Reports
Cox Creek Dredge Material Containment Facility: Exterior Sedimentary Environment 2015
2019, Gillmor, A., Connallon, C., Sylvia E.R., and Van Ryswick, S.
File Reports, Coastal and Estuarine Geology, File Report 17-08
Executive Summary
File Reports, Coastal and Estuarine Geology, File Report 17-08
Executive Summary
The Cox Creek site is a dredged material containment facility (DMCF) located in the Baltimore Harbor. The site is an upland dredged material placement site anchored to land, with a diked containment area projecting into the Harbor. The Cox Creek DMCF was first operational during the 1960s through 1984. Between 2002 and 2006, the Cox Creek DMCF site underwent modifications in order to accept additional dredged material from the Baltimore Harbor. In the past, Baltimore Harbor material was placed in the Hart-Miller Island Dredge Material Containment Facility (HMI DMCF). However, the HMI DMCF stopped accepting dredged material at the end of 2009. As a result, the Cox Creek DMCF became more active in receiving material dredged from the Baltimore Harbor; with the first large inflow received in 2012. To date, the Cox Creek DMCF has received approximately two million cubic yards of dredged material.
In order to assess any effects of the reactivation and current operations of the Cox Creek DMCF, surficial sediment has been collected from ten consistent monitoring sites around the exterior of the facility: nine (9) monitoring sites adjacent to the area and one site designated as a reference site. Sediment samples were collected annually between 2006 and 2010. No exterior sampling was done in 2011 and 2012 due to little or no discharge from the facility. Annual exterior sampling resumed in 2013. Results of the 2015 monitoring are presented in this report.
Maryland Environmental Service (MES) collected the samples and the Maryland Geological Survey (MGS) was responsible for textural and chemical analyses of the samples and interpretation of the results. Samples consisted of undisturbed sediments collected at the sediment-water interface. The sediments were analyzed for textural properties and 51 elements including total nitrogen (N), carbon (C), phosphorus (P), sulfur (S), cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), lead (Pb) and zinc (Zn).
Data from sediments collected on October 7, 2015 are presented in this report. Placed in a broader context with the results of ongoing monitoring, the data show:
- Sediments adjacent to the Cox Creek DMCF are generally fine grained, primarily sand-silt-clays and silty clays. The sand content has ranged from approximately 3% to 70% over time, with an average of 22-24%. Historically, the exterior sedimentary environment becomes more clayey (Clay to Mud Ratio increases to greater than 0.40) across a gradient from northwest to southeast. During 2015, the sandiest sediments were located adjacent to the DMCF at stations CC-3 and CC-6, and the most clayey sediments were located to the southeast at stations CC-5, CC-7 and CC-8.
- The amount of total carbon present in the sediments is approximately 3.5% by dry weight. The proportion of sedimentary organic carbon contributed by planktonic primary production is approximately 40% and the proportion contributed by transport of terrigenous organic matter is approximately 60%. The proportions of sedimentary phosphorus contributed by planktonic and terrigenous sources are approximately 28% and 72%, respectively. The proportion of planktonic organic matter which is preserved in the sediments may be affected by initial planktonic growth, bacterial decomposition within the sediment, and proximity to additional inputs of terrestrial carbon (usually coal). These ratios vary little from year to year.
- The amount of total sulfur present in the surficial sediments is approximately 0.5% by dry weight. The total sulfur content of the sediment has been generally stable to decreasing over time. The ratio of total sulfur to planktonic carbon (S:Cplanktonic) can be more sensitive to changes in sedimentation. A decrease in S:Cplanktonic may be interpreted as an increase in sedimentation rate, where the rate of biogenic sulfide formation is outpaced by the increased rate of Cplanktonic burial.
- Compared relative to the Effects Range Low, a toxicological screening value, the sediments adjacent to the Cox Creek DMCF contain elevated levels of Cr, Cu, Hg, Ni, Pb and Zn present at at-least one sampling station. Sedimentary concentrations of Cr, Ni and Zn are additionally above the related Effects Range Median at at-least one sampling station.
- Compared relative to the grain-sized normalized concentration (i.e. the sigma levels), the sedimentary concentrations of Cd, Mn, and Ni conform to the background behavior for the Northern Chesapeake Bay sediments.
- Compared relative to the grain-sized normalized concentration (i.e. the sigma levels), the sedimentary concentrations of the remaining target metals Cr, Cu, Pb and Zn are elevated with respect to the background behavior for Northern Chesapeake Bay sediments.
- Compared relative to the grain-sized normalized concentration (i.e. the sigma levels) eighty percent of the sampling stations are enriched in Zn in 2015. All of the sampling stations were enriched with Cr, Cu, Fe and Pb in 2015. However, these sedimentary concentrations remain similar to metals concentrations specific to the Baltimore Harbor. Over time (2006-2015), there has been no observable increase in size of the area with metals enrichment nor has there been any upward trend in the magnitude of metals enrichment (as expressed in sigma levels) in the sediments adjacent to the facility. We interpret the stability of spatial pattern and size and absence of increasing temporal trend as indicative of no outward effects from the Cox Creek DMCF operations to the exterior sedimentary environment.
- Comparisons relative to the reference site have been of limited utility due to the dynamic grain-size composition observed at this station. Interpretations of temporal and spatial trends are therefore considered more informative.
