Hydrogeologic Investigations of Pesticide Spills - ACS Symposium

9 Hydrogeologic Investigations of Pesticide Spills 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

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.

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

160

EVALUATION O F PESTICIDES IN GROUND WATER

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


9.

MOON A N D HENRY

Hydrogeologic Investigations of Pesticide Spills

161


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


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

162

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)


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



9.

M O O N A N D HENRY


163

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


164

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


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



9.

MOON A N D HENRY


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 .



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.


% C m το

Ο

70

ο

m

5

H η

m

*V

ΤΙ

ο

δ ζ

r c

$

ON ON

9.


ο

MOON A N D HENRY


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

on next

page


168

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


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


Hydrogeologic Investigations of Pesticide Spills - ACS Symposium

Recommend Documents