How to Use ESD to Protect Aquatic Resources Richard Klein 1 In this portion of the workshop we’ll get into the technical details of ESD. But because of the complexity of ESD we’re going to present more of an overview then an in-depth how-to. But we’re also going show you where to find some great guidance documents that make it easy to grasp the how-to’s. Most of these documents were prepared by Tom Schueler of the Chesapeake Stormwater Network. 1 Key ESD Guidance Documents Plus ESD Chapter 5 http://www.mde.state.md.us/Programs/WaterPrograms/SedimentandStormwater/home/index.asp 2 The following presentation is based on these two Maryland Department of the Environment guidance documents. The one on the left – the sediment control specs – is still in draft form and has not been officially adopted. Of course the 2000 Stormwater Design Manual is official including the new Chapter 5 which sets forth how ESD is to be applied. A word of caution though. Many of the specifics of how to apply ESD to a site are still being ironed-out. So you may find that your county or even MDE applies ESD requirements in ways subtly different from that presented here. 2 ESD Principles Design the project to cause the smallest area of disturbance; To minimize erosion, divert off-site runoff or convey it and on-site runoff in wellvegetated channels, pipes or other erosion resistant structures Maintain sheetflow and natural overland flow processes wherever feasible. Confine the area of disturbance to the portion(s) of the site with the: Least erodible soils and flattest slopes; Greatest distance from wetlands, streams, floodplains, etc.; and Least contiguous forest. Minimize new impervious area with practices such as: Short road lengths, narrow road widths; minimum number of parking spaces, smallest parking stalls practical, and other Better Site Design measures; Substitute porous pavement, permeable pavers, etc. for conventional asphalt-concrete, and Use multi-story construction for parking and buildings. Locate impervious surfaces upslope of permeable soils suited for ESD practices; Identify open space areas that can be converted to forest; Identify important resource areas that can be expanded (e.g. stream buffers); Use ESD Practices to minimize offsite pollution, erosion, and maintain groundwater recharge. 3 Here is my attempt to distill ESD down to basic principles. This list is a compilation of the guidance points presented in both MDE documents. How about if we take a few minutes to read through this list. If you see something unclear then we can discuss it now. But the rest of this portion of the workshop will be covering these principles in further detail. 3 ESD Practices Practice Category Number of Practices Alternative Surfaces 3 Nonstructural Practices 3 Micro-Scale Practices 9 4 Chapter 5, of the new Stormwater Design Manual, lists 15 ESD Practices. These practices are grouped into these three categories. 4 ESD Alternative Surfaces Reinforced Turf Permeable Pavements Green Roof 5 These are the three Alternative Surface practices. From a water quality perspective, a Green Roof is the least effective because it doesn’t provide groundwater recharge. However, a Green Roof does provide heating-cooling benefits. No other practice does this. ESD Practices can be combined in a train that negates the limitations of any single measure. So a Green Roof, which doesn’t provide recharge, can drain to a Dry Well which would release roof runoff into the soil. Permeable pavers and Reinforced Turf can be used for parking spaces, streets, sidewalks, patios etc., though I’d hate to have to cross either in high heels, not that I wear high heels. 5 ESD Nonstructural Practices 6 These three Nonstructural Practices are intended to serve very short sections of impervious surfaces which adjoin flat pervious areas such as grass or woods. The idea is that the relatively small volume of runoff from impervious surfaces will mostly soak into the adjoining pervious area where pollutants will be removed and recharge will occur. These are my least favorite practices. My bias comes from some studies showing the pollutants are mostly retained in surface soils and may be washed into nearby waters during severe, scouring runoff events. Also, runoff must always be in sheet flow and I’ve seen too many situations where accumulations of leaves, twigs, litter creates channel flow. The channel flow then discharges into a nearby waterway along with most of the pollutant load. 6 ESD Microscale Practices 7 I view these nine micro-scale practices as being the most effective. With the exception of Rainwater Harvesting, these practices force runoff to pass through a column of planting soil, which has a high-pollutant removal capacity. The pollutants are then stored well below the effects of surface runoff. Additionally, most provide excellent groundwater recharge which is critical to maintaining dry-weather inflow to wetlands, streams, and other aquatic systems. Finally, most micro-scale practices can be designed to manage the one-year storm thought to be key to preventing stream channel erosion. 7 ESD Concept Design Phase Site & Resource Mapping Site Fingerprinting & Development Layout Locate ESD Practices 8 Chapter 5 calls for this three step process when designing an ESD Concept Plan. And it’s the concept plan which most clean water advocates will see. This is because most volunteer and professional clean water advocates become aware of a proposed development project when notice is given of a Planning Board or Commission hearing. The ESD Concept Plan will usually be part of a subdivision or site plan. So understanding these three components of the Concept Plan preparation process is essential to determining if every reasonable opportunity has been utilized to fully protect aquatic resources with ESD. 8 Site & Resource Mapping Buffers: • • • Forest Stream Wetland Critical areas Existing drainage areas Forests Floodplains HighlyHighly-erodible soils on: • • Slopes >15% Slopes ≥25% Rivers Soils: • • Springs/seeps Streams: • • Clay ≥15% Permeable Intermittent Perennial Wetlands • • • Nontidal Special State Concern Tidal 9 At a minimum, the Concept Plan should show all of these features which occur on the site. The Limits of Disturbance and impervious areas should be laid out to avoid these features. On most development sites this leaves lots of room for buildings, streets, parking areas, and other structures. 9 Shoppes @ Apple Green Example 10 In the next series of slides we’ll show you how to verify that the Concept Plan accurately depicts key features. For this illustration I’ll use a commercial project proposed for a 40-acre site in northern Calvert County. This project is called the Shoppes @ Apple Green. I’ve been helping 161 families in the adjoining community with concerns about this project. While the families are not opposed to the Shoppes per se, they do have some very serious and legitimate questions about stormwater management and the flawed wastewater treatment system proposed for the project. 10 Site & Resource Mapping Shoppes Example http://websoilsurvey.nrcs.usda.gov/app/ 11 The US Department of Agriculture Web Soil Survey is one of the best resources for identifying sensitive features and other key characteristics. To start Web Soil Survey click the green button. . 11 12 After starting Web Soil Survey you can find a site using an address, coordinates, or other options. For the Shoppes I used the polygon Area Of Interest tool to outline the 40-acre site, which produced the soils map you see here. 12 Highly Erodible Soils – Slopes >25% None >25% >0.35 >15% 13 Here are the first pair of layers I selected for the Shoppes site using the Soil Data Explorer. On the left you see the soil erodibility layer for the site. The MDE documents use two definitions for highly-erodible soils. Both begin with an erosion factor greater then 0.35. The dark blue areas in the map on the left have an erodibility >0.35. In the Chesapeake and Coastal critical area a soil is highly-erodible if it has a K value greater then 0.35 and is on a slope steeper then 15%. Elsewhere in Maryland the slope must be greater then 25%. The Shoppes is not in the critical area so there’s no restriction on development, though it would be good to avoid the dark blue most erodible soils. 13 Highly Permeable Soils B A >6’ B B >6’ C B >6’ 14 A system known as Hydrologic Soil Groups is used to rate the permeability of soil. There are four soil categories: A, B, C, and D. The A soils are the most permeable, producing the least runoff. D soils are the opposite. A typical A soil would be very sandy with considerable depth to the water table. D soils may be very clayey or have a shallow depth to the water table or bedrock. Most ESD practices can be used on A or B soils, while C soil are marginal or D soils are very restricted. So impervious areas should be arranged so sufficient permeable A or B soil remains downslope to install ESD Practices. A shallow depth to the water table can also restrict the use of ESD Practices. But the map on the right shows this is not an issue on the Shoppes site. 14 High Clay Soils >15% 15 Clay is responsible for the muddy appearance or turbidity of water even when days have passed since the last rain. Clay particles are also the most damaging to aquatic ecosystems. The draft erosion and sediment control standards call for special attention when soils with a high clay content are within the proposed Limits Of Disturbance. Such a soil is composed of more then 15% clay, as opposed to silt, sand, or gravel. Once the draft standards become effective, an erosion and sediment plan must show how clay soils and runoff will be managed to prevent excessive turbidity. 15 Existing Drainage Areas MERLIN Maryland's Environmental Resources & Land Information Network http://www.mdmerlin.net 16 The Concept Plan usually shows the hills, valleys, and other site topography with contour lines. You should compare the topography shown on the plan with other references such as the USGS topo maps available on Web Soil Survey and the MERLIN site. Consider verifying topography in the field. Take the plan out to areas adjoining the site to see if the ridges, slopes, and valleys look the same. Drainage areas are separated by hilltops and ridgelines. On the right you see drainage areas delineated with dashed red lines. 16 Resource Map & Fingerprint Composite Site Resource Map Site Fingerprint Map 17 We could keep going but I suspect you get the idea of how to verify site resources. On the left is a composite map of all the resources identified thus far. On the right the Site Fingerprint map shows an area bounded by a yellow dashed line. This area is free of constraints while mostly being on or upslope of permeable soils suited for ESD Practices. 17 ESD Concept Design Phase Site & Resource Mapping Site Fingerprinting & Development Layout Locate ESD Practices 18 Now that the site fingerprint has been defined the plan designer can move on to locating buildings, parking areas, and other structures within the fingerprint so they drain to ESD Practices. 18 Locating Alternative Surface & Nonstructural Practices Alternative Surface Green Roof Permeable Pavement Reinforced Turf Nonstructural Practices Disconnect Rooftop Disconnect Non-Rooftop Sheetflow Conservation Hotspot Runoff Hydrologic Soil Group Slope All A, B, C A, B, C <30% OK ≤5% Not OK ≤5% Not OK A, B, C A, B, C ≤5% ≤5% ≤5% Not OK 19 This table lists some, though not all, of the criteria for locating two categories of ESD Practices within the fingerprint area: Alternative Surfaces and Nonstructural Practices. Of course HSG is Hydrologic Soil Group. Slope is measured in feet per 100 feet and is expressed as a percent. So an area which rises or falls 5 feet for every 100 feet of horizontal distance has a 5% slope. A hotspot is any land use likely to generate unusually toxic runoff, such as a gas station or vehicle repair shop. Practices designed to infiltrate runoff should not be used at hotspots because of the groundwater contamination potential. Again, there are additional location criteria. 19 Locating Micro-Scale Practices Rainwater Harvesting Submerged Gravel Wetland Landscape Infiltration Infiltration Berm Dry Well MicroMicro-Bioretention Rain Garden Swale Enhanced Filter Soil Slope All C-D A-B <2% 0% Avoid slough or landslidelandslide-prone ≤10% A-B All Avoid clay or compacted All DA (square feet) Large enough to maintain inflow ≤10,000 Small enough to prevent flow concentration ≤500 ≤30% ≤20,000 <5% ≤2,000 <5% ≤4% <one acre Hotspot Runoff No No OK if no other infiltration No No if designed to infiltrate No No 20 This table shows siting constraints for the nine micro-scale practices. Note that most have a very small drainage area. This means they must be located at or very near the edge of impervious surfaces. Furthermore, the impervious surfaces must be designed with a number of small drainage areas. This is actually easier then it sounds. So, a first step in reviewing a Concept Plan is to verify that all impervious surfaces drain to an ESD Practice. 20 Environmental Site Design Computations 21 Once you’ve verified that all impervious surfaces do drain to an ESD Practice then we get to the ESD computations. This box contains the criteria which ESD must meet. The box also provides the formulas for computing runoff depths or volumes that must be treated to meet the ESD criteria to the Maximum Extent Practicable. I know these computations may look a bit intimidating, but… 21 Chesapeake Stormwater Network http://www.chesapeakestormwater.net/ Tom Schueler 22 …fortunately, Tom Schueler of the Chesapeake Stormwater Network has produced these two tools which make the computations far easier. A bit later I’ll show you how to get to these two documents on the CSN website. 22 Unified Stormwater Sizing Criteria Water Quality Volume (WQV) • Recharge Volume (Rev) • 1-Year Storm (2.4(2.4- to 3.03.0-inches in 24 hours) Overbank Flood Protection Volume (Qp) • 0.070.07- to 0.380.38-inches of impervious surface runoff infiltrated Channel Protection Storage Volume (Cpv) • 0.90.9- to 1.01.0-inches of runoff from impervious surfaces 1010-Year Storm (4.3(4.3- to 5.65.6-inches in 24 hours) Extreme Flood Volume (Qf) • 100100-Year Storm (5.9(5.9- to 8.18.1-inches in 24 hours) 23 The 2000 Maryland Stormwater Design Manual contained these five criteria for sizing structural, end-ofpipe practices. ESD employs these same criteria, but in a different way. The first criteria, Water Quality, applies to all development projects. New development projects, but not redevelopment, must meet Recharge volume. Sites discharging to tidal waters or located on the Eastern Shore may be exempt from the other three requirements, but most other projects in Maryland must meet the Channel Protection criteria. Except for some interjurisdictional watersheds, local agencies may require Overbank or Extreme Flood control when flooding problems exist. 23 Minimum ESD Requirements MDE Design Manual Definition (5.2.3) Must Treat WQV & ReV With ESD Practices Water Quality Volume Frederick, Washington, Allegany & Garrett Counties: Impervious surface runoff from 0.9-inches of rain. Rest of Maryland: Impervious surface runoff from one inch of rain. Hydrologic Soil Group Recharge Volume (inches) A 0.38 B 0.26 C 0.13 D 0.07 24 ESD must be used on every site to the Maximum Extent Practicable. In the ESD chapter of the 2000 Stormwater Design Manual, MEP is defined as treating the Water Quality Volume and the Recharge Volume with ESD Practices. However, the goal should be to treat the Channel Protection Volume as well. But if this can’t be done then the plan designer gets to deduct the runoff treated with ESD from the Channel Protection requirement and, if required, the Overbank and Extreme Flood volumes. These deductions were not previously allowed, which created unnecessary problems. 24 Maximum Extent Practicable COMAR 26.17.02.06.A.2 The MEP standard is met when channel stability and 100 percent of the average annual predevelopment groundwater recharge are maintained, nonpoint source pollution is minimized, and structural stormwater management practices are used only if determined to be absolutely necessary. 25 This language appears in the Minimum Control Requirements section of the stormwater regulations. To me this regulation calls for substantially more then just treating the water quality and recharge volume with ESD practices. For example, it has been a point of debate whether the ReV actually maintains groundwater recharge at 100% of the predevelopment amount. As will be seen a bit later in this presentation, few Practices keep post-development pollution releases at pre-development levels, which to me is contrary to the definition of “minimized.” I suspect this text will be a source of considerable contention as more projects are reviewed under the ESD regulations. 25 ESD Sizing Criteria Same Runoff as Woods In Good Condition Hydrologic Soil Group Woods In Good Condition Runoff Curve Number Inches of Runoff From 2.7” Rainfall A 38 0.00” B 55 0.12” C 70 0.55” D 77 0.87” 26 The goal of ESD is to restore runoff equivalent to Woods In Good Condition. In other words, the criteria is intended to reduce the volume of runoff from a developed site to the volume which would have flowed from the same land when it was covered by healthy woodland. Of course prior to development most sites are not Woods in Good Condition. They are a mixture of cropland, pasture, forest and other land uses. This mix generates more runoff, more pollution, and allows less recharge then Woods in Good Condition. As a result the waters draining the site are already degraded by some accelerated erosion, pollution, and diminished dry-weather flow. In using ESD Practices to restore the runoff regime of Woods In Good Condition, the waters draining the development site will return to a healthier condition. 26 27 The ESD computations begin by requiring the plan designer to determine the Rainfall Target. This is accomplished with Table 5.3 of the ESD chapter. This excerpt from Table 5.3 is for Hydrologic Soil Group B. Let’s say we have a site that’s completely underlain by B soils and is proposed to become a parking lot, which is 100% impervious. The Rainfall Target would be determined by entering the table on the left at an imperviousness of 100%. Then move right until you hit the first green cell. Note the number at the top of the column of that first green cell, which becomes the Rainfall Target. 27 Rainfall Target PE = 2.6 inches 28 Again, begin at the proposed impervious area on the left and move right to the first green cell then go up to PE row. In the case of our 100% impervious, B-soil parking lot the Rainfall Target is 2.6 inches. Of course PE is the symbol for the Rainfall Target. 28 Example: ESD Practice to Treat 10,000 Square Feet of Roof Design Factors Hydrologic Soil Group AA-B ≤ 10,000 ft2 Drainage Area LI Surface Area ≥ 2% of DA LI Depth: HSG A ≤12’ 12’ B ≤5’ No hotspot runoff 29 Now for an example of how to run the ESD computations. For this example I’ll use one of my favorite ESD Practices – Landscape Infiltration. Here you see some of the more critical design factors. LI can be used on A or B soils. Each practice cannot drain more then 10,000 sq ft; a quarter-acre. The surface area of the LI must be equal to at least 2% of the drainage area. Assuming the depth to water table, bedrock, or poor soils permits, the LI can be 12 ft deep on A soils or 5 ft deep on B. Since LI’s infiltrate they cannot serve hotspot uses. Like all other micro-scale practices, an LI cannot receive more runoff then the Channel Protection volume; the one-year storm. 29 Landscape Infiltration (LI) Computations For 10,000 Square Feet of Roof Factor Symbol Value A 10,000 ft2 Minimum Surface Area Hydrologic Soil Group Imperviousness Water Quality Volume Recharge Volume Rainfall Target Recharge Factor Af HSG I WQV ReV PE Rv ESD Volume To Meet PE ESDv A * 0.02 = 200 ft2 B 100% 1.0 inches 0.26 inches 2.60 inches (Table 5.3) 0.05+0.009(I) = 0.95 PE*RV*A/12 = 2,058 ft3 Drainage Area 30 This table shows the factors used to compute the volume of ESD treatment provided by the Landscape Infiltration practice . The drainage area is 10,000 sq ft and 100% impervious. The LI must have a surface area of at least 200 sq ft. Since the soil is B then practice depth cannot exceed 5 ft. The Rainfall Target is 2.6 inches, Water Quality Volume is 1.0 inches, and the Recharge Volume is 0.26 inches. The Recharge Factor is computed using this equation then combined with the Rainfall Target and Drainage Area to get the volume required to meet the ESD requirement, which is 2,058 cubic feet. 30 Landscape Infiltration (LI) Computations For 10,000 Square Feet of Roof Factor LI surface area Symbol Value Af 800 ft2 Practice Ponding Depth 1 ft Practice Storage Depth 3.5 ft PE 2.60 inches ESD Treatment Required ESDV PE*RV*A/12 = 2,058 ft3 ESD Treatment Provided ESDV (Af*1’ *1’)+(Af*3.5’ *3.5’*0.4) = 1,920 ft3 PE 1,920 ft3 * 12/A = 2.30 inches Rainfall Target Rainfall Treated 31 In this table we compute the ESD volume provided by the Landscape Infiltration Practice. We start off with a surface area of 800 sq ft, which exceeds the 200 sq ft minimum. The surface ponding depth is 1 foot and the practice depth is 3½ feet, which is less then the 5 foot maximum. From the previous table we know we need an ESD volume of 2,058 cubic feet to meet the Rainfall Target, but the next to last line of this table shows we only have 1,920 cubic feet of ESD volume. However, the last line shows that the Rainfall Treated exceeds the Recharge depth of 0.26 inches and the Water Quality depth of one inch. So two of the three applicable ESD requirements has been met. 31 Meeting Rainfall Target (PE) Increase Landscape Infiltration Size To Meet The Rainfall Target ESDV Rainfall Target = 2,058 ft3 Increase surface area (Af) from 800 ft2 to 870 ft2 Practice Ponding Depth = 1 ft (same) Practice Storage Depth = 3.5 ft (same) ESDV=(Af*1’ *1’)+(Af*3.5’ *3.5’*0.4)=2,088 ft3 ESDV Exceeds Rainfall Target 32 Since the first design didn’t meet the Rainfall Target we try making the practice bigger. In this example the surface area is increased from 800 square feet to 870. The ponding and storage depth remains the same. By making the surface area a bit larger we increase ESD volume to 2,088 cubic feet which exceeds the amount required to meet the Rainfall Target. We also could have tried increasing storage depth, reducing impervious area, using a Green Roof, and other options to meet the target. The volume provided in the practice can be deducted from Overbank or Extreme Flood volumes if either is required. 32 ESD Computations Mostly Same For Other Micro-Scale Practices 33 The ESD computations just illustrated for Landscape Infiltration are much the same for the other eight micro-scale practices. 33 Alternative Surfaces & ESD Computations Reinforced Turf Permeable Pavements 34 Now we’ll take a look at the ESD computations for Alternative Surfaces. Again there are three Alternative Surface Practices: Green Roofs, Permeable Pavement, and Reinforced Turf. 34 Runoff Curve Number (RCN) http://www.wsi.nrcs.usda.gov/products/W2Q/H&H/docs/other/TR55_documentation.pdf 35 The Alternative Surface ESD computations are based on Runoff Curve Numbers or RCNs. The document on the left – TR55 – is the best reference for RCNs. RCNs range from 30 to 98. The higher the RCN the greater the runoff depth for a given rainfall amount. As the table on the right shows, RCNs are a product of hydrologic soil groups and land use. For a given land use A soils have a lower RCN and, therefore, will produce less runoff during a specific rainfall depth when compared to the same use on a B, C or D soil. 35 36 The RCN for Woods in Good Condition on an A soil is 38 to 40 and that for impervious surfaces is 98. This table, which is also from TR55, shows that the Good Woods does not produce runoff until 3.5 inches of rain have fallen in a 24-hour period. For the impervious surface, with an RCN of 98, the same 3.5-inches of rainfall produces 3.27 inches of runoff. In other words, 93% of the rain falling on the impervious surface becomes runoff. 36 Alternative Surfaces Effective RCN Reinforced Turf RCN Surfacing Material A B Grass (open space) 39 61 C 74 D 80 37 For Alternative Surfaces the MDE manual provides Effective RCNs which reflect the reduced volume of runoff from these surfaces. For example a conventional roof has an RCN of 98 while an eight-inch thick green roof has an RCN of 77. Hydrologic soil groups don’t come into play because the permeable portion of a green roof overlays impermeable layers to prevent leakage into the underlying building. Of course hydrologic soil groups are factors for permeable pavement and reinforced turf. 37 Alternative Surface ESD Computation Woods RCN (HSG=B) 55 Conventional Roof RCN 98 Green Roof (8”) Effective RCN 77 Rainfall Target (PE) 2.60 inches Green Roof Runoff Depth 0.80 inches Runoff Treated By Green Roof 1.80 inches Use DryDry-Wells To Treat Recharge requirement (0.26 inches). 38 Here we see how the Effective RCNs are used to compute the remaining Rainfall Target (PE). From previous slides we used a PE of 2.6 inches. With an Effective RCN of 77 the Green Roof produces 0.80 inches of runoff from the Target Rainfall of 2.6 inches. Since 1.80 was treated with the Green Roof the Water Quality requirement has been met. Another ESD Practice, like a Dry Well, could be installed at each downspout to treat 0.26 inches of roof runoff to meet the Recharge requirement. Other ESD practices could be used to treat the balance of the Rainfall Target. 38 Nonstructural ESD Computation 39 Now for the last of the three ESD groups – Nonstructural Practices. 39 Nonstructural PE 40 For Nonstructural Practices credit is given towards the Rainfall Target. The credit depends upon the length of grass, woods, or other permeable surfaces runoff from impervious surfaces must flow over to reach an outlet. Hydrologic soil groups do not come into play, except to determine if an area is suitable for Nonstructural Practices. 40 Nonstructural ESD Computation PE from Table 5.3 (HSG=B) 2.60 inches Western Shore 4545-foot flow path PE value 0.60 inches Remaining PE To Be Treated Elsewhere 2.00 inches 41 Let’s assume we provided a 45 foot flow path length for roof runoff and the project is on the Western Shore. The Rainfall Target or PE credit for this practice is 0.60 inches. The bottom table shows how the Nonstructural Practice credit is counted towards the Rainfall Target for the impervious area draining to the disconnect. The designer would need to explore the possibility of using ESD practices elsewhere on the site to meet the Maximum Extent Practicable requirement. 41 ESD Project Computations 42 This table shows how the treatment provided in ESD practices throughout a site are combined to determine if the Rainfall Target was met for the site as a whole. According to this table, ESD practices provided treatment volume in excess of the Rainfall Target for all of the drainage areas. So the site as a whole complies with the Environmental Site Design to the Maximum Extent Practicable requirement. 42 Chesapeake Stormwater Network http://www.chesapeakestormwater.net/ 43 Again, these two Chesapeake Stormwater Network resources will make it much easier to determine if a Concept Plan meets ESD requirements. 43 Chesapeake Stormwater Network http://www.chesapeakestormwater.net/ 44 When you go to this web address, the page on the left will appear. To download the two resources click Read More at the end of this first paragraph, which is headed “June 2010 - New and Improved ESD to MEP spreadsheet released for MD designers.” 44 http://mawaterquality.org/capacity_building/ESDToolsWebcast.htm http://mawaterquality.org/capacity_building/ESDToolsWebcast.htm 45 In May, the Chesapeake Stormwater Network did an introductory webcast on Environmental Site Design. This webcast can be viewed at the address given at the bottom of this slide. Taking a look at this webcast would provide another perspective on how Environmental Site Design works. 45 Download ESD Chapter 5 http://www.mde.state.md.us/Programs/WaterPrograms/SedimentandStormwater/stormwater_design/index.asp 46 Additionally, download ESD Chapter 5 from the 2000 Maryland Stormwater Design Manual. There are three ESD design examples in Chapter 5. Spending an hour or so running these design examples through the CSN spreadsheet will make you an ESD expert – Well, at least more comfortable with the computations. 46 Redevelopment Definition Existing Site Impervious Area (IA) Greater Than 40% Example 100 acre site ÷ 41 acres of existing impervious area = 41% IA = Treat As Redevelopment 47 Now on to Redevelopment. The year 2000 MDE Stormwater Design Manual treated redevelopment projects differently then green field or new development. The 2007 Act continued this tradition, though the aquatic resource protection requirements for redevelopment were strengthened. Here we have the definition of redevelopment and an example. A redevelopment project is one where more than 40% of a site is covered by existing impervious surfaces. 47 Redevelopment The Best Hope for Restoring Urban-Suburban Waters 48 Our most degraded waters are located in urban and older suburban areas. These are the very areas where recreational opportunities are most sorely needed. What a tragedy it is that the waters located closest to most Maryland homes is unfit for our use. Redevelopment offers what may be our best hope for restoring these waters. As each urban-suburban home and building is redeveloped the new ESD regulations will require installing water quality protection measures. Over time this will result in gradual improvements. How much time? Well Philadelphia uses an approach similar to ESD and officials there think up to 59% of the existing impervious area might be retrofitted by 2035. 48 Limits Of Disturbance (LOD) 49 While the entire site is used to determine if the 40% existing impervious area threshold is crossed, the actual requirements only apply to the Limits Of Disturbance. Of course the LOD is the outer boundary of the portion of a site where earth-moving, demolition, vegetation removal, and other disturbances will occur. The “redevelopment” plan on the left shows no LOD, which should be cause for denying approval. The Shoppes plan on the right shows the LOD. If the site were more then 40% impervious, which it isn’t, then any existing impervious areas within the LOD would need to meet the following redevelopment requirements. 49 Redevelopment Requirements Reduce existing impervious area within the Limits Of Disturbance (LOD) by at least 50%; or Implement ESD practices to the Maximum Extent Practicable (MEP) to provide water quality treatment for at least 50% of existing impervious area within the LOD; or Use a combination of impervious area reduction and ESD implementation for at least 50% of existing impervious areas. And… 50 This slide shows the three preferred Environmental Site Design options for meeting the new redevelopment requirements. Redevelopment projects must only meet the Water Quality volume requirement; not the recharge, channel protection, overbank, or extreme flood requirements. Though the local approving authorities have the option of requiring any of these four. If there’s a net increase in impervious area then this area must be treated with ESD. The ESD practices must meet the water quality, recharge, and channel protection volume to the MEP. 50 …if you can’t do that, then… Use on-site structural BMP; or An off-site structural BMP to provide water quality treatment for an area equal to or greater than 50% of existing impervious areas; or A combination of impervious area reduction, ESD implementation, and on-site or off-site structural BMP for an area equal to or greater than 50% of existing impervious area within the LOD. And… 51 But if an applicant finds the three preferred ESD options too difficult then MDE included these structural end-of-pipe alternatives. The applicant can also go offsite if the requirements can’t be meet within the bounds of the redevelopment project. 51 …if you can’t even do that then… Use a combination of ESD and an on-site or off-site structural BMP; Retrofitting including existing BMP upgrades, filtering practices, and off-site ESD implementation; Participate in a stream restoration project; Pollution trading with another entity; Design criteria based on watershed management plans developed according to §E of this regulation; Pay a fee-in-lieu; or Request a partial waiver of the treatment requirements if ESD is not practicable. 52 And if you can’t meet the alternative requirements onsite or offsite then MDE made the following final provisions available. As you can see, those designing redevelopment have considerable latitude in how ESD requirements will be met. There’s been considerable hue and cry about the onerous nature of the redevelopment requirements. Frankly, I don’t get this consternation. 52 Old & New Redevelopment Requirement Comparison Existing Impervious Area That Must Be Treated Old New 20% 50% 690 1,724 WQV Treated (cubic feet/acre): Redevelopment New Development 3,449 53 This slide contrasts redevelopment requirements with those for new development. Though more runoff must be treated with the 2007 requirements, its still half of that required for developing a cropfield, forest or other vacant property. 53 http://www.cwp.org/CBSTP/index.html 54 For further detail on redevelopment please view this recent PowerPoint presentation from the Chesapeake Stormwater Network and the Center for Watershed Protection. We understand it will be posted soon at the web address you see at the bottom of the screen. 54 Costs of Clean Water Cost/Impervious Acre Urban Redevelopment ESD $191,000 Urban Green Street Retrofit $167,100 Stream Channel Restoration $35,600 Rainwater Harvesting $32,500 New Development with ESD $46,500 New Development pre-ESD $31,700 55 Here are some cost figures provided in the preceding redevelopment webcast. As you can see the costs can be quite significant. However, the value of the benefits are far greater. Consider the following. A home located near visibly polluted water sells for 20% less than comparable homes. A 2008 Kansas State University study documented that nationwide excessive nutrient inputs alone cost $4.3 billion annually due to lost recreation opportunities, increased water treatment, and other factors. 55 Aquatic Resources Protection Effectiveness of ESD vs. Structural Practice 56 Before bringing this portion of the workshop to a close I have few slides showing which practices are the most effective in protecting aquatic resources. 56 Unified Stormwater Sizing Criteria Water Quality Volume (WQV) • Recharge Volume (Rev) • 1-Year Storm (2.4(2.4- to 3.03.0-inches in 24 hours) Overbank Flood Protection Volume (Qp) • 0.070.07- to 0.380.38-inches of impervious surface runoff infiltrated Channel Protection Storage Volume (Cpv) • 0.90.9- to 1.01.0-inches of runoff from impervious surfaces 1010-Year Storm (4.3(4.3- to 5.65.6-inches in 24 hours) Extreme Flood Volume (Qf) • 100100-Year Storm (5.9(5.9- to 8.18.1-inches in 24 hours) 57 As you’ll recall the 2000 Maryland Stormwater Design Manual contained these five criteria for sizing structural, end-of-pipe practices. These same criteria apply to ESD, though they are computed differently. 57 ESD Practices & Sizing Criteria All practices can meet Water Quality Volume; Most practices can meet Recharge Volume, though the Green Roof cannot; Some micro-scale practices can meet Channel Protection Volume; and Runoff treated in all ESD practices cannot exceed Cpv, but can be deducted from Overbank and Extreme Flood volumes. 58 Here you see which of the 2000 criteria can be met with ESD Practices. Most ESD practices can meet the Water Quality Volume and Recharge criteria. Some can even meet the Channel Protection volume. The storage provided in all ESD practices can be deducted from the Channel Protection, Overbank, and Extreme Flood requirements. 58 Pollutant Removal (%) Total Suspended Solids Nitrogen Dry Pond 49 24 20 29 88 Wet Pond 80 31 52 57 70 Wetland Pond 72 24 48 47 78 Filtering Practice 86 32 59 37 37 Bioretention 59 46 65 81 N/A Infiltration 89 42 65 86 N/A Open Channel 81 56 24 65 -25 Phosphoru Copper Bacteria s National Pollutant Removal Performance Database Version 3, September, 2007, Center for Watershed Protection, 8390 Main Street, Ellicott City, MD 21043. 410.461.8323 http://www.cwp.org/Resource_Library/Center_Docs/SW/bmpwriteup_092007_v3.pdf 59 In this table the pollutant removal capability of structural and ESD practices is shown. The three ponds are exclusively end-of-pipe structural practices while the other four can be. However, a number of the ESD Practices are smaller versions of filtering, bioretention, infiltration, and open channel practices. Filtering, bioretention, and infiltration generally have the highest pollutant removal rates. These practices also move pollutants well below the path of high-volume runoff events which would scour contaminants from surface soils. Finally, these three practices are usually designed to provide groundwater recharge. Therefore, filtering, bioretention, and infiltration are generally the most effective in protecting aquatic resources. 59 High Quality (Tier II) Waters http://www.mde.maryland.gov/ResearchCenter/Data/waterQualityStandards/Antidegradation/index.asp http://www.mde.maryland.gov/ResearchCenter/Data/waterQualityStandards/Antidegradation/index.asp 60 MDE has identified high quality waters throughout the state. As the name implies, these waters are of exceptional quality and tend to support species which are unusually sensitive to watershed development impacts. If you are reviewing a project located in the watershed of one of these aquatic resources then please contact CEDS for advice on the need for additional safeguards beyond what is normally required under ESD. 60 Maryland Environmental Resources & Land Information Network http://www.mdmerlin.net/atlaslaunch.html 61 The Maryland Environmental Resources & Land Information Network website, also known as MERLIN, can provide a wealth of information about a site. I urge you to use this resource to see if two uniquely sensitive features may be affected by each project you review. The first feature is a Wetland of Special State Concern. There are 405 WSSC’s in Maryland and most support an aquatic threatened or endangered species. WSSC’s are indicated with yellow on the MERLIN maps. In this screenshot there are four streams designated WSSCs. The other feature is a Sensitive Species Project Review Area. As the name implies SSPRAs are established to alert project reviewers that there’s a uniquely sensitive resource within the area. If one of your projects may affect a WSSC or SSPRA then please contact CEDS for advice on how to determine if more is needed then just full ESD implementation. 61 Total Maximum Daily Loads http://www.mde.state.md.us/Programs/WaterPrograms/TMDL/Sumittals/index.asp http://www.mde.state.md.us/Programs/WaterPrograms/TMDL/Sumittals/index.asp 62 You should also check this MDE webpage to see if a project is within the drainage area of a waterway with a Total Maximum Daily Load aka TMDL. If it is then the waterway is receiving excessive inputs of one or more pollutants. Most of the TMDL pollutants can be released from land uses regulated by the ESD requirements. If this is the case then take a look at opportunities to employ ESD practices which are particularly effective at removing the TMDL pollutant. 62 ESD Compliance Checklist We’d like to add your checklist to the CEDS-ESD Compliance Database. So please forward a copy of your completed checklist to: CEDS-ESD 811 Crystal Palace Court Owings Mills, MD 21117 or Fax: 410-654-3028 or [email protected] 63 This checklist was prepared by CEDS for this workshop. The checklist serves as a general guide for what to look for as you review an ESD concept plan and the supporting computations. If you use the checklist could you forward a copy to CEDS. We hope to compile a database of checklist entries for use in assessing how well ESD is being implemented in each watershed, county, municipality, and statewide. All information we receive will be kept confidential. We’ll also provide you with periodic summaries. In the next three slides I’ll give a few examples of checklist items to note while reviewing these documents. 63 Sample ESD Plan 64 So here’s the first of three sample ESD plans. Here we have a small commercial development site. All of the parking area, driveway, sidewalks, patio, and a portion of the roof drains to ESD Practices. The ESD practices are : Landscape Infiltration, Dry Wells, and permeable pavers. However, only the red area on the roof drains to ESD Practices. The rest of the roof will drain to offsite structural practices. The untreated roof area amounts to 30% of overall site imperviousness. In this case we would ask why the roof area is not being treated with ESD. If the designer ran out of suitable soils or space then we would ask what efforts were made to reduce impervious area, use a Green Roof, or other ESD options. 64 Easton Airport Redevelopment Plan 65 Here we have a redevelopment ESD plan. The orangetan is the existing 116 acres of impervious area, a tenth of which will be removed. The pink-red is 31-acres of new impervious area. The blue rectangles are proposed micro-bioretention areas, which of course is an ESD micro-scale practice. The green areas are existing dry ponds which will be converted to extendeddetention to meet Overbank requirements. Channel protection is not required since this site is on the Eastern Shore. From this plan it appears that more then the required 50% of existing impervious area is being treated with ESD practices as well as all of the new impervious area. However, the LOD hasn’t been defined so its hard to tell. 65 Shoppes @ Apple Green 66 Here we have the Shoppes @ Apple Green stormwater plan. Of course we used the Shoppes to illustrate Site & Resource Mapping. In fact you see the final site fingerprint map on the right bounded by the yellow line. The plan on the left shows the current stormwater proposal for the 40 acre site. The 25-acres of proposed impervious area will all drain to the single, end-of-pipe structure – a micropool pond. The headwaters of the northern stream will be buried beneath the shopping center along with the buffer. There will not be any recharge for the northern stream. Of course this is a far cry from a plan consistent with ESD. By the way, Calvert County issued a waiver of ESD requirements for this site in May. 66 Apple Greene Existing 1970s Regional Pond 67 But it could be worse. How you say? Well this was the approved stormwater scenario for the Shoppes as of 2008. Calvert County had approved a site plan allowing the applicant to utilize a dilapidated 1970s regional pond as the sole stormwater management. There’s 2,000 feet of stream channel between the regional pond and the Shoppes site. Yes, nearly a halfmile of stream would have been exposed to the full pollutional and channel eroding effects of 25-acres of impervious surface runoff. But this approach has been abandoned in favor of the onsite, end-of-pipe structure. A step in the right direction but not enough to protect the rights of downstream property owners. 67 For A No-Cost Initial Review For Additional ESD Opportunities Forward Project Plans To… Richard Klein Community & Environmental Defense Services 811 Crystal Palace Court, Owings Mills, MD 21117 ceds.org ~ [email protected] 410410-654654-3021 ~ 11-800800-773773-4571 68 If you wish, we would be delighted to take an initial look at a concept plan for additional opportunities to enhance aquatic resource protection through ESD. There’s no charge for this quick look for clean water advocates. Just drop the plans in the mail to the address you see here along with a note telling us who you are, how to get in touch with you, and describe any specific questions you have. This brings this presentation to a close. Any questions? 68
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