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Offices in Illinois, Iowa, Minnesota, and Wisconsin 2901 International Lane, Suite 300, Madison, WI 53704-3133 (608) 242-7779 (800) 446-0679 FAX: (608) 242-5664 WEB ADDRESS: www.msa-ps.com 1 MEMO To: Water Resources Management Commission From: Eric Thompson, P.E., CFM Subject: Preliminary Cost Estimates – Pond Dredging Date: March 17, 2010 Introduction The City of Middleton’s stormwater management system contains 96 structural BMPs which collectively are effective at removing 41.3% of the annual Total Suspended Solids (TSS) within stormwater runoff (as defined by NR216 and applicable modeling guidelines). This level of TSS reduction is above the minimum 40% threshold required by NR216 and places the City in compliance with their WPDES permit. Most of the 96 BMPs in the City’s stormwater management system (and all the most important BMPs) are wet detention ponds. According to current WDNR guidance, wet detention ponds must maintain a permanent pool depth of at least three feet to achieve 100% of the predicted TSS removal rate. Many of the ponds in the City’s stormwater management system have been in place for years and are accumulating large amounts of sediment. Once a significant number of these ponds, or a select few very important ponds have accumulated sediment to the point where they have less than three feet of permanent pool depth the TSS capture efficiency of the ponds will be compromised and the City will fall out of WPDES permit compliance. It will then be necessary to implement a plan to maintain the ponds through a dredging program. This memo provides a cost estimate for dredging out seven selected ponds in the City. Dredging Cost Estimates The tables below and on the following page, as well as the attached images provide a summary of a preliminary dredging program for a selected group of seven wet detention ponds. Cost Estimate Dredging Estimate Pond Number Stormwater Quality Plan Pond Number Pond Name Construction Year Construction 8% Engineering 25% Contingency Total 1 28.01 Orchid Heights North Pond 1995 $89,000 $7,120 $22,250 $118,370 2 28.01 Orchid Heights South Pond 1997 $79,000 $6,320 $19,750 $105,070 3 2.0102 South Pond 2002 $869,000 $69,520 $217,250 $1,155,770 4 1.01 Confluence Pond 1998 $1,246,000 $99,680 $311,500 $1,657,180 5 5.01 7th Addition to Middleton Hills 2004 $11,000 $3,000 $2,750 $16,750 6 6.01 Outlot 10, Middleton Hills 1995 $60,000 $4,800 $15,000 $79,800 7 49.01 West Metro Business Park 1991 $73,125 $5,850 $18,281 $97,256 Total $3,230,196 ---PAGE BREAK--- ---PAGE BREAK--- PROCESS EQUIPMENT FOR DEWATERING STAGING AREA PERMANENT SEDIMENT BASIN REMOVE MATERIAL FROM ACCESS ROUTE DETENTION BASIN PROCEDURES TO ORIGINAL CONDITION 4. RESTORE SITE TO LANDFILL 3. TRANSPORT SEDIMENT 2. DEWATERING PROCESS 1. HYDRAULIC SEDIMENT REMOVAL POND1.dgn 3/17/2010 3:24:53 PM barbh ---PAGE BREAK--- SEDIMENT BASIN FROM PERMANENT REMOVE MATERIAL DEWATERING PROCESS STAGING AREA FOR PARKING LOT ACCESS FROM TO ORIGINAL CONDITION 4. RESTORE SITE 3. TRANSPORT TO LANDFILL 2. DEWATERING PROCESS 1. HYDRAULIC SEDIMENT REMOVAL DETENTION BASIN PROCEDURES POND2.dgn 3/17/2010 3:27:36 PM barbh ---PAGE BREAK--- PROCESS EQUIPMENT DEWATERING STAGING AREA FOR ACCESS ROUTE ENCOUNTERED WHEN SOLID BOTTOM IS DOWN TO ELEVATION 923.00 OR PERMANENT SEDIMENT BASIN REMOVE MATERIAL FROM 4. RESTORE SITE TO ORIGINAL CONDITION 3. TRANSPORT TO LANDFILL 2. DEWATERING PROCESS 1. HYDRAULIC SEDIMENT REMOVAL DETENTION BASIN PROCEDURES POND3.dgn 3/17/2010 3:29:06 PM barbh ---PAGE BREAK--- 4. RESTORE SITE TO ORIGINAL CONDITION 3. TRANSPORT TO LANDFILL 2. DEWATERING PROCESS 1. HYDRAULIC SEDIMENT REMOVAL DETENTION BASIN PROCEDURES 902.00 TO AN ELEVATION OF MATERIAL REMOVED LOWER AREA TO HAVE 903.00 TO AN ELEVATION OF MATERIAL REMOVED UPPER AREA TO HAVE DEWATERING PROCESS STAGING AREA FOR POND4.dgn 3/17/2010 3:30:42 PM barbh ---PAGE BREAK--- STAGING AREA FOR DEWATERING PROCESS PERMANENT SEDIMENT BASIN REMOVE MATERIAL FROM CONDITION 4. RESTORE SITE TO ORIGINAL 3. TRANSPORT TO LANDFILL 2. DEWATERING PROCESS REMOVAL 1. MECHANICAL SEDIMENT DETENTION BASIN PROCEDURES POND5.dgn 3/17/2010 3:33:00 PM barbh ---PAGE BREAK--- 4. RESTORE SITE TO ORIGINAL CONDITION 3. TRANSPORT TO LANDFILL 2. DEWATERING PROCESS 1. HYDRAULIC SEDIMENT REMOVAL DETENTION BASIN PROCEDURES BASIN DOWN TO 916.00 REMOVE MATERIAL FROM STAGING AREA FOR DEWATERING PROCESS ACCESS ROUTE POND6.dgn 3/17/2010 3:34:27 PM barbh ---PAGE BREAK--- 4. RESTORE SITE TO ORIGINAL CONDITION 3. TRANSPORT TO LANDFILL 2. DEWATERING PROCESS 1. HYDRAULIC SEDIMENT REMOVAL DETENTION POND PROCEDURES BOTTOM SEDIMENT BASIN REMOVE 6" MATERIAL FROM DEWATERING PROCESS STAGING AREA FOR POND7.dgn 3/17/2010 3:35:33 PM barbh