What is MPA and how can it be used to differentiate ground water under surface influence?

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.