Attachment 3. ERG TechMemo Solar Stormwater SERC Site.pdf

Environmental Research Group, L.L.C. | 6049 Falls Road | Baltimore, MD 21209 Phone 410.366.5170 | Facsimile 410.366.5176

TECHNICAL MEMORANDUM

Stormwater Best Management Practices and Post-Construction Considerations To: Jacob Bradd, Smithsonian Institute (SI)

Anthony Richards, SI Kris Kinaitis, SI Anthony (Sal) Saladrigas, SI

Copy: Kay Toye, Environmental Research Group (ERG) Jim Pritchard, ERG

From: Amy A. Cervantes, ERG Date: 20 June 2025

A meeting was held on April 29, 2025 to discuss applicable stormwater requirements associated with the addition of a solar array at The Smithsonian Environmental Research Center (SERC) near Edgewater in Anne Arundel County, Maryland.

Details provided during the meeting include the location of the new solar array. No specifications have been developed, and the array is planned to be in an existing forested area near the Woodlawn House. It is not anticipated that the entire area will become impervious; only the solar panel design and base will increase impervious areas and runoff coefficients. The SI staff is looking at different locations and design alternatives and any potential stormwater related issues those alternatives may cause. The SI staff understands there will be stormwater construction of best management practices (BMPs) and associated requirements but is also assessing the post-construction requirements and their potential impacts to long-term project costs, and compliance obligations.

Summary of Findings

• The four sites identified by SERC staff were evaluated based on slope and soil composition in comparison to Maryland Department of the Environment (MDE) recommendations for BMPs for solar arrays.

• All three sites have slopes over 10% and therefore additional structural terraces or berms will be required to maintain appropriate stormwater flow conditions.

• Post-construction requirements were enumerated depending on the selected location;

however, the designer should specify the schedule and maintenance requirements for each BMP and structure.

Discussion

In addition to requirements described in the Maryland Stormwater Design Manual, Volumes I and II (MDE, October 2000, Revised May 2009), MDE developed the Stormwater Design Guidance

– Solar Panel Installations and Technical Memorandum #8-Solar Panels. The supplement includes guidance for various conditions to limit the impacts of erosion for solar panel installation. Non-rooftop disconnection to treat runoff should incorporate factors such as slope, vegetated surfaces, soil types, and proposed groundcover. Additionally, Technical Memorandum #8 specifies the need to protect the surface below the drip line of the solar panels, where concentrated flow has the potential to cause erosion. It is recommended to have a level surface ‘splash pad’ of gravel embedded to minimize erosion.

The guidance for non-rooftop disconnection, as described in Maryland Stormwater Design Manual, Volumes I and II, Chapter 5.N-1, is applicable for hydraulic soil groups (HSG) A, B, or C.

Preliminary slope and soil type were identified for the four proposed locations of the new solar array at SERC (Table 1), based on data from the United States Department of Agriculture Natural Resources Conservation Service, Web Soil Survey.

Table 1: Pre-Development Soil Conditions

Soil Name Map Unit Name Slope (%) HSG Rating Acres Sites #1 & #2

CRD Collington and Annapolis soils 10-15 B 1.1 MaB Marr-Dodon complex 2-5 B 4.4 MaC Marr-Dodon complex 5-10 C 4.8 MaD Marr-Dodon complex 10-15 C 5.4 Site #3 MaB Marr-Dodon complex 2-5 B 4.4 MaC Marr-Dodon complex 5-10 C 4.8 MaD Marr-Dodon complex 10-15 C 5.4 MDE Marr and Dodon soils 15-25 C 0.00 Site #4 CMA Colemantown silt loam 0-2 C/D* 0.1 CRD Collington and Annapolis soils 10-15 B 0.8 DnB Donlonton fine sandy loam 2-5 D 3.3 MaC Marr-Dodon complex 5-10 C 2.9 MaD Marr-Dodon complex 10-15 C 6.1 MDE Marr and Dodon soils 15-25 C 0.1

*If a soil is assigned to a dual hydrologic group (A/D, B/D, or C/D), the first letter is for drained areas and the second is for undrained areas. Only the soils that in their natural condition are in group D are assigned to dual classes.

Considerations and Recommendations

Design and Site Selection:

Mitigation factors to aid in managing the stormwater that enters streams near a given solar facility include designing grading and associated stormwater controls to minimize hydrological changes to streams and wetlands, and designing controls to maintain the existing flow regime to streams and wetlands.

From the data presented above, all four sites currently under consideration for the new solar array at SERC have the appropriate HSG to implement the recommended stormwater design guidance for solar panel installations from MDE. Nonstructural methods promoting disconnection of impervious cover will reduce runoff by promoting overland filtering and infiltration.

Recommendations for areas below 5% slopes require no structural BMPs; however, the design should include a disconnection flow path that is greater than or equal to the width of the solar panel, as shown below in Figure 1. The disconnection flow path is the spacing between the solar panels in the downgradient direction.

For areas with slopes between 5-10%, other BMPs, such as level spreaders that reduce concentrated flow and improve infiltration, will need to be utilized to help redirect the runoff, as shown below in Figure 2.

For Sites #1 and #2, the slopes indicated above 10% are 6.5 acres of 15.7 total acres (41%). For Site #3, the slopes indicated above 10% are 4.8 acres of 14.6 total acres (33%). For Site #4, the slopes indicated above 10% are 7 acres of 13.3 total acres (52%). For those areas with slopes above 10%, MDE recommends that a series of terraces or berms may be required to maintain sheetflow. These terraces may be readily constructed of landscaping stones, timber, or earthen berms. All sites will require additional structural terraces or berms to maintain sheetflow to some extent; however, Site #3 has the smallest area with slopes between 5-10%, and would therefore have the least additional BMP requirements.

The selected design must state the maintenance to be completed and the period for completion.

This maintenance schedule should be included in the MDE approved stormwater management plan.

Before construction, applicable permits and designs must be approved by MDE and Anne Arundel County. These permits would include but are not limited to a National Pollution Discharge Elimination System (NPDES) permit with appropriate Stormwater Pollution Prevention Plan (SWPPP) and Erosion and Sediment Control Plan (ESC).

Construction:

During construction standard stormwater and erosion control measures must be taken including but not limited to the requirements per NPDES approved permit to implement site specific SWPPP and ESC measures. Additional compaction should be minimized during construction and re-loosening or aerating compacted areas should be completed prior to planting cover vegetation and final grade.

Post-Construction Management:

By the Maryland Stormwater Management and Erosion and Sediment Control Guidelines for State and Federal Projects guidance, the owner of the property shall maintain in good condition and promptly repair and restore stormwater management BMPs, vegetation, erosion/sediment control measures, and other protective devices. Such repairs or restoration, and maintenance shall be completed in accordance with MDE-approved plans. The design MDE approved maintenance schedule should be documented and followed post-construction.

All installed BMPs must meet plan requirements and as-builts must be maintained by SI. For areas meeting the minimum design requirements for slopes 5% and under, ongoing maintenance of areas receiving disconnected runoff is no different than that required for other lawn or landscaped areas. The areas receiving runoff should be protected from future compaction (e.g., by planting trees or shrubs along the perimeter).

For instances of slopes between 5-10%, level spreaders or energy dissipaters, once installed, have minimal maintenance requirements. MDE Technical Memorandum #9, Maintenance Schedules, details minimum requirements for maintenance schedules for standard BMPs. However, depending on the design selected and maintenance schedule specified, inspections should assess BMP sedimentation, if flow is concentrated, adequate access to the level spreader, and evidence of erosion. Annual inspections could be recommended to trigger maintenance operations such as sediment removal, spot revegetation, and level spreader repair. Ideally, inspections should be conducted in the non-growing season when it is easier to see the flow path and could be completed by on-site staff.

Similarly, any established terraces and berms should be inspected as required by MDE approved plans as well as the designer and may be completed annually to ensure they are functioning as design and erosion is limited.

Attachments

Attachment A - Stormwater Design Guidance – Solar Panel Installations, 2013, MDE Attachment B – Technical Memorandum #8: Solar Panels, 2018, MDE- Sediment and Stormwater Plan Review Division, Water and Science Administration Attachment C – Chapter 5 N-1 (Page 5.57 to 5.65), Maryland Stormwater Design Manual, Volumes I and II, (October 2000, Revised May 2009), MDE Attachment D – Web Soil Survey, 2025, USDA-Natural Resources Conservation Service Attachment E – Maryland Stormwater Management and Erosion and Sediment Control Guidelines for State and Federal Projects, 2015, MDE- Sediment and Stormwater Plan Review Division, Water and Science Administration Attachment F – Technical Memorandum #9: Maintenance Schedules, 2018, MDE- Sediment and Stormwater Plan Review Division, Water and Science Administration

Attachment A – Stormwater Design Guidance – Solar Panel Installations

Maryland Department of the Environment

Stormwater Design Guidance – Solar Panel Installations Revisions to Maryland’s stormwater management regulations in 2010 require that environmental site design (ESD) be used to the maximum extent practicable (MEP) to mimic natural hydrology, reduce runoff to reflect forested wooded conditions, and minimize the impact of land development on water resources. This applies to any residential, commercial, industrial, or institutional development where more than 5,000 square feet of land area is disturbed. Consequently, stormwater management must be addressed even when permeable features like solar panel installations exceed 5,000 square feet of land disturbance.

Depending on local soil conditions and proposed imperviousness, the amount of rainfall that stormwater requirements are based on varies from 1.0 to 2.6 inches. However, addressing stormwater management does not mean that structural or micro-scale practices must be constructed to capture and treat large volumes of runoff. Using nonstructural techniques like disconnecting impervious cover reduces runoff by promoting overland filtering and infiltration. Commonly used with smaller or narrower impervious areas like driveways or open roads, the Disconnection of Non-Rooftop Runoff technique (see pp. 5.61 to 5.65 of the 2000 Maryland Stormwater Design Manual1) is a low cost alternative for treating runoff in situations like rows of solar panels.

When non-rooftop disconnection is used to treat runoff, the following factors should be considered:

• The vegetated area receiving runoff must be equal to or greater in length than the disconnected surface (e.g., width of the row of solar panels)

• Runoff must sheet flow onto and across vegetated areas to maintain the disconnection

• Disconnections should be located on gradual slopes (≤ 5%) to maintain sheetflow. Level spreaders, terraces, or berms may be used to maintain sheetflow conditions if the average slope is steeper than 5%. However, installations on slopes greater than 10% will require an engineered plan that ensures adequate treatment and the safe and non-erosive conveyance of runoff to the property line or downstream stormwater management practice.

• Disconnecting impervious surfaces works best in undisturbed soils. To minimize disturbance and compaction, construction vehicles and equipment should avoid areas used for disconnection during installation of the solar panels.

• Groundcover vegetation must be maintained in good condition in those areas receiving disconnected runoff. Typically this maintenance is no different than other lawn or landscaped areas. However, areas receiving runoff should be protected (e.g., planting shrubs or trees along the perimeter) from future compaction.

Depending on the layout and number of panels installed, the disconnection of non-rooftop runoff technique may address some or all of the stormwater management requirements for an individual project. Where the imperviousness is high or there is other infrastructure (e.g., access roads, transformers), additional runoff may need to be treated. In these situations, other ESD techniques or micro-scale practices may be needed to provide stormwater management for these features.

Example 1 – Using Non-Rooftop Disconnection Where the Average Slope ≤ 5%

Several rows of solar panels will be installed in an existing meadow. The soils within the meadow are hydrologic soil group (HSG) B and the average slope does not exceed 5%. Each row of panels is 10 feet wide and the distance between rows is 20 feet. The rows of solar panels will be installed according to Figure 1 below. In this scenario, the disconnection length is the same as the distance between rows (20 feet) and is greater than the width of each row (10 feet). Therefore, each row of panels is adequately disconnected and the runoff from 1.0 inch of rainfall is treated.

Figure 1. Typical Installation - Slope ≤ 5%

Example 2 – Using Non-Rooftop Disconnection Where the Average Slope ≥ 5% but ≤ 10%

Several rows of solar panels will be installed in an existing meadow. The soils within the meadow are hydrologic soil group (HSG) B and the average slope is greater than 5% but less than 10%. Each row of panels is 10 feet wide and the distance between rows is 20 feet. The rows of solar panels will be installed as shown in Figure 2 below. The disconnection length is the same as the distance between rows (20 feet) and is greater than the width of each row (10 feet). However, in this example, a level spreader (typically 1 to 2-foot wide and 1 foot deep) has been located at the drip edge of each row of panels to dissipate energy and maintain sheetflow.

Discussion

To meet State and local stormwater management requirements, ESD must be used to the MEP to reduce runoff to reflect forested conditions. While all reasonable options for implementing ESD must be investigated, minimally, the runoff from 1 inch of rainfall must be treated. In each of the examples above, there may be additional opportunities to implement ESD techniques or practices and reduce runoff that should be explored. However, simply disconnecting the runoff from the solar panel arrays captures and treats the runoff from 1.0 inch of rainfall. Where imperviousness is low and soil conditions less optimal (e.g., HSG C or D), this may be sufficient to completely address stormwater management requirements. In more dense applications or in sandy soils, additional stormwater management may be required.

Conclusion

The primary purpose of Maryland’s stormwater management program is to mimic natural hydrologic runoff characteristics and minimize the impact of land development on water resources. Any land development project that exceeds 5,000 square feet of disturbance, including solar panel projects, must address stormwater management. However, for solar panels, stormwater management may be provided in a cost-effective manner by disconnecting each row of panels and directing runoff over the vegetated areas between the individual rows.

Resources

1 2000 Maryland Stormwater Design Manual, Volumes I and II, MDE, October 2000 (http://www.mde.state.md.us/programs/Water/StormwaterManagementProgram/MarylandStormwaterDesignMa nual/Pages/Programs/WaterPrograms/SedimentandStormwater/stormwater_design/index.aspx)

Figure 2. Typical Installation – Slope ≥ 5% but ≤ 10%

Attachment B – Technical Memorandum #8: Solar Panels

TECHNICAL MEMORANDUM #8

TO: Applicants and Designers for State and Federal Projects

FROM: Sediment and Stormwater Plan Review Division Water and Science Administration

DATE: March 30, 2018

SUBJECT: Solar Panels

On May 22, 2012 Maryland passed House Bill 1117 establishing that the impervious surface for solar panels includes only the foundation or base supporting the solar panel.

The best way to handle solar array projects is to think about them in much the same way as any other project. MDE requires that Environmental Site Design (ESD) be provided for the impervious area requiring treatment (IART) and the target rainfall (PE). For a solar array project this would be the base/posts for the panels as well as any other impervious areas within the LOD such as access roads, pads, sheds, etc. If the treatment cannot be provided at the source, compensatory water quality management for the IART could potentially be provided elsewhere in the watershed. As for the water quantity component of ESD, the impervious area may be small enough that management of the channel protection volume would not be required. This assessment will have to be made on a case-by-case basis.

Other considerations include the impact the changes will have on the hydrology/drainage pattern as well as erosion and sediment control. The Stormwater Design Guidance for Solar Panel Installations (January 2013) on MDE's website addresses this. When water falls off the solar panels it hits the ground below. That surface below the drip line is going to be hit by concentrated flow and susceptible to erosion. The surface needs to be protected with some sort of "splash pad". Gravel would work as would soil stabilization matting. More important than having a level surface is maintaining sheet flow across the contours (i.e. down the slope). This would be achieved most effectively if the splash pad were embedded so that it is flush with the ground surface. Because matting is thin and the grass grows through it, it may be the better surface. Matting comes in permanent and temporary variations. The permanent is preferable. Carefully consider maintenance and mowing requirements when making the selection.

Regarding erosion and sediment control, even if there is no proposed grading, the entire work area should be included in the limit of disturbance. The ground surface will be disturbed and exposed by equipment during the installation process, and therefore sediment controls are necessary for the entire work area. Same day stabilization alone is not a viable option although stabilization should be implemented as quickly and efficiently as possible.

Attachment C – Chapter 5 N-1 (Page 5.57 to 5.65), Maryland Stormwater Design Manual

Chapter 5. Environmental Site Design.............................Nonstructural and Micro-Scale Practices

N-1. Disconnection of Rooftop Runoff

Rooftop disconnection involves directing flow from downspouts onto vegetated areas where it can soak into or filter over the ground. This disconnects the rooftop from the storm drain system and reduces both runoff volume and pollutants delivered to receiving waters. To function well, rooftop disconnection is dependent on several site conditions (e.g., flow path length, soils, slopes).

Applications:

There are many opportunities for disconnecting rooftops in both new and redevelopment designs.

Runoff may be directed to undisturbed natural areas (e.g., vegetated buffers) or landscaped areas (e.g., lawns, grass channels). Rooftop disconnection is possible in commercial, industrial, and residential settings given the constraints listed below.

Performance:

The PE values shown in Table 5.6 may be applied to the ESD sizing criteria when the contributing rooftop area is adequately disconnected. Rev requirements (see Chapter 2) are also addressed when the PE from Table 5.6 meets or exceeds the soil specific recharge factor listed in Section 2.2.

Constraints:

The following constraints are critical when considering the use of rooftop disconnection to capture and treat stormwater runoff:

Space: A permeable, vegetated treatment area equal to the flow path length must be available down gradient from the downspout to effectively disconnect rooftop runoff.

Additional treatment using micro-scale practices may be used to fully meet PE requirements.

Topography: Runoff must be conveyed as sheetflow from the downspout and across open areas to maintain proper disconnection. Level spreaders may be needed at the downspout to dissipate flow. Additionally, disconnected downspouts should be located on gradual slopes (≤ 5%) and directed away from buildings to both maintain sheetflow and prevent water damage to basements and foundations. If slopes are too steep (> 5%), a series of terraces or berms may be required to maintain sheetflow. These terraces may be readily constructed of landscaping stones, timber, or earthen berms.

Soils: Downspout disconnections work best in undisturbed, sandy soils that allow runoff to infiltrate. Clayey soils or soils that have been compacted by construction equipment greatly reduce the effectiveness of this practice and soil amendments may be needed.

5.57 Supp.1

Chapter 5. Environmental Site Design............................Nonstructural and Micro-Scale Practices

Figure 5.4 Disconnection of Rooftop Runoff

Plan View

Profile

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Chapter 5. Environmental Site Design.............................Nonstructural and Micro-Scale Practices

Drainage Area: The rooftop area to each downspout should be small enough to prevent concentration of flow within the permeable treatment area. Disconnections may not be feasible for large rooftops or those with a limited number of downspouts.

Reconnections: Disconnections are ineffective if runoff flows onto impervious areas located directly below the downspout. This practice may not be feasible if there are large areas of imperviousness close to downspouts.

Design Guidance:

The following conditions should be considered when designing rooftop disconnections:

Conveyance: Runoff from disconnected downspouts shall drain in a safe and non-erosive manner through vegetated areas to the property line or downstream BMP.

Treatment: Disconnections shall meet the following conditions:

o A pervious area at least 15 feet long (12 feet for Eastern Shore projects) shall be available down gradient of disconnected downspouts. The length of the disconnection flow path may be increased up to 75 feet to address larger values of PE as shown in Table 5.6.

o Disconnections shall be located on an average slope of 5% or less. Terraces, berms, or similar grade controls may be used where average slopes exceed 5%.

o The drainage area to each disconnected downspout shall be 500 ft2 or less.

o Disconnected downspouts shall be at least 10 ft. from the nearest impervious surface of similar or lower elevation to prevent reconnection.

Table 5.6. ESD Sizing Factors for Rooftop Disconnection

Disconnection Flow Path Length (ft.)

Western

Shore 15 30 45 60 75

Eastern Shore 12 24 36 48 60

PE (in.) = 0.2 0.4 0.6 0.8 1.0

Landscaping: Areas receiving disconnected rooftop runoff shall be identified and notations related to grading and construction operations included on the landscaping plans.

Disconnections should be directed over HSG A, B, or C (e.g., sands, sandy loams, loams).

HSG D or soils that are compacted by construction equipment may need to be tilled and/or amended to increase permeability. Groundcover should be provided after any soil amendments are used. Turf grass is the most common groundcover in residential applications. However, trees and shrubs as well as other herbaceous plants will enhance infiltration and evapotranspiration of runoff.

5.59 Supp.1

Chapter 5. Environmental Site Design............................Nonstructural and Micro-Scale Practices

Construction Criteria:

The following items should be addressed during the construction of projects with planned rooftop disconnections:

Erosion and Sediment Control: Erosion and sediment control practices (e.g., sediment traps) shall not be located in vegetated areas receiving disconnected runoff.

Site Disturbance: Construction vehicles and equipment should avoid areas receiving disconnected runoff to minimize disturbance and compaction. Should areas receiving disconnected runoff become compacted, scarifying the surface or rototilling the soil to a depth of four to six inches shall be performed to ensure permeability. Additionally, amendments may be needed for tight, clayey soils.

Inspection:

A final inspection shall be conducted before use and occupancy approval to ensure that sizing for treatment areas have been met and permanent stabilization has been established.

Maintenance Criteria:

Maintenance of areas receiving disconnected runoff is generally no different than that required for other lawn or landscaped areas. The areas receiving runoff should be protected from future compaction (e.g., by planting trees or shrubs along the perimeter). In commercial areas, foot traffic should be discouraged as well.

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Chapter 5. Environmental Site Design.............................Nonstructural and Micro-Scale Practices

N-2. Disconnection of Non-Rooftop Runoff

Non-rooftop disconnection involves directing flow from impervious surfaces onto vegetated areas where it can soak into or filter over the ground. This disconnects these surfaces from the storm drain system, reducing both runoff volume and pollutants delivered to receiving waters.

Non-rooftop disconnection is commonly applied to smaller or narrower impervious areas like driveways, open section roads, and small parking lots and is dependent on several site conditions (e.g., permeable flow path length, soils, slopes, compaction) to function well.

Applications:

There are many opportunities for disconnecting impervious surfaces in both new and redevelopment designs. Runoff may be directed as sheetflow to undisturbed natural areas (e.g., vegetated buffers) or landscaped areas (e.g., lawns, grass channels). Non-rooftop disconnection is possible in commercial, industrial, and residential settings given the constraints listed below.

Performance:

The PE values shown in Table 5.7 below may be applied to the ESD sizing criteria when the contributing developed area is adequately disconnected. Rev requirements (see Chapter 2) are also met when the PE from Table 5.7 meets or exceeds the soil specific recharge factor listed in Section 2.2.

Constraints:

The following constraints are critical when considering the use of non-rooftop disconnection to capture and treat stormwater runoff:

Space: A permeable, vegetated treatment area equal to the minimum flow path length needed for treatment must be available down gradient of the impervious cover to effectively disconnect runoff. If the flow path length is insufficient, additional treatment may be provided using micro-scale practices.

Topography: Runoff must be conveyed as sheetflow onto and across open areas to maintain proper disconnection. Additionally, disconnections should be located on gradual slopes (≤ 5%) and directed away from buildings to both maintain sheetflow and prevent water damage to basements and foundations. If slopes are too steep (> 5%), a series of terraces or berms may be required to maintain sheetflow. These terraces may be readily constructed of landscaping stones or timber.

Soils: Non-rooftop disconnection works best in undisturbed, sandy soils that allow runoff to infiltrate. Clayey soils or soils that have been compacted by construction greatly reduce the effectiveness of this practice.

5.61 Supp.1

Chapter 5. Environmental Site Design............................Nonstructural and Micro-Scale Practices

Drainage Area: The impervious area to each discharge location should be small enough to prevent flow concentration onto permeable treatment areas. Disconnections may not be feasible for large blocks of impervious cover or areas with limited discharge points.

Hotspot Runoff: Disconnections should not be used to treat hotspots that generate higher concentrations of hydrocarbons, trace metals, or toxicants than are found in typical stormwater runoff and may contaminate groundwater.

Design Guidance:

The following conditions should be considered when designing non-rooftop disconnections:

Conveyance: Runoff from disconnected areas shall drain in a safe and non-erosive manner through vegetated areas to the property line or downstream BMP.

A 1 to 2 foot wide gravel (typ. No. 67 stone) transition strip should be provided from the disconnected area to the vegetated area to assure that runoff will flow in a safe and non-erosive manner.

Treatment: Disconnections shall meet the following conditions:

o The flow path or “disconnection” through vegetated areas shall be at least 10 feet and shall not exceed 75 feet. The flow path may be increased to address larger values of PE to a maximum of 1 inch as shown in Table 5.7.

o The maximum contributing impervious flow path length shall be 75 feet, and the maximum contributing pervious flow path shall be 150 feet.

o Disconnections shall be located on an average slope of 5% or less. Terraces, berms, or similar grade controls may be used where average slopes exceed 5%.

o The drainage area to each disconnection shall be 1,000 ft2 or less.

o Disconnections shall be at least 10 ft. from the nearest impervious surface of similar or lower elevation to prevent reconnection.

Table 5.7. ESD Sizing Factors for Non-Rooftop Disconnection

Ratio of Disconnection Length to Contributing Length Impervious

Ratio 0.2:1 0.4:1 0.6:1 0.8:1 1:1

Pervious Ratio 0.1:1 0.2:1 0.3:1 0.4:1 0.5:1

PE (in.) = 0.2 0.4 0.6 0.8 1.0

Landscaping: Areas receiving disconnected runoff shall be identified and notations related to grading and construction operations included on the landscaping plans.

Disconnections should be directed over HSG A, B, or C (e.g., sands, sandy loams, loams).

HSG D and soils that are compacted by construction equipment may need to be tilled and/or amended to increase permeability. Groundcover vegetation should be provided after any soil

Supp. 1 5.62

Amy Cervantes Highlight

Chapter 5. Environmental Site Design.............................Nonstructural and Micro-Scale Practices amendments are used. Turf grass is the most common groundcover in residential applications. Trees and shrubs as well as other herbaceous plants will enhance infiltration and evapotranspiration of runoff.

Construction Criteria:

The following should be addressed during construction of projects with non-rooftop disconnections:

Erosion and Sediment Control: Erosion and sediment control practices (e.g., sediment traps) shall not be located in areas designated for non-rooftop disconnections.

Site Disturbance: To minimize disturbance and compaction, construction vehicles and equipment should avoid areas receiving disconnected runoff. Should areas receiving disconnected runoff become compacted, scarifying the surface or rototilling the soil to a depth of four to six inches shall be performed to ensure permeability. Additionally, amendments may be needed for tight, clayey soils.

Inspection:

A final inspection shall be conducted before use and occupancy approval to ensure that adequate treatment areas and permanent stabilization has been established.

Maintenance Criteria:

Maintenance of areas receiving disconnected runoff is generally no different than that required for other lawn or landscaped areas. The areas receiving runoff should be protected from future compaction (e.g., by planting trees or shrubs along the perimeter). In commercial areas, high foot traffic should be discouraged as well.

5.63 Supp.1

Chapter 5. Environmental Site Design............................Nonstructural and Micro-Scale Practices

Fig. 5.5 Non-Rooftop Disconnection

Profile

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Chapter 5. Environmental Site Design.............................Nonstructural and Micro-Scale Practices

Figure 5.6 Non-Rooftop Disconnection

Isometric

5.65 Supp.1

Attachment D – Web Soil Survey

Soil Map—Anne Arundel County, Maryland

Natural Resources Conservation Service

Web Soil Survey National Cooperative Soil Survey

5/12/2025

365530 365600 365670 365740 365810 365880 365950 366020 366090 366160

365530 365600 365670 365740 365810 365880 365950 366020 366090 366160

38° 53' 56'' N

3'

'' W 38° 53' 56'' N

2'

5' ' W

38° 53' 42'' N

3'

'' W

38° 53' 42'' N

2'

5' ' W

N

Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 18N WGS84 0 100 200 400 600

Feet 0 40 80 160 240

Meters Map Scale: 1:3,020 if printed on A landscape (11" x 8.5") sheet.

Soil Map may not be valid at this scale.

MAP LEGEND MAP INFORMATION

Area of Interest (AOI) Area of Interest (AOI)

Soils Soil Map Unit Polygons

Soil Map Unit Lines

Soil Map Unit Points

Special Point Features Blowout

Borrow Pit

Clay Spot

Closed Depression

Gravel Pit

Gravelly Spot

Landfill

Lava Flow

Marsh or swamp

Mine or Quarry

Miscellaneous Water

Perennial Water

Rock Outcrop

Saline Spot

Sandy Spot

Severely Eroded Spot

Sinkhole

Slide or Slip

Sodic Spot

Spoil Area

Stony Spot

Very Stony Spot

Wet Spot

Other

Special Line Features

Water Features Streams and Canals

Transportation Rails

Interstate Highways

US Routes

Major Roads

Local Roads

Background Aerial Photography

The soil surveys that comprise your AOI were mapped at 1:12,000.

Warning: Soil Map may not be valid at this scale.

Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale.

Please rely on the bar scale on each map sheet for map measurements.

Source of Map: Natural Resources Conservation Service Web Soil Survey URL:

Coordinate System: Web Mercator (EPSG:3857)

Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required.

This product is generated from the USDA-NRCS certified data as of the version date(s) listed below.

Soil Survey Area: Anne Arundel County, Maryland Survey Area Data: Version 23, Sep 6, 2024

Soil map units are labeled (as space allows) for map scales 1:50,000 or larger.

Date(s) aerial images were photographed: Jun 20, 2022—Aug 13, 2022

The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident.

Soil Map—Anne Arundel County, Maryland

Natural Resources Conservation Service

Web Soil Survey National Cooperative Soil Survey

5/12/2025

Map Unit Legend

Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI

CRD Collington and Annapolis soils, 10 to 15 percent slopes

1.1 7.0%

MaB Marr-Dodon complex, 2 to 5 percent slopes

4.4 28.1%

MaC Marr-Dodon complex, 5 to 10 percent slopes

4.8 30.4%

MaD Marr-Dodon complex, 10 to 15 percent slopes

5.4 34.5%

Totals for Area of Interest 15.8 100.0%

Soil Map—Anne Arundel County, Maryland

Natural Resources Conservation Service

Web Soil Survey National Cooperative Soil Survey

Hydrologic Soil Group—Anne Arundel County, Maryland

Conservation Service

Web Soil Survey National Cooperative Soil Survey

5/12/2025

365530 365600 365670 365740 365810 365880 365950 366020 366090 366160

365530 365600 365670 365740 365810 365880 365950 366020 366090 366160

38° 53' 56'' N

3'

'' W 38° 53' 56'' N

2'

5' ' W

38° 53' 42'' N

3'

'' W

38° 53' 42'' N

2'

5' ' W

N

Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 18N WGS84 0 100 200 400 600

Feet 0 40 80 160 240

Meters Map Scale: 1:3,020 if printed on A landscape (11" x 8.5") sheet.

Area of Interest (AOI)

Soils Soil Rating Polygons

A

A/D

B

B/D

C

C/D

D

Not rated or not available

Soil Rating Lines A

A/D

B

B/D

C

C/D

D

Not rated or not available

Soil Rating Points A

A/D

B

B/D

C

C/D

D

Not rated or not available

Water Features Streams and Canals

Transportation Rails

Interstate Highways

US Routes

Major Roads

Local Roads

Background Aerial Photography

The soil surveys that comprise your AOI were mapped at 1:12,000.

Warning: Soil Map may not be valid at this scale.

Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale.

Please rely on the bar scale on each map sheet for map measurements.

Source of Map: Natural Resources Conservation Service Web Soil Survey URL:

Coordinate System: Web Mercator (EPSG:3857)

Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required.

This product is generated from the USDA-NRCS certified data as of the version date(s) listed below.

Soil Survey Area: Anne Arundel County, Maryland Survey Area Data: Version 23, Sep 6, 2024

Soil map units are labeled (as space allows) for map scales 1:50,000 or larger.

Date(s) aerial images were photographed: Jun 20, 2022—Aug 13, 2022

The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident.

Hydrologic Soil Group—Anne Arundel County, Maryland

Natural Resources Conservation Service

Web Soil Survey National Cooperative Soil Survey

Hydrologic Soil Group

Map unit symbol Map unit name Rating Acres in AOI Percent of AOI

CRD Collington and Annapolis soils, 10 to 15 percent slopes

B 1.1 7.0%

MaB Marr-Dodon complex, 2 to 5 percent slopes

B 4.4 28.1%

MaC Marr-Dodon complex, 5 to 10 percent slopes

C 4.8 30.4%

MaD Marr-Dodon complex, 10 to 15 percent slopes

C 5.4 34.5%

Totals for Area of Interest 15.8 100.0%

Hydrologic Soil Group—Anne Arundel County, Maryland

Natural Resources Conservation Service

Web Soil Survey National Cooperative Soil Survey

Description

Hydrologic soil groups are based on estimates of runoff potential. Soils are assigned to one of four groups according to the rate of water infiltration when the soils are not protected by vegetation, are thoroughly wet, and receive precipitation from long-duration storms.

The soils in the United States are assigned to four groups (A, B, C, and D) and three dual classes (A/D, B/D, and C/D). The groups are defined as follows:

Group A. Soils having a high infiltration rate (low runoff potential) when thoroughly wet. These consist mainly of deep, well drained to excessively drained sands or gravelly sands. These soils have a high rate of water transmission.

Group B. Soils having a moderate infiltration rate when thoroughly wet. These consist chiefly of moderately deep or deep, moderately well drained or well drained soils that have moderately fine texture to moderately coarse texture.

These soils have a moderate rate of water transmission.

Group C. Soils having a slow infiltration rate when thoroughly wet. These consist chiefly of soils having a layer that impedes the downward movement of water or soils of moderately fine texture or fine texture. These soils have a slow rate of water transmission.

Group D. Soils having a very slow infiltration rate (high runoff potential) when thoroughly wet. These consist chiefly of clays that have a high shrink-swell potential, soils that have a high water table, soils that have a claypan or clay layer at or near the surface, and soils that are shallow over nearly impervious material. These soils have a very slow rate of water transmission.

If a soil is assigned to a dual hydrologic group (A/D, B/D, or C/D), the first letter is for drained areas and the second is for undrained areas. Only the soils that in their natural condition are in group D are assigned to dual classes.

Rating Options

Aggregation Method: Dominant Condition

Component Percent Cutoff: None Specified

Tie-break Rule: Higher

Hydrologic Soil Group—Anne Arundel County, Maryland

Natural Resources Conservation Service

Web Soil Survey National Cooperative Soil Survey

Conservation Service

Web Soil Survey National Cooperative Soil Survey

5/12/2025

365360 365400 365440 365480 365520 365560 365600

365360 365400 365440 365480 365520 365560

38° 53' 46'' N

3'

'' W 38° 53' 46'' N

2'

9' ' W

38° 53' 36'' N

3'

'' W

38° 53' 36'' N

2'

9' ' W

N

Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 18N WGS84 0 50 100 200 300

Feet 0 20 40 80 120

Meters Map Scale: 1:1,590 if printed on A portrait (8.5" x 11") sheet.

Area of Interest (AOI)

Soils Soil Map Unit Polygons

Soil Map Unit Lines

Soil Map Unit Points

Special Point Features Blowout

Borrow Pit

Clay Spot

Closed Depression

Gravel Pit

Gravelly Spot

Landfill

Lava Flow

Marsh or swamp

Mine or Quarry

Miscellaneous Water

Perennial Water

Rock Outcrop

Saline Spot

Sandy Spot

Severely Eroded Spot

Sinkhole

Slide or Slip

Sodic Spot

Spoil Area

Stony Spot

Very Stony Spot

Wet Spot

Other

Special Line Features

Water Features Streams and Canals

Transportation Rails

Interstate Highways

US Routes

Major Roads

Local Roads

Background Aerial Photography

The soil surveys that comprise your AOI were mapped at 1:12,000.

Warning: Soil Map may not be valid at this scale.

Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale.

Please rely on the bar scale on each map sheet for map measurements.

Source of Map: Natural Resources Conservation Service Web Soil Survey URL:

Coordinate System: Web Mercator (EPSG:3857)

Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required.

This product is generated from the USDA-NRCS certified data as of the version date(s) listed below.

Soil Survey Area: Anne Arundel County, Maryland Survey Area Data: Version 23, Sep 6, 2024

Soil map units are labeled (as space allows) for map scales 1:50,000 or larger.

Date(s) aerial images were photographed: Jun 20, 2022—Aug 13, 2022

The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident.

Soil Map—Anne Arundel County, Maryland

Natural Resources Conservation Service

Web Soil Survey National Cooperative Soil Survey

MaB Marr-Dodon complex, 2 to 5 percent slopes

0.8 11.1%

MaC Marr-Dodon complex, 5 to 10 percent slopes

3.8 51.2%

MaD Marr-Dodon complex, 10 to 15 percent slopes

2.8 37.4%

MDE Marr and Dodon soils, 15 to 25 percent slopes

0.0 0.4%

Totals for Area of Interest 7.5 100.0%

Soil Map—Anne Arundel County, Maryland

Natural Resources Conservation Service

Web Soil Survey National Cooperative Soil Survey

Conservation Service

Web Soil Survey National Cooperative Soil Survey

5/12/2025

365360 365400 365440 365480 365520 365560 365600

365360 365400 365440 365480 365520 365560

38° 53' 46'' N

3'

'' W 38° 53' 46'' N

2'

9' ' W

38° 53' 36'' N

3'

'' W

38° 53' 36'' N

2'

9' ' W

N

Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 18N WGS84 0 50 100 200 300

Feet 0 20 40 80 120

Meters Map Scale: 1:1,590 if printed on A portrait (8.5" x 11") sheet.

Area of Interest (AOI)

Soils Soil Rating Polygons

A

A/D

B

B/D

C

C/D

D

Not rated or not available

Soil Rating Lines A

A/D

B

B/D

C

C/D

D

Not rated or not available

Soil Rating Points A

A/D

B

B/D

C

C/D

D

Not rated or not available

Water Features Streams and Canals

Transportation Rails

Interstate Highways

US Routes

Major Roads

Local Roads

Background Aerial Photography

The soil surveys that comprise your AOI were mapped at 1:12,000.

Warning: Soil Map may not be valid at this scale.

Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale.

Please rely on the bar scale on each map sheet for map measurements.

Source of Map: Natural Resources Conservation Service Web Soil Survey URL:

Coordinate System: Web Mercator (EPSG:3857)

Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required.

This product is generated from the USDA-NRCS certified data as of the version date(s) listed below.

Soil Survey Area: Anne Arundel County, Maryland Survey Area Data: Version 23, Sep 6, 2024

Soil map units are labeled (as space allows) for map scales 1:50,000 or larger.

Date(s) aerial images were photographed: Jun 20, 2022—Aug 13, 2022

The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident.

Hydrologic Soil Group—Anne Arundel County, Maryland

Natural Resources Conservation Service

Web Soil Survey National Cooperative Soil Survey

MaB Marr-Dodon complex, 2 to 5 percent slopes

B 0.8 11.1%

MaC Marr-Dodon complex, 5 to 10 percent slopes

C 3.8 51.2%

MaD Marr-Dodon complex, 10 to 15 percent slopes

C 2.8 37.4%

MDE Marr and Dodon soils, 15 to 25 percent slopes

C 0.0 0.4%

Totals for Area of Interest 7.5 100.0%

Hydrologic Soil Group—Anne Arundel County, Maryland

Natural Resources Conservation Service

Web Soil Survey National Cooperative Soil Survey assigned to one of four groups according to the rate of water infiltration when the soils are not protected by vegetation, are thoroughly wet, and receive precipitation from long-duration storms.

The soils in the United States are assigned to four groups (A, B, C, and D) and three dual classes (A/D, B/D, and C/D). The groups are defined as follows:

Group A. Soils having a high infiltration rate (low runoff potential) when thoroughly wet. These consist mainly of deep, well drained to excessively drained sands or gravelly sands. These soils have a high rate of water transmission.

Group B. Soils having a moderate infiltration rate when thoroughly wet. These consist chiefly of moderately deep or deep, moderately well drained or well drained soils that have moderately fine texture to moderately coarse texture.

These soils have a moderate rate of water transmission.

Group C. Soils having a slow infiltration rate when thoroughly wet. These consist chiefly of soils having a layer that impedes the downward movement of water or soils of moderately fine texture or fine texture. These soils have a slow rate of water transmission.

Group D. Soils having a very slow infiltration rate (high runoff potential) when thoroughly wet. These consist chiefly of clays that have a high shrink-swell potential, soils that have a high water table, soils that have a claypan or clay layer at or near the surface, and soils that are shallow over nearly impervious material. These soils have a very slow rate of water transmission.

If a soil is assigned to a dual hydrologic group (A/D, B/D, or C/D), the first letter is for drained areas and the second is for undrained areas. Only the soils that in their natural condition are in group D are assigned to dual classes.

Rating Options

Aggregation Method: Dominant Condition

Component Percent Cutoff: None Specified

Tie-break Rule: Higher

Hydrologic Soil Group—Anne Arundel County, Maryland

Natural Resources Conservation Service

Web Soil Survey National Cooperative Soil Survey

Conservation Service

Web Soil Survey National Cooperative Soil Survey

5/12/2025

365730 365780 365830 365880 365930 365980 366030 366080 366130 366180

365730 365780 365830 365880 365930 365980 366030 366080 366130 366180

38° 53' 53'' N

2'

4' ' W

38° 53' 53'' N

2'

4' ' W

38° 53' 43'' N

2'

4' ' W

38° 53' 43'' N

2'

4' ' W

N

Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 18N WGS84 0 100 200 400 600

Feet 0 30 60 120 180

Meters Map Scale: 1:2,280 if printed on A landscape (11" x 8.5") sheet.

Area of Interest (AOI)

Soils Soil Map Unit Polygons

Soil Map Unit Lines

Soil Map Unit Points

Special Point Features Blowout

Borrow Pit

Clay Spot

Closed Depression

Gravel Pit

Gravelly Spot

Landfill

Lava Flow

Marsh or swamp

Mine or Quarry

Miscellaneous Water

Perennial Water

Rock Outcrop

Saline Spot

Sandy Spot

Severely Eroded Spot

Sinkhole

Slide or Slip

Sodic Spot

Spoil Area

Stony Spot

Very Stony Spot

Wet Spot

Other

Special Line Features

Water Features Streams and Canals

Transportation Rails

Interstate Highways

US Routes

Major Roads

Local Roads

Background Aerial Photography

The soil surveys that comprise your AOI were mapped at 1:12,000.

Warning: Soil Map may not be valid at this scale.

Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale.

Please rely on the bar scale on each map sheet for map measurements.

Source of Map: Natural Resources Conservation Service Web Soil Survey URL:

Coordinate System: Web Mercator (EPSG:3857)

Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required.

This product is generated from the USDA-NRCS certified data as of the version date(s) listed below.

Soil Survey Area: Anne Arundel County, Maryland Survey Area Data: Version 23,…