1. Is this Seepage A Problem?
With your host
Adam Powers

3. Round 1

4. Is this Seepage a Problem?
Question 1: Mike M.
This Deer Lodge County dam has ponding water and numerous sand boils at the toe of the dam. If you look closely, sand is actively moving (boiling).
Is this Seepage a Problem?
HINT:
The dam is not very high

5. #1 a.
Sand boils often signify high uplift pressures in the foundation. They also can be a sign that internal erosion of the foundation is occurring, a potentially serious problem.

6. #1 b last
However, this seepage is not a serious problem for this Deer Lodge County dam
The “boiling” sands appear to be moving only at the surface. Since the dam is not that high, there is not enough driving head from the reservoir to move the finer foundation soils from the foundation and cause backward erosion to initiate.
As a precaution, a sand filter was installed, and piezometers are regularly measured (with no warning signs).

7. Is this Seepage a Problem?
Question 2: Brent Z.
This Powell County Dam has an over-steepened downstream slope, with ponding water and water loving vegetation at the toe. However, the embankment is mostly dry.
Is this Seepage a Problem?
HINT:
The foundation is glacial till, interbedded clay and silt

8. Yes, this Seepage is a Problem.
A year after construction of a stability berm on the downstream face of the dam, a “blow out” occurred at the edge of the berm. Material was rapidly eroding back towards the dam. Without intervention, failure was imminent.
Rapid response and nearby stock piled materials saved the day.

9. There are a couple of theories on the cause of the blowout:
Construction of the new berm concentrated foundation seepage at the edge of the berm
The location of the blow out was reported to be where top soil was stockpiled and later removed.

10. #2 c. last
Many older dams were built without foundation preparation. As a result, they often have a layer of organic clay that acts like a cap that can pressurize a foundation. Even a slight penetration of this cap can cause a blow out and backward erosion.
Organic Clay
Sandy Gravel
Always be cautious when doing any kind of construction activity at the toe of the dam.

11. Is this seepage a problem? Should we be concerned about a blowout?
Question 3: Ben F.
This Teton County Dam has ponding water, green grass and cattails at the toe. Piezometers show water levels above ground surface when the reservoir is full. However the embankment is dry.
Is this seepage a problem?
Should we be concerned about a blowout?
HINT:
The water bearing zone in the foundation is believed to be competent bedrock

12. Internal Erosion Failure Components
For internal erosion and blowout that leads to dam failure there are several factors that must be present:
Internal Erosion Failure Components
Reservoir Loading:
Flaw Exists:
Continuation:
Progression:
Unsuccessful detection and Intervention
Dam Breaches
Reservoir at or above threshold level
Erosion initiates
Unfiltered Exit exists
Continuous stable roof, evidence of worsening conditions

13. Reservoir at or above threshold level
Erosion initiates (flaw in embankment)
Unfiltered exit exists (nothing to stop particle movement)
Continuous stable roof

14. #3 c. last
It is uncertain if the seepage is a problem, fortunately, not all of the internal erosion components are present
Internal Erosion Failure Components 
Piezometers 5’ above ground surface at full pool (High foundation pressure)
Reservoir Loading:
Flaw Exists:
Continuation:
Progression
Unsuccessful detection and Intervention
Dam Breaches x
None that are obvious 
Unfiltered exit present – no filters at toe ?
Unsure if water bearing layer would support continuous “roof”. No evidence of worsening conditions. x
Careful monitoring underway to detect developing problems

15. However, the downstream face looks to be in good condition.
Question 4: Tim K.
Q #4
This photo shows evidence of erosion near the upstream gate of this Choteau county dam.
However, the downstream face looks to be in good condition.
Is this caused by seepage and is this seepage a problem?

16. Yes, this Seepage was a Problem.
Seepage that is moving soil into deteriorated outlets can go undetected for years. Failure often occurs suddenly with no warning

17. #4 b last
A new tool is in development to help dam owners rehabilitate their outlet works before failure occurs

18. STATE
CONSULTANTS 2 2

19. Round 2

20. Is this Seepage a Problem?
Question 5: Ben F.
A sinkhole suddenly appeared on the downstream face of this Granite County dam, along with cloudy water from a toe drain
Is this Seepage a Problem?

21. Yes, this Seepage was a Problem BUT…… Not as bad as it could have been
When soil above or around a backward erosion pipe is unable to “hold a roof” the following occurs:
• backward erosion pipes form but soon collapse, resulting in general movement of the soil above.
• If the collapse is upward, it can lead to the development of a near‐vertical cavity (stope) in
the embankment
Yes, this Seepage was a Problem BUT……
Not as bad as it could have been

22. #5 b last
If the embankment soils would have been able to “hold a roof”, the backward erosion could have made it back to the reservoir and failed the dam
So, in general sinkholes on the upstream face are more of a concern than sinkholes on the downstream face.

23. Is this seepage that caused these sinkholes a problem?
Question 6: Tim K.
During a low pool inspection of this northern Lewis and Clark County dam, sinkholes were discovered on the upstream face
Is this seepage that caused these sinkholes a problem?
HINT:
The sinkholes were below normal pool level, on the right abutment

24. #6 a.
Yes and No…..
Upstream face sinkholes are always a serious concern, however these sinkholes are unique…….
The glacial foundation of this dam is full of large boulders. Further investigation revealed that the sinkholes extend vertical deep below the dam

25. #6 b. last
The sinkholes were patched to prevent migration of soils into the foundation.
However, over the past 15 years, sinkholes have continually reappeared in the reservoir pool.
So YES, this seepage is a problem, as migration of soils is undesirable, but NO, these sinkholes are not believed to be putting the dam at risk.
Frequent inspections and seepage monitoring is ongoing at this high hazard dam.

26. Is this Seepage a Problem?
Question 7: Mike M.
A seep on the left groin of this Granite county dam was getting progressively worse, with measurable sediment accumulation
Is this Seepage a Problem?
HINT:
The sediment was determined to be coming from infilling in left abutment bedrock

27. #7a.
Yes, this Seepage was a Problem - No doubt, the dam was well on its way to an internal erosion piping failure.

28.     x x Back to our internal erosion checklist:
Internal Erosion Failure Components 
Occurs when reservoir above certain level
Reservoir Loading:
Flaw Exists:
Continuation:
Progression
Unsuccessful detection and Intervention
Dam Breaches
Abutment / embankment contact may have been improperly prepared during construction  
Unfiltered exit present 
Seepage and sediment increasing x
Careful monitoring and dye tests were key to figuring out the issue and designing a repair x

29. Successful in using “Upstream Control” (grouting).
Seepage and Internal Erosion were completely stopped

30. Issues – Downstream Control
Decided against using “Downstream Control” (Seepage Berm)
#7d (last)
Issues – Downstream Control
High flows (150 cfs) –
Difficult to filter out fines, sand size filter needed
Sand does not have sufficient permeability to handle large flows
Sediment will clog filter – main issue
Internal erosion far advanced, concentrated flow
Potential to make problem migrate
Uncertainty with how far to go with blanket/drainage system, would need to extend outlet works at high cost
Berm not needed for stability, no upward gradients

31. This Madison County Dam has a history of reservoir sinkholes
Question 8: Brent Z.
This Madison County Dam has a history of reservoir sinkholes
The toe drain pipe has some sediment
Some odd sand boils appear below the dam
Is this Seepage a Problem?

32. The downstream face of the embankment is dry
No, the seepage is not a problem, as long as the reservoir stays relatively low (the reservoir seeps and does not stay full for long). Should the reservoir stay at full pool for an extended period of time, there are some concerns.
#8a.
It is suspected that the seepage moves deep into the foundation from the reservoir.
The downstream face of the embankment is dry
The sand boils are well below the toe of the dam

33. Regarding the sediment in the toe drains:
#8b.
Regarding the sediment in the toe drains:
Back in 1959, during a grouting attempt to stop seepage , the State used dynamite in the grout holes to increase grout intake. This may have damaged the embankment/toe drain, so the sediment may not be reflective of internal erosion.
State does not get points because of the use of dynamite, regardless of how good their answer is.

34. #8c. last
DH3 is a key piezometer to measure whenever reservoir gets to full pool. Any change in measured water levels in DH3 is a big warning sign that a problem is developing in the dam.
Early grouting efforts may have damaged the dam, problems will likely only show up when dam is at full pool.

35. STATE
CONSULTANTS 3 4

36. Bonus Round
Audience gets to choose contestant

37. Is the Seepage at this Dam a Problem?
Question 9: Audience Choose Contestant
During an inspection, white sediment was found at the toe of this Judith Basin County dam.
Is the Seepage at this Dam a Problem?

38. #9 a.
Early investigations indicated high foundation pressure exist (piezometers at toe showed above ground water levels) and geology could support internal erosion

39. High pressure in foundation as evidenced by sand boils (see video)

40.    ? x To our internal erosion checklist:
Internal Erosion Failure Components
Internal Erosion Failure Components 
When reservoir exceeds a certain, high uplift pressures exist
Reservoir Loading:
Flaw Exists:
Continuation:
Progression
Unsuccessful detection and Intervention
Dam Breaches 
Cracks through confining layer, possibly from improperly abandoned boreholes 
Unfiltered exit present, no filter at toe ?
Bedrock in foundation may limit progression of internal erosion x
Detection through regular inspection

41. Intervention through construction of seepage berm
#9 d
Intervention through construction of seepage berm

42. STATE
CONSULTANTS 3 5
If audience chooses consultant to answer question

43. STATE
CONSULTANTS 4 4
If audience chooses state to answer question