Introduction

Power Generation, Transmission, and Use

Markets, Regulation, and Oversight

Impacts of Power Generation and Transmission

Looking Ahead

Appendices

CEIR Report Map

PPRP Home

Maryland Power Plants and the Environment (CEIR-18)

4.6.3 Disposition and Beneficial Use

Beneficial Use

When properly engineered and correctly applied, CCBs can be utilized in manufacturing, civil engineering, mine restoration, and agricultural applications (see Table 4-9). The beneficial use of CCBs as raw materials in applications that are environmentally sound, technically safe, and commercially competitive leads to a reduction in disposal, which may contribute to reduced GHG emissions. The most direct contribution to reducing GHG emissions occurs when fly ash is used as a supplementary material in concrete and concrete products. By substituting fly ash in place of cement, the carbon emissions associated with cement production (an energy-intensive process) are avoided. Each ton of fly ash utilized represents approximately one ton of CO2 avoided. A continued increase in the beneficial utilization of Maryland CCBs will likely lead to:

Table 4-9 CCBs Produced in Maryland and Common Uses

CCB Type Source in Md Common Uses Across United States Current Uses in Md
Class F Fly Ash Brandon Shores,
H.A. Wagner,
Morgantown,
Dickerson,
Chalk Point
Concrete, cement, grout, road base, structural fill, soil stabilization Concrete, cement, grout
Class C Fly Ash C.P. Crane Concrete, cement, grout, soil stabilization, coal mine reclamation, agriculture Disposed
Class F Bottom Ash Brandon Shores,
H.A. Wagner,
Morgantown,
Dickerson,
Chalk Point
Concrete, cement, grout, road base, structural fill, soil stabilization, traction control Concrete, cement, grout
Boiler Slag C.P. Crane Abrasive grit, roofing shingles Abrasive grit, roofing shingles
FBC Fly Ash/Bottom Ash Warrior Run Concrete, cement, grout, coal mine reclamation, agriculture Coal mine reclamation
FGD Material Brandon Shores,
Morgantown,
Dickerson,
Chalk Point
Wallboard, concrete, cement, agriculture Wallboard, cement

 

Click to OpenUse of CCBs in Highway EmbankmentsBeneficial use of CCBs in Maryland has historically included predominantly large-scale fill applications as in highway embankments and mine reclamation. However, over time the use of CCBs in encapsulated forms, such as cement, concrete, wallboard, and roofing tile has become more prevalent. Such changes are driven by industry practice, technology, costs of natural materials, regulations and guidelines, public perception, and demands for sustainability in the commercial marketplace. Of the approximately 1.5 million tons of CCBs produced by Maryland power plants in 2014, just over 200,000 tons were placed in disposal sites. More than 350,000 tons of CCBs were used in concrete and cement, and another 500,000 tons were used in wallboard manufacture. Coal mine reclamation is the third largest use of CCBs in Maryland, with about 360,000 tons of alkaline CCBs being used to reclaim surface coal mines in Western Maryland. Other, smaller scale uses included agricultural amendments, and the manufacture of roofing tiles, blasting grit, and grouts. Figure 4-40 shows the locations of Maryland’s 7 active coal-fired power plants (in addition to one plant that closed in 2012), and highlights some of the beneficial use sites and disposal sites across the state. Figure 4-41 highlights the quantity of CCBs generated and disposed by Maryland’s coal-fired power plants annually.

 

Figure 4-40 Locations of CCB Generation, Use, and Disposal in Maryland

Figure 4-40 - map of location of CCB Generation, use and disposal in Maryland

Figure 4-41 CCB Generation and Disposal (2014 Data)

Figure 4-41 - Bar chart of CCB Generation and Disposal

Fly ash, bottom ash, boiler slag, and FGD material have different primary beneficial uses because each type of CCB has distinct physical and chemical properties suited to specific applications (see Table 4-9). Fly ash is used in the largest quantities and the widest range of applications among the CCBs because of its pozzolanic properties. In Maryland, sale of fly ash to the cement, grout, and ready-mix concrete industries is the predominant use of Class F fly ash. The relatively uniform spherical shape and particle distribution of fly ash improves properties of flowable fill and the fluidity of these cementitious materials. The manufacture of cement, concrete, and grout is also the primary beneficial use for bottom ash in Maryland. Nationwide, this material is also used as road base/sub base, structural fill, and snow and ice control. Boiler slag is taken up in more specialized applications, such as abrasive grit and roofing tiles. 100% of the boiler slag produced in Maryland is sold to these industries. Since the first FGD scrubbers were installed in Maryland in 2010, the majority of FGD material generated in Maryland has been marketed to wallboard manufacturers as a replacement for natural gypsum. This use accounted for more than 90% of the total FGD material produced in Maryland in 2014. The small percentage of FGD material that was disposed is primarily comprised of “off-spec gypsum” that could not be sold because it did not meet the standards required by industry for wallboard manufacturing.

Disposal

The first permitted and lined CCB landfill in Maryland (the Millennium Landfill) began operation in 2011. This landfill is fully compliant with current state and federal CCB disposal regulations. However, prior to 2008, there were no regulations in Maryland governing the disposal of CCBs (see Section 4.6.2). CCBs were disposed in unlined landfills and were sometimes used as fill in applications that, under current state and federal regulations, constitute disposal. While high percentages of Maryland CCBs are currently going into beneficial uses and current disposal practices are more protective of ground water, these legacy ash disposal sites continue to have the potential to leach constituents into ground water.

One possible way to mitigate this impact is to “mine” the previously disposed CCBs for sale to the cement manufacturers and ready-mix concrete industries. The success of marketing freshly produced CCBs to cement manufacturers and ready-mix concrete industries has produced a demand for these materials within the industry. As older coal-fired power plants are retired, and in some cases, replaced by gas-fired generating units, cement manufacturers and ready-mix concrete industries are willing to consider, and pay for, previously disposed CCB materials. One successful example of this kind of project is described in Section 4.6.4.

 

Pozzolanic

Pozzolan is a type of material that, when added in the process of mixing cement, improves the strength of the resulting solid.

Formerly owned by GenOn.

Use of CCBs in Highway Embankments

In an effort to assuage the environmental uncertainty associated with using CCBs as structural fill, PPRP has been monitoring water quality at two Maryland sites in which CCBs were used to construct highway embankments, namely the Route 213/301 overpass in Centerville on the Eastern Shore, and the Interstate 695 overpass near Baltimore. As with any fly ash beneficial use site, the potential exists for ground water quality degradation, primarily caused by elevated levels of sulfate and trace elements. Several design features provide mitigative controls to minimize adverse environmental impact compared to other CCB fill sites. These include the shallow fill thickness, the steep embankment slopes, and the presence of asphalt or concrete pavement. 

The water quality data for these sites indicate that the potential for leachate to form in the fly ash is being realized, despite the fact that the majority of the fly ash used in the embankments is covered with impermeable pavement. The data further indicate that the leachate constituents, including calcium, sulfate, arsenic, sodium, and chloride, are being attenuated in the underlying native soils, possibly due to adsorption and precipitation reactions. Additionally, concentrations of arsenic, calcium, and sulfate are further attenuated in the underlying ground water at both sites. These findings suggest that overall, leachate from the fly ash has a negligible impact on ground water quality.

For future fly ash use for structural fill to be as environmentally effective as at these overpass study sites, proper design features tailored to the specific hydrogeologic conditions of the site must be incorporated. The benefits of fly ash utilization for embankment construction offset the minimal potential for environmental degradation.

Photo of a highway embankment in Maryland

Route 213 highway embankment site, Centerville