Pollutants of Concern Monitoring: A Low-Intensity, Budget-Conscious Stormwater Sampling Method to Identify Highly Polluted Areas for Potential Management Action
Finding sources of urban pollutants in urban landscapes can be very difficult and time consuming yet TMDL and other water quality objectives are difficult to address without locating and abating more highly polluted source areas. Although stormwater monitoring is very effective in identifying highly polluted watersheds, it is very expensive to implement at multiple locations and at a spatial scale that conforms closer with the scales of management. To meet TMDL targets for PCBs and mercury in the San Francisco Bay Area and help focus management effort most cost effectively, a regional reconnaissance study design was developed by the Regional Monitoring Program for Water Quality in San Francisco Bay (RMP) to identify drainages with disproportionate pollutant concentrations and loads. To help ensure applicability to management questions and replicability by multiple practitioners, a stakeholder process over multiple storm seasons was used to guide and refine the design over time. The resulting sampling method is flexible enough that it can be used to mobilize for sampling to any part of the region depending on where the storm will hit; decisions about sampling-mobilization can be made closer to real time as a storm begins rather than needing multiple days of advance warning and planning; and a single field team can sample multiple locations in a single storm event. This method has now been applied over four wet seasons and refined to the point where it is now applicable to other regions of California and any pollutant that is found in stormwater.
The method has three key steps. First a desktop GIS analysis of land use and contaminant source areas within urban drainages around the region is used to identify potential areas of interest as well as specific sampling locations. These locations are then reconnoitered to identify a shorter list of safe sites for sampling during storm events. The shortlisted urban drainages are then monitored at a reconnaissance level using appropriately prepared clean sampling equipment and a time-weighted composite design (since flow is not monitored) during a single storm event. Previous analysis of well sampled locations provided evidence that single event monitoring, in comparison to monitoring over multiple storm events and wet seasons, could adequately characterize whether a urban drainage system was likely highly polluted or not and required further investigation for potential management action.
In this presentation we will discuss the methods and results from successfully sampling 70 watersheds using this approach and describe its applicability to other stormwater programs in California. Using this method, the sites could be ranked from highest to lowest water quality and compared to other information as a tool for carrying out further sampling or doing other follow up surveys to locate actual source properties of interest. Additionally, the RMP piloted a project to explore the use of alternative un-manned “remote” suspended sediment samplers (the Hamlin and Walling Tube samplers), both of which are designed to enhance settling and capture of suspended sediment particles from the water column. Samples were collected at eight of the 70 locations using the remote Hamlin and Walling devices. The results of this pilot show that there is promise in using even lower cost, unattended sampling devices to identify urban stormwater drainages that are highly polluted with any pollutants that strongly attach to sediment particles such as PCBs and mercury, trace metals, phosphorus, PAHs, and chlorinated pesticides such as DDT, and modern use pesticides such as pyrethroids.
Alicia Gilbreath works in the Clean Water Program for the San Francisco Estuary Institute. She has primarily focused on high and low-intensity stormwater monitoring around the San Francisco Bay Area to identify highly polluted areas of interest and to support modeling to estimate pollutant loads into the estuary. Alicia is smitten with creeks, storm drains, ditches, and green infrastructure. Her most proud accomplishment: she has two 8-year old boys that love nothing more than throwing on their waders and heading outside for some fun during storms.