Environmental Impacts on Sediments

(A TOSC Fact sheet)

Sediment Contamination at the Ashland/NSP Lakefront Site

Lake Superior sediments located adjacent to the Ashland/NSP property have been contaminated by volatile organic compounds (VOCs) and polynuclear aromatic hydrocarbons (PAHs). The contamination extends up to 700 feet from shore and is confined between Ellis Street pier and the city dock (see Figure 1). The contamination is estimated to cover 9-10 acres of the lake; this "exclusion zone" has signs and buoys in place to keep people from coming into contact with the sediments and to keep the sediments from being disturbed.

The sediment samples were collected in the winter. A grid pattern, extending from the marina to the city beach and about 1000 feet from shore, was set up on the ice of Lake Superior. Borings were made through the ice and into the sediments. These sediment borings were collected, tagged and sent to a lab to be analyzed.

Contaminants found in the sediments

Contaminants known as non-aqueous phase liquids (NAPLs) were found in sediment borings between a wood chip layer and a sand layer, near the sediment surface. The amount of contamination decreases with the depth of sediment and stops at or above the Miller Creek aquitard (a natural clay layer).

Sediments were analyzed and a wide range of VOCs and PAHs were identified. Examples of levels of contamination are listed below. There are "hot spots" in the sediments where the contamination levels are higher.

This chart shows contaminant levels in some of the soil borings taken.
VOC	Amount ( m g/kg)	AET-L ( m g/kg)	AET-H ( m g/kg)
VOC	Amount ( m g/kg)	AET-L ( m g/kg)	AET-H ( m g/kg)

VOC Amount ( m g/kg) AET-L ( m g/kg) * AET-H ( m g/kg) *

Benzene 2,400 Not available Not available

Toluene 5,900 Not available Not available

Xylene 16,500 40 120

PAH Amount ( m g/kg) AET-L ( m g/kg) AET-H ( m g/kg)

Naphthalene 170,000 2,100 2,700

Benzo(a)pyrene 13,000 1,600 3,600

* AET-L = Apparent Effects Threshold-Low (at this level, adverse effects are probable but expected infrequently)

AET-H = Apparent Effects Threshold-High (at this level, adverse effects are probable). These terms refer to the effects upon microorganisms living in sediments. Source: "National Sediment Quality Survey," USEPA Sept 1997.

The Midwest Hazardous Substance Research Center, Michigan State University.
Please contact us if you have any comments or questions.