DENR Releases Groundwater Reconnaissance Well Water Sampling Summary

Monday, August 17, 2015 - 12:00am

The N.C. Department of Environment and Natural Resources today posted a summary of results from a reconnaissance sampling of groundwater quality in the vicinity of Duke Energy’s Allen Steam Station, Buck Steam Station and Marshall Steam Station coal-fired power plants.

The study provides a limited evaluation of the distribution of metals and other parameters that may be naturally occurring in the groundwater, and that may also be associated with coal burning activities. 
This study was managed by the DENR Division of Water Resources Mooresville Regional Office and involved the collection of samples from twenty-four (24) water supply wells near the above mentioned coal–fired steam stations. In accordance with the Coal Ash Management Act, the groundwater samples collected were analyzed for the same constituents and parameters as the private and public wells tested near coal ash facilities under the well water testing program, and in support of the comprehensive site assessments. Test well locations were chosen for this study based on the following criteria:

• Located in areas that are not hydraulically connected to groundwater beneath Duke Energy’s coal-fired power plant facilities
• Positioned across surface water and groundwater divides from the facilities
• Situated in the same geologic units as the coal ash impoundments and private wells already being tested near coal ash facilities
• Targeting “newer” water supply wells to minimize the influence of older, potentially poorly constructed wells or aging well maintenance issues that could affect the samples. The tested reconnaissance water supply wells were installed between from 1996 and 2013.

The water samples collected from the 24 wells were analyzed for heavy metals and the other parameters as the agency’s well water testing program. The results from the limited study were sent to the N.C. Department of Health and Human Services for health risk assessments. 
The following are the results of the limited study:
• 13 well owners received “Do Not Drink” from the DHHS for exceedences for either DHHS’ health screening levels or state Interim Allowable Maximum Contaminant Levels, or IMAC. Twelve of the wells had exceedences for chromium 6 and vanadium, as well as one exceedance for iron and manganese.
• 7 well owners received “Do Not Drink” recommendations for vanadium and resample recommendations for chromium 6. 
• 4 well owners received incomplete sample results with recommendations for resampling for chromium 6. 
• 0 wells had exceedences of federal drinking water standards.

The source of contamination in a well, whether determined to be naturally occurring or not, does not influence its potential impact on health. Wells that exhibit constituent concentrations higher than the applicable health screening level, determined by the DHHS, may represent an increased health risk. Well testing results were sent to DHHS to perform a health risk evaluation, which have been mailed to residents along with potential well treatment options to remove or reduce contaminants from well water if needed. Individual results will be made available when DENR has confirmed receipt of results to well owners via certified mail.

Groundwater samples collected from the water supply wells in these study areas that met these criteria are believed to be representative of similar water quality conditions near the coal-fired plants in the DWR Mooresville Region. 

While the groundwater reconnaissance study provides data for staff to develop a better understanding of background concentrations of metals and other parameters, limitations and additional factors must be taken into consideration: 

• Concentrations of naturally occurring metals and other water quality parameters in groundwater can, in some cases, vary significantly over fairly short distances and depths in the subsurface
• Local groundwater quality is affected by a number of different variables, including but not limited to, the particular soil and rock chemistry in which a well is installed and the natural pH and oxidation state of the groundwater
• Well construction is an important consideration with respect to evaluating groundwater results since the turbidity of groundwater produced, the age, condition, depth and type of well casing used, pump and filtration equipment, position of the pump within a well, and the interval of an aquifer, or aquifers, affected by water production are all factors that potentially complicate the assessment of ground water site conditions 
• Unknown susceptibility to other sources of impacts to groundwater such as septic systems and residential household and property applications of chemicals

While these factors limit the study results’ use as a statistical evaluation, the data is useful to illustrate the distribution of certain constituents throughout the area sampled. 

In carrying out the Coal Ash Management Act, DENR is also overseeing a comprehensive groundwater assessment of drinking water wells near all 14 of the state’s facilities with coal ash ponds. The comprehensive groundwater assessments will be the driving force behind the agency’s efforts to determine whether any contaminants in wells are naturally occurring or from the coal ash ponds. DENR will require Duke Energy to provide well owners with alternative drinking water supplies if the agency determines any contamination came from the coal ash ponds.