UNITED STATES ENVIRONMENTAL PROTECTION AGENCY WASHINGTON D

. C. , 20460 O FF I CE O F CHE MICAL SAFE TY A N D PO L L UT I ON PREVENT IO N 

### MEMORANDUM

SU BJE C T :

FROM:

THR U :



### TO: PC Code : 116002 , 116004 DP Barcod e: 419489 , 427507 Response t o Re g is trant 's Re buttal on th e Drinkin g Wate r N umbers Used b y HED 

### in S upport o f the Remo v al of Graz in g R es triction s for Lactating Dairy Animal s o n T ricl o py r T EA (P C C od e 116002 ) an d B E E (PC Co d e 116004) Larry Liu, P h .D, Che mist 

# -f ;

/' / Env iron m enta l Ri sk B r a n c h 5 

## LA/' Enviro nmen ta l F ate and Effects Divis i on (7507 P ) 

## I


## · Ob/ 0 

# 'f /I S-- Mah Shamim , Ph.D. Branch Chief 

# JYtlti**~** 

## I Enviro nmen tal Risk B ranch 5 

# I/**ff~** Env iro nme nta l Fate and Effects Divis i on (7507 P ) Mindy Ondish , Ri sk Manager Rev iewe r Reuben Baris. Risk Manager , RM-25 H

e rbic ide Branch R

egistrati o n Division (7505P) Je nn ifer Ty l er, Che m ist RA B I 

### Health Effects Divis ion (7509P)
EFED has reviewed comme n ts received from the registrant (Dow AgroSc iences LLC) regardi n g tr i clopy r dri nki n g water EECs used in the Acute and Ch r o nic Agg r egate Di e tary ( F ood and Drin k in g W ate r ) Ex p os ure a nd Ris k Assess m ent fo r th e Pro pose d Livestock To l era n ce C h a nges on three labe l s [triclopyr T EA (EPA. R eg. No. 627 19

- 37) , and tr i clopyr B EE (EPA Reg
. No. 62719-552 and 627 1 9-63 7)]. S ince the proposed removal of a grazing r estriction for lac tating dairy an imals does not change the dr inking water assessment , E FED is referring to the last assessment comp leted on 6 / 17/2002 (see anachment)
. I n this drinking water assessment, EF ED reco m mended va lu es of 1, 049 ppb and 390 ppb fo r acute a n d ch r on i c d rinki n g wate r EECs
. In r es po nse , th e r eg istrant s uggested that a va lu e of 4 0 0 pp b s h ou ld be u sed fo r ac ute and c hro ni c dr inkin g wate r E E Cs beca use the labe l s in clude the setback d istance from th e app l icat i o n site to a functiona l potab le water intake and the in take mu st be turned off unt il th e tr ic lopyr concentration in t he intake water is less than 400 ppb. EFED concurs with the registrant that 400 ppb s ho uld be used for ac u te and chronic dr i nking water EEC.MEMORANDUM UNITED STATES ENVIRONMENTAL PROTECTION AGENCY WASHINGTON , D.C. 20460

OFFICE OF PREVENT I ON. PEST I CIDES ANO TOXIC SUBSTANCES

PC Code: 116002 DPBarcode: 

### D 283 

## " f I 

## 5 SUBJECT: Revi se d Tier 1 Esti mate s for Drinking Water Concentrations Resulting from T riclopyr Use for Aquatic Weed Control DAT E : 1 7 June 2002 FROM : Miche le M aho ne y, Agronomist 

### fl<.**~~l/18/oz** Ian Kennedy, Hydrologist 

### -r-**tS-~-** 

# __ 1...,, / Environmental Risk Branch II · - ..-**~ -~**  ig"f ..;,... 2 • .:1c:n.. Environmental Fate and Effects Division (7507C) TO: Jim Tompkin s

THRU: Registration Divi sion (7505C) Dana Vogel Health Effects D i vision (7509C) 

# 1 Tom Bailey , Branch Chief 

# rr-----o7Jl7 Environmental Risk Branc h II
.../ Environmenta l Fate and Effects Divi si on (7507C)
Summary: EFED has calculated suggested setback di stances fo r triclopyr ap p l ications near dr inki ng water intakes and made predictions for peak and ann u a l average dri nkin g water concentrati ons resulting from direc t applicati on of t riclopyr TEA to surface water at such se tbacks. For the setback d istances discu ssed b e low the estimated peak (acute) drinking wa ter concentration ran ges up to I 049 ppb and the estimated annual average drinking water concentrati on ranges up to 390 ppb. Discussion: The estimated environmental concentrations (EEC's) we r e based on treatment of an area of a lak e at the maximum ap pl ication rate of2
. 5 ppm , at se tback distance s wh ich a re dependent on the size of the area treated
. EFED calculated setbacks to be used in order to ke ep the annua l average concentration be low 400 ppb and then used th ese setbacks in calcu lati n g annual average and peak EEC's.Estimates were made using the one-dimensional convection-dispersion equation

The dimen s ionless parameters in this equation are C 

# = c/c0, 't 

# = vt

l l , Z 

### = xll, P 

# = vl/D, 

### μ 

# = ln(2)Llvt 112 • Where c is the conc e ntration , c 0 the initial concentration , 

### l the l ength of the water body , 

### x is distance along the water body, 

### v i s the water flow rate, 

### D is a dispersion coefficient and t lll. is the half-life of the chemical. The dimensionless paramete r 

### Pis known as the Peclet number and can be u sed to tell how much a pulse will spread as it flows the length of the system. The so luti on to this equation, as s umin g an initial constant concentration between two points i s (Toride et al., 1 995)



# - = 

# L (- 1) ' e- μ r l - 

### -erfi ' - -e 4r

C ' · [ 

# l I {(Z-Z

. )

- r ) f,!r pz_ P [(Z-Z,> +r f C

0 i=O 2 

# .J 4 

### r I P 1r 

## +i(1+ P(Z 

## + Z;)+ Pr)e " erfr (

# (Z~ 

# ' )f]

where the 

### Z ; are the start and end of the applicatio n zone , converted to dimensionless parameters in th e same manner as Z , above. The function erfc(x) is the complementary error function and is defi n e d as

The yearly average concentration at different distances downstream was then calcu l ated and used to detennine the setback distance needed to keep the annua l average concentration below 40 0 ppb. The e quati on uses only one spac e dimension, so only the len gth of the application area was considered. This length was calc ul ated from the application area by assuming the treated area had proportions id entical to those of the Index Reservoir (640m x 82m) and using the long side of the resu lting rectangle as the length of the app lication (and because we cons idered only one dimension, the width of the lake). Thus for a 4 acre (16000 m 2 ) app li cation area, we would assume a long , skinny lake 45m wide , w ith an application the full width and 360m lon g . These lengths are listed in Table I below , and shown graph i cally in Figure I. Note that this does not ass um e th e entire lake i s treated , and app licat ions to other areas of the lake at different times would add to the EEC's presente d here
. The index reservoir. whic h is a flooded stream channel, 2should represent the type of water body geometry likely to transport a direct application most efficiently to a water intake. Such a water body i s also more likely to have lower di spersion, as assumed here. than a water body with more complex geometry. Parameters used fo r t hi s calculation were D 

# = 0
.0005 m2 /s and and a ha lf- li fe of t riclopyr of 142 days. Flow veloci t ies ranged between 2.28 m/day and 6.28 m/day , depending on the size of the application area, and were chosen to maximize the annual average concentrat i ons. The flow velocities used in previou s direc t application EEC calculations ranged between 1.75 m/day and I 2.2 m/d ay, so th ese flow rates fa ll squarely into that range. These flow rates are somewhat lower than those used in previous modeling done for the registrant , but were chosen as conservative values. Higher water velocities would mo ve the chemical mo re quickly and result in lower annual ave rage concentration s. Lower wate r veloc ities will allow more time for the chemical to degrade before reaching the setback p oint. The dispersion va l ue of 0.0005m 2 /s is fa irl y s mall, lower than that used in model ing subm itted by the registrant, and was chosen because small dispersion values result in more conservative EEC's. This value is on the low end of d i spers i on values for lakes (Chapra, 1997). Decreasing the di s persion to zero wou ld result in p l ug flow , where the chemical moves in a sing le slug the size of the appl ication area withou t sp reading. Suc h a scenario wou l d res u lt in somewhat h igher annua l average and peak concentrations. For the listed appl ication areas and se tbacks, annual average concentrations would remain below 400 ppb. Peak concentrations wou l d increase to around 1150 ppb for all four cases. Note that for t reatment areas of 8

- I 6 and**~** 16 ac r es, the setback distances l is t ed in the tab l e are greater th an those on the proposed labe l. The proposed label doe s not specify a maximum area that can be treated

- the largest area is simply 

### Figu r e 1. relative si z es of applica tion ar

eas listed as**I** 6 acres. Here**the" ~**  1 6 acre" category was as sumed to be 32 acres, and the treated length and setback was calculated using this area. The sizes and shapes of the treated areas are shown in Figure 1
. Setbacks are the distance downst ream from the downstream end of each of these areas, and are not s hown in th e figure. Treated a reas greater than 32 acres were not considered in t h is assessment , but setback d i stances would need to i ncrease proport i onall y for larger ap pl ication areas . EFED believes the se calculations pre sented here rep resent a more protective estimate of EEC's. Flow rate s we re chosen to maximize annual average conce ntrat i ons for each of the four cases considered. The dispers i on value was used was small, which a l so results in somewhat h i gher EEC's. G r eater d is p e r s ion and a n y c h ange in flow rate wo ul d lead to lowe r p redic ted annua l
3average EEC's
. Finally , the convection dispersion equation was solved in only one space dimension, so on ly longitudinal mixing of triclopyr was considered. This i s equivalent to an app li cation over the entire width of the l ake
.



### Table 1. 

### Input Sizes, Setbacks an d EECs Area Treate d Setback Distance flow rate Concentration (ppb)
acres 

### m 2 length (m) feet meters 

### m/day annual avg peak 

### sA 16187 360 1000 300 2
. 28 382 821 4-8 32375 500 1400 425 3. 1 3 384 894 8-16 64750 710 2000 600 4.44 389 983 216 129500 

### lOOO 2600 792 6.28 390 10 4 9


### Ref e rences Chapra, S. C. (1997)
. 

### Surface Water Quality Modeling. McGraw Hill , New York , p. 149 Toride, N., F
. J. Leij , and M. Th. van Genuchten, 1995. 

### The CXTFITCodefor Estimating Transport Parameters from laboratory or Field Tracer Experiments. US DA-ARS , U.S. Salinity Lab oratory Re search Report No. 13 7

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