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HomeMy WebLinkAboutStorm water management assessment memorandum Revised July 30,2014 Storm Water Management System Assessment Memorandum — FOR — Orono Truck Station Hennepin County, Minnesota Inspected by:Tom Christianson Prepared by:Jessica Tello Approved by: Brady Busselman,PE Prepared By: � - 763-476-6010 wwwsambatek.com engineering surveying planning environmental 12800 Whitewater Dr,Suite 300,Minnetonka,MN 55343 Table of Contents I. Introduction..........................................................................................................................................2 II. Site Description ...................................................................................................................................2 WetlandStatus........................................................................................................................... 6 III. Existing Conditions.............................................................................................................................7 Vegetation ................................................................................................................................. 7 DrainageArea............................................................................................................................ 8 InletStructure............................................................................................................................. 8 Outlet Control Structure............................................................................................................... 9 Survey....................................................................................................................................... 9 Evaluation................................................................................................................................ 12 IV. Recommendations.............................................................................................................................13 V. Appendix............................................................................................................................................14 Page 2 of 20 Storm Water Management System Assessment Orono Truck Station I. Introduction Hennepin County Property Services retained MFRA, Inc. to conduct a storm water management system assessment at the Orono Truck Station and outline recommended maintenance. This technical memorandum details the findings of the inspection and outlines recommendations for repair and maintenance. This facility was inspected on January 20�antl March 4th, 2014 under frozen winter conditions. A follow-up inspection was completed on June 11th to observe those aspects of the storm water management system that were under snow antl ice cover. A storm water management system questionnaire was submitted to the facility's manager; however, as of the date of this report a response has not been received (see blank questionnaire in the Appendix of this report). II. Site Description With the exception of the west pond topo survey, the following diagrams were gathered from a technical memorandum furnishetl by Hennepin County Property Services, titled "Storm Water Pond Inspection" and dated 11/4/2005. The Orono Truck Station contains two ponds; the east retention pontl was built in 2002, the west pond was an existing wetland that is being used for storm water treatment. The 2005 memorantlum addresses the east pond conditions, but did not include a review of the west pontl. The ponds receive runoff from the facility's buildings, landscaped areas and paved areas. Figure 1 shows the locations of the ponds on site. , �� : � e, w; � ,s • `` « '~ t ��� wa�wwurr 1 ' � ',t ; }�t.. " "� wewrT"'."... '4 .�.� f"� " `�y Y9° R '� .kc � � �.�ji�a ��. € � " '� "a �t'�f n � � � 3 .�`, " 5 F y jJ ^ �+ �,y� . � � ",�K'. �p,. w d� q � �vlY .+i'� � 'A' ,j `6 . . .. � �h � ��� �� j,�l , t I �i.�~ �� s�� t ��'G�� ��. � i � ��� �f,-v�I4f F'. '�^^'.;"'T�'S��'' ;k '���. �1 R � �di'�1m.� � ,Y ��y°� p { }''t{�� ��Y . / � '.M j * y� ' S ^f� .f A .�i If.' ���1` },.'. � � ' { } r � . ♦-.� 'rilyr��!r `� �9� ;.4 �� '�.. � ,aw�,.�w..j,� � '... �` � e:'�• l 7 , � . . , � �. . . .. . . , � _',� " N 4..^-.",...�.-:. ..._�y..,...... ~ ��� .,, •�' \.. .. . ._ _ , ,�• '� yi �R �4. .t {�j. d'�<.�'�f� �� .. .r:,+.�;_ • ♦�' �.^!'�. ��ri , .. � ��Y*� �., c�_ i _ ��M1�'�� A _ { y: ,� � ,� .. F N � . .: �„''''�*-'%'"� •` >�f �' �. �' =�� � ` ,: ,. .�..--.��. .s �� <- - n �� ,� �',... . .... . . .� !��-'"""��.� �a � .9 E, ` � , "' II/11�E fI11�lf��f t11E�E1T ItEt ;N`" ___,;,, %,���!► i' .. . ., . � r , , - i , , � i • ,,s.'y �.j ,I- . � _ rr .r G�... � � ' ' _ � ' - �'� ' _ East'Pond ; -�s-. � �, '' 1�tVest Pond 3 �� '� � '-=- �, �, t .�; 1", ' �• ' �„ ` --�'1 ` `, , � � F . • 1 j � 1 .. .. .._,-���1 ��.,.• ..,1 . ( � • � �E I � . , . �. � � �► ....��.. ... ^ '. . _ . ' �. , � i. �.t. '� `*�� 1 ti�' '�1 �'. ; ��,r ''. • �� j� '�..� .. _'_..` --ar--{r���'�=RI �u-' . - .. 1� .'f � _.. • .z . Y ..'f^"'*"'�+"'—�""'= ` . . . . �- ,j .... ` ':� ♦ 'i4� �� , . �- .� y . ... .�: � . �,a49.vr • �� -� ,,'�: '� ��, ,, . South Ditch _ , , ,, � � ,' ,. �_ - � - - � - � - ~ � � , . . . r�,��� � �, � �' . _. � ..._. y '� _ � � Figure 1 —West and East Pond Locations Page 3 of 20 Storm Water Management System Assessment Orono Truck Station East Pond Figure 2 shows the grading plan for the east retention pond. The inlet structure is a 15-inch HDPE pipe that drains into the retention pond from the north. The outlet control structure is an 18-inch corrugated metal standpipe connectetl to an 18" carbon steel pipe that flows approximately 60 feet to the southwest and discharges through a flared end section. Both the inlet antl the outlet drain onto rip rap for energy dissipation. The design pond bottom is at an elevation of 933, and the top of the standpipe is at an elevation of 938.65. No details were provided on the design of the standpipe, and it is unknown whether the opening at the top of the pipe is the only outlet designed for this pond. The outlet control structure is shown in Figure 3. �' � �r � � � �,°,.�� 'r� 'i � �4 ♦ � �, "�"�'�°j",.�r►''�`'ryr' � � ; �� �! �� �,.+�s �°�'4.„y, i � ti � 1 � 1 � � � t� �' � I/ ,+ t w..�� t .r+�"`�+' "4 ��, � Il� � . � � ���` ���'�c'�'��2 pw� `��.�rw � �'� �� �,�� R �_ �� _ "rs., .� � � � 1 cv�'�' � ��� s a+k � �" .a � � � e M. ���, � � ��,�p � � � 4 ._ � � � ., y �bq , � .�� A+��'� � Wa` rr�,a� x., �aV a4A �� t � �� ° S»�i � � �: ..( -N :W., �.. � �a� � 'y��, s . , myj*�.�F � � !H � � � n�Y s � � f {�f.,"�4 � � ..d . ,s�,�A ,,pc� ,�=s xwr ' �yA � ��' �� � ,� ����ti„ i� � � a Y�''a �i �, .r° '� °"� ca e9 � 1 �y .� � fi�� _ z:�+�7��`'��+ � ,� � �, � _ �,. , "���,�.. ,� �." �� f� W ° � A `. � � � ,� a w � .•�,•�{''��.e.r�w .s �'�� �4� �. � � �" � "� - � _ - •• � '� Figure 2—East Retention Pond Grading Plan Page 4 of 20 Storm Water Management System Assessment Orono Truck Station 55.� L� i8" CS PIPE + kf'RON ! t.ax �o�. �r�ts��a�su���— �xtsrt�c s►�,� � TOF t� ��'' CII�` • , • � �'Tdtl�'�P4E� !!�.l�� • ' � _ • . � ..,,....�,., � . ' . , � , � ' - ..".�'.:.,._....�.."..,._:.._ "_.. � ' • a • . �+ ` � �' " • � � ��� ' ' � �����`;�' . „ , . , � :� , 'F51.�.�Qt'I Figure 3—Outlet Control Structure Profile Page 5 of 20 Storm Water Management System Assessment Orono Truck Station West Pond Figure 4 shows a topo survey of the west pond. Runoff from the truck station facility appears to discharges to the west pond through an 18 inch flared end section. It also appears that runoff flows from the east pond through a ditch on the south side of the facility and into a culvert which drains into the west pond. Runoff also appears to flow overland from the facility directly into the south ditch before draining into the west pond. The outlet from the west pond appears to be a 30 inch flared end section adjacent to the inlet from the truck station facility. f "��i" F � }y� ' Y��`K �.��: ; 1 r " � . ,.. �1�' Y' f� .<,L,'��f.'.�'�si"+��" . �M��1'� Y ��a� [��t,�^ � �Civ� y�^[ �..�e.'k'E.' y ... . y. �.t t u' s�,. � -t,� h: � 4 � �,( C" r-� � �°'` P� ." +`` .. 3' �� �"'"��y . .. ?N,�..' ✓ r� r x �� .. � �f «. �,� "`��v �' ;�5�F`��,. ? � . gr'�!` �. 1°�t� l .i_�,I yF '..�e e 3�,� � � ��: ��. 't+�-n-.�V� .��..o.. a �y... ����� -.,i.�'d , � ,'� �c t4� '�. .tf�:,� + '���F EI t'..: �• � � 4� ` 1` ��~� � � `�1` .::�+nr� ,.. ���p 4 r �''�', !3 b: 1�. i ^ se;i .,td� ���`� p• �d • � 7 i � �.' �}, �. ,M ; E i �it � i� ,»ra. r+, ..%-a A A � t �` .� J: �� aw.:..� a � '�4ia,� :� y I � , - � ;� � � �}� w k4. � � �X � �^ .*"", yi����i� .� '" ��Fq a•�b �x '�i �R4}k� +�� '�t A.' d$ � �, '�4 v� ° j,�,. R c y �' �. � : 4� �"4't—�r _I .0 �ai!� � �;; �` '�TM '�k + "C ��g��'�; . �,.�,,,. ��i����������":�1 ,• ! Ck,� �"�M ��`s�1� .¢�� a.r , , � .�F� � �, _� � � �r� "+�r��t�3r� b� �e wr� �� i t"` ► ry,�a� � R ; ��t� ;�, 'u. �r� f .:S 4 E. � .� ',`'� �aY_:E.��r'S y1 � ` �1F"' �,�Y �- ���' I ; \ s /" �`, � �� �,� ,� •"� � .. �.r4+""' r',', � J �••• + r " � '" �a. �W'�'. I�1: � �: •j f �4 Y �. �" 6 '� �` �t� . ; �i�,,,,v�,..11M«.... r e.� � ' { •y 4., * "� �� i�'`�1 \�1�\� � � F q ^'�,,._„�� �f� �. :1, ! t,�• c� �,;a �?" F;���Y. \Llt�' . 1. �6'��{ � t 1 �. � ' t.�� �'° ;,'.�r�/'R "i 1)g,g�i�' . � �t" i �' ,j�34 �f�t�.7 �� .(; � ` � �: . , ����,�l . ? � -�� . ��"!".:/� �i.` a � I, ♦+sy '�+C i �l. �'.�' �.. � S , �'�'wa�L ':7 / i:.:���r a� � 4,� ..�. � �y �� � r 9 i.: .r i .+'M�'�R.•��': ' y *i g °. y� `��t.G� '0. 9 O t ` ' �! � 4' , •� �` t � �� � f ! �1 /ii�+�+1D �,r`r �'r^�'�r;x''� 9 t��1 � 6 � "��.:.`� , C' q St�. °r y� ".���"+'"i -. S� � ti (� � f�'�� y �. � �} r�,�~ . .�� .�_ � ,�aD�. �i `rr e .t 1 r I�. :"+5' "� �..: •(�k_ :. � � #� � k�.:t.� . :.i?'. k N7{.J��� � 9,. \ V..94 9h�`+n ' yy �{C . 4 ' �,�t r,i x a'dz �� � ��z����'�` �� � �'r> ��t�'.y. >:,;� . . . kre�" 'e`'��... - �. � . �"*�`� � e'� ", k y - ;zv. �,,ti,.,��,� , .R.. , �..� M e � � ;> � ,� <',x ����`i �: r-,��w� . � . i+i';�. i � � ,,`�. � ...�..' °� +w s�� r �� e, � . y fi� �1 / 4 . �� ' ,• �""�. � /' Y�,{t i P� � .v ���—.9Yr �` �7 i t �pd , • '' .r �y � r i� i I ► � T '� o' i� i <w i � � / � . • �. � � L e . ;� :o � 3 6 � 1 i �t: � '� {i. � �y' ' ..d�' �'' t_ �' J y; s.� ,"`�„ i.;ur•rr_ ,k:' � ��4 t. ;f +r. � :� � � .i ,�; �; ��!�. *�.a�, ..��::• �.. ��'f, ., .� �� .'. Figure 4-West Pond Topo Survey Page 6 of 20 Storm Water Management System Assessment Orono Truck Station Wetland Status National Wetland Inventory (NWI) maps were reviewed to tletermine the jurisdictional status of the storm water management system. Based on Figure 5, no wetlands are present in the vicinity of the East pond. The west pond is a part of an existing wetlantl. � � l � � r�•� � � :..� -� `,�`�� ' ,� :� f• ����q� ���'��1'��lA'.��T.'� =.�<. �w�tw �.. � . '� � ' '+`' �_� 1 � �� ' - . ��� �,--'Y .. �. �' ^ , , , � ,Ff i rt�, , #""`��',�`�`�a���� ta�j + �„-.. ., ' ' 'r� ,�,. �, , .rr.. �:�� �,' Fi�+� . . '"� �; l � rj ,,. �� � �. . ��;�� l't-.�, � � r�. �"� � ��✓�"<, '� � �( � �� :r'� , :c � � !r` � � ����� � , . '� �� '`�'� � 1.•� "� /�p�;� • c y}1 , ;� �p".' _'� t ' v f f.�' Y - ` . .:c ... 'T� .. ! .� _� * ge.• F�S'}� ������i,. �'�' Oron ix�,�;St� ion `-» • �.. :�• � � r'� *' ��+` �+''�; � •.oL W ,4~,. �,�.:� LL��o ruckSt � n'+�'� : . ��. �;S"'1 ' �j �'re.�� R �+ � ��'�1�1 Q r y � ; , R •;y � �' w. �r.�,� .4. � �ro' �� �� ,Tr � y�� ... - }N�. �, ��k . ar ,�� � ��'•� � � �t±�� f� �,t ♦ . E�li 4,' �•` � +r 4 �� S � ^~• �` �� A• ' � { *��� �,� � . . P . s '+� ' y � ,'.. :'I� ��. �g �'9. y �":. .P ,+ L' :� � � '�C. 't�4'��Y�•,'�i �` � . � 6' � ��' �� � ' � � ' �' V�- .���"``� �:. ��� �t � fl A a 3�� Y ,` ��� �.�i� • ` t �� it �''+` �"'.'s • �r X� _ � . . r` ; . . ��• i �''s __ �t �r'S�e i ,r"f �� ��' •I�p�, ... _ ���ayt.�...... i_. . .. . /�d�'SlYMiT��'<-..k.'.. !v ' T1 ... y�, _f � ., _ � ,... � • �a . � , --. ._.x.: � >.: � �'�f- i r... �: . � ... :� , , �:,,.. r t, �ry.= +�t Figure 5-National Wetland Inventory Map(1/9/14) Page 7 of 20 Storm Water Management System Assessment Orono Truck Station III. Existing Conditions The Orono Truck Station storm water management system was inspectetl on January 20th(east pond) and March 4th (west pond). Skies were cloudy and temperatures were in the low 30's at the time of the first inspection, antl skies were cloudy and temperatures were in the teens at the time of the second visit. A follow-up inspection was performed on June 11th to observe those aspects of the storm water management system that were untler snow and ice cover. The purpose of these inspections was to evaluate the existing vegetation, runoff sources, inlet and outlet contlitions and pond condition (including a determination of the depth of accumulated sediment). Photographs taken during the inspection are included in the Appendix of this report. Vegetation Due to snow cover at the time of MFRA's first site visit, a thorough review of the vegetation could not be completed. At the follow-up inspection, it was observed that the east pond area is almost completely covered with cattails. Cattails typically do not grow in water deeper than 2 feet, and the maturity of these plants intlicates that the permanent water level of the pond is consistently at or below 2 feet. The west pond is also densely covered with cattails, which is not abnormal for a wetland with shallow standing water. Buckthorn was noted in the west pond surround. Both cattails and buckthorn are considered an invasive species and could be removed; however, their presence does not affect the ponds' performances. Additionally, the "Storm Water Pond Inspection" prepared by HDR in 2005 noted the need for a vegetated buffer to be reestablished near the northeast corner of the east pond. At the time of the inspection, it appeared as though this maintenance issue had been resolved and a lack of vegetated buffer was not observed. Table 1 lists the plant material that was visible at the time of the inspection, most of which is appropriate in a storm water pond. Page 8 of 20 Storm Water Management System Assessment Orono Truck Station Table 1 —Vegetation Onsite East Pond Common Name Scientific Name Smooth Sumac Rhus labra Hone Locust Gleditsia triacanthos American Elm Ulmus americana Reed Canary Grass Phalaris arundinacea Common Milkweed Asclepias syriaca Canada Goldenrod Solida o canadensis Cattail T ha S . Common Burdock Arctium minus Vi inia Cree er Parthenocissus a►vensis Common Buckthom Rhamnus cafhartica Smooth Brome Bromus inermis Lea S u e Eu horbia esula Box Elder Acer ne undo Field Bindweed Convovulvus arvensis Basswood Tilia americana Riverbank Gra e V'�tas ri aria Drainage Area The retention ponds receive runoff from the facility's buildings, landscaped areas and paved areas. No new impervious areas are known to have been added to the facility since the ponds'construction in 2002. Inlet Structure East Pond The 2005 technical memorandum noted that a side bank near the inlet of the east pond had experienced erosion problems. Vegetation has filled this area and the erosion issue is no longer apparent. Due to snow cover at the time of MFRA's first site visit, an inspection of the both ponds' inlet structures could not be completed.At the time of the second inspection, the 15 inch HDPE inlet pipe was being encroached upon by vegetation. This vegetation should be cleared to allow for better flow and maintenance access. The inlet pipe was in otherwise good condition and no erosion was noted. West Pond The west pond inlet structure appears to be an 18 inch flared end section that receives runoff from the truck station facility(the west pond also appears to receive runoff from the east pond through a culvert crossing under the road). At the time of the second inspection, the 18 inch flared end section and riprap were in good condition. A small amount of vegetation has begun to grow inside the flared end section and should be removed to prevent clogging of the system. Page 9 of 20 Storm Water Management System Assessment Orono Truck Station Outlet Control Structure East Pond Due to snow cover at the time of MFRA's first site visit, an inspection of the outlet control structures for both ponds could not be completed. The 2005 technical memorandum noted that a grate should be added to the 18 inch corrugated metal standpipe. At the time of the second inspection, it was observed that this maintenance issue hatl been resolved and that the standpipe and surrountling riprap were in good condition. The standpipe drains south to a ditch where runoff then flows overland to the west pond. The downstream carbon steel pipe is in good condition and no erosion was evident in the ditch. West Pond The outlet structure of the west pond appears to be a 30 inch flared end section. This flared entl section is adjacent to the 18 inch flared entl inlet and causes concern for short circuiting of the wet pond. At the time of the inspection, the outlet was clear of vegetation and in good condition. Survey East Pond A survey of the setliment depth was taken at two points in the east pond: between the inlet and outlet structures, antl in the eastern section of the pond. A viable thirtl point coultl not be surveyed due to the density of cattails. The coordinates of the two points have been provided so that their exact location may be revisited. Survey point locations are shown in Figure 6. ..t N r t � E � *. � '.�' •� 'r,,.,,�'�`",�„ti �/ � +� # �� .�"� � w ��~ '` �� i � � � t a.�""�' �,�, �I�"` _ _"_'"� �j' � �r,.,�w+.ir.eru'e�° � ! �� { 'ti �,...�1 � � C / ` � r �� � �' ( � � 'r-4i4' ` � �l � � � ► ��i� 1 +'- / � �q� 1 r �/ ��. �--� ' 938'. �� ` + r � • � at � �— � ��..� ' , �� A�� } �1 -� _V r '". ` � �'93�'- ♦ i / � � � - 1t� � �qr y f • ,: , > ? i n a ' .L + r -� �,t� `= / . �,� y" l �� ' / �9�� r. .� � e, ei`p ++� � .tt � e'�' ',,,r►�"" , ���y � � / .I�c '�y ` 'i r�6 �r� ,L '' � .^' � M' �� 6 �► � j � , ' . ,. ',.• '�IG.... ' ,,„„.�"" .� 3�irj� � I .•�,,,,,. ' � •. � ,�p — $ ' i „� s ... ..•' ... .... �+'!. � � . � �'' -' �. ! j ` / � p� Figure 6—Survey Point Locations East Pond Page 10 of 20 Storm Water Management System Assessment Orono Truck Station Table 3-Surve Measurements East Pond Rod Readin A roximate Elevation To of Stand i e 2.66 937.58 Invert of Stand i e" 5.21 935.03 Location:OR-1, Between Inlet and Outlet Structures Coordinates: 152682.197,438536.391,850.432 To of Ice 6.02 934.22 To of Sediment from Ice 1.0 933.22 Bottom of Sediment from Ice 1.7 932.52 De th of Sediment 0.7 ft Location:OR-2, East Section of Pond Coordinates: 152708.701,438593.500,848.914 To of Ice 5.97 934.27 To of Sediment from Ice 0.7 933.6 Bottom of Sediment from Ice 0.5 932.8 De th of Sediment 0.8 ft *Known elevation from 2005 report used as benchmark It appears that an average of 0.75 feet of sediment has accumulated on the bottom of the basin. Page 11 of 20 Storm Water Management System Assessment Orono Truck Station West Pond A survey of the setliment depth was taken at two points in the west pond. The west pond area is dense with cattails and a third point a distance from the first two was not feasible. The coordinates of the two points have been provided so that their exact location may be revisited. Survey point locations are shown in Figure 7. �yp� �` � ��p �z��p'�'�. '���y,�"'�jr [ �� £� � s't' 4'yf�� �1~ tY, �� i h��'7��.��1`+w1S`�jy§: "p ..e � '�F cF^.i$��,��� �s FP' .f� ,,-� �' `� �I �a"�a r r r d u, ....r-; '�` . ,�ak� a �{R ��,� �, �' 1r a�F :. y ��:1:'lG�f;'. 3@'�� d'' �' � � :� '�"�',�,�`r.=.� �� z �'�r' ;�"' . �� � .1 y . �{� ±u1�4�,.a�. �F. � . ' �.< . �.�"�'''k` .�, �.,�� ����-0s`� °��.�� T"'�� �,� w` t� � �.'.. � i,k���,c}� "'E�, ., �, af' �` �,� � a�y� :,��"R &� � . '� 2 f� ��:,a. .r,. ��,�.>. 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" +. `�' w,, ,�+"'� g�¢ �{ a «t„w .r+ � '�F * Figure 7—Survey Point Locations West Pond Page 12 of 20 Storm Water Management System Assessment Orono Truck Station Table 4—Survey Measurements West Pond Rod Reading Approximate Elevation Location:OR-1 152665.567,438197.848,838.386 Top of Sediment from Ice 1.0 NA Bottom of Sediment from Ice 2.6 NA Depth of Silt 1.6 ft Location:OR-2 152674.771,438167.812,838.797 Top of Sediment from Ice 1.0 NA Bottom of Sediment from Ice 1.8 NA Depth of Silt 0.8 ft Note: No benchmark elevation was available It appears an average of 1.2 feet of sediment has accumulated on the bottom of the basin. No standing water was observed in the west pond and the sediment deposition could be described as mud or slush like. Evaluation The East pond has been in operation for 12 years and during that time appears to have been functioning properly. However, the maturity and prevalence of cattails in the east pond is an indication that the permanent water level in the East pond is below 2 feet. The design permanent water level of the east pond could not be determined from the 2005 technical memorandum or from the survey provided by Hennepin County Property Services. The 2005 technical memorandum noted no sediment accumulation in the East pond, and it is assumed no removal of sediment has occurred since the pond's construction in 2002. The West pond was already in place at the time the East pond was constructed. It is unknown how long the West pond has been in use. No record of maintenance activity in the West pond was available, and it is assumed no removal of sediment has occurred in the West pond. Page 13 of 20 Storm Water Management System Assessment Orono Truck Station IV. Recommendations As previously stated, a follow-up site visit will be completed in spring 2014 to observe the inlet structures, outlet control structures, vegetation, and sheet flow perimeters. A completed Stormwater Basin Questionnaire has not yet been received from the facilities manager. Completion of this survey would allow for greater understanding as to whether the ponds are functioning properly or if problems are arising with inlet/outlet structures, vegetation, or erosion. Based on the first inspection, the following actions are recommended: �► Any vegetation encroaching on the inlet, outlet, or emergency overflow structures should be removed. This maintains proper flow through the pond and ensures that all structures are accessible for maintenance. y Further analysis of the east pond outlet control structure design should be completetl to verify if the permanent water level in the pond is at the design elevation. This analysis should include review of adtlitional design documents (subject to availability) as well as visual inspection of the outlet control structure, which will be completed as part of the follow-up inspection in spring 2014. If the permanent water level is lower than the design elevation, further evaluation should be completed to determine the cause of the low water level. y Accumulated sediment should be removed from the east pond. A scaled drawing of the pontl was not available, and no estimate of sediment to be removed has been calculated. y Accumulated setliment should be removed from the west pond. Since the west pond is a wetland area and there is no documentetl record of a stormwater maintenance plan, approval from the Minnehaha Creek Watershed District will be required prior to performing maintenance activities in the pond. A scaletl drawing of the pond was not available, and no estimate of sediment to be removed has been calculated. � The buck thorn near the west pond is an invasive species. It could be removed and the area routinely mowed to prevent reestablishment, but its removal does not affect performance of the pontl. As noted above, approval from the Minnehaha Creek Watershed District will be needetl prior to performing maintenance activities in the west pond. � We recommend that Hennepin County consider a 15-year cycle of sediment survey antl removal for both ponds. �► Please refer to the attached maintenance schedule. When removing vegetation, care should be taken not to allow any removed vegetation to clog the outlet structure, to re-stabilize bare areas to prevent erosion, and to avoid exposing the pond to hazardous chemicals. A permit is not required to perform sediment removal in retention ponds. However, in June of 2012 the MPCA published Managing Stormwater Sediment Best Management Practice Guidance for Municipalifies, which outlines how to efficiently test and remove sediment from retention ponds. Since the purpose of the stormwater pond is to collect and retain pollutants, sediment should be tested according to this guidance document and the sediment disposed of properly. Page 14 of 20 Storm Water Management System Assessment Orono Truck Station V. Appendix Photos �� �� �� � ` � y� . � �#:�Y � ' �Sr i . � '�' C �,` ;�i� rs 4 , �� "` � � �'� �-- � ` �'� s�� „�'� , . . _ r� .�, � � •�'� �� � i ,� t t M� 3` � , . . , ... ,, , ��:, �. �LL�. ���;� � . ... � � . ' " { Y ' � , %"` `-+ti.:.. . � �'�`e ��'�'��� �1,�1��'1i,V• �� .�,s:, � �� •i����" ��► 1� � � :�,'� . � . ,� ' ' �4 '� � �.�� , ,-��,��� � � � �� . � , �:t �►, � w+� �` �:;� �� 1��i ' T =+� � �� '� �y�. , � t�i.�� ��l ��' ,�� �` �, 5 .��' �,� t � +� �� ��:,h '� fi 3 �'"r ,� �p„ k� �� ,q�'' ��:.ti i�� _��' _ ` �� � ., , . . •�, -;a .. S'���,r� .k,�'�\` ��� :� i Figure 8—Photograph of East Retention Pond from West � . , • . , �.. R ' . ... �� � .+" -Y , '� ' . � _ i �.4 � t� �� � ! ,�' � �1+,�� . .s,� �������,.e� � � � �� - - � � � �, '/ /�� ' � _ ! ` t r,� �'` � I . � ., � „ � `�r , 3�. `. ` � � 6',li►.�` — � •�t.. � �� ,�, � � � � � ' \ ti.. , � �,�, � .i-!'�" �«" � � -� �� ,F;,_ ; � � � � �� ���`' ��� � r��� \ � � , r �• '� _ � , : � •, .+ ,�:'. "'� i ;_ -- � c � � �� ' t " � � " . . ` �. � , f �y �; � e. 'f . �� '=" ,;� � � �, '� �\�� , `� { , i � . i�` I i: "� � � � ' .. . - � �, , � ���r �� -. 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'� ,�?���`�. `� ��a+� i°�' � ��,i .� s4� �� 4;� c, �j ��' ���A i "-� P � Y'+G�, d '`� �,µ '� ��` �Q�.�O� a. x �.. 3 b^'�`y�i� ,r ��4L .-�i,�c-`' �� _` _ '+i r �. ' d�"ry_. . �y'`'� y i ,:� '�:��,. �� ¢ ��� f . � �, ,r '�� �� � .����. ' _, ! _. _ ' P {' . '� . e �j '� �.� k �' ` �'�� � ��� 7 ' .e t„ep�A 4?' .�.;��y.1`'� �' A yp s�'v ''��� ''g�. t -. ".� „;i� ��;^.� i° Ff�.'C F� "^�... 4 ,� :'� ` ' . , � ..', -rp,�,�, � s� ,�y,'r��r i ,.w �tis'��, - � ,. ,"�w ; ,� � �� j .p w'.. fi�F,r+ .. `�; . . "#�.f t ° ...� *� ,`�'d. ; `�. �G�:v- "' ws ;, ,._ �t� _• � . Figure 15—Photograph of 18"FES Inlet on Left and 30"FES Outlet on Right Page 19 of 20 Storm Water Management System Assessment Orono Truck Station Storm Water Pond Maintenance Schedule Maintenance Procedure Frequency Item Wetland Monitor wetland vegetation health and composition and replant lost vegetation. Spring and Fall,additionally as Vegetation Remove all wetland vegetation encroaching on inlet,outlet,and emergency needed to allow visual overflow structures. ins ection of the ond Non-native or The pond and pond surround should be inspected for the presence of non-native Spring and Fall,additionally as Invasive and invasive vegetation. Identified species should be removed—through mowing needed to allow visual Vegetation or other means recommended by the DNR.All vegetation on the berm which inspection of the pond im edes access to ond should be removed. Erosion Inspect pond and pond surround for bare or eroded soils,repair damaged areas. Spring and Fall,additionally as needed after large storm events or washouts occur Debris Inspect pond and pond surround for debris;dispose of all debris properly. Spring and Fall,additionally as debris build u is noticed Inlet and Outlet Inspect inlet and outlet structures(including all corresponding grates and orifices) Spring and Fall,additionally as Structures for clogging and damage.Remove sediment or debris from the structures. any problems with drainage are Replace damaged grates/valves. noted A report, including photos,should be made in conjunction with any cleanings or repairs to document the pond's condition.Frequent removal of sediment from outlets may be a sign of other unde�ying problems,such as erosion and loss of sediment stora e de th in the ond. Easily Inspect risers,barrels,embankments,and pipes for damage. Repair or replace Every one to three years, Accessible any damaged components. additionally as problems with Pond pond function arise Component A report,induding photos,should be made in conjunction with any repairs or re lacements to document the ond's condition. Hard to Reach Remotely inspect(i.e.televise)components that are not easily accessible,such as Every five to ten years, Pond under-drains,reverse slope pipes,or submerged/buried pipes.Repair or replace additionally as problems with Components damaged components. pond function arise A report,including photos,should be made in conjunction with any repairs or replacements to document the ond's condition. Sediment Visually monitor sediment depth during routine inspections.Complete survey of Monitor yearly, survey every 5 sediment depth and remove sediment when pond functionality is impaired. to 10 years,remove on a 5 to 10 or 15 year cycle based on rate of sediment accrual Normal The pond water elevation should be inspected to ensure that the normal water Annually,and more than 72 Water Level level is being maintained.Water levels below the outlet structure may signify a hours after large rainfall events For Retention leak in the outlet system.Water levels that remain above the outlet structure for Ponds lon er than 72 hours after a rainfall event ma si ni a clo in the s stem. Mosquitoes If problems with mosquitoes arise,possible solutions are participating in a As needed mosquito control program through the state or hiring a private contractor. Presence of mosquitoes may be a sign of another underlying problem,such as shallow onds in the pond embankment and sta nation. Page 20 of 20 Storm Water Management System Assessment Orono Truck Station Stormwater Basin Questionnaire Please complete the following survey and return it via fax, mail, or email. 1. Have any issues been noted during rain events, i.e.,water ponding in unwanted areas, plugged outlets, or draining taking longer than 48 hours? 2. Have any changes in vegetation occurred, such as vegetation dying or the presence of a new plant species? 3. Have any possible hazardous materials entered the basin from vehicles or agricultural runoff? 4, Have any impervious surfaces been added to the basin's drainage area since its installation? 5. Have any noticeable erosion or washout problems occurred? 6. Has any maintenance been performed on the basin/storm sewer system since the basin's installation? 7. Do you have any additional comments about the basin's performance? All questions can be addressed to Jessica Tello at 763-259-6679 or jtello .mfra.com . Thank you! TECHNICAL MEMORANDUM HDR ENGINEER/NG, INC. STORM WATER POND INSPECTION HENNEPIN COUNTY, MINNESOTA Orono Truck Station Facility 11/4/2005 Reviewed by: Mike Johnson P.E. CFM, Dave Johnson Prepared by: Foad Hussain TABLE OF CONTENTS INTRODUCTION................................................................................................................................ 2 PONDDESCRIPTION......................................................................................................................... 2 WetlandsStatus.................................................................................................................................3 PONDCONDITION ............................................................................................................................ 4 ExistingVegetation..............................................................................................................................4 RunoffSources.....................................................................................................................................4 InletStructure.......................................................................................................................................4 OutletStructure....................................................................................................................................4 SedimentElevation Survey..................................................................................................................4 OverallAssessment........................................................................................................................... 5 RECOMMENDATIONS...................................................................................................................... 5 APPENDIX—PHOTOGRAPHS.......................................................................................................... 8 11/4/2005 HDR PROJECT#32560 1 HENNEPIN COUNTY,MINNESOTA ORONO TRUCK STATION FACILITY STORM WATER POND EVALUATION TECHNICAL MEMORANDUM HDR ENG/NEER/NG, INC. INTRODUCTION HDR Engineering, Inc. (HDR) was retained by Hennepin County Property Services to perform an inspection of the storm water pond and to make recommendations for long-term and short-term maintenance of the pond at the Orono Truck Station Facility. This technical memorandum describes the information collected during the pond inspection, documents the pond condition, and provides recommendations for the maintenance of the pond. HDR conducted an on-site inspection of the pond on October 19, 2005. At the time of the inspection, the pond was not drained and was near the normal pool elevation. POND DESCRIPTION The Orono wet detention pond was built in 2002 at the east corner of the facility. It was designed to receive storm water runoff from the Orono Truck Station site, which includes the facility building, landscaped areas, and roads and paved parking lot. A plan view of the pond design contours is provided in Figure 1. � B A 5.� Tj �� " ' �'�, ^ _�� _ _Y'�^ - � S ��� ` t"`�1, '� . � — • '4 i . _.,,; _ ��fti�k i ty' -- _. -- -""''�' ! I .• .�= ; �;�i , `��. 1 's•- _. ' a�r _�>�5 I � � ! - � �' t l, fi� 1 .� �.` � �y ti7 �`� j J , _t_ __ - _ _ -».•. - ! y _ � -- � � _ 0 .- - 1� 1 -_ �r1.r _ _ ' u � , t � .p� .a. P�F1Qf^ .��:r.•y��;f".J -E_►.�� =r � � ' � E�iu I 6' G�P -- � _ - � �i+,.ert . 9as..,� ..-� f L, 1' � �_x ��y'V-�' '�+s�. —�.r: ~' '�5 ti.,y, _ � - �~ ` � ''t � 'i:,^ r�. -- C�' L � � - 4��' T /�r� ��.j�,.�' ��+� - ^ - �- -yw- - � l JJ` J � 1 �_ ,Ti°'-�_A��'✓Y' .,y;' 'f.- �a{ Jii~ ^ � ��,L ) ..i �, • ' - ` '' 1 ��I �� --•���— »^ _ _ -=_wi"S+��/ �-'�- ,w v-'"��F�=l 1��'�r � 1 e; � y __ � .� ..YIC.-1f7�Z^' _`�-_r'SL'-_7/ - _ ��11\'._7Sr_vY':�.��` 1' 1 �� Y �Y r � f�^ - "� � � '� ' �� ` �'�� - ~5 `l ��,• L " �� - L � � �. •- L'��Y�= ^ IL +��•� :11 � ,wt -� L 1' � ' L J r �� e Figure 1 - Pond Layout Plan View The Orono detention pond consists of one inlet and one outlet structure. The inlet structure consists of a 15-inch polyethylene pipe and is located on north side of the pond. The outlet structure consists of a corrugated metal standpipe, which has a diameter of 18 inches, and is located on the west corner of the pond. The downstream end of the metal pipe consists of a concrete flared end section without a trash guard/grate. Rock riprap was placed on the edge/foot of the inlet and the outlet structures to prevent erosion. Storm water enters the detention pond through the inlet culvert and is stored until it reaches the maximum storage capacity of the pond. The approximate bottom elevation of the pond per the design drawings is 933 ft as shown in Figure 1. The highest elevation up to which the water can be stored in the pond is 938.65 ft (top of standpipe), as shown in Figure 2. 11/4/2005 HDR PRO.IECT#32560 2 HENNEPIN COUNTY,MINNESOTA ORONO TRUCK STATION FACILITY STORM WATER POND EVALUATION TECHNICAL MEMORANDUM HDR ENG/NEERING, INC. 56.D Lt iB" CS ?1PE + APRON.t� 1.01L � . PROP. F1N[SHEq St1RFACE E%ISt1NG 5t1RFAC� � T� OF t6' CMAP . � � STANDPIP� = 938.65` � � • FLCp'L1Mdf. ELEV = 935.00'� FLr7WLIt� ELEY = 935.�7'' ' PI,AC� APRON . . Figure 2 - Pond Standpipe Culvert Profile Wetlands Status A review of the National Wetland Inventory (NWI) was performed to investigate the jurisdictionai status of the pond. The Orono Truck Station pond does not appear to be part of the NWI as shown in Figure 3. � y ,� �.L:. .r j.. ,. �.�. ,r:. . ,_y 5� ..t�y,.�• �r � :.�:.�•,.,� T yy�}� y' �•{, , • 5 �: ��`4• _ I F �.1. ����' '..t� �:.'��y,�"ti��• �.,'. ,_t` i 5' . • :�-5i�'��.":''�5`,° :i•, •J•-�, ' - ';7':• ���,,-S;;�•�'`'.�`•'. � •�'� •ti r .••r . ,?� , .. .. 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Figure 3 - NWI Wetland Location Map 11/4/2005 HDR PRo,IECT#32560 3 HENNEPIN COUNTY,MINNESOTA ORONO TRUCK STATION FACILITY STORM WATER POND EVALUATION TECHNICAL MEMORANDUM HDR ENG/NEER/NG, INC. POND CONDITION A site visit was conducted by HDR to assess the existing condition of the Orono storm water detention pond on October 19, 2005. The purpose of the pond site visit was to inspect the pond condition, assess its current performance, and perform level surveying to determine the approximate depth of the sediments deposited on the pond bottom. Photographs taken during the site visit are included in the Appendix of this report. Existing Vegetation Almost the entire periphery of the Orono Pond was covered by medium size vegetation, except the northeast side bank of the pond (area around/near inlet). However, no vegetation was observed near the center of the pond. The pond periphery (except the northeast corner) supports a medium population of reeds and sedges, which are extended into the pond. The assessment team was able to walk through the vegetation without any problem. Overall, the vegetation supported by the pond is normal and desirable for the pond operation. The northeast side bank of the pond lacks a vegetative buffer strip and is experiencing erosion. The balance of the pond surface is open water. Runoff Sources The drainage area of the Orono wet detention pond consists of the paved parking lot, truck station building, roads, landscape areas, and storage facility. The visual inspection of the Hennepin County Orono wet detention pond revealed the pond site is moderately clean and no floating debris was observed in the pond. However, some garbage/trash (bottles, cans, etc.) were noticed at the side banks and near the outlet structure of the pond. Inlet Structure The inlet structure of the Orono wet detention pond appeared to be in good shape. The inlet culvert/pipe discharging the runoff into the pond had no visible problems. However, no grate was observed over the inlet culvert/pipe. Moreover, no sediment deposition in the inlet pipe was observed during the inspection visit. Rock riprap was provided around inlet structure and at the foot of the pipe to prevent erosion. It was noticed that the side bank near the inlet of the Orono pond has experienced erosion problems. Since no vegetation protection is available in that part of the pond, the soil has eroded away and some cracks in the side bank were observed. Outlet Structure The outlet structure at the Orono wet detention pond was located and visually inspected. The metal standpipe installed at the outlet structure had no visible problems. Rock riprap was placed around the outlet structure and the bottom of the pipe to prevent erosion. Sediment Elevation Survey The purpose of the elevation survey was to take several measurements as close to the pond bottom as possible to try to ascertain the amount of sediment deposited in the pond. The Orono pond had vegetation around the perimeter and open water for most of the pond surface area. Depth measurements were taken at points in the pond that could be safely accessed by the survey team. The invert of the downstream end of the outlet structure was at an elevation of 934.31 ft per the design drawings and was used as a reference elevation. Elevation measurements were taken at several locations within the pond (Table 1). 11/4/2005 HDR PRo.IECT#32560 4 HENNEPIN COUNTY,MINNESOTA ORONO TRUCK STATION FACILITY STORM WATER POND EVALUAT/ON TECHN/CAL MEMORANDUM HDR ENG/NEERING, INC. Table 1- Summary of Pond Level Measurements Staff Location �taff R�ading *HI , Ei�vs�an ' (�) ��� ��� "*Invert of the d/s end of the outlet structure 9.54 943.85 934.31 To of the d/s end of the outlet structure 8.00 943.85 935.85 Invert of stand i e 8.82 943.85 935.03 Invert of Inlet PE i e 8.36 943.85 935.49 To of Inlet PE i e 7.04 943.85 936.81 Ed e of water 8.63 943.85 935.22 Ed e of water 8.62 943.85 935.23 Bottom of ond 5 ft from outlet 11.22 943.85 932.63 Bottom of ond 8-10 ft from outlet 11.42 943.85 932.43 Ed e of water 8.72 943.85 935.13 Bottom of ond 5 ft from inlet 10.95 943.85 932.90 Bottom of ond 8-10 ft from inlet 10.98 943.85 932.87 '`HI=HEIGHT OF THE INSTRUMENT. "'`INVERT OF THE DOWNSTREAM END OF OUTLET STRUCTURE WAS KNOWN(934.31 FT). Based on the measurements taken during the survey, the amount of sediment accumulation in the Orono pond appears to be negligible. Given that the water surFace elevation in the pond is not above the design elevation, the pond outlet (standpipe) appears to be functioning and appropriately draining the pond. Overall Assessment Given that the Orono wet detention pond was constructed in early 2002 and has been in operation for approximately 2.5-years, it appears to be in good shape and is functioning as intended. The presence of vegetation along the boundary of the pond indicates that influent storm water brings plentiful amounts of nutrients and some percentage of these nutrients is being removed from the storm water discharge flows. Although the side bank near the inlet structure has undergone erosion and needs immediate attention, it appears that almost all of the storm water pond components are present, intact, and functioning. The amount of sediment in the pond is negligible. RECOMMENDATIONS Based on HDR's inspection and assessment of the pond conditions, few recommendations are proposed to improve or sustain the pond's performance. The recommendations are presented in a tabular format in Table 2. Additional discussion relating to an action item is noted in the Comment Item column and the related comments are provided following the table. 11/4/2005 HDR PRo.IECT#32560 5 HENNEPIN COUNTY,MINNESOTA ORONO TRUCK STATION FACILITY STORM WATER POND EVALUATION TECHNICAL MEMORANDUM HDR ENGINEERING, INC. Table 2—Action Items Action �tem �escriptian Recornmended Time ��rr�nt to Comp�ate ltem The side bank near the northeast corner of the pond As soon as possible. A has experienced erosion and requires immediate repair measures. The vegetative buffer strip should be reestablished in that part of the pond to prevent further deterioration of the side bank. The grates should be installed over the inlet culvert and As soon as possible B the outlet culvert (downstream end) of the Orono wet detention pond. The vegetation around the downstream end of the During normal, C outlet structure of the pond should be trimmed where it scheduled maintenance impedes access to the outlet structure requiring periodic and as needed. inspection. A periodic inspection of the pond should be scheduled As needed D to keep the pond in operating and optimum condition. Comment Item A The northeast periphery of the Orono pond has undergone erosion and some cracks were observed in the side bank during the inspection visit. It was also noticed that the northeast side bank consists of the low cohesive soil with lots of small pebbles and rocks which might be due to construction of the storage facility (constructed after the pond ) further north of the pond. The top soil of the northeast side bank should be immediately replaced with the fertile cohesive soil and a seed mix should be sprinkled to develop a vegetative buffer strip in this part of the pond. The vegetative buffer strip will not only provide slope stability to the side bank but also improve the water quality and pollutant removal efficiency of the pond. Comment Item B The grate over the inlet structure and outlet structure (d/s end) at the Orono wet detention pond was not seen during the inspection visit. The provided design plan sheets do not include/show a grate over the inlet structure and the downstream end of the outlet structure. It is recommended that the grates should be installed over the inlet and outlet structure to trap the trash and debris and improve the water quality of the Orono wet detention pond. Comment Item C The degree and density of the vegetation around and in the pond is appropriate at this time. If the vegetation at the location of the inlet and outlet structures becomes excessive and impedes access for visual inspections, it should be thinned as needed. The growth of large trees should only be allowed where they will not impede the performance of the inlet and outlet structures and will not compromise bank stability. 11/4/2005 HDR PRO,IECT#32560 6 HENNEPIN COUNTY,MINNESOTA ORONO TRUCK STATION FACILITY STORM WATER POND EVALUATION TECHNICAL MEMORANDUM HDR ENG/NEERING, INC. Comment Item D A periodic inspection schedule should be compiled and followed. Table 3 provides a suggested maintenance and inspection schedule. Table 3— Maintenance and Inspection Schedule Maintenance Item Description Frequency Remove accumulated trash and debris from the pond side Twice per year slopes, embankments, and inflow and outflow structures. Mosquito control As necessary Storm damage/ Site spill incident As necessary, especially after extreme weather events or uncontained material spill that may flow to the pond. Remove excessive vegetation growth that impedes access to As needed during the pond structures. growing season to maintain access. Perform visual inspection of pond inlet and outlet structure. Twice per year. Remove accumulated debris that may impede the inlet or outlet flows. Perform or schedule repairs as needed. Perform an annual inspection of the pond to make sure it is Annually operating as desired. It is recommended that a digital photo reference point should be established from which annual maintenance assessment can be made and the pond condition photo-documented. The pond should be drained and the following items should be checked: ❖ embankment subsidence ❖ cracking or excessive tree growth on the embankment ❖ damage to the outlet standpipe ❖ sediment accumulation at the outlet ❖ sediment accumulation around the inlet •3 inadequacy or failure of bank or other erosion controls ❖ changes to the pond configuration ❖ changes to the contributing watershed that may affect the pond Sediment removal 5-to 15-year cycle, 10 year interval recommended 11/4/2005 HDR PRO,IECT#32560 7 HENNEPIN COUNTY,MINNESOTA ORONO TRUCK STATION FACILITY STORM WATER POND EVALUATION TECHNICAL MEMORANDUM HDR ENG/NEERING, INC. APPENDIX - PHOTOGRAPHS � , � � :, � ��`Y " �i�i �'' �'.:"�` ' � ; � �� � ' � � _ , � a�� . �,�. ,: ,. k�,'"^�,�� -�_�`. '�a . �� �( ` 1* `'���� '4� i . , 'r .d 1 ; tA� '� ' � `'`� _ i" ' �4r L j�'. , : !'�'. '�i� �� ^,�, f�'� ,t, ��` rs .+a; �" ��±,. 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("ti' -�.� � ..� _� �;' � d�_ �� . ��,(.� �t �.. x �� �y� E'°�t� '3 . w��,y' r� ._+gar�`n+P*a �+f1�1:iy :� /�j�'� �..t� +4'r <. tit,�, s� '��� �Q' i � ����1 fd.. a4�„y �:,hy q� �. �`, ' , � �'E ��1, � g�(R�w�o� � 7 � �'' .r � �{ x+"'r: �e �'� � � �.'.;r' b kli�i r �i' `v�' ,. �y�jX�B� r�,W;--.. '� ...���'-7� 3���.1� '�}�a� ` y g��a ��� � ,a'.�` ' ' ¢c.i�:m�j� �q '1� T d ' ti . �r 9t r � �-j . ��». . , + a e`���� '►`�`� �'� ..4s 1'� 'd �y •:.� > y ..r , — � R,(V�'�G a..� ` ��. �� ,�1'.y'�'1�a t �.;.. .,� :^�_..-- - � f�'` i`� �'- � �,y;.. i.�� ., � �6` ',�s.<< �'+`'�, • ' .._� - . , p .,,� 4'��t,, .:.:., ' ���t ♦ 7�, `� �, .�«f., �.-y'`�+�`�'�ca��. ;��,� '�"t ..;w'"�.S�,'� .'.�' ��`� . �_ !�"� a'�,��iyk '1 ��'�a�� '•'���`��j�'�_ i. �.. ... ,� ,� s,�1°�" ��� - ~-�—i .' :� +�,�l�.: ... :�.p X {�� �� ��' !,,'�. - ��'s; ' a� -:-��r�f -,�,�� �;�;+r„ �.�..� "''�fri�= . . ,. :'.�r� q�F��"+��1 �� o:� �. !�� r. � �� � Q�� � � r ,f>' ��,� p►a� �p,�ee �'_. ' �� �� i _►���� y�.: rye �� a *'� , . ,r`' '�Yi �� . _ ��� �9�� a.�c•!"�� s, �,�, � « �,� '`''*[ F.�j �" �! �T \ �'� , � ,� '��y �'`+.�,�` t �p, N '�y "s.n�,4 � �� �' `� ��t��' '`�4' � A �p �!i .':�t�"��'t'' �: ft.. R • �.��,�� � ��� �.�, kq�i.� ,'���;�1.� ;� ''.;�..; ��l��� �, �. �- � -� `'� ,�,�� �tC- C �aa,".�'�3T .M � ' i. ��``�;�' i - �t;M^i�_m(,,�,�v,�� � �. ��'�.� � �`�,a✓- i1 �� � � '� ����''�� 4..�` t�d/Ll ;1� �!• `��'��ib:'i�""\�.,�'� �►`� "� ��,�'e ��.�I.Yi�-�f�Y,� ���q��.,dii��'�1���ai��.A._ A�F�yy, a� ��<�L � � � � `E .. ,c �i. e � (/�+� �� �f�;�+ �� ��` a'�,�'` ��`' ....�'.ry' .r�"� � � �1. \ �:.+. -. •�!w A� . ..ri .. u,. � �. „a��.} �'#� ������-����,�� _ Photo 5: Downstream End of the Outlet Structure of the Orono Pond 11/4/2005 HDR PRO,IECT#32560 12 HENNEPIN COUNTY,MINNESOTA ORONO TRUCK STATION FACILITY STORM WATER POND EVALUATION Orono Truck Before Stormwater System After Stormwater System Station Updates U�da#es West Pond, southeast . �� d { , . � West Pond, southeast corner d , � >;�`�� ,..r, ' � . ��� �' ����» � �.� x � �. �.���' corner at southwest '�a�,� Y f� rt t ��,. � � '�� � : at southwest corner of a ", � corner of parking lot. ����, r+ �!��w + ��; _; ��';? parking lot. Note cast iron , Note open mouth (12 �_ ��� ��' , '� cover on gently sloped rough ___ inch plus diameter)of ' � surfaced concrete apron. steeply sloped , �,;,. '� �� Stormwater flows into a � � ;�:; corrugated steel drain �,a•..� precast concrete basin and pipe—often hidden by � -� then horizontally onto rip rap � • ~� �`� tall grass or snow. �,^ in photo below. � :_�"''� , - �� / �~i�;.. � �'&d�. . y'� •r ' � w. k t�� '��, , . � � . ,. " �'f._..�` . . - �.�� T .. .. , .. . . West Pond, southeast � '`' ' '* ��� : West Pond, southeast corner. comer. Note steeply � , „ #"�,�aa."�` � . �_ � Note open rip rap for sloped corrugated steel , �'»*� � � � � stormwater drainage, '� �' = :.�" '''~ � �t`, � enclosed i e is one, rate � drain pipe(12 inch plus � �.�` �.f�� ,�a+ �b�i p�p 9 g , , �� .', � �� '"��+ in lace over o en mouth of -�!'"-. diameter)terminating "`�' :, / p p �,. � / ' • ,�. ��tr�.v . . , !�'���ii ��� ,� , j / �. underwater. Note open � ' � � �R . horizontal concrete "' . t� mouth of horizontal =;• , �,,, �;��` ' �� stormwater pipe on left. �� � ; ��"�''� concrete stormwater � '�� . �, .� �,+ � . �• pipe on left. ; r ��. �,� '�i��`.. �s::... - ` s� ` t. s •.�•y�} .p ��_ 1 � � '...'�� . :�...�y�.r' � � � ,� t '�. •.!b f�'.�} .���.' �,.., i,4 2� �t tR '�����+������"����_ . '� � �4 South edge of parking � �s<�� W F� � �' South edge of parking lot � `�'� "�; � lot near center. Photo "& ��p¢�� 3� i"' near center. Photo shows rip �l�: a . shows one of several � '��"���J��;�° �'•i'!, rap reinforced drainage area ;� �°� � � : �� ��`t�. eroded drainage areas �e ���!, ��'� K leading down rip rap covered � r°� �� leading to the east/west , . �;�,�`� �¢ surface into the east/west ���� -�` '` Y��� .� ;�.�� � .,��� ditch draining into Lake 1.; � ��' ditch draining into Lake �.; �y� �._q � ' ' Minnetonka. �,�� "� `'� ' ,�t,J :� ,� Minnetonka. Other eroded � ������_���r � �-;, ° �;�'-,. '�.� • • areas have been seeded and ;,� ` '.� ��� _ . recontoured to direct �;�� � � , , ���d��r: , stormwater to the rip rap area �p� `� + � �� � � v �iop n ie� shown in phota , _..�� ��