FINAL ELF EMF SURVEY REPORT
MARY WALTER ELEMENTARY SCHOOL FACILITY

Prepared by Louis S. Vitale, Jr. JULY 12, 1994 Copyright ©1995 VitaTech Engineering, LLC

1.0 INTRODUCTION

The objective of this document is to analyze the extremely low frequency (ELF) electromagnetic field (EMF) data presented in the Mary Walter Elementary School Contour Measurement Report (28-29 April 1994), examine simulated electric and magnetic field levels under various loads, evaluate practical field management (mitigation) strategies to reduce EMF exposure, and provide ELF EMF exposures and risk assessment information regarding schools and children.

1.1 Site Description

The 64,000-square foot Mary Walter Elementary School building with 31 acres of property is located on State Road 835 in Morrisville, Virginia. From the adjacent VEPCO Morrisville substation, a single circuit (three phase) wide-delta configured 525 KV transmission line (circuit #569) transverses school property along a northeast unfenced/unmarked 235-foot right-of-way (ROW) easement. Maximum conductor sag (closest point to ground) is 42 feet when conductor reaches 190 F⁰ under heavy loads. The main school building is 360 feet, and the new classroom building is 260 feet, from the 525 KV transmission line center conductor. There is a playground area between the school and transmission lines. Within the school there are 29 classrooms and several common areas (hallways, library, cafeteria, office, lounge, etc.), a student computer lab with 22 computers, television monitors, and assorted projectors.

There is also a single circuit (three phase) 34.5 KV overhead distribution line 240 feet from the main school building (front) that runs parallel to State Road 835. An underground 34.5 KV three phase service drop originating from the utility pole near the main driveway (entrance) supplies electrical power to the main and new building ground mounted transformers. Recently, the ground mounted transformers have been enclosed with a securable fence to restrict access and limit magnetic field exposure.

The Morrisville substation is adjacent to the southwest school property line. At the substation three 525 KV transmission lines interconnect: main feeder (circuit #573) from the North Anna nuclear steam generation station, feeder (circuit #572) from the Mount Storm fossil fuel steam generation station, and the Loudoun substation feeder (circuit #569) which transverses the school property. There is also a 115 KV transmission line, supplied from a 525-115 KV step-down transformer at the substation, that runs to the Remington Patton substation.

2.0 MARY WALTER ELEMENTARY SCHOOL CONTOUR SURVEY REPORT

A comprehensive ELF EMF on-site survey was performed 28-29 April 1994 at the Mary Walter Elementary School facility. The author, Mr. Louis Vitale who is Chief Engineer at VitaTech Engineering, managed the on-site survey project with assistance from Mr. Craig Wakefield, Supervisor of Maintenance/Facilities at the Fauquier County Public School System. All EMF data was recorded and witnessed under Mr. Wakefield's direct supervision during the two day on-site EMF survey.

On Thursday, 28 April 1994, a short meeting was held with Ms. Lois Adkins, school principal, regarding the on-site EMF survey process. After the meeting, EMF data collection began at 1 P.M. with her approval, and proceeded until 6 P.M.. The next day work resumed at 1 P.M., and the on-site EMF survey was completed by 4 P.M. The final Mary Walter Elementary School Contour Measurement Report was delivered via Federal Express to Mr. Wakefield's office on 9 June 1994. Another original copy of the aforementioned report with color plots is attached to this document. This report will be referred to as the M.W.E.S. Contour Measurement Report in this document.

2.1 Electrical Surveys-Main & New Buildings

A basic electrical survey was performed on the switchgear panels, distribution transformers, and grounding systems in both the main and new buildings. Refer to pages 2 and 3 of the M.W.E.S. Contour Measurement Report for details. The bonded water pipe ground conductors from each switchgear panel (neutral-ground buss) were measured with a Fluke 33 True RMS Clamp Meter for excessive ground currents: none were recorded. It should be noted that we could not locate the supplemental ground rods required by the National Electric Code (NEC) sections 250-81 and 250-83. A licensed electrician should locate the ground rods or install same according to local code requirements. In each building normal ground current levels were measured on the neutral-ground conductors from the distribution transformers.

In conclusion, the electrical survey did not measure any excess currents on the grounding systems (switchgear panels & distribution transformers) under normal operating conditions. Excess currents usually indicate potentially serious electrical problems that generate significantly high magnetic field levels around the conductive path to ground (grounding conductor, water pipe, and ground rod).

2.2 Overview-Outdoor & Indoor Survey Paths

Fourteen survey paths were recorded during the two-day, on-site EMF survey (refer to pages 4-7 of the M.W.E.S. Contour Measurement Report for details). On the next page the outdoor and indoor survey paths are listed in Table 1:

Table 1. Outdoor & Indoor Survey Paths

The outdoor survey paths contain four perimeter surveys (property line, main & new buildings, playground areas, and new building), two radial surveys (from main & new buildings to under the transmission line), and a front survey (from main entrance to street/distribution line to transmission line). New building indoor survey paths include all the classrooms, hallway perimeter (normal conditions), and hallway perimeter during special power/ground current tests. Finally, the main building survey paths include the outer classroom loop, and inner classroom/office/library loop plus the gym/cafeteria/kitchen areas.

2.21 Survey Instrument-FieldStar 1000 Gaussmeter

All magnetic flux measurements, except for the computer monitor MPR II compliance tests, were recorded with a triple-axis Dexsil Corporation FieldStar 1000 microprocessor-controlled gaussmeter (serial #31400009). This unit was factory calibrated according to ANSI/IEEE Standard 644-1987 on 5/24/93. Inside the gaussmeter three onthogonal coils simultaneously detect both horizontal (x-axis and y-axis) and vertical (z-axis) magnetic fields at 60 Hz. The microprocessor instantly converts the magnetic field levels of each axis (x,y,z) to magnetic flux (milligauss) readings and simultaneously calculates the resultant R_rms (root-means-square) vector according to the following formula:

When collecting path data, a nonmetallic survey wheel is attached to the FieldStar 1000 gaussmeter and the unit is programmed to record mapped magnetic flux data at selected (1-foot) intervals. Along each path the distance is automatically logged by the survey wheel and the relative direction entered on the keyboard. After completing the path surveys, magnetic flux data with distance and directional information is uploaded to a 486 computer, and processed by the FieldStar graphics software (version 2.55) into detailed hatch and profile plots (see pages 11-39 of the M.W.E.S. Contour Measurement Report for details). All plots display a record number, DOS file name, time/date stamp, ID path number, and the following statistical data (in milligauss) defined below:

Peak - maximum magneticfield (flux) value measured in group.

Mean - arithmetic average of all magnetic field (flux) values collected.

Standard deviation - is calculated using the formula below:

where B is the magnetic field (flux) and N is the number of samples

Median, L5 and L95 - calculated by first dividing the data set range into 1000 equal intervals or bins, then assigning each data point to a bin as the data is plotted. After the data has been assigned to bins, the number of points in each of the bins is summed beginning at zero. When the total number of points in the sum reaches 5% of the total the mid-point of that bin is labeled L95 or the magnetic field (flux) value above which the data is 95% of the time. Continuing the sum until 50% of the total is reached, the mid-point of that bin is then the median. When the sum reaches 95% of the total number of points in the data set, the mid-point of this bin is then L5 or the level above which the magnetic field (flux) value is 5% of the time.

2.22 New Building-Ground Current Tests

The hallway magnetic flux levels were lower than near the walkway and doorway columns in the new building. Refer to the Perimeter-hallway new building B1 profile plots, M.W.E.S. Contour Measurement Report. Each column and footing is reinforced with metal rods that conductively connect the steel roof and metal support frame to the ground. Only two sources can produce elevated magnetic flux levels in the reinforced columns: electrical ground currents and/or electromagnetically induced currents (see Section 2.41 for details) from the 525 KV transmission line.

The electrical systems of both building are grounded to a common metal water pipe mounted to the metal roof frame just above the walkway/hallway ceiling tiles. Electrical ground currents normally travel along the water pipes and may leak current onto the metal roof frame. Although the electrical surveys (see Section 2.1) did not detect any abnormal switchgear and transformer ground currents, it is possible to have leakage currents from electrical equipment or several grounded-neutral receptacles scattered around the building. These currents naturally migrate along multiple paths to the nearest earth grounds, thereby inducing elevated magnetic fields in the water pipes and reinforced columns.

It was necessary to perform a Ground Current Test to classify the source of current traveling in the reinforced columns: electrical ground currents and/or electromagnetically induced currents. Mr. Wakefield identified elevated levels around the outside doorway columns and three other spots (now defined as points) in the new building during a previous survey with VEPCO: walkway column (point A), walkway wall (point B), and the outside wall (point C) in classroom #9. Refer to page 6 and indoor path plots B1, G1 & H1 of the M.W.E.S. Contour Measurement Report.

The Ground Current Tests was performed under the following power conditions: both building energized, new building de-energized, and both buildings de-energized. Each marked point was measured under the test conditions listed in Table 2, below:

*Path B1 recorded on Thursday @ 16:03; all other data recorded on Friday between 15:30-15:45

Table 2. Ground Current Test Chart

First, reference data was recorded at each point with both buildings energized. Next, the new building was de-energized, and points A, B & C decreased by 5-10%. Finally, both buildings were completely de-energized, and all three points remained absolutely unchanged. Refer to the Perimeter-hallway new building path plots G1 and H1 in the M.W.E.S. Contour Measurement Report.

There was a 5-10% decrease in magnetic flux levels only after the new building was de-energized. This basically proves the electrical ground currents originate only from within the new building. However, if the magnetic flux levels diminish by 5-10% after eliminating all electrical ground current sources, then obviously 90% of the column currents are generated from electromagnetic induction between the 10,000-square foot steel roof and the 525 KV transmission line. Conclusively, there is an additive magnetic flux effect in each reinforced column from the combined electrical ground currents and electromagnetically induced currents.

It is not cost effective to locate, reduce, or reroute the rather insignificant electrical ground current sources in the new building. This is a typical electrical phenomena in most commercial/industrial buildings including public schools. Also, nothing can be done to reroute the electromagnetically induced roof and column currents. The only solution is to reduce the magnetic field levels from the 525 KV transmission line, thereby reducing the electromagnetically induced currents in the 10,000-square foot metal roof.

2.3 Indoor Equipment Data

Magnetic flux data from energized equipment in the main office, computer room, library, and kitchen were recorded at 4-inch and 18-inch intervals. Refer to pages 8 & 9 in the M.W.E.S. Contour Measurement Report. Energized office and library equipment measurements were generally typical. However, the opaque projector and right side of the film strip projector measured 174 mG and 1270 mG, respectively. Any projector with magnetic flux levels exceeding 100 mG should be magnetically shielded to reduce exposure to teachers and students. Kitchen equipment levels were typical except for the floor mixer, which appears to have an improper grounding problem. Electrician should examine and repair floor mixer.

The gym transformer measured 300 mG directly on top and 1.56 mG around the Blue Line Safety Zone installed by the school. Finally, the main and new building transformers are all enclosed within safety fences.

2.31 Computer Room VDT Emission Data

Video display terminals (VDTs) were checked for electric and magnetic field compliance to the Swedish MPR II VDT emissions standards with the MEDA PLM-100WB wideband gaussmeter and Radiation Technology, Inc. Tracer TR-100 electric field monitor. The Swedish MPR II VDT electric and magnetic field emission standards are presented on the next page in Table 3:

Table 3. Swedish MPR II Emission Standards

All VDT monitors in the main office, computer room, and library areas complied with the Swedish MPR II emission standards. Note: the computer room became warm and uncomfortable (77.4 F^ø/57% H) fifteen minutes after students entered the classroom. Apparently, the combined head load from computers, VDTs, printers, and students exceeds the HVAC cooling capacity in the computer room.

2.4 Radial Electric & Magnetic Field Measurements

Electric and magnetic field measurements were recorded along a 310-foot continuous radial line at 10-foot intervals from the northwest corner of the new building to under and beyond the 525 KV transmission line. Refer to page 10 of the M.W.E.S. Contour Measurement Report for details. Electric fields, measured in volts per meter (V/M), were recorded 6 feet above the ground in the vertical plane with the Electric Field Measurements Model 160 (serial #160-3-60-594) electric field meter. This is a single-axis electric field meter that was recently calibrated by the manufacturer.

At 200 feet from the new building, the vertical electric field levels reached a maximum of 2,200 V/M, diminished to 380 V/M directly under the 525 KV transmission line center conductor, and then increased to 1,040 V/M near the tree line. Normally, the maximum electric field level occur near the outer conductors as demonstrated above. When the conductors are arranged in a delta configuration, the resultant electric field level significantly decreases under the center conductor because of the partial-cancellation effects between conductors. The above electric field data also conforms to the simulated electric field profile data calculated by the Southern California Edison Fields 2.0 software (see Section 5.1 for details).

Around the playground equipment, the electric and magnetic field levels were also recorded. Metal playground equipment (i.e., swings, basketball hoops, climbing ladder, etc.) distorted the vertical electric field lines and intensified the readings above the equipment. This is a typical phenomena around grounded metal objects such as playground equipment within a uniform electric field from a transmission line.

Electric and magnetic fields produced by the 525 KV transmission line transfers energy (power) from the lines to nearby conductive animate (i.e., children, teachers, etc.) and inanimate (i.e. playground equipment, metal roof, etc.) objects. These nearby conductive objects experience two distinct phenomenon: electrostatic induction from the electric fields and electromagnetic induction from the magnetic fields.

2.41 Electrostatic Induction

Alternating currents and voltages are induced from electric fields coupling with conductive animate and inanimate objects. The actual current consists of minute movements of charged particles: electrons in metallic conductors and ionic conduction in body tissues and fluids. The voltages and currents induced directly into humans are of concern if they are high enough to cause direct biological, physiological, and psychological effects.

If the conductive object is grounded, the induced current that travels through the object to the ground is called the short-circuit current (units in amperes). Generally, in humans and animals the short-circuit current flows from head to feet (called body currents). Examples of measured short-circuit currents in 1,000 V/M and 2,000 V/M electric fields similar to those around the playground area are presented below:

When a person touches a conductive object isolated from ground within an electric field, a perceptible current (tingling sensation) or shock may occur. This can also happen when the person is insulated and the object is grounded. The amount of current is determined by the electric field strength, size of the object, and how well both the object and person are insulated from the ground. Shocks are classified as average perception, secondary, and primary. The average perception level for a man (180-lbs.) is about 1.0 mA, for a woman 0.67 mA, and for a child under 0.50 mA. Secondary shocks cause no direct physiological harm, but they may annoy a person and cause muscles to react involuntarily. Although difficult to define, the lower average secondary shock level for an average sized man is about 2.0 mA.

Primary shocks can be harmful. The lower level is described as the current at which 99.5 percent of subjects can still voluntarily "let-go". Research determined that the average let-go current for men (180 lbs.) is 9 mA and 6 mA for women (120 lbs.). It isestimated at 4.5 mA for children. The National Electrical Safety Code (N.E.S.C.) specifies 5 mA as the maximum allowable short-circuit current from vehicles, trucks, and equipment near transmission lines. The American National Standard Institute (ANSI) allows up to 0.5 mA leakage current from portable household appliances and 0.75 mA from fixed appliances (ANSI 1973). Finally, in addition to potential shocks, there may be a perceptible skin (tingling) and vibrating hair sensation, depending on the humidity and weather, directly under the 525 KV transmission line conductors.

Safety Notes:

1)Students should never play directly under the 525 KV transmission lines: no kites, model airplanes, ropes, long conducting poles, etc.  Refer to "Living and Working Around High-Voltage Power Lines" written by Bonneville Power Administration in Appendix. Electricity from the 525 KV transmission lines will arc or "flashover" through the air to any grounded conductive object approaching too close. VEPCO will provide the recommended N.E.S.C. safe distance and vehicle clearance requirements.

2)Check playground equipment grounds and definitely replace metal chain on dosing tank with a plastic equivalent.

2.42 Electromagnetic Induction

A conductive object, animate or inanimate, coupled by a magnetic field induces currents and voltages by electromagnetic induction. Magnetic fields from transmission lines will normally induce voltages at the open ends of long, partially grounded, parallel (conductors) fences, wires, and exposed pipes. Normally, one end of the conductor is grounded and the earth serves as the remainder of the loop. A person that closes the loop can experience a shock. Threshold and let-go levels are the same for electromagnetically coupled currents.

During the Ground Current Test (see Section 2.11), the electromagnetic induction currents were identified as the primary source of magnetic flux from the reinforced columns of the new building. These currents originate in the 10,000-square foot steel metal roof, which is electromagnetically coupled to the nearby transmission line, and migrate to the earth through the reinforced columns. Finally, there is also an electromagnetic induction coupling effect with the aluminum window frames and doorway lintels. This phenomena produces distorted and intensified magnetic flux levels around the window frames and doors from circulating currents.

Alternating magnetic fields also induce electric fields and currents inside humans. Magnetically induced body currents flow primarily in peripheral loops (called eddy currents) perpendicular to the field; however, current at the center (body) is near zero. It should be noted that electrostatic induction tends to induce higher body currents than electromagnetic induction (eddy currents). Humans cannot perceive (sense) magnetic fields produced by any source including transmission lines. Only very high levels (>100 Gauss) will cause a flickering visual sensation. This effect disappears when the field is removed, apparently without permanent damage to the visual system.

2.5 Outdoor Survey Plots-Magnetic Flux Assessment

There are two types of outdoor survey plots in the M.W.E.S. Contour Measurement Report: hatch and profile. Hatch plots translate the sampled data (R_rms resultant magnetic flux at one-foot intervals-see Section 2.21 for definitions) into colored lines that represent magnetic flux levels by defined ranges along the survey path. A key defines the range limits for each sampled data point by color and line size.

Profile plots (color and black-and-white) display sampled magnetic flux data as a function of distance. Color profile plots show the horizontal (x-axis and y-axis) and vertical (z-axis) components plus the R_rms resultant sampled magnetic flux data. The black-and-white profile plots only show the R_rms resultant.

2.51 Front Door/Street/Transmission Line

The first outdoor survey, identified as path A1, began at the front door, main building, proceeded straight to Route 835 under the 34.5 KV single-circuit distribution line, and turned 90 degrees, continuing down Route 835 under the 525 KV transmission line.

The front door path is under 3 mG until nearly 15 feet from the distribution line, Point A, indicating the predominate field in front of the school is from the transmission line, not the distribution line. From Point A, the level increases toward the transmission line, reaching a maximum peak of 76.7 mG under the center conductor. In the color profile plot, notice the vertical z-axis flux level: it predominates from the start point at the front door, and continues past Point A for almost 200 feet before intersecting with the horizontal x-axis, approximately 150 feet from the center conductor.

2.52 Perimeter-Property & Transmission Line

The second outdoor survey, identified as path B1, began on State Road 835 (front of school) and circumnavigated the school property line, under and parallel to the transmission lines, and back to the main building front doorway. Refer to Perimeter-Property & Transmission Line images: Hatch plot (image 1) & Profile plot (image 2).

In the black-and-white profile plot, the level exceeded 2.8 mG for nearly 100 feet after the start point (due to the distribution line on State Road 835), then dropped to .5 mG from Point A to Point C along the fence line. About 175 feet after Point C, the transmission line effects increased from 2.8mG to 71 mG directly under the conductors before Point D, then diminished to 40 mG parallel to the conductors peaking before Point E a second time at 71 mG. Levels continued to decline from Points F-G until they returned to 2.8 mG after Point H at the front of the school.

2.53 Perimeter-Main & New Building

The third outdoor survey, identified as path C1, began at the front door, main building, proceeded around the main building perimeter, along the gym and kitchen area, then around new building perimeter, and back to the front door. Refer to: Hatch plot (image 1) & Profile plot (image 2).

In the color profile plot (notice how the vertical z-axis field predominates), the front levels diminished from 3.75 mG at the doorway to 1.75 mG (Point A) around the turn, slightly increased to 2.5 mG along the parking lot side to Point B, decreased to 1 mG around the gym between Points C and D, then increased to 4 mG at Point E near the main building transformers. The levels dropped off around the playground from Point E to Point G midway, increased to around 7 mG along the new building perimeter facing the transmission line, and diminished back to the front door.

2.54 Perimeter-Playground Areas

The fourth outdoor survey, identified as path D1, began near the new building (linear graphic distorts actual path), turned toward the paved playground area which is between the transmission line and the school, then turned toward the school flowing a path around the playground structure near the school buildings, and back along the perimeter of the new building past the transformer.

In the color profile plot, (notice how vertical z-axis field predominates except near the transmission line between Points A and B), the level increased from 7 mG near the new building to over 15 mG at Point A before reaching a 21 mG peak at Point B, then the levels steadily diminished back towards the school to under 3 mG around the playground structure, and elevated back up to 7 mG near the new building wall facing the transmission line.

2.55 Radial-Main Building/Transmission Line

The fifth outdoor survey, identified as path E1, began at the outside front corner of the main building and followed a radial line under and past the 525 KV transmission line. Refer to: Hatch plot (image 1) & Profile plot (image 2).

In the color profile plot, the start point measured 3.52 mG at the main building (outside front corner wall), then steadily increased at a non-linear 1/r² rate until it peaked under the center conductor at 51.6 mG, and dropped off in a similar contour on the other side. Notice the vertical z-axis flux level: it predominates from the start at the front corner of the main building and continues for more than 200 feet before intersecting with the horizontal x-axis, approximately 175 feet from the center conductor.

2.56 Radial-New Building/Transmission Line

The sixth outdoor survey, identified as path F1, began at the outside front corner of the new building and followed a radial line under and past the 525 KV transmission line.

In the color profile plot, the start point measured 6.44 mG at the new building (outside front corner wall), then steadily increased at a non-linear 1/r² rate until it peaked under the center conductor at 50.4 mG, and dropped off in a similar contour on the other side. Again, notice the vertical z-axis flux level: it predominates from the start at the front corner of the main building and continues for more than 200 feet before intersecting with the horizontal x-axis, approximately 175 feet from the center conductor.

2.57 Perimeter-New Building Only

The seventh outdoor survey, identified as path G1, began at the outside front corner of the main building, proceeded along the main building, walkway and new building perimeter, then around the new building perimeter, and back along the walkway to the main building back outside corner.

In the color profile plot (notice how the vertical z-axis field predominates, except over the underground service drop), the main front corner level increased from 2.5 mG to 4.25 mG between walkway Points A and B (due primarily to the electromagnetically induced column and electrical ground currents-see Sections 2.22 and 2.42 for details). The levels decreased along the common area new building perimeter to 3.0 mG at Point C, then elevated to 4.25 mG moving toward the transmission line at Point D, and increased around the transformer fence between Points E and F, peaking at 5.12 mG over the underground service drop (see peak in the horizontal x-axis). From Point F the level has dropped to 2.5 mG and continues to taper off around the new building, walkway, and main building perimeters.

2.6 Indoor Survey Plots-Magnetic Field Assessments

There are two types of indoor survey plots in the M.W.E.S. Contour Measurement Report: hatch and profile. Hatch plots translate the sampled data (R_rms resultant magnetic flux at one-foot intervals-see Section 2.21 for definitions) into colored lines that represent magnetic flux levels by defined ranges along the survey path. A key defines the range limits for each sampled data point by color and line size.

Profile plots (color and black-and-white) display sampled magnetic flux data as a function of distance. Color profile plots show the horizontal (x-axis and y-axis) and vertical (z-axis) components plus the R_rms resultant sampled magnetic flux data. The black-and-white profile plots only show the R_rms resultant.

2.61 Classrooms-New Building

The first indoor survey, identified as path A1, began in the walkway between buildings, looped through every new building classroom and around the hallway, and finally, terminated back in the walkway.

In the black-and-white (color plots would be too complex to visually decipher) profile plot, the walkway start point measured 2.75 mG, increased to 3.8 mG near the walkway column, declined to 2.5 mG before turning into classroom #9, then elevated near the wall and declined again to 2.5 mG in the hallway (due primarily to electromagnetically induced column currents-see Section 2.42 for details). All the classrooms, regardless of transmission line proximity and orientation to each classroom, have elevated 3-4 mG levels near the aluminum window frames and columns (due to electromagnetically induced window frame and column currents-see Section 2.24) as compared to the hallway 1.4-2.0 mG levels.

2.62 Perimeter-Hallway New Building

The second indoor survey (recorded under normal power conditions), identified as path B1, began in the walkway between buildings, looped around the new building hallways to the outside doors, then back to the walkway.

In the color profile plot (notice how the vertical z-axis field predominates), the walkway start point measured 2.75 mG, increased to 4.6 mG near the walkway column (due to electromagnetically induced and electrical ground column currents-see Section 2.42 for details), and declined to 1.8 mG around the new building hallway turn, Point A. Compared to the 1.4-1.8 mG hallway levels, the outside doorway levels, Points B & C, were elevated (due to electromagnetically induced column and door lentils currents-see Section 2.42).

2.63 Classrooms-Outer Loop Main Building

The third indoor survey, identified as path C1, began in the main building hallway near classroom #20, looped through every outer classroom in the main building, and finally terminated outside classroom #33.

Refer to page 7 image.

In the two black-and-white (color plots would be too complex to visually decipher) profile plots, all the classrooms, regardless of transmission line proximity and orientation to each classroom, have elevated 2.0-4.32 mG levels near the aluminum window frames and columns (due to electromagnetically induced window frame and column currents-see Section 2.24) compared to the average 1.5 mG hallway level.

2.64 Gym & Cafeteria Areas

The fourth indoor survey, identified as path D1, began at the gym entrance, circumscribed the gym perimeter, looped around the cafeteria, passed through the kitchen, and then continued back out through the cafeteria to the entrance area.

In the black-and-white (color plots would be too complex to visually decipher) profile plot, the gym entrance start point measured 2.0 mG and decreased to 1.0 mG around the gym perimeter before it peaked to 2.75 mG between the gym and cafeteria hallway. The cafeteria perimeter averaged 1 mG and the kitchen area peaked at 3.96 mG (due to the refrigerators and freezers), which incidentally is normal.

2.65 Classrooms-Interior Loop Main Building

The fifth indoor survey, identified as path F1, began in the main building hallway near classroom #21, looped through every inner classroom in the main building including the main office and library areas, and finally terminated outside classroom #32.

In the black-and-white (color plots would be too complex to visually decipher) profile plots, all the classrooms, regardless of transmission line proximity and orientation to each classroom, have elevated 1.0-2.0 mG levels near the aluminum window frames and columns (due to electromagnetically induced window frame and column currents-see Section 2.24) compared to the average 0.8 mG hallway level. There is a 5 mG spike from the lounge soda machine in room #28.

2.66 Perimeter-Hallway New Building

The sixth indoor survey (recorded with only the new building de-energized), identified as path G1, began in the walkway between buildings, looped around the new building hallways to the outside doors, and then back to the walkway.

In the color profile plot (notice how the vertical z-axis field predominates, except in the walkway), the walkway start point measured 2.25 mG, increased to 3.48 mG near the walkway column (due only to electromagnetically induced column currents, not electrical ground currents-see Section 2.42 for details), and declined to 1.0 mG around the new building hallway turn, Point A. Compared to the average 1.2 mG hallway levels, the outside doorway levels, Points B & C, were elevated (due only to electromagnetically induced column and door lentils currents-see Section 2.42).

2.67 Perimeter-Hallway New Building

The seventh indoor survey (recorded with both buildings de-energized), identified as path H1, began in the walkway between buildings, looped around the new building hallways to the outside doors, and then back to the walkway.

In the color profile plot (notice how the vertical z-axis field predominates, except in the walkway), the walkway start point measured 3.48 mG near the walkway column (due only to electromagnetically induced column currents, not electrical ground currents-see Section 2.42 for details), and declined to 1.0 mG around the new building hallway turn, Point A. Compared to the average 1.2 mG hallway levels, the outside doorway levels, Points B & C, were elevated (due only to electromagnetically induced column and door lentils currents-see Section 2.42).

3.0 RECORDED & SIMULATED EMF LEVELS UNDER VARIOUS LOADS

Recorded electric and magnetic field data was introduced in section 2.4, Radial Electric & Magnetic Field Assessment, and in the Outdoor & Indoor survey plots sections 2.5 and 2.6. This data represents a visual snap-shot of the EMF profile around the Mary Walter School due exclusively to the transmission line current load at that time and date. As seasonal weather and power demand varies, the EMF profile adjusts accordingly--expanding and constricting around the school property. Therefore, it is critically important to compare recorded and simulated EMF profiles under various load conditions: average, winter & summer peaks, future winter & summer peaks, and maximum thermal. Valid mitigation strategies must consider all load conditions.

3.1 Comparison VEPCO Load & Recorded Data

An outdoor radial-main building/transmission line profile plot (see section 2.55) was recorded on Thursday, 28 April 1994 at 14:36. In order to compare the recorded data profile to the simulated software profile, the actual transmission line phase current for that moment in time was required. Upon request Mr. D. E. Koone, Director -Transmission Standards and Technology at VEPCO, provided transmission line Load Information for 28 April 1994 at 14:30: 815.6 MWatt; -84.2 MVAR; and, 522.7 KV. Phase current for each conductor (assumed balanced) was calculated to be 905.5 Amperes. Phase current and transmission line conductor information (i.e., size, bundles, configuration, height, ground wires, etc.) were entered into EMF simulation software, Fields version 2.01, written by Southern California Edison.

The EMF-simulated software output, titled Mary Walter E.S.: 525 KV Transmission Line Profile-VEPCO data 4/28/94 at 14:30: 815.6 MW (905.5 Amps), is presented in Appendix A. Provided are magnetic and electric field profiles plots, E (electric) and B (magnetic) maximum values, and the input variables. Profile plots and the maximum field table show both the magnetic and electric field levels as a function of distance from the center conductor. Boundary lines for the parking lot, main building, new building, right-of-way, and transmission line are hand marked on each output sheet.

The above recorded and simulated magnetic flux data were imported into a spreadsheet including two data points from the Outdoor Perimeter-main & new building (see subsection 2.53) survey for extrapolation purposes. A very impressive graphic, titled Transmission Line Loads Vs. Distance, Actual Data & Simulated Load, presented on page 17, was generated from the combined data. The calculated data tracked and correlated with the recorded data. Note: the two imported data points are slightly higher because of induced column/window currents and electrical equipment sources emanating from the main building. Also the electric field profiles closely match (some distortion due to elevation changes) the recorded data on page 10.

3.2 Simulated Peak Summer & Winter, Future & Thermal Loads

Upon request, VEPCO also provided load information for the 1993 summer and 1993 winter peak loads, projected 2003 summer and 2004 winter loads, and the maximum thermal load. Calculated phase currents and transmission line conductor information (i.e., size, bundles, configuration, height, ground wires, etc.) were entered into Fields version 2.01 EMF simulation software. Detailed simulated EMF output data for the peak summer & winter, future, and maximum thermal loads are in Appendix A.

Magnetic flux data from the simulated April 1994, summer/winter 1993 peaks, projected summer/winter peaks 2003/2004, and maximum thermal loads were imported into a spreadsheet and plotted. Refer to the Transmission Line Loads Vs. Distance, Simulated Software Comparison presented on page 18 for details. Except for the worst-case maximum thermal load of 3000 Amperes, the other simulated loads converge around 5.7 mG (ñ 0.9 mG) and 3.05 mG (ñ 0.5 mG) at the New Building and Main Building outside walls, which are 260 feet and 360 feet from the center conductor, respectively.

Presented in Table 6 below are recorded and simulated magnetic flux data points for under the transmission line center conductor, R/W (right-of-way), playground equipment-front (on radial line from the main building front corner to lines), new building walls, main building walls, and the parking lot boundaries:
 

.Table 6. Recorded & Simulated Magnetic Flux (mG) Levels

In review, the flux levels under the center conductor to the unmarked right-of-way (75 feet away) are extremely high (greater than 30 mG) regardless of the demand and season. Furthermore, flux levels remain significant (greater than 10 mG) near the front playground equipment (160 feet away) and elevated (greater than 5 mG) at the new building wall. Only at the main building-wall do the flux levels decline to around 3 mG under normal and projected seasonal peak loads.

Preliminary Recommendations

The objective of this section is to present practical field management (mitigation) strategies. Practical does not infer the proposed solutions can be implemented without significant costs. The decision to mitigate depends on the ability to implement. Only VEPCO has the authority and resources to relocate, underground, reconfigure, or passive field cancel the Morrisville-Loudoun 525 KV transmission line. Since everything in the power industry is colossal in scale, the estimated costs to implement any of the proposed VEPCO solutions are between $100,000 to $3,000,000.

The Fauquier County Public School System has the authority and resources (although limited) to implement three possible mitigation solutions: relocate (switch) the parking lot and playground areas; abandon the new classroom building, or reduce the magnetic field levels with active field cancellation inside the new classroom building. According to Mr. Wakefield, it would cost (estimated) $70,000 to flip-flop (switch) the parking lot and playground. Installing an active field cancellation system would cost (estimated) between $30,000-$50,000, depending on the overall magnetic flux reduction criteria.

4.1 VEPCO Field Management Alternatives

Feasible and cost effective magnetic field management (mitigation) options are limited because the power industry has been reluctant to acknowledge a causal effect between magnetic field exposure and health. Several years ago in response to public pressure, the Electric Power Research Institute (EPRI) initiated an extensive mitigation research program. Unfortunately, little of this EMF mitigation research has transferred into practical solutions. VEPCO does not have an industry-tested and approved solution to consider when challenged to mitigate a transmission line magnetic field problem. Each mitigation solution is unique, and the costs generally proportional to the uniqueness of the solution. Therefore, designating (by committee or dictum) acceptable (tolerable) magnetic flux limits (boundaries) around school property is critical--this one constraint will significantly influence mitigation alternatives and costs.

There are other complex political and legal issues regarding any mitigation actions implemented by VEPCO. Basically, if VEPCO were to agree to mitigate, they are acknowledging a possible health risk which could be interpreted as precedent setting. Other VEPCO customers along transmission lines would demand similar field management solutions. This could bankrupt VEPCO, unless they passed the incurred mitigation costs to all customers. Since most customers do not live along transmission line corridors, they would be outraged by the higher monthly electric bills, and probably challenge the increased rate in court with a class action lawsuit. So, do not expect VEPCO to voluntarily mitigate your transmission line magnetic field problem.

4.11 Relocate 525 KV Transmission Line

If the two transmission line towers (#569-156 & #569-157) located on school property were moved 130 feet to within 30 feet of the opposite right-of-way boundary, then flux levels would diminish by 30% at the playground equipment-front, 50% at the new building-wall, 54% at the main building-wall, and 70% at the parking lot. Existing and moved transmission line levels under two extreme conditions, recent April 1994 (VEPCO Data) and future Winter 2004 data, are presented below in Table 7:

Appendix B includes detailed relocated (moved) simulated EMF output transmission line data for April 1994 (VEPCO Data) load, winter 2004 projected peak load, and maximum thermal load. Also, moved maximum thermal load magnetic flux conditions diminished by 34% at the playground equipment-front, 46% at the new building-wall, 57% at the main building-wall, and 70% at the parking lot.

Finally, the estimated cost to install two new 525 KV transmission line towers, suspend over 2,000-feet of new wire for each phase conductor, and remove the old towers could cost between $250,000-$500,000. This is not a trivial mitigation project.

4.12 Underground 525 KV Transmission Line

Magnetic fields emanating from an underground transmission line are extremely low because of self-cancellation between the conductors inside a steel conduit pipe and attenuation of the pipe. For example, if the attenuation effect of the steel conduit pipe is neglected, the estimated peak magnetic flux level is 29 mG directly above the phase conductors for a 600 Ampere load buried 3.5 feet below the ground. Experimental measurements have recorded pipe attenuation factors up to 94%. Applying the 94% attenuation figure reduces the 29 mG above ground magnetic flux level to only 1.7 mG.

The previous example can also be applied to a theoretical buried 525 KV transmission line by doubling the current to 1,200 amps (close to the projected 2003/2004 summer & winter peak loads) and doubling the above ground level to 58 mG. Applying the 94% attenuation figure reduces the above ground (3.5 feet) magnetic flux level to only 3.48 mG. Furthermore, there are no electric fields that emanate from underground transmission lines. This is a rather extraordinary reduction in both magnetic and electric field levels, but the estimated costs to install a 525 KV underground transmission line is staggering.

Transmission line voltage significantly impacts the feasibility, installation, and life-cycle (operation & maintenance costs) costs for underground transmission lines. Currently, there are only a few experimental 525 KV underground transmission lines in the United States. Several northeastern utilities (New York, Connecticut, Rhode Island, etc.) have 345 KV underground transmission lines; however, most underground transmission lines are 230 KV and lower, especially in urban areas.

There are two types of conventional 345 KV high voltage underground systems: high pressure fluid filled (HPFF) and high pressure gas filled (HPGF). The HPFF system places three paper-insulated cables inside a steel pipe filled with a special pressurized fluid that is constantly circulating. Heat exchangers are also necessary to dissipate thermal conductor heat from the circulating fluid. Pressurizing plants with heat exchangers would be located at intervals. The HPGF system uses paper-insulated cable with pressurized nitrogen gas, and does not require special pressurizing plants.

Assuming the HPFF system was selected to underground 1,500 feet of 525 KV transmission line from the substation to State Road 835, the estimated installation costs could exceed $3,000,000, including removal of the existing towers and conductors. Furthermore, the life-cycle costs to operate and maintain the underground HPFF line are typically twice the installation costs.

4.13 Reconfigure 525 KV Transmission Line

On each 525 KV transmission line tower, the phase conductors (wires) are individually secured with two high voltage insulators fashioned to form a V-string. The three phase conductors are geometrically arranged to form an isosceles triangle known as a wide horizontal delta (center conductor elevated with respect to the outer two conductors). Unfortunately, the wide horizontal delta produces the highest magnetic flux levels of any single-circuit transmission line configuration because of the wide separation between the two outer phase conductors (isosceles base-64.5 feet) relative to the apex center conductor (isosceles sides-34.32 feet each).

Phase current, relative conductor geometries and line sag significantly affect the magnetic flux levels emanating from any transmission line. Various configuration schemes have been experimentally tested and the 6-Wire Configuration (vertical delta, double-circuit/split phase) produces the lowest magnetic flux levels (assumed all phase currents are balanced). Simulated Existing (from Table 6) and 6-Wire Configuration transmission line flux levels (in mG) are compared below in Table 8 for both VEPCO Data (April 1994) and future peak winter 2004 levels:
 

Listed in Appendix C is the 6-Wire Configuration simulated EMF output data for April 1994 (VEPCO Data), winter 2004 projected peak load, and maximum thermal load. The maximum thermal load conditions are also remarkably low: centerline 23.63 mG; edge of R/W 10.75 mG; playground equipment-front 3.29 mG; new building-wall (260') 1.04 mG; main building-wall (360') 0.42 mG; and, parking lot (640') 0.08 mG.

The estimated cost to implement the 6-Wire Configuration from the substation to Route 835 is between $500,000-$1,250,000. The existing 525 KV transmission line would have to be temporarily moved while the 6-wire configuration is installed.

4.14 Passive Field Cancellation-525 KV Transmission Line

A passive field cancellation scheme to reduce magnetic flux levels at the right-of-way edge was presented by R.A. Walling, J.J. Paserba and C.W. Burns in an IEEE paper titled, Series-Capacitor Compensated Shield Scheme for Enhanced Mitigation of Transmission Line Magnetic Fields. Basically, this scheme involves encircling the transmission line with a heavy gaged capacitor-compensated rectangular wire loop support on insulated poles to form a self-induced passive field cancellation system.

The authors reported a reduction between 57-82% in magnetic flux levels at the edge of the right-of-way (ROW) and between 37-51% nearly 500 feet from the ROW centerline. The wide variation in field reduction is due to nonlinear asymmetrical effects. This is a very simple and cost-effective mitigation technology; however, it has not been applied except in experimental research. The estimated costs to research, design, and install a passive field cancellation system is between $100,000-$175,000.

4.2 Fauquier County Public School Field Management Alternatives

Predicated upon the assumption that VEPCO will not implement any of the mitigation alternatives discussed in section 4.1, it may be incumbent upon the Fauquier County Public School System to consider their own field management alternatives. Unfortunately, there are only three possible field management alternatives available to the school district: abandon the new classroom building; relocate (switch) the parking lot & playground areas; and, active field cancellation technology. Therefore, designating acceptable magnetic flux limits around school buildings, playground areas, and sport fields will ultimately determine mitigation alternatives and costs.

Schools, commercial businesses, and residential property owners all have limited field management options when located near high current/magnetic field transmission and distribution lines. The resultant (R_rms) magnetic flux profile from a high current (balanced) three phase transmission line diminishes at a nonlinear 1/r² rate, as demonstrated in the recorded and simulated data presented on page 17, Transmission Line Loads Vs. Distance-Actual Data & Simulated Load.

The resultant (R_rms) magnetic flux level is a function of distance and cumulative phase currents which change instantaneously according to demand (day, time, temperature, diurnal and seasonal peaks). This is illustrated on page 18, Transmission Line Loads Vs. Distance-Simulated Software Comparison, and in Table 6, Recorded & Simulated Magnetic Flux (mG) Levels, on page 19. Except during maximum thermal load which only occurs (if at all) for 15-20 minutes, the average magnetic flux levels around the school for typical and worst-case peak winter loads (1993/2004) converge as follows:

4.21 Abandon-New Classroom Building

If 5.70 mG (ñ 0.90 mG) is unacceptable at the new classroom building-wall (260 feet), then the new classroom building should be abandoned and used as a warehouse. Until a new classroom building is constructed near the existing parking lot, move all playground equipment and locate temporary classroom buildings at least 640 feet from the transmission lines where the levels are only 0.98 mG (ñ 0.17 mG). Build a new delivery road and parking lot between the abandoned building and playground areas. Note, the main classroom building-wall (360 feet) levels will be 3.05 mG (ñ 0.50 mG).

Install a six-foot high, well-grounded, metal fence 160 feet from the center conductor parallel to the transmission line corridor where levels are 13.42 mG (ñ 2.21 mG). The fence would isolate students, teachers, and vehicles from both high electric and magnetic field levels emanating from the transmission line.

This is a very expensive alternative estimated between $2,000,000-$3,000,000, depending on architectural/engineering (A&E) and building construction costs.

4.22 Relocate Parking Lot & Playground

If 5.70 mG (ñ 0.90 mG) is acceptable at the new classroom building-wall (260 feet), then move all the playground equipment to the existing parking lot side where the levels are only 0.98 mG (ñ 0.17 mG). Build a new delivery road and parking lot between the new classroom building and old playground areas. Note, the main classroom building-wall (360 feet) levels will be 3.05 mG (ñ 0.50 mG).

Install a six-foot high, well-grounded, metal fence 160 feet from the center conductor parallel to the transmission line corridor where levels are 13.42 mG (ñ 2.21 mG). The fence would isolate students, teachers, and vehicles from both high electric and magnetic field levels emanating from the transmission line.

The estimated cost according to Mr. Wakefield to flip-flop (switch) the parking lot and playground areas plus build a new delivery road is $70,000. Installing a six-foot high metal isolation fence would cost (estimate) between $2,500-$7,500, depending on the materials and construction methods.

4.23 Active Field Cancellation-New Classroom Building

Close to a single-circuit horizontally arrayed transmission line, the near field resultant R_rms magnetic field vector elliptically rotates in space during each 60-Hz cycle. Whereas, the far field (greater than 150 feet) resultant R_rms vector for a single-circuit horizontally arrayed line is linearly polarized and rotates during each 60-Hz cycle inboth the horizontal and vertical planes. Actual recorded data from the main building to the transmission line (see section 2.55, Radial-Main Building/Transmission Line for details) graphically illustrates the horizontal (x-axis and y-axis), vertical (z-axis), and calculated R_rms components. Note how the y-axis magnetic flux level, parallel to the transmission line, dropped below 0.50 mG after 150 feet from the center conductor. Only the z-axis (vertical) component predominates after 150 feet with the x-axis (horizontal) component, perpendicular to the transmission line, rapidly falling-off as it approaches the new classroom building.

Furthermore, the sections listed below validate the z-axis predominance along radial lines, around the playground/school perimeters, and within the new school building:

Indoor classrooms generally displayed a complex triple-axis magnetic flux profile produced from several electromagnetically induced magnetic flux sources: steel roof, reinforced columns, aluminum window frames, and doorway lintels (see section 2.42). Although the indoor classroom profiles do not generally show a z-axis predominance, a major quantity of the electromagnetically induced currents are generated in the steel roofs and window frames from the vertically polarized z-axis magnetic fields. Therefore, if the transmission line z-axis vertical magnetic fields are reduced, then the outside perimeter building z-axis and inside electromagnetically induced magnetic flux levels will also proportionally diminish.

Only active field cancellation technology can effectively mitigate (reduce) far field magnetic field sources from a transmission or distribution line. Basically, active field cancellation technology senses a magnetic field from a source and generates an opposing cancellation field. Ideally, if two 180-degree out-of-phase magnetic fields of equal magnitude intersect, the resultant magnetic field is cancelled (nullified). The effectiveness (reduction ratio) of an active field cancellation system is limited by the following factors: magnitude, spatial uniformity and gradient of the field source; volummetric size of the selected cancellation area; number of required cancellation coils (one coil per axis); geometry, placement, and size of the cancellation coils; and the power and stability of the active feedback, closed-loop, cancellation system.

There are two basic cancellation coil systems, enclosed and external:

The estimated cost for an active field cancellation system is between $30,000-$50,000, depending on the overall magnetic flux reduction criteria. This includes: engineering and project design, consultation fees, cancellation coils, weather proof enclosure, 6-foot fence, installation work, test and evaluation. All playground equipment should be moved closer to the classroom buildings. Also a non-metallic fence should be installed to isolate the coils and the transmission line corridor from both students and teachers.

5.0 FINAL CONCLUSION & RECOMMENDATIONS

Generally, the average simulated magnetic flux level at the new classroom building-wall is 5.70 mG and only varies by ñ 0.90 mG between a typical April 1994 day, winter peak 1993 day, and a predicted 2004 winter peak day. Average levels for the playground equipment-front, main building-wall, and parking lot-boundary are presented below as a function of distance from the transmission line:
 

Are the above magnetic flux levels acceptable? If not, then what maximum limits are acceptable to the school board, administration, teachers, and parents? Currently, there are no federal or state maximum acceptable limits, except a 200 mG right-of-way edge limit for transmission lines in Florida and New York. It should be noted that the typical Morrisville-Loudoun 525 KV right-of-way edge levels range from 29 mG (April 1994) to 45.42 mG (2004 winter peak).

This report addressed the potential shock hazards from induced voltages and currents as a result of electrostatic and electromagnetic coupling. However, it is beyond the scope of this report to render an opinion regarding maximum magnetic flux limits and potential long term EMF health effects.

Final Recommendations

It would be prudent to mitigate (reduce) the magnetic flux levels inside the new classroom building to below 3 mG (limit based upon the 1992 Swedish Residential Study, not the opinion of the author) under all normal transmission line load conditions (diurnal and seasonal peak loads). Therefore, a minimum reduction factor of 55% is necessary to achieve the 3 mG limit for a worst-case 6.6 mG predicted 2004 winter peak level at the new building-wall. This can be achieved as follows by VEPCO or the Fauquier County Public School System (FCPSS):

This completes the Final ELF EMF Survey Report,

Mary Walter Elementary School Facility.

Appendix A

Simulated EMF Output Data:
VEPCO Data: April 28, 1994 at 14:30 hours
Summer 1993 peak load: 1010 MW (1114 Amps)
Summer 2003 projected peak load: 1109 MW (1222 Amps)
Winter 1993 peak load: 1019 MW (1121 Amps)
Winter 2004 projected peak load: 1168 MW (1286 Amps)
Maximum thermal load: 2728 MW (3000 Amps)

Appendix B

Relocated Transmission Line Simulated EMF Output Data
VEPCO Data: April 28, 1994 at 14:30 hours
Winter 2004 projected peak load: 1168 MW (1286 Amps)
Maximum thermal load: 2728 MW (3000 Amps)

Appendix C

6-Wire Configuration Line Simulated EMF Output Data
VEPCO Data: April 28, 1994 at 14:30 hours
Winter 2004 projected peak load: 1168 MW (1286 Amps)
Maximum thermal load: 2728 MW (3000 Amps)

Appendix D

Living & Working Around High-Voltage Power Lines

Appendix E

Collected ELF EMF Exposure & Risk Assessment Information:

New York Survey of Magnetic Fields Around Schools ...
Microwave News-School EMFs Alarm Parents and Teachers ...
Microwave News-Slater School Case Moves Forward
Microwave News-Swedish Studies...
EMF Hazard Free School Zone-National EMR Alliance
House Bill H.R. 1494 Congressman Miller, 103rd Congress