Microscopic Particulate Analysis (MPA) to support GWDI

Modified on: Tue, 18 Apr, 2023 at 3:02 PM


Groundwater under the direct influence of surface water (GWDI) include sources such as open channel contamination (cracked well casing), systems receiving recharge from a nearby surface source and surface sources as creeks and rivers.

The Microscopic particulate analysis (MPA) test (which evolved from the analysis of Giardia and filtration efficiency determination) is a test used to determine the likelihood of groundwater being directly influenced by nearby sources of surface water. 

The consensus method (US EPA) attempts to equate quantitatively the significant occurence of primary and secondary indicator organisms to a relative risk score for a particular water supply. The range of values for each bio-indicator was taken from data submitted from participating US laboratories across the country. 

The method Abstract clearly indicates that surface water influence on a groundwater source cannot be determined solely on the basis of one or two MPA's; other pertinent information is required. 

The microindicators targeted are Giardia cysts, coccidia and helminths, pigment bearing diatoms, other chlorophyl containing algae, blue/green & brown algae, insect parts and larvae, soil and awater mites, sessile or free-swimming rotifers and plant debris.

For more details on what this analysis entails, please see here a link to the US EPA method (EPA 910-9-92-029, October 1992) 


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