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TECHNICAL MEMORANDUM <br /> HDR ENG/NEER/NG, INC. <br /> INTRODUCTION <br /> HDR Engineering, Inc. (HDR) was retained by Hennepin County Property Services to perform an <br /> inspection of the storm water pond and to make recommendations for long-term and short-term <br /> maintenance of the pond at the Orono Truck Station Facility. This technical memorandum <br /> describes the information collected during the pond inspection, documents the pond condition, and <br /> provides recommendations for the maintenance of the pond. <br /> HDR conducted an on-site inspection of the pond on October 19, 2005. At the time of the <br /> inspection, the pond was not drained and was near the normal pool elevation. <br /> POND DESCRIPTION <br /> The Orono wet detention pond was built in 2002 at the east corner of the facility. It was designed to <br /> receive storm water runoff from the Orono Truck Station site, which includes the facility building, <br /> landscaped areas, and roads and paved parking lot. A plan view of the pond design contours is <br /> provided in Figure 1. <br /> � B A 5.� Tj �� " ' �'�, ^ _�� _ _Y'�^ - � S ��� <br /> ` t"`�1, '� . � — • '4 <br /> i . _.,,; _ ��fti�k i ty' <br /> -- _. -- -""''�' ! I .• .�= ; �;�i , <br /> `��. 1 's•- _. ' a�r _�>�5 I <br /> � � ! - � �' t <br /> l, fi� 1 .� �.` � �y ti7 <br /> �`� j J , _t_ __ - _ _ -».•. - ! y <br /> _ � -- � � _ 0 .- - 1� 1 <br /> -_ �r1.r _ _ ' u � , <br /> t � .p� .a. P�F1Qf^ .��:r.•y��;f".J -E_►.�� =r <br /> � � ' � <br /> E�iu I 6' G�P -- � _ - � <br /> �i+,.ert . 9as..,� ..-� f L, 1' � �_x ��y'V-�' <br /> '�+s�. —�.r: ~' '�5 ti.,y, _ � - �~ ` � ''t � 'i:,^ r�. <br /> -- C�' L � � - <br /> 4��' T /�r� ��.j�,.�' ��+� <br /> - ^ - �- -yw- - � l JJ` J � 1 �_ ,Ti°'-�_A��'✓Y' .,y;' 'f.- �a{ Jii~ ^ � ��,L ) ..i <br /> �, • ' - ` '' 1 ��I �� <br /> --•���— »^ _ _ -=_wi"S+��/ �-'�- ,w v-'"��F�=l 1��'�r � 1 e; � y __ � .� <br /> ..YIC.-1f7�Z^' _`�-_r'SL'-_7/ - _ ��11\'._7Sr_vY':�.��` 1' 1 �� Y �Y r � f�^ <br /> - "� � � '� ' �� ` �'�� <br /> - ~5 <br /> `l ��,• L " �� - L � � �. •- L'��Y�= ^ IL +��•� :11 � ,wt -� L 1' � ' L J r �� e <br /> Figure 1 - Pond Layout Plan View <br /> The Orono detention pond consists of one inlet and one outlet structure. The inlet structure <br /> consists of a 15-inch polyethylene pipe and is located on north side of the pond. The outlet <br /> structure consists of a corrugated metal standpipe, which has a diameter of 18 inches, and is <br /> located on the west corner of the pond. The downstream end of the metal pipe consists of a <br /> concrete flared end section without a trash guard/grate. Rock riprap was placed on the edge/foot of <br /> the inlet and the outlet structures to prevent erosion. <br /> Storm water enters the detention pond through the inlet culvert and is stored until it reaches the <br /> maximum storage capacity of the pond. The approximate bottom elevation of the pond per the <br /> design drawings is 933 ft as shown in Figure 1. The highest elevation up to which the water can be <br /> stored in the pond is 938.65 ft (top of standpipe), as shown in Figure 2. <br /> 11/4/2005 <br /> HDR PRO.IECT#32560 2 HENNEPIN COUNTY,MINNESOTA <br /> ORONO TRUCK STATION FACILITY <br /> STORM WATER POND EVALUATION <br />