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There are two systems at Adams Station
are located about three miles downstream from the Onstead project.
They treat discharges from two different mines in the area that are only
about a quarter mile apart. They are both in the 3.3 pH range and
of course, have no alkalinity. The first system known as 06 is what is
called an anoxic limestone drain (ALD) which means that it is enclosed
to prevent oxygen from getting into the water that would cause the metals
to drop out and result in armoring of the limestone (clogging its porous
nature with iron deposits), making it unable to neutralize the acid in
the water. The system was constructed in 2003 and due to heavy rain events
in 2003 and 2004 suffered damage to the anoxic limestone bed which necessitated
the construction of a bypass around the system to carry excess water and
prevent pressure from building up in the system. This caused us to
have to seek more money to correct the situation. This was done and the
system is now performing satisfactorily. The system cost over $200,000
to complete.
The second system known as 07 was constructed
at the same time as 06. It had large concentrations of metals and was considered
a “killer” discharge. Nothing lived in the stream below the entry point
of this discharge. It was constructed as a vertical flow SAPS (successive
alkalinity producing systems); much the same as the Onstead
system. It too suffered from the same rain events and required considerable
repair work. The repairs were made and the system is now operational. This
project cost in excess of $300,000 when it was done.
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System 1:
Natural wetlands are characterized by water-saturated
soils or sediments with supporting vegetation adapted to reducing conditions
in their rhizosphere. Constructed wetlands are man-made ecosystems that
mimic their natural counterparts. Often they consist of shallow excavations
filled with a flooded gravel, soil, and organic matter to support wetland
plants, such as Typha, Juncus, and Scirpus sp. Treatment depends on dynamic
biogeochemical interactions as contaminated water travels through the constructed
wetland. ALDs are **abiotic systems consisting of buried limestone
cells that passively generate bicarbonate alkalinity as anoxic water flows
through.
Anoxic limestone drains (ALD) are
buried cells or trenches of limestone into which anoxic water is introduced.
The limestone dissolves in the acid water, raises pH, and adds alkalinity.
Under *anoxic conditions, the limestone does not coat or armor with
Fe hydroxides because Fe+2 does not precipitate as Fe(OH)2 at pH <6.0.
ALDs improved the capability of wetlands to meet effluent limitations without
chemical treatment. Since 1990, ALDs have also been constructed as stand-alone
systems, particularly where AMD discharges from deep mine portals.
**"Abiotic" refers to nonliving
objects, substances or processes.
*Anoxic means lack of oxygen. An
adjective usually used to desribe a microbial habitat.
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System 2:
SAPS combine treatment concepts from both
wetlands and ALDs. Oxygenated water is pre-treated by organic matter removing
O2 and Fe+3, and then the anoxic water flows through an ALD at the base
of the system. Limestone ponds are ponds built over the upwelling of a
seep and the seep is covered with limestone for treatment. OLCs are surface
channels or ditches filled with limestone. Armoring of the limestone with
Fe hydroxides decreases limestone dissolution by 20 to 50%, so longer channels
and more limestone is required for water treatment. Successive alkalinity
producing systems (SAPS) combine the use of an ALD and an
organic substrate into one system. Oxygen concentrations in AMD are often
a design limitation for ALDs.
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