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1
- #1
EngrInfo
Civil/Environmental
- Apr 9, 2003
- 7
Last week an engineer from USEPA in Cincinnati, OH confirmed a grown concern of mine with arsenic in water distribution systems that needs further discussion.
First a little arsenic background:
• US recently adopted a lower standard for arsenic in drinking water from 50 ppb to 10 ppb.
• Removal processes using iron media seems to be the industry trend gaining momentum. Negative ions of arsenic are attracted to the positive ions of iron where arsenic is held by electrostatic force to the iron surface. Arsenic adsorption continues until the media achieves a saturation point (balanced positive and negative charges). This is a passive arsenic removal system where change in the arsenic oxidation state is not required. Recharge of the media occurs with a change in the pH that effects the charge of the media thus releasing the arsenic.
• Many water distribution systems have iron piping having similar charged iron elements.
• These pipelines are actually removing and storing arsenic from the source water.
• Treatment changes effecting the pH such as the introduction of chlorine for the first time, corrosion control adjustment, or even a biofilm will change the ionic balance of the arsenic-iron adsorption resulting in a decreased adsorption capacity of the iron pipe.
• A decreased adsorption means the arsenic re-enters the water at a much higher concentrations, perhaps exceeding the arsenic LD50 toxic levels.
• Even water systems with low levels of arsenic (concentrations below laboratory detection levels) in the water supply that have accumulated months or years of arsenic adsorption could result in short-term very toxic levels of arsenic laden water following temporary chlorination or a biofilm release (during flushing for example).
Every regulatory agency looks at the source for contaminants in the drinking water. Only DBP’s, lead and copper are regulated in US with regard to distribution system effects.
The EPA official indicated that they have collected hydrant flush samples from at least 20 distribution systems in Ohio. Nineteen of the 20 samples resulted in arsenic levels over the proposed standard (and apparently, many of these systems had little to no arsenic detected in the source water). Samples were collected during the flush cycle well after the water cleared up and the results continued to show arsenic levels over the proposed standard. The EPA official confirmed that change in pH or water chemistry (treatment change) will affect the release of arsenic from the distribution system (their samples were only from flushing and not treatment change). So higher arsenic levels would be found in these situations. This information is very preliminary, has not been published, and quantitative values were not given (other than the values were over the proposed standard). Based on my discussions with the EPA official, the immediate operational solution is this: Maintain a treatment change very gradually to reduce the quantity of arsenic release (by the way, there are also issues related to radium and copper storage and releases).
Obviously, more distribution sampling is required to better define the situation; however, here are a few discussion points (note: I’m not a pipeline salesman, nor do I have a preference for type of pipeline in drinking water systems):
Iron pipe vs. Plastic pipe: Should systems having ductile or cast iron piping be required to remove more arsenic from the source, monitor the distribution system for arsenic, conduct more frequent flushing or unidirectional flushing (UDF)…
Iron and Manganese in Source Water: Being a secondary standard, there are many areas in the country that do not treat for iron and manganese. In these areas it is essential to flush the pipelines (iron or plastic pipe systems) because of accumulated iron and manganese deposits in the distribution. Samples from a trailer park distribution system in US revealed arsenic levels in the PPM range from these flush samples (where the source was in compliance with the arsenic standard). Perhaps iron and manganese is no longer a secondary standard, but rather a primary standard due the ability of these materials to remove arsenic and cause uncontrolled high releases of arsenic, a primary drinking water standard? Should iron and manganese treatment be mandatory?
Arsenic Treatment: System having iron piping, do they treat just below the MCL, or go further to reduce effects of re-adsorption on the distribution iron piping?
Biofilm Prevention: Biofilms on distribution pipelines (plastic and iron) have an ionic charge that could affect the arsenic. Should operators focus on biofilm reduction/prevention programs to control biofilm development? For example: implement a variable chlorine residual program (i.e. week 1 @ 0.2 mg/l, week 2 @ 1.2 mg/l, week 3 @ 0.5 mg/l, week 4 @ 1.0 mg/l) w/ flushing during high chlorine residual periods to prevent the biofilm growth due to adaptation (bacteria and other biofilm elements may adapt to the chlorine residual at constant and low levels).
Treatment Process: Corrosion control treatment at the source can change the ionic status of the iron pipe distribution system. The pink water episodes resulting from iron and manganese treatment systems may actually be causing more harm than known. Should the importance of providing a consistent and stable treated water supply be emphasized? Would this effect the type of treatment system chosen (i.e. use of proprietary media vs. greensand for iron/manganese removal)?
Mandatory Disinfection: It was stated during the development of the Total Coliform Rule (TCR) that the detection of coliform bacteria in the distribution system increased by seven-fold over the previous bacteria monitoring program. As a result, there are more TCR failures over the last 13 years when compared to the prior years. This failure rate caused many water systems to chlorinate on a continuous basis; however, others continue to fight the problem in states that don’t require mandatory disinfection. Will the arsenic release from 6-months of arsenic accumulation in the distribution pipeline (where release is caused by mandatory temporary chlorination resulting from a TCR failure) actually cause more harm? Should mandatory disinfection be considered in those states the presently do not require mandatory disinfection that also have areas of arsenic in the groundwater?
Perhaps arsenic is over-rated: However, people smarter than I indicate otherwise pointing the finger at diabetes and heart disease (in addition to the various cancers) resulting from arsenic in drinking water. Perhaps the whole regulatory process needs to analyze contaminant threshold levels and their impacts with regard to length of exposure. Personally, I would like to see more epidemiologic studies to see if there is a possible link. But I have a feeling this would be extremely complicated and many years down the road.
Comments, suggestions, arguments welcome.
First a little arsenic background:
• US recently adopted a lower standard for arsenic in drinking water from 50 ppb to 10 ppb.
• Removal processes using iron media seems to be the industry trend gaining momentum. Negative ions of arsenic are attracted to the positive ions of iron where arsenic is held by electrostatic force to the iron surface. Arsenic adsorption continues until the media achieves a saturation point (balanced positive and negative charges). This is a passive arsenic removal system where change in the arsenic oxidation state is not required. Recharge of the media occurs with a change in the pH that effects the charge of the media thus releasing the arsenic.
• Many water distribution systems have iron piping having similar charged iron elements.
• These pipelines are actually removing and storing arsenic from the source water.
• Treatment changes effecting the pH such as the introduction of chlorine for the first time, corrosion control adjustment, or even a biofilm will change the ionic balance of the arsenic-iron adsorption resulting in a decreased adsorption capacity of the iron pipe.
• A decreased adsorption means the arsenic re-enters the water at a much higher concentrations, perhaps exceeding the arsenic LD50 toxic levels.
• Even water systems with low levels of arsenic (concentrations below laboratory detection levels) in the water supply that have accumulated months or years of arsenic adsorption could result in short-term very toxic levels of arsenic laden water following temporary chlorination or a biofilm release (during flushing for example).
Every regulatory agency looks at the source for contaminants in the drinking water. Only DBP’s, lead and copper are regulated in US with regard to distribution system effects.
The EPA official indicated that they have collected hydrant flush samples from at least 20 distribution systems in Ohio. Nineteen of the 20 samples resulted in arsenic levels over the proposed standard (and apparently, many of these systems had little to no arsenic detected in the source water). Samples were collected during the flush cycle well after the water cleared up and the results continued to show arsenic levels over the proposed standard. The EPA official confirmed that change in pH or water chemistry (treatment change) will affect the release of arsenic from the distribution system (their samples were only from flushing and not treatment change). So higher arsenic levels would be found in these situations. This information is very preliminary, has not been published, and quantitative values were not given (other than the values were over the proposed standard). Based on my discussions with the EPA official, the immediate operational solution is this: Maintain a treatment change very gradually to reduce the quantity of arsenic release (by the way, there are also issues related to radium and copper storage and releases).
Obviously, more distribution sampling is required to better define the situation; however, here are a few discussion points (note: I’m not a pipeline salesman, nor do I have a preference for type of pipeline in drinking water systems):
Iron pipe vs. Plastic pipe: Should systems having ductile or cast iron piping be required to remove more arsenic from the source, monitor the distribution system for arsenic, conduct more frequent flushing or unidirectional flushing (UDF)…
Iron and Manganese in Source Water: Being a secondary standard, there are many areas in the country that do not treat for iron and manganese. In these areas it is essential to flush the pipelines (iron or plastic pipe systems) because of accumulated iron and manganese deposits in the distribution. Samples from a trailer park distribution system in US revealed arsenic levels in the PPM range from these flush samples (where the source was in compliance with the arsenic standard). Perhaps iron and manganese is no longer a secondary standard, but rather a primary standard due the ability of these materials to remove arsenic and cause uncontrolled high releases of arsenic, a primary drinking water standard? Should iron and manganese treatment be mandatory?
Arsenic Treatment: System having iron piping, do they treat just below the MCL, or go further to reduce effects of re-adsorption on the distribution iron piping?
Biofilm Prevention: Biofilms on distribution pipelines (plastic and iron) have an ionic charge that could affect the arsenic. Should operators focus on biofilm reduction/prevention programs to control biofilm development? For example: implement a variable chlorine residual program (i.e. week 1 @ 0.2 mg/l, week 2 @ 1.2 mg/l, week 3 @ 0.5 mg/l, week 4 @ 1.0 mg/l) w/ flushing during high chlorine residual periods to prevent the biofilm growth due to adaptation (bacteria and other biofilm elements may adapt to the chlorine residual at constant and low levels).
Treatment Process: Corrosion control treatment at the source can change the ionic status of the iron pipe distribution system. The pink water episodes resulting from iron and manganese treatment systems may actually be causing more harm than known. Should the importance of providing a consistent and stable treated water supply be emphasized? Would this effect the type of treatment system chosen (i.e. use of proprietary media vs. greensand for iron/manganese removal)?
Mandatory Disinfection: It was stated during the development of the Total Coliform Rule (TCR) that the detection of coliform bacteria in the distribution system increased by seven-fold over the previous bacteria monitoring program. As a result, there are more TCR failures over the last 13 years when compared to the prior years. This failure rate caused many water systems to chlorinate on a continuous basis; however, others continue to fight the problem in states that don’t require mandatory disinfection. Will the arsenic release from 6-months of arsenic accumulation in the distribution pipeline (where release is caused by mandatory temporary chlorination resulting from a TCR failure) actually cause more harm? Should mandatory disinfection be considered in those states the presently do not require mandatory disinfection that also have areas of arsenic in the groundwater?
Perhaps arsenic is over-rated: However, people smarter than I indicate otherwise pointing the finger at diabetes and heart disease (in addition to the various cancers) resulting from arsenic in drinking water. Perhaps the whole regulatory process needs to analyze contaminant threshold levels and their impacts with regard to length of exposure. Personally, I would like to see more epidemiologic studies to see if there is a possible link. But I have a feeling this would be extremely complicated and many years down the road.
Comments, suggestions, arguments welcome.