Reports
Cox Creek Dredge Material Containment Facility Exterior Monitoring: Exterior Sedimentary Environment 2014
2017, Gillmor, A., Sylvia, E.R., and Van Ryswick, S.
File Reports, Coastal and Estuarine Geology, File Report 16-01
Executive Summary
The Cox Creek site is a dredged material containment facility (DMCF) located in the Baltimore Harbor. The site is an upland disposal 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 has recently become more active in receiving material dredged from the Baltimore Harbor; first large inflow was received in 2012. To date, the Cox Creek DMCF has received approximately 2 million cubic yards of dredged material.
In order to assess any effects of the reactivation and operations of the Cox Creek DMCF, ten monitoring sites were established 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. Exterior sampling resumed in 2013, representing the sixth year of monitoring during active operations and continued for a seventh year in 2014. Results of the 2014 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 samples collected on October 21, 2014 are presented in this report. Placed in a broader context with the results of ongoing monitoring (2006-2014), the data show:
- Sediments around the Cox Creek DMCF are generally fine grained and exhibit a gradient of higher sand content close to the dike, diminishing outwards toward the channel and downstream. This distribution pattern has been reproduced during all monitoring years.
- As derived from the total N and total P content of the sediment, the sediments adjoining the Cox Creek DMCF study area receive the majority of their organic matter from terrigenous sources rather than planktonic sources.
- The sulfur to carbon ratio is lower than that measured further into the Harbor, indicating that the area is slightly more disturbed or has a higher sedimentation rate than further into the Harbor.
- Certain target metals, including Cd, Mn, and Ni, remain within background levels found in the northern Chesapeake Bay. The remaining target metals, including Cr, Cu, Fe, Pb and Zn, are elevated above background levels. Forty percent of the sites are enriched in Zn. Ninety to 100 percent of the sites were significantly enriched with Cr, Cu, Fe, Pb.
- Target metals in the study area follow the general patterns seen in the 1994 - 1997 Baltimore Harbor Spatial Mapping studies (BHSM, Baker et al, 1997, Mason et al 2004). The sediments exterior to the Cox Creek DMCF appear enriched in Fe and Pb, and to a lesser extent, in Cr, Cu and Zn relative to some, but not all, areas of Baltimore Harbor.
- Physically and chemically, the reference site is not representative of sediments immediately exterior to the DMCF. Large variations in sediment texture have occurred at the reference site; for example the % sand has ranged more than 50% (from > 60% in 2007 to < 10% in 2008) and the clay-to-mud ratio (CMR) ranged more than 20%. The reference site helps provide spatial coverage which suggest additional external source of regional metals, but may not be a good gauge to measure changes due to operation of the DMCF. Therefore changes due to operation of the DMCF are best evaluated through monitoring any changes to the exterior sediments over time.
- The spatial pattern of the metals concentrations, expressed as sigma level contours, for all elevated metals (Cr, Cu, Pb and Zn) depicts the entire area of sediments adjoining the Cox Creek DCMF as significantly enriched in these metals. The local sigma maximum was observed at sampling station #8 during the 2014 event, located to the southeast of the DMCF, consistent with most preceding monitoring years. Over time (2006-2014), 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, size and magnitude as indicative of no outward effects from the Cox Creek DMCF operations to the exterior sedimentary environment.
