Common regulatory practices in onsite wastewater programs: a willing suspension of disbelief.
Estimated daily wastewater flow from residences is a common prescribed number in nearly every prescriptive onsite wastewater code. This number is expressed as gallons per day (GPD), is often prescribed as a "per bedroom" number, and literally dictates the ultimate "size" of an onsite wastewater system. The particular number varies wildly from jurisdiction to jurisdiction, but in general falls between 120 GPD per bedroom and 200 GPD per bedroom. A typical three-bedroom home, therefore, would have a projected daily flow of between 360 GPD and 600 GPD as the basic figure for calculating the overall size of the soil absorption system (a soil loading rate being the other variable). There is little debate that these projected usage figures are "conservative." The regulatory justification for "conservative" design standards of any ilk generally revolves around the potential variability among any group of circumstances. Water use among individual families certainly varies around some mean, and because these wastewater systems often serve only one single family, the wastewater system design criteria must lean, the argument goes, toward the excessive users.
Where, however, does the cost-benefit of being "conservative" cross the line toward the absurd? Unfortunately, we seldom ask ourselves these kinds of questions, even for this simple issue of wastewater volume. Taken from a property owner's perspective, however, the cost can be extraordinary. Our range of prescriptive flows cited above and calculated with a reasonable and common soil loading rate of 0.4 GPD/[ft.sup.2] for a conventional gravity-fed trench system could occupy between 2,500 and 3,500 square feet of a property, and the actual installation costs for these two systems would vary according to size, one being 1.4 times the other based on the different estimated flow figures. In my experience, perhaps more insidious but unfortunately less quantifiable, is the circumstance where a particular property does not provide "adequate space" for the required (prescribed size) wastewater system. That is, this one prescribed number is the basis upon which our regulatory system prohibits an owner from constructing the home he or she wishes to have. Sometimes alternative plans with fewer bedrooms are necessary, and often "bedrooms" are simply relabeled on a house plan to circumvent the prescribed requirements (I would like to compare the ratio of homes on sewer versus on onsite systems that have an "exercise room". ... no closet allowed, of course). Either way, the market value of the home is likely negatively impacted.
What is the real story regarding water usage? Most studies show per capita daily usage in the U.S. is between 40 and 60 gallons. A 1999 study of 1,200 households showed only 10% exceeded 100 GPD per capita, and one might imagine that the higher prescribed code numbers (200 GPD per bedroom) are established to include those marginal large flows just to be conservative. Our codes, however, tend to take these per capita numbers, adjust them for "safety," then assume each bedroom includes two water-consuming inhabitants because "it is possible." Our typical three-bedroom home is assumed, always, to have SIX occupants. In my view, that assumption and the potential consequences are where our standard system drifts toward the absurd, and where our defense of this methodology requires a continued willingness to suspend disbelief.
U.S. census data show the average household size is 2.6 people, but we recognize we cannot reasonably, for a single residence, adopt an average for practical application in this case. How common are households, however, that have six or more occupants, as we have assumed of our typical three-bedroom home? Census data identifying households of six or more have hovered around 3% of U.S households since 1990 (down rapidly from 11% in 1970). In onsite wastewater regulation, a three-bedroom home, sized for six liberal users of water, is infinitely more common than 3% of permit proposals.
In Illinois, the department of public health-prescribed daily wastewater flow is 200 GPD per bedroom, representing two occupants per bedroom with all occupants consuming water at virtually twice the per capita average. I am uncertain how a statistician might go about calculating the probability that these two demonstrably rare events coincide. I am willing to suggest, however, that this is rare enough that we (the regulatory community) should not expect every single property owner to shoulder the cost (in dollars and in disrupted dreams) of these statistical outliers. And yet that is precisely what we have done and continue to do.
And what is the monetary cost? I made that calculation on an annual basis for Illinois' citizens with a few reasonable assumptions. I only proposed that the Illinois 200 GPD/bedroom might be reduced to 120 GPD/bedroom (a more reasonable but still conservative prescriptive figure assuming six occupants in every home). I calculated that all included permits were for three-bedroom homes at 360 GPD rather than 600 GPD (some would be more and some less). I assumed the 0.4 GPD/[ft.sup.2] soil loading rate to calculate system size for all systems (some would be better, some worse). I took a $2.50 per square foot cost for installation (given to the department of public health by installation contractors in central Illinois). I only calculated cumulative excess cost between the 200 GPD and 120 GPD flows for new systems (I did not include repairs/replacement). That resulted in 4,900 new soil absorption systems (average per year) each with 900 [ft.sup.2] of absorption area rather than the current required 1,500 [ft.sup.2]. This "savings" to Illinois' citizens simply by adopting a "more reasonable" prescribed flow at $2.50 per square foot of installed absorption capacity is $1,500.00 per system and $7.35 million per year cumulative.
Now, my installer friends may not like a proposal to remove over $7 million from their annual Illinois revenue stream, and my regulator friends will have any number of reasons to justify these prescriptive figures (they have had this fight before with the property owner whose four-bedroom home just became two bedrooms, an exercise room, and a sewing room). Ultimately, however, it comes down to some (much .... most) of the regulatory community's unwillingness to participate in the "management" of onsite wastewater systems. That means providing options to property owners to control their water use (time dosing can set flow limits on an hourly daily or weekly basis), establishing oversight to assure system watertightness (no extraneous contributions to the wastewater volume), monitoring system performance and compliance with the accepted restrictions, and holding the property owner accountable if he or she does not meet their agreed-upon obligations. This makes our onsite wastewater programs an "activity" (ongoing), rather than an "event" (permit-inspect-forget). I know where there is over $7 million that the state of Illinois could scoop up (OK, maybe split with the property owners) every year to fund onsite wastewater activities.
Prescribed daily design flows are not the only element of our typical codes that should be dragged out into the light of day, so to speak. In my view, however, it is one of the more revealing examples of how this common regulatory program, and we who administer the programs, persistently resist being interrupted by facts and by reason. Batman lives!
Corresponding Author: Anthony Smithson, 287 Southfield, Vernon Hills, IL 60061.
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|Title Annotation:||GUEST COMMENTARY|
|Publication:||Journal of Environmental Health|
|Date:||Oct 1, 2010|
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