HEAVY METALS IN LEGACY SEDIMENTS ABOVE A LOW HEAD DAM IN THE BUSHKILL CREEK, EASTON, PA: IMPLICATIONS FOR DAM REMOVAL

The Bushkill Creek is a tributary to the Delaware River and flows southeast through Northampton County before joining the Delaware in Easton, PA (Steiner 1996). Flow path is about 34.5 km and the drainage basin is approximately 205 km². Several low head dams remain on the lower reaches of Bushkill Creek from mills of the 1800s to early 1900s with potential for removal. The purpose of this study is to determine the concentrations of heavy metals in legacy sediment behind the Third Street Dam, in Easton the last dam prior to the confluence with the Delaware River. Data will aid in determining if removing the dam and mobilizing sediment will release important trace metals to the area downstream of the dam as the channel readjusts its dimensions. Grain size classification and analysis for trace metals was conducted on ten cores collected above the Third Street dam. Concentrations of lead, copper and cadmium were measured for each texturally distinctive layer within the cores. Cores were classified into two to three distinctive strata based on textural characteristics. Chemical concentration was measured using atomic absorption spectroscopy. Lead concentrations ranged from 50-200 micrograms per gram of dry sediment and the upper strata have higher concentrations of lead than the lower strata. Copper concentration were less than 50 micrograms per gram of dry sediment and showed little trends within the strata of the cores. Cadmium concentration measured negligible (<0.61 ug/g) in comparison to the copper and lead concentrations in all strata of the cores. Arsenic is to be tested as an additional trace element in this study. Chemical concentration data will be combined with a detailed survey of the channel and HEC-RAS modeling to estimate channel profile readjustment and potential for transport of heavy metals in legacy sediments.