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Home My WebLink AboutBLD2015-00216 - 05 STORMWATER • • ��so o0,_ JEFFERSON COUNTY 4 �`:,;, +3 DEPARTMENT OF COMMUNITY DEVELOPMENT h . :,q �C "$ 621 Sheridan Street • Port Townsend • Washington 98368 *(4.& NG�O 360/379-4450 • 360/379-4451 Fax http://www.co.jefferson.wa.us/commdevelopment/ Stormwater Calculation Worksheet MLA# PROJECT/APPLICANT NAME: Igo (I_"AN—)4 •%tt',A i 't .4is 1,IA., DETERMINING STORMWATER MANAGEMENT REQUIREMENTS: This stormwater calculation worksheet should be completed first to classify the proposal as "small,""medium,"or"large." The size determines whether a Stormwater Site Plan is required in conjunction with a stand-alone stormwater management permit application, building permit application, or other land use approval application that involves stormwater review. The basic information will also be helpful for completing a Stormwater Site Plan, if required. r-- ^�o PARCEL SIZE (I.E., SITE1 -� f�C (cam a ll/7 '- Size of parcel :), % acres An acre contains 43,560 square feet. Multiply het creage by this figure. Size of parcel in square feet_ �Fa�Le sq/ft J1 A JUN 2 5 2015 J JEFFERSON COUNTY Land-disturbing activity is any activity that results in movement of earth, or a change in the ex'stingazpil gpggmtlyp *wand non-vegetative) and/or the existing soil topography. Land disturbing activities include, but are nalinted to clearing, grading, tilling, excavation, and compaction associated with stabilization of structures and road construction. Native vegetation is vegetation comprised on plant species, other than noxious weeds,that are indigenous to the coastal region of the Pacific Northwest and which reasonably could have been expected to naturally occur on the site. Examples include species such as Douglas fir,western hemlock,western red cedar, alder, big-leaf maple, and vine maple; shrubs such as willow,elderberry, salmonberry, and salal; herbaceous plants such as sword fern,foam flower, and fireweed. LAND DISTURBING ACTIVITY, CONVERSION OF NATIVE VEGETATION, AND VOLUME OF CUT/FILL Calculate the total area to be cleared, graded,filled, Answer the following two questions related to excavated,and/or compacted for proposed development conversion of native vegetation: project. Include in this calculation the area to be cleared for: Does the project convert%acres or more of Construction site for structures ,F� sq/ft native vegetation to lawn or landscaped areas? Drainfeld,septic tank, etc. ( J so/ft Circle: Yes Oa Well, utilities,etc. d sq/ft Does the project convert 2 4 acres or more of native vegetation to pasture? Driveway, parking,roads, etc. 0 sq/ft Circle: Yes co Lawn, landscaping, etc. 0 sq/ft Other compacted surface, etc. 0 sq/ft Indicate Total Volumes of Proposed: Total Land Disturbance 0 sq/ft Cut Fill _ (cu/yd) [over] stormwater talc worksheet Rev 9-9-2010–REV 9/9!2010 I 0 0 Impervious surface is a hard surface that either prevents or retards the entry of water into the soil mantle as under natural conditions prior to development. A hard surface area which causes water to run off the surface in greater quantities or at an increased rate of flow from the flow present under natural conditions prior to development. Common impervious surfaces include, but are not limited to roof tops, walkways, patios, driveways, parking lots or storage areas, concrete or asphalt paving, gravel roads, packed earthen materials, and oiled, macadam or other surfaces which similarly impede the natural infiltration of stormwater. STORMWATER CALULATIONS-IMPERVIOUS SURFACE NEW EXISTING Structures (all roof area) (ILA XS2, '1a sq/ft Structures(all roof area) 51_19 sq/ft Sidewalks D sq/ft Sidewalks sq/ft Patios 0 sq/ft Patios sq/ft Solid Decks D sq/ft Solid Decks sq/ft (without infiltration below) (without infiltration below) _ - Driveway, parking, roads, etc 0 sq/ft Driveway, parking, roads, etc_ Z• Other sq/ft Other sq/ft Total New -1 7q sq/ft Total Existing LP sq/ft TOTAL NEW+TOTAL EXISTING* ?..-131-1 sq/ft 1 *This amount will be used BY STAFF to check total lot coverage. IIT�Sollowing questions will help determine whether the proposed project is considered development or redevelopment. DEVELOPMENT v. REDEVELOPMENT Divide the total existing impervious surface above by the size of the parcel and convert to a percentage: % Does the site have 35%or more of existing impervious surface? Circle: Yes No FURTHER INSTRUCTIONS: If the answer is yes, the proposal is considered redevelopment and the attached Figure 2 should be used to determine the applicable Minimum Requirements. If the answer is no, the proposal is considered new development and the attached Figure 1 should be used. At this juncture, the applicant should refer to the applicable Flow Chart to determine the Minimum Requirements for stormwater management. DCD staff will help verify the classification of the project and the application requirements. For proponents of "small" projects who must comply only with Minimum Requirement #2-Construction Stormwater Pollution Prevention-an additional submittal is not required. The proponent is responsible for employing the 12 Elements to control erosion and prevent sediment and other pollutants from leaving the site during the construction phase of the project. Pick up the Construction Stormwater Pollution Prevention (SWPP) Best Management Practices (BMPs) Packet. Proponents of"medium" projects-those that must meet only Minimum Requirements #1 through #5-and for "large" projects-those that must meet all 10 Minimum Requirements-are required to submit a Stormwater Site Plan. DCD has prepared a submittal template of a Stormwater Site Plan, principally for rural residential projects. Complete the template in the Stormwater Site Plan Instructions and Submittal Template or prepare a Stormwater Site Plan using the step-by-step guidance in the Stormwater Management Manual. APPLICANT SIGNATURE By signing the Stormwater Calculation Worksheet, I as the applicant/owner attest that the information provided herein is true and correct to the best of my knowledge. I also certify that this application is being made with the full knowledge and consent of all owners of the affected property. (LANDOWNER OR AUTHORIZ D REPRESENTATI %SI NATURE) (DATE) FOR OFFICE USE ONLY SMALL MEDIUM LARGE REDEVELOPMENT___ _ Stormwater Site Plan: Yes No stormwaler cak worksheel Rev 9-9-2010—REV 919/2010 2 • • ¢,SOJV cO � 4w . JEFFERSON COUNTY IFOIERVE I-z.4 �` ., DEPARTMENT OF COMMUNITY DEVELOPMENT JUN 2 5 . , ,C 1 2015 i 621 Sheridan Street • Port Townsend • Washington 98368 I J I & $ JEFFERSON COUNTY �`S$ING�O httttp://www.co.jefferrsonwa.us/ommdevelopmenti (--_—DEPT.OF COMMUNITY DEVELOPMENT Stormwater Calculation Worksheet MLA# PROJECT/APPLICANT NAME: • (v_a Ab^I 'h A,,inv- Al 1 IlL AM S IR.I DETERMINING STORMWATER MANAGEMENT REQUIREMENTS: This stormwater calculation worksheet should be completed first to classify the proposal as"small,""medium,"or"large." The size determines whether a Stormwater Site Plan is required in conjunction with a stand-alone stormwater management permit application, building permit application, or other land use approval application that involves stormwater review. The basic information will also be helpful for completing a Stormwater Site Plan,if required. r p PARCEL SIZE(I.E.,SITE) Size of parcel - J , L t, acres An acre contains 43,560 square feet. Multiply the acreage by this figure. Size of parcel in square feet_7z1, 4C- sq/ft r 1 _ I Land-disturbing activity is any activity that results in movement of earth, or a change in the existing soil cover (both vegetative and non-vegetative) and/or the existing soil topography. Land disturbing activities include, but are not limited to clearing, grading, filling, excavation, and compaction associated with stabilization of structures and road construction. Native vegetation is vegetation comprised on plant species, other than noxious weeds,that are indigenous to the coastal region of the Pacific Northwest and which reasonably could have been expected to naturally occur on the site. Examples include species such as Douglas fir, western hemlock,western red cedar, alder, big-leaf maple,and vine maple; shrubs such as willow, elderberry, salmonberry, and salal; herbaceous plants such as sword fern,foam flower,and fireweed. LAND DISTURBING ACTIVITY,CONVERSION OF NATIVE VEGETATION,AND VOLUME OF CUT/FILL Calculate the total area to be cleared,graded,filled, Answer the following two questions related to excavated,and/or compacted for proposed development conversion of native vegetation: project. Include in this calculation the area to be cleared for: y� Does the project convert' acres or more of Construction site for structures ,C/ sq/ft native vegetation to lawn or landscaped areas? Drainfeld, septic tank, etc. (J sq/ft Circle: Yes No Well, utilities,etc. d sq/ft Does the project convert 2 Y2 acres or more of native vegetation to pasture? Driveway, parking,roads,etc. sq/ft Circle: Yes Lawn, landscaping, etc. 0 sq/ft Other compacted surface, etc. 0 sq/ft Indicate Total VgltimPC of Proposed: 1 Total Land Disturbance - C) sq/ft Cut l [ri- ( /Y If r !r11 1 'H JUN 2 5 2015 ;I [over] -J l.i i I` i JEFFERSON COUNTY "FT OF COMMUNITY DEVELOPMENT 1 stormwater calc worksheet Rev 9-9-2010—REV 9/9/2010 1 • • Impervious surface is a hard surface that either prevents or retards the entry of water into the soil mantle as under natural conditions prior to development. A hard surface area which causes water to run off the surface in greater quantities or at an increased rate of flow from the flow present under natural conditions prior to development. Common impervious surfaces include. but are not limited to roof tops, walkways, patios, driveways, parking lots or storage areas, concrete or asphalt paving, gravel roads, packed earthen materials, and oiled, macadam or other surfaces which similarly impede the natural infiltration of stormwater. STORMWATER CALULATIONS-IMPERVIOUS SURFACE NEW EXISTING Structures(all roof area) (VA X52) '12g sq/ft Structures(all roof area) (� sq/ft Sidewalks sq/ft Sidewalks sq/fl Patios Q sq/ft Patios sq/ft Solid Decks C) sq/ft Solid Decks sq/ft (without infiltration below) (without infiltration below) - -'� Driveway, parking, roads, etc 0 sq/ft Driveway, parking, roads,etc_ Z '�{r- 143 osl! ' ' Other sq/ft Other sq/ft Total New 77N sq/ft Total Existing �/G./ -C) sq/ft TOTAL NEW+TOTAL EXISTING* �J� sqlft `This amount will be used BY STAFF to check total lot coverage. • The following questions will help determine whether the proposed project is considered development or redevelopment. DEVELOPMENT v. REDEVELOPMENT Divide the total existing impervious surface above by the size of the parcel and convert to a percentage: % Does the site have 35%or more of existing impervious surface? Circle: Yes No FURTHER INSTRUCTIONS: If the answer is yes, the proposal is considered redevelopment and the attached Figure 2 should be used to determine the applicable Minimum Requirements. If the answer is no, the proposal is considered new development and the attached Figure 1 should be used. At this juncture, the applicant should refer to the applicable Flow Chart to determine the Minimum Requirements for stormwater management. DCD staff will help verify the classification of the project and the application requirements. For proponents of "small" projects who must comply only with Minimum Requirement #2—Construction Stormwater Pollution Prevention—an additional submittal is not required. The proponent is responsible for employing the 12 Elements to control erosion and prevent sediment and other pollutants from leaving the site during the construction phase of the project. Pick up the Construction Stormwater Pollution Prevention (SWPP) Best Management Practices (BMPs) Packet. Proponents of"medium" projects—those that must meet only Minimum Requirements #1 through #5—and for "large" projects—those that must meet all 10 Minimum Requirements—are required to submit a Stormwater Site Plan. DCD has prepared a submittal template of a Stormwater Site Plan, principally for rural residential projects. Complete the template in the Stormwater Site Plan Instructions and Submittal Template or ' prepare a Stormwater Site Plan using the step-by-step guidance in the Stormwater Management Manual. APPLICANT SIGNATURE By signing the Stormwater Calculation Worksheet, I as the applicant/owner attest that the information provided herein is true and correct to the best of my knowledge. I also certify that this application is being made with the full knowledge and consent of all owners of the affected property. OP Cs� QI1.QA 2.0 kS-- (LANDOWNER OR AUTHORIZ D REPRESENTATI a SI NATURE) (DATE) FOR,OFFICE USE ONLY SMALL MEDIUM LARGE REDEVELOPMENT Stormwater Site Plan: Yes No r.. stormwater caic worksheet Rev 9-9-2010—REV 919120W 2 .andard Conditions for Residenti evelopment in Jefferson County • . LIGHTING: Lighting fixtures shall be designed and hooded to prevent the light source from being directly 1 y visible from outside the boundaries of the property. The intensity or brightness of all lighting, during construction and after project completion shall not adversely affect the use of surrounding properties or adjoining rights-of-way. Exterior lighting for residential uses shall not exceed twenty feet (20') in height from the finished grade, excepting when such lighting is an integral part of a building or structure. Ground level lighting is encouraged_ 2. BUILDING HEIGHT: The building height is not to exceed 35 feet. 3. OUTDOOR STORAGE: Outdoor residential storage shall be maintained in an orderly manner and shall create no fire, safety, health or sanitary hazard. 4. UNLICENSED VEHICLES: Not more than 2 unlicensed vehicles shall be stored on any lot unless totally screened from view of neighboring dwellings and rights-of-way. Such screening shall meet all applicable performance and development standards specific to the district in which the storage is kept, and shall be in keeping with the character of the area. Screening shall meet the requirements of Chapter 18.30 JCC. Outdoor storage of 3 or more junk motor vehicles is prohibited except in those districts where specified as an automobile wrecking yard or junk(or salvage) yard and allowed as a permitted use in Table 3-1 or Chapter 18.18 JCC, and such storage shall meet the requirements of JCC 18.20.100,Automobile wrecking yards and junk (or salvage) yards. In no case, shall any such junk motor vehicles be stored in a critical area. 5. PARKING: A minimum of two (2) on-site parking spaces shall be provided for the single family residence. 6. This permit has been reviewed consistent with JCC 18.40.130 & 140. Notice: this permit does not excuse the applicant from complying with other local, state and federal ordinances, regulations or statues, applicable to the proposed development, but consistent with RCW 90.58. Future development beyond that specified in this permit shall require further review. 7. BMPs:The project shall adhere to the Best Management Practices (BMPs) to control stormwater, erosion and sediment during construction. BMPs shall address permanent measures to stabilize soil exposed during construction, and in the design and operation of stormwater and drainage control systems. 8. NOTICE: This permit does not excuse the proponent from complying with other local, state, and federal ordinances, regulations, or statutes applicable to the proposed development, but consistent with RCW 90.58. Development pursuant to this permit shall be undertaken subject to the applicable policies and performance standards of the Jefferson County Shoreline Management Master Program and the Jefferson County Unified Development Code. If during excavation or development of the site an area of potential archaeological significance is uncovered, all activity in the immediate area shall be halted, and the Administrator shall be notified at once. The Federal Endangered Species Act rules to protect threatened Chinook and Summer-run Chum salmon became effective on January 8, 2001. Bull trout have been listed as threatened since early 2000. Under the ESA, any person may bring lawsuit against any individual or agency that"takes" listed species (defined as causing harm, harassing, or damaging habitat for the listed species). In addition, the National Marine 2013-03-075FR_StdConditions 3/7/2013 1 Fisheries Service can levy pena P es. Portions of Jefferson County, includi g marine waters, are included as "critical habitat"for a listed species. Development of property along any marine shoreline, freshwater shoreline, or floodplains could harm habitat if protective measures are not taken- To minimize the potential to damage habitat, all property owners developing adjacent to marine shoreline, freshwater shoreline, or floodplains are advised to do the following: All development activities should avoid unstable slopes, wetlands, and forested areas near surface waters Remove minimal vegetation for site development, especially large trees Allow trees that have fallen into surface waters to remain there Infiltrate stormwater from buildings and driveways onsite through drywells rather than discharging directly into surface waters or roadside ditches The Federal Bald and Golden Eagle Protection Act requires landowners within 660 feet (1/8th of a mile) of an eagle nest to consult with the US Fish and Wildlife Service. This Eagle Act prohibits anyone from "taking" bald eagles. This federal law defines the term "take" and describes the possible legal consequences when a"take" occurs. Among other actions, "take" includes a disturbance of bald eagles or their habitat. Under federal law a permit may still be required for activities that impact bald eagles or their habitat. Contact the US Fish and Wildlife Service (http://www.fws.gov/pacific/eagle/) to learn more about how this law affects your project. Any individual, group, or agency can bring suit for a listed species"taking", even if you are in compliance with Jefferson County development codes. The risk of a lawsuit against you can be reduced by consulting with a professional fisheries habitat biologist, and following the recommendations for site development provided by the biologist. For more information, contact the National Marine Fisheries Service in Seattle, or the U.S. Fish and Wildlife Service. 2013-09-06 SFR_StdConditions 9/6/2013 2 . • 3.1.2 Downspout Dispersion Systems (BMP T5.10B) Downspout dispersion systems are splash blocks or gravel-filled trenches, which serve to spread roof runoff over vegetated pervious areas. Dispersion attenuates peak flows by slowing the runoff entering into the conveyance system, allowing some infiltration, and providing some water quality benefits. Applications & Downspout dispersion may be used in all subdivision lots where Limitations downspout full infiltration, full dispersion, and bioretention/rain gardens are not feasible. Runoff Modeling In WWHM,roof areas maybe modeled as grassed surfaces (landscape) if for Roof roof runoff is dispersed according to the requirements of this section on Downspout lots greater than 22,000 square feet, and the vegetated flowpath is 50 feet Dispersion or larger through undisturbed native landscape or lawn/landscape area that meets BMP T5.13. If the available vegetated flowpath is 25 to 50 feet, use of a dispersion trench allows modeling the roof as 50% impervious/50%landscape. This is done in WWHM on the Mitigated Scenario screen by entering the roof area into one of the entry options for dispersal of impervious area runoff. For WWHM2012, see Appendix III-C in this Volume. Design Criteria 1. Use downspout trenches designed as shown in Figures 3.1.5 and 3.1.6 for all downspout dispersion applications except where splash blocks are allowed below. 2. Splash blocks shown in Figure 3.1.7 may be used for downspouts discharging to a vegetated flowpath at least 50 feet in length as measured from the downspout to the downstream property line, structure,slope over 15%, stream, wetland,or other impervious surface. Sensitive area buffers may count toward flowpath lengths. 3. Cover the vegetated flowpath with well-established lawn or pasture, landscaping with well-established groundcover,or native vegetation with natural groundcover. The groundcover shall be dense enough to help disperse and infiltrate flows and to prevent erosion. 4. If the vegetated flowpath(measured as defined above)is less than 25 feet,a perforated stub-out connection per Section 3.13 may be used in lieu of downspout dispersion.A perforated stub-out may also be used where implementation of downspout dispersion might cause erosion or flooding problems, either on site or on adjacent lots.For example,this provision might be appropriate for lots constructed on steep hills where downspout discharge could culminate and might pose a potential hazard for lower lying lots, or where dispersed flows could create problems for adjacent off-site lots. This provision does not apply to situations where lots are flat and on-site downspout dispersal would result in saturated yards. Perforated stub-outs are not appropriate when seasonal water table is<1 foot below trench bottom. Volume III—Hydrologic Analysis and Flow Control BMPs—December 2014 3-11 • • Setbacks Local governments may require specific setbacks in sites with slopes over 40%, land slide areas,open water features,sprint ,weIls,and septic tank drain fields.Adequate room for maintenance . cess and equipment should also be considered.Examples of setbacks cc monly used include the following: 1. All infiltration systems should b- .t least 10 feet from any structure, property line,or sensitive area except slopes over 40%). \2. All infiltration systems mu be at least 50 feet from the top of any slope \over 40%.This setback ay be reduced to 15 feet based on a geotechnical evaluatio but in no instances may it be less than the bufer width. 3. For sites -th sep'c systems,infiltration systems must be downgradient of the drai -le unless the site topography clearly prohibits subsurface flows from in e ecting the drainfield. Volume III—Hydrologic Analysis and Flow Control BMPs—December 2014 3-10 • • Note:For all other types of projects, the use of a perforated stub-out in lieu of downspout dispersion shall be as determined by the Local Plan Approval Authority. 5. For sites with septic systems,the discharge point of all dispersion systems must be downgradient of the drainfield. This requirement may be waived if site topography clearly prohibits flows from intersecting the drainfield. Design Criteria for Dispersion Trenches I. A vegetated flowpath of at least 25 feet in length must be maintained between the outlet of the trench and any property line,structure,stream, wetland,or impervious surface. A vegetated flowpath of at least 50 feet in length must be maintained between the outlet of the trench and any slope steeper than 15%. Sensitive area buffers may count towards flowpath lengths. 2. Trenches serving up to 700 square feet of roof area may be simple 10- foot-long by 2-foot wide gravel filled trenches as shown in Figure 3.1.5. For roof areas larger than 700 square feet,a dispersion trench with notched grade board as shown in Figure 3.1.6 or alternative material approved by the Local Plan Approval Authority may be used.The total length of this design must not exceed 50 feet and must provide at least 10 feet of trench per 700 square feet of roof area. 3. Maintain a setback of at least 5 feet between any edge of the trench and any structure or property line. 4. No erosion or flooding of downstream properties may result. 5. Have a geotechnical engineer or a licensed geologist,hydrogeologist, or engineering geologist evaluate runoff discharged towards landslide hazard areas.Don not place the discharge point on or above slopes greater than 15%or above erosion hazard areas without evaluation by a geotechnical engineer or qualified geologist and jurisdiction approval. 6. For purposes of maintaining adequate separation of flows discharged from adjacent dispersion devices,the outer edge of the vegetated flowpath segment for the dispersion trench must not overlap with other flowpath segments,except those associated with sheet flow from a non- native pervious surface. Volume III—Hydrologic Analysis and Flow Control BMPs—December 2014 3-12 • • . . e level outlet • ° d ° Qo o o n° .° • d 8 >° 7d d0 8 o010 pp a.0q a _— • 0 0 0O 00 pen • _, 00• o p . n_ 0 Q . e .00 a o o . o 'pQn ple a • ' 6'min d>oop a°0do 0.0.ti o o n' e o.0 4"pert pipe .ed o°O�7id ndo0� 18'min .s0pov.0 0000D°„o we 3/a washed rock O ap0 . Q0.°04 Oen. 0�. no p n . n 0 0 p °.n. •p0°y...Q.. .0 o.p°. Doll o.p o.o. o. . 0 .o . ° 24'min TRENCH X-SECTION NTS slope —• small catch basin or yard drain 2'x10' level trenches 5700 sq.fl Type I CB >700 sq.ft. standard dispersion trench wi notched grade board length 10'per 700 sq.ft, of roof area PLAN VIEW OF ROOF MTC Figure 3.1.5-Typical Downspout Dispersion Trench Source: King County Volume III—Hydrologic Analysis and Flow Control BMPs—December 2014 3-13 • • /pipe O.D. r-o � t'-0 xtnn 111131 end cap or plug flow to second dispersal trench ■ ^ clean out wye from pipe it necessary R ° 1 u 4° o 4"orb"perbrat?d pipe laid flaUlevet a notched _� o p° gradeboard �. A° 2"x2'notches =v. 0 9 type ICBw/eD lid copier(locking) ICB is.ac. A type 's/sol id cover _ a it1 r� 11111111111111•1 .41— Q a R intluentpip? (max design 1� Qo66 fbws0.5CFS per trench) �'�A Y _ v¢ clean out vow from pipe • I flan to otter branching CB's PLAN as rec -nary NTS pipe O.D. I it O.C. galvanized boles r-o /1.-0 }w—2" try __ s.;;{{,,,, �r �b "` �;�.n ¢a ar w 2"grade 2'x12" `y, ``.g,, , a, ,'; pressure 44.4.,,:''' ''.4:;:.'■N¢a e9 ti.` board notches 2" treated grade 2.L1 ° o .�•.t: 4"ore'perforated to ani N '';f:':.4• a4 ,4 pipe laid flat 9 ° NOTES: o * )t ~ _ui ra 4"x4'support post 'y ( , p� . dean(s5%fines) 1.This trench shall be construced so *° i+i- -3N"avashed rock as to prevent point dischargeand.br in 1 B. I,'.,.7 erosion. IX filter fabrb '�>' � 2.Trenches may he placed no cbser than 50 feet tc one another.(100 feet "15%. mexfer flow ccntroNuaterclaalily along fbwlire) treatment in rural areas. 3.Trench and grarw board must be level.A Iig n to fol bw co nto urs of sin. SECTION A-A 4.Support post spacing as required by NTS soil conditions to ensure grade board remains level. Figure 3.1.6 - Standard Dispersion Trench with Notched Grade Board Volume III—Hydrologic Analysis and Flow Control BMPs—December 2014 3-14 ! • Design Criteria for Splashblocks A typical downspout splashblock is shown in Figure 3.1.7. In general, if the ground is sloped away from the foundation and there is adequate vegetation and area for effective dispersion, splashblocks will adequately disperse storm runoff. If the ground is fairly level, if the structure includes a basement,or if foundation drains are proposed, spla hhblocks with downspout extensions may be a better choice because the discharge point is moved away from the foundation. Downspout extensions can include N-piping to a splashblock/discharge point a con%derable distance from the d'awnspout,as long as the runoff can travelrthrough a well-vegetated area as 1-scribed below. The fo owing apply to the use of splashblocks: 1. Maint.-n a vegetated flowpath offat least 50 feet between the discharge point an any property line, structure, slope steeper than 15%, stream, wetland, 1. ,e,or other impervious surface. Sensitive area buffers may count towar• owpath lengtps. 2. A maximum o 00 squaro feet of roof area may drain to each splashblock. 3. For purposes of mai .'ning adequate separation of flows discharged from adjacent dispel-ski devices,the vegetated flowpath segment for the splashblock must not Overlap with other flowpath segments, except those associated with sheet low from a non-native pervious surface. 4. Place a splashbloci k or a pad o crushed rock(2 feet wide by 3 feet long by 6 inches deep)at each ds spout discharge point. 5. No erosion or flooding of downstre..0 properties may result. 6. Have a geotechnical engineer or a lice ed geologist, hydrogeologist, or engineering geologist evaluate runoff..scharged towards landslide hazard areas. Do not place Splashblocks o sr above slopes greater than 15%or above erosion hazard areas with.ut evaluation by a professional engineer with geotechnical expert e or a licensed geologist,hydrogeologist,or engineering geolog t, and approval by the local Plan Approval Authority. 7. For with septic systems,the discharge point mu be downslope of the primary and reserve drainfield areas. This requir i ent may be waived if site topography clearly prohibits flows from int: secting the drainfield or where site conditions (soil permeability,distan e between systems,etc.) indicate that this is unnecessary. Volume III—Hydrologic Analysis and Flow Control BMPs—December 2014 3-15 • • • Design Criteria for Splashblocks A typical downspout splashblock is shown in Figure 11.7. In general, if the ground is sloped away from the foundation and there is adequate vegetation and area for effective dispersion, splashblocks will adequately disperse storm runoff. If the ground is fairly level, if the structure includes a basement, or if foundation drains are proposed, splashblocks with downspout extensions may be a better choice because the discharge point is moved away from the foundation. Downspout extensions can include piping to a splashblock/discharge point a considerable distance from the downspout,as long as the runoff can travel through a well-vegetated area as described below. The following apply to the use of splashblocks: 1. Maintain a vegetated flowpath of at least 50 feet between the discharge point and any property line, structure, slope steeper than 15%, stream, wetland, lake,or other impervious surface. Sensitive area buffers may count toward flowpath lengths. 2. A maximum of 700 square feet of roof area may drain to each splashblock. 3. For purposes of maintaining adequate separation of flows discharged from adjacent dispersion devices,the vegetated flowpath segment for the splashblock must not overlap with other flowpath segments,except those associated with sheet flow from a non-native pervious surface. 4. Place a splashblock or a pad of crushed rock(2 feet wide by 3 feet long by 6 inches deep) at each downspout discharge point. 5. No erosion or flooding of downstream properties may result. 6. Have a geotechnical engineer or a licensed geologist,hydrogeologist, or engineering geologist evaluate runoff discharged towards landslide hazard areas. Do not place Splashblocks on or above slopes greater than 15%or above erosion hazard areas without evaluation by a professional engineer with geotechnical expertise or a licensed geologist,hydrogeologist,or engineering geologist, and approval by the Local Plan Approval Authority. 7. For sites with septic systems,the discharge point must be downslope of the primary and reserve drainfield areas. This requirement may be waived if site topography clearly prohibits flows from intersecting the drainfield or where site conditions (soil permeability, distance between systems, etc.)indicate that this is unnecessary. Volume III—Hydrologic Analysis and Flow Control BMPs—December 2014 3-15 p • • /pipe O.D. mn rain end cap or plug low to second dispersal trench 11.11.^ clean outwpe from pipe if necrsant I. vo 0 4"or6"perbraed pipe laid fla91eveI notched ❑° 4. g r de board • qa 2'k 2"notches n 9 type I C B verso lid cote r(loc king) 18'O.C. ° j type I CB w/sol id cove r _ a iii a �I -'R-' o a a influent pipe (maxdesign w 1� �jG1u6 flow.0.5CFSpertreneh) .!_■ 4 v' v4 clean outwle from pipe i ° tlowtoother • branching C S's PLAN as necessary NTS j pipe O.D. `f ' l 2 gatvanizei bolts f'-0 r-o �1 t� Iii .--- •r 0 2"grade ss -" ° '' preure ��§ a e ,y board notches 4,- Y as 4"orb'perforated treated grade ' �S a a of board a C .4 -..erg, pipe lak flax "va Yg,�o2' . NOTES: 4"x 4'sup port post k'• ck4 „ c_.lean(55%fines) 1.This trench shall be construced so 'P„ 1+le -31*"washed rock ast prevent pointdischargeandior tfA 9 erosion. • G ',.V.:,?r.% 2.Trenc hes may be placed no c loser fitter fabric than 50 feet+o one another.(100 feet along fbwline) 15 t118xfCYflOVCCYItfoUWeteYglalib} 3.Trenchardgradeboardmustbe treatrrert in rural areas. level.Align to follow contoursofsir. SECTION A-A 4.Support post spacing as required by NTS so it co rditbns to ensure g rade board remains I=_vel. Figure 3-1.6-Standard Dispersion Trench with Notched Grade Board Volume III—Hydrologic Analysis and Flow Control&MPs—December 2014 3-14 • 0 house 1 _ t... ..,._.L......1 Roof downspout serves up to 700 sf. Of roof MEM .............. 50' min. Vegetated �- flow path Splash !== block ti •;,.nos Downspout extension NTS Splash block Figure 3.1.7-Typical Downspout Splashblock Dispersion Vob ne III—Hydrologic Analysis and Flow Control BMPs—December 2014 3-16 • • 3.1.3 Perforated Stub-Out Connections (BMP T5.10C) A perforated stub-out connection is a length of perforated pipe within a gravel-filled trench that is placed between roof downspouts and a stub-out to the local drainage system. Figure 3.1.8 illustrates a perforated stub-out connection. These systems are intended to provide some infiltration during drier months. During the wet winter months,they may provide little or no flow control. Applications& Perforated stub-outs are not appropriate when seasonal water table is less Limitations than one foot below trench bottom. In ` ojects subject to Minimum Requirement#5 (see Vol e I), perfo ted stub-out connections may be used only whe .11 other higher priority n-site stormwater management BMPs are . feasible,per the criteria fo each of those BMPs. Select the to Lion of the connection to allow .. maximum amount of runoff to infiltr e into the ground (ideally . •ry,relatively well drained, location). To faci ' ate maintenance,do •t locate the perforated pipe portion of the syste under impervioug or heavily compacted (e.g., driveways and parkinareas) surfaces. Use the same setbacks as for infiltration trenches in Section 3.J 1. Have a licensed geologist,hydrogeologist, or engineering geologist evaluate potential runoff disc arges towards landslide hazard areas. Do not place the perforated portion f the pipe on or above slopes greater than 20%or above erosion hazard are. without evaluation by a professional engineer with geotechnical experti - or qualified geologist and jurisdiction approval. For sites with septic systems,the perfor:ted portion of the pipe must be downgradient of the drainfield primary a • reserve areas. This requirement can be waived if site topograp' will clearly prohibit flows from intersecting the drainfield or where site onditions(soil permeability, distance between systems,etc.)indicate that th is unnecessary. Design Criteria Perforated stub-out connections consist of at leas 10 feet of perforated pipe per 5,000 square feet of roof area laid in a 1ev- 2-foot wide trench backfilled with washed drain rock.Extend the drain •ck to a depth of at /least 8 inches below the bottom of the pipe and cover t e pipe. Lay the ' pipe level and cover the rock trench with filter fabric an. 6 inches of fill / (see Figure 3.1.8). Runoff Model /J Any flow reduction is variable and unpredictable.No compu.-r modeling Representation techniques are allowed that would predict any reduction in fib, rates and volumes from the connected area. Volume III—Hydrologic Analysis and Flow Control BMPs—December 2014 3-17