(477d) Experimental Investigation Using a Contaminant-Monitoring Sytem in Storm Drains: A Dichotomous Preliminary Risk Assessment

As humans have built cities using concrete, asphalt, and large areas of impervious materials, they have potentially disturbed the normal hydrologic circle, and have learned that they must build storm drains to convey excess rainwater and prevent flooding.  But these storm drains have a drawback in that they can also lead to pollution of natural environments if they carry contaminants such as antifreeze, fertilizers, paints, used motor oil, tossed pet waste, cigarette butts, and litter. Everything other than pure water is a potential contaminant that degrades water quality. Pollution sources entering storm drains include: automobile emissions, residential wastes, agricultural runoff, urban activities, construction runoff, and businesses [Hyperspective Studios, 2002].

In the summer of 2010, in conjunction with the UAB Occupational Health and Safety (OHS) Department, Dr. Robert W. Peters, and two of his graduate students conducted a project involving a risk assessment of contamination of runoff water flowing into storm drains on the UAB campus [Lackey et al., 2010].  The project was successful enough to spin off into further studies but it had one key shortcoming: it considered only the effects of point sources on storm drains and largely ignored the effects of non-point sources.  The details of that study, as well as the steps that will be taken to address that shortcoming, and what further studies the results will lead to, are listed below.

To begin the study, the UAB OH&S Department gave the civil engineering graduate research assistants a series of overhead maps of the UAB campus that have marked storm drain inlet locations from a previous study. The study took place over two main strategic areas on the UAB campus, one that contained the majority of storm drains on the western academic side of campus, and the other that contained the majority of the storm drains on the eastern side of campus which is more focused on medical research.  The students were helped by the inlet locations provided on the maps by O&HS, but there were several differences between the locations given on each map and the actual locations of the inlets. Therefore, the project involved an update on the actual locations of each inlet as well as a risk assessment of the likelihood of dumping unwanted chemicals.

In the study, the students identified four main types of inlets:

1. Standard Covered Curbside: The type that contain a concrete or iron cover and engulf large volumes of water from adjacent roadways and parking lots during a rainstorm.
2. Uncovered Grate: These are often found in the middle of parking lots or on pedestrian walkways. Occasionally, these are even found in grassy areas where irrigation is common.
3. Combination Curbside Grate:  Essentially a combination of Types A and B, these are found in the same areas as Type A.
4. Elongated Grate: Found in the same types of areas as Type B, and extremely common at entrances of parking decks.

In addition to the types, each inlet was also assigned a risk assessment value of 0 to 3 based on the priority of its labeling. A color was assigned to each as well for easier readability:

0   (blue) – Marker already present on drain inlet

1   (green) – Low dumping risk

2   (yellow) – Moderate dumping risk

3   (red) – High dumping risk

Some of the criteria for determination of the risk as 1, 2, or 3 are as follows:

1. Default condition; generally assigned unless the inlet was near a probable pollution source such as a trash receptacle, dumpster, laboratory entrance, or parking space.
2. Assigned if the inlet was near a potential moderate pollution source, such as a laboratory entrance or trash can, or if the inlet was on or adjacent to a parking space.
3. Assigned if the inlet was next to a dumpster or other probable major pollution source, or two conditions or more that would result in “2” applied.

The major results of the study, in terms of number of inlets of each type and risk factor, are displayed below in Table 1 and Table 2.

                                                     Table 1. Summary of type and risk factor of inlets in Strategic Area 1 (Main Campus).

Table 2. Summary of type and risk factor of inlets in Strategic Area 2 (Medical Campus). 

In late 2012, the O&HS department decided that they not only want to install warning stencils on the UAB campus, but also sensors that would detect whenever harmful chemicals are present.  The idea was expanded on to not only call for "artificial nose" chemical sensors but also a contaminant monitoring system that would map out the data from each sensor in real-time and send alerts to concerned parties whenever harmful chemicals are detected.  Despite an initiative to cut costs as much as possible, the budget only calls for 50 of these "artifical noses".  Therefore, priority needs to be assigned to the drains most in need of monitoring.  When determining this, it turns out that anthropogenic point sources that result from dumping, while being the best criteria for whether or not to use a warning stencil, are not neccessarily the best criteria to decide whether a storm drain is a good candidate for a contaminant monitoring system, or at least not the only criteria.  In order to complete the picture, non-point sources such as emissions from traffic must also be considered.  O&HS has determined that 11th Avenue and University Boulevard are the roads on the UAB campus that have the highest traffic, and therefore the most at risk for contamination by traffic emissions.  Some other adjacent roads have also been determined to have significant traffic. 

Therefore, it would be best to expand the study to a two-phase, or dichotomous, risk assessment.  The scale will be expanded from 1-5, and storm drains which are adjacent to high-traffic roads will have their risk factor raised by two, while storm drains which are adjacent to medium-traffic roads will have their risk factor raised by one.  The new scale will become:

0: marked storm drain not on a high-or-medium-traffic road.

1: unmarked low point-source risk storm drain not on a high-or-medium-traffic road or marked storm drain on a medium-traffic road.

2: unmarked medium point-source risk storm drain not on a high-or-medium-traffic road, unmarked low point-source risk storm drain on a medium-traffic road, or marked storm drain on a high-traffic road.

3: unmarked high point-source risk storm drain not on a high-or-medium-traffic road, unmarked medium point-source risk storm drain on a medium-traffic road, or unmarked low point-source risk storm drain on a high-traffic road.

4: unmarked high point-source risk storm drain on a medium-traffic road, or unmarked medium point-source risk storm drain on a high-traffic road.

5: unmarked high point-source risk storm drain on a high-traffic road.

Storm drains which receive overall risk values of 5 will be the first to be monitored, followe.d by those with values of 4, and then those with values of 3, either until all 50 sensors have been placed or those of the 50 not meant to monitor "blank" base cases will be used.  A "blank" would be one assigned a risk value of 0 or 1 that is used to determine if labeling or proximity to either point or non-point sources really does have an effect on contamination.  And once the target drains are determined, the next phase of the project, which involves installing the sensors into the storm drains and beginning to analyze data generated by the contaminant-monitoring system, may proceed.

References Cited:

Hyperspective Studios, 2002. “Storm Drains”, website: http://protectingwater,com/storm-darins.html; website accessed: October 16, 2012.

Lackey, D.A., A.N. Kajale, R.W. Peters, and J.D. Hagan, 2010. “The Effects of Labeling Storm Drains on the University of Alabama at Birmingham Campus”, Poster paper presented at the Alabama Water Resources Conference, Orange Beach, Alabama (September 8-10).