Identifying Metal Pollutants in Stormwater Runoff
Naval Facilities Engineering and Expeditionary Warfare Center has developed a Geographic Information System-based methodology to identify and quantify non-point sources of metal pollutants in storm water runoff.
By Vern Novstrup and Ron Tsumura, EIT
The Department of the Navy is addressing a multitude of stormwater-related issues regarding compliance with its stormwater National Pollutant Discharge Elimination System permits. Many U.S. Navy installations continue to struggle with the permit requirements due to low benchmark concentrations of metal pollutants in stormwater runoff from industrial areas and particularly stringent acute toxicity requirements. In most cases, copper and zinc are two problematic metals that have been recognized through Toxicity Identification Evaluations (TIE) as the primary cause of toxicity.
At Naval Base San Diego, Calif., copper concentration in stormwater must not be greater than 63.6-μg/L and zinc concentration must not be greater than 117-μg/L. Note, however, these are only benchmark concentrations and not limits. Depending on the region, copper and zinc benchmarks may be less stringent.
In many areas, runoff from industrial and non-industrial areas is mixed in common stormwater conveyances, making it difficult to pinpoint which entities may be responsible for elevated metals concentrations. Naval Facilities Engineering and Expeditionary Warfare Center (NAVFAC EXWC) has developed a new Geographic Information System (GIS) methodology enabling identification and quantification of non-point sources of metal pollutants that was successfully demonstrated at selected Navy sites.
The objective was to provide Naval Base San Diego and other applicable bases a GIS-based methodology and Non-point Source Storm water Management tool to help identify and quantify significant non-point sources of metal pollutants (particularly copper and zinc) that contribute to benchmark exceedances at stormwater outfalls.
PREDICTING POTENTIAL ISSUES
The primary function of the tool is predictive. The function is based off a multi-linear regression equation developed to model a pollutant (one was developed for copper and another for zinc). The equation includes explanatory variables that each represents a significant source of the pollutant as identified by statistical analysis such as building material, parking lot, and industrial activity. The statistical analysis involves taking all the potential sources of the pollutant identified in the site characterization and narrowing down the possible sources to the most statistically relevant ones. In the equation, each coefficient represents the “weight” of the variable relative to each other.Other functions include generating graphs of historical storm water quality data and management of stormwater quality data, inspections and best management practices.
This project employed a GIS approach to track significant non-point sources of copper and zinc as a result of the following reasons:
- NAVFAC has an existing GIS infrastructure;
- Good visual display of results;
- The future of data management associated with maps is GIS;
- Model is non-proprietary;
- Streamlines installation annual storm water BMP inspections;
- It is low maintenance;
- The developed GIS-model is applicable Navy-wide;
- GIS data may be uploaded to the Navy’s GIS server and Navy installations worldwide may access the data.
CASE STUDY DETAILS
The GIS based methodology has enabled identification and quantification of metal pollutant sources in stormwater runoff and a colored layer transposed over Naval Base San Diego.
Participants conducted a site characterization to identify potential metal pollutant point sources, particularly for copper and zinc. Using GIS and handheld Global Positioning System (GPS) technologies, key information such as industrial operations, building materials, traffic density, parking lot data, roadways, outside storage areas, etc. were captured on a survey template and imported into GIS software in order to calculate broad range estimates of potential metal concentrations, identify potential material sources, and predict which drainage basins need the most attention. The methodology incorporates into a decision support tool that enables selection of appropriate best management practices and/or nonstructural source reduction measures to comply with NPDES permit requirements.
Among the benefits, this approach simplifies Storm Water Pollution Prevention Plan-required Best Management Practice assessments; utilizes an existing GIS platform; and provides a visual analysis (graphical display) of metal pollutant “hotspots.”
Application of this methodology is recommended as an iterative process where user input can be used for identifying, eliminating, and mitigating point sources of metals in storm water runoff. The cost of a handheld GIS/GPS device for use during BMP assessments formatted with BMP checklist is approximately $10,000. The device may also be available for rental.
The development and validation of the stormwater runoff methodology for identifying metals was made possible by the Navy Environmental Sustainability Development to Integration Program (www.nesdi.navy.mil). The site is a comprehensive resource of technologies and processes that have been or are being developed, addressing environmental needs identified by Navy personnel to promote Navy operations.