Evaluation of Pesticides in Ground Water - ACS Publications

10 Monitoring Ground Water for Pesticides S. Z. Cohen, C. Eiden, and M . N. Lorber

Evaluation of Pesticides in Ground Water Downloaded from pubs.acs.org by UNIV OF LEEDS on 10/04/15. For personal use only.

Office of Pesticide Programs (TS-769C), U.S. Environmental Protection Agency, Washington, DC 20460

At least 17 pesticides have been found in ground water in a total of 23 states as a result of agricultural practice. These results have been obtained through three different types of monitoring studies: (1) large-scale retrospective, (2) smallscale retrospective, and (3) small-scale prospective. The first two types of studies survey areas where the pesticide(s) in question has already been used. The third type of study is an intensive field study where the pesticide is applied and monitoring begins at time zero. Often, soil core data are at least as important as ground-water data. The ability to draw meaningful conclusions from large-scale studies is greatly diminished unless the studies have a statistical, stratified design. The purpose of this paper is threefold: to describe the three study types; suggest guidelines for ground-water sampling, soil sampling and well construction; and update the data summary of pesticides in ground water from agricultural practice. In 1984, Cohen e t a l . r e v i e w e d l e a c h i n g and m o n i t o r i n g d a t a on 12 d i f f e r e n t p e s t i c i d e s found i n ground water i n a t o t a l o f 18 d i f f e r e n t s t a t e s as a r e s u l t o f a g r i c u l t u r a l p r a c t i c e (V) · They a l s o e s t a b l i s h e d c r i t e r i a f o r p r e d i c t i n g whether c e r t a i n p e s t i c i d e s c o u l d l e a c h t o ground water as a r e s u l t o f normal use. In the l e s s t h a n 2 y e a r s s i n c e t h a t paper was p u b l i s h e d , t h e numbers o f p e s t i c i d e s found i n ground water have i n c r e a s e d s i g n i f i c a n t l y as have the number o f s t a t e s found t o have p e s t i c i d e s i n ground w a t e r . Seventeen p e s t i c i d e s have now been found i n t h e ground water o f 23 s t a t e s as a r e s u l t o f a g r i c u l t u r a l p r a c t i c e ( F i g u r e 1, T a b l e I ) . (As d e s c r i b e d i n t h e " O c c u r r e n c e " s e c t i o n a t t h e end o f t h i s paper, many a d d i t i o n a l f i n d i n g s can be a t t r i b u t e d t o poor d i s p o s a l p r a c t i c e s , m i x i n g - l o a d i n g o p e r a t i o n s , e t c . and a r e n o t i n c l u d e d i n t h i s c o u n t . ) T h i s s i g n i f i c a n t i n c r e a s e i s more l i k e l y due t o an i n c r e a s e i n t h e q u a l i t y and q u a n t i t y o f s t u d i e s r a t h e r t h a n an i n c r e a s e i n This chapter not subject to U.S. copyright. Published 1986, American Chemical Society


F i g u r e 1. Numbers o f p e s t i c i d e s found i n ground a result of a g r i c u l t u r a l practice.

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E V A L U A T I O N O F PESTICIDES IN G R O U N D WATER

Table I .

T y p i c a l P o s i t i v e Results of P e s t i c i d e M o n i t o r i n g i n t h e U.S.t


Pesticide

Use*

Alachlor Aldicarb (sulfoxide & sulfone)

H I, Ν

Atrazine Bromacil Carbofuran Cyanazine DBCP DCPA (and a c i d products) 1,2-Dichloropropane Dinoseb Dyfonate EDB

Η Η I, Ν Η Ν Η

Metolachlor Metribuzin Oxamyl Simazine 1,2,3-Trichloropropane

MD, AR, MA, NY, VA, ΡΑ,

ΙΑ, NE, ΡΑ AZ, CA, F L , ME, NC, NJ, OR, R I , TX, WA, WI IA, NE, WI, MD FL NY, WI, MD ΙΑ, PA AZ, CA, HI, MD, SC NY

Ν

CA, MD, NY, WA

Η I Ν

NY IA CA, F L , GA, SC, WA, AZ, MA, CT ΙΑ, PA IA NY, RI CA, PA, MD CA, HI

Η Η I, Ν Η Ν (impurity)

t T o t a l o f 17 d i f f e r e n t p e s t i c i d e s *H - h e r b i c i d e I = insecticide N = nematicide

State(s)

Ground-Water

Typical Positive, ppb 0.1-10 1-50

0.3-3 300 1-50 0.1-1.0 0.02-20 50-700 1-50 1-5 0.1 0.05-20 0.1-0.4 1.0-4.3 5-65 0.2-3.0 0.1-5.0

i n a t o t a l o f 23 d i f f e r e n t

states.


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the problem. However, o u r knowledge o f t h e t r u e e x t e n t o f p e s t i c i d e o c c u r r e n c e i n ground water has i n c r e a s e d o n l y s l i g h t l y . This i s not t o s a y t h a t EPA has been i d l e i n the i n t e r i m . On t h e c o n t r a r y , t h e r e has been a tremendous i n c r e a s e i n a c t i v i t y i n t h i s a r e a . The problem i s t h a t t h e t a s k i s enormous. The t a s k i s t o c h a r a c t e r i z e the e x t e n t o f c o n t a m i n a t i o n o r e x t e n t o f p o t e n t i a l c o n t a m i n a t i o n , i n terms o f : 1. p e s t i c i d e s i n g e n e r a l and the n a t i o n as a whole; 2. s p e c i f i c p e s t i c i d e s and groups o f p e s t i c i d e s , e.g., nematicides; 3. s p e c i f i c crop growing a r e a s , e.g., c i t r u s ; 4. a r e a s a s d e f i n e d by s p e c i f i c f i e l d c o n d i t i o n s , e.g., soil p e r m e a b i l i t y and ground-water depth; 5. a r e a s as d e f i n e d p o l i t i c a l l y , e.g., counties; 6. i n d i v i d u a l p e s t i c i d e s , t h e r e l a t i o n s h i p between t h e i r p r o p e r t i e s , f i e l d c o n d i t i o n , and the mechanisms o f l e a c h ing. These c h a r a c t e r i z a t i o n s are n e c e s s a r y i n o r d e r t o make b e t t e r i n f o r m e d r e g u l a t o r y d e c i s i o n s on p e s t i c i d e r e g u l a t i o n and d r i n k i n g w a t e r contaminant r e g u l a t i o n s . C l e a r l y , no s i n g l e m o n i t o r i n g o r p r e d i c t i v e e x e r c i s e can address a l l of these i s s u e s . What needs t o be done, i n the case of m o n i t o r i n g s t u d i e s , i s t o c l e a r l y s t a t e and l i m i t t h e o b j e c t i v e s o f t h e s t u d i e s , and then d e s i g n t h e s e s t u d i e s so t h a t they c o n t a i n c o n s i d e r a t i o n s f o r h y d r o g e o l o g y , p e s t i c i d e usage, and s t a t i s t i c s . T h i s paper w i l l d i s c u s s t h r e e study t y p e s which, c o l l e c t i v e l y , c a n be used t o c h a r a c t e r i z e t h e problem i n t h e s i x d i f f e r e n t ways d e s c r i b e d above. Large-scale r e t r o s p e c t i v e p r o b a b i l i t y , s m a l l - s c a l e r e t r o s p e c t i v e , and s m a l l s c a l e p r o s p e c t i v e s u r v e y s a r e d e s c r i b e d below. The two o t h e r p u r p o s e s o f t h i s paper a r e t o o f f e r some g u i d e l i n e s f o r t h e conduct of t h e s e s t u d i e s and t o update t h e d a t a summary o f p e s t i c i d e s i n ground w a t e r from a g r i c u l t u r a l p r a c t i c e . But f i r s t i t would be h e l p f u l t o l i s t some o f t h e t o o l s a v a i l a b l e t o d e s i g n t h e s e studies. I t i s important to note that p o t e n t i a l p e s t i c i d e l e a c h e r s can be and have been i d e n t i f i e d (^, 2 ) . C r i t e r i a are a v a i l a b l e t o a s s e s s ground-water v u l n e r a b i l i t y f o r p e s t i c i d e a p p l i c a t i o n (J^, _3, 4_) · The acronym "DRASTIC" d e s c r i b e s a scheme f o r combining w e i g h t e d e v a l u a t i o n s o f seven d i f f e r e n t h y d r o g e o l o g i c a l parameters i n t o a s c o r e , which i s an i n d i c a t o r o f r e l a t i v e ground-water c o n t a m i n a t i o n p o t e n t i a l f o r a county o r subcounty r e g i o n ( 3 ) . Also, r e g i o n a l p e s t i c i d e s a l e s d a t a (_5) and county l e v e l c r o p d a t a ( 6 ) a r e a v a i l a b l e t o t h e p u b l i c , w h i l e more s p e c i f i c and c o n f i d e n t i a l s a l e s o r use d a t a c a n be p r o v i d e d t o the EPA by t h e p e s t i c i d e i n d u s t r y ( " r e g i s t r a n t s " ) . F i n a l l y , s t a t i s t i c a l s u r v e y methods a r e a v a i l a b l e ( 7 - 1 1 ) . Thus v a r i o u s t o o l s a r e a v a i l a b l e which can be i n t e g r a t e d i n t o s t u d i e s d e s i g n e d t o s a t i s f y c e r t a i n o b j e c t i v e s as d e s c r i b e d above. Large-Scale Retrospective

Studies

The o b j e c t i v e o f l a r g e - s c a l e r e t r o s p e c t i v e ground-water s t u d i e s i s co c h a r a c t e r i z e the e x t e n t o f o c c u r r e n c e o f p e s t i c i d e s i n w e l l s over a l a r g e a r e a . These s t a t i s t i c a l s u r v e y s c o v e r m u l t i c o u n t y


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o r m u l t i s t a t e a r e a s and t y p i c a l l y i n v o l v e sampling of more than 100 w e l l s . They a r e complex and e x p e n s i v e s u r v e y s and are u s u a l l y done f o r s p e c i f i c p e s t i c i d e s a f t e r d e t e r m i n a t i o n of a human h a z a r d c o n c e r n and a f t e r documented w e l l c o n t a m i n a t i o n . T h i s type of s u r v e y can a l s o be u s e f u l t o s t a t e o r o t h e r a g e n c i e s who would l i k e t o make e s t i m a t e s about p e r c e n t a g e s of w e l l s contaminated by v a r i o u s c h e m i c a l s u s i n g m u l t i r e s i d u e methods. A b r i e f d i s c u s s i o n of some p r i n c i p l e s of p r o b a b i l i t y s u r v e y s f o l l o w s . F u l l e r e x p l a n a t i o n of the b a s i c methods and t h e o r i e s of survey s t a t i s t i c s a r e given elsewhere (7-11). P r o b a b i l i t y s u r v e y s a r e s u r v e y s where samples a r e s e l e c t e d by a s p e c i f i e d random p r o c e s s . The p o p u l a t i o n from which the samples w i l l be s e l e c t e d i s c a l l e d the u n i v e r s e or the t a r g e t p o p u l a t i o n . The d a t a c o l l e c t e d from t h e s e s u r v e y s a r e used t o make i n f e r e n c e s about the t a r g e t p o p u l a t i o n of w e l l s which may be c a t e g o r i z e d i n v a r i o u s ways. Some examples o f t a r g e t p o p u l a t i o n s a r e w e l l s i n : ° a l l corn-growing c o u n t i e s where p e s t i c i d e X i s a p p l i e d t o >10% of the l a n d a r e a ; ° c e r t a i n ground-water b a s i n s i n the s o u t h e a s t ; ° the U n i t e d S t a t e s ; ° the S t a t e of F l o r i d a ; ° areas with h i g h l y vulnerable hydrogeologies i n a certain state, etc. Once the t a r g e t p o p u l a t i o n has been d e f i n e d , two p r i n c i p l e s s h o u l d be c o n s i d e r e d . F i r s t , s t a t i s t i c a l c o n c l u s i o n s drawn from the s t u d y a r e not r e l i a b l y a p p l i c a b l e o u t s i d e the t a r g e t p o p u l a t i o n . Second, i f w e l l s are a r b i t r a r i l y e x c l u d e d from s a m p l i n g a t l a t e r s t a g e s of the s u r v e y d e s i g n or e x e c u t i o n , the s t a t i s t i c a l v a l i d i t y of the study s u f f e r s s i g n i f i c a n t l y . The c o n v e r s e i s t r u e - w e l l s c a n t be a r b i t r a r i l y i n c l u d e d . T h i s i s a c o r o l l a r y of the s t a t e ment t h a t a l l sampling u n i t s ( w e l l s , farm f i e l d s , e t c . ) must have a non-zero p r o b a b i l i t y of s e l e c t i o n . O t h e r w i s e , water q u a l i t y r e s u l t s from w e l l s s e l e c t i v e l y chosen may r e f l e c t a p a r t i c u l a r w e l l - c o n s t r u c t i o n o r " a q u i f e r - m a t e r i a l e f f e c t , " and w i l l not be r e p r e s e n t a t i v e of a l l the water i n the s p e c i f i c a q u i f e r t h a t i s under study ( 1 2 ) . H e l s e l and Ragone make use of an example where w e l l s from two a r e a s a r e s e l e c t i v e l y chosen, one s e t of w e l l s a r e s c r e e n e d i n c o a r s e g r a v e l s , the second s e t b e i n g screened i n a v a r i e t y of m a t e r i a l s . R e s i d u e c o n c e n t r a t i o n s may d i f f e r between the two s e t s , r e f l e c t i n g the d i f f e r e n c e i n l i t h o l o g i e m a t e r i a l s s u r r o u n d i n g the w e l l s c r e e n s , and not the d i f f e r e n c e s i n p e s t i c i d e use p a t t e r n s . A f t e r the sample p o p u l a t i o n has been d e t e r m i n e d and the c o n s t r a i n t s u n d e r s t o o d , an o v e r a l l e x p e r i m e n t a l d e s i g n can be constructed. The major p o s s i b i l i t i e s a r e simple random s a m p l i n g , random s a m p l i n g w i t h i n g e o g r a p h i c a l or s p a t i a l c l u s t e r s , and s t r a t i f i e d random s a m p l i n g . ( I n t h i s paper, "random s a m p l i n g " i s a c o n v e n i e n t term w h i c h means sampling of e q u a l o r p r o p o r t i o n a t e p r o b a b i l i t y and w i t h o u t r e p l a c e m e n t . ) In a l l c a s e s , a c r i t i c a l s t e p i s the d e t e r m i n a t i o n o f the sample s i z e . There a r e e s t a b l i s h e d ways f o r c a l c u l a t i n g the r e q u i r e d numbers, η (7_, 9-11); but b a s i c a l l y η i s a f u n c t i o n of the d e s i r e d p r e c i s i o n of the c o n c l u s i o n (where p r e c i s i o n i m p l i e s a l i m i t on the p r o b a b i l i t y , say .05, t h a t the c o n c l u s i o n s d i f f e r from the t r u e answer by a t most a s p e c i f i e d f


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p e r c e n t a g e ( s a y 15%) o f t h e t r u e answer, t h e t a r g e t p o p u l a t i o n s i z e , and t h e c o s t p e r sample. Often, p r o b a b i l i t y surveys are designed i n stages. This i s e s p e c i a l l y t h e case when the t a r g e t p o p u l a t i o n i s l a r g e and s u c c e s s i v e s t a g e s a r e n e c e s s a r y t o reduce t h e p o t e n t i a l number o f w e l l s , f a r m s , e t c . , t o be sampled. Once t h e t a r g e t p o p u l a t i o n has been i d e n t i f i e d , i t i s c a r v e d up i n t o c o n v e n i e n t p o p u l a t i o n s e g ments such as c o u n t i e s , e n u m e r a t i o n d i s t r i c t s , b a s i n s , e t c . These segments a r e c a l l e d p r i m a r y sampling u n i t s ( P S U ' s ) . The next s t e p i n s t a g e d d e s i g n i s t o randomly s e l e c t some PSU's f o r f u r t h e r study. T h i s s u b p o p u l a t i o n o f randomly s e l e c t e d PSU's i s r e f e r r e d t o as t h e f i r s t s t a g e sample. I n a two-stage d e s i g n , w e l l s a r e then randomly s e l e c t e d from the sample frame f o r f i e l d s a m p l i n g , i . e . , water a n a l y s i s . B e f o r e t h e s p e c i f i c s u r v e y types a r e d i s c u s s e d , some advantages of p r o b a b i l i t y s u r v e y s s h o u l d be mentioned. Such s u r v e y s a r e e f f i c i e n t i n t h a t r e s u l t s from a r e l a t i v e l y s m a l l number o f samples can be used t o draw r e l i a b l e c o n c l u s i o n s about a l a r g e t a r g e t popu lation. The p r o b a b i l i t y approach a l s o r e d u c e s p o s s i b l e s e l e c t i o n b i a s r e s u l t i n g from the ' l e t ' s g r a b a sample here because i t l o o k s good' p h i l o s o p h y . P u t i n d i f f e r e n t words, "the major ob s t a c l e t o random s e l e c t i o n i s c o n v e n i e n c e - i f i t i s more c o n v e n i e n t t o s e l e c t sampling p o i n t s i n a p a r t i c u l a r f a s h i o n , the p r o c e s s i s p r o b a b l y not random and s h o u l d be a v o i d e d " (12)· In simple random s a m p l i n g , samples a r e randomly s e l e c t e d from the t a r g e t p o p u l a t i o n , where t h e t a r g e t p o p u l a t i o n i s u s u a l l y w e l l s , but may be the ground water under farms, g o l f c o u r s e s , e t c . T h i s d e s i g n s t r a t e g y i s g e n e r a l l y o n l y recommended i n l i m i t e d c i r c u m s t a n c e s f o r s t u d i e s o f p e s t i c i d e s i n ground water because o f e x p e c t e d h i g h v a r i a n c e s i n t h e s t a t i s t i c a l c o n c l u s i o n s and t h e f a c t t h a t i t does n o t a l l o w one t o i n c o r p o r a t e knowledge o f f i e l d con d i t i o n s i n t o the design. One example where t h i s approach makes sense i s when the p o p u l a t i o n t o be sampled i s v e r y n a r r o w l y d e f i n e d and i s known t o be r e l a t i v e l y homogeneous. For example, a t a r g e t p o p u l a t i o n c o u l d be w e l l s o f s i m i l a r c o n s t r u c t i o n i n a k a r s t l i m e stone r e g i o n o f a two county a r e a dominated by one s o i l t e x t u r e , e.g., a loamy sand. I n t h i s c a s e , e s t i m a t e s r e s u l t i n g from s i m p l e random s a m p l i n g would l i k e l y have a lower v a r i a n c e compared t o o t h e r r e g i o n s c o n t a i n i n g w i d e l y v a r y i n g types o f s o i l and s u b s u r f a c e h y d r o g e o l o g y . Thus knowledge o f ground-water v u l n e r a b i l i t y was used t o l i m i t t h e t a r g e t p o p u l a t i o n , b u t was n o t a p a r t o f t h e s t a t i s t i c a l design. The second type o f random s a m p l i n g , which has some s p a t i a l c o n t r o l on t h e sample d i s t r i b u t i o n , i s a s p e c i a l case o f s t r a t i f i e d random s a m p l i n g . No examples o f t h i s type c o u l d be found i n t h e l i t e r a t u r e p e r t a i n i n g t o w e l l sampling d e s i g n ; however, an example of t h i s second type o f random s a m p l i n g p e r t a i n i n g t o s o i l core s a m p l i n g was found and i s d i s c u s s e d i n t h e s e c t i o n on s o i l s a m p l i n g under s m a l l - s c a l e r e t r o s p e c t i v e s t u d i e s . As r e g a r d s w e l l sampling d e s i g n a p o s s i b l e d e s i g n s t r a t e g y i s as f o l l o w s : The w e l l s o f t h e e a s t e r n shore o f a m i d - A t l a n t i c s t a t e a r e i d e n t i f i e d as t h e t a r g e t population. G r i d s c o r r e s p o n d i n g t o 5 mi χ 5 mi a r e a s a r e l a i d o v e r a map o f t h a t r e g i o n o f t h e s t a t e . One o r more w e l l s a r e then randomly sampled w i t h i n each g r i d s e c t i o n . T h i s study type


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may have l i m i t e d a p p l i c a t i o n t o a r e a s which c o n t a i n l a r g e h y d r o g e o l o g y and human a c t i v i t y ( e . g . , d i s p o s a l s i t e s ) d a t a gaps and i n the s i t u a t i o n s when the time r e q u i r e d f o r an a p p r o p r i a t e r e c o n n a i s s a n c e a n a l y s i s i s too l o n g . In such a s i t u a t i o n , t h i s may be c o n s i d e r e d a p r e l i m i n a r y study which would l e a d t o the g e n e r a t i o n of h y p o t h e s e s and the i n i t i a t i o n of a d d i t i o n a l s t u d i e s . The t h i r d type of random sampling d i s c u s s e d i n t h i s paper i s s t r a t i f i e d random s a m p l i n g . The p r i n c i p a l weakness of s i m p l e r a n dom sampling i s t h a t i t does not use r e l e v a n t i n f o r m a t i o n or j u d g e ment t h a t we have about the environment, i . e . , about p e s t i c i d e s l e a c h i n g t o ground w a t e r . F o r example, i t would i n c o r p o r a t e our knowledge t h a t a r e a s w i t h loamy sands o v e r l y i n g s o l u t i o n l i m e s t o n e a q u i f e r s are p a r t i c u l a r l y v u l n e r a b l e to p e s t i c i d e p o l l u t i o n . This knowledge can be used i n s t r a t i f i e d random s a m p l i n g . In t h i s s u r v e y approach, the t a r g e t p o p u l a t i o n i s d i v i d e d i n t o s u b p o p u l a t i o n s o r s t r a t a t h a t a r e i n t e r n a l l y more homogeneous than the t a r g e t p o p u l a t i o n as a whole ( 1 1 ) . Then s p e c i f i e d numbers of samples a r e randomly s e l e c t e d from each s t r a t u m . Recommended s t r a t i f i c a t i o n v a r i a b l e s a r e ground-water v u l n e r a b i l i t y and p e s t i c i d e usage. Human o r w e l l p o p u l a t i o n d e n s i t y may be used or i t may be used as a ' s i z e m e a s u r e , a w e i g h t i n g f a c t o r t o i n c r e a s e the p r o b a b i l i t y t h a t c e r t a i n a r e a s may be s e l e c t e d . The s t r a t a s h o u l d be c o n s t r u c t e d so t h a t they a r e m u t u a l l y e x c l u s i v e and a c c o u n t t o t a l l y f o r the t a r g e t p o p u l a t i o n . 1

F o l l o w i n g i s an example of a s t r a t i f i e d random s u r v e y . EPA's O f f i c e o f D r i n k i n g Water and O f f i c e of P e s t i c i d e Programs (OPP) a r e j o i n t l y d e s i g n i n g a n a t i o n a l s t r a t i f i e d random s u r v e y w i t h the h e l p of s t a t i s t i c a l and h y d r o g e o l o g y c o n t r a c t o r s . The s u r v e y i s b e i n g d e s i g n e d i n t h r e e s t a g e s - s e l e c t c o u n t i e s , s e l e c t county segments, s e l e c t w e l l s . As of t h i s w r i t i n g , the d e s i g n of the second and t h i r d s t a g e s i s u n c e r t a i n . However, i n the f i r s t stage the s t r a t i f i c a t i o n v a r i a b l e s a r e p e s t i c i d e usage ( 5 , 6) and ground-water v u l n e r a b i l i t y ( 3 ) . A l l c o u n t i e s i n the U.S. a r e b e i n g c a t e g o r i z e d a c c o r d i n g t o whether they have h i g h , medium, low o r uncommon p e s t i c i d e usage and h i g h , medium, o r low ground-water v u l n e r a b i l i t y . Thus a l l c o u n t i e s i n the U.S. w i l l be p l a c e d i n t o one of the 12 (3x4) strata. The number of c o u n t i e s w i l l p r o b a b l y be near 200 and w i l l be d e t e r m i n e d u s i n g the c r i t e r i a d e s c r i b e d above ( d e s i r e d precision, etc.) T h e r e a r e t h r e e advantages of s t r a t i f i e d random sampling f o r l a r g e t a r g e t p o p u l a t i o n s , when p r o p e r l y done, r e l a t i v e to s i m p l e random s a m p l i n g . The o v e r a l l v a r i a n c e f o r the e s t i m a t e s s h o u l d be s i g n i f i c a n t l y l o w e r . T h e o r e t i c a l l y , t h e r e i s an i n v e r s e square r e l a t i o n s h i p between the number of s t r a t a and the v a r i a n c e , a l t h o u g h p r a c t i c a l l y the r e s u l t s a r e u s u a l l y l e s s d r a m a t i c (_7, pp. 133-5). The second advantage i s t h a t e s t i m a t e s can be p r o v i d e d f o r c e r t a i n s u b d i v i s i o n s of the p o p u l a t i o n . F o r example, EPA s t a f f d e s i r e s to draw m e a n i n g f u l c o n c l u s i o n s about the h i g h - h i g h s t r a t u m i n the n a t i o n a l s u r v e y - the c o u n t i e s w i t h h i g h p e s t i c i d e use and h i g h ground-water v u l n e r a b i l i t y . The t h i r d advantage i s t h a t the p o s s i b i l i t y t h a t c e r t a i n segments of the t a r g e t p o p u l a t i o n may n o t be sampled a t a l l can be e l i m i n a t e d . F o r example, i f t h e r e i s a s m a l l but s i g n i f i c a n t c o t t o n - g r o w i n g a r e a i n a s t a t e , which i s of

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i n t e r e s t , t h a t a r e a c a n be made i n t o i t s own s t r a t u m , w i t h s i m i l a r treatments to other crop areas. T h i s d i s c u s s i o n has emphasized t h e t h e o r y and b a s i c p r i n c i p l e s of p r o b a b i l i t y sampling o f w e l l s i n a l a r g e a r e a . The next two s e c t i o n s a d d r e s s s t u d i e s o f a r e a s of a few a c r e s o r l e s s . The g u i d e l i n e s f o r w e l l sampling i n those s e c t i o n s a r e a p p r o p r i a t e f o r t h i s s e c t i o n as w e l l .


Small-Scale

Retrospective

Studies

F o r a s m a l l - s c a l e r e t r o s p e c t i v e s t u d y , p a r t i c i p a n t s e n t e r and s t u d y a f i e l d i n which a p e s t i c i d e has been used over a p e r i o d o f t i m e . The purposes of s m a l l - s c a l e r e t r o s p e c t i v e s t u d i e s a r e t o d e t e r m i n e whether t h e p e s t i c i d e ( s ) i n q u e s t i o n has l e a c h e d t o ground water i n c e r t a i n f i e l d s , and t o c h a r a c t e r i z e t h e l e a c h i n g p a t t e r n i n t h e s o i l p r o f i l e a t a given point i n time. This s e c t i o n contains d i s c u s s i o n s on s i t e s e l e c t i o n , s i t e c h a r a c t e r i z a t i o n , t h e number and l o c a t i o n o f o b s e r v a t i o n w e l l s , w e l l c o n s t r u c t i o n and s a m p l i n g , and s o i l sampling. Site Selection. a site

The f o l l o w i n g c r i t e r i a a r e i m p o r t a n t

i n choosing

( 2 2 , 14)·

1) There s h o u l d be documented p r i o r usage of t h e p e s t i c i d e i n the f i e l d s i t e , p r e f e r a b l y f o r s e v e r a l p r e v i o u s y e a r s . I f p o s s i b l e , t h e f i e l d s h o u l d be s e p a r a t e h y d r o g e o l o g i c a l l y and p h y s i c a l l y from o t h e r f i e l d s where t h e p e s t i c i d e under s t u d y has been p r e v i o u s l y u s e d . T h i s a v o i d s t h e p o s s i b i l i t y o f r u n o f f from o t h e r f i e l d s c o n t a m i n a t i n g t h e s t u d y f i e l d s and l e a c h i n g from o t h e r f i e l d s c o n t a m i n a t i n g t h e u n d e r l y i n g a q u i f e r . 2) be

Land owner/farmer c o o p e r a t i o n i s e s s e n t i a l s i n c e he/she c l o s e l y i n v o l v e d i n the study.

will

3) I t i s preferable to i n s t a l l observation wells s p e c i f i c a l l y d e s i g n e d f o r the purposes o f t h e s t u d y . G u i d e l i n e s f o r w e l l c o n s t r u c t i o n a r e g i v e n i n t h e w e l l c o n s t r u c t i o n s e c t i o n . Howe v e r , e x i s t i n g w e l l s c a n be used i f s u f f i c i e n t i n f o r m a t i o n i s a v a i l a b l e to c h a r a c t e r i z e the w e l l s . I f e x i s t i n g wells are u s e d , t h e h i s t o r y o f t h e w e l l - c o n s t r u c t i o n w i l l be n e c e s s a r y . The w e l l s h o u l d be r e j e c t e d from t h e s t u d y i f t h e s e d a t a a r e not complete. Some p e r t i n e n t q u e s t i o n s t o a s k a r e : What i s t h e w e l l depth? A t what d e p t h i s i t screened? W i t h what m a t e r i a l i s t h e w e l l annulus f i l l e d , i . e . , g r a v e l , cement? Was t h e w e l l sealed properly? Does t h e w e l l have a d e v i c e t o p r e v e n t backs i p h o n i n g i n s t a l l e d i n i t ? Of what m a t e r i a l i s t h e w e l l c a s i n g constructed? There s h o u l d be o n l y one s h o r t s c r e e n o r p e r f o r a t i o n i n the c a s i n g . Well casings with several screens or perf o r a t i o n s a t d i f f e r e n t depths s h o u l d be r e j e c t e d from the s t u d y . The w e l l c a s i n g may be i n a d e q u a t e f o r m o n i t o r i n g c e r t a i n o r g a n i c s i f i t i s c o n s t r u c t e d w i t h any type o f p l a s t i c s o r p l a s t i c i z e r s known t o a d s o r b o r g a n i c s . 4)

Uniform s o i l

c h a r a c t e r i s t i c s on t h e f i e l d

are d e s i r a b l e .

178



U n i f o r m i t y i n t h i s c o n t e x t r e f e r s t o s l o p e and t e x t u r e . I d e a l l y , the f i e l d s h o u l d have a s l o p e o f l e s s than 2%, and i f p o s s i b l e , t h e r e s h o u l d be o n l y one s o i l s e r i e s on t h e f i e l d . I f more than one s o i l s e r i e s i s on t h e f i e l d , a l l t h e s e r i e s s h o u l d be of the same t e x t u r e , i . e . , a l l s h o u l d be sandy loams. This c r i t e r i o n does n o t p r e c l u d e the p o s s i b i l i t y o f l a y e r e d s o i l s ( s o i l s w i t h d i s t i n c t h o r i z o n s ) as l o n g as the e n t i r e f i e l d i s c h a r a c t e r i z e d by t h i s l a y e r e d s o i l . The more u n i f o r m the f i e l d , the e a s i e r w i l l be t h e i n t e r p r e t a t i o n o f r e s u l t s . Soil Conservation Service s o i l surveys give s u f f i c i e n t l y d e t a i l e d information to characterize a f i e l d . Characterizing a Site. The s o i l i n the f i e l d must be c h a r a c t e r ized. A minimum o f the f o l l o w i n g k i n d s of i n f o r m a t i o n s h o u l d be recorded: ° p e r m e a b i l i t y o f the i n d i v i d u a l s o i l l a y e r s as a f u n c t i o n o f d e p t h down t o t h e water t a b l e ; ° o r g a n i c matter; ° bulk d e n s i t y ; ° p a r t i c l e s i z e d i s t r i b u t i o n of sand, s i l t , and c l a y as a f u n c t i o n of d e p t h , i f d i s t i n c t l y d i f f e r e n t h o r i z o n s e x i s t i n the s o i l column down t o t h e water t a b l e ; ° a v a i l a b l e water h o l d i n g c a p a c i t y , as d e f i n e d by the d i f f e r e n c e of f i e l d c a p a c i t y and w i l t i n g p o i n t , b o t h o f which s h o u l d a l s o be a s c e r t a i n e d f o r the s o i l ; ° SCS s o i l s e r i e s c l a s s i f i c a t i o n f o r the s o i l s of t h e study s i t e , i f information i s a v a i l a b l e . The h y d r o g e o l o g y o f t h e f i e l d must be c h a r a c t e r i z e d . I n many cases, only semiquantitative analyses are necessary. Some p o i n t s to consider a r e : ° t y p e s , d e p t h s , and e x t e n t of l a y e r s of reduced p e r m e a b i l i t y such as c l a y pans and s i l t - c l a y l e n s e s ; ° w a t e r t a b l e d e p t h below t h e s u r f a c e as a f u n c t i o n of time; t h e water t a b l e may f l u c t u a t e s e a s o n a l l y w i t h r a i n f a l l / r u n o f f e v e n t s and snowmelt; ° t h e d i r e c t i o n of ground-water f l o w ( c o n s t r u c t i o n of a f l o w - n e t ) ; ° type of a q u i f e r ( c o n f i n e d , u n c o n f i n e d , a r t e s i a n ) ; ° g e o l o g i c m a t e r i a l s c o m p r i s i n g t h e a q u i f e r (sand and g r a v e l , g l a c i a l t i l l , carbonates, e t c . ) ; ° h y d r a u l i c c o n d u c t i v i t y ( s ) (K m /day) - whether t h e l o c a l p o r t i o n o f t h e a q u i f e r i s c h a r a c t e r i z e d by one Κ ( i s o t r o p i c ) o r s e v e r a l Κ values ( a n i s o t r o p i c ) ; ° transmissivity; ° whether t h e a q u i f e r has r e c h a r g i n g o r d i s c h a r g i n g c h a r a c t e r i s t i c s ; ° any man-made a c t i v i t i e s t h a t may a f f e c t t h e water l e v e l o f t h e a q u i f e r such as ground-water pumpage. 2

C l i m a t o l o g i c a l i n f o r m a t i o n f o r the s i t e w i l l be n e c e s s a r y . P r e c i p i t a t i o n d a t a , a i r temperature and pan e v a p o r a t i o n d a t a , and any use o f i r r i g a t i o n water must be c a r e f u l l y r e c o r d e d . Irrigation and n a t u r a l r e c h a r g e i s a c r i t i c a l a s p e c t of p e s t i c i d e l e a c h i n g .

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A water b a l a n c e d e t a i l i n g t h e water i n p u t s and o u t p u t s from t h e f i e l d c a n be used t o e s t i m a t e r e c h a r g e . I n p u t s t o t h i s b a l a n c e i n c l u d e p r e c i p i t a t i o n and i r r i g a t i o n . The o u t p u t s w h i c h can be e s t i m a t e d a r e r u n o f f and évapotranspiration, and t h e remainder can be assumed t o be r e c h a r g e . Number and L o c a t i o n o f O b s e r v a t i o n W e l l s . The p r e c i s e amount o f p e s t i c i d e which was a p p l i e d t o t h e s o i l s u r f a c e and i s a v a i l a b l e f o r l e a c h i n g i s known as t h e s o u r c e term. F o r p e s t i c i d e s which a r e a p p l i e d d i r e c t l y t o t h e s o i l , such as g r a n u l e s o r l i q u i d formul a t i o n s s p r a y e d o n l y onto t h e s o i l s u r f a c e , t h e s o u r c e term c a n be assumed t o be e q u a l t o t h e t o t a l amount o f a p p l i c a t i o n . However, i f the p e s t i c i d e i s s p r a y e d onto a d e v e l o p i n g canopy, then some o f t h e p e s t i c i d e w i l l be i n t e r c e p t e d by t h e p l a n t and w i l l be u n a v a i l a b l e f o r l e a c h i n g . The s o u r c e term o b v i o u s l y cannot be e s t i m a t e d a c c u r a t e l y w i t h o u t p o s t - a p p l i c a t i o n s a m p l i n g , which i s why landowner r e c o r d s a r e i m p o r t a n t . E s t i m a t i o n of the source term i s c r i t i c a l f o r t h e i n t e r p r e t a t i o n o f a l l subsequent d a t a c o l l e c t i o n e f f o r t s , a s w e l l as f o r m o d e l i n g purposes ( i f t h a t w i l l be p a r t o f the use o f f i e l d d a t a ) . A n o t h e r c r i t i c a l i n f o r m a t i o n need f o r e i t h e r a r e t r o s p e c t i v e o r a p r o s p e c t i v e s t u d y i s the d i r e c t i o n o f ground-water f l o w . I f i t can be d e t e r m i n e d from p r e e x i s t i n g h y d r o g e o l o g i c a l i n f o r m a t i o n on the s t u d y s i t e , t h e n the d e s i g n and placement o f the m o n i t o r i n g w e l l s c a n be d e t e r m i n e d . I f the d i r e c t i o n o f ground-water f l o w cannot be d e t e r m i n e d from e x i s t i n g d a t a , and p r e v i o u s l y i n s t a l l e d w e l l s a r e p r e s e n t on the p r o p e r t y , they c a n be used t o t r y t o e s t a b l i s h the ground-water f l o w n e t . U n d e r s t a n d i n g the d i r e c t i o n o f ground water f l o w i s n e c e s s a r y to d e t e r m i n e t h e l o c a t i o n o f m o n i t o r i n g w e l l s . The minimum number of w e l l s i t e s i s suggested t o be 4 f o r one study s i t e . (Federal R e g u l a t i o n s i n 40 CFR P a r t 256, s u b p a r t F o f the Resource C o n s e r v a t i o n and Recovery A c t s u g g e s t a t l e a s t f o u r m o n i t o r i n g w e l l s as the minimum number f o r l a n d f i l l s . ) A " w e l l s i t e " c a n be d e f i n e d as a c l u s t e r o f t h r e e w e l l s , l o c a t e d v e r y n e a r each o t h e r , which p e n e t r a t e t h r e e depths o f the a q u i f e r , i . e . , each w e l l i s s c r e e n e d a t a d i f f e r e n t d e p t h t o o b t a i n 3 d i m e n s i o n a l sampling o f the a q u i f e r a t each w e l l s i t e . The f i r s t w e l l i s p l a c e d c e n t r a l l y w i t h r e s p e c t t o t h e s t u d y s i t e u p - g r a d i e n t and o u t s i d e o f t h e s t u d y s i t e boundary; t h e second w e l l i s p l a c e d c e n t r a l l y w i t h r e s p e c t t o the study s i t e and down-gradient and o u t s i d e o f t h e s t u d y s i t e boundary; and t h e t h i r d and f o u r t h on e i t h e r s i d e o f t h e c e n t e r o f the study s i t e w i t h i n t h e t h e s t u d y s i t e b o u n d a r i e s . Once the w e l l s a r e i n p l a c e , ground-water samples c a n be t a k e n f o r water q u a l i t y measurements. Assuming t h e f i e l d has had s e v e r a l y e a r s o f s e a s o n a l p e s t i c i d e use, p e s t i c i d e s may be d e t e c t e d i n w e l l samples any time of the y e a r . However, t h e two o p t i m a l times f o r sampling beneath and j u s t down-gradient o f t h e f i e l d a r e n o t l o n g f o l l o w i n g a p p l i c a t i o n i n l a t e s p r i n g and e a r l y summer, and d u r i n g the w i n t e r - s p r i n g snowmelt p e r i o d ( c a . M a r c h ) . Experience has shown t h a t l e a c h i n g p e s t i c i d e s t y p i c a l l y contaminate v e r y s h a l l o w ground water beneath the f i e l d w i t h the f i r s t major p e r i o d of r e c h a r g e f o l l o w i n g a p p l i c a t i o n ; i . e . , w i t h s p r i n g r e c h a r g e f o l l o w i n g a p p l i c a t i o n i n t h e s p r i n g f o r p e s t i c i d e s i n the N o r t h e a s t ,

180

EVALUATION O F PESTICIDES IN G R O U N D WATER

o r w i t h summer r a i n f o r s p r i n g a p p l i e d p e s t i c i d e s i n the S o u t h e a s t , Because of the temporal changes i n ground-water q u a l i t y ( 1 5 - 1 7 ) , w e l l s s h o u l d be sampled b e g i n n i n g a t the o n s e t of the sampling program and c o n t i n u i n g t h r o u g h the w i n t e r and i n t o the next s e a s o n .


W e l l C o n s t r u c t i o n . The s e l e c t i o n of a d r i l l i n g method f o r t h i s phase of work s h o u l d be based on the a b i l i t y of a p a r t i c u l a r method t o a c h i e v e the o b j e c t i v e s of a d r i l l i n g program, which i n c l u d e the f o l l o w i n g p o i n t s from L u h d o r f f and S c a l m a n i n i ( 1 8 ) : 1)

t h e a b i l i t y t o p e n e t r a t e a l l a n t i c i p a t e d f o r m a t i o n s and m a t e r i a l s , t o p e n e t r a t e a t a d e s i r e d r a t e , and t o c o n s t r u c t a b o r e h o l e of d e s i r e d d i a m e t e r f o r the a n t i c i p a t e d w e l l , as w e l l as f o r the placement of a g r a v e l o r sand pack and n e c e s s a r y f o r m a t i o n s e a l i n g m a t e r i a l such as b e n t o n i t e o r cement;

2)

i d e n t i f i c a t i o n of l i t h o l o g y o r development of a g e o l o g i c l o g of a l l f o r m a t i o n s and m a t e r i a l s p e n e t r a t e d , i n c l u d i n g p h y s i c a l c h a r a c t e r i s t i c s and v i s u a l d e s c r i p t i o n of c o l o r , t e x t u r e , e t c . ;

3)

c o l l e c t i o n of samples of a q u i f e r f l u i d s d u r i n g the d r i l l i n g p r o c e s s and p r i o r t o w e l l c o n s t r u c t i o n , w h i l e a t the same time minimizing p o t e n t i a l f o r cross-contamination ("cleanliness" i s a key i s s u e i n d r i l l i n g - t h e r e s h o u l d be no c o n t a m i n a t i o n from s u r f a c e s o i l s and w a t e r , i n a d d i t i o n t o c r o s s - c o n t a m i n a t i o n between l a y e r s ) ;

4)

c o l l e c t i o n of " u n d i s t u r b e d " s o i l samples from the c e n t e r l i n e or s i d e w a l l of the b o r e h o l e ( t h i s o b j e c t i v e o f t e n r e q u i r e s the d r i l l i n g t o be h a l t e d w h i l e s o i l samples a r e t a k e n from the bottom of the i n c o m p l e t e b o r e h o l e ) ;

5a)

c o m p l e t i o n of the b o r e h o l e i n t o a m o n i t o r i n g w e l l d u r i n g the i n i t i a l c o n s t r u c t i o n p r o c e s s , i . e . , c o n s t r u c t i n g a w e l l as the b o r e h o l e i s d r i l l e d o r c o n s t r u c t i n g a w e l l i n the b o r e h o l e i m m e d i a t e l y a f t e r the d r i l l i n g t o o l s a r e removed; or

5b)

c o m p l e t i o n of a m o n i t o r i n g w e l l i n the b o r e h o l e f o l l o w i n g a time l a p s e f o r i n t e r p r e t a t i o n of g e o l o g i c o r g e o p h y s i c a l d a t a from the b o r e h o l e .

Though g e o p h y s i c a l l o g g i n g of the b o r e h o l e i s d e s i r a b l e i n many s i t u a t i o n s , the a d d i t i o n a l expense and equipment n e c e s s a r y may be p r o h i b i t i v e . F o r the s m a l l e r , more s h a l l o w w e l l s used i n s m a l l - s c a l e ground-water s t u d i e s t h i s i s not n e c e s s a r y . There a r e many d r i l l i n g t e c h n i q u e s a v a i l a b l e f o r w e l l construction: h o l l o w stem; f l i g h t auger; d i r e c t c i r c u l a t i o n rotary d r i l l i n g ; cable tool d r i l l i n g ; reverse c i r c u l a t i o n rotary d r i l l i n g ; and a i r r o t a r y d r i l l i n g . B a r c e l o n a , Gibb and M i l l e r (1983) p r o v i d e a more d e t a i l e d d i s c u s s i o n of each ( 1 9 ) .


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F o r the purposes of a s m a l l - s c a l e r e t r o s p e c t i v e o r p r o s p e c t i v e s t u d y , t h e h o l l o w stem, c o n t i n u o u s - f l i g h t auger i s recommended. The h o l l o w - s t e m auger i s m o b i l e and i n e x p e n s i v e t o o p e r a t e . I t i s c a p a b l e o f d r i l l i n g a p p r o x i m a t e l y 150 f e e t i n t o u n c o n s o l i d a t e d material. ( P r a c t i c a l e x p e r i e n c e i n d i c a t e s t h a t 100 f e e t may be successfully drilled.) The r i g i s equipped w i t h a removable p l u g t h a t h e l p s i n the d r i l l i n g p r o c e s s , but t h a t i s i n s e r t e d i n s i d e the h o l l o w stem of t h e auger and i s , t h e r e f o r e , e a s i l y removable. The d r i l l i n g p r o c e d u r e uses no d r i l l i n g f l u i d s , t h e r e b y m i n i m i z i n g c o n t a m i n a t i o n problems between the b o r e h o l e m a t e r i a l s and t h e d r i l l i n g p r o c e s s ( 2 0 ) . Once the b o r e h o l e has been d r i l l e d t o t h e d e s i r e d d e p t h , t h e p l u g i s removed from i n s i d e the h o l l o w stem and a s m a l l - d i a m e t e r w e l l c a s i n g , 1 l / 4 " - 2 " , (3-5 cm) can be i n s e r t e d i n s i d e t h e h o l l o w stem. The hollow-stem auger c a n then be p u l l e d out o f the b o r e h o l e l e a v i n g the w e l l c a s i n g i n p l a c e , which c a n then be e a s i l y g r o u t e d i n . S o i l c o r e samples c a n a l s o be o b t a i n e d d u r i n g t h e d r i l l i n g p r o c e s s b y i n s e r t i n g a Shelby Tube o r a s p l i t spoon ( s p l i t b a r r e l ) sampler i n s i d e the h o l l o w stem, l o w e r i n g t h e assembly t o the bottom o f the h o l e and d r i v i n g t h e sampling tube i n t o t h e u n d i s t u r b e d p r o f i l e ( 2 1 ) . These c o r e samples w i l l be used f o r l i t h o l o g i e i d e n t i f i c a t i o n . C r o s s - c o n t a m i n a t i o n o f d r i l l e d m a t e r i a l s and s o i l samples c o l l e c t e d f o r l i t h o l o g i e i d e n t i f i c a t i o n c a n be m i n i m i z e d d u r i n g d r i l l i n g by i n s t a l l i n g temporary c a s i n g as t h e d r i l l i n g p r o c e e d s , and r e v e r s i n g t h e d r i l l s p i n i n p l a c e . A f t e r t h e f i r s t w e l l h a s been d r i l l e d from the s o i l s u r f a c e t o the d e s i r e d d e p t h , u s u a l l y the water t a b l e and below, t h e s o i l c o r e s from t h i s s i t e may be used f o r l i t h o l o g i e i d e n t i f i c a t i o n , as mentioned. F o r any o t h e r w e l l s d r i l l e d o n the same p l o t , i n which a Shelby Tube o r s p l i t spoon sampler a r e n o t u s e d , t h e f i r s t 18" o f e a r t h c a n be removed w i t h a s h o v e l r e d u c i n g t h e p o s s i b i l i t y o f s o i l from t h e s e upper zones from c o n t a m i n a t i n g the lower d r i l l i n g d e p t h s . This i s d e s i r a b l e f o r r e t r o s p e c t i v e s t u d i e s as t h e f i r s t 18" o f s o i l o f t e n c o n t a i n s the h i g h e r c o n c e n t r a t i o n s o f p e s t i c i d e s . In most c a s e s the h o l l o w - s t e m auger w i l l produce a s u f f i c i e n t l y deep b o r e h o l e f o r a s m a l l - s c a l e ground-water s t u d y d e s i g n e d t o d e t e c t the l e a c h i n g o f p e s t i c i d e s from normal a g r i c u l t u r a l u s e . Where deeper w e l l s a r e needed o r where c o n s o l i d a t e d f o r m a t i o n s a r e encountered o t h e r t e c h n i q u e s may be r e s e a r c h e d f o r t h e i r a p p l i c a bility. Once a new w e l l i s i n p l a c e i t needs t o be d e v e l o p e d . Well development r e f e r s t o t h e procedure used t o c l e a r the w e l l - s c r e e n of f i n e s i l t s and c l a y s produced d u r i n g d r i l l i n g . Pumping t h e w e l l u n t i l sediment f r e e - f l o w i s e s t a b l i s h e d o r by u s i n g a surge b l o c k t o l o o s e n c l o g g e d m a t e r i a l a r e recommended ( 2 1 ) . F o r t h e purposes of s m a l l and l a r g e s c a l e ground-water s t u d i e s , a l l w e l l s s h o u l d be c o n s t r u c t e d w i t h a s i n g l e , s h o r t s c r e e n a t a known depth (12). Once a s c r e e n e d c a s i n g h a s been lowered i n t o the b o r e h o l e t o the depth of i n t e r e s t , q u a r t z sand, f r a c sand o r pea g r a v e l s h o u l d be f i l l e d i n around and a few i n c h e s above t h e s c r e e n e d i n t e r v a l . Expandable g r o u t s h o u l d be used t o f i l l i n the annulus above t h e s c r e e n t o t h e s u r f a c e around the w e l l . The e n t i r e l e n g t h o f t h e c a s i n g from s u r f a c e t o t h e s c r e e n e d i n t e r v a l s h o u l d be g r o u t e d i n


182


t o p r e v e n t seepage from the s u r f a c e down a l o n g the c a s i n g ( 2 1 ) . The p e r m e a b i l i t y of g r o u t s e a l s i s f u r t h e r d i s c u s s e d by Kurt and Johnson (1982) ( 2 2 ) . I t i s recommended t h a t cement s e a l s be used, and b e n t o n i t e s e a l s be a v o i d e d . The recommended m o n i t o r i n g w e l l d i a m e t e r i s 2 i n c h e s (5 cm) (23). The type of w e l l c a s i n g i s i m p o r t a n t , and w i l l be d e t e r m i n e d by the types of compounds sampled f o r . The f o l l o w i n g m a t e r i a l s were ranked by the U.S. G e o l o g i c a l Survey (USGS) as t o t h e i r i n e r t n e s s and s u i t a b i l i t y as c a s i n g m a t e r i a l s : g l a s s , T e f l o n , s t a i n l e s s s t e e l , g a l v a n i z e d s t e e l , PVC, b l a c k p i p e , f i b e r g l a s s . From the a f o r e m e n t i o n e d USGS memorandum a c o m b i n a t i o n of m a t e r i a l s f o r w e l l c a s i n g i s recommended, s p e c i f i c a l l y , "a T e f l o n or s t a i n l e s s s t e e l s c r e e n and c a s i n g i n the water b e a r i n g zone and PVC c a s i n g f o r the remainder of the h o l e . " T h i s p r o c e d u r e i s recommended f o r b o t h v o l a t i l e and n o n - v o l a t i l e p e s t i c i d e s of expected low c o n c e n t r a t i o n l e v e l s i n a n o n - c o r r o s i v e environment, i . e . , pH g r e a t e r than 5, no i r o n p r e c i p i t a t i o n , and low c o n c e n t r a t i o n s of o r g a n i c s o l v e n t s . Whenever PVC i s u s e d , no o r g a n i c - b a s e d s o l v e n t s or s e a l e r s s h o u l d be used because of the p o s s i b i l i t y of c o n t a m i n a t i o n . J o i n t s of c a s i n g s h o u l d be threaded and screwed t o g e t h e r , not g l u e d t o g e t h e r . As w i t h w e l l c o n s t r u c t i o n and d r i l l i n g method p r e c a u t i o n s , a l l sampling d e v i c e s s h o u l d be c a r e f u l l y c l e a n e d p r i o r t o u s e . T h e r e a r e many suggested methods. C u r r e n t p r a c t i c e a t the U.S. G e o l o g i c a l Survey recommends a hot d e t e r g e n t s c r u b w i t h an i n organic detergent, p r e f e r a b l y a sulfonated detergent, followed by a d i s t i l l e d water r i n s e f o r p l a s t i c and T e f l o n p a r t s and an o r g a n i c s o l v e n t r i n s e f o r m e t a l p a r t s ( 2 4 ) . A l l sampling d e v i c e s s h o u l d be p r e - r i n s e d w i t h the w e l l water to be sampled. W e l l Sampling. B e f o r e a w e l l i s sampled, i t must be purged of i t s s t a n d i n g water or s t o r a g e water u n t i l the w e l l y i e l d s r e p r e s e n t a t i v e a q u i f e r water upon pumping. Storage water i s water t h a t "does not come i n t o c o n t a c t w i t h the f l o w i n g ground w a t e r " (25, 26). In the p a s t , the most common method used t o o b t a i n a r e p r e s e n t a t i v e a q u i f e r sample was t o f l u s h the w e l l - b o r e by pumping a s p e c i f i e d number of w e l l - b o r e volumes of w a t e r . T h i s p r o c e d u r e i s c o n s i d e r e d o u t d a t e d , and i s not a d v i s e d . The f o l l o w i n g e x c e r p t i s a c o m p i l a t i o n of the i n f o r m a t i o n compiled by Gibbs and o t h e r s o u t l i n i n g recommendations f o r the c o l l e c t i o n of ground-water samples (25). 1) A two or t h r e e hour pumping t e s t s h o u l d be conducted on each m o n i t o r i n g w e l l t o be sampled. A n a l y s i s of the pump t e s t d a t a and o t h e r h y d r o l o g i e i n f o r m a t i o n s h o u l d be used t o d e t e r m i n e the f r e q u e n c y a t which samples w i l l be c o l l e c t e d and the r a t e and p e r i o d of time each w e l l s h o u l d be pumped p r i o r t o c o l l e c t i n g the sample. I f pumping t e s t s cannot be c o n d u c t e d , s l u g t e s t s may be s u b s t i t u t e d t o p r o v i d e the needed h y d r o l o g i e i n f o r mation. 2) In g e n e r a l , p e r i s t a l t i c and T e f l o n pumps are recommended f o r s m a l l d i a m e t e r , 2" (5 cm) w e l l s . The p e r i s t a l t i c pump i s used t o h e l p e v a c u a t e the c a s i n g .

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183


The U.S. G e o l o g i c a l Survey r e q u i r e s t h a t t h e s p e c i f i c conductance and temperature s t a b i l i z e b e f o r e t a k i n g a water sample t h a t i s c o n s i d e r e d r e p r e s e n t a t i v e o f t h e a q u i f e r ; t h i s i s t h e OPP/EPA p o l i c y , as w e l l . The pH o f t h e sample s h o u l d be r e c o r d e d t o + 0.1. There a r e no s e t number o f w e l l c a s i n g volumes t o be pumped·


These s m a l l 2" w e l l s s h o u l d n o t be overpumped t o t h e p o i n t of d r y n e s s . A pumping r a t e slow enough t o a l l o w t h e w e l l t o r e c h a r g e o r r e c o v e r i s recommended. Overpumping c a n cause e x c e s s i v e s i l t and c l a y f i n e s t o be drawn from t h e w e l l ( 2 7 ) * Measurement of c h e m i c a l parameters i s b e s t a c c o m p l i s h e d w i t h an i n - l i n e c l o s e d measurement c e l l ( 2 5 ) . When t h e v a l u e s of t h e i n d i c a t o r parameters a r e observed t o v a r y l e s s than +_ 10% o v e r t h r e e c o n s e c u t i v e w e l l - b o r e s t o r a g e volumes, t h e w e l l may be presumed t o have been a d e q u a t e l y f l u s h e d f o r r e p r e s e n t a t i v e sampling. When i n - l i n e measurement c e l l s a r e n o t p r a c t i c a l , s t a n d a r d pH and c o n d u c t i v i t y meters and thermometers a r e u s e d . A l l c o n t a i n e r s used f o r measurements must be r i n s e d 3 times w i t h r e p r e s e n t a t i v e w e l l water. 3) Once t h e water has been determined t o be r e p r e s e n t a t i v e o f t h e a q u i f e r , t h e p e r i s t a l t i c pump s h o u l d be removed. A T e f l o n b l a d d e r pump o r p o s i t i v e d i s p l a c e m e n t pump s h o u l d be used t o c o l l e c t t h e a c t u a l water samples. A t l e a s t 1 l i t e r o f r e p r e s e n t a t i v e w e l l w a t e r s h o u l d be pumped through t h e b l a d d e r pump before sampling. The b l a d d e r pump (3 f e e t l o n g ) i s i n s e r t e d i n t o t h e w e l l and f i l l s p a s s i v e l y w i t h w a t e r . The T e f l o n b l a d d e r i n s i d e o f t h e pump i n f l a t e s w i t h N2 gas and d i s p l a c e s the water sample up a T e f l o n tube and i n t o t h e sample c o n t a i n e r . I t i s important t h a t t h e r e i s enough water t o c o m p l e t e l y c o v e r the pump i n o r d e r t o p r e v e n t t h e i n t r o d u c t i o n o f a i r i n t o the water sample. Sampling d e v i c e s s h o u l d be s e l e c t e d t h a t m i n i m i z e t h e i n t r o d u c t i o n o f a i r and gas bubbles i n t o t h e sample (28, 2 9 ) . F o r w e l l s w i t h o u t enough water t o c o v e r t h e b l a d d e r , a T e f l o n o r s t a i n l e s s s t e e l b a i l e r r e s e m b l i n g a l o n g , narrow bucket may be used ( 2 7 ) . A l l c o l l e c t i o n c o n t a i n e r s s h o u l d be r i n s e d 3 times w i t h r e p r e s e n t a t i v e w e l l water p r i o r t o collection. Most p e s t i c i d e s s t i l l i n u s e a r e n o t v o l a t i l e o r g a n i c s . However, f o r v o l a t i l e o r g a n i c s , t h e f o l l o w i n g p r o c e d u r e s a r e recommended (30)· 1) A s i l i c o n / T e f l o n septum capped v i a l i s recommended f o r t h e c o l l e c t i o n o f v o l a t i l e o r g a n i c compounds. T h i s a l l o w s t h e l a b o r a t o r y c o n d u c t i n g t h e c h e m i c a l a n a l y s e s t o withdraw a sample t h r o u g h t h e septum t o p , m i n i m i z i n g t h e sample's exposure t o air. 2) F i l l t h e v i a l u n t i l a p o s i t i v e meniscus forms a t t h e t o p . a e r a t i n g t h e sample w h i l e s e a l i n g t h e c o n t a i n e r .

Avoid

184



3) Look f o r a i r b u b b l e s by t u r n i n g the c o n t a i n e r u p s i d e down. Any bubbles a r e an i n d i c a t i o n of t r a p p e d a i r and the sample s h o u l d be d i s c a r d e d and a new sample c o l l e c t e d . Because p e s t i c i d e s may degrade a f t e r c o l l e c t i o n , the f o l l o w i n g s t e p s may be c o n s i d e r e d t o m i n i m i z e t h a t breakdown. 1) F o l l o w c o l l e c t i o n p r o c e d u r e s o u t l i n e d above. 2) Wrap the g l a s s sample c o n t a i n e r i n aluminum f o i l o r use amber g l a s s b o t t l e s o r use T e f l o n sample c o n t a i n e r s t o s h i e l d p e s t i c i d e s from the e f f e c t s of s u n l i g h t . 3) D e a e r a t e samples w i t h N 2 , He or A r gas when they a r r i v e i n the lab. 4) S t o r e samples a t 4°C u n t i l a n a l y s i s , o r i f samples a r e c o l l e c t e d i n T e f l o n b o t t l e s they can be f r o z e n u n t i l a n a l y s i s . 5) E x t r a c t the samples as soon as p o s s i b l e , p r e f e r a b l y w i t h i n 2 weeks. DO NOT f r e e z e samples i n g l a s s c o n t a i n e r s . F r e e z i n g may c r a c k g l a s s c o n t a i n e r s . A l t h o u g h T e f l o n c o n t a i n e r s can be s h i p p e d w i t h f r o z e n samples, f r e e z i n g and thawing p r o c e d u r e s may d i s t u r b the c h e m i c a l e q u i l i b r i a of s o l u t e s i n s o l u t i o n , and i s t h e r e f o r e not recommended ( 3 1 ) . S o i l Sampling. S o i l s a m p l i n g p r o v i d e s i n f o r m a t i o n on u n s a t u r a t e d zone p e s t i c i d e m i g r a t i o n , and as s u c h , i s a c r i t i c a l component of r e t r o s p e c t i v e and p r o s p e c t i v e s t u d i e s . F o r t h i s r e a s o n , s o i l s a m p l i n g f o r a r e t r o s p e c t i v e f i e l d study s h o u l d a d e q u a t e l y d e s c r i b e p e s t i c i d e f a t e h o r i z o n t a l l y ( o v e r the e n t i r e f i e l d s u r f a c e ) and v e r t i c a l l y ( t h r o u g h the v a r i o u s s o i l h o r i z o n s t o the ground w a t e r ) . U n l i k e water s a m p l i n g , t h i s can be a c c o m p l i s h e d w i t h o n l y a s i n g l e sampling date. This requirement r e s u l t s i n a s i g n i f i c a n t savings of r e s o u r c e s i n c o n t r a s t t o a p r o s p e c t i v e f i e l d s t u d y , which r e q u i r e s s e v e r a l s o i l s a m p l i n g d a t e s over t i m e . O b v i o u s l y , the t i m i n g of t h i s s o i l sampling d a t e i s c r i t i c a l . I t should occur f o l l o w i n g a time p e r i o d when the p r e v i o u s a p p l i c a t i o n would have s p r e a d out i n the p r o f i l e and l e a c h e d , i f t h a t i s what i t would do. F o r a s p r i n g a p p l i c a t i o n , t h i s i s u s u a l l y i n the f a l l , f o r example. Few examples of e x p e r i m e n t a l d e s i g n s f o r s o i l sampling were found i n the l i t e r a t u r e . T o u r t e l o t and M i e s c h (32) d i s c u s s the e s t i m a t i o n of the t o t a l g e o c h e m i c a l v a r i a t i o n of a s h a l e u n i t u s i n g a d e s i g n a p p r o a c h c a l l e d a " h i e r a r c h i a l a n a l y s i s of v a r i a n c e . " T h i s i s one approach which c o u l d be a p p l i e d t o the v a r i a n c e of p e s t i c i d e r e s i d u e s i n a s o i l p l o t s t u d y i n the f o l l o w i n g manner. F o r a p l o t of v a r i a b l e s o i l c h a r a c t e r i s t i c s : a) d e t e r m i n e a r e a s of v a r i a b l e s o i l types ( t e x t u r e s , % o r g a n i c m a t t e r ) on the f i e l d , and c o n s i d e r these d i f f e r e n t " a r e a s " l e v e l 1 of the h i e r a r c h i a l a n a l y s i s of v a r i a n c e ; b) d e t e r m i n e , by g r i d placement, s e c t i o n s w i t h i n each " a r e a " t o be sampled, and c o n s i d e r t h e s e " s e c t i o n s " l e v e l 2 of the d e s i g n ; and c) d e t e r m i n e , randomly, the number of samples per g r i d be t a k e n , and c o n s i d e r t h i s l e v e l 3 of the d e s i g n .

s e c t i o n to


10.

COHEN ET AL.


185

S e v e r a l p r o c e d u r e s may be used as t o where t o take samples w i t h i n a g r i d placement: a t i n t e r s e c t i o n p o i n t s o f the g r i d , i n t h e c e n t e r of the g r i d s e c t i o n s , and a t o p p o s i t e c o r n e r s o f the g r i d s e c t i o n s . The number o f samples t a k e n per g r i d s e c t i o n s h o u l d be a t l e a s t two f o r t h e purposes o f sample comparison w i t h i n a g i v e n g r i d s e c t i o n . L e v e l s 1, 2, and 3 a l l o w f o r comparison o f the v a r i a n c e i n t h e parameter i n q u e s t i o n ( h e r e , p e s t i c i d e r e s i d u e c o n c e n t r a t i o n s i n s o i l ) as a f f e c t e d by d i f f e r e n c e s between samples from " a r e a s " o f d i f f e r e n t s o i l c h a r a c t e r i s t i c s , d i f f e r e n c e s between samples from g r i d " s e c t i o n s " o f t h e same s o i l c h a r a c t e r i s t i c s , and d i f f e r e n c e s between samples from the same g r i d " s e c t i o n " . The p e r c e n t a g e o f v a r i a n c e c o n t r i b u t e d by each l e v e l o f the d e s i g n f o r the p e s t i c i d e r e s i d u e i n v o l v e d o f i n t e r e s t c a n be d e t e r m i n e d (32)« Krumbein and S l a c k (33) i l l u s t r a t e d e t a i l s o f t h e c a l c u l a t i o n s i n v o l v e d i n computing t h e v a r i a n c e components. The sample v a r i a n c e c o n t r i b u t e d by a n a l y t i c a l t e c h n i q u e , l e v e l 4, c a n be e s t i m a t e d by d u p l i c a t e a n a l y s e s of t h e samples. T h e r e are then 4 l e v e l s o f v a r i a n c e which a r e a d d i t i v e and t h e i r sum i s e q u a l t o t h e t o t a l v a r i a n c e o f t h e s o i l p l o t as a whole, i f sampling and a n a l y s e s b i a s e s a r e absent t h r o u g h o u t t h e experimental design procedure (32). For a p l o t where a l l s o i l c h a r a c t e r i s t i c s a r e homogenous, l e v e l 1, d e s c r i b e d above, would n o t be n e c e s s a r y , and t h e r e would be 3 l e v e l s o f v a r i a n c e t o compare. The use o f a g r i d t o s e l e c t s e c t i o n s t o be sampled has been r e f e r r e d t o as " r e g u l a r l y spaced" s a m p l i n g , a s opposed t o random s e l e c t i o n procedures, ( 3 2 ) . A systematic sampling procedure, such as a g r i d i s recommended, (34, 3 5 ) . The p r e c e d i n g d i s c u s s i o n i s i l l u s t r a t i v e and i s one s t r a t e g y f o r s o i l c o r e s a m p l i n g . EPA c o n t i n u e s t o i n v e s t i g a t e t h i s i s s u e . B a s i c a l l y , t h e g u i d a n c e which t h e a u t h o r s g i v e t o p e s t i c i d e companies and o t h e r s i s 1) l o c a t e s o i l c o r i n g s i t e s i n an X p a t t e r n or o t h e r r e g u l a r l y spaced p a t t e r n as d e s c r i b e d above, and 2) choose a t l e a s t 5 s i t e s p e r 1 t o 3-acre p l o t . G e n e r a l l y , s o i l probes and hand augers a r e used t o c o l l e c t s o i l c o r e s from depths near t h e s u r f a c e . Probes a r e s t a i n l e s s s t e e l t u b e s , a p p r o x i m a t e l y 2.5 cm i n d i a m e t e r sharpened and b e v e l l e d on one end, and f i t t e d w i t h a Τ h a n d l e t h a t i s used t o push the probe i n t o t h e s o i l . Augers a r e used where probes w i l l not p e n e t r a t e t h e s o i l . Augers a r e t w i s t e d o r screwed i n t o t h e ground. They a r e 3-20 cm i n d i a m e t e r . Augers c o l l e c t a d i s t u r b e d sample by v i r t u e o f t h e t w i s t i n g motion used t o i n s e r t t h e tube i n t o the s o i l . Probes and hand augers a r e d e s i g n e d t o sample t h e upper 2 meters o f s o i l ( 3 6 ) . S h e l b y tubes and s p l i t b a r r e l samplers a r e used f o r deeper s o i l c o r e sampling as mentioned e a r l i e r under w e l l c o n s t r u c t i o n . Cross contamination of s o i l l a y e r s during the coring process s h o u l d be a v o i d e d . T h i s c a n be a c c o m p l i s h e d e i t h e r by i n s t a l l i n g temporary c a s i n g as d r i l l i n g p r o c e e d s , o r by d r i l l i n g t o a p o i n t , r e v e r s i n g t h e s p i n o f t h e auger f l i g h t t o c a r r y l o o s e s o i l out o f the h o l e , and e n s u r i n g t h a t t h e s o i l a t t h e s u r f a c e i s stamped down. S o i l samples s h o u l d be t a k e n t o the d e p t h o f p e s t i c i d e pene t r a t i o n a t each sampling e v e n t , and then a l i t t l e f u r t h e r t o e n s u r e



186

t h a t a l l t h e p e s t i c i d e i s a c c o u n t e d f o r . T h i s d e p t h can be e s t i mated w i t h a computer s i m u l a t i o n model, by judgement and e x p e r i e n c e , o r t h e sampling can be t o a c e r t a i n d e p t h , t h r e e f e e t f o r example. When t h e p e s t i c i d e n e a r s t h a t l e v e l , the sampling d e p t h can be i n c r e a s e d by i n c r e m e n t s such as a f o o t a t a t i m e . The l o c a t i o n o f the ground water s h o u l d be c o n s i d e r e d when d e t e r m i n i n g the t o t a l d e p t h of s o i l s a m p l i n g , w i t h deeper sampling f o r a deeper g r o u n d water l e v e l . Sampling s h o u l 4 be done i n 6 - i n c h i n c r e m e n t s . Each i n d i v i d u a l sample s h o u l d o r i g i n a t e from a c o n t i n u o u s core w h i c h has been t a k e n t o t h e p r e d e t e r m i n e d t o t a l d e p t h o f s a m p l i n g . R e s o u r c e s p e r m i t t i n g , t h e r e s h o u l d a l s o be a t l e a s t one s e t o f deep c o r e s t o c h a r a c t e r i z e t h e p r o f i l e t o the ground water, i f the s o i l p r o f i l e has n o t a l r e a d y been e s t a b l i s h e d from p a s t o r current well d r i l l i n g procedures. Small Scale P r o s p e c t i v e

Studies

These s t u d i e s a r e done by p e s t i c i d e r e g i s t r a n t s and o t h e r s c i e n t i f i c r e s e a r c h e r s , and a r e u s u a l l y a s s o c i a t e d w i t h t h e p e s t i c i d e - u s e r e g i s t r a t i o n process. The p r i m a r y o b j e c t i v e o f t h i s study type i s to c h a r a c t e r i z e the subsurface f a t e of a p a r t i c u l a r p e s t i c i d e , i . e . , e s t a b l i s h the l e a c h i n g p o t e n t i a l i n a c o n t r o l l e d study. A p r o s p e c t i v e s t u d y d e s i g n attempts t o f o l l o w t h e p e s t i c i d e from t h e time i t i s a p p l i e d t o t h e s u r f a c e and u n t i l i t has degraded, r e a c h e d the s a t u r a t e d zone, o r r e a c h e d a d e p t h s i g n i f i c a n t l y g r e a t e r than the r o o t zone. As such, p a r t i c u l a r emphasis i s p l a c e d on s o i l coring. S i n c e many o f the d e t a i l s of r e t r o s p e c t i v e and p r o s p e c t i v e s t u d i e s a r e s i m i l a r , such as c o n s t r u c t i n g w e l l s and e x t r a c t i n g samples, o n l y the d i f f e r e n c e s between t h e two w i l l be c o v e r e d i n the f o l l o w i n g s e c t i o n s . S i t e S e l e c t i o n and C h a r a c t e r i z a t i o n . The most i m p o r t a n t c r i t e r i a f o r s i t e s e l e c t i o n i s t h a t t h e r e s h o u l d be no p r i o r use o f t h e p e s t i c i d e i n q u e s t i o n on t h e f i e l d s i t e . T h i s demands a landowner/ f a r m e r who keeps c a r e f u l r e c o r d s o f h i s f i e l d and method o f a p p l i c a t i o n f o r the p e s t i c i d e of i n t e r e s t . A l l other c r i t e r i a , i n c l u d i n g h y d r o g e o l o g i c c o n s i d e r a t i o n s , s o i l homogeneity, e x i s t i n g w e l l i n f o r m a t i o n , and new w e l l c o n s t r u c t i o n a r e s i m i l a r i n t h e p r o s p e c t i v e and r e t r o s p e c t i v e s t u d y . C h a r a c t e r i z a t i o n of a p r o s p e c t i v e f i e l d s i t e i s similar to retrospective f i e l d s i t e characterization. C o l l e c t i o n o f S o i l and Water Samples. S o i l sampling p r o v i d e s i n f o r m a t i o n on u n s a t u r a t e d zone p e s t i c i d e m i g r a t i o n , and as such, i s the most c r i t i c a l d a t a t h a t w i l l come out of a p r o s p e c t i v e f i e l d s t u d y . F o r t h i s r e a s o n , s o i l sampling programs s h o u l d a d e q u a t e l y d e s c r i b e p e s t i c i d e f a t e h o r i z o n t a l l y , v e r t i c a l l y , and t e m p o r a l l y (over time). One s e t of s o i l samples s h o u l d be t a k e n p r i o r t o p e s t i c i d e a p p l i c a t i o n , t o ensure that the f i e l d i s f r e e of r e s i d u e s . Another s e t of samples s h o u l d be t a k e n on t h e same day as p e s t i c i d e a p p l i c a t i o n o r on t h e day a f t e r a p p l i c a t i o n . Three t o f o u r more s e t s of samples s h o u l d be taken o v e r the c o u r s e of the season, p a r t i c u l a r l y a f t e r r a i n f a l l e v e n t s t o demonstrate the e f f e c t s of water


10.

C O H E N ET AL.

187


i n f i l t r a t i o n on p e s t i c i d e l e a c h i n g . One s e t s h o u l d be t a k e n a f t e r the w i n t e r f a l l o w p e r i o d a t s p r i n g t i m e d u r i n g snowmelt. S o i l c o r e s w i l l need t o be timed w i t h i r r i g a t i o n e v e n t s i n f i e l d s u s i n g i r r i gation practices. One s e t o f w e l l samples s h o u l d be t a k e n p r i o r t o p e s t i c i d e a p p l i c a t i o n t o e n s u r e t h a t the w e l l water i s f r e e o f r e s i d u e . Water sampling s h o u l d then o c c u r f o l l o w i n g major r e c h a r g e e v e n t s , i . e . , major storms p r o d u c i n g r e c h a r g e . Placement and number o f well s i t e s i ss i m i l a r to retrospective f i e l d s i t e s . One i m p o r t a n t d i f f e r e n c e between a p r o s p e c t i v e and r e t r o s p e c t i v e study i s the a p p l i c a t i o n and a n a l y s i s o f t r a c e r s . Davis (1980) d i s c u s s e d t y p e s o f t r a c e r s t h a t a r e a v a i l a b l e ( 3 7 ) . The a d d i t i o n o f t r a c e r s a l o n g w i t h the p e s t i c i d e i s v a l u a b l e f o r t h e following reasons: 1)

t r a c e r s allow the researcher t o track moves down the s o i l p r o f i l e .

t h e "water f r o n t " a s i t

2)

t r a c e r s a l l o w f o r the d e t e r m i n a t i o n o f t h e " r e t a r d a t i o n f a c t o r " , R, o f the p e s t i c i d e as i t t r a v e r s e s down the u n s a t u r a t e d zone. R i s d e f i n e d as a r a t i o o f the d i s t a n c e o f t r a v e l o f the water front t o the distance of t r a v e l of the p e s t i c i d e f r o n t .

3)

t r a c e r s a l l o w f o r the d e t e r m i n a t i o n o f a phenomena known as "macropore f l o w " , which i s t h e r a p i d f l o w o f a s m a l l p o r t i o n o f water through macropores, e.g. worm h o l e s , r a p i d l y through t h e s o i l p r o f i l e a t t h e o n s e t o f a storm, d i r e c t l y t o t h e a q u i f e r . T r a c e r s a p p e a r i n g a t the w e l l f o l l o w i n g a storm c a n a l l o w f o r macropore f l o w a n a l y s i s .

4)

t r a c e r s a l l o w f o r the d e t e r m i n a t i o n o f the (K) i n t h e s a t u r a t e d zone.

hydraulic

conductivity

C h l o r i d e and bromide a r e t h e t r a c e r s o f c h o i c e . T r a c e r s must be a p p l i e d a t t h e time o f p e s t i c i d e a p p l i c a t i o n , so t h a t the movement of t h e t r a c e r can be d i r e c t l y c o r r e l a t e d t o the movement o f p e s t i cide. However, i n a more d e t a i l e d s t u d y , Tennyson and S e t t e r g r e n (38) found t h a t bromide moved more r a p i d l y i n s o i l - w a t e r than would be e x p e c t e d from the l a b o r a t o r y d e t e r m i n e d s o i l h y d r a u l i c conductivity (K). R a d i o a c t i v e m a t e r i a l s , o r g a n i c dyes, g a s e s , and f l u o r o c a r b o n s are n o t recommended f o r use as t r a c e r s . The f l u o r o c a r b o n s have been used s u c c e s s f u l l y , though they have n o t been used e x t e n s i v e l y t o d a t e (39)· A f t e r the a p p l i c a t i o n o f p e s t i c i d e and t r a c e r , t h e p r o c e d u r e s p r e v i o u s l y o u t l i n e d s h o u l d be f o l l o w e d f o r m o n i t o r i n g s o i l and ground w a t e r . Occurrence of P e s t i c i d e s

i n Ground Water

At l e a s t 17 p e s t i c i d e s have been found i n ground water i n a t o t a l of 23 s t a t e s as a r e s u l t of a g r i c u l t u r a l p r a c t i c e . These d a t a are summarized i n T a b l e I and F i g u r e 1 as w e l l as i n the d i s c u s s i o n below. Two o f t h e s e p e s t i c i d e s , 1,2-D and 1,2,3-TCP, a r e n o t u s u a l l y c o n s i d e r e d t o be p a r t o f t h e a c t i v e i n g r e d i e n t s but a r e s y n t h e t i c by p r o d u c t s of the a c t i v e i n g r e d i e n t s . U n l i k e t h e 1984



188

summary (_1), the term " a t l e a s t " has t o be used. T h i s i s because of the s i g n i f i c a n t i n c r e a s e i n the number of d a t a g e n e r a t o r s as w e l l as i n the d a t a g e n e r a t e d . I t i s d i f f i c u l t t o keep t r a c k of so much knowledge. The n e x t update of t h i s s t a t i s t i c w i l l r e q u i r e e i t h e r a d d i t i o n a l c o a u t h o r s o r a q u a l i f i e r such as "...many more than X p e s t i c i d e s . . . " . H o p e f u l l y , the next update w i l l be more c o n c l u s i v e as a r e s u l t of more s y s t e m a t i c and r i g o r o u s l y d e s i g n e d surveys. At p r e s e n t , we cannot y e t determine the e x t e n t of the p r o b l e m . The EPA i s d e s i g n i n g a n a t i o n a l s t a t i s t i c a l s u r v e y which w i l l attempt t o answer t h i s q u e s t i o n ( d e s c r i b e d b e l o w ) . In a d d i t i o n , EPA's O f f i c e o f P e s t i c i d e Programs (OPP) c o n t i n u e s t o i n v o l v e i t s e l f i n v a r i o u s f i e l d p r o j e c t s around the U.S. i n c o l l a b o r a t i o n w i t h s t a t e , c o u n t y , and USGS s t a f f . These s t u d i e s and o t h e r s which a r e b e i n g done o r have been done s i n c e 1984 a r e v e r y i n t e r e s t i n g and a r e worth h i g h - l i g h t i n g below. The a u t h o r s r e g r e t i f key, c u r r e n t s t u d i e s a r e not mentioned i n the s y n o p s i s below. The i n t e n t was t o l i s t o n l y the most r e c e n t and e x c i t i n g s t u d i e s of w h i c h the a u t h o r s have p e r s o n a l knowledge. They a r e l i s t e d i n no p a r t i c u l a r o r d e r by c h e m i c a l , s t a t e and agency. F o l l o w i n g t h i s summary o f r e c e n t p r o j e c t h i g h l i g h t s i s a more complete summary of m o n i t o r i n g r e s u l t s o r g a n i z e d by c h e m i c a l . Aldicarb. Union Carbide C o r p o r a t i o n continues to monitor f o r a l d i c a r b around the U.S. w i t h the a s s i s t a n c e of l o c a l government officials. As w e l l , more m e c h a n i s t i c s t u d i e s c o n t i n u e on i t s s u b s u r f a c e p e r s i s t e n c e and m o b i l i t y i n Long I s l a n d and F l o r i d a (40-43). OPP i s i n the m i d s t of a r e g u l a t o r y d e c i s i o n on t h i s c h e m i c a l , a p u b l i c use-by-use r i s k - b e n e f i t a n a l y s i s . R e g i o n a l A s s e s s m e n t s . OPP i s c o l l a b o r a t i n g w i t h the Water R e s o u r c e s D i v i s i o n o f USGS and l o c a l u n i v e r s i t i e s on a m u l t i - y e a r study of c e r t a i n a r e a s of the High P l a i n s o r O g a l a l l a A q u i f e r as w e l l as c e r t a i n a r e a s i n the San J o a q u i n V a l l e y . The o b j e c t i v e i s t o study the r e l a t i o n s h i p between a g r i c u l t u r a l l a n d use on groundwater q u a l i t y i n t h e s e a r e a s . 1

N a t i o n a l Survey. E P A s O f f i c e of D r i n k i n g Water and OPP a r e d e s i g n i n g a n a t i o n a l s t a t i s t i c a l s u r v e y of p e s t i c i d e s i n e x i s t i n g d r i n k i n g w a t e r w e l l s . The g o a l s are t o make s t a t i s t i c a l e s t i m a t e s about n a t i o n w i d e o c c u r r e n c e , t o r e l a t e the o c c u r r e n c e t o f i e l d c o n d i t i o n s ( p e s t i c i d e usage and h y d r o g e o l o g y ) , and t o make broad e s t i m a t e s of the p o p u l a t i o n exposed. T e c h n i c a l d e t a i l s were des c r i b e d above under " L a r g e - S c a l e R e t r o s p e c t i v e S t u d i e s . " A f i n a l r e p o r t i s e x p e c t e d i n 1989. D i b r o m o c h l o r o p r o p a n e (DBCP) i n C a l i f o r n i a and H a w a i i . DBCP has now been found i n 2500 p r i v a t e d o m e s t i c , p u b l i c , and i r r i g a t i o n w e l l s i n C a l i f o r n i a , and was r e c e n t l y found t o have l e a c h e d 400 f e e t downward through the u n s a t u r a t e d or vadose zone ( 4 4 ) . California S t a t e Assembly B i l l 1803, passed i n 1984, r e q u i r e s the s t a t e h e a l t h department t o m o n i t o r 40 p r i o r i t y p e s t i c i d e s and o t h e r organics. The r e m a i n i n g use of DBCP on p i n e a p p l e s i n H a w a i i was c a n c e l l e d ( 4 5 ) . In a c o l l a b o r a t i v e e f f o r t between EPA and USGS,

10.

COHEN ET AL.

189


a f i e l d by f i e l d ground-water v u l n e r a b i l i t y r e c o n n a i s s a n c e was performed on Maui ( 4 6 ) .

analysis


Iowa. The S t a t e o f Iowa G e o l o g i c a l Survey and the Department o f Water, A i r , and Waste Management c o n t i n u e t o a g g r e s s i v e l y m o n i t o r f o r p e s t i c i d e s i n ground w a t e r i n many a r e a s o f t h e s t a t e (47-50)» EPA/OPP i s c o l l a b o r a t i n g w i t h the U n i v e r s i t y o f Iowa and t h e IGS i n a two-year s t r a t i f i e d random s u r v e y o f w e l l s and farm f i e l d s i n f o u r types o f h y d r o g e o l o g i c e n v i r o n m e n t s . E t h y l e n e Dibromide (EDB). R e s u l t s o f a c o l l a b o r a t i v e study o f EDB between USGS and EPA/OPP i n southwest G e o r g i a were r e c e n t l y p u b l i s h e d ( 5 1 ) . A f o l l o w up p r o j e c t i s c o n t i n u i n g . The S t a t e o f F l o r i d a has been s u c c e s s f u l l y s t r u g g l i n g w i t h d e t e c t i o n s o f EDB i n a p p r o x i m a t e l y 1000 p r i v a t e and p u b l i c w e l l s (11% p o s i t i v e s ) , r e s u l t i n g i n exposure t o g r e a t e r than 50,000 p e o p l e ( 5 2 ) . L a b o r a t o r y r e s e a r c h on the s u b s u r f a c e f a t e o f EDB c o n t i n u e s (53, 5 4 ) . Cape Cod. EPA/OPP i s c o l l a b o r a t i n g w i t h the Cape Cod P l a n n i n g and Economic Development Commission and the USGS t o d e s i g n and conduct a s m a l l - s c a l e r e t r o s p e c t i v e s t u d y o f ground-water q u a l i t y under g o l f courses t r e a t e d w i t h p e s t i c i d e s . The USGS d i s t r i c t o f f i c e i s a l s o l e n d i n g some t e c h n i c a l s u p p o r t t o t h i s e f f o r t . Two o t h e r r e c e n t C a l i f o r n i a r e p o r t s a r e worth h i g h l i g h t i n g . The C a l i f o r n i a Department o f Food and A g r i c u l t u r e r e c e n t l y completed and r e p o r t e d on a u s e f u l c o m p u t e r i z e d w e l l i n v e n t o r y d a t a base f o r a g r i c u l t u r a l p e s t i c i d e s i n ground water from n o n p o i n t s o u r c e s (55)« A 1983 r e p o r t by R a m l i t A s s o c . showed t h a t the number o f p e s t i c i d e s found i n ground water as a r e s u l t o f p o i n t s o u r c e p o l l u t i o n g r e a t l y outnumbered t h o s e from n o n p o i n t s o u r c e s ( 5 6 ) * This l a t t e r report u n d e r s c o r e s the need t o determine c o n t a m i n a t i o n s o u r c e s so t h a t p r o p e r r e m e d i a l and r e g u l a t o r y a c t i o n s a r e t a k e n . F o l l o w i n g i s a c h e m i c a l - s p e c i f i c summary o f ground-water monitoring r e s u l t s . T h i s i s an update o f t h e 1984 t a b u l a t i o n , which a l s o c o n t a i n e d e n v i r o n m e n t a l c h e m i s t r y d a t a (I) · In order f o r a p e s t i c i d e t o be i n c l u d e d on t h i s l i s t , t h e r e must be a n a l y t i c a l c o n f i r m a t i o n , t h e r e must be l a b and/or c o n t r o l l e d f i e l d d a t a w h i c h demonstrate some l e a c h i n g p o t e n t i a l i n c e r t a i n environments, and t h e f i n d i n g s must be t i e d t o a g r i c u l t u r a l p r a c t i c e . The same c r i t e r i a a p p l i e d t o t h e 1984 t a b u l a t i o n . The c h e m i c a l s a r e l i s t e d i n a l p h a b e t i c a l o r d e r . The d a t a a r e summarized by c h e m i c a l and by s t a t e i n T a b l e I and F i g u r e 1, r e s p e c t i v e l y . There a r e a d d i t i o n a l r e p o r t s o f p e s t i c i d e s i n ground water, b u t t h e r e p o r t s o n l y s a t i s f y two o f t h e t h r e e c r i t e r i a f o r i n c l u s i o n on t h e l i s t . The t h r e e p e s t i c i d e s i n q u e s t i o n a r e a r s e n i c i n Texas and EDB and a t r a z i n e i n Hawaii. These r e p o r t s a l l f o c u s on n o n p o i n t s o u r c e s o f p e s t i c i d e s l e a c h i n g t o ground w a t e r . However, t h e e x t e n t o f o c c u r r e n c e o f p e s t i c i d e s i n ground water from a g r i c u l t u r a l and i n d u s t r i a l p o i n t s o u r c e s i s a l s o n o t known. A s e p a r a t e i n v e s t i g a t i o n i n t o t h i s t o p i c would be w a r r a n t e d .


190


Alachlor. A l a c h l o r has been found r e c e n t l y i n Iowa (47-50), P e n n s y l v a n i a ( 5 7 ) , and Maryland ( 5 8 ) . The s t u d i e s would a l l be c l a s s i f i e d as l a r g e - s c a l e r e t r o s p e c t i v e . A l l s t u d y d e s i g n s had s t r o n g h y d r o g e o l o g i c a l components, but had l i t t l e , i f any, p r o b a b i l i s t i c components. I n the more l o c a l i z e d a r e a s the l a t t e r components would not be n e c e s s a r y . The Iowa f i n d i n g s have been i n p r i v a t e w e l l s , p u b l i c w e l l s , and o b s e r v a t i o n w e l l s i n v a r i o u s a r e a s around the s t a t e and h y d r o g e o l o g i c environments r a n g i n g from a l l u v i a l to k a r s t l i m e s t o n e . I n P e n n s y l a v a n i a , the USGS r e p o r t e d s i x p o s i t i v e s i n a network of a p p r o x i m a t e l y 82 o b s e r v a t i o n and r e s i d e n t i a l w e l l s i n c e n t r a l P e n n s y l v a n i a sampled f o r p e s t i c i d e s . L i k e w i s e , i t was found i n f o u r p u b l i c and p r i v a t e w e l l s out o f 30 w e l l s sampled i n v a r i o u s l o c a t i o n s on M a r y l a n d ' s E a s t e r n S h o r e . Most p o s i t i v e s f a l l i n the 0.1-10 ppb range. A l a c h l o r has now been found i n f o u r s t a t e s ' ground w a t e r . Aldicarb. As n o t e d p r e v i o u s l y (JL), the a l d i c a r b s p e c i e s u s u a l l y found a r e the b i o o x i d i z e d m e t a b o l i t e s , a l d i c a r b s u l f o x i d e and a l d i c a r b s u l f o n e . The o n l y new s t a t e w i t h a r e p o r t o f a l d i c a r b i n ground water i s Rhode I s l a n d . The f i n d i n g r e s u l t e d from a water q u a l i t y i n v e s t i g a t i o n by the USGS i n the v i c i n i t y o f p o t a t o f i e l d s (59). The w e l l s c r e e n s g e n e r a l l y ranged between 15 and 50 f e e t (4.6 - 15.2 m) deep. As T a b l e I i n d i c a t e s , a l d i c a r b has now been found i n the ground water o f 15 s t a t e s . The f i n d i n g s have been i n o b s e r v a t i o n , i r r i g a t i o n , and p r i v a t e domestic w e l l s but a p p a r e n t l y not i n p u b l i c w e l l s . Based on work c i t e d p r e v i o u s l y (1) and o t h e r more r e c e n t work (42, 6 0 ) , r o u g h l y 2000 w e l l s n a t i o n w i d e have been found t o c o n t a i n a l d i c a r b r e s i d u e s , a t l e v e l s t y p i c a l l y r a n g i n g from 1 t o 50 ppb t o t a l a l d i c a r b r e s i d u e s . These s t u d y d e s i g n s would be c l a s s i f i e d under a l l t h r e e s t u d y t y p e s . The s i t e s e l e c t i o n p r o c e s s has been p u r p o s i v e i n n a t u r e w i t h a heavy emphasis on s o i l t y p e , w e l l d e p t h , and p e s t i c i d e a p p l i c a t i o n t i m i n g w i t h r e s p e c t to r e c h a r g e events and c r o p growth. A t r a z i n e . A t r a z i n e was found i n the same P e n n s y l v a n i a s u r v e y mentioned i n the a l a c h l o r d i s c u s s i o n above. A t r a z i n e was r e p o r t e d i n 21 of t h o s e w e l l s . I t was a l s o r e p o r t e d i n t h r e e p u b l i c w e l l s i n the M a r y l a n d s u r v e y mentioned i n the a l a c h l o r d i s c u s s i o n . I t has now been r e p o r t e d i n f i v e s t a t e s ' ground water a t l e v e l s t y p i c a l l y r a n g i n g between 0.3 and 3.0 ppb. B r o m a c i l . There a r e no new p o s i t i v e s o f b r o m a c i l t o r e p o r t , a l t h o u g h i t i s seldom a n a l y z e d f o r i n w e l l s u r v e y s . Carbofuran. The o n l y new s t a t e w i t h a r e p o r t o f c a r b o f u r a n i n ground water i s M a r y l a n d . The f i n d i n g was beneath t e s t p l o t s on M a r y l a n d ' s E a s t e r n Shore i n a s m a l l - s c a l e p r o s p e c t i v e s t u d y , and p o s i t i v e s t y p i c a l l y exceeded 5 ppb. A t r a c e r was a p p l i e d . More d e t a i l s cannot be g i v e n due t o the f a c t t h a t the i n f o r m a t i o n i s c o n s i d e r e d by the r e g i s t r a n t , FMC, to be c o n f i d e n t i a l b u s i n e s s i n f o r m a t i o n ( 6 0 ) . C a r b o f u r a n has now been r e p o r t e d i n t h r e e s t a t e s ' ground water, a t l e v e l s t y p i c a l l y r a n g i n g between 1 and 50 ppb. I t s h o u l d be noted t h a t c a r b o f u r a n ground-water m o n i t o r i n g has r a r e l y attempted t o d e t e c t the t o x i c m e t a b o l i t e s , 3-OH and 3-keto

10.

C O H E N ET AL.

Monitoring

191

Ground Water for Pesticides

carbofuran. T h i s i s a d e f i c i e n c y which s h o u l d future monitoring.

be a d d r e s s e d i n


C y a n a z i n e . T h i s c h e m i c a l had n o t been found i n ground water as o f the time t h e 1984 l i s t (1_) was w r i t t e n . The new f i n d i n g s a r e i n n o r t h e a s t e r n Iowa (47-49) and c e n t r a l P e n n s y l v a n i a ( 5 7 ) . In the Iowa s t u d i e s , c y a n a z i n e was found a t low l e v e l s i n t h r e e w e l l s and a s p r i n g i n i n c i p i e n t k a r s t and k a r s t a r e a s . Cyanazine was r e p o r t e d at 1.1 ppb i n one o f t h e 82 w e l l s i n t h e c e n t r a l P e n n s y l v a n i a s t u d y where t h e water l e v e l i n t h e w e l l was a p p r o x i m a t e l y 75 f e e t below land surface. DBCP. No a d d i t i o n a l s t a t e s have r e p o r t e d DBCP f i n d i n g s . DBCP was r e p o r t e d i n w e l l s o f f i v e s t a t e s ( 1 ) .

I n 1984,

DCPA (and a c i d p r o d u c t s ) . No a d d i t i o n a l s t a t e s have r e p o r t e d DCPA findings. I t was r e p o r t e d i n New York ground water ( 1 ) . These c h e m i c a l s a r e n o t u s u a l l y i n c l u d e d i n ground-water m o n i t o r i n g programs. 1,2-Dichloropropane. 1,2-D was r e c e n t l y r e p o r t e d i n a t l e a s t seven s h a l l o w w e l l s i n w e s t e r n Washington i n a s s o c i a t i o n w i t h s o i l i n j e c t i o n i n strawberry f i e l d s (61). The p u r p o s i v e w e l l s e l e c t i o n s i n t h i s r e t r o s p e c t i v e s t u d y were done w i t h s t r o n g bases i n h y d r o g e o l o g y and p e s t i c i d e usage i n f o r m a t i o n . 1,2-D has now been r e p o r t e d i n f o u r s t a t e s ground water a t l e v e l s g e n e r a l l y r a n g i n g between 1 and 50 ppb. 1

D i n o s e b . No a d d i t i o n a l s t a t e s have r e p o r t e d d i n o s e b f i n d i n g s . I t had been found i n New York ground water ( 1_). This chemical i s not u s u a l l y i n c l u d e d i n ground-water m o n i t o r i n g programs. D y f o n a t e . T h i s c h e m i c a l was n o t on t h e 1984 l i s t . I t was found a t 0.11 ppb i n a s p r i n g d r a i n i n g a s o l u t i o n l i m e s t o n e a q u i f e r i n n o r t h e a s t Iowa ( 4 9 ) . I t i s a marginal leacher; i . e . , i t s p e r s i s t ence and m o b i l i t y a r e l e s s than most o f t h e o t h e r ground-water contaminants (,2). EDB. Four a d d i t i o n a l s t a t e s have r e p o r t e d EDB i n ground water. EDB was found i n 14 p u b l i c , p r i v a t e , and o b s e r v a t i o n w e l l s , o u t of 95 w e l l s sampled, t a p p i n g s h a l l o w u n c o n f i n e d and deeper c o n f i n e d a q u i f e r s i n w e s t e r n Washington (6^2, 6 3 ) . EDB has been found i n s e v e r a l w e l l s i n southwest A r i z o n a a t sub-ppb l e v e l s , i n c l u d i n g community w e l l s i n Phoenix ( 6 4 ) . C o n t a m i n a t i o n o f over 220 p u b l i c and p r i v a t e w e l l s was r e p o r t e d i n w e s t e r n M a s s a c h u s e t t s and w e s t e r n C o n n e c t i c u t where i t had been used i n t h e C o n n e c t i c u t R i v e r V a l l e y (65, 6 6 ) . I n many c a s e s t h e s e l a r g e - s c a l e r e t r o s p e c t i v e s t u d i e s have i n v o l v e d s a t u r a t i o n s a m p l i n g . That i s , e v e r y p o s s i b l e t h r e a t e n e d w e l l was sampled. I n such s i t u a t i o n s , a s t a t i s t i c a l / p r o b a b i l i s t i c d e s i g n i s m e a n i n g l e s s and n o t r e q u i r e d . EDB has been found i n t h e ground water o f e i g h t s t a t e s a t w i d e l y v a r y i n g l e v e l s which u s u a l l y range between 0.05 and 20 ppb.

192


Metolachlor. Both s t a t e r e p o r t s of m e t o l a c h l o r a r e new. I t was found i n 4 out o f 82 w e l l s sampled i n the USGS c e n t r a l P e n n s y l v a n i a study ( 5 7 ) . M e t o l a c h l o r was a l s o found i n a w e l l i n an i n c i p i e n t k a r s t a r e a and two s p r i n g s d r a i n i n g a s o l u t i o n l i m e s t o n e a q u i f e r i n n o r t h e r n Iowa (^8, 4 9 ) . C o n c e n t r a t i o n s t y p i c a l l y range between 0.1 and 0.5 ppb.


Metribuzin. T h i s p e s t i c i d e i s a r e c e n t a d d i t i o n t o the l i s t . It was found i n t h r e e o b s e r v a t i o n w e l l s i n n o r t h e r n Iowa a t l e v e l s r a n g i n g from 0.09 to 4.35 ppb ( 4 8 ) . Oxamyl. The Rhode I s l a n d w e l l s out o f range from 1 ppb. Oxamyl

o n l y new s t a t e r e p o r t i n g oxamyl i n ground water i s ( 5 9 ) . I t was found i n a t l e a s t f o u r o b s e r v a t i o n 11 sampled. T y p i c a l l e v e l s o f oxamyl i n ground water to 60 ppb, w i t h the Rhode I s l a n d r e s u l t s c l o s e r t o 1 has now been found i n the ground water of two s t a t e s .

Simazine. Simazine was r e c e n t l y found i n e i g h t out of 82 w e l l s sampled i n c e n t r a l P e n n s y l v a n i a ( 5 7 ) . I t was a l s o found i n one w e l l a t the d e t e c t i o n l i m i t i n the p r e v i o u s l y mentioned Maryland study (58). Simazine has been found i n the ground water of t h r e e s t a t e s a t l e v e l s t y p i c a l l y r a n g i n g between 0.2 and 3.0 ppb. Trichloropropane. 1 , 2 , 3 - T r i c h l o r o p r o p a n e (TCP) had been a byp r o d u c t of the m a n u f a c t u r e of d i c h l o r o p r o p e n e / d i c h l o r o p r o p a n e nematicides. I t i s u n c e r t a i n whether t h i s p e r s i s t e n t and m o b i l e i m p u r i t y i s s t i l l p r e s e n t i n p e s t i c i d e f o r m u l a t i o n s . TCP has been found i n s m a l l - s c a l e and l a r g e - s c a l e r e t r o s p e c t i v e s t u d i e s i n C a l i f o r n i a and Hawaii s o i l and ground water (67, 68). I t was found a t l e a s t 10 f e e t down i n the s o i l p r o f i l e s i n H a w a i i , and i n w e l l s i n Oahu and the C e n t r a l V a l l e y o f C a l i f o r n i a . Positives t y p i c a l l y range between 0.2 and 2 ppb i n the s o i l and i n ground water. Concluding

Remarks

The e x t e n t of the problem o f p e s t i c i d e s i n ground water i s not known. What we have i s a c o l l e c t i o n of m o n i t o r i n g s t u d i e s , conc e i v e d w i t h d i f f e r e n t o b j e c t i v e s and u s i n g d i f f e r e n t d e s i g n s t r a t e g i e s , a l t h o u g h most a r e v a r i o u s s c a l e s o f r e t r o s p e c t i v e s t u d i e s . (Most of these have e i t h e r been c i t e d i n the p r e s e n t work o r p r e v i o u s l y (1))· T h e r e f o r e the r e a d e r i s c a u t i o n e d about making g e n e r a l i z a t i o n s about the r e s u l t s so f a r . F o r example, i t would be easy to l o o k a t F i g u r e 1 and c o n c l u d e t h a t Iowa has a worse ground-water p r o b l e m t h a n , s a y , M i s s o u r i . However, F i g u r e 1 may o n l y r e f l e c t the f a c t t h a t the Iowa S t a t e government has a v e r y a c t i v e m o n i t o r i n g program, e s p e c i a l l y when one c o n s i d e r s t h a t M i s s o u r i has a p o t e n t i a l h i g h use of n e m a t i c i d e s i n permeable s o i l s over s o l u t i o n limestone a q u i f e r s . Perhaps the next update of t h i s g e n e r a l assessment w i l l be more c o n c l u s i v e and w i l l c i t e a d d i t i o n a l good m o n i t o r i n g s t u d i e s which c o n t a i n s e v e r a l of the key elements d e s c r i b e d e a r l i e r i n t h i s paper. L i k e w i s e , improvements i n our p r e d i c t i v e c a p a b i l i t i e s s h o u l d enable us to be more c o n c l u s i v e i n our assessments.

10.

C O H E N ET AL.


193

Acknowledgment s The a u t h o r s g r a t e f u l l y acknowledge t h e a s s i s t a n c e o f t h e S t a t i s t i c s Team o f OPP's T o x i c o l o g y Branch f o r s e v e r a l h e l p f u l suggestions. L i k e w i s e , George DeBuchananne o f DeBuchananne & A s s o c i a t e s and L e s M c M i l l i o n o f EPA-Las Vegas were i n v a l u a b l e s o u r c e s o f i n f o r m a t i o n on w e l l c o n s t r u c t i o n and h y d r o g e o l o g y .


Literature Cited

1. Cohen, S.Z.; Creeger, S.M.; Carsel, R.F.; Enfield, C.G. In "Treatment and Disposal of Pesticide Wastes"; Krueger, R.F.; Seiber, J.N., Eds.; ACS SYMPOSIUM SERIES No. 259, American Chemical Society: Washington, DC, 1984; pp. 297-325. 2. Cohen, S.Z. "List of Potential Ground-Water Contaminants," Office of Pesticide Programs (TS-769C), Environmental Protection Agency, Washington, DC 20460, August 28, 1984. 3. Aller, L.; Bennett, T.; Lehr, J.H.; Petty, R.J. "DRASTIC: A Standardized System for Evaluating Ground Water Pollution Potential Using Hydrogeologic Settings," EPA/600/2-85/018, Robert S. Kerr Environmental Research Laboratory, Environmental Protection Agency, Ada, Oklahoma 74820. 4. Helling, C.S.; Gish, T.J. "Soil Characteristics Affecting Pesticide Movement Into Ground Water," 189th ACS National Meeting, PEST 2, Florida, 1985. 5. "1984 Herbicide Market Study," Doane Marketing Research, Inc., Princeton, New Jersey 08540; 1984 (also available are reports on insecticides and specialty crops). 6. "1982 Census of Agriculture, Volume 1, Geographic Area Studies," Bureau of the Census, Department of Commerce, 1984. 7. Cochran, W.G. "Sampling Techniques Second Edition"; John Wiley & Sons, Inc.: New York, 1967; Chaps. 2, 5. 8. Nelson, J.D.; Ward, R.C. Ground Water 1981, 19, 617-625. 9. Mason, R.E.; McFadden, D.D.; Iannachione, V.G.; McGrath, D.S. "Survey of DBCP Distribution in Ground Water Supplies and Surface Water Ponds," EPA 68-01-5848, Research Triangle Institute, Research Triangle Park, North Carolina 27709. 10. Williams, B. "A Sampler on Sampling"; John Wiley & Sons, Inc.: New York, 1978. 11. Snedecor, G.W.; Cochran, W.G. "Statistical Methods Seventh Edition"; The Iowa State University Press: Ames, Iowa, 1980; Chap. 21. 12. Helsel, D.R.; Ragone, S.E. "Evaluation of Regional GroundWater Quality in Relation to Land Use: U.S. Geological Survey Toxic Waste-Ground-Water Contamination Program", 1984, Water Resources Investigations Report 84-4217, 33 pages. 13. "RCRA Permit Writer's Manual Ground-Water Protection 40 CFR Part 264, Subpart F," U.S. EPA, 1983. 14. "Field Agricultural Runoff Monitoring (FARM) Manual," Smith, C.N.; Brown, D.S.; Dean, J.D.; Parrish, R.S.; Carsel, R.F., U.S. EPA, EPA-600/3-85/043, 1985, 300 pages. 15. Porter, K. S.; Trautmann, N.M. "Seasonality in Ground Water Quality," EPA Office of Research and Development, Las Vegas, NV; in press.


194

EVALUATION OF PESTICIDES IN GROUND WATER

16. Keith, S.J.; Wilson, L.G.; Fitch, H.R.; Esposito, D.M. Ground Water Monitoring Review 1983, 2, 21-32. 17. Hallberg, G.R.; Libra, R.D.; Bettis, A.E.; Hoyer, B.E. "Hydrologie and Water Quality Investigations in the Big Spring Basin," 1984, Iowa Geological Survey, Open-File Report, 231 pages. 18. Luhdorff, G.; Scalmanini, J. "Ground Water and the Unsaturated Zone Monitoring and Sampling," National Water Well Assoc.; unpublished training manual, 359-365. 19. Barcelona, M.J.; Gibb, J.P.; Miller, R.A. "A Guide to the Selection of Materials for Monitoring Well Construction and Ground-Water Sampling," 1983, 111. State Water Survey, Contract Report 327. 20. Scalf, M.R.; McNabb, J.F.; Dunlap, W.J.; Cosby, R.L.; Fryberger, J. "Manual of Ground Water Sampling Procedures", National Water Well Association/Environmental Protection Agency Series. 21. "Quality of Water Branch Technical Memorandum No. 85.09," U.S. Department of the Interior Geological Survey, April 22, 1985. 22. Kurt, C.E.; Johnson, R.C. Ground Water. 1982, 20(4), 415-419. 23. Nacht, S.J. Ground Water Monitoring Review. 1983, 3, 23-8. 24. Feltz, H. U.S. Geological Survey, Reston, VA., July 1, 1985, personal communication. 25. Wilson, L.C.; Rouse, J.V. Ground Water Monitoring Review. 1983, 1, 103-108. 26. "Ground Water and the Unsaturated Zone Monitoring and Sampling", National Water Well Assoc.; unpublished training manual, pp. 257-262. 27. ibid. pp. 143-148. 28. Schuller, R.M.; Gibb, J.P.; Griffin, R.A. Ground Water Monitoring Review. 1981, Spring, 42-46. 29. Gibb, J.P.; Barcelona, M.J. J. Am. Water Works Assoc. 1984, May, 48-51. 30. Holden, P.W. "Primer on Well Water Sampling for Volatile Organic Compounds," Water Resources Research Center, University of Arizona, U.S. Department of the Interior, 1978. 31. Steinheimer, T. U.S. Geological Survey, Central Analytical Lab, Aravada, CO, July 9, 1985, personal communication. 32. Tourtelot, H.A.; Miesch, A.T. The Geological Society of America-Special Papers. 1975, 155, 107-119. 33. Krumbein, W.C.; Slack, H.A. Geol. Soc. Am. Bull. 1956, of 67(6), 739-762. 34. Hormann, W.D.; Karlhuber, B.; Ramsteiner, K.A. Proc. Eur. Weed Res. Coun. Symp. Herbicides-Soil. 12-3, 129-140. 35. Reed, J.F.; Rigney, J.A. J. Am. Soc. Agron. 1947, 39, 26-40. 36. Mason, B.J. "Preparation of Soil Sampling Protocol: Techniques and Strategies," U.S. Environmental Protection Agency, 1982. 37. Davis, S.N.; Thompson, G.M.; Bentley, H.W.; Stiles, G. Ground Water. 1980, 18, 14-23. 38. Tennyson, L.C.; Settergren, C.D. Water Resources Bulletin. 1980. 16, 433-437. 39. Thompson, G.M.; Hayes, J.M. Water Resources Research. 1979, 15, 546-554.

10.

COHEN

40. 41. 42.

43. Evaluation of Pesticides in Ground Water Downloaded from pubs.acs.org by UNIV OF LEEDS on 10/04/15. For personal use only.

44. 45. 46. 47. 48. 49. 50. 51. 52. 53. 54. 55. 56. 57.

ET

AL.


195

Jones, R.L.; Back, R.C. Environ. Toxicol. Chem. 1984, 3, 9-20. Miles, C.J.; Delfino, J.J. J. Agric. Food Chem. 1985, 33, 455-460. Porter, K.S.; Lemley, A.T.; Hughes, H.B.; Jones, R.L. In "Second International Conference on Ground-Water Quality Research Proceedings", National Center for Ground Water Research, Oklahoma State University, Stillwater, OK, in press. Lemley, A.T.; Zhong, W. J. Agric. Food Chem. 1984, 32, 714719. Cohen, D.B. "Ground Water Contamination By Toxic Substances: A California Assessment," 189th ACS National Meeting, PEST 91, Florida, 1985. "Dibromochoropropane; Intent to cancel Registrations of Pesticide Products Containing Dibromochloropropane (DBCP)", EPA Fed. Reg. 50, 1122-1130, 1985. Cohen, S.Z. "DBCP Use on Certain Pineapple Fields on Maui Implications for Potential Drinking Water Contamination," TS-769C, U.S. EPA, Washington, DC 20460, 1985. "Hydrogeology, Water Quality, and Land Management in the Big Spring Basin, Clayton County, Iowa," Iowa Geological Survey Open File Report 83-3, Iowa City, IA, 1983. "Ground Water Quality and Hydrogeology of Devonian-Carbonate Aquifers in Floyd and Mitchell Counties, Iowa," Iowa Geological Survey Open File Report 84-2, Iowa City, IA, 1984. "Hydrogeologic and Water Quality Investigations in the Big Spring Basin, Clayton County, Iowa 1983 Water-Year," Iowa Geological Survey Open File Report 84-4, Iowa City, IA, 1984. Kelly, R., Iowa Department of Water and Waste Management, Des Moines, IA, 1984 and 1985, personal communications. McConnell, J.B.; Hicks, D.N.; Lowe, L.E.; Cohen, S.Z.; Jovanovich, A.P. "Investigation of Ethylene Dibromide (EDB) in Ground Water in Seminole County, Georgia," USGS Circular 933; Reston, VA, 1984. Reich, A. Florida Dept. Health & Rehab. Serv. - Env'l Epi. Sect.; personal communications, 1985. Jungclaus, G.; Cohen, S.Z. "Hydrolysis of Ethylene Dibromide," Environ. Sci. Technol., in review. Weintraub, R.A.; Jex, G.W.; Moye, H.A. "Degradation of 1,2Dibromoethane in Florida Ground Water and Soil," American Chemical Society 189th National Meeting, PEST 110, Florida, 1985. "Agricultural Pesticide Residues in California Well Water: Development and Summary of a Well Inventory Data Base for Non-Point Sources", Environmental Hazards Assessment Program, Cal. Dept. Fd. Ag., Sacramento, CA, 1985. Litwin, Y. "Groundwater Contamination by Pesticides: A California Assessment", Ramlit Assoc., Berkeley, CA, 1983. Buchanan, J.W.; Loper, W.C.; Schaffstall, W.P.; Hainly, R.A. "Water Resources Data Pennsylvania Water Year 1983 Volume 2. Susquehanna and Potomac River Basins," USGS/WRD/HD-84/060, U.S. Geological Survey; Harrisburg, PA, 1984.


196

EVALUATION OF PESTICIDES IN GROUND WATER

58· "Results of a Maryland Groundwater Herbicide Survey Fall 1983," Office of Environmental Programs, Dept. Health and mental Hygiene; Annapolis, MD, 1984. 59. Johnston, H.E., United States Geological Survey, Providence, RI, July 24, 1985, personal communication, and subsequent contacts with that office. 60. EPA/Office of Pesticide Programs confidential business information files. 61. "EDB Contamination Survey, Skagit County, WA" , EPA - Drinking Water Branch, Seattle, WA; 1984. 62. "Results and Implications of the Investigation of Ethylene Dibromide in Ground Water in Western Washington," Washington Department of Social Services and Health, Water Supply & Waste Section, Olympia, WA, 1985. 63. Plews, G.; Baum, L., ibid., personal communication. 64. "Results of Ethylene Dibromide (EDB) Sampling in Arizona," Ambient Water Quality Surveys and Data Management, Division of Environmental Health Services, Phoenix, AZ, in press. 65. Wing, S.; Robinson, B.R., Connecticut Dept. Env. Protection; personal communications, 1984. 66. Higgins, J., Massachusetts Dept. Env. Qual. Engg. - Western Region, Springfield, MA; personal communication, 1984. 67. Wong, W., Arizumi, T., Hawaii Department of Health, personal communication, 1983. 68. Cohen, D., California State Water Resources Control Board, personal communication, 1985. RECEIVED April 1, 1986

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