Utilities around the country have developed preliminary closure plans for surface impoundments storing coal ash, gypsum, and other coal combustion residuals (CCR). Some ash ponds are already in the process of closing. To close, the utility must either remove the CCR and redispose of it elsewhere, or prepare the site and close and cap it in place.

In litigation and through the media, citizen groups have argued in favor of closure by removal, but either option is available under EPA’s regulations. Closure in place is allowed only if the utility can demonstrate satisfaction of environmental performance standards, and closure by removal allows for reduced long term regulatory obligations. In that sense, the regulations provide a bit of an incentive to close by removal.

On the other hand, the regulations also recognize a benefit in closing as soon as reasonably possible. The longer the closure process takes, the more time ash is left unsecured and at risk of exposure to the elements.

So how long should the closure process take? One data point is how long it would take to excavate the CCR and transport it for redisposal elsewhere. For larger CCR units, the task is daunting.

To illustrate, consider an ash pond storing 10 million cubic yards of CCR. That’s a large pond, but some hold more than twice as much. Let’s assume there are landfills within 10 miles that can accept that much material, although that may well not the case. Let’s also assume the utility can mobilize an unlimited supply of triaxle dump trucks. The capacity of such a truck can reach up to 24 yards, depending on the configuration, but weight restrictions may limit the volume. To round out the scenario, let’s assume each truck hauls off 20 cubic yards per trip.

For an ash pond of 10 million cubic yards, that’s 500,000 truck trips. Five hundred thousand truck trips.  If you assume one truck every 10 minutes, 24 hours per day, 7 days per week, 365 days, that’s 9.5 years of truck traffic. A more realistic five day schedule would consume more than 13 years.

In this scenario, trucks loaded with ash will travel 5 million miles over local roads and highways. While some power plants are in isolated locations, others are located in or near neighborhoods and towns. Is that kind of traffic by homes and local schools really the best solution for the people who live near these facilities? The project would require 81 million ton-miles on local roads and highways over that 13 year period. That has significant consequences for state and local highway departments.

The primary argument in favor of closure by removal has to do with the potential for ash to be in contact with groundwater, especially if the pond is located near a stream or river. If that happens, the concern is the potential for metals or other constituents that occur naturally in coal to migrate and be detected in monitoring wells. We’ll know more about that when groundwater monitoring results become available next year.

On the other hand, even if that occurs, there is more than one way to address it. Depending on local factors, it may be possible to consolidate ash where the ground is higher or the water table is lower, or to build a subsurface barrier between the ash and groundwater flow. It is also possible that the dewatering itself will reduce the potential for interaction with groundwater, as EPA has acknowledged.[1] If there is a source of drinking water in the vicinity, it can and should be tested as well.

Subsurface hydrology can be complex and difficult to sort out. However, with closure by removal, the air emissions from diesel traffic are clearly and immediately available for local exposure. The diesel traffic associated with our excavation scenario would amount to approximately 500 pounds of volatile organic compounds, 1,900 pounds of carbon monoxide, 8,200 pounds of nitrous oxides, 195 pounds of PM2.5, and 211 pounds of PM10, all available for respiration by anyone in the area.[2] That’s on top of 1.6 million tons of carbon dioxide.[3]

To emphasize, these are conservative estimates in that they assume no work stoppages, no weather delays, no holidays, and consistent loading of one truck every ten minutes. It assumes a normal work week of five days, but with a 24-hour operation of three shifts per day, which may not be possible. The mileage and emission figures only reflect the trip from the ash pond to the landfill. That doesn’t count the return trip back to the ash pond, diesel consumed while the trucks idle, the trips to and from the truck’s point of origin, or the use of equipment necessary to excavate, stage and load the ash, all of which adds additional environmental impacts. This also assumes zero accidents and zero spillage, which may not be realistic based on a half-million truck trips. The concerns grow commensurately if an ash pond has more than 10 million cubic yards or available landfill capacity is farther than 10 miles away.

What does all this mean for ash pond closures? For some ponds, especially the smaller ones, excavation may well make sense, depending on site-specific considerations. However, for larger units, it’s harder to see closure by removal as the best option. Where common sense measures are reasonably available to manage ash that is capped in place, that may well prove to be the better alternative—even before considering cost, with environmental issues and local impacts as the primary consideration.

[1] “As noted, EPA’s risk assessment shows that the highest risks are associated with CR surface impoundments due to the hydraulic head imposed by the impounded water. Dewatered CCR surface impoundments will no longer be subjected to the hydraulic head so the risk of releases, including the risk that the unit will leach into the groundwater, would be no greater than those from CCR landfills.” 80 Fed. Reg. 21,301, 21,342 (Apr. 17, 2015).

[2] Based on pollutant estimates per mile for a Class VII heavy duty truck as found in Table 2 of EPA, Average In-Use Emissions from Heavy-Duty Trucks, No. EPA420-F-08-027 (Oct. 2008).

[3] Assuming 1.456 grams of carbon dioxide per mile from diesel consumption.