py^fioS'eJmh^. ip/RO University of Nebraska Lincoln Institute of Agriculture and Natural Resources May 20, 1994 Mr. Dennis Grams, Reeional Administrator USEPA Region VII 726 Minnesota Avenue Kansas City, Kansas 66101 Water Center Oftice of the Director 103 Natural Resources Hall Lincoln, NE 68583-0844 (402) 472-3305 FAX (402) 472-3574 mM f^,int»niPf? S .^ ffAC (TDlliier: ov LP 5 .2.0'^^ ^' Dear Dennis: It was a pleasure to meet Lynn at the antique show. I ended up purchasing the swan buttermold and Mary got another vaporizer for her collection. At an auction last weekend five small oil cans were sold. You will have to tell me how to disdnguish a good oil can from a run-of-the-mill one. Enclosed is a copy of a summary discussing the advantages of the irrigation altemative as the containment and mass renioval remedy for the North Landfill and Far-Mar-Co subsites in Hastings. An expanded version will be included in the 60% design report for the North Landfill subsite thai Geraghty & Miller will be submitting to Diane Easley. I have the two big consulting firms on board albeit reluctantly since there isn't any big money for them in this treatment technique. The irrigation altemative should benefit the PRPs and EPA and provide the necessary containment and mass removal in the process. The approach is novel in that both the PRPs and the EPA will be promoting a pragmatic and innovative solution. This summer we will be conducting a sprinkler irrigation pilot project at the NAD subsite and downgradient from die Far-Mar-Co subsite. The pilot projecl (the proposal is enclosed) is funded by USDA and participants include University of Nebraska researchers from the Water Center, the Center for Electro-Optics in die Department of Electrical Engineering, the Department of Biosystems Engineering, and the Conservation and Survey Division. The project will attempt to fine-tune the methodology for any aberrance that may be site specific to Hastings. I really don't think there will be any site-specific problems; however, confirmation is always important. Two weeks ago we discussed a meeting. Should you and I first meet in Lincoln or Kansas City to discuss strategy and then have a follow-up meeting with Glen Curtis, Diane Easley, and Susan Hoff? I'm not sure of the best way to keep this exciting and innovative approach on track. Please suggest the course of action you think best; I'll be in Baltimore until Friday, May 27. Best regards. y- 7 Roy F. Spalding .Associate Director & Director, Water Sciences Laboratory Enclosures University of Nebraska-Lincoln iH^.ROO. University of Nebraska at Omaha 190477 University of Nebraska Medical Center
Transcript
py^fioS'eJmh^. ip/RO
University of Nebraska Lincoln
Institute of Agriculture and Natural Resources
May 20, 1994
Mr. Dennis Grams, Reeional Administrator USEPA Region VII 726 Minnesota Avenue Kansas City, Kansas 66101
Water Center Oftice of the Director
103 Natural Resources Hall Lincoln, NE 68583-0844
(402) 472-3305 FAX (402) 472-3574
mM
f ,int»niPf? S . ^ f f A C
(TDlliier: ov LP 5 . 2 . 0 ' ^ ^
^'
Dear Dennis:
It was a pleasure to meet Lynn at the antique show. I ended up purchasing the swan buttermold and Mary got another vaporizer for her collection. At an auction last weekend five small oil cans were sold. You will have to tell me how to disdnguish a good oil can from a run-of-the-mill one.
Enclosed is a copy of a summary discussing the advantages of the irrigation altemative as the containment and mass renioval remedy for the North Landfill and Far-Mar-Co subsites in Hastings. An expanded version will be included in the 60% design report for the North Landfill subsite thai Geraghty & Miller will be submitting to Diane Easley. I have the two big consulting firms on board albeit reluctantly since there isn't any big money for them in this treatment technique. The irrigation altemative should benefit the PRPs and EPA and provide the necessary containment and mass removal in the process. The approach is novel in that both the PRPs and the EPA will be promoting a pragmatic and innovative solution.
This summer we will be conducting a sprinkler irrigation pilot project at the NAD subsite and downgradient from die Far-Mar-Co subsite. The pilot projecl (the proposal is enclosed) is funded by USDA and participants include University of Nebraska researchers from the Water Center, the Center for Electro-Optics in die Department of Electrical Engineering, the Department of Biosystems Engineering, and the Conservation and Survey Division. The project will attempt to fine-tune the methodology for any aberrance that may be site specific to Hastings. I really don't think there will be any site-specific problems; however, confirmation is always important.
Two weeks ago we discussed a meeting. Should you and I first meet in Lincoln or Kansas City to discuss strategy and then have a follow-up meeting with Glen Curtis, Diane Easley, and Susan Hoff? I'm not sure of the best way to keep this exciting and innovative approach on track. Please suggest the course of action you think best;
I'll be in Baltimore until Friday, May 27.
Best regards.
y-7 Roy F. Spalding .Associate Director & Director, Water Sciences Laboratory
Enclosures
University of Nebraska-Lincoln
iH^.ROO.
University of Nebraska at Omaha
190477
University of Nebraska Medical Center
THE SPRINKLER IRRIGATION ALTERNATIVE
Several very imponant technical, administrative, and economic reasons make sprinkler
irrigation the most pragmatic altemative to contain and treat contaminated ground water from the
North Landfill and Far-Mar-Co subsites. The conventional pump and dreat approach used at
individual subsites is neither technically nor administratively feasible where contaminant plumes
from two or more sites have commingled. A coordinated approach that provides an integrated
solution is warranted. The following discussion examines some of the advantages of a single
focused approach to contain and remove volatile organic compounds ft-om the commingled
plume.
Technical Considerations
Several laboratory and field smdies have demonstrated that there is a significant loss of
volatile compounds when water containing these compounds is applied to the land. Litton and
Guymon (1988) have summarized many of the studies reported in the literature. Many of the soil
volatilization investigations were soil column studies. In the laboratory Wilson et al. (1981)
investigated the fate and transpon of TCE in sandy, low organic soils under unsaturated
conditions. TCE concentrations of 900 and 180 jag/L were applied at a steady state rate of 14
cm/day to packed soil columns equipped with vapor traps. The air above the column was
exchanged once every eight minutes. At the higher influent concentration 58% of the total mass
of the applied TCE was volatiUzed while 88% was volatilized at the lower concentration. There
is very little information in the literature conceming the volatihty of EDB; however, a few
studies have quantified the volatilization losses of dibromochloropropane CDBCP), a nematocide
with a volatility similar to that of EDB, from soils. Castro and Belser (1968) reported that
volatilization was the dominant loss mechanism from soils and subsequent studies by other
investigators have shown that the volatilization losses may be significant. Litton and Guymon
(1993) confirmed that volatilization accounted for at least 85% of the DBCP loss in Hanford
sandy loam soils and that trace amounts of DBCP in contaminated ground water could be
removed by appUcation to agricultural lands.
Volatilization of an organic compound is strongly dependent upon the vapor presstu-e and die
solubility of the chemical although other factors such as mrbulence and molecular diffusion can
influence volatilization. Henry's Law relates the vapor pressure of a chemical to its aqueous
concentration if the chemical is of low solubility. Henry's Law is expressed as Pc = HCc where
Pc is the vapor or partial pressure of the chemical, H is Henry's Law constant (atm-m^mol), and
Cc is the molar concentration of the chemical in water. Henry's constant can be approximated by
dividing the sattu-ated vapor pressure by the aqueous solubility of the substance. The partitioning
of the chemical between the water and ah phases can predicted by Ca = HCw where Ca is the
concentration of the chemical in air (mass/volume), Cw is the concentration of the chemical in
the water (mass/volume) and H is the dimensionless Henry's constant which is obtained by
multiplying H in atm-m^/mol by the constant 41.57. In an open system the concentration in air is
constantiy diluted with chemical-free air; consequently, the dilution volume approaches infinity
and allows for further reduction in the aqueous concentration. The VOCs detected at the Nonh
Landfill and the Far-Mar-Co subsites are listed in Table 1 in order of their relative volatihty.
Their Henry's constant, dimensionless Henry's constant, and other physical-chemical properties
also are hsted.
TABLE 1. PHYSICAL-CHEMICAL CHARACTERISTICS OF SELECTED VOCS (listed in order of decreasing volatihty)
Compound Solubility Vapor Pressure Boiling Point Henry's K Henry's K
(mg/L) (mm Hg) CC) (atm-m^/mol) (dimensionless)
1,1-DCE
vinyl chloride
1,2-transDCE
1,1,1,-TCA
carbon tet (Ci)
PCE
TCE
chiorofonn
EDB
DBCP
5,000
2,800
6,300
4,400
795
150
1,100
10,000
4,250
700
590
2,994
390
74
115
18.6
76
199.4
13.8
0.8
32
-14
49
75
77
121
87
61
131
196
1.9X10-1
8.1 X 10-2
6.7X10-2
3.0 X 10-2
2.3 X 10-2
1.5 X 10-2
9.1 X 10-3
2.9 X 10-3
8.2 X 10^
5.6X10"^
7.9
3.4
2.8
1.25
0.96
0.62
0.37
0.12
3.4 X 10-2
2.3X10-2 •
The process that occiu^ when volatile organic compounds vaporize from water is not well
understood on a microscopic level. While it is generally conceded that increases in surface area
at the air-water interface result in increased volatilization, the molecular velocities created by the
sheering effects of small droplet formation may dramatically increase volatilization. Thus VOCs
dissolved in irrigation water would be much more likely to vaporize from water apphed through
a sprinkler irrigation system than from water applied via funow urigation (a 12(X)-foot long
stream of water =0.1 ft deep open to the atmosphere) and least likely to vaporize from a drip
irrigation system, which is designed to minimize evaporation. The Orange County Water District
(1989) investigated the extent of TCE removal through both drip and sprinkler irrigation
systems. Volatilization losses averaged 42% in the drip irrigation system with source TCE
concentrarions ranging from 17.3 to 18.3 )ig/L. Volatilization efficiency was much greater widi
sprinkler irrigation which removed an average of 97.3% of the =24 )j.g/L TCE in the source
water. The removal efficiency increased with smaller droplet size (99.5%) and increasing
trajectory height and fall distance (97.7%). The greatest removal efficiency (99.5%) was realized
with stationary nozzles producing fine uniform sprays and continuous, steady flows. Med-Tox
Associates (1989) reponed that TCE-contaminated ground water with concentrations ranging
from trace to 90 \ig/L has been used to drip irrigate crops used for human consumption since at
least 1985 and probably longer. In California high water intake crops like lettuce also showed no
detectable DCE residue after being irrigated by DCE-contaminated irrigation water.
Wood et al. (1985) evaluated a series of spray nozzles with a wide range of water flow rates
and spray pattems at several sites with VOC contamination as high as 10^ |.ig/L. The removal
efficiency increased with decreased droplet size and increased spray trajectory. Fog nozzles
which require pressm-es greater than 20 psi and full cone nozzles operating at low pressiu-e (<10
psi) and a 24-foot upward trajectory provided the most effective treatment removing more than
99% of the contaminants. Removal amounts greater than 99% could not be quantified with the
sampUng and analytical methods employed. Similar experiments with EDB-contaminated water
are not reponed in the literature.
Volatilization losses during furrow or gravity irrigation have not been tested; however, given
that vaporization can occiu- at the flowing water-atmosphere interface large losses would be
anticipated.
There is littie doubt diat TCE and carbon tetrachloride (CT) at the Nonh Landfill and Far-
Mar-Co subsites can be effectively treated using sprinkler irrigation. Because the effectiveness of
sprinkler irrigation in treating EDB was questionable, column droplet experiments were
conducted. The experiments measured the volatilization of TCE, CT, and EDB from three
droplet sizes (135 jam, 225 ]-m, and 3(X) jam) and two relatively shon (62 cm and 125 cm) fall
distances. The experiments were performed in die Center for Electro-Optics laboratory in die
Depanment of Electrical Engineering and the samples were analyzed in the Water Sciences
Laboratory at the University of Nebraska. Initial EDB concentrations of = 1 |ig/L were treated to
levels less 30 rjg/L (pans per uillion), which is well below the MCL of 50 r^g/L. At
concentrations approaching 4,)ag/L and a fall distance of 125 cm (4 ft), 99% of the EDB was
volatilized.
This summer additional laboratory and field experiments will be performed to ftuther
evaluate sprinkler irrigation as an altemative technique for remediation of VOC-contaminated
ground water. Funded by USDA these experiments performed by scientists in the Water Center,
the Center for Electro-Optics, the Depanment of Biological Systems Engineering, and the
Conservation and Survey Division of the University of Nebraska wiU measure the effects longer
fall distances and droplet size have on volatility. The field experiments will be conducted in
Hastings on farmland presently cropped to small grains and sprinkler irrigated with ground water
containing VOCs. The objective is to fine-tune the treatment technique by determining the most
efficient nozzles and trajectories.
Modeling has shown that irrigation will contain the primary contaminants TCE, CT, and
EDB at agreed upon ARRAs. Recent capture zone models by Geraghty and Miller (1994)
indicate that pumping the existing irrigation well 16(X) feet east of well 1-49 at 1350 gpm for 4
months will capture the contaminants at concenttations equal to or greater than the ARRA levels
at bodi sites. The pumped water will be sprayed on two quaners (=320 acres) of row crops 0.5
miles soutii of the well. Transpon modehng also has shown that over time pulsed pumping will
provide the necessary containment and mass removal (S.S. Papadopulos and Assoc., 1993). Risk
assessment modeling for emissions volatiUzed during sprinkler irrigation indicate that risk to
health under a worst case scenario is de minimus. The emphasis of this approach is pragmatic. It
is containment with mass removal. It does not propose to remove all VOCs to maximum
contaminant levels as does the much discredited pump and treat altemative.
Administrative Considerations
This procedure would simultaneously expedite solutions for two subsites. USEPA Region 7
would become one of the first regions to implement a rapid, innovative, and economic altemative
at two Superfund subsites. Since the irrigation well is in place and one of the pivots already is
operating, the design and construction could be quickly implemented. This would eliminate the
need for the customary remediation design phase for the Far-Mar-Co subsite and allow for a final
100% design for both sites before the end of this year. The sprinkler irrigation altemative would
permit timely response to the immediate problem of downgradient excursion of the
contaminants. With containment in place, problems of less immediacy such as upgradient source
control at the North Landfill subsite and source control at the Far-Mar-Co subsite can be
addressed.
The common goal would also promote cooperation between PRPs from both sites and EPA.
It is warranted hot only from an administrative standpoint but is die only practical procedure for
containment of the two commingled plumes. When the plumes have commingled, the
conventional altemative is by natm-e adversarial because it fosters conflict between PRPs from
adjacent sites which wastes resources and accomplishes litde for health and die environment.
Economic Considerations
The sprinkler irrigation treatment altemative provides a beneficial use for the treated water
and eliminates the cosdy disposal of the discharged water. Inherent in the treatment altemative is
irrigation, a farming practice that is vital to the successful production of small grains in central
Nebraska and which will remain an economically viable practice as long as there is a market for
smaU grains. Only slight modification of the existing pivot is needed to promote maximum
volatilization. The cost of the second pivot would be approximately $33,000. Additional costs
would be incurred for trenching and piping from the containment site to the irrigated quaners.
Operation and maintenance of the sprinkler systems would be only slightiy more expensive than
it is for the each of the odier 71,000 center pivots in operation in Nebraska. Thus the costs of die
proposed altemative treatment are much lower than the conventional treatment which has
averaged = $25 million per site. With the sprinkler irrigation altemative the City of Hastings,
Dutton-Lainson Co., Morrison Enterprises, and additional PRPs have the potential to save more
than $50 million.
References
Castro, CE. and N.O. Belser. 1968. Biodehalogenation. Reductive dehalogenatiom ofthe
biocides ethylene dibromide, l,2-dibromo-3-chloropropane, and 2,3-dibromobutane in soil.
Environ. Sci. and Technol. 2: 779-783.
Geraghty and MiUer. 1994. 60% design repon for the North Landfill subsite, Hastings ground
water contamination site, Hastings, NE.
Litton, G.M. and G.L. Guymon. 1988. Literature review conceming the fate of DCE, TCE, and
DBCP in agricultural water during irrigation and percolation through sod. Prepared for the
Santa Ana Watershed Project Authority by Dept of Civil Engineering, University of
CaUfomia, Irvine, CA. 94 p.
Litton, G.M. and G.L. Guymon. 1993. Laboratory experiments evaluating the transport and fate
of DBCP in Hanford sandy loam. J. Environ. Qual. 22(2): 311-325.
Med-Tox Associates. 1989. Public health risk assessment for the OCWD/IRWD proposed
trichloroethylene containment program, Irvine, Cahfomia. Prepared for the Orange County
Water District, Fountain Valley, CA. 7 p.
Orange County Water District. 1989. Results of an investigation of TCE removal during
sprinkler and drip irrigation in the Irvine area. Orange County Water District, Irvine CA. 30
P-S.S. Papadopulos and Associates. 1993. Draft final remedial investigation Far-Mar-Co subsite,
Hastings ground water contamination site, Hastings, NE. Repon prepared for Morrison
Transpon and fate of selected organic pollutants in sandy soil. J. Environ. Qual. 10(4).
Wood, P.R., R.F. Lang, and LL. Payan. 1985. Anaerobic transformation, transpon, and removal
of volatile chlorinated organics in ground water (pp. 493-511). In Ground Water Quality
(CH. Ward, W. Giger and P.L. McCarty, eds.). John Wiley & Sons.
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TITLE D i r e c t o r Nebraska A g r i c u l t u r a l ExoerirTient S t a t i o n
Title of Proiect Sprinkler L'nsaLioii as a Remedial Teciiiiique for VOC-Coii[aminated Grouudv.'ater
.Abstract This research investigation is designed to demonstrate that spraying small droplets of VOC-contaminated v/ater through sprinkler irrigation systems is botii an environmentally acceptable and technically efficient m.ethod for remediating VOC-contaminated groundwater. Both laborator)' and. field studies will be conducted.
Kev Words volatile organic chemicals, groundwater remediation
.lu.stificatiori Nebraska togetlier v/ith other major sm.ali-grain producing states has numerous sites v/here the groundwater bas been contaminated by chlorinated and brominated •.olatile organic chemicals (VOCs) as a result of fumigating stored grain v/ith these compounds, hi order to better evaluate Qie impact of this source of VOC :ontaminaLion on drirJdng water supplies, the USEPA requested in 1991 that imall-grain producing states initiate sam.pling of private v/eU.s in ccmniunities that ••lad grain storage facilities. Tiic study focused on community water supplies in :owns where USDA had grain bins (USEPA, 1992). In Nebraska aioiie dieie v/ere 41 communities where USDA had grain storage bins. Ihidcr SupeiTund legislation. USDA as well as orivate businesses are responsible for remediating sites v 'here concentrations of the fumigants in groundwater exceed the standards set by the Safe Drinking V/ater Act. lh Nebraska private businesses and tlie USDA already have spent millions of dollars for clean-up. For USDA ;-emediation v/ill require a sizable expendimre from an already tight budget.
Packed tower aeration and granular activated carbon (GAC) adsorption are the most frequently used teclinologies to routinely remediate VOC-contaminated groundwater because they have the proven capability of removiiig more tlian 99% of the VOCs under a wide variety cf conditions. Installation of the tower and/or regeneration of the GAC and disposal of the contaminants are factors that contribute to the high costs of these remedial techniques.
hi the proposed metiiod, VOCs are stripped from the contaminated groundwater as it is discharged as an aerosol fro.m tlie spri.nkler no/:zle of an irrigation system. Diludon of the air-bome emissions quickly rnuiimizes the health risk to levels «i0~6_ Xhe total annual emissions will not approach Nebraska A.ir Pollution Control Rules standards of 2.5 tons VOCs per year (NDEQ Title 129). ^Hic VOC-free v/ater is then applied to the crop. The seasonal pumping by irrigation wells is sufficient to contain tlie majority of VOC contaminant plumes.
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Prelirnuiaiw laboratory studies siiow that ihs. proposed sprinkler irrigation remedial technique is a verv effective metiiod for rem.oving ethylene dibromide (EDB), tricliloroeLhylene (TCE), and carbon teti-achioride (CCU) from groundwater. Tnis procedure would be a more cost effective miethod for containing the plume of contaminadon, remediating the groundwater, and disposing of some VOCs than the presently used teclinologies. In many areas of the United States irrigation systems are already in place, v/hich negates the cosdy altemative of aerarion tow'er installadon. Because most VOC groundv/ater remediation procedures use pump-and-treat technologies, excess treated water is wasted. In several areas of Nebraska groundwater mining has caused significant declines in the water table. In tlie area of the proposed pilot project, a groundv/ater control area has been estabhshed to regulate v/ithdrawals to protect the long-temi agricultural p.roductivity ofthe area. Conservation of groundv/ater is inlierent in the proposed sprinkler irrigadon technique.
Objectives' Tnis investisation is both a iaboratorv research T roiect and a ileld pilot nro^ect to determine the criteria necessaiw to voladlize VOCs from groimdwater and to test die apphcation of aerosol volatilization in sprinkler irrigation. Degradation .rates of volatiles released to die amiosphere will be estimated by laboratopy ultraviolet laser experiments.
Procedures Laboratop/ experiments: Laboratory experiments will be conducted using the experimental apparatus shov/ii in Figure 1. Tnis equipment and experimental apparatus v/ere used to obtain die preliminarv data for EDB, TCE, and CCLi. Ln dhe proposed laboratory studies dichloroethylene (DCE) and vinyl cliloride will be Lnvesdgated to detemiine the deg.ree to v/hich these compounds can be remediated using smaU aerosols. This phase of die research will provide die evidence needed to detennine the usefulness of sprLnlder inigadon as a means for site remediation of mixed plumes containing ^ flXr , TCE, CCI4, DCE, and vinyl crdoride.
The second phase of the proposed laboratory research is to carr>' out a system.adc invesdgation into the fundam.ental chemical and physical m.echanisms of die volatilizadon process. The physico-chemical constants (Table 1) for CCk, TCE, DCE, and EDB indicate diat voiadiization is more favorable for CCI4, TCE, and DCE dian EDB. Our prelLminary work, however, indicates that EDB is voladlized v/ith the same efficiency as TCE. ' fliis behavior is not understood, but our current hypodiesis is that Henry's Law is based on volatihzation from a solurion into die headspace of a container and not of volatihzadon from a solution in the aerosol form. As pan of die proposed experimental research, studies will be conducted to establish constants for aerosols containing VOCs of interest in ihis proposal.
EDB CCU 1, 1,2-TCE L 1-DCE I, 2-:rans DCE
4250 794.5
1,100 5,000 6,3CO
13, 115 76
590 390
Table I. Physico-chemiical charactenstics of selected VOCs in groundwater.
Compound Solubility Vapor Pressm'e Henrv's K (mgyL) (mm Hg) (arm-in^/mole)
8.1 X 10- 2.9 X 10--1.2 X 10-2 1.5 X 10-2 5.3 X 10-3
The third phase of die experimental laboratory work is to investigate the effectiveness of using uldaviolet rays to decompose VOCs after dieir release into the air thus reducing their potential mteraction with the ozone layer. In the proposed research either nitrogen lasers (?v = 337 nm) or excimer lasers (A = 243
nm, /\ = 193 nm) wih be used to illuminate gaspHHsstsamples of EDB, CCI4, TCE, DCE, and vinyl chloride contained in a syndietic fused silica cell widn ultraviolet (UV) rays. The pulsed lasers v/ill seiwe as concentrated sources of ultraviolet radiation to simulate die UV radiation from the sun interacting widn VOCs released into the enviromnent. Tnese studies shoukLprovide data on the half lives of these VOCs and the resulting chemical species diat would be expected from die interacdon v/ith ultraviolet radiation. The idendficadon of chemical species in the test cell v/iU be accomi^lished using a HP 5890 gas chi-omatograoh v/ith periodic mass selective detector confimiadon.
Field demonstradons: Tests, of the efficacy of usuig sprinkler irrigadon for VOC remediadon will occur at two sites with VOC-contaminated groundv/ater. Bodi sites are Superfund subsites and are located near Hastings, Nebraska. The first demonstradon site is a farm located on the former site of a Naval Ammunition Depot. We have received permission from the farmer to conduct the proposed experiment. Presently, he is irrigating his crops with the VOC-contaminated groundwater, which contains as much as 680 ppb TCE and 460 ppb trichloroethane (Woodward-Clyde Consultants, 1990). The well is equipped widn a T-.L linear drive sprinkler system which can be easily modif ed and monitored for diis project.
Tne second site wdll be used to test the efficacy of sprinkler irrigation for remediating EDB and CCU-contaminated water from a grain storage area. It.is likely that this sprinkler irrigadon system will be installed by private industries, who are the potentiaUy responsible pardes.
The field demonstradon projects will compare the voiadiization efficiencies for die four compounds using droplet sizes and faU distances that are based on the results of the laboratory experiments. Sprinkler heads (nozzles) that best sunulate tlie most efficient droplet sizes and fall distances determined in the Iaboratorv'
experiments will be installed on die ami. Droplets at various fall distances wid be scanned for size and shape using a high speed photographic image acquisidon prol e (Hawkes et al., 1993). To maintain die necessary droplet size DOOSter pumps may be needed to ensure minimum pressures at the sprinkler heads. Sam^ples of the Held spray will be coUected in large, iced, rectangular dishes arranged in a configuradon diat best collects the sprinider spray in the shortest period of tune.
Sam.ples of field spray v/id be immediately transferred to 40-ml screw-top VOC vials with Teflon-lined septa. Samples v/ill be analyzed at an on-site laboratoiy using EPA Method 601/602 and an O I Analytical high perfonnance system udlizing purge and trap gas chromatography v/idi P.ID/ELCD detection. With tliis system a sample of water is sparged widi an inert gas, die .liberated organics are concentrated on a sorbant trap, and die contents of die d'ap are diemially desorbed onto the GC column. The sample components are then separated v/ith a megabore capiUary column, and detected with photoionization and electrolydc conductiviry detectors connected in series. Adi sampling :m.d analyses will follov/ strict quality assurance and quality control guidelines diat inchide one field blanlc and one field duplicate, for every ten or fewer v/ater samples and one trip blank for each sampling event.
Research Timetable July, 1993 to September, 1993. InstaU nozzles on sprin>der irrigation system^ and
conduct TCE and TCA experiments.
September, 1993 to June, 1994. Conduct laboratory experimients.
June, 1994 to August, 1994. InstaU nozzles at CCU and EDB-conta.rninated site and conduct volatilization expenmerits.
August, 1994 to June, 1995. hiterpret data and v/rite report.
Literature Review an(;i CinreDl ES'MAZLh Preliminaiy laboratory suidies on die use of sma.n aerosol particles for remediadon of EDB, TCE, and CCU are very encouraging (Table 2). Tnese laborator>-experiments, conducted at the Center for Electro-Optics in the Departmient of Mechanical Engineering at the University of Nebraska (UNL), v/ere designed to evaluate die relative efficiency of contaminant removal via volatUization that occurs when VOC-contaminated water is sprayed during simulated modified surinkler irrigation.
Aerosol particles of a known size were generated using a Thermal Systems Inc. Model 3450 Vibrating Orifice Aerosol Generator. The primary components of the generator are a variable now rate syringe pump and a micron-sized orifice mounted on a piezoelectric ceramic crystal and driven by a frequency generator. Small
panicles are fomied by forcuig liquid to pass through die smaU orifice v/hile simultaneously usins die piezoelectric ceramic crystal to apply a high frequency penurbation to die flowing liquid column (Berglund and Liu, 1973). Instabihdes in die fluid column as it exits die orifice result in fluid breakup and formation of uniform sized droplets. Based on the assumption of uniform particle size, a 'dieoredcal panicle diameter can be calculated using die foLlov/ing reladonship,
/:)theor = 317(Q/y)l/3, v/here D is the dieoredcal diameter in.microns, Q is die liquid flow rate in cc/min, and/is die piezoelectric frequency in kHz. Tne aerosol stream can be dispersed and/or diluted using an independendy controUed flow of air dirough die system. .After generation, die aerosol droplets faU through the controUed evaporation coluiim and are coUected and funneled into 40-md screw-top ampoules at die exit of die column. Figure 1 is a schematic of the complete laboratory apparadis.
Tilt samples in sealed ampoules were transported to the Water Center's Water Sciences Laboratory for extracdon and analysis. Volaules were extracted and analyzed following the procedures oudined in U. S. Environmental Protection .-\gency (EPA) micthod 504, a miediod diat is specifica.Uy for the detemiinadcn nf Ultra trace levels of EDB. A HP 5890 gas ciiromiatograph equipped 'widi an electron capture detector was used in die analyses. The detection limits were 50 parts per triUion (ppt) for EDB, 300 ppt for TCE, and 100 ppt for CCU- Several samples also were analyzed using a gas chromatograph with a mass selective detector (GC-MSD) for positive confiimadon of die volatiles. Preliminary results indicate 98% removal of the voladle contaminants from die smaU (300 jam diameter) aerosol droplets (Table 2).
Tnese data support earlier reports (Enviromnental Science and Engineering, 1986) diat indicated that some compounds are more easily removed through aeradon dian v/ould be estimated based on Henry's Law constant alone. Given the vapor pressure and aqueous solubility of a VOC, its propensity to be volatilized can be estimated by its Henry's Law constant (K). K is the rado of the partial pressure in atmospheres to the solubility in moles/m^. The physico-chenucal constants for volatiles of concem in Hastings' groundwater are Usted in Table 1. Henry's Law v/ould predict EDB to be about 15 times less likely to be stripped with aeration dian TCE.
Table 2. VOC
Effect of droDlet size and fall length on volatilization efficiency. Droplet 62-cm F;iU 125-cmFaJi
Facilities and Equipment The Center for Electro-Optics and the Water Center's Water Sciences Laboratory at die University of Nebraska have unique facilides for conducting die proposed experimental research. Much of the expertise in dealing with aerosols is a result of approximately one miUion dollars of funded reseajch in a 10-year period by the Department of Defense to invesdgate the interactions of high power lasers with aerosols. The proposed research of die volatilizadon of chemdcal compomids is similar to past research conducted on detecting and neutralizing chemical warfare agents. A high level of expertise in environmental analytical chemistry has Ixen assembled at the Water Sciences Laboratory. The laboratory currentiy is engaged in uroiects totaling more dian S5.7 miUion.
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Bodi centers have miUions of doUars of state-of-the-art equipment that can be UtiUzed on the project. Equipment at the Center for Electro-Opdcs consists of excimer and nitrogen lasers, drop voiadiization set-up widi rnonodispersed Berglund-Liu generator, phase Doppler particle sizing equipm.ent, laser imaging equipment, optical vibradon uables, and video im.aging processing equipment. Water Sciences Lahorator)' instrumentation includes an HP 5890 GC/MS.D :uid additional gas chromatographs with EC detectors.
Collaborative Arrangements
Dr. Roy F. Spalding, Director of the Water Sciences Laboratory, Hydrochemist and Professor of Agronomy at the University of Nebraska v/iU direct the analytical smdies.
Dr. Dennis R. Alexander, Director Center Electro-optics and Professor of Mechanical Engineering at die University of Nebraska wiU direct the laboratory droplet studies.
Dr. Derrel L. Manin, Associate Professor of Biological Systems Engineering, wiU coordinate field droplet sizing and shape measurem.ents and assist with nozzle instaUadon.
Ms Mary E. Exner, Research Chemist and Associate Professor in the Conservadon and Survey Division at the University of Nebraska, wiU coordinate both field and laboratory quality control and quality assurance.
Cqrriculum Vitae of Investigators Vitae of the research team are on the foUowing pages.
References Berglund, R.N. and B.Y.H. Liu. 1973. Generadon of monodispersed aerosol standards. Environmental Science and Technology 7: 147-153.
Lnvironmental Science and Engmeering, Inc. 1986. Removal of Volatile Organic Chemicals from Potable Water. Noyes Data Coiporation, Park Ridge, NJ, p.27-28.
Hawkes, R.D., D.L. Mardn, and G.E. Meyer. 1993. In-flight digital image analysis of sprinkler drops. Opdcs in Agriculture and Forestry. SPIE-Tne Lnternadonal Society for Optical Engineering. SPIE Proceedings. Vol. 1836 (in press).
U. S. Environmental Protecdon Agency. 1992. Summary report of contamLnated v/ater supplies associated with past srain bin fumigation. Region " /U. Kansas City, KS.
Woodward-Clyde Consultants. 1990. Final Remedial Livesdgadcn P.cport. Hastings East hidustrial Park Remedial Investigation/Feasibility Smdy Plastings, Nebraska.
