low-flow groundwater sampling - groundwater monitoring equipment

Low-Flow Groundwater SamplingUsing In-Situ ® Inc. TROLL® 9500 Water Quality Instrument and Flow-Sense SoftwareJune 2008

OverviewThis document provides a description of low-flow sampling techniques, a summary of federal low-flow guidance documents, and outlines the operation of a TROLL 9500 instrument using Flow-Sense software.

What is low-flow groundwater sampling?Low-flow groundwater sampling is an increasingly accepted method of collecting groundwater samples with a strict set of guidelines to ensure consistent sample representation and quality.

Groundwater is extracted from the well at a very low rate (<500 mL/min) so that drawdown of the water level is minimized. Water samples from the more hydrogeologically conductive areas of the aquifer around the well screen are monitored with water quality instruments for stability to indicate the change from stagnant well water to representative formation water. After the water quality parameters stabilize, a sample of formation water can be taken with a minimal amount of geochemical disruption to the sample.

Why use low-flow groundwater sampling methods and a TROLL 9500 instrument?

Meet sampling plan or scope of work requirements.•Improve sample quality.•Improve sample representativeness.•Reduce wastewater created by large volumes of •sample purging.Reduce field time by setting up sampling events •with Flow-Sense software in the office.Reduce field time with automated data collection •and stabilization of water quality parameters.Eliminate errors created by manual field recording •and manual data transcription.Create more detailed sampling summaries, records, •and reports.Save time and money with quick and easy digital •report formats.Produce professional reports that can be inserted •directly into your project deliverables.Provide a complete calibration history of the •sampling event to ensure sample validation.Create a digital sampling record that can be easily •replicated by other technicians.Save time and money by digitally organizing •sampling events.

Using In-Situ ® Inc. TROLL® 9500 Water Quality Instrument and Flow-Sense Software

Low-flow federal guidance summaryThe following points summarize federal guidelines that dictate the requirements of a low-flow groundwater sampling event.

SummaryLow-flow1. refers to the velocity that is imparted during pumping to the formation pore water adjacent to the well screen, not necessarily the flow rate of water discharged by the pump.Low-flow purging2. can be used on any well capable of being pumped at a constant rate of 1.0 L/min or less without continual drawdown of the water level in the well.A typical 3. flow rate from a pump during low-flow purging is approximately 0.1 to 0.5 L/min.Continuous discharge 4. pumps with variable flow rates are preferred (Grundfos, Fultz, Nomad, Keck, Proactive). Cyclic discharge is also acceptable (bladder pumps). Dedicated pumps are preferred. Grab sampling devices such as bailers, Kemmerer samplers, and inertial-lift devices cannot be used. Peristaltic pumps are discouraged because of loss of VOCs, degassing, and pH and oxidation reduction potential (ORP) changes.You must have a 5. water level indicator for initial readings and drawdown monitoring with accuracy (±0.01 ft. /3 mm).Flow cells6. are preferred for monitoring, especially for dissolved oxygen (DO) and ORP readings, which will be altered if exposed to atmosphere.Calibration 7. of multi-parameter equipment is required once a day, with periodic checks.The pump should be placed at the mid-point of the 8. submerged well screen.Drawdown9. in any well should not exceed 0.1 m/0.33 ft./4 in. or 25% of the distance from the top of the well screen to the pump intake.Stabilization parameters:10.

pH: ±0.2 pH unitsa. Conductivity: ±3% of readingb. DO: ±10% of reading or 0.2 mg/L, whichever is c. greaterORP: ±20 mVd. Turbidity: ±10% of the prior reading or ±1.0 e. NTU, whichever is greater (not always required)

Flow cell sample rate 11. measurement frequency should be based on the time required to completely evacuate one volume of the flow cell, associated tubing and pump volume.

Stabilization12. is reached when three consecutive readings meet the stabilization criterion listed above when sampled at the established rate. Field reporting requirements:13.

Equipment calibration reporta. Site specific data (project name, site, well b. number, well depth, well diameter, screen length, casing type, pump type, tubing type)Initial water levelc. Pump placement/type (relative to well screen d. and static water level)Final pumping ratee. Final stabilized drawdownf. Water quality measurements (date, time, g. temperature, pH, ORP, conductivity, DO, turbidity)

Required field equipmentGraduated cylinder•Overflow 5-gallon buckets (2)•Pump and tubing•Sample jars•TROLL 9500 low-flow sampling system•Visqueen and other PPE•Water level indicator•


TROLL 9500 instrument connection and calibrationConnect to the TROLL 9500. Open Win-Situ 4. 1. The Connection Wizard will start. Choose a 2. Direct connection to One device.

Choose3. Com 1 for a serial port connection.


Choose a Baud Rate of 4. 19200.

Choose a name for your connection or use the default (5. COM1-19200).


The software should automatically connect to the device and list available parameters.6.

Check your battery capacity and confirm that at least 50% of battery capacity remains. If you want to change 7. batteries, insert two new D cell batteries now.Synchronize the TROLL 9500 clock with the clock on your computer. Make sure the computer clock is accurate. 8. Click Edit.

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Select 9. Clock. Click Next >.

Select 10. Synchronize With Computer Clock. Click Finish.


To calibrate, highlight 11. Parameters. Click Quick Cal.

Choose the parameters to calibrate. Click 12. Next >.


Fill the Cal Cup with Quick Cal solution. Click 13. Run. Wait for pH, conductivity, and DO to automatically stabilize. (It may take a few minutes.)

Choose 14. Use Vented Cable for your barometric channel. Click OK.


Take the TROLL 9500 instrument and invert it so that the sensors point up. Unscrew the black end cap above 15. the sensors. Empty out enough Quick Cal solution so that the DO sensor membrane is exposed to air. Replace the black cap, but leave the hole in the threads open to the atmosphere. Click Run.

When the calibration is complete, the software will automatically generate digital calibration reports and save 16. them on your hard drive. Click Yes to view them.


The calibration report is generated with the following data:17.

The TROLL 9500 instrument will reset. The Win-Situ® 4 dashboard will reappear. Highlight the 18. Flow-Sense Wizard. Click Start.

9500


Click 19. Verify Units to make sure you are collecting data in the units desired for your project and reporting requirements. Highlight each parameter and select the units you want. Click OK.

The Flow-Sense software will open.20.


Collect all the well sampling logs, sheets and information from previous sampling events. Enter all the 21. sampling project information in the Flow-Sense Wizard sequence. First enter the project and site information. Click Next >.

Enter well information. Click 22. Next >.


Enter pump information. Click 23. Next >.

Enter pumping rate and drawdown information. 24. Click Next>.


Select channels and enter the stabilization criteria. This information should be in your sampling plan, but 25. are listed below for reference. You can enter the American Society for Testing and Materials (ASTM) or USEPA ranges here. To use a percentage instead of a range, enter a range and a percentage, and the program will default to the percentage. Click on Notes to see or record any information on the sampling event. Turbidity is not listed in this example, but the turbidity stabilization range should be ±1.0 NTU or 10%. Do not click Start until the flow and drawdown values have stabilized. When the values are stable, click Start.Click 26. < Back at any time to change your settings.


After the stabilization sequence begins, the information shown in the following screens is being collected. The 27. left column records the latest water quality parameter reading. The right column lists the stabilization targets. The center column lists the current value.The software needs at least three water quality parameter readings to run a 3-point running average and to 28. calculate the stabilization values. For the sample set (A, B, C), [(Max-Min)/A] X 100 = Running Average.This screen also includes the start time of the sampling event, the number of water quality readings collected 29. so far, the total elapsed sampling time, and time left until the next readings are recorded.When all the values in the center column are less than the corresponding values in the right column, 30. stabilization has occurred. Click Accept and collect the groundwater sample. Click Graph to present the stabilization readings graphically. The graph depicts movement away from complete stabilization.


After accepting the stabilization values, a Low Flow Notes window will appear. Enter any extra information 31. about the sampling event here.

The 32. Save As screen will appear, and the sampling event will be saved automatically (by project, site, well ID, and date). Rename the file as desired.


The data file is automatically logged under the Flow-Sense data folder on the Win-Situ® 4 software, in 33. alphabetical or chronological order.

To print the groundwater data collection record for a specific well and date, simply highlight the appropriate 34. sampling event. Click File, Export To Excel.The data is converted into Excel®, but In-Situ® Inc. has developed a formatted template that will organize all 35. your data into an integrated data sheet. Just right click on the data spreadsheet tab in the lower left corner of the screen and click Insert.


A window will that displays available Excel® templates. Double-click the InSituLowFlow template to create 36. the data sheet. You may have to locate the file “InSituLowFlow.xlt” in the “templates” directory located in the Win-Situ® 4 software installation directory.


A formatted data sheet is created. It can be pasted or loaded into any sampling report and customized with 37. your company’s logo.

For more information contact In-Situ Inc.221 East Lincoln Avenue Fort Collins, CO 80524 1-800-446-7488 (toll-free in U.S. & Canada 1-970-498-1500 (international & domestic) Internet: www.in-situ.comIn-Situ, the In-Situ logo, ® and ™ are trademarks or registered trademarks of In-Situ Inc. © 2008, In-Situ Inc., Fort Collins, CO USA. Teflon is a registered trademark of E.I. du Pont de Nemours and Company USA and other countries. Excel is a registered trademark of Microsoft Corporation.


Open the Flow-Sense data folder and highlight the desired well to sample the well again on another date. All 38. the site data entered for this sampling event will be available for future use. Click Start From Template.

ReferencesASTM Guideline D6771-02. July 2002. 1. Standard Practice for Low-Flow Purging and Sampling for Wells and Devices Used for Ground-Water Quality Investigations.Puls, R. W. and M.J. Barcelona. April 1996.2. Low-Flow (Minimal Drawdown) Ground-Water Sampling Procedures. U.S. Environmental Protection Agency, Office of Research and Development. Publication: EPA/540/S-95/504. http://www.epa.gov/ahaazvuc/download/issue/lwflw2a.pdfU.S. Environmental Protection Agency, Region 1. 30 July 1996. 3. Low Stress (low flow) Purging and Sampling Procedure for the Collection of Ground Water Samples from Monitoring Wells. SOP #: GW 0001. http://www.epa.gov/region1/measure/well/lowflow8.pdfYeskis, D. and B. Zavala. May 2002. 4. Ground-Water Sampling Guidelines for Superfund and RCRA Project Managers. U.S. Environmental Protection Agency, Office of Solid Waste and Emergency Response. Publication: EPA 542-S-02-001. http://www.epa.gov/tio/tsp/download/gw_sampling_guide.pdf

These guidelines are federal and regional suggestions. Review with your local regulator.

http://www.epa.gov/ahaazvuc/download/issue/lwflw2a.pdf

http://www.epa.gov/region1/measure/well/lowflow8.pdf

http://www.epa.gov/region1/measure/well/lowflow8.pdf

http://www.epa.gov/tio/tsp/download/gw_sampling_guide.pdf

low-flow groundwater sampling - groundwater monitoring equipment

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