The above graph depicts actual data for three parameters of water pollution always associated with storm water runoff: BODs, CODs, and TSSs.
This useful graphic refers to a study of runoff from impervious urban surfaces, turning quantitative and temporal data into an easily understood picture.
Although the study that produced it is not about Hudson (Hudson’s data is discussed in the next section), the graph ably depicts the rate at which contaminants are removed from impervious surfaces during the kinds of rain events associated with summer cold fronts: violent thunder storms accompanied by sudden deluges (on the graph see “Time vs. Flow”).
This graph was chosen for the weather conditions that shaped it. Year after year, similar conditions threaten the integrity of Hudson’s waste water collection system, though only episodically and less so of late. Since Hudson expanded the capacity of its waste water treatment plant, the only “combined sewer overflows” of untreated sewage and runoff into the environment have occurred as the result of large summer thunderstorms.
(The only other condition which might stress the storage capacity of Hudson’s combined sewer system is a sudden snow melt, a test passed earlier this year without incident.)
Known as a study of First Flush Effect, changes in the concentration of hazardous compounds and pathogens found in runoff are determined by data collected before, during, and immediately after major wet-weather events.
During the single event depicted in the graph, notice how quickly the concentrations of Biological Oxygen Demand (BOD) drop off in relation to the volume of runoff caused by rainfall.
The drop in Total Suspended Solids (TSS) was less precipitous, but also impressive.
These are the rapid rates at which compounds found on all impervious urban surfaces were washed away by rain following three days of dry weather.
Where storm sewers feed into waste water treatment plants, as in Hudson, these environmentally hazardous compounds are captured by filtration. With Hudson’s newly expanded treatment plant, the collection system is nearly at an optimum regarding the waste water that the city generates.
But if city government has its way, this arrangement may soon change. Even though we have data recommending that we continue to capture these pollutants (and at evermore efficient rates), Hudson’s current grant application is conditioned on the goal of diverting all of the city’s runoff directly into the bays and river.
This has less to do with ecological science and common sense than it does available public money for engineering projects.
HUDSON’S SINGLE STUDY
In a three-month study of combined sewer overflows for the City of Hudson in 1979 (Cahn Engineers), data for BODs and TSSs were taken once in July and November, and thrice in September and October each.
Hudson’s First Flush Effect study was made available to the public in February of this year. Presumably Hudson’s data describes combined sewer discharges above and beyond the surface runoff depicted in the graph, but the rapid rates of decrease in BOD and TSS concentrations are the same in both studies, and so are the implications.
Because only huge summer downpours concern us here, the following were the City of Hudson’s First Flush Effect figures for July 31, 1979.
To match the above graph, Hudson’s numbers need only be multiplied by 10. But the key to understanding the rate at which contaminants are washed off Hudson’s surfaces is a ratio which expresses before and after conditions (where before means “peak pollutant concentrations generally found at the beginning of storms,” and after means “pollutant concentration after first flush subsides”).
Immediately preceding a rainstorm in Hudson in July 1979, the number for BODs was 133 mg/L, and for TSSs the figure was 385 mg/L.
75 minutes later, the figures for these compounds had dropped to 13.5 and 99 respectively.
For Biological Oxygen Demand, a ratio of 133/13.5 = 9.9
For Total Suspended Solids, a ratio of 385/99 = 3.9
Citing the “general guidelines” for estimating the magnitude of a first flush effect, the Cahn engineers identified as “large” anything above 4.0.
There is no reason to suspect that these rates would have changed since the 1979 study.
But even though “the magnitude of first flush” in Hudson can be large by standard measures of contaminant concentrations – which means that we’re already capturing most of these first flush contaminants for treatment – the city continues to guard its counter-intuitive plans which utterly disregard this data.
Based on ideas developed before Hudson’s treatment plant upgrade, the ultimate goal to dump all of the city’s runoff into the river unfiltered remains unchanged. The federal funding the city is currently seeking would move us nearer to the goal of abandoning the successful capture of first flush contaminants.
For residents of the City of Hudson, challenging old and fixed ideas – especially where easy money is concerned – always meets with stiff opposition. In the long term, this makes for an increasingly passive citizenry.
Even in the course of an official Public Hearing, the sort of politician who habitually excludes public participation may attempt to shut down what he derides as mere “opinion” that is “going far afield” (though the conclusions are drawn from the above pertinent data).
When a public comment is based on an empirical study which some may regret was ever made public (its release was due only to public pressure), it is all too often the case in Hudson that someone in a position of authority will still find some way to object.
The public has been forced to wait since 2003 for its right to weigh in on the sewer issues that were the subject of Thursday’s hearing, and which are discussed above. Technically speaking, that 11-year deprivation constitutes an injustice about which we’ll be hearing more.
Due to the unprofessional badgering of the public by a particularly domineering official, Thursday’s formal Public Hearing lasted less than 10 minutes. Of that injustice we shall also be hearing more.
Where the health of the environment is at stake, it’s more than fair to interrogate the motives of those who blatantly abuse their positions of power to harass and silence dissent.
Whether the motive is money or power, the negative environmental consequences of this kind of arrogant governance are always the same everywhere.