I would not have been surprised by this, at all, given the relative ratios in Environmental Engineering (don't quote me on this, but I perceived it as about 60:40 in favor of women) as compared to Computer Science at my alma mater (that was, ahem, not 60:40 -- closer to 4:96).

Edit for context: major American research university, 2000 - 2004. The bulk of people I knew at university would be late twenties or early thirties now.