buzzi hercules hydrogeology
TRANSCRIPT
GEOLOGIC AND HYDROGEOLOGIC CONDITIONS AT AND IN THE REGION SURROUNDING THE HERCULES LIMESTONE QUARRY,
STOCKERTOWN, PENNSYLVANIA
Assessment of the Potential Impacts of Quarry Dewatering on
Local Groundwater and Surface Water Resources with an Emphasis on
Proposed Deepening of the East Pit to 50 ft msl
Stream losses were determined to be ~30 million gallons per day or ~ 46 cfs
Pumping from quarry was ~ 54 Million Gallons per day or ~ 84 cfs
A recirculation cell was hypothesized
WQIZ
The U.S.G.S. speculated that there could be a “Hypothesized Fracture Zone with Large Hydraulic Conductivity.”
Risser, 2006
West quarry inflow zone
PADEP-05
PADEP-02
PADEP-04
PADEP-03
PADEP-06
MW-3
MW-2
MW-1
MW-6R
MW-8
MW-4
PADEP-01
Grout Curtain
WQIZ
ESSROC Quarry
Naz
aret
h
In an attempt to eliminate the hypothetical recirculation, a grout curtain was installed in 2008.
Data generated during and since the installation of the grout curtain provided for an expanded understanding of hydrogeologic conditions
The previous conceptualization was of a single, unconfined aquifer as the source of the quarry inflow. The boundaries were assigned based on a combination of the observed limits of stream flow losses in the Bushkill and Schoeneck Creeks and water balance, assuming a uniform, standard recharge rate.
Data from the post-grouting period supports a conclusion that there are two distinct groundwater systems: a shallow unconfined system which occurs
in the epikarst zone and a deep confined system.
The currently proposed quarry deepening would occur wholly within the unconfined aquifer zone. .
Buzzi Cement Plant
WQIZ
ESSROC Quarry
Stockertown
Tatamy Naz
aret
h
The grout curtain failed to eliminate WQIZ inflows, but achieved a maximum reduction of flow of approximately 10%
Various investigators hypothesized that the conduit flow bypassed the curtain in the subsurface by flowing around the ends.
The questions which had to be answered were:
Does extraction from the WQIZ derive water from the Bushkill Corridor? Is there a conduit of large conductivity? Are the two groundwater zones distinct hydraulically? Will extending the depth to 50 ft msl adversely impact local or regional water resources?
The answers to those questions required a re-assessment of both the geology and
hydrogeology of the quarry and the surrounding area.
U D
Surface Expression of Karst trend
Prominent Karst Feature
Fold axis
Fault Trace
Explanation
Ojb
Ob
Ojb
Ojb
Ob Ob
Groundwater Flow
Bushkill Creek
Geologic Contact
Outcrop of Jacksonburg Fm
Fault Inferred Location
West quarry inflow zone
Beginning of influent stream conditions
Ob Beekmantown Group
Geology
U D
Surface Expression of Karst trend
Prominent Karst Feature
Fold axis
Fault Trace
Explanation
Ojb
Ob
Ojb
Ojb
Ob Ob
Groundwater Flow
Bushkill Creek
Geologic Contact
Outcrop of Jacksonburg Fm
Fault Inferred Location
West quarry inflow zone
Beginning of influent stream conditions
Ob Beekmantown Group
.
There is a pervasive SW-to-NE trend of all
structural features
Geology
Karst solution features follow the same general SW-NE trend and also plunge
toward the NE.
Geology
U D
Surface Expression of Karst trend
Prominent Karst Feature
Fold axis
Fault Trace
Explanation
Ojb
Ob
Ojb
Ojb
Ob Ob
Groundwater Flow
Bushkill Creek
Geologic Contact
Outcrop of Jacksonburg Fm
Fault Inferred Location
West quarry inflow zone
Beginning of influent stream conditions
Ob Beekmantown Group
The hypothetical conduit of Risser would be off trend and would, of
necessity, have to plunge SW.
Geology
U D
Surface Expression of Karst trend
Prominent Karst Feature
Fold axis
Fault Trace
Explanation
Ojb
Ob
Ojb
Ojb
Ob Ob
Groundwater Flow
Bushkill Creek
Geologic Contact
Outcrop of Jacksonburg Fm
Fault Inferred Location
West quarry inflow zone
Beginning of influent stream conditions
Ob Beekmantown Group
In fact, both the trend and plunge of the hypothetical feature are not plausible: the trend would be inconsistent with the entire tectonic setting and the plunge, if present, would have to be eastward.
Geology
Hydrogeology
The quarry is in the outcrop area of the Jacksonburg Formation near the contacts with the Martinsburg Fm (up section) and Epler Fm (down section). Within the outcrop area of the pelitic Martinsburg Formation the stream is effluent. The reach of stream over the paleokarst Jacksonburg Formation is perched above an aquifer which is in the epikarst zone. The reach of stream from the contact of the Epler Formation with the Jacksonburg Formation is a classic, influent karst stream characterized by few tributaries, surface drains, predominant subsurface drainage, closed depressions, sinking streams, in-stream ponors…
It was necessary to pressure grout the curtain which could only be accomplished by reducing aquifer pressures through a series of relief wells.
Indications of Two Groundwater
Systems
Hydrogeology
“When the pressure relief wells were opened to provide for grout injection, there was an immediate response in wells MW-3 and MW-6.”
Hydrogeology Indications of Two
Groundwater Systems
There is an upwelling zone in the standing water of the WQIZ; Water jets out of seams/cracks in the standpipes of capped wells in the WQIZ with 15-ft high standpipes; Water rose to a height 48 ft above the quarry floor during grouting Grout and rock fragments were ejected from pressure relief wells
Indications of Two Groundwater
Systems
Hydrogeology
West quarry inflow zone
PADEP-05
PADEP-02
PADEP-04
PADEP-03
PADEP-06
MW-3
MW-2
MW-1
MW-6R
MW-8
MW-4
PADEP-01
Unconfined zone wells did not respond to the operation of pressure relief wells
Indications of Two Groundwater
Systems
West quarry inflow zone
PADEP-05
PADEP-02
PADEP-04
PADEP-03
PADEP-06
MW-3
MW-2
MW-1
MW-6R
MW-8
MW-4
PADEP-01
Unconfined zone wells responded to precipitation and stream flow.
Indications of Two Groundwater
Systems
Hydrogeology
Temperatures of unconfined zone groundwater followed stream water temperatures through the fall-winter months. Confined zone groundwater remained nearly constant.
Indications of Two Groundwater
Systems
Hydrogeology
Unconfined groundwater has remained unaffected over a period of time during which the volume of quarry extraction increased.
Indications of Two Groundwater
Systems
Hydrogeology
Buzzi does not pump groundwater. The water in the WQIZ flows freely upward into the stilling basins and it is pumped from those ponds to the Bushkill
Indications of Two Groundwater
Systems
Hydrogeology
In other words, there is no active hydraulic influence pulling water against the prevailing hydraulic gradient.
Indications of Two Groundwater
Systems
Hydrogeology
After 19 years of artesian flow into the WQIZ under significant hydraulic pressure, there has been no adverse effect on aquifer performance.
Indications of Two Groundwater
Systems
Hydrogeology
The flows into the WQIZ do not exert a hydraulic influence on either unconfined groundwater or the Bushkill Creek.
Indications of Two Groundwater
Systems
Hydrogeology
Absence of responses in unconfined groundwater to confined zone stresses – especially in interposed wells
Hydrogeology
U D
Surface Expression of Karst trend
Prominent Karst Feature
Fold axis
Fault Trace
Explanation
Ojb
Ob
Ojb
Ojb
Ob Ob
Groundwater Flow
Bushkill Creek
Geologic Contact
Outcrop of Jacksonburg Fm
Fault Inferred Location
West quarry inflow zone
Beginning of influent stream conditions
Ob Beekmantown Group
The geology imparts a significant directional anisotropy to the groundwater system.
Hydrogeology
West quarry inflow zone
PADEP-05
PADEP-02
PADEP-04
PADEP-03
PADEP-06
MW-3
MW-2
MW-1
MW-6R
MW-8
South Sump
‘V’ Sump
East Sump (drained)
MW-4
PADEP-01
Hydrogeology
Currently approved for deepening to 0 ft msl from current floor at 100 ft msl. October 3, 2011 report addressed Special Condition 22 for hydrogeology and highwall integrity. Concern regarding hydrology is that further deepening could have impact on local hydrogeology. Conducted a hydraulic test in June 2011 using south sump.
Quarry Deepening
Proposed mine deepening area
West Quarry Inflow Zone
Quarry Deepening
MW-8
MW-6R
MW-2
MW-3
MW-4
MW-1
Quarry Deepening The sump was dewatered at a rate of 1,800 gpm in July, 2011 – local effects were monitored in perimeter wells.
Sump
Quarry Deepening
MW-8
MW-6R
MW-2
MW-3
MW-4
MW-1
Quarry Deepening The drawdown of unconfined water within the sump was ~ 12 ft. The volume of water extracted was approximately 4 X 106 ft3 (30 million gallons). At a porosity of 4% (high) and an aquifer thickness of 100 ft, that is equivalent to the storage over an area of ~ 24 acres.
Sump
Quarry Deepening
MW-8
MW-6R
MW-2
MW-3
MW-4
MW-1
Quarry Deepening Sump rebound was at a rate of 0.15 ft hr-1. Total rebound was 11.5 ft over a 7-day recovery period. The calculated Darcian hydraulic conductivity is 2 ft day-1 to 4 ft day-1.
Sump
Quarry Deepening
MW-8
MW-6R
MW-2
MW-3
MW-4
MW-1
Quarry Deepening There were NO responses in any well to either the dewatering at 1,800 gpm or to the post-extraction recovery… Except MW-3 which is along-strike of the sump.
Sump
Quarry Deepening
MW-8
MW-6R
MW-2
MW-4
MW-1
Sump
Quarry Deepening
MW-3
MW-8
MW-6R
MW-2
MW-3
MW-4
MW-1
The structural geology imparts are pronounced, along-strike directional anisotropy along a generally SW-NW direction.
.
Quarry Deepening
MW-8
MW-6R
MW-2
MW-3
MW-4
MW-1
.
The structural geology imparts a cross-strike barrier to flow and even to hydraulic communication. .
Quarry Deepening
Cross-Strike Cross-Strike
The directional anisotropy is also the condition within the confined aquifer
MW-8
MW-6R
MW-2
MW-3
MW-4
MW-1
As a result of the directional anisotropy, drawdown of the unconfined aquifer to accommodate mining to 50 ft msl will be in an along-strike direction and will be bound by the north and south boundary faults. The Bushkill in the along-strike direction is a perched stream unconnected to groundwater and is already lined
.
Quarry Deepening
MW-8
MW-6R
MW-2
MW-3
MW-4
MW-1
With a footprint area of ~ 50 acres and a depth of 50 ft, the dewatering can be maintained with an extraction rate of ~2,600 gpm for a total daily volume of ~ 2.6 MGD.
.
Quarry Deepening
Highwall Integrity/Stability
Quarry Deepening
Two Distinct Structural Trends Quarry Deepening
Quarry Deepening
Quarry Deepening
Quarry Deepening
The Markland Analysis revealed that there are areas along the southern highwall where instabilities could occur, but that the potentially causal structural features do not extend vertically beyond one bench or only marginally into the next highest bench. Routine mitigation measures are adequate to stabilize the potentially unstable zones
Quarry Deepening
Conclusions
There are two hydraulically distinct aquifers: • a shallow unconfined zone which occurs
predominantly in the epikarst zone;
• a deep confined aquifer which is the principal source of WQIZ inflow water
Conclusions
The pattern of unconfined aquifer dewatering is controlled by geologic structure. The cone of depression appears to be elongate in a SW-NE ellipse, constrained between faults which create no-flow boundaries to cross-strike flow.
Conclusions
Mining to el. 50 ft msl will have little impact on local or regional water resources. Using data from sump dewatering test, the east pit dewatering will require ~ 2,000 gpm, or an additional 2.5 MGD…. … an increase of 4% to 5% above current discharge.
U D
Surface Expression of Karst trend
Prominent Karst Feature
Fold axis
Fault Trace
Explanation
Ojb
Ob
Ojb
Ojb
Ob Ob
Groundwater Flow
Bushkill Creek
Geologic Contact
Outcrop of Jacksonburg Fm
Fault Inferred Location
West quarry inflow zone
Beginning of influent stream conditions
Ob Beekmantown Group
The speculation that there could be a “conduit of large conductivity” is inconsistent with all data and observations.
Conclusions
MW-8
MW-6R
MW-2
MW-3
MW-4
In 2009 the loss of water from the Bushkill increased from 30 MGD to ~38 MGD with no change to the rate or volume of WQIZ inflows. It is not possible that a portion of water lost to swallow holes could travel in the unconfined aquifer away from the quarry while the remainder flows toward the quarry.
.
The source of WQIZ water is not the Bushkill Creek
Conclusions
MW-8
MW-6R
MW-2
MW-3
MW-4
Groundwater elevations in the two aquifers within the Bushkill Corridor are similar – at some locations, are under a negative pressure gradient at some locations, and at some locations there is a positive pressure gradient. .
The source of WQIZ water is not the Bushkill Creek
Conclusions