Groundwater Residue Sampling Design - ACS Publications

Chapter 1

Groundwater Residue Sampling Overview of the Approach Taken by Government Agencies 1

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Ralph G. Nash , Charles S. Helling , Stephen E. Ragone , and Anne R. Leslie 4

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EPL Bio-Analytical Services, Inc., Box 1708, Decatur, IL 62525 Agricultural Research Service, U.S. Department of Agriculture, Beltsville, MD 20705 Office of the Assistant Director for Research, U.S. Geological Survey, 104 National Center, Reston, VA 22092 Office of Pesticide Programs, U.S. Environmental Protection Agency, Mail Stop H7506C, Washington, DC 20460

Downloaded by 80.82.77.83 on December 25, 2017 | http://pubs.acs.org Publication Date: June 20, 1991 | doi: 10.1021/bk-1991-0465.ch001

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Recognition that nitrogen applied as f e r t i l i z e r may reach groundwater has been known for two to three decades. It is only in the past decade that evidence has become available suggesting pesticides may leach to groundwater, also. The evidence, though mostly anecdotal, has raised the nation's awareness of the potential for contamination of our water resources, the need to ascertain the extent of the problem, and ways to prevent i t . Because of the complexity of natural systems, an interdisciplinary study approach i s needed to provide information for cost-effective solutions to the problem. The Problem Water resources are an aggregation of numerous dynamic, individual and interactive ground- and surface-water systems. These multiphase and multicomponent systems have their own hydrogeologic and m i n é r a l o g i e characteristics and are found in a variety of climatic settings. Therefore, the time i t takes contaminants to reach and move throughout the system can vary from days to centuries. The pathways through which contaminants are transported also vary and, depending on conditions, may move between groundwater and surface water or from one aquifer to another. Contaminants may also transfer between the aqueous phase and the s o l i d and gaseous phases. These factors may also affect the contaminant's ultimate fate by determining the reaction types or extent that can cause alteration (Ragone, S.E. Water-Quality Contamination: A Systems Approach Towards Its Protection and Remediation. In Proc. of the Conf. The Environment: Global Problem - Local Solutions Hofstra Univ. Long Island, New York, June 7-8, 1990). 0097-6156/91/0465-0001$06.00A) © 1991 American Chemical Society

Nash and Leslie; Groundwater Residue Sampling Design ACS Symposium Series; American Chemical Society: Washington, DC, 1991.

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GROUNDWATER RESIDUE SAMPLING DESIGN

Scope T h i s book emphasizes approaches needed t o study the e f f e c t of agrochemicals on groundwater. Most of t h e p r i n c i p l e s t h a t apply t o agrochemicals apply t o other anthropogenic substances. These are s p e c i f i c a l l y r e l a t e d t o two main sources of p o t e n t i a l agrochemical contamination of groundwater: n i t r o g e n and p e s t i c i d e s . Nitrogen. Nitrogen, an e s s e n t i a l element f o r p l a n t growth, i s c y c l e d and r e c y c l e d throughout the environment i n a s e r i e s of t r a n s p o r t and t r a n s f o r m a t i o n steps known as t h e n i t r o g e n c y c l e . Atmospheric N gas i s i n c o r p o r a t e d i n t o p l a n t t i s s u e and s o i l through symbiotic n i t r o g e n f i x a t i o n processes. Other inputs occur through p l a n t residues, animal wastes, commercial fertilizer, atmospheric d e p o s i t i o n , and l i g h t e n i n g . Organic forms (plant r e s i d u e s and animal wastes) of n i t r o g e n undergo mineralization, i . e . , transformation t o ammonium-, n i t r i t e - , and n i t r a t e - N , the three s p e c i e s a s s i m i l a t e d by p l a n t s and s o i l microorganisms. The n i t r o g e n source ( n a t u r a l or manmade), then, i s immaterial. Nitrogen l o s s e s from s o i l , i n a d d i t i o n t o p l a n t uptake, can i n c l u d e d e n i t r i f i c a t i o n (conversion t o gaseous n i t r o g e n oxides and N ) and ammonia v o l a t i l i z a t i o n . Groundwater contamination can r e s u l t when an excess of n i t r o g e n , p r i m a r i l y n i t r a t e N, i s present and when p e r c o l a t i o n occurs.


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Commercial n i t r o g e n inputs t o the United States cropland during 1985-87 averaged 9.6 m i l l i o n m e t r i c tons Ν per year. By comparison, inputs from other sources (manure, crop r e s i d u e , r a i n f a l l , b i o l o g i c a l f i x a t i o n ) were estimated as 8.3 t o 9.8 m i l l i o n metric tons ( 2 ) . S i g n i f i c a n t i n f l u x of n i t r a t e - N t o groundwater may d e r i v e from g e o l o g i c a l d e p o s i t s (2) or from f o r e s t s , pastures, and human wastes ( 3 ) . Nitrogen from a g r i c u l t u r a l use may be a p o t e n t i a l problem where Ν f e r t i l i z e r consumption i s g r e a t e s t . On t h a t b a s i s the Corn B e l t s t a t e s of Iowa, I l l i n o i s , and Indiana are p a r t i c u l a r l y l a r g e consumers, as w e l l as Nebraska, Michigan, and Kansas (4). On a state-wide p e r acre b a s i s , Ν use i n Iowa and Indiana g r e a t l y exceeds t h a t i n l a r g e s t a t e s such as C a l i f o r n i a and Texas. State use i s c o n s i s t e n t with cropping p a t t e r n s : among the four major cash crops i n the United S t a t e s , Ν use i s dominated by corn (4.6 m i l l i o n metric tons) and wheat (1.6 m i l l i o n m e t r i c tons) , with c o t t o n and soybean use of Ν f a r l e s s (5). Except f o r cotton, n i t r o g e n use has g r e a t l y i n c r e a s e d when comparing 1965 and 1985 production years. T i l e d r a i n s provide an e a r l y warning o f p o s s i b l e groundwater n i t r a t e - N and p e s t i c i d e contamination problems


1. NASH ET AL

Overview of Groundwater Residue Sampling

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from a g r i c u l t u r a l use. At the l e a s t , these r e s i d u e s w i l l be t r a n s p o r t e d r e l a t i v e l y q u i c k l y i n t o s u r f a c e waters. The four s t a t e s with the most area under t i l e drainage are I l l i n o i s (ca. 3.1 m i l l i o n ha), followed by Iowa, Indiana, and Ohio, a l l i n the Corn B e l t (6). Nelson (7) evaluated Ν found i n t i l e drainage water from the Eastern Corn B e l t and concluded t h a t , on average, 7 kg ha y d e r i v e d from n a t u r a l background and 20 kg ha" y' , from f e r t i l i z e r s . In a d d i t i o n t o being a source of contamination, t h i s c l e a r l y represents a s i g n i f i c a n t economic l o s s .


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The n a t i o n a l p i c t u r e of Ν i n groundwater was summarized i n 1985 by a major survey—124,000 w e l l s over a 25 y p e r i o d (8). Expressed as n i t r a t e - N , the r e s u l t s showed t h a t 80.4% o f the w e l l s contained 10 ppm. The >10 ppm represents the h e a l t h advisory l e v e l (HAL) f o r n i t r a t e - N , r e f l e c t i n g concern about development of methemoglobinemia i n i n f a n t s d r i n k i n g t h i s water. There have been a number of reviews concerning n i t r a t e - N and groundwater q u a l i t y , e s p e c i a l l y as r e l a t e d t o a g r i c u l t u r a l p r a c t i c e s , and t h a t by H a l l b e r g (9) i s among the most recent. Pesticides. P e s t i c i d e s i n ground water have become a concern p r i m a r i l y i n the past decade. There a r e two p o s s i b l e reasons f o r t h i s , one s c i e n t i f i c and one analytical. Much e a r l y research f a i l e d t o demonstrate t h a t p e s t i c i d e l e a c h i n g t o groundwater was o c c u r r i n g , though this was partially because of limited investigations. F i r s t i t was g e n e r a l l y b e l i e v e d t h a t p e s t i c i d e s would not leach because most degrade t o innocuous compounds [within hours t o ( f o r some of the formerly used c h l o r i n a t e d hydrocarbon p e s t i c i d e s ) years] and they a l s o tend t o adsorb t i g h t l y t o s o i l . Second, our a n a l y t i c a l c a p a b i l i t y has increased t o the p o i n t t h a t p a r t s - p e r - b i l l i o n (ppb) d e t e c t i o n l i m i t s i s o f t e n r o u t i n e and p a r t s - p e r - t r i l l i o n (ppt) l e v e l s have been reported (20-12). I t i s now g e n e r a l l y accepted t h a t some p e s t i c i d e s w i l l leach t o groundwater: what i s more s u r p r i s i n g i s how r a p i d l y t h i s may occur. Leaching depends upon the chemical, soil, site, weather, and management. Agrochemicals whose adsorption i s low, e s p e c i a l l y i f coupled with an i n h e r e n t l y slow tendency t o degrade i n s o i l , are more a t r i s k t o excessive l e a c h i n g . Conversely, s o i l s t h a t are coarse t e x t u r e d and with low organic matter content u s u a l l y i n c r e a s e the v u l n e r a b i l i t y of u n d e r l y i n g groundwater, a l l other t h i n g s being equal. Important s i t e f a c t o r s i n c l u d e shallow depth t o groundwater, the presence of s i n k h o l e s , o r improperly s e a l e d abandoned w e l l s . Weather may be the most dominant f a c t o r i n c e r t a i n cases (Table I) when high r a i n f a l l occurs s h o r t l y a f t e r a p p l i c a t i o n , producing high r u n o f f


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and f a s t , deep p e r c o l a t i o n i n macropores. Within the f i f t h category, management, the improper storage, use, and disposal of pesticides, including t h e i r containers, i n c r e a s e s t h e p r o b a b i l i t y of groundwater contamination. High a p p l i c a t i o n r a t e s a l s o i n c r e a s e the r i s k o f l e a c h i n g . On t h e p o s i t i v e s i d e , as mentioned e a r l i e r (Figure 1), recommended h e r b i c i d e r a t e s have tended t o d e c l i n e as newer, more a c t i v e and/or s e l e c t i v e compounds a r e developed. Table I i l l u s t r a t e s three cases of deep and/or very r a p i d agrochemical movement. Bromacil [5-bromo-6-methyl3-(1-methylpropyl)-2,4(1H,3H)-pyrimidinedione] leached t o 4.9 m w i t h i n 4 months i n a F l o r i d a sand (12). A l a c h l o r [ 2 - c h l o r o - N_- ( 2 , 6 - d i e t h y l p h e n y l ) - N_(methoxymethyl)acetamide], atrazine [6-chloro-N-ethylN'-(1-methylethyl)-1,3,5-triazine-2,4-diamine],cyanazine {2-[[4-chloro-6-(ethylamino-l,3,5-triazin-2-yl]amino]-2m e t h y l p r o p a n e n i t r i l e , and carbofuran (2,3-dihydro-2,2dimethyl-7-benzofuranyl methylcarbamate) were a l l detected i n shallow (ca. 0.6 t o 1.5 m) groundwater 6 d f o l l o w i n g p e s t i c i d e a p p l i c a t i o n t o a Maryland s i l t loam (13). In the l a t t e r case, l e a c h i n g was a t t r i b u t e d t o macropore flow i n the n o - t i l l p l o t s , because over 4 cm o f r a i n f a l l occurred beginning 12 h a f t e r a p p l i c a t i o n . In the t h i r d case, n i t r a t e and bromide ions were found i n t i l e drainage (1.1 m depth) beneath an Iowa loam w i t h i n 1 h a f t e r a p r e c i p i t a t i o n event; the authors (14) s t a t e d t h a t flow p r e d i c t i o n s based on the usual c o n v e c t i v e - d i s p e r s i o n flow equations would not have p r e d i c t e d such r a p i d movement, hence macropore flow was suspected. Table I.

Three Examples of Deep o r Fast P e s t i c i d e Leaching

Pesticide

State

Soil

Bromacil Florida sand A t r a z i n e Maryland s i l t l o a m II II Alachlor II II Cyanazine II Carbofuran " NO3-, Br" Iowa Loam

Time

Depth m

Reference

4 mon HAL of 10 ppm n i t r a t e - N . Among domestic w e l l s , 3 contained high p e s t i c i d e l e v e l s and 8, n i t r a t e - N . (23) An a d d i t i o n a l , recent review (24) has r e p o r t e d t h a t 39 p e s t i c i d e s have been detected i n groundwater from 34 U.S. s t a t e s or Canadian p r o v i n c e s . Besides nonpoint sources, these s t a t i s t i c s i n c l u d e some commercial p o i n t sources such as samples c o l l e c t e d near p e s t i c i d e supply and mixing sites. Study Approach Any study of ground water q u a l i t y must be cognizant of the regulatory aspects, primarily those of the U.S. Environmental P r o t e c t i o n Agency (USEPA). Two approaches have been d e s c r i b e d t o i n v e s t i g a t e groundwater q u a l i t y and i t s amelioration [The U.S. G e o l o g i c a l Survey, Water Resources D i v i s i o n (USGS/WRD) (Ragone, S.E. Water-Quality Contamination: A Systems Approach Towards I t s P r o t e c t i o n and Remediation. In Proc. of the Conf. The Environment: G l o b a l Problem - L o c a l S o l u t i o n s H o f s t r a Univ. Long I s l a n d , New York, June 7-8, 1990) and the U.S. Department of A g r i c u l t u r e , A g r i c u l t u r a l Research S e r v i c e (USDA/ARS) (1)]. Both provide a framework t o guide the a l l o c a t i o n of resources t o study a wide-ranging and complex problem. The i n d i v i d u a l researcher, or r e s e a r c h team t h a t a c t u a l l y conducts the groundwater research or monitoring, needs a d d i t i o n a l guidance over and above U.S. agency programs. Most of the chapters i n t h i s book were w r i t t e n by investigators that have conducted some aspect of groundwater q u a l i t y research, or a t a minimum have provided i n v e s t i g a t i v e t o o l s t h a t can be a p p l i e d t o best design and execute research on agrochemical movement/loss from the r o o t or vadose zones and groundwater. USEPA. Regulation i s a t o o l (by r e q u i r i n g c e r t a i n p r e r e g i s t r a t i o n information) t o minimize the p o t e n t i a l f o r agrochemicals t o reach groundwater. The USEPA-mandated laboratory and field studies needed for pesticide r e g i s t r a t i o n i n the United States, r e q u i r e information on the m o b i l i t y and p e r s i s t e n c e i n the environment. C e r t a i n p e s t i c i d e s may be r e s t r i c t e d based on v a r i o u s r i s k factors, e.g., those showing actual leaching to groundwater or movement deep i n t o the r o o t zone, those showing p o t e n t i a l t o leach (through evidence of high


1. NASH ET AL.

Overview of Groundwater Residue Sampling

mobility and persistence), t o x i c o l o g i c a l concern.

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USGS/WRD. A h i e r a r c h i a l approach, t h a t i n c l u d e s p o i n t , nonpoint, and c o n t i n e n t a l s t u d i e s has been d e s c r i b e d elsewhere (25). The approach f o r the t h r e e contamination type problems i s s i m i l a r i n t h a t i t e s t a b l i s h e s the hydrogeologic framework i n which the d i s t r i b u t i o n of contaminant mass i s i d e n t i f i e d . The approaches d i f f e r i n d e t a i l because of s c a l e . For p o i n t - s o u r c e s t u d i e s , the focus i s on the s c a l e of lithologie variability. Groundwater contamination from a p o i n t source may -have an o v e r a l l a r e a l dimension from s e v e r a l m t o >1 km t o as small as

Groundwater Residue Sampling Design - ACS Publications

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