Archive for March 2013

Slashing pollution, saving water – the classic win-win (but ignored by society)

March 24, 2013

In this entry, we’re going small-bore, looking at a rather localized and somewhat parochial issue. But one that highlights some of the challenges we face in moving society toward sustainable water, in stimulating deep conservation.

Barton Springs is the natural discharge point of the Barton Springs segment of the Edwards Aquifer, which lies to the south/southwest of Austin, Texas. Nitrate levels in Barton Springs have been increasing in recent years. And, according to a USGS report, a good deal of it is from wastewater sources. Who could have guessed? I mean, besides anyone who gave this matter a moment’s notice.

Nitrate in BSZ-USGS

The graphic above shows the growth of those wastewater sources from 1990 to 2010. The top line of graphics shows the growth in number of OSSFs. That stands for on-site sewage facility, the Texas rules-speak name for what are popularly known as “septic” systems. The bottom line shows TLAP systems. That stands for Texas land application permit. In this type of wastewater system, the effluent is spewed out over an area that is “irrigated” mainly just to make the water go “away” rather than for an actual irrigation benefit, such as an improved landscape or growing a marketable crop. In the most used type of “septic” system – consisting of an “aerobic treatment unit” (ATU) and a couple of spray rotors – the wastewater is also spewed out over the ground, with little regard for the value of the water, or of the environmental impacts. Such as increasing the nitrate levels in Barton Springs.

As these graphics show, the density of the “septic” systems has increased very dramatically over the 2 decades they cover. Growth in the number of TLAP systems, while not so dramatic, was also considerable. Given the nature of those systems, spewing the water over land surfaces that, in the case of OSSFs, are not “qualified” at all and, in the case of TLAPs, are addressed in a rather cursory manner, it should not have been the least bit surprising that nitrate levels would be rising in the waters that drain out of this watershed. Indeed, particularly when combined with increases in pollution it was known would occur simply because development was occurring there, it should have been readily anticipated that this would be so.

The level of nitrate in Barton Springs is approaching 2 mg/L. The often quoted limit for nitrate in drinking water is 10 mg/L. This is what is termed the “enforcement limit”, the level at which definitive action would be required to reduce nitrate loadings into the groundwater. But there is another limit in the rules, 2 mg/L, which is termed the “preventative action limit”. That is the level at which actions to stem the shedding of nitrate into the groundwater – preventative action – are to be considered. We are there!  So it’s time to start taking preventative action, no?

The tragedy here is that this did not have to happen. Preventative action has been available all throughout those 2 decades. Wastewater could have been managed by means which would have greatly blunted, perhaps essentially eliminated, the shedding of nitrates from these wastewater sources. AND this could have been done at very low overall cost, perhaps at NO cost – or even at a savings – in terms of global life-cycle costs of this water management function, while at the same time conserving water. In any case, the tide can certainly be turned going forward by moving practice to those methods.

First, here is what is wrong with the currently prevailing methods. The ATU employs a technology, activated sludge, which is inherently unstable, and so typically suffers “excursions” in its treatment quality, particularly when used in the essentially unsupervised on-lot environment. As my realtor cousin once said of them, “They puke solids.” In any case, the ATU does not remove nitrogen from the wastewater. Spraying this effluent over the ground surface also limits the amount of denitrification – the biologically-mediated conversion of nitrate to nitrogen gas – attained in the soil. These on-lot systems spew the effluent onto the ground without regard to whether it’s raining or how wet the ground is. All this results in a nitrate-rich effluent being dispersed in a manner that heightens the likelihood a good bit of it would be shed, rather than assimilated in the plant/soil ecology, and so would appear in the waters that drain from this watershed.

That shedding of nitrate can be greatly blunted, perhaps even essentially eliminated, by a shift in the type of OSSF used. First, a treatment unit employing recirculating gravel filter (RGF) technology can be designed to remove a majority of the nitrogen from the wastewater prior to dispersal. This is a very robust, inherently stable treatment process, so it can consistently produce this high-quality, denitrified effluent in the lightly supervised on-lot operating environment. The major proof-of-concept field study of this technology was a project I ran on Washington Island, Wisconsin, in which nitrogen reduction of over 60%, and in some cases approaching 90%, was consistently achieved by systems subject to all the vagaries of operating in the on-lot environment. So using the RGF instead of the ATU for treatment will eliminate over half the nitrogen loadings prior to dispersal, consistently and reliably.

Then, instead of spewing it into the air, this effluent can be dispersed in a subsurface drip irrigation field. With the level of nitrogen in the effluent reduced, it is much more evenly matched to the uptake rate by plants. This dispersal method will also enhance in-soil denitrification. Together, these assure consistently more complete assimilation of the nitrogen that is dispersed into the soil. And subsurface dispersal eliminates runoff of effluent during rainy weather. The result is that very little nitrate will leach or flow “away” to appear in the waters that drain from the watershed.

The RGF/drip strategy is also a deep conservation measure, that can move us toward sustainable water. Drip rather than spray dispersal can greatly serve the water economy by displacing potable water with this effluent to defray irrigation demands. Because spray dispersal entails a potential for contact with this partly treated water (which is also questionably disinfected, the reasons for which we won’t get into here), the spray heads are set away from the house, off somewhere on the lot where they won’t be “obtrusive”. But the improved landscaping, the plants that might be irrigated in any case, are typically up around the house, so these spray systems are hardly ever arrayed to serve that landscaping. Because the drip lines are subsurface, there is very low contact hazard, so the water can be dispersed anywhere on the lot where the owner chooses to install irrigated landscaping, and the effluent routed to that drip field would defray irrigation usage, pretty much gallon for gallon through the peak irrigation season.

Also, irrigation efficiency of drip is inherently much greater than for spray. In any case, the rules require the design dispersal rate for spray systems to be very low, so not much irrigation benefit could be derived even if it did operate at higher efficiency. The rules allow the application rate for drip to be significantly higher, much more in line with irrigation rates through the peak irrigation season. So, in combination with the high irrigation efficiency of drip, a much higher irrigation benefit can be derived from drip dispersal.

Further, the rules do not require the area over which effluent is sprayed to be “qualified” in any meaningful way, in regard to soil depths and plant cover. In contrast, drip fields must have at least 6 inches of soil beneath the drip lines and 6 inches of cover over them. In the Hill Country terrain of the Barton Springs watershed, this often requires importing soil to attain these depths. Soil is often “enhanced” to create improved landscaping in any case, so with drip the OSSF dispersal field is typically placed in the best soils available on the lot. Better soil increases irrigation efficiency by providing more soil moisture storage capacity, and with there being more soil volume to “absorb” the water even when the soil is already wet from rainfall, it provides for better assimilation of nutrients.

The bottom line is that with higher quality pretreatment, including significant nitrogen reduction, and drip dispersal, the shedding of nitrate would be greatly blunted, if not essentially eliminated, and a very high percentage of the annual effluent flow could contribute to defraying water used for irrigation. The first benefit would halt whatever portion of the nitrate increases in Barton Springs that have been due to OSSFs. The second benefit is a bonus, one that is very valuable to this water-challenged region. I’ve been designing this type of OSSF for over 20 years, and it has been approved by all the local jurisdictions. Therefore, it is clear that these are benefits which can be readily realized, which could have been attained all along.

So why weren’t they? We won’t belabor the details here, but the installed cost of the RGF/drip system would be somewhat higher than an ATU/spray system. And that’s why the latter are so ubiquitous, because first cost typically rules the day. However, the life-cycle costs would be similar, at least if the cost of the water saved is taken into account. (Whether the cost of that water shows up on a monthly bill would depend on if the home were served by a well or by a piped water system.) Other savings derive from much lower power costs (also a benefit in regard to energy sustainability), from lower equipment replacement costs, and from not requiring chlorine for disinfection (another insult to the environment that is avoided by subsurface drip systems). So nitrate reduction could be realized at very low, or no, cost on a global, life-cycle basis.  Again, the barrier is first cost.

These same technologies could be just as readily used in those TLAP systems. In those systems, land application is, in theory, operated so that nitrogen loadings match plant uptake and in-soil denitrification rates. That could be much more readily, and cost efficiently, attained using the denitrifying RGF system for treatment and subsurface drip irrigation for dispersal. The shedding of nitrate could be further attenuated by placing the drip fields in areas that would be irrigated in any case. This improved landscaping would have better soils than the rangeland and cedar breaks typically constituting the dispersal fields in TLAP systems, to which the water is routed simply to make it go “away”, with no intent of defraying irrigation water usage in the development the TLAP system serves.

Again, the RGF/drip strategy is an exemplar of deep conservation – integrating water efficient practices, instead of water wasting practices, into the very fabric of development. Indeed it could be called to question why any responsible entity in this increasingly water-challenged region would allow water to be so gratuitously wasted, when there are readily available – and globally cost efficient – methods that can blunt that water waste, to realize the resource value of what is now being so foolishly managed solely and exclusively as if it were a nuisance. That both state and local regulatory systems embrace and support those wasteful methods is testament to the institutional resistance to deep conservation.

Going forward, however, a win-win situation is there for the taking. At the same time that water use efficiency could be greatly enhanced, further increases in nitrate being shed into this watershed can be essentially eliminated by shifting to the appropriate technologies. Over time, the existing sources could also be phased out. As people come to value the water being thrown away in their sprayfields, the spray systems may be replaced with drip irrigation fields, arrayed to irrigate their highest value landscaping.

This could be spurred on if there continue to be water curtailments due to drought, since the drip field would “drought-proof” the landscaping it serves. That’s because water curtailments in all the local drought contingency plans impact only exterior water use. The wastewater dispersed in the drip field would derive from interior water use, which is not curtailed, so the landscaping over the drip field could continue to be irrigated through the drought.

Then too, as the ATUs wear out, or the owners get tired of the frequent replacement costs (or the stench they often produce), they could be retrofitted to an RGF, obtaining the nitrogen reductions in the treatment system as well. Together with the drip field replacing the spray system, again this would greatly blunt, if not essentially eliminate, the nitrate being shed by the existing OSSFs.

This is a fairly impressive list of benefits, for both water quality and water quantity, from simply plugging in the appropriate technologies for the circumstances at hand. As noted, the barrier is the first cost of those appropriate technologies, along with the inertia of the wastewater management field of practice, and the sad fact that ATU/spray systems are accorded what amounts to a “most favored status” in the OSSF rules system in Texas.

The latter two factors are matters of reforming the “culture” of the field, but the first cost issue is a ubiquitous problem in regard to all manner of efforts to enhance water sustainability. Society has not figured out how to send to those who incur the first costs the signal sent by the global life-cycle costs. The result is that choices are made which may well serve the short-term interests of those who bear those first costs but poorly serve the long-term best interests of society.

A solution to that conundrum could be provided by appropriate regulation to attain ends which do serve the long-term best interests of society. Like requiring OSSFs in nitrogen-sensitive watersheds to meet nitrogen reduction standards, while simultaneously significantly defraying irrigation demands on “original” water supplies. Here in Texas, society has not yet gotten around to considering its long-term best interests in these regards. So we’ve seen, and no doubt will continue to see, increases in the level of nitrate measured in Barton Springs. And all that water running through those wastewater systems will continue to be indeed wasted.

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Irrigation Efficiency – a new “reservoir” for your city

March 11, 2013

Let’s start this one with a BIG NUMBER. To quote the web site of the Alliance for Water Efficiency, “The efficiency of overhead irrigation, such as rotors and pop-up sprayheads, is typically 50 percent and rarely exceeds 70 percent. The efficiency of a well-designed drip irrigation system can reach nearly 100 percent.” This indicates that irrigation efficiency could be as much as DOUBLED by converting to drip. Or, to put it more graphically, the same amount of irrigation would be accomplished using HALF THE WATER! System-wide, that would be a VERY BIG number.

OLYMPUS DIGITAL CAMERA

But wait a minute. Take a close look at the irrigation “system” in the above picture, a not at all atypical scene along the streets of my city, Austin. That 50-70% efficiency estimate is for a “designed” spray system – using rotors and spray heads, laid out in a pattern that provides head-to-head throw of water, uniformly covering the area to be irrigated, and hopefully with the spray arcs set so that very little water sprays over areas not intended to be irrigated, like sidewalks and driveways. What do you suppose the “efficiency” of the spray operation in the picture would be, spreading much of the water on the sidewalk and street? Maybe 20%? Or less?!

Now sure this picture was selected exactly because it serves as a particularly bad example, but as noted it is not all that atypical. One morning, I rode my bike through my South Austin neighborhood and took note of all the irrigation going on that day, at about 25 houses in all. Of those, only a couple were “solid set” systems using pop-up spray heads. The rest were hose-end sprinkler applications. And in only one of the operating systems was there no overspray onto pavement! Most of them were dropping A LOT of the water onto pavement, creating rivulets running along the curb, just like we see in that picture above. It’s a small sample of the entire city, to be sure, but it indicates that these low-efficiency operations are more common than well-designed spray systems.

So it may be that converting those irrigation operations to subsurface drip would perhaps TRIPLE – or more – the efficiency. System-wide, that is a VERY, VERY BIG number! As the title of this piece notes, it would be sort of like a whole new “reservoir” for your city’s water supply.

A “reservoir” of relieved capacity at just time it is most needed! That’s because water savings obtained by increasing irrigation efficiency comes directly off the peak demand, since that is driven almost exclusively by irrigation water use in this region. And it was purported by the City of Austin that a growth in peak demand created the need to build the new water treatment plant it is presently constructing sooner rather than later. So, as is no doubt the case in many cities, measures to increase irrigation efficiency would be particularly valuable to the overall system, allowing sufficient service to be provided without having to increase their peak supply capacity. Yet these measures generally remain quite neglected, in terms of any programs explicitly aimed to stimulate, promote or require them.

This highlights that increasing the efficiency of irrigation operations could be a huge water saver. Not in one big fell swoop, but by the multiplicity of many, many small actions. And that is probably why aggressively pursuing irrigation efficiency has been pretty much neglected as a part of most city’s water conservation programs – it would require the stimulation of many individual actions, through education, incentives and/or mandates. The city bureaucracies no doubt consider that “too hard” – much easier to just build more capacity, which is under its unilateral control, they think, even though an ever-expanding supply is not sustainable. And, as just noted, is unlikely to be the most cost efficient strategy. To move toward sustainable water, it’s clear we will have to take on “distributed” measures like irrigation efficiency at some point. So why not now, BEFORE we put ourselves in hock for expanded peak supply capacity that could be avoided?

The application efficiency – accurately routing the water onto the plants you want to irrigate – is only part of the overall efficiency. Other aspects must also be addressed to maximize the savings. One of them is the quality and depth of the soil. The more soil over the irrigated area and the higher its “sponge effect”, the more water it can hold, so more water would be held in the soil until the plant roots can take it up, rather than draining through the soil and being lost to the plants. Because more depth of good quality soil also allows more rainwater to infiltrate and holds more rainfall in the root zone, irrigation can be delayed longer after a rainfall, also saving water. And because improving the soil reduces runoff, so blunting stormwater management problems, it’s a win-win-win sort of strategy.

Requiring a minimum depth of soil was urged by a resolution of Austin’s Resource Management Commission in early 2006, and was considered by the water conservation task force later that year, but it wasn’t included in the water conservation program, reportedly due to objections from builders. You see, builders are totally focused on the installation cost and aren’t impacted by the long-term costs of having to “over-water” because there’s not much soil there to hold the water. So the city, in its infinite wisdom, chose not to impose that cost on the builders, rather to in effect subsidize them by enduring the inefficient irrigation that results, so driving a perceived need to provide more water treatment capacity, for which the rest of us will pay.

This illustrates the insidious nature of allowing today’s first cost issues to dominate what should be a long-term strategy. This is a ubiquitous problem plaguing many efforts to instill deep conservation practices.

Another aspect of irrigation efficiency is watering at the optimum time. You don’t want to lose water to runoff or leaching below the root zone because watering took place when the soil was still “too wet” – either because the area had been recently watered or because there had been recent rainfall. To maximize this aspect of efficiency requires either real-time expert management, consistently applied – which simply does not happen, is not practical, for most irrigation systems – or using an irrigation control system which can sense when irrigation is needed. “Smart” irrigation control systems that can do this are readily available, and are cost efficient for high usage systems, where savings would be most significant.

All these factors highlight the importance of good system design. As noted, it is likely that a lot of irrigation water runs through systems that are not designed at all, rather are simply a movable sprinkler at the end of a hose.

As noted, those hose-end systems may operate at very low efficiency. Look again at the picture, at the low regard for watering efficiency exhibited by setting the sprinkler on the sidewalk. Now I would speculate that the person who did this is not doing it because he is dumb, rather he is simply using the piece of equipment that he has, to get water onto the parkway strip between the sidewalk and the street. He is doing this, so gratuitously wasting a lot of water, rather than financing a highly efficient drip irrigation system, which is exactly the best way to water areas like the parkway strip between the sidewalk and the street in that picture. And no one is really telling him he should not be wasting water like that.

The Austin Water utility’s propaganda does say that intentionally spreading water on pavement is considered illegal, so I don’t mean that literally no one is telling this person that “irrigating the sidewalk” is not legal. I mean that he is not receiving any signal through either the billing system or through any incentive program that wasting water in this manner is not in the public interest, that it is so economically inefficient, that he – and all the rest of us – are paying for his wastefulness by financing increased water supply capacity, needed only for peak demands that are driven by that wastefulness.

It is also notable that considerable efficiency may be gained simply by better educating people who are using well-designed systems about the actual need for irrigation. One city’s conservation department compared actual irrigation rates to ET (evapotranspiration) rates obtained from weather stations and found that most users were drastically over-irrigating. This launched an effort to educate their irrigators, which reduced irrigation water usage city-wide substantially.

All this highlights the systematic neglect of irrigation efficiency on the part of most cities. It seems rather basic that they need to examine the various means of increasing irrigation efficiency that were reviewed above. They need to come up with estimates of the system-wide water savings that could be attained by widespread application of those measures and of the costs of implementing those actions. This then would reveal the price of this “relieved capacity”, and that could be compared with the price to be charged for adding that same supply capacity to the system. Then the city could incentivize deep conservation actions, like highly efficient irrigation systems, at the level that reflects their real value to the overall water supply system. Or they could mandate those that are clearly fiscally efficient for the end user (despite perhaps being more costly to the builder) – like requiring drip irrigation in all new projects – to forestall, or even avoid entirely, having to do things like spend a billion dollars to expand treatment capacity.

So back to that person who set the sprinkler on the sidewalk, you’ve got to figure out if the fiscal signals you can reasonably send will influence this behavior in a meaningful manner, and if not, then how efficiency could be enforced in order to proliferate it. This is an effort that most cities have so far chosen not to pursue, and so irrigation efficiency, despite that BIG NUMBER noted at the beginning, remains a neglected stepchild. Changing this might have, by itself, allowed Austin to delay construction of its new water treatment plant by a decade or more. How many more cities could, in essence, gain a new reservoir’s worth of capacity simply by investing aggressively in irrigation efficiency?