Reports
Masonville Dredged Material Containment Facility Exterior Sedimentary Environment 2014
2017, Gillmor, A., Sylvia, E.R., and Van Ryswick, S.
File Reports, Coastal and Estuarine Geology, File Report 16-02
Executive Summary
The Masonville Dredged Material Containment Facility (DMCF) is located in The Baltimore Harbor. The site is an upland disposal site anchored on land, and has a diked containment area projecting into the Patapsco River. The site is designed to accept dredged material from The Baltimore Harbor that would have historically been sent to the Hart-Miller Island (HMI) DMCF. The HMI DMCF stopped accepting dredged material at the end of 2009.
This is the seventh year of active exterior monitoring at Masonville DMCF. Ten (10) sites were sampled annually from 2006 to 2010 to provide site-specific baseline data on conditions prior to use of the containment facility. The results of ongoing monitoring data are evaluated multiple ways, including; 1.) general comparison to a site-specific pre-construction monitoring event via plotting of trends over time, 2.) general comparison to regional concentrations, in particular the concentration distributions determined for the Baltimore Harbor in 1996, 3.) detailed comparison against a regional baseline behavior, specifically a grain-size normalized concentration prediction for specific metals, which is a shared interpretative technique with HMI, 4.) detailed comparison against toxicological screening levels and 5.) general comparison relative to a presumed upgradient sampling station. Construction of the Phase I dikes were completed by the end of 2010 and the Masonville DMCF began accepting dredged material. Due to limited discharge from the facility, external sediment samples were not collected in 2011 or 2012. External monitoring was resumed in 2013 and sediment samples were collected at the established ten sites. Nine (9) monitoring sites were adjacent to the footprint of the dike and one (1) additional site was designated as a reference site. Maryland Environmental Service (MES) collected the samples and the Maryland Geological Survey (MGS) was responsible for analyses and interpretation of the sediment data.
The sediment samples were collected on October 21, 2014. Samples consisted of undisturbed sediments collected at the sediment-water interface. The samples were analyzed for textural properties and 51 elements, including carbon (C ), nitrogen (N), sulfur (S), phosphorus (P), cadmium (Cd) chromium (Cr), copper (Cu), iron (Fe), manganese (Mn), mercury (Hg), nickel (Ni), lead (Pb) and zinc (Zn).
Placed in context of ongoing monitoring (2006-2013), the 2014 data showed agreement with earlier data, including the following findings:
- Sediments adjacent to Masonville DMCF are fine grained, primarily silty-clays. The sand content is low, ranging from approximately 2 to 20%, with an average of 12-14%. Small changes adjacent to the facility may be attributable to construction activities. The reference station ME-REF shows the most variability in grain size, ranging from approximately less than 10 to more than 80 % sand. Historically, the exterior sedimentary environment becomes more clayey (Clay to Mud Ratio greater than 50%) across a gradient from east to west. During 2014, a pattern is visible of clayey sediments deposited exterior to the DMCF.
- The proportions of organic Carbon and Phosphorus in sediment contributed by planktonic primary production and by transport of terrigenous organic matter, respectively, has changed very little compared to previous years. The input is consistent with sediments in the rest of the Baltimore Harbor, i.e. the terrigenous Carbon input decreases toward the mouth of the Harbor.
- The total Sulfur content of the sediment has changed little through the years. The S:Cplanktonic ratio is slightly more responsive to changes in sedimentation. A decrease in S:Cplanktonic often interpreted as an increase in sedimentation rate, where the rate of biogenic sulfide formation is outpaced by the increased rate of Cplanktonic burial, with lows during 2007, 2010, 2013 and 2014. These may indicate influxes of new sediment.
- Cd, Fe, Mn, and Ni are within background levels found for the Northern Chesapeake Bay.
- The remaining target metals in the study area are relatively enriched above the grain-size concentration prediction, which suggest local sources. There appears to be a source of Cr, Cu, Pb and Zn north of the Masonville DMCF site. In 2014, all four of these enriched metals approach background levels (<3 sigma) southeast (downgradient) of the site. Additionally, concentrations of Cr and Cu decreased slightly from the preceding years’ averages and Pb and Zn were of comparable concentrations.
- The reference site (ME-REF) is not representative of the area immediately adjacent to the DMCF. ME-REF is likely influenced by proximity to mouth of the Patapsco River. Interpretation of spatial and temporal changes are a better gauge to assess potential changes due to operation of the dredged material containment facility. In broad overview, the 2014 monitoring results show that the sediments around the DMCF were slightly more coarse-grained (more sandy) compared to the previous years’ samples; they also contained slightly lower concentrations of certain regionally-enriched metals.
