changes in water chemistry can result in dissolution of these sinks, leading to releases of manganese into the bulk water or formation of new manganese-containing precipitates or scales with different compositions. Such changes in water chemistry can result from changes in treatment, source water quality, or due to blending of multiple sources with varying chemical profiles (USEPA 2006 and prior references). HEALTH IMPACTS AND REGULATORY REQUIREMENTS Health Impacts

Manganese is a necessary element for human nutrition. Humans typically meet their

dietary requirement for manganese by consuming food which contains manganese. According to the Food and Nutrition Board of the National Academy of Sciences (2001), an adequate intake level of manganese for adult men is 2.3 mg per day and for adult women is 1.8 mg per day. Manganese can be found in nuts, grains, fruits, legumes, tea, leafy vegetables, infant formula, and some meat and fish.

Manganese has rarely caused toxic effects when ingested orally (USPEA, 2003). However, manganese poisoning has occurred due to inhaling high levels of manganese, generally in an occupational setting. At toxic levels, manganese attacks the central nervous system and can cause, according to the USEPA (2003) ataxia, dementia, anxiety, a “mask-like” face, and manganism, which is a syndrome similar to Parkinson’s disease.

USEPA’s Integrated Risk Information System (IRIS) includes oral, inhalation and carcinogenicity health risk assessments for manganese. The IRIS recommendations for human exposure are as follows. The manganese Reference Dose for Chronic Oral Exposure (RfD) is 1.4x10-1mg/kg-day. The manganese Reference Dose for Concentration for Chronic Inhalation Exposure (RfC) is 5x10-5mg/m3. The human carcinogenicity classification for manganese is D; not classifiable as to human carcinogenicity. Manganese in Drinking Water

For adults, ingested manganese is regulated by homeostatic mechanisms in the body

(Menezes-Filho et al. 2009), which may be the reason that toxicity due to ingestion appears to be rare. (A homeostatic mechanism can be described as self-regulating through negative feedback.) Ljung and Vahter (2007) indicate that the homeostasis may not be completely established in infants and they may have a more sensitive nervous system. Manganese retention is higher in infants than adults based on hair and blood samples which have shown that manganese levels


decrease with age (Ljung and Vahter 2007). Research has indicated that children may absorb more ingested manganese than adults (Dorner et al. 1989). Absorption of ingested manganese on a per pound body mass basis may be enhanced by a growth-related high demand for iron (Mena et al. 1969).

Bouchard et al. (2010) conducted a study that included a comparison of manganese exposure from drinking water and diet, with manganese concentration in children’s hair samples. The authors point out that drinking water consumption of manganese has been of less concern because the intake from water is much less than that from eating food (except for infants). In this study, the investigators determined that manganese intake from drinking water was very small, at least two orders of magnitude less than manganese ingested from foods. However, intake of water was significantly associated with manganese content of hair and intake from food was not. Bouchard et al. (2010) conclude that their findings indicate that manganese from drinking water is metabolized differently than manganese from food.

Menezes-Filho (2009) reviewed existing research on the effects of manganese on children, including studies involving exposure via drinking water. The investigators determined that while manganese is recognized as a neurotoxin, research on the effects of manganese exposure on children is sparse. However, the researchers concluded that the evidence of adverse effects from manganese exposure on children is substantive enough to deserve further research. These findings agree with those of Ljung and Vahter (2007). Ljung and Vahter (2007) reviewed available literature on manganese exposure through drinking water, specifically focusing on the World Health Organization health-based guideline value for manganese. The authors point out that no single study has made a determination of a toxic level of manganese for children and infants, and that evidence does point to there being a higher risk for toxicity in children than adults. Ljung and Vahter (2007) also point out that it was unclear whether manganese exposure affects both younger children and older children or whether symptoms apparent in older children are the result of infant exposure. The authors conclude that more research is needed to understand the causal relationship between manganese exposure and children’s health.

Bouchard et al. (2010) recently conducted an investigation into the relationship between manganese and children’s Intelligence Quotient (IQ) as well as the relationship between drinking water manganese exposure and manganese present in children’s hair samples (discussed above). This study included 362 children in southern Quebec between the ages of 6 and 13 years of age. The median concentration of manganese in the household drinking water was 34 µg/L (with a range of 1 – 2,700 µg/L). The authors found that a 10-fold increase in manganese concentration at the tap was associated in a reduction of 2.4 IQ points. These data were adjusted for other factors, including family income and maternal intelligence. The authors conclude that these findings “support the hypothesis that low-level, chronic exposure to manganese from drinking water is associated with significant intellectual impairments in children” (Bouchard et al. 2010).

Spangler and Reid (2010) completed a study evaluating the degree of correlation between groundwater and airborne manganese concentrations and cancer age-adjusted mortality rates at the county level in North Carolina. Cancer related mortality rates per 100,000 were obtained over a 4-year period from 1997-2001 and correlated, by county, with average air manganese levels and mean groundwater manganese concentration. The mean groundwater manganese concentrations by county were estimated from the North Carolina Geological Survey groundwater database using samples taken between 1973 and 1979. The authors did not mention


if the water quality data used for this study was obtained from wells used strictly for potable supply, what proportion of the population considered by the study depended on groundwater as their water source or if any treatment was in place for those individuals consuming groundwater.

Ignoring these obvious shortcomings, the study concluded that groundwater manganese positively correlated with total cancer, colon cancer and lung cancer county level death rates. Spangler and Reid (2010) estimated that for each one log increase in groundwater manganese, total cancer mortality rates at the county level increased by 12.1 deaths per 100,000. Using the same methodology, the authors estimated for each one-log increase in groundwater manganese, there was a 2.84 and 7.73 times increase in colon and lung cancer deaths per 100,000 respectively. Co-occurrence with other contaminants

Manganese oxides and oxyhydroxides have been shown to be important in scavenging

dissolved trace metals such as lead (Dong et al. 2003) and arsenic (Ouvrard et al. 2002) from natural waters. The scavenging properties of manganese oxides are so good that it forms the basis for the use of the precipitation of manganese dioxide as an analytical method to pre-concentrate trace metals such as aluminum, cadmium, copper, nickel, lead, vanadium, zinc, and rare earth elements (Umashankar et al. 2002). Thus, legacy manganese may pose a health risk due to the possible release of co-occurring regulated inorganic contaminants (Schock and Holm 2003; Schock 2005). These regulated contaminants are typically monitored (per regulatory requirements) after drinking water has been treated but prior to distribution, and therefore utilities don’t typically monitor these contaminants in the distribution system. It appears possible that during releases of legacy manganese, drinking water customers could be exposed to other contaminants at levels greater than maximum contaminant levels for those contaminants. As discussed in Friedman et al. (2010), Schock and Holm (2003), Schock (2005) and others under certain conditions, such as during disequilibrium or dissolution events caused by changing water chemistry, contaminant releases may not necessarily be visible to consumers.

Friedman et al. (2010) described accumulation trends and contaminant behavior for two broadly-divided groups – trace metal cations and anionic compounds. Trace metal cations include barium, lead, nickel, and radium isotopes. These elements have a strong affinity for hydrous manganese oxides (HMOs) and an apparent affinity for phosphate precipitates and/or phosphate surface groups. Their accumulation by adsorption/co-precipitation mechanisms is typically enhanced under conditions of elevated pH and when potentially competitive cations (e.g., calcium, magnesium) are present at low concentrations. Trace anionic compounds include the oxoacids arsenate, chromate, and vanadate, as well as complexes of uranyl. These compounds have a strong affinity for HMOs and hydrous ferric oxides. Their accumulation by adsorption/co-precipitation mechanisms is typically enhanced under conditions of low pH and when potentially competitive anions (e.g., bicarbonate, phosphate, silicate) are present at low concentrations.

Sandvig et al. (2008) describe how scales on lead piping (such as lead service lines) consist of multiple layers with the surface-most layer being somewhat lower in total lead, but high in amorphous compounds of other elements such as iron and manganese. The authors hypothesized that changes in water chemistry that increase the solubility of the iron and


manganese minerals could destabilize the structure of the surface-most layer, releasing lead-rich particles. Cantor (2006) discusses a case study for the Madison Water Utility in which a full lead service line replacement program was undertaken. The study concluded that the combination of lead service lines (LSL) with iron/manganese scales may put individual sites at risk for high levels of total and particulate lead. The researchers demonstrated that lead concentrations at residences prior to LSL replacement were erratic, and remained erratic for four years after replacement due to lead particulate matter dislodging from pipe walls and arbitrarily becoming entrained in water samples. Dissolved lead concentrations were immediately reduced with LSL replacement. Scale analysis (Schock et al. 2006) verified that the lead compounds were intermingled with manganese and iron scale layers.

Lytle et al. (2004) did not find a relationship between arsenic and manganese levels, or between arsenic and any other major constituents of the pipe and hydrant flush solids collected from 15 midwestern utilities. The authors concluded that arsenic associated with distribution system solids varies widely, is difficult to predict, and likely depends on a combination of many factors such as water chemistry, pipe material and age, flushing procedures and frequency, and solids retention and exposure time.

Welsh et al. (2010) was unable to find an overall correlation between the accumulation of trace metals and the amount of manganese in scales on lead service line samples taken from 21 utilities. However correlations were found between amounts of certain trace metals including barium, nickel, chromium and the amount of manganese in scale taken from individual utilities. The authors concluded that while manganese may not control trace metal accumulation, manganese scale destabilization can still release accumulated metals. Regulatory Requirements

Table 1 provides a summary of regulatory requirements related to manganese from

selected countries and regulatory agencies. Three of the six agencies have set a health-based regulatory limit for manganese, and all six have set non-enforceable aesthetic-based limits.


Table 1. Summary of Manganese-Related Regulatory Requirements

United States

In the United States, manganese is considered an aesthetic problem and is not regulated

with the objective of protecting public health. The USEPA currently does not regulate manganese as part of the National Primary Drinking Water Standards. The USEPA has set a Secondary Maximum Contaminant Level (SMCL) for manganese of 0.05 mg/L. SMCLs are non-enforceable levels set by the USEPA to indicate that concentrations above these levels may cause aesthetic problems (such as color or taste), cosmetic problems (such as staining), or technical effects (due to staining or corrosion).

In 2004, the USEPA completed an evaluation of the need to develop a primary drinking water standard for manganese. The USEPA concluded that, based on available data, manganese did not present a meaningful opportunity for health risk reduction. Therefore, the USEPA has set a Drinking Water Health Advisory Value (HAV) for manganese of 0.3 mg/L (USEPA 2004). An exposure of this level of manganese on a daily basis is not expected to result in adverse health effects. With respect to acute exposure to manganese, the USEPA has set one-day and 10-day HAVs at 1 mg/L. The USEPA does indicate that for infants, the acute exposure HAV is 0.3 mg/L due to concerns regarding absorption and excretion in infants. Since these HAVs have been established, some research, described previously, has been completed that suggest concerns regarding manganese exposure for children and the co-occurrence of manganese with other drinking water contaminants. Additionally, legacy manganese presents the possibility of periodic releases of accumulated manganese (and associated trace contaminants) that could result in periods of acute or sub-chronic exposure and differing health impacts.

Country/Agency Year Cited

Country Specific Designation

Health Based Value

Aesthetic Objective

Resource

Australia/National Resource

Management 2004 Guideline Value 0.5 mg/L 0.1 mg/L Australian Drinking Water

Guidelines

Canada/ Health Canada 2010

Maximum Acceptable

Concentration 0.05 mg/L Guidelines for Canadian Drinking Water Quality

European Union 2007 0.05 mg/L

European Communities(Drinking

Water)(NO. 2) Regulations Japan/Ministry of

Health 2004 Standard Value 0.05 mg/L 0.01 mg/L Revision of Drinking Water

Standards in Japan

United States/USEPA 2011

Secondary Maximum

Contaminant Level 0.05 mg/L

USEPA http://water.epa.gov/drink/c

ontaminants/index.cfm World Health Organization 2008 Guideline Value 0.4 mg/L

0.05-0.1 mg/L

Guidelines for Drinking Water Values


World Health Organization Guidelines The World Health Organization (WHO) has established a guideline level of 0.4 mg/L for

manganese. The WHO guidance notes that this is significantly higher than what is considered acceptable from an aesthetic standpoint, with customers generally finding water containing manganese concentrations below 0.05 - 0.1 mg/L aesthetically acceptable. Other Countries

Canada’s guidelines for drinking water quality establishes an aesthetic objective for

manganese of less than or equal to 0.05 mg/L. The European Union has established a Directive value of 0.050 mg/L for manganese. Japan has established a drinking water standard of 0.05 mg/L for manganese, and a supplemental target value of 0.01 mg/L. MANGANESE OCCURRENCE Presence of Manganese in Source Water

Manganese can be present in many waters including groundwater, surface water sources

(such as rivers) and lakes and reservoirs. Each source type has different characteristics (such as contact time with manganese-bearing soil and rock, oxidation/reduction potential, etc.) that generally govern the amount of manganese in solution. Between 1984 and 1986, the National Inorganic and Radionuclide Survey (NIRS) collected data from 989 U.S. community public water systems (PWSs) served by ground water in 49 states and found that 68% of the ground water PWSs reported detectable levels of manganese, with a median concentration of 10 µg/L. Supplemental survey data from PWSs supplied by surface waters in five states reported occurrence ranges similar to those of ground water PWSs. Overall, the detection frequency of manganese in U.S. ground water is high (approximately 70% of sites assayed have measurable manganese levels) due to the ubiquity of manganese in soil and rock, but the levels detected in ground water are generally below levels of public health concern (U.S. EPA 2003). Similarly, manganese is detected in about 97% of surface water sites (at levels far below those likely to cause health effects) and universally in sediments and aquatic biota tissues (at levels which suggest that it does not bioaccumulate; U.S. EPA 2003).

Casale et al (2002) evaluated manganese concentrations in source waters from utilities that provided data to the 1996 AWWA WaterStats Database. Approximately 35% of the 349 groundwater systems participating in the survey reported source water manganese concentrations exceeding 50 µg/L. Approximately 40% of the 428 surface water systems participating in the survey reported source water manganese concentrations exceeding 50 µg/L.

Kohl and Medlar (2006) found that source water manganese levels were much greater in groundwater sources compared to surface water sources. However they also concluded that manganese levels measured in bulk water samples collected from distribution systems were similar for groundwater and surface water utilities.


Frequency of Manganese Treatment There are approximately 153,530 public drinking water systems in the United States,

51,651 of which are community water systems. 78% of these systems, representing 30% of the population (88,032,021 persons), are served by groundwater (USEPA, 2009). According to the USEPA Community Water System Survey (2006), 73.5% of survey respondents use groundwater as their primary water source, and 13% of the groundwater systems provide treatment for manganese (removal or sequestration), while 21% of the surface water systems provide treatment for manganese. The survey also states that 23% of treatment plants provide treatment for removal or sequestration for iron. As can be seen in Figure 3, which presents various treatment objectives for surface water and groundwater treatment plants, manganese treatment is a frequent treatment objective. The incidence of manganese control as a treatment objective is roughly on the same order as taste and odor control. It is very difficult to extrapolate these results to determine the actual number of manganese treatment plants nationwide, since survey results can have many biases, based on the number and types of systems that responded.

Kohl and Medlar (2006) report that for the 242 systems included in their utility survey, manganese levels entering the distribution system were almost always less than 50 µg/L. Seventy two percent of the surveyed utilities had less than 20 µg/L of manganese entering the distribution system. While it is encouraging to note that treatment systems appear to effectively remove manganese from source water, there is no way to determine from this information the quantity of manganese that was loaded into the distribution system prior to treatment implementation, nor the quantity of manganese that continues to accumulate, albeit at very low rates, due to a wide variety of system-specific factors. Thus, analysis of current treatment practices probably yields little useful information with regard to determining existing quantities of legacy manganese.

Further details on methods and efficacy of treatment of manganese can be found in the Remediation and Preventive Strategies discussion below.


Figure 3. Groundwater and Surface Water Treatment Objectives, Including

Manganese Removal (Source: USEPA, 2006). Occurrence within the Distribution System

Until now, the accumulation of legacy manganese in distribution systems has not been a

topic of focused study. Instead the current understanding of how manganese accumulates in distribution systems has come indirectly from the work of a few utilities and researchers studying distribution system flushing efficacy, contaminant presence in the distribution system, and pipe scales. This section summarizes the quantity of distribution system manganese observed during these investigations. Hydrant Flush Manganese Concentrations

This section includes information on manganese levels observed during hydrant flushing

(both grab sample results and results of solid samples) from various researchers. Numeric results for bulk water samples collected during flushing are compiled in Table 2. Numeric results for

0 20 40 60 80 100

Algae Control

Corrosion Control

Primary Disinfection

Secondary Disinfection

Disinfectant By‐product Control

Dechlorination

Oxidation

Iron Removal

Manganese Removal

Taste/Odor Control

TOC Removal

Particulate/Turbidity Removal

Softening (Hardness Removal)

Recarbonation

VOCs Removal

Inorganics Removal

Radionuclides Removal

Security

Mussel Control

Fluoridation

Other

Percentage Surface Water PlantsPercentage Groundwater Plants

% of Systems Providing Treatment to Meet Objectives


solid samples collected during flushing are compiled in Table 3. Additional information associated with the studies compiled in Tables 2 and 3 is provided below.

A large utility in Alaska (EES 2001) conducted a pilot flushing program in summer 2001 and monitored, among other water quality parameters, manganese presence in the flushed water. Table 2 presents the average total manganese level from bulk water samples collected at the beginning and end of flushing. Typically, the total manganese concentration dropped to a concentration below the Secondary Maximum Contaminant Level (SMCL) of 0.050 mg/L within flushing five pipe volumes.

Friedman et al. (2003) conducted a study focusing on the impact of flushing velocity on solids within the distribution system. As part of this research, 10 utilities participated in 19 hydrant flushes to determine if higher velocities removed more or different types of material. Grab samples were collected at the beginning, mid-point, and end of each hydrant flush. The researchers conducted data analysis on the manganese concentrations of these grab samples to develop a “normalized theoretical mass,” an estimate of the mass of manganese removed over pipe surface area. These estimated masses are reported in Table 2. Additionally, the researchers conducted 16 hydrant flushes during which particulates were captured (at 10 utilities) to describe the nature of distribution system deposits and evaluate flushing performance. Manganese comprised 0 to 2.5% of the captured particulates in these tests.

Lytle et al. (2004) studied arsenic levels in 67 distribution system solid samples collected from 15 groundwater drinking utilities in Ohio, Michigan, and Indiana with sources containing iron and arsenic. As part of this study, the investigators quantified the elemental composition, including manganese, of hydrant flush samples and pipe interior solids. Tables 2 and 3 include Lytle’s findings with respect to the presence of manganese in hydrant flush and pipe solid samples.

Manganese complaints increased in Madison, Wisconsin in 2005 (Schlenker et al. 2008, Madison Water Utilities 2007), especially in a neighborhood served by a single well containing manganese. A single sample collected from a customer’s tap in this neighborhood had a manganese concentration of 224,000 g/L. At this time, twenty-four groundwater wells supplied Madison with drinking water. On average, the wells had a manganese level of 28 g/L, with 21 of the wells producing water below 50 g/L (Schlenker et al. 2008). The wells with the three highest manganese levels ranged from 53 g/L to 124 g/L. Madison Water Utility collected 2,075 samples at 1,118 properties served by the utility, collecting the majority of these samples in locations served by wells with the highest levels of manganese. Of these samples, 90% were less than 50 g/L. Eleven of the samples (0.6%) collected had manganese levels greater than 300 g/L. Upon repeat testing at these 11 locations, all were less than 300 g/L. The highest manganese samples were often collected from infrequently used hose bibs or unoccupied properties. Madison Water Utility also analyzed data to determine whether locations served by the high manganese wells had higher manganese levels than those seen throughout the service area. Three of the four high manganese wells served locations with a higher number of samples in the 50 –149 g/L range (9 – 15%) than the rest of the service area (3.5%) (Madison Water Utilities 2007), demonstrating that while samples containing relatively high levels of manganese were present throughout the distribution system, more were located in areas served by high manganese wells.


As discussed earlier, a medium-sized utility in Washington State (HDR 2008) conducted a pilot flushing program in 2007 and monitored manganese presence in the flushed water. Table 2 presents the average total manganese level of samples collected at the beginning of flushing hydrants. Investigators determined that while the surface water supply contains a very low level of manganese, relatively high levels of manganese had accumulated due to the fact that this piping is located in a new undeveloped subdivision where stagnant water conditions exist, thereby creating an environment conducive to the settling of these solids. The study does not include information on manganese levels at the end of flushing efforts.

Friedman et al. (2010) investigated the elemental composition of 26 hydrant flush solids and 46 pipe scale solids collected from 20 participating utilities. The researchers noted that 11 of the 20 utilities reported manganese concentration at the distribution system entry point to be greater than 10 g/L. Results for manganese levels in hydrant flush solids are included in Table 3 and in Figure 2.


Table 2. Compilation of Manganese Levels Measured in Bulk Samples Collected During Various Hydrant Flushing Studies

Utility/ Data

Source

State Source Water Type

Pop. Served

Finished Water

Mn (µg/L)

Dist. System Bulk Water Mn

(µg/L)

Sample Type

Pipe Material in Flush

Zone

Hydrant Flush Bulk Water or Surface Loading

MnEES 2001 AK Surface

and Ground water

52,000 < 20 Beginning of flush

Asbestos cement and cast

iron

1,000µg/L1

End of flush

Asbestos cement and cast

iron

20 µg/L1

HDR 2008

WA Surface 47,000 1.4 Loop A11

Old, unlined cast iron

42.7 µg/L

Loop A21

New cement-

lined ductile

iron

54.3 µg/L

Friedman et al. 2003

AK Surface and

Ground water

52,000 < 20 ANC-5 Asbestos-Cement

6.5 mg/ft2 2

ANC-13

Asbestos-Cement

3.4 mg/ft2 2


NH ND – 150

DOV-3 Unlined Cast Iron

0.6 mg/ft2 2


VA <10 NNH-3 Unlined Cast Iron

13.1 mg/ft2

2

NNI-4 Ductile Iron

2.9 mg/ft2 2


OR <10 POR-6 Unlined Cast Iron

35.7 mg/ft2

2

POR-12

Unlined Cast Iron

14.1 mg/ft2

2

1 Average of total manganese values collected during hydrant flushing. 2 Manganese concentrations observed during the flush were used to estimate the mass of Mn removed normalized to pipe surface area flushed.


Table 3. Compilation of Manganese Levels in Hydrant Flush Solids from Various Studies Utility/ Data

Source State Source

Water Type

Pop. Served

Source Water

Mn (µg/L)

Distribution System (Bulk Water)

Mn (µg/L)

Sample Pipe Material in Flush

Zone

Hydrant Flush Solid

Mn (µg/g)/(%wt)

Utility 1 (Lytle 2004)

OH Ground-water

2 9

1-1 Cast Iron

89/0.01

1-2 Asbestos Cement

2,295/0.23

1-3 94/0.01

1-4 1061/0.11

1-5 139/0.01


OH < 10

2-1 Cast Iron

10,579/1.06

2-2 Cast Iron

981/0.10

2-3 Cast Iron

3,576/0.36

2-6 1,591/0.16

2-7 1,612/0.16

2-8 679/0.07

2-9 360/0.04

2-10 1,958/0.20


OH 1014

5-1 1,611/0.16

5-2 9,876/0.99

5-3 12,028/1.20

5-4 17,881/1.79

5-5 13,521/1.35

5-6 10,833/1.08


MI 19 6-1 523/0.05

6-2 330/0.03

6-3 698/0.07

6-4 434/0.04


MI < 107 5 6

7-2 682/0.07


OH 20 15-1 526/0.05

15-2 460/0.05


Utility/ Data Source


Pop. Served

Source Water

Mn (µg/L)


Mn (µg/L)


Zone

Hydrant Flush Solid

Mn (µg/g)/(%wt)

15-3 1,237/0.12

15-4 776/0.08

15-5 1,254/0.13

Utility W (Friedman et al.

2010

Ground-water

7,000 0.04 W-D Cast Iron

240/0.02

W-E Cast Iron

177/0.02

W-F Cast Iron

99.6/0.01

Utility CL (Friedman et al.

2010)

Ground-water

28,000 CL-F: 0.4 CL-F Cast Iron

1,192/0.12

CL–G: 0.1 CL-G Cast Iron

614/0.06

Utility SA (Friedman et al.

2010)

Ground-water and

Surface

60,000 SA-D: 1.2 SA-E: 0.3

SA-D

Cement-lined

1,461/0.15

SA-E Cement-lined

3,509/0.35

Utility G (Friedman et al.

2010)

Ground-water

5,000 0.2 G-A Cast Iron

488/0.05

Utility J (Friedman et al.

2010)

Ground-water

145,000 J – A-D, G-J: 55.4

J-E, F: 7.8

J-A Cast Iron

1,235/0.12

J-B Cast Iron

30.11/0.003

J-C Cast Iron

387/0.04

J-D Cast Iron

390/0.04

J-E Cast Iron

760/0.08

J-F Cast Iron

322/0.03

J-G Cast Iron

443/0.04

J-H Cast Iron

1,459/0.15

J-I Cast Iron

613/0.06

J-J Cast 1,091/0.11


Utility/ Data Source


Pop. Served

Source Water

Mn (µg/L)


Mn (µg/L)


Zone

Hydrant Flush Solid

Mn (µg/g)/(%wt)

Iron

Utility NC (Friedman et al.

2010)

Ground-water

200

30.0

NC-A

PVC

210/0.02

Utility ST (Friedman et al.

2010)

Ground-water

15,000 ST-C: <0.01

ST-D: 1.9

ST-C Cement-Lined

2,949/0.30

ST-D Cast Iron

845/0.09

Utility K (Friedman et al.

2010)

Ground-water

8,000 9.0 K-C Cast Iron

825/0.08

K-D Cast Iron

396/0.04

Pipe scale

As described earlier, Lytle et al. (2004) and Friedman et al. (2010) investigated the

composition of distribution main scales from numerous utilities. Results for manganese occurrence are presented in Table 4. Figure 4 summarizes manganese occurrence levels observed by Friedman et al. (2010) from pipe specimens, hydrant flushed solids, and all solid samples in the data set (n=58). The median Mn level was 790 µg/g (0.08% wt), and the average level was 7,320 µg/g or about 0.73 % weight. The standard deviation was 31,200 µg/g. The Mn level for the bulk of the samples was between 300 µg/g and 2000 µg/g. In the most extreme case, a specimen of HDPE pipe that has been exposed to water with an average manganese level 50 g/L for a period of nearly eight years had a developed a thick, friable layer comprised of 23.2 wt% manganese.


Figure 4. Cumulative occurrence profile for manganese in deposit samples (Source: Friedman et al. 2010).

Schock et al. (2008) conducted research on the accumulation of contaminants on lead

pipe scales. The authors emphasize that this study was not conducted to quantify, on a national level, contaminant accumulation in pipe scales. This research analyzed the pipe scales from 91 lead pipe specimens obtained from 26 utilities in eight states. These samples were collected over 15 years and represented both surface water and groundwater sources of supply. The average and median manganese levels were 17,451 and 4,960 mg of manganese per kg of pipe scale (approximately 1.75 and 0.50 % by weight), respectively, with a maximum measurement of 177,200 mg/kg. Manganese was categorized as a “major contaminant,” according to the presence by weight in the pipe scale.

0%

20%

40%

60%

80%

100%

100 1,000 10,000 100,000 1,000,000

Sam

ple

Perc

entil

e

Manganese Concentration (μg/g)

All Solid Samples Pipe Specimens Hydrant Flush Solids


Table 4. Compilation of Manganese Levels in Pipe Section Solids from Various Studies Utility 1 (Source) State Source

Water Type

Pop. Served

Distribution System (Bulk

Water) Mn (µg/L)

Sample Pipe Material

Pipe Section Solid Mn

(µg/g)/(% wt)


OH < 10

2-4 Cement-lined iron

10,187/1.02


1,112/0.11


OH 292 3-1 PVC 5,141/0.51

3-2 PVC 1,267/0.13Utility 4 (Lytle

2004) IN < 10

< 10


638/0.06

4-2 Cast iron 609/0.06


MI 19 6-5 Cast iron 553/0.06


MI < 107 5 6

7-1 Cast iron 1,242/0.12


MI 1106

8-1 Cast iron 18,591/1.86

8-2 Cast iron 20,585/2.06

8-3 Cast iron 6,897/0.69


OH < 10 9-1 Cast iron 287/0.03


MI 24 10-1 Cast iron 1,804/0.1810-2 Cast iron 1,090/0.1110-3 Cast iron 744/0.0710-4 Cast iron 585/0.0610-5 Cast iron 219/0.0210-6 Cast iron 1,838/0.1810-7 Cast iron 469/0.0510-8 Cast iron 1,417/0.1410-9 Cast iron 318/0.0310-10 Cast iron 936/0.0910-11 Cast iron 415/0.0410-12 Cast iron 860/0.0910-13 Cast iron 312/0.0310-14 Cast iron 627/0.0610-15 Cast iron 186/0.0210-16 Cast iron 324/0.0310-17 Not

Available 884 2 /0.09


Utility 1 (Source) State Source Water Type

Pop. Served


Water) Mn (µg/L)



(µg/g)/(% wt)


OH 30 3

36 3 34 3 77 3 30 3 38 3

11-1 Not Available

312/0.03

11-2 Not Available

660/0.07

11-3 Not Available

2,083/0.21


MI 55

12-1 Not Available

88/0.01


MI 13-1 Cement 1454/0.15

13-2 PVC 290/0.03

13-3 PVC 1143/0.11


MI 50 14-1 Asbestos Cement

632/0.06


OH 20 15-6 Plastic 882/0.09

(Schock et al. 2008)

Lead 4,9604/1.75

Utility W (Friedman et al.

2010)

Ground-water

7,000 0.04 W-A Cast Iron 447/0.05

W-B Cast Iron 976/0.10

W-C Cast Iron 816/0.08

Utility CL (Friedman et al.

2010)

Ground-water

28,000 CL-A,B: 0.06

CL-C: 0.03

CL-A Cast Iron 400/0.04

CL-B Cast Iron 362/0.04

CL-C Cast Iron 372/0.04

CL-D Cast Iron 1,393/0.14

CL-E Cast Iron 580/0.06

Utility SA (Friedman et al.

2010)

Ground-water and

Surface

60,000 0.1 SA-B Cement-Lined

313/0.03

Utility CH (Friedman et al.

2010)

Ground-water

11,000 pop

0.3 CH-A Steel 1,319/0.13

Utility RW (Friedman et al.

2010)

Ground-water

6,300 0.5 RW-A Galvanized Iron

635/0.06

RW-B Galvanized Iron

1,628/0.16


Utility 1 (Source) State Source Water Type

Pop. Served


Water) Mn (µg/L)



(µg/g)/(% wt)

Utility IN (Friedman et al.

2010)

Ground-water and

Surface

57,000 6.6 IN-B Ductile Iron 1,342/0.13

IN-C Ductile Iron 691/0.07IN-D Ductile Iron 654/0.07

Utility CC (Friedman et al.

2010

Ground-water

1,900 3.9 CC-A Cast Iron 46.69/0.01CC-B Cast Iron 28.95/0.003CC-C Cast Iron 14.12/0.001CC-D Cast Iron 21.65/0.002

Utility DN (Friedman et al.

2010)

Surface 1,200,000 <6.0 DN-A Cast Iron 1,144/0.11

DN-B Cast Iron 514/0.05

Utility CA (Friedman et al.

2010)

Ground-water and

Surface Water

100,000 0.2 CA-A Steel 1,166/0.12

CA-B Cast Iron 139/0.01

Utility PC (Friedman et al.

2010)

Ground-water and

Surface

8,000 0.02 PC-A Galvanized Iron

2,597/0.26

PC-B Galvanized Iron

2,790/0.28

Utility WDB (Friedman et al.

2010)

Ground-water

1,200 50.0 WDB-A HDPE 232.4/0.02

Utility WA (Friedman et al.

2010)

Ground-water

6,000 11.1 WA-A Cast Iron 3,714/0.37WA-B Cast Iron 129/0.01WA-C Cast Iron 386/0.04WA-D Cast Iron 2,292/0.23

Utility B (Friedman et al.

2010)

Ground-water and

Surface Water

100,000 0.1 B-A Ductile Iron 928/0.09

B-B Ductile Iron 715/0.07

B-D Cast Iron 402/0.04

Utility ST (Friedman et al.

2010)

Ground-water

15,000 < 0.01 ST-A Cast Iron 3,925/0.39

Utility K (Friedman et al.

2010)

Ground-water

8,000 9.0 K-A Cast Iron 938/0.09

1 Listed in same manner used to designate utilities in literature. 2 This result was listed as a hydrant flush sample, but other information indicates it was a pipe section sample. 3 Note: These samples were collected in a building. 4 The median measurement from 91 samples.


General Observations Regarding Manganese Occurrence in the Distribution System As mentioned at the beginning of this section, a specific study to quantify of the amount

of manganese that may accumulate in distribution systems has not been attempted. At present, estimates of the quantity of accumulated manganese can only be made indirectly from information gathered by other studies. Nonetheless, by assessing data from the flushing and pipe solids studies described above some general observations can be made:

Manganese can be detected in solids mobilized by flushing and in solids found on

pipe walls. Higher levels of manganese have been found in pipewall solids compared to those solids mobilized by flushing.

While the amount of manganese found in mobilized solids or pipe wall solids can vary widely, the amount of manganese is typically less than 1% by weight. Based on analysis performed by Friedman et al. (2010), the preponderance (60%) of pipe wall solids analyzed contained between 0.03% and 0.2% by weight manganese. Schock et al 2008 observed from 7 mg/kg to nearly 18% by weight in 91 lead pipe scales, with the average being approximately 1.8% and a median of approximately 0.5%.

The amount of manganese released by flushing can vary widely. Estimates by Friedman et al. (2010) of the mass of manganese released per unit area of pipe flushed during flushing ranged from 0.6 mg/ft2 to 35.7 mg/ft2.

While it is reasonable to assume that there is a positive correlation between bulk water manganese concentrations in the distribution system and mass loading of manganese in pipe wall solids, insufficient data exists to prove that this is true.

The loading of manganese accumulated in a distribution system (mg/ft2 pipe area) can vary widely within the distribution system. This implies that manganese accumulation may occur over broad areas of the distribution system with low loading of accumulated manganese or in localized area of high loadings of accumulated manganese. Variables such as water chemistry, pipe material, age of pipe, operational history, and hydraulic characteristics, as well as history of main cleaning techniques will impact the degree of accumulation observed.

DIRECT AND INDIRECT IMPACTS OF LEGACY MANGANESE PRESENCE IN THE DISTRIBUTION SYSTEM

Kohl and Medlar (2006) concluded that consumer pressure is typically the motivation for

utilities to implement or modify manganese treatment and/or apply system maintenance practices (e.g., flushing) to improve aesthetic quality. According to the authors, many utilities, particularly those with seasonal or intermittent Mn problems, do not feel they can justify the cost for major treatment improvements simply to achieve a reduction in customer complaints, i.e., they believe there needs to be a health-based driver. However, there may be the potential for public health issues under certain release scenarios as discussed above. Also, it is worth noting that from the customer’s perspective, palatability and other aesthetic properties are often a major factor in their perception of the safety of the water. It appears that some utilities believe it is


more cost-effective to increase O&M activities (e.g., distribution system flushing or pigging) rather than incur large capital costs to retrofit or add onto existing treatment plants. This is a completely rational approach as long as utilities recognize the total and life-cycle costs of enhanced distribution system O&M, as well as intangible issues and costs, which although difficult to quantify, suggest that most consumers would be willing to pay an additional price for water that consistently meets their expectations for aesthetics.

In addition to aesthetic and the possibility of health impacts, manganese accumulation within the distribution system can cause impacts on utility infrastructure and operational practices. For example, some utilities have adopted the approach of “don’t stir anything up” thereby limiting proactive and important valve and hydrant exercising programs, as well as implementation of flushing programs. Some of these impacts, referred to as direct impacts, have relatively straightforward expenses associated with them, they are directly related to manganese occurrence, and/or they involve purchasing equipment or require additional power. However, other impacts, referred to as indirect impacts, are difficult to monetize, such as the impacts to customer acceptance of the available water quality and trust in the water purveyor. Currently, there is very little peer-reviewed (or non peer-reviewed) and published data related to quantification of direct and indirect impacts associated with legacy manganese. Direct Impacts Utility Equipment and Customer Devices

The release of legacy manganese into distribution system water can result in costs

associated with reimbursing customers for stained clothing or replacement of utility equipment such as valves or piping subject to scale and sediment. For example, a city in Washington State (serving 3,500 people), received 34 water quality-related customer complaints in August and September 2007. The causes of the dirty, cloudy, and/or rusty water complaints were determined to be iron and manganese precipitation and dissolved carbon dioxide (cloudy complaints). The City considered multiple alternatives for addressing the iron and manganese, including installing individual filters at residents’ homes. They estimated the initial cost of filters to be $200 - $500 per affected customer and replacement filters would cost $20 apiece. The filters would need to be replaced every three to six months. The literature does not appear to contain information on utility costs for compensating customers for items stained during laundering or other costs for replacing household equipment specific to issues associated with legacy manganese.

As described in an issue paper by Dickinson and Pick (2002), in industrial cooling systems, manganese scales degrade heat exchanger performance and are commonly believed to promote corrosion due to formation of under-deposit conditions. (Under-deposit refers to conditions where a deposit causes a localized concentration of specific chemical promoting accelerated corrosion.) The direct galvanic action of manganese dioxide in the corrosion process is less well recognized and can promote severe localized attack. Manganese deposition in cooling water circuits degrades corrosion resistance, lowers heat exchanger efficiency, and reduces biocide performance. These effects incur significant costs to the electric power industry through increased fuel consumption, more frequent and extensive cleanups, higher chemical treatment costs, and in some cases, significant capital costs for component replacement. The


authors state that concerns over manganese fouling are less universal than those related to calcium, silica, or iron due to the often low or undetectable levels of manganese in cooling water supplies. The corrosive impact of manganese deposition in systems relying on these waters can lead to the necessity of replacing condenser tubing, causing expenses that far exceed costs associated with the more common mineral scalants.

Manganese deposition is often present as a thin film on plastic pipe or cement-lined pipe, resulting in diameter reduction, or can become incorporated into the corrosion scale of cast iron pipes (see Figure 5), resulting in increased roughness, decreases in the Hazen-Williams C-factor and increases in pipe friction. These phenomena can result in lower pressures and/or increased energy requirements associated with pumping.

Figure 5. Manganese coating on a galvanized pipe specimen.

There is limited documentation on the degree to which legacy manganese can reduce C-

factors in distribution system pipes. However Grob (2011) recently described in a trade journal the results from air scouring water mains of a small Ohio town which had experienced manganese deposition in its distribution system. C-factors were measured in an 8” pipe section before and after air scouring. After removal of the manganese containing solids by air scouring the C-factor improved from 67 to 96 signifying that, in part, legacy manganese was responsible for some of the reduction in C-factor. (Greater C-factors indicate less pipewall friction. Less pipewall friction creates less resistance to the movement of water). However it is impossible to determine from the information provided how much of the reduction in C-factor was directly caused specifically by manganese deposition compared to that caused by corrosion products in general.

Grigg (2010) investigated the secondary effects of corrosion control on distribution system equipment. As the authors noted, the manganese problems experienced by utilities are not related to corrosion control, but manganese is interrelated with other effects of deposition and accumulation. Table 5 presents Grigg’s analysis of scaling impacts to distribution system equipment.


Table 5. Impacts of Scaling to Distribution System Equipment Equipment Impacts Caused by ScalePipes Beginning with tuberculation in unlined cast

iron pipes, all raw and treated water supply pipes are subject to some form of corrosion and/or scaling.

Pumps Pumps are vulnerable to failure due to excessive scaling. Scales can cause problems ranging from lower efficiency to outright failures.

Valves Due to the presence of moving parts (similar to pumps), valve function can be inhibited or blocked by scales.

Meters Loss of accuracy and periodic meter replacement are caused by scaling (and corrosion).

(Adapted from: Grigg 2010) Cost of Prevention

Kohl and Medlar (2006) report that the median and 90th percentile of treated water

manganese leaving the WTPs of the surveyed utilities were 22 and 50 µg/L, respectively. Customer complaints continued to occur even in systems at the median level, presumably due to a combination of periodically mobilized legacy manganese and the SMCL being too high to consistency control aesthetic issues. Thus, even for utilities that have Mn removal strategies in place, Mn still presents an ongoing challenge with regard to customer service. The authors recommend that utilities treat manganese to a level which prevents manganese accumulation in the distribution system as opposed to allowing manganese to enter the distribution system, which may or may not cause water quality problems. Though it is hard to quantify, the author’s indicate that prevention will save money on customer service calls and flushing.

There are numerous engineering reports describing the cost of new treatment associated with addressing water quality problems such as manganese. However, Kohl and Medlar (2006) developed a cost model for addressing manganese through treatment. This model reviewed costs associated with using different treatment processes to reach varying concentrations in finished drinking water. As part of this model, the costs associated directly with treating manganese and operational costs due to manganese treatment were estimated in addition to the consumer benefit associated with preventing manganese problems in the distribution system. The cost model includes assumptions and inputs such as influent concentration of manganese, a treated water target for manganese concentration, per capita consumption costs, unaccounted-for-water, plant sizes, industrial consumption, population served by a given plant size, estimate of the number of persons who may experience problems at a manganese concentration of 50 g/L, and cost to an individual consumer if problems with manganese are experienced in the household. Kohl and Medlar (2006) made a conservative estimate that one percent of the residential population may experience staining, discoloration, or sediment. The researchers assigned an individual cost of $150 per year for consumers affected by manganese problems. This number was developed by


considering the costs of direct impacts such as lost and destroyed clothes, purchasing bottled water, attending meetings, cleaning the clothes and dish washers, and etc. and indirect impacts of aggravation and loss of consumer confidence. This study determined that the source of manganese does not affect treatment cost. According to the cost model, the researchers concluded that each individual dollar spent by the utility to prevent manganese problems in the distribution system results in a greater benefit to the customer versus if customers had to deal with manganese problems on an individual basis.

Cost of Mitigation

These are costs associated with addressing manganese once it has entered the distribution

system and become problematic. Manganese mitigation in the distribution system includes measures such as flushing or pipe cleaning. Hasit et al. (2004) conducted a detailed cost and benefit analysis associated with utility flushing programs. The objectives of this study were to identify the performance parameters for assessing the water quality benefits of flushing operations and to evaluate the costs and benefits of flushing. It is important to note that the study did not specifically focus on flushing effectiveness for Mn removal, and depending on the type of legacy manganese present (loose sediment, adhered film, co-mingled with iron scale) the effectiveness of flushing at removing the manganese will vary substantially. Hasit et al (2004) provides metrics that can be used to develop system-specific basic unit costs, such as:

Production cost of water flushed Disposal cost of water flushed Average labor costs Average cost of operating vehicles Total cost of flushing equipment

In addition to the Hasit et al. (2004) report, additional flushing cost estimates are

available for systems that have found manganese to be a component of their water quality issues in the distribution system. A utility in Alaska conducted a pilot flushing project which improved distribution system water quality, including significantly lower total manganese levels measured at the hydrant. To conduct unidirectional flushing of 16,160 feet of water main, 328 hours of field work and planning were completed. This project also made an estimate of the amount of time needed to conduct planning and fieldwork for future unidirectional flushing efforts and the cost of new equipment.

A medium-sized utility in Washington (HDR 2008) conducted a pilot flushing program in December 2007. This effort involved flushing approximately 6 miles of distribution system mains. As part of this effort, estimates were made regarding the number of hours necessary for conducting further flushing of the distribution system. As shown in Table 6, the estimate differentiates between the amount of effort necessary to conduct flushing the first time and the amount of effort needed to conduct repeat flushing of an area.


Table 6. Estimated Hydrant Flush Labor Efforts Department First Effort

(Hours per Mile)Repeat Effort (Hours per Mile)

O&M – Water 37.4 30.7 Engineering/GIS 11.4 0.0 Public Information 0.8 0.8 Overall 49.6 31.5

(Source: HDR 2008) Indirect Impacts

Kohl and Medlar (2006) point out that while utilities are responsive to public pressure, it

is difficult to justify additional treatment to meet the objective of reducing customer complaints if the water quality meets the SMCL of 0.050 mg/L. However, Kohl and Medlar (2006) point out that while indirect costs to both utilities and customers are difficult to quantify, it appears that most customers would be willing to pay more for water that is aesthetically acceptable the majority of the time. Especially because many consumers tend to use taste, odor, and appearance as surrogates for safety of the drinking water supply (which was justified with respect to manganese presence by Schlenker et al. 2008).

Hasit et al. (2004) tried to include indirect impacts in the cost benefit analysis of flushing. The investigators include an evaluation of the benefits of reducing customer complaints, improving water quality, and meeting regulatory requirements. Aesthetic Impacts and Customer Acceptability

Historically, legacy manganese has been perceived as a nuisance contaminant because of

its ability to aesthetically degrade water quality at relatively low levels. Even today, most utilities’ perception of whether they have a “manganese problem” is attributable to customer complaints about discoloration, color, staining, and/or taste. Customers have to rely on their observations (taste, smell, and appearance) of drinking water at the tap as an indicator of the safety of the water supply. As a contaminant that impacts drinking water aesthetics, manganese control is important for meeting customer criteria of a drinking water that appears safe to drink. Additionally, few customers will find a water supply that negatively affects their ability to launder clothing to be acceptable, even on an intermittent basis. Kohl and Medlar (2006) state that customer complaints continued to occur even in systems at the median level of 20 g/L, presumably due to a combination of periodically mobilized legacy manganese and the secondary MCL being too high to consistently control aesthetic issues. The authors note that manganese presence in drinking water can cause “black water” or dirty water complaints, clothes and fixture staining, and, at relatively high levels, a metallic taste. These problems are caused by particulate manganese (Mn(IV)). In one common scenario, manganese enters a household tap in the dissolved, Mn(II) form, but is oxidized to Mn(IV) by bleach and hot water, resulting in stained clothing.

As described earlier, Madison, Wisconsin experienced problems with high levels of manganese at household taps. Investigators found a positive relationship between manganese


and the turbidity of flushed drinking water (Schlenker et al. 2008). They found that the average manganese level observed at a turbidity of 1 NTU (criteria for determining an area had been adequately flushed) was 82 g/L and none of the samples with a turbidity of 1 NTU had manganese levels of 300 g/L (USEPA’s HAV). In samples which had a turbidity of 5 NTU (which were visibly discolored or cloudy), manganese concentrations were greater than 1000 g/L (the 1-day and 10-day HAVs for adults). These results supported the public information campaign to advise people to avoid drinking discolored or dirty water (Schlenker et al. 2008).

Two publications were identified that contain more stringent recommendations (compared to the USEPA SMCL) for consistent control of aesthetic impacts due to manganese in drinking water. These are summarized in Table 7. In addition to these recommended levels, both Ljung and Vahter (2007) and Bouchard et al. (2010) recommend that international manganese guidelines be revisited.

Table 7. Finished Water Manganese Levels Recommended in Literature

Recommended Manganese Goal

(mg/L)

Objective Source Notes

0.01

Control aesthetic problems

Knocke (2004) The median treated water concentration reported from the

National Inorganic and Radionuclide Survey (NIRS) found that 68% of the

groundwater public water systems (PWSs) reported detectable levels of Mn, with a median concentration of

0.01 mg/L (USEPA, 2003)Control

manganese deposition

Kohl and Medlar (2006)

Manganese deposition in distribution systems can occur at concentrations as

low as 0.02 mg/L. Utility Uncertainty

Releases of legacy manganese and co-occurring contaminants can have a negative impact

on the utility’s efforts to ensure a safe drinking water supply. Additionally, a utility with legacy manganese in their distribution system cannot predict upcoming releases and, as a result, is typically in a response mode when it comes to manganese. The utility will not know there is a problem until receiving customer complaints. This might lead to wide-spread, unplanned flushing efforts, unplanned pipe cleaning efforts, public outreach and education, and possibly rate increases associated with implementation of mitigation strategies. The unpredictable release of manganese (and co-occurring contaminants) into the distribution system can also negatively impact public confidence in the water provider. This lack of confidence can have far-reaching repercussions on the utility’s public information and educational efforts and other aspects of effective utility management.

For example, some utilities have avoided implementation of proactive valve and hydrant exercising programs so as to avoid stirring up accumulated sediments and creating discolored water events. The lack of these preventative maintenance programs can expose utilities to


uncertainty during emergency situations such as fires or main break events, since it may be difficult to locate or operate valves that have not been exercised. Purposeful removal of accumulated legacy manganese and accumulated sediments through ongoing hydrant and valve exercising that typically accompanies a well-organized unidirectional flushing program can enhance utility certainty and responsiveness during emergency events. REMEDIATION AND PREVENTIVE STRATEGIES

To date, most studies involving manganese have revolved around lowering the amount of

manganese entering the distribution system thereby reducing the possibility of a manganese-related colored water event. Less research has focused on managing the consequences of manganese after it has entered the distribution system. Once manganese has entered the distribution system, techniques for managing the consequences of its presence are limited. In this section methods for controlling a) the amount of manganese entering distribution systems and b) mitigating the effects of manganese once it is present in the distribution system are discussed. Control of Manganese Prior to Entering the Distribution System Manganese Control Technologies

Numerous water treatment technologies or processes are capable of controlling or

removing manganese from source water. Kohl and Medlar (2006) provide an excellent summary of manganese removal and treatment technologies. In their review Kohl and Medlar (2006) classify manganese removal technologies into the following categories:

In situ Biological Chemical oxidation/physical separation Oxide-coated media Physical separation Ion exchange Incidental precipitation (softening) Sequestration

While not a removal technique and not discussed by Kohl and Medlar (2006), blending is

another effective method for controlling manganese concentration entering the distribution system. Table 8 summaries key manganese treatment techniques and their basis of operation.


Table 8. Summary of Manganese Treatment Techniques Treatment Category Subcategory Basis of OperationIn-situ aeration Surface water Full lake or hypolimnetic aeration to suppress

release of soluble Mn from anoxic lake or reservoir sediments into the water column.

Groundwater Adjustment (increase) in redox potential caused by injection of oxygenated water within zone of influence of withdrawal well. Injected water creates conditions that form insoluble Mn(IV) in the native groundwater. The Mn(IV) is retained in aquifer materials when the native water is withdrawn for use.

Biological Biological oxidation of Mn(II) under aerobic conditions forming insoluble Mn(IV) which is retained by the biofilm or substrate material.

Chemical oxidation/ physical separation

Chlorine Oxidation of Mn(II) by chemical oxidants to insoluble Mn(IV). Oxidation is typically followed by physical separation of particulate Mn(IV) from the treated water using one of several processes. Effective solid/liquid separation processes include sedimentation/media filtration, low pressure membranes and dissolved air flotation.

PermanganateOzoneChlorine dioxide

Physical separation Reverse osmosis/nano filtration membrane

Soluble Mn(II) in its ionic +2 state is separated from source water when water is passed through a polymeric membrane under pressure.

Oxide-coated media Greensand Glauconite sand is pre-coated with MnO2(s) and activated by permanganate or chlorine. Mn removal is by a two step process of Mn(II) adsorption followed by oxidation to Mn(IV) at the sand’s surface.

Pyrolusite Mineral MnO2 (pyrolusite) is used rather than pre-coated glauconite sand. Soluble Mn removal mechanism is similar.

Induced oxide-coated media

Existing filter media is coated in-situ by MnO2(s) in the presence of chlorine using background Mn in the source water or short term exposure to permanganate. After in-situ coating, soluble Mn is then removed per the mechanism similar to greensand and pyrolusite. Media is continuously or intermittently regenerated in the presence of chlorine.

Ion Exchange Soluble Mn(II) is removed by a cation exchange process in which Mn2+ replaces hydrogen or sodium ions on active sites on the cation exchanger.


Incidental precipitation (softening)

Lime or hydroxide addition (softening) increasing treated water pH to 9.5 or greater causing precipitation of insoluble Mn. Insoluble Mn is incorporated into softening solids and removed by sedimentation and filtration.

Sequestration Addition of sequestering agents (typically polyphosphates) that maintain Mn(II) in solution by binding Mn(II) to sequesterant and delaying oxidation of Mn(II) to insoluble Mn(IV) for the period of time that the treated water remains in the distribution system. Unlike other processes, sequestration does not remove manganese from the treated water.

Readers who desire to obtain additional information regarding treatment techniques are

encouraged to consult Kohl and Medlar (2006) or Casale et al (2002). AWWA Water Quality and Treatment, a Handbook on Drinking Water (2011) and AWWA Water Treatment, Principles and Design (2005) are also excellent resources for the interested reader.

Prevalence of Treatment Technologies

There are no comprehensive surveys of water treatment facilities that have determined

the prevalence of particular manganese treatment technologies. Casale et al (2002) performed a survey of manganese treatment technologies at 101 surface, groundwater and surface and groundwater blend plants operated by American Water Works Services Company. Of the approximately 50 surface water plants surveyed (the exact number of surface water plants surveyed was not stated) 47 plants practiced chemical oxidation, with the remaining plants practicing aeration or sequestration. Groundwater plants used a wider variety of treatment technologies. Of the approximately 50 groundwater plants surveyed (again the exact number of groundwater plants surveyed was not stated), 11 used aeration, 26 chemical oxidation, 11 oxide-coated media, 19 sequestration and 3 other processes. It is evident that some of the groundwater plants are using multiple processes for treating manganese. It should be noted that the large number of reported aeration systems were actually for iron treatment and not manganese removal.

Casale et al (2002) also analyzed the 1996 AWWA WaterStats database and concluded that of 492 groundwater systems, 28.5% used permanganate, 18.1% used Fe/Mn control processes and 6.9% used oxide-coated media. For 543 surface water systems surveyed for WaterStats database, Casale et al (2002) concluded 35.7% used permanganate, 7.9% used Fe/Mn control processes and 0.2% used oxide-coated media. In both cases it is not clear if permanganate addition was for manganese control or other treatment objectives. Nor were details of the ‘Fe/Mn control’ technologies were specified.


Control of Manganese After Entering the Distribution System Distribution System Mitigation

As described in the previous section, manganese can be controlled or removed from

source waters by several different methods and technologies. Nonetheless, it is very likely that trace amounts of manganese will find its way to the distribution system. This is due in part to the limitation of each treatment methods or to the initial understanding that manganese is not a problem at all (i. e., manganese is present at levels below the secondary MCL of 0.050 mg/L and consequently the water utility has not implemented a plan for manganese control/removal ). To mitigate problems caused by manganese reaching distribution systems, water utilities can implement several strategies including a) periodic flushing; b) pigging distribution lines; c) chemical addition for finished water stabilization; and d) pipe replacement. Periodic Flushing

Pipe flushing consists of forcing high velocity water through the distribution system with

the purpose of dislodging and removing precipitates. The use of periodic flushing by water utilities to mitigate and prevent the accumulation of precipitated materials in the distribution system has been widely employed (Chadderton et al. 1993; Friedman et al. 2002; Hasit et al. 2004; Husband et al. 2008; Kohl and Medlar 2006; Schock et al. 2005). Hasit et al (2004) conducted a detailed cost and benefit analysis associated with water utility flushing programs. Moreover, the investigation identified the performance parameters for assessing the water quality benefits of flushing operations. The researchers found that the majority of utilities surveyed utilize some type of flushing program on a yearly basis to primarily address and minimize customer complaints. Concurring, Kohl and Medlar (2006) stated that consumer pressure is typically the driver for utilities to employ or modify manganese treatment and/or implement distribution system mitigation practices such as flushing. Although periodic flushing is a common practice, it does not guarantee successful results. Schock et al (2005) reported that Hopkinton, Mass., continued to receive red water complaints even after instituting a flushing program to eliminate precipitated iron from the water mains.

As part of a flushing pilot study in an undisinfected groundwater system (EES, in-house files, 2004), the investigators determined that manganese formed a very adherent coating on PVC piping that could not be fully removed using flushing, even at velocities greater than 6 feet per second (see Figure 6). Although an adherent film remained, significant quantities of accumulated iron, manganese, and bacteria were removed during the flushing trial. The majority of the manganese that could be removed was removed at 6 fps, and no additional benefit was observed when flushing at 10 fps for manganese. However, additional iron was removed at 10 fps, as summarized in Table 9.


Figure 6. Manganese coating on 6-inch PVC pipe before and after flushing at 10fps.

Table 9. Summary of Bulk Water Quality during Flushing

Sample Time HPC Coliform Iron

Bacteria Sulfur

Bacteria Turbidity* Total

Fe Diss. Fe Total Mn

Diss. Mn

(cfu/mL) (per 100

mL) (per Liter) (per Liter) (NTU) (mg/L) (mg/L) (g/L) (g/L) LV 0 11:18 4,000 <1 2,900,000 64,000 8.6 6.92 <0.03 490 <10 LV 1 11:19 11,000 <1 4,400,000 8,000 8.6 1.32 <0.03 110 <10 LV 2 11:20 31,000 <1 20,000,000 130,000 17.6 2.25 <0.03 60 <10 LV 3 11:21 7,000 <1 12,000,000 64,000 14.4 4.37 <0.03 140 <10 LV 4 11:22 15,000 <1 7,200,000 8,000 19.3 3.96 <0.03 390 <10

LV End 11:30 530 <1 430,000 16,000 1.4 0.037 <0.03 10 <10

HV 0 11:37 1,200 <1 2.53 HV 1 11:38 920 <1 430,000 16,000 2.15 0.37 <0.03 30 <10 HV 2 11:39 830 <1 2.35 HV 3 11:40 750 <1 500,000 96,000 2.62 1.06 <0.03 30 <10 HV 4 11:41 450 <1 1.8

HV End 11:44 500 <1 180,000 48,000 1.44 0.21 <0.03 10 <10 *Field measurement LV=Low velocity (6 fps) HV=High velocity (10 fps) Pigging Distribution Lines

Pigging consists of pushing an object, termed a pig1, through the water distribution line to

dislodge and carry away precipitated solids. Similarly to flushing, pigging has also been extensively employed by water utilities to mitigate the accumulation of precipitated materials in the distribution system. The different types of pigs used for pipe cleaning in drinking water applications as well as their classification and pig launching methods are described elsewhere

1The term pig is derived from the term Pipeline Inspection Gauge. Pigs are designed for a number of uses; in this case the reference is to a cleaning pig.


(Huben 2005). However, to the authors’ best knowledge; there is no peer-reviewed literature that has investigated pigging performance and costs associated with using this mitigation technique to control legacy manganese. Finished Water Stabilization

In theory, by reducing desorption and dissolution events, finished water stabilization can

be employed to mitigate distribution systems affected by manganese accumulation. As presented in Table 10, Friedman et al, 2010 summarize water quality conditions that can impact deposit and trace contaminant stability.

Table 10. Water quality conditions that impact deposit and trace contaminant

stability

Water Quality Characteristic Description of Impact

Provide a stable pH within the distribution system (±0.2 units)

The following processes are highly sensitive to pH: adsorption and desorption of trace elements; precipitation/solubilization of precipitates capable of serving as accumulation sinks; precipitation/solubilization of trace contaminant compounds; and deposit stability.

When implementing purposeful pH adjustment, utilities should be aware of potential release impacts and perform distribution system monitoring.

Provide a stable oxidation-reduction potential (ORP) within the distribution system (± 20%)

The nature and stability of mineral deposits is dependent on ORP. These include deposits that may serve as accumulation sinks (e.g., FeCO3, α-FeOOH), as well as chemical precipitates directly involving trace elements (e.g., Cr(OH)3, PbO2, UO2).

Provide a stable orthophosphate concentration within the distribution system (± 20%)

Orthophosphate can react with common inorganic elements to produce precipitates that may serve as accumulation sinks or low-solubility passivation layers. In either case, it is important to maintain a near-constant concentration to promote stability of these solids.

When implementing purposeful phosphate addition, utilities should be aware of potential release impacts and perform distribution system monitoring.

Provide adequate corrosion control

Reduce the formation of iron corrosion scale and tubercles. Reduce the occurrence of red water episodes. Promote the stability of cement-mortar linings. Reduce the leaching of inorganics from cementitious materials.

Avoid uncontrolled blending of surface water and groundwater

Groundwater and surface water supplies typically have very different water quality profiles, including mineral/ionic distribution, NOM concentrations, and ORP. The uncontrolled blending, or periodic switching back-and-forth, of these different source types can prevent formation of stable corrosion scales and contribute to the release of existing scales and associated contaminants.

Avoid uncontrolled blending of free chlorinated and choraminated waters

The uncontrolled blending, or periodic switching back-and-forth, can cause dramatic changes in ORP and disinfectant residual type and concentration, thus impacting scale stability.

Source: Friedman et al. 2010


Pipe Replacement Although not specifically to mitigate legacy manganese accumulation in water

distribution systems, pipe replacement has been used by water utilities for a long time to solve iron pipe corrosion issues (McNeill and Edwards 2001). Thus, pipe replacement could be a very effective technique used as a last resort for water utilities that have a severe case of metals accumulation in their distribution system, although it would only be an effective long-term solution if coupled with a rigorous control optimization program at the treatment plant. Metals accumulation could then be integrated into a Capital Improvement Plan that governs pipe replacement for a specific utility. Residuals Management

Potentially, residuals management could be an important factor when mitigating legacy

manganese in distribution systems. It is a common practice to allow the flushed liquid/solid material to flow to the nearby storm water run-off drain as there is no established procedure governing the disposal of such residuals. However, this scenario could change and it might be necessary to investigate and classify the type of solid residuals produced when mitigating legacy manganese and verify if the residuals pass the Toxicity Characteristic Leaching Procedure (TCLP) as co-contaminants might be present as well. This could be useful in setting a standard procedure to capture, dewater, and dispose the solid material to a landfill and comply with potential future regulations. CONCLUSIONS

Legacy manganese is a wide ranging topic touching on many areas: chemistry, treatment,

costs, consumer confidence and potentially health effects. Based on information gathered for this review, several observations are made regarding legacy manganese and its relevance to the water treatment industry.

Because of its costs to utilities, impact on consumer confidence and possible, but unproven

detrimental impact on public health, legacy manganese is an issue worthy of the drinking water industry’s attention.

The complexity of manganese chemistry along with inherent features of distribution systems (spatially covering a large area, variations in infrastructure age, design features, time varying hydraulics, time dependant changes in water chemistry), suggests that it is more difficult to control accumulation and release in the distribution system than to prevent entry of manganese into the distribution system. However even the most effective treatment system will still permit trace levels of manganese to enter the distribution system.

It is likely that utilities tend to underestimate the cost impacts of accumulated Mn. In general utilities consider the cost impacts of accumulated Mn as an O&M expense rather than a problem to be solved by capital improvements.

Mn events seriously erode customer confidence in a utility. The erosion of consumer confidence is generally not considered by utilities in estimating the cost of accumulated Mn.


Utilities could benefit from more information on the direct and indirect costs associated with legacy manganese. Further information could assist in selecting appropriate treatment and/or prevention measures and in educating consumers on the costs and benefits of spending capital and/or maintenance dollars on addressing legacy manganese.

On average, the percentage on a weight basis of accumulated Mn in pipe scales is small. However, percent weight analyses represent relative occurrence and must be interpreted with caution. There are wide variations in the amount of accumulated Mn in distribution system.

Available data indicate that accumulated Mn may be spatially localized in distribution systems (as opposed to being uniformly distributed throughout the distribution systems). If true, localized control of manganese in the distribution system which focuses on the manganese impacted zone, rather than system wide control should be considered as an approach to deal with legacy manganese.

Some research appears to show that manganese impacts on public health may need to be revisited. These public health impacts may be caused directly by manganese exposure (as demonstrated in Bouchard et al. 2010) or through exposure to other contaminants that can negatively affect public health and which are found to co-occur with manganese.

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