Surface Water Filtration and Groundwater Under the Influence Investigations

contaminated spring water, bottled water, groundwater under the influence, microscopic particulate analysis   direct filtration, pilot filter testing evaluation, slow sand filters, diatomaceous earth, pall filter, cartridge filters

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During the past 15 years giardiasis and cryptosproridiosis has been recognized as one of the most frequently occurring waterborne diseases in the United States.

The occurrence and detection of this parasite and drinking water source identification and protection has become a matter of urgent concern to those responsible for water utility operation in endemic areas.   Because of these concerns the Surface Water Filtration Rule was established and protocols were developed for determining if a source was characterized as surface water, groundwater, or groundwater under the influence of source water. As part of the Surface Water Filtration Rule all community water supplies identified as surface water require a minimum of filtration rather than just disinfection prior to consumption. The Surface Water Filtration Rule has lead to the development of a protocol to evaluate the performance of filtration plants. The protocol is similar to the method used for the Groundwater Under the Influence Investigations, except the risk rankings and interpretations are based on a combination of the system configuration, source water quality, degree of particle reduction, and distribution of particles.

Since as the Director for the Center for Environmental Quality has conducted research in pilot filtration plant performance and optimization, the laboratory has been involved in the evaluation of a number of bench-scale, pilot, and full-scale filtration plants in Pennsylvania, New York, and New Jersey.   The laboratory Director has worked on projects using diatomaceous earth filtration, slow sand filtration, direct filtration, submicron filters, cartridge filters and upflow filtration systems.   In addition, we have conducted bench scale and pilot scale experiments to assist in optimization of pretreatment process and filtration of water supplies and has developed protocols and conducting testing to assist in the development of solid flux loadings for secondary clarifiers for a wastewater applications and living filtration systems for on-site wastewater disposal systems.

Microscopic Evaluation Technique for Filtration Plant Performance

The purpose of this procedure is to evaluate the performance of public water supply filtration systems. A minimum of 300 gallons of both raw and finished water should be collected. The evaluation is based on the filtration plants ability to remove Giardia sized and larger particles. In addition to the MET evaluation, the evaluator should also consider the operational conditions of the plant, physical condition of the plant/ raw water, and effluent quality of the finished water.

Each analysis culminates in a filtration performance rating which reflects the overall effluent quality. The rating is always accompanied by an explanation which details the justification of the assessment. Filtration Plants with Excellent and Good ratings are reported as "Acceptable Filtration Performance". Filter which are rated Questionable or Poor are reported as "Unacceptable Filtration Performance".

The amounts of each of several specific groups of particulate matter and microorganisms are recorded. These groups include: small particulate debris, large particulate debris, cellular plant debris, diatoms, and other algae, protozoa, insects and crustaceans, nematodes, and rotifers. Also, pollen grains, Giardia, and other parasitic protozoa should be noted.

No of Specific Particles in a Category
Avg. Field at 100x

None  0
Rare  1 - 50
++  Few  51 - 100
++++ Moderate > 200


Excellent- These systems remove essentially all of the Giardia sized debris and that which is much smaller. There is no evidence of turbidity breakthrough to indicate any risk for Giardia contamination of the effluent and 300 gallons of effluent can be observed in a single sample without any Giardia sized particles reaching the rare level (+).

Good-300 gallons of effluent can be observed in a single subsample without significant amounts of Giardia sized particles present, i.e., the levels of diatoms, algae, and protozoa remain a the few (++) level.

Questionable-Giardia sized particles are at the moderate (+++) level in samples which represent 300 gallons of effluent. These systems have filtration which does not provide the obvious assurance for Giardia removal as in the above two ratings. It is not possible to comfortably predict the potential for Giardia breakthrough with this result.  Facility evaluations rely heavily on information obtained in the operations survey.

Poor-These systems are unable to remove Giardia sized particles and are therefore vulnerable for Giardia passage through the facility. Subsamples represent 300 gallons of effluent, and Giardia sized debris is in the moderated (+++) to many (++++) range. Operational changes are required to improve the effluent quality. The facility must be reevaluated to determine whether correction of the problem was achieved. Corrections must be performed within a reasonable time period and public notified if the potential for Giardia contamination remains.

Advanced Stormwater Design