Date: 201908
Local time of day: 0001-0600
Location: ZZZ.Airport, US
Aircraft: A320
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Taxi
Airspace: Class B ZZZ
ATC / advisory: Ground ZZZ
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine; Flight Crew Instrument
Human factors: Communication Breakdown; Situational Awareness
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Hazardous Material Violation
Detector: Person Ground Personnel; Person Dispatch
When detected: Taxi
Result: Flight Crew Became Reoriented; Flight Crew Returned To Gate; General Flight Cancelled / Delayed; General Maintenance Action; General Work Refused
Contributing factors: Human Factors; Manuals
Primary problem: Human Factors

Narrative: After beginning our taxi last night in ZZZ; we were immediately informed by ZZZ Ground that the Company needed us to return to the gate. The First Officer checked with ZZZ Ops who informed us that 2 shipments of dangerous goods were placed next to each other and needed to be moved. I was surprised because we hadn't been informed of any dangerous goods on the aircraft.After returning to the gate; I inquired about the dangerous goods and was told by ZZZ Ops that we had dry ice and 44 boxes with 800+ pounds of lithium-ion batteries in our cargo bay. I inquired further with ZZZ Ops about the 800+ pounds of lithium-ion batteries and was told that we weren't informed about dangerous goods because it was an 'excepted quantity.' I then phoned Dispatch; who ultimately conferenced with Load Planning and the [Chief Pilot] to learn the rules about lithium-ion batteries as cargo in the plane; and specifically if 800+ pounds was an 'excepted quantity.' They attempted twice to get an answer from the Dangerous Goods Hot-line; but first got no answer and then got an agent who was unable to look up any information about our flight and could not provide us with any information whatsoever.At this point I conferred with both Dispatch and the [Chief Pilot] and we concurred that without more information all of the 'dangerous goods;' including the 44 boxes of lithium-ion batteries; should be removed from the flight.I went to the ramp to see what was really in the cargo bay and observed multiple large boxes displaying a 'flammable battery' icon being removed from the forward cargo bay (photos attached). The 44 boxes were labeled with a gross weight of 12.44 kg; or 27.43 lbs; for a total gross weight of 1207 pounds of boxes containing lithium-ion batteries -- if the information provided to us by Ops was accurate.The only FOM [Flight Operations Manual] guidance I was able to find was for lithium-ion batteries carried for personal use; not as cargo. Is it allowed for a passenger aircraft to carry 800+ pounds of lithium-ion batteries as cargo and the pilots are not informed because this is an 'excepted quantity?'




Synopsis: A320 Captain reported ground return due to Dangerous Cargo shipping irregularities; including documentation and handling errors. Hazmat cargo subsequently removed due to insufficient safety information provided.