Paper Presented at 2005 USSD Conference

Transcription

1 ABSTRACT A Case History Dewatering the Saluda Dam Howard W Gault PG, Paul C Rizzo Associates Inc Raymond Ammarell, PE South Carolina Electric & Gas, Harry Bagherzadeh PG Griffin Dewatering, Kerry McCarney GIT Paul C Rizzo Associates Inc. The Saluda Dam Remediation included the construction of a Roller Compacted Concrete Berm (1.3 million cubic yards) and a Rock fill Berm (3.5 million cubic yards) along the downstream toe of an existing earthen dam in order to withstand a future seismic event similar to the Charleston earthquake of An excavation to non-liquefiable soils or bedrock was required prior to Berm construction. To accomplish this construction, the installation and operation of an extensive groundwater dewatering system was required to protect from slope instability due to unstable and wet dam soils, to lower pore pressure, and to control groundwater elevation and seepage within the excavations. Failure to control water during and after dewatering could result in flooding of the excavation, unstable or unworkable sub-grade, uplift of construction features, safety issues, delays in the project, loss of fines from the dam, or a host of unstable conditions such as boils, springs, blowouts, seeps, or piping effects. Catastrophic conditions with this unique dam could have arisen due to the fact that Columbia, South Carolina was just eight-miles downstream of the Dam and over 120,000 lives would have been at stake had a Dam breach occurred. Obviously, this dewatering challenge was incredibly exceptional in that an entire dam was to be dewatered, not just an individual excavation. Dewatering efforts were centered on construction efforts and construction schedules, which didn t always agree. In addition, construction of the dewatering system needed to keep up with the fast-paced construction schedule. Pumps were sometimes turned off and on to test the effects of pumping on the soils or bedrock at certain locations. Dewatering became critical if a deep well malfunctioned above an excavation location. Furthermore, if there was a location where the pore pressures were too high to begin or continue excavation, deep wells or eductor lines had to be drilled on a very short notice to avoid costly delay charges from the General Contractor. Additional complications arose with the reluctance of Dam contractors to assume the responsibility for the dewatering and related safety impacts on dam stability. Perhaps the biggest challenge occurred when the plans changed from an excavation start in the center cells to a simultaneous start of excavation of both the northern and southern cells. This Paper will present a case history of the design and implementation of the dewatering system required to facilitate the remediation of the Saluda Dam. The paper will discuss initial design, field modifications, contractual difficulties, and related topics. Introduction Construction of the new Berm at Saluda Dam required a great amount of new information about the hydrogeology of Saluda Dam. The original design was based on five lines of nested piezometers and two pump tests. During installation of the dewatering system, over 1200 wells, piezometers and instruments

2 have been installed on and at the toe of Saluda Dam. The Engineer logged all of the boreholes associated with these wells. The Owner and Engineer have learned much from the installation of a constructionstability monitoring system and construction de-watering system. These data were used to modify the original design to accommodate varying subsurface conditions. The implementation of the dewatering program of the Dam was based on an understanding of flow and pore pressures within the Dam far more compete than many large structures. Subsurface information was collected every 10 to 20 feet during the installation of the dewatering program. Detailed description of the subsurface was made of subsurface material every 100 feet as well. Records of well development and response to pumping exist for all of the wells on the site. This large effort resulted in a large database of subsurface information. The dewatering system was designed and installed in real time with regard to this data. Small design changes were made because of geology, and geometry. The initial design was based on an understanding of the geology based on pre-construction drilling, a limited number of nested piezometers and two aquifer tests. By constantly updating a subsurface data base the Engineer was able to modify the dewatering system during its installation and adapt it to varying subsurface conditions. Geologic mapping of the foundation provided much more detailed information of the subsurface and permitted further refinements of the hydrogeologic model. Figure 1 Geologic Map of the Excavation for Saluda Dam The Geologic Map of the excavation will be published by the South Carolina Geologic Survey. A Dewatering Chronology Investigative efforts at the Saluda Dam began in 1989 with a conventional geotechnical investigation aimed at confirming the static and dynamic stability of the dam. Based on the results of the analyses presented, the dam required remediation to comply with current FERC parameters of seismic loading due to predictions of wide-scale liquefaction. During the 1989 investigation a number of nested piezometers were installed to augment a limited existing system. Data collected from these piezometers allowed the creation of a flow net to model flow within the Dam. Pumping tests were performed by RIZZO at the Saluda Dam site during 2000 and 2001 at two different locations. These tests were performed in the underlying rock. Pump Test 1

3 was located in the schist and Pump Test 2 was in the gneiss. Tests in each rock type were performed once with water levels in the pumping well maintained above the screened interval (to avoid transient conditions) and secondly with maximum drawdown. Based on drawdown data, transmissivity and specific capacity values in the 2 main aquifers (schist and gneiss) were estimated. These values allowed RIZZO to the design the dewatering system. However, the most important observation made during pre-design pump-testing was that pumping within the fractured rock affected water levels within the overlying soil. As presented below, the validity of this assumption is crucial to the success of the dewatering program. Packer tests were performed by RIZZO at six locations near in 2000 and 2001 as part of a hydrogeological study of the site. Four of these packer tests were conducted to 250-feet below ground surface to assess deep permeability. Significant permeability was detected at depth in several of these tests. In addition, falling head tests were also performed in April of 2000 at nine piezometers screened within the dam and underlying residual soils. These tests provided in-situ measurements of the permeability of the soil within the screened interval of the piezometer. Upon gathering results, hydrogeologic conditions at the dam and the downstream toe were interpreted. Ranges of hydraulic conductivity in each hydrostratigraphic horizons, storativity values, and degree of confinement were determined. In addition, optimum spacing was approximated using the radius of influence of deep wells. The plan was to install deep wells on 100-foot spacing so that there would be well interference. We would also install a row of eductors at the edge of the excavation to intercept any water flowing through the dam. Installation and operation of an extensive groundwater dewatering system was required to protect from slope instability and to control groundwater within the toe excavations required to construct the RCC Berm and Rockfill Berms. RIZZO designed the groundwater control system and Griffin Dewatering Southeast, L.L.C. (Griffin) was selected as the dewatering contractor to drill, install, operate, and maintain the groundwater control system(s) under a unit-price contract. Barnard Construction of Montana was awarded a lump-sum contract to build the 1.5 mile long back up dam on September 15, 2002.

4 Griffin selected Miller Drilling, Inc. (Miller) as the drilling subcontractor and mobilization to the job site began on April 22, Miller mobilized two Schramm Air Rotary rigs on , one additional Air Rotary on , and one Barber Rig on Subsequently as the job progressed, Miller drilling mobilized a second Barber rig and six Sonic rigs. Drilling began on April 24, 2002 with a soil piezometer. Drilling and installation continued from April of 2002 until May of During this time, 94 deep wells, 824 eductor wells, 80 vibrating wire piezometers, 48 rock piezometers, 73 soil piezometers, 43 vacuum wells, 25 well points, and 80 inclinometers were installed. During installation RIZZO geologists logged every borehole. Yield tests were performed on all of the pumping wells and compared to an always increasing database of subsurface information. Total footage drilled is presented on Table 1 Table 1 Drilled Footage Description Drilled Depth (ft) DEEP WELLS 23,308 EDUCTORS 39,201 SOIL PIEZOMETERS 2,950 ROCK PIEZOMETERS 3,622 INCLINOMETERS 7,323 SHALLOW WELLS 3,777 VIBRATING WIRE PIEZ. 5,320 GRAND TOTAL 85,500 Saluda Dam Hydrological Model Water flow within and beneath Saluda dam is controlled by geologic conditions and the construction methodology. Ground water flow beneath the Dam conforms to the general Hydrogeologic model for the Piedmont Physiographic province where fractures within the rock control permeability and water is stored within the residual soils. This concept of permeable rocks below water-storing residual soils formed the basis of the design of the dewatering system. To a large degree the success of the dewatering program was due to

5 the validity of this model. Water was pumped from fractures within the rock and in time drained the overlying soil. To understand the flow of water through Saluda Dam a review of construction methodology is required. Saluda Dam is a semi- hydraulically filled earth dam that was constructed from 1929 to At the time of construction it was the largest dam in the world (Morse, 1942). Construction methodology consisted of dumping soil on cleared ground along the upstream and downstream limits of the dam, washing the dumped soil piles and allowing the fines to flow to a puddle core. This results in a dam composed of three zones: an interior core composed of fines, surrounded upstream and downstream by a washed fill zone which is depleted of fines which is in turn bounded on the out side of the dam with dumped fill. The top of the dam is constructed of compacted fill. Modification over the years included the addition of drains and rock fill benches. The top of the Dam was raised in 1988 to increase the reservoir capacity during maximum floods. During the 1988 and 1989 subsurface investigation of Saluda dam the effectiveness of these construction methods were evaluated. A number of instruments were installed in the Dam to augment the existing system. Based on data from these instruments, a potentiometric model of flow through the dam was developed. Perhaps the most significant control of water flow beneath the dam is the clayey residual soil layer, which can be a very effective aquatard. This clayey residual soil is the uppermost soil horizon in most of the soil beneath the Dam. This clayey soil does not exist in the bottom of the old Saluda river valley where it has been removed by erosion. A very good approximation of the location of this clayey soil layer can be seen on the Topographic map of Saluda Dam make in 1927 prior to dam construction. In that very little grubbing was done prior to the construction of Saluda Dam, the original ground surface approximates the uppermost boundary of this clay layer. An organic layer was encountered in many borings that penetrated this layer. In locations where this layer was disturbed or removed during construction of the Dam, the 1927 Topographic map is inaccurate. However, the validity of the map was largely confirmed during the installation of the dewatering system. There is a high degree of correlation between the top of residual soil found during drilling and the elevations on the 1927 topographic map.

6 Where residual soil is well developed, it grades downward from clay to silt to silty sand. Just below the silt the texture of the parent rock becomes visible. Texture and fractures of the parent rock can be described and mapped. This residual soil is part of the aquifer beneath the dam and controls the storage of water for the aquifer. Fractured rock below the residual soil controls permeability. The soil and rock are two parts of one aquifer system (Trainer, 1988; LeGrand, 1988). This characteristic allowed the construction of a dewatering program that pumped water from the rock and drained water from overlying soil. A number of drains and tunnels were constructed over the years. These features further complicate water flow through the dam. During the installation of the Dewatering system the location of many of these features were confirmed. These features conduct various amounts of water. Interviews with long time site workers indicate that some produce sediment after heavy rainfall events. There have been numerous sink holes in the dam over the years which may explain the sediment. These features will largely become irrelevant after the Berm is completed as the permeability of the rock fill and filters at the excavation/toe of Dam contact will control their drainage in the future. INSTALLATION Drilling methodology must be carefully chosen when drilling through an embankment dam. Conventional air rotary could in an extreme case cause a breach if air under high pressures were to communicate with the reservoir. Additionally, Saluda Dam has a 10 to 20-foot layer of rip-rap on the downstream side. In the past this rockfill layer would be penetrated by conventional air rotary methods, a casing installed and the borehole advanced with wash rotary methods. This time consuming process was not appropriate for in excess of 800,000 linear feet of drilling associated with the larrge number of instruments and eductors installed during the dewatering program. Deep wells were nominally 9-inch diameter and installed with casement advancement systems. Both Barber drill rigs and conventional air rotary drill rigs with Odex systems were employed to advance steel casing into rock. Barber rigs have two tables and can advance a casing independent of the drill bit. This allows the bit to be inside of the casing

7 in soft material and in front of the casing in hard material. This is very advantageous. The boreholes were left open in most cases. In the few cases that sand was encountered during well development a 6-inch PVC casing was installed. Eductors were originally planned to be installed by wash rotary methods, but the drilling subcontractor proposed using Sonic drilling method to advance these boreholes. Sonic drilling uses sound waves to liquefy the material just in front of the drill bit and water to remove the cuttings. This drilling process results in a clean, straight borehole, that is superior to one made by wash rotary methods. Side-by-side tests proved that Sonic drilling resulted in a well that yielded more than wash rotary, or in a later test, a Barber rig. Sonic drilling was also four or more times faster than wash rotary methods. The Sonic drills could penetrate the rip-rap in a mater of minutes and advance a ten foot rod through the soft Dam soils in a few seconds. There were liquefaction concerns about Sonic drilling as well however when these drills were used for sampling, concerns about liquefaction was put to rest. Sonic technology can obtain a nearly undisturbed sample inside of the drill rods and it is unreasonable to expect liquefaction on the outside. Liquefaction associated with Sonic drilling occurs just in front of the drill bit. Well points were installed were access by truck mounted rigs was impossible. Such as, in an old creek bed on the north side of the Dam. The well points were jetted in from crane. This allow for the machinery to operate away from soft ground. While this makes for an effective well, it is very messy and can easily overwhelm drainage and erosion system downhill. Schedule with help of Scott Howard of the South Carolina Geologic Survey, For stability reasons, excavation for the Berm was planned in nominally 250-foot long cells. A number of these cells were considered critical with requirements for critical and non-critical cells with regard to how many could be open at one time. In practice the Contractor was able to open one southern cell and a northern cell at the same time. The initial schedule envisioned construction starting in the Center cells and substantially completing the RCC prior to start of the rockfill north and south cells. However, in August 2001, just as the wells for the Center cells were being completed, the selected contractor proposed the idea of starting in both of the northern and southern cells while doing preparatory work in the central cells. The resulting schedule change cut six-months from the project schedule and was well-received e the Owner and other interested parties.

8 Prior to this schedule change, dewatering was ahead of schedule and after it was not. The number of drill rigs was increased to 8 working at one time. Additional eductors and shallow wells were installed in the footprint of the cells to accelerate the dewatering of the soils. Water levels in the first cells excavated were below the bottom of the excavation a few weeks before excavation started, and the progress of dewatering exceeded that of excavation such that the rest of the cells were dewatered months in advance of their excavation. During this schedule change, the dewatering program received considerable focus from the owner, contractor and regulator. Outside experts were brought in to advise the engineer. Many suggestions were made. Some were adopted others rejected. One major change to the dewatering system was made to the eductor design after an initial operational test of two test eductor systems, which were installed on May 12, Originally, eductor wells were drilled by a Sonic rig advancing 8-inch sonic casing through riprap and overburden and stopping approximately five feet before reaching bedrock. Upon reaching total depth, a 2-inch PVC Schedule. 40 eductor pipe with a 5- foot screen was installed and a sand pack and bentonite seal was installed. Test Eductor System One was installed in alluvial materials and yielded approximately 75 GPM from 10 eductors. Test Eductor System Two was installed near the dam in fill and residual materials. The system yielded approximately 10 GPM from 10 eductors. Based on the advice of an outside expert, RIZZO directed Griffin to change the eductor well design installation so that a 3-inch well screen was installed in the borehole and a select filter gravel was placed in the annulus between the drill casing and the 3 well screen and a bentonite seal installed at least 10 ft. deep depending on depth of rip rap. Upon completion of well development the eductor unit consisted of 2 inch X 1 ¼ inch single pipe eductor was installed inside the 3 screen. Approximately 150 eductor wells were installed with this new design. The first eductor system included 10 wells with the original 2 design and the rest with the new 3 design. The system was put into operation on October 15, The 10-eductor wells that were installed with original design produced approximately 10 GPM. However, when the rest of the eductors were put into operation, the flow rate reduced to 1 GPM. RIZZO was immediately informed of the results. Obviously the new design was not working. RIZZO directed Griffin to go back to the original design. Griffin proposed a solution to fix the problem on the installed eductor wells by adding a packer between the 2 and 3 pipes. The eductor wells were removed from the 3 pipe and a packer was placed at each well before re-starting the system. An improvement was made resulting in increasing flow rate to 5 GPM.

9 In addition, Griffin was directed to install eductors located within the footprint of the Berm using a jetting method. This method was suspended after installation of 28 eductor wells because of excess jetting water flowing into adjacent excavation areas. Many other concerns needed to be addressed during the course of installing the dewatering system on the dam. At times, up to eight drill rigs and their support trucks were working on narrow long benches. Maneuvering rigs, trucks, forklifts, trucks, and other vehicles on the cut benches was difficult as precaution had to be taken that no piece of equipment was blocking another piece of equipment from getting on or off of a bench. In addition, discharge lines needed to service all pumping wells and eductor systems over the entire 1.5 mile long dam and discharge into the Saluda River just downstream of the dam without impeding construction or dewatering traffic. Power lines were a concern when drilling on the bench at the crest of the dam and often had to be shut down. Further complications included the reluctance of various Dam contractors wanting to be responsible for dewatering and related safety impacts on dam stability. All three of the short-listed large dam contractors expressed reservations about dewatering and were reluctant to assume the responsibility for schedule delays. Standby charges for the Dam Contractor could have caused major cost overruns. Such a unique design required flexibility to deal with variations in subsurface and often, drilling methods or pre-determined drilling depths were changed from boring location to boring location or even halfway through a boring. Factors in site conditions included subsurface geology (material types, fill versus residual soils properties, degree and continuity of fracturing and water within fractures), subsurface hydraulic conditions including permeabilities and thicknesses of different materials, groundwater occurrence, groundwater paths, groundwater elevation, and recharge conditions. A unit-price contract was very advantageous as well, as it allowed the flexibility to change the plan of with minimal additional costs. The operation and maintenance of the dewatering systems was conducted 24 hours a day, 7 days a week. The water levels and flow rate from each well and eductor system (a total of 19 each 500ft) was monitored on a daily basis and recorded. The primary electrical power was provided by the Owner. Standby generators were located at each power drop and were ready for operation if the primary power was lost.

10 Results With a few minor exceptions, we were able to excavate and construct the Berm under dry conditions. Exceptions occurred near both abutments where rock was shallow and the distance between the Lake and the excavation relatively short. Minor flow through near surface fractures was common and controlled by the contractor. As shown on table 2, 82 percent of the water was intercepted by the deep wells: Table 2 TOTAL WELL YEILDS The deep wells by design removed the artesian pressure Deep Wells 565,341,000 gal on the up-stream side and underneath the excavation Shallow Wells 2,668,000 gal. thereby removing the source of water from the soils. Eductors 73,631,000gal. After a few months of deep well pumping there was no Grand total 641,640,000 gal. water for the eductors in the center of the excavation to pump. The upstream eductors primary role was to intercept the small amount of water flowing through the Dam prior to it reaching the slope of the excavation. Shallow wells were installed where soils were too deep for eductors to work effectively. There is a strong east west foliation (perpendicular to the dam) along the schistosity of the rock. There apparently is a fairly good hydraulic connection to the reservoir along this foliation especially along the rock soil interface. All of the wells installed were designed to intercept this zone the eductors and shallow wells from above and the deep wells from below. Based on our knowledge of the geology and pumping results, the Dam was divided into six main sections with different properties that would react differently to dewatering. Although the initial plan called for a Deep Well every 100 feet and an eductor every 10 feet along the upstream side of the excavation, the actual locations and spacing varied depending on the schedule and nature of the subsurface. These six Zones are shown on the Figure 2 and described in the text that follows:

11 Figure 2 Excavation and Ground Water Zones Zone 1 is within the southern abutment of the dam and extends from the southern limit of the Dam to near the boundary between Cell S-3A and S-3B. There is a northwest trending diabase dike at the north boundary of Zone 1. This diabase dike is an effective hydrologic boundary between rock to the south and rock to the north. Within zone 1 the Dam is thin (the distance between the Lake the downstream side of the Dam is relatively short). There is a relatively thin soil above rock. Rock in this zone is gneiss of the Lake Murray Gneiss formation. This rock is very hard but also closely fractured in the near subsurface. The combination of fractures and a relatively short distance between the Lake and the toe drain results in a relatively high rate of flow through the rock and thin soil beneath the dam. Historically this flow emanated at Harmon Spring and other unnamed springs near the down-stream side of the southern part of the Dam. Drains and tunnel were installed at the toe of the Dam from Station northward. This area which includes Cells S1 through S3B was dewatered by six deep well all located in the northern half of the zone. Two deep wells were installed on the downstream edge of the excavation to lower water levels associated with Harmon Spring. No wells were required in the southern part of the zone where the bottom of the excavation was higher than the water level in the reservoir. Eductors were installed at 20- foot spacing for along most of the upstream side of the excavation and in the middle of the excavation near the location of Harmon Spring. There were a number of eductors in the center of the excavation that were drilled but never put into operation because the deep well system lowered water levels below the top of rock before the eductors could be put in operation. The deep wells produced an average of 4 to 2 GPM with a range of 12 to 1 GPM Zone 2 is bounded by the Diabase dike to the south and the contact with schistose rock to the north in Cell C-7/8. This northern contact also delineates the left bank of the historic Saluda River flood plain. It is evident that the Lake Murray Gneiss was more resistant to weathering than the schist to the north. Recent geologic mapping has uncovered several faults below the old riverbed. These faults may be due to unloading or reaction to a hereto-unknown stress field. Zone 2 is characterized by a much thicker layer of residual soil than Zone 1. Although both zones are underlain by Lake Murray Gneiss the residual soils in Zone 2 can be as much as 60 feet thick. Residual soil grades downward from clay to silt and silty-sand. The clayey top layer of this residual soil layer forms a very effective aquitard.

12 Below this aquitard and within the residual soil the soils were completely saturated prior to pumping. This area was dewatered by 24 Deep wells installed on 100 foot spacing with a small number inside and downstream of the excavation. One of the deep wells near the southern edge of the zone exhibited flowing artesian conditions. Eductors were installed at 20 foot spacing along the upstream edge of the excavation except where old valleys were shown on the 1927 topographic map. Ten-foot spacing was employed in these area were it was suspected that there might be higher flow through the dam in these area. Eductor were installed in the center of the excavation. A number of shallow wells were installed in the northern end of the zone to drain soils prior to excavation. The deep well wells in this zone made an average of 11 to 7 GPM over time with an instantaneous range of 28 to 1 GPM. Zone 3 extends from the schist/gneiss contact in Cell C-7/8 to midway in Cell C-5 and is characterized by thin to non-existent soils overlying well-fractured schistose rock. There is also a shallow southward dipping (N 40 W, 35 SW) Lamprophyre dike. This well fractured dike controls groundwater flow in Zone 3. There are many close spaced fractures (the likely result of cooling) within this rock which facilitate ground water flow. There is also alluvial sediments associated with the old Saluda River flood plain in this Zone. This zone was dewatered by eight deep wells most of which intercepted the Lamprophyre dike. These wells made an average of 36 to 22 GPM over time and with an instantaneous range of 70 to 3 GPM. Shallow wells were installed along the upstream edge of the excavation at 50-foot spacing. Shallow wells were used instead of eductors because the depth to rock was over 90 feet the maximum depth that an eductor can effectively work. Control boxes were installed on these shallow wells so that the pump would turn itself off when the well was evacuated and restart after a pre determined amount of time. Zone 4 is underlain area of quartz plagioclase mica schist (QMS) extending from the mafic dike northward to the granitic intrusive. Zone 4 is characterized by thin to non-existent soils overlying well-fractured schistose rock. This rock the same formation as in Zone 3, however the Lamprophyre dike is not intersect the dewatering system. This results in much lower yields. This zone was dewatered by ten deep wells which averaged 6 to 7 GPM over time and with a range of 30 to 0.5 GPM. Eductors at 10-foot spacing were installed at the upstream edge of the excavation. The eductors exhibited artesian conditions in the north half of the zone. Zone 5 is characterized by a granitic intrusive body which extends from cell C-1 to N-3. There is a relatively thick residual soil layer above the rock in this zone. There is a poorly developed east-west lineation within the granitic rock body. However, much of the flow through this rock occurs along subhorizontal exfoliation fractures. This zone was dewatered There is a strong east west foliation in all of these zones along the schistosity of the rock. There apparently is a fairly good hydraulic connection to the reservoir along this foliation especially along the rock soil interface. Zone 5 was dewatered by 12 deep wells which made an average over time of 15 GPM and an instantaneous range of 120 to 1 GPM. No eductors were required in this zone. Apparently, the flow through the exfoliation fracture was efficient enough to remove any water from the overlying residual soils. Zone 6 extends from N-3 to the northern limit of the Dam and is characterized by schist and has similarities to Zone 4 in that it is schistose and Zone 1 in that the excavation was relatively close to the reservoir. This area includes N3 through N1 and was dewatered by seven deep wells. Much like Zone 1 water flowed through fractures into the excavation during excavation and also like in Zone 1 the contractor was able to control this seepage with small submersible pumps. Two additional areas were also of interest from a dewatering perspective and they are: Zone 7 - An area of the excavation near the Saluda River. This zone was dewatered by 4 deep wells. Because of construction activity in this area eductors were not employed, but would have helped had there been room. During excavation a small amount of seepage was noted through the alluvium in this location.

13 Zone 8 a small area between the excavation and one of the existing ash this pond was used as part of the erosion and sedimentation system during the early phase of construction and could not be drained prior to excavation A row of eductors and two deep wells kept the excavation dry in this area. CONCLUSION There was not a simple one size fits all solution to dewatering at this site. Design and procedures had to be adjusted to fit the geology, geometry and schedule. Nevertheless, the excavation was at all time dry enough to work in. the overall construction schedule was never impacted. The selected contractual method for dewatering unit price allowed for multiple, rapid design changes with minimal cost impact. References: Dennis, Allen J., Sacks, Paul E. and Maher, Harmon D., 1987b, Nature of the Late Alleghanian Strike-Slip Deformation in the Eastern South Carolina Piedmont: The Irmo Shear Zone, in Secor, Donald T., (editor), Anatomy of the Alleghanian Orogeny as seen from the Piedmont of South Carolina and Georgia: Carolina Geological Society Field Trip Guidebook, pp Griffin Dewatering Corporation, 2001, Company web site, LeGrand, Harry E., 1988, Region 21 Piedmont and Blue Ridge, in: Back, W., Rosenshien, J.s., and Seaber, P.R., eds., Hydrogeology: Geol. Soc. Amer., The Geology of North America, Boulder Colorado. V-O2. Maher, Harmon D., 1987, D 3 Folding in the Eastern Piedmont Associated with Alleghanian Thrusting, in: Secor, Donald T., (editor), Anatomy of the Alleghanian Orogeny as seen from the Piedmont of South Carolina and Georgia: Carolina Geological Society Field Trip Guidebook, pp.1-18 Morse, Fredrick T., 1942, Power Plant Engineering and Design: Van Nostrand Company, New York, 703 p.

14 Sacks, Paul E., and Dennis, Allen J., 1987, The Modoc Zone D 2 (Early Alleghanian) in the Eastern Appalachian Piedmont, South Carolina and Georgia, in: Secor, Donald T., (editor), Anatomy of the Alleghanian Orogeny as seen from the Piedmont of South Carolina and Georgia: Carolina Geological Society Field Trip Guidebook, pp Secor, Donald T., 1987, Regional Overview, in: Secor, Donald T., (editor), Anatomy of the Alleghanian Orogeny as seen from the Piedmont of South Carolina and Georgia: Carolina Geological Society Field Trip Guidebook, pp.1-18 Secor, Donald T Geology of the Eastern Piedmont in Central South Carolina in: Secor, Donald T. (editor) Southeastern Geological Excursion, Geological Soc. Amer. Guidebook for Geological Excursions Held in Connection with the Meeting of the Southeastern Section of the Geological Society of America Columbia South Carolina April 4 to 10, 1988 Scholz, Christopher H., 1988, The Mechanics of Earthquakes and Faulting, Cambridge University Press, 439 p. Trainer, Frank. W., 1988, Hydrogeology of the Plutonic and Metamorphic Rocks, in: Back, W., Rosenshien, J.s., and Seaber, P.R., eds., Hydrogeology: Geol. Soc. Amer., The Geology of North America, Boulder Colorado. V-O2.