Reports
Urieville Lake Sediments Study, Kent County, Maryland; Reconnaissance Survey of Sediments at Urieville Lake
2020, Gillmor, A., Van Ryswick, S., Sylvia, E.R., Connallon, C., and Nicholson, B.
File Reports, Coastal and Estuarine Geology, File Report 20-01
Executive Summary
In response to a request by the Resources Assessment Service (RAS) of the Maryland Department of Natural Resources (DNR) as a recommendation under the State Lakes Protection and Restoration Fund legislation project recommendation process, the Maryland Geological Survey (MGS) was contracted to perform a study on the sediments within an approximate one acre of Unieville Lake, located in Kent County, Maryland. The sediments are slated to be dredged; therefore, physical and chemucal characterization is required to ascertain if the sediments are well-suited to the current intended end-use. The intended end-use 1s as a soil conditioner to be applied to an agricultural field. Three cores were collected from each of the four quadrants, totaling twelve vibracores. Cores were homogenized as follows: the first meter of Cores Al, A2 and A3 was combined to form Composite A from quadrant A, and similarly for the remaining Cores B, C, and D. The fieldwork for this study occurred in November 2019.
A suite of various geotechnical, environmental and agricultural analyses were performed on the sediment samples. The analysis suite was as prescribed in Table A2-3 of the Maryland Department of the Environment's (MDE) Innovative Reuse and Beneficial Use of Dredged Material Guidance Document, since the anticipated end-use of these freshwater sediments is to be as soil, fill, or soil conditioner. This document outlines the pathways to innovatively and beneficially reuse dredged material, and classifies sediments into three Categories based on the physical and chemical characteristics. Category 1 has comparatively low concentrations and is pernussible to place on residential properties. Dredge material to be reused as soil, soil amendment or soil conditioner to be applied to agricultural lands should also meet Category 1. Category 2 has greater concentrations than Category 1 and is recommended to be placed on non- residential properties. Category 3 has greater concentrations than Category 2 and is recommended to be placed on properties such as Brownfields where it can be maintained under a protective cap to limit rainfall infiltration. In all cases, the end user may choose to blend the dredge material with other soil amendments to ensure that the physical and chemical characteristics of the dredge material are acceptable for use for an intended lesser Category.
The physical properties of the sediments accumulated within the study area of Uneville generally consisted of a surficial layer of dark colored, soft, organic-rich watery muds, followed by an intermediate layer of silty sands and muddy sands, followed by a denser clay-rich layer at depth. There was some heterogeneity and/or depositional disturbance inferred. The physical and geotechnical analyses were performed on composited material, and all four grain size classes (clay, gravel, sand and silt) are present in each composite. The most common grain size in the sediment was sand (47%), followed by clay (27%), silt (18%) and gravel (8%).
The results of the nutrient and agricultural analyses found these sediments to contain 7 to 30 mg/kg of extractable phosphorus, 0.2 to 0.3 mg/kg of nitrogen-from-nitrate and 43.7 to 54.3 mg/kg of nitrogen-from-ammonium. These sediments also contained 0.71 to 1.4% of total organic carbon, sediment pH of 5.9 to 6.4 and cation exchange capacities of 4 to 5 mulli-equivalents per 100 grams.
Of the various environmental and chemical analyses performed on the material, most indicated sediment concentrations well below the most sensitive screening level or no detectable concentrations.
There were only three compounds which prompted some additional consideration. There were concentrations of Arsenic (As) and Thallium (Tl) present in all four sediment composites at concentrations above the default Category 1 residential screening levels for these metals [0.68 mg/kg (milligrams per kilogram) and 0.078 mg/kg, respectively], and a concentration of benzo[a]pyrene also above the default Category 1 residential screening level for this compound (0.11 mg/kg). The default Category 1 screening levels are based on a hazard quotient of 0.1 and a lifetime cancer risk of 1 in one million (106), and it is common to perform all screening at this most sensitive level as a first step. However, if evaluating a single or few components which are present above the most sensitive screening level, then the evaluator may shift the assumptions of risk and use the screening levels derived from a lifetime cancer msk of 1 in one hundred thousand (105) (USEPA). Doing so would raise the screening levels by an order of magnitude for each of these three substances, and in this case the material would likely be permitted to be used as a Category 1 manufactured soil, soil amendment or soil conditioner.
At this time, it is anticipated that this material may be reused as a Category 1 manufactured soil, soil amendment or soil conditioner with the As, Tl and benzo[a]pyrene concentrations present. This is contingent upon review and acceptance of the order of magnitude adjustment by all permitting parties.
