United States 

 Environmental Protection 

 Agency 

Occurrence Analysis for Potential Source Waters 

 for the Second Six-Year Review of 

National Primary Drinking Water Regulations 
Office of Water (4607M) 

EPA 815-B-09-004 

October 2009 

www.epa.gov/safewater 
EPA-OGWDW Occurrence Analysis for Potential Source Waters EPA 815-B-09-004 

for the Second Six-Year Review of NPDWRs 

Table of Contents 

Executive Summary...................................................................................................................ES-1 

1. Introduction.......................................................................................................................... 1-1 

2. Cost Savings......................................................................................................................... 2-1 

2.1 Magnitude of Possible MCL Increase.......................................................................... 2-1 

2.2 Relative Source Water Concentration.......................................................................... 2-2 

2.3 Co-Occurring Contaminants ........................................................................................ 2-2 

2.4 Treatment Technology................................................................................................. 2-3 

2.4.1 Ion Exchange (Barium)........................................................................................ 2-3 

2.4.2 Granular Activated Carbon (Alachlor, Diquat, 1,1-Dichloroethylene, Lindane, 

Picloram, 1,1,1-Trichloroethane).........................................................................................2-4 

2.4.3 Packed Tower Aeration (1,1-Dichloroethylene, 1,1,1-Trichloroethane)............. 2-4 

2.4.4 Oxidation (Glyphosate)........................................................................................ 2-4 

2.4.5 Lime Softening (Barium)..................................................................................... 2-4 

2.4.6 Reverse Osmosis and Electrodialysis (Barium)................................................... 2-5 

3. Contaminant Characteristics and Sources............................................................................3-1 

4. Contaminant Occurrence Data Sources ............................................................................... 4-1 

4.1 NAWQA ......................................................................................................................4-1 

4.2 STORET ...................................................................................................................... 4-4 

4.3 PDP ..............................................................................................................................4-4 

4.4 Contaminant Occurrence ............................................................................................. 4-4 

4.4.1 Alachlor................................................................................................................ 4-5 

4.4.2 Barium.................................................................................................................. 4-7 

4.4.3 1,1-Dichloroethylene ...........................................................................................4-8 

4.4.4 Diquat................................................................................................................... 4-9 

4.4.5 Glyphosate ......................................................................................................... 4-11 

4.4.6 Lindane .............................................................................................................. 4-12

4.4.7 Picloram ............................................................................................................. 4-14

4.4.8 1,1,1-Trichloroethane......................................................................................... 4-16 

5. Conclusions.......................................................................................................................... 5-1 

6. References............................................................................................................................ 6-1 

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EPA-OGWDW Occurrence Analysis for Potential Source Waters EPA 815-B-09-004 

for the Second Six-Year Review of NPDWRs 

Table of Exhibits 

Exhibit ES-1. Current MCLG/MCL Values and Possible MCLG Values ............................... ES-2 

Exhibit 1-1. Current MCLG/MCL Values and Possible MCLG Values.....................................1-2 

Exhibit 2-1. Magnitude of Possible Change ................................................................................2-1 

Exhibit 2-2. Summary of Treatment Technologies......................................................................2-3 

Exhibit 3-1. Potential Sources of the Contaminants ....................................................................3-1 

Exhibit 3-2. TRI On-site and Off-site Reported Disposal of or Otherwise Release of (in pounds) 

Alachlor for facilities in All Industries by State (2006) .............................................................. 3-2 

Exhibit 3-3. TRI State Total Reported Disposal of or Otherwise Released Pounds of Alachlor for 

facilities in All Industries (2006).................................................................................................3-3 

Exhibit 3-4. TRI On-site and Off-site Reported Disposal of or Otherwise Release of (in pounds) 

Barium for facilities in All Industries by State (2006) ................................................................3-4 

Exhibit 3-5. TRI State Total Reported Disposal of or Otherwise Released Pounds of Barium for 

facilities in All Industries (2006).................................................................................................3-5 

Exhibit 3-6. TRI On-site and Off-site Reported Disposal of or Otherwise Release of (in pounds) 

Barium Compounds for facilities in All Industries by State (2006) ............................................3-6 

Exhibit 3-7. TRI State Total Reported Disposal of or Otherwise Released Pounds of Barium

Compounds for facilities in All Industries (2006) ....................................................................... 3-8 

Exhibit 3-8. TRI On-site and Off-site Reported Disposal of or Otherwise Release of (in pounds) 

Lindane for facilities in All Industries by State (2006) ............................................................... 3-9 

Exhibit 3-9. TRI State Total Reported Disposal of or Otherwise Released Pounds of Lindane 

Compounds for facilities in All Industries (2006) ..................................................................... 3-10 

Exhibit 3-10. TRI On-site and Off-site Reported Disposal of or Otherwise Release of (in pounds) 

Picloram for facilities in All Industries by State (2006)............................................................3-11 

Exhibit 3-11. TRI State Total Reported Disposal of or Otherwise Released Pounds of Picloram

Compounds for facilities in All Industries (2006) ..................................................................... 3-12 

Exhibit 3-12. TRI On-site and Off-site Reported Disposal of or Otherwise Release of (in pounds) 

1,1,1-Trichloroethane for facilities in All Industries by State (2006)........................................3-13 

Exhibit 3-13. TRI State Total Reported Disposal of or Otherwise Released Pounds of 1,1,1-

Trichloroethane Compounds for facilities in All Industries (2006)...........................................3-14 

Exhibit 4-1. NAWQA Study Units .............................................................................................. 4-2 

Exhibit 4-2. CWS Dataset Summary by System Size.................................................................. 4-3 

Exhibit 4-3. CWS Summary by Water Source ............................................................................4-3 

Exhibit 4-4. Distance from NAWQA Sampling Stations to Nearest CWS Facility....................4-3 

Exhibit 4-5. Summary of Alachlor Occurrence Based on Maximum Sample Values for Locations 

in NAWQA ..................................................................................................................................4-5 

Exhibit 4-6. Summary of Alachlor Occurrence Based on Maximum Sample Values for Locations 

in STORET ..................................................................................................................................4-5 

Exhibit 4-7. NAWQA Occurrence Data for Alachlor Based on Maximum Sample Values....... 4-6 

Exhibit 4-8. Summary of Alachlor Occurrence for Raw Water Samples in USDA Agricultural 

Marketing Service Pesticide Data Program .................................................................................4-6 

Exhibit 4-9. Summary of Alachlor Occurrence for Finished Water Samples in USDA 

Agricultural Marketing Service Pesticide Data Program............................................................. 4-6 

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EPA-OGWDW Occurrence Analysis for Potential Source Waters EPA 815-B-09-004 

for the Second Six-Year Review of NPDWRs 

Exhibit 4-10. Summary of Barium Occurrence Based on Maximum Sample Values for Locations 

in NAWQA ..................................................................................................................................4-7 

Exhibit 4-11. Summary of Barium Occurrence Based on Maximum Sample Values for Locations 

in STORET ..................................................................................................................................4-7 

Exhibit 4-12. NAWQA Occurrence Data for Barium Based on Maximum Sample Values....... 4-8 

Exhibit 4-13. Summary of 1,1-Dichloroethylene Occurrence Based on Maximum Sample Values 

for Locations in NAWQA............................................................................................................4-8 

Exhibit 4-14. Summary of 1,1-Dichloroethylene Occurrence Based on Maximum Sample Values 

for Locations in STORET............................................................................................................4-9 

Exhibit 4-15. Plot of 1-1-Dichloroethylene NAWQA Occurrence Data..................................... 4-9 

Exhibit 4-16. Crop and Noncrop Diquat Application for California in 2005............................ 4-10 

Exhibit 4-17. Estimates of National Annual Pesticide Use for Crops.......................................4-10 

Exhibit 4-18. Summary of Glyphosate Occurrence Based on Maximum Sample Values for 

Locations in NAWQA ...............................................................................................................4-11 

Exhibit 4-19. Summary of Glyphosate Occurrence Based on Maximum Sample Values for 

Locations in STORET................................................................................................................4-11 

Exhibit 4-20. Plot of Glyphosate NAWQA Occurrence Data ................................................... 4-12 

Exhibit 4-21. Summary of Lindane Occurrence Based on Maximum Sample Values for 

Locations in NAWQA ...............................................................................................................4-12 

Exhibit 4-22. Summary of Lindane Occurrence Based on Maximum Sample Values for 

Locations in STORET................................................................................................................4-13 

Exhibit 4-23. Plot of Lindane NAWQA Occurrence Data ........................................................4-13 

Exhibit 4-24. Summary of Lindane Occurrence for Raw Water Samples in USDA Agricultural 

Marketing Service Pesticide Data Program ...............................................................................4-13 

Exhibit 4-25. Summary of Lindane Occurrence for Finished Water Samples in USDA 

Agricultural Marketing Service Pesticide Data Program........................................................... 4-14 

Exhibit 4-26. Summary of Picloram Occurrence Based on Maximum Sample Values for 

Locations in NAWQA ...............................................................................................................4-14 

Exhibit 4-27. Summary of Picloram Occurrence Based on Maximum Sample Values for 

Locations in STORET................................................................................................................4-14 

Exhibit 4-28. Plot of Picloram NAWQA Occurrence Data....................................................... 4-15 

Exhibit 4-29. Summary of Picloram Occurrence for Raw Water Samples in USDA Agricultural 

Marketing Service Pesticide Data Program ............................................................................... 4-15 

Exhibit 4-30. Summary of Picloram Occurrence for Finished Water Samples in USDA 

Agricultural Marketing Service Pesticide Data Program........................................................... 4-15 

Exhibit 4-31. Summary of 1,1,1-Trichloroethane Occurrence Based on Maximum Sample Values 

for Locations in NAWQA..........................................................................................................4-16 

Exhibit 4-32. Summary of 1,1,1-Trichloroethane Occurrence Based on Maximum Sample Values 

for Locations in STORET..........................................................................................................4-16 

Exhibit 4-33. Plot of 1,1,1-Trichloroethane NAWQA Occurrence Data .................................. 4-17 

Exhibit 5-1. Summary of Potential Cost Savings Factors – Occurrence .....................................5-2 

Exhibit 5-2. Summary of Potential Cost Savings Factors – Treatment .......................................5-2 

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EPA-OGWDW Occurrence Analysis for Potential Source Waters EPA 815-B-09-004 

for the Second Six-Year Review of NPDWRs 

Abbreviations and Acronyms 

ATSDR Agency for Toxic Substances & Disease Registry 

BAT Best Available Technology 

CF Coagulation/Filtration 

CWS Community Water System 

DBP Disinfection Byproduct 

EDR Electrodialysis 

EPA U.S. Environmental Protection Agency 

GAC Granular Activated Carbon 

GIS Geographical Information System 

GW ground water 

IX Ion Exchange 

LDC Legacy Data Center 

LS Lime Softening 

MCL Maximum Contaminant Level 

MCLG Maximum Contaminant Level Goal 

MSBA Multi-Stage Bubbling Aeration 

NAICS North American Industry Classification System

NAWQA National Water Quality Assessment 

NCFAP National Center for Food and Agricultural Policy 

NCOD National Contaminant Occurrence Database 

ND no data reported 

NPDWR National Primary Drinking Water Regulation 

OPP U.S. Environmental Protection Agency, Office of Pesticide Programs 

OX Oxidation 

PAC Powdered Activated Carbon 

PDP U.S. Department of Agriculture Pesticide Data Program 

POTW Publicly Owned Treatment Works 

POU Point-of-Use 

PTA Packed Tower Aeration 

PUR California Pesticide Use Reporting Database 

PWS Public Water System 

RCRA Resource Conservation and Recovery Act 

RO Reverse Osmosis 

SDWA Safe Drinking Water Act 

SDWIS/FED Federal Safe Drinking Water Information System 

SW surface water 

TRI Toxics Release Inventory 

UI Underground injection 

USDA U.S. Department of Agriculture 

USGS U.S. Geological Survey 

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EPA-OGWDW Occurrence Analysis for Potential Source Waters EPA 815-B-09-004 

for the Second Six-Year Review of NPDWRs 

Executive Summary 

The U.S. Environmental Protection Agency (EPA) has completed its second Six-Year Review 

(Six-Year Review 2) of national primary drinking water regulations (NPDWRs). The 1996 Safe 

Drinking Water Act (SDWA) Amendments require the U.S. Environmental Protection Agency 

(EPA or the Agency) to periodically review existing NPDWRs. Section 1412(b)(9) of SDWA 

reads: 

 ...[t]he Administrator shall, not less than every 6 years, review and revise, as 

appropriate, each primary drinking water regulation promulgated under this title. 

Any revision of a national primary drinking water regulation shall be promulgated 

in accordance with this section, except that each revision shall maintain, or 

provide for greater, protection of the health of persons. 

The primary goal of the Six-Year Review process is to identify NPDWRs for possible regulatory 

revision. Although the statute does not define when a revision is “appropriate,” as a general 

benchmark, EPA considered a possible revision to be “appropriate” if, at a minimum, it presents 

a meaningful opportunity to: 

• improve the level of public health protection, and/or 

• achieve cost savings while maintaining or improving the level of public health protection. 

For Six-Year Review 2, EPA obtained and evaluated new information that could affect a 

NPDWR, including information on health effects (USEPA, 2009e), analytical feasibility 

(USEPA, 2009b), treatment feasibility (USEPA, 2009f), and finished water occurrence (USEPA, 

2009a). EPA identified new health effects assessments that indicate the possibility to raise 

maximum contaminant level goal (MCLG) values for a number of regulated contaminants. 

Consequently, EPA reviewed data on contaminant occurrence in source water to determine if 

there is a meaningful opportunity to achieve cost savings while maintaining or improving the 

level of public health protection. This document describes this review. 

Exhibit ES-1 shows the current MCLG values for contaminants for which new health effects 

assessments indicate a possible MCLG that is higher than the MCLG in the NPDWR. The new 

health effects information results in a wide range of possible MCLG increases. The lowest 

relative increase is 2 times the current MCLG for both diquat and picloram. The highest relative 

increase is 150 times the current MCLG for the upper bound possible MCLG for lindane. 

The exhibit also shows the current maximum contaminant level (MCL) values, most of which 

equal the MCLG values. The possible MCLG value for each contaminant is higher than the 

corresponding current MCL value. Thus, a revision to the MCLG for a contaminant would affect 

its MCL, which could reduce costs for drinking water systems that control the contaminant to 

meet the MCL. 

ES-1 
EPA-OGWDW Occurrence Analysis for Potential Source Waters EPA 815-B-09-004 

for the Second Six-Year Review of NPDWRs 

Exhibit ES-1. Current MCLG/MCL Values and Possible MCLG Values 

Contaminant 

Current MCLG/MCL 

(mg/L) 

Possible MCLG 

(mg/L) 

Alachlor1 zero (MCLG) 

0.002 (MCL) 0.04 

Barium1 2 6 

1,1-Dichloroethylene2 0.007 0.35 

Diquat1 0.02 0.04 

Glyphosate1 0.7 14 

Lindane (gamma-Hexachlorocyclohexane) 2 0.0002 0.001 – 0.03 (depending on risk 

factors used for uncertainty) 

Picloram2 0.5 1 

1,1,1-Trichloroethane1 0.2 14 

1. New health effects information during Round 2 indicates a possibility to increase MCLG. 

2. New health effects information during Round 1 indicated a possibility to increase MCLG. EPA made a decision in Round 1 

not to revise the NPDWR because the revision was a low priority. 

The potential for and magnitude of cost savings related to MCL changes depend on four factors: 

• The magnitude of increase in the MCL 

• The concentration of the contaminant in the source water, relative to the current MCL 

and the possible MCLG 

• The presence of co-occurring contaminants treated with the same technology and their 

relative importance to the design and operation of the treatment technology 

• The specific treatment technology currently employed. 

EPA’s analysis of the potential for cost savings was constrained to readily available data. The 

data available to characterize contaminant occurrence was especially limited because there is no 

comprehensive dataset that characterizes source water quality for drinking water systems. Data 

from the National Water Quality Assessment (NAWQA) program conducted by the U.S. 

Geological Survey (USGS); EPA’s STORET (short for STOrage and RETrieval) data system, 

which are part of EPA’s Office of Ground Water and Drinking Water’s National Contaminant 

Occurrence Database (NCOD); and U.S. Department of Agriculture (USDA) Pesticide Data 

Program (PDP) water monitoring survey provide useful insights into potential contaminant 

occurrence in source water. However, these data are not based on random or representative 

sampling events and, therefore, cannot be used directly to derive quantitative estimates of 

national occurrence in drinking water sources. 

Nevertheless, the available data indicate relatively infrequent contaminant occurrence in 

potential source waters at the levels of interest. The NAWQA data, which provide the most 

extensive coverage of potential source waters, indicate that only alachlor is found in 

concentrations that exceed the possible MCLG. In particular, two contaminants – glyphosate and 

picloram – are not found at levels above either the current MCLG or the possible MCLG in any 

of the three datasets. Diquat, which is not included in any of these datasets, has the potential to 

occur infrequently in source water given its less frequent use compared to the other pesticides in 

the table (alachlor, glyphosate, lindane, and picloram) and its tendency to dissipate quickly from 

surface water and be immobile in soils. 

ES-2 
EPA-OGWDW Occurrence Analysis for Potential Source Waters EPA 815-B-09-004 

for the Second Six-Year Review of NPDWRs 

Without national estimates of contaminant occurrence in drinking water sources, EPA cannot 

determine how many systems currently treat for the contaminants listed in Exhibit ES-1. EPA 

also does not have national data regarding the treatment technologies being utilized to control 

these contaminants. Some technologies have higher potential for operational cost savings; 

however, co-occurrence considerations for all of the Best Available Technologies could diminish 

the potentially affected system’s ability to alter treatment for possible higher MCLGs. 

Despite the possibility for changes in MCLG values that range from 2 to 150 times higher than 

current MCLs, the available occurrence data for potential drinking water sources indicate 

relatively low contaminant occurrence in the concentration ranges of interest. As a consequence, 

EPA cannot conclude that there is a meaningful opportunity for system cost savings. 

ES-3 
EPA-OGWDW Occurrence Analysis for Potential Source Waters EPA 815-B-09-004 

for the Second Six-Year Review of NPDWRs 

1. Introduction 

The U.S. Environmental Protection Agency (EPA or the Agency) has completed its second SixYear Review (Six-Year Review 2) of national primary drinking water regulations (NPDWRs). 

The 1996 Safe Drinking Water Act (SDWA) Amendments require the Agency to periodically 

review existing NPDWRs. Section 1412(b)(9) of SDWA reads: 

 ...[t]he Administrator shall, not less than every 6 years, review and revise, as 

appropriate, each primary drinking water regulation promulgated under this title. 

Any revision of a national primary drinking water regulation shall be promulgated 

in accordance with this section, except that each revision shall maintain, or 

provide for greater, protection of the health of persons. 

The primary goal of the Six-Year Review process is to identify NPDWRs for possible regulatory 

revision. Although the statute does not define when a revision is “appropriate,” as a general 

benchmark, EPA considered a possible revision to be “appropriate” if, at a minimum, it presents 

a meaningful opportunity to: 

• improve the level of public health protection, and/or 

• achieve cost savings while maintaining or improving the level of public health protection. 

For Six-Year Review 2, EPA implemented the protocol that it developed for the first Six-Year 

Review (USEPA, 2003), including minor revisions developed during the current review process 

(USEPA, 2009d). EPA obtained and evaluated new information that could affect a NPDWR, 

including information on health effects (USEPA, 2009e), analytical feasibility (USEPA, 2009b), 

treatment feasibility (USEPA, 2009f), and finished water occurrence (USEPA, 2009a). EPA 

identified new health effects assessments that indicate the possibility to raise maximum 

contaminant level goal (MCLG) values for a number of regulated contaminants. Consequently, 

EPA reviewed data on contaminant occurrence in source water to determine if there is a 

meaningful opportunity to achieve cost savings while maintaining or improving the level of 

public health protection. This document describes this review. 

Exhibit 1-1 shows the current MCLG values for contaminants for which new health effects 

assessments indicate a possible MCLG that is higher than the MCLG in the NPDWR. The new 

health effects information results in a wide range of possible MCLG increases. The lowest 

relative increase is 2 times the current MCLG for both diquat and picloram. The highest relative 

increase is 150 times the current MCLG for the upper bound possible MCLG for lindane. 

Exhibit 1-1 also shows the current maximum contaminant level (MCL) values, most of which 

equal current MCLG values (the MCL for alachlor is higher because it is limited by analytical 

feasibility). The possible MCLG value for each contaminant is higher than the corresponding 

current MCL value. Thus, a revision to the MCLG for the contaminant would affect its MCL, 

which could reduce costs for drinking water systems that control the contaminant to meet the 

MCL. 

1-1
EPA-OGWDW Occurrence Analysis for Potential Source Waters EPA 815-B-09-004 

for the Second Six-Year Review of NPDWRs 

Exhibit 1-1. Current MCLG/MCL Values and Possible MCLG Values 

Contaminant 

Current MCLG/MCL 

(mg/L) 

Possible MCLG 

(mg/L) 

Alachlor1 zero (MCLG) 

0.002 (MCL) 0.04 

Barium1 2 6 

1,1-Dichloroethylene2 0.007 0.35 

Diquat1 0.02 0.04 

Glyphosate1 0.7 14 

Lindane (gamma-Hexachlorocyclohexane) 2 0.0002 0.001 – 0.03 (depending on risk 

factors used for uncertainty) 

Picloram2 0.5 1 

1,1,1-Trichloroethane1 0.2 14 

1. New health effects information during Round 2 indicates a possibility to increase MCLG. 

2. New health effects information during Round 1 indicated a possibility to increase MCLG. EPA made a decision in Round 1 

not to revise the NPDWR because the revision was a low priority. 

In making its recommendation to revise or take no action regarding an MCLG, EPA needs to 

determine whether there is a meaningful opportunity for cost savings while maintaining the same 

level of protection. This report provides the information EPA reviewed for this evaluation and 

the basis for the Agency’s decisions. This report provides the information EPA reviewed for this 

evaluation and the basis for the Agency’s decisions. 

During the First Six-Year Review, EPA made a recommendation not to revise several NPDWRs 

for which an increase in MCLG was possible, including several under consideration during the 

current review: 1,1-dichloroethylene, lindane, and picloram. EPA’s recommendation was based 

on its determination that there was a low potential for cost savings. This meant that a revision 

was a low priority activity for the Agency because of competing workload priorities, 

administrative costs associated with rulemaking, and the burden on States and the regulated 

community to implement any regulatory change that resulted. 

This technical support document addresses the potential for cost savings, which depends on the 

potential cost savings impact at the system level and the number of systems affected. Section 2 

provides a discussion of the factors affecting the potential for cost savings for each contaminant 

of interest. Section 3 discusses the sources of these contaminants and current usage of some of 

the contaminants. Section 4 summarizes water quality data that is readily available to 

characterize contaminant occurrence. Section 5 concludes the paper with a summary of 

information regarding whether possible changes to the MCLGs constitute a meaningful 

opportunity to reduce costs while maintaining health protection. USEPA (2009a) provides 

occurrence analysis information for other contaminants included in the Six-Year Review 2. 

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2. Cost Savings 

The potential for and magnitude of cost savings related to MCL changes depend on four factors: 

• The magnitude of increase in the MCL 

• The concentration of the contaminant in the source water, relative to the current MCL 

and the possible MCLG 

• The presence of co-occurring contaminants treated with the same technology and their 

relative importance to the design and operation of the treatment technology 

• The specific treatment technology currently employed. 

The potential cost savings is generally limited by the most constrained factor for a specific 

treatment facility. The following sections address each of these factors. 

2.1 Magnitude of Possible MCL Increase 

In general, the potential for cost savings is positively correlated with the magnitude of the MCL 

increase. A larger MCL increase can mean a greater number of systems affected and more 

significant changes in treatment operations. This factor can be limited, however, in the case of 

co-treatment. If co-occurring contaminants are present, even a large increase in the MCL for one 

contaminant may not permit a dramatic change in treatment operations, because the treatment 

system must continue operations sufficient to meet the MCLs for the other contaminants. 

Exhibit 2-1 presents the magnitude of possible change for the contaminants of interest. 

Exhibit 2-1. Magnitude of Possible Change 

Contaminant Magnitude of Possible MCLG/MCL Increase 

Alachlor 20 times higher (based on MCL) 

Barium 3 times higher 

1,1-Dichloroethylene 50 times higher 

Diquat 2 times higher 

Glyphosate 20 times higher 

Lindane (gamma-Hexachlorocyclohexane) 5 to 150 times higher (depending on risk factors for uncertainty) 

Picloram 2 times higher 

1,1,1-Trichloroethane 70 times higher 

One potential operational change that is highly dependent on the magnitude of the MCL increase 

is the degree of blending used by a treatment system. Some systems treat only a portion of the 

source water to a level well below the MCL and then blend the treated water with untreated 

water, resulting in blended water with contaminant concentrations below the MCL. An MCL 

increase could result in a system reducing the quantity of water being treated and increasing the 

quantity of untreated water in its blending operation. This change could result in reduced 

operating costs such as labor costs for operating the treatment system and, potentially, reduced 

energy costs for pumping water through the treatment process. 

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EPA-OGWDW Occurrence Analysis for Potential Source Waters EPA 815-B-09-004 

for the Second Six-Year Review of NPDWRs 

2.2 Relative Source Water Concentration 

If an MCL increases, there are two potential scenarios for a treatment system that could result in 

cost savings: 

• The source water concentration is greater than the current MCL, but less than the possible 

higher MCL 

• The source water concentration is greater than both the current and possible higher 

MCLs. 

The potential cost savings under the first scenario are greater than under the second, because a 

system could cease treatment for the contaminant altogether. The potential for ceasing treatment, 

however, may be limited by the presence of co-occurring contaminants. A system may need to 

continue treatment for the other contaminants. The number of systems that face each scenario 

depends, in part, on the magnitude of the MCL increase as well as the distribution of the 

contaminant in source waters. 

Under the SDWA, public water systems (PWSs) are required to conduct compliance monitoring, 

and EPA is collecting monitoring data from a sample of systems. These data, however, reflect 

post-treatment water quality. Comprehensive data for source water quality (i.e., prior to 

treatment) is not readily available. EPA has identified three sources of data that characterize 

contaminant occurrence in potential source waters: the National Water Quality Assessment 

(NAWQA) program conducted by the U.S. Geological Survey (USGS), and EPA’s STORET 

(short for STOrage and RETrieval) data system, which are part of EPA’s Office of Ground 

Water and Drinking Water’s National Contaminant Occurrence Database (NCOD), and the U.S. 

Department of Agriculture (USDA) Pesticide Data Program (PDP) water monitoring survey. 

Section 4 addresses data from these sources. 

2.3 Co-Occurring Contaminants 

As discussed above, the presence of co-occurring contaminants is an important limiting factor 

affecting the cost savings that can be achieved for an MCL increase. Co-occurring contaminants, 

however, are significant only when the same treatment process that is used to remove the target 

contaminant also removes the co-occurring contaminant(s). For example, a system with 

coagulation/filtration to remove turbidity, followed by granular activated carbon (GAC) to 

remove lindane, could realize a cost savings as a result of an increase in the lindane MCL if the 

GAC system can be adjusted without a significant effect on turbidity removal. If, however, the 

GAC process also removed other regulated organic contaminants, the system may not be able to 

adjust its GAC operation despite a change in the lindane MCL. 

When the same treatment process removes multiple contaminants, potential cost savings depend 

on the relative importance of each contaminant to the design and operation of the process. If the 

contaminant with the MCL increase controls operation, and removal of other contaminants is less 

sensitive to operational changes, there may be a greater opportunity for cost savings, at least to 

the point where changes begin to affect co-occurring contaminant removal. On the other hand, if 

a co-occurring contaminant controls operations, and the contaminant with the MCL increase is 

removed as an additional benefit, a system may not be able to adjust operations. 

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EPA-OGWDW Occurrence Analysis for Potential Source Waters EPA 815-B-09-004 

for the Second Six-Year Review of NPDWRs 

2.4 Treatment Technology 

Exhibit 2-2 summarizes the Best Available Technologies (BATs) for each of the seven 

contaminants. 

Exhibit 2-2. Summary of Treatment Technologies 

Contaminant 

Best Available Treatment 

Technologies 

Small System Compliance 

Technologies 

Alachlor GAC GAC, POU GAC, PAC 

Barium IX, LS, RO, EDR CF, IX, LS, RO, EDR, POU IX, POU 

RO 

Diquat GAC GAC, POU GAC, PAC 

Glyphosate OX OX 

1,1-Dichloroethylene PTA, GAC PTA, GAC, MSBA, Aeration (diffused, 

tray, shallow tray) 

Lindane (gammaHexachlorocyclohexane) GAC GAC, POU GAC, PAC 

Picloram GAC GAC, POU GAC, PAC 

1,1,1-Trichloroethane PTA, GAC PTA, GAC, MSBA, Aeration (diffused, 

tray, shallow tray, spray) 

GAC = Granular Activated Carbon; IX = Ion Exchange; LS = Lime Softening; POU = point-of-use; RO = Reverse Osmosis; 

EDR = Electrodialysis; OX = Oxidation (Chlorine or Ozone); CF = Coagulation/Filtration; PTA = Packed Tower Aeration. 

Sources: 40 CFR 141.61 and 141.62, USEPA 1998. 

The potential for cost savings (e.g., chemical use, energy, media replacement) vary by treatment 

technology (i.e., some technologies, once in place, are more amenable to operational changes 

than others). The following sections provide discussions of the factors affecting the potential cost 

savings for each technology in Exhibit 2-2. 

2.4.1 Ion Exchange (Barium) 

Increasing the MCL for a target contaminant in an ion exchange system could allow for greater 

run times before regeneration or replacement of the ion exchange resin. This longer run length 

would mean a reduction in regeneration chemical use, with associated cost savings, or a 

reduction in the cost of replacement resin/media. Alternatively, by changing bed depth, a system 

can reduce the quantity of resin or media present, with similar cost savings. Therefore, these cost 

savings could be large relative to the total operating cost of the technology, particularly if the 

magnitude of the MCL change is large. 

Also, ion exchange systems are more likely than other systems to be operated for the removal of 

a single contaminant. This is particularly true of systems with contaminant-specific resins. Thus, 

co-occurring contaminants may be less of a concern for some systems using this technology. 

Even when operated to remove multiple contaminants, this technology is amenable to changes in 

the resin used. If one contaminant’s MCL increases such that it is no longer a concern, the 

system can switch to a contaminant-specific resin (e.g., resin designed for arsenic removal) that 

is more efficient for removal of co-occurring contaminants, with potential cost savings. 

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2.4.2 Granular Activated Carbon (Alachlor, Diquat, 1,1-Dichloroethylene, 

Lindane, Picloram, 1,1,1-Trichloroethane) 

Similar to ion exchange, granular activated carbon (GAC) systems treating for a contaminant 

with an increased MCL may be able to extend their run length before regeneration or 

replacement of the GAC media or decrease the bed depth to reduce the GAC quantity. Cost 

savings could be large relative to the total operating cost of the technology, particularly if the 

magnitude of the MCL change is large. 

Unlike ion exchange, however, GAC removes a wide spectrum of organic and inorganic 

compounds including disinfection byproduct (DBP) precursors, and is more likely to be used for 

the removal of multiple contaminants. Thus, co-occurring contaminants may limit or eliminate 

the potential for cost savings, depending on which contaminant(s) have the greatest influence on 

GAC operation. Also, although all GAC media are not the same, there is less potential for a 

change in GAC media to result in significant cost savings. 

2.4.3 Packed Tower Aeration (1,1-Dichloroethylene, 1,1,1-

Trichloroethane) 

An increased MCL could allow packed tower aeration (PTA) systems treating for 1,1-

dichloroethylene or 1,1,1-trichloroethane to reduce the air-to-water ratio, resulting in reduced 

energy cost for blowers. Blower energy costs, however, make up a small portion of total 

operating costs. Thus, the cost savings could be small relative to the total operating cost of the 

technology. 

Also like GAC, PTA can remove a wide range of contaminants, specifically volatile 

contaminants, and is more likely to be used for the removal of multiple contaminants. Thus, cooccurring contaminants may eliminate the potential for cost savings or limit the savings to the 

extent 1,1-dichloroethylene or 1,1,1-trichloroethane treatment controls the PTA system’s air-towater ratio. 

2.4.4 Oxidation (Glyphosate) 

With an increased MCL, systems using oxidation to treat for glyphosate could reduce the dose of 

chlorine or ozone, resulting in reduced chemical cost. Chlorination and ozonation, however, 

typically are installed for the primary purpose of disinfecting drinking water. In other words, 

there would almost always be a co-occurring contaminant (i.e., bacteria, viruses, and parasites) in 

these systems, and glyphosate treatment would be a secondary benefit of the system. Cost 

savings in these systems would be limited to the extent glyphosate treatment controls the 

chemical dose. Although chemical costs make up a large portion of operating cost for these 

technologies, the ability to reduce these costs significantly would likely be small because of 

disinfection needs. It is unlikely that systems would be able to cease their oxidation treatment 

because of an increase in the glyphosate MCL, given the need for disinfection. 

2.4.5 Lime Softening (Barium) 

An increased MCL may allow lime softening systems to reduce the dose of treatment chemicals 

(coagulant or lime), resulting in reduced cost. Similar to oxidation, however, lime softening 

systems also are typically installed for another primary purpose (e.g., solids and/or hardness 

removal). The treatment of the contaminant with the increasing MCL would likely be a 

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EPA-OGWDW Occurrence Analysis for Potential Source Waters EPA 815-B-09-004 

for the Second Six-Year Review of NPDWRs 

secondary benefit of the system. Cost savings would be limited to the extent the contaminant 

with the MCL increase controls the coagulant or lime dose. Although chemical costs make up a 

moderate portion of operating cost for this technology, the ability to reduce these costs 

significantly would likely be small because of treatment needs for other contaminants. It is 

unlikely systems would be able to cease lime softening treatment, given the need to continue 

removal of solids and/or hardness. 

2.4.6 Reverse Osmosis and Electrodialysis (Barium) 

These two technologies generally achieve a very high removal rate for a wide variety of 

contaminants. Although some operational adjustments may be possible (e.g., changes in blending 

ratios), these changes would not have a dramatic effect on operating costs unless there are no cooccurring contaminants. These technologies are very likely to be used for removal of multiple 

contaminants, thereby limiting the potential for cost savings due to an MCL change for one 

contaminant. 

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3. Contaminant Characteristics and Sources 

Toxic pollutants can be introduced to surface water through natural sources as well as human 

activities. Exhibit 3-1 provides a brief summary of the uses and potential sources for the 

pollutants of interest. 

Exhibit 3-1. Potential Sources of the Contaminants 

Contaminant 

Sources of Potential 

Release to the 

Environment Description/Uses 

Environmental Fate and 

Transport 

Alachlor Agricultural runoff 

Herbicide used for weed control: 

corn, soybeans, sorghum, peanuts, 

and beans. 

Low absorption to soil; soluble 

and highly mobile in water; 

leaches to groundwater. 

Barium 

Industrial waste; drilling 

waste ground application, 

offshore drilling waste 

water; copper smelting; 

erosion of natural 

deposits. 

Naturally occurring metal; used in oil 

and gas drilling mud, jet fuel, 

pesticides, paint, bricks, ceramics, 

glass, and rubber. 

Leaching and erosion of natural 

deposits into groundwater; 

atmospheric deposition; 

precipitate out of aquatic media 

as insoluble salt; adsorb to 

suspended solids in surface 

water; not mobile in soil systems. 

1,1-

Dichloroethylene

Atmospheric emissions or 

wastewater discharge 

from manufacturing 

plants. 

Industrial chemical used in making 

adhesives, synthetic fibers, 

refrigerants, food packaging, and 

coating resins. 

Hydrophobic; highly volatile; if 

spilled on land, may leach to 

groundwater. 

Diquat

Agricultural runoff; 

manufacturing wastewater

discharges. 

Herbicide used to control plant 

growth in aquatic environments and 

as agricultural and residential 

herbicide. 

Permanently adsorbs to soil; 

rapidly adheres to sediments 

when released to water; 

immobile. 

Glyphosate

Direct discharge during 

application; manufacturing

wastewater discharges. 

Herbicide used on food and non-food 

field crops as well as a plant growth 

regulator. 

Strongly adsorbs to soil, 

immobile; unlikely to leach to 

groundwater; likely to adhere to 

sediments when released to 

surface water by aquatic use and 

erosion. 

Lindane (gammaHexachlorocycloh

exane)

Agricultural runoff; 

atmospheric emissions; 

rain and snow deposition.

Insecticide used to treat a variety of 

crop seeds; all agricultural 

application of this chemical will cease 

by October 2009. 

Volatile; sorbs to soil, leaching to 

groundwater (soluble in water at 7 

mg/L). 

Picloram

Runoff from agricultural, 

forest, and rights-of-way 

application. 

Herbicide used to control feed crop 

pastures, nonfood crops (rights-ofway), and in forestry. 

Highly soluble and mobile in 

water; leaches to groundwater, no 

degradation. 

1,1,1-

Trichloroethane

Atmospheric emissions or 

wastewater discharge 

from manufacturing 

plants, discharge or 

leaching from landfills. 

Industrial chemical used as a solvent 

and in production of 

hydrofluorocarbons. 

Highly volatile; sorbs to soil, 

leaching to groundwater; 

atmospheric deposition; moderate 

solubility. 

Sources: USEPA OPP 2006; ATSDR 2005; ATSDR 2007; ATSDR 2002; USEPA 2002; USEPA 1995a; USEPA 1993; USEPA 

2006c; USEPA 1995b; USEPA 2007; ATSDR 2006. 

3-1
EPA-OGWDW Occurrence Analysis for Potential Source Waters EPA 815-B-09-004 

for the Second Six-Year Review of NPDWRs 

EPA collected the most recently reported state level releases and disposal data for the pollutants 

of concern from EPA’s Toxic Release Inventory (TRI). This data identifies states that are most 

likely to have anthropogenic sources of the contaminants of interest that are reported to the TRI, 

which excludes agricultural applications of pesticides. No release or disposal were reported for 

1,1-dichloroethane, diquat, or glyphosate. The following table and map exhibits show the total 

number of pounds of each pollutant of interest reportedly released or disposed of on-site to 

different media, the total off-site disposal/releases, and a graphical representation of the total 

releases/disposal. 

Alachlor releases occurred only in Iowa in 2006 (see Exhibit 3-2 and Exhibit 3-3). Most of the 

274 pounds were released to air; 12 pounds were discharged to water. 

Exhibit 3-2. TRI On-site and Off-site Reported Disposal of or Otherwise Release of 

(in pounds) Alachlor for facilities in All Industries by State (2006) 

 

State 

Air1

(a) 

Surface 

Water 

Discharges2

(b) 

Underground 

Injection3

(c) 

On-site 

Landfill 

Disposal4

(d) 

Other Onsite 

Releases5

(e) 

Total On-site 

Disposal or 

Other 

Releases 

(f)=(a)+(b)+ 

(c)+(d)+(e) 

Total Offsite 

Disposal 

or Other 

Releases6

(h) 

Total Onand Off-site 

Disposal or 

Other 

Releases 

(i)=(f)+(h) 

Iowa 262 12 0 0 0 274 0 274 

Total 262 12 0 0 0 274 0 274 

Source: USEPA, 2008 

ND: no data reported 

1. Includes fugitive and point source air releases. Fugitive emissions are all releases to air that are not released through a confined 

air stream. Fugitive emissions include equipment leaks, evaporative losses from surface impoundments and spills, and releases 

from building ventilation systems. Point source air emissions occur through confined air streams such as stacks, vents, ducts, or 

pipes. 

2. Releases to water include discharges to streams, rivers, lakes, oceans, and other bodies of water. This includes releases from 

contained sources, such as industrial process outflow pipes or open trenches. Releases due to runoff, including storm water runoff 

are also reportable to TRI. 

3. Underground injection is the subsurface emplacement of fluids through wells including Class I, II, III, IV, or V wells. 

4. Total On-Site Disposal to Class I UI RCRA Landfills and other Landfills. 

5. Includes land treatment, surface impoundments, and other land disposal. Other disposal is the disposal of the toxic chemical to 

land at the facility that does not fall into one of the other on-site land releases listed. Other disposal includes such activities as 

placement in waste piles and spills or leaks. 

6. Disposal of toxic chemicals in waste to off-site locations include discharges to Publicly Owned Treatment Works (POTWs) or 

disposal at other off-site facilities. Other off-site disposal facilities may include underground injection, landfills, 

solidification/stabilization (metals), water treatment (metals), surface impoundments, land treatment, waste broker, or other unknown 

off-site facilities. 

3-2
EPA-OGWDW Occurrence Analysis for Potential Source Waters EPA 815-B-09-004 

for the Second Six-Year Review of NPDWRs 

Exhibit 3-3. TRI State Total Reported Disposal of or Otherwise Released Pounds 

of Alachlor for facilities in All Industries (2006) 

National releases and disposal of barium were reported to be approximately 6.8 million pounds 

in 2006. Exhibit 3-4 and Exhibit 3-5 show that Arizona reported the greatest release and 

disposal of 2.5 million pounds (36.3%) followed by Kansas (0.65 million pounds), Oregon (0.63 

million pounds), and Pennsylvania (0.55 million pounds). In Arizona all releases and disposal 

came from the electric utilities sector (NAICS 2211) and most was disposed of in on-site 

landfills. The total release directly to surface water in 2006 was 6,640 pounds. Nebraska reported 

the highest release to surface water of 3,913 pounds. 

3-3
EPA-OGWDW Occurrence Analysis for Potential Source Waters EPA 815-B-09-004 

for the Second Six-Year Review of NPDWRs 

Exhibit 3-4. TRI On-site and Off-site Reported Disposal of or Otherwise Release of (in 

pounds) Barium for facilities in All Industries by State (2006) 

 

State 

Air1

(a) 

Surface 

Water 

Discharges2

(b) 

Underground 

Injection3

(c) 

On-site 

Landfill 

Disposal4

(d) 

Other Onsite 

Releases5

(e) 

Total Onsite 

Disposal or 

Other 

Releases 

(f)=(a)+(b)+ 

(c)+(d)+(e) 

Total Offsite 

Disposal 

or Other 

Releases6

(h) 

Total Onand Offsite 

Disposal 

or Other 

Releases 

(i)=(f)+(h) 

Alabama 4 313 0 0 0 317 2,927 3,244 

Alaska 4,808 ND 0 0 0 4,808 177,652 182,460 

Arizona 4,529 ND 0 2,273,949 235 2,278,713 173,489 2,452,202 

California 1,607 ND 0 622,433 18 624,058 112 624,170 

Colorado 28,643 0 0 0 9,547 38,190 0 38,190 

Connecticut 3 ND 0 0 0 3 2,565 2,568 

Delaware 35 11 0 0 0 46 0 46 

Georgia 98 ND 0 0 0 98.1 10,350 10,448 

Idaho 29 ND 0 164,671 0 164,700 0 164,700 

Illinois 56 0 0 0 0 56 46,878 46,934 

Indiana 6 ND 0 0 0 6 28,353 28,359 

Iowa 715 0 0 0 0 715 32,395 33,110 

Kansas 7,533 0 0 131,690 0 139,223 507,055 646,278 

Kentucky 79,829 250 0 0 0 80,079 0 80,079 

Louisiana 0 ND 0 16,000 0 16,000 1,980 17,980 

Michigan 2 0 0 0 0 2 88,487 88,489 

Minnesota 8.8 ND 0 0 0 8.8 1,005 1,014 

Nebraska 55,056 3,913 0 0 22,524 81,493 379,261 460,754 

New Jersey 130 ND 0 0 0 130 6,387 6,517 

New York 0 314 0 6,072 0 6,386 8,700 15,086 

North Carolina 31.4 501 0 0 0 532 3,110 3,642 

Ohio 10,230 1,089 18,086 82,086 0 93,405 81,556 174,961 

Oregon 0 7 0 631,136 90 631,233 12 631,244 

Pennsylvania 1,556 0 0 335,647 0 337,203 213,707 550,910 

Puerto Rico 0 ND 0 0 0 0 5 5 

South Carolina 274 ND 0 0 0 274 48 322 

South Dakota 1,000 ND 0 47,646 0 48,646 0 48,646 

Tennessee 0 ND 0 0 0 0 33,629 33,629 

Texas 2,511 242 0 44,385 0 47,138 57,339 104,477 

Utah 503 0 0 107,604 0 108,107 30,017 138,124 

Virginia 0 ND 0 0 0 0 40,470 40,470 

Washington 49 ND 0 0 0 49 14 63 

West Virginia 0 ND 0 0 90,000 90,000 0 90,000 

Wisconsin 0 ND 0 0 0 0 31,850 31,850 

Total 199,246 6,640 18,086 4,463,319 122,414 4,791,619 1,959,353 6,750,972 

Source: USEPA, 2008 

ND: no data reported 

1. Includes fugitive and point source air releases. Fugitive emissions are all releases to air that are not released through a confined air 

stream. Fugitive emissions include equipment leaks, evaporative losses from surface impoundments and spills, and releases from 

building ventilation systems. Point source air emissions occur through confined air streams such as stacks, vents, ducts, or pipes. 

2. Releases to water include discharges to streams, rivers, lakes, oceans, and other bodies of water. This includes releases from 

3-4
EPA-OGWDW Occurrence Analysis for Potential Source Waters EPA 815-B-09-004 

for the Second Six-Year Review of NPDWRs 

Exhibit 3-4. TRI On-site and Off-site Reported Disposal of or Otherwise Release of (in 

pounds) Barium for facilities in All Industries by State (2006) 

 

State 

Air1

(a) 

Surface 

Water 

Discharges2

(b) 

Underground 

Injection3

(c) 

On-site 

Landfill 

Disposal4

(d) 

Other Onsite 

Releases5

(e) 

Total Onsite 

Disposal or 

Other 

Releases 

(f)=(a)+(b)+ 

(c)+(d)+(e) 

Total Offsite 

Disposal 

or Other 

Releases6

(h) 

Total Onand Offsite 

Disposal 

or Other 

Releases 

(i)=(f)+(h) 

contained sources, such as industrial process outflow pipes or open trenches. Releases due to runoff, including storm water runoff are 

also reportable to TRI. 

3. Underground injection is the subsurface emplacement of fluids through wells including Class I, II, III, IV, or V wells. 

4. Total On-Site Disposal to Class I UI RCRA Landfills and other Landfills. 

5. Includes land treatment, surface impoundments, and other land disposal. Other disposal is the disposal of the toxic chemical to land 

at the facility that does not fall into one of the other on-site land releases listed. Other disposal includes such activities as placement in 

waste piles and spills or leaks. 

6. Disposal of toxic chemicals in waste to off-site locations include discharges to Publicly Owned Treatment Works (POTWs) or 

disposal at other off-site facilities. Other off-site disposal facilities may include underground injection, landfills, solidification/stabilization 

(metals), water treatment (metals), surface impoundments, land treatment, waste broker, or other unknown off-site facilities. 

Exhibit 3-5. TRI State Total Reported Disposal of or Otherwise Released Pounds 

of Barium for facilities in All Industries (2006) 

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EPA-OGWDW Occurrence Analysis for Potential Source Waters EPA 815-B-09-004 

for the Second Six-Year Review of NPDWRs 

National releases and disposal of barium compounds were reported to be approximately 224.7 

million pounds in 2006. Exhibit 3-6 and Exhibit 3-7 show that Texas reported the greatest 

release and disposal of 16.5 million pounds (7.4%) followed by North Dakota (13.9 million 

pounds) and Michigan (12.6 million pounds). In Texas, 94% of the reported releases and 

disposal came from the electric utilities sector (NAICS 2211) and 2% came from the chemical 

sector (NAICS 325). The total release directly to surface waters in 2006 was approximately one 

million pounds. Illinois reported the highest release to surface water of 123,897 pounds followed 

by Tennessee (119,997 pounds) and South Carolina (75,055 pounds). 

Exhibit 3-6. TRI On-site and Off-site Reported Disposal of or Otherwise Release of (in 

pounds) Barium Compounds for facilities in All Industries by State (2006) 

State 

Air1

(a) 

Surface 

Water 

Discharges2

(b) 

Underground 

Injection3

(c) 

On-site 

Landfill 

Disposal4

(d) 

Other Onsite 

Releases5

(e) 

Total Onsite 

Disposal or 

Other 

Releases 

(f)=(a)+(b)+ 

(c)+(d)+(e) 

Total Offsite 

Disposal or 

Other 

Releases6

(h) 

Total Onand Off-site 

Disposal or 

Other 

Releases 

(i)=(f)+(h) 

Alabama 39,293 68,042 0 1,819,037 8,852,004 10,778,376 53,416 10,831,793

Alaska 26,894 ND 0 149,061 1,243 177,198 1,243 178,441 

Arizona 19,259 ND 0 1,618,845 5,576,154 7,214,258 19,112 7,233,370 

Arkansas 53,429 75,026 0 3,243,243 344,456 3,716,153 37,327 3,753,480 

California 12,052 260 0 7,838 0 20,150 14,516 34,666 

Colorado 14,733 930 0 4,810,972 415 4,827,050 3,911,998 8,739,048 

Connecticut 2,545 7 0 0 0 2,553 99,338 101,891 

Delaware 10,601 10,593 0 280,000 0 301,194 149,119 450,313 

Florida 27,228 10,727 0 1,789,344 2,411,543 4,238,842 342,315 4,581,157 

Georgia 66,339 62,809 0 817,488 7,801,677 8,748,313 62,617 8,810,930 

Hawaii 64 ND 0 0 0 64 50,896 50,960 

Idaho 7,456 ND 0 10,634 48,573 66,663 47,000 113,663 

Illinois 154,529 123,897 0 476,000 4,822,273 5,576,699 3,562,257 9,138,956 

Indiana 95,425 34,454 0 4,983,355 3,765,383 8,878,617 819,017 9,697,633 

Iowa 186,258 5,515 0 1,341,054 1,894,000 3,426,827 1,451,238 4,878,065 

Kansas 93,805 747 0 3,461,575 1,995,885 5,552,012 0 5,552,012 

Kentucky 58,941 67,955 0 2,671,201 2,648,100 5,446,197 1,891,428 7,337,625 

Louisiana 49,943 30,962 541 2,012,600 1,012,871 3,106,376 1,338,912 4,445,289 

Maine 1,448 4,600 0 82,130 0 88,178 18,197 106,375 

Maryland 8,048 896 3 38,246 197,754 244,947 954,092 1,199,039 

Massachusetts 3,684 1,061 0 9,572 228,932 243,249 103,068 346,317 

Michigan 64,032 39,122 0 5,807,055 4,307,884 10,218,093 2,364,276 12,582,369

Minnesota 52,501 2,860 0 2,942,269 5,575,059 8,572,689 782,215 9,354,903 

Mississippi 4,106 20,656 51,600 1,043,777 91,925 1,160,464 93,627 1,254,090 

Missouri 161,647 16,584 0 1,673,048 5,398,947 7,250,226 103,723 7,353,948 

Montana 114,897 795 0 8,398,812 165,155 8,679,659 440,377 9,120,036 

Nebraska 59,038 5 0 1,828,368 10 1,887,421 336,671 2,224,092 

Nevada 898 0 0 841,677 53,390 895,965 35 896,000 

New 

Hampshire 1,267 ND 0 0 13,000 14,267 3,558 17,825 

New Jersey 8,128 39 0 0 0 8,167 289,375 297,542 

3-6
EPA-OGWDW Occurrence Analysis for Potential Source Waters EPA 815-B-09-004 

for the Second Six-Year Review of NPDWRs 

Exhibit 3-6. TRI On-site and Off-site Reported Disposal of or Otherwise Release of (in 

pounds) Barium Compounds for facilities in All Industries by State (2006) 

 State 

Air1

(a) 

Surface 

Water 

Discharges2

(b) 

Underground 

Injection3

(c) 

On-site 

Landfill 

Disposal4

(d) 

Other Onsite 

Releases5

(e) 

Total Onsite 

Disposal or 

Other 

Releases 

(f)=(a)+(b)+ 

(c)+(d)+(e) 

Total Offsite 

Disposal or 

Other 

Releases6

(h) 

Total Onand Off-site 

Disposal or 

Other 

Releases 

(i)=(f)+(h) 

New Mexico 13,880 2,100 0 3,683,605 1,210,133 4,909,718 755 4,910,473 

New York 23,342 13,186 0 607,765 25 644,317 1,250,835 1,895,152 

North Carolina 24,666 58,290 0 299,831 3,545,025 3,927,812 427,201 4,355,012 

North Dakota 41,053 20,722 0 1,645,308 5,347,505 7,054,588 6,849,716 13,904,304

Ohio 70,988 34,283 0 1,671,929 3,663,861 5,441,061 3,723,633 9,164,694 

Oklahoma 23,899 15,920 0 1,069,250 396,268 1,505,337 395,945 1,901,282 

Oregon 15,617 3,939 0 250,000 0 269,556 40,196 309,752 

Pennsylvania 42,320 29,942 0 1,229,599 193,816 1,495,677 3,196,635 4,692,313 

Puerto Rico 2,847 0 0 0 0 2,847 0 2,847 

Rhode Island 5 18 0 0 0 23 10,343 10,366 

South Carolina 25,317 75,055 0 674,795 912,137 1,687,303 596,404 2,283,707 

South Dakota 1,120 120 0 588,856 0 590,095 169,306 759,401 

Tennessee 20,231 119,997 0 1,310,070 4,012,858 5,463,156 5,514,045 10,977,201

Texas 143,884 43,683 0 10,620,521 2,444,136 13,252,225 3,289,907 16,542,131

Utah 4,498 80 0 3,314,131 180,397 3,499,106 44,609 3,543,715 

Vermont 0 ND 0 0 0 0 29,485 29,485 

Virginia 5,159 37,270 0 1,027,000 516,161 1,585,590 432,784 2,018,374 

Washington 1,048 3,105 0 26,143 1,010,646 1,040,942 88,564 1,129,506 

West Virginia 6,418 15,186 0 3,141,468 1,089,119 4,252,191 1,159,751 5,411,941 

Wisconsin 51,094 8,283 0 285,180 656,674 1,001,231 1,743,425 2,744,655 

Wyoming 41,688 4,987 0 6,068,618 675,635 6,790,928 678,126 7,469,054 

Total 1,957,560 1,064,708 52,144 89,671,269 83,061,028 175,754,568 48,982,625 224,737,194

Source: USEPA, 2008 

ND: no data reported 

1. Includes fugitive and point source air releases. Fugitive emissions are all releases to air that are not released through a confined air 

stream. Fugitive emissions include equipment leaks, evaporative losses from surface impoundments and spills, and releases from 

building ventilation systems. Point source air emissions occur through confined air streams such as stacks, vents, ducts, or pipes. 

2. Releases to water include discharges to streams, rivers, lakes, oceans, and other bodies of water. This includes releases from 

contained sources, such as industrial process outflow pipes or open trenches. Releases due to runoff, including storm water runoff are 

also reportable to TRI. 

3. Underground injection is the subsurface emplacement of fluids through wells including Class I, II, III, IV, or V wells. 

4. Total On-Site Disposal to Class I UI RCRA Landfills and other Landfills. 

5. Includes land treatment, surface impoundments, and other land disposal. Other disposal is the disposal of the toxic chemical to land 

at the facility that does not fall into one of the other on-site land releases listed. Other disposal includes such activities as placement in 

waste piles and spills or leaks. 

6. Disposal of toxic chemicals in waste to off-site locations include discharges to Publicly Owned Treatment Works (POTWs) or 

disposal at other off-site facilities. Other off-site disposal facilities may include underground injection, landfills, solidification/stabilization 

(metals), water treatment (metals), surface impoundments, land treatment, waste broker, or other unknown off-site facilities. 

3-7
EPA-OGWDW Occurrence Analysis for Potential Source Waters EPA 815-B-09-004 

for the Second Six-Year Review of NPDWRs 

Exhibit 3-7. TRI State Total Reported Disposal of or Otherwise Released Pounds 

of Barium Compounds for facilities in All Industries (2006) 

As shown in Exhibit 3-8 and Exhibit 3-9, nationally only 10 pounds of lindane were reportedly 

released and disposed of in 2006 from three states including Arkansas, Ohio, and Utah. Half of 

the 10 pounds were released into the air, while the other 5 pounds were disposed of at off-site 

facilities. 

3-8
EPA-OGWDW Occurrence Analysis for Potential Source Waters EPA 815-B-09-004 

for the Second Six-Year Review of NPDWRs 

Exhibit 3-8. TRI On-site and Off-site Reported Disposal of or Otherwise Release of (in 

pounds) Lindane for facilities in All Industries by State (2006) 

 

State 

Air1

(a) 

Surface 

Water 

Discharges2

(b) 

Underground 

Injection3

(c) 

On-site 

Landfill 

Disposal4

(d) 

Other Onsite 

Releases5

(e) 

Total On-site 

Disposal or 

Other 

Releases 

(f)=(a)+(b)+(c)

+(d)+(e) 

Total Offsite 

Disposal or 

Other 

Releases6

(h) 

Total On- and 

Off-site 

Disposal or 

Other 

Releases 

(i)=(f)+(h) 

Arkansas 1 ND 0 0 0 1 0 1 

Ohio 0 0 0 0 0 0 5 5 

Utah 4 ND 0 0 0 4 0 4 

Total 5 0 0 0 0 5 5 10 

Source: USEPA, 2008 

ND: no data reported 

1. Includes fugitive and point source air releases. Fugitive emissions are all releases to air that are not released through a confined 

air stream. Fugitive emissions include equipment leaks, evaporative losses from surface impoundments and spills, and releases from 

building ventilation systems. Point source air emissions occur through confined air streams such as stacks, vents, ducts, or pipes. 

2. Releases to water include discharges to streams, rivers, lakes, oceans, and other bodies of water. This includes releases from 

contained sources, such as industrial process outflow pipes or open trenches. Releases due to runoff, including storm water runoff 

are also reportable to TRI. 

3. Underground injection is the subsurface emplacement of fluids through wells including Class I, II, III, IV, or V wells. 

4. Total On-Site Disposal to Class I UI RCRA Landfills and other Landfills. 

5. Includes land treatment, surface impoundments, and other land disposal. Other disposal is the disposal of the toxic chemical to 

land at the facility that does not fall into one of the other on-site land releases listed. Other disposal includes such activities as 

placement in waste piles and spills or leaks. 

6. Disposal of toxic chemicals in waste to off-site locations include discharges to Publicly Owned Treatment Works (POTWs) or 

disposal at other off-site facilities. Other off-site disposal facilities may include underground injection, landfills, 

solidification/stabilization (metals), water treatment (metals), surface impoundments, land treatment, waste broker, or other unknown 

off-site facilities. 

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Exhibit 3-9. TRI State Total Reported Disposal of or Otherwise Released Pounds 

of Lindane Compounds for facilities in All Industries (2006) 

National releases and disposal of picloram were reported to be approximately 51.8 thousand 

pounds in 2006. As shown in Exhibit 3-10 and Exhibit 3-11, while three states reported releases 

(Michigan, Missouri, and Texas), 99% of the releases and disposal were in Texas. All of the 

reported releases and disposal came from the chemical sector (NAICS 325) and most was 

disposed of in on-site landfills. The total release directly to surface water in 2006 was only 350 

pounds, all of which was reported in Michigan. 

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Exhibit 3-10. TRI On-site and Off-site Reported Disposal of or Otherwise Release of 

(in pounds) Picloram for facilities in All Industries by State (2006) 

 State 

Air1

(a) 

Surface 

Water 

Discharges2

(b) 

Underground 

Injection3

(c) 

On-site 

Landfill 

Disposal4

(d) 

Other Onsite 

Releases5

(e) 

Total On-site 

Disposal or 

Other 

Releases 

(f)=(a)+(b)+(c)

+(d)+(e) 

Total Offsite 

Disposal 

or Other 

Releases6

(h) 

Total On- and 

Off-site 

Disposal or 

Other 

Releases 

(i)=(f)+(h) 

Michigan 14 350 0 0 0 364 0 364 

Missouri 46 ND 0 0 0 46 8 54 

Texas 201 0 0 51,133 0 51,334 0 51,334 

Total 261 350 0 51,133 0 51,744 8 51,752 

Source: USEPA, 2008 

ND: no data reported 

1. Includes fugitive and point source air releases. Fugitive emissions are all releases to air that are not released through a confined 

air stream. Fugitive emissions include equipment leaks, evaporative losses from surface impoundments and spills, and releases from 

building ventilation systems. Point source air emissions occur through confined air streams such as stacks, vents, ducts, or pipes. 

2. Releases to water include discharges to streams, rivers, lakes, oceans, and other bodies of water. This includes releases from 

contained sources, such as industrial process outflow pipes or open trenches. Releases due to runoff, including storm water runoff 

are also reportable to TRI. 

3. Underground injection is the subsurface emplacement of fluids through wells including Class I, II, III, IV, or V wells. 

4. Total On-Site Disposal to Class I UI RCRA Landfills and other Landfills. 

5. Includes land treatment, surface impoundments, and other land disposal. Other disposal is the disposal of the toxic chemical to 

land at the facility that does not fall into one of the other on-site land releases listed. Other disposal includes such activities as 

placement in waste piles and spills or leaks. 

6. Disposal of toxic chemicals in waste to off-site locations include discharges to Publicly Owned Treatment Works (POTWs) or 

disposal at other off-site facilities. Other off-site disposal facilities may include underground injection, landfills, 

solidification/stabilization (metals), water treatment (metals), surface impoundments, land treatment, waste broker, or other unknown 

off-site facilities. 

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Exhibit 3-11. TRI State Total Reported Disposal of or Otherwise Released Pounds 

of Picloram Compounds for facilities in All Industries (2006) 

National releases and disposal of 1,1,1-trichloroethane were reported to be approximately 119.8 

thousand pounds in 2006. Exhibit 3-12 and Exhibit 3-13 show that Louisiana reported the 

greatest release and disposal of 57.0 thousand pounds (47.6%) followed by Minnesota (36.3 

thousand pounds) and New Mexico (10.8 thousand pounds). In Louisiana all releases and 

disposal came from the chemical sector (NAICS 325) and most was released into the air. The 

total release directly to surface water in 2006 was only 53 pounds. Louisiana also reported the 

highest release to surface water of 47 pounds. 

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Exhibit 3-12. TRI On-site and Off-site Reported Disposal of or Otherwise Release of 

(in pounds) 1,1,1-Trichloroethane for facilities in All Industries by State (2006) 

 State 

Air1

(a) 

Surface 

Water 

Discharges2

(b) 

Underground 

Injection3

(c) 

On-site 

Landfill 

Disposal4

(d) 

Other Onsite 

Releases5

(e) 

Total On-site 

Disposal or 

Other 

Releases 

(f)=(a)+(b)+(c)

+(d)+(e) 

Total Offsite 

Disposal or 

Other 

Releases6

(h) 

Total Onand Off-site 

Disposal or 

Other 

Releases 

(i)=(f)+(h) 

Arkansas 102 ND 0 0 0 102 0 102 

California 272 ND 0 0 0 272 90 362 

Illinois 1 0 0 0 0 1 21 22 

Indiana 500 ND 0 0 0 500 0 500 

Kentucky 1,620 4 0 0 0 1,624 0 1,624 

Louisiana 57,018 47 0 0 0 57,065 1 57,066 

Minnesota 36,337 ND 0 0 0 36,337 0 36,337 

Mississippi 1 0 0 0 0 1 0 1 

Missouri ND ND ND ND ND ND 0 0 

Nebraska 10 0 0 11 0 21 0 21 

New Jersey 1 2 0 0 0 3 200 203 

New Mexico 0 ND 0 0 10,806 10,806 0 10,806 

Ohio 840 0 0 0 0 840 255 1,095 

Pennsylvania 500 0 0 0 0 500 5 505 

Texas 1,468 0 0 0 0 1,468 0 1,468 

Utah 9,654 ND 0 0 0 9,654 4 9,658 

Virginia 10 ND 0 0 0 10 0 10 

Total 108,334 53 0 11 10,806 119,204 576 119,780 

Source: USEPA, 2008 

ND: no data reported 

1. Includes fugitive and point source air releases. Fugitive emissions are all releases to air that are not released through a confined 

air stream. Fugitive emissions include equipment leaks, evaporative losses from surface impoundments and spills, and releases from 

building ventilation systems. Point source air emissions occur through confined air streams such as stacks, vents, ducts, or pipes. 

2. Releases to water include discharges to streams, rivers, lakes, oceans, and other bodies of water. This includes releases from 

contained sources, such as industrial process outflow pipes or open trenches. Releases due to runoff, including storm water runoff 

are also reportable to TRI. 

3. Underground injection is the subsurface emplacement of fluids through wells including Class I, II, III, IV, or V wells. 

4. Total On-Site Disposal to Class I UI RCRA Landfills and other Landfills. 

5. Includes land treatment, surface impoundments, and other land disposal. Other disposal is the disposal of the toxic chemical to 

land at the facility that does not fall into one of the other on-site land releases listed. Other disposal includes such activities as 

placement in waste piles and spills or leaks. 

6. Disposal of toxic chemicals in waste to off-site locations include discharges to Publicly Owned Treatment Works (POTWs) or 

disposal at other off-site facilities. Other off-site disposal facilities may include underground injection, landfills, 

solidification/stabilization (metals), water treatment (metals), surface impoundments, land treatment, waste broker, or other unknown 

off-site facilities. 

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Exhibit 3-13. TRI State Total Reported Disposal of or Otherwise Released Pounds 

of 1,1,1-Trichloroethane Compounds for facilities in All Industries (2006) 

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4. Contaminant Occurrence Data Sources 

EPA has identified three sources of data that provide information on contaminant occurrence in 

source water: USGS’ NAWQA Program, EPA’s STORET data system, and USDA’s Pesticide 

Data Program (PDP) water monitoring survey. This section provides background information on 

these three sources as well as occurrence summary data for the seven contaminants of interest. 

4.1 NAWQA 

In 1991, USGS implemented the NAWQA Program, in part, to characterize the condition of 

streams, rivers, and ground water in the U.S. 

From 1991-2001, the NAWQA Program conducted interdisciplinary assessments, including 

water chemistry, hydrology, land use, stream habitat, and aquatic life, and established a baseline 

understanding of water-quality conditions in 51 of the Nation's river basins and aquifers, referred 

to as Study Units (USGS, 2006a). Exhibit 4-1 depicts these study units. 

USGS selected these Study Units to reflect important hydrologic and ecological resources; 

critical sources of contaminants, including agricultural, urban, and natural sources; and a high 

percentage of population served by municipal water supply and irrigated agriculture. These areas 

account for more than 70 percent of total water use (excluding thermoelectric and hydropower) 

and more than 50 percent of the population’s supply of drinking water (Gilliom, 2006). 

The Study-Unit design used a rotational sampling scheme; therefore, sampling intensity varied 

year to year at the different sites. During the first decade, 20 investigations began in 1991; 16 in 

1994; and 15 in 1997. During the time period 2001-2012, rotational monitoring will continue in 

42 of the 51 Study Units. 

USGS has made most of this data available through the NAWQA Warehouse. EPA collected and 

analyzed all available water quality sampling data for the seven contaminants of interest. EPA 

selected the maximum reported concentration for each contaminant analyzed at each location. 

The results shown below are based on these maximum concentrations and, therefore, represent 

upper bounds on contaminant occurrence in the NAWQA database. 

The NAWQA data include latitude and longitude fields for the water quality sampling stations. 

EPA used these data along with latitude and longitude data in the Federal Safe Drinking Water 

Information System (SDWIS/FED) for community water system (CWS) facilities (e.g., intake 

well or treatment plant) to characterize the proximity of NAWQA sampling stations to these 

systems. EPA used a 2007 data extract of system, facility, and location information from 

SDWIS/FED for the analysis. EPA developed an initial dataset that contained 108,243 facility 

location records for 40,875 active CWSs that did not purchase water. EPA selected the records 

for facilities associated with water sources: infiltration gallery, intake, reservoir, roof catchment, 

spring, well, and well head. Treatment plant location records were also retained if a PWS had 

none of the facilities associated with source water. Because there are no NAWQA monitoring 

stations outside the contiguous 48 States, EPA removed records for Alaska (AK), Hawaii (HI), 

Puerto Rico (PR), and the Northern Mariana Islands (NMI), resulting in a final dataset of 

106,351 facility records for 40,013 CWS. Exhibit 4-2 provides a breakdown of the CWS by 

system size and Exhibit 4-3 provides a breakdown by source water type. 

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Exhibit 4-1. NAWQA Study Units 

Source: Gilliom, 2006a. 

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Exhibit 4-2. CWS Dataset Summary by System Size 

Dataset 25 - 500 

501 – 

3,300 

3,301 – 

10,000 

10,001 – 

100,000 >100,000 Total 

Total CWS with facility location 24,131 10,382 3,492 2,566 304 40,875 

(%) (59%) (25%) (9%) (6%) (1%) (100%) 

CWS excluding AK, HI, PR, NMI 23,660 10,162 3,414 2,484 293 40,017 

(%) (59%) (25%) (9%) (6%) (1%) (100%) 

Source: SDWIS/FED 2007 data extract 

Exhibit 4-3. CWS Summary by Water Source 

Dataset GW SW Total 

Total CWS with facility location 36,251 4,624 40,875 

(%) (89%) (11%) (100%) 

CWS excluding AK, HI, PR, NMI 35,666 4,347 40,013 

(%) (89%) (11%) (100%) 

Source: SDWIS/FED 2007 data extract 

GW: ground water, SW: surface water (includes 454 CWS with ground water under the influence of surface water)

Using a geographical information system (GIS), EPA estimated the distance between each CWS 

facility and the nearest NAWQA sampling site. Exhibit 4-4 shows results for 11 distance 

categories, including the number, cumulative number, and cumulative percent of NAWQA 

stations in each category. For example, 1,179 or 12.3% of the NAWQA sites are located within 

0.5 miles of a CWS facility. Almost half of the NAWQA stations are within three miles of a 

CWS facility, and over 65% are within five miles. This location analysis does not, however, 

demonstrate that the water sources monitored by the NAWQA sampling sites are the drinking 

water sources for the nearest CWS facility; it only demonstrates relative proximity. 

Exhibit 4-4. Distance from NAWQA Sampling Stations to Nearest CWS Facility 

Distance in Miles NAWQA Total Cumulative Cumulative % 

<0.5 1,179 1,179 12.3% 

0.5-1 834 2,013 21.1% 

1-2 1,456 3,469 36.3% 

2-3 1,183 4,652 48.7% 

3-5 1,592 6,244 65.4% 

5-10 1,642 7,886 82.6% 

10-15 587 8,473 88.7% 

15-20 267 8,740 91.5% 

20-25 172 8,912 93.3% 

25-50 434 9,346 97.8% 

>50 206 9,552 100.0% 

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Although many of the NAWQA sampling sites are located within 5 to 10 miles of a CWS 

facility, the same cannot be said of the CWS facilities. There are approximately 4 times more 

CWS systems and 10 times more facilities than there are NAWQA sampling sites. 

4.2 STORET 

EPA manages two databases that contain water quality data for waterways in the United States 

(http://www.epa.gov/storet/). The Legacy Data Center (LDC) contains archived data through the 

end of 1998, while STORET is an active database updated each month with new water quality 

data beginning in 1999. It also includes all LDC data. STORET is a repository for data collected 

by local, state and federal agencies, Indian tribes, universities, and volunteers. Data downloads 

for a location vary over time as contributors revise their data. It contains raw biological, 

chemical, and physical data on surface and ground water for all 50 states and U.S. territories and 

jurisdictions. EPA collected and analyzed all available water quality data for the seven 

contaminants of interest. 

4.3 PDP 

The USDA established the PDP in 1991 to collect data pertaining to pesticide residues in food 

consumed by infants and children. In 1996, Congress expanded the program to include pesticide 

residues in drinking water. Implementation of this portion of the program was initiated in 2001. 

The databases are produced annually and contain the following data collected through December 

2006: 

• pesticide residual concentrations in drinking water, bottled water, vegetables, grains, 

grain products, nuts, dairy products, fruits, poultry, beef, and pork for approximately 372 

pesticides 

• results from consumables originating in 43 countries, 50 states, Washington D.C., and 

Puerto Rico 

The drinking water data are used to support the Food Quality Protection Act authorized in 1996 

by Congress. Sampling occurs in regions of interest for a minimum of two years to track 

variations throughout different growing seasons. When the study began in 2001, it was limited to 

treated water at community water systems in New York and California. In 2002, monitoring 

efforts expanded to include five additional systems in Colorado, Kansas, and Texas; these 

locations were eliminated after 2003. The study expanded in 2004 to include Michigan, North 

Carolina, Ohio, Oregon, Pennsylvania, and Washington, as well as add source or raw water 

samples. Treatment plant personnel collect PDP samples from the raw and treated water flows, 

attempting to synchronize the collection of samples so that the sample collected after treatment is 

theoretically from the same aliquot of water sampled at the intake. 

4.4 Contaminant Occurrence 

The following sections discuss the occurrence of six of the seven contaminants of interest, and 

present summary data (maximum concentration values) from the NAWQA, STORET, and PDP 

databases. Each summary table juxtaposes the occurrence data with the current MCLG value (or 

MCL value when it is greater than the MCLG) and one or more possible MCLG values that are 

based on new health risk information. EPA also plotted the NAWQA data to demonstrate the 

spatial extent of the sampling locations and occurrence of the contaminants. 

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EPA did not identify any readily available water quality data for diquat. The Agency, therefore, 

obtained available information on diquat use and environmental fate and transport to characterize 

potential source water occurrence. 

4.4.1 Alachlor 

Exhibit 4-5 and Exhibit 4-6 provide comparisons of the maximum alachlor concentrations 

found at locations in the NAWQA and STORET databases, respectively, with the current MCL 

(which is greater than the MCLG) and the possible MCLG value. Exhibit 4-7 presents a spatial 

representation of the NAWQA data. Less than 0.4% of NAWQA sampling locations have a 

maximum concentration that exceeds the current MCL and only one has a concentration that 

exceeds the possible MCLG. STORET data show that less than 1.4% of sampling locations have 

maximum concentrations above the MCL and none have samples exceeding the possible MCLG. 

Exhibit 4-8 and Exhibit 4-9 show alachlor raw water concentrations and finished water 

concentrations, respectively, from the PDP database. None of the samples contained alachlor 

concentrations that exceeded the current MCL or possible MCLG. 

Exhibit 4-5. Summary of Alachlor Occurrence Based on Maximum Sample Values 

for Locations in NAWQA 

Number of Locations (% of locations) 

Occurrence Result Surface Water Ground Water Other Total 

Total locations 2,125 (100.0%) 6,785 (100.0%) 326 (100.0%) 9,236 (100.0%) 

All samples are nondetect 1,601 (75.3%) 6,665 (98.2%) 305 (93.6%) 8,571 (92.8%) 

At least one detection 524 (24.7%) 120 (1.8%) 21 (6.4%) 665 (7.2%) 

Maximum concentration exceeds 

current MCL1 (0.002 mg/L) 32 (1.5%) 2 (0.03%) 1 (0.31%) 35 (0.38%) 

Maximum concentration exceeds 

possible MCLG (0.04 mg/L) 1 (0.05 %) 0 (0.0%) 0 (0.0%) 1 (0.01%) 

Source: USGS 2006b (national data from 1992 to 1/1/2008). 

1. The current MCLG is zero. Because of analytical limitations, EPA cannot determine the number of samples that do not 

exceed the current MCLG. Consequently, EPA reports the number exceeding the current MCL, instead of the MCLG. 

Exhibit 4-6. Summary of Alachlor Occurrence Based on Maximum Sample Values 

for Locations in STORET 

Occurrence Result Number of Locations (% locations) 

Total locations 2,252 (100.0%) 

All samples are nondetects 1,669 (74.1%) 

At least one detection 583 (25.9%) 

Exceeds current MCL1 (0.002 mg/L) 40 (1.8%) 

Exceeds possible MCLG (0.04 mg/L) 0 (0.0%) 

Source: USEPA 2006b (national data 1/1/2002 to 9/20/2006). 

1. The current MCLG is zero. Because of analytical limitations, EPA reports the number exceeding the current MCL, instead 

of the MCLG. 

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Exhibit 4-7. NAWQA Occurrence Data for Alachlor Based on Maximum Sample 

Values 

Exhibit 4-8. Summary of Alachlor Occurrence for Raw Water Samples in USDA 

Agricultural Marketing Service Pesticide Data Program 

Occurrence Result Number of Samples (% total samples) 

Total Samples 1,121 (100%) 

Nondetect 1,118 (99.73%) 

Detected quantity 1 3 (0.27%) 

Exceeds current MCL (0.002 mg/L) 0 (0%) 

Exceeds possible MCLG (0.04 mg/L) 0 (0%) 

Source: USDA (2004, 2005, and 2006) Detection limits range from 7.8 X 10-6 mg/L to 45 X 10-6 mg/L. 

1. Detected quantities range from 16.3 X 10-6 mg/L to 44 X 10-6 mg/L. 

Exhibit 4-9. Summary of Alachlor Occurrence for Finished Water Samples in 

USDA Agricultural Marketing Service Pesticide Data Program 

Occurrence Result Number of Samples (% total samples) 

Total Samples 2,511 (100%) 

Nondetect 2,492 (99.24%) 

Detected quantity 1 19 (0.76%) 

Exceeds current MCL (0.002 mg/L) 0 (0%) 

Exceeds possible MCLG (0.04 mg/L) 0 (0%) 

Source: USDA (2001, 2002, 2003, 2004, 2005, and 2006). Detection limits range from 5 X 10-6 mg/L to 49.5 X 10-6 mg/L. 

1. Detected quantities range from 16.3 X 10-6 mg/L to 145 X 10-6 mg/L. 

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4.4.2 Barium 

Exhibit 4-10 and Exhibit 4-11 provide comparisons of maximum barium concentrations for 

locations in the NAWQA and STORET databases, respectively, with the current MCLG and 

possible MCLG values. Exhibit 4-12 presents a spatial representation of the NAWQA data. 

These data indicate that less than 1% of the total sampling locations for this contaminant have 

maximum concentrations between the current MCLG and the possible MCLG value. Although 

barium occurs in detected quantities at most of the NAWQA sampling locations, less than 0.1% 

of ground water sampling locations and no surface water sampling locations in NAWQA report 

maximum concentrations above the current MCLG. Likewise, the STORET data indicate less 

than 0.5% of detections exceed the current MCLG value. 

Exhibit 4-10. Summary of Barium Occurrence Based on Maximum Sample Values 

for Locations in NAWQA 

Number of Locations (% of locations) 

Occurrence Result Surface Water Ground Water Other Total 

Total locations 417 (100.0%) 4,326 (100.0%) 121 (100.0%) 4,864 (100.0%) 

All samples are nondetects 1 (0.2%) 42 (1.0%) 0 (0.0%) 43 (0.9%) 

At least one detection 416 (99.8%) 4,284 (99.0%) 121 (100%) 4,821 (99.1%) 

Exceeds current MCLG (2.0 

mg/L) 0 (0.0%) 3 (0.07%) 0 (0.0%) 3 (0.06%) 

Exceeds possible MCLG (6.0 

mg/L) 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.0%) 

Source: USGS 2006b (national data from 1992 to 1/1/2008). 

Exhibit 4-11. Summary of Barium Occurrence Based on Maximum Sample Values 

for Locations in STORET 

Occurrence Result Number of Locations (% locations) 

Total locations 16,595 (100.0%) 

All samples are nondetects 2,299 (13.9 %) 

At least one detection 14,296 (86.1%) 

Exceeds current MCLG (2.0 mg/L) 234 (1.4%) 

Exceeds possible MCLG (6.0 mg/L) 163 (1.0%) 

Source: USEPA 2006b (national data 1/1/2002 to 9/20/2006). 

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Exhibit 4-12. NAWQA Occurrence Data for Barium Based on Maximum Sample 

Values 

4.4.3 1,1-Dichloroethylene 

Exhibit 4-13 and Exhibit 4-14 provide comparisons of maximum 1,1-dichloroethylene 

concentrations for locations in the NAWQA and STORET databases, respectively, with the 

current MCLG and possible MCLG values. Exhibit 4-15 presents a spatial representation of the 

NAWQA data. These data indicate that less than 0.1% of NAWQA locations have maximum 

concentrations between the current MCLG and the higher possible MCLG values. STORET 

results indicate higher occurrence frequencies above both the current MCLG and possible 

MCLG values. The STORET results are driven by the 157 sampling locations in Phoenix, 

Arizona, that have a maximum sample above the MCL of 0.007 mg/L. Five of these locations 

also account for those having a maximum sample that exceeds 0.35 mg/L. 

Exhibit 4-13. Summary of 1,1-Dichloroethylene Occurrence Based on Maximum 

Sample Values for Locations in NAWQA 

Number of Locations (% of locations) 

Occurrence Result Surface Water Ground Water Other Total 

Total locations 211 (100.0%) 5,467 (100.0%) 110 (100.0%) 5,788 (100.0%) 

All samples are nondetects 183 (86.7%) 5,346(97.8%) 107 (97.3 %) 5,636 (97.4%) 

At least one detection 28 (13.3%) 121 (2.2%) 3 (2.7 %) 152 (2.6%) 

Exceeds current MCLG (0.007 

mg/L) 1 (0.5%) 0 (0.0%) 0 (0.0%) 1 (0.02%) 

Exceeds possible MCLG (0.35 

mg/L) 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.0%) 

Source: USGS 2006b (national data from 1992 to 1/1/2008). 

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Exhibit 4-14. Summary of 1,1-Dichloroethylene Occurrence Based on Maximum 

Sample Values for Locations in STORET 

Occurrence Result Number of Locations (% locations) 

Total locations 2,448 (100.0%) 

All samples are nondetects 1,498 (61.2%) 

At least one detection 950 (38.8%) 

Exceeds current MCLG (0.007mg/L) 165 (6.7%) 

Exceeds possible MCLG (0.35 mg/L) 5 (0.2%) 

Source: USEPA 2006b (national data from 1/1/2002 to 5/1/2007). 

Note: 97.14% of reported detection limits for the nondetect samples were at or below the current MCLG of 0.007 mg/L and 

99.81% were at or below the possible MCLG of 0.35 mg/L. 

Exhibit 4-15. Plot of 1-1-Dichloroethylene NAWQA Occurrence Data 

4.4.4 Diquat 

Water quality results for diquat were not available in either NAWQA or STORET. To 

characterize potential source water occurrence, EPA obtained pesticide application estimates 

because diquat’s primary uses are as an algaecide, defoliant, desiccant, and herbicide (USEPA, 

1995a). There are two sources of national pesticide use: 

• Pesticide Use Database developed by the National Center for Food and Agricultural 

Policy (NCFAP) in 1997 and CropLife Foundation in 2002 

• Pesticide Use Maps developed by the USGS for the Pesticide National Synthesis Project. 

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NCFAP estimates indicate overall cropland application of almost 270,000 pounds in 1997, 

primarily on potato and alfalfa crops (NCFAP, 2000). The NCFAP based these estimates on its 

own estimates of State-level pesticide diquat application patterns for the period 1994-1998 and 

State-level crop acreage for 1997 from the USDA Census of Agriculture. The diquat application 

estimates – annual pounds of active ingredient applied per acre per crop per year – are based on a 

wide variety of agricultural pesticide survey sources. Thus, the diquat use estimates reflect 

several limitations: they do not include noncropland applications, the data sources vary in 

quality, and state-level pesticide use data gaps are filled using data for nearby states. 

The CropLife Foundation updated NCFAP’s analysis to use crop acreage estimates from the 

2002 Census of Agriculture and State-level diquat usage patterns based on survey data collected 

from 1999 through 2004. The annual diquat use estimate is 217,649 pounds (Gianessi and 

Reigner, 2006). Because the CropLife Foundation study uses the same method as the NCFAP to 

derive State-level diquat use estimates, the national estimate has similar limitations. 

More detailed pesticide application data from California indicates the potential for crop usage 

estimates to understate total diquat use. The State maintains a comprehensive Pesticide Use 

Reporting (PUR) database. Exhibit 4-16 provides a summary of detailed pesticide application 

estimates for 2005, which indicate that total diquat use is three times higher than reported crop 

use. Major non-crop uses include right-of-way (24,521 pounds active ingrediant or lb a.i.) and 

landscape (15,689 lb a.i.) applications. Both of these uses exceeded the two top crop uses: alfalfa 

for forage (11,138 lb a.i.) and potatoes (5,104 lb a.i.). 

Exhibit 4-16. Crop and Noncrop Diquat Application for California in 2005 

Use1 Pounds Percent of Total 

Crop Application 17,375 25% 

Non Crop Application 51,150 75% 

Total Application 68,525 100% 

Source: California Pesticide Use Database available at http://pesticideinfo.org/Detail_ChemUse.jsp?Rec_Id=PC33217#working

1. Crop total comprises the following use categories: alfalfa for forage, potatoes, clover for forage, wine grapes, cabbage, and 

almonds. Non-crop total includes all other use categories. 

Of the pesticides addressed in this document, diquat has the lowest national estimate for use on 

crops. Exhibit 4-17 provides national crop use estimates for diquat and the other pesticides 

included in this report that were developed by Gianessi and Reigner (2006) and provided on-line 

in an Excel file. These data suggest that even if the actual national use of diquat is several times 

greater than the crop use estimate indicates, diquat would have one of the lowest annual usage 

rates in terms of pounds applied. 

Exhibit 4-17. Estimates of National Annual Pesticide Use for Crops 

Pesticide Annual Pounds Type 

Alachlor 6,269,543 Herbicide 

Diquat 217,649 Herbicide 

Glyphosate 102,325,419 Herbicide 

Lindane 1,698,309 Insecticide 

Picloram 1,915,653 Herbicide 

Source: Gianessi and Reigner (2006) and on-line Excel file at http://www.croplifefoundation.org/cpri_npud2002.htm

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The USGS estimated county-level pesticide usage for 2002 based on crop acreage estimates in 

the 2002 Census of Agriculture and state-level diquat application rates for the period 1999-2004 

developed by the CropLife Foundation (USGS, no date), which implemented the NCFAP 

method for estimating pesticide usage (Gianessi and Reigner, 2006) and, therefore, has similar 

limitations. The USGS estimates total diquat application to crops of approximately 200,000 

pounds per year, with potatoes accounting for almost 90% of these applications (USGS, no date). 

Diquat use on crops occurred primarily in regions of New England, the Great Lakes states, North 

Dakota, the Pacific Northwest, California, and Florida. 

USEPA (1995a) notes that although diquat is persistent (i.e., it does not hydrolyze and is 

resistant to degradation), it becomes immobile when it adsorbs to soil particles and, therefore, is 

not expected to contaminate ground water. Furthermore, diquat dissipates quickly from surface 

water because it adsorbs to soil sediments, vegetation, and organic matter; the estimated half-life 

in surface water is 1 to 2 days, based on a study of two ponds in Florida (USEPA, 1995). These 

factors indicate the possibility of low occurrence in drinking water sources. 

4.4.5 Glyphosate 

Exhibit 4-18 and Exhibit 4-19 provide comparisons of maximum glyphosate concentrations for 

locations in the NAWQA and STORET databases, respectively, with the current MCLG and 

possible MCLG values. 

Exhibit 4-20 presents a spatial representation of the NAWQA data. Although these data are 

sparse, they indicate that none of the sampling locations for this contaminant have maximum 

concentrations between the current MCLG and the possible MCLG values. 

Exhibit 4-18. Summary of Glyphosate Occurrence Based on Maximum Sample 

Values for Locations in NAWQA 

Number of Locations (% of locations) 

Occurrence Result Surface Water Ground Water Other Total 

Total locations 4 (100.0%) 37 (100.0%) 0 (100.0%) 41 (100.0%) 

All samples are nondetects 0 (0.0%) 37 (100%) 0 (0.0%) 37 (90.2%) 

At least one detection 4 (100%)2 0 (0.0%) 0 (0.0%) 4 (9.8%) 

Exceeds current MCLG (0.7 

mg/L) 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.0%) 

Exceeds possible MCLG (14.0 

mg/L) 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.0%) 

Source: USGS 2006b (national data from 1992 to 9/30/2005). 

Exhibit 4-19. Summary of Glyphosate Occurrence Based on Maximum Sample 

Values for Locations in STORET 

Occurrence Result Number of Locations (% locations) 

Total locations 241 (100.0%) 

All samples are nondetects 180 (74.7 %) 

At least one detection 61 (25.3 %) 

Exceeds current MCLG (0.7 mg/L) 0 (0.0%) 

Exceeds possible MCLG (14.0 mg/L) 0 (0.0%) 

Source: USEPA 2006b (national data from 1/1/2002 to 5/1/2007). 

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Exhibit 4-20. Plot of Glyphosate NAWQA Occurrence Data 

4.4.6 Lindane 

Exhibit 4-21 and Exhibit 4-22 provide comparisons of maximum lindane concentrations for 

locations in the NAWQA and STORET databases, respectively, with the current MCLG and 

possible MCLG values. Exhibit 4-23 presents a spatial representation of the NAWQA data. 

These data indicate that less than 0.1% of NAWQA locations and 0.3% of the STORET 

locations have maximum concentrations between the current MCLG and the higher possible 

MCLG values. Exhibit 4-24 and Exhibit 4-25 show lindane raw water concentrations and 

finished water concentrations, respectively, from the PDP database. No samples contained 

lindane above the current MCLG or possible MCLG values. 

Exhibit 4-21. Summary of Lindane Occurrence Based on Maximum Sample Values 

for Locations in NAWQA 

Number of Locations (% of locations) 

Occurrence Result Surface Water Ground Water Other Total 

Total locations 1,846 (100.0%) 6,127 (100.0%) 222 (100.0%) 8,195 (100.0%) 

All samples are nondetects 1,718 (93.1%) 6,120 (99.9%) 220 (99.1%) 8,058 (98.3%) 

At least one detection 128 (6.9%) 7 (0.1%) 2 (0.9%) 137 (1.7%) 

Exceeds current MCLG 

(0.0002 mg/L) 1 (0.05%) 0 (0.0%) 0 (0.0%) 1 (0.01%) 

Exceeds possible MCLG 

(0.001 mg/L) 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.00%) 

Exceeds possible MCLG (0.03 

mg/L) 0 (0.0 %) 0 (0.0%) 0 (0.0%) 0 (0.0%) 

Source: USGS 2006b (national data from 1992 to 9/30/2005). 

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Exhibit 4-22. Summary of Lindane Occurrence Based on Maximum Sample Values 

for Locations in STORET 

Occurrence Result Number of Locations (% locations) 

Total locations 2,691 (100.0%) 

All samples are nondetects 2,017 (75%) 

At least one detection 674 (25%) 

Exceeds current MCLG (0.0002 mg/L) 7 (0.26%) 

Exceeds possible MCLG (0.001 mg/L) 1 (0.04%) 

Exceeds possible MCLG (0.03 mg/L) 1 (0.04%) 

Source: USEPA 2006b (national data from 1/1/2002 to 5/1/2007). 

Exhibit 4-23. Plot of Lindane NAWQA Occurrence Data 

Exhibit 4-24. Summary of Lindane Occurrence for Raw Water Samples in USDA 

Agricultural Marketing Service Pesticide Data Program 

Occurrence Result Number of Samples (% total samples) 

Total Samples 1,116 (100%) 

Nondetect 1,116 (100%) 

Detected quantity1 0 (0%) 

Exceeds current MCL (0.0002 mg/L) 0 (0%) 

Exceeds possible MCLG (0.001 mg/L) 0 (0%) 

Exceeds possible MCLG (0.03 mg/L) 0 (0%) 

Source: USDA (2004, 2005, 2006). Detection limits range from 10 X 10-6 mg/L to 66 X 10-6 mg/L. 

1. There are no detected quantities. 

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Exhibit 4-25. Summary of Lindane Occurrence for Finished Water Samples in 

USDA Agricultural Marketing Service Pesticide Data Program 

Occurrence Result Number of Samples (% total samples) 

Total Samples 2,181 (100%) 

Nondetect 2,181 (100%) 

Detected quantity 1 0 (0%) 

Exceeds current MCL (0.0002 mg/L) 0 (0%) 

Exceeds possible MCLG (0.001 mg/L) 0 (0%) 

Exceeds possible MCLG (0.03 mg/L) 0 (0%) 

Source: USDA (2001, 2002, 2003, 2004, 2005, 2006). Detection limits range from 10 X 10-6 mg/L to 66 X 10-6 mg/L. 

1. There are no detected quantities. 

4.4.7 Picloram 

Exhibit 4-26 and Exhibit 4-27 provide comparisons of maximum picloram concentrations for 

locations in the NAWQA and STORET databases, respectively, with the current MCLG and 

possible MCLG values. Exhibit 4-28 presents a spatial representation of the NAWQA data. 

Exhibit 4-29 and Exhibit 4-30 show picloram raw water concentrations and finished water 

concentrations, respectively, from the PDP database. Data from all three sources indicate no 

occurrence of this contaminant above the current MCLG and the higher possible MCLG values. 

Exhibit 4-26. Summary of Picloram Occurrence Based on Maximum Sample 

Values for Locations in NAWQA 

Number of Locations (% of locations) 

Occurrence Result Surface Water Ground Water Other Total 

Total locations 971 (100.0%) 4,603 (100.0%) 198 (100.0%) 5,772 (100.0%) 

All samples are nondetects 947 (97.5%) 4,588 (99.7%) 198 (100.0%) 5,733 (99.3%) 

At least one detection 24 (2.5%) 15 (0.3%) 0 (0.0%) 39 (0.7%) 

Exceeds current MCLG (0.5 

mg/L) 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.0%) 

Exceeds possible MCLG (1.0 

mg/L) 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.0%) 

Source: USGS 2006b (national data from 1992 to 9/30/2005). 

Exhibit 4-27. Summary of Picloram Occurrence Based on Maximum Sample 

Values for Locations in STORET 

Occurrence Result Number of Locations (% locations) 

Total locations 870 (100%) 

All samples are nondetects 745 (85.6%) 

At least one detection 125 (14.4%) 

Exceeds current MCLG (0.5 mg/L) 0 (0%) 

Exceeds possible MCLG (1.0 mg/L) 0 (0%) 

Source: USEPA 2006b (national data from 1/1/2002 to 5/1/2007). 

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Exhibit 4-28. Plot of Picloram NAWQA Occurrence Data 

Exhibit 4-29. Summary of Picloram Occurrence for Raw Water Samples in USDA 

Agricultural Marketing Service Pesticide Data Program 

Occurrence Result Number of Samples (% total samples) 

Total Samples 1,122 (100%) 

Nondetect 1,120 (99.82%) 

Detected quantity 1 2 (0.18%) 

Exceeds current MCL (0.5 mg/L) 0 (0%) 

Exceeds possible MCLG (1.0 mg/L) 0 (0%) 

Source: USDA (2004, 2005, 2006). Detection limits range from 22 X 10-6 mg/L to 4,407 X 10-6 mg/L. 

1. Detected quantity is 37 X 10-6 mg/L. 

Exhibit 4-30. Summary of Picloram Occurrence for Finished Water Samples in 

USDA Agricultural Marketing Service Pesticide Data Program 

Occurrence Result Number of Samples (% total samples) 

Total Samples 1,876 (100%) 

Nondetect 1,875 (99/95%) 

Detected quantity 1 1 (0.05%) 

Exceeds current MCL (0.5 mg/L) 0 (0%) 

Exceeds possible MCLG (1.0 mg/L) 0 (0%) 

Source: USDA (2001, 2003, 2004, 2005, 2006). Detection limits range from 22 X 10-6 mg/L to 5,000 X 10-6 mg/L. 

1. Detected quantity is 37 X 10-6 mg/L. 

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4.4.8 1,1,1-Trichloroethane 

Exhibit 4-31 and Exhibit 4-32 provide comparisons of maximum 1,1,1-trichloroethane 

concentrations for locations in the NAWQA and STORET databases, respectively, with the 

current MCLG and possible MCLG values. Exhibit 4-33 presents a spatial representation of the 

NAWQA data. The NAWQA data indicate that none of the sampling locations for this 

contaminant have maximum concentrations between the current MCLG and the possible MCLG 

values. Fewer than 0.3% of the STORET locations have maximum concentrations between the 

current MCLG and the possible MCLG. 

Exhibit 4-31. Summary of 1,1,1-Trichloroethane Occurrence Based on Maximum 

Sample Values for Locations in NAWQA 

Number of Locations (% of locations) 

Occurrence Result Surface Water Ground Water Other Total 

Total locations 210 (100.0%) 5,468 (100.0%) 110 (100.0%) 5,788 (100.0%) 

All samples are nondetects 146 (69.5%) 5,043 (92.2%) 101 (91.8%) 5,290 (91.4%) 

At least one detection 64 (30.5%) 425 (7.8%) 9 (8.2%) 498 (8.6%) 

Exceeds current MCLG (0.2 

mg/L) 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.0%) 

Exceeds possible MCLG (14 

mg/L) 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.0%) 

Source: USGS 2006b (national data from 1992 to 1/1/2008). 

Exhibit 4-32. Summary of 1,1,1-Trichloroethane Occurrence Based on Maximum 

Sample Values for Locations in STORET 

Occurrence Result Number of Locations (% locations) 

Total locations 3,429 (100.0%) 

All samples are nondetects 2,304 (67.2%) 

At least one detection 1,125 (32.8%) 

Exceeds current MCLG (0.2 mg/L) 5 (0.1%) 

Exceeds possible MCLG (14 mg/L) 0 (0.0%) 

Source: USEPA 2006b (national data from 1/1/2002 to 1/1/2008). 

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Exhibit 4-33. Plot of 1,1,1-Trichloroethane NAWQA Occurrence Data 

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5. Conclusions 

In this report, EPA addressed contaminants that the Six-Year Review 2 identified as having 

possible MCLG increases based on new health effects information. A possible MCLG increase 

and accompanying MCL increase raises the possibility of cost savings among systems treating 

for the contaminant. The potential for cost savings from possible MCL increases is systemspecific and depends on various factors including the magnitude of the MCL increase, the 

concentration of a contaminant in a system’s source water, the specific treatment technology in 

use, and the extent to which co-occurring contaminants control the operation of a specific 

technology. Exhibit 5-1 and Exhibit 5-2 present a summary of this information. 

The new health effects information results in a wide range of possible MCL increases (see 

Exhibit 5-1). The lowest relative increase is 2 times the current MCL for both diquat and 

picloram. The highest relative increase is 150 times the current MCL for the upper bound 

possible MCLG for lindane. 

EPA’s analysis of the potential for cost savings was constrained to readily available data. The 

data available to characterize contaminant occurrence was especially limited because there is no 

comprehensive dataset that characterizes source water quality for drinking water systems. Water 

quality data from the NAWQA Program, STORET data system, and PDP provide useful insights 

into potential contaminant occurrence in source water, even though they are not based on random 

or representative sampling events and, therefore, cannot be used directly to derive quantitative 

estimates of national occurrence in drinking water sources. 

Nevertheless, the summary of the available data in Exhibit 5-1 shows relatively infrequent 

contaminant occurrence in potential source waters at the levels of interest. The NAWQA data, 

which provide the most extensive coverage of potential source waters, indicate that only alachlor 

is found in concentrations that exceed the possible MCLG. In particular, two contaminants – 

glyphosate and picloram – are not found at levels above either the current MCLG or the possible 

MCLG in any of the three datasets. Diquat, which is not included in any of these datasets, has the 

potential to occur infrequently in source water given its less frequent use compared to the other 

pesticides in the table (alachlor, glyphosate, lindane, and picloram) and its tendency to dissipate 

quickly from surface water and be immobile in soils. 

Without national estimates of contaminant occurrence in drinking water sources, EPA cannot 

determine how many systems currently treat for the contaminants listed in Exhibit 5-2. EPA also 

does not have national data regarding the treatment technologies being utilized to control these 

contaminants. As Exhibit 5-2 shows, some BATs have higher potential for operational cost 

savings; however, co-occurrence considerations for all of the BATs could diminish the 

potentially affected system’s ability to alter treatment for possible higher MCLGs. 

Despite the possibility for changes in MCLG values that range from 2 to 150 times higher than 

current MCLs, the available occurrence data for potential drinking water sources indicate 

relatively low contaminant occurrence in the concentration ranges of interest. As a consequence, 

EPA cannot conclude that there is a meaningful opportunity for system cost savings. 

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Exhibit 5-1. Summary of Potential Cost Savings Factors – Occurrence 

Occurrence Summary (percent of sample locations) 

Exceed Current MCLG or 

MCL 

Exceed Current MCLG or 

MCL 

Contaminant 

 Magnitude 

of 

Increase1 NAWQA STORET PDP NAWQA STORET PDP 

Alachlor 20 0.38% 1.8% 0.0% 0.01% 0.0% 0.0% 

Barium 3 0.1% 1.4% -- 0.0% 1.0% -- 

Diquat 2 -- -- -- -- -- -- 

Glyphosate 14 0.0% 0.0% -- 0.0% 0.0% -- 

1,1-Dichloroethylene 50 0.02% 6.7% -- 0.0% 0.2% -- 

Lindane 5 to 150 0.01% 0.26% 0.0% 0.0% 0.04% 0.0% 

Picloram 2 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 

1,1,1-Trichloroethane 50 0.0% 0.1% -- 0.0% 0.0% -- 

--: No data were available. 

1. Number indicates times higher the possible MCLG is than the current MCL. For example the possible MCLG for 

alachlor (0.04 mg/L) is 20 times higher than the current MCL (0.002 mg/L). 

Exhibit 5-2. Summary of Potential Cost Savings Factors – Treatment 

Contaminant Best Available Technology 

Cost Savings 

Potential of 

Technology 

Presence of 

Co-occurring 

Contaminants 

Could Limit 

Savings 

Alachlor Granular Activated Carbon High Yes 

Ion Exchange High Yes 

Lime Softening Moderate Yes 

Reverse Osmosis Low Yes Barium 

Electrodialysis Low Yes 

Diquat Granular Activated Carbon High Yes 

Glyphosate Oxidation (Chlorine or Ozone) Low Yes 

Packed Tower Aeration Low Yes 1,1-Dichloroethylene Granular Activated Carbon High Yes 

Lindane Granular Activated Carbon High Yes 

Picloram Granular Activated Carbon High Yes 

Packed Tower Aeration Low Yes 1,1,1-Trichloroethane Granular Activated Carbon High Yes 

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6. References 

ATSDR (Agency for Toxic Substances & Disease Registry). 2007. Toxicological Profile for 

Barium. Available online at: http://www.atsdr.cdc.gov/toxprofiles/tp24.html. August. 

ATSDR (Agency for Toxic Substances & Disease Registry). 2006. Toxicological Profile for 

1,1,1-Trichloroethane. Available online at: http://www.atsdr.cdc.gov/toxprofiles/tp70.html. July. 

ATSDR (Agency for Toxic Substances & Disease Registry). 2005. Toxicological Profile for 

Barium. Available online at: http://www.atsdr.cdc.gov/toxprofiles/tp24.html. August. 

Gianessi, L. and N. Reigner. 2006. Pesticide Use in U.S. Crop Production: 2002 With 

Comparison to 1992 and 1997 – Fungicides & Herbicides. Washington, D.C.: CropLife 

Foundation. 

Gilliom, R.J., J.E. Barbash, C. G. Crawford, P.A. Hamilton, J.D. Martin, N. Nakagaki, L.H. 

Nowell, J.C. Scott, P.E. Stackelberg, G.P. Thelin, and D.M. Wolock. 2006. The Quality of Our 

Nation’s Waters—Pesticides in the Nation’s Streams and Ground Water, 1992–2001: U.S. 

Geological Survey Circular 1291. Reston, VA: U.S. Department of the Interior, U.S. Geological 

Survey. 

NCFAP (National Center for Food and Agricultural Policy). 2000. Pesticide Use in U.S. Crop 

Production: 1997. National Summary Report. Washington, D.C.: NCFAP. 

USEPA. 2009a. Analysis of Occurrence Data from the Second Six-Year Review of Existing 

National Primary Drinking Water Regulations. EPA 815-B-09-006. 

USEPA. 2009b. Analytical Feasibility Support Document for the Second Six-Year Review of 

Existing National Primary Drinking Water Regulations. EPA 815-B-09-003. 

USEPA. 2009c. Development of Estimated Quantitation Levels for the Second Six-Year Review 

of National Primary Drinking Water Regulations. EPA 815-B-09-005. 

USEPA. 2009d. EPA Protocol for the Second Review of Existing National Primary Drinking 

Water Regulations (Updated). EPA 815-B-09-002. 

USEPA. 2009e. Six-Year Review 2 – Health Effects Assessment – Summary Report. EPA 822-

R-09-006. 

USEPA. 2009f. Water Treatment Technology Feasibility Support Document for Chemical 

Contaminants for the Second Six-Year Review of National Primary Drinking Water Regulations. 

EPA 815-B-09-007. 

USEPA. 2009g. Consideration of Other Regulatory Revisions in Support of the Second Six-Year 

Review of the National Primary Drinking Water Regulations. EPA 815-B-09-008. 

USEPA. 2008. TRI Explorer – Geographic Report. Online at: 

http://www.epa.gov/triexplorer/geography.htm?year=2006, accessed March 2008. 

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for the Second Six-Year Review of NPDWRs 

USEPA. 2007. Toxicological Review of 1,1,1-Trichloroethane. Available online at: 

http://www.epa.gov/ncea/iris/toxreviews/0197-tr.pdf. August. 

USEPA. 2006a. Drinking Water Contaminants Consumer Fact Sheets. Accessed online at: 

http://www.epa.gov/OGWDW/hfacts.html. 

USEPA. 2006b. STORET Database. Online at http://www.epa.gov/storet/, accessed 9/20/06. 

USEPA. 2006c. Addendum to the July 2002 Lindane Reregistration Eligibility Decision (RED). 

Available online at: 

http://www.epa.gov/pesticides/reregistration/REDs/lindane_red_addendum.pdf. July. 

USEPA. 2003. EPA Protocol for Review of Existing National Primary Drinking Water 

Regulations. EPA 815-R-03-002. June. 

USEPA. 2002a. Report of the Food Quality Protection Act (FQPA) Tolerance Reassessment 

Progress and Risk Management Decision (TRED): Diquat Dibromide. Washington, D.C.: 

USEPA, Prevention, Pesticides and Toxic Substances. 

USEPA. 2002b. Toxicological Review of 1,1-Dichloroethylene. 2002. Available online at: 

http://www.epa.gov/NCEA/iris/toxreviews/0039-tr.pdf. June. 

USEPA. 1998. Small System compliance Technology List for the Non-Microbial contaminants 

Regulated Before 1996. EPA Report 815-R-98-002. Washington, D.C.: USEPA Office of Water. 

USEPA. 1995a. Reregistration Eligibility Decision (RED) Diquat Dibromide. EPA 738-R-05-

016. Available online at: http://www.epa.gov/oppsrrd1/REDs/0288.pdf . July. 

USEPA. 1995b. Reregistration Eligibility Decision (RED) Picloram. Available online at: 

http://www.epa.gov/oppsrrd1/REDs/0096.pdf. August. 

USEPA. 1993. Reregistration Eligibility Decision (RED) Glyphosate. Available online at: 

http://www.epa.gov/oppsrrd1/REDs/old_reds/glyphosate.pdf. September. 

U.S. Environmental Protection Agency Office of Pesticide Programs (USEPA OPP). 2006. 

Cumulative Risk from Chloroacetanilide Pesticides. Available online at: 

http://www.epa.gov/oppsrrd1/cumulative/chloro_cumulative_risk.pdf. March. 

USGS. 2006a. About NAWQA Study Units. December. Accessed online at: 

http://water.usgs.gov/nawqa/studies/study_units.html

USGS. 2006b. National Water Quality Assessment (NAWQA) Program. Online at 

http://infotrek.er.usgs.gov, accessed 8/28/06. 

USGS. No date. Pesticide National Synthesis Project: 2002 Pesticide Use Map – Diquat 

(http://water.usgs.gov/nawqa/pnsp/usage/maps/show_map.php?year=02&map=m1950, accessed 

March 2008). 

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