DECIDING WHEN TO INTERVENE

Introduction

The Wisconsin Department of Natural Resources (WDNR) through Short Elliott Hendrickson Inc. (SEH) recently completed an Ecological Risk Assessment (ERA) for the contaminated sediment in an area that comprised approximately 4.05 hectares of the harbor that extends from 92 to 213 m off shore from Kreher Park in water less than 3.05 m deep and between jetties to the east and west. Previous investigations have identified the contaminants of concern as volatile organic compounds (VOCs) and polycyclic aromatic hydrocarbon compounds (PAHs). The contaminants are associated with black tarry materials and appear to be most concentrated at the interface of a wood chip layer (that covers a large part of the area to an average depth of 22.5 cm) and the underlying fine sands and silty sands. The contamination was generally present in the upper 3.05 m of the sandy sediment and decreased with depth till underlying, cohesive parent materials were reached.

Contaminants sources

Given the large area of bottom sediment contaminated and the visible black, tarry characteristics associated with the contamination, there is only a limited number of possible contributing sources to this type of contamination. A major contributing source was likely releases of coal tar wastes from the Manufactured Gas Plant (MGP) that operated up on the bluff from the late 1800s until 1947. MGPs generated gas for residential heating and lighting from heating coal in retorts. Coal tars were a by-product of the gas generation process. Disposal of waste products were largely unregulated during the period of active coal gas production. Coal tars from the Ashland MGP have been identified in the ravine off of the bluff, the deep groundwater aquifer, and in the filled area of the Ashland Lakefront property.

As more and more MGP sites are being investigated around the state, coal tar wastes are being found in the bottom sediment of surface waters associated with a large number of the sites. Even 40-50 years after the MGPs have ceased operating, the coal tar wastes have remained at or near the sediment surface and at a depth to impact aquatic resources on a continuing and long-term basis. Organic and metal compounds from MGP wastes are toxic to bottom-dwelling organisms and can be released from bottom sediment by various means to the overlying water in dissolved forms, associated with suspended particulates, or as separate oils, all of which may be available and toxic to fish and other aquatic organisms. Coal tar wastes may contain thousands of organic compounds of which there is the ability to routinely analyze and identify only a portion. Many of the unidentified may be as equally toxic as those that can be identified.

Ecological risk assessment

The purpose of the ERA was to estimate the current and future risks and impacts from contaminants of concern present in the surface waters and sediment of the site to plants, fish, and other aquatic organisms that would normally occupy the site habitats and birds and wildlife that may use the habitats as part of their foraging base. A previous assessment looked at the risks to human health from exposure to the site contaminants.

The ERA used a weight of evidence approach to link the observed and measured sediment and water contamination found at the site to actual and predicted impacts to fish and other aquatic organisms that may use the harbor area off of the Lakefront property. The weight of evidence approach depends on using multiple methods of associating the contaminants levels to effects to different organisms who are exposed to the contaminants by different exposure routes.

The weight of evidence of impacts was built on the following:

• Representative fish, water column, and benthic test organisms were exposed to sediment, and water was collected from the contaminated site and a clean site in a series of laboratory toxicity tests.
• Samples of the organisms inhabiting the bottom substrates of the site were collected to look at the number and diversity of species present and compared with those from uncontaminated sites.
• Review of the results of studies conducted on other sites with the same groups and levels of the contaminants of concern and methods of exposure to organisms occurred.
• The use of published guidelines or criteria that relate sediment and water concentrations of the contaminants to effects on fish and other aquatic organisms, and a comparison of these guideline/criteria concentrations to measured concentrations found at the site occurred.

Integration of the above study components leads the WDNR to conclude that the ecological risks associated with the contaminated sediment off of the Ashland Lakefront property are likely to be high for the present and for the long-term. Given the bottom characteristics, PAHs will not attenuate or naturally beak down over time as evidenced by their toxicity 50-60 years after being released to the harbor. Risks and impacts to the insects, worms, crustacea, and other species that inhabit the bottom substrates for all or some portion of their life cycles and for water column organisms such as immature fish, are expected to be highest. The bottom-dwelling community serves as part of the food chain that supports higher trophic levels or larger consumers such as fish. It is likely the bottom dwelling community is limited as a food source at the site, and those organisms that can survive may accumulate PAH contaminants and pass them onto higher level consumers. Immature fish impacted by the site contaminants also means a possible loss of a food base for higher level consumers and loss of fish stock to the bay and the lake. The health of larger fish utilizing the area may also be impaired.

Some of the PAH contaminants at the site have the unique characteristic of having their toxicity to bottom-dwelling and water column organisms such as fish enhanced or increased by sunlight that can penetrate through the water to the bottom substrates and activates the PAHs in the process (Table 1). In all the above cases, the direct evidence indicates that the shallow nearshore habitat off the Ashland Lakefront property is impaired and not supporting a healthy, balanced community of aquatic organisms. These impacts may have secondary impacts to higher trophic level organisms such as birds and wildlife that use the habitat as a foraging base.

Feasibility study for sediment remediation

Based on the results of the ERA, the WDNR will be undertaking a feasibility study to evaluate remedial alternatives for the contaminated sediment of the site. The overall objective for remediating the contaminated sediment off of the Lakefront property is to protect the unique resources of the Chequamegon Bay and Lake Superior Ecosystems. All necessary means will be taken to protect these resources from any degree of degradation or impairment.

Summary of ecological risk assessment - weight of evidence

Benthic Community:

• Adsorbed chemical PAH and VOC concentrations in sediment
• Exceedance of several different sediment effects benchmarks for PAHs and VOCs concentrations in sediment
• Impacted benthic community per Spring 1998 survey
• Toxicity study results indicate PAH contaminated sediment is toxic to benthic organisms
• UV exposure results indicate PAH contaminated sediment is toxic to benthic organisms
• Degradation of lower order food chain microorganism populations based on microbial enumeration bioassays

Aquatic Community:

• Adsorbed chemical PAH and VOC concentrations in sediment
• Exceedance of several different sediment effects benchmarks for PAHs and VOCs concentrations in sediment
• PAH concentrations in sediment at levels comparable to those associated with tumors in fish at other sites
• Exceedance of accute and chronic criteria for water quality during wave action
• Reports of sheen and odors in surface waters above contaminated sediment
• Potential for release of more heavily contaminated deeper sediment due to natural or anthropogenic disturbances
• Toxicity study results indicate PAH contaminated sediment is toxic to fish fry
• UV exposure results indicate PAH contaminated sediment is toxic to fish fry and daphnia magna

Terrestial Community:

• HHRA indicated risk of cancer to humans from exposure to sediment or contaminated water
• Lower order food chain impacted - decreases quantity and quality of fish and other food sources
• Potential for uptake of PAH contaminants by terrestial organisms feeding on lower order aquatic or benthic organisms that may bioaccumulated contaminants

Identification

Site identification:

• Planning on a Watershed basis
• Assessment on a Watershed basis
• Other sediment remediation projects
• Fish consumption advisory monitoring
• Wildlife monitoring programs
• Other

Ashland Harbor site identification:

• Known coal gasification site
• Other coal gasification sites with serious problems
• Expansion of local Wastewater Treatment Facility

Tiered approach

• Comparison of contaminant concentrations with reference/background sites
• Comparison with existing effect-based sediment guidelines
• Simple partitioning models for non-polar organic compounds
• Site specific studies that integrate sediment chemistry, laboratory toxicity/bioaccumulation, and field studies
• Fate and transport modeling
• Human health and ecological risk assessments

Field collections at Ashland Harbor site

Sediment chemistries:

• 80 locations @ 30.5 m grid spacing
• Sediment depths to 7.5 m
• PAHs, VOCs and others

Surface water samples:

• High wind and wave periods

Biological studies:

• Benthic macroinvertebrates - 4 habitat types and tissue PAH concentrations
• Fish studies - tissue PAH concentrations and fish health assessment

Ashland Harbor sediment toxicity testing

4 Sample sites:

• Reference wood and sand
• Contaminated wood and sand
• Results expressed in Toxic Units

Solid phase tests:

• Hyalella azteca
• Chironomus tentans
• Lumbriculus variegatus

Sediment Elutriate tests:

• Daphnia magna (48 Hr)
• Pimephales promelas (7 day)

Photo-enhanced Toxicity tests:

• Lumbriculus variegatus
• Daphnia magna
• Pimephales promelas
• 2-4 hours Ultraviolet exposure
• Results expressed in Toxic Units

Table 1. PAH Sediment Concentrations and Related Toxicity Units at the Study Sites

Type of Bottom Substrate Sampled	Total PAHs mg/kg (dry wt.)	Sum of UV Toxic PAHs1 Organic Carbon Normalized mg PAH/kg TOC	Total Toxic Units2
			Based on dry wt.	Organic Carbon Normalized
Reference sand	.424	40.9	1	7
Contaminated sand	.145	15	7	119
Reference wood	6.543	41.1	31	14
Contaminated wood	370.2	8,294	1,711	3,728

1. PAHs identified to be associated with phototoxic effects based on the literature - anthracene, benzo(a)pyrene, dibenzo(a)anthracene, pyrene, benzo(k)fluoranthene, and benzo(g,h,i)perylene.

2. Based on Ingersoll HA 28 d ERM values or Effect Range - Median values. ERM values associated with frequent or probable adverse biological effects.

Sediment concentration of the PAH compound/HA 28 d ERM concentration for the PAH compound = Toxic Units.

Toxic Units for individual PAHs at a site are summed to derive a Total Toxic Unit value for the sample site.