Paper No. 23
Presentation Time: 9:00 AM-6:00 PM
ASSESSMENT OF AQUATIC ECOSYSTEM HEALTH AT THE PIKE HILL COPPER MINE SUPERFUND SITE, VERMONT
The Pike Hill Copper Mine operated from 1847 to 1919 and exploited Besshi-type massive sulfide deposits. The site, which is now a Superfund site, is drained by Pike Hill Brook and by an unnamed tributary that flows into Cookville Brook, and both brooks drain into the Waits River, which flows into the Connecticut River. The aquatic ecosystem health was assessed using a variety of approaches that investigated surface-water quality, sediment quality, and various ecological indicators. Copper and Cd concentrations in surface waters reached or exceeded the USEPA hardness-based chronic water-quality criteria in most of Pike Hill Brook sites and some sites on the tributary to Cookville Brook. USEPA Biotic Ligand Model-based criteria for Cu, which replaced the hardness-based criteria in 2007, were generally lower than hardness-based criteria at a given stream site resulting in more exceedances and thus suggesting a greater degree of impairment. Riffle-habitat benthic invertebrate richness and abundance data correlated strongly with the extent of impact based on water quality. Similarly, fish community assessments documented degraded conditions throughout most of Pike Hill Brook, whereas the tributary to Cookville Brook was less degraded.
The sediment environment also indicates regions of impairment. On the basis of probable effects concentrations, sediment impairment was dominated by elevated Cu, and localized elevated Cd and Zn. Uncertain toxic effects were predicted throughout both brooks on the basis of equilibrium-partitioning sediment benchmarks, with one downstream exception that indicated no toxic effects. Laboratory toxicity testing on sediment indicated chronic toxicity to the amphipod Hyalella azteca and the midge Chironomus dilutus at some sites in both streams. Interestingly, toxicity was not indicated for either species in sediment from the most acidic metal-rich location, likely due to the low lability of Cu remaining in the sediment. Depositional habitat invertebrate richness and abundance data generally agreed with sediment toxicity and other ecosystem-health indicators.
In general, degraded surface-water and sediment quality, particularly from Cu, appears to be the dominant cause of toxicity. The biological community begins to recover at the most downstream locations in both brooks.