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HomeMy WebLinkAbout801034015 Drainage Report STORMWATER SITE PLAN ROGER AND MARIE BROWN Report Prepared for: Roger and Marie Brown PO Box 1043 Port Hadlock, W A 98339 APPROVED STORMW A TER PLAN June 30, 2004 JUl 2 2 2004 Report By: Tillman Engineering P.O. Box 1375 Port Hadlock, Washington 98339 (360) 379-966] Table of Contents June 30, 2004. ....... ........ ...... .......... ............. ............ .......... ..... ........ ................................ .............. ................ I I. PROJECT OVERVIEW 3 II. PLOT PLAN - (See Attachment 'A', Site Plan) 3 III. CONDITIONS SUMMARY 3 IV. OFF SITE ANALYSIS 4 V. ANALYSIS AND DESIGN OF STORMWATER FACILITIES 4 VI. SPECIAL REPORTS AND STUDIES 5 VII. BASIN AND COMMUNITY PLANNING AREAS 5 VIII. OTHER PERMITS 5 2.5.1 Minimum Requirement #1: Preparation of Storm water Site Plans 6 2.5.2 Minimum Requirement #2: Construction Storm water Pollution Prevention (SWPP) 6 2.5.3 Minimum Requirement #3: Source Control of Pollution 9 2.5.4 Minimum Requirement #4: Preservation of Natural Drainage Systems and Outfalls 9 2.5.5 Minimum Requirement #5: On-site Storm water Management 9 2.5.6 Minimum Requirement #6: Runoff Treatment 10 2.5.7 Minimum Requirement #7: Flow Control 10 2.5.8 Minimum Requirement #8: Wetlands Protection 11 2.5.9 Minimum Requirement #9: Basin/Watershed Planning 11 2.5.10 Minimum Requirement #10: Operation and Maintenance 12 ATIACHMENT I ATIACHMENT II S.C.S. MAP OF THE PROJECT LOCATION SITE PLANS Roger Brown Stormwater Site Plan (no address assigned) Center Road Chirnacum, W A 98325 June 30, 2004 Page 2 I. PROJECT OVERVIEW The applicant is under corrective order by Jefferson County Superior Court, Stipulated Order with Respect to Assessor's Parcel No. 801034015, Jefferson County Case No. 04-2-00060-1. The action commenced by Jefferson County is the result ofa complaint filed by northerly neighbor on APN 801034015 which alerted County officials to earthwork activities in violation of provisions within the County Unified Development Code (UDC). Mr. Brown has undertaken significant earthwork over time to re-grade his property in anticipation of construction of a single-family residence. According to Jefferson County, the earthworks have taken place over an approximate ten-year time period with increased activity during the past fifteen months. In the most recent earthmoving activities, a homesite bench was excavated from a hillside along the south property line and fill placed in a wetland ravine near the north property line. In addition to site generated fill, off-site generated fill was disposed of on the property. An unknown quantity of roadside ditch cleaning spoils, perhaps as much as several hundred yards of fill material, were deposited on the site by Jefferson County Public Works crews. It is unknown when the ditch spoils were placed on this site. Mr. Brown contacted Tillman Engineering, Inc. after enforcement actions resulted from the violation to assist the project and gain compliance under the UDC. II. PLOT PLAN - (See Attachment 'A', Site Plan) III. CONDITIONS SUMMARY The subject property contains previous development including driveways, clearings, earthwork cuts and fills, a travel trailer used as Brown's residence, and several vehicles. Most of the subject property is northerly sloping at mild grades of approximately 2-5 percent, with local steep areas offill near the north property line of approximately fifty percent (50%). The site is within the Center Valley, which contains Chirnacum Creek, with the river an unknown distance to the north of the property. The Brown property is at higher elevation that properties to the immediate east and west, and lower elevation than the property to the immediate south. Much of the site is bare earth, including relatively large areas where recent earthwork activities have taken place. Volunteer grasses and weeds cover portions of the site. Areas along the north property line, east property line, and Center Road contain native trees and vegetation. Surface Soil Conditions The native site soils are mapped in the Soil Survey of Jefferson County Area, Washington, August 1975, by the Soil Conservation Service (SCS). The dominant soil type mapped in the project vicinity is Alderwood gravelly loamy sand (AIC) and Cassolary sandy loam (CfD). See the attached pages from the soil survey for specific soil profile descriptions. Several soil log holes have been evaluated on the site by Creative Design Solutions of Port Angeles for determination of on-site septic system capacity. These soil logs verified presence of very shallow native soils underlain by relatively impervious subsoil units. Storm Drainaee Prior to Brown's grading activities, the site was likely to have contained an intermittent drainage corridor, namely a ravine. It is also likely that the ravine contained a wetland associated with the drainage. Discussions with Jefferson County personnel Linda Atkins, Susan Porto, and Molly Pearson indicate that a Roger Brown Stormwater Site Plan (no address assigned) Center Road Chimacum, W A 98325 June 30, 2004 Page 3 drainage was known to exist on the Brown property. Current investigations have located a wetland continuing northerly off of the Brown property toward confluence with a year-round stream that flows to Chimacum Creek approximately one mile north of the site. That stream is located approximately thirty feet easterly of the Brown property. Storm drainage patterns on the Brown site have been interrupted by earthwork activities. The site grading is irregular, with depressions and pockets of standing water during wet weather. The former ravine still directs storm drainage to the wetland at the north, but fill potentially disrupts the timing of and possibly the quantity of stormwater reaching the wetland, and stream system beyond. IV. OFF SITE ANALYSIS As with most projects, there is the potential for off-site transport of eroded soils. Implementation of erosion controls and timing of earthmoving activities to coincide with the summer dry season will reduce the ris!c of sedimentation to the adjacent property, and the wetland and stream system. There is contribution to site stormwater from adjacent properties to the south due the northerly sloping landform. There are no conveyances onto or across the site as it currently exists, although as noted above, there may have been a corridor in the past. As noted above, the subject parcel is located up-gradient of a wetland system that is feeds a year-round stream tributary to Chimacum Creek. It is important to maintain to the extent practical stormwater flows to the wetland and stream beyond. V. ANALYSIS AND DESIGN OF STORMWATER FACILITIES As an enforcement action for earthmoving activities that have occurred over an approximate ten year period, this project does not follow the typical analysis for storrnwater facilities. Since the extent of and original hydrology of the wetland no longer exists, the rate of flow to the wetland is impossible to calculate and therefore numerical analysis is irrelevant. At best, the original conditions can be physically mimicked in the attempt to restore hydrology to the wetland that has been impacted by filling. Runoff from most of the site will be directed, through grading operations, to flow toward the wetland. The remaining wetland depends on continued flow of stormwater through the Browns property. Since the flow through the ravine that feeds surface water to the wetland has been interrupted, an attempt must be made to restore the flows. To that end, the site is being regraded to approximate a more natural landform shape. The regrading is not intended to be an exact restoration of the landform. It is noted that no pre- development documentation exists that show the original landform shape, and the grading contour proposed on the plans are an interpretation based on current topography of the site. Stormwater runoff from the existing developed areas such as the driveway will remain uncontrolled to the Center Road ditchline. Several other areas of the site, including the east and west edges, will remain in an undisturbed condition and will flow runoff as they have historically. Stormwater from the proposed residence will be collected via gutters and downspouts on the building, and conveyed through a tightline pipe to a catchbasin and then to the level-spreader infiltration ditch. Runoff from the parking areas will be routed across lawn areas, which act as a filter strip prior to entering the ditch. Prudent actions and maintenance of these facilities will ensure long term water quality and quantity control. The infiltration trench will put most of the site runoff back into the ravine in a spread-out manner. In times of high runoff, stormwater may top the infiltration trench and the trench will then act as a level spreader. The level spreader will sheet flow stormwater across the surface of the ground to the wetland. A wetland buffer enhancement plan by Olympic Wetland Resources will be utilized to provide planting and revegetation of the graded area. After permanent vegetation is established, exposed soils will be minimized and risk of erosion from the project area will be minimal. Roger Brown Stormwater Site Plan (no address assigned) Center Road Chimacum, W A 98325 June 30, 2004 Page 4 The current re-grading project alters approximately 10,000 sf of site cover, and the total site impervious . area will be approximately 15000 square feet including future residence, shop/garage, parking areas and the existing access driveways. It is noted that the site impervious coverage is limited to 25% of the gross site area, or approximately 17,000 square feet, under the requirements of the UDC. The re-grading proposes to move approximately 600 to 800 cubic yards of material from the wetland buffer to an area previously identified as a possible homesite. The fill site is outside of County prescribed buffers from the existing Type 5 stream and Category II wetland. VI. SPECIAL REPORTS AND STUDIES Roger Brown Wetland Revegetation Plan, May 2004, by Olympic Wetland Resources SEP A Checklist, May 2004, by Tillman Engineering, Inc. VII. BASIN AND COMMUNITY PLANNING AREAS There is no known basin plan for this locale. VIII. OTHER PERMITS The enforcement action seeks compliance with a stormwater permit. The proponent has applied for this permit previously, and that application is currently held pending receipt of this report. A building permit, together with the associated septic system permit and electrical work permit will be required for the construction of the proposed residence. At the time of this plan, the proponent has submitted a septic system permit, but has not applied for the residential permit. Roger Brown Storrnwater Site Plan (no address assigned) Center Road Chimacum, WA 98325 June 30, 2004 Page 5 2.5.1 Minimum Requirement #1: Preparation of Stormwater Site Plans All projects meeting the thresholds in Section 2.4 shall prepare a Stormwater Site Plan for local government review. Stormwater Site Plans shall be prepared in accordance with Chapter 3 of this volume. This project proposes the current grading of approximately 600 to 800 cubic yards of material and approximately 10 - 12,000 sf ofland disturbing activity to grade the excavation. The proponent also proposes construction of an approximate 4000 SF residence and an approximate 3500 sf shop/garage building with approximately 7000 estimated SF of related parking area and driveways. The driveways are already in existence. Minimum requirements 1 through 10 of the current Stormwater Manual for Western Washington will apply for all new impervious surfaces and converted pervious surfaces. 2.5.2 Minimum Requirement #2: Construction Stormwater Pollution Prevention (SWPP) Element 1: Mark Clearing Limits The project requires no clearing. A silt fence will be placed at the northerly toe of the fill to act as a barrier to clearing additional property. The future buildings will be built entirely on previously disturbed area, and clearing limits are not applicable. Element 2: Establish Construction Access Construction access for the project site is existing at the present time in the form of a developed driveway from Center Valley Road. No additional work is required. Center Road will be checked at the end of each work day and cleaned, if required. Sediment from cleaning activities will be disposed of in an appropriate manner. Element 3: Control Flow Rates No offsite flows are anticipated during construction. All stormwater run-off will be infiltrated on-site and infiltration trenches, swales, inlets and stormwater conveyance systems will be protected from sediment during construction. Element 4: Install Sediment Controls The duff layer, native topsoil, and natural vegetation will be retained in an undisturbed state to the maximum extent practicable-. Silt fence will be placed downslope of earth disturbing activity, as required, to prevent sediment from entering undisturbed areas. Other sediment control BMPs will be utilized, if required. Element 5: Stabilize Soils All exposed and unworked soils not target for wetland revegetation (see Olympic Wetland Resources report) shall be stabilized by application ofBMP C120, Temporary and Permanent Seeding, and BMP Roger Brown Stormwater Site Plan (no address assigned) Center Road Chimacum, W A 98325 June 30, 2004 Page 6 C121, Mulching, to protect the soil from the erosive forces of raindrop impact and flowing water, and wind erosIOn. From October 1 through April 30, no soils shall remain exposed and unworked for more than 2 days. From May I to September 30, no soils shall remain exposed and unwoIked for more than 7 days. This condition applies to all soils on site, whether at final grade or not. These time limits may be adjusted by the local permitting authority if it can be shown that the average time between storm events justifies a different standard. Work on this construction site will not exceed the capability of the contractor to to Ie-stabilize the disturbed soils, meeting the timing conditions listed above. Element 6: Protect Slopes The e)(isting fill slope is to be moderated under the proposed grading plan, reducing it's gradient. That revised slope is to be re-vegetated in conformance with the Roger Brown Buffer Revegetation Plan, May 2004 by Olympic Wetland Resources. Element 7: Protect Drain Inlets Storm drain inlets (there is only one), will be protected by filter fabric curtain around the basin. This is detailed in the plans. Element 8: Stabilize Channels and Outlets One permanent surface swale is anticipated for this site. Stabilization, including armoring material, will be made by a maintained grass lining to prevent erosion for this project. Element 9: Control Pollutants All pollutants, including waste materials and demolition debris, that occur on-site during construction, will be handled and disposed of in a manner that does not cause contamination of stormwater. Cover, containment, and protection from vandalism will be provided for all chemicals, liquid products, petroleum products, and non-inert wastes present on the site (see Chapter 173-304 WAC for the defInition of inert waste). Maintenance and repair of heavy equipment and vehicles involving oil changes, hydraulic system drain down, solvent and de-greasing cleaning operations, fuel tank drain down and removal, and other activities which may result in discharge or spillage of pollutants to the ground or into stormwater runoff will be conducted using spill prevention measures, such as drip pans. Contaminated surfaces will be cleaned immediately following any discharge or spill incident. Emergency repairs may be performed on-site using temporary plastic placed beneath and, if raining, over the vehicle. Wheel wash, or tire bath wastewater, will be discharged to a separate on-site treatment system or to a sanitary sewer. Application of agricultural chemicals, including fertilizers and pesticides, will be conducted in a manner and at application rates that will not result in loss of chemical to stormwater runoff. Manufacturers' recommendations will be followed for application rates and procedures. Roger Brown Stormwater Site Plan (no address assigned) Center Road Chimacum, W A 98325 June 30, 2004 Page 7 Management of pH -modifYing sources will prevent contamination of runoff and stormwater collected on the site. These sources include, but are not limited to, bulk cement, cement kiln dust, fly ash, new concrete washing and curing waters, waste streams generated from concrete grinding and sawing, exposed aggregate processes, and concrete pumping and mixer washout waters. Element 10: Control De-Watering HigWy turbid or otherwise contaminated dewatering water, such as from construction equipment operation, clamshell digging, concrete tremie pour, or work inside a cofferdam, will be handled separately from stormwater at the site. Other disposal options, may include: 1) infiltration, 2) transport off-site in vehicle, such as a vacuum flush truck, for legal disposal in a manner that does not pollute state waters, 3) on-site treatment using chemical treatment or other suitable treatment technologies. -- Dewatering is not anticipated for this project. Element 11: Maintain BMPs All temporary and permanent erosion and sediment control BMPs will be maintained and repaired as needed to assure continued performance of their intended function. All maintenance and repair will be conducted in accordance with BMPs. Sediment control BMPs will be inspected weekly or after a runoff-producing storm event during the dry season and daily during the wet season. All temporary erosion and sediment control BMPs will be removed within 30 days after final site stabilization is achieved or after the temporary BMPs are no longer needed. Trapped sediment will be removed or stabilized on site. Disturbed soil areas resulting from removal of BMPs or vegetation will be permanently stabilized. Element 12: Manage The Project As stated in Element 5, work on this linear construction site will not exceed the capability of the contractor to re-stabilize the disturbed soils, meeting the appropriate timing conditions. The following activities are exempt from the seasonal clearing and grading limitations: 1. Routine maintenance and necessary repair of erosion and sediment control BMPs; 2. Routine maintenance of public facilities or existing utility structures that do not expose the soil or result in the removal of the vegetative cover to soil; and 3. Activities where there is one hundred percent infiltration of surface water runoff within the site in approved and inStalled erosion and sediment control facilities. Inspection and Monitoring - All BMPs shall be inspected, maintained, and repaired as needed to assure continued performance of their intended function. Roger Brown Stormwater Site Plan (no address assigned) Center Road Chimacum, W A 98325 June 30, 2004 Page 8 Whenever inspection and/or monitoring reveals that the BMPs identified in the Construction SWPPP are inadequate, due to the actual discharge of or potential to discharge a significant amount of any pollutant, the SWPPP shall be modified, as appropriate, in a timely manner. Maintenance of the Construction SWPPP - The Construction SWPPP shall be retained on-site or within reasonable access to the site. The Construction SWPPP shall be modified whenever there is a significant change in the design, construction, operation, or maintenance of any BMP. 2.5.3 Minimum Requirement #3: Source Control of Pollution All known, available and reasonable source control BMPs shall be applied to all projects. Source control BMPs shall be selected, designed, and maintained according to this manual. The contractor will utilize appropriate BMP's should the need arise for preventing stormwater from coming into contact with pollutants. 2.5.4 Minimum Requirement #4: Preservation of Natural Drainage Systems and Outfalls Natural drainage patterns shall be maintained, and discharges from the project site shall occur at the natural location, to the maximum extent practicable. The manner by which runoff is discharged from the project site must not cause a significant adverse impact to downstream receiving waters and down gradient properties. All outfalls require energy dissipation. One of the elements of this drainage plan is to restore the natural drainage pattern in the central portion of the site to the maximum extent practical. The outlet of site-generated stormwaters is in the original wetland, on the proponent's property. All undisturbed natural drainage patterns within the project limits will be preserved and maintained in their natural state. 2.5.5 Minimum Requirement #5: On-site Stormwater Management Projects shall employ On-site Stormwater Management BMPs to infiltrate, disperse, and retain stormwater runoff onsite to the maximum extent feasible without causing flooding or erosion impacts. Roof Downspout Control BMPs, functionally equivalent to those described in Chapter 3 of Volume III, and Dispersion and Soil Quality BMPs, functionally equivalent to those in Chapter 5 of Volume V, shall be required to reduce the hydrologic disruption of developed sites. Stormwater runoff from the site will be infIltrated after the water quality storm flows are treated with appropriate bioswales and with sediments removed at a catch basin. The location of the infiltration/level spreader trench will maximize infIltration back to the wetland to the extent possible. It is noted that the northerly neighber's home is within the wetland itself and stormwater flows around and perhaps under his garage and residence. The preservation of the natural system and minimizing effects of flooding or stormwater impacts are at odds in this case. Application ofBMP C120, Temporary and Permanent Seeding, and BMP C121, Mulching, will minimize any potential for erosion. Roger Brown Stormwater Site Plan (no address assigned) Center Road Chimacum, W A 98325 June 30, 2004 Page 9 2.5.6 Minimum Requirement #6: Runoff Treatment Thresholds The following require construction of stormwater treatment facilities o Projects in which the total of effective, pollution-generating impervious surface (PGIS) is 5,000 square feet or more in a threshold discharge area of the project, or o Projects in which the total of pollution-generating pervious surfaces (pGPS) is three-quarters (3/4) of an acre or more in a threshold discharge area, and from which there is a surface discharge in a natural or man-made conveyance system from the site. This project technically required treatment facilities due to area of pollution-generating pervious surfaces, i.e. the parking and driveway areas. However, the driveway has existed for a long period of time preceding this project report, and directs runoff into the brushy areas alongside of the road. The water quality ofthis project would not be improved with additional stormwater treatment facilities. 2.5.7 Minimum Requirement #7: Flow Control Applicability Projects must provide flow control to reduce the impacts of increased stormwater runoff from new impervious surfaces and land cover conversions. The requirement below applies to projects that discharge stormwater directly, or indirectly through a conveyance system, into a fresh water - except for: discharges into the Columbia River, Lakes Sammamish, Silver (Cowlitz Co.), Union (King Co.), Washington, and Whatcom; discharges into a wetland; (See Minimum Requirement #8 for flow control requirements applicable to discharges to wetlands) Any exempted areas shall meet the following requirements: o The area must be drained by a conveyance system that is comprised entirely of manmade conveyance elements (e.g., pipes, ditches, outfall protection, etc.) and extends to the ordinary high water line of the receiving water; and o Any erodible elements of the man made conveyance system for the area must be adequately stabilized to prevent erosion; and o Surface water from the area must not be diverted from or increased to an existing wetland, stream, or near-shore habitat sufficient to cause a significant adverse impact. Local governments may petition Ecology to exempt projects in additional areas. A petition must justify the proposed exemption based upon a hydrologic analysis that Roger Brown Stormwater Site Plan (no address assigned) Center Road Chimacum, W A 98325 June 30, 2004 Page 10 demonstrates that the potential stormwater runoff from the exempted area will not significantly increase the erosion forces on the stream channel nor have near field impacts. All post development stormwater run-off generated by this project will be returned to the natural wetland hydrology. 2.5.8 Minimum Requirement #8: Wetlands Protection Applicability The requirements below apply only to projects whose stormwater discharges into a wetland, either directly or indirectly through a conveyance system. These requirements must be met in addition to meeting Minimum Requirement #6, Runoff Treatment. Thresholds The thresholds identified in Minimum Requirement #6 - Runoff Treatment, and Minimum Requirement #7 - Flow Control shall also be applied for discharges to wetlands. Standard Requirement Discharges to wetlands shall maintain the hydrologic conditions, hydrophytic vegetation, and substrate characteristics necessary to support existing and designated uses. A wetland can be considered for hydrologic modification and/or stormwater treatment in accordance with Guide Sheet 1B in Appendix I-D of the Stormwater Manual. The plan proposes restoration, to the extent practicable, of the hydrologic conditions and hydrophytic vegetation. 2.5.9 Minimum Requirement #9: BasinIWatershed Planning Projects may be subject to equivalent or more stringent minimum requirements for erosion control, source control, treatment, and operation and maintenance, and alternative requirements for flow control and wetlands hydrologic control as identified in BasinIWatershed Plans. BasinIWatershed plans shall evaluate and include, as necessary, retrofitting urban stormwater BMPs into existing development_and/or redevelopment in order to achieve watershed-wide pollutant reduction and flow control goals that are consistent with requirements of the federal Clean Water Act. Roger Brown Stormwater Site Plan (no address assigned) Center Road Chimacum, W A 98325 June 30, 2004 Page II Standards developed from basin plans shall not modify any of the above minimum requirements until the basin plan is formally adopted and implemented by the local governments within the basin, and approved or concurred with by Ecology. There are no basin plans applicable to this project. 2.5.10 Minimum Requirement #10: Operation and Maintenance An operation and maintenance manual that is consistent with the provisions in V olume V of the Stormwater Manual shall be provided for all proposed stormwater facilities and BMPs, and the party (or parties) responsible for maintenance and operation shall be identified. At private facilities, a copy of the manual shall be retained on site or within reasonable access to the site, and shall be transferred with property to the new owner. For public facilities, a copy of the manual shall be retained in the appropriate department. A log of maintenance activity that indicates what actions were taken shall kept and be available for inspection by the local government. An operation and maintenance manual has been developed for the stormwater facilities and BMP's related to this project and a copy will be given to the owner for their reference and implementation and to be kept on site. A copy is attached to this stormwater report. Roger Brown Stormwater Site Plan (no address assigned) Center Road Chimacum, W A 98325 June 30, 2004 Page 12 -if I'JGTCH\ 3HEET NUMBER ,: ;:)~ ~c.. N t i r I ,I I I o o o o 10 , (\J ~o .. ..... <ll ro o U) o o o :l'( I II..~. 'b: <:0., '~j: ',s-'-' ~ d o o '" ~~ o o o .,. o o o '"