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Introduction to the Groundwater Monitoring Program - April 2001

1.0 - Introduction

2.0 - Sampling Methodology

3.0 - Water Level Measurements

4.0 - Historical Analytical Results

Figures

Figure 1   Potentiometric Surface Map, January 1997

Figure 2   Potentiometric Surface Map, October 1997

Figure 3   Potentiometric Surface Map, January 1998

Figure 4   Potentiometric Surface Map, November 1998

Figure 5   Potentiometric Surface Map, September 1999

Figure 6   Potentiometric Surface Map, December 1999

Figure 7   Potentiometric Surface Map, March 2000

Tables

Table 1   Summary of Groundwater Monitoring Program

Table 2   Well Pump Information, December 2000

Table 3   Summary of Groundwater Elevations

Table 4   Summary of Groundwater Information Through March 2000

Table 5   Target Analytes for the RL74 Monitoring Program

Table 6   Groundwater VOC Analytical Results

Table 7   Groundwater Metals Analytical Results

Table 8   Groundwater VOC Analytical Results for Off-post Public Private Water Wells

1.0 - Introduction

In 1991, during routine water well testing conducted by TDH, dissolved TCE, PCE, and 1,2‑DCE were detected above MCLs in well 16. In 1992, a groundwater sample was collected from each well at CSSA to evaluate the extent of contamination. A groundwater monitoring program was established in 1994 so that groundwater flow directions, elevations, and contaminant concentrations could be monitored over time. A summary of wells included in the program and the dates they were sampled is provided in Table 1.

A Quarterly Groundwater Report was prepared for each of these previous sampling events. Reports for May 1994 through April 1996 are listed in the List of Previous Monitoring Reports, behind the �Groundwater Monitoring� tab. Complete reports for the January 1997, November 1998, September 1999, December 1999, and March 2000 are also included behind the �Groundwater Monitoring� tab in Volume 5. All work pertaining to the groundwater investigation up through June 1996 is summarized in the Groundwater Investigation and Associated Source Characterization Report (Parsons ES, 1996).

Starting with the June 2000 sampling event, a revised reporting approach was initiated. This �Introduction� was prepared in an effort to simplify subsequent monitoring reports and eliminate redundancy. This introduction summarizes data from August 1991 through March 2000 sampling events, and describes the typical sampling methodology. A short event-specific report will be prepared for each event (starting with the June 2000 event) to describe event-specific analytical and groundwater measurement results, as well as to describe any deviations from the typical sampling methodology that may have been necessary.

2.0 - Sampling Methodology

As shown in Table 1, the wells sampled as part of CSSA's groundwater monitoring program include Wells 1, 2, 10, 11, 16, D, G, H, I, MW1, and MW2. Offsite wells that have been sampled include Wells LS-7, RFR-8, RFR-3, and JW-30. Well LS-7 has been regularly sampled since December 1999. Additional wells are currently (as of February 2001) being installed at CSSA. Once installation and development of these wells is complete, they will be added to the monitoring program. Sampling of additional off-site wells is also being planned.

Wells 3 and 4 are not typically sampled due to their proximity to Well 2. AFCEE, CSSA, and Parsons ES reached this consensus during the Technical Interchange Meeting (TIM) on February 13, 1997.

Well G, although it is included in the monitoring program, has not been sampled since December 1999. Groundwater levels at that time, and until September 2000, were presumed to be below the bottom of the sucker rods in the well. However, in December 2000, the water level increased to 206.54 feet BTOC, well above the level in September 1999 (298.83 ft BTOC) when the well was last sampled, but still no sample could be collected. Therefore, it has been concluded that the sucker rods are no longer operational.

Wells 9 and 10 are connected to the water distribution system at CSSA; thus, they are equipped with dedicated high capacity pumps through which groundwater samples can be collected. These dedicated pumps in the water-supply wells are often in use during weekdays and are typically turned off during weekends. Wells 1 and 11 are also sampled through dedicated high-capacity pumps, although they have been taken off the CSSA water distribution system. Well I is powered by a windmill and will be pumping any time there is sufficient wind energy. Dedicated slow-purge/low-flow QED bladder pumps were installed in Wells 2, 16, D, MW1, and MW2. Information regarding each CSSA well, including pump depths and types as of December 2000, is included in Table 2.

The first step of the quarterly groundwater sampling procedure is to measure the static water level in every available CSSA well with an electronic water level indicator (e-line). The only exception is Well 10, which is measured by the air-line method. The water level in offsite Well LS-7 is not measured before sampling because the sample is collected from a spigot and, thus, no suitable opening exists for placing an e-line probe into this well.

The next step is to stabilize groundwater conditions in the well. In order to stabilize groundwater conditions before collecting a sample, several steps are taken at each well prior to filling the appropriate bottles with groundwater. The first of these actions is to evacuate any water within the pump system by purging several gallons from the well. Next, groundwater pH, conductivity, and temperature are monitored.

After these parameters stabilize, the samples are collected and placed into the appropriate bottles and sent to the laboratory for analysis. Detailed groundwater sampling procedures can be found in Section 2.1.5 of the Field Sampling Plan, Volume 1-4. Purging methodology is described in Section 2.1.5.1 of the DO23 SAP Addendum, Volume 1-4.

Table 2 - Well Pump Information, December 2000

Well ID

Well Type

Pump Type

Pump Depth (ft bgs)

Total Depth (ft bgs)

Casing Depth (ft bgs)

Comments

Well 1

Production

(inactive)

Electric Submersible

420

432

135

Pump depth based on Ashworth, 1976. Well depth based on 1997 video survey. Well removed from water distribution system at CSSA in September 1999.

Well 9

Production

Electric Submersible

504

534

23

Pump depth based on 1997 well upgrade. Well depth based on 1997 video survey.

Well 10

Production

Electric Submersible

528

559

390

Both well and pump depths are based on Ashworth, 1976.

Well 11

Production

(inactive)

Electric Submersible

510

529

213

Pump depth based on 1997 well upgrade. Well depth based on 1997 video survey.

Well 2

Monitoring

QED Bladder

239

350

205

 

Well 3

Monitoring

No pump installed.

NA

NA

205

Well can be sampled with portable low-flow pump system.

Well 4

Monitoring

No pump installed.

NA

NA

200

Well can be sampled with portable low-flow pump system.

Well 16

Monitoring

QED Bladder

350

431

200

 

MW1

Monitoring

QED Bladder

310

320

140

 

MW2

Monitoring

QED Bladder

349

361

141

 

Well D

Monitoring

QED Bladder

250

263

205

Water level was below pump depth in September 1999, December 1999, March 2000, and June 2000.

Well G

Livestock

Sucker Rods/Gasoline motor

N/A

N/A

N/A

Sucker rods are no longer operational. No data available for this well.

Well H

Livestock

Sucker Rods/Electric motor

N/A

N/A

N/A

Sucker rods are no longer operational. No data available for this well.

Well I

Livestock

Sucker Rods/Windmill

252

362

250

Pump depth based on Ashworth, 1976.

3.0 - Water Level Measurements

Water level measurements are collected at CSSA as part of the regular sampling protocol. Water well upgrades were performed on CSSA Wells 1 and 11 between May 7 and 13, 1997, and on Well 9 between November 17 and 20, 1997. The upgrades included the installation of a PVC e-line measuring tube in both wells. Prior to the upgrades, Well 11 water levels were measured by the air-line method.

Several groups of privately owned domestic wells and a municipal water district are located along the western and southwestern boundaries of CSSA. The domestic wells are grouped geographically, and include the Jackson Woods subdivision wells, Ralph Fair Road wells, Leon Springs Villas wells, Hidden Springs Estates wells, and the I-10/Old Fredericksburg Road wells. These domestic/municipal wells are primarily completed in the Lower Glen Rose formation and yield less than 10 gal/min. The Jackson Woods subdivision group has 31 wells and is the largest group of domestic wells. The Fair Oaks Water Company (Fairco) operates 43 large capacity municipal wells near CSSA. Most of these open-borehole completion wells are completed across all three of the Middle Trinity aquifer (the Lower Glen Rose, Bexar Shale, and Cow Creek formations).

The impact of pumping by adjacent municipal and subdivision water wells upon the water table at CSSA is unknown. However, in September 1999, Parsons ES initiated a well survey in the vicinity of CSSA. From data currently available, it appears that Fairco conducts the most significant pumping in the area. In August 1999, Fairco pumped approximately 1.8 million gallons per day (mgpd) for residential use. Additional information about the Fairco wells, and other offsite wells near CSSA, is included in the Offsite Well Survey Report (Volume 5 behind the �Groundwater Investigation� tab).

3.1 - Basewide Flow Direction and Gradient

Groundwater potentiometric elevations using e-line and air-line measurements taken during each of the monitoring events from January 1997 through March 2000 are depicted in Figures 1 through 7, respectively. Figure 5 includes the weekly average water level (1036.80 feet MSL) measured by Fairco for Fairco Well 20 during the week of September 8, 1999.

Groundwater gradients and flow directions, as shown on the potentiometric surface maps, are approximate and general in nature. Drawing concrete conclusions from these maps regarding the natural groundwater gradient at CSSA is not appropriate for several reasons. Groundwater elevation data is collected from different types of wells, such as production wells, stock wells, and a few monitoring wells. These wells are screened in different groundwater zones or through multiple zones. The historical groundwater elevation data being analyzed was measured using a mixture of air and electrical lines. Air-lines are not as accurate as e-lines, which makes a direct correlation between the two tenuous. When groundwater levels are collected, surrounding production wells are often pumping; thus, not showing the true static water level condition at CSSA. Furthermore, significant local area pumping occurs near CSSA. Local pumping likely influences the groundwater gradient and flow directions at CSSA and may be the reason that groundwater flow directions have fluctuated greatly from southeast to southwest over time. To assume, then, that CSSA�s groundwater flow direction is naturally to the south or southwest may not be correct. The natural general groundwater flow direction for the area, however, is towards the southeast. Upon installation of the current and future cluster wells at CSSA, additional information about groundwater flow directions will be gathered. Historical groundwater elevations from October 1992 through December 2016 are shown in Table 3.

The average groundwater elevation decrease for the January 1998 and November 1998 monitoring events do not include groundwater level data for Wells 1, 9, 10, or I since the pumps at these wells were often in operation at that time. Well 1 was removed from the water distribution system at CSSA in September 1999. The average elevation decrease for the March 2000 event does not include a groundwater level datum from Well 4, which was dry. Regular pumping at Well 11 was discontinued due to the presence of coliform in this well. The total average rise in groundwater elevations from January 1997 to November 1998 was 175.5 feet. The rise is predominantly the result of extended rainfall in the latter parts of 1997 and 1998. The sharp decline observed in the groundwater elevation average in September 1999, and the continued declines in December 1999 and March 2000, are likely due to the inferred increase in water demand by surrounding residential and commercial developments and due to drought conditions that occurred throughout 1999 and have persisted into 2000. Approximate groundwater gradients, flow directions, and average changes in groundwater elevation during each sampling event from October 1997 through March 2000 are shown in Table 4.

Pumping in most water-supply wells was halted at least 48 hours prior to water level measurement. In Figure 3, however, water level measurements from Wells 9 and 10 were not used due to active pumping at that time. The water level measurement for Well 11 was also not used in Figure 3 because the measurement represents the localized influence of this pumping. Likewise, water level measurements from Well 10 were also excluded from Figures 4 through 6 due to active pumping. The water levels measured in Wells 9 and 11 during the March sampling event were possibly being influenced by the pumping occurring in Well 10 (see Figure 7). Water level measurements taken from Wells 10 and 11 during October 1997 appear to be flawed and were therefore not included in Figure 2. The groundwater elevations measured in Wells 10 and 11 during October 1997 significantly exceeded those in all other wells at that time and Wells 10 and 11 were pumping in the days prior to the measurements.

Table 4 - Summary of Groundwater Information Through March 2000

Date of Monitoring Event

Approximate Flow Direction

Approximate Gradient (ft/ft)

Average Change in Water Level (ft)*

October 1997

South

0.002

105.4

January 1998

South-southeast

0.003

-43.4

November 1998

South-southeast

0.013

113.5

September 1999

Southwest

0.007

-188.4

December 1999

Southwest

0.004

-4.9

March 2000

South-southeast

0.009

-9.3

Of the 15 wells that have been sampled during groundwater monitoring at CSSA, TCE and/or PCE have been detected in 10 of them. These compounds have never been detected in CSSA�s water supply wells 9 and 10, and they have never been detected in agricultural supply wells G, H, and I, which are all located in the north pasture. The highest concentrations of TCE and PCE have consistently been detected in Wells 16 and D, in the central portion of the facility. TCE and PCE concentrations in these wells, and in monitoring wells MW1 and MW2, located roughly 2,000 feet south of Wells 16 and D, have exceeded MCLs.

Groundwater naturally contains metals. Of the metals analyzed at CSSA, lead concentrations have most frequently exceeded the MCL. Prior to June 2000, lead concentrations at Wells 1, 2, 3, G, H, and I have exceeded the MCL, though not consistently. As of March 2000, the only other metal exceeding the MCL was nickel at Well 16 in September 1999.

4.0 - Historical Analytical Results

All groundwater samples collected as part of the RL74 monitoring program were analyzed for the following VOCs: 1,1-dichloroethene (1,1-DCE), bromodichloromethane, chloroform, cis-1,2-dichloroethene (cis-1,2-DCE), dibromochloromethane, methylene chloride, trans-1,2-dichloroethene (trans-1,2-DCE), tetrachloroethene (PCE), trichloroethene (TCE), and vinyl chloride using EPA Method SW8260. This list of analytes was agreed upon by the EPA at the February 3, 2000 TIM, and by the TNRCC in a letter dated October 5, 1999. The list of target analytes for the RL74 monitoring program are provided in Table 5. Historical analytical results for VOC concentrations in groundwater samples from August 1991 through March 2000 are summarized in Table 6.

All groundwater samples collected as part of the RL74 monitoring program were also analyzed for metals. The metals tested for include: arsenic, barium, cadmium, chromium, copper, lead, mercury, nickel, and zinc. Historical analytical results for metals concentrations in groundwater are summarized in Table 7.