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HomeMy WebLinkAbout963302106 Stormwater MgmtSTORMWATER SITE PLAN Block 21; Irving Park Addition Jefferson County, WA ~~"~ o¥ Prepared for: Mr. Arnold Wood 2155 Discovery Road Port Townsend, WA 98368 Prepared by: Colette M, Kostelec, P.E. P.O. Box 2085 Port Townsend, WA 98368 May 4, 2001 STORMWATER SITE PLAN Block 21; Irving Park Addition TABLE OF CONTENTS PROJECT OVERVIEW ................................................................................... , ................ , ................................. 1 H. PLOT PLAN ..................................................................................................................................................... 1 III. PRELIMINARY CONDITIONS SUMMARY ............................................................................................. 1 IV. OFF-SITE ANALYSIS ................................................................................................................................... 2 V. STORMWATER RUNOFF CONTROL FACILITIES ............................................................................... 2 A. Minimum Requirement #2: Preservation of Natural Drainage Systems ............................................ 2 B. Minimum Requirement #3: Source Control of Pollution. .................................................................. 2 C. Minimum Requirement g4: Runoff Treatment BMPs ....................................................................... 3 D. Minimum Requirement #5: Streambank Erosion Control ................................................................. 3 E. Minimum Requirement #6: Wetlands ................................................................................................ 4 F. Minimum Requirement #7: Water Quality Sensitive Areas .............................................................. 4 G. Minimum Requirement #8: Off-Site Analysis and Mitigation .......................................................... 5 H. Minimum Requirement #9: Basin Planning ....................................................................................... 5 I. Minimum Requirement #10: Operation and Maintenance ................................................................... 5 J. Minimum Requirement #11: Financial Liability .................................................................................. 5 VI. SPECIAL REPORTS AND STUDIES .................. ~ .................. , ............................. , ....................................... 6 VII. BASIN AND COMMUNITY PLANNING AREAS ...................................................................................... 6 VIII. OTHER PERMITS ....................................................................................................................................... 6 IX. LARGE PARCEL Ne Ao B. C. D. E. F. G. H. I. J. K. L. M. N. O. ESC ESC ESC ESC ESC ESC ESC Reqmrement Reqmrement Requirement Reqmrement Requirement Reqmrement Reqmrement EROSION AND SEDIMENT CONTROL PLAN ........................................................ 6 #1: Stabilization and Sediment Trapping ............................................................. 7 #2: Delineate Clearing and Easement Limits ....................................................... 7 #3: Protection of Adjacent Properties .................................................................. 7 g4: Timing and Stabilization of Sediment Trapping Measures ........................... 8 #5: Cut and Fill Slopes ......................................................................................... 8 #6: Controlling Off-Site Erosion .......................................................................... 8 #7: Stabilization of Temporary Conveyance Channels and Outlets .................... 8 ESC Reqmrement #8: Storm Drain Inlet Protection .......................................................................... 9 ESC Requirement #9: Underground Utility Construction .................................................................... 9 ESC Requirement #10: Construction Access Routes ........................................................................... 9 ESC Requirement #11: Removal of Temporary BMPs ................................................................... 10 ESC Requirement #12: Dewatering Construction Sites .................................................................. 10 ESC Requirement #13: Control of Pollutants Other Than Sediment on Construction Sites ........... 10 ESC Requirement #14: Maintenance ............................................................................................... 11 ESC Requirement #15: Financial Liability ...................................................................................... 11 MAINTENANCE AND OPERATIONS ...................................................................................................... 11 APPENDIX A RESULTS OF COMPUTER SIMULATIONS OF STORM EVENTS AND SIZING OF STORMWATER FACILITIES Stormwater Site Plan Block 21; Irving Park Addition May 4, 2001 STORMWATER SITE PLAN Block 21; Irving Park Addition I. PROJECT OVERVIEW This Stormwater Site Plan has been prepared for Block 21 and it's adjacent vacated fights-of- way in the Irving Park Addition in unincorporated Jefferson County, Washington (Parcel Number 963302106). The site is generally located between the intersections of Discovery Road, State Highway 20 and Florence Avenue. A vicinity map for the site is provided on Figure 1. The site is approximately 2.85 acres and is divided into 8 building lots. Sheet CO 1 shows the site boundaries and existing site topography. Following clearing of the site, a Notice of Voluntary Correction was issued by Jefferson County. The Correction Order requires submittal of a Large Parcel Erosion and Sediment Control Plan. This is a comprehensive report that provides information and analysis for the successful implementation of stormwater controls during and after construction at the site in fulfillment of the requirements of the Department of Ecology's Stormwater Management Manual for the Puget Sound Basin (the "Technical Manual") dated February 1992. The proposed development of the site will include installation of a water service line with eight service connection stub-outs from the Jefferson County Public Utility District's eight- inch water main that currently exists along the site's southern property boundary. Also proposed is a 16-foot wide access road terminating in a cul-de-sac with a radius of 40 feet. Existing site grades will be modified to allow for drainage from the access road and creation of an infiltration pond. Proposed grades are shown on Sheet C03. II. PLOT PLAN The following Sheets are included as part of this Stormwater Site Plan: Sheet C01 - Existing Site Plan Sheet C02 - Erosion & Sediment Control Plan Sheet C03 - Permanent Stormwater Control Plan Sheet C04 - Construction Details III. PRELIMINARY CONDITIONS SUMMARY The project site is approximately 2.85 acres and slopes down approximately 12 feet fi'om the northern property boundary to the southwest comer at a 3% grade. A gentle ridge-line runs north-south in the center of the property. Sheet CO 1 shows existing topographic contours. Surrounding land uses are single-family residential. Stormwater Site Plan Block 21; Irving Park Addition 1 May 4, 2001 F. PROJECT SITE {. VAC AVENUE TRACE ALDER --CEDAR FLORENCE AVENUE LAWRENCE SPRUCE STREET STREET AVENUE LAKE MAPLE ST. CARROLL STEVENS RAILROAD SEE MAP ABOVE NOT TO SCALE AVEI AVE MA Y4, 1 The site soils are mapped by the Soil Conservation Service as Dick loamy sand. These soils have a standard profile of loamy sand to a minimum of 60 inches in depth. They are excessively drained and according to the Soil Survey have a permeability range of 6 to 20 inches per hour. However, Table 11I-3.1 of the Technical Manual provides an infiltration rate of 2.41 inches per hour for loamy sand and this was used in the hydrologic modeling for the site. IV. OFF-SITE ANALYSIS No off-site water currently impacts the project site. V. STORMWATER RUNOFF CONTROL FACILITIES The Technical Manual identifies 11 minimum requirements that must be addressed in all stormwater management plans. These requirements are identified, described and addressed below. Minimum Requirement # 1 is Erosion and Sediment Control and that is addressed in Section IX of this report (Large Parcel Erosion and Sediment Control Plan). A. Minimum Requirement #2: Preservation of Natural Drainage Systems [Technical Manual - Natural drainage patterns shall be maintained, and discharges from the site shall occur at the natural location, to the maximum extentpracticable. Objective: To preserve and utilize natural drainage systems to the fullest extent because of the multiple stormwater benefits these systems provide.] As described above, topography slopes toward the southwest comer of the property at a grade of approximately 3 %. However, based on the soil types typical of the Dick Series, runoff from the site is currently very low. This stormwater plan proposes collection, treatment and infiltration of the nmoff caused by the development, thereby preserving the natural drainage pattern. B. Minimum Requirement #3: Source Control of Pollution [Technical Manual - Source control BMPs shall be applied to all projects to the maximum extent practicable. Source control BMPs shall be selected, designed, and maintained according to an approved manual. Objective: The intention of source control BMPs is to prevent stormwater from coming in contact with pollutants. They are a cost-effective means of reducing pollutants in stormwater, and therefore should be a first consideration in all projects.] The only anticipated on-site pollutant source will be the access road. Runoff from the road will be collected and treated in a bioswale adjacent to the access road. Sheet C03 shows Stormwater Site Plan Block 21; Irving Park Addition May 4, 2001 ' proposed stormwater control and treatment improvements. The recommended grass seed mix (hydroseeding preferred) for the bioswale is provided on Sheet C04. C. Minimum Requirement #4: Runoff Treatment BMPs ~echnical Manual - All projects shaH provide treatment of stormwater. Treatment BMPs shah be sized to capture and treat the water quality design storm, defined as the 6-month, 24- hour return period storm. The first priority for treatment shah be to infiltrate as much as possible of the water quality design storm, only if site conditions are appropriate and groundwater quality will not be impaired. Objective: The purpose of runoff treatment is to reduce pollutant loads and concentrations in stormwater runoff using physical, biological, and chemical removal mechanisms.] See Item C above. D. Minimum Requirement #5: Streambank Erosion Control [Technical Manual - Stormwater discharges to streams shah control streambank erosion by limiting the peak rate of runoff from individual development sites to 50 percent of the existing condition 2-year, 24-hour design storm while maintaining the existing condition peak runoff rate for the lO-year, 24-hour and lO0-year, 24-hour design storms. Ob/ective: To reduce streambank erosion that results from increased runoff due to development. The standard is intended to reduce the frequency and magnitude of bankfull flow conditions, which are highly erosive and increase dramatically as a result of development.] Typically, hydrologic analysis is used to design a stormwater control system that limits site runoff to less than pre-development conditions. In this case, since infiltration is proposed as the permanent stormwater control system, pre-existing conditions are not relevant. The proposed system is based on infiltrating all of the stormwater runoff during a 100-year, 24- hour storm event. Hydrologic modeling has been performed to size the infiltration pond (see Appendix A for modeling assumptions and results). The modeling was performed using the computer model HydroCad. For modeling purposes, it was assumed that all of the access road runoff plus the runoff from the individual building sites would go to the infiltration pond. Based on the Technical Manual's Table III-1.3, impervious surface coverage of 33% can be assumed for single-family residential development at a density of 2.8 dwelling units per acre (2.85 acres/8 units). The remaining 67% of each building site is assumed to be landscaped with runoff calculated assuming 75% lawn in good condition. For the purpose of the design of the system for this site, a permeability of 2.41 inches per hour (0.003 feet per minute) has been used. Stormwater Site Plan Block 21; Irving Park Addition May 4, 2001 Based on a 100-year storm event (2.75 inches of precipitation), a pond with bottom dimensions of 20 feet x 120 feet and side slopes of 2 horizontal:l vertical and a depth of 2 feet will be required. That configuration will provide for one foot of freeboard during the 100-year storm event. The pond configuration and location is shown on sheet C03. The pond should be seeded (hydroseeding preferred) with the recommended grass seed mix provided on Sheet C04. E. Minimum Requirement #6: Wetlands [Technical Manual - Stormwater discharges to wetlands must be controlled and treated to the extent necessary to meet the State Water Quality Standards, as appropriate. Discharges to wetlands shall maintain the hydroperiod and flows of existing site conditions to the extent necessary to protect the characteristic uses of the wetland. Created wetlands that are intended to mitigate for loss of wetland acreage, function and value shall not be designed to also treat stormwater. In order for constructed wetlands to be considered treatment systems, they must be constructed on sites that are not wetlands and they must be managed for stormwater treatment. Stormwater treatment BMPs shall not be built within a natural vegetated buffer, except for necessary conveyance systems as approved by the local government. Objective: To ensure that wetlands receive the same level of protection as any other waters of the state. Wetlands are extremely important natural resources which provide multiple ' stormwater benefits, including groundwater recharge, flood control, and streambank erosion protection. They are easily impacted by development unless careful planning and management are conducted Wetlands can be severely degraded by stormwater discharges from urban development due to pollutants in the runoff and also due to disruption of natural hydrologic functioning of the wetland system. Changes in water levels and the duration of inundations are of particular concern.J No wetlands have been identified at the project site. F. Minimum Requirement #7: Water Quality Sensitive Areas [Technical Manual- Where local governments determine that the Minimum Requirements do not provide adequate protection of water quality sensitive areas, either on-site or within the basin, more stringent controls shall be required to protect water quality. An adopted and implemented basin plan (Minimum Requirement #9) may be used to develop requirements for water quality sensitive areas that are tailored to a specific basin. Objective: To ensure protection of water quality in sensitive areas.J No basin study is available for the analysis of impacts to potential water quality sensitive areas. The proposed stormwater control facilities are designed to meet the requirements of Stormwater Site Plan Block 21; Irving Park Addition May 4, 2001 the Technical Manual for treatment and infiltration of stormwater runoff generated by the development. G. Minimum Requirement 08: Off-Site Analysis and Mitigation [Technical Manual - All development projects shall conduct an analysis of off-site water quality impacts resulting from the project and shall mitigate these impacts Objective: To ensure that future impacts from the project will be controlled and/or existing impacts will not be aggravated by the project] Since the proposed on-site stormwater control facilities will treat and infiltrate stormwater runoff, thereby mimicking existing site conditions, it is anticipated that no mitigation will be necessary off-site. H. Minimum Requirement #9: Basin Planning [Technical Manual - Adopted and implemented watershed-based basin plans may be used to modify any or all of the Minimum Requirements, provided that the level of protection for surface or groundwater achieved by the basin plan will equal or exceed that which would be achieved by the Minimum Requirements in the absence of a basin plan. Objective: To promote watershed-based planning as a means to develop and implement comprehensive water quality protection measures. Primary objectives of basin planning are to reduce pollutant loads and hydrologic impacts to streams and wetlands.J No basin studies are available related to stormwater for this area. I. Minimum Requirement #10: Operation and Maintenance [Technical Manual - An operation and maintenance schedule shall be provided for all proposed stormwater facilities and BMPs, and the party (or parties) responsible for maintenance and operation shall be identified. Objective: To ensure that stormwater control facilities are adequately maintained and operated properly. J Operation and maintenance of all stormwater control facilities, including erosion and sediment control BMPs are discussed in Section X of this report (Maintenance and Operations). J. Minimum Requirement #11: Financial Liability [Technical Manual- Performance bonding or other appropriate financial instruments shall be required for all projects to ensure compliance with these standards. Stormwater Site Plan Block 21; Irving Park Addition May 4, 2001 Objective: To ensure that development projects have adequate financial resources to fully implement storrnwater management plan requirements and that liability is not unduly incurred upon local governments.] The property owner(s) will assume all financial liability associated with the operation and maintenance of the temporary erosion and sediment control and permanent stormwater quality control facilities. VI. SPECIAL REPORTS AND STUDIES No special reports or studies are available for the site. VII. BASIN AND COMMUNITY PLANNING AREAS No basin studies are available related to stormwater for this area. VIII. OTHER PERMITS This report is being prepared to accompany a Master Land Use Application Form for a Stormwater Permit. Building and septic permits will be obtained from the County by the individual lot owners. IX. LARGE PARCEL EROSION AND SEDIMENT CONTROL PLAN Since the proposed new development involves creation of greater than 5,000 square feet of impervious surfaces and greater than one acre of land disturbing activities, it requires a Large Parcel Erosion and Sediment Control Plan ("LPESC Plan"). This section of the Stormwater Site Plan, in conjunction with Sheets C02 and C04 of this report, constitutes the LPESC Plan for this development. The purpose of the LPESC Plan is to provide for the interception and treatment of all potential silt-laden runoff that could occur during clearing, grading, construction, and site stabilization. The goal of the LPESC Plan is to assure that no silt-laden runoff leaves the site during construction and site stabilization. Sheet C02 identifies Erosion and Sediment Control Best Management Practices (BMPs) to be used during construction and site stabilization at the site. Sheet C04 provides construction details for the BMPs. Erosion and Sediment Control BMPs are designed fa:st and foremost to prevent erosion and secondly to deal with sediment produced from unavoidable erosion. The Technical Manual identifies 15 minimum requirements for erosion and sediment control that must be addressed in an LPESC Plan. Each of these requirements is described and addressed below. Stormwater Site Plan Block 21; Irving Park Addition 6 May 4, 2001 A. ESC Requirement #1: Stabilization and Sediment Trapping [Technical Manual - All exposed and unworked soils shall be stabilized by suitable application of BMPs. From October 1 to April 30, no soils shall remain unstabilized for more than 2 days. From May 1 to September 30, no soils shall remain unstabilized for more than 7 days. Prior to leaving the site, stormwater runoff shall pass through a sediment pond or sediment trap, or other appropriate BMPs.J The following BMPs will be used at the site to meet this requirement: Mulching (with straw) is to be used for all exposed areas of the site during construction and after seeding to protect and insulate geminating seeds. The straw application rate shall be 75 to 100 pounds or two to three bales per 1,000 square feet of exposed area. The depth of application shall be a minimum of two inches. Straw mulch must be kept moist or will be tacked down to prevent it being blown away by wind. · Gravel base on the access road shall be applied as soon as feasible after grading. Soil stockpiles will be stabilized or protected with sediment trapping measures to prevent soil loss. B. ESC Requirement #2: Delineate Clearing and Easement Limits [Technical Manual- In the field, mark clearing limits and/or any easements, setbacks, sensitive/critical areas and their buffers, trees and drainage courses.] Silt fencing will be used for protection of adjacent properties (as discussed in the next section). C. ESC Requirement 03: Protection of Adjacent Properties [Technical Manual - Properties adjacent to the project site shall be protected from sediment deposition.] The following BMPs will be used on-site to meet this requirement. Silt Fencing Silt fencing shall be installed as shown on Sheets C02 and C04 to prevent sediment carried by stormwater runoff from leaving the site. Filter fabric shall be purchased in a continuous roll cut to the length of the barrier to avoid use of joints. When joints are necessary, filter cloth shall be spliced together only at a support post, with a minimum six-inch overlap, and both ends securely fastened to the post. Stormwater Site Plan Block 21; Irving Park Addition May 4, 2001 Posts shall be spaced a maximum of six feet apart and driven securely into the ground a minimum of 30 inches, where physically possible. A trench shall be excavated approximately 8 inches wide and 12 inches deep along the line of posts and upslope from the barrier. The trench shall be constructed to follow the contour. D. ESC Requirement #4: Timing and Stabilization of Sediment Trapping Measures [Technical Manual- Sediment ponds and traps, perimeter dikes, sediment barriers, and other BMPs intended to trap sediment on-site shall be constructed as a first step in grading. These BMPs shall be functional before land disturbing activities take place.] The silt fencing will be constructed and installed prior to all other site disturbing activities. E. ESC Requirement 05: Cut and Fill Slopes [Technical Manual - Cut and fill slopes shall be designed and constructed in a manner that will minimize erosion. In addition, slopes shall be stabilized in accordance with ESC Requirement #1.] Cut and fill slopes will be constructed around the infiltration pond and bi#swale. Slopes will be seeded and mulched as described in "A" above. F. ESC Requirement #6: Controlling Off-Site ErOsion [Technical Manual - Properties and waterways downstream from development sites shall be protected from erosion due to increases in the volume, velocity, and peak flow rate of stormwater runoff from the project site.J No increase in the volume, velocity or flow rate of runoff is anticipated from the project site. G. ESC Requirement #7: Stabilization of Temporary Conveyance Channels and Outlets [Technical Manual - All temporary on-site Conveyance channels shall be designed, constructed, and stabilized to prevent er#si#n from the expected velocity of flow frorn a 2- year, 24-hour frequency storm for the developed condition. Stabilization adequate to prevent erosion of outlets, adjacent streambanks, slopes and downstream reaches shall be provided at the outlets of all conveyance systems.J No temporary conveyance channels are anticiPated. Stormwater Site Plan Block 21; Irving Park Addition 8 May 4, 2001 H. ESC Requirement #8: Storm Drain Inlet Protection [Technical Manual - All storm drain inlets made operable during construction shall be protected so that stormwater runoff shall not enter the conveyance system without first being filtered or otherwise treated to remove sediment.] Straw bales will be installed in the bioswale as shown on Sheets C03 and C04 until the grass is established to prevent erosion of the swale and to protect the cross-culvert leading to the infiltration pond. I. ESC Requirement 09: Underground Utility Construction [Technical Manual- The construction of underground utility lines shall be subject to the following criteria. Where feasible, no more than 500feet of trench shall be opened at one time. Where consistent with safety and space considerations, excavated material shall be placed on the uphill side of trenches. Trench dewatering devices shall discharge into a sediment trap or sediment pond. J No more than 500 feet of trench shall be open at any time during underground utility Construction. No dewatering is anticipated at this site. J. ESC Requirement #10: Construction Access Routes [Technical Manual - Whenever construction vehicle access routes intersect paved roads, provisions must be made to minimize the transport of sediment (mud) onto the paved road. If sediment is transported onto a road surface, the roads shall be cleaned thoroughly at the end of each day. Sediment shall be removed from roads by shoveling or sweeping and be transported to a controlled sediment disposal area. Street washing shall be allowed only after sediment is removed in this manner.] A stabilized construction entrance will be provided as shown on Sheets C02 and C04 in order to prevent erosion by construction vehicles and tracking of sediment off-site. Material used for the stabilized construction entrance shall be quarry spalls, four inches to eight inches in size. The rock pad shall be at least 12 inches thick and 100 feet long; the width shall be the full width of the vehicle ingress and egress area. Additional rock shall be added periodically to maintain proper function of the pad. Any sediment that is transported to paved areas will be swept and deposited in a controlled area. Stormwater Site Plan Block 21; Irving Park Addition May 4, 2001 K. ESC Requirement #11: Removal of Temporary BMPs [Technical Manual - All temporary erosion and sediment control BMPs shall be removed within 30 days afler final site stabilization is achieved or after the temporary BMPs are no longer needed. Trapped sediment shah be removed or stabilized on site. Disturbed areas resulting from removal shah be permanently stabilized.] The silt fencing will be removed within 30 days after the site is stabilized. All disturbed areas resulting from the removal of the BMPs shall be stabilized. L. ESC Requirement #12: Dewatering Construction Sites [Technical Manual - Dewatering devices shah discharge into a sediment trap or sediment pond. J No dewatering is anticipated during construction at this site. M. ESC Requirement #13: Control of Pollutants Other Than Sediment on Construction Sites [Technical Manual - All pollutants other than sediment that occur on-site during construction shall be handled and disposed of in a manner that does not cause contamination of storrnwater.] Other potential pollutants besides sediment associated with construction activities include chemicals (pesticides, fertilizers, paints, oils, gasoline, etc.) and wastes such as paper, wood, concrete debris, garbage, and sanitary wastes. These must be controlled to prevent damage to neighboring properties and off-site watercourses. Although the construction of the access road and installation of underground utilities are not anticipated to be a source of other pollutants, it is anticipated that this Stormwater Site Plan will be applied to development of the individual lots and therefore the following best management practices are recommended. Good housekeeping practices are the most economical and effective way to control these potential pollutants. Weather-resistant storage will be provided for chemicals to be used on- site. Wastes will be removed promptly and will be disposed of at authorized facilities. Storage sheds and dumpsters will be regularly monitored for leaks and repaired as necessary. Workers will be reminded about proper storage and handling of materials. Washout from concrete trucks will be disposed of into a designated area that will later be backfilled (slurry pit), or in an area where the material can harden, be broken up and then put in a dumpster. In no case will concrete washout occur in a location subject to surface water runoff or closer than 50 feet from a storm drain. Stormwater Site Plan Block 21; Irving Park Addition 10 May 4, 2001 N. ESC Requirement #14: Maintenance [Technical Manual - All temporary and permanent erosion and sediment control BMPs shall be maintained and repaired as needed to assure continued performance of their intended function. All maintenance and repair shall be conducted in accordance with an approved manuaL] Operation and maintenance of all stormwater control facilities, including erosion and sediment control BMPs, are discussed in Section X of this report (Maintenance and Operations). O. ESC Requirement 015: Financial Liability [Technical Manual- Performance bonding, or other appropriate financial instruments, shall be required for all projects to ensure compliance with the approved erosion and sediment control plan.] The developer/property owners assume responsibility for the continued maintenance of the erosion control BMPs identified in this report. X. MAINTENANCE AND OPERATIONS The major reason for BMP failure is poor maintenance. For this site, all of the Large parcel Erosion and Sediment Control BMPs will be inspected regularly, particularly before, during and after a major storm event. In addition, a routine "end of day check" will be implemented during construction to make sure that all control practices are working properly, and to repair any that are not, prior to leaving the site unsupervised overnight or over a weekend. All temporary erosion and sediment control measures shall be removed within 30 days after final site stabilization is achieved or after the temporary BMPs are no longer needed. Trapped sediment shall be removed or stabilized on-site. Disturbed soil areas resulting from removal shall be permanently stabilized. Straw mulching: mulched areas shall be checked periodically, especially follow~g severe storms. Additional straw shall be added and damaged areas shall be repaired as necessary. Seeded areas: seeded areas shall be inspected for failure and reseeded as necessary. A follow-up survey shall be made after one year and areas shall be reseeded as necessary. Construction access road: the construction entrance and exit shall be maintained in a condition that prevents tracking of mud onto the public rights-of-way. Periodic top dressing with two-inch stone, as conditions demand, shall be made. All materials spilled, dropped, washed, or tracked from vehicles onto roadways or into storm drains shall be removed immediately. Stormwater Site Plan Block 21; Irving Park Addition 11 May 4, 2001 Filter fence: the filter fence shall be inspected immediately after each rainfall, and at least daily during prolonged rainfall, and repaired as necessary. Sediment shall be removed when it reaches approximately one-third the height of the fence, especially if heavy rains are expected. Any sediment deposits remaining in place after the filter fence is no longer needed shall be dressed to conform to the existing grade, prepared and ~seeded. Straw bales: straw bale barriers shall be inspected immediately after each runoff-producing rainfall and at least daily during prolonged rainfall. Close attention must be paid to the repair of damaged bales, end runs, and undercutting beneath bales. Necessary repairs shall be made promptly. Sediment deposits shall be removed after each runoff-producing rainfall. They must be removed when the level of deposition reaches approximately one-half the height of the barrier. Any sediment deposits remaining in place after the straw bale barrier is no longer required shall be dressed to conform to the existing grade, prepared and seeded. Bioswales: the vegetated bioswales must be mowed regularly to promote growth and pollutant uptake. Grass cuttings must be removed promptly and disposed in a way so that no pollutants can enter the infiltration pond. Sediment should be removed from the bioswale when they build up to 6 inches at any spot, cover biofilter vegetation, or otherwise interfere with biofilter operation. Use of equipment like a Ditch Master is recommended over a backhoe or dragline. If the equipment leaves bare spots they must be re-seeded immediately. Bioswales must be inspected periodically, especially after periods of heavy runoff. Sediment removal and reseeding should be done as necessary. Fertilizer use must be done carefully to avoid impacts to groundwater. Homeowners in this development should be made aware of the maintenance recommendations in this report. Infiltration Pond: the infiltration pond should be inspected on a monthly basis, and more frequently if a large storm occurs, when it is first placed into service. Thereafter, once it is determined that there are no potential sediment problems, inspection can be reduced to a semiannual basis with additional inspections following the occurrence of a large storm (e.g. approximately 1 inch in 24 hours). Establishing a healthy stand of vegetation on the basin side slopes and floor is important as it will not only prevent erosion and sloughing, but will also provide a natural means of maintaining relatively high infiltration rates. Inspection of the basin should include an evaluation of the vegetation and follow-up with reseeding of bare spots. Grass bottoms in infiltration basins seldom need replacement since grass serves as a good filter material. Stormwater Site Plan Block 21; Irving Park Addition 12 May 4, 2001 APPENDIX A RESULTS OF COMPUTER SIMULATIONS OF STORM EVENTS AND SIZING OF STORMWATER FACILITIES Data for Wood: lOOyr/postdev/enti, re site/pond TYPE IA 24-HOUR RAINFALL= 2.75 IN Prepared by Colette U. Kostelec, P.E. HydroCAD 5.11 001496 (c) 1986-1999 Applied Microcomputer Systems Page 1 4 May.01 WATERSHED ROUTING <~ :~UBC~TCHHENT F---] RERCH ~POND LINK SUBCATCHMENT I POND 1 = Post-development = Infiltration Pond 20x120x2 -> POND 1 -> Data for Wood: lOOyr/postdev/entire site/pond TYPE IA 24-HOUR RAINFALL= 2.75 IN Prepared by Colette M. Kostelec, P.E. HydroCAD 5.11 001496 (c) 1986-1999 Applied Microcomputer Systems Page 2 4 May 01 SUBCATCHMENT I Pos t -deve I opmen t PEAK= .59 CFS @ 8.02 HAS, VOLUME= .25 AF ACRES CN .25 98 .86 98 1.74 68 2.85 8O access road 33% imperv, bldg sites landscaped areas Method Comment SBUH METHOD TYPE ZA 24-HOUR RAZNFALL= 2.75 IN SPAN= 0-48 HRS, dt=.l HRS Tc (min) CURVE NUMBER (LAG) METHOD L=400' s=.03 '/' Segment ID: 8.8 5~ 50 45 40 ~5 30 25 15 B5 ,/ SUBCATCHMENT 1 RUNOFF Po~-d~velopmen% AREA-- ~.85 ~C To= 8, B MTN CN= 80 SBUH METHOD TYPE lA 24-HOUR RAINFALL= 2,75 IN PEAK= .59 CF5 ~ 8,02 HR5 UOLUME= ,25 AF TIME Data for Wood- lOOyr/postdev/entire site/pond TYPE IA 24-HOUR RAINFALL= 2.75 IN Prepared by Colette M. Kostelec, P.E. HydroCAD 5.11 001496 (c) 1986-1999 Applied Microcoaputer Systeas Page 3 4 May 01 POND I · Infiltration Pond 20x120x2 Qin = Qout= .59 CFS @ 8.02 HRS, VOLUME= .25 AF .15 CFS @ 17.95 HRS, VOLUME= .25 AF, ATTEN= 75%, LAG= 595.8 MIN ELEVATION CON.AREA INC.STOR CUM.STOR WET.AREA STOR-IND METHOD (FT) (SF) (CF) (CF) . (SF) 0.0 0 0 0 0 · 2 2513 168 168 2513 .4 2627 514 681 2633 · 6 2742 537 1218 2753 · 8 2858 560 1778 2875 1 . 0 2976 583 2362 2999 1 . 2 3095 607 2969 3125 1.4 3215 631 3600 3251 1.6 3337 655 4255 3380 1 . 8 3460 680 4935 3509 2.0 3584 704 5639 3640 PEAK STORAGE = 2442 CF PEAK ELEVATION= 1.0 FT FLOOD ELEVATION= 2.0 FT START ELEVATION= 0.0 FT SPAN= 0-48 HRS, dr=.1 HRS Tdet= 215.6 MIN (.25 AF) # ROUTE INVERT OUTLET DEVICES 1 P 0.0' EXFILTRATION V= .003 FPM over SURFACE AREA ,55 ,50 25 20 PON© 1 INFLOW & OUTFLOW In~i I±.ro~ ion Pond 20x120x2 STOR--IND METHOD PEAK STOR= 2442 CF PEAK ELEU= 1 FT QIn-- ,59 CF5 Qout=_i 5 CFS LAG= 595. 8 M]iN TIME FLORENCE / VD 1929 RVAL = 1, OD' JRES: PERFORMED BY FIELD TRAVERSE SECOND ELECTRONIC TOTAL ITE AND STEEL TAPE, 16, T, 30 N,,R, 1 W, ,WM, WITH CAP 'A, WOOD PLS 23911' -~PDGRAPHIC CONTOUR REE __~~------~ EASEMENT WATER MAIN POWER -U~T~NDERGROUND ~ w[AVED ROAD 100' 150' , , DA~: ~Y~ ~1 $C~: ~ $HO~ CO1 / / WITH CAP dA, WOOD PLS 23911' RAPHIC CONTOUR TREE } OF STRAW BALE SH£ET CO5 ~~AD EASEMENT 8~ WATER MAIN _~I~UNDERGRDUND PHONE CABLE u~.UNDERGRDUND POWER FLORENCE SILT FENCE AVE, PAVE~ ~ = ~0' ~ ' 100' 150' DAT~. M~ Y 4, 2001 $c~: AS SHOWN C02 / / TH CAP ~A, WDDD PLS 23911' GRAPHIC CONTOUR FLE1RENCE~ AVE, ,  D ROAD -q ~ "-' D ROAD (SEE SHEET CO4) ~ 100' 150' E LVERT AND SWALE OUTLETS TO POND DATE: MA Y 4, 2001 AS SHOWN C03 PROVIDE FULL INORE$S/EGf CONS TR UCTION ACCESS R OA /6" QUARRY SPALLS ELEVATION R CULVERT; 12" FOR SWALE 7TION 'WALE >OND I~AT~: MA Ir 4, 2001 C04