trying to calculate trade volume?

I'm trying to calculate trade volume for cc's. Here is one item returned from the Cryptopia GetMarkets api:

{"TradePairId":1261,"Label":"$$$/BTC","AskPrice":0.00000034,"BidPrice":0.00000033,"Low":0.00000031,"High":0.00000037,"Volume":679217.98580777,"LastPrice":0.00000034,"BuyVolume":23714498.59283377,"SellVolume":11239801.32898952,"Change":0.0,"Open":0.00000034,"Close":0.00000034,"BaseVolume":0.23164978,"BuyBaseVolume":1.13929174,"SellBaseVolume":28943846.84960915}

I googled previously and found a thread where trade volume was described as the total of buy volume and sell volume. The item above has:

* BuyVolume = 23714498.59283377
* SellVolume = 11239801.32898952
* Volume = 679217.98580777

However, BuyVolume + SellVolume != Volume for the numbers above.

Does the Volume value above represent the volume available to trade? That would seem unusual b/c in that case BuyVolume and SellVolume would appear to indicate that the full available volume for the CC was bought and sold multiple times over the course of the day.