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lity modeling studies are contained in reports dated April 16, 1991 and December 20, 1991. latter report includes corrections to the first report and includes the effect of seepage. Both orts are available from VBWD, but only the results of the December 20, 1991 report are ussed here. The mean summer average phosphorus concentration for Lake Olson (through 0) is 0.045 mg/L.The water quality modeling predicted that, under ultimate development 1 ditions, the mean summer average phosphorus concentration of Lake Olson would rise to lae 47 mg/L without the addition of water from the Olson Lake Estates pond, and would rise 0.049 mg/L with the addition of water from the Olson Lake Estates pond. The incremental rease from 0.047 to OA49 mg/L is approximately 4%. The effect of dilution is a major reason t the predicted incremental increase in the phosphorus concentration is small. For example, volume of water which would flow from the Olson Lake Estates pond to Lake Olson during runoff events of a 10-year magnitude or less is from 2 to 4% of the volume in Lake Olson available for mixing. When the volume of Lake DeMontreville is added in, the Olson Lake Estates pond discharge is only 1 to 2% of the total volume available in Lakes Olson and DeMontreville. The model predicted that the small increase in phosphorus concentration would be nearly undetectable in terms of Secchi disc transparency and the percent of summer with algae blooms. The results of water quality sampling conducted by the Washington Soil and Water Conservation District in 1992 and VBWD in 1993 at the Olson Lake Estates pond appear to support the model assumptions. Historical data indicates the existing and future desired uses of Lakes Olson and DeMontreville have often conflicted with their water quality during the late summer period. According to MPCA surveys;Secchi disc transparencies less than 2 meters are associated with water quality conditions which result in impaired swimming conditions. Secchi disc transparencies were less than ? meters during the late summer period of 1988 through 1991. Application of an algicide during the late summer period has been necessary to control algal blooms, and make the lakes more enjoyable for recreational use, especially swimming. During the years when an algicide was not applied (i.e. 1988-1990), the conflict between water quality and usage was essentially the same in both lakes. As discussed previously, application of an 91a algicide during 19nd-T�esu-Ite-d in a greater improvementn i transparency-m-Lake Olson than in Lake DeMontreville. Thus, during years when algicide application has occurred, the conflict between water quality and usage has been less in Lake Olson than in Lake DeMontreville. During 1993, no water quality/usage conflict was noted in Lake Olson. Section 3.2 -- Water Quality Management Plan identifies Lake Olson as a Category I lake, based on its existing and desired recreational uses. Further description of this water quality classification is included in Section 3.2. 4.2.8.6 VBWD Water Quality Management Goals As shown in Table 5 of Section 3.2 -- Water Quality Management Plan, VBWD's management goal for Lake Olson is restoration of the lake's water quality so that the existing: and future desired recreational use no longer conflict with the lake's water quality during the late summer period. The current recreational use of the lake indicates the that the Lake Olson would be a Category I waterbody, however, the lake's late summer water quality data have generally suggested it to be a Category II water body, Although VBWD's current goal is restoration to achieve a Category I rating, VBWD may need to revise this goal based on further water quality testing results and hydrologic and nutrient budget results under ultimate watershed land use conditions. VBWD will complete hydrologic and nutrient budgets of Lake Olson, depending on the availability of funds. VBWD will then, establish final management goals for the lake. Water quality goals established for Long Lake and Lake DeMontreville will consider the water quality 23\82\045\SEC4.RPT\KMH 28 DRAFT: June 23, 1994