In Situ Treatment Technology - Chapter 2 pptx

The concept of lifecycle design and its use ongroundwater was first published in 1985 in one of the author’s books, Groundwater Treatment Technology.. First, the lifecycle, as originally

Nyer, Evan K "Lifecycle Design"

In Situ Treatment Technology

Boca Raton: CRC Press LLC,2001

Retardation vs Biochemical ActivityActive Management

Lifecycle Design for In SituTreatment MethodsDetermining the Time Required to Complete a Lifecycle in Groundwater RemediationReferences

The lifecycle concept helps to focus the designer on the main strategies necessary

to successfully remediate a site The concept of lifecycle design and its use ongroundwater was first published in 1985 in one of the author’s books, Groundwater Treatment Technology The simple basis for the lifecycle concept is that groundwaterremediations are unique, and that the requirements for the project will change overthe life of the project One must design for the entire life of the project, not just theconditions found at the beginning Since 1985, we have continued to use the concept

of lifecycle on groundwater treatment designs However, over the years there havebeen three major interpretations of the lifecycle This chapter will review each ofthe main interpretations of the lifecycle of a groundwater remediation, and withinthe review, show how design concepts have changed in groundwater remediationover the last two decades

There are two reasons that this book contains an entire chapter on the lifecycledesign concept First, the lifecycle, as originally described in 1985, was an earlyindicator that we would not be able to reach ‘clean’ with pump and treat systems.Understanding the lifecycle of a groundwater remediation will help us understandthe limitations of pump and treat, and help us understand the possible limitations

of any in situ treatment method Second, in situ treatment remediations will gothrough a lifecycle Once again, the conditions at the beginning of the project willnot be the same as the conditions during the middle of the project, and the conditionscontinue to change as the project progresses to the end The design of the in situ

remediation must encompass all of the conditions to be found during the remediation,and not be solely based upon the initial conditions

LIFECYCLE DESIGN FOR PUMP AND TREAT SYSTEMS

In 1985 the main treatment technology was pump and treat There was littlediscussion on remediation methods The main discussion was on the type of tech-nology used to remove the organics and metals from the water withdrawn as theresult of the pump and treat system The main use of the lifecycle curve was toprovide a model that could be used to design the groundwater treatment system.There were three main lessons learned from using the original lifecycle model:concentration changes over time; capital costs were an important considerationbecause of the limited time each piece of equipment would be used; and operatorexpenses were a significant part of the treatment costs

CONCENTRATION CHANGES WITH TIME

There are three patterns that contaminant concentrations follow over the life ofthe project These patterns are summarized in Figure1 First, there is the constantconcentration exhibited by a leachate If we do not remove the source of contami-nation, then the source will replace the contaminants as fast as they can be removedwith the groundwater pumping system Until the source of contamination is reme-diated, the concentration will remain the same We normally think of “mine” leachate

or “landfill” leachate, but anytime there is a continuous source of contamination,

we are dealing with a leachate A NAPL or a large clay lens impregnated withdissolved contaminants can also represent a source of contamination As the watermoves around the clay lens and/or the NAPL diffuses into the groundwater, a welldownstream of the lens will show a continuous concentration of the contaminant.Several other examples of sources have developed as we have gained experiencewith remediation LNAPLs have been found to be a continual source in two majorlocations First, LNAPL can be sorbed in the vadose zone Rainwater (or othersurface water) can cause a vertical migration of the contaminants into the ground-water Second, the smear zone can act as a source of continual contaminants Thesmear zone is created when the change in groundwater levels causes a subsequentchange in the level of the LNAPL floating on top of the water This allows the

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LNAPL to sorb to the soil over a wide vertical zone When the water rises again,the sorbed LNAPL does not float out of the soil; it stays sorbed to the soil Thiscreates an area that has relatively low permeability to both water and air carriersmaking it difficult to remediate However, the smear zone is still in contact withboth the vadose zone and the aquifer, and the organic compounds making up theLNAPL can diffuse into either area DNAPLs can cause the same type of effect inthe aquifer As the DNAPL travels down through the aquifer, a portion is sorbed tothe soil While these areas may have a reduced permeability to water movement,water can still move through the affected zone, picking up contaminants Thesezones can also act as a diffusion source of organic contaminants

The second possible pattern arises when the contamination plume is being drawntoward the groundwater removal system This mainly happens with municipal drink-ing water wells In this situation the concentration increases over time The well isoriginally clean, but becomes more contaminated as the plume is drawn toward thewell It is important to recognize when this situation will occur Since the concen-tration will rise over time, the original treatment system must be overdesigned toallow for increases in concentration This will allow the treatment system to bedesigned for the entire life of the project The curve shown in Figure1 represents

a large plume, or a situation where the source of the contaminant has not beenremoved Smaller plumes, which have had their source of contamination controlled,will increase and then decrease The center of the plume will be drawn toward thelow hydraulic head created by the large amount of pumping Once the center of theplume is pumped, the concentration will start to decrease This process can take along period of time, in many cases even decades

The final pattern is associated with remediation In this case, the original source

of contamination is removed The pumping system is placed near the center of the

Figure 1 Time effect on concentration.

plume This should be the area of highest concentration, and the place where thewater will bring the maximum amount of mass of contaminants to the withdrawalpoint for removal from the aquifer As the pumping continues, the concentration ofthe contaminants decreases over time The rate of decrease is fast at the beginning

of the project, slows, and then finally stops decreasing, or reaches an asymptote.The author originally thought that this was the result of just retardation, naturalchemical and biochemical reactions, and the dilution of the surrounding groundwater

As discussed in Chapter 1, we now realize that the geology and micro flow patternsplay an important role in the lifecycle pattern of remediation While the beginningpart of the lifecycle curve is concerned with the main body of the contamination,further along in the lifecycle minor sources of contaminants control the shape of thecurve When we were designing our first groundwater treatment systems, we wereonly concerned with the beginning part of the lifecycle curve In fact, recognizingwhat occurred during the beginning of the remediation curve was a giant step towardproper design of groundwater treatment systems

In the early 1980s, the main problem with groundwater treatment designs wasthat the concentration values used to determine the type of technology and treatmentsystem size were overly conservative It was common, at the time, to summarize allthe concentrations found in the monitoring wells and use the maximum concentrationfound in the highest concentration well as the initial concentration for the ground-water treatment system This often led to the incorrect selection of technology Whenthe pumping wells were installed and the system finally turned on, the actualconcentrations found at the influent to the treatment plant were significantly lowerthan the design concentrations

Most treatment systems do not get more efficient as the influent concentrationdecreases Metal removal and biological treatment systems can have a catastrophicfailure if the influent concentration drops below a minimum level The selectionamong other technologies can be based on total pounds of contaminant that have to

be removed For example, one of the main costs of carbon adsorption is the ment of the spent carbon This is related to the total mass of contaminants that areremoved Carbon adsorption will be skewed as a high cost technology if the wrongconcentration is employed in its evaluation As a result, many treatment systemsfailed to meet discharge standards, or were not economical on their first day ofoperation

replace-Even if the original design did work, this design approach produced treatmentsystems that were no longer effective after a short period of time In 1985, thelifecycle concept was introduced so that the designers realized that their treatmentsystem design would have to treat changing concentrations over the life of theequipment and the remedial program

The concept of the concentration change over the lifecycle of the project waspromoted to show that the treatment design would have to be flexible on anygroundwater treatment system installation No matter what the type of contaminant

or the geological setting, the lifecycle curve of remediation was consistent In 1985

we were mainly worried about the beginning portion of the lifecycle curve because

we were mainly interested in the design of groundwater treatment systems and theeffect of the changing concentration on the actual design We did not think too much

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about the later part of the curve We were not sure if it was a period of slow decrease

in concentration and the lifecycle curve would be a straight line if the time was put

on a log scale, or if it was a true flattening of the curve and the concentrations hadstopped decreasing While several studies were already available to tell us that thecurve was probably flat, they were mainly in the hydrogeological literature Theengineers and hydrogeologists were kept separate at the time, and the design engi-neers were simply told to design a groundwater treatment system based on the results

of the remedial investigation The first part of the curve was a major advance in thetreatment design method; the concentration would decrease as the remediation pro-gressed The last part of the curve was a simple guess, and we did not realize itsimportance at the time

CAPITAL COSTS

Another factor that we faced in the early 1980s was the lack of experience indesigning capital equipment for groundwater remediations Engineers who haddesigned wastewater treatment systems were the best source of experience at thetime Most of the first designers transferred from the wastewater area This wassimilar to many hydrogeologists during the same period who transfered from the oilfields One problem with wastewater as a background for the groundwater field wasthe length of time that the project would last Municipal systems are designed tolast up to 50 years Industrial systems are expected to last at least 20 years Mostequipment used in the field will have a 5 to 20 year life expectancy Municipalsystems switched from steel tanks to concrete tanks in order to extend the life ofthose unit operations Pumps and other equipment with moving parts have a lowerlife expectancy, and tanks and reaction vessels have a longer life expectancy Thecost of equipment in wastewater treatment is figured over the life expectancy of theequipment However, the cost of equipment on a groundwater cleanup must be based

on the time the equipment is used on the project with an upper limitation on the lifeexpectancy of the equipment

Chapter 1 discussed that the total time for the mass removal portion of a cleanupwould probably be much less than the 20 years necessary for an industrial wastewaterproject In the previous section of this chapter, we saw that even if the life of theproject is 10 years, all of the equipment would probably not be needed for the entiretime As the concentration decreases, some of the equipment would have completedits function The second part of the lifecycle design switched our thinking from thelength of time that the equipment would last to the length of time the project wouldneed the equipment The difference can be significant

In 1985, we were mainly interested in equipment associated with groundwaterpump and treat systems The example prepared then was based on a biologicaltreatment system The lesson still holds true today for the type of equipment that

we apply on groundwater remediations The example below was produced in 1985,but will show the same results as the example that we will provide in a section later

in this chapter, Lifecycle Design for In Situ Treatment Methods We have updated

the interest rate in the example below, and the daily costs produced will be slightlydifferent from the original 1985 calculations (Nyer and Senz 1995).

Let us assume that the cost of equipment for a submerged, fixed film, biologicaltreatment system is $100,000 If we set the amount of time that we need theequipment and the interest rate that we have to pay for the equipment, then we cancalculate the daily cost of the equipment

One formula for calculating costs would be

where C = cost per time period n; Cap = capital cost ($100,000 in our example); i

= the interest rate; and n = the period of time

We will assume that the interest rate is 9 percent If the equipment is used for

10 years, the daily cost is $43/day If the equipment is only needed for 5 years, thedaily cost is $70/day At 2 years, the daily cost is $156/day, and at 1 year, the dailycost is $299/day All of these figures assume that we have no use for the equipmentafter its usefulness is finished on this project Figure2 summarizes the daily cost ofequipment when used for various periods of time

As can be seen, the cost of equipment gets significantly higher as the time ofuse decreases The normal method of comparing the cost of treatment by differenttechnologies is to base the comparison on cost of treatment per 1,000 gallons ofwater treated At a flow of 25,000 gpd, the cost of treatment goes from $1.72/1000gallons at 10 years to $11.96/1000 gallons at 1 year Using the treatment equipment

Figure 2 Capital cost as a function of time.

in which a particular piece of equipment is only needed for a short period of time.

An obvious solution to short-term use is to rent the equipment, or to use it overseveral different projects This would allow the equipment to be capitalized over 10years even though it was only required for 1 year on a particular project

Of course, any equipment that is to be used for more than one project will have

to be transported from one site to the next The equipment will have to be portable.For example, the design engineer needs a 15,000 gallon storage tank They have achoice of one tank 17 feet in diameter and 10 feet in height, or two tanks 12 feet

in diameter and 10 feet in height If the equipment is to be used only a short period

of time, the proper choice is the two 12 foot diameter tanks The legal limit for awide load on a truck is 12 feet In general, to be transported by truck, the treatmentequipment should also be less than 10 feet in height and 60 feet in length Railtransport can take slightly wider, higher, and longer units, but to be able to reachmost destinations in the United States, shipment by truck should be assumed in thedesign

Most of the equipment used today on groundwater pump and treat systems, and

in fact, on all remediation systems, are portable Most of the pump and treat systemsare for very small flows A 100 gpm unit is considered a medium to high flow system.Even for larger flow systems it is not hard to make an air stripper portable A 750gpm packed tower air stripper would be significantly less than 12 feet in diameter.Biological units have been designed in rectangular tanks to be able to fit on trucks.All carbon adsorption units are portable Other equipment has also taken on theshapes and limitations necessary to make them portable In 1985 portability wasintroduced as part of the lifecycle design requirements for groundwater treatmentsystems Today we accept portability as part of the unique requirements on mostgroundwater remediation systems

In the mid-1990s, a new practice started to become acceptable Many smallremediation projects, such as gasoline stations, are starting to use equipment that

no longer has a long life expectancy Small systems can cost more to move thanthey are worth Plastics and other less expensive materials are being used forconstruction The life expectancy of the equipment in these systems is on the order

of 5 years The equipment is thrown away after it is used at the site

As will be discussed later in the chapter, one of the main problems with usingair as the carrier is that the lifecycle occurs over a short period of time This cancreate situations that have a large variation of organic concentration in the air streamover a 6 month to 2 year period Chapter 6 provides a case history for the lifecycledesign of an air treatment system In this case the site was divided into three sections

As the VES in each section was brought on line, its air stream was sent to a highconcentration treatment system When the concentration reached lower levels, theair stream was switched to a low concentration treatment system, and the next section

was brought on line and sent to the high concentration treatment system Thislifecycle design allowed the high concentration system to be used over a longerperiod of time on the project and to be designed at a lower flow rate.

OPERATOR EXPENSES

One final area that has to be discussed under lifecycle design is operator expenses.Any system that requires operator attention will cost more to operate than a systemthat does not require operators All wastewater treatment systems should have oper-ator expenses factored into the design With groundwater treatment systems, thisfactor takes on added importance The main reasons for this importance are therelative size of a groundwater treatment system, the remote locations of many sites,and the many remediations that occur at properties no longer active or sold to newowners Once again, the engineer cannot take a design developed for wastewatertreatment systems and reduce its size for groundwater treatment Most groundwatertreatment systems will be very small in comparison to wastewater treatment systems,and most wastewater systems are associated with an active industrial plant Theoperator costs, therefore, become more significant when dealing with groundwatertreatment system designs

In the 1980s we thought that most groundwater treatment systems would requireregular operator attention Current systems are designed so that they work withoutregular operators These new system designs use various automatic analyzers andtelemetry systems in order to inform a central office if the system needs attention.Remote locations and inactive sites have forced this change in approach for manyremediations

The significance of the cost of operator attention can still be shown by analyzingthe relative cost of regular operator attention Let us look at the biological treatmentsystem example once again Assume that a 15 hp blower is required for the system

at $0.06/kwhr In addition, chemicals and miscellaneous costs are $3.00/day At a

10 year life expectancy for the equipment, the daily costs would be:

30 percent, power to 18 percent and chemicals to 2 percent At just one shift perday, the operator is now the main expense of the treatment system

Daily costs for the project double if an operator is required for an 8 hour daywhen compared to operating with no personnel The costs triple at two shifts per

Figure 3 Ratio of daily cost with no operator.

Figure 4 Ratio of daily cost with 8 hr/day operator attention.

day, and costs quadruple when around-the-clock attention is required These costsare summarized in Figure6 As can be seen from these data, the design engineercannot ignore the effect of the operator on treatment system costs Even when weextend the curve below the 8 hour day operator attention data point, we see thatsmall amounts of operator attention can still add significant costs to the remediation.The designer should spend a significant amount of effort on minimizing the operatortime required for a particular design.

The effect of the operator does not decrease even as the size of the equipmentincreases significantly Figure7 represents the relative costs from a treatment systemfive times the size of the present example and requiring 24 hours per day of operatorattention The operator still represents over one-third the cost of treatment Even asthe total cost of the treatment system approaches $500,000, the design engineer musttake special precaution to keep the required operator attention to a minimum

In summary, there are three main factors that must be considered when ing a lifecycle design for a groundwater treatment system First, the concentrationmay change over time The treatment design must meet the requirements at thebeginning of the project, at the middle of the project, and at the end of the project.Second, because of the relatively short time that equipment is needed on groundwaterprojects, portable or inexpensive equipment should be considered Finally, due tothe relatively small size of groundwater equipment and the strong possibility ofoperation at an inactive site, manpower costs from operators become a significant,

perform-if not controlling, factor in equipment design(Nyer 1989)

As you can see, all of the above discussions relate to groundwater treatmentsystems It was a given that the groundwater was going to be pumped above-groundand treated It was assumed that this would clean the aquifer The only question was

Figure 5 Ratio of daily cost with 24-hr/day operator attention.

Figure 6 Daily cost of treatment with variable operator attention.

Figure 7 Ratio of daily cost for a $500,000 treatment system with 24-hr/day operator attention.