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�� Roger Peitso � Building Official WENCK City of Orono � . . Responsive partner. Exceptional outcomes. Around the mid-2000's our ISTS work on Big Island was questioned because we disagreed with some ISTS practitioners' soil interpretations. In response, we decided to install piezometers and monitoring wells on the properties highlighted above. The first set of piezometers and wells were installed at 170 Big Island for the Palm family and monitored for three years. The results of the monitoring showed that the features in the soil were relict. Documentation was submitted to the City of Orono and an ISTS was permitted and installed. Subsequent to that investigation, additional piezometers and monitoring wells were installed at other properties in 2007-2008. Over 10 years of monitoring has occurred on Big Island. Concurrently, we were monitoring others sites in Hennepin County in similar soils at varying landscape positions. Here is what we have learned so far: Lester soils with slopes in excess of approximately 6% on summits, shoulders, and upper back slopes do not receive enough water (rain and run- on) to maintain saturation in the topsoil or subsoil for long enough durations to cause an anaerobic condition that could affect ISTS effluent treatment. When observing the Big Island sites at the wettest and highest water times of year (including May 18 and 22, 2014 when Lake Minnetonka approached the 100-year high water level), no free water was observed in any of the piezometers or monitoring wells. The soil texture, slope, and upper landscape positions of these sites shed water down slope and prolonged seasonal saturation does not occur. Investigation at 540 Big Island The property was first investigated in 2007 with the completion of soil borings in the central portion of the lot near the top of a rise. The top of the rise is a logical location for a cabin and the soil borings were completed in the general vicinity with the purpose of determining ISTS suitability. The soil parent material for the area features high chroma loam soils with threads of calcium carbonates (often misidentified as low chroma iron reductions) and reddish iron concretions. These features were observed on the soil borings at 540 Big Island. These soil features are a result of the soil parent material, and not a fluctuating seasonal water table. Saturated conditions were not observed in the soil borings, or in the three piezometers and one monitoring well installed in October 2007 and monitored through 2014, so an in-ground trench system is proposed. In conclusion, the site is suitable for a subsurface drain field. Seven years (2007-2014) of site-specific well and piezometer monitoring data indicate the site does not experience seasonal saturation within 6 feet of the surface, even during record high water levels and record precipitation (2014). Observed soil mottling is due to calcium carbonates and iron concretions, and not due to seasonal soil saturation. Any observed redoximorphic features should be considered relict, and not representative of current hydrologic conditions. 3 T:`�2015\Technical Memo_Flnal 030Si6.docx