One aerobic wetland system
has been completed and two are currently in construction. The completed
system was constructed along Monastery Run, a tributary to Loyalhanna
Creek in Westmoreland County. The NRCS and Monastery Run Coalition have
also constructed aerobic wetlands along this stream. The area is located
near the bottom of a syncline in the flooded Pittsburgh coal seam, resulting
in a number of high volume, net alkaline discharges with elevated iron
concentrations. Water quality and flows were monitored for the BAMR
system from May 1994 through April 1995, prior to completion of design.
During that time, flows fluctuated from 0 to 1,750 gpm (0 to 110.4 L/s).
The system was designed to treat the average flow of 689 gpm (43.5 L/s).
The project, consisting of the construction of 9.5 acres (3.86 hectares)
of treatment wetland divided into four cells, was completed in November
1998. The system operated very effectively for a number of months, until
the spring of 1999. At that time, flows reached a level never measured
prior to construction – more than 2,400 gpm (151.4 L/s) (flows
during the spring of 2000 have reached nearly 3,000 gpm (189 L/s)).
This problem was exacerbated by artesian up-wellings of AMD occurring
within cells 2 and 3 of the treatment system, causing this influent
to have inadequate retention time. While these up-wellings were known
to exist prior to construction, and therefore were not unexpected, the
volume of flow entering from the up-wellings was much greater than expected.
While the iron load being removed in the system remained quite impressive
(as high as 519 lbs/day (235 kg/day)), the concentrations in the discharge
increased considerably. One action taken to improve this situation was
the construction of an additional internal dike in cell 2 to prevent
short-circuiting of a major artesian up-welling. The most effective
action taken to date has been to run a siphon pipe from the discharge
across the stream to an aerobic treatment facility constructed by the
NRCS that was being underutilized. This additional retention time resulted
in outstanding iron removal in all but the highest flow conditions.
This treatment system routinely discharges less than 1 mg/L of iron,
with the exception of springtime conditions.
There has been much speculation concerning the flow increases observed
from BAMR’s system. One possibility is that there may have been
boreholes within the area used for treatment that were improperly sealed
and uncovered by the construction excavation. Nevertheless, significant
improvement has been observed in the appearance of Monastery Run and
Loyalhanna Creek. The three wetland treatment systems that have been
constructed are removing approximately 1,000 lbs/day (453.6 kg/day)
of iron, which equates to more than 180 tons per year (136 tons per
year) of iron precipitate that is not depositing on the substrate of
these streams. St. Vincent College, which owns the ground where the
systems were constructed, is conducting ongoing biological stream assessments
to further evaluate stream recovery.
Return
to AMD Stakeholders' page
