What is MPA and how can it be used to differentiate ground 
water under surface influence? 
The premise behind the use of microscopic particulate analysis 
(MPA) is that surface waters are subject to contamination by 
pathogens such as Giardia and that there are other organisms whose 
natural habitat is limited to surface waters.  If these surface water 
organisms are found in ground water, then the water is subject to 
contamination with Giardia cysts and other pathogens.  Indicators of
surface water contamination of ground waters include: Giardia, 
coccidia including Cryptosporidium, diatoms and certain other algae, 
rotifers, green plant material, and insect parts.