1. 7.4.4 BMP Considerations
    1. Increased storage
    2. Decreased velocity
    3. Pollution control/water quality
      1. 7.5 Mined Lands

Pennsylvania Stormwater Best Management Practices Manual
Chapter 7
Implement numerous infiltration BMPs throughout the site instead of just one.
Stormwater should not be conveyed into concentrated runoff flow paths. Broad and shallow
flow dispersion is most effective. Minimizing impervious surfaces should aid in decreasing
runoff, in general. (Virginia DCR)
Impounded water causes soil saturation and loss of cohesion, and produces stress from the
weight of the water. Differences in hydraulic head and steep hydraulic gradients can result in
sinkhole development. For these reasons, shallow basins with overflow channels are
preferred over one large, deep basin. Basins, if they must be used, must have synthetic
liners to prevent failure and sudden loss of water into a subsurface drain.
Diligence and site maintenance can influence the ultimate success of the stormwater plan.
Seal all exploratory boreholes to eliminate surface water entry.
Minimize earth disturbance when installing stormwater structures. Disturbing the upper,
cohesive soils can lead to subsidence and future collapses. (Newton, 1987)
Management of stormwater structures usually ends after construction. In karst, however,
BMPs need to be inspected, cleaned, maintained, and possibly repaired. Sinkholes should
be promptly and properly repaired. Inspection and maintenance schedules must be
addressed in the plans.
Pay specific attention to the integrity of piping of all types. Evidence of pipe leakage or
sagging should be immediately addressed because these areas quickly become the focus for
soil loss into subsurface voids that leads to subsidence and sinkhole collapse.
All stormwater management designs for karst areas must include details for sinkhole repair
during and after construction. The sinkhole repair plan should appear on the construction
drawings and also be made a part of the site’s Operation and Maintenance Plan. The
sinkhole repair plan should be flexible to accommodate a variety of failure modes and
locations. A qualified individual should oversee the repair work.
7.4.4 BMP Considerations
The conventional stormwater BMPs presented for traditional development activities are generally
applicable and effective in karst areas. However, these are not necessarily the
most
effective or
appropriate. (McCann & Smoot, 1999) (Virginia DCR) The following are some conventional
examples of karst area BMPs:
Increased storage
Dry detention pond
Wet retention with lined settling ponds
Shallow detention ponds
Vegetated Roof
Increased infiltration
Runoff spreaders
Porous pavement
Improved sinkholes / Class V injection well (See Crawford, 1989, Chapter 3)
Perforated pipes
Bioretention cells / rain gardens
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2006
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Pennsylvania Stormwater Best Management Practices Manual
Chapter 7
Decreased velocity
Increased vegetation density / vegetated swales
Terraced slopes
Rip rap (preferably using carbonate rock)
Pollution control/water quality
Filter berms
Gravel or sand filtration systems
Peat moss or activated carbon filtration
Constructed wetlands (lined)
Increased vegetation density / rain gardens
Rip rap
Compost
7.5 Mined Lands
Disturbed lands that have been strip or surface mined, or are underlain by deep mine
excavations, are one of the most difficult areas on which to apply stormwater BMPs. The
drainage of rainfall that has percolated through residual mine wastes on the land surface, or
infiltrated the existing land surface and drained into deep mines and subsequently found its way
to the surface from mine tunnels, has produced one of the most severe water quality conditions in
Pennsylvania. Thousands of miles of streams within the state are devoid of aquatic life because
of the extreme acidity of surface waters that are polluted by abandoned mine discharges. This
condition is considered by most experts to be the single greatest pollution issue in the state,
simply because it has no obvious or easy solution.
Since this acid drainage from abandoned mines begins as rainfall on the surface, the obvious
solution would seem to be to redirect any rainfall away from any surface materials containing
mine wastes, and assure that as little infiltration as possible took place above deep mine layers.
The exclusion of all infiltration BMPs in these areas would negate many of the BMPs described in
Chapter 6, other than the vegetated roof systems and the capture/reuse measures. One
important consideration is that the use of vegetation to remove or change the chemical form of
pollutants in acid mine drainage could also include the pollutant load from new impervious
surfaces where suitable. A great deal of research has been directed toward the use of wetland
systems as passive AMD treatment technologies (PADEP, 2005). These systems form part of a
larger strategy for abandoned mine reclamation (PADEP, 1998) in those watersheds where the
problem is widespread.
All of this very important water quality research does not address the specific problem created by
new development or redevelopment on mined lands. Where the potential exists for runoff from
new development to come into contact with mine wastes, then surface drainage design should
convey runoff to surface swales and channels free of any mine waste residual. If detention basins
are used for rate mitigation, they should be lined if situated on surface mined lands or over deep
mines. Water quality measures will need to rely on intensive maintenance programs for new
development, and control of pollutant application, especially fertilizers, herbicides and pesticides.
If porous pavements are designed, the sub-surface beds must be lined, so that the primary
function will be detention rather than volume reduction by infiltration. Finally, the land
development plan should place special emphasis on protection of existing vegetation and
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2006
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