I'll have to answer in pieces to give the best type of a "total" answer..
1. One of the first rules: Don't touch the dam.
This is strictly regulated: FERC to DWR example quote: "3. You are reminded that you may not proceed with collection of shear wave velocity data until we authorize your proposed plan for drilling."
If DWR wants to emplace sensors anywhere in the dam embankment (especially the core) it is a significant step that has to be planned, coordinated, and mostly "explained why" in communications and authorization from FERC.
This is because if you do something stupid you can introduce a leakage path that may lead to a serious problem. I'm not saying the engineers are not intelligent, it is just that there is a very high safety protocol that has to be maintained in dam operations. ex: Any sensors into the core or other zones have to be carefully emplaced to have "filter stops" to prevent an introduction of a "guided" leakage path.
2. Who (engineer or lowly manager) wants to trigger an intense "what's going on, do you have a problem?" response from FERC if someone wants to figure out an unexplained anomaly (such as Greenage). Unless there is a collective will in "belief" that there is a real puzzle that needs to be investigated, they likely will take "heat" from upper management, directors, and the Board in triggering a FERC intensive inquiry. You can degrade your career with triggering an investigation where the starting point is "I really don't know" (re: the anomaly). In a Pro-active High Reliability Systems World -> A boldness should be encouraged by upper management to support someone who actively wants to identify problems proactively, even if it's a minor atypical anomaly in a typical dam performance expectation.
3. DSSMRs (Dam Safety and Surveillance Monitoring Reports) are the life blood of critical independently performed inspections, usually by outside contractor experts, to meet the very extensive FERC DSSMR report requirements & standards. FERC's required DSSMRs of full inspections & reviews are done less frequently than the annual CA Division of Safety of Dams (DSOD) Inspections. Look at it as a hierarchy of safety inspections.
4. Below is a 2012 DSSMR findings & response document (GEI Consultants [DSSMR inspectors for this FERC report], DWR as responders to the findings of DSSMR items, and FERC as the agency that this report & actions are filed with). There are key points in this DSSMR report that shed light on the Green Area anomaly question. (a) GEI gave a glowing report on the performance of the main dam (i.e. the Green Area was not mentioned). (b) Monument surveys were mentioned, but no information was stated as to how many of the 100 dam surface monuments are part of the regular survey. (there was mention of "threshold levels" in terms of "methods and actions" on any data - but this too was not fully detailed). (c) ONLY 3 of the original 56 Piezometers still work at the dam. So the dam mostly does not have the ability to determine reference internal water levels (phreatic line) within the dam. Thus, no mention of the Green Area, no mention of settlement issues (mainly a "glowing" report). This could very likely discourage anyone from initiating or speaking out in concerns of this Greening anomaly.
5. Somewhere buried in my mounds of documents - I ran across communications where FERC is asking DWR to determine the Phreatic line within the dam. (I'll need to keep digging to find it again). This FERC request may be linked to the fact that the dam has only 3 working Piezometers left.
6. Because of (1)(2)(3)(4) there becomes a potential significant hurdle in someone triggering an "investigation" into the atypical Greening. The "system" says that there is nothing of issue (DSSMR report), other than the DSOD Inspection reports continually repeating, "we should watch this grass". The net effect of the redundant safety procedures between FERC, DSSMR's, Independent Contractors desiring continuing business, DSOD, DWR's sensitivity to meeting "good standing with FERC" for re-licensing - creates a net environment that could greatly discourage any Green Spot "alarm" raising by engineers or managers. Worse, this Green Spot defies the typical known world of phreatic line behavior if the complexities of the prior postings - i.e. if not forensically researched with a high grade of expertise (history, stages, seasonal consolidation in construction, differential settlement sharp slope transition, phreatic line anomalies, clogged drain zone sections, seepage silt/soil "shelf forming", etc).
Original Oroville main dam sensors & instrumentation - 56 hydraulic piezometers of which only 3 function today. 100 Survey Monuments on the outside layer of the dam to measure settlement.
Glowing DSSMR report - no mention of Green Area - DWR notes only 3 piezometers work (out of the original 56) - no info on number of survey monuments tracked AND the "threshold" level to "action"
