Located to the north of the Central Slag Disposal Area, SCU 28 comprises present and former slag quarrying and aggregate processing areas (Figure 5-1). Clean slag has long been known as a suitable aggregate for use as a construction fill. Heckett Multiserv currently operates the aggregate production operation in this area. In 1997 approximately 100,000 tonnes of aggregate were processed and sold.

Despite the fact that slag has been deposited in this area for over 70 years, few environmental issues have been identified in the aggregate quarrying areas. Reportedly, no drums or liquid wastes of any kind have been discovered in the past 30 years of quarrying (pers. comm., D. Hemmings, Heckett Multiserv). Notwithstanding this, industrial wastes such as caster slag and blast furnace flue dust have been deposited on top of the slag mound.

The results of testing performed by JDAC in 2000/2001 indicate that one borehole location, MCES-003-MW, is located within this area. Soil samples collected from this borehole did not exceed CCME commercial guideline values. Groundwater from the same location exceeded the Canadian Drinking Water Quality Guideline values for certain heavy metals (sodium, chloride, barium, and iron), EPA 625, PAHs and HCNs.

These contaminants are consistent with coal tar contamination. Groundwater concentrations of petroleum hydrocarbons exceeded the NSDEL Tier 1 criteria. As mentioned above, elevated levels of sodium and chloride are expected in a marine environment, and the remainder of the contaminants are consistent with those found in the Tar Ponds. It is noted that the groundwater is not used as a source of potable water.

The majority of open space in this area is covered with granular materials. Slopes at certain locations show signs of surface erosion. Overland drainage in the area may present the possibility of siltation and sediment impacts to receiving waters.

Potential environmental issues associated with the North Slag Disposal Area include fill and groundwater contamination associated with industrial waste disposal, including heavy metals, and petroleum hydrocarbon. Petroleum impacts may also have resulted from leakage from the Tank Farm area. The potential also exists for coal tar (PAH, HNC) or PCBs contamination to have impacted groundwater and subsurface soils due to infiltration from the Tar Ponds. Coal tar-contaminated sediment may be present, beneath the fill in this area.

Blast furnace slag was widely used as a fill material in this area. Various heavy metals are known to be present in blast furnace slag, but often in a highly immobile state. An important part of future environmental testing at this site will be the appropriate evaluation of heavy metal impacts in relations to their environmental risk.