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5 12/24/03 <br /> EXHIBIT A <br /> Water Filtration Plant Filter Clogging Study <br /> SCOPE OF WORK <br /> During the last four years, the City of Everett drinking water treatment facility at Lake <br /> Chaplain has experienced periodic filtration difficulties (i.e. clogging events). These <br /> clogging events have mostly occurred during the summer-stratified period in Lake <br /> Chaplain. The objective of this proposed research project is to determine how the <br /> vertical distribution of planktonic organisms in Lake Chaplain varies relative to the depth <br /> of the intake structure, and to assess whether possible solutions such as changing the <br /> depth from which water is withdrawn from Lake Chaplain could reduce the incidences of <br /> clogging. This will be accomplished by determining the biomass and vertical distribution <br /> of detritus,bacteria and phytoplankton in the vicinity of the intake, as well as determining <br /> the vertical distribution of plankton at a deep water sampling location in Lake Chaplain. <br /> Particular attention will be paid to microorganisms and detritus in the 0.1 to 10µm size <br /> range, as particles in this size range are most likely to clog drinking water filters. <br /> However, particles ranging from 10 to 2000 p.m (i.e. moderate to large phytoplankton and <br /> zooplankton sized particles) will also be quantified. Close attention will be paid to how <br /> the depth distribution of planktonic organisms relates to thermal stratification in Lake <br /> Chaplain and the depth of the intake structure. <br /> Based on data collected previously from this reservoir, it appears to be a classic <br /> oligotrophic system (i.e. low nutrients, low plankton biomass, and high water clarity). <br /> Because oligotrophic lakes usually have strongly nutrient limited epilimnia (= surface <br /> layer) during the summer stratified period, it is common for deep oligotrophic lakes to <br /> have phytoplankton biomass maxima in the metalimnion. [The metalimnion is the <br /> transitional thermal layer between the warm/well mixed but nutrient depleted epilimnion <br /> and the cold/poorly mixed nutrient enriched hypolimnion (=bottom layer)]. In the <br /> limnological literature this phenomena is commonly known as a "deep chlorophyll <br /> maxima" Based on initial descriptions of the intake structure and typical epilimnetic <br /> depths in lakes/reservoirs similar to Lake Chaplain, it is quite likely that the intake <br /> structure in Lake Chaplain is taking water from the depth in the water column where <br /> small sized planktonic organisms are most concentrated during the summer stratified <br /> period. By determining the depth distribution of planktonic organisms in Lake Chaplain <br /> it will be possible to determine whether extending the intake structure upwards into the <br /> epilimnion or downwards into the hypolimnion wi 11 result in a reduced incidence of <br /> clogging events at the drinking water treatment facility. Because of the reservoir's <br /> morphology in the vicinity of the intake structure, it would be least costly to extend the <br /> intake structure into the epilimnion where due to severe nutrient limitation plankton <br /> biomass tends to be lower during the summer stratified period. However, because water <br /> temperature is an important component of drinking water quality, in the long term it may <br /> be best to extend the intake structure so that it can take water from the hypolimnion were <br /> 16 <br />