Monitoring Optical Brighteners Helps Track Watershed Pollution
The Lynnhaven River and its tributaries in Virginia Beach, VA, are currently in violation of the state’s water quality standards ...
The Lynnhaven River and its tributaries in Virginia Beach, VA, are currently in violation of the state’s water quality standards for fecal coliform bacteria and dissolved oxygen in shellfish waters. As a result, many segments of the river are listed as impaired on Virginia’s 303(d) Total Maximum Daily Load Priority List.
Sampling pads studied under black light. The control pad on the left is negative (no brighteners) and the one to the right tests positive.
To better understand the problem, in 2004 the City of Virginia Beach investigated potential sources of sanitary wastewater that may be entering the Lynnhaven River via the storm drainage system. The city’s consultant used an innovative technique to detect human waste signatures: monitoring for a particular class of dyes added to many laundry detergents.
Optical Brightener Monitoring
Optical brightener monitoring (OBM) is a promising new technique to screen for a surrogate of human bacterial contamination in storm drainage outfalls and receiving waters. Optical brighteners are dyes that are added to many laundry detergents. These brighteners adsorb onto natural fibers and cause them to appear whiter. Since laundry effluent is predominantly associated with sanitary wastewater, and since optical brighteners (OBs) decompose relatively slowly, they serve as ideal indicators of illicit discharges in storm drains.
While these dyes are invisible to the naked eye, they appear as an easily detectable bright glow under an ordinary black light. Storm drain outfalls that consistently tests positive for the presence of OBs are likely to have one or more sources of sanitary wastewater in the upstream collection system.
Apart from detecting OBs, there are other analytes characteristic of sanitary wastewater, such as caffeine, nicotine, pharmaceutical and personal care products. Currently, there are no cost-effective standard testing methods established for these agents. One main difference between testing for OBs and other analytes is that OBM is not just a “grab sample.” For locations that are not tidally influenced, sample collection devices are left in place for a period of seven to 10 days and a composite sample is collected, integrating data across that period of interest.
Although OBM has its merits as a screening tool, it has limitations. It is not likely to detect sanitary wastewater from most commercial buildings, which often lack laundry facilities. Also, if the centralized laundry rooms in apartment complexes have a separate discharge point and plumbing, then depending on the actual sampling point there is the possibility that the discharge could go undetected.
The required equipment and testing set-up for OBM are relatively simple, and chief among them are:
- brightener-free cotton pads available from any scientific laboratory,
- sampling cages made of galvanized steel wire mesh, interlock snap swivel hooks, and monofilament fishing lines,
- liquid nails to avoid causing damage to structures, and
- a 4-6 watt long-wave fluorescent ultraviolet light for analyzing the samples.
Monitoring for OB is a simple procedure. Optical brightener-free cotton pads are used to monitor storm sewer outfalls. If the retrieved sample pad glows under a long-wave ultraviolet black light, the premise is made that there is an illicit discharge of sanitary wastewater in the system.
In-house testing was conducted using optical brightener-free cotton pads to determine the intensity of the fluorescent reaction for various detergent dilution levels and pad exposure times. Commercially available laundry detergent was used to prepare solutions with concentrations ranging from 1 ounce of detergent in 50 gallons of water to 10 ounces of detergent in 1 gallon of water. Exposure times of one minute, five minutes, and one hour were selected. A sterile, OB-free cotton pad was used in each test. After the pad was allowed to dry in a dark room, each pad was viewed under the UV light and assigned a rank ranging from 0 to 5, where 0 = no sign of optical brightener and 5 = strongest visibility of optical brightener.
Also, in order to compare the consistency of results obtained by different testers, two independent readings were taken for each sample. The first reading was taken immediately after the samples had dried. The presence of OBs was detected on every sampling pad, even on the most diluted solution exposed for a minute. A different person performed the second reading three days later. The results of the second reading were lower than those of the first test reading, possibly due to break down of the optical brighteners over time.
Optical brightener monitoring sampling sites in the Lynnhaven River Watershed.
This exercise of in-house testing was performed to determine the feasibility of collecting grab (instantaneous) samples for those sites subject to tidal conditions. Outfalls subject to tidal conditions pose problems for OBM, since what is being monitored may in fact be due to contamination in the river and not the storm drainage system. As such, a logical solution is to collect grab samples at these sites. In the grab sampling effort, the OB-free cotton pads were dunked in the outfalls for a couple of minutes and retrieved for drying and analysis. Grab sampling was conducted on the premise that OBs can be detected on a sampling pad in the most diluted solution exposed for a minute.
Monitoring, Site Selection
Base maps of storm water drainage and sanitary sewerage systems were obtained from the city, including planimetrics, street centerlines and the Lynnhaven River Watershed boundary. The initial set of 25 sampling sites were located on storm sewer outfalls leading into the Western Branch of the Lynnhaven River and the next set of 25 sites were located on the Eastern Branch of the Lynnhaven River.
In the initial set of sampling locations, approximately 21 miles of storm sewer running parallel to sanitary sewers were studied. In the second set of locations, approximately 16 miles of storm sewer running parallel to sanitary sewers were studied.
In general a sampling site was selected using the following guidelines:
- those areas served by both storm sewer and sanitary sewerage systems,
- outfalls where the sanitary and storm sewers run parallel for a significant distance and/or cross each other at several locations,
- ease of access at the site, and
- provided outfall is not tidally influenced.
Field crews carried detailed maps of each sampling location showing the storm sewer system upstream of the outfall location. If the site conditions were different than initially assessed, such as tidal influence at the outfall, lake backwater effects, or difficult access, the field crew moved upstream of the outfall until they located a drainage structure with favorable conditions. If a structure with favorable conditions was not located within a few hundred feet of the outfall, the field crew discarded the sampling location.
Great care was exercised to ensure that the monitoring data collected was of good quality. Special care was taken when handling the samples to prevent cross-contamination. Once the samples were retrieved and dried, they were observed under a black light twice before the results were recorded.
Of these 50 locations, eight sites tested positive for the presence of optical brighteners in the initial sampling. To confirm initial readings and pinpoint the sources of sanitary sewage entering the storm sewer system, more detailed OB monitoring was performed at those sampling sites and the associated upstream storm sewer systems. Based on the results of the detailed monitoring, seven sites have potential contamination from sanitary wastewater.
At 14 outfalls subjected to tidal conditions, grab sampling was performed. Of these locations, five sites tested positive for presence of optical brighteners.
Optical brightener monitoring is an emerging technique to quickly and cost-effectively detect the contamination of stormwater by sanitary wastewater. Unlike more expensive techniques, OBM facilitates a more comprehensive survey of the study area. Results obtained through this study of the Lynnhaven River Watershed will help to plan and implement effective local actions to improve water quality and safeguard public health. WW
About the Authors:
Seshadri Iyer is Senior Water Resources Engineer, URS Corp. He may be contacted at e-mail: email@example.com. Michael Barbachem is Vice President, URS Corp. ; e-mail: firstname.lastname@example.org. Steve McLaughlin is Project Manager, City of Virginia Beach, Dept. of Public Works and Engineering; e-mail: email@example.com. William Johnston is Stormwater Administrator, City of Virginia Beach; e-mail: firstname.lastname@example.org