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Richard Lloyd of Tesla, who previously published a widely-reported estimate of 2 km for the UMLACA/Volcano's range, has recently made another interesting discovery.
First, some background: Three days after the Ghouta attack, the Syrian news agency reported that Syrian soldiers who entered Jobar discovered an underground chemical weapons store, and that some of them suffered from "suffocation". This was quickly dismissed as a desperate attempt to divert attention, and the equipment was estimated to be related to explosives production or to protection from a chemical attack. This blog too did not find that report useful.
However, Mr. Lloyd managed to identify in a video of the location two items which perfectly match the sarin IEDs used against Syrian soldiers in Jobar, as reported in the final UN report. This attack was of special interest as it was the only one where the UN detected sarin in a soldier's blood sample (despite a one month delay in sampling).
See here the full report.
Update: An anonymous contributor below noted that the soldiers were attacked by the IEDs just 250m from the likely launch location of the August 21st attack. Besides further strengthening the connection between the two attacks, it provides another important indication: Since the Syrian army has reported being attacked while advancing into this area on August 24th, it is likely that the area (and rocket launch location) was under opposition control on August 21st.
Update: The UN reported that two cylinders seized in August by the Syrian Army tested positive for sarin. It is reasonable to assume this report relates to the IEDs found in Jobar.
Conclusion: The underground store discovered by the Syrian Army in Jobar was indeed a chemical weapons store.