Bunker Hill, Idaho

Ecological Restoration Demonstration

Introduction

The Bunker Hill Superfund site in the Coeur d'Alene River Basin is the second largest Superfund site in the nation., Mining and smelting of Zn, Pb, Cd, and As rich ores from 1916 into the 1980s have resulted in heavy metal contamination of mountain soils. Revegetation of these soils along with metal contaminated mine tailings will limit the spread of contaminents via the Coeur d'Alene River system.

Success in restoration is both environmentally and politically important. Specially designed mixtures of residuals (such as biosolids and wood ash) applied to the surface of these soils can restore a vegetative cover.

Basis for Treatment

Phytotoxicity was caused by: i) high concentrations of trace metals, ii) low pH, iii) low soil nutrients and organic matter, and iv) poor soil physical properties. Co-utilization of residuals can correct these problems. Wood ash has a high calcium carbonate equivalent that cures soil acidity. Biosolids limit metal toxicity, provide organic matter that both improves soil tilth,and provides a substrate for soil microbes, and is a slow release nutrient source. Surface application of the biosolids/ash mixture creates a new soil horizon that is capable of supporting plant growth and helps to remedy problems in the subsoil.

Characteristics of the soils and materials.

	Zinc	Cadmium	Lead	pH	Carbon	Nitrogen
	mg/kg	mg/kg	mg/kg		%	%
Typical soil	50	0.5	10	5.5	3.5	0.2
Soil in plots	10000	17	3000	6.4	0.4	0.02
High N biosolids	620	2.5	75	8.0	32	5.0
Low N biosolids	1700	22	380	6.5	26	2.8
Wood Ash	410	3.4	55	11	18	0.1
Logyard Waste	86	0.5	15	7.2	9	0.2

Project Goals

The overall goal of this program at Bunker Hill was to investigate methods for establishment of stable, long-term vegetated and healthy ecosystems. Specific objectives include:

• To reduce erosion.
• To achieve a self-sustaining plant cover
• To reduce metal phytoavailability.
• To develop application technique efficacy.
• To determine appropriate combinations of residuals such as biosolids, logyard waste and woodash.

Phase I. Demonstration Plots

High and low nitrogen biosolids were applied at 55 and 110 dry Mg/ha. Wood ash from power generation was applied at a constant rate of 220 wet Mg/ha to provide 50 Mg/ha calcium carbonate equivalent. In addition, logyard waste was added at a fixed volume ratio of 1:5. Materials were mixed with a front end loader and were applied using an Aerospread on a Rottne chassis. The machine has sufficient traction to access the existing terrain and can accurately distribute the mixture up to 50 m from the roadway.

Phase II. Research Plots

A second phase of this research was installed in October 1997, Small plots were designed to test the best amendment mixtures and the effect of different organic sources for large-scale restoration efforts.

Results

Phase I. Low-N biosolids mixtures provided rapid and lush growth of a variety of native seeded and volunteer plants. Ammonia volatilization from high-N biosolids caused initial toxicity to emerging seedlings, but subsequent reseeding proved to be highly sucessful. Metals in grass harvested from these plots in 1997-8 are comparable to plants grown on uncontaminated soils.

Metals in plants collected from Phase I plots (8/97).

	Zinc	Cadmium	Copper	Phosphorus	Potassium
	µg/g	µg/g	µg/g	mg/g	mg/g
Normal grass	20-150	<1.5	6-15	>1.5	>20
Control	215	0.4	3.9	0.6	10
Low N biosolids
Low rate	70	1.0	7.2	3.8	33
High rate	105	2.0	8.5	3.6	29
High N biosolids
Low rate	84	1.0	9.9	3.7	26
High rate	65	0.8	9.9	5.5	24

Phase II. All organic amendment treatments showed vigorous growth by the following spring. Biomass production was far better in them than controls or conventional treatments.

Conclusions

• Application of a mixture of biosolids and ash is highly successful in revegetation and erosion control. A vigorous combination of grasses and legumes on the plots indicate a self-sustaining vegetative cover. The mixture also appears to be highly adhesive.
• High initial ammonia concentrations can result in reduced initial germination. Delayed seeding can eliminate this problem.
• Plant measurements indicate that "supermulch" treatments can result in biomass far exceeding control soils and conventional hydroseeding techniques.

Cooperators

Sally Brown & Chuck Henry, University of Washington

Harry Compton & Scott Fredericks, US EPA National Superfund

John Tindall, Idaho Divison of Environmental Quality

Rufus Chaney, USDA-ARS

Acknowledgements: Northwest Biosolids Management Association, Ram Enterprises, and US EPA Region 10

Suppliers: Biosolids from King County, Everett, Tacoma, and Cowlitz County, WA, and Post Falls, Hayden, and Coeur d'Alene, ID; ash from Avista Utilities, Louisiana Pacific and Kimberly-Clark; logyard waste from Crown Pacific

Other Associated Projects

Coeur d'Alene River Basin West Page Swamp Wetland Restoration Project

Upper Arkansas River, Colorado: Ecological Restoration Demonstration