[Home] [Master Table of Contents]

[Table of Contents] [Next Section]

Sampling and Analysis Plan - Addendum Specific to Field Sampling Plan for Delivery Order TO42

Section 3 - Groundwater Well Sampling

Under this task order, a total of five rounds of quarterly groundwater sampling will occur between March 2002 and September 2003. For the first two events (March 2002 and June 2002), the samples will be collected in conjunction with groundwater sampling already funded under Air Education and Training Command (AETC) contract delivery order 5084. Beginning September 2002, this task order will solely fund all quarterly groundwater monitoring and reporting for the CSSA program. As the drilling of new wells progresses and the existing quarterly monitoring under DO 5084 expires, the amount of wells to be sampled under this order will increase. At the beginning of this task order, only 32 on-post wells will be sampled. By the end of the TO42 period of performance, a total of 49 on-post wells will have been incorporated into the quarterly monitoring program. Additionally, up to 40 off-post private and public wells will be sampled quarterly between September 2002 and September 2003. Table 9 indicates the number of wells and sampling parameters that will be funded under this contract. A breakdown of quarterly sampling events by well and analyte is provided in Appendix F.

Sampling of the wells will be based on AFCEE Handbook procedures with exceptions as appropriate for the hydrogeology at the site. The wells will be purged in accordance with low-flow sampling techniques. QA/QC sampling and analysis will be performed to meet requirements in the QAPP. Purge water will be containerized and transported for treatment by a GAC treatment system (set up under RL74) prior to discharge at CSSA�s Outfall 002.

3.1 - Water Level Measurements

Water level measurements will be obtained from on-site wells that provide good access for an electric measuring device. The depth to water will be measured to the nearest 0.01-foot with respect to the surveyed reference point on the top of the casing. If no clear reference point exists, the reading will be obtained from the north side of the well casing as a reference point. Water supply wells have supplied gauging tubes for obtaining water levels.

In the past, supply wells were shut down before a quarterly event (no more than 48 hours) to allow the aquifer to equilibrate. Parsons will notify CSSA Environmental at least 7 days prior to a sampling event to allow adequate time to arrange well shut down. Therefore, water level monitoring should ensue at the beginning of each sampling quarter. This will also allow CSSA to resume normal pumping operations as quickly as possible. Since sampling rounds can last for 5 days or more, it is recommended that all water levels be collected in a single initiative so atmospheric and meteorological effects can be minimized. Data from all well transducers and the weather station also need to be downloaded as part of each quarterly event.

Table 9 - Sample Quantities and Analytical Parameters

3.2 - Groundwater Sampling Methods

In general, the overall goal of any groundwater sampling program is to collect representative water samples with little or no alteration in water chemistry. Analytical data obtained in this manner may be used for a variety of purposes depending on regulatory requirements. CSSA has initiated a low-flow sampling program for all the installation�s monitoring wells, while drinking water and livestock wells are equipped with either high capacity downhole pumps or windmills. Other well sets include low-yielding perched aquifer wells (AOC 65), Westbay^� multi-port samplers, on- and off-site public supply wells, and offsite domestic wells. There are five types of well sampling that will be routinely carried out over the course of this task order. These types of wells and sampling techniques are addressed below.

3.2.1   On-Site Wells with Dedicated Low-Flow Bladder Pumps

An important goal of any monitoring program is collection of data truly representative of conditions at the site. It is generally accepted that water in the well casing is non-representative of the formation water and needs to be purged prior to collection of ground-water samples. However, water in the screened interval may indeed be representative of the formation, depending on well construction and site hydrogeology. To this end, CSSA implemented a low-flow sampling strategy in many of the groundwater monitoring wells. Using low-flow purging and sampling techniques can often mitigate sampling-induced turbidity problems. The following discussion and procedures are excerpted from the USEPA guidance entitled Low-Flow (Minimal Drawdown) Ground-Water Sampling Procedures (USEPA 1995).

Low-flow refers to the velocity with which water enters the pump intake and is imparted to the formation pore water in the immediate vicinity of the well screen. The objective is to pump in a manner that minimizes stress (drawdown) to the system to the extent practical, taking into account established site sampling objectives. Typically flow rates on the order of 0.1 -0.5 liters per minute (L/min) are used; however, some extremely porous formations can be successfully sampled at flow rates to 1 L/min. Isolation of the screened interval water from the overlying stagnant casing water may be accomplished using low-flow minimal drawdown techniques. When the pump intake is located within the screened interval most of the water pumped will be drawn in directly from the formation with little mixing of casing water or disturbance to the sampling zone.

CSSA utilizes a QED Well Wizard^TM system for collecting low flow samples. The sampling device consists of a pressurized nitrogen gas canister, pneumatic controller, gas injection tubing, a bladder pump, a drop pipe with inlet (deeper wells only), and discharge tubing. Prior knowledge of the well construction is necessary to assist in purging. At a minimum, any stagnant water remaining in the pump tubing needs to be purged so the sampler can be assured that fresh, representative groundwater is being collected at the sampling port. A minimum purge volume is defined as the amount of water held in storage within the 3/8-inch discharge tubing. Water may stagnate within the discharge tubing between sampling events since it is held by a check valve located at the pump. Table 10 lists the current and anticipated low-flow pump systems to be sampled at CSSA. An estimated minimum purge volume to evacuate stagnate water is also included in this table. As well construction ensues and actual completion information becomes available, this table will require updating.

Well purging is nearly always necessary to obtain samples of water flowing through geologic formations in the screened interval. Rather than using a general but arbitrary guideline of purging three casing volumes prior to sampling, water quality measurements will be used to establish stabilization time for several parameters (e.g., temperature, pH, specific conductance, and turbidity) on a well-specific basis. Data on pumping rate, drawdown, and volume required for parameter stabilization can be used as a guide for conducting subsequent sampling activities. The following recommendations should be considered:

Prior to sampling, all sampling device and monitoring equipment should be calibrated according with manufacturer�s recommendations and the SAP (Volume 1-4: Sampling and Analysis Plan). Calibration of pH should be performed with at least two buffers that bracket the expected range.

During sampling events conducted after significant rain events or when the water table is elevated more than 100 feet above pumps, extra care shall be taken to slowly increase nitrogen pressure in the low-flow sampling system. These procedures are intended to decrease stress on the pump systems and reduce the possibility of damaging pump bladders.

Table 10 - Low-Flow Pump Installation Data and Minimum Tubing Purge Volumes

The USEPA recommends that the water level be checked periodically to monitor drawdown in the well as a guide to flow rate adjustment. The goal is minimal drawdown (<0.1 meter) during purging. At CSSA, it is unlikely that the dedicated bladder pumps can create such a drawdown in the main karstic aquifers (e.g., LGR and CC). In lower yielding intervals (perched aquifer or BS wells) this goal may be difficult to achieve under some circumstances due to geologic heterogeneity within the screened interval, and may require adjustment based on site-specific conditions and personal experience.

Water quality indicator parameters should be continuously monitored during purging. The water quality indicator parameters monitored can include temperature, pH, conductivity, and turbidity. The last two parameters are often most sensitive. Pumping rate, drawdown, and the time or volume required to obtain stabilization of parameter readings can be used as a future guide to purge the well. Measurements should be taken every 3‑5 minutes. Stabilization is achieved after all parameters have stabilized for three successive readings at some volume beyond the minimum purge requirements. Three successive readings should be within � 1^◦ F (� 0.5^◦ C) for temperature, � 0.1 for pH, � 5% for conductivity, and � 10% for turbidity.

Sampling can be initiated upon parameter stabilization. If an in-line device is used to monitor water quality parameters, it should be disconnected or bypassed during sample collection. Sampling flow rate may remain at established purge rate or may be adjusted slightly to minimize aeration, bubble formation, turbulent filling of sample bottles, or loss of volatiles due to extended residence time in tubing. Typically, flow rates less than 0.5 L/min are appropriate. The flowrate for volatile sampling should approach 0.1 L/min. Generally, volatile (e.g., solvents and fuel constituents) and gas sensitive (e.g., Fe ²⁺, CH₄, H₂S/HS^-, alkalinity) parameters should be sampled first. The sequence in which samples for most inorganic parameters are collected is immaterial unless filtered (dissolved) samples are desired. Filtering should be done last, and in-line filters should be used. Water samples should be collected directly into this container from the pump tubing.

3.2.2   Shallow Wells Sampled by the Bailer Method

On occasion, shallow perched aquifer wells not equipped with any pumping apparatus will require sampling. Currently, this group of wells include AOC-65- CS-MW-1, CS-MW-2A, CS-MW-2B, CS-MW-3, and CS-MW-4. Two of these wells are routinely dry; therefore, sampling of these wells may be implicitly related to precipitation events rather than quarterly events. At CSSA, these types of wells usually do not freely yield water, and are usually purged to dryness before attaining any minimum purging requirement. Samples are collected after a sufficient volume of groundwater has accumulated within the wellbore to obtain an adequate sample volume.

Before each monitoring well is purged and sampled, the water level will be measured within �0.01 foot with respect to the reference point on the top of the casing. Using the static water level, well casing diameter, and total depth of the well, one well casing volume is calculated and recorded. Purging of low-yielding observation points is performed by removing up to three well casing volumes from each monitoring well, or until the well has gone dry. The water is removed via a decontaminated or disposable Teflon bailer and placed in a drum or other leakproof container. The field crew may find that a disposable bailer is not adequate for purging because of its lack of rigidity, thus a decontaminated rigid bailer may be used. Purging and sampling will be performed in a manner that minimizes agitation of sediments in the well and formation. Equipment will not be allowed to free-fall into the well, and the bailer will be lowered into the water column slowly. All purged groundwater produced from these wells requires treatment at the CSSA GAC.

Groundwater samples will be collected in the order of increasing anticipated contamination when possible. Careful use of the bailer will minimize sample agitation and contact with air. A clean length of nylon cord will be used for raising and lowering the bailer in each well. The bailer rope should not be allowed to touch the ground during sampling. For every 0.5 well volumes removed, measurements of pH, temperature, and specific conductivity are collected and recorded in the logbook. Because of the nature of these wells, turbidity will not be a stabilization criterion. Ideally, when at least three subsequent measurements are within 10 percent of each other, it is indicative that water is being removed from the aquifer rather than from the well casing. However, if the well goes dry before three well volumes, this standard may not be achievable. When a low-yield monitoring well is bailed dry before three well volumes are removed, the sample will be collected as soon as the volume of recovered fluid is sufficient for sampling.

3.2.3   Westbay� Multi-Port Samplers

Westbay^� multi-port wells will be monitored and sampled monthly from December 2002 until September 2003. Samples from these wells will be obtained on a monthly frequency plus immediately after a qualifying precipitation event. In general, CSSA will be responsible for collection of data from the Westbay^� wells. Parsons will supply one field technician per ground water sampling event. Groundwater samples will be collected from discrete intervals using the Westbay^� device for a period of 12 months. Sampling frequency will utilize the following scheduling parameters:

Note: The samples will be collected within 72 hours of the rain event. This allows for samples to be collected on Monday should the rain event occur on Friday. After each sampling event the data will be evaluated to determine if monthly or other sampling is necessary.

The sampling and use of the multi-port monitoring devices require specialized training provided by Westbay^�. At a minimum, two persons each from both CSSA and Parsons will be trained on the correct use and procedures of obtaining meaningful data. Requirements for measurement, purging, and sampling will be provided by Westbay at that time.

3.2.4   Deep Wells Sampled by the Bailer Method

Quarterly groundwater events include deeper, larger diameter wells that may be routinely sampled but are not equipped with any sampling device. Currently, there are no wells scoped for this design under TO 42, but the need may eventually arise periodically (e.g., CS-3 and CS-4 are not equipped with pumps). Their diameter and depth preclude bailing as a feasible purging alternative. Samples collected from such wells will be obtained by bailer grab samples. The same field methodology for shallow wells will be implemented for collecting deeper samples utilizing a bailer. A single measurement for pH, temperature, and conductivity will be recorded to document the water quality. Other instances that may occasionally include this sampling method are Wells CS-3 and CS-4 (CS-G will have a low-flow pump and CS-H an electric pump).

3.2.5   On-Site Water Production Wells

Water production wells available for groundwater monitoring are purged only to remove water from the pump column. Currently, these include CS-1, CS-9, CS-10, and CS-11. Purged groundwater is typically pumped into the distribution system at CS-1, CS-9, and CS-10. CS-11 is currently off-line, therefore the well is purged directly onto the ground surface. Wells with pumps are purged 10 to 15 minutes prior to sampling. Temperature, pH, turbidity, and conductivity will be taken prior to and during purging. Well purging will be performed until temperature, pH, turbidity, and conductivity values stabilize. Stabilization is defined for pH as � 0.1 unit, temperature � 1�F, turbidity as � 10 percent, and conductivity as � 5 percent. Successive measurements will be taken at 5-minute intervals. All purge information will be recorded in the field logbook. Samples are collected from the water faucet tap located at or near the top of the wellhead.

3.2.6   Off-Site Domestic and Public Supply Wells

Under TO 42, offsite groundwater samples will be collected from select offsite public and domestic supply wells. Nearly all these wells are equipped with a submersible water pump, a bladder-type pressure chamber or booster pump, and possibly a large storage capacity cistern. These wells are purged and sampled with the same criteria as the on-post drinking water wells. Most offsite well locations require a signed access agreement and a minimum of 72-hours notification to the owner before accessing the site.

Because of the variability of system configurations, some ingenuity is required to assure that the pump is running and that a representative sample is being obtained. Most wells with pressure tanks can be operated by opening a faucet to create a pressure drop, thereby energizing the well pump. Cisterns and booster pumps often operate the well pump with some type of level switch (float or pressure), and therefore may require some manipulation to energize the pump. This can be accomplished either by draining water from the cistern to activate the switch, or manually engaging the switch at its location. Carrying an extra garden hose to direct purge water to an unobtrusive location is highly recommended. Public supply wells will be operated by the owners or their representatives only.

The sampler must ensure that the pump is running when the sample is actually being collected. CSSA has already retrofitted several off-post domestic wells with wellhead sampling ports. All samples must originate at or as near to the wellhead as possible prior to other system influences, which include pressure tanks, booster pumps, water softeners, and/or cisterns.

3.3 - Groundwater Sample Identification

To keep groundwater sampling information orderly and consistent, a naming convention was established as part of the DQOs. Consistent use of a standardized naming convention allows for better database management and ease of use. Nomenclature has been established to distinguish the following data types:

Table 11 lists valid sample identification codes for wells currently sampled, in addition to the new wells described in this work plan. All sampling locations have a geographic prefix followed by an alphanumeric designator. The following are examples of geographic coding:

Some offsite well locations are treated with one or more GAC units. The GAC units are designated as unit �A� or unit �B.� There is currently only one location with multiple GAC systems (RFR-10). Each GAC system consists of two canisters (#1 and #2) that are operated in series, with sampling ports following each canister. Occasionally, samples are collected after individual canisters to evaluate their condition and monitor for hydrocarbon breakthrough. Other infrequent samples include entry point (EP) samples collected at public supply wells, and water samples collected from a point-of-use faucet (tap) such as in a kitchen or washroom.

It is imperative that sampling conventions be applied consistently. For those occasions when sampling does not fit the valid sample identifications (e.g., a new GAC system), the field crew will contact the project or task manager to assign a new unique sample identifier.

Table 11 - Valid Groundwater Sample Identifications

3.4 - Groundwater Sampling Parameters

With the exception of the Westbay multi-port samplers, all wells are sampled on a quarterly basis for VOCs and metals constituents. Depending on the location and circumstance, all wells are sampled for either the AFCEE QAPP v3.0 list of VOC analytes (Full List VOCs), or the reduced list of analytes (Short List VOCs) of compounds detected at CSSA. Metals analysis requires the same nine parameters for each sampling event. In addition, new wells will be sampled for natural water quality parameters during the quarterly monitoring event following their installation. All groundwater samples will be analyzed for those parameters and methods listed in Table 12.

Currently, all off-post drinking water wells require the full analyte list for VOCs. CSSA is reviewing wells where a reduction of analytes to the short list for future events is appropriate to obtain approval from regulators. The project manager, or designee, will prepare a list of sampling parameters for each well prior to each quarterly event. No analyses for inorganics or natural water quality parameters are submitted for laboratory analyses from off-post sampling locations.

All newly-installed monitoring wells will be sampled for the Full List of VOCs, metals, and groundwater quality parameters during its inaugural sampling event. Subsequent monitoring events will utilize the approved Short List VOCs, if appropriate in conjunction with metals analyses. After the initial sampling event, natural water quality parameter sampling is no longer required.

Table 12 - Sampling Parameters from Groundwater Definitive Data Samples

[Next Section]