9220 Wightman Road, Suite 120 Montgomery Village, Maryland Phone Fax

Transcription

1 9220 Wightman Road, Suite 0 Montgomery Village, Maryland Engineers Planners Landscape Architects Surveyors Phone Fax

2 STORMWATER MANAGEMENT SUMMARY Project: Wildwood Manor Shopping Center MHG Proj. No.: SM File #: Date: March 2018 Background Drainage OVERALL SITE INFORMATION The project is located on Old Georgetown Ave. (Route 187) between Rock Spring Drive and Democracy Boulevard; approximately 0.25 miles south of Exit-1 of I-270. The acre site is currently zoned CRT-1.25, C-0.5, R-0.75, H-50. Proposed plans are for a new mixed use building with an underground garage to be constructed on the existing parking lot. Additional surface parking improvements are also proposed. The existing site is 67% impervious, thus it is considered a redevelopment site. Under existing conditions on-site drainage is conveyed through an existing closed system through the adjacent property to the South. The offsite storm drain system also serves properties across Old Georgetown Ave. and parts of Old Georgetown Ave. and continues into a public system within the Rossmore Drive. Proposed conditions primarily drain to the same offsite storm drain system. Approximately 0.5 acres are diverted to storm drain within the Berkshire Drive right-of-way. All runoff ultimately discharges to Luxmanor Branch of Lower Rock Creek. Lower Rock Creek and its tributaries have a Class I-P State water use designation. STORMWATER MANAGEMENT ESD MEP Stormwater management for the proposed site is designed such that environmental site design (ESD) techniques have been integrated to the maximum extent practicable (MEP). In addition to stacking the proposed building over structured parking, the stormwater concept consists of micro-bioretention facilities and green roof. Site limitations preclude the complete use of ESD practices to meet the stormwater management requirement and existing shallow storm drain infrastructure makes most structural stormwater management practices infeasible. Water Quality management is provided using ESD to the MEP, but full quantity management is not practical through ESD measures. A shallow underground filtration system is proposed to manage stormwater quantity management. The site limitations and ESD techniques are described in more detail as follows: Wildwood Manor Shopping Center March 2018 SWM Summary Page 1 MHG Project No

3 Site Limitations: The subject property is currently developed including an existing storm drain system that connects to the adjacent developed property. The system on the adjacent property is prohibitively shallow to support widespread use of volume-based structural stormwater practices. Flow-based structural practices are only viable in the locations that are already dedicated to ESD techniques. Underlying soils have been identified as having infiltration rates at or below 0.30 in/hr. The minimum infiltration rate for stormwater practices that rely on infiltration as a means of treatment is 0.52 in/hr, thus the existing soils are unsuitable for these types of practices. Green Roof: An extensive greenroof is proposed for approximately 50% of the proposed building area. The green roof is designed to have 8 of planting media over a series of other roofing layers to manage the root systems and drainage of the media as well as provide waterproofing and insulation for the rooftop. The exact percentage of green roof will not be determined until the building design is finalized and space required for mechanical equipment is known. The green roof area along with the remainder of the roof area is designed to contribute to the downstream planter box micro-bioretention system, PB-2. Micro-Bioretention: Three micro-bioretention facilities are proposed to manage the majority of the proposed pavement and to supplement management of the roof area. Micro-bioretention practices are designed to temporarily pond runoff at the surface as well as temporarily detain and filter runoff through a cross section of planting media, gravel, and sand. Because of the existing shallow storm drain system, the microbioretention facilities are limited in depth and the shallowest facility is designed with 24 of soil. Planter box micro-bioretention facilities are also proposed where space is limited for grading and the facility is adjacent to buildings. Underground Filtration: A large diameter pipe array storage system is proposed to temporarily store the CPv remainder volume upstream from an underground cartridge filtration system. The system is designed to treat runoff from the existing parking lot area. Treated water and overflow water is conveyed through the bypass chamber of the proposed filtration system to the proposed onsite storm drain system and finally to an existing offsite storm drain system. The facility is located near the northeast corner of the property in order to provide adequate depth and cover to discharge into the existing storm drain system. Wildwood Manor Shopping Center March 2018 SWM Summary Page 2 MHG Project No

4 SUMMARY OF ESD PRACTICES Green Roof: Green roof technology is proposed for approximately 50% of the rooftop area. Pervious Pavement: Pervious pavement was considered; however the underlying soils are not suitable according to the project geotechnical study. Reinforced Turf: Reinforced Turf was not explored because the expected use of the paved areas is to intense for reinforce turf. Disconnection of Rooftop Runoff: In general the site is too dense for disconnection to be feasible. The limited open space areas are dedicated to other ESD practices. Disconnection of Non-Rooftop Runoff: In general the site is too dense for disconnection to be feasible. The limited open space areas are dedicated to other ESD practices. Sheetflow to a Conservation Area: No onsite conservation areas exist. Rainwater Harvesting: Rainwater harvesting was not explored because year-round demand cannot be practically provided. Submerged Gravel Wetland: Available open space areas are dedicated to other micro-scale practices. Landscape Infiltration: Landscape infiltration was not explored because the development is located on poor soils. Infiltration Berms: Infiltration berms are not proposed because the site is too dense for berms to be practical. The limited open space areas are dedicated to other ESD practices. Dry Wells: The rooftop area is too large for dry wells to be a practical management technique. The rooftop area is planned to be managed by other ESD techniques. Micro-Bioretention: Micro-bioretention is proposed to treat portions of the proposed paved area and roof area. Rain Gardens: Rain gardens were not proposed because alternate and more efficient ESD measures are proposed in the open space areas. Swales: The site does not have obvious linear treatment areas and the limited open space areas are dedicated to other ESD practices. Wildwood Manor Shopping Center March 2018 SWM Summary Page 3 MHG Project No

5 SWM COMPUTATIONS WILDWOOD MANOR SHOPPING CENTER MHG PROJECT No Table of Contents ESD Sizing Criteria 1-3 ESD Micro-Scale Treatment Summary 4 Average Treatment PE Calculation 5 ESD Micro-Scale Reduced RCN Calculation 6 CPv Remainder Calculation 7 Green Roof Design 8 Micro-Bioretention Design: MB-1 9 Micro-Bioretention Design: MB-2 10 Micro-Bioretention Design: PB-1 11 Micro-Bioretention Design: PB-2 SF1 ESDv Calculation 13 CMP Storage Volume Computation 14 SF1 Sizing Computation 15

6 DATE: 3/5/18 CHECKED BY: Macris, Hendricks & Glascock, P.A. PROJECT No.: Wightman Road, Suite 0 PAGE: 1 Montgomery Village, MD Phone: (301) Fax: (301) Site Data: Total Drainage Area (DA): 149,110 SF = 3.42 Acres Total Impervious (I) Area: 109,510 SF = 2.51 Acres = 73.4% Determine Target P E : Drainage Area Hydrologic Soil Group (HSG) Distribution HSG A B C D HSG DA (SF) 149,110 SF % of Total DA 0.0% 0.0% 0.0% 100.0% HSG I Area (SF) 109,510 SF HSG %I 0.0% 0.0% 0.0% 73.4% HSG RCN HSG P E * 0.0'' 0.0'' 0.0'' 1.8'' *See Abridged Rainfall Targets/RCN Reductions Table(s) Below Target RCN = 77 x 100% = 77.0 Target Rainfall = P E = 1.8'' x 100% = 1.80'' WILDWOOD MANOR SHOPPING CENTER Environmental Site Design (ESD) Sizing Criteria HYDROLOGIC SOIL GROUP A %I RCN* P E = 1.0'' 1.2'' % % HYDROLOGIC SOIL GROUP B %I RCN* P E = 1.0'' 1.2'' % % HYDROLOGIC SOIL GROUP C %I RCN* P E = 1.0'' 1.2'' % % HYDROLOGIC SOIL GROUP D %I RCN* P E = 1.6'' 1.8'' 2.0'' 70% % %

7 Proposed Disturbed Area: PAGE: 2 Total Disturbed Area (LOD): 89,781 SF = 2.06 Acres Impervious Area (I) Within LOD: 63,081 SF = 1.45 Acres = 70.26% Determine Q E : R V = the dimensionless volumetric runoff coefficient = (I) where I is percent impervious cover = (70.26%) = 0.68 Q E = Runoff depth in inches that must be treated using ESD practices = P E x R V = 1.8'' x 0.68 = 1.23'' Determine ESD V : ESD V = Runoff volume used in the design of specific ESD practices (P E )(R V )(A) = where A is the drainage area (in square feet) (1.8'')(0.68)(89781) = = 9,189 CU FT

8 Minimum ESD Target: PAGE: 3 As a minimum, ESD shall be used to address both Re v and WQ v requirements Determine RE V : Re V = Groundwater Recharge volume component of ESD V (S)(R V )(A) = (0.06'')(0.68)(89781) = = 306 CU FT SOIL SPECIFIC RECHARGE FACTOR (S) HSG (S) % AREA (S)(%A) A % 0 B % 0 C % 0 D % 0.06 COMPOSITE S = 0.06 Determine WQ V : Wq V = Water Quality volume component of ESD V = 1.0" Eastern Zone and 0.9" Western Zone (P E )(R V )(A) = where A is the drainage area (in square feet) (1'')(0.68)(89781) = = 5,105 CU FT

9 JOB #: DATE: 1/18/2018 Macris, Hendricks & Glascock, P.A. PAGE: Wightman Road, Suite 0 Montgomery Village, MD Phone: (301) Fax: (301) ESD SUMMARY TREATMENT IMPERVIOUS UNIT NO. FACILITY DESCRIPTION AREA (SF) AREA (SF) P E (IN) R V ESD V MB-1 Micro-Bioretention Facility 17,600 5, ,165.7 MB-2 Micro-Bioretention Facility 13,400 8, ,802.7 PB-1 Planter Box Micro-Bioretention 20,000 16, ,196.0 PB-2 Planter Box Micro-Bioretention 20,000 20, ,698.2 GR-1 Green Roof 10,000 10, ,345.8 TOTALS 81, , ,208.4 AVG. PE 1.71 R V = (I) (P E )(R V )(A) (ESD V ) ESD V = PE = where I is percent impervious cover (RV)(A)

10 DATE: 3/6/18 CHECKED BY: Macris, Hendricks & Glascock, P.A. PROJECT No.: Wightman Road, Suite 0 PAGE: 5 Montgomery Village, MD Phone: (301) Fax: (301) Average Treatment P E for Development Area It is not practicable for all parts of the development area to drain to stormwater facilities. It is therefore necessary to average the treated ESDv from all drainage areas over the entire development area. This is accomplised using the relationship between P E and ESDv such that the ESDv term is the summation of all treated stormwater volumes, while the site data is based on the development area. Determine Avg. Treatment P E for Total Site: P E = (ESD V ) (RV)(A) Treated ESDv = 8,208 CU FT (From ESD SUMMARY Sheet) Disturbed Area (LOD) = 89,781 SF Rv = 0.68 Avg. P E = (8208) (0.68)(89781) Avg. Treatment P E = 1.61 Target P E = Avg. Treatment P E = 1.80'' 1.61'' ESDv Required = 9189 cu ft ESDv Provided = 8208 cu ft

11 DATE: 3/5/18 CHECKED BY: Macris, Hendricks & Glascock, P.A. PROJECT No.: Wightman Road, Suite 0 PAGE: 6 Montgomery Village, MD Phone: (301) Fax: (301) Design Treatment P E= 1.61'' Use 1.6'' Site Data: WILDWOOD MANOR SHOPPING CENTER Environmental Site Design (ESD) Sizing Criteria Total Drainage Area (DA): 149,110 SF = 3.42 Acres Total Impervious (I) Area: 109,510 SF = 2.51 Acres = 73.4% Determine Reduced RCN: Drainage Area Hydrologic Soil Group (HSG) Distribution HSG A B C D HSG DA (SF) 0 SF 0 SF 0 SF 149,110 SF % of Total DA 0.0% 0.0% 0.0% 100.0% Site %I 73.4% 73.4% 73.4% 73.4% HSG RCN* Design P E 0.0'' 0.0'' 0.0'' 1.6'' *See Abridged Rainfall Targets/RCN Reductions Table(s) Below Design RCN = 78 x 100% = 78.0 See Page for Additional CPv Requirements HYDROLOGIC SOIL GROUP A %I RCN* P E = 1.4'' 1.6'' 1.8'' 70% % % HYDROLOGIC SOIL GROUP B %I RCN* P E = 1.4'' 1.6'' 1.8'' 70% % % HYDROLOGIC SOIL GROUP C %I RCN* P E = 1.4'' 1.6'' 1.8'' 70% % % HYDROLOGIC SOIL GROUP D %I RCN* P E = 1.4'' 1.6'' 1.8'' 70% % %

12 DATE: 3/5/18 CHECKED BY: Macris, Hendricks & Glascock, P.A. PROJECT No.: Wightman Road, Suite 0 PAGE: 7 Montgomery Village, MD Phone: (301) Fax: (301) UNIFIED STORMWATER SIZING CRITERIA TREATMENT VOLUME DETERMINATION CHANNEL PROTECTION VOLUME (Cpv) DESIGN RAINFALL (P) = 2.6 in SITE AREA (A) = SF PROPOSED CONDITION RCN = 78.0 (From Reduced RCN Calculation Page ) S = (1000/RCN) - 10 (Equation 2.3, TR-55, USDA NRCS 1986) = (1000/78 ) - 10 = 2.8 Q (P - 0.2S) 2 1 = (P + 0.8S) ( *2.8) 2 = ( *2.8) = 0.86'' V design = Q 1 x A = 0.86'' x SF x FT/IN = 6434 CF EXISTING CONDITION RCN = 77.0 (For Woods in Good Condition) S = (1000/RCN) - 10 (Equation 2.3, TR-55, USDA NRCS 1986) = (1000/77 ) - 10 = 3 Q (P - 0.2S) 2 1 = (P + 0.8S) ( *3) 2 = ( *3) = 0.80'' V woods = Q 1 x A WILDWOOD MANOR SHOPPING CENTER = 0.8'' x SF x FT/IN = 5985 CF CPv = V design - V woods = 6434 CF CF = 449 CF

13 DATE: 8/10/16 CHECKED BY: Macris, Hendricks & Glascock, P.A. PROJECT No.: Wightman Road, Suite 0 PAGE: 8 Montgomery Village, MD Phone: (301) Fax: (301) WILDWOOD MANOR SHOPPING CENTER Green Roof Design Facility GR-1 Site Data: Green Roof Area (GR) = 10,000 sq ft Design Equations: From Environmental Site Design (ESD) Process & Computations (1) ESD V = (ESD V /ft 2 )(GR) ESD Values for Green Roofs Roof Thickness RCN ESD V /ft 2 Equiv. P E (in.) 2'' '' '' '' '' Facility Requirements: For P E = 1.0 in Roof Thickness = 4'' Facility Design: Roof Thickness = 8'' P E = 1.70 in Roof Area = 10,000 sq ft ESD V /ft 2 = ESD V = 1340 CF

14 DATE: 1/15/17 CHECKED BY: Macris, Hendricks & Glascock, P.A. PROJECT No.: Wightman Road, Suite 0 PAGE; 9 Montgomery Village, MD Phone: (301) Fax: (301) WILDWOOD MANOR SHOPPING CENTER Micro-Bioretention Design Facility MB-1 Site Data: HSG A B C D Total Trib. Area (DA) 0 sq ft 0 sq ft 0 sq ft 17,600 sq ft 17,600 sq ft Imp. Area (I) 0 sq ft 0 sq ft 0 sq ft 5,000 sq ft 5,000 sq ft Determine R V : R V = the dimensionless volumetric runoff coefficient = (I) where I is percent impervious cover = (28.41%) = 0.31 Maximum Runoff Volume: V = (P x R V x A) / = (2.6 x 0.31 x 17600) / = 1,166 cu ft Upstream ESDv Provided= 0 cu ft Maximum Runoff Volume = 1,166 cu ft Effective Drainage Area: Upstream ESD V Provided = 0 cu ft or 0% of Maximum Runoff Volume Effective Drainage Area = x 100% = sq ft Design Equations: From 2000 Maryland Stormwater Design Manual ESDv = (P E )(R V )(A) P E = (ESDv)() (Rv)(A) Facility Design: A f = 810 sq ft (4.6% DA) Bottom Storage Area = 810 sq Elev ' Top Storage Area = 980 sq Elev ' Storage Depth = 0.50' Temp. Ponding Volume = 448 cu ft Planting Media Depth = 3.5 ft (2.0'-3.5') Sand Layer Depth = 0.5 ft Porosity (n) = 0.40 Media Storage Volume = 1,296 cu ft Total ESDv Provided = 1,744 cu ft ESDv exceeds Max. Runoff Volume Total ESDv Provided = 1,166 cu ft P E = ()(ESDv) (Rv)(A) = ()(1166) (0.31)(17600) P E = 2.60 in Enhanced (Y or N): N

15 DATE: 1/15/17 CHECKED BY: Macris, Hendricks & Glascock, P.A. PROJECT No.: Wightman Road, Suite 0 PAGE; 10 Montgomery Village, MD Phone: (301) Fax: (301) WILDWOOD MANOR SHOPPING CENTER Micro-Bioretention Design Facility MB-2 Site Data: HSG A B C D Total Trib. Area (DA) 0 sq ft 0 sq ft 0 sq ft 13,400 sq ft 13,400 sq ft Imp. Area (I) 0 sq ft 0 sq ft 0 sq ft 8,500 sq ft 8,500 sq ft Determine R V : R V = the dimensionless volumetric runoff coefficient = (I) where I is percent impervious cover = (63.43%) = 0.62 Maximum Runoff Volume: V = (P x R V x A) / = (2.6 x 0.62 x 13400) / = 1,803 cu ft Upstream ESDv Provided= 0 cu ft Maximum Runoff Volume = 1,803 cu ft Effective Drainage Area: Upstream ESD V Provided = 0 cu ft or 0% of Maximum Runoff Volume Effective Drainage Area = x 100% = sq ft Design Equations: From 2000 Maryland Stormwater Design Manual ESDv = (P E )(R V )(A) P E = (ESDv)() (Rv)(A) Facility Design: A f = 2,000 sq ft (14.9% DA) Bottom Storage Area = 2,000 sq Elev ' Top Storage Area = 2,300 sq Elev ' Storage Depth = 0.50' Temp. Ponding Volume = 1,075 cu ft Planting Media Depth = 2.0 ft (2.0'-3.5') Sand Layer Depth = 0.5 ft Porosity (n) = 0.40 Media Storage Volume = 2,000 cu ft Total ESDv Provided = 3,075 cu ft ESDv exceeds Max. Runoff Volume Total ESDv Provided = 1,803 cu ft P E = ()(ESDv) (Rv)(A) = ()(1803) (0.62)(13400) P E = 2.60 in Enhanced (Y or N): N

16 Determine RE V : Re V = Groundwater Recharge volume component of ESD V (S)(R V )(A) = (0.06'')(0.62)(13400) = = 42 CU FT SOIL SPECIFIC RECHARGE FACTOR (S) HSG (S) AREA (sq ft) % AREA (S)(%A) A % 0.00 B % 0.00 C % 0.00 D , % 0.06 COMPOSITE S = 0.06 S = Re V = 0.06 in 42 cu ft Enhanced Filter - Stone Reservoir Design: A f = 2,000 sq ft Depth (D) = 1.0 ft Porosity (n) = 0.4 Vol. of Stone = 2,000 cu ft Vol. of Storage= 800 cu ft P E in Stone Reservoir = ()(ESDv) Total Facility Treatment Provided: (Rv)(A) = ()(800) (0.62)(13400) = 1.15 in ESDv treated by Filter = 1,803 cu ft ESDv treated by Enhancement = N/A Total ESDv Treatment = 1,803 cu ft P E treated by Filter = P E treated by Enhancement = Total P E Treatment = 2.60 in N/A 2.60 in

17 Determine 10-Year Discharge: Design Rainfall = 5.1 in Proposed Condition RCN = 91.4 Runoff = 4. in Proposed Condition Tc = 0.10 Hours Initial Abstraction = Ia = (200/91.4) -2 = Ia/P = (0.188)/5.1 IN = tc = 0.1 Hours or 0.10 Hours Minimum From TR55: qu 1010 CSM/IN OR CFS/AC/IN Determine 10-Year WSEL: qi = (4. IN)(1.578 CFS/AC/IN)(0.31 Ac.) = 2 CFS Inlet Weir Crest = ' Inlet Weir Length = 5.0' c = 3.1 Q 10 = 2.0 CFS Q = c * L * H 1.5 H = WSEL 10 = 0.26' '

18 DATE: 1/15/17 CHECKED BY: Macris, Hendricks & Glascock, P.A. PROJECT No.: Wightman Road, Suite 0 PAGE; 11 Montgomery Village, MD Phone: (301) Fax: (301) WILDWOOD MANOR SHOPPING CENTER Micro-Bioretention Design Facility PB-1 Site Data: HSG A B C D Total Trib. Area (DA) 0 sq ft 0 sq ft 0 sq ft 20,000 sq ft 20,000 sq ft Imp. Area (I) 0 sq ft 0 sq ft 0 sq ft 16,000 sq ft 16,000 sq ft Determine R V : R V = the dimensionless volumetric runoff coefficient = (I) where I is percent impervious cover = (80%) = 0.77 Maximum Runoff Volume: V = (P x R V x A) / = (2.6 x 0.77 x 20000) / = 3,337 cu ft Upstream ESDv Provided= 0 cu ft Maximum Runoff Volume = 3,337 cu ft Effective Drainage Area: Upstream ESD V Provided = 0 cu ft or 0% of Maximum Runoff Volume Effective Drainage Area = x 100% = sq ft Design Equations: From 2000 Maryland Stormwater Design Manual ESDv = (P E )(R V )(A) P E = (ESDv)() (Rv)(A) Facility Design: A f = 460 sq ft (2.3% DA) Bottom Storage Area = 460 sq Elev 0.00' Top Storage Area = 460 sq Elev 1.00' Storage Depth = 1.00' Temp. Ponding Volume = 460 cu ft Planting Media Depth = 3.5 ft (2.0'-3.5') Sand Layer Depth = 0.5 ft Porosity (n) = 0.40 Media Storage Volume = 736 cu ft Total ESDv Provided = 1,196 cu ft P E = ()(ESDv) (Rv)(A) = ()(1196) (0.77)(20000) P E = 0.93 in Enhanced (Y or N): N

19 DATE: 1/15/17 CHECKED BY: Macris, Hendricks & Glascock, P.A. PROJECT No.: Wightman Road, Suite 0 PAGE; Montgomery Village, MD Phone: (301) Fax: (301) WILDWOOD MANOR SHOPPING CENTER Micro-Bioretention Design Facility PB-2 Site Data: HSG A B C D Total Trib. Area (DA) 0 sq ft 0 sq ft 0 sq ft 20,000 sq ft 20,000 sq ft Imp. Area (I) 0 sq ft 0 sq ft 0 sq ft 20,000 sq ft 20,000 sq ft Determine R V : R V = the dimensionless volumetric runoff coefficient = (I) where I is percent impervious cover = (100%) = 0.95 Maximum Runoff Volume: V = (P x R V x A) / = (2.6 x 0.95 x 20000) / = 4,117 cu ft Upstream ESDv Provided= 1,340 cu ft Maximum Runoff Volume = 2,777 cu ft Effective Drainage Area: Upstream ESD V Provided = 1340 cu ft or 32.55% of Maximum Runoff Volume Effective Drainage Area = x 67.45% = sq ft Design Equations: From 2000 Maryland Stormwater Design Manual ESDv = (P E )(R V )(A) P E = (ESDv)() (Rv)(A) Facility Design: A f = 700 sq ft (3.5% DA) Bottom Storage Area = 700 sq Elev ' Top Storage Area = 700 sq Elev ' Storage Depth = 1.00' Temp. Ponding Volume = 700 cu ft Planting Media Depth = 3.5 ft (2.0'-3.5') Sand Layer Depth = 0.5 ft Porosity (n) = 0.40 Media Storage Volume = 1,0 cu ft Total ESDv Provided = 1,820 cu ft P E = ()(ESDv) (Rv)(A) = ()(1820) (0.95)(13490) P E = 1.70 in Enhanced (Y or N): N

20 DATE: 2/3/17 CHECKED BY: Macris, Hendricks & Glascock, P.A. PROJECT No.: Wightman Road, Suite 0 PAGE: 13 Montgomery Village, MD Phone: (301) Fax: (301) WILDWOOD MANOR SHOPPING CENTER (Effective Drainage Area To SF1) UNIFIED STORMWATER SIZING CRITERIA TREATMENT VOLUME DETERMINATION CHANNEL PROTECTION VOLUME (Cpv) DESIGN RAINFALL (P) = 2.6 in DRAINAGE AREA (A) = SF PROPOSED CONDITION RCN = 89.0 (Unmanaged RCN for Drainage Area) S = (1000/RCN) - 10 (Equation 2.3, TR-55, USDA NRCS 1986) = (1000/89 ) - 10 = 1.2 Q (P - 0.2S) 2 1 = (P + 0.8S) ( *1.2) 2 = ( *1.2) = 1.56'' V design = Q 1 x A = 1.56'' x SF x FT/IN = 3835 CF Effective Drainage Area Summary Table: SF-1 Contributing DA = 0.68 AC Contributing DA Runoff Volume = 3,835 CF ESDv Provided = 1,340 CF or 0.35% of Required ESDv % remaining ESDv Required = 65% Effective DA = 0.4 AC (Contrib. DA x % Remain. ESDv Req'd) Max runoff to SF-1 = 2,493 CF CPv Remainder = 449 CF

21 MACRIS, HENDRICKS AND GLASCOCK, P.A WIGHTMAN ROAD SUITE 0 DATE: 03/06/18 MONTGOMERY VILLAGE, MARYLAND CHECKED BY: JOB NO.: PAGE: 14 STAGE-STORAGE COMPUTATIONS FOR CMP STORAGE SYSTEM PIPE SYSTEM DIAMETER = CROSS SECTIONAL AREA OF PIPE = EFFECTIVE LENGTH OF PIPE = LOWER INVERT IN PIPE SYSTEM = UPPER INVERT IN PIPE SYSTEM = 4.0 FT CMP PIPE SYSTEM.57 FT 50 FT FT FT H1 1 AREA A1 2 H2 3 AREA A2 4 LENGTH VOLUME 5 VOLUME ELEVATION FT (D/S) FT (U/S) (A1+A2)/2 FT FT 3 AC-FT FT FT FT FT FT FT FT FT FT FT FT FT FT FT FT FT FT FT H1 = ELEVATION - LOWER INVERT IN PIPE SYSTEM 2. AREA A1 = AREA OF PONDED WATER AT LOWER END OF PIPE = Dia 2 x A/Dia 2 (FOR H1/Dia FROM ATTACHED TABLE) 3. H2 = ELEVATION - UPPER INVERT IN PIPE SYSTEM 4. AREA A2 = AREA OF PONDED WATER AT UPPER END OF PIPE = Dia 2 x A/Dia 2 (FOR H2/Dia FROM ATTACHED TABLE) 5. VOLUME = AVERAGE AREA x EFFECTIVE LENGTH

22 MACRIS, HENDRICKS AND GLASCOCK, P.A WIGHTMAN ROAD, SUITE 0 DATE: 3/6/2018 MONTGOMERY VILLAGE, MD JOB NO.: PAGE: 15 WILDWOOD MANOR SHOPPING CENTER - SF1 STORMFILTER DESIGN - PER M.D.E. SWM DESIGN MANUAL Section Filtering Treatment Criteria The required filter bed area (A f ) is computed using the following equation. A f = (WQ v ) (d f ) / [ (k ) (h f + d f ) (t f )] where: A f = Surface area of filter bed (ft 2 ) WQ v = water quality volume (ft 3 ) = 449 d f = filter bed depth (ft) = 0.58 k = coefficient of permeability of filter media (ft/day) = 8.7 h f = average height of water above filter bed (ft) = 0.75 t f = design filter bed drain time (days)* = 1.67 * 1.67 days is recommended maximum for sand filters. so: A f = 13.5 sqft Then given a surface area of 7.3 ft 2 per each cartridge: Number of Stormfilter Cartridges Required = 2