[Work Plan Index] [Next Section]

9.1 - Statement of Objective

This addendum to the work plan describes activities in support of the installation of twelve monitoring wells. The wells will be installed in four cluster sets composed of three wells each. The wells in each cluster will monitor three units of the Middle Trinity aquifer underlying CSSA. Each well cluster shall consist of a shallow well in the Lower Glen Rose (LGR), a mid-depth well in the Bexar Shale (BS), and a deep well in the Cow Creek (CC) Limestone. The target drilling depths beneath CSSA are scoped as identified below:

The actual drilling depths will vary based on the local topography and/or proximity to structural features (e.g., faults). The given depths are generalized for the CSSA vicinity, and were established for scope delineation and cost estimating purposes. During the actual fieldwork, drilling depths will extend to the appropriate formational contacts. If necessary, total drilling footage greater than that in the statement of work (SOW) will be addressed with a scope modification as field conditions warrant.

The primary objective and placement of these wells are designed to aid in the horizontal and vertical delineation of the solvent plume in the Middle Trinity aquifer, as well as provide integral data for the hydrogeologic conceptual site model (RL83-Task 4) and numerical groundwater model (RL74). A secondary objective of this effort will be to characterize the vadose zone (which includes the Upper Glen Rose Limestone) for the presence of perched groundwater and contaminant migration. This drilling effort will be conducted in conjunction with monitoring well installations contracted under DO23. The drilling tasks for both these efforts will be performed concurrently such that the usable data from each study can be maximized. This work plan and associated Sampling and Analysis Plan (SAP) will provide guidance for the installation of the DO23 wells.

Figure 9.1.1 illustrates the proposed drilling locations of the RL83 and DO23 wells. A list of the new wells is provided in Table 9.1.2. The new DO23 wells will be designated as MW3, MW4, and MW5. The RL83 cluster well locations will be denoted as MW6, MW7, MW8, and MW9. As part of the nomenclature, each well name will be appended by a suffix that identifies the monitored interval:

Table 9.1.2 - Proposed Monitoring Well Nomenclature

9.2 - Schedule

It is anticipated that two drilling rigs will concurrently install the monitoring wells during the field effort. Additionally, a well development crew will begin once the drilling program is well under way. After the wells are developed, screening samples will be collected by CSSA to determine if VOCs are present in the groundwater. Based on the results of these screening samples, drilling locations may be altered which better suit the plume delineation. Table 9.1.3 provides a tentative timeline for the progression of the work. It is anticipated that each well cluster will take approximately 20 days to install and develop. Fieldwork for this effort is expected to last approximately two months.

Table 9.1.3 - Proposed Well Installation and Development Schedule

Rig 1	Rig 2	Development Crew
Install MW6 (3 wells)	Install MW8 (3 wells)
Install MW9 (3 wells)	Install MW3-LGR (1 well)	Develop MW6 and MW8 clusters
Install MW5-LGR (1 well)	Install MW7 (3 wells)	Develop MW3-LGR and MW-9 cluster
Install MW4-LGR (1 well)	Develop MW7 cluster	Develop MW5-LGR and MW4-LGR
Construct well completions	Construct well completions	IDW management and demobilization activities
Note: Wells will be developed in the order that they are completed. A minimum of 48 hours will be allowed for the annular seals to set before well development begins. Well development can be performed prior to the installation of the surface completions. The surface completions will be constructed in batches to maximize resources.

9.3 - General Requirements

The following paragraphs describe the planned field activities and procedures. More detailed discussions on the procedures are in the RL83 Sampling and Analysis Plan Addendum.

The wells will be designed and constructed per the AFCEE’s Model Field Sampling Plan (MFSP) version 1.1 criteria and the RL83 SAP. The wells shall be drilled to avoid potential cross contamination of the various hydrogeologic zones by setting multiple strings of protective casing. All wells will be drilled using air rotary methods in accordance with the MFSP. The drilling subcontractor will implement "air-mist" drilling techniques which will help reduce volatile emissions from the borehole, help suppress the dust plume, and prevent the formation of hardened "clumps" along the borehole walls in moist zones. At each cluster, wells will be spaced no closer than 15 feet apart. Representative lithologic samples will be collected continuously from the deepest boring (referred to as the corehole) at each cluster.

As each zone is penetrated by the corehole, the zone will be geophysically logged, packer-tested, and sampled prior to the installation of casing. Any remaining protective casing string or well that penetrates that same hydrologic unit will be reamed without coring, and completed based on lithologic and geophysical data obtained for the corehole. A single-shot declination tool will be used to check the plumbness and straightness of the boreholes and monitoring wells. The declination tool will be run in the borehole every 50 feet of advancement. The declination of the borehole will not deviate more then 2 degrees. This will ensure that any downhole equipment can easily be installed at a later date.

Each cluster will be drilled in its entirety before proceeding to the next cluster. The identified procedure for installing each well cluster will follow a phased approach. Protective surface casing will be installed in each borehole prior to proceeding to the next hydrologic unit. Only one wellbore at each cluster will be continuously cored and sampled, which ultimately will become a triple-cased well to monitor the Cow Creek Limestone that is the deepest member of the Middle Trinity aquifer.

The deepest well of each cluster (CC well) will be drilled before the mid-depth well (BS well) and the shallow well (LGR well). The deepest well will be continuously cored and all reasonable attempts will be made to maintain and mark the original orientation of the cores. All core will be retained for future reference and potential archival at the Texas Bureau of Economic Geology (BEG) University of Texas-San Antonio (UTSA).

Upon penetration of each geologic member, the resultant borehole will be logged with borehole geophysical tools. Four geophysical logs will be used: natural gamma ray (GR), caliper (CAL), spontaneous potential (SP), and both short (16") and long (64") resistivity logs. All logs will be digitally recorded. The logs will be presented as charts and electronic digital files. The information attained will provide the basis for developing the baseline comparison between geophysical log response to changes in lithology, fractures, or porosity.

Up to 20 feet of rock core from each corehole will be submitted for fracture analysis to an offsite laboratory. The intervals will be determined after review of downhole geophysical interpretations to determine the zones of interest. The results of the fracture analyses will determine the number, relative dip, and relative size of fractures present in the core. The fracture analysis will assist in comparing the strike and dip of primary/secondary jointing (or faulting) patterns which may dictate preferential flow of both groundwater and contaminants.

As an independent study, CSSA will be responsible for the collection and analyses of core samples for geophysical testing. The goal of the geophysical testing will be to determine matrix characteristics of selected core intervals. CSSA will be responsible for the selection of the geophysical analyses, and the tabulation of the generated data. CSSA can provide the tabulated data to Parsons ES for incorporation into the "Groundwater Investigation" section of Volume 5 of the CSSA Environmental Encyclopedia.

A total of six samples (1 near-surface sample and 5 subsurface samples) for volatile organic compounds (VOC) and inorganic analyses will be obtained from each of the 4 coreholes. Sample depths will be based on field measurement of volatiles (using a photoionization detector), visible contamination or staining, zones of fracturing or secondary porosity features, or intervals of saturation. One groundwater grab sample will be obtained from each hydrologic zone for background metals and aqueous cations/anions from the corehole prior to being cased.

Injection packer testing will be performed in each hydrologic zone at two intervals determined from the lithologic core and geophysical results for a total of six tests per corehole. Two inflatable packers will be used to seal off a discrete zone to test for transmissive properties. Water will be injected into the formation at a measurable rate and pressure. From this test, an estimate of transmissive properties of the zone will be calculated.

The general well completion design will result with a 4-inch diameter well with no more than 25 feet screen open to the surrounding be open borehole throughout the thickness of the formational member. Each zone will be cased-off from the underlying unit before drilling resumes. All well surface casing will be composed of welded low-carbon steel pipe. All annular seals (grout) will be emplaced via tremie pipe. The interior well casing and screen will be composed of flush-threaded 304 stainless steel and will be constructed with an appropriately sized filter pack. A bentonite seal and Portland cement slurry will be used to seal the remaining annular space. Wells will be completed with 4-foot square concrete pads with locking well protectors and protector posts in accordance with state regulations. At drilling locations that may be prone to flooding, wells will be flush-mounted surface completions without the use of protector posts. The interior cap in each flush-mounted well will be outfitted with a pressure relief valve. This will prevent the intrusion of surface water into the well, while allowing atmospheric and wellbore pressures to be equilibrated to facilitate easy cap removal.

The drilling effort will result with single-cased wells in the Lower Glen Rose (310 feet), double-cased wells in the Bexar Shale (380 feet), and doubletriple-cased wells in the Cow Creek Limestone (450 feet). Protective casing will be installed no more then 105 feet into the underlying formational member. The actual casing depth will be dependent on the nature of the geologic contact. Geophysical data will be key information in identifying the optimum depth to install the casing. The casing depth the Lower Glen Rose wells will vary based on the presence of perched water zones, but past experience has shown that between 150 feet and 200 feet of surface casing should be sufficient.

The second string of casing in the Cow Creek well and the primary protective casing in the Lower Glen Rose and Bexar Shale wells will be no larger than 8-inch ID (8-5/8 inch OD) low-carbon steel casing completed within a borehole with a nominal diameter of 12-1/4 inches. This casing completion will result with an annular space of 1-13/16 inches. A minimum of 24 hours will pass after the emplacement of casing grout before proceeding to the next lower hydrologic unit within the borehole.

The primary protective surface casing on each Cow Creek monitoring well will be no larger than 12-inch ID steel casing completed within a borehole with a nominal diameter of 16-1/4 inches. This casing completion will result with an annular space of 2-1/2 inches. A minimum of 24 hours will pass after the emplacement of casing grout before proceeding to the next lower hydrologic unit within the borehole.

The interior 4-inch ID 304 stainless steel casing and screen will be installed in each well to limit the amount of open borehole to less than 25 feet. The nominal diameter of the borehole will be 7-7/8 inches. The casing and screen will be centered within the borehole using centralizers at 50-foot intervals.

The well screen will be constructed of 304 stainless steel wire-wrapped screen with a slot size of 0.050-inches (50-slot), with no more than a 25-foot intake. The annular space will be filled with a 4/10 or 6/9-mesh filter pack from the base of the borehole to height of 2 feet above the top of the screened interval. The filter pack will be emplaced via tremie pipe from the base of the borehole to the top of the designated screened zone. A 100 percent sodium bentonite seal with a maximum thickness of 5 feet will be emplaced within the borehole above the filter pack.

Beginning with small lifts, a Portland/bentonite grout mixture will be slowly pumped into the annular space using a side-discharge tremie pipe. The slurry will be injected until grout flows freely at the surface. The annular space will be checked periodically for settlement, and will be topped off as needed. The grout will be allowed to cure for at least 48 hours prior to well development.

The drilling contractor will develop each well by using surging, bailing, and pumping techniques. The well development requirements will follow the MFSP and the RL83 SAP.

Waste management will include the handling of both drill cuttings and groundwater. Air rotary method will produce a significant volume of drill cuttings and groundwater. One transportable 20-yard rolloff box will be placed at each well cluster to contain soil cuttings. An additional rolloff box (covered, lined, and leak-proof) will be placed near the water treatment plant for processing through a granular activated carbon (GAC) unit. Groundwater produced during the drilling activities and well development, as well as decontamination water, will be transported to this rolloff container via suction truck for the settlement of suspended solids. The resulting fluids will be pumped off the top for treatment in the GAC unit. The remaining solids and drill cuttings will be profiled using TCLP analyses, and transported to a permitted landfill. For those solids that are deemed non-hazardous, CSSA may opt for an alternative recycling or disposal method at CSSA.

A full decontamination of equipment will take place between hydrologic zones and before relocating to different well clusters.

To prevent sample contamination from the onsite sampling equipment and machinery, decontamination will be conducted using the following procedures outlined in the MFSP. A decontamination pad, large enough to fully contain the equipment to be cleaned, will be set up. One or more layers of heavy plastic sheeting will be used to cover the ground surface. Sampling equipment that will come into direct contact with samples will not be allowed to come in contact with the plastic.

Drill rigs, drill pipe and other equipment that does not come into contact with the sample medium will be decontaminated with a steam cleaner before initial use and after each borehole is completed. Drill bits will be decontaminated with a steam cleaner prior to use at each boring or monitoring well location. If the hot water cleaning alone is found to be ineffective, the equipment may be scrubbed with laboratory-grade detergent, then rinsed with high-pressure steam. All visible dirt, grime, grease, oil, loose paint, etc., will be scrubbed until it has been removed. When possible, drilling will proceed from the "least" to the "most" contaminated sites.

The casing pipe and centralizers will either be certified clean by the manufacturers or if necessary, decontaminated by steam cleaning. Prior to well development, equipment such as pumps or surge blocks will be decontaminated by flushing or pumping laboratory-grade detergent solution, potable water, then ASTM Type II Reagent water (Reagent Grade II water) through the internal components. The exterior of the pump inlet hose will be steam cleaned.

Sampling equipment includes augers, continuous-core samplers, hand trowels, bailers, pH meters, conductivity meters, shovels, knifes, spatulas, and composition bowls that directly contact samples. This equipment will be cleaned in accordance with the SAP.

9.4 - Well Monitoring Systems

Upon completion of well development, dedicated bladder pumps will be installed in each of the new wells under the current DO23 and RL83 SOWs. Each pump system will consist of a Teflon™ and stainless steel bladder pump, Teflon-lined tubing, and a lockable wellhead apparatus. The use of the pumping system is currently being re-evaluated by CSSA. If significant changes to the sampling method are made, the SOW will need to reflect the changes so that all contractual obligations are met.

Additionally, four In Situ Troll downhole dataloggers will be installed in selected wells. Each datalogger continuously collects and stores information regarding static water level, water temperature, and pH. Locations for the transducers will be selected based upon initial water level and chemistry data.

9.5 - Reporting Procedures

A well installation report shall be prepared to document the activities associated with installation of the four sets of cluster wells. The report shall include boring logs, well completion and development logs, well design diagrams. The hydrogeologic conceptual model (CSM) will be updated with cross sections and associated hydrogeologic diagrams based upon the new data generated from the well installations.

[Next Section]