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Wet Area - DWR-FERC correspondence - DWR asking to relocate drill hole to facilitate DWR's to help figure out Green Wet Area

DWR is seeking to determine the cause of the Green - Wet Spot area on the left midslope area of the dam. Here is a snip from 2016 DWR's response to FERC in asking to move the FERC requested toe monitoring drill site where DWR is asking if it could be instead drilled near the Wet Spot area. DWR notes that this hillside should have "severely fractured weathered rock". This evidence points to DWR suspecting penetration into the left embankment from percolating ground table water - thus causing the Wet Area. This Wet Area still needs a horizontal component to distribute the seepage - that is where the "layer 2 and layer 3" construction history may indicate a residual clay "fines" mixed in with the Zone 3 embankment layer compaction (forming a "flow shelf").

2016 FERC doc - DWR wants to relocate (from FERC request) a proposed drill hole to 670ft Left Bank near Green Wet Area to help understand the cause of the Seepage.

Map from DWR to FERC on relocation request for piezometer sensor based drill/test/monitoring hole.

More Wet Area & Greenage Discussion - Recent DWR photo shows large plant growth Apr 13, 2017

Oroville's main Earth Fill Dam has a 20 ft wide vertical "Drain Zone" comprised of gravels, cobbles, and boulders that extends the full width of the Dam to drain any water seepage that penetrates through the clay based center. Seepage is intended, by design, to migrate down this vertical drain zone to a horizontal collection drain zone to the toe of the dam (see drainage zone post link for dam schematic design).

The Dam & thus the "Drain Zone" on this far side of the Dam has a natural "shelf" (horizontal type of run). Thus, any "seepage" into the Drain Zone will flow more sideways than vertical on this natural boundary abutment "shelf". IF the "Drain Zone" is not capturing the full seepage in this "sideways run", an amount of the "seepage" could "escape" and produce the "Green Wet Area (vegetation)". New image from DWR shows how large the plant growth has become (keep in mind the distance away from the camera - the vegetation size is larger in comparison due to its location mid-slope of the dam - camera shot at/near the top). Note how focused the greening of the Wet Area is verses the absence of lush growth below and just above. This gets back to a horizontal flow mechanism assumed related to the construction phases of compacting layer 2 top to starting emplacement of layer 3 (bottom).

Another Clue to this puzzle is that greening is identifiable "upslope" and further up the seam of the Dam to Natural Ground boundary further up the abutment. The Abutment may be contributing to this flow (east to west)- OR - revealing that the flow extends to the abutment (west to east).

History of images & discussion posts on "Long Standing Wet Area":

Wet Area - DWR-FERC correspondence - DWR asking to relocate drill hole to facilitate DWR's to help figure out Green Wet Area

Oroville Earth Fill Dam Design - Drainage Zone (gravel cobble boulders) to collect seepage & Wet Area location

Water Seepage Discussion - Dark discoloration markings on Finished Dam + two "downslope" large wet areas in early operation

Water Seepage Issue - Answer from "layered" construction of earthen dam? - (problematic "Wet Area" aligns at seam of Layer 2 & 3)

More Info: Mid-slope Main Dam Erosion channels from unaddressed "Weepage" inside of dam

2014/2015 Dam Inspection Reports: "Long Standing..Wet Area" - midslope dam backside seepage (being ignored?)

Apr 13 - Large Vegetation Growth in Wet Area - little to no growth below and just above this zone. Inferred waterflow notable in comparison to greenage near DWR exploratory well (DWR is seeking to get clues to the Wet Area via water data/sensors to understand this problem).

Matching Greening at elevation locations in 2015 to this Apr 13 image above. Upslope Greening along the Dam to the Earth Abutment boundary infers seepage flow at higher elevations. Whether this flow is supplemental to the Wet Area OR if it is another clue to the penetration of non captured seepage ??

Heated Discussion - "Leak" in Dam - Public meeting with DWR - April 27

The DWR sponsored "information Q&A" meeting became heated when the "Leak" in the dam was brought up. Apparently, there was a professional moderator handling the Q&A with the packed hall of concerned residents. Here is a transcript of a particularly heated interchange with a resident, a male "chief DWR engineer", and the moderator.

= = = April 27 2017 DWR informational meeting interchange responding to a question from a resident speaking of the "green" wet area on the left side of the dam & asking DWR about this "Leak":

Resident: "There is a leak above the Hyatt power plant...its been there for years…grass doesn't grow unless you've got water…when the lake level goes down...you can see the grass die..because the water is not going through…you got water...you pressurize the dam to the most its been pressurized in the history of that dam…and now...with the green patches... where the grass is growing..were saying that leak..nobody wants to talk about it at your office?...I mean… there's water coming through…let the water out before it all comes out..on us."

DWR Chief Engineer: "The um, the, the dam was built..the regulators know about it….we..we inspect it...when we monitor it...it is not going through the dam…"

Resident: "Sure and you inspected and you monitored that spillway too…"..[crosstalk]

2nd resident, woman: "...they've had the same problem at another dam…and it failed.."

Moderator: "So, so I really need to… to ask people who are… who've asked to speak.. I..I just want to make sure we get your comments sir..so…"

Resident: "Well I hadn't got an answer…[inaudible]"

Moderator: "Well….I think what...what you're hearing.."

Resident: "About the leak…"

Moderator: "Well, what I understand that, what, you're hearing from the chief engineer, is, that.. it.. but it doesn't.. you..you..let's just hear that again, okay ..:"

DWR Chief Engineer: "That…that…leak…its…its a natural spring that has been documented...for decades….and we are measuring it on an annual basis…and… [crosstalk - crowd noise]

Moderator: Shhh…ok…lets…lets...let him answer the question.. okay?…

DWR Chief Engineer: "Do you have anything to add on that?"

end clip - of interchange.

My Discussion/commentary:

= = = I've never seen a "natural spring" flow uphill. The horizontal bench of the "wet area" green vegetation actually increases in elevation the further it is from the left abutment. The assumption is that a "natural spring" does not exist from "inside" of an earthen dam. IF there were to be a "spring" it would have to originate from upslope on the left abutment then would have to defy gravity and flow up in elevation". So why has DWR drilled a "test hole" near the green wet area at the left abutment in 2016 (DWR asking FERC) as DWR wants to figure out what is causing this seepage?

= = = So? How's the decades of Monitoring & measuring been going? Here are the California Division of Safety of Dams (DSOD) Inspection reports on "their monitoring" -

CA Division of Safety of Dams Inspection Report 2014 - Recommendation to implement a method to "monitor the mid-slope seepage" on the backside mid-slope of Oroville's earthen dam

CA Division of Safety of Dams Inspection Report 2015 - Stronger Recommendation to "investigate" wet area "to ensure the long term stability of the slope"

2016 FERC doc - DWR wants to relocate (from FERC request) a proposed drill hole to 670ft Left Bank near Green Wet Area to help understand the cause of the Seepage.