Using the WQRF Contaminant Occurrence Map to Research Groundwater and Arsenic
By Kim Redden
If you’ve been in the water treatment industry for any length of time, you likely have heard about the need for a comprehensive national water quality dataset for private wells. Since private wells are not federally regulated, there is no national on-going data collection for these drinking water sources. As we’ve witnessed in California and plenty of other areas across the United States, private well water quality can be a potential concern for public health and corrected with proper POU/POE treatment. The objective to collect private well data at a national scale is quite a large undertaking and would require a somewhat complex network and funding to process samples. There are, however, some resources already available to research public water systems (PWS) using groundwater and some states provide private well data on their websites (such as this one from Wisconsin: https://www.uwsp.edu/cnr-ap/watershed/Pages/WellWaterViewer.aspx).
WQRF Contaminant Occurrence Map
The Water Quality Research Foundation (WQRF) has funded a national data collection effort and mapping tool for water quality occurrence data of public water systems. The data collection, statistical analyses and mapping tool were conducted and developed by Corona Environmental Consulting. The mapping tool is an illustration of the occurrence data and a way to make the information accessible to the public (www.WQRF.org/map). The project successfully collected data for 57 contaminants over a 10-year period, from January 2009 to December 2018. This data collection effort resulted in over 59 million data points, one of the largest datasets on water quality available.
The data collection focused on regulated drinking water contaminants that have an enforceable level (MCL or action level) above the health-based goal level (MCLG). The data collection also included secondary contaminants with aesthetic issues, including iron, hardness, manganese, pH, chlorine and chloramine. The data collection methodology included a call for information to all the states, as well as used US EPA’s Fourth Unregulated Contaminant Monitoring Rule (UCMR4) occurrence data. US EPA’s State Drinking Water Information System (SDWIS) was also used to collect data on system size, system type, source water and addresses to geolocate the data for the online mapping tool.
The scope of the data collection is public water systems; however, the mapping tool does allow users to customize the occurrence data shown by use of several different data filters, including source-water type. As a result, the mapping tool can be used to review groundwater data and how that may compare to surface water or groundwater under the direct influence of surface water for a specific contaminant. The map’s other data filters allow for the user to see occurrence based on various statistical summaries, year and PWS size and type.
Observations about arsenic
Data for arsenic was collected from 46 states, resulting in 596,013 data records from 64,694 public water systems. The researcher performed several different statistical analyses to compare what types of circumstances affect the occurrence of arsenic. Statistical analyses included all data collected and were not based on sample location, i.e. untreated or treated water. As a result, these analyses did not reflect a system’s compliance with drinking water standards or the water quality at a consumer’s tap. For the national 50th percentile or median, which could be considered an appropriate statistic to review what is typical, the arsenic concentration was non-detect. Further, if looking at the national 95th percentile for a representation of what is more a worst-case scenario, the arsenic concentration was 17 µg/L. As suspected, the data showed groundwater had the highest 95th percentile arsenic levels compared to other source waters (see Figure 1). A statistical analysis also compared arsenic occurrence and system size, and the analysis found that arsenic concentrations were highest for the very small systems compared to larger systems.
Using the Contaminant Occurrence Map
Of the 46 states that provided data, not all had data available for all the requested contaminants due to a variety of reasons. Therefore, white space on the map indicates no data available for that area and non-detect data points indicate that data was available with a non-detect result. As the data collection effort included regulated contaminants where the concentrations are compliant with the Safe Drinking Water Act (SDWA) but above non-enforceable health-based goals, it’s important to understand that occurrence data does not necessarily indicate a SDWA violation. The map displays statistical summaries for all the data collected to show occurrence. It is not designed to be used to track SDWA violations. SDWA compliance is calculated on a specific schedule and based on yearly running averages. Additionally, it’s important to note the address for each data point from SDWIS may be an office building and not the treatment plant itself, so state level or regional level is the most appropriate use of the map (as opposed to a zip-code level).
This new mapping tool may not fully close the data gap for wells, but it provides access to an immense amount of data for groundwater and customized searches for researching contaminants, systems and source waters. Additional data in the coming years will make it an even more effective tool for reviewing contaminant occurrences across the United States.
About the author
Kimberly Redden, WQRF Foundation Relations & Research Manager, has a Bachelor’s Degree in chemistry from North Central College and Master’s Degree in public health from Elmhurst College. She has worked for WQA since 2013 in Regulatory and Technical Affairs as well as the Professional Certification and Training Departments.
About the organization
The Water Quality Research Foundation, formerly the Water Quality Research Council (WQRC), was formed in 1952 to serve on behalf of the Water Quality Association (WQA) as a universally recognized, independent research organization. The mission of WQRF is advancing knowledge and the science of high quality, sustainable water. WQRF’s vision is water quality improvement through relevant research. https://www.wqrf.org/