20031023 Ver 1_Staff Report_20040305

Martin Marietta
Rocky Point Mine
Page 1 of 2
March 5, 2004
File Memorandum
From: Danny Smith
Subject: Martin Marietta Materials
Rocky Point Quarry
1635 MM Road, Rocky Point, NC 28457
DWQ #03-1023
Pender County
NCDWQ staff has concerns that the mine pit will cause removal of wetland hydrology.
These concerns stem from the following issues:
1) The excavated mine pit is approximately 537 acres, it is approximately 50 feet
deep, and dewaters approximately 1.2 to 4 MGD (million gallons per day)
(pumping averages estimated from May 16, 2003 and May 2, 2003 Memorandum
from Kimley Horn and Associates.)
2) The dewatering of the mine and depth of the mine face changes the hydraulic
gradient of the groundwater.
3) The cone of depression of the groundwater extends beyond the face of the mine
(as per Kimley-Horne Memorandum dated May 9, 2002). [Note: Rick Shiver of
Division of Water Quality has worked with a similar mining operation that has
had a cone of depression estimated to extend in excess of 5000 linear feet beyond
the perimeter of the mine footprint.
4) It was explained in Martin Marietta Materials' February 17, 2003, response
document that the life of the mine site may extend to 20 years (if future permits
are secured for mine expansion).
5) Martin Marietta Materials has used DRAINMOD, to predict the influence of
forestry ditches on tracts B, C, E, G1, and G2. This effort was undertaken to
address/secure the necessary wetland determinations and to address NPDES
permit condition regarding dewatering issues. The model assumed that an
impermeable layer is present at a depth of 10 feet. However, it is the
understanding of DWQ staff that this layer has lower permeability, rather than
being a complete impermeable layer.
6) It is unclear to DWQ staff how far the layer of low permeability extends beyond
the footprint of the mine. Also, unknown are the variations of hydraulic
conductivity of this layer and if the feature is uniformly present.
7) It is the understanding of DWQ staff that the site is mined by the removal of
overburden. The rock material is then shot with explosives to enable the material
to be accessed and available for processing.
Martin Marietta
Rocky Point Mine
Page 2 of 2
Like other mined materials, explosives cause fractures. Limestones (carbonate
terrains) are soluble and are naturally susceptible to the formation of networks of
fractures that can convey water rapidly. As such, the mining efforts can
intercepts these natural conduits. This coupled with rapid dewatering of the
groundwater from the pit can result in impacts beyond the face of the mining
efforts.
8) In the Martin Marietta Materials and NCDWQ meeting dated February 12, 2004,
it was explained by Martin Marietta Material that the elevation of the water in the
mine pit, when reclamation is complete, is expected to be approximately 8 and 10
feet above MSL. With respect wetland drainage, this may result in additional
wetland drainage.
To address the above concerns, NCDWQ needs to know where the wetlands are
located (this is a typical requirement in any certification application) and the wetlands
need to be monitored to ensure that the hydrology remains intact. This information will
enable DWQ to determine whether impacts to wetlands have occurred beyond what has
been proposed. If impacts are determined, NCDWQ can then revisit the matter with
Martin Marietta to ensure/achieve the appropriate compliance with wetland and water
quality standards, NPDES Permits, Section 401 and 402 of the Clean Water Act.
Finally, NCDWQ is also concerned and appreciates the serious issue of time
constraints at Rocky Point Facility (Martin Marietta has explained that there is
approximately six months rock available at the active mine site. It is NCDWQ
experience and belief that securing the delineation of the H1 and H2, resolving the
monitoring plan details, and well placement locations can easily be accomplished within
this time frame.