Monitoring Well Development

1. Monitoring Well Development Purpose Factors Affecting Well Development Time Interval Between Installation & Development Procedures, Criteria & Documentation Time Interval Between Development & Sampling Redevelopment

2. Well Development Purpose • Primary ground water sampling objective: representative sample • Formation damage due to monitoring well installation adversely affects natural conditions: • Decreased saturated zone yield (adjacent to the well) • Increased particulate matter and ground water turbidity • Various changes in ground water chemistry due to increased turbidity, aeration and oxidation, degassing, or addition of drilling fluids

3. Well Development Purpose • Stress the well and surrounding formation to • Create a graded filter pack and/or • Remove particulate matter and fluids from well installation

4. Well Development Purpose • Proper well development • Ensures good hydraulic communication between the well and surrounding formation • Minimizes head loss • Enhances well yield • Restores and stabilizes ground water chemistry • Facilitates the collection of lower-turbidity ground water samples

5. Well Development Purpose • Reduction and stability of turbidity by well development? • Helps to ensure collection of representative ground water samples • Helps to minimize silting of the well screened interval • Sample filtration is not a substitute for proper well development • Some monitoring wells are difficult to develop, e.g., wells installed in clay-rich sediments

6. Factors Affecting Well Development Activities • Property Hydrogeology • Drilling Method • Monitoring Well Design • Non-Aqueous Phase Liquids • Other Considerations

7. Factors Affecting Well Development Activities • Property Hydrogeology • Consolidated geologic materials (bedrock) • Unconsolidated geologic materials • Coarse-grained sediments (sand and gravel outwash) • Fine-grained sediments (clay- and silt-rich till or lacustrine deposits)

8. Factors Affecting Well Development Activities • Property Hydrogeology • Monitoring wells installed in unconsolidated, fine-grained sediments are the most challenging to develop • Low ground water yield • Difficult to create a graded filter pack • Generation of excessive silt and clay may damage (clog) filter pack

9. Factors Affecting Well Development Activities • Drilling Method • Affects the ability of the formation to produce representative ground water sample to some extent • Methods that cause greater formation damage: • Augers (shearing/smearing) • Rotary (shearing/smearing, injecting fluids or air) • Methods that cause lesser formation damage: • Direct-push • Rotosonic

10. Factors Affecting Well Development Activities • Monitoring Well Design • Monitoring wells can be difficult to develop • Small inside-diameter casing and screen, generally 2” or less • Installed in lower-yielding saturated zones • Screen • Length & placement depend on hydrogeology & regulatory program • Generally use 0.010” slot screens (finer-grained saturated zones) • Over-screening may cause turbidity problems • Filter pack • Gradation should be appropriate for screen slot-size (90% retained) • Thickness > 2” may require increased development effort

11. Factors Affecting Well Development Activities • Non-Aqueous Phase Liquids (LNAPL or DNAPL) • Check for the presence of NAPLs prior to well development • Were petroleum products or solvents stored or used at the property? • Inspect down-hole drilling equipment, cuttings and core samples • Screen the well water column with an interface probe or clear bailer

12. Factors Affecting Well Development Activities • Non-Aqueous Phase Liquids (LNAPL or DNAPL) • Ohio EPA recommends not developing monitoring wells that contain NAPL to avoid: • Distributing the NAPL throughout the filter pack and screened formation interval • Generating contaminated purge water • Increasing the difficulty of NAPL recover efforts

13. LNAPL & DNAPL

14. Factors Affecting Well Development Activities • Other Considerations • Turbidity-sensitive COCs (metals) • Regulatory requirements • Well accessibility • Development purge water • Personal protective equipment needed? • Temporary storage and transportation? • Disposal options?

15. Well Installation / Development Time Interval • Time interval between well installation and development? • Avoiding pulling uncured grout into the filter pack and screen during development • Generally a concern with grout slurries • If solid grouting materials are used (bentonite granules), less danger of contaminating the filter pack and screened interval

16. Well Installation / Development Time Interval • Ohio EPA recommends a 48-hour time interval, however… • A shorter time frame may be justified based on well construction, grout type, and conditions under which grout was installed

17. Well Development Procedures • Monitoring well development procedures alleviate formation damage and help improve ground water sample quality: • Surging the well screened interval • Removing purge water from well by bailing or pumping • Monitoring stabilization criteria (to evaluate the effectiveness of surging and/or removing purge water)

18. Well Development Procedures • “Well development” and “well purging” are not synonymous • Removal of purge water without surging does not adequately develop wells installed in coarse-grained sediments or bedrock • While purging without surging may be an appropriate approach for wells installed in silt or clay, development should always include measurement and evaluation of purge water stabilization criteria

19. Well Development Procedures • During surging, water is forced back and forth through the filter pack, and optimizes the hydraulic interconnection between the well and adjacent formation by • Removing fine sediment • Grading and stabilizing the filter pack and formation (if unconsolidated)

20. Well Development Procedures • Surging is generally not recommended for wells installed in silts or clays • Mobilization of fine sediment may clog filter pack • Surging will not necessarily improve the interconnection between the well and a silty or clayey formation

21. Surge Blocks

22. Surge Blocks

23. Surging

24. Surging

25. Well Development Criteria • Development is considered complete after the following criteria are met: • At least 3 times the standing water volume (well & filter pack) has been removed • Water quality parameters have stabilized over at least 3 successive well volumes (temp, pH, cond., DO, ORP) • Purge water: clear of sediments, turbidity < 10 NTUs • Sediment thickness in the well is < 10% of the screen length

26. Well Development Criteria • What if a turbidity of 10 NTUs or less cannot be achieved? Additional criteria: • Verify that the well has been properly constructed (If the purge water pH > 9, grout contamination may be present in the filter pack) • Consider using other well development methods • Turbidity measurements have stabilized within 10% over at least 3 successive well volumes

27. Well Development Criteria • Other criteria to consider: • Volume of fluids added during drilling and well installation (remove) • Is the well behaving as expected based on known hydrogeologic conditions (e.g., static water level, yield, slug test results)

28. Well Development Criteria Water Quality Parameters (ASTM D6771-02) Water Quality Parameter Stabilization Criteria • pH • Specific Conductance • Temperature • Turbidity • Oxidation-Reduction Potential • Dissolved Oxygen • +/- 0.2 S.U. • +/- 3% • +/- 0.5o C • +/- 10% when > 10 NTUs • +/- 20 mV • +/- 10% or +/- 0.2 mg/L, whichever is greater

29. Well Development Criteria • Duration of well development activities? Varies with: • Well diameter • Screen length and type (slot size) • Filter pack thickness • Water column height • Formation type • Development method

30. Well Development Criteria • Adequate development may take less than 2 hours or more than two days, and should always be based on attaining water quality stabilization criteria (duration by itself is not a criteria)

31. Well Development Methods • “Predevelopment” procedures • Recommended methods for monitoring wells: • Surging and Pumping • Inertial Lift Pump • Overpumping • Bailing • Method should be appropriate for the formation materials screened

32. Well Development Methods • Predevelopment: activities performed before or during well installation to facilitate well development • Purge turbid water generated during drilling from boring before installing well • Surge and purge after the screen and filter pack installed and before installing grout • Better filter pack installation, less time needed for subsequent development efforts

33. Well Development Methods • Surging and Pumping • Typically performed with an electric submersible or bladder pump with or without a surge block • No surge block? The pump must be of sufficient weight and diameter to effectively surge the well • Surge block may be attached to the pump or a separate assembly • Recommended for gravel, sand or bedrock wells • Surging is not recommended for silt or clay wells

34. Well Development Methods • Inertial Lift Pump • Consists of a ball valve connected to flexible tubing; surge block typically available as a separate attachment • Water is purged from the well by lifting and dropping the pump in a continuous up-and-down motion (manually or automatically)

35. Well Development Methods • Inertial Lift Pump • Advantages: inexpensive, portable, and easy to operate • Disadvantages: slow; surging may cause clogging of filter packs installed in finer formations • Recommended for wells installed in bedrock, gravel, sand, silt or clay (surging is not recommended for wells installed in silt or clay) • Recommended for direct-push wells with pre-packed screens

36. Inertial Lift Pump

37. Inertial Lift Pump

38. Inertial Lift Pump

39. Well Development Methods • Overpumping • Process of repeatedly pumping a well at a relatively high rate to induce quick drawdown and then allowing the well to recover • Performed with an electric submersible pump (larger-diameter wells) or a peristaltic pump (smaller-diameter, shallow wells)

40. Well Development Methods • Overpumping • Removes fine sediments from the screen and filter pack but does not grade the filter pack (unidirectional flow, no surging) • Unidirectional flow may reduce filter pack K due to bridging • Less effective than surging and pumping or an inertial lift pump for well installed in bedrock, gravel or sand • Acceptable method for well installed in silt or clay

41. Well Development Methods • Bailing • Lowering and lifting a bailer through a well water column will surge the filter pack • Most effective with a steel to stainless steel bailer (need weight) • May be able to fit bailer with flange to serve as a surge block • Effective at removing sediment from bottom of well screen

42. Well Development Methods • Bailing • Slow and labor intensive • Always causes some surging action (may not want to surge screen every time you remove water) • Less effective than surging and pumping or inertial lift pumps for wells installed in bedrock, gravel or sand • For wells installed in silt or clay, inertial lift pumps or overpumping are likely to produce better results

43. Well Development Methods • The following methods are discussed in the TGM, but are more appropriate for water supply well development than monitoring well development: • Backwashing – allow water that has been purged from the well to flow back through the pump intake and create a surging effect • Air-Lift Pumping and Air Surging – well development by air injection

44. Well Development Documentation • Well Development Field Form • Important documentation demonstrating that the well is ready to produce representative ground water samples • Also useful information for future reference, e.g., for selecting sampling methods or evaluating the need for redevelopment

45. Well Development Documentation • Well Development Field Form • Information recorded typically includes • Well construction details and development methods used • Water level data (at least initial and final water levels) • Volume purged and estimated purge rate • Stabilization parameter measurements and observations (e.g., purge water clarity, sediment removed, odor, etc.)

46. Well Development Documentation

47. Well Development / Sampling Time Interval • Time interval between well development and sampling? Depends on the following factors: • Hydrogeologic conditions • Drilling methodology and well construction • Well development methodology • Regulatory program and data quality objectives

48. Well Development / Sampling Time Interval • Prior to sampling a newly developed (or redeveloped well), need to consider if the well has attained • Physical equilibrium (return to static water level conditions) • Chemical equilibrium (may be difficult to determine)

49. Well Development / Sampling Time Interval • Ohio EPA recommends the following post-development time intervals prior to ground water sample collection: • 24 hours for shallow (< 25 feet bgs), small diameter (< 2-inch ID) monitoring wells installed using direct-push methods • 72 hours for deeper (25 to 50 feet bgs) direct-push monitoring wells or larger diameter (2 to 4-inch ID) monitoring wells installed using augers or rotary drilling methods • One week (7 days) for deep (> 50 feet bgs) monitoring wells installed in unconsolidated sediments or bedrock monitoring wells

50. Well Development / Sampling Time Interval • Wells installed in silt, clay or shale may require a longer post-development stabilization period than wells installed in gravel, sand or more permeable bedrock types