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HomeMy WebLinkAboutSouthold Demonstration Site - Aldicarb calculations - 1983 Aldicarb Calculations South old Demonstration Site New York State Fertilizer and Pesticide Demonstration Project October 1983 Center for Environmental Research 468 Hollister Hall Cornell University Ithaca, New York 14853 ALDICARB CALCULATIONS Southold Demonstration Project In the final report for the Southold Demonstration Site of the New York State Fertilizer and Pesticide Demonstration Project, Table VI-2 presents the results of our simulation of aldicarb movement below the Depot Lane Transect in Southold, N. Y. Included are the dates when the simulation shows aldicarb entering the groUJld water and the average concentrations of these recharge plumes. The following explanation provides greater detail about the simulation, including the many simplifying assumptions inherent in its design. Table A-2 also provides the dates when the simulation shows aldicarb to decay below 7 ppb along the Depot Lane transect UJlder two different half life assumptions. These dates are meant merely to illustrate what may happen at this site if the assumptions are correct, not to predict with any accuracy what will occur. Because of the great UJlcertainty in the decay rate assumptions, these dates are not included in the Final Report of the Southold Demonstration Project. Depot Lane Transect In 1980 the Suffolk County Department of Health Services had a series of geologic test holes and observation wells drilled along Depot Lane in Cutchogue in order to obtain information about how aldicarb and other contaminants move through the North Fork's aquifer. The transect cuts across the North Fork from north to south and runs parallel to ground-water flow in both the northerly and southerly directions. Private wells were sampled by the County in the Spring of 1980, and the observation wells were tested a year later. Aldicarb contamination was found up to 100 feet below the water table near the center of the transect and at shallower depths (up to 40 feet below the water table) at the northern and southern extremities, with concentrations ranging from one to 149 ppb (Baier and Robbins, 1982). Aldicarb Simulation The Depot Lane transect was divided into 13 areas (Figures 1 and 2), and the farmers were surveyeu about their aldicarb use on fields within each of these regions. The aldicarb application rates for each field in an area were averaged, and fields where no aldicarb was applied were included in the averaging. Results are shown in Table 1. For our simulations, the adsorption partition coefficient was set at 0.09 in the root zone and at 0.0 below the root zone, indicating that only a small percent of the aldicarb contained in the soil water would be adsorbed to soil particles in the root zone, and none below this. zone. These numbers were calculated from a linear regression relating adsorption coefficients to soil organic matter derived from the results of four field and laboratory experiments (Kain and Steenhuis, 1982). The greatest uncertainty in modelling aldicarb is its rate of attenuation in the root zone, unsaturated zone, and saturated zone. The half-life, or time that it takes for half of the aldicarb to decay to nontoxic byproducts, CX) It) q 0", "0 ;\' 0", ,,~ ;\'/ .9", o~ 2 "0&..""" ~IIO 0"".:> <II.:> "" ~ i :i ~" ~ . . " 8 ~ ~ . . . g . o ~ o ~ ,.: Z ." '0 .c ;; 0 en U .. ~ c: :! - .. c: " ...J '0 Q. .. C ,.: .. .. = - 01 " c: 01 0 u:: .. . "-0 .!! ~ !: " c: " -e " .l:! ." .. - .2 ." .. ~ " ~ " .. .:; 3 ,.. Or.gon Rd. Middle lmR ROld MIln ROld .. .. 2 3 . .. 5 Clllchoglll Harbor 8 9 10 11 12 13 2. Str.,mline / / / / / / MSL L.LS- ;; .! .2 \ .. --40 \ ~ .! \ W -&0 \ -50 \ , -100 Sill Wat., Wldg. --__ _1____ ---- ----- '- -120 Clly Bound.,y - ------- _ _.i ~'~l" ~~. _140 -150 . 3 . , 8 a 10 11 12 13 14 15 16 17 18 19 20 Distance from North Shore 11000 It ) Flgur. 2. Simulated aldlcarb p.lumes along the Depot Lane transect, Southold, N.Y. Table 1 Aldicarb use on areas along the Depot Lane transect, 1975 to 1979 A1dicarb Applied (lb active ingredient/A) Area" 1975 1976 1977 1978 1979 Total 1 0.5 0.0 0.0 0.0 0.0 0.5 2 2.5 0.6 1.0 1.0 1.0 6.1 3 0.4 0.7 1.1 1.1 1.1 4.4 4 0.1 1.4 2.3 2.3 2.3 8.4 5 1.1 1.9 2.4 2.4 2.4 10.2 6 0.5 1.8 2.5 3.7 3.7 12.2 7 0.0 0.0 0.0 0.0 0.0 0.0 8 1.7 2.0 2.0 2.9 2.9 11. 5 9 1.6 3.7 3.7 4.6 4.6 18.2 10 2.1 2.6 2.6 3.8 3.8 14.9 11 2.1 4.0 4.0 5.2 3.7 19.0 12 0.0 0.2 0.2 0.2 0.0 0.6 13 1.7 1.7 1.7 1.7 1.7 8.5 is shortest in the root zone where microbial populations speed the decaying process, and longest in the saturated zone because of the lower temperatures and low rates of microbial activity. Unfortunately, laboratory and field experiments on these half-lives are few, and the results are inconclusive. A previous review summarizing studies on aldicarb degradation in a variety of soils showed ranges in half-lives from one to 231 days (Kain and Steenhuis, 1982). This review indicated that for Long Island soil types, a 50 day half-life was reasonable for the root zone, which was assumed to be 30 cm deep. This was increased to 100 days for the next 30 centimeters in depth because microbial populations diminish with increasing depth (Pacenka and Porter, 1981). For the remainder of the unsaturated zone, a half-life of 10 years was used. The 50 day root zone half-life is from Kain and Steenhuis (1982). The other numbers were derived by calibrating our model with field data from a potato field on the North Fork studied by Intera (1980) and a deep soil core taken at the Long Island Horticultural Research Laboratory (unpublished data). The simulation results indicating the dates. and concentrations of aldicarb leaching to the ground water are shown in Table 2. Dates of aldicarb decay are presented for two potential half-lives, three years and ten years, chosen somewhat arbitrarily to represent a range of possible half-lives for aldicarb in ground water. Aldicarb's half-life in ground water is highly speculative, however, because no laboratory data are available for its half-life at 150C and pH of 6, conditions typical of Long Island's ground water (see Table 3). Without an accurate estimate of the half-life in ground water, any simulation of aldicarb's disappearance has to be based on speculation alone. Field and laboratory research currently underway will better define aldicarb's half-life under Long Island conditions. Until these data become available, simulations which predict specific dates of disappearance are likely to be misleading. We felt that 4 the table of simulation results gives a false impression of accuracy. For this reason, the estimated dates of aldicarb decay presented in Table 2 were not retained in the final reDort for the Southold Demonstration Site. Assumptions Implicit in the Ground-Water Simulations The flow system. The velocities of the aquifer are calculated from data in the study conducted by the Suffolk County Department of Health Services (Baier and Robbins, 1982). These calculations assume that the aquifer is composed of uniform material. Variations in the material which undoubtedly occur will cause the actual flows to be slightly different. The Suffolk County Department of Health Services estimate that time of travel calculations would be accurate to within ~ 25 percent. Disllersion. The process of dispersion was modelled in the unsaturated flow where dispersion is quite significant. In the saturated zone dispersion was not explicitly accounted for. Instead, a simplifying assumption was made that all aldicarb within the plume is evenly distributed throughout the plume and therefore that the concentration in the plume is uniform. This is comparable to assuming that all dispersion occurs within the unsaturated zone before the aldicarb enters the aquifer and that no dispersion occurs after that. The fact that these simplifying assumptions only approximate reality means that the simulation results must be used carefully with an appreciation for their limitations. An additional word of caution needs to be made about the interpretation of the aldicarb decay dates in this table. These dates represent the times when the entire plume of aldicarb from each area along the transect would be expected to decay below 7 ppb, not the times for 5 Table Z Simulation Results Showing Dates When Aldicarb Would Reach Ground Water and Would Decay to Concentrations Below 7 ppb Along the Depot Lane Transect in Southold, N. Y. A B C D E F G Area Year Aldicub Year All Aldicarb Average Aldicarb Number of Date When Date When Stream Tube First Reaches Hu Reached The Concentration in Years {or Watel' Avenge Aldicarb Average Aldicarb Number Water Table Water Table Recharge Water Starting at the Concentration Concentration at the Water Water Table to Would Be Below Would Be Below Table {ppbl Be Discharged 7 ppb Assuming 7 ppb Assuming from the 3 Year Half Life 10 Year Half Life Aquifer 1979 1979 40.8 . 1983 1983 , 1979 1984 51.6 18 1993 ZOOl 3 1979 1984 2.3.6 3Z 1989 zaaz . 1979 1984 38.9 53 1991 ZOO9 5 1979 1984 55.7 91 1993 Z014 6 1977 1982 61.6 143 1991 2013 7 NA.. NA.. NA.. NA** NA*. NA*. 8 1976 1981 78.0 60 1992 2016 9 1976 1981 109.9 51 1993 2021 10 1976 1981 99.4 .5 1992 2019 11 1976 1981 118.4 ,9 1993 2010 1, 1977 1980 5.0 ,0 1977 1977 13 1976 1981 61.8 8 1989 1989 In these cases the contaminated water would be dischar~ed from the aquifer before the aldicarb would decay to a concentration below 7 ppb. 'II. Not computed because no aldicarb was applied to this section. 'II.. Very little aldicarb was applied to Area *12. and simulated recharge concentrations from this area are always less than 7 ppb. Explanation of Columns in Table 2 A . Area. Stream tube, Number ~ Area numbers refer to the numbered areas and corresponding stream tubes which receive the recharge from those areas as depicted in Figures 1 and 2. B . Year Aldicarb First Reaches Water Table - This gives the year in which aldicar"b would have first reached the water table according to the simulation. Note that the greater the distance between the land surface and the water table, the longer the time between when aldicarb is applied at the surface and when it reaches the water table. C . Year All Aldicarb Has Reached the Water Table - After this year all aldicarb is in the saturated zone and none remains in the unsaturated zone according to the simulation. o . Averalle Aldicarb Concentration in Recharlle Water at the Water Table - This is the average concentration of aldicarb in water entering the saturated zone between the time when aldicarb first reaches the water table and the time when it has all reached the water table. E . Number of Years for Water StartinlZ at the Water Table to be Discharlled from the AQuifer - This gives the time it,takes for water to travel throuih the stream tube to the Sound or Bay. This is an upper limit on the amount of time that contaminated water could remain in tee stream tube. F . Date When Aldicarb Concentration Would Be Below 7 JJ1)b Assuminll a 3 Year Half Life - Asauming first order decay this iives the year that the concentration given in column 0 would decay to below the 7 ppb guideline. The number of years tbat decay would require is added to the year in column C to get the year in column E. G . Date When AveraR:e A1dicarb Concentration Would Be Below 7 l1Pb AssuminlZ 10 Year Half Life - The same as the calculation for tbe 3 year balf life only now using a ten year half lile. 6 Table 3 Laboratory data on half-lifes (in days) of aldicarb and its degradation products in water at various p3's and temperatures. pH Source 5.5 6.0 7.0 7.5 8 8.5 Aldicarb 150C 3240 1900 170 b 250C 266 245 266 a Aldicarb Sulfoxide 150C 440 360 10 b NA NA 73 c 4221 422 42 d 250C 679 161 23 a NA 154 22 c Aldicarb Sulfone 150C 450 125 5 b NA 2n 52 c 1458 145 15 d 250C 420 77 10 a NA 84 10 c 597 60 6 d Sources: a) Chapman and Cole (1982). b) Hansen and Spiegel (1982). c) Hansen et a1. (1983) (Note: Values labelled "NA" are not yet available but will be at the conclusion of the experiments). d) Lemley (1983) (Note: These data are extrapolated from experiments conducted at pH's 11 to 13). which wells at individual houses would be expected to exceed the standad.. Alclicarb was applied to potato farms along the uepot Lane transect for the fi'le years between 1975 and 1979. The .Jlumes of aldicarb contamination will advance though the ground water underlying the transect, preceded and followed by aldicarb-free water representing recharge from before and several years after the application period. Individual wells would therefore in most cases be expected to exceed the 7 ppb sta,dard for a shorter period of time than 'i- 0 dates in our table, which represent 7 aldicarb disappearance nlume rather than at along its path. in the moving stationary sites The transect also portrays a wor_e th311 usual case for aldicarb in SouthalL's ground water because approximately half of the land along Depot Lane is devoted to potato farl.,lng, whereas in Southold as a whole only approximately 41 percent of the land is used for any type of agriculture. ~'or Eastern Long Islan-i, faming accounts for less than 20.'''' of the ~ ntal land use. 8 REFERENCES Baier, J.H., and S.F. Robbins. 1982. Report on the Occurrence and Movement of Agricultural Chemicals in Groundwater: North. Fork of Suffolk County. Suffolk County Department of Health Services, Bureau of Water Resources. C1apman, R.A., and C.M. Cole. 1982. Observations on the Influence of Water and Soil pH on the Persistence of Insecticides. J. Environ. Sci. Health B17(5):487- 504. Hansen, J.L. and M.H. Spiegel. 1983. Long Term Hydrolysis Studies of A1dicarb Sulfoxide and A1dicarb Sulfone. Union Carbide Corp., unpublished Report. Hansen, J.L., R.R. Romine and M.H. Spiegel. 1982. Hydrolysis Studies of Aldicarb, Aldicarb Sulfoxide and Aldicarb Sulfone. Environmental Toxicology and Chemistry 2:147- 153. ;(dn, D.P. and T.S. Steenhuis. 1983. Adsorption Partition Coefficients and Degradation Rate Constants and Half-Lifes of Selected Pesticides Compiled from the Literature. Unpublished Manuscript. Cornell University, Ithaca, New York. Lemley, A.T. 1983. Unpublished Results. Department of Design and Environmental Analysis, Cornell University, Ithaca, N.Y. Pacenka, S. and K.S. Porter. 1981. Preliminary Regional Assessment of the Environmental Fate of the Potato Pesticide, A1dicarb, Eastern Long Island, New York. Center for Environmental Research, Cornell University, Ithaca, New York.