CITY OF MERCER ISLAND DEVELOPMENT SERVICES GROUP

Transcription

1 DEVELOPMENT SERVICES GROUP 9611 SE 36TH STREET MERCER ISLAND, WA PHONE: Inspectin Requests: Online: VM: Intrductin Small prjects that nly trigger Minimum Requirements #1-5, include prjects that: a. Result in 2,000, but < 5,000 square feet f new plus replaced hard surface area b. Have a land disturbing activity f 7,000 square feet, but < ¾ acres f vegetatin cnverted t lawn r landscaped areas r < 2.5 acres f native vegetatin cnverted t pasture, r c. Result in a net increase f impervius surface f 500 square feet, but < 5,000 square feet f new plus replaced hard surface area. Minimum Requirements #1-5 (and assciated sectins f the City s submittal package) include: MR#1 - Strmwater Site Plans (Sectin A) MR#2 - Cnstructin Strmwater Pllutin Preventin (Sectin B) MR#3 - Surce Cntrl (Sectin A) MR#4 - Preservatin f Natural Drainage Systems and Outfalls (Sectin A) MR#5 - On-site Strmwater Management (Sectins A, C, and D) What are the benefits f LID? Single-family residential rain garden Lw Impact Develpment (LID) prvides many benefits t cmmunities n a large and small-scale. Nt nly can it make yur neighbrhd a greener and mre aesthetically pleasing place t be, it simultaneusly reduces flding, imprves water quality, and imprves grundwater recharge. LID can enhance the lcal envirnment, prtect public health, and imprve cmmunity livability. What is n-site strmwater management? On-site strmwater management is a strmwater and land use management strategy that mimics hw water at a site wuld naturally react prir t develpment, and uses design techniques fr infiltratin, filtratin, strage, evapratin and transpiratin. Instead f cnveying and detaining strmwater in large facilities lcated at the bttm f drainage areas, LID addresses strmwater thrugh small, distributed features lcated at the lt level. Permeable pavement driveway Single-family residential rain garden 1

2 What are Best Management Practices (BMPs)? A best management practice (r BMP) is a structural r management practice designed t prevent r reduce the release f pllutants. Strmwater management BMPs are cntrl measures taken t mitigate changes t bth quantity and quality f urban runff caused thrugh changes t land use. Generally, BMPs fcus n water quality prblems caused by increased impervius surfaces frm land develpment. BMPs are designed t reduce strmwater vlume, peak flws, and/r pllutin thrugh infiltratin, filtratin, strage, evapratin, and transpiratin. Types f LID BMPs Biretentin Rain gardens Permeable pavement Rf dwnsput cntrls Dispersin Sil quality and depth Vegetated rfs Rainwater harvesting Single-family residential rain garden Permeable pavement driveway Rain garden cllecting rad runff Rain garden cllecting rad runff 2

3 Which BMPs shuld be evaluated? Prjects that trigger Minimum Requirements #1-5 are required t implement List #1 (see belw) r the LID perfrmance standard (refer t the Strmwater Manual adpted in Sectin f the City s municipal cde). List #1 Fr each categry, select the first feasible item n the list: Lawn and landscaped areas Pst-cnstructin sil quality and depth Rfs Biretentin during installatin 1. Full dispersin r dwnsput full infiltratin systems 2. Rain gardens r biretentin 3. Dwnsput dispersin systems 4. Perfrated stub-ut cnnectins 5. On-site detentin Other hard surfaces 1. Full dispersin 2. Permeable pavement, rain gardens, r biretentin 3. Sheet flw dispersin r cncentrated flw dispersin Permeable pavement installatin 4. On-site detentin List #2 Prjects that trigger the full set f Minimum Requirements #1-9 are required t implement List #2 r the LID perfrmance standard in accrdance with the Strmwater Manual adpted in Sectin f the City s municipal cde. On-site detentin is added t the feasibility evaluatin fr List #2 (similar t List #1 abve) if all f the ther n-site strmwater management BMPs are determined t be infeasible fr Rfs and Other hard surfaces. Established biretentin facility 3

4 Hw t Implement Minimum Requirement #5 (On-Site Strmwater Management) Lawn & landscaped areas Step 1: Calculate areas by surface type (Sectin A) Rfs Other hard surfaces (e.g., driveways, patis, sidewalks) Step 2: Refer t List #1 r List #2. This tip sheet fcuses n implementing List #1 (Sectin A). Step 3: Evaluate the infeasibility f BMPs (Sectin C) in pririty rder based n: Design criteria, limitatins, and infeasibility criteria (Sectin C) Cmpeting needs criteria (Vlume V, Chapter 5 f the Strmwater Manual) Step 4: Select the first BMP that is cnsidered feasible fr each surface type (Sectin C) Step 5: Dcument the infeasibility (narrative descriptin and ratinale) fr each BMP that was nt selected (Sectin C) 4

5 DEVELOPMENT SERVICES GROUP 9611 SE 36TH STREET MERCER ISLAND, WA PHONE: Inspectin Requests: Online: VM: Benefits f Healthy Sils Reduced need fr irrigatin, fertilizers, and pesticides Decreased strmwater runff Decreased ersin Imprved plant health Marketable buildings and landscapes TIP SHEET: POST-CONSTRUCTION SOIL MANAGEMENT 5 Step Implementatin Prcess Step 1 Retain and prtect native vegetatin and sil Identify areas f the site that will nt be disturbed during cnstructin (cleared, graded, r driven n). Fence thse areas t prevent impacts during cnstructin. If neither sils nr vegetatin are disturbed, these areas d nt require amendment. Step 2 Lsen cmpacted subsil, if needed In disturbed areas (cmpacted by cnstructin traffic): Scarify the tp 4 inches f subsil Step 3 Restre sils that are disturbed during cnstructin Three ptins t restre disturbed sils include: Pht surce: City f Prt Angeles Befre Pht surce: City f Prt Angeles After Use a cat-munted ripper, tractr-munted disc, r tiller t mix the first lift f tpsil int the subsil (knwn as scarifying, ripping, r tilling) Use the equipment listed in the previus bullet t scarify (till r rip) sils t a depth f 12 inches befre tilling in at least 8 inches f cmpst Optin 1: Till cmpst (1.75 inches fr turf areas; 3 inches fr planting beds) int existing sil, r Optin 2: Stckpile and reuse existing tpsil (amend if needed t meet 5% rganic matter cntent fr turf areas; 10% rganic matter cntent fr planting beds), r Optin 3: Imprt 6 inches f cmpst-amended tpsil (25% cmpst fr turf areas; 40% cmpst fr planting beds) and scarify (till r rip) int existing sil in tw 3-inch lifts 5

6 TIP SHEET: POST-CONSTRUCTION SOIL MANAGEMENT 5 Step Implementatin Prcess (cnt.) Step 4 Add mulch t planting beds Spread mulch (carse bark r wd chips) in the spring r fall (after planting) t cntrl weeds, reduce the need fr irrigatin, and prevent ersin. Apply 1 t 2 inches f mulch n planting beds and arund shallw-rted annuals. Apply 2 t 4 inches f mulch arund trees and wdy perennials, but make sure t keep mulch 2 t 3 inches away frm tree trunks. Step 5 Prtect restred sils frm ersin and re-cmpactin Prevent runff frm rads r pen slpes nt amended sil areas. Cmpst blankets are an apprved ersin cntrl Best Management Practice (BMP) that can be used during cnstructin and then tilled int the existing sil at the end f the cnstructin prcess prir t planting. Once sils have been amended, vehicle traffic shuld be prhibited t prevent re-cmpactin frm ccurring. Exemptins The fllwing prtins f the prject area are exempt frm sil amendment requirements: Areas cvered by an impervius surface, r Areas incrprated int a drainage facility, r Structural fill r engineered slpes On till slpes greater than 33% Pht surce: City f Prt Angeles Cmpst ptins require tilling t a depth f 8 Planting bed Turf Stckpile and reuse existing tpsil if it meets the rganic matter cntent requirements Native, undisturbed sil 1.75 f cmpst r 6 f cmpst-amended tpsil tilled in t an 8 depth f mulch 3 f cmpst r 6 f cmpst-amended tpsil tilled t an 8 depth