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below the driveway. The large number mature and developing trees add significant stability to the soil <br /> below the driveway, mitigating potential concerns over erosion. <br /> The proposed location of a walkout structure on the Gronberg survey is well situated to minimize <br /> required grading and take advantage of the steady and gradual slope above the bluff line and to <br /> position the rear wall of the foundation just above the stable "shelf' created by the construction of a <br /> driveway bed more than a century ago. Per the Gronberg survey, only minimal grading will be required <br /> on the sides of the structure, and virtually no grading will be required in the front or rear of the structure. <br /> Given the unique contour created by the construction of the driveway bed, positioning the structure <br /> further away from the bluff zone may actually create a greater potential for erosion of soil above the <br /> driveway bed. Positioning the structure immediately above the driveway bed "shelP' appears to be the <br /> most stable position for a structure near the allowed building envelope in the Gronberg survey. Having <br /> a relatively flat and demonstrably stable 15 foot wide area immediately behind the proposed structure <br /> alleviates concems over erosion immediately behind the structure. <br /> Additional factors mitigate the concern for erosion from the proposed structure on the Gronberg survey: <br /> (i) the slope of the hill immediately below the top of the bluff line near the location of the proposed <br /> structure is significantly less than the 30% slope threshold marginally found in areas near the wetland <br /> that cause this to be defined as a bluff, (ii) the area at the bottom of the bluff, often a concern for <br /> lakeshore bluff management, is not at risk for erosion from waves, ice or even standing water, as a <br /> result of thickly developed_vegetation throughout the wetland area. <br /> Recommendations: <br /> The survey shows that the basement floor is planned for elevation 981 feet. Assuming the footings will <br /> be about 4 feet lower for frost cover indicates a required depth of excavation to about 977 feet for <br /> footing placement, and refilling to 981 feet. <br /> The survey also indicates that about a dozen trees will require removal for the house foundation. It is <br /> recommended that these trees and their root systems be completely removed and the resultant <br /> openings backfilled with lean clay developed from the basement excavation. The lean clay should be <br /> spread in half foot lifts and compacted to 95 percent of maximum density up to the planned walkout <br /> grade of the rear yard (allowing for surface topsoil). When the walkout area has been raised to its <br /> planned grade, the rear footing line should be re-dug through the compacted fill to footing grade. <br /> All excavations will require silt fencing to prevent down slope erosion protection. The rear yard fill in the <br /> walkout area should be immediately protected after excavation, with commercial netting and straw. <br /> Your engineer and surveyor should design all runoff discharge from the new house, yards, walks and <br /> driveways. The use of rain gardens or small retention ponds is recommended, and can be readily <br /> designed for one or both sides of the proposed structure with minimal grading. <br /> With careful attention to slope protection during and after construction, it is my opinion that existing <br /> soils at this site have sufficient stabi(ity to allow construction of a home at the site indicated on the <br /> Gronberg and Associates survey without the risk of any material soil erosion. <br /> I hereb cert' that this re ort was re ared b me �►s��r�, ,;f i f 1�;;t ' <br /> Y �Y p P P Y .� , �• . �• ^�t �, <br />� and that I am a duly Licensed Professional Engineer ,�����;,'���'�����r�� �,s��;,q�`�:���'�.'�� <br /> � under the laws of the State of Minnesota. ;��;�° °��% ���° '.��y= <br /> . ..` �..L•�):`C°.__C�Q �'�� = �o 'N'p�^'.. ` . <br /> a , � t,:v:. 67M1� � <br /> � : �t�i4�:.'.•:'..�:'�r�j. � � : �"{'"�h^ii C.:'�i���e: <br /> (/ /wA/ j��'ry(� l/. .. � X �llr�ir.�..:.. o + � t..�• y � + <br /> �� L�r/!N� {� f�[S. ,r.�..:;� $ C�ril����i•.Ti.y""I' <br /> �•�,•�. i f ^ ' . <br /> � �;� 107;6 ��q�; ;ti?.' 14736 :,`Q; <br /> r.g�. ♦ i'I�'°y _ 'f o � <br /> � Carl E. Anderson, P. E., P. G. � ',,�"�`•'�..��''���.` '•���`'°••°�..."����:`� <br /> Registration Number 10736 `��;����y���`� '�.,�F�`N�,.� <br />