Hydrogeologic Investigations of Pesticide Spills - ACS Symposium

Jul 23, 2009 - If properly designed, monitor-well networks can also aid in determining the ... For example, a monitoring program designed to supply in...
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Ralph E. Moon and Carol D. Henry Geraghty & Miller, Inc., Ground Water Consultants, 14310 North Dale Malory Highway, Tampa, FL 33618

A major reason for installing monitor wells is to provide early warning of ground-water contamination. If properly designed, monitor-well networks can also aid in determining the effectiveness of ground-water protection measures. The ultimate effectiveness of monitor wells is dependent upon a clear definition of the desired results. For example, a monitoring program designed to supply information for litigation is quite different from one implemented to determine whether local agricultural practices adversely affect ground-water quality. Monitoring based upon a regulatory philosophy of zero discharge to ground water will require a monitoring system substantially different in design from one reflecting a regulatory philosophy of containment within the boundaries of a disposal site. Whatever the reason for installing a ground-water monitoring system, its design should be based on demonstrated hydrogeologic principles and site-specific data. C o n t a m i n a t i o n o f g r o u n d w a t e r w i t h p e s t i c i d e s c a n o c c u r i n two d i s t i n c t l y d i f f e r e n t s i t u a t i o n s , those o r i g i n a t i n g from widespread a g r i c u l t u r a l use and those a t t r i b u t e d t o a s p e c i f i c p o i n t s o u r c e loss. Each o f these s i t u a t i o n s r e q u i r e s a d i f f e r e n t approach t o ground-water m o n i t o r i n g . Cases o f widespread p e s t i c i d e c o n t a m i n a t i o n can r e s u l t from unusually high application rates under shallow water-table c o n d i t i o n s , on e x t r e m e l y porous s o i l s , o r near g e l o g i c c o n d u i t s t h a t c o n n e c t t h e s u r f a c e t o deeper a q u i f e r s . In these c a s e s , sampling o f e x i s t i n g p u b l i c and p r i v a t e w a t e r - s u p p l y w e l l s g e n e r a l l y forms t h e b a s i s o f the ground-water m o n i t o r i n g . In other cases of p e s t i c i d e c o n t a m i n a t i o n on g r e a t expanses o f l a n d , t h e ground-water m o n i t o r i n g network has been d e s i g n e d t o i d e n t i f y t h e " c l e a n " p o t a b l e s o u r c e s o f ground water r a t h e r than t h e e x t e n t o f t h e c o n t a m i n a t i o n . The f o c u s o f t h i s paper i s on s p i l l s and p o i n t s o u r c e l o s s e s o f p e s t i c i d e s , which a r e g e n e r a l l y a s s o c i a t e d w i t h t h e manufacture and 0097-6156/ 86/ 0315-0159$06.00/ 0 © 1986 A m e r i c a n C h e m i c a l Society

Garner et al.; Evaluation of Pesticides in Ground Water ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

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d i s p o s a l of p e s t i c i d e s . Commonly, the ground-water c o n t a m i n a t i o n s t e m s from l e a k y p i p e s , used drums, l a g o o n s , l a n d f i l l s , and waste s t r e a m s on p l a n t p r o p e r t y . The h y d r o g e o l o g i c i n v e s t i g a t i o n of p e s t i c i d e c o n t a m i n a t i o n i s e s s e n t i a l l y no d i f f e r e n t from the h y d r o g e o l o g i c i n v e s t i g a t i o n o f most o t h e r hazardous c h e m i c a l c o n s t i t u e n t s . The purpose o f the i n v e s t i g a t i o n i s to i d e n t i f y the v e r t i c a l and h o r i z o n t a l e x t e n t of c o n t a m i n a t i o n so t h a t u l t i m a t e l y the c o n t a m i n a t i o n c a n be i s o l a t e d and the a q u i f e r r e m e d i a t e d . The r e g u l a t o r y and h y d r o l o g i e r e q u i r e m e n t s o f the m o n i t o r i n g p l a n c o n s i s t o f f o u r b a s i c e l e m e n t s : p r o b l e m i d e n t i f i c a t i o n , h e a l t h and s a f e t y requirements, monitor-well network design, and drilling and well-installation techniques. Problem

Identification

A l l i n v e s t i g a t i o n s of ground-water c o n t a m i n a t i o n problems i n v o l v e the same b a s i c c o n s i d e r a t i o n s , namely the l o c a t i o n and n a t u r e of the s o u r c e s o f the c o n t a m i n a t i o n , the mechanisms f o r i n t r o d u c i n g the c o n t a m i n a n t s i n t o the ground, the paths of f l o w t h r o u g h the g r o u n d water system, and the l o c a t i o n s of w e l l s , s p r i n g s , and s u r f a c e - w a t e r b o d i e s where the contaminants u l t i m a t e l y leave the ground-water system. A d e t a i l e d r e v i e w o f the h i s t o r y of the s i t e can p r o v e e x t r e m e l y u s e f u l i n d e f i n i n g the l o c a t i o n and n a t u r e o f s o u r c e s o f contamination. Installation of m o n i t o r w e l l s and water-quality sampling are the methods for defining subsurface transport of contaminants. Site History. A e r i a l photographs p r o v i d e v a l u a b l e i n f o r m a t i o n to h e l p d i r e c t the c o u r s e of a ground-water i n v e s t i g a t i o n . I t has been s a i d by t h o s e i n the l e g a l p r o f e s s i o n t h a t "The p a l e s t i n k s u r p a s s e s the v a l u e o f the f i n e s t memory." A c c e s s t o h i s t o r i c a l photographs s u p p o r t s t h i s statement, o f t e n r e v e a l i n g o l d a c t i v i t i e s long s i n c e f o r g o t t e n by the most f a i t h f u l employees. P e r s o n n e l i n t e r v i e w s can be h e l p f u l , but the b e s t way t o e s t a b l i s h a c h r o n o l o g i c a l sequence o f d i s p o s a l and s t o r a g e p r a c t i c e s i s t h r o u g h s c r u t i n y o f photographs, c o n s u l t i n g reports, corporate documents, and governmental records ( F e d e r a l and s t a t e r e g u l a t o r y a g e n c i e s ) . Waste D i s p o s a l P r a c t i c e s . Maps showing p r e v i o u s waste d i s p o s a l s i t e s may h e l p e x p l a i n the r e s u l t s o b t a i n e d from the a n a l y s i s o f g r o u n d w a t e r samples. I n f o r m a t i o n t h a t l o c a t e s s t o r a g e a r e a s and e f f l u e n t d i s c h a r g e p o i n t s , c h a r a c t e r i z e s waste streams, and p r o v i d e s c h e m i c a l a n a l y s e s o f s o i l , s u r f a c e w a t e r , and ground water can a l s o h e l p t o d e f i n e the waste d i s p o s a l p r a c t i c e s o f a f a c i l i t y . In a d d i t i o n , i d e n t i f y i n g a d j a c e n t l a n d owners and l a n d use p r a c t i c e s a r e b e n e f i c i a l when i t i s n e c e s s a r y t o e x p l a i n the p r e s e n c e o f ground-water c o n s t i t u e n t s t h a t c o u l d be a t t r i b u t e d t o u p g r a d i e n t p r a c t i c e s . Geology. D r i l l i n g l o g s o f o n - s i t e water w e l l s , o n - s i t e m o n i t o r w e l l s , f o u n d a t i o n b o r i n g s , and water w e l l s owned by a d j a c e n t property owners, t o g e t h e r w i t h d a t a o b t a i n e d from the U.S. G e o l o g i c a l Survey and state agencies, c a n be u s e f u l i n d e s i g n i n g a g r o u n d - w a t e r monitoring p l a n and/or r e c o v e r y program. Lithologie descriptions o b t a i n e d f r o m t h e s e s o u r c e s can d e f i n e the d e p t h to the water t a b l e , c h a r a c t e r i z e t h e s o i l t y p e s , and e s t a b l i s h t h e d e g r e e t o w h i c h

Garner et al.; Evaluation of Pesticides in Ground Water ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

9.

MOON A N D HENRY

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a q u i f e r s a r e i s o l a t e d from o r c o n n e c t e d t o one a n o t h e r . Geologic information helps t o e s t a b l i s h t h e p o t e n t i a l r i s k t o underground d r i n k i n g water s u p p l i e s and t o p r e d i c t t h e d i r e c t i o n and r a t e o f movement o f t h e p e s t i c i d e plume. F i e l d Reconnaissance. F i e l d reconnaissance techniques f o r e v a l u a t i n g ground-water contamination i n c o r p o r a t e s e v e r a l methods o t h e r than v i s u a l and o l f a c t o r y d e t e c t i o n . B i o l o g i c i n d i c a t o r s , f o r example, can demonstrate t h e p r e s e n c e o f p e s t i c i d e s i f t h e p l a n t community i s s p a r s e ( h e r b i c i d e s ) o r u n u s u a l l y dense ( i n s e c t i c i d e s ) . On a v i s i t t o the h i s t o r i c l o c a t i o n o f a South F l o r i d a DDT f o r m u l a t i o n s i t e (15 y e a r s o l d ) , o l f a c t o r y d e t e c t i o n o f p e s t i c i d e l o s s was n o t a p p a r e n t . I n s p e c t i o n o f t h e p l a n t community, however, showed s e v e r a l l a r g e c i r c u l a r p a t c h e s (20 f e e t i n d i a m e t e r ) o f dense, l o w - l y i n g v e g e t a t i o n at t h e s i t e . Removal o f t h e p l a n t s and s o i l w i t h a p i c k a x a l o n g t h e periphery o f the community r e s u l t e d i n t h e immediate r e l e a s e o f p e s t i c i d e , which was c o n f i r m e d w i t h an o r g a n i c v a p o r a n a l y z e r and by smell. Hydrogeologic Considerations. The d i r e c t i o n and r a t e o f movement o f a contaminant plume c a n change i n r e s p o n s e t o h y d r o l o g i e c o n d i t i o n s . Recharge from p r e c i p i t a t i o n , t h e m o l e c u l a r d e n s i t y o f t h e p e s t i c i d e , and t h e h y d r a u l i c g r a d i e n t ( s l o p e o f t h e water t a b l e ) a r e p r e d i c t a b l e conditions that control t h e h o r i z o n t a l and v e r t i c a l extent of contamination. S p r i n g s , s t r e a m s , l a k e s , and r i v e r s a r e p r i n c i p a l a r e a s where c o n t a m i n a n t s a r e d i s c h a r g e d from ground-water s y s t e m s . Stormwater d i t c h e s , i r r i g a t i o n w e l l s , community w e l l f i e l d s , d o m e s t i c wastewater s p r a y f i e l d s , i n f i l t r a t i o n ponds, i n d u s t r i a l impoundments, and l e a k i n g municipal sewer l i n e s may a l t e r t h e ground-water f l o w p a t t e r n by c r e a t i n g a r t i f i c i a l p o i n t s o f r e c h a r g e and d i s c h a r g e . These p o s s i b l e h y d r o l o g i e i n f l u e n c e s s h o u l d be taken i n t o a c c o u n t when a n a l y s e s o f g r o u n d - w a t e r samples show o r g a n i c compounds t h a t seem u n r e l a t e d t o the l o c a t i o n o f t h e i n f e r r e d s o u r c e s . Health

and S a f e t y

Requirements

Worker h e a l t h and s a f e t y a r e among t h e b a s i c c o n s i d e r a t i o n s i n a ground-water i n v e s t i g a t i o n o f c h e m i c a l s w i t h harmful p r o p e r t i e s . However, most i n s t a n c e s o f p e s t i c i d e c o n t a m i n a t i o n o t h e r than l o s s e s o f f r e e p r o d u c t , i n v o l v e ground-water and s o i l c o n c e n t r a t i o n s much lower than those p o s i n g an immediate o c c u p a t i o n a l h e a l t h t h r e a t . In i n s t a n c e s where f r e e p r o d u c t i s l o s t , vacuum r e c o v e r y systems a n d / o r a b s o r b e n t s may be used t o remove t h e s u r f a c e concentrations before t h e ground-water i n v e s t i g a t i o n begins. These actions, normally t a k e n as t h e f i r s t s t e p i n t h e r e m e d i a l a c t i o n p l a n , o f t e n r e n d e r t h e l a n d s u r f a c e a t t h e s i t e n e a r l y c l e a n b e f o r e the g r o u n d water problem i s s t u d i e d . P r o t e c t i v e wear and a s s o c i a t e d equipment a r e r e q u i r e d t o s a f e guard the worker. I n t h e f i e l d w h e r e no d e t e c t a b l e airborne p e s t i c i d e emissions a r e p r e s e n t , b u t where t h e p o t e n t i a l f o r s k i n contact i s h i g h , a hard h a t w i t h s p l a s h p r o t e c t o r , s a f e t y g l a s s e s , chemically r e s i s t a n t outer c l o t h i n g , gloves and b o o t s w i t h taped w r i s t s and a n k l e s , and i n n e r s u r g i c a l g l o v e s would p r o v i d e a c o n s e r v a t i v e dress f o r f i e l d p r o t e c t i o n . The p r e s e n c e o f d e t e c t a b l e

Garner et al.; Evaluation of Pesticides in Ground Water ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

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concentrations of p e s t i c i d e d u s t or vapor r e q u i r e s supplemental respiratory protection ranging from a combination particulater e m o v i n g f i l t e r and o r g a n i c v a p o r / p e s t i c i d e f i l t e r t o a heavy d u t y c a n i s t e r s i m i l a r l y equipped. Work c o n d i t i o n s t h a t r e q u i r e personal p r o t e c t i o n above t h i s l e v e l may n e c e s s i t a t e a réévaluation o f the d r i l l i n g o r s a m p l i n g l o c a t i o n s f o r ground-water m o n i t o r i n g . The s p e c i f i c r e g u l a t o r y r e q u i r e m e n t s o f a H e a l t h and Safety Plan are d e s c r i b e d i n " S t a n d a r d O p e r a t i n g S a f e t y G u i d e s . " (1)

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Monitor-Well

Design

The o b j e c t i v e s of i n s t a l l i n g a m o n i t o r - w e l l network must be c l e a r l y d e f i n e d b e f o r e c h o o s i n g the s p e c i f i c l o c a t i o n s , numbers, and dimens i o n s o f the w e l l s . The p r e f e r r e d d e s i g n depends on the p r o p o s e d uses of the monitor-well network, the dimensions and chemical c h a r a c t e r i s t i c s of the contaminant plume, and the s i t e hydrogeology. L o c a t i o n and Number. The l o c a t i o n o f a m o n i t o r w e l l r e f e r s t o b o t h i t s a r e a l l o c a t i o n i n r e l a t i o n to the waste s o u r c e and i t s v e r t i c a l l o c a t i o n o r d e p t h i n the uppermost or o t h e r a q u i f e r . The number and l o c a t i o n s o f the w e l l s depend on s e v e r a l f a c t o r s , i n c l u d i n g r e g u l a t o r y c o n s t r a i n t s and the c u r r e n t l e v e l of knowledge o f the site h y d r o g e o l o g y and water q u a l i t y . S t a t e and F e d e r a l r e g u l a t i o n s , f o r i n s t a n c e , g e n e r a l l y r e q u i r e t h a t a m i n i m a l number o f m o n i t o r w e l l s be i n s t a l l e d a t o r near the s o u r c e o f ground-water c o n t a m i n a t i o n , i n b o t h the u p g r a d i e n t and downgradient d i r e c t i o n s . However, i f o n l y s c a n t h y d r o g e o l o g i c d a t a a r e a v a i l a b l e , i t may not be p o s s i b l e t o determine in advance the horizontal and vertical direction of ground-water f l o w . In t h e s e c a s e s , a presumed f l o w d i r e c t i o n , based on the l o c a t i o n s of s u r f a c e water b o d i e s , the topography, and o t h e r s u r f a c e i n d i c a t i o n s , i s used t o d e s i g n a t e the p r o p o s e d m o n i t o r - w e l l l o c a t i o n s , b o t h u p g r a d i e n t and downgradient o f the waste s o u r c e s . A d d i t i o n a l w e l l s a r e g e n e r a l l y r e q u i r e d f o r c h a r a c t e r i z a t i o n of the s i t e hydrogeology. W e l l s m o n i t o r i n g d i f f e r e n t a q u i f e r s o r d i f f e r e n t zones w i t h i n a s i n g l e a q u i f e r a r e g e n e r a l l y i n s t a l l e d f o r two r e a s o n s : (1) t o i d e n t i f y h y d r a u l i c c h a r a c t e r i s t i c s of and the r e l a t i o n s h i p between the d i f f e r e n t zones or a q u i f e r s , and (2) to c h a r a c t e r i z e the g r o u n d water quality at d i f f e r e n t depths. Characterization of site h y d r o g e o l o g y a l s o i n v o l v e s i n v e s t i g a t i n g the p r e s e n c e o f c o n f i n i n g layers. To demonstrate the e f f e c t i v e n e s s of a c o n f i n i n g l a y e r i n preventing the downward m i g r a t i o n of a plume, f o r i n s t a n c e , i t i s o f t e n n e c e s s a r y to i n s t a l l w e l l s to a d e p t h b e n e a t h the c o n f i n i n g l a y e r i n o r d e r t o c o l l e c t water samples and measure water l e v e l s d u r i n g a pumping t e s t . I f the c o n f i n i n g l a y e r i s r e l a t i v e l y impermeable o r i f the h y d r a u l i c g r a d i e n t i s upward, m o n i t o r i n g of deeper a q u i f e r s may not be r e q u i r e d . Where s h a l l o w and deep w e l l s are needed, t h e y commonly a r e i n s t a l l e d a t the same l o c a t i o n and are r e f e r r e d to as p a i r e d w e l l s or c l u s t e r w e l l s . The c h o i c e of w e l l l o c a t i o n s can be i n f l u e n c e d by the t y p e s o f wastes o r c o n t a m i n a n t s and t h e i r p r o p e n s i t y t o m i g r a t e from the waste sources. Heavy o r g a n i c s , f o r i n s t a n c e , are l i k e l y to migrate to d e e p e r a q u i f e r s zones, where t h e i r movement i s not t o t a l l y dependent on ground-water f l o w d i r e c t i o n s but may be p a r t l y c o n t r o l l e d by the slope o f the top o f the uppermost c o n f i n i n g d e p o s i t s . Thus, i n

Garner et al.; Evaluation of Pesticides in Ground Water ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on March 11, 2018 | https://pubs.acs.org Publication Date: July 17, 1986 | doi: 10.1021/bk-1986-0315.ch009

9.

M O O N A N D HENRY

Hydrogeologic Investigations of Pesticide Spills

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d e s i g n i n g a m o n i t o r - w e l l network t o d e t e c t h e a v i e r - t h a n - w a t e r s o l v e n t plumes, c o n s i d e r a t i o n must be g i v e n t o i n s t a l l i n g w e l l s a t t h e base o f t h e uppermost a q u i f e r t o d e t e c t g r a v i t y f l o w o f p u r e p r o d u c t away from the s i t e . S h a l l o w m o n i t o r w e l l s a l s o must be i n s t a l l e d t o d e t e c t d i s s o l v e d components moving i n t h e d i r e c t i o n o f ground-water flow. O f t e n , t h e p r e l i m i n a r y c h a r a c t e r i z a t i o n w e l l s c a n be i n c o r p o r a t e d i n t h e permanent m o n i t o r - w e l l network. However, i n c a s e s where the i n i t i a l presumed ground-water f l o w d i r e c t i o n t u r n s o u t t o be i n c o r r e c t , due t o t h e i n f l u e n c e s o f n e a r b y pumping w e l l s , tidal fluctuations, ground-water mounds, o r o t h e r h y d r a u l i c phenomena, a d d i t i o n a l r e g u l a t o r y w e l l s may be r e q u i r e d . Dimensions. The d i m e n s i o n s o f a w e l l r e f e r t o i t s d e p t h , c a s e d i n t e r v a l , l e n g t h o f the screened o r open-hole s a m p l i n g interval, s c r e e n s l o t s i z e , and b o r e h o l e , s c r e e n , and c a s i n g d i a m e t e r s . The l e n g t h o f t h e sampling i n t e r v a l depends on t h e purpose o f t h e w e l l , the site hydrogeology, and t h e ground-water quality. A very p r e l i m i n a r y i n v e s t i g a t i o n t o d e t e r m i n e w h i c h , i f any, contaminants h a v e m i g r a t e d from a s i t e may i n v o l v e t h e i n s t a l l a t i o n o f o n l y a few s h a l l o w w e l l s w i t h a 3 t o 10 f t s c r e e n e d i n t e r v a l a t t h e water t a b l e . Once c o n t a m i n a n t s a r e i d e n t i f i e d , deeper w e l l s may be i n s t a l l e d t o d e t e r m i n e how t h o s e c o n t a m i n a n t s may have m i g r a t e d v e r t i c a l l y . In d e t e r m i n i n g t h e l e n g t h o f t h e s a m p l i n g i n t e r v a l f o r t h e deeper h o l e s , a balance should be sought between s a m p l i n g a s m a l l i n t e r v a l t o b e t t e r d e f i n e t h e contaminant plume and s a m p l i n g a l a r g e r i n t e r v a l t o a v o i d m i s s i n g t h e plume. I f pumping t e s t s a r e t o be p e r f o r m e d , w e l l s i n t h e same a q u i f e r s h o u l d be s c r e e n e d o r o p e n e d t o t h e same i n t e r v a l s ; f u l l y penetrating wells are generally preferred. S l o t s i z e s o f t h e s c r e e n s a r e chosen t o maximize w e l l y i e l d so that r e l i a b l e water samples and w a t e r - l e v e l drawdown d a t a c a n be c o l l e c t e d d u r i n g s p e c i f i c - c a p a c i t y and o t h e r f i e l d t e s t s . To accompl i s h t h i s , s i e v e a n a l y s e s c a n be performed on s p l i t - s p o o n samples from t h e i n t e r v a l t o be m o n i t o r e d . A g r a i n - s i z e d i s t r i b u t i o n curve c a n be f i e l d p l o t t e d and a n a l y z e d t o e s t a b l i s h t h e s c r e e n s l o t s i z e and t h e s i z e o f t h e g r a v e l pack. F o r w e l l s i n s t a l l e d i n competent b e d r o c k , i t may be w i s e s t n o t t o i n s t a l l a s c r e e n b u t t o l e a v e t h e h o l e open f o r maximum y i e l d . In t h e s e c a s e s , a s u r f a c e c a s i n g i s i n s t a l l e d t o p r e v e n t t h e c o l l a p s e o f t h e u n c o n s o l i d a t e d sediments and p o s s i b l e downward m i g r a t i o n o f c o n t a m i n a n t s . The d i a m e t e r o f a w e l l i s d i c t a t e d by i t s proposed u s e s , i t s d e p t h , and t h e d e p t h t o w a t e r . Wells i n s t a l l e d f o r water-level measurements o n l y a r e commonly o n l y 1-1/4 t o 2 i n c h e s i n d i a m e t e r . W e l l s t o be sampled c a n a l s o be t h i s s m a l l , b u t c o n s i d e r a t i o n s h o u l d be g i v e n t o t h e d e p t h o f t h e w e l l and t h e d e p t h t o water. Centrif u g a l pumps a n d p e r i s t a l t i c pumps c a n be u s e d f o r s a m p l i n g i n small-diameter w e l l s , i f t h e d e p t h t o water i s l e s s t h a n 25 f e e t ( i n c l u d i n g drawdown caused by t h e pumping); o t h e r w i s e , bailing i s required. Because b a i l i n g i s l e s s e f f i c i e n t t h a n pumping, i t i s often preferable to i n s t a l l a larger-diameter w e l l ; a submersible pump t h e n c a n be u s e d f o r s a m p l i n g . I f automatic water-level r e c o r d i n g i n s t r u m e n t s a r e t o be i n s t a l l e d o r i f g e o p h y s i c a l l o g g i n g i s t o be performed on t h e w e l l s , i t i s g e n e r a l l y a d v i s a b l e t o i n s t a l l 4-inch-diameter or l a r g e r diameter w e l l s . The d i a m e t e r o f t h e b o r e h o l e s h o u l d be s u f f i c i e n t t o i n s t a l l t h e c a s i n g and/or s c r e e n and a

Garner et al.; Evaluation of Pesticides in Ground Water ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

164

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

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minimum 3 - i n c h - t h i c k g r a v e l pack. The g r o u t e n v e l o p e a l s o s h o u l d be a t l e a s t 3 i n c h e s t h i c k t o i n s u r e t h a t i t c o m p l e t e l y surrounds the well. Materials. Polyvinyl chloride (PVC), black carbon steel, and s t a i n l e s s s t e e l a r e commonly used m a t e r i a l s f o r c a s i n g s and s c r e e n s . PVC and b l a c k c a r b o n s t e e l a r e l e s s e x p e n s i v e , but a r e sometimes not c o m p a t i b l e w i t h contaminants found i n the ground water. Although g e n e r a l l y immune t o c h e m i c a l a t t a c k by most n a t u r a l l y o c c u r r i n g compounds, PVC may adsorb o r l e a c h o r g a n i c compounds (2^ _3, 4_) ; t h u s , PVC must be used w i t h c a r e i n s i t u a t i o n s where t h e r e i s a p o s s i b i l i t y of o r g a n i c c o n t a m i n a t i o n . Where PVC i s deemed a p p r o p r i a t e , g e n e r a l l y S c h e d u l e 40 s h o u l d be used f o r w e l l s l e s s t h a n 200 f e e t deep and S c h e d u l e 80 f o r deeper w e l l s . Cement and o t h e r a d h e s i v e s s h o u l d be a v o i d e d ; j o i n t s s h o u l d be t h r e a d e d and c o u p l e d o r f l u s h j o i n t e d . B e c a u s e g a l v a n i z e d s t e e l i s not c o r r o s i o n - r e s i s t a n t , i t s h o u l d n o t be u s e d i n plumes of an a c i d i c n a t u r e , o r i n water w i t h h i g h e l e c t r i c a l c o n d u c t i v i t y due t o c h l o r i d e s or s u l f a t e s . Stainless s t e e l i s much more r e s i s t a n t t o c o r r o s i o n and can o f t e n be used i n p l a c e o f g a l v a n i z e d s t e e l , but i s s e v e r a l times more e x p e n s i v e . For t h i s r e a s o n , w e l l s can be c a s e d w i t h a cheaper g a l v a n i z e d s t e e l above the water t a b l e and w i t h more e x p e n s i v e s t a i n l e s s s t e e l c a s i n g o r s c r e e n below the water t a b l e . The g r a d i n g o f a g r a v e l pack i n a w e l l s h o u l d be based on a s i e v e a n a l y s i s o f the f i n e s t a q u i f e r m a t e r i a l s o f the s c r e e n e d zone. The s c r e e n s l o t opening s h o u l d r e t a i n 90 p e r c e n t o r more o f the g r a v e l pack m a t e r i a l . The g r a v e l pack m a t e r i a l s h o u l d be c l e a n , w i t h well-rounded grains that are smooth and uniform. These c h a r a c t e r i s t i c s i n c r e a s e the p e r m e a b i l i t y and p o r o s i t y o f the pack material. Drilling

and W e l l

Installation

Techniques

S e v e r a l methods a r e a v a i l a b l e f o r the d r i l l i n g and i n s t a l l a t i o n of monitor w e l l s . The advantages and d i s a d v a n t a g e s r e l a t i n g t o ease of c o n s t r u c t i o n , c h a r a c t e r o f f o r m a t i o n s p e n e t r a t e d , w e l l d i a m e t e r and d e p t h , r i s k s o f c o n t a m i n a t i o n , and i n t e n d e d use o f the w e l l have been r e p o r t e d by s e v e r a l i n v e s t i g a t o r s Ç 5 , _6_> _ 7 ) . A l l f i e l d personnel should be thoroughly familiar with w e l l s p e c i f i c a t i o n s , quality a s s u r a n c e / q u a l i t y c o n t r o l p r o c e d u r e s , and s a f e t y p l a n s and r e q u i r e ments p r i o r t o i n s t a l l a t i o n o f m o n i t o r w e l l s . Drilling. Common d r i l l r i g s a v a i l a b l e f o r m o n i t o r - w e l l i n s t a l l a t i o n i n c l u d e c a b l e t o o l , a i r r o t a r y , mud rotary, reverse rotary, and h o l l o w - s t e m auger. The c a b l e t o o l r i g r e p e a t e d l y l i f t s and drops a d r i l l b i t , d r i l l stem, d r i l l i n g j a r s , and rope s o c k e t . The d r i l l b i t c r u s h e s h a r d r o c k o r l o o s e n s u n c o n s o l i d a t e d m a t e r i a l and mixes the l o o s e n e d p a r t i c l e s w i t h water t o form a s l u r r y o r s l u d g e . The s l u d g e i s removed a t i n t e r v a l s by a sand pump or a b a i l e r . A mud r o t a r y r i g c u t s a b o r e h o l e by r o t a t i n g a b i t i n t o the f o r m a t i o n m a t e r i a l s and removing the c u t t i n g s by c o n t i n u o u s c i r c u l a t i o n of a d r i l l i n g f l u i d . In a c o n v e n t i o n a l r o t a r y system, mud i s pumped down t h r o u g h the d r i l l p i p e and out t h r o u g h n o z z l e s i n the bit. The mud f l o w s upward i n the a n n u l a r space around the d r i l l p i p e to the s u r f a c e , where i t i s c h a n n e l e d i n t o a s e t t l i n g p i t and a

Garner et al.; Evaluation of Pesticides in Ground Water ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

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9.

MOON A N D HENRY

Hydrogeologic Investigations of Pesticide Spills

165

storage b a s i n . Although the w a l l of the borehole i s e f f e c t i v e l y s e a l e d w i t h t h e mud, l a r g e q u a n t i t i e s o f f l u i d c a n be l o s t t o t h e formation p r i o r to s e a l i n g . In reverse r o t a r y , the d r i l l i n g f l u i d i s water which f l o w s down t h e a n n u l a r space around t h e d r i l l rods and up i n s i d e t h e d r i l l rods t o t h e s u r f a c e . To p r e v e n t c a v i n g , t h e f l u i d l e v e l must always be kept a t ground l e v e l . Hollow-stem auger rigs a r e commonly used for drilling i n u n c o n s o l i d a t e d m a t e r i a l w i t h enough c l a y so t h a t t h e b o r e h o l e w i l l stand without caving. An auger stem i s t u r n e d and pushed as t h e auger f l i g h t s c a r r y m a t e r i a l t o the surface. A i r r o t a r y d r i l l r i g s a r e used f o r c o n s o l i d a t e d m a t e r i a l s . A i r i s c i r c u l a t e d through t h e d r i l l p i p e , o u t through p o r t s i n t h e d r i l l b i t , and upward i n t h e a n n u l a r space around t h e d r i l l p i p e . T a b l e I d e s c r i b e s t h e r e l a t i v e advantages and d i s a d v a n t a g e s o f different d r i l l i n g rigs. F o r i n s t a n c e , a h o l l o w - s t e m auger i s v e r y e c o n o m i c a l f o r d r i l l i n g i n u n c o n s o l i d a t e d m a t e r i a l s and p r o v i d e s good s o i l samples, p a r t i c u l a r l y above t h e water t a b l e . Mud r o t a r y i s u s e f u l f o r d r i l l i n g i n r u n n i n g sands and s i l t s , i s m o d e r a t e l y e x p e n s i v e , b u t p r o v i d e s poor s o i l samples. A i r r o t a r y i s expensive and p r o v i d e s poor s o i l and r o c k samples, b u t i s v e r y r a p i d ; r o c k fragments c a n g e n e r a l l y be i d e n t i f i e d , b u t o t h e r c h a r a c t e r i s t i c s such as f r a c t u r i n g cannot. S m a l l zones o f c o n t a m i n a t i o n c a n be m i s s e d . C l e a r l y t h e type o f r i g c a n be chosen o n l y a f t e r c a r e f u l c o n s i d e r a ­ t i o n o f t h e f o r m a t i o n s t o be d r i l l e d , time and budget c o n s t r a i n t s , and sampling r e q u i r e m e n t s . W e l l I n s t a l l a t i o n and Development. Once b o r e h o l e s a r e completed, w e l l s s h o u l d be i n s t a l l e d a c c o r d i n g t o d e t a i l e d w e l l s p e c i f i c a t i o n s . The f o l l o w i n g i s a s e t o f good p r a c t i c e s a p p l i c a b l e t o most w e l l installations. ο ο ο

ο

ο ο

ο

ο ο

The g r a v e l pack s h o u l d be i n s t a l l e d by t h e t r e m i e method t o a s s u r e p r o p e r placement, A f i n e sand pack s h o u l d be i n s t a l l e d above t h e g r a v e l pack t o p r e v e n t m i g r a t i o n of the o v e r l y i n g cement i n t o the g r a v e l pack, I f s u r f a c e c a s i n g i s i n s t a l l e d f o r a bedrock w e l l , g r o u t s h o u l d be emplaced by t h e p r e s s u r e t r e m i e method t o i n s u r e a complete s e a l around t h e w e l l . Grout s h o u l d be a l l o w e d t o s e t f o r a t l e a s t 24 h o u r s . A m e t h o d s u c h a s t h e plumb bob m e t h o d s h o u l d be u s e d t o determine i f t h e c a s i n g a n d b o r e h o l e a r e plumb a n d t r u e . C e n t r a l i z e r s s h o u l d be a t t a c h e d t o w e l l s as n e c e s s a r y , A l l f l u i d and mud produced by t h e d r i l l i n g o p e r a t i o n s s h o u l d be r e t a i n e d i n p o r t a b l e mud p i t s f o r p r o p e r d i s p o s a l , A l l equipment s h o u l d be c l e a n e d between each w e l l i n s t a l l a t i o n to p r e v e n t c r o s s - c o n t a m i n a t i o n . S p e c i f i c c l e a n i n g procedures s h o u l d be o u t l i n e d i n t h e w e l l s p e c i f i c a t i o n s , To the extent possible, drilling of the borehole and i n s t a l l a t i o n o f t h e w e l l s h o u l d be a c c o m p l i s h e d i n a c o n t i n u o u s manner. T h i s w i l l m i n i m i z e t h e r i s k o f c r o s s - c o n t a m i n a t i o n , A w a t e r - l e v e l measurement s h o u l d be t a k e n upon c o m p l e t i o n o f well installation, W e l l s s h o u l d be d e v e l o p e d u n t i l t h e pumped o r b a i l e d water i s c l e a r o r u n t i l s u c c e s s i v e pH and s p e c i f i c conductance v a l u e s remain s t a b l e .

Garner et al.; Evaluation of Pesticides in Ground Water ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

Garner et al.; Evaluation of Pesticides in Ground Water ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

Size

Fluids

Drilling

Rate

Quality of Soil/Rock Samples

I n s t a l l i n g Grout o r G r a v e l Pack

Drilling

Hole

Slow

Excellent

Easy

Water

Unlimited

Rapid

Poor

Easy

None o r s m a l l amounts o f water

Unlimited

Slow

F a i r t o Poor

Easy

Mud

Unlimited

100 f t

Rapid

Good Above Water T a b l e Good

Moderate

Difficult i f a n n u l a r space i s limited

None

Up t o 1 2 - i n c h

About

Formations

Unconsolida­ ted

Low

AugerHollow-Stem

Sometimes Difficult

Water

Unlimited

Unlimited

Unlimited

Unlimited

Unlimited

Depth

Restrictions

Unconsol­ idated Formations

Unlimited

Unlimited

Moderate

Reverse Rotary

Most Materials

Moderate t o H i g h

Mud R o t a r y (Conventional)

Drillable Formations

Rotary High

Air

Methods

Moderate

Tool

Comparisons o f D r i l l i n g

Cost

Cable

Table I.

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% C m το

Ο

70

ο

m

5

H η

m

*V

ΤΙ

ο

δ ζ

r c

$

ON ON

9.

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ο

MOON A N D HENRY

Hydrogeologic Investigations of Pesticide Spills

E l e v a t i o n s o f measuring p o i n t s on w e l l s s h o u l d a q u a l i f i e d s u r v e y o r t o t h e n e a r e s t 0.01 f o o t .

be determined

167

by

Recordkeeping. Keeping complete, accurate drilling logs is a c r i t i c a l a s p e c t o f w e l l d r i l l i n g and i n s t a l l a t i o n t e c h n i q u e s . Table I I l i s t s items t h a t may be i n c l u d e d i n a w e l l l o g , depending on t h e type o f w e l l and t h e s p e c i f i c a t i o n s f o r s a m p l i n g . This i s a d e t a i l e d l i s t and i n many c a s e s , i t may n o t be n e c e s s a r y t o r e c o r d a l l t h e items l i s t e d . G e n e r a l l y , as much d e t a i l as t h e d r i l l i n g technique c a n p r o v i d e s h o u l d be r e c o r d e d by t h e f i e l d i n s p e c t o r . Some items t h a t may n o t seem c r i t i c a l a t t h e t i m e o f d r i l l i n g may p r o v i d e i n s i g h t t o unanswered q u e s t i o n s o r a m b i g u i t i e s t h a t may a r i s e d u r i n g a n a l y s i s of the data. Items such as l e n g t h o f c a s i n g and number o f c a s i n g l e n g t h s s h o u l d be checked by the f i e l d i n s p e c t o r . In some c a s e s , samples may be numbered by a random numbering system; these v a l u e s s h o u l d be r e c o r d e d i n f i e l d n o t e s . A record of f i e l d or t r i p b l a n k s s h o u l d a l s o be k e p t . Any c h e c k i n g i n t h e f i e l d o f w a t e r q u a l i t y p a r a m e t e r s , i . e . , pH and c o n d u c t i v i t y , s h o u l d be r e c o r d e d . In g e n e r a l , t h e f i e l d i n s p e c t o r s h o u l d u n d e r s t a n d t h e c r i t i c a l n a t u r e of h i s o r h e r t a s k , and s p e c i f i c g u i d e l i n e s f o r r e c o r d i n g f i e l d n o t e s s h o u l d be e s t a b l i s h e d p r i o r t o t h e d r i l l i n g program.

Table

ο ο ο ο ο

ο

ο

II.

I n f o r m a t i o n t o I n c l u d e on D r i l l i n g

Logs

Name o f c o n t r a c t o r , d r i l l e r , i n s p e c t o r L o c a t i o n o f s i t e and s p e c i f i c b o r e h o l e l o c a t i o n B o r e h o l e number Date - s t a r t / f i n i s h Soil Characteristics depth g r a i n s i z e and t e x t u r e angularity moisture content D r i l l i n g operations rate loss of c i r c u l a t i o n use o f water/mud c o r e diameter c o l o r o f c i r c u l a t i n g water core r e c o v e r y d i a m e t e r o f auger o r c o r e type c o r e b a r r e l s i z e o f d r i v e hammer and f r e e f a l l d i s t a n c e t o d r i v e hammer blows p e r f o o t t o d r i v e sample f o r c e t o push t h i n w a l l samples Well m a t e r i a l s / c h a r a c t e r i s t i c s casing - type, diameter, i n t e r v a l screen - type, diameter, i n t e r v a l , s l o t s i z e grout - type, i n t e r v a l t o t a l d r i l l e d depth open h o l e i n t e r v a l sand pack - t y p e , i n t e r v a l p r o t e c t i v e c a s i n g - t y p e , diameter Continued

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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 I — C o n t i n u e d

Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on March 11, 2018 | https://pubs.acs.org Publication Date: July 17, 1986 | doi: 10.1021/bk-1986-0315.ch009

ο ο ο

Samples - number, d e p t h , t y p e , s i z e S t a b i l i z e d water l e v e l Rock C h a r a c t e r i s t i c s d e p t h u n i t / f o r m a t i o n and member names color hardness fracturing coatings or f i l l i n g s (or lack o f ) i n j o i n t s or seams angle of bedding, s c h i s t o s i t y , o r other p l a n a r features luster thickness of bedding planes degree o f w e a t h e r i n g decomposition strength weathering r o c k a l t e r a t i o n o t h e r than by w e a t h e r i n g induration rock q u a l i t y c a v i t i e s or voids

Literature Cited

1. 2. 3. 4. 5. 6. 7.

"Standard Operating Safety Guides." Office of Emergency and Remedial Response, Hazardous Response Support Division, Environ­ mental Response Team, November, 1984. Miller, G.D. Proc. 2nd Natl. Sym. Aquifer Restoration and Ground-Water Monitoring, 1982, p. 236. Houghton, R.L.; Berger, M.E. Proc. 3rd Natl. Sym. Aquifer Restoration and Ground-Water Monitoring, 1983; p. 203. Barcelona, M.J.; Gibb, J.P.; Millar, R.A.; "A Guide to the Selection of Materials for Monitor Well Construction and Ground Water Sampling;" Illinois Water Survey; Champaign, Illinois; 1983; p. 39. Briggs, G.F.; Fieldler, A.G., Eds.; In "Ground Water and Wells;" Johnson Division, UOP, Inc.; St. Paul, Minnesota, 1980 edition; p. 209. Richter, H.R.; Collentine, M.G; Proc. 3rd Natl. Sym. Aquifer Restoration and Ground-Water Monitoring, 1983, p. 194. Minning, R.; Proc. 3rd Natl. Sym. Aquifer Restoration and Ground-Water Monitoring, 1983, p. 194.

RECEIVED April 7, 1986

Garner et al.; Evaluation of Pesticides in Ground Water ACS Symposium Series; American Chemical Society: Washington, DC, 1986.