United States Office of Ground Water EPA/816-R-99-014o

Environmental and Drinking Water (4601) September 1999

Protection Agency 

The Class V Underground Injection

Control Study

Volume 15

Experimental Technology Wells
September 30, 1999

Table of Contents

Page

1. Summary ............................................................... 1

2. Introduction ............................................................. 2

3. Experimental Tracer Study Wells ............................................. 5

3.1 Prevalence of Wells ................................................. 6

3.2 Injectate Characteristics and Injection Practices ............................ 8

3.2.1 Injectate Characteristics ........................................ 8

3.2.2 Well Characteristics and Operating Practices ........................ 9

3.3 Potential and Documented Damage to USDWs ........................... 20

3.3.1 Injectate Constituent Properties ................................. 21

3.3.2 Observed Impacts ........................................... 21

3.4 Best Management Practices .......................................... 22

3.5 Current Regulatory Requirements ...................................... 23

3.5.1 Federal Programs ............................................ 23

3.5.2 State and Local Programs ..................................... 25

4. Experimental ATES System Wells ............................................ 26

4.1 Prevalence of Wells ................................................ 26

4.2 Injectate Characteristics and Injection Practices ........................... 27

4.2.1 Injectate Characteristics ....................................... 27

4.2.2 Well Characteristics and Operating Practices ....................... 27

4.3 Potential and Documented Damage to USDWs ........................... 33

4.3.1 Injectate Constituent Properties ................................. 33

4.3.2 Observed Impacts ........................................... 34

4.4 Best Management Practices .......................................... 35

4.5 Current Regulatory Requirements ...................................... 37

4.5.1 Federal Programs ............................................ 37

4.5.2 State and Local Programs ..................................... 37

Attachment A: State and Local Program Descriptions .................................. 38

References ................................................................... 48
September 30, 1999 1

EXPERIMENTAL TECHNOLOGY WELLS

The U.S. Environmental Protection Agency (USEPA) conducted a study of Class V

underground injection wells to develop background information the Agency can use to evaluate the risk

that these wells pose to underground sources of drinking water (USDWs) and to determine whether

additional federal regulation is warranted. The final report for this study, which is called the Class V

Underground Injection Control (UIC) Study, consists of 23 volumes and five supporting appendices. 

Volume 1 provides an overview of the study methods, the USEPA UIC Program, and general findings. 

Volumes 2 through 23 present information summaries for each of the 23 categories of wells that were

studied (Volume 21 covers 2 well categories). This volume, which is Volume 15, covers Class V

experimental technology wells.

1. SUMMARY

Experimental technology injection wells have been reported in seven states and are used to test

new or unproven technologies. Experimental “tracer study” wells, which inject chemical tracers for the

purpose of studying ground water and hydrogeologic parameters, comprise the vast majority of wells

classified as experimental wells for the purpose of this study. Experimental technologies also have been

recently applied in Class V wells associated with Aquifer Thermal Energy Storage (ATES) systems,

which store thermal energy by injecting heated and/or cooled water into an aquifer. The existence of

experimental wells varies widely from state to state because, in some instances, different definitions of

“experimental well” are used by different states. The definitions used by the states may not necessarily

correspond to the USEPA definition of experimental well that was included the Class V study

questionnaire.

Experimental Tracer Study Wells

Many different types of substances are injected into experimental tracer study wells. Examples

of these substances include organic dyes, inert gases, short half-life radionuclides, rare earth metals, and

inorganic or organic compounds. Only one experimental well was reported for which injectate did not

meet the primary maximum contaminant levels (MCLs), secondary MCLs, and health advisory levels

(HALs), this being the tracer study well at the Naturita, Colorado site, where contaminated native

ground water was used as a tracer carrier. The injectate for this tracer well exceeded MCLs for

sulfates and chloride, and contained arsenic and molybdenum at levels greater than HALs.

The injection zone characteristics for experimental technology injection wells vary widely

depending upon the purpose of the well. Wells used for tracer studies may inject into contaminated

aquifers, sometimes including aquifers that serve as drinking water supplies.

No contamination incidents were reported for experimental tracer study wells. In addition,

experimental tracer study wells are not vulnerable to illicit discharges because injectate quality is
September 30, 1999 2

controlled by the conditions of the experiment being conducted. Tracer study wells generally release

tracers in small quantities. 

According to the state and USEPA Regional survey conducted for this study, six states have a

total of 396 documented experimental tracer study wells: South Carolina, Colorado, Nevada, Idaho,

Texas, and Washington. More than 97 percent of the documented tracer study wells exist in South

Carolina (207 wells or 52%) and Nevada (179 wells or 45%). Most of the tracer study wells in South

Carolina and Nevada are being operated at U.S. Department of Energy facilities. The States of

Massachusetts, Florida, and Mississippi indicated that they may have experimental wells, but that they

could not provide an estimate of how many actually exist. The Texas and Washington UIC programs

identified five and two experimental wells operating in their states, respectively, but did not provide any

information concerning the types of wells (they may in fact be something other than tracer study wells). 

The Illinois UIC program reported two experimental wells that are most likely no longer operating. 

Survey responses from the other states indicated that they had no experimental wells.

The experimental technology wells in South Carolina, Nevada, and Washington are individually

permitted by the state. Idaho authorizes shallow injection wells (<18 feet deep) by rule, provided that

inventory information is supplied and use of the well does not result in contamination of a USDW. 

Deep injection wells (>18 feet deep) in Idaho must obtain an individual permit. Experimental wells in

Texas and Colorado are permitted by rule, but the wells in Colorado must have a construction permit.

ATES System Wells

Heated or cooled process water, which may originate from native ground water, surface water,

or potable water, are injected into aquifers for ATES systems. Experimental ATES wells inject water

into the same aquifer from which it was withdrawn. While no contamination incidents were reported for

ATES system wells, several reports mentioned that the concentration of constituents in ground water

receiving fluids from some ATES wells were higher than background levels. Experimental ATES

system wells are not vulnerable to illicit discharges because injectate quality is controlled by the

conditions of the process operation. In particular, experimental ATES systems inject treated water for

which injectate quality must be controlled. No UIC programs reported any operating ATES system

wells in the survey responses. ATES systems, however, were recently operated in Minnesota and

New York, and are in operation in several European countries.

2. INTRODUCTION

Under the existing UIC Program regulations in 40 CFR 146.5(e), Class V injection wells

include “injection wells used in experimental technologies.” Experimental technology is defined in 40

CFR 146.3 as “a technology which has not been proven feasible under the conditions in which it is

being tested.” As part of this study, USEPA conducted a survey of state and USEPA Regional staff

who administer Class V UIC programs in order to collect information on experimental technology

wells. Unfortunately, the UIC program personnel who identified “experimental wells” in their survey

responses did not use the same criteria to classify these types of wells, and in some cases, did not apply
September 30, 1999 3

the definition of experimental well that appeared on the survey questionnaire itself. The questionnaire

defined “experimental well” as follows:

DEFINITION: Experimental wells are used to test new technologies. Wells will not be

classified as experimental if the technology can be considered under an established well

subclass. For example, a well used for bioremediation will be classified as an aquifer

remediation well.

Despite this intended definition, the survey respondents classified many different types of wells

as experimental. For example, certain state UIC programs included injection wells used for dye tracer

studies in the experimental well category while other programs did not identify tracer study wells as

experimental wells. Tracer study wells are used to conduct experiments (e.g., characterization of

aquifers); however, the tracer study well technology itself is generally not considered an experimental

technology, and would therefore not fit the USEPA definition of an experimental well. Other survey

respondents included “experimental” solution mining, aquifer remediation, food processing, or aquifer

storage and recovery injection wells in the experimental well category. However, these wells are not

true experimental wells under the USEPA experimental well definition, either because they are not

intended to test new injection technologies or because they fit within another established well subclass. 

For the purposes of this volume, wells that were identified by UIC programs as “experimental wells”

were recategorized if another Class V sub-category appeared to be more appropriate. In other words,

wells that USEPA believes are better classified under one of the other Class V well types -- even if

considered experimental by the survey respondents -- are not discussed in this volume, but are

discussed in the volume for the appropriate well type.

To be more specific, the following sections identify the different kinds of wells classified as

experimental by the survey respondents and describe where and how they are covered the Class V

Study.

Tracer Study Wells

Some UIC Programs identified tracer study wells as experimental wells since these wells

injected ground water tracers (also called tracer tests). Other programs, however, did not identify

these wells as experimental wells. A ground water tracer is “matter or energy carried by ground water

which will give information concerning the direction of movement and/or velocity of the water and

potential contaminants which might be transported by the water.... Tracers can also help with the

determination of hydraulic conductivity, porosity, dispersivity, chemical distribution coefficients, and

other hydrogeologic parameters” (Davis, et. al., 1986 as cited in Holmbeck-Pelham, 1998). While

tracers may exist in the subsurface due to natural or anthropogenic reasons, in the context of this

discussion the only tracers that are relevant are those deliberately introduced through injection wells.

Tracer study wells may not be considered experimental wells under the USEPA definition, as

these wells are not intended to test new injection technologies. However, tracer study wells do not fit
September 30, 1999 4

neatly into any other well category discussed in this report. Therefore, tracer study wells are discussed

in Section 3 of this volume. 

Aquifer Thermal Energy Storage Wells

An aquifer thermal energy storage (ATES) system stores thermal energy by injecting heated

and/or cooled water into an aquifer. This energy can then be used at a later time. ATES system

injectate (whether heated or cooled) generally is returned to the same aquifer from which it was

previously withdrawn; however, in some cases, the injectate may have come from a different aquifer or

from surface water. The heated or cooled water stored in the aquifer can be reused (for heating or

cooling) by pumping the water to the surface. 

Although no active ATES systems were identified in the survey, experimental ATES systems

were recently operated in Minnesota and New York (Marseille and Wicke, 1992; Hoyer, et. al.,

1994). ATES system wells are considered experimental injection wells because they are designed to

test new injection technologies. These systems are discussed in Section 4 of this volume.

Solution Mining Wells

The Arizona and Colorado UIC programs identified injection wells as experimental wells since

these wells tested innovative solution mining technologies. Solution mining involves injecting a fluid

(e.g., sulfuric acid or sodium bicarbonate) into an underground mineral formation through an injection

well, and then extracting the mineral-laden fluid through a recovery well for further processing to

recover the mineral of interest. In the past, solution mining wells operated for experimental purposes

have been rule authorized as Class V injection wells, while solution mining wells operated for

commercial purposes may be permitted as Class III injection wells.

Although these wells have been handled this way in the past, USEPA now believes such wells

are more appropriately classified as Class III solution mining wells. In fact, the only remaining solution

mining well that was initially regulated as a Class V experimental well has been, or is in the process of

being, permitted as a Class III well. In the future, all such wells will also be permitted as Class III

wells. Therefore, these wells are not considered in this Class V Study. Volume 12 covers other

solution mining wells that qualify as Class V wells.

Experimental Aquifer Remediation Injection Wells

Several UIC programs identified innovative aquifer remediation technologies as experimental

wells. For example, the survey respondents identified the following experimental aquifer remediation

technologies:

• Chlorine for remediation of aquifer bacterial contamination;

• Ethanol for remediation of aquifer nitrate contamination; 

• Calcium polysulfide for remediation of aquifer hexavalent chromium contamination;
September 30, 1999 5

• Ground water to prevent migration of contaminants in aquifers; and

• Gas-phase or aqueous-phase nutrients for studies of experimental ground water in situ

bioremediation systems.

For this study, aquifer remediation wells identified as “experimental” by survey respondents are

not considered experimental because they do not test new injection technologies. Instead, they are

covered along with other aquifer remediation wells in Volume 16 of this report.

Aquifer Storage and Recovery Injection Wells

The Tennessee UIC Program identified one injection well as an experimental well. This well is

used by a municipal water company for drinking water storage. Aquifer storage and recovery wells are

used to emplace and then retrieve drinking water from an aquifer. Typically, ground water (or surface

water) is treated to drinking water standards and is injected back into an aquifer. The treated water is

then retrieved during times of high water usage for distribution to customers.

The Tennessee UIC Program indicated that this injection well was permitted as an experimental

well because, although aquifer storage and retrieval system technology has been demonstrated in other

states, this is the first such system to be constructed in Tennessee. However, USEPA believes this well

is the same as other such wells throughout the nation, and therefore covers it along with other aquifer

storage and recovery wells in Volume 21 of this study.

Food Processing Wells

The West Virginia UIC Program reported that one experimental injection well is operating

within the state. This well, which is located at a goat cheese factory, consists of a drain field that

contains wood chips. The state reported that this well was classified as an experimental well because it

did not fit into any other state program category. However, USEPA considers this to be a food

processing well and covers it along with other such wells in Volume 6 of this report.

3. EXPERIMENTAL TRACER STUDY WELLS

This section provides the following information on experimental tracer study wells: 

(1) prevalence; (2) injectate characteristics and well operating practices; (3) potential and documented

impacts on USDWs; (4) practices for effectively installing, operating, and removing tracer study wells;

and (5) federal, state, and local programs governing the installation, operation, and removal of this well

type.
September 30, 1999 6

3.1 Prevalence of Wells

For this study, data on the number of tracer study wells were collected through a survey of state

and USEPA Regional UIC programs. The survey methods are summarized in Section 4 of Volume 1

of the Class V Study. Table 1 lists the number of experimental tracer study wells in each state by

USEPA Region, as determined from the survey using the categorizations described above in Section 2. 

The table includes the documented and estimated number of tracer study wells in each state, along with

the source and basis for any estimate, when noted by the survey respondents. If a state is not listed in

Table 1, it means that the UIC program responsible for that state indicated that no tracer study wells

are currently operating in the state. As described above, wells that were originally identified by UIC

programs as “experimental” were reclassified if the wells were better addressed under another

established injection well category. Table 1 does not include these particular wells.

As shown in Table 1, a total of 396 documented Class V experimental tracer study wells have

been identified. None of the UIC programs reported “estimated” numbers for experimental tracer

study wells. However, Florida, Massachusetts, and Mississippi reported that the true inventory of

experimental wells is “unknown.” The Texas and Washington UIC programs provided no information

on the nature or purpose of the experimental wells existing in their states.

There may be considerable temporal variation in the tracer study well inventory data

because, unlike some of the other Class V injection well categories, tracer study wells have a limited

operating life. Operating permits or rule authorizations for tracer study wells generally expire at the

conclusion of the experiment being conducted (e.g., when a tracer study for aquifer characterization is

concluded). The duration of operating permits and rule authorizations for tracer study wells reported in

the survey responses ranged in duration from two months to 10 years. Therefore, the numbers

reported in Table 1 may be considered only as a “snapshot” of the tracer study well inventory.

Of the 396 operating Class V experimental tracer study wells, 179 are in Nevada and 207 are

in South Carolina. These two states account for more than 97 percent of the documented experimental

wells in the U.S. All of the experimental tracer study wells reported by the Nevada UIC program are

associated with the proposed Yucca Mountain High Level Radioactive Waste Repository Site

Characterization Project (YMSCP) operated by the U.S. Department of Energy (DOE). Some of

these 179 wells at the Yucca Mountain site have reportedly been plugged and abandoned. In addition,

nearly all of the experimental wells documented in South Carolina are tracer study wells or aquifer

remediation injection wells associated with environmental remediation projects at the DOE Savannah

River Site. The survey questionnaire for South Carolina did not identify how many of the wells are

tracer study wells and how many are aquifer remediation wells. Because no additional information is

available concerning the purpose of the experimental wells reported by the South Carolina UIC

program, all of South Carolina’s wells are included in the tracer study well inventory.
September 30, 1999 7

Table 1. Inventory of Experimental Tracer Study Wells in the U.S.

State Documented 

Number of Wells

Estimated Number of Wells

Number Source of Estimate and Methodology

USEPA Region 1

MA 0 Unknown NA

USEPA Region 2 -- None

USEPA Region 3 - None

USEPA Region 4

FL 0 Unknown NA

MS 0 Unknown NA

SC 207 207 Permit Program Data.

USEPA Region 5

IL 0 NR Permit Program Data. Two experimental wells reported to be used to inject

compressed air are believed no longer to be operating.

USEPA Region 6 

TX 5 NR Permit Program Data. The Texas UIC program reported 5 experimental wells

in the state, but provided no information concerning the purpose of the wells.

USEPA Region 7 -- None

USEPA Region 8

CO 2 NA Permit Program Data.

USEPA Region 9

NV 179 179 Permit Program Data.

USEPA Region 10

ID 1 1 IDWR Injection Well Permit Application No. 63-W-47, October 26, 1990, 

provided by Ms. Jane Talllman, Idaho Department of Water Resources.

WA 2 NR Permit Program Data. The Washington UIC program reported 2 experimental

wells in the state, but provided no information concerning the purpose of the

wells.

All USEPA Regions

All States 396 > 396 Total estimated number counts the documented number when the estimate is

unknown or NR.

NA Not available

NR Although USEPA Regional or state officials reported the presence of the well type, the estimated number of wells was

not reported.

Unknown Questionnaire completed, but number of wells is unknown
September 30, 1999 8

Two state UIC programs -- Colorado and Idaho -- reported one or two operational Class V

experimental tracer study wells. Altogether, these programs comprise less than 1 percent of the documented

tracer study wells in the nation. 

The Colorado UIC Program reported two operational experimental tracer study wells. One well is

being operated at an experimental mining operation in Idaho Springs, Colorado. The Colorado UIC

program also reported three “experimental” aquifer remediation wells and one “experimental” solution mining

well that have been recategorized for the purpose of this study, as described in Section 2.

The Idaho UIC Program reported that one experimental well is being operated in Eagle Island State

Park by Boise State University (as part of a university graduate student research project). This project

involves the construction of both a tracer injection well and monitoring wells used to study ground water

contaminant migration in shallow aquifers. 

3.2 Injectate Characteristics and Injection Practices

The following sections describe the injectate characteristics and injection practices for experimental

tracer study wells. 

3.2.1 Injectate Characteristics

Tracers used for injection well experiments may include organic dyes, rare earth metals, and other

organic and inorganic compounds (e.g., rare earth metals, Rhodamine WT dye, chloride, bromide, and

organic solutes) (Holmbeck-Pelham, 1998). Short half-life radioisotopes may also be used as long as the

likelihood of contaminating drinking water is extremely low, or the site is already contaminated with

radionuclides. For some tracer study wells, only general information is available concerning injectate

characteristics. For these wells, examples of tracers and injectate data are presented below.

• Boise State University Department of Geology. The permit issued by the Idaho Department of

Water Resources for the injection well tracer study limits the injectate to heated ground water

derived from the same aquifer from a nearby well (IDWR, 1990). The project description in the

permit application indicates that tracer solutions of chloride and bromide ions would be used in the

tracer test (BSU, 1990). However, neither the permit application nor the permit for the injection

well included any concentration data for the tracer solutions or identified the specific chloride and

bromide ion compounds used in the tracer well tests.

• Bureau of Mines Stope Leaching Project Tracer Study. The U.S. Department of the Interior,

Bureau of Mines (BOM) submitted an application in 1992 for authorization to inject potable water

and sodium chloride (NaCl) tracer into a man-made fractured crystalline rock mass at the Colorado

School of Mines (CSM) Experimental Mine Facility in Idaho Springs, Colorado. In all three tests,

the injectate (potable water provided by the Idaho Springs Municipal Water Department) was

mixed with a NaCl tracer. The concentration of NaCl in the injectate was 7,000 ppm, 3,000 ppm,

and 6,000 ppm during the three tests. 
1

 A stope is an excavation in the form of steps made by the mining of ore from steeply inclined or

vertical veins.

September 30, 1999 9

• Naturita Uranium Site Tracer Study. In 1998, the United States Geological Survey (USGS)

applied for approval to conduct a small-scale tracer study of an aquifer in Colorado contaminated

with uranium, vanadium, sodium chloride, sodium bicarbonate, sulfuric acid, and ammonium sulfate. 

The USGS applied for approval to conduct five tracer tests at the Naturita site. Each test would

inject native ground water with 1,000 ppm potassium bromide (ppm as bromide) into the aquifer. 

The native ground water used as a tracer carrier is contaminated with uranium, chloride, and sulfates

at levels greater than drinking water maximum MCLs, and with molybdenum and arsenic at levels

greater than HALs. Concentrations of strontium in the native ground water are also elevated above

background concentrations. Native ground water (i.e., tracer carrier) quality data are summarized in

Table 2 (USGS, 1999).

• Yucca Mountain Site Characterization Project (YMSCP). Although many other chemicals are

being used (e.g., helium, lithium bromide, synthetic colloids, and short half-life radionuclides), the

most commonly injected tracer for YMSCP tracer study wells is sulfur hexafluoride gas. Tracers

approved by the Nevada UIC program for the Yucca Mountain project are shown in Table 3. Not

all of these tracers have been used.

During 1996 and 1997, the YMSCP injected sulfur hexafluoride to conduct tracer and ventilation

testing at the site (USDOE, 1996). Additionally, lithium bromide was mixed with water and was

used as a tracer to tag construction, dust control, and drilling water. Other tracers used in testing at

the YMSCP include sodium iodide, pentafluorobenzoic acid (PFBA), and fluorescent microspheres.

3.2.2 Well Characteristics and Operating Practices

Examples of well characteristics and operating practices for tracer study wells are presented below.

Bureau of Mines Stope Leaching Project Tracer Study

The BOM conducted three tracer tests at the stope leaching research project. The research project

involved the control of fluids released into a simulated stope filled with fractured rock.1 The fractured rock

was formed by blasting the in-place rock mass and by creating associated fracture patterns in the

surrounding bedrock. While some fluid introduced into the formation is lost in the fractures, the remaining

fluid is collected and recycled back into the formation for the duration of the tracer study (BOM, 1993).
September 30, 1999 10

Table 2. Summary of Native Ground Water (Tracer Carrier) Analyses at the

Naturita Site 1989 -1994 (USGS, 1998)

Parameter

Background Ground

Water Quality

(mg/l)

Onsite Ground

Water Quality

(mg/l) MCL (mg/l) HAL (mg/l)

Aluminum <0.09 <0.10 0.05-0.2 (S) --

Ammonium <0.10 0.26 -- --

Antimony <0.003 <0.003 0.006 0.003 (NC)

Arsenic <0.01 0.03 0.05 0.002 (C)

Barium <0.1 <0.1 2.0 2.0 (NC)

Boron <0.1 0.2 -- 0.6 (NC)

Bromide <0.1 0.4 -- --

Cadmium <0.001 <0.001 0.005 0.005 (NC)

Calcium 155 243 -- --

Chloride 8.2 546 250.0 (S) --

Chromium (total) <0.01 <0.01 0.1 0.1 (NC)

Cobalt <0.05 <0.05 -- --

Copper <0.02 <0.02 1.3 --

Cyanide <0.01 <0.01 0.2 0.2 (NC)

Fluoride 0.3 1.4 4.0 --

Iron <0.03 <0.05 0.3 --

Lead (at tap) <0.01 <0.01 0.015 --

Magnesium <0.01 5.1 -- --

Mercury (inorganic) <0.0002 <0.0002 0.002 0.002 (NC)

Molybdenum <0.01 0.29 -- 0.04 (NC)

Nickel <0.04 <0.04 0.1 0.1 (NC)

Nitrate (as N) 1.7 2.7 10.0 --

Phosphate <0.1 0.4 -- --

Potassium 1.9 41 -- --

Selenium <0.005 0.01 0.05 --

Silica <0.005 0.01 -- --

Silver <0.01 <0.01 0.1 (S) 0.1 (NC)

Sodium 48 997 -- --

Strontium 1.2 5.5 -- 17.0 (NC)
Table 2. Summary of Native Ground Water (Tracer Carrier) Analyses at the

Naturita Site 1989 -1994 (USGS, 1998)

(Continued)

Parameter

Background Ground

Water Quality

(mg/l)

Onsite Ground

Water Quality

(mg/l) MCL (mg/l) HAL (mg/l)

September 30, 1999 11

Sulfate 348 1200 500.0 --

Sulfide <0.1 <0.1 -- --

Thallium <0.01 <0.01 0.002 0.0005 (NC)

Tin <0.005 <0.005 -- --

Uranium 0.012 2.2 0.02 –

Vanadium <0.01 6.4 -- --

Zinc 0.057 <0.005 5.0 (S) 2.0 (NC)

-- means no MCL or health advisory level specified

(S) means the reported value is a secondary MCL (no notation means the value is a primary MCL)

(NC) means the reported health advisory level is for non-cancer effects

( C ) means the reported health advisory level is for a 10-4 cancer risk
September 30, 1999 12

Table 3. Nevada UIC-Approved Tracers for Yucca Mountain Site Characterization Project, Yucca

Mountain, Nevada

NV UIC Approved Tracers for the Yucca Mountain

Project

Pyridone

Sodium Chloride

Lithium Bromide

Fluorescent Microspheres

Polystyrene Spheres

Sulfur Hexafluoride (SF6) - gaseous tracer

Nitrogen 

“SUVA” Cold-MP (tetra-fluorethane) (gas)

2,4,6- Trifluorobenzoic Acid

2,4,5- Trifluorobenzoic Acid

2,3,4- Trifluorobenzoic Acid

2,3,6- Trifluorobenzoic Acid

2,3,4,5- Tetrafluorobenzoic Acid

2,3,4,6- Tetrafluorobenzoic Acid

3,4,5-Trifluorobenzoic Acid

2,3- Difluorobenzoic Acid

2,4- Difluorobenzoic Acid

2,5- Difluorobenzoic Acid

2,6- Difluorobenzoic Acid

3,4- Difluorobenzoic Acid

3,5- Difluorobenzoic Acid

Pentafluorobenzoic Acid

NV UIC Approved Tracers per 1996

Modification

Sodium Tungstate Dihydrate

Sodium Molybdate Dihydrate

Sodium Fluoride

Fluorescein, sodium derivative

Potassium Fluoride

Magnesium Fluoride

Magnesium Iodide

Helium

Neon

Krypton

Xenon

Argon

Sodium Iodide

Sodium Bromide

Potassium Iodide

Potassium Bromide
September 30, 1999 13

Three tracer tests were conducted in a stope filled with fractured rock, into which tracer fluid was

injected. This research project involved the filling of the stope with tracer fluid, which subsequently flowed

into the fractured rock. The Situation Statement for the project approved the use of cementious grout and

superplasticizer for the control of water flow in the rock fractures. A USEPA Region 8 toxicologist

indicated that these grouting materials are toxicologically insignificant (BOM, 1993). After the tracer tests

were initiated, the BOM requested and obtained approval to use alternative grouting materials, including

“Hey’di Special System” and “Hey’di K-11” waterproofing grouts (USEPA Region 8, 1993a; BOM,

1993a).

The first tracer test was conducted by injecting approximately 4,000 gallons of potable water with

7,000 ppm of NaCl tracer into the man-made fracture formation (stope). The injectate flowed through the

stope and exited through a bulkhead, and then flowed through a pipe to a sump. Samples were taken from

the pipe before the water reached the sump. The NaCl tracer was detected in fluids at a concentration

ranging between 1,000 and 1,500 ppm NaCl. Approximately 3,000 gallons of tracer fluid were lost through

fractures adjacent to the bulkhead. Almost all of the lost fluid was recovered in the sump and was

transported to the Idaho Springs Municipal Waste Water Treatment Plant for disposal. On three different

occasions, the stope was flushed with 4,000 gallons of potable water without any tracer to dilute the tracer

in the fractures and to test the grouting measures used to seal the leaking fractures. This first tracer test

resulted in considerable fluid loss through the fractures. As a result, the leaking fractures were surface

grouted both inside and outside the stope with Portland cement grout and Hey’di waterproofing grouts

(BOM, 1993a; BOM 1993b).

The second tracer test was conducted using a total of 8,000 gallons of potable water with 3,000

ppm of NaCl tracer. The water samples used for this test were obtained from the same locations as were

the samples in the first tracer test and were analyzed for certain constituents (BOM, 1993b).

The third tracer test and a constant head test were completed in September 1994. Water samples

were taken during this test at the same locations as during the first and second tests. A total of 8,114 gallons

of potable water with 6,000 ppm NaCl tracer was injected into the stope. After the test’s conclusion, in

May 1994, a total of 3,603 gallons of fluid were recovered in the sump. The stope was subsequently

flushed with 8,185 gallons of potable water without tracer. Over a period of about four months, USEPA

Region 8 approved the reuse of the tracer solutions in drilling operations, and required that the concentration

of the tracer solution be diluted to no greater than 1,000 ppm NaCl prior to reuse (USEPA Region 8,

1994).

USEPA limited the concentration of the sodium chloride tracer to no more than 7,000 ppm and

required that BOM analyze fluid samples from the system sump for several constituents. Analyses were

required prior to the beginning of the tracer test, two months after the beginning of the tracer test, and

quarterly, thereafter. Ten samples were taken during the first tracer test, and analytical results are shown in

Table 4 (these data are representative of the injectate and ground water).
September 30, 1999 14

Table 4. Analytical Data for Recovered Injectate - BOM Stope Leaching Project

Sample Number MCL

(mg/l)

Parameter 10-1 10-2 10-3 10-4 10-5 10-6 10-7 10-8 10-9 10-10 1-1

Arsenic <0.005 <0.005 0.005 0.005 0.005 <0.005 0.005 0.006 <0.005 <0.005 <0.005 0.05

Cadmium 0.005 <0.005 0.019 0.016 0.016 0.009 0.014 0.017 0.017 0.016 <0.005 0.005

Copper 0.18 0.046 0.53 0.52 0.40 0.16 0.49 0.52 0.51 0.53 0.005 1.3

Lead 0.010 0.006 0.035 0.030 0.040 0.085 0.034 0.042 0.026 0.030 <0.005 0.015

Mercury 0.0011 0.0002 0.0026 0.0012 0.0008 0.0010 0.0006 0.0006 0.0005 0.0029 <0.0001 0.002

Zinc 0.72 0.28 3.3 3.4 3.9 2.7 3.7 3.6 3.5 3.6 1.2 5.0 (S)

Silver <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0002 0.1 (S)

Gross Alpha

(pCi/L)

90 +/- 25 23 +/- 13 320 +/-

40

300 +/-

50

280 +/-

40

130 +/-

30

340 +/-

50

340 +/-

50

360 +/-

50

290 +/-

40

19 +/- 20 15.0

Gross Beta

(pCi/L)

64 +/- 15 25 +/- 10 170 +/-

20

160 +/-

20

140 +/-

20 

81 +/- 17 170 +/-

20

180 +/-

20

160 +/-

20

170 +/-

20

30 +/- 31 --

Sample Number

Parameter 2-1 2-2 1-1

Fluoride 0.5 1.1 <0.5 4.0

Sulfate (SO4) 470 780 450 500.0

-- means no discharge limit, MCL, or health advisory level specified

(S) means the reported value is a secondary MCL (no notation means the value is a primary MCL)
September 30, 1999 15

USGS Naturita Uranium Site Tracer Study

Each of the five proposed tests at this site, introduced in Section 3.2.1, would inject 50 gallons of

native ground water with 1,000 ppm potassium bromide tracer into the aquifer. Monitoring would be

conducted at two existing monitoring wells and 12 newly installed wells at the site. The USGS reported that

injection and monitoring wells would be installed approximately 150 yards from the San Miguel River. The

river recharges the alluvial aquifer during high water season, while the aquifer discharges to the river during

the low water season. Unconfined ground water occurs in the alluvial aquifer at depths ranging from zero to

18 feet below ground surface (USGS, 1998). The USGS predicted that the tracer tests would result in

elevated concentrations of potassium (K+) and bromine (Br-). Local ground water concentrations of K+

would increase from approximately 40 mg/l to 540 mg/l, and local concentrations of Br- would increase

from less than 5 mg/l to 1,000 mg/l. Bromide concentrations in the aquifer would be comparable in

magnitude to concentrations of sodium and sulfate in the aquifer, prior to any dispersion (USGS, 1998). 

The USGS did not provide any information concerning well characteristics or operating data for the

experimental well operation. 

Boise State University Department of Geology

A diagram of the injection well in use at the Boise State University (BSU) tracer study site is shown

in Figure 1. The well has a 4.5 inch diameter Schedule 40 PVC casing slotted from 8 feet deep to 38 feet

deep, with a vented cap and a concrete and granular bentonite seal to 6 feet deep. The well is 6 inches in

diameter. In the permit application for the proposed injection well, BSU requested exemption from a

requirement to install 18 feet of steel surface casing (BSU, 1990).

Heated ground water containing chloride or bromide ions (i.e., the tracers) is injected into this well. 

The ground water containing the injected tracer solution is withdrawn from the aquifer through monitoring

wells to determine the flow characteristics of the aquifer. The permit issued by the Idaho Department of

Water Resources limits the flow of injectate into the injection well to no more than 10 gallons per minute on

a weekly average, and limits the source of the injectate to heated ground water taken from a water

production well located in the same aquifer zone as the injection well. 

Yucca Mountain Site Characterization Project

The YMSCP is studying the hydrological and geological properties of rock formations around

Yucca Mountain. Three wells are injecting tracers to study hydrological characteristics of the saturated

zone. Three more wells may be constructed, if necessary. Other injection wells and boreholes are injecting

approved tracers to tag the drilling water or air. The tracers will allow project managers to identify water or

air from ground water and gas sources other than the water or air being injected into the well (Land, 1997).
September 30, 1999 16

Figure 1. Schematic Diagram of Tracer Study Injection Well, Boise State University Department

of Geology

Source: BSU, 1990

During 1996, YMSCP researchers injected 4.6 ft3 of sulfur hexafluoride to conduct tracer and

ventilation testing at the site (USDOE, 1996). Additionally, 30,465 ounces of lithium bromide were mixed

with 9,374,000 gallons of water. The mixture was used to tag construction, dust control, and drilling water. 

Other tracers used for this test include sodium iodide, pentafluorobenzoic acid (PFBA), and fluorescent

microspheres. 

During 1997, YMSCP scientists continued using sulfur hexafluoride as a tracer in

drilling and testing activities at the site (USDOE, 1997a). The total annual amount of this tracer used in

operations, drilling activities, and testing activities is approximately 215,000, 38, and 215,000 ft3,

respectively.
September 30, 1999 17

During 1997, researchers also performed tests using several different tracers, including helium,

lithium bromide, and various dyes. Tables 5 and 6 show the amounts and concentrations of selected dyes

and tracers used in research at the site in 1997. In order to tag construction, dust control, and drilling water,

researchers also used approximately 1.4 ft3 of helium in eight tracer tests and 15,000 ounces of lithium

bromide (diluted in over 4.6 million gallons of water). Table 7 provides a side-by-side comparison of

analytical results characterizing ground water collected from a tracer test injection well and a drinking water

well at the Yucca Mountain site. Figure 2 shows a schematic diagram of an injection well used for multistrata tracer studies.

Table 5. 1997 Dye Usage, Yucca Mountain Site Characterization Project,

Yucca Mountain, Nevada

Dye Amount Used (liters) Average Concentration (mg/l)

FD&C Blue #1 2.3522 8,750

No. 8006 FD&C Yellow #6 0.13 9,200

FD&C Red #40 2.2493 8,250

Sulfo rhodamine b 2.5718 1,830

Lissamine FF 0.118 1,900

Source: USDOE, 1997a

Table 6: 1997 Tracer Injection Analysis, Yucca Mountain Site Characterization Project, Yucca

Mountain, Nevada

Tracer

Amount

Injected (kg)

Peak Concentration

(mg/l)

Mass

Recovered (kg) Percent Recovered

LiBr (Lithium ion) 14.6 (Li) 0.56 9.5 (Li) 65

LiBr (Bromide ion) 165.1 (Br) 9.4 115 (Br) 69

PFBA 12.12 0.83 10.24 84

Fluorescent Microspheres 0.0085 2.0 million/L 0.0013 15

2,6-DFBA 11.3505 0.251 8.0 70

Pyridone 3.018 0.0437 0.038 1.9

Source: USDOE, 1997b
September 30, 1999 18

Table 7. 1997 Semi-annual Ground Water Sampling Results, Yucca Mountain Site

Characterization Project, Nevada

Constituent

Concentration mg/l (except as noted)

Tracer Testing Injection Well Drinking Water Well

Total Dissolved Solids 241 241

Electrical Conductivity (Fmo/cm) 294 270

Calcium 13 13

Magnesium 0.34 2.0

Sodium 56 44

Potassium 2.0 5.6

Sulfate 17 16

Chloride 7.6 7.5

Nitrate 1.3 2.0

Bicarbonate 100 100

Carbonate ND ND

Fluoride 1.7 1.6

Arsenic ND ND

Iron ND ND

Manganese ND ND

Copper ND ND

Zinc ND ND

Barium ND ND

Boron 0.14 0.14

pH (units) 8.04 7.62

Cadmium ND ND

Chromium ND ND

Lead ND ND

Mercury ND ND

Molybdenum NR ND

Nickel NR ND
Table 7. 1997 Semi-annual Ground Water Sampling Results, Yucca Mountain Site

Characterization Project, Nevada (Continued)

Constituent

Concentration mg/l (except as noted)

Tracer Testing Injection Well Drinking Water Well

September 30, 1999 19

Selenium ND ND

Silver ND ND

Tungsten ND ND

Gross Alpha (pCi/L) 2.1±1.8 2.7±1.5

Gross Beta (pCi/L) 0.7±2.1 4.5±2.2

Silica 41 35

Lithium 0.06 0.043

Strontium 0.043 0.049

Bromide ND ND

Iodide ND ND

Pentafluorobenzoic Acid ND ND

2,6-Difluorobenzoic Acid ND ND

Fluorescent Microspheres ND ND

Pyridone ND ND

NR - Not Reported ND - Not Detected

Source: USDOE, 1997b
September 30, 1999 20

Figure 2. Schematic Diagram of Pneumatic Packed Tracer Injection Well for Geologic Strata

Tracer Studies at Yucca Mountain Site

(Source: http://www.ymp.gov/about/science/e_sci/pneuma.htm) USDOE, No date.

3.3 Potential and Documented Damage to USDWs

The chemical quality of fluids released into experimental tracer study wells is not necessarily the best

indicator of the potential damage that these wells can have on USDWs. The risk associated with

experimental wells is largely a function of the receiving ground water and aquifer characteristics as well as the

objective of the experimental project. 

In some cases, tracer study wells intentionally introduce a tracer into the ground water at a specific

concentration and location, knowingly exceeding drinking water standards. This being the case, a direct

comparison of injectate quality to drinking water standards is useful, but does not tell the whole story about

the potential for experimental wells to endanger USDWs. It is also necessary to consider the potential

effects of experimental well operations by evaluating ground water monitoring data for these well systems. 

In general, operators of experimental injection wells are required to collect ground water quality data from

monitoring wells situated in the vicinity of the injection well. Monitoring is required to determine whether the

experimental well operation is having the desired effect and to determine whether the operation is having any

effects beyond its zone of operation (e.g., the tracer is migrating beyond the aquifer formation).
September 30, 1999 21

Section 3.3.1 identifies the injectate constituents likely to exceed drinking water standards and

reviews the properties of these constituents that most influence risk (e.g., toxicity, persistence, and mobility in

ground water). Section 3.3.2 then summarizes available ground water monitoring results and other

information on observed impacts associated with experimental well operations.

Numerous boreholes intersecting many different geologic strata or levels have been drilled for tracer

studies at the Yucca Mountain Site. Tracer study injection wells use inflatable rubber bladders to separate

the different geologic segments (“packing them off”). These balloon-like devices allow DOE to study if and

how gases move through the various strata. Tracer gases are injected into these boreholes and the

circulating gas pressure, found in each strata, is then measured to determine how much gas can be recovered

back from the rock.

3.3.1 Injectate Constituent Properties

The primary constituent properties of concern when assessing the potential for Class V wells to

adversely affect USDWs are toxicity, persistence, and mobility. The toxicity of a constituent is the potential

of that contaminant to cause adverse health effects if consumed by humans. Appendix D to the Class V

Study provides information on the health effects associated with contaminants found above drinking water

standards or health advisory limits in the injectate of experimental wells and other Class V wells. As

discussed in Section 3.2.1, the contaminants that have been observed above MCLs and/or HALs in

experimental well injectate are chloride, strontium, sulfates, uranium, molybdenum, and arsenic.

Persistence is the ability of a chemical to remain unchanged in composition, chemical state, and

physical state over time. Appendix E presents published half-lives of common constituents in fluids released

in experimental wells and other Class V wells. All of the values reported in Appendix E are for ground

water. Caution is advised in interpreting these values because ambient conditions have a significant impact

on the persistence of both inorganic and organic compounds. Appendix E also provides a discussion of

mobility of certain constituents found in the injectate of experimental wells and other Class V wells.

3.3.2 Observed Impacts

Ground water monitoring data are not available for all of the experimental injection wells for which

injectate data and other permit data were reported. Potential effects on ground water quality identified in the

survey conducted for this study include:

• Migration of tracers from the study zone into drinking water aquifers; and

• Migration of contaminants (e.g., uranium, strontium) from reinjection of native contaminated ground

water.

The experimental tracer study well at the Naturita, Colorado site was the only well that did not meet

primary MCLs, secondary MCLs, and HALs. The injectate for this tracer well exceeded MCLs for sulfates

and chloride, and contained arsenic and molybdenum at levels greater than HALs. However, in this case,
September 30, 1999 22

the injectate was not being injected into an aquifer of drinking water quality. In particular, the natural

concentrations of strontium and uranium in the receiving aquifer were higher than normal background levels.

None of the state UIC programs documented any incidents of USDW contamination (i.e.,

exceedance of drinking water standards) from the operation of experimental tracer study wells. 

The majority of experimental tracer study wells reported by state and USEPA Regional UIC

programs are used to inject tracers (e.g., organic dyes, noble gases, short half-life radionuclides) into ground

water. These tracers are used to determine the characteristics of the ground water. In tracer study well

experiments, these compounds are injected in low concentrations. Therefore, negative ground water

impacts are unlikely. As discussed in Attachment A, state UIC programs generally require that tracer wells

be permitted and operated so as not to affect ground water quality. Given this requirement, no incidents of

USDW contamination have been reported from the operation of experimental technology wells.

3.4 Best Management Practices

Best management practices (BMPs) for experimental tracer study wells are similar to the best

management practices for aquifer remediation wells (see Volume 16), and include proper site characteristics,

design, construction, maintenance, operation, monitoring, and closure. BMPs for tracer study wells are

primarily related to the concentration and characteristics of the tracer. In general, tracers are injected in low

concentrations with either potable or native ground water. Ideal tracers do not affect the flow regime or

experience significant chemical, biological, or physical reactions during the test(s) (Holmbeck-Pelham,

1998). Tracer injectate concentrations can be minimized by using tracers of unique isotopic signatures. 

These signatures can allow the researcher to distinguish between natural and introduced compounds. In

some cases, environmentally benign tracer compounds such as sodium and potassium salts can be used as

tracers. However, for other applications, tracers with more unique signatures are required. While stable

and radioactive isotopes fit this description, their use can raise concerns about residual radioactivity. This

radioactivity can be minimized by using radioactive isotopes that have short half-lives.

Another potential concern for tracer study wells is the use of existing ground water as a tracer

carrier. Many tracer studies are conducted at aquifer remediation sites where ground water is already

contaminated with metals, organic compounds, or other constituents. The use of contaminated ground water

as a tracer carrier could potentially spread this contamination to other areas, if the tracer wells and

monitoring wells are not sited properly. However, the nature of the tracer study or the lack of potable water

may require the use contaminated ground water. Therefore, careful siting of both the injection and

monitoring wells will preclude any spreading of contamination. The potential for contamination can also be

reduced by minimizing the concentration and quantity of the injectate required for the tracer study.
September 30, 1999 23

3.5 Current Regulatory Requirements

Several federal, state, and local programs exist that either directly manage or regulate experimental

wells, or impact them indirectly through broad based water pollution prevention initiatives.

3.5.1 Federal Programs

On the federal level, management and regulation of Class V experimental wells fall primarily under

the UIC program authorized by the Safe Drinking Water Act (SDWA), as discussed below. Some states

and localities have used these authorities, as well as their own authorities, to extend the controls in their areas

to address endemic concerns associated with experimental wells. Because more than 97 percent of the

documented experimental wells are owned or operated by DOE, applicable DOE environmental control

programs are also summarized below.

SDWA

Class V wells are regulated under the authority of Part C of SDWA. Congress enacted the SDWA

to ensure protection of the quality of drinking water in the United States, and Part C specifically mandates

the regulation of underground injection of fluids through wells. USEPA has promulgated a series of UIC

regulations under this authority. USEPA directly implements these regulations for Class V wells in 19 states

or territories (Alaska, American Samoa, Arizona, California, Colorado, Hawaii, Indiana, Iowa, Kentucky,

Michigan, Minnesota, Montana, New York, Pennsylvania, South Dakota, Tennessee, Virginia, Virgin

Islands, and Washington, DC). USEPA also directly implements all Class V UIC programs on Tribal lands. 

In all other states, which are called Primacy States, state agencies implement the Class V UIC program, with

primary enforcement responsibility.

Experimental wells currently are not subject to any specific regulations tailored just for them, but

rather are subject to the UIC regulations that exist for all Class V wells. Under 40 CFR 144.12(a), owners

or operators of all injection wells, including experimental wells, are prohibited from engaging in any injection

activity that allows the movement of fluids containing any contaminant into USDWs, “if the presence of that

contaminant may cause a violation of any primary drinking water regulation . . . or may otherwise adversely

affect the health of persons.” 

Owners or operators of Class V wells are required to submit basic inventory information under 40

CFR 144.26. When the owner or operator submits inventory information and is operating the well such that

a USDW is not endangered, the operation of the Class V well is authorized by rule. Moreover, under

section 144.27, USEPA may require owners or operators of any Class V well, in USEPA-administered

programs, to submit additional information deemed necessary to protect USDWs. Owners or operators

who fail to submit the information required under sections 144.26 and 144.27 are prohibited from using their

wells.

Sections 144.12(c) and (d) prescribe mandatory and discretionary actions to be taken by the UIC

Program Director if a Class V well is not in compliance with section 144.12(a). Specifically, the Director
2

 May 2003 is the deadline including an 18-month extension.

September 30, 1999 24

must choose between requiring the injector to apply for an individual permit, ordering such action as closure

of the well to prevent endangerment, or taking an enforcement action. Because experimental wells (like

other kinds of Class V wells) are authorized by rule, they do not have to obtain a permit unless required to

do so by the UIC Program Director under 40 CFR 144.25. Authorization by rule terminates upon the

effective date of a permit issued or upon proper closure of the well. 

Separate from the UIC program, the SDWA Amendments of 1996 establish a requirement for

source water assessments. USEPA published guidance describing how the states should carry out a source

water assessment program within the state’s boundaries. The final guidance, entitled Source Water

Assessment and Programs Guidance (USEPA 816-R-97-009), was released in August 1997.

States must conduct source water assessments which are comprised of three steps. First, a state

must delineate the boundaries of the assessment areas in the state from which one or more public drinking

water systems receive supplies of drinking water. In delineating these areas, states must use “all reasonably

available hydrogeologic information on the sources of the supply of drinking water in the state and the water

flow, recharge, and discharge and any other reliable information as the state deems necessary to adequately

determine such areas.” Second, the state must identify contaminants of concern, and for those contaminants,

the state must inventory significant potential sources of contamination in delineated source water protection

areas. Class V wells, including experimental wells, should be considered as part of this source inventory, if

present in a given area. Third, the state must “determine the susceptibility of the public water systems in the

delineated area to such contaminants.” States should complete all of these steps by May 2003 according to

the final guidance.2

DOE Environmental Control Programs

Approximately 99 percent of the experimental injection wells reported in the UIC survey

questionnaires are experimental tracer study wells being operated at DOE facilities as part of the its ongoing

aquifer remediation programs. A representative of the DOE Office of Science and Technology familiar with

the aquifer remediation program at the DOE Oak Ridge Reservation in Oak Ridge, Tennessee indicated that

she did not believe that the Department has established any standardized procedures for the construction

and operation of tracer study wells (Phillips, 1999). A representative of the USEPA National Risk

Management Research Laboratory who has worked with DOE on development of experimental tracer study

techniques for aquifer characterization indicated that experimental tracer study wells operated by DOE are

not subject to standardized design procedures but are designed on a site-specific basis (Parker, 1999). 

DOE is subject to federal and state environmental regulations concerning the design and operation of

injection wells, including federal and state UIC regulations. DOE also has a system of Directives (DOE

Orders) that have been developed by the Department to implement environmental protection programs. 

DOE Order 5400.5, Radiation Protection of the Public and the Environment, establishes standards and

requirements for operations of DOE and DOE contractors with respect to protection of members of the

public and the environment against undue risk from radiation. DOE Order 5400.1, General Environmental
September 30, 1999 25

Protection Program, establishes environmental protection program requirements, authorities, and

responsibilities for DOE operations for assuring compliance with applicable federal, state, and local

environmental protection laws and regulations, executive orders, and internal department policies. Under

these and related DOE Orders, DOE is required to obtain operating permits for tracer study wells operated

at their facilities in states with UIC permit programs, and is required to comply with ground water protection

standards and other environmental regulations related to construction and operation of underground

injection wells.

3.5.2 State and Local Programs

Six states -- Colorado, Idaho, Nevada, South Carolina, Texas, and Washington -- have

documented Class V experimental wells. Two of these states, Nevada and South Carolina, have more than

97 percent of the current documented well inventory. In addition, Illinois staff report that two experimental

wells have been recorded but are most likely no longer operating at this time.

In Colorado, USEPA Region 8 directly implements the Class V UIC program. For the BOM Stope

Leaching Project Tracer Study and the USGS Naturita Uranium Site Tracer Study conducted in that state,

USEPA Region 8 staff indicate that individual UIC permits were not required but that both projects were

rule authorized and subject to the general program requirements described above in Section 3.5.1. USEPA

Region 8 staff also indicate that, for the Naturita project, the rule authorization was valid for three years from

the date of issuance and the results of the tracer test had to be reported to USEPA. Both projects were also

required to comply with Colorado Department of Public Health and Environment Regulations (USEPA

Region 8, 1993).

The other states listed above have primacy for the Class V UIC program and have established a

range of requirements for their programs. Specifically:

C Idaho authorizes shallow injection wells (<18 feet deep) by rule, provided that inventory information

is supplied and use of the well does not result in contamination of a USDW. Deep injection wells

(>18 feet deep) must obtain an individual permit. Both shallow and deep wells must satisfy

operating requirements to ensure that no violation of the state’s water quality standards for ground

water occurs.

C Illinois has established rules for its Class V UIC program that are intended to be identical in

substance to USEPA’s rules in 40 CFR Part 144. The state applies inventory requirements and

uses a permit-by-rule approach to ensure non-endangerment of USDWs. The state may require an

individual permit to ensure no violation of drinking water requirements.

C Nevada requires experimental wells to obtain individual permits, based on detailed information about

the facility.

C South Carolina requires experimental wells to obtain individual permits, based on detailed

information about the facility. South Carolina’s operating requirements for experimental wells are
September 30, 1999 26

identical to the requirements for Class II and III injection wells. Monitoring requirements are the

same as those for Class III wells.

C Texas authorizes Class V wells, including experimental wells, by rule. The state applies mandatory

requirements and uses a permit-by-rule approach to ensure non-endangerment of USDWs. In

addition, the state applies specific construction standards for Class V wells.

C Washington individually permits experimental wells.

4. EXPERIMENTAL ATES SYSTEM WELLS

An aquifer thermal energy storage (ATES) system stores thermal energy by injecting heated and/or

cooled water into an aquifer for use at a later time. ATES system injectate (whether heated or cooled)

generally is returned to the same aquifer from which it was previously withdrawn; however, in some cases,

the injectate may have come from a different aquifer or from surface water. The heated or cooled water

stored in the aquifer can be reused (for heating or cooling) by pumping the water to the surface. Although

no operating ATES systems were identified in the survey responses as currently being active, experimental

ATES systems were recently operated in Minnesota and New York (Marseille and Wicke, 1992, Hoyer,

et. al., 1994). ATES systems are considered to be experimental injection wells because they are intended to

test new injection technologies. These systems are therefore discussed in this volume of the report, and are

not discussed in other report volumes.

4.1 Prevalence of Wells

No UIC program reported any operating ATES system wells. ATES system wells, however, were

recently operated in New York and Minnesota.

There may be considerable temporal variation in the experimental well inventory data

because, unlike some of the other Class V injection well categories, experimental wells have a limited

operating life. Operating permits or rule authorizations for experimental wells generally expire at the

conclusion of the experiment being conducted (e.g., when an experimental injection technology is

demonstrated as either viable or not viable). Therefore, ATES system wells may be operated in the future,

although none were reported to be operating at present.

4.2 Injectate Characteristics and Injection Practices

Although no ATES system wells are currently known to be operating, their injectate characteristics

and injection practices are described here because they have been used recently and may be used again in

the future. Because injectate data for ATES system wells were not available, Section 4.2.1 presents

general characteristics of ATES system injectate. Section 4.2.2 presents ATES system injection practices. 
September 30, 1999 27

4.2.1 Injectate Characteristics

Injectate data for experimental ATES systems were not available, and therefore only a general

discussion of injectate characteristics is included in this section. Injectate for ATES systems is commonly

heated water, or in some cases cooled water, that is being returned to the same aquifer from which it was

withdrawn. In some cases, the water that is injected may come from a different aquifer or from a surface

water source. In addition, cleaning agents may be injected into ATES system wells during well operation

and maintenance activities to prevent plugging of the well due to scaling or other causes. The Minnesota

Franconia-Ironton-Galesville Experimental ATES System provides an illustrative example of this type of

well. Based on the review of the literature, an ATES system was operated in a confined aquifer system in

St. Paul, Minnesota, referred to as the Franconia-Ironton-Galesville (F-I-G) aquifer (Hoyer, et. al., 1994). 

The injectate was ground water that had been heated and softened. 

4.2.2 Well Characteristics and Operating Practices

ATES injection wells are used to store thermal energy to supply process cooling, space cooling,

space heating, and ventilation air preheating; they may be used with or without heat pumps. Waste or byproduct energy, ambient air, and renewable energy (e.g., solar energy) are often used as energy sources for

ATES systems (Morofsky, 1997).

An ATES system is composed of one or more pairs of fairly conventional water supply wells drilled

into an aquifer (Hall and Raymond, 1992). The well spacing is chosen to minimize interference and thermal

short-circuiting during operation, which is normally seasonal. ATES systems are designed to maximize the

amount of cold or heat stored in each cycle of ground water withdrawal and injection (Mirza, 1994). During

the operation, ground water is withdrawn from one well, heated or chilled in a heat exchanger, and then

returned for storage in the same aquifer through a second well. The stored thermal energy is recovered

when the second well is pumped and the hot or cold water is again circulated through a heat exchanger and

then returned to the aquifer through the first well. Different system types may be selected based on local

geology, geography, climate conditions, and general applications. ATES systems have been classified into

four main types: 

1. Storage of warm water;

2. Storage combined with process cooling;

3. Storage for combined space cooling and heating; and

4. High-temperature ATES systems.

For the first type, in the summer, warm surface water is pumped through a heat exchanger to heat

ground water that is pumped from a cool part of the aquifer. The heated water is then stored in a warm part

of the aquifer; in the winter, the water is withdrawn and used as a source of energy to a heat pump system. 

The second and third types are similar and used for industrial process cooling and space heating and cooling. 

The third type, however, differs in that the systems are designed for optimal space cooling while space

heating is complemented by the use of heat pumps. Typical users of ATES systems are commercial building

owners and district heating networks (Andersson and Sellberg, 1992). Approximately 83% of 55 systems
September 30, 1999 28

reviewed (from Canada, Germany, The Netherlands, and Sweden) were for commercial building

applications, 13% for process cooling, and 4% for residential applications (Chant and Morofsky, 1992, Hall

and Raymond, 1992). 

ATES systems can potentially be used for seasonal and short-term energy storage at temperatures

ranging from 2oC to more than 100oC. In Sweden, several low-temperature systems (<25oC) have

operated since before 1990. These systems also generally involve the use of heat pumps in combination

with the seasonal storage (Andersson and Sellberg, 1992). Many systems have storage temperatures in the

range of 12 to 40oC, while there are fewer -- one study found only six -- high-temperature systems (greater

than 85oC). In 1992, high temperature systems were considered experimental (Jenne, et. al., 1992). One

experimental high-temperature system was constructed to study scaling caused by over saturation

(Andersson and Sellberg, 1992). 

Potentially suitable aquifers for ATES systems are widely available throughout the U.S. The

capacity of an aquifer limits the flow rate of an ATES system. The effective porosity of the aquifer affects

the volume of aquifer required to store a volume of heated or chilled water. This consequently affects the

size of an ATES well field required to store a specified quantity of energy (Hall and Raymond, 1992). 

Maximum flow rates range from 30 to 1,000 m3/hour (Andersson and Sellberg, 1992). ATES system wells

may be operated in either confined or unconfined aquifers. Operation in a confined aquifer would inhibit

heated water from migrating out of the formation.

The configuration of ATES systems also varies widely depending upon the application. Although

information on ATES systems in the U.S. is limited, information characterizing these systems in Europe is

believed to be representative of systems in the U.S. For example, in Switzerland, one experimental ATES

system has a large diameter central well (2.2 meters), from which two networks of six horizontal drains (0.2-

meter diameter, 25-meter length) were driven into the soil at the level of two sandy aquifers (depths of 7 and

24 meters). The storage volume is 100,000 m3 with a flow rate of 5-20 m3/hour (Jollien, et. al., 1992). 

This system is illustrated in Figure 3. Schematic diagrams of three other experimental ATES systems,

recently operated in Europe, are included in Figures 4 through 6.
September 30, 1999 29

Figure 3. Schematic Diagram of Dorigny, Switzerland ATES System

Source: Jollien, et. al., 1992
September 30, 1999 30

Figure 4. Schematic Diagram of Stuttgart, Germany ATES System 

Source: Adinolfi and Ruck, 1992
September 30, 1999 31

Figure 5. Schematic Diagram of Impounded ATES System at

University of Stuttgart, Germany

Source: Adinolfi and Ruck, 1992
September 30, 1999 32

Figure 6. Schematic Diagram of Combined Process ATES System, Malmö, Sweden

Source: Andersson and Selberg, 1992

Separately, in New York, an experimental ATES system (which is believed to no longer be

operating) consisted of six wells, each 55 meters in depth, with a 0.305-meter diameter steel bushing fitted

with a 15.2-meter long screen, of 0.2-meter diameter. The screen is surrounded by a 0.46-meter diameter

fine gravel envelope that extends 6.1 meters above the screen for a total height of 21.3 meters. The casing

above the gravel pack is enclosed in cement grout. The well pump is within the casing above the screen and

within the water table at a sufficient distance to allow for draw down. The 25-millimeter clearance around

the pump on all sides of the well casing allows for recharge. The wells are located in glacial outwash sand

and gravel sediments (manetto gravel). The ground water table is 12.2 meters below surface grade

(Marseille and Wilke, 1992).

Finally, in Minnesota, one recent field-test facility of an ATES project was conducted in the

Franconia-Ironton-Galesville (F-I-G) confined aquifer in St. Paul, Minnesota. Researchers assessed the

feasibility of designing, constructing, and operating the ATES system in a confined aquifer at temperatures as

high as 150oC. The storage and source wells were spaced 225 meters apart (Hoyer, et. al., 1994). 
September 30, 1999 33

4.3 Potential and Documented Damage to USDWs

The chemical quality of fluids released into ATES system wells is not necessarily the best indicator of

the potential for these wells to threaten USDWs, because the risk associated with experimental wells is

largely a function of the receiving ground water and aquifer characteristics as well as the objective of the

experimental project. For example, injection of heated and softened ground water into the experimental

ATES facility located in Minnesota lowered ground water temperature, raised ground water pH, and

resulted in the mobilization of silica into the ground water from the native quartz deposits in the receiving

formation. Although data are not available for other metals, it is possible that changes to the chemistry of the

ground water resulting from injection of heated and softened water or other treated water could mobilize

toxic metals (e.g., chromium, arsenic) if they are also present in the formation.

This being the case, a direct comparison of injectate quality to drinking water standards is useful, but

does not tell the whole story about the potential for experimental wells to endanger USDWs. It is also

necessary to consider the potential effects of ATES system well operations by evaluating ground water

monitoring data for these systems. In general, operators of experimental injection wells are required to

collect ground water quality data from monitoring wells situated in the vicinity of the injection well. 

Monitoring is required to determine whether the experimental well operation is having the desired effect and

to determine whether the operation is having any effects beyond its zone of operation (e.g., is heated water

injected into an ATES system aquifer formation migrating beyond the formation).

Section 4.3.1 identifies the injectate constituents likely to exceed drinking water standards. Section

4.3.2 then summarizes available ground water monitoring results and other information on observed impacts

associated with experimental well operations.

4.3.1 Injectate Constituent Properties

The constituents that may exceed MCLs and HALs in ATES system well injectate include chlorine,

arsenic, and chromium. Biological constituents (represented by total coliforms) may also be present in some

ATES system wells. In addition, although not present in the injectate itself, ground water monitoring data for

experimental injection wells indicate that trihalomethanes may be created in the aquifer through chemical or

physical reaction between the injectate and the ground water or receiving formation.

Appendix D to the Class V Study describes the critical or adverse toxicological effects noted in the

studies that served as the basis for the MCLs or HALs for these constituents. Appendix E to the study

presents data on the persistence and mobility of these and other constituents in ground water.
September 30, 1999 34

4.3.2 Observed Impacts

Ground water monitoring data are not available for ATES system experimental injection wells. 

However, several potential effects on ground water quality were identified as a result of the survey

conducted for this study, including production of trihalomethanes in ground water from injection of treated

(chlorinated) water into aquifers; and mobilization of minerals from receiving formations into ground water

from injection into aquifers.

Although experimental ATES system well operations were not reported to result in contamination of

a USDW to concentrations greater than drinking water standards, elevated concentrations in ground water

above background concentrations resulting from physical or chemical reaction of the injectate with the

ground water or ground water formation were notable for some experimental injection wells. Potential

impacts that may result directly from injectate characteristics or from physical or chemical reactions are

discussed further in Section 4.4.2. 

Injectate used for ATES systems (e.g., water used for heating or cooling systems) may not meet

primary and secondary drinking water standards. Operation of ATES systems may also result in changes in

ground water temperature and geochemistry, and water treatment chemicals used in these operations may

migrate outside the ATES system aquifer. Literature sources indicate that the experimental ATES system

formerly operated in Minnesota affected the characteristics of the underlying aquifer.

In general, ATES operations induce geochemical changes to native waters through the introduction

of non-native waters or heat (Holm, et. al., 1987). Some of the geochemical changes that occur include

precipitation-dissolution reactions, ion exchange, and mixing. All of these types of reactions may occur to

different extents and at different times during ATES operation. In the case of the experimental F-I-G

aquifer ATES system in St. Paul, Minnesota, the ATES operations caused the character of the geochemistry

of the native ground water to change from a calcium-magnesium-bicarbonate water system near saturation

with calcite, aragonite and dolomite, to a sodium-bicarbonate water system. The ATES system testing also

caused changes in ground water pH, alkalinity, dissolved silica, and most major ion concentrations. Ground

water sampling data from the ATES operations on the F-I-G aquifer indicate that the ATES system raised

the native water temperature; slightly lowered the pH; and slightly increased the concentration of chloride,

fluoride, and silica above background levels (Hoyer, et. al., 1994).

In addition to the direct effects of geochemical and heat changes (within the aquifer and its close

surroundings), there are other potential risks including (Andersson and Sellberg, 1992):

• Leakage of toxic substances like glycol, brine, etc.;

• Emission of CFC gases (see discussion below on methane);

• Growth of pathogenic bacteria; and

• Change of water composition in the aquifer due to chemical treatment.

Some aquifer systems have had high concentrations of dissolved gases such as methane while others

have had no major chemical contamination (Chant and Morofsky, 1992). Reaction of methane with HCl
September 30, 1999 35

used as a water treatment chemical could result in the production of CFCs. Scaling and clogging were cited

as the biggest operational problem with ATES systems; the injection of HCl prevented scaling but increased

corrosion and potential environmental impacts. The changes in aquifer chemistry included pH and hardness

(over saturation for calcium carbonate) (Jollien, et. al., 1992).

4.4 Best Management Practices

Research suggests certain characteristics are key to successful performance of ATES wells. This

research generally defines successful performance in terms of energy storage and system operation, and not

necessarily in terms of ground water quality. Best management practices begin with design of the system and

continue through construction and installation, characterization of the aquifer, and operation and maintenance

of the well.

Proper design of wells includes attention to the entire well field and its relationship to the storage

aquifer. In addition, the water well design for the ATES facility requires that the energy management plan of

the facility be known. Poor design and installation of a number of ATES wells has led to poor performance. 

Factors responsible for poor efficiency and specific yield include inadequate recognition of geochemical and

biologically induced degradation with time and temperature changes, use of improper water well design,

incorrect siting, insufficient quality control during well construction, and not understanding the demands

placed on the well during its service. ATES operation requires wells and drains that are designed to

withstand seasonal changes in flow direction, accommodate large changes in temperature on a cyclical basis,

and operate with little maintenance.

Aquifer characterization, including site-specific investigations, is a critical step for well design. The

characterization involves understanding the regional and local geology and hydrogeology, including analysis

of all operating water wells within a 2 to 3 mile radius of the ATES facility. Test wells are screened and

developed until the suspended solids in the discharge water are less than 1 ppm. A test well with more than

1 ppm of sediment during sustained pumping indicates either that it is not properly designed, installed or

developed, or that the aquifer has features that have not been taken into consideration. Test drilling and

pumping tests also yield water quality information and indicate whether or not dissolved gases may be

present under the confining aquifer pressure. The presence of gases can later lead to problems in installation

and pollution from gases escaping into formations intersected by the well bore. For well drilling, mud can

invade the fine pores of the aquifer formation. Proper well development ensures that all the mud that has

migrated into the aquifer formation is pulled back out of the aquifer zone immediately adjacent to the gravel

pack. If not, wells will eventually clog within a few years after commissioning (Mirza, 1994). 

The most significant problems affecting the operation of experimental ATES systems are caused by

scaling, clogging, and corrosion. Microbes play a crucial role in these processes and are relevant to water

quality (Seppaenen, 1994). However, most of the hydrochemically related clogging and corrosion problems

in ATES systems can be predicted and prevented by proper design, construction, operation (including water

treatment), and performing complete and careful pre-investigation. Scaling of heat exchangers and clogging

of wells, gravel pack, and adjacent aquifer(s) caused by chemical precipitates has frequently occurred in

ATES systems. The precipitation of carbonates has especially occurred in systems operating above 85oC
September 30, 1999 36

and iron and manganese oxides in systems operating below 40oC (Jenne, et. al., 1992). The content of

phosphonates or dissolved organic matter in the ground water serves as natural inhibitors for growing

carbonate crystals (Andersson and Sellberg, 1992). Conventional treatments for scaling utilize hydrochloric

acid, sodium hydroxide, or ion exchange (with a large consumption of regeneration chemicals) (Koch and

Ruck, 1992). To avoid problems associated with conventional water treatment, chemicals and processes

are used to prevent scaling (i.e., mineral deposits inside pipes); the use of small amounts of carbon dioxide

has been found to be a preferable treatment alternative (Koch and Ruck, 1992).

Clogging by iron bacteria slime is a potential risk mainly in low-temperature systems and in waters

with an iron concentration of at least 1 mg/l. Major bacterial growth is also a risk with redox potential (Eh)

values between 200 and 400 mV and pH values between 5.5-7.5. Corrosion usually occurs in slightly

acidic water and with total dissolved solids greater than approximately 1,000 mg/l (Driscoll, 1986 as cited in

Jenne, et. al., 1992).

At the ATES facility in St. Paul, Minnesota, the water injected into the aquifer was treated by an

ion-exchange water softener to decrease calcium carbonate precipitation and scaling within the ATES

system. Previous operation of the system with a calcium carbonate precipitator filter protected the aquifer

and injection well from scaling and clogging problems, but scale build up required the heat exchangers to be

shut down for eight hours at a time so that the filters could be replaced (Hoyer, et. al., 1994).

The principal technical problems with warm surface water storage systems has been biofouling of the

surface water heat exchanger, clogging of injection wells, and clogging of recovery wells during production. 

The biofouling problem has been solved through use of a specially designed air bubble filter in front of the

surface water open-hole inlet. Frequent cleaning with acid has been used to remove iron precipitation in the

tubes and the heat exchanger. In one system, the source of the iron precipitation was considered to be from

the mixing of lake water containing elevated iron with oxidized aquifer water (relatively free of iron). The

oxidized water oxidized the iron rich water when mixed in one of the wells, which caused a delayed

precipitation reaction to occur in tubes and fittings. This problem was proposed to be resolved with an in

situ oxidation of the dissolved iron (Andersson and Sellberg, 1992).

ATES well operations are also frequently hindered by the presence of a specific bacteria species,

Legionella. Factors to control the survival and propagation of Legionella include:

• Maintaining pH and alkalinity of the ground water below 5.5 or above 8.1 (tolerance range).

• Preventing scaling and corrosion (of cooling towers) with the addition of organic phosphorous

compounds and corrosion inhibitors such as zinc and chromate.

• Adding commercially available biodispersants to ensure Legionella associated with biofilms are

exposed to disinfectant and high alkalinity conditions.

• Reducing concentrations of metals, such as manganese and zinc, to levels that do not support the

growth of Legionella. Low levels of certain metals (such as iron, zinc, and potassium) enhance

growth of Legionella.

• Maintaining temperatures of water systems below 5oC or above 65oC. Legionella have been

isolated at temperatures between 5.7 and 63oC.
September 30, 1999 37

• Selecting biocides detrimental to both Legionella and the specific microflora found in association

with this microorganism.

• Keeping the environment aerobic. Legionella have been isolated at dissolved oxygen content

between 0.3 to 9 mg/l (Hicks and Stewart, 1988 as cited in Seppaenen, 1994).

• Using treatment chemicals responsibly and only in the amounts and frequencies necessary to control

bacterial growth, biofouling, and other system operating parameters.

4.5 Current Regulatory Requirements

4.5.1 Federal Programs

ATES system wells are covered by the UIC regulations discussed in Section 3.5.1 of this volume.

4.5.2 State and Local Programs

No UIC program reported any operating ATES wells. Therefore no state regulatory requirements

currently apply.
September 30, 1999 38

ATTACHMENT A

STATE AND LOCAL PROGRAM DESCRIPTIONS

This attachment does not describe every state’s program requirements; instead it focuses on the six

states where experimental tracer study wells are known to exist: Colorado, Idaho, Nevada, South Carolina,

Texas, and Washington. Altogether, these six states have a total of 396 documented experimental tracer

study wells. The program in Illinois is also described because that state reports two experimental wells that

are most likely no longer operating.

Colorado

Colorado is a Direct Implementation state. However, the state engineer issues permits to construct

wells. The Water Well Construction Rules (2 Colorado Code 402-2) (CCR) apply to well construction

contractors and drillers and to the construction of water wells, test holes, dewatering wells, monitoring and

observation wells, and well plugging and sealing (abandonment). The rule specifies that excavations that do

not penetrate through a confining layer between aquifers recognized by the state engineer may be designed,

constructed, used, and plugged and sealed by authorized individuals, as specified in the rule, who are not a

licensed well construction contractor. Wells constructed for sampling, measuring and test pumping for

scientific, engineering, and regulatory purposes that do not penetrate a confining layer may be constructed by

an authorized individual. 

Idaho

Idaho is a Primacy state and has promulgated regulations for the underground injection control

program in the Idaho Administrative Code (IDAPA), Title 3, Chapter 3. Deep injection wells are defined as

more than 18 feet in vertical depth below the land surface (37.03.03.010.11 IDAPA). Wells are further

classified, with Class V Subclass 5X25 defined as experimental technology wells (37.03.03.025.01.z

IDAPA).

Permitting

Construction and use of shallow injection wells is authorized by rule, provided that inventory

information is provided and use of the well does not result in unreasonable contamination of a drinking water

source or cause a violation of water quality standards that would affect a beneficial use (37.03.025.03.d.

IDAPA). Construction and use of Class V deep injection wells may be authorized by permit

(37.03.03.025.03.c IDAPA). The regulations outline detailed specifications for the information that must be

supplied in a permit application (37.03.03.035 IDAPA).

Operating Requirements

Standards for the quality of injected fluids and criteria for location and use are established for ruleauthorized wells, as well as for wells requiring permits. The rules are based on the premise that if the

injected fluids meet MCLs for drinking water for physical, chemical, and radiological contaminants at the
September 30, 1999 39

wellhead, and if ground water produced from adjacent points of diversion for beneficial use meets the water

quality standards found in Idaho’s “Water Quality Standards and Wastewater Treatment Requirements,”

16.01.02 IDAPA, administered by the Idaho Department of Health and Welfare, the aquifer will be

protected from unreasonable contamination. The state may, when it is deemed necessary, require specific

injection wells to be constructed and operated in compliance with additional requirements (37.03.03.050.01

IDAPA (Rule 50)). Rule-authorized wells “shall conform to the drinking water standards at the point of

injection and not cause any water quality standards to be violated at the point of beneficial use”

(37.03.03.050.04.d IDAPA).

Monitoring, recordkeeping, and reporting may be required if the state finds that the well may

adversely affect a drinking water source or is injecting a contaminant that could have an unacceptable effect

upon the quality of the ground waters of the state (37.03.03.055 IDAPA (Rule 55)). The permit for the

BSU Department of Geology tracer study well also prohibits the injection well operation from degrading

ground water or harming “beneficial uses” of ground water, and requires that Idaho water quality standards

not be exceeded.

Plugging and Abandonment

The Idaho Department of Water Resources (IDWR) has prepared “General Guidelines for

Abandonment of Injection Wells,” which are not included in the regulatory requirements. IDWR expects to

approve the final abandonment procedure for each well. The General Guidelines recommend the following:

• Pull casing, if possible. If casing is not pulled, cut casing a minimum of two feet below land surface;

• Measure the total depth of the well;

• Perforate the casing if is left in place. Neat cement with up to 5% bentonite can be pressure-grouted

to fill the hole. As an alternative, when the casing is not pulled, coarse bentonite chips or pellets may

be used to fill the hole. If the well extends into the aquifer, the chips or pellets must be run over a

screen to prevent any dust from entering the hole. No dust is allowed to enter the bore hole because

of the potential for bridging. Perforation of the casing is not required for this alternative;

• If well extends into the aquifer, a clean pit-run gravel or road mix may be used to fill bore up to ten

feet below top of saturated zone or ten feet below the bottom of casing, whichever is deeper, and

cement grout or bentonite clay used to surface. The use of gravel may not be allowed if the lithology

is undetermined or unsuitable;

• Place a cement cap at top of the casing if it is not pulled, with a minimum of two feet of soil overlying

filled hole/cap; and

• Abandonment of well must be witnessed by IDWR representative.
September 30, 1999 40

Financial Responsibility

No financial responsibility requirement exists for rule-authorized wells Permitted wells are required

by the permit rule to demonstrate financial responsibility through a performance bond or other appropriate

means to abandon the injection well according to the conditions of the permit (37.03.03.35.03.e IDAPA). 

Illinois

Illinois is a Primacy state. The Illinois Environmental Protection Agency (IUSEPA), Bureau of Land

has promulgated rules establishing a Class V UIC program in 35 Illinois Administrative Code (IAC) 704 that

are intended to be identical in substance to USEPA rules in 40 CFR 144.

Permitting

Any underground injection, except into a well authorized by permit or rule, is prohibited. The

construction of any well required to have a permit is prohibited until the permit has been issued (704.12.

IAC). Injection into Class V wells is authorized by rule until requirements under future regulations become

applicable (704.146 IAC). Under the state’s rules, basic information must be submitted, including the

activities to be conducted, location of the facility, principal activities, operator information, list of other

permits, topographic map of the facility, when required by the IUSEPA (702.123 IAC). Wells used in

experimental technologies are required to submit the following information:

• Location of each well;

• Date of completion of each well;

• Identification and depth of the formation(s) into which each well is injecting;

• Depth of each well;

• Casing and cementing record, tubing size, and depth of packer;

• Nature of the injected fluids;

• Average and maximum injection pressure at the wellhead;

• Average and maximum injection rate;

• Date of last mechanical integrity test, if any (704.148(b) IAC).

Operating Requirements

Owners or operators of wells authorized by rule must submit inventory information (704.148 IAC). 

In addition, IUSEPA may require submission of other information deemed necessary by IUSEPA (704.149

IAC). This may include information about the performance of ground water monitoring, analysis of injected

fluids, and description of the geologic strata through which and into which injection is taking place. 

If at any time the IUSEPA learns that a Class V will may cause a violation of primary drinking water

regulations under 40 CFR 142, it will require the injector to obtain an individual permit, issue a permit that

requires the injector to take such action, including closure of the well, as may be necessary to prevent the
September 30, 1999 41

violation, or take enforcement action. If a Class V well may be otherwise adversely affecting the health of

persons, the IUSEPA may prescribed such actions as may be necessary to prevent the adverse effect.

Mechanical Integrity Testing 

If the IUSEPA determines that a well lacks mechanical integrity, it may order immediate cessation of

injection (704.142(f) IAC). However, the regulations do not establish a specific requirement for mechanical

integrity testing for Class V wells A permit for a Class V well may include requirements for demonstration of

mechanical integrity (704.190 IAC).

Nevada

Nevada is a Primacy state in which the Division of Environmental Protection (DEP) administers the

UIC program. The statute specifically defines injection wells used in experimental technologies as Class V

wells (445A.849.16 NRS).

Nevada Revised Statutes (NRS) §§ 445A.300 - 445A.730 and regulations under the Nevada

Administrative Code (NAC) §§ 445A.810 - 445A.925 establish the state’s basic underground injection

control program. The injection of fluids through a well into any waters of the state, including underground

waters, is prohibited without a permit issued by the DEP (445A.465 NRS), although the statute allows

both general and individual permits (445A.475 NRS and 445A.480 NRS). Furthermore, injection of a fluid

that degrades the physical, chemical, or biological quality of the aquifer into which it is injected is prohibited,

unless the DEP exempts the aquifer and the federal USEPA does not disapprove the exemption within 45

days after notice of it (445A.850 NRS).

Regulations, particularly Chapter 445A NAC, “Underground Injection Control,” define and

elaborate these statutory requirements. First, they provide that any federal, state, county, or municipal law

or regulation that provides greater protection to the public welfare, safety, health, and to the ground water

prevails within the jurisdiction of that governmental entity over the Chapter 445A requirements (445A.843

NAC). 

Permitting

The UIC regulations specify detailed information that must be provided in support of permit

applications, including proposed well location, description of geology, construction plans, proposed

operating data on rates and pressures of injection, analysis of injectate, analysis of fluid in the receiving

formation, proposed injection procedures, and corrective action plan (445A.867 NAC). The DEP may

modify the permit application information required for a Class V well.
September 30, 1999 42

Siting and Construction

The state specifies, among other siting requirements, that the well must be sited in such a way that it

injects into a formation that is separated from any USDW by a confining zone that is free of known open

faults or fractures within the area of review. It must be cased from the finished surface to the top of the zone

for injection and cemented to prevent movement of fluids into or between USDWs (445A.908 NAC).

Operating Requirements

Monitoring frequency for injection pressure, pressure of the annular space, rate of flow, and volume

of injected fluid is specified by the permit for Class V wells. Analysis of injected fluid must be conducted

with sufficient frequency to yield representative data. Mechanical integrity testing is required once 5 years,

by a specified method (445A.913.5 NAC and 445A.916 - 445A.920 NAC). For the YMSCP site, the

concentration of injected chemicals “will not result in the injected water exceeding state or federal drinking

water standards or in degradation of waters of the state” according to officials at Nevada’s Bureau of Water

Pollution Control (Land, 1997).

Plugging and Abandonment

A plugging and abandonment plan and cost estimate must be prepared for each well, and reviewed

annually. Before abandonment, a well must be plugged with cement in a manner that will not allow the

movement of fluids into or between USDWs (445A.923 NAC).

Financial Responsibility

Class V wells may be required to provide a bond in favor of the state either equal to the estimated

cost of plugging and abandonment of each well or, if approved by DEP, a sum not less than $50,000 to

cover all injection wells of the permit applicant in the state (445A.871 NAC). However, if adequate proof of

financial responsibility is presented, the bonding requirements may be waived or reduced. 

South Carolina

South Carolina is a Primacy state. The state’s underground injection control program is

implemented by the Department of Health and Environmental Control (DHEC). The UIC regulations, found

in Chapter 61 of the state regulations (SCR), divide Class V wells into two groups, with experimental wells,

defined as “injection wells used in experimental technologies,” found in group (A) ((R61-87.10E.(1)(g)). 

The same requirements apply to experimental wells as are applied to other Class V(A) wells. 
September 30, 1999 43

Permitting 

Experimental wells, as Class V(A) wells, are prohibited except as authorized by permit (R61-

87.10.E.(2)). The permit application must include a description of the activities to be conducted, the name,

address, and location of the facility, the names and other information pertaining to the owner and operator, a

description of the business, drawings of the surface and subsurface construction of the well, and proposed

operating data, including average and maximum daily rate and volume of fluid to be injected, average and

maximum injection pressure, and source and an analysis of the chemical, physical, biological, and

radiological characteristics of the injected fluid (R61-87.13.G(2)). The movement of fluids containing

wastes or contaminants into USDWs as a result of injection is prohibited if the waste or contaminant may

cause a violation of any drinking water standard or otherwise adversely affect the health of persons (R61-

87.5).

Siting and Construction

Siting and operating criteria and standards for Class V(A) wells require logs and tests, which will be

specified by DHEC in the permit, to identify and describe USDWs and the injection formation. 

Construction standards are the same as those applied to drinking water wells. 

Injection may not commence until construction is complete, the permittee has submitted notice of

completion to DHEC, and DHEC has inspected the well and found it in compliance 

(R61-87.13U).

Operating Requirements

DHEC will establish maximum injection volumes and pressures and such other permit conditions as

necessary to assure that fractures are not initiated in the confining zone adjacent to a USDW and to assure

compliance with operating requirements (R61-87.13V). Operating requirements for Class V(A) wells are

not distinguished in the state regulations from operating standards for Class II and III wells (R61-87.14). 

Injection pressure at the wellhead may not exceed a maximum calculated value to ensure that injection does

not initiate new fracturing or propagate existing fractures in the confining zone adjacent to the USDW.

Monitoring requirements will be specified in the permit. Monitoring requirements for Class V(A)

wells are the same as those for Class III wells, and may include installation of monitoring wells in the

injection zone and adjacent zones as necessary to detect the dispersion and migration of injection fluids

within and from the injection zone. Monitoring of the fluid levels and water quality in the injection and

monitor wells at specified intervals and submission of monitoring results will be specified in the permit. 

However, reporting of monitoring results to DHEC is required at least quarterly (R61-87.14.G and I(1)). 
September 30, 1999 44

Mechanical Integrity

Prior to granting approval for operation, DHEC will require a satisfactory demonstration of

mechanical integrity. Tests will be performed at least every 5 years (R61-87.14.G).

Plugging and Abandonment

A plugging and abandonment plan must be prepared and approved by DHEC (R61-87.12.B and

.15).

Texas

Texas is a Primacy state. The Injection Well Act (Chapter 27 of the Texas Water Code) and Title 3

of the Natural Resources Code provide statutory authority for the underground injection control program. 

Regulations establishing the underground injection control program are found in Title 30, Chapter 331 of the

Texas Administrative Code (TAC).

Permitting

Underground injection is prohibited, unless authorized by permit or rule. (331.7 TAC) By rule,

injection into a Class V well is authorized , although the Texas Natural Resources Control Commission

(TNRCC) may require the owner or operator of a well authorized by rule to apply for and obtain an

injection well permit (331.9 TAC). No permit or authorization by rule is allowed where an injection well

causes or allows the movement of fluid that would result in the pollution of a USDW. A permit or

authorization by rule must include terms and conditions reasonably necessary to protect fresh water from

pollution (331.5 TAC). Experimental wells are not specifically identified in the rules as Class V wells, but

the category is not limited to the well types specified in the rules (331.11 (a)(4) TAC).

Siting and Construction

All Class V wells are required to be completed in accordance with explicit specifications in the rules,

unless otherwise authorized by the TNRCC. These specifications are:

• A form provided either by the Water Well Drillers Board or the TNRCC must be completed.

• The annular space between the borehole and the casing must be filled from ground level to a depth

of not less than 10 feet below the land surface or well head with cement slurry. Special requirements

are imposed in areas of shallow unconfined ground water aquifers and in areas of confined ground

water aquifers with artesian head.

• In all wells where plastic casing is used, a concrete slab or sealing block must be placed above the

cement slurry around the well at the ground surface; and the rules include additional specifications

concerning the slab.

• In wells where steel casing is used, a slab or block will be required above the cement slurry, except

when a pitless adaptor is used, and the rules contain additional requirements concerning the adaptor.
September 30, 1999 45

• All wells must be completed so that aquifers or zones containing waters that differ significantly in

chemical quality are not allowed to commingle through the borehole-casing annulus or the gravel

pack and cause degradation of any aquifer zone.

• The well casing must be capped or completed in a manner that will prevent pollutants from entering

the well.

• When undesirable water is encountered in a Class V well, the undesirable water must be sealed off

and confined to the zone(s) of origin (331.132 TAC).

Operating Requirements

None specified. Chapter 331, Subpart H, “ Standards for Class V Wells” addresses only

construction and closure standards (331.131 to 331.133 TAC).

Mechanical Integrity Testing

Injection may be prohibited for Class V wells that lack mechanical integrity. The TNRCC may

require a demonstration of mechanical integrity at any time if there is reason to believe mechanical integrity is

lacking. The TNRCC may allow plugging of the well or require the permittee to perform additional

construction, operation, monitoring, reporting, and corrective actions which are necessary to prevent the

movement of fluid into or between a USDW caused by the lack of mechanical integrity. Injection may

resume on written notification from the TNRCC that mechanical integrity has been demonstrated (331.4

TAC).

Plugging and Abandonment

Plugging and abandonment of a well authorized by rule is required to be accomplished in accordance

with §331.46 TAC (331.9 TAC). In addition, closure standards specific to Class V wells provide that

closure is to be accomplished by removing all of the removable casing and filling the entire well with cement

to land surface. Alternatively, if the use of the well to be permanently discontinued, and if the well does not

contain undesirable water, the well may be filled with fine sand, clay, or heavy mud followed by a cement

plug extending from the land surface to a depth of not less than 10 feet. If the use of a well that does contain

undesirable water

is to be permanently discontinued, either the zone(s) containing undesirable water or the fresh water zone(s)

must be isolated with cement plugs and the remainder of the well bore filled with sand, clay, or heavy mud to

form a base for a cement plug extending from the land surface to a depth of not less than 10 feet (331.133

TAC).

Financial Responsibility

Chapter 27 of the Texas Water Code, “Injection Wells,” enacts financial responsibility requirements

for persons to whom an injection well permit is issued. A performance bond or other form of financial

security may be required to ensure that an abandoned well is properly plugged (§ 27.073). Detailed

financial responsibility requirements also are contained in Chapter 331, Subchapter I of the state’s UIC
September 30, 1999 46

regulations (331.141 to 331.144 TAC). A permittee is required to secure and maintain a performance bond

or other equivalent form of financial assurance or guarantee to ensure the closing, plugging, abandonment,

and post-closure care of the injection operation. However, the requirement, unless incorporated into a

permit, applies specifically only to Class I and Class III wells (331.142 TAC).

Washington

Washington is a Primacy state. Chapter 173-218 of the Washington Administrative Code (WAC)

establishes the underground injection control program. Under the program, the policy of the Department of

Ecology (WDOE) is to maintain the highest possible standards to prevent the injection of fluids that may

endanger ground waters which are available for beneficial uses or which may contain fewer than 10,000 mg/l

total dissolved solids (TDS). Consistent with that policy, new Class V injection wells that inject industrial,

municipal, or commercial waste fluids into or above a USDW are prohibited (172-218-090(1) WAC), and

existing wells that inject industrial, municipal, or commercial waste fluids into or above a USDW must obtain

a permit to operate. All other Class V injection well owners and operators must notify the WDOE and

supply required inventory information (172-218-090 (2) and (3) WAC).

Permitting 

A permit must specify conditions necessary to prevent and control injection of fluids into the waters

of the state, including all known, available, and reasonable methods of prevention, control, and treatment;

applicable requirements in 40 CFR Parts 124, 144, 146; and any conditions necessary to preserve and

protect a USDW. Any injection well that causes or allows the movement of fluid into a USDW that may

result in a violation of any primary drinking water standard under 40 CFR Part 141 or that may otherwise

adversely affect the beneficial use of a USDW is prohibited (173-218-100 WAC). The state’s Waste

Discharge Permit Program, which prohibits the discharge of pollutants into waters of the state (which include

ground water) without a permit (Chapter 173-216 WAC) does not apply to the injection of fluids through

wells which are regulated by the UIC control program (173-216-010 WAC). 

Siting and Construction

The state’s minimum standards for construction and maintenance of wells require notice before

construction, reconstruction, or abandonment of a well, and submission of complete records describing

construction or alteration of a well (173-160-050 and 173-160-055 WAC).

Wells are required to be planned and constructed to be adapted to the geologic and ground water

conditions at the well site and designed to facilitate conservation of ground water (173-160-065 WAC).

The natural barriers to ground water movement between aquifers must be maintained, and aquifers

or strata penetrated during drilling must be sealed to prevent impairment of water quality or cascading water. 

All sealing must be permanent and prevent movement of surface or ground water into the annular space. 

Sealing shall prevent the movement of ground water either upward or downward from zones that were

cased off because of poor quality. When cement grout is use in sealing, it must be set in place 72 hours
September 30, 1999 47

before additional drilling takes place, unless special additives are mixed with the grout that cause it to set in a

shorter period of time. All grouting must be performed by tremmying the mixture from the bottom of the

annular space to the surface in one continuous operation. The annual space to be grouted shall be a

minimum four inches larger than the permanent casing. When casing diameter is reduced, a minimum of 8

feet of casing overlap is required and the bottom of the annular space between the casings shall be sealed

with a watertight packer. The remainder of the annular space must be pressure grouted with bentonite or

neat cement (173-160-075 WAC).

Operating Requirements

The water quality standards for ground waters establish an antidegradation policy. The injectate

must meet the state ground water standards at the point of compliance (173-200-030 WAC).

Plugging and Abandonment

All wells not in use must be securely capped so that no contamination can enter the well

(173-160-085 WAC).
September 30, 1999 48

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September 30, 1999 51

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