KSA Engineer - Alan Draper, P.E.
The following article contains 4 things you need to know as a city manager or water system operator regarding the presence and removal of arsenic in your municipal water system.
1. Why is there arsenic in our community water system, and where does it come from?
Arsenic has always been in drinking water and is naturally occurring. Arsenic is actually a common element in the earth’s crust. Weathering of rock formations, volcanoes, forest fires and manmade processes like smelting ore release arsenic into the atmosphere. Arsenic is transported primarily by water and, as a result, arsenic concentrates in groundwater. All aquifers contain some amount of arsenic. Some aquifers contain groundwater with larger concentrations of arsenic than currently deemed safe to drink. While arsenic levels in groundwater fluctuate day to day, overall arsenic levels have not significantly changed in most aquifers in the last 15 years. However, advanced medical research has lead rule makers to reassess the safe level of arsenic in drinking water. Arsenic in drinking water may only be removed by completing a treatment process.
2. At what level does arsenic become dangerous to our municipal water system, and at what levels do we need to begin to plan and then act on any arsenic removal processes?
In 2001, the Environmental Protection Agency adopted a new standard for maximum contaminant limit for arsenic that limits arsenic content to 10 parts per billion (ppb). This replaced EPA’s old standard of 50 ppb. The new rule went into effect in 2006 and is intended to address the long term, chronic effects of exposure to low concentrations of inorganic arsenic. Arsenic levels over 10 ppb are in violation of the EPA rule and will require treatment. Most water supplies in violation have received a letter from EPA or, in Texas, from the Texas Commission on Environmental Quality (TCEQ) outlining compliance deadlines. The previous year’s Consumer Confidence Report will also contain a measurement of arsenic levels and determination if an arsenic violation exists. If a water system has arsenic levels above 10 ppb, planning for and implementation of treatment should begin immediately.
3. What's involved in the removal of arsenic from our city water system? Are there multiple methods (i.e. aggressive, less aggressive, organic) that can be used to remove or reduce the levels of arsenic in our potable water? Can arsenic ever be completely 100% removed from our community water?
Several treatment methods effectively remove arsenic from groundwater. The most common systems involve either absorption of arsenic by a filter media, precipitation of arsenic followed by filtration, or membrane treatment such as reverse osmosis. Each system differs significantly and the best treatment method must be selected after considering the specific water quality and existing infrastructure of the system.
Each treatment method is very effective and will lower finished water arsenic levels to 3-4 ppb. Reverse osmosis will remove up to 95% of arsenic. Typically, arsenic treatment systems are designed with a primary treatment stream and an untreated side stream. The two streams are combined to achieve a finished water arsenic level of 7-8 ppb which is below the 10 ppb EPA limit. The minimum arsenic level technically feasible to achieve through treatment is approximately 3 ppb. EPA evaluated this limit while generating the current rule and found that excessive cost of achieving a 3 ppb level did not justify the added benefits.
4. My community has just been cited for elevated levels of arsenic, what's next?
The first step is to review the agreed or administrative order in detail with particular emphasis on the ordering provisions. This section will identify any assessed fines and also provide a compliance schedule. Both EPA and TCEQ are currently issuing orders for arsenic violations and each agency has different procedures. However, each agency typically allows approximately 120 days to develop an arsenic treatment study and compliance plan and each mandates a deadline for completing treatment equipment installation and obtaining compliance with the standard. Each agency also requires quarterly progress updates. This is the perfect time to bring in an engineering consultant. A consultant will be needed to complete the engineering report and will assist with correspondence with the regulatory agencies.