Acid mine drainage site in Virginia. Metal and coal mines within the Chesapeake Bay basin are being studied to learn the limitations of 

new remote sensing techniques. Contrary Creek in the Piedmont Pyrite Belt in southern Virginia is an ideal test site because it has 

neutral seeps entering a severely acidified stream. The stream bed is yellow orange from acidic flocculates and precipitates. Dried 

yellow flocculates extend over the creek banks. In contrast, a neutral tributary in the background (arrow) is red from iron precipitated 

by bacteria in neutral, iron-rich ground water. 

Author collecting a sample of iron flocculate produced by microbial activity in acidic water.

Microbial and Spectral Reflectance Techniques to Distinguish 

Neutral and Acidic Drainage

"Acid mine drainage from coal affects 

drinking water quality, property values, 

and stream habitat for fish and other 

organisms. Coal is an important 

resource that fuels our industrial 

economy. So new techniques are needed 

in conjunction with mining to stop acids 

and metals from leaking into streams. 

New remote sensing techniques can 

locate sites of leakage because they use 

diagnostic wavelengths of light to 

distinguish between acidic and neutral 

water. Bacteria are known to use a 

variety of strategies to precipitate toxic 

metals. Stopping the metals from 

moving downstream from the mining sites 

can protect our land and water and keep 

our industrial base functioning."

Acidic drainage is common in places 

where high-sulfur coal and sulfidebearing rocks have been mined, but not 

properly reclaimed. Although mining 

and reclamation methods that stop acidic 

drainage from forming or from leaving 

the site are currently used throughout the 

United States, numerous old abandoned 

mines continue to produce acid mine 

drainage (AMD) from underground 

tunnels and mine waste piles. As the 

tunnels fill with water and water 

percolates through the waste piles, the 

sulfide minerals oxidize producing acids, 

iron, and other metals that leak into 

streams. These produce yellow ferric 

oxy-hydroxide (FeOOH) and sulfate 

("yellow boy") flocculates and 

precipitates that encrust rocks, logs, 

leaves, and streambeds. Acidified 

streams are considered to be dead 

systems because they have no fish.

Acid drainage from abandoned coal 

mines is affecting thousands of miles of 

rivers in the eastern United States.

Eleanora Iberall Robbins

U.S. Department of the Interior

U.S. Geological Survey

USGS Fact Sheet FS–118–99

June 1999 Printed on recycled paper
Yellow flocculates ("yellow boy") from an acidic site are colonized by numerous colorless bacteria (arrows), as seen using a light 

microscope.

Red flocculates from a neutral site are formed by iron-coated bacteria called Gallionella that look like braids, as seen using a light 

microscope.

Different microbial communities can 

participate in the production of these 

acidic and neutral iron oxide flocculates. 

The acidophilic bacteria that create ironrich flocculates in acidic water are often 

Thiobacillus species. These bacteria 

derive energy from oxidizing the iron or 

sulfide in pyrite, FeS2, which is the most 

common sulfur-bearing mineral in coal. 

Oxidation of pyrite produces sulfuric acid 

and iron flocculates that appear yellow 

and yellow-orange in sunlight. In 

contrast, neutral pH water contains a 

different group of bacteria, as well as 

fish, frogs, and turtles. Where neutral 

water contains iron, the neutralophilic 

iron-depositing "iron bacteria" such as 

Gallionella derive energy from iron 

oxidation. 

U.S. Geological Survey (USGS) 

scientists are finding that neutral 

drainage is sometimes being 

mistaken for acidic drainage 

because both involve the 

formation of iron oxide-rich 

materials. 

Iron-rich flocculates can form 

naturally in places where ironbearing, anoxic ground water 

discharges into streams. In these 

near-neutral pH settings, flocculates 

have red and red- orange hues in the 

visible spectrum and are composed 

of ferric oxy-hydroxide minerals. 

These iron-bearing materials are 

natural and are even found in the 

oldest rocks on Earth.

USGS scientists are adapting 

microbial techniques to learn about 

the processes that form the acidic and 

neutral iron oxide-rich flocculates.
ACID PRECIPITATE

NEUTRAL PRECIPITATE

This false color composite image uses the digital multispectral 

video (DMSV) and selected filters to show acidic water as yellow 

and neutral water as red. The DMSV instrument was mounted in a 

fixed-wing aircraft and flown at an altitude of 1,650 m above the 

site. The filters that produced this image have central wavelengths 

of 450 nm (blue), 650 nm (red), and 750 nm (near-infrared). The 

straight line crossing the middle of the image is U.S. Route 522, and 

the central rectangle is the bridge across Contrary Creek. (Image 

supplied by John Anderson, Topographic Engineering Center, U.S. 

Army Corps of Engineers.)

New technology that allows above-ground measurements of 

reflected light is being tested to characterize mine drainage on the 

basis of the spectral properties of various iron minerals. 

Cooperative work between the USGS, the Army Corps of 

Engineers, and the Pennsylvania Department of Environmental 

Protection, demonstrates that certain remote sensing tools can be 

used to differentiate between acidic and neutral waters because 

the iron flocculates in acid water have distinctly different spectral 

signatures from those formed in neutral water. A hand-held, field 

spectroradiometer produces graphical displays showing that the 

yellow-hued flocculates in acidic water have higher spectral 

reflectances than the red-hued flocculates formed in neutral water. 

An aerial technique using a 4-channel, digital multispectral video 

system (DMSV) can create digital composite images of the 

flocculates using specific wavelength filters. The images show a 

uniformly bright yellow or yellow-green signal above acidic 

water having yellow flocculates when the filtered video channels 

are combined in certain ways. 

Scientists are developing spectral reflectance techniques that 

differentiate between acid and neutral materials.

Spectral reflectance graphs show data from 

abandoned coal mine discharges in the 

Southern Anthracite coalfield of central 

Pennsylvania. The hand-held 

spectroradiometer produced distinctly 

different spectral reflectance graphs for 

acid (Markson discharge) and near-neutral 

(Tracy discharge) discharges. The yellow of 

the acidic flocculates has higher spectral 

reflectance than the red of neutral 

flocculates.

40

30

20

10

0

% REFLECTANCE

WAVELENGTH (nm)

400 500 600 700 800 900

COMPARATIVE SPECTRAL SIGNATURES FROM PENNSYLVANIA DISCHARGES AND ENVIRONS

APRIL 18, 1996

Concrete pad

Light asphalt road

Dark asphalt road

Markson

Markson

Light road

Senescent grass

Tracy

Swatara headwaters
False color composite image of the area around the Markson discharge from an abandoned underground coal mine in 

Pennsylvania. Where anoxic water from the mine discharges to the surface and becomes aerated, the yellow acid-type 

flocculates form (arrows). Other yellow pixels in the image along the edge of Rausch Creek may be sites where pyritebearing mine waste was piled along the bank and where yellow flocculates are collecting in slack-water pools. In this 

image, trees are red, the road is blue, and Rausch Creek water, having no iron-rich flocculates, is blue and green. 

For More Information Contact:

Is acid still leaking from sites and mines that are thought to have 

been reclaimed? Have all the places that leak acids and metals 

into streams been identified? Remote sensing from the air can 

help answer such questions. Aerial measurements allow the 

examination of places that are remote or cover large areas. 

Regulatory agencies could use an objective scientific tool such as 

remote sensing to monitor coal mining permits and to check the 

effectiveness of efforts to prevent pollution. Other agencies need 

to report on the health of all our Nations's streams, even the 

remote ones, to meet requirements of the Clean Water Act. 

Although more work is needed to refine the techniques at 

disparate localities and different hydrological or seasonal 

conditions, preliminary data suggest that multispectral imagery 

can be used as an objective tool for resource and regulatory 

agencies that manage water quality and mining reclamation in 

coal-mining regions. 

Federal and State regulatory agencies are using these data to 

help make land-use decisions.

Eleanora I. (Norrie) Robbins

U.S. Geological Survey

956 National Center

Reston, VA 20192

(703) 648-6527 (work)

(703) 648-6419 (fax)

nrobbins@usgs.gov