See press release, New hydrology report exposes Sabal Trail pipeline risk to Floridan Aquifer, and this report is also available in PDF.
Schreuder, Inc. Water-Resources & Environmental Consultants
Directional Horizontal Drilling (HDD) under the
At Suwannee River State Park
Hydrogeologic Issues of Concern
In any review of potential environmental consequences related to the use of Horizontal Directional Drilling (HDD), both the geotechnical and scientific communities can be expected to raise serious concerns when such drilling is done around karst areas, and in regions which over lie the Floridan Aquifer System (FAS), which includes the Upper Floridan Aquifer, and the karstic geologic subsurface features at the location proposed in Volume I of the Southeast Market Pipelines Project (herein referred to as the Proposed Project) Final Environmental Impact Statement (FEIS), Within this report, the text in Italics is taken from the FEIS report Any addition or changes by the Author are in non—italics script.
Proposed Project Description
The Proposed Project involves the installation of a 36-inch diameter pipeline from a point in Choctaw County, Alabama to a point in Martin County, Florida. The Proposed Project is to be implemented by Florida Southeast Connection, LLC, Transcontinental Gas Pipe Line Company, LLC and Sabal Trail Transmission, LLC (the Companies). This report focuses on one section of the overall proposed pipeline installation—the proposed sub-surface crossing of the proposed pipeline under the Suwannee River in north Florida at the Suwannee River State Park.
Proposed Project Location
The Proposed Project is located at the Suwannee River State Park in Suwannee County. Florida (Figure 1 (A) Proposed Project Site in Hamilton County and (B) Proposed Project Site in Suwannee County). A close-up view of the HDD crossing under the Suwannee River is provided in Figure 2 (FEIS Page E-11), which also shows the springs within a one-mile radius of the crossing. It should be noted that there are several errors in the number and location of the springs in FEIS Page E-11. This report will provide evidence that there are many more springs near the proposed crossing. This report will also provide evidence that the direction of ground water flow south of the HDD location is actually reversed from the direction shown in this FEIS Page E-11.
Site-Specific Issues of Concern
According to the text on FEIS Page 3-41, the Companies propose to place the pipeline in a subsurface pathway under the Suwannee River. To accomplish this, the Companies propose to use the HDD method to install pipelines at 29 locations. The Companies state that none of the HDD installations would occur within the carbonate bedrock of the FAS and there are no springs in proximity to the installations. Therefore, the Companies states that HDD operations would not impact springs, but could impact nearby wells.
These statements are clearly in error, because on FEIS Page 3-30 it states that five of the proposed HDD would encounter carbonate rock and be located in proximity to mapped springs, including the Suwannee River. There is a contradiction in the FEIS as it is written. Not only are there springs located in the Suwannee River State Park area, but significant fracture traces also have been identified along with nearby cave systems. We maintain that the HDD method will have significant and potentially highly damaging if not catastrophic impacts on the Upper Floridan Aquifer, on the ground water quality in the area, and on the unique and world-renowned Falmouth Cave Complex.
The HDD Method
According to the description in the FEIS (Page 2):
…the first step in an HDD is to drill a small diameter (8 inch) pilot hole from one side of the crossing to the other using a drill rig. At the Suwannee site the total borehole length will be approximately 4000 feet. As the pilot hole progresses, segments of drill pipe are inserted into the hole to extend the length of the drill The drill bit is steered and monitored throughout the process until the desired pilot hole had been completed. The pilot hole is then enlarged using several passes of successively larger reaming tools, Once reamed to a suflicient size, a prefabricated segment of pipe is attached to the drill string on the exit side of the hole and pulled back through the drill hole toward the drill rig. Depending on the substrate, drilling and pull back can last anywhere from a few days to a few weeks.
The HDD method utilizes a slurry referred to as drilling mud, which is composed of 95 percent water and bentanite, a naturally occurring clay mineral that can absorb up to 10 times its weight in water. Bentonite-based drilling mud is a non-toxic, non-hazardous material that is also used to construct potable water wells throughout the United States. The drilling mud is pumped under pressure through the inside of the drill pipe, and flows back (returns) to the drill entry point along the outside of the drill pipe. The purpose of the drilling mud is to lubricate the drill bit and convey the drill cuttings back to the drill entry point where the mud is reconditioned and re-used in a closed, circulating process. It also forms a cake on the rock surface of the borehole, which helps to keep the drill hole open and maintain circulation of the drilling mud system. Because the drilling mud is pressurized, it can be lost, resulting in an inadvertent release or ”frac-out,” if the drill path encounters fiactures or fixtures that offer a path of least resistance. or near the drill entry and exit points where the drill path has the least amount of ground cover.
The bentonite slurry is pumped through the drill stem at a rate of 750 gallons per minute (gpm) at a pressure of 1,500 pounds per square inch (psi). When the drill bit encounters a fracture, crack, or cavity. the mud flow from the drill bit will immediately follow the weak zone. If this is a filled in sinkhole it may lift up the sediment, causing it to come to the surface (free-out). If the drill bit encounters a cavity the mudflow will enter the cavity at the operational flow rate and pressure. This could have a potentially catastrophic effect on the karstic system, causing major extensive sinkhole collapses in the area.
The potential for this outcome was observed by Schreuder, Inc. in 1997 at the Heritage Pines housing development proposed by the US Home Corporation. The project site was in the northwest corner of Pasco County. A local well driller had just completed the installation of a 12-inch diameter irrigation supply well. He was “raw-hiding” the well to remove drilling sediment. The term “raw-hiding” refers to a technique whereby the driller lowers a pipe to the bottom of the well and injects a slug of air. This air will cause a sudden fast upward flow of groundwater in the borehole all the way to land surface. The drillers normally employ an air pump capable of delivering 1500 cubic feet of air per minute at pressures ranging from 100 to 200 psi. After the first several “slugs” the driller observed that the ground around the well casing began to collapse. He immediately stopped his work, gathered his tools, and moved off site. The collapse of the soil around the well casing as a result of his “raw-hiding” the well was the beginning of a massive sinkhole collapse. Eventually a total of more than 670 sinkholes formed. some as large as one-half acre. The geotechnical engineer estimated that up to 2 million cubic yards of soil had collapsed into the karstic subsurface. The sudden discharge of a flow of mud at a rate of 750 gpm and a pressure of 1,500 psi is similar to the “raw-hiding” effect of the well development at the Heritage Pines site. This potential consequence of the HDD must be considered as a major threat to the karst environment at the Suwannee River State Park and surrounding areas.
Anticipated Impacts from the HDD at Suwannee River State Park Site
The anticipated impacts of HDD, many of which are not addressed in the FEIS, are described in the following sections.
Size of the Borehole and Volume of Material to be Removed
The length of the proposed HDD is considerable (Figure 3), and the borehole and the volume of material to be removed are substantial. The final diameter of the borehole which will be drilled in the limestone of the Upper Floridan Aquifer is not mentioned in the FEIS. To accommodate a 36-inch external diameter steel pipe the final borehole diameter may be 40 inches or larger in diameter. In this paper the final diameter is estimated to be 40 inches. This is a very large hole The outside diameter of the steel gas line pipe will be 36 inches. After the installation is complete, there will be a 4 inch annular space between the gas pipeline and the rock wall. This annular space will create a very significant hydraulic pathway through which groundwater will flow from a higher potentiometric surface to a lower one. This connection will significantly change the potentiometric surface in the Upper Floridan Aquifer. In the FEIS no consideration has been given to the impacts that this new man-made hydraulic connection will have on the interface between the regional groundwater flows, the spring systems, and the surface water flows. The volume of lime-rock which will be removed to accommodate the installation of the gas pipeline under the Suwannee River is very large. Assuming a final borehole diameter of 40 inches and a borehole length of 4,000 feet, a total of 34,900 cubic feet (1293 cubic yards) of lime-rock will be drilled out. This is equivalent to a total of 72 trucks each carrying 18 cubic yards of rock material. This calculation does not include the bentonite clay residual in this rock volume, which could well be another 8 or more truck loads of material. The volume of the resulting cavity might create instability in the overlying surface. This issue is not addressed within the FEIS.
Subsurface Hydraulic and Water Quality Impacts
The diameter of the interior of the borehole will be 40 inches. Assuming that the annular space between the outside of the gas pipeline and the rock wall is a net four inches, the open area is 1.66 flz. Assuming a groundwater flow velocity ranging from 1 ft/sec to 6 fl/sec. the groundwater flow through the annular space can range from 1.07 million gallons per day (mgd) to 6.44 mgd.
The FEIS does not assess the impacts of the proposed action on the groundwater environment at the Suwannee River State Park Site. The cover of bentonite clay on the rock wall of the borehole will gradually be eroded by groundwater flow and thus will provide a large source of finely suspended solids which will cause turbidity in the groundwater for a very long time. The FEIS does not address the occurrence of this contamination and the impacts that it will have on the long-term water quality in the springs, caves and the river itself. In paragraphs 3 on FEIS page 3-41 and in paragraph 1 on FEIS page E-5 there is an implication that the bentonite and other additives are: “also used in other rotary drilling applications such as water well drilling and completion”. In Florida, water wells installed in the FAS are drilled using the reverse air circulation method. Bentonite mud is rarely used to install a potable water supply well in the FAS in Florida because the use of mud during the drilling of a potable water supply well impacts the recently completed well with suspended solids. preventing the groundwater samples from that well to meet the turbidity standard (2.00 NTU), postponing the use of the well for a undetermined period of time as a water supply well. The HDD borehole can and should be considered a 3,500 feet horizontal well in the FAS. The mud cake will contaminate the groundwater for a very long indeterminate period of time. The evidence of this long-term aquifer contamination most likely will not be observed in the downstream springs for some time after the completion and installation of the HDD installed pipeline. The FEIS does not include any consideration of this matter or address this major long-term threat to the regional quality of the groundwater and in particular to the quality of the groundwater flowing through the nearby caves. This omission in the overall Proposed Project assessment is a serious failure of the Companies to objectively assess the potential environmental impacts of their proposed actions.
Structural Geologic Concerns
At the proposed river crossing location, three fracture trace alignments are shown in FEIS Figure 3.3.1-3 (Sabal Trail Project, Horizontal Directional Drill Crossing at the Suwannee River Hamilton and Suwannee Counties, Florida) on Page 3-35. A copy of this referenced exhibit is included in this report as Figure 4. Two of these alignments are in the same location and direction as the river alignment at the location where the HDD project is proposed. Fractures in the limestone and dolomite formation composing the FAS are a result of past geologic events (Ocala Uplift). Most fractures are trending northeast and northwest and often intercept one another. Examples are evident in the Proposed Project area. Fractures in limestone may or may not add a significant additional hydraulic conductivity to the FAS. If these fractures at the HDD Proposed Project site have high hydraulic conductivity, they may cause a significant obstacle to the HDD process. The Companies failed to conduct a range of geophysical investigations to determine the exact location of these fractures and they did not conduct an exploratory drilling program to determine the potential hydraulic conductivity of these two fractures at the proposed HDD Proposed Project site.
Regional Impacts on Springs and Caves
There are 269 springs and caves in the US. (Table 1). Of this total, 258 caves and springs occur in Florida. The majority are in the northern and western parts of the state (Figure 5). The large number of caves and springs is the result of the geologic history of the State related to depositional and geological processes which created a very large and extensive karst environment. The large number of caves and springs are also an indication of the hydraulic connectivity between the surface-water and groundwater systems. A recent tracer study illustrates the horizontal connectivity through the FAS between the various cave and spring systems (Figure 6). The locations of the caves and springs mentioned in this study are shown in Figure 7. It is important to note that the potential for the development of caves and springs is directly related to the location where fractures interact. There are two fracture traces trending southwest to northeast along the Suwannee River (Figure 4). There is another fracture trending southeast to northwest along the Withlacoochee River. At the interpolated intersection of these traces, several caves and spring are found, notably Lime Spring, Edwards Spring and Suwanacoochee Cave.
The Falmouth Spring and Cave System is world renowned. Many divers have contributed to the mapping of this extensive cave system. The mapped extent of the cave system is shown in Figure 8. The northern most leg of this system extends 9,000 feet (1.7 miles) from the southeast to the northwest. The southern leg is 11,265 feet long. The numbers along each leg of this system indicate the depth of water in the cave system measured during exploration, Both legs trend towards the Suwannee River. The Falmouth Cave system is shown to extend to Lime Spring (Figure 5), which is directly south of the HDD Proposed Project site and may be hydraulically connected to the southwest-northeast fracture to the north of the Suwannee River. Any mud intrusion in this fracture could move towards Lime Spring and possibly into the Falmouth Cave System.
In Figure 9 the Cathedral-Falmouth System is presented to illustrate the negative numbers along both legs of the cave system, which indicate the approximate depth in feet NGVD. This is by necessity an approximation. The number was calculated by subtracting the depth of water (Figure 7) from the average level of the potentiometric surface of the FAS (Figure 10). The purpose of this analysis was to determine if the operational depth on the HDD traverse below the Suwannee River was within the depth interval of the Falmouth Cave system. The depth of the HDD borehole will be -40 ft NGVD (Figure 3). The bottom of the Falmouth Cave system ranges from -135 ft NGVD to -91 ft NGVD. No information was available to determine the elevation of the ceiling of the Falmouth Cave system, but the occurrence of sinkholes in the area may indicate that the ceiling elevations can vary greatly from close to land surface to an elevation of the recorded bottom of the Falmouth Cave System.
The research presented herein indicates that there is the potential for a major impact to occur to the karst system during the execution of the proposed HDD Proposed Project under the Suwannee River at the Suwannee River State Park site. A sudden release of the mud flow at 1,500 psi may cause a collapse in the FAS. If that happens there will be a potentially massive occurrence of numerous sinkholes resulting in a catastrophic collapse of overburden materials into the underlying caves and springs along the river. Unless the applicant is required to conduct a thorough and detailed geophysical investigation along the proposed borehole alignment, and all other environmental and cultural concerns associated with the entire length of the proposed pipeline are adequately addressed, this Proposed Project should not be allowed to proceed as designed.
June 23 2016
Peter J. Schreuder
Florida PG 1043,
AIPG CPG 8373
Figure 2: Close-Up View of the Location of the Proposed HDD Crossing of the Suwannee River (FEIS Page E-11)
Figure 4: FEIS Page E-35, HDD Crossing at the Suwannee River, Hamilton and Suwanee Counties, Florida
Figure 9 Elevations of the Bottom (Floor) of the Cathedral-Falmouth Cave System in Feet NGVD (Sheck Exley + Peter Schreuder)
Table 1: Inventory of Caves and Spring in the USA http://caveatlas.com/cave_systems.asp (4 pages in report)
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