True or false. Arsenic is colorless, tasteless and odorless in water. True. Same exercise: Arsenic only exists in one form, or species. False. So, you know the basics of arsenic and most likely more. But, are your employees and customers also well-versed? We reached out to some of the water treatment industry”s leading presenters and experts on this topic and posed some common questions that should help determine an arsenic IQ.
Arsenic is among the top candidates for news coverage and newspaper headline appearances. For example, in June, WaterTech e-News Daily™ published several arsenic-related news stories, such as, “One out of eight wells tested in N.J. in violation of safe limits for many contaminants.” Testing results from the Private Well Testing Act by the Department of Environmental Protection (DEP) in New Jersey showed that one out of eight wells were in violation of safe limits for arsenic and other potentially harmful contaminants.
Who is responsible for spreading this news, conveying a potential health risk and educating customers?
Since arsenic, like many other contaminants, is in the news and being discussed among the public, customer awareness is heightened. However, misinformation can be as dangerous as being uninformed. “Developing an awareness and sensibility to arsenic has to be done from the ground-up,” notes Jim Pardini, Isolux business manager for MEL Chemicals Inc.
What is arsenic and how does it enter water supplies?
As mentioned, arsenic is an odorless, colorless and tasteless semi-metal element that can enter drinking water naturally through the erosion of natural deposits in the Earth, making groundwater susceptible. There are also cases where arsenic can enter water through other means, such as agricultural runoff.
What forms can the contaminant arsenic occur in water?
Two forms: Trivalent arsenic (As(III), or arsenite) or pentavalent arsenic (As(V), or arsenate).
What is the maximum contaminant level (MCL) for arsenic?
The Environmental Protection Agency”s maximum contaminant level (MCL) for arsenic is 10 parts per billion (ppb). In 1975, the U.S. set the maximum level for arsenic in drinking water at 50 ppb. In 2001, after years of research and concern regarding the long-term effects of consuming arsenic, EPA lowered the MCL to 10 ppb.
What is the difference between As(III) and As(V)?
“As(III) is found in areas with wells that do not have enough oxygen,” educates Kevin Osborn, Layne Christensen”s sales manager/engineer for its residential and commercial division. And, continues Osborn, given As(III)”s charge, it is not as easy to remove from water as As(V).
As(III) is an uncharged species in plus-3 form. Therefore, As(III), unlike As(V) which maintains a charge, cannot be effectively removed using an adsorption media.
As a result of this challenge, is it important to know which species of arsenic is present, and is there a test to make this determination?
Field and laboratory testing are available to identify total arsenic in water. Additional speciation testing is available at a more expensive price. But, before recommending treatment and implementing a system, how important is knowing the species of the arsenic?
“In designing a treatment system, it is almost as important to know what type (species) of arsenic are present as well as the total amount of arsenic present,” explains Shaun Lettau, media replacement coordinator for AdEdge Water Technologies LLC. “Arsenic(III) is much more difficult to treat and therefore, requires oxidation or other considerations that will significantly affect operating and maintenance costs.”
In sites that are currently in operation, continues Lettau, these tests are valuable when issues arise and systems are not performing up to expectations.
Can customers assume that once As(III) is not found in their well water after testing that any arsenic moving forward will have a charge, or be in the As(V) state?
No. Well chemistry changes throughout seasons and for many other variables. As(III) could not be present at all for years, adds Osborn, and for whatever reason enough oxygen does not get into the well and As(V) becomes As(III).
Furthermore, explain the experts, if a system is already in place that once treated As(V) and new testing shows arsenic is present, it is a good reason to recommend a speciation test and check equipment.
If As(III) is present, should I first convert it to As(V) then treat? Yes.
Most technologies available for arsenic treatment are highly effective and more practical for As(V), so treating As(V) is more cost effective for the customer. It is always economical for the homeowner to oxidize than not. This oxidation conversion is commonly achieved using chlorine.
Explains Lettau, arsenic can be treated using treatment technologies such as:
- Oxidation-filtration. Using an oxidizer to change any As(III) to As(V) and existing ferrous iron into ferric iron, which allows the arsenic and iron to be co-precipitated and filtered out.
- Coagulation-filtration. Adding a chemical or coagulant, such as ferric chloride or potassium permanganate to operate the same way as oxidation-filtration in areas without a large amount of natural iron.
- Reverse osmosis (RO). This technology is very effective in removing a large number of contaminants. However, when considering as an arsenic treatment one needs to realize it will only remove As(V) effectively. Also, if oxidizers, such as bleach are used as a pretreatment, the water will need to be de-chlorinated prior to passing through the RO membrane to prevent damage to the membrane.
- Anion exchange. Many of the comments stated above for RO apply to using anion exchange resins as well. They are only effective at removing As(V) and residual chlorine added pretreatment to oxidize the arsenic will need to be removed prior to the resin to prevent damaging the resin.
Also, discuss proper regeneration techniques with suppliers and follow the manufacturer”s instructions for use and disposal. Some manufacturers, says Osborn, offer to take used materials back for reuse purposes.
The importance of protecting the solution
Having a complete laboratory water analysis, including parameters that can negatively impact arsenic removal media, are extremely important. According to Laura Maass, MPH, who is the high purity special applications project coordinator for Atlas Watersystems Inc., pH significantly impacts arsenic media performance in addition to competing ions that may include iron, manganese, vanadium, sulfate, phosphate, hardness, silica, total dissolved solids, suspended solids and hydrogen sulfide.
“Each arsenic media manufacturer has guidelines, which should be followed in order to obtain the greatest arsenic removal capacity,” advises Maass. “Pretreatment for the media”s specific competing ions is recommended in order to extend the arsenic removal media capacity and to reduce media replacement costs for the consumer.”
The key to ensuring an arsenic removal system continues to provide effective arsenic removal after installation is to monitor the entire system”s performance. Fluctuating arsenic levels, effectiveness of pretreatment, amount of water processed through the system each day and any other changes to the well water quality will all impact the performance of an arsenic removal system, adds Maass.
“Since arsenic is odorless and tasteless, periodic servicing and testing of all pretreatment and periodic testing of the arsenic removal system before and after the arsenic removal tank(s) is the only way to determine when the arsenic media requires replacement,” says Maass.
Knowing your territory
Is there a resource to use as a guideline to determine if your area and customers are prone to arsenic contamination in well water?
Yes. U.S. Geological Survey provides “A Retrospective Analysis on the Occurrence of Arsenic in Ground-Water Resources of the United States and Limitations in Drinking-Water-Supply Characterizations,” which contains a map of known risk areas for arsenic. This map can be found at http://pubs.usgs.gov/wri/wri994279/pdf/wri994279.pdf.
In known risk areas, how often should testing be performed?
In May, the National Ground Water Association (NGWA) issued a press release urging private well owners to “test their water regularly” for bacteria, nitrate and anything of local concern, citing the possibility of arsenic and uranium in some central and northeastern Massachusetts bedrock wells.
The press release also detailed an alarming trend. According to the NGWA”s press release, it was reported that from May 7 to 11 only 10 of about 1,500 owners of private wells in Northborough, Mass. tested their water for arsenic and uranium in response to a letter sent to all residents a year ago by Jamie Terry, board of health agent.
Is there an opportunity for dealers to educate customers on the importance of testing for arsenic in areas that are specifically being asked to test their wells for this contaminant? The answer is clearly defined above.
NGWA recommends testing a private well “regularly.” But, how frequent is suffice and what do the experts recommend for known risk areas?
As mentioned, well water chemistry changes from year to year and season to season. Therefore, ongoing testing is needed and although frequency can vary, depending on many circumstances, the experts agree that once a year is a good rule of thumb.
“At least once a year a private well owner should test their water,” says Osborn, adding that dealers should test water six to nine months after a system is implemented to ensure effectiveness and functionality. “Even in non-high risk areas for arsenic, if you are on a private well, you should test for arsenic.”
And, concurs Maass, well owners who have not previously had an arsenic issue should be on alert due to potential well chemistry changes. “Throughout my 13 years of working in fields related to arsenic removal, I have often seen some wells go from non-detectable arsenic to levels above the primary drinking water level (MCL) of 0.010 mg/L in just one year,” she says.
What will determine a need for increased testing frequency?
“Many areas should be tested more often (than once a year), especially those with high levels of arsenic (over 50 µg/L) or systems that are nearing their projected media life,” adds Lettau.
Also, many areas or individual community water systems require testing from a certified laboratory on a regular basis, depending on the location and application of the system, continues Lettau. This testing can be as often as each month, but more often the tests are required quarterly or bi-annually. Additionally, Lettau says, if it is an application that does not require a test from a certified lab, such as a residential customer, there are arsenic field test kits that produce reasonably accurate results within 15-20 minutes.
What are some common pitfalls that dealers and end customers make when dealing with arsenic contamination?
The answer: Not testing and considering other variables and contaminants in water that can have an affect on water chemistry and system performance, answers Pardini. During testing, for example, get a phosphate or phosphorous reading. Why?
“The big thing that people do not test for because at this point in time they do not show any type of harm to the individual, but can impact treatment, is phosphates,” notes Osborn. Phosphate and arsenic are roughly in the same family on the periodic element table. And, adds Osborn, “The majority of technologies cannot decipher between the two contaminants so they want to remove both.”
Also, consider silica. Silica can become a gel-like substance on membranes and affect equipment performance, adding to costs and exposing customers to risk. “Phosphates and silica are the two most significant competing ions in relation to arsenic adsorption,” says Lettau. “They are in much higher concentrations than arsenic in the water giving them the competing effects. They can take up the limited number of adsorption sites leaving fewer for arsenic to adhere to.”
Also, remember, oxygen will affect water samples for arsenic testing. Since there is potential for oxygen to affect the water sample, consider field kits that can basically rule out the chance of oxidation, adds Osborn.
What are some other issues that can affect treatment?
In addition to finding out the total arsenic present in the water, and depending on the treatment options decided on, dealers should also consider pH, iron, manganese and vanadium as competitive ions or contaminants that can interfere or hinder system performance.
According to Lettau, interferents or inhibitors can actually change the chemical properties of the media, which can either plug or foul the media and reduce adsorption capacity dramatically. “Iron, manganese and sulfides are the three common parameters,” he says. “Other issues can be loss of flow across the media or poor performance if proper pretreatment is not employed. Water containing high levels of iron or manganese in excess of the MCLs should be pretreated prior to using adsorption media technology, for instance.”
Testing and identifying pretreatment needs are crucial steps that dealers must take prior to putting in a system to treat arsenic. “Take the extra step to do all the testing,” concludes Osborn. “It will make a world of difference down the line for the homeowner.”