Abstract
The coal industry has long been viewed as providing only negative impacts to the environment and not as a possible resource to utilize, where practical, to benefit local communities. In January of 1994, the Maryland Department of Natural Resources - Freshwater Fisheries Division (DNR) and Mettiki Coal Corporation (MCC) of Oakland, Maryland entered into a cooperative agreement to construct a trout rearing facility within the coal company's 10 million gallons per day acid mine drainage treatment system to supplement the DNR stockings in the newly revitalized North Branch of the Potomac River.
Due to pyrite oxidization and a lack of alkaline buffering capacity in the Freeport coal strata, seven thousand gallons per minute of acidic water containing oxidized sulfide minerals must be pumped through MCC's acid mine drainage (AMD) treatment systems and elevated to Federal standards prior to discharge into the upper North Branch of the Potomac River. Utilizing hydrated lime, aeration, flocculation, sedimentation, and sludge recirculation, MCC's treatment imparts superior trout propagation qualities to the discharge (pH of 8.1, dissolved oxygen of 8.0 ppm, temperature ranges of from 52 to 60 o F ) and has allowed for weight gain throughout the typically dormant winter months.
Presently, 30,000 brown trout (Salmon trutta), rainbow trout
(Oncorhynchus mykiss) , and cutthroat trout (Oncorhynchus clarki) are suspended
in floating net pens within the systems' discharge collection pond where pH,
flow, temperature, feed assimilation, and growth rates were compared with
typical stream diversion hatcheries. Growth rates, lack of significant disease,
and quality parameters coupled with ideal temperatures suggests treated acidic
mine effluent can offer successful fish propagation opportunities.
Introduction
During the past century, as the vast timber and coal resources of western Maryland were utilized for the expansion and growth of the nation, many of the areas' streams and rivers were impacted due to a limited understanding of the effects this extraction could have on the environment. The lack of laws requiring restoration of the land or accountability for water impacts after extraction was a reflection of this lack of understanding and many streams that once held vast numbers of native trout became devoid of aquatic life due to siltation and acidity loading. As the nation became more cognizant of its effects on the environment and as laws were enacted to reverse the levels of deterioration, a restoration of aquatic habitat has been noticed in the remote areas of western Maryland.
Although not often recognized for its efforts, companies within
the mining industry -- Mettiki Coal Corporation in particular -- have been
instrumental in the turnaround and restoration of historically impacted streams
and rivers such as the north branch of the Potomac River which has its source in
extreme western Maryland.
Apart from the aesthetic visual impacts to the landscape during
the extraction of coal reserves and concerns about possible post mining land use
restrictions, water degradation has been the most widely recognized image of
coal mining and mineral extraction. (Caruccio 1994)
Acid mine drainage can be generally categorized as occurring when
iron sulfides -- collectively termed pyrites -- oxidize in the presence of
oxygen and water in the absence of calcareous buffering materials to produce
high concentrations of sulfate and ferrous iron. The ferrous iron is further
oxidized in nature to form ferric oxyhydroxides or "yellow boy" which imparts
the typical red or yellow discoloration to stream beds characteristic of acid
drainage. (Sengupta 1993) The most widely used treatment techniques to mitigate
acid production include neutralization by alkaline addition and oxidization to
precipitate the iron and other metals as hydroxide sludge.
Treatment
Mettiki Coal Corporation operates a drift mine which enters the
outcrop of the 8 1/2 foot Freeport coal seam and dips down starting at a 25%
grade towards the Potomac River. Present working sections of the mine are
between 2 to 2.5 miles from the mine entrance with an average depth of cover of
600 feet. Over 5 miles of conveyor beltlines transport the raw coal from
underground to the surface where the preparation plant cleans the coal of
impurities. The coal is then loaded either on rail or trucks for transport to
markets.
The water which pools in the lower elevations of the mine is stage
pumped through the mine to an underground sump and then conveyed to the surface
via a combination of one 400 hp Layne, one 450 hp Goulds, or one Peabody Floway
800 hp deep well turbine pumps and treated at the AMD plant. Under normal
conditions, flow rates of 2000, 4000, 6000 or 8000 gal/min are maintained
depending upon what pump or combination of pumps are placed in operation.
Treatment options consists of two identical High Density Sludge treatment
systems each capable of treating 3000 gal/min and one Techniflo in line aeration
system presently capable of treating 2000 gal/min.
Raw water enters the ferric tank and is mixed with a hydrated lime
slurry. The slurry is made from clear water taken from the settling basins or
can be mixed from the raw AMD. Lime addition is controlled by Great Lakes pH
probes located at the effluent end of the ferric tanks. The neutralized water
reports to the aeration tank through 12 inch PVC pipe and is aerated using 10 hp
splash aerators in the HDS system. The aerated water then discharges through a
sluice-way where Stockhausen polymer is added prior to its entering the 25 ft. x
280 ft. x 14 ft. clarification basin for precipitation of the hydroxide sludge
(Figure 1).
The in-line aeration system differs from the above in the
oxidization step. Oxidization is accomplished by an air inductor that entrains
air by a venturi device which is powered solely by the pressure of the raw water
pump. Post aeration treatment involves anionic polymer addition to aid
flocculation of the metal hydroxides and clarification in a concrete 115 ft. by
14 ft. circular clarifier.
Metallic hydroxide accumulation in the bottom of the clarifiers is
raked and suctioned to a sludge disposal tank via two Hazelton sludge pumps or
centerwell pump. Final sludge disposal into old underground workings is
accomplished by Goulds 125 hp disposal pumps.
Scientists within the environmental department at MCC realized
that the consistent water quality discharged from the AMD treatment process
contained ideal trout parameters early in 1993 and contacted the Maryland Region
1 Fisheries division of the Maryland DNR in July of 1993 to see if an experiment
within the treatment system could be instituted. After several site visits and
discussions, a test batch of 400 brown and rainbow trout were delivered in
September of 1993 and monitored for approximately 2 months to gauge
viability.
When the quality characteristics were confirmed to be ideal for
trout propagation, discussions between MCC and the Maryland DNR began towards
developing a trout propagation partnership within the treatment facility. The
design was based upon the net pen technology being developed by J. Michael Dean
below the Army Corps of Engineers Jennings Randolph Dam on the North Branch of
the Potomac River.
Rearing Facility
2 ft. x 2 ft. x 2 ft. floating dock sections of polyethylene cubes are connected three or four wide with locking plugs to form a stable dock for net support and access. Boat cleats are inserted within a 15 ft. x 20 ft. opening to support a 9 ft. deep nylon net to contain the trout throughout the growth season. The net mesh size can be varied to accommodate various sizes of trout. Fingerlings are placed in the nets at approximately 60 per pound size ranges (3 inch in length). Nets are cleaned periodically by pulling sections up upon the floats and hosing with water sprays (Figure 2 ).
Fish are fed measured amounts of specially formulated trout pellets supplied by Zeigler Brothers, Inc. of Gardners, Pennsylvania. Typical protein and fat content is 38 and 12 percent respectively. Towards the end of the growth season, canthaxanthin is added to the feed to enhance the coloration of the flesh. Pellet sizes ranging from #8 to 3/16 inch are fed at Mettiki depending upon fish sizes and nutritive requirements. Feeding is accomplished using solar powered automatic feeders which dispense a set amount of feed hourly throughout the day. Feed rates are strictly controlled and determined utilizing a percent feed to average body weight throughout the year. Fish are weighted bi-weekly to access growth and weight accumulation and records are maintained throughout the year. This data is then used to determine feed rate increases and overall rearing performance.
Typical growth in hatchery trout at the end of the growing season approaches 2.2 fish per pound (.5 pounds each) when fed at the typical feed rate of 1.2 % body weight. Fish at MCC have exceeded 1.0 fish per pound when fed this 1.2% ration - reflecting the ability to convert food to flesh throughout the typically dormant winter months (Piper 1982). Fish are stocked throughout Garrett and Allegheny counties in western Maryland from the facility between March and June of each year. Careful attention to native species and the impact of hatchery fish on the genetic pool limits the areas into which non-native species (especially browns) are stocked. Positive imput received from local fisherman suggests that size characteristics are an important and appreciated attribute.
Conclusions
This cooperative facility has afforded the Maryland Department of
Natural Resources , Region 1 Fisheries a much needed cold water resource and has
allowed for more trout to be stock into the newly revitalized North Branch of
the Potomac River - deemed "unsalvageable" as little as 10 years ago. Combined
efforts from Federal, State, and Local concerns coupled with Mettiki Coal
Corporations' alkaline inputs have had such a beneficial effect on the North
Branch water quality that in May 1996, trout were stocked for the first time
from the Wilson, Maryland bridge over the Potomac down to the Jennings Randolph
Dam - an area that even 5 years ago was written off. Keeping in mind that the
Mettiki facility imputs the equivalent of 4 tons per day of calcium carbonate
alkalinity into the Potomac at Wilson, Maryland, one can see that the coal
industry has become an integral part of aquatic restoration efforts within the
North Branch drainage basin.
References
1. Caruccio, Frank T. and Gwendelyn Geidel. "Acid Mine Drainage:
The Problems and its Solutions." Proceedings of the International Land
Reclamation and Mine Drainage Conference (Pittsburgh, PA April 1994).
2.
Sengupta, M. "Environmental Impacts of Mining - Monitoring, Restoration, and
Control." Lewis Publishers , Boca Raton, Fl. 1993, pp 3-25.
3. Piper,
Robert G. et. al., "Fish Hatchery Management." U.S. Department of the Interior,
1982. 1-14, pp 208-234.
4. Stnickney, R., "Culture of Salmonid Fishes.",
CRC Press, Boca Raton, FL., 1992,p 52.