| 
|
By David Venhuizen, P.E.
I’ve been corresponding with this vendor of composting toilets who tirelessly repeats the theme that we “shouldn’t” be flushing water to create wastewater, that most of our wastewater management problems would go away if we “just” stopped doing that. In a recent exchange, I retorted that the question of what is the least problematic method of management—flushing our wastes with water and reclaiming it, or not using the water to begin with by employing alternative technology—is amenable to engineering analysis. I suggested that when that analysis is executed—and it indeed shows that using composting toilets is the superior option—then he may assert that using flush toilets is as inherently “evil” as he claims. “It seems that our problem in attempting to communicate about this matter,” I wrote, “is that you begin with that premise, based upon ideology, rather than arrive at it, based upon an engineering analysis.”
As I reflected on that, it struck me that the field of onsite wastewater treatment is rife with situations just like this, where ideology pre-empts engineering. This is generally true of the field as a whole—the “dichotomy view” that I wrote about a couple issues ago is a case in point—and is true in regard to many of the details. And, indeed, we do have a widespread problem in this field when attempting to communicate on the level of engineering because of the sway that ideology holds.
An example is a recent encounter with a state regulatory system, when it was suggested that a low-pressure-dosed (LPD) field be used for a project. It is a matter of some curiosity to me that, while most regulatory jurisdictions recognize the concept of pressure distribution within a dispersal field, very few recognize the LPD concept, as it is set forth in the publication out of North Carolina State University, Design and Installation of Low-Pressure Pipe Waste Treatment Systems (1982). For those not familiar with the concept, it proposes the use of very narrow trenches, which are fairly shallow. Effluent is intermittently pressure-dosed into these trenches through small-diameter, perforated PVC pipes, enforcing a dose/rest loading cycle and assuring that—unlike in the conventional gravity trench—the entire field area, including much of the trench sidewall, is always engaged in the dispersal process. The concept thus actuates the three main criteria that have been observed to enhance soil treatment mechanisms: uniform distribution, dosing and resting cycles, and shallow placement of effluent in the root zone. This was a major engineering advancement in this field, and one that has been practiced for over 20 years. Rampant failures resulting from use of this method have not been reported, so one is left to presume that the operating theory is sound and this concept is indeed a valuable addition to our “toolbox.” Thus, based upon engineering analysis, it should be a readily accepted concept. Anywhere.
However, the rules in the state in question do not recognize the concept and require a minimum trench width of 1 foot. This was not based on engineering analysis, finding that the concept as presented in that manual was “wrong”; it is simply an article of their ideology that trenches “must” be at least that wide. Since it was made quite clear that this—or any other—rule of that state would not be changed, or even varied, no matter what engineering analysis was provided to support a change, one might say that the entire rule system of that state is an ideology.
This sort of thing is not at all uncommon. In two other states, I encountered rules that require all on-lot systems to use a design flow criterion of 200 gallons/day/bedroom in one case and of 212.5 gallons/day/bedroom in the other, both ridiculously high amounts. Looking into it, I found that this is driven by an ideology that the methods used for on-lot wastewater management cannot be trusted, and in particular, the soil loading rates were seen as no better than a wild guess, so a huge “factor of safety” was being applied. Rather than apply engineering analysis to derive methods that would work and then implementing the institutions to support them, or even simply rationalize the soil loading rates, the rule-writers chose to “penalize” all systems of any type by requiring them to be hugely oversized—a triumph of ideology over engineering that actually retards the supposed goal of that ideology by fiscally discouraging improved systems that could cope with problematic conditions.
Drip irrigation dispersal is another method that seems to be regulated more by ideology than by engineering analysis. In two states, I have seen rules for drip irrigation that were very obviously written around a specific commercial “package” and in each case, the specification of equipment presupposed that the effluent routed to the drip irrigation field would be poorly treated, containing significant levels of solids—again the ideology that no on-lot treatment method is to be trusted. So all systems using drip irrigation, regardless of the quality and reliability of the pretreatment system employed, have to use a drip system that may be needlessly costly, needlessly complex—and thus needlessly failure-prone—and needlessly expensive to operate and maintain. The end result of these ideologically driven rules is that the use of drip irrigation—the method that practically maximizes those three principles of optimal soil treatment noted above—is retarded, almost certainly to the detriment of public health and environmental values.
Design standards applied to drip irrigation fields is another area where ideology often trumps any sort of rational engineering analysis. In one state, a drip irrigation field following at least secondary pretreatment may be installed with as little as 6 inches of soil between the drip emitters and a limiting condition. While we will not belabor it here, the best science available indeed indicates that this is a sound decision, at least if the pretreatment system is a sand filter. However, this same rule system also requires that a drip emitter may be installed no closer than 10 feet from a slope break where a seep might occur. Matric potential is the only force that can draw water laterally any distance from the emitter, but this would be highly unsaturated flow, which would never produce a seep. There is no force that would cause water coming out of a drip emitter to be driven even one foot sideways, as saturated flow that could produce a seep, before it could traverse at least a 6-inch vertical depth through the soil. And if the water is good to go into the groundwater after traversing the 6-inch vertical depth, what possible hazard could it pose even if it did surface in a seep at the edge of the field? But the ideology is that the slightest possibility of any seep containing any effluent-derived water is a hazard. This ideology is of course rooted in concerns about conventional dispersal fields receiving septic tank effluent. Engineering analysis of the actual situation is simply not considered—the ideology is blind to that.
A hoped-for antidote to this problem of ideology negating engineering is to go to a “performance code.” One must question, however, if a performance code would ever be adopted, given what a tight hold ideology seems to have on rules systems. There would have to be wholesale modifications of not just the rule language but also the very philosophy of the rules systems, and I have not observed that either “the heart” or an understanding of the need for it exists to tackle this endeavor in most states. On-lot wastewater management is simply not a high enough priority to merit the effort. And that itself is an ideology.
So our composter salesman friend can be forgiven, I guess, for hewing to an ideology that sees flush toilets as unfailingly evil without any regard to context or practicality, as the entire field of onsite wastewater treatment is dominated by people and institutions that hew to ideologies without any regard to practical outcomes; the preceding examples are just a small sampling. In many, if not most, cases these ideologies will not move aside to even allow engineering analysis to shed light on the matter, much less to displace the ideology. If we expect to see progress and expansion of this field and, thus, more opportunities to enhance the bottom lines of practitioners in this field, that fealty to ideology at the expense of engineering must be eliminated. As noted, that is a huge challenge, perhaps the greatest one facing this field.
DAVID VENHUIZEN, P.E., is based in Austin, TX. Comments,
suggestions, and your own anecdotes about this field can be
sent to Venhuizen at waterguy@venhuizen-ww.com.
OW - November/December 2005 |
