1. Is Land Use and Land Cover a Factor in EMC Determination and Selection?
Kenya L. Goodson1, Chancee’ Lundy1, Anouk Savineau2, Jonathan Champion3
1 Nspiregreen, LLC; 601 Pennsylvania Avenue NW, Washington, DC 20004
2 LimnoTech; 1015 18th Street NW, Washington, DC 20036
3 District Department of Environment; 1200 First Street NE, Washington, DC 20002
ABSTRACT
The District of Columbia is developing a Consolidated Total Maximum Daily Load
Implementation Plan (TMDL IP) to reduce loads for 23 TMDL pollutants in the MS4
area, including bacteria, sediment, nutrients, metals, organics, PCBs, oil and grease,
BOD, and trash. The methodology for the MS4 TMDL IP includes calculating the
existing pollutant loads, determining the gap between the waste load allocations and the
existing loads, and determining the amount of BMP implementation necessary to close
the gap. Storm water event mean concentrations (EMCs) were used to estimate the loads
for all pollutants of concern. This presentation will summarize the research and analysis
undertaken to establish the most representative EMCs for the District of Columbia MS4
area.
Several different sets of EMCs, developed at different times for different purposes, were
used to establish the TMDLs. The requirement to develop a Consolidated TMDL IP
provided an opportunity to identify and apply a consistent set of EMCs to support
modeling of pollutant load estimations. Three different analyses were conducted to
evaluate the most appropriate set of EMCs for use in the TMDL IP, including
1. A review of EMCs used to develop TMDLs in the district
2. A review of EMCs reported in literature for various land use classes
3. An evaluation of District MS4 outfall monitoring data to develop DC-specific
EMCs
Research demonstrates that different land use and land cover (LULC) affect event mean
concentration. In an effort to determine the significance of LULC in the District of
Columbia, LULC EMCs from the literature and DC-specific EMCs were compared.
Literature for LULC EMCs from US and international sources was compiled and
analyzed for statistical trends. The median EMC calculated from the literature was
compared to the DC-specific EMCs for each pollutant. The median values were less
variable for nutrients and TSS. Bacterial values were more variable. Toxic contaminants
were more challenging to compare because of the lack of data for LULC EMCs. The
calculated EMC values using the average values per land use type identified from the
literature didn’t correlate with the monitored EMC values.