4A - Amendment to the Conditional Use Permit for the RV Resort Village at the Preserve

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MEMO January 16, 2007 Page 3 of 3 Wastewater strength parameters and discharge limits must also be established, on which the wastewater treatment facility design is based. The RV resort will be utilized as a permanent residence for a period of each year and not as transient type usage with weekly turnover. Therefore, wastewater strengths will more closely match typical domestic wastewater rather than the more concentrated wastewater associated with campground and marina dump stations. The following wastewater strengths will be utilized for treatment facility design. Total suspended solids - 500 mg/l 5-day biochemical oxygen demand - 400 mg/1 Total nitrogen(TN) - 80 mg/1 Ammonia(NH4) - 15 mg/1 Total phosphorus - 30 mg/1 Fats, oils and grease - 60 mg/1 These values are 1.5 to 2 times those of published data for domestic wastewater. However, those typical values are for systems that include infiltration and inflow that dilute strengths. The RV resort collection system will have considerably less infiltration and inflow than average municipal systems. In addition, the estimated wastewater flows are lower than those for residential homes, so wastewater strengths are more concentrated. The wastewater strengths will be reviewed by the MPCA during permitting and may be subject to revision based on review comments with respect to the proposed treatment facility. The option of adding a dump station to collect wastewater from the RV units after they have been on the road for a week(coming up from the south each spring) will also be considered during final design. Starting up the mechanical treatment plant each spring with concentrated dump waste may cause problems. The first 15 to 20 units that show up each spring will utilize a dump station so the concentrated wastewater(which also contains additives/deodorizers) can be metered in during the startup and not adversely affect the biological process. This parameter will be discussed with the treatment unit manufacturer to see how it may also be utilized to facilitate startup each spring of the wastewater treatment facility. Conventional soil treatment systems would be difficult to construct with the limited suitable area remaining on site, and would be subject to a minimum 180-day permit review period along with significant site soils and groundwater modeling/monitoring. MPCA design guidance for large subsurface wastewater treatment system (LSTS)permitting option 1 (fast track recommended by the MPCA)requires an end-of-pipe limit for total nitrogen of 10 mg/1. Design of the wastewater treatment facility and related subsurface disposal area for the RV resort utilize this option for the NPDES permitting and will be submitted to the MPCA. The subsurface disposal field of this type of system is not utilized for any type of additional soil treatment. Loading rates are based on hydraulic capacity of the site soils and how that relates to mounding of disposal water. This allows more flexibility in location of the subsurface disposal areas and utilization of the area above them. WSN has reviewed the new design flow of 24,850 gpd with the manufacture of wastewater treatment equipment used for the treatment facility design. No modifications are needed to the secondary treatment units. Depth of the anoxic tank shown on sheet 15 will be increased from 10 feet to 12 feet to allow additional contact time for total nitrogen reduction. This is the only change required to the wastewater treatment facility based on the current average daily flow of 24,850 gpd.