Download - Buzzi Hercules Hydrogeology

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

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Grout Curtain

WQIZ

ESSROC Quarry

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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

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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.

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Surface Expression of Karst trend

Prominent Karst Feature

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Fault Trace

Explanation

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Groundwater Flow

Bushkill Creek

Geologic Contact

Outcrop of Jacksonburg Fm

Fault Inferred Location


Beginning of influent stream conditions

Ob Beekmantown Group

Geology

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Fault Trace

Explanation

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Groundwater Flow

Bushkill Creek

Geologic Contact






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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

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Fault Trace

Explanation

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Ojb

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Groundwater Flow

Bushkill Creek

Geologic Contact






The hypothetical conduit of Risser would be off trend and would, of

necessity, have to plunge SW.

Geology

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Fold axis

Fault Trace

Explanation

Ojb

Ob

Ojb

Ojb

Ob Ob

Groundwater Flow

Bushkill Creek

Geologic Contact






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


Systems

Hydrogeology


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Unconfined zone wells did not respond to the operation of pressure relief wells


Systems


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Unconfined zone wells responded to precipitation and stream flow.


Systems

Hydrogeology

Temperatures of unconfined zone groundwater followed stream water temperatures through the fall-winter months. Confined zone groundwater remained nearly constant.


Systems

Hydrogeology

Unconfined groundwater has remained unaffected over a period of time during which the volume of quarry extraction increased.


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


Systems

Hydrogeology

In other words, there is no active hydraulic influence pulling water against the prevailing hydraulic gradient.


Systems

Hydrogeology

After 19 years of artesian flow into the WQIZ under significant hydraulic pressure, there has been no adverse effect on aquifer performance.


Systems

Hydrogeology

The flows into the WQIZ do not exert a hydraulic influence on either unconfined groundwater or the Bushkill Creek.


Systems

Hydrogeology

Absence of responses in unconfined groundwater to confined zone stresses – especially in interposed wells

Hydrogeology

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Fold axis

Fault Trace

Explanation

Ojb

Ob

Ojb

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Groundwater Flow

Bushkill Creek

Geologic Contact






The geology imparts a significant directional anisotropy to the groundwater system.

Hydrogeology


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South Sump

‘V’ Sump

East Sump (drained)

MW-4

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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

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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

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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

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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

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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

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Sump

Quarry Deepening

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The structural geology imparts are pronounced, along-strike directional anisotropy along a generally SW-NW direction.

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Quarry Deepening

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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

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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

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Quarry Deepening

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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.

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Quarry Deepening

Highwall Integrity/Stability

Quarry Deepening

Two Distinct Structural Trends 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.

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Fold axis

Fault Trace

Explanation

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Ob

Ojb

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Groundwater Flow

Bushkill Creek

Geologic Contact






The speculation that there could be a “conduit of large conductivity” is inconsistent with all data and observations.

Conclusions

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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.

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The source of WQIZ water is not the Bushkill Creek

Conclusions

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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

Download - Buzzi Hercules Hydrogeology

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