20031023 Ver 1_Technical Memo_20020309

C=F1 Kimley-Horn
m and Associates Inc.
T e c h n i c a l M e m o r a n d it m
=7,
Date: May 9, 2002
Project: MARTIN MARIETTA AGGREGATES, Rocky Point, NC.
Subject Mine Dewatering, Surface and Ground Water Monitoring Plan
1.0 Introduction
Martin Marietta Aggregates (MMA) operates a limestone aggregate quarry in Rocky Point, North
Carolina. MMA, in cooperation with and in response to a request from the North Carolina
Department of Environment and Natural Resources (NCDENR) Division of Water Quality
(DWQ), will document its dewatering and monitoring program to provide information on the
present and future mine operations and mine expansion. The requested modifications From DWQ
were detailed in a letter from Mr. Rick Shiver, DWQ to Mr. Robert Winchester, MMA, dated
March 5, 2002, and clarification on April, 16, 2002 meeting with DWQ/MMA staff. This
document has been prepared to address the issues requested in the March 5 letter, and as clarified
during the April 16 meeting.
2.0 Background
2.1 Site Setting
The Rocky Point quarry has operated in its present location since 1984. Figure 1 provides a
general location map of the quarry and Figure 2 presents an aerial photograph of the quarry as of
February 2002. The quarry produces approximately 4,000 tons per day of product from the
Eocene age Castle Hayne limestone, a semi-consolidated sandy limestone ranging in thickness in
the quarry area from 5 to 18 feet. The product zone is overlain by sands and clayey sands ranging
in thickness From 20 to 30 feet. Below the producing zone is a thin confining unit that separates
the Castle Hayne limestone from the underlying Peedee aquifer. The confining unit is composed
of clay, silty clay and sandy clay ranging in thickness from, on average, 25 to 35 feet The Cape
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Martin Marietta Aggregates
Rocky Point Quarry
Fear River is located to the east and south of the quarry area, a distance of approximately 1.5 to 2
miles from the active boundary of the quarry. The topography of the area is generally of low
relief, ranging from 25 ft. above mean sea level (msl) on the western side of the quarry to a low of
5 ft. msl near the Cape Fear River. The areas east and south of the quarry are generally poorly
drained soils and well-drained sandy ridges. There are some wetland areas and/or drainage
swales that are all part of the Cape Fear floodplain area or tributaries to the Crape Fear River.
2.2 Local Hydrogeology
Water table elevations in the area occur from ground surface in the wetland areas near the Cape
Fear River to 3 to 10 feet below ground surface in the upland areas as reported in MMA ground
water monitoring well records. The hydraulic connection between the near-surface water table,
water levels within the overburden and water levels within the limestone is somewhat variable.
From a regional perspective and over seasonal time scales, these three zones respond to ground
water changes predominantly as a single hydrogeologic unit. However, their properties are
sufficiently different that in the short term, and in local areas, strong vertical gradients can
develop and the units can respond quite differently to changes in ground water pressures.
Trexler, B. D., (1974)1 provides a good description of the hydraulic properties of the Castle
Ilayne formation and Giese, G. L., J. L. Eimers and R. W. Coble (1997) provide a regional
discussion of the major water-bearing units of' the North Carolina Coastal Plain which includes
the Rocky Point Quarry area.
3.0 Purpose of the Dewatering, Surface and Ground Water Monitoring Plan
Operation of the quarry requires dewatering of the overburden and the Castle Hayne Limestone
This generally results in depression of the water table within the quarry area to an elevation of 2
to 5 ft. msl. The cone of depression created by dewatering extends outside of the active mining
front.
Trexler, B. D., 1974. Pc trographv, Poroslly, and Hydraulic Conductivity of the Castle Havne Aquifer,
CastlcHarne, Nor•117 Carolina. Master's Thesis, North Carolina State University, Raleigh, NC.
Giese, G. L., J. L. Eimers and R. W. Coble, 1997. SinurlaNnn of Gromid-Water Flmt, in the Coastal
Plain Aquifer SI'StCrn of North Carolina. U. S. Geological Survcy Professional Paper 1404-M.
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May 9, 2002
Martin Marietta Aggregates
Rocky Point Quarry
DWQ, in their letter of March 5, 2002 regarding compliance with NDPES permit conditions and
potential impacts on nearby wetlands, requested the following (paraphrased):
¦ Develop alternative site specific pumping and monitoring plans. The pumping plans should
consider ways to minimize the impacts of dewatering. The monitoring plans must depict the
cone of depression associated with the mining and future mine expansion.
¦ Install monitoring wells along a transect or in several directions from the dewatering location
to detect the effects of purnping.
¦ Consider the utility of alternative methods of hydrating areas effected by pumping, such as
spray irrigation or other alternatives.
Pursuant to the April 16 meeting, MMA agreed to, among other tasks, prepare a ground water
monitoring and pumping plan that would include the above as goals and specifically include:
¦ Target monitoring well locations,
¦ Develop frequency, goals, and methods for monitoring, and
¦ Identify reporting format and frequency.
This Technical Memorandum presents a ground water monitoring and pumping program, target
well locations, and monitoring frequency to provide information on the shallow and intermediate
ground water levels outside the active mine area.
The monitoring program, presented herein, assumes mine operations will continue their
expansion to the east and south, but this will be dictated by the mine reserves and economics. If
the mine operations plan is modified, the pumping and monitoring plan will also be modified to
achieve the above goals.
The specific goals of the monitoring program are:
1. Monitor shallow and intermediate ground water levels outside of the mine area to provide
background information on water table elevations prior to mine expansion.
2. Monitoring the extent of the cone of depression created by mine dewatering.
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Rocky Point Quarry
3. Monitor water levels outside of the proposed perimeter recharge ditch(es) to monitor and
manage recharge to the shallow ground water system and to monitor the efficiency of impact
minimization for areas outside of the mine area.
4. Monitor shallow ground water levels near areas suspected to be wetlands.
5. Manage pumping, discharge points and recharge ditches to minimize impacts from mine
dewatering.
6. Monitor hydrological affects of pumping.
3.1 Pumping and Dewatering Plan
Pi-escni Deivaterin, Mclhoch; awlOpci-alions: Dewatering for the present mine operations is
accomplished by float-controlled pumps set in two sumps located near the eastern perimeter and
southern perimeter, inside the mined-out area (Figure 3). Trenches along the base of the mining
face direct seepage toward the sumps and maintain a relatively dry working environment for the
mining equipment. The pumps are activated based on level-controlled floats, and estimates of
total purnpage are made from the pump capacity and hours of operation.
Total pumpage is estimated to vary from 3 to 5 million gallons per day (mgd). The eastern sump
is scheduled to be moved farther south and east to better control the ground water levels in areas
(if and G2 (Figure 3). Discharge from the east sump currently is to Strawberry Branch (east of
the mine). The southern sump is positioned to dewater areas Fl and F2 and to provide water for
product washing.
PumpitW and Dewaler-in, Plan: The goals of the proposed pumping and dewatering plan are:
1. Dewater the mine face sufficiently to allow the equipment to operate efficiently and
safely.
2. Minimize the an1nu1t of water necessary to be pumped consistent with goal Number 1.
3. Limit the spread of' the cone of depression from dewatering activities to the planned
mining area using perimeter recharge ditches and discharge management.
4. Use discharge points to minimize hydrologic impact to adjacent streams and/or wetlands
from dewatering activities and to promote natural hydroperiod and hydrologic fluctuation
in those areas.
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Rocky Point Quarry
,Wethodolo .v: Figure 3 illustrates the existing dewatering sumps and the proposed new east
sump location. It is proposed that the current pumping regime (location of pumps, location of
discharges) continue through the initial phase of the monitoring. MMA is proposing a new
pumping plan with a discharge to the original discharge location and monitoring the effects of the
relocation. By phasing the pumping plan during the initial monitoring plan collection of baseline
data can be initiated immediately while the appropriate measures to implement the proposed
pumping plan can be undertaken (relocation 01' pump, maintenance of existing ditches,
construction of new recharge ditches and potentially installation of water control and dissipation
structures).
For the proposed pumping plan, the new east sump will be located to the south (of the present
sump location) to better focus dewatering activities in the GI and G2 areas. Discharge fi-om the
new east swap will be directed into a new recharge ditch (typical section contained in Figure 3)
that forrns the northern border for area G2. This recharge ditch will confine the dewatering cone
of depression to the areas south of the ditch and isolate the Strawberry Branch area from the
dewatering activities. SwTace water discharges from this ditch will be directed into the unnamed
tributary to Strawberry Branch to support and maintain its hydroperiod to the extent practicable
during mining activities.
The south SUMP provides dewatering of the F I and F2 areas, and provides some overlap with the
new east sump area of influence in the boundary area between areas F and G. Ground water
derived from the south sump will be directed into a perimeter recharge ditch that parallels the
western and southern boundary of area FI, and then directed northward to be discharged into the
unnamed tributary to Strawberry Branch or directed southward to maintain hydrology and/or base
flow to adjacent areas. Figure 3 provides the planned location of the sumps and recharge ditches.
The results of the initial monitoring plan will be evaluated to determine appropriate recharge
ditch cross section and any potential amendments needed to the proposed pumping plan.
Implementation oflhc: P/an: The following specific actions will be implemented to initiate the
pumping and dewatering plan:
1. The east sump will be relocated to the new, more southerly location.
2. The discharge point for the new east sump will be directed into a new recharge ditch as
shown in Figure 3
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May 9, 2002
Martin Marietta Aggregates
Rocky Point Quarry
3. The new recharge ditch will be constructed along the northern boundary of area G2, and
continue along the eastern boundary to the unnamed tributary of Strawberry Branch (see
typical section on Figure 3).
4. The pumping volume will be accurately recorded for the old and new east sump as well as the
existing south sump.
5. A rain gage will be used to provide on-site precipitation data.
6. The discharge point for the south sump will be modified to direct excess water not needed for
product washing into the recharge ditch along the western and southern border of area F.
This recharge ditch will be inspected to determine if unobstructed flow can occur along the
entire planned pathway to the unnamed tributary, or 1f control structures on side culverts are
necessary to maintain head levels and flow within the ditch.
7. Records of quantities pumped from each sump will be maintained on a daily basis on site for
later consolidation and presentation in an annual report format.
3.2 Surface and Ground Water Monitoring Plan
The goal of the surface and ground water monitoring plan is to gather sufficient information to
identify the area of influence of the dewatering activities and to provide information for
management of the dewatering and recharge activities so as to minimize adverse impacts from
dewatering outside of the mine area.
Melhodology: In order to accomplish the above stated goal of the monitoring program, a series
of ground water monitoring wells and monitoring well nests will be installed. Figure 4 illustrates
the three types of wells planned. These are:
1. Shallow wells, generally less than 10 feet deep, designed to monitor shallow ground water
levels in suspected wetland areas to document hydrodynamics for these systems.
2. Overburden wells, generally installed to a depth between 10 feet and 20 feet from ground
surface. These wells are designed to monitor the local ground water table surrounding the
mine area, monitor the expansion of the cone of depression from the pit dewatering and to
provide information on the efliciency of the perimeter recharge ditch.
3. Limestone wells, installed into the limerock unit being mined to provide vertical flow
information, when used in conjunction with the overburden wells, monitor the extent of
H TNM0111850101Final GW_Monitcring_Plan.doc 6 0110
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Martin Marietta Aggregates
Rocky Point Quarry
expansion of the cone of depression ti-om the dewatering activities, and provide information
on the hydraulic head relationship between the overburden and limestone Units.
Shallow aquifer monitoring locations are proposed in areas G1, G2, Hl, and H2 (Figure 5). Each
monitoring location will consist of a free-water surface monitoring well to monitor for wetland
hydrology, and a "nest" of 3 to 4 piezometers (depending on soil stratigiaphy) to assess soil water
movement and vertical/horizontal flow gradients in the areas of suspected wetlands. The
objectives of the monitoring nests are to I ) document the presence, or lack thereof, of the water
table near the surface sufficient to meet wetland hydrology criteria, and 2) correlate groundwater
flow with the deeper aquifer monitoring wells to demonstrate the relationship (if any) with the
deeper groundwater systems in these geomorphic features. A sketch of the monitoring well and
piezometer "nest" is shown as an inset in Figure 4. All monitoring wells will be installed using
appropriate methodology to meet applicable regulatory requirements for hydrologic monitoring
purposes. All wells installed will be surveyed and tied to permanent benchmarks.
The data from the monitoring well and piezometers will be collected daily and on a limited basis
by continuous recorder dataloggers attached to each well/piezometer. The units will be
programmed such that readings will be collected daily. The dataloggers will be downloaded on a
monthly basis, at a minimum, to inspect proper function of the monitoring equipment.
The shallow monitoring locations were identified tlu-ough a field evaluation meeting with the US
Army Corps of Engineers (COE) staff (Mickey Sugg) held on April 30, 2002. The areas visited
during that meeting identified by the COE as suspected wetland areas are those included for
shallow aquifer monitoring on parcels G1, G2, Hl, and 112. A jurisdictional determination (JD)
as to the extent of wetland areas was not performed at that time, so monitoring locations were
determined as the closest approximation to location as discussed in the field. Additional
information regarding the influence of drainage ditches on suspected wetland areas and the extent
of hydric/non-hydric soils is requi?-ed by the C.OE to determine wetland boundaries. Wetland
delineation efforts are on-going and may supplement the proposed plan (contained here) as
necessary.
The overburden and limestone wells will be located in two transects of 3 well nests each, oriented
east and south of the F and G areas. Each well nest location will include a well screened in the
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Rocky Point Quarry
overburden and a well screened in the limestone unit. This configuration will provide both
horizontal and vertical definition of hydraulic gradients, and in combination with the information
on unit hydraulic conductivities, will provide quantitative information on ground water flow rates
Each of the overburden and limestone monitoring wells will be measured daily. A limited
number of shallow water table wells will also be instrumented with continuous recorders but,
because of the number of monitoring locations, and the number of peizometers, manual
monitoring on a monthly basis may be performed to supplement water table well data with the
piczometer data.
The physical location of the wells will be dictated by the planned mine expansion. At this time, it
is anticipated that mining operation will continue in FI and is intended to expand into areas GI
and G2. Based on this planned development, the two transacts ofoverburden and limestone wells
and the shallow wells should provide sufficient information to closely evaluate the impacts of
mine dewatering. This proposed plan may be modified, however, if the mine expansion plans are
modified or if analysis of the ground water data indicate that changes are necessary in the
monitoring program.
Scheduling of installation of the monitoring network will be determined in conjunction with mine
operators and DWQ regulatory personnel to meet the necessary terms for permit compliance and
sound environmental management. Figure 5 illustrates the planned location for the monitoring
wells and Table I provides the planned monitoring well designation, monitoring frequency and
construction details.
4.0 Summary
The above dewatering, surface and ground water monitoring program will provide information on
dewatering activities, impacts and ground water table elevations near sensitive suspect wetland
systems, provide information on the regional ground water table, monitor the impacts of mine
dewatering on the overburden and limestone geologic units surrounding the mine and provide a
method of managing the perimeter recharge ditches to minimize the expansion of the cone of
depression in the water table aquifer from mine dewatering activities. The program includes two
transects of overburden wells and limestone wells and areally distributed shallow wells based on
HLPNr0111850101Final.GW.Monitoring Plandoc 80(1o
May 9, 2002
Martin Marietta Aggregates
Rocky Point Quarry
the planned mine expansion program. The location and timing of well installation may be
modified based on mine operations and permit compliance needs. The results of the monitoring
plan will be used to assess the proposed pumping plan and to develop amendments to the plan, if
necessary.
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Martin Marietta Aggregates
Rocky Point Quarry
Table 1: Surface and Ground Water Monitoring Well Program
Rocky Point Quarry, Pender County, NC

Location No.
Well Type Planned Total

Depth (ft) Screen Length

(ft) Monitoring

Frequency
1 OB 15 5 DM
1 LS 35 5 DM
2 OB 15 5 DM
2 LS 35 5 DM
2 S11 Varies Varies DM
2 PI Varies Point location PM
3 OB 15 5 DM
3 LS 35 5 DM
3 S11 Varies Varies DM
3 P1 Varies Point location PM
4 OB 15 5 DM
4 LS 35 5 DM
5 S11 Varies Varies DM
5 PI Varies Point location PM
6 S11 Varies Varies DM
6 PI Varies Point location PM
7 S11 Varies Varies DM
7 PI Varies Point location PM
Notes: OB = Overburden Well
LS = Limestone Well
SH = Shallow Water Table Well
PI Piezometer
DM - Daily Measurement
PM = Periodic Measurement
H:TW0111850101Final GW Monitoring Plan doc 10 of 10
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5/9/02 NA 011195010 4
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