Presentation on theme: "Lake Whetstone Sediment Removal by Hydraulic Dredging"— Presentation transcript:
1 Lake Whetstone Sediment Removal by Hydraulic Dredging Millions have lived without love. No one has lived without water.Turkish businessman, 1998October 16, 2013 Public MeetingMontgomery County Department of Environmental ProtectionWatershed Management Division
2 Today’s Agenda Montgomery County background What is a Watershed & Runoff?Intro to Stormwater and the MS4 ProgramProject OverviewProject ObjectivesProject Impacts and BenefitsDesign and Permitting TimelineWhat to Expect During Construction
3 Montgomery County, MD 500 sq. miles 1,000,000 people 11/2/2011Montgomery County, MD500 sq. miles1,000,000 peopleSecond only to Baltimore City within Maryland in average people per square mile184 languages spokenAbout 12% impervious surface overallAbout the size of Washington DCOver 1,500 miles of streamsTwo major river basins:PotomacPatuxentEight local watershedsDistrict of ColumbiaBrief history and tidbits about MoCo.EXPLAIN imperviousPotomac 88% of MCPatuxent 12% of MCOf the 184 languages spoken the top 5 non English spoken are: Spanish, Chinese (Mandarin), Korean, Vietnamese, Amharic (Ethiopia)Impervious: Not allowing water to soak through the ground.
4 What is a Watershed?A watershed is an area from which the water above and below ground drains to the same place.Different scales of watersheds:Chesapeake BayEight local watershedsNeighborhood (to a storm drain)
5 Seneca Watershed Drainage Area: 210 square miles Great Seneca Watershed Drainage Area: 62.5 square milesWhetstone Run Watershed Drainage Area: 4.81 square milesLake Whetstone Drainage Area: 3.28 square miles
6 Volume/Timing of Runoff 11/2/2011What is Runoff?Water that does not soak into the ground becomes surface runoff. This runoff flows over hard surfaces like rooftops, driveways and parking lots collecting potential contaminants and flows:Directly into streamsInto storm drain pipes, eventually leading to streamsInto stormwater management facilities, then streamsBrief history and tidbits about MoCo.EXPLAIN imperviousStormwater is water that originates from storms… becomes runoffTwo Major Issues:Volume/Timing of RunoffWater Quality
7 What is the County doing to protect our Streams? 11/2/2011What is the County doing to protect our Streams?Must meet regulatory requirementsFederal Clean Water Act permit programMS4 = Municipal Separate Storm Sewer SystemApplies to all large and medium Maryland jurisdictionsCounty programsRestore our streams and watershedsAdd runoff managementMeet water quality protection goalsReduce pollutants getting into our streamsEducate and engage all stakeholdersIndividual actions make a differenceFocus on watersheds showing greatest impactsFederal Clean Water Act NPDES: National Pollutant Discharge Elimination System MS4: Municipal Separate Storm Sewer System PermitMS4 Permit sets priorities for all Watershed7
8 MS4 permit, what is it? Montgomery County is responsible for: What goes into our storm drain pipesWhat comes out of themWhat flows into the streamsRequires additional stormwater management for 20 percent of impervious surfaces (4,292 acres = 6.7 square miles). That’s about three times the size of Takoma Park.That’s equivalent to 3,307 football fields!
9 Watershed Management Division Stormwater Facilities MaintenanceInspections and MaintenanceStormwater Permit CoordinationReporting, Monitoring, and Watershed OutreachWatershed RestorationStormwater Retrofits and Stream RestorationRainScapesConstruction ManagementOversees project constructionAdministers contracts and procurementCan add own photo for your own projects.
10 Water Quality Protection Charge Part of the Montgomery County property tax billFunds are used to maintain existing storm water management facilitiesFunds projects to minimize stormwater pollution, protect property and infrastructure and restore our rivers and streams
11 Resources For information such as: Local watershed groups www6.montgomerycountymd.gov/dectmpl.asp?url=/Content/dep/water/localgroups.aspRegional and national groupsGeneral informationLiving a Green Life: My Green Montgomery
12 Project Selection Improve stormwater function Requested by Montgomery Village FoundationLocated in a key watershed (Great Seneca Creek)
14 Hydraulic DredgeHydraulic dredges work by sucking a mixture of bottom sediments and water from the lake. A cutterhead is a mechanical device that has rotating blades or teeth to break up or loosen the bottom sediments so that it can be pumped through the dredge.
16 Turbidity CurtainsTurbidity is a measure of water clarity; how much material suspended in water decreases the passage of light through the water
17 Hydraulic Dredging Procedure Underwater surveys to measure the amount of sediment to be removedHydraulically remove lake bottom sedimentsPump sediment slurry through the pipeline to the dewatering area
18 Dredged Material Volume Remove approximately 20,000 cy of sediments within two dredge areas
26 Bathymetric Survey A Study of Sediment Depth of Lake Whetstone Performed by JMT in April 2013
27 Lake Whetstone Dredging Project proposed to dredge approximately 20,000 cubic yard of sediments from the Lake.Dredging to occur in northern and southern ends of the Lake.Dredging performed by hydraulic dredging methods.Approximately 2,000 truck Loads of sediment to be removed from the Lake after being Processed.
28 Dredging Area 1 – Northern End Dredged volume for Area 1 is approximately 5,000 cy
29 Dredging Area 2 – Southern End Dredged volume for Area 2 is approximately 15,000 cy
30 Sediment Characteristics In October 2011 sediments samples were taken and tested for contaminants.Results showed elevated levels of PAHs and metals.Facilities in Maryland that have permits to handle these Sediments.CLEAN EARTH out of HagerstownSOILSAFE out of Brandywine.
31 Sediment Characteristics In July 2013 Sediments borings were taken at each proposed dredging location and tested for their Characteristics needed for the design of the Hydraulic dredging.Testing includedMoisture ContentGradation AnalysisAtterberg LimitsSpecific GravityTesting to determine how easily the sediments can be pumped and dewatered.
32 Dewatering & Staging Area Truck Traffic 7:00 AM to 5:00 PM Week DaysApproximately 2,000 truck loads of sediment hauled away from site.
33 Project AreaExisting Recreational area will be graded and used for dewatering operation.Parking area will be used for office trailer, construction sanitary facility, employee car parking, and equipment storage.Access to site will be from Montgomery Village Ave. onto Lake Shore Drive, turn onto Island Side Drive , then down the Road to the Boat Dock Area.A Construction Fence will be provided around entire AreaThere will be several pipes from the Dewatering Plant area going across the Path next to the Lake for the Dredging Operations.
34 Restoration of SiteDewatering Area to be restored to existing conditions after completion of the Dredging.
35 PermitsAll local, state and federal permits will be obtained for this project.
36 Project ImpactsRecreational – Closure of picnic area and parking lot; No boating on Lake; impact to path around the Lake.Traffic – construction traffic enters and exits construction site, Lake Shore Drive and Island Side Drive will be shared by residents and construction trucks for the duration of the project.Neighborhood – construction and traffic noise will typically occur Monday – Friday, 7AM to 5PMCan add own photo for your own projects.
37 Project Impacts Environmental Some trees will be removed. Rookery on island – working with DNR to minimize the impactTurbidity – Turbidity is a measure of water clarity. Contractor is required to comply with MDE requirement on turbidity for water discharged back to lake.Aquatic Biota – Minimal impact to aquatic biota in Lake
38 Project BenefitsEnvironmental – Improve storm water management function of the Lake, improve aesthetic appearanceRecreation – Improve boating access areaCan add own photo for your own projects.
39 Tentative Schedule Permit submittal - October 2013 Approvals – March 2014Contractor Selection –March 2014Construction – June 2014Can add own photo for your own projects.
40 What to expect during construction DurationSite preparation and mobilization - approximately 1 monthDredging - approximately 6 monthsSite restoration - approximately 1 monthConstruction HoursMonday through Friday, 7AM – 5PM; Some work may be performed after 5:00 PM or on weekends for maintenance of equipmentNoiseContractor is required to comply with Montgomery County Noise Ordinance.Can add own photo for your own projects.
41 What to expect during construction SafetySite will be fenced for safety.TrafficImpacts to traffic from truck entering and exiting construction site during the day. Lake Shore Drive and Island Side Drive will see increased traffic volumeSedimentContractor will be required to comply with Montgomery County Sediment Control Permit and not track dirt onto roads
42 Questions? For more information: Julia Liu, 240-777-7762