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Final Well Installation Report

Section 2 - Well Installation Methodology

2.1 - Scope

Under TO42, a total of 17 groundwater MWs were drilled and installed, and five existing wells were modified from their original construction. The following wells were installed (or upgraded) in each of the LGR, BS, and CC:

Table 2.1 - List of Wells Installed or Upgraded Under TO42

One well, CS-WB04, was constructed to monitor all of the above-mentioned formations. The four Westbay^� Multi-port Sampling System (WB) wells also monitor the base of the Upper Glen Rose (UGR). Data were also gathered from supplementary work performed at three off-post private wells: JW-32, LS-7, and RFR-10.

2.2 - Determination of Well Locations

The primary objective of the selection of TO42 well locations was to obtain more data points to better delineate and monitor, both vertically and horizontally, two solvent plumes within CSSA. One plume (Plume 1) is believed to originate in the areas of solid waste management units (SWMU) O-1 and B-3 affecting supply well CS 16, and another plume (Plume 2) has been associated with area of concern (AOC) 65 in the southwestern portion of the facility. Specific drilling locations were determined with significant involvement from the CSSA Environmental Office, and subsequent review by AFCEE and the EPA. After project data quality objectives (DQOs) were formulated, and in preparation for the new well installations, Parsons geologists conducted site surveys of potential well sites between November 14 and December 13, 2001. Findings, conclusions, and recommendations of the survey were submitted to CSSA in the TO42 Site Survey Report, May 2002. The DQOs were revised before commencement of fieldwork later in 2002. Several wells were removed while others were added to the program. It was decided early on in the process to construct four wells as WB sampling systems. These wells were located with consideration of the effects that faulting and fault blocks might have on the movement of Plume 2 through the southwest portion of CSSA. Additional well upgrades were also included at that time, but these did not affect siting of new wells. The changes that affected well installation work are described in TO42 Modification 01, July 2002.

Table 2.2 is a list of the wells eventually installed and the rationale for their placement. Well locations are illustrated in Figure 2.1.

Table 2.2 - New Well Locations and Rationale for Their Location

2.3 - Work Plan Development

2.3.1   Original TO42 Statement of Work (September 2001)

Construction of the wells at CSSA under TO42 was per AFCEE�s Model Field Sampling Plan (MFSP) version 1.1 criteria and the TO42 Sampling and Analysis Plan (SAP) Addendum. As planning and work progressed, some conditions changed and occasionally new information became available, warranting changes to the work plan. Three modifications to the TO42 Work Plan were approved to reflect these changes. Changes not relative to the TO42 well installation subtask are not discussed here.

In general, under the initial Statement of Work (SOW), a total of 24 new MWs were to be installed. Half of these wells were to be arranged in shallow clusters around Building 90 and off-post locations. Major upgrades were planned for two existing on-post wells to bring the wells into conformity with current CSSA well construction requirements. Minor upgrades for two CSSA supply wells were also scheduled. Construction of a settling basin was planned to hold drilling fluids and cuttings awaiting sampling and disposal. A draft version of the SAP was issued in January 2002. A revision to the project DQOs between the draft and final issues of the SAP prompted a change in the SOW, discussed in Section 2.3.2.

2.3.2   TO42 Modification 01, July 2002

Numerous changes to TO42 project work followed reformulation of DQOs prior to the onset of fieldwork. The scope of work and well completion methods were extensively revised, and as a result, many new well sites were relocated. The total number of new wells to be installed was reduced to 17, and total well upgrades were increased to eight. Eliminated from the program were CS-MW3-CC, CS-MW4-CC, CS-MW5-BS, and CS‑MW5-CC. These wells were to complement existing LGR MWs. It followed that total logging, sampling, and low-flow pump emplacements would be reduced accordingly. Changes in well completions included dropping the protective surface casing requirement except for four wells sited in areas of known groundwater contamination. All subsurface soil/rock sampling and injection packer testing was deleted from the program. The 12 shallow cluster wells at AOC-65 were replaced by four WB wells located around Building 90 and select off-post locations.

Regulatory approval of the use of a settling basin was hindered with permitting issues. As a result, preparations were made for the use of semi-mobile rolloff containers for drilling fluid containment. Permanent benchmarks were to be installed to facilitate surveying of on-post features and infrastructure.

These changes to the work plan document were described in the revised Data Quality Objectives, Groundwater Contamination Investigation, (April 22, 2002) and in the TO42 Sampling and Analysis Plan Addendum, May 2002.

2.3.3   TO42 Modification 02, September 2002

Modification 02 did not impact TO42 well installation fieldwork.

2.3.4   TO42 Modification 03, February 2003

In October and November 2002, during drilling of CS-MW1-BS and CS-MW1-CC, groundwater from the BS interval was found to contain VOCs. The detections necessitated triple-casing methodology for wells that would be screened in the underlying CC. Triple-casing was used to prevent contamination migration between the formations.

2.3.5   Work Plan Deviations

Some activities deviated from the Work Plan as drilling progressed. Most notable deviations were replacement of locations MW15-LGR and MW15-CC with CS‑MW11B‑LGR. One WB well was drilled to a depth, which penetrated the CC. Other activities incorporated into the project resulted in utilization of FLUTe^� borehole liners, Hydrophysical^� Logging (HpL) surveys, and optical televiewer services. Locations of the WB wells were refined in late summer 2003 after further review of AOC‑65 geophysical survey results. One WB well was located off-post near RFR‑10 and would be completed through the CC, and three LGR WB wells were sited in the AOC‑65 vicinity. Well CS‑MW11B‑LGR was added as a result of observations and data obtained during the drilling of MW11A-LGR. Inner casing requirements for MW16-CC were altered to allow for a wider inner diameter to accommodate a higher capacity pump. Three wells, CS-MW2-LGR, MW12-CC, and MW18-LGR, required additional hours for redevelopment due to elevated pH of the formation water within the screened interval. A second video log was made of completed MW18-LGR to inspect casing and screen integrity.

2.4 - Monitoring Well Construction

Well construction design followed specifications used for previous RL83 MW installation work at CSSA. MW construction materials included low-carbon steel outer casings, 4-inch diameter Schedule 80 polyvinyl chloride (PVC) risers, 25 feet of 4‑inch diameter stainless steel well screen, clean sand, bentonite, and cement-bentonite grout. Inner casing utilized at CS-MW16-CC was Certa-Lok^� Schedule 40 PVC. The WB wells had 1.5‑inch PVC casing with multiple purge and 0.125-inch button valve sampling ports in packer-isolated zones. Surface completions were basically the same for all MWs, and included a 4‑foot square concrete pad around a steel well protector placed over the well. Bollards extending three feet above ground surface were placed at each outside corner of each well pad.

Conventional MW installation under TO42 generally proceeded the same as during the previous RL83 program. A safety and quality assurance/quality control (QA/QC) exclusion zone was set up around the drill rig and area of drilling. A containment area immediately surrounding the wellhead and the drilling table of the rig was erected using sturdy boards and heavy plastic liner. The size of the exclusion zone depended on the well location and the anticipated volume of water that might be produced. Wells at each drilling location were cored and reamed using air rotary methods in accordance with the SAP. The drilling subcontractor, GeoProjects International (GPI), implemented �air-mist� drilling techniques to help reduce volatile emissions from the borehole and suppress dust produced by drilling. Water for injection during drilling was obtained from well CS-9, which provided a non-chlorinated on-site source. Routine quarterly groundwater sampling at CS-9 monitors the quality of the injection water.

Continuous core samples were collected by a split-barrel sampler advanced into the subsurface at 10‑foot increments. The corehole outside diameter was either 4.0 or 4.25 inches, depending on the bit used. Visual observations of the core were logged, and included color, hardness, texture, and other lithologic features. Cores were screened by photoionization detector (PID) to monitor for the presence of VOCs. The core was marked with red and black wax pencil so the black score runs from top to bottom on the left side of the core. The core was then boxed and digitally photographed. All core was retained for future reference and potential archival at the University of Texas-San Antonio (UTSA). A data CD is included in Appendix A with photographic documentation of the core and fieldwork.

A �TOTCO� single shot declination tool was used to check borehole plumbness every 50 feet of advancement during reaming of the wells. As per the Work Plan, the borehole declination was not to deviate more than 2 degrees from true vertical as per AFCEE specifications. An exception to the 1 degree plumbness specification in the AFCEE MFSP was granted in November 1999 during the RL83 well installations. Results of the declination surveys are included in Appendix A.

Geo Cam, Inc., of San Antonio, Texas geophysically logged each new corehole. After logging, the wells were subjected to discrete interval groundwater (DIGW) sampling at selected zones. Sampling was followed by reaming (widening the diameter of the hole) using a 7‑⁷/₈-inch diameter tri-cone drill bit (often referred to as an 8‑inch drilled borehole). At some wells the LGR section was reamed a second time, to a 16‑³/₈-inch diameter to allow for triple-casing. The geophysical logging and DIGW sampling procedures are described in further detail in Sections 2.8 and 2.9, respectively. Parsons geologists carefully reviewed the logs, then selected a final reaming depth. Frequently a corehole was partially backplugged with bentonite as the final constructed depth selected for a well was above the total cored depth. After reaming and thorough cleaning by forced air-lifting, a 25‑foot, Schedule 304 stainless steel, continuous-wrap screen was installed at an interval determined by geophysical logging and DIGW sampling results. The diameter of each well screen is 4 inches and wire-wound slot size is 0.050 inch.

Using decontaminated 1.5-inch tremie pipe and approximately 1 to 2 gallons per minute (gpm) of clean water, sand was washed down to settle in the annulus between the well screen and the rock formation, to a depth 2 feet above the top of the screen. Dehydrated bentonite chips were then added to create a 5‑foot thick plug above the sand. These uncoated pellets (coated chips have been associated with acetone detections in groundwater) were added slowly to prevent bridging in the upper portions of the well. The bentonite pellets were then allowed to hydrate for a minimum of 4 hours before proceeding with grouting in the remaining annular space above. The annular space was pressure-grouted in separate lifts, from bottom to surface using a thick but pumpable slurry of water and Portland cement mixed with 3 to 5 percent bentonite powder, to a density of 14.5 pounds per gallon.

All investigation-generated water, soils, and cuttings were sampled and analyzed. Water produced from known contaminated zones, and any other water containing tetrachloroethene (PCE) or trichloroethene (TCE) was treated at the on-post granular activated carbon (GAC) system and released at Texas Pollutant Discharge Elimination System (TPDES) permitted Outfall 002. Concentrations of VOCs in all other fluid and solid media were either not detected or less than Texas Risk Reduction Program (TRRP) Tier 1 Residential Primary Contaminant Levels (PCLs), and the media was discharged on-post as per the EPA and Texas Commission on Environmental Quality (TCEQ)-approved CSSA RCRA Facility Investigation and Interim Measures Waste Management Plan.

2.5 - Westbay Well Construction

To better profile the upper portions of the LGR and the basal layers of the UGR in the AOC‑65 area, three WB multi-port well systems were constructed. These wells were completed 312 to 314 feet below ground surface (bgs) without penetrating the major water-bearing zone at the base of the LGR. One WB well was constructed off-post and downgradient from the AOC‑65 area to monitor the entire Middle Trinity horizon (511 feet bgs).

2.5.1   WB Borehole Construction

The start of the WB installation process was the same as that of the conventional MWs. An exclusion zone was set up around the area of coring and the drill rig. Containment around the wellhead was erected using boards and plastic liner. Wells at each drilling location were cored by GPI using air rotary methods in accordance with the SAP. Continuous core samples were collected by a split-barrel sampler advanced into the subsurface at 10-foot increments. Corehole diameters are 4.25 inches, except the bottom portion of WB‑04 where a 4‑inch bit was employed. The drilling subcontractor used no foaming agents or other drilling additives, only clean, non-chlorinated, raw water from well CS-9.

Visual observations of the core were logged including color (using a Munsell^� comparison chart), hardness, texture, and other lithologic features. Cores were screened by PID to monitor for the presence of VOCs. The core was marked with red and black wax pencil so the black score runs from top to bottom on the left side of the core. The core was then boxed and photographed. A data CD is included in Appendix A with photographic documentation of the core and fieldwork. The coreholes were geophysically logged and had video surveys completed by Geo Cam. Parsons and GPI then performed standard DIGW sampling at selected zones utilizing GPI�s dual packer apparatus. The wells were developed and the discharge transported to the on-post GAC system for treatment. Following development, each corehole was temporarily sealed by flexible FLUTe liner technology pending HpL by COLOG. After COLOG, the wells were resealed with FLUTe liners until emplacement of WB systems.

2.5.2   Interim Sealing of WB Boreholes

A lapse of several weeks occurred between significant operations at the four WB wells after coring. The holes were left open between coring, HpL, and then final completion. To prevent contaminant communication between separate hydrologic zones in the coreholes, flexible FLUTe liners were installed. The liners were installed prior to scheduled inactivity in WB operations, then later removed the day before activities resumed at a well.

CSSA and Parsons selected FLUTe technology after cooperative research and consideration. Four liners were purchased by CSSA and manufactured by FLUTe according to specifications provided by CSSA in collaboration with Parsons. The products consisted of one 540‑foot liner for WB-04, and three 335‑foot liners for WB-01, -02, and -03, and are made of urethane-coated nylon fabric in tubular form. Ancillary installation and removal equipment was rented from FLUTe.

Liners were delivered on large reels in an inverted (inside-out) state. Liner tops were clamped onto a metal head, which in turn was clamped to the rim of short, temporary surface casings. The liners were filled with clean water causing them to descend into a hole. The liners everted (unrolled) into the holes under the weight of the added water. Clean water inside the liners acted as pressurizing fluid. The material became pressed against the well walls, closing-off transmissive and permeable zones. Each liner�s descent rate was dependent upon the rate groundwater was forced back into the formation (permeability) ahead of the descending liner. A wellhead roller stationed at the well guided the liner off its storage reel and into the well. Once installed, the flexible liners sealed the coreholes against vertical flow of subsurface contaminants. The head of clean water within the liner was maintained above the head of groundwater to maintain positive pressure of the liner against the borehole wall. Shallow piezometers and other neighboring wells were monitored on a weekly basis to ensure the liner did not go slack due to possible groundwater fluctuations. Clean water was added to the liner as needed to ensure the positive pressure.

Each liner came with a tether attached to its inside bottom. The tether extended from the inside bottom of an installed liner up to the ground surface, and was used to pull the liner out. The process of liner removal was generally the opposite of installation. The cord was pulled upward and the liner was peeled off the well walls from the bottom up. Clean water was periodically pumped out of the inside of the liner as it was pulled upward. The liner exited the wellhead inverted (inside-out) and was flattened out as it was re-wound onto its reel.

2.5.3   WB Well Installation

All lithologic, geophysical, and video logs were carefully reviewed before final well specifications were given to Westbay personnel. Special consideration regarding possible faults, fractures, and joints, water-bearing zones, karstic, and other geologic features was given toward selection of WB monitoring intervals. Final designs were a result of consultation between Parsons geologists, CSSA, and Westbay personnel.

The WB apparatus was assembled by sections at CSSA according to Parsons� final specifications. The plastic-wrapped sections were transported to the corresponding corehole. There, the sections were assembled by spline lock without screws or glue. Trained Westbay personnel carried out the installation of each WB system. GPI provided a winch truck and operators to assist with lowering the WB apparatus into the coreholes several sections at a time. Once the PVC pipe reached the water level in the corehole, clean water was added to the casing interior to counter buoyancy. There was no communication between the inside contents of the casing and the formation waters that filled each separate annular space. Installation of the WB apparatus involved no reaming, outer casing, and grouting as in conventional CSSA MWs.

The packers were inflated after an entire WB string was assembled and inserted. Packers included on designated depths of the PVC were inflated with clean water and effectively isolated the selected sampling intervals. Then Westbay personnel used a MOSDAX^� pressure probe to profile each newly installed well. Pressures were checked in each interval. Based on the readings obtained, Westbay was able to assure that each zone was isolated and that the packers had sealed properly. Parsons supervised and documented the installations. Detailed construction specifications of each WB well are itemized in the Completion Report, MP38 Monitoring Wells: WB01, WB02, WB03, and WB04 prepared by Westbay Instruments, Inc., in Appendix A.

2.6 - Surface Completions

MWs were completed above ground level. Conventional MW risers extend approximately 2.5 feet above ground surface, and 1.5 feet at the WB wells. The WB risers are completed shorter to accommodate the tripod and equipment assembled over the wellhead during sampling. A 6‑inch-square lockable well protector was installed over each monitoring wellhead. These housings consist of a 5-foot length of square tubing set 2 feet into concrete, leaving a remaining stick-up of 3 feet. The top portion of the square tubing is sealed, hinged, and provided with a lockable hasp.

A concrete pad, 4 feet square and 6 inches thick, was constructed around each well. A 2‑inch-diameter brass monument permanently stamped with the MW identification was set into the concrete pad. Prior to setting, the concrete pad was swept with a broom to create a non-slip surface. Protective bollards, consisting of 4-inch-diameter carbon steel in 5‑foot lengths, were installed at the corners of each well pad to provide protection to the aboveground portion of the well. The bollards were set in cement 2 feet below grade, leaving 3 feet above grade. The steel well protector was painted white and the bollards were painted in traffic safety yellow.

2.7 - Lithologic Core Logs

During the drilling of MWs, the core was brought up from depth and the lithology was noted in standard log format. The core descriptions were grouped into intervals of similar lithology. Dunham�s Carbonate-Rock Classification System (1962) was used to classify the mostly mudstone, limestone, and dolomite lithologies encountered in the subsurface. A Munsell color comparison chart was employed to consistently express the color and hue of the retrieved core. The core was described with respect to porosity, faults, fractures, fossils, texture, hardness, and recovery ratios. These characteristics aid lithologic and hydraulic correlation between wells.

A PID was used to monitor the core for VOCs at the time of retrieval. The lithologic and well construction logs for each well can be found in Appendix A.

2.8 - Geophysical and Hydrophysical Logging

2.8.1   Geo Cam

Standard geophysical logging of TO42 coreholes and wells was performed by Geo Cam, a subcontractor of GPI. There was no difference in Geo Cam�s logging procedures between RL83 and TO42. Geo Cam logging parameters consisted of spontaneous potential (SP), gamma ray, caliper, and electrical resistivity. Copies of geophysical logging sheets are located in Appendix B.

2.8.2   COLOG

Another Parsons subcontractor, COLOG, applied its proprietary HpL and Borehole Imaging Processing System^� (BIPS) as well as heat-pulse flowmeters (HPFs) to characterize subsurface hydraulic characteristics at four coreholes within the AOC-65 plume. In contrast to Geo Cam parameters, this type of logging had not previously been employed at CSSA. Characterization was achieved by:

HpL and HPF were performed under both non‑stressed, or ambient conditions, and stressed, or pumping conditions, to fully evaluate the water-bearing horizons intersecting the well. Tools, methods, computer programming, and calculations are explained in greater detail in the COLOG Hydrophysical and Geophysical Logging Results Report, in Appendix C.

2.8.2.1   Hydrophysical Logging

HpL was conducted in two runs, which included an ambient groundwater profile, and pumping (stressed method) while injecting deionized (DI) water. During this process, FEC changes in the fluid column were recorded. These changes occurred when electrically contrasted formation water was drawn back into the corehole by pumping, or by naturally occurring subsurface pressures (for ambient flow characterization). A downhole wireline HpL tool, which simultaneously measures FEC and temperature, was employed to log the physical and chemical changes of the emplaced fluid.

Additionally, prior to emplacement of DI water, ambient FEC and temperature (FEC/T) logs were acquired to assess the ambient fluid conditions within the corehole. During these runs, no pumping or DI emplacement was performed, and precautions were taken to preserve the existing ambient hydrogeological and geochemical regime. These ambient water quality logs were performed to provide baseline values for the undisturbed subsurface groundwater conditions prior to testing. Computer programs utilized the data generated for identification and evaluation of the hydraulically conductive intervals and quantification of the interval-specific flow rates.

2.8.2.2   Optical Televiewer

The optical televiewer, or BIPS, was based on direct optical observation of the borehole wall face. Precise measurements of dip and direction of bedding and joint planes, along with other geological features, were possible in both air and clear fluid-filled boreholes.

The BIPS tool directly imaged the borehole wall face. As the instrument was lowered, the raw analog video signal from the camera was transmitted uphole via coaxial wireline to televiewer surface instrumentation, where the analog signal was digitized and recorded. Features were picked by COLOG throughout each well by visual inspection of the digital images and analyzed by computer. Orientations were based on magnetic north and were corrected for declination.

2.8.2.3   Heat-Pulse Flowmeter

The HPF-4293 is a high-resolution device for measuring vertical fluid movement within a borehole. Corehole fluid was heated and thermally tagged with an electrical heater grid. Flow rate was determined by measuring the time between the grid discharge and the peak when the thermal pulse of water reached a thermistor sensor. The HPF can measure flow from 0.01 to 1.5 gpm. The HPF was run at discrete intervals within a borehole selected after review of previously run logs (temperature, gamma, resistivity, HpL, caliper, acoustic televiewer, etc.).

2.9 - Discrete Interval Groundwater Sampling

Discrete intervals were selected for collection of screening samples because of their potential hydraulic characteristics based on interpretation of the geologic and geophysical logs. The general strategy was to gather groundwater data from permeable zones throughout the local portion of the Middle Trinity Aquifer. Yield of these zones is dependent upon many factors such as porosity, permeability, and transmissivity. Other major factors affecting sample collection are seasonal affects on groundwater levels. Some zones that could be easily sampled during wet seasons may be dry during the late summer and fall months. Analytical and general flow data provide information relevant to plume delineation and potential migration pathways for groundwater contamination.

The parameter list, assembled and refined during previous well installation projects, comprises acetone, cis-1,2-dichloroethene (cis-1,2-DCE), trans‑1,2‑dichloroethene (trans‑1,2‑DCE), isopropanol (IPA), methyl ethyl ketone (MEK), PCE, TCE, and toluene. All samples were analyzed by DHL Analytical, in Round Rock, Texas. Though acetone and toluene are under consideration as possibly resulting from the drilling and sampling processes, they have not been ruled out as actual groundwater contaminants. These two contaminants appear sporadically throughout the sample results. There is no known history of extensive acetone use at CSSA. Toluene would most likely have been a fractional constituent of another substance; however, constituents commonly associated with toluene, such as benzene, ethyl benzene, and xylenes, have not been identified in the sampled areas.

Each interval was normally purged of at least three volumes of water, or until the water was clear. Occasionally time constraints, low-flow zones, and persistent turbidity problems caused some samples to be collected before normal purging quantity and quality standards could be completely satisfied. In some instances, purging was carried out over an extended period of time for critically located intervals exhibiting poor yield. In these cases a sample was collected after alternating periods of pumping and recovery. Some zones exhibiting good flow had to be purged of larger volumes to reduce turbidity prior to sampling. Most of the intervals selected for WB DIGW samples in the LGR correspond stratigraphically from well to well. This allows for direct observation of changes in contaminant concentrations in specific zones and layers at various distances from the source area. The differences in depths are due to surface elevation variations and geologic displacement.

Unless stated otherwise, DIGW samples were collected in 4.25-inch diameter coreholes utilizing a dual packer apparatus with an open interval of 12 feet. Packers were inflated by compressed nitrogen gas. A 1.5 horsepower (Hp) pump was affixed between the packers on the end of a 1‑inch diameter pipe string (5‑to 21‑foot sections). Pipe lengths were selected to achieve the specific depths requested by Parsons. A large packer assembly with an interval of 64 feet was utilized in RFR‑10. The packer systems were assembled, maintained, and operated by GPI in the same manner as during earlier RL83 work. Parsons field personnel collected the samples and supervised the efforts.

2.10 - Monitoring Well Development

MW development was performed by air-lifting, bailing, and pumping. Each well was surged using the drill rig immediately after reaming to the final drilling depth. Bailing was accomplished by winch truck after the drill rig had mobilized to the next well location. Pumping usually took place after the majority of work around the well was finished.

2.10.1   Air-Lifting

Air-lifting was performed after a well had been reamed to its final depth, but before casing emplacement. At this point, the bottom portion of a well was still an uncased borehole. Compressed air was injected downhole via the drill pipe string to within 20 feet of the total depth of the well. This process flushed out drilling foam remnants and the majority of loose, heavy sediments produced during final stages of reaming. At selected intervals, the driller jetted the well by releasing bursts of air pressure in the saturated column, causing the sediments to become suspended and airlifted to the surface where they were expelled and collected in the rig containment pit. This process was also used to clean out well holes before each stage of casing installation in the double-and triple-cased wells.

2.10.2   Bailing

New wells were bailed following a minimum of 48 hours after grouting, and prior to any pumping. The bailing apparatus used was a 6‑foot steel dart-valve with a 3-gallon capacity bailer. Drilling subcontractor personnel operated the bailing apparatus. A pump installation truck (Smeal^�) was backed over each well and the bailer was lowered and raised by a motorized cable reel. The bailer was first gently lowered to the bottom of the constructed well, and then raised several feet. The cable was marked at that point so the operator would have an indication as to when the bailer approached the bottom of the screen. This allowed rapid descent of the bailer in the well while preventing the heavy bailer from striking the screen bottom. In general, the bailer was lowered down into the well screen and then quickly raised to surge the screened interval. This draws out fine particulates from the sand filter and surrounding borehole walls.

Bailing helped remove sediments that may have been difficult to remove by pumping. Parsons geologists occasionally monitored color, odor, pH, conductivity, and specific conductivity of bailed groundwater. It was not necessary to achieve stabilization of these field parameters at this time. Bailing time averaged approximately 4 hours per well per Work Plan specifications. Groundwater in some wells cleared quickly; other wells remained highly turbid and were bailed for more hours over several efforts. Bailing continued until visible sediments were no longer observed in the discharge. Bailed groundwater was contained and volumes were measured out in 55-gallon drums. When necessary, the drummed water was transported to the GAC via GPI vacuum truck. In general, the BS wells exhibited greater fine turbidity during development than LGR or CC wells. Occasionally a BS well could be bailed �dry.� In such cases bailing was suspended until the well recovered sufficiently for bailing to resume.

2.10.3   Pumping

Once visible sediment was removed by air-lifting and bailing, well development was completed by pumping. Each completed MW was pumped with a decontaminated, 1 hp Grundfos submersible pump rated at 5 gpm. The pump was attached to flexible tubing and hand-lowered by drilling subcontractor personnel. The pump was suspended within the screened section, approximately 2 feet off the bottom of each well. A portable generator supplied power for the pump.

The developed volume of each well was monitored by flowmeter. Field parameters, including turbidity, odor, temperature, pH, conductivity, and specific conductivity, were periodically monitored. This process usually continued until the water removed from the wells was clear, field parameters stabilized, and the volume withdrawn surpassed the estimated volume of water injected during drilling. Strict adherence to this procedure was not always feasible in the case of BS screened intervals. As with bailing, low yield BS wells were pumped �dry� before the requisite volume of groundwater could be evacuated. As a result, development at these wells entailed repeated cycles of short-term pumping and recovery.

Stabilization was achieved when water appeared foam- and sediment-free, turbidity remained within 10 nephelometric turbidity units (NTUs), temperature was +/- 1.0˚C, pH +/‑0.1 units within a range of 6.5 to 8, and conductivity +/- 5 percent, all for a period of at least 30 minutes. Pumping was normally maintained for at least 6 hours, even after the above conditions had been met. Developed groundwater from wells that showed contamination during drilling and/or discrete interval testing was discharged into rolloff containment for characterization.

2.11 - Transducer Installation

A total of 21 transducers were purchased by CSSA from In Situ, Inc. for permanent installation in selected wells. The systems consist of five Troll 4000 sensors (100 pounds per square inch [psi]), eight miniTroll sensors (4 x 100 psi and 4 x 300 psi), and eight Troll 9000 sensors (4 x 100 psi and 4 x 300-psi). All transducers are equipped to measure temperature and downhole pressure, which can be converted to water level. Each unit is rated for a specified psi submergence suspended from a polyethylene-coated data cable. Each transducer is automatically compensated for barometric effects through a vented sleeve within the cable jacket. All transducers are fully programmable, and include datalogging capability on either linear, logarithmic, or event-based modes.

Each transducer was set to a depth (Table 2.3) within the water column that was anticipated to fall within the seasonal extremes while still operating within the sensor 100‑psi (231 feet of water) rating. During installation, each sensor was referenced to the static water in the respective well as measured from the top of the well casing. To conserve battery power and minimize data points, the transducers were programmed to monitor the head and temperature every 15 minutes, but only record data points that showed a net change of 0.25 feet from the prior reading, or twice daily, whichever occurred first. The reference level (calibration) was checked and the data downloaded from each transducer on a routine basis, which coincided with the quarterly groundwater sampling event.

The Troll 4000 probes are equipped with a built-in datalogger capable of storing over 500,000 data points between data downloads. Data are stored within the on-board datalogger in the form of a �test,� and are easily retrieved from the sensor using a remote computer node at the wellhead. Three of these transducers were installed in each unit of the Middle Trinity Aquifer at the CS-MW9 cluster to record the effects of recharge/discharge within and between the various members of the aquifer. The fourth transducer was installed at CS-MW4-LGR in hopes of gaining insight regarding interaction between groundwater and surface water recharge along Salado Creek. The fifth transducer was installed at CS-MW16-LGR to measure effects of the water level on contaminant concentrations, and is co-located with the northern weather station.

The Troll 9000 probes are also equipped with a built-in datalogger capable of storing 16 programmable tests with 4 megabytes (MB) of memory which will store over 1 million data points. These probes are capable of monitoring up to nine sensors simultaneously, and these particular probes are equipped to measure conductivity, water level, and temperature. The four 100‑psi probes are currently being used in the Contract F41624-00-D-8024, Task Order 0058 (TO58) recharge study, and are installed in wells CS-MW1-CC, CS-MW2-CC, CS-MW11A-LGR, and CS-MW12-CC. Troll 9000 probes are submerged to a depth within the screened interval of the well so that continual flow through the aquifer is recorded, and not stagnated water within the casing column.

The miniTroll probes are equipped with a built-in datalogger capable of storing 16 programmable tests with 1 MB of memory which will store up to 220,000 data points. Three of the 100‑psi miniTrolls are installed in wells CS-MW11B-LGR, CS-MW18-LGR, and CS-MW19-LGR, while the 300‑psi miniTrolls are installed in wells CS-MW16-CC, CS‑1, CS-9, CS-10, and CS-11.

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