The Environmental Protection Agency’s (EPA) coal combustion residuals rule (CCR Rule) requires coal ash pond owners to evaluate background groundwater quality conditions at regulated landfills and impoundments with respect to certain naturally-occurring parameters. Most owners have already initiated the eight groundwater monitoring events required to establish background and downgradient groundwater quality as part of their Detection Monitoring Program (DMP). The deadline to complete these is October 2017. Additionally, impending changes to the CCR Rule will now make inactive surface impoundments subject to those same groundwater monitoring obligations as are currently required for existing impoundments. Although an extension will be provided to owners of inactive impoundments to comply with the new requirement, the following information is still important to consider.
Evaluating Your Data
As an owner, it is critical to evaluate your data now and make adjustments, if necessary, to:
Waiting to initiate this assessment until after all eight monitoring events are complete could hinder your flexibility and/or ability to validate or refute a statistical exceedance of background. Failure to identify errors or potential issues early on could prematurely force you to close an unlined impoundment or implement corrective action (e.g., groundwater remediation), which might otherwise be avoided.
According to the CCR Rule, downgradient wells must be compared to background levels for Appendix III constituents. However, the first eight sampling events include both Appendix III (detection monitoring) and Appendix IV (assessment monitoring) constituents. It is important to evaluate and validate data as it becomes available to verify whether an exceedance of a parameter has occurred, especially since this data will be used to determine whether further action is necessary.
Additionally, it is beneficial to assess whether your background values or MCLs will be used for development of groundwater protection standards, and then directly compare downgradient concentrations to the higher of those two levels.
Spotting Red Flags
There are no hard and fast rules when looking at limited data, but let common sense guide you. Some of the most common early warning signs that your data requires further attention include:
Isolated data spikes (particularly elevated anomalies) can generally be classified as:
These scenarios have similar potential causes. Unfiltered sample results are influenced by the amount of sediment in the sample. Highly turbid samples or unstable field parameters could indicate that purge rates are too high or there are problems with well construction. This could result in elevated metal concentrations in samples that would consequently not be representative of the actual groundwater quality. Although sample filtration would reduce turbidity, the CCR Rule requires unfiltered (total) sample analysis for metals. This reinforces the need for correct well construction, properly designed filter pack/screen, and the use of appropriate purging techniques.
If more than one background monitoring well is present, inconsistent data among these wells could also be a red flag, and could indicate the presence of an upgradient source. Additionally, while sample mislabeling may seem like an obvious source of error, it happens more often than you might think. Also, while it is uncommon for laboratory errors to result in data spikes of inorganic constituents such as those included in Appendix III or Appendix IV, all data should undergo an independent (non-laboratory) validation process.
Consistently High or Upward Trending Concentrations in Isolated Wells
After two or three monitoring events, consistently elevated concentrations in isolated wells (either upgradient or downgradient) more likely reflect actual groundwater conditions rather than sampling inconsistencies or laboratory errors.
Recognizing upward trending data can also assist in identifying a problem. It should be established whether elevated concentrations or increasing trends are apparent in multiple downgradient wells or a single well. Elevated or upward trending data in a single well could indicate a poorly-constructed well or the presence of another source of contamination.
Elevated Concentrations in Downgradient Wells
Consistently elevated concentrations in downgradient wells (as a group) compared to the background well(s) can be an indicator of a release from a CCR unit. If concentrations in your downgradient wells as a group appear to appreciably exceed your background well concentrations, this may be indicative of a release. However, if only one well appreciably exceeds, it could indicate an alternate source of contamination, or may indicate other errors such as well construction or sampling errors.
Inconsistent or Unexpected Groundwater Levels
In addition to evaluating groundwater quality, it is important to evaluate whether groundwater levels are consistent with what were anticipated in the Conceptual Site Model. Higher than expected groundwater levels in one or more wells may indicate there is a higher water-bearing zone than thought, resulting in decreased separation between the base of the impoundment and the uppermost aquifer. Additionally, an observation of potential hydraulic connectivity like this could be indicative of a more serious issue, like a leaking impoundment.
If you identify these warning signs in your data, do not wait until all eight initial events are conducted to evaluate potential causes. Once these eight events are complete and a statistically significant exceedance is identified, the timeframe for action is limited. In this case, you will only have 90 days to either (1) confirm and demonstrate the cause of the exceedance is due to an error in sampling, analysis, statistical evaluation, or natural variation; (2) identify an alternate source; or (3) initiate an assessment monitoring program. Although conducting a statistical evaluation on an abbreviated data set (less than eight events) could provide insight as to the ultimate outcome of your data, you should not rely solely on these results, as they may be unreliable due to the margin of error inherent in a small data set. However, if historical data exist, it could be very helpful in conducting a preliminary evaluation.
Identifying issues early on in the process, and making necessary adjustments to your monitoring program, will make it easier to verify and document an exceedance within the 90-day period provided. Engaging scientists and statisticians with the expertise to identify these key warning signs will help keep you ahead of the game and potentially avoid costly corrective actions (or premature unit closure) down the line.
Please stay tuned for additional blogs addressing this topic.