Stormwater Committee Statement

April 14, 2010 abridged 

To Mayor E. Hauptman: 

Dear Mr. Mayor:   

            The following is a revision to the report from the Storm Water Sub Committee (SWSC) on the progress in providing the Council and the CCI with a draft of the Code for Storm Water Management.  This is a progress report based on the committee meeting of 13 April 2010.  It represents the general approach and update on our work in fulfilling the charge to provide a draft Code for Dunes City for the management and control of storm water run off.  The SWSC members present were D. Bellemore, L. Riechel, J. Stead, G. Burke (Vice-Chair) and G. Wasserburg (Chair).  L. Ekelund, (the Planning Secretary) was present and took notes and will prepare the minutes.  Our next meeting will be on 20 April at 2-4PM at the Dunes City Hall. 

            We submit the following outline, which states our approach to the charge given to us.  It is requested that this outline be put on the Dunes City web site and replace the earlier efforts that were prepared in 2007.  This would inform the interested general Dunes City citizens of our approach and provide a basis for future discussion. 

OUR APPROACH:   

            The draft code that will be ultimately presented is to be considered as either a separate ordinance/code or as an addition to the existing Erosion Control Ordinance (#193).  In either case, a modification to Codes #193 and #173 must be made.  These modifications must include a specific reference to storm water management as defined in a separate ordinance/code or as an addition to the existing Erosion Control Ordinance (#193) and include reference to Storm Water Management within the appropriate sections of the existing Dunes City code and the responsibility for maintenance, construction and upgrading of all streets under the regulatory control of the City.  Inspection by the City will be undertaken on site prior to the construction of the impervious surfaces with the documented plans prepared by a licensed engineer or erosion control expert in consideration of storm water management.  These plans should include a maintenance procedure and schedule.  The site will then be inspected after completion of the construction and approved for appropriate storm water control.  This inspection will be done prior to final approval of the site by the City.  The site subsequently will be subject to inspection every four years to verify whether the storm water management system is still adequately functional or if the property owner(s) is (are) required to clean out the holding system.  These rules will apply to all existing residences that have added impervious surfaces in excess of 500 sq ft subsequent to the establishment of the storm water code.  For developments, the above will apply to the whole development considered as a single unit. 

STORM WATER DEFINITION AND ISSUES: 

            We define "Storm Water" as those conditions in which the rate and duration of rainfall exceeds the rate at which water can penetrate into the ground surface and pass into the ground water table.  These conditions result in water runoff that causes channeling and erosion and transports debris across property lines, down roads and fill existing drainage systems, flowing into the lakes. 

            It has become evident that more diffuse sources of water pollution, such as stormwater runoff from construction sites, are significant contributors to water quality problems.  Sediment runoff rates from construction sites are typically 10 to 20 times greater than those from agricultural lands, and 1,000 to 2,000 times greater than those of forestlands.  During a short period of time, construction activity can contribute more sediment to streams than can be deposited over several decades, causing physical and biological harm to our Nation's waters (EPA 833-F-00-013 January 2000 (revised December 2005) Fact Sheet 3.0).  Further, the presence of impermeable surfaces (including roofs, parking lots, driveways and roads) provide sources of high levels of flow and runoff that greatly increase channeling, erosion and debris transport.  This involves transport due to severe storms to neighboring properties and transport into the lakes, which are a principle source of drinking water.  The septic waste systems in use in the City must be secure so that under conditions of stormwater conditions, they do not pollute the lakes and drinking waters sources used by the community. 

            The issue is considered to cover three different areas.  These are: 1) In preparation of and during construction; 2) Post construction and long-term maintenance; 3) Maintenance of common areas, roads and culverts.  Of these areas, items 1) and 2) place requirements on the owners/contractors who have been licensed to carry out new construction or owners of property on which the construction is completed.  Area 3) is the responsibility of Dunes City and also involves Lane County and the State of Oregon for roads and drainages under their control for both maintenance and construction. 

            In treating this problem we have taken the precipitation conditions of 3.14" over a six-hour period (0.53" per hour) for Dunes City as the design basis (100 year storm, Hydrometeorological Design Studies Center-NOAA/National Weather Service 1325 East-West Highway-Silver Spring, MD 20910 - Aug 20 02:08:05 2009).  We note that the amount of rainfall used above is not significantly different than the amount expected for a two-year storm, two-hour duration storm. 

            The simplest case considered is the construction of impermeable surfaces on properties with existing residences.  The following proposal is under consideration: 

STORM WATER CODE FOR EXISTING RESIDENCES: 

            Owners of an existing developed site of a single family residence that propose creation of new impermeable surfaces in excess of 500 sq. ft. are required to submit a plan to the Dunes City Planning Secretary (for evaluation of an engineer or hydrologist knowledgeable about storm water control).  The approval of the Planning Secretary will be based on that review and is required prior to issuance of a permit and the initiation of the construction.  The plan must show the drainage system that is to be installed will be capable of carrying off or containing 3.1 inches of rainfall in a 6-hour period.  The plan must show the proposed drainage system for the proposed improvements as well as the nature of all improvements on the property and the existing related drainage systems including the septic tank and drain field, the rain gutter drainage system, etc.  For paved surfaces, the nature of the construction used, with the impermeable surface is to be laid over a high permeability sub-grade to avoid pavement failure.  The storm water runoff is to be directed into drainage system of filter strips, bio-retention areas, infiltrator systems or retention ponds that direct sheet flow into the retention area in order to prevent channeling.  The approval of the site inspector is required prior to the issuance of a permit.  The plan should include the position of the septic tank and drainfield and show that these sensitive areas will not be subject to channeling and erosion by the rainfall.  The requirement that debris flow in excess of one cubic foot may not be transported into adjacent properties or drainages is to serve as a guiding requirement.  The drainage area and containment of the impermeable area is to be inspected at least once every four years to ensure that it is able to drain properly. 

            We are in the process of considering the Storm Water Management issue for new construction of a single family residence on a property unit less than or equal to one acre.  The final submitted document is intended to be written in a self-consistent fashion and related to existing codes and regulations in a clear and self-explanatory manner. 

Respectfully, D. Bellemore, L. Riechel, J. Stead, G. Burke (Vice-Chair) and G.J. Wasserburg (Chair), 13 April 2010