Risk-Ranking Coal Ash Impoundments

February 12, 2016.  The 2014 Coal Ash Management Act, Session Law 2014-122 , required the Department of Environmental Quality (then the Department of Environment and Natural Resources) to propose classifications for  coal ash impoundments in the state as High, Intermediate or Low Risk. The risk classification determines both how quickly the impoundment must be closed and whether closure requires removal of the coal ash for beneficial reuse or disposal in a lined landfill. Only Low Risk impoundments can be closed by de-watering and capping the coal ash in place.  The General Assembly designated Dan River Steam Station, Riverbend, Asheville and the Sutton Plant as high risk by law;  DEQ and the Coal Ash Management Commission have responsibility for classifying the remaining 10 coal ash sites.

Statutory Criteria for Risk Classification. The law, in G.S. 130A-309.211,  listed factors to be considered in classifying the impoundments:

(1)        Any hazards to public health, safety, or welfare resulting from the impoundment.
(2)        The structural condition and hazard potential of the impoundment.
(3)        The proximity of surface waters to the impoundment and whether any surface waters are contaminated or threatened by contamination as a result of the impoundment.
(4)        Information concerning the horizontal and vertical extent of soil and groundwater contamination for all contaminants confirmed to be present in groundwater in exceedance of groundwater quality standards and all significant factors affecting contaminant transport.
(5)        The location and nature of all receptors and significant exposure pathways.
(6)        The geological and hydrogeological features influencing the movement and chemical and physical character of the contaminants.
(7)        The amount and characteristics of coal combustion residuals in the impoundment.
(8)        Whether the impoundment is located within an area subject to a 100‑year flood.
(9)        Any other factor the Department deems relevant to establishment of risk.

DEQ’s Proposed Risk Classifications. On January 29, 2016,  DEQ  released a report providing information to support proposed classifications for most coal ash impoundments.  (Several impoundments have temporary classifications pending complete information on impacts to water supply wells.)  DEQ has based its risk classifications on three “key factors” — one each for groundwater, surface water and dam safety risks:

Groundwater Risk Factor: The number of people served by water supply wells within 1500 feet and down-gradient of the impoundment’s compliance boundary that are potentially or known to be exposed to groundwater contamination related to the impoundment. DEQ used a scale based on the number of people affected by well contamination:  0 people = Low Risk; 11-20 people = Intermediate Risk and  >  30 people = High Risk.  Transitional  classifications of Low/Intermediate Risk and Intermediate/High Risk cover the gaps between the three basic categories.

Surface Water Risk Factor:   The impoundment’s location relative to the 100-year floodplain.   Impoundments located outside of the 100-year floodplain or contained by a stream valley embankment with an engineered discharge (such as a spillway) have been classified as Low Risk. Impoundments sited along the run of a river, in the floodplain, and within the 100-year flood level are classified as  High Risk.

Dam Safety:  Structural integrity and maintenance as reflected in dam safety inspections.    Impoundments that received a Notice of Deficiency  identifying non-structural deficiencies at the last dam safety inspection have been classified as Intermediate Risk.  Impoundments that received a Notice of Deficiency identifying structural deficiencies  at the last inspection have been classified as High Risk. One important note —  a number of impoundments have a High Risk dam safety rating because of structural deficiencies identified in the last inspection, but DEQ has discounted that factor in the overall facility risk rating by assuming  the impoundments will be Low Risk once the structural deficiencies has been corrected.

Other Risk Factors.  The DEQ  report describes a number of  “other considerations”  that were not given the same weight in risk classification as the key factors. “Other considerations”  for groundwater and surface water risk include significant site conditions such as:  toxicity of contaminants exceeding groundwater standards; the extent of groundwater contamination; proximity of coal ash to the water table; potential impact of groundwater contamination on surface waters; location of the impoundment in a stream or drainage way; the water quality classification and use of  nearby surface waters; and proximity to a drinking water intake.

How DEQ Arrived at Each Proposed Classification.  The exact method DEQ used to arrived at the overall classification for each site is something of a mystery.   We know the three “key factors” largely drove the classification because the report tells us that. But there is no explanation of how (or whether) DEQ also used the information on “other considerations”  or even how the three key factors were weighted.

Example: Buck Steam Station.  Looking in greater depth at the classification of  one coal ash facility  provides a little more insight into DEQ’s classification decisions. DEQ has  temporarily  given Buck Steam Station a Low-Intermediate classification until the department receives additional information on impacts to water supply wells. If no well users near Buck Steam Station are  affected  by contamination associated with the impoundments (or well users have an alternate water source),  DEQ intends to classify the Buck  impoundments as Low Risk. Well impacts will be the deciding factor in the proposed classification. Buck rated as Low Risk under the key factor for surface water impacts because the impoundments are outside the 100-year flood plain. The three impoundments at Buck rated as  High Risk for dam safety, but DEQ assumed the  impoundments would  be Low Risk once the deficiencies have been corrected.

Looking  beyond the three key factors,  however, Buck rated as  high risk on a number of other groundwater and surface water parameters including:   contaminants exceeding state groundwater standards at or beyond the compliance boundary;  proximity of coal ash to the water table;  and discharge of contaminated groundwater to surface waters. It rated Intermediate risk based on the use of adjacent surface waters (the Yadkin River has been classified for water supply) and proximity to a drinking water intake. On some other parameters related to surface water, Buck Steam Station rated as low or intermediate risk.  See pages 92-99  for the entire list of risk ratings for the Buck impoundments.

The Buck classification seems to be fairly representative. Overall,  the  “other considerations”  discussed at great length in the report are  irrelevant to DEQ’s proposed classifications.  The one exception has to do with groundwater; after focusing the “key factor” for groundwater on impacts to down-gradient water supply wells, DEQ has deferred classification of several sites to get additional information on up-gradient and side-gradient wells.   It is also unclear how DEQ weighted different risk levels for the three key factors to arrive at an overall classification.   The Cape Fear Steam Station  was ranked Low Risk for groundwater (no impacted wells); High Risk for surface water (all of the impoundments are in the 100-year floodplain); and High Risk for  half of those impoundments because of dam safety deficiencies. But the facility as a whole received a classification of Intermediate Risk.

There may be more method to the  proposed classifications than it appears. It is possible that DEQ weighted the key factors and “other considerations”  or viewed some conditions as mitigating others.  Since the report does not provide any explanation, it is difficult to know.  The Coal Ash Management Act itself did not provide any guidance on how to translate nine statutory criteria into three risk classifications. Normally, that gap would be filled through rulemaking.   In the absence of  rules (or even a clear explanation in the DEQ report), it is hard to identify  the principles underlying the classification decisions.  The approach to groundwater risk classification may be particularly controversial since an impoundment that contains a very large volume of coal ash; extends below the water table; has documented groundwater standard violations at or beyond the compliance boundary; and discharges contaminated groundwater to surface water could be classified as Low Risk as long as no existing water supply wells users are affected.

Next Steps.  DEQ has scheduled public meetings on the proposed classifications as required under the law.  Those meetings will take place in March.  The final decisions on classification will be made by the Coal Ash Management Commission.  (Assuming the Commission can be reconstituted in time; see an earlier post on the Commission’s inability to act because  appointments to the Commission violated the N.C. Constitution.)