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Home My WebLink About200518 Stormwater Design Report_04-08-2021 INTRODUCTION The Midwest Welding and Machine shop site plan consists of a 21,741 sq. ft. building and associated improvements located on Lot 9, Block 2 of Nelson Meadows Subdivision in Bozeman, Montana. A combination of site grading, curb and gutter, curb inlet, riser inlet, dry well, Duraslot surface drain and underground Stormtech SC-310 storage chambers will be used to manage stormwater runoff for the development of the site. The proposed underground Stormtech SC-310 stormwater storage system and dry well were sized for the 10-year, 2-hour storm and checked for the half inch requirement. Supporting stormwater calculations are attached to this report. A Drainage Area Map is included in Appendix A. Calculations for each individual drainage area are included in Appendix B. Groundwater depth information is included in Appendix C. Excerpts from the original Nelson Meadows Subdivision Stormwater Report are included in Appendix D. A Stormwater Facilities Inspection and Maintenance Plan is included in Appendix E. DRAINAGE AREAS Drainage Area 1 Drainage Area 1 consists of the largest portion of the site including the west portion of the parking lot and landscaping and majority of the proposed building. Runoff from this drainage area flows via curb and gutter and underground storm drain piping from the roof downspouts to Infiltration System #1 (Stormtech SC-310) at the northwest corner of the site. The proposed Stormtech infiltration chambers are designed to detain stormwater runoff using the arch-shaped chambers and void space in the surrounding washed rock while the runoff infiltrates into the ground. The footprint of these chambers will be over-excavated down to native gravels to remove any existing slow-draining layer of soil beneath the chambers. This excavation will be back-filled with a well- draining gravel to ensure infiltration. The chambers were sized by applying an infiltration rate for native gravel subgrades to the footprint area of the chambers to determine the discharge (infiltrate rate) from each system. This discharge rate was then compared to the proposed inflow rates from the contributing areas to the systems during the 10-year 2-hour storm event to determine the required detention volume for the system. The half inch requirement was also checked; however, it was found that the 10-year, 2-hour storm governed the design and required 1,560 cubic feet of storage. 1,694 cubic feet of storage is provided in Infiltration System #1 including the surrounding washed rock using a stone porosity of 40%. The gravel infiltration rate used for these sizing calculations is 3.9 inches per hour. This infiltration rate was calculated from the infiltration rate of 2.6 inches per hour for gravel per the DEQ Circular- 8, Appendix C, Table 2, and was increased by 50% because pre-treatment is provided to the chambers in the form of the isolator row. This infiltration rate of 3.9 inches/hour is believed to be extremely conservative. Recent stormwater designs on other projects within the City with sub- surface infiltration systems have included percolation tests to verify on-site infiltration rates, and produced rates of 40-100inches/hour. Drainage Area 2 Drainage Area 2 consists of the portion of the parking lot and landscaping south of the building. Runoff from this drainage area flows via curb and gutter and a storm drain pipe located underneath a Duraslot surface drain to a 24” riser inlet. The riser inlet serves as a method of pre-treatment for the adjacent drywell which it flows into. The proposed Drywell #1 is designed to retain stormwater runoff in the slotted manhole and within the void space in the surrounding washed rock. The footprint of the drywell will be over-excavated down to native gravels to remove any existing slow-draining layer of soil beneath the chambers. This excavation will be back-filled with a well- draining gravel to ensure infiltration. This system was sized for the 10-year, 2-hour storm and was checked for the half inch requirement. It was found that the 10-year, 2-hour storm governed the design and required 1,074 cubic feet of storage. 1,083 cubic feet of storage is provided in Drywell #1 including the surrounding washed rock using a stone porosity of 40%. Drainage Area 3 Drainage Area 3 consists of a small portion of the site including a portion of the building and the landscaped area between the building and Nelson Road. Runoff from this drainage area flows from the roof downspout across the landscaped area and into the Nelson Road Right-of-Way (R.O.W.). The original Nelson Meadows Subdivision Stormwater Design Report did not account for the future development of the lots within the subdivision. Instead, the subdivision stormwater infrastructure was sized for the R.O.W.s and portions of the existing un-developed lots that naturally drain into the R.O.Ws. A C coefficient for existing pasture land of 0.23 was used in the original calculations for the portions of the lots that naturally drain into the R.O.W.s. It was determined using AutoCAD that the approximate area of Lot 9, Block 2 that was accounted for as existing pasture land was 0.62 acres. Using 0.62 acres and a C coefficient of 0.23, the runoff for the 10-year 2-hour storm was calculated to be 421 cubic feet. The runoff from Drainage Area 3 was calculated to be 364 cubic feet. Therefore, it is acceptable to allow the runoff from Drainage Area 3 to flow into the Nelson Road R.O.W. Drainage Areas 4 and 5 Drainage Areas 4 and 5 consists of sections of 5-foot-wide concrete sidewalk on the north side of the building. The runoff from these sidewalks will flow directly into two separate trench drains (Trench Drain #1 and #2). Each trench drain was sized for the 10-year, 2-hour storm and was checked for the half inch requirement. It was found that the 10-year, 2-hour storm governed the design and required 27 cubic feet of storage for Trench Drain #1 and 31 cubic feet of storage from Trench Drain #2. 71 cubic feet of storage is provided in Trench Drain #1 and 88 cubic feet of storage is provided in Trench Drain #2 including the surrounding washed rock using a stone porosity of 40%. Drainage Area 6 Drainage Area 6 consists of portions of the north landscaped area between the building and property line and west portion of the lot which contains the 12’ all-weather access lane for maintenance of the sanitary sewer main. These areas will drain with their historical drainage pattern with the same volume as before construction. Currently the lot has slight vegetative cover and drains generally to the north. After construction it will be landscaped on the north portion of the lot and the gravel access road will remain. Therefore, Drainage Area #6 remains un-changed from historical drainage patterns and no stormwater improvements are located in this area. DEPTH TO GROUNDWATER Groundwater monitoring was performed by Morrison Maierle in 2018 for Nelson Meadows Subdivision. The monitoring wells nearest to Lot 9, Block 2 were used to verify that the proposed stormwater infrastructure for Midwest Welding and Machine is above the high groundwater table. Monitoring Well (MW) #6 was used for Infiltration System #1 and MW #2 was used for Dry Well #1. MW #6 had a measured high groundwater recording of approximately 5 feet below ground surface in April 2018. MW #2 had a measured high groundwater recording of approximately 5.5 feet below ground surface in April 2018. Approximately 2.25 feet of separation from groundwater is provided for Infiltration System #1. Approximately 0.05 feet of separation is provided for Dry Well #1. It is neither economical nor practical to ensure 3 feet separation between the high groundwater table and the bottom of the underground stormwater storage systems. See Appendix C for more groundwater depth information. G:\C&H\20\200518\Design Reports\Storm\200518 Stormwater Design Report.Docx APPENDIX A DRAINAGE AREA MAP APPENDIX B DRAINAGE AREA, INFILTRATION/RETENTION SYSTEM AND PIPE SIZING CALCULATIONS DRAINAGE AREA #1 INFILTRATION SYSTEM #1 1. Calculate Area and Weighted C Factor Contributing Area DA #C Area (ft 2)C * AreaHardscape10.95 38097 36192 Landscape 1 0.20 1525 305Total3962236497 A = Area (acres)0.91 C = Weighted C Factor 0.92 2. Calculate Infiltration Rate Existing Soil Condition =Native gravel Infiltration Rate (in./hr) =2.6 Per DEQ Circular 8, App C Infiltration Rate (in./hr) =3.9 increase by 50% if using pre-treatmentInfiltration Rate (ft/sec) =0.0000903 Infiltration Length (ft) =49.22Infiltration Width (ft) =28.17 Infiltration Area (sf) =1386.53 Total Area (acres) =0.91 acres Weighted C =0.92 Discharge Rate (cfs) =0.13 cfs Inf. Rate (ft/sec) x Inf. Area (sf) 3. Calculate Required Stormtech Volume Duration(min)Duration (hrs)Intensity (in/hr)Qin (cfs)Runoff Volume Release Volume Required Storage (ft3) 108 1.80 0.44 0.37 2371.4 811.32 1560.04 109 1.82 0.43 0.36 2379.0 818.83 1560.19 110 1.83 0.43 0.36 2386.6 826.34 1560.29 111 1.85 0.43 0.36 2394.2 833.85 1560.35 112 1.87 0.43 0.36 2401.7 841.37 1560.37 113 1.88 0.42 0.36 2409.2 848.88 1560.34 114 1.90 0.42 0.35 2416.7 856.39 1560.27 115 1.92 0.42 0.35 2424.1 863.90 1560.15 116 1.93 0.42 0.35 2431.4 871.42 1560.00 117 1.95 0.41 0.35 2438.7 878.93 1559.80 Check the half inch requirement (per DSSP II.A.4) 1. Determine Area of Hardscape within Drainage Area #1 Contributing Area Area (ft2 ) Hardscape 38097 2. Calculate 1/2" runoff volume over hardscape (aka Runoff Reduction Volume [RRV] as calculated in Montana Post- Construction Storwater BMP Manual - Equation 3-1) RRV = [P*Rv*A]/12 P = Water quality rainfall depth 0.50 inches Rv = Dimensionless runoff coefficient 0.92 0.05 + 0.9*I I = Percent impervious cover (decimal)0.96 decimal A = Entire drainage area 0.91 acres RRV = Runoff Reduction Volume 0.035 acre-ft RRV = Runoff Reduction Volume 1511 cubic feet Because the runoff volume from the 10-yr, 2-hr storm (for flood control) is greater than the runoff volume produced by the half inch rainfall (for water quality) the proposed InfiltrationSystem #1 is sized to handle the larger volume (1,560 cf). DRAINAGE AREA #1 ROOF DOWNSPOUT PIPE ROUTED TO INFILTRATION SYSTEM #1 1. Summary of Roof Area and C Factor Contributing Area DA #C Area (ft2 )C * Area Hardscape 1 0.95 17661 16778 Total 17661 16778 A = Area (acres)0.41 C = Weighted C Factor 0.95 2. Calculate Tc (Time to Concentration) Tc Overland Flow (on roof with pitch of 1/4" to 12") Tc = 1.87 (1.1-CCf)D1/2/S1/3 Storm S = Slope of Basin (%)2.1%Return (yrs)CfC = Rational Method Runoff Coefficient 0.95 2 to 10 1 Cf = Frequency Adjustment Factor 1.1 11 to 25 1.1 D = Length of Basin (ft)81 26 to 50 1.251 to 100 1.25 Tc Overland Flow (minutes)1.3 Tc Total =5.0 (5 minute minimum) 3. Calculate Flow (Rational Formula)Q = CIA C = Weighted C Factor 0.95 (calculated above) I = 0.78 Tc-0.64 (in/hr)3.83 (25-yr storm) A = area (acres)0.41 (calculated above) Q 25-yr Flow Rate (cfs)=1.47 MANNING'S EQUATION FOR PIPE FLOW (PROVIDED CAPACITY)Pipe: 1 Location:Roof Downspout pipe INPUT D=8 inchesd=7.50 inchesMannings Formula n=0.013 mannings θ=57.7 degrees Q=(1.486/n)ARh2/3S1/2 S=0.0124 slope in/in R=A/P A=cross sectional area P=wetted perimeter V=(1.49/n)Rh2/3S1/2 S=slope of channel Q=V x A n=Manning's roughness coefficient Solution to Mannings Equation Area,ft2 Wetted Perimeter, ft Hydraulic Radius, ft velocity ft/s flow, cfs PVC 0.013 0.34 1.76 0.19 4.43 1.51 PE (<9"dia)0.015 PE (>12"dia)0.02 PE(9-12"dia)0.017 CMP 0.025 ADS N12 0.012 HCMP 0.023 Conc 0.013 Manning's n-values d θ D DRAINAGE AREA #2 DRY WELL #1 1. Calculate Area and Weighted C Factor Contributing Area DA #C Area (ft 2)C * Area Hardscape 2 0.95 16240 15428Landscape20.20 2514 503Total1875415931 A = Area (acres)0.43 C = Weighted C Factor 0.85 2. Calculate Required Volume Q = CIA V=7200Q C = Weighted C Factor 0.85I = intensity (in/hr) 0.41 (10 yr, 2hr storm)A = Area (acres)0.43Q = runoff (cfs)0.15 V = REQUIRED VOL (ft3)1074 Check the half inch requirement (per DSSP II.A.4) 1. Determine Area of Hardscape within Drainage Area #2 Contributing Area Area (ft 2)Hardscape 16240 2. Calculate 1/2" runoff volume over hardscape (aka Runoff Reduction Volume [RRV] as calculated in Montana Post- Construction Storwater BMP Manual - Equation 3-1) RRV = [P*Rv*A]/12 P = Water quality rainfall depth 0.50 inches Rv = Dimensionless runoff coefficient 0.83 0.05 + 0.9*I I = Percent impervious cover (decimal)0.87 decimal A = Entire drainage area 0.43 acres RRV = Runoff Reduction Volume 0.015 acre-ft RRV = Runoff Reduction Volume 648 cubic feet Because the runoff volume from the 10-yr, 2-hr storm (for flood control) is greater than the runoff volume produced by the half inch rainfall (for water quality) the proposed retention facility #1 is sized to handle the larger volume (1,074 cf). 1. Calculate Drywell Volume Porous Media in Drywell Washed Rock Porosity of Media 40.00% Media Offset Dist. From Drywell (ft)12.1 Media Void VolumeMedia Bed Depth (below MH)0.05 Media Volume (ft2)2581.12 Media Storage Volume (ft2 1032 Manhole Volume Manhole Volume (ft3)50 Proposed Manhole Depth (ft)4 (round up to nearest 3") Provided Storage Volume (ft3)1,083 DRAINAGE AREA #2 HDPE PIPE BELOW DURASLOT TO DRY WELL #1 1. Calculate Area and Weighted C Factor Contributing Area DA #C Area (ft2 )C * Area Hardscape 2 0.95 16240 15428 Landscape 2 0.20 2514 503Total1875415931 A = Area (acres)0.43 C = Weighted C Factor 0.85 2. Calculate Tc (Time to Concentration) Tc Overland Flow Tc = 1.87 (1.1-CCf)D1/2/S1/3 Storm S = Slope of Basin (%)0.9%Return (yrs)Cf C = Rational Method Runoff Coefficient 0.85 2 to 10 1 Cf = Frequency Adjustment Factor 1.1 11 to 25 1.1 D = Length of Basin (ft)118 26 to 50 1.2 51 to 100 1.25 Tc Overland Flow (minutes)3.4 Tc Total =5.0 (5 minute minimum) 3. Calculate Flow (Rational Formula) Q = CIA C = Weighted C Factor 0.85 (calculated above) I = 0.78 Tc-0.64 (in/hr)3.83 (25-yr storm) A = area (acres)0.43 (calculated above) Q 25-yr Flow Rate (cfs)=1.40 MANNING'S EQUATION FOR PIPE FLOW (PROVIDED CAPACITY)Pipe: 2 Location:HDPE pipe below Duraslot INPUT D=10 inchesd=9.38 inches Mannings Formula n=0.013 mannings θ=57.7 degrees Q=(1.486/n)ARh2/3S1/2 S=0.01 slope in/in R=A/P A=cross sectional area P=wetted perimeter V=(1.49/n)Rh2/3S1/2 S=slope of channel Q=V x A n=Manning's roughness coefficient Solution to Mannings Equation Area,ft2 Wetted Perimeter, ft Hydraulic Radius, ft velocity ft/s flow, cfs PVC 0.013 0.53 2.20 0.24 4.44 2.36 PE (<9"dia)0.015 PE (>12"dia)0.02 PE(9-12"dia)0.017 CMP 0.025 ADS N12 0.012 HCMP 0.023 Conc 0.013 Manning's n-values d θ D DRAINAGE AREA #3 RUNOFF VOLUME FROM DA #3 1. Calculate Area and Weighted C Factor Contributing Area DA #C Area (ft2 )C * Area Hardscape 3 0.95 5021 4770Landscape30.20 3117 623 Total 8138 5394 A = Area (acres)0.19 C = Weighted C Factor 0.66 2. Calculate Required Volume Q = CIA V=7200Q C = Weighted C Factor 0.66 I = intensity (in/hr) 0.41 (10 yr, 2hr storm)A = Area (acres)0.19 Q = runoff (cfs)0.05 V = REQUIRED VOL (ft3)364 Check the quantity of stormwater allocated from the subdivision design 1. Determine Area of portion of Lot 9 that was included in Nelson Road pond Contributing Area DA #C Area (ft2 )C * Area Existing Pasture Land NR-11 0.23 27136 6241 Total 27136 6241 A = Area (acres)0.62 C = Weighted C Factor 0.23 2. Calculate Volume allocated to Lot 9 from the Nelson Meadows Subdivision design Q = CIA V=7200Q C = Weighted C Factor 0.23 I = intensity (in/hr) 0.41 (10 yr, 2hr storm) A = Area (acres)0.62 Q = runoff (cfs)0.06 V = ALLOCATED VOL (ft3)421 Because the runoff volume from the 10-yr, 2-hr storm for DA #3 (which drains to the Nelson Road R.O.W.) is less than the runoff volume allocated to the 0.62 acre portion of Lot 9 from the Nelson Meadows Stormwater design it is allowable to have the runoff from DA #3 to flow into the Nelson Road R.O.W. DRAINAGE AREA #4 TRENCH DRAIN #1 1. Calculate Area and Weighted C Factor Contributing Area DA #C Area (ft 2 )C * Area Hardscape 4 0.95 384 365 Landscape 4 0.20 179 36 Total 563 401 A = Area (acres)0.01 C = Weighted C Factor 0.71 2. Calculate Required Volume Q = CIAV=7200Q C = Weighted C Factor 0.71 I = intensity (in/hr) 0.41 (10 yr, 2hr storm) A = Area (acres)0.013 Q = runoff (cfs)0.004 V = REQUIRED VOL (ft3)27 Check the half inch requirement (per DSSP II.A.4) 1. Determine Area of Hardscape within Drainage Area #4 Contributing Area Area (ft2)Hardscape 384 2. Calculate 1/2" runoff volume over hardscape (aka Runoff Reduction Volume [RRV] as calculated in Montana Post- Construction Storwater BMP Manual - Equation 3-1) RRV = [P*Rv*A]/12 P = Water quality rainfall depth 0.50 inches Rv = Dimensionless runoff coefficient 0.66 0.05 + 0.9*I I = Percent impervious cover (decimal)0.68 decimal A = Entire drainage area 0.01 acres RRV = Runoff Reduction Volume 0.000 acre-ft RRV = Runoff Reduction Volume 16 cubic feet Because the runoff volume from the 10-yr, 2-hr storm (for flood control) is greater than the runoff volume produced by the half inch rainfall (for water quality) the proposed Trench Drain #1 is sized to handle the larger volume (27 cf). 1. Calculate Trench Drain Volume Porous Media in Drywell Washed Rock Porosity of Media 40.00% Trench Depth 1.0Trench width 1.0 Trench Length 71 Trench Volume (ft3)71 DRAINAGE AREA #5 TRENCH DRAIN #2 1. Calculate Area and Weighted C Factor Contributing Area DA #C Area (ft 2 )C * Area Hardscape 5 0.95 475 451 Landscape 5 0.20 67 13 Total 542 464 A = Area (acres)0.01 C = Weighted C Factor 0.86 2. Calculate Required Volume Q = CIAV=7200Q C = Weighted C Factor 0.86 I = intensity (in/hr) 0.41 (10 yr, 2hr storm) A = Area (acres)0.012 Q = runoff (cfs)0.004 V = REQUIRED VOL (ft3)31 Check the half inch requirement (per DSSP II.A.4) 1. Determine Area of Hardscape within Drainage Area #5 Contributing Area Area (ft2)Hardscape 475 2. Calculate 1/2" runoff volume over hardscape (aka Runoff Reduction Volume [RRV] as calculated in Montana Post- Construction Storwater BMP Manual - Equation 3-1) RRV = [P*Rv*A]/12 P = Water quality rainfall depth 0.50 inches Rv = Dimensionless runoff coefficient 0.84 0.05 + 0.9*I I = Percent impervious cover (decimal)0.88 decimal A = Entire drainage area 0.01 acres RRV = Runoff Reduction Volume 0.000 acre-ft RRV = Runoff Reduction Volume 19 cubic feet Because the runoff volume from the 10-yr, 2-hr storm (for flood control) is greater than the runoff volume produced by the half inch rainfall (for water quality) the proposed Trench Drain #1 is sized to handle the larger volume (31 cf). 1. Calculate Trench Drain Volume Porous Media in Drywell Washed Rock Porosity of Media 40.00% Trench Depth 1.0Trench width 1.0 Trench Length 88 Trench Volume (ft3)88 APPENDIX C GROUNDWATER DEPTH INFORMATION N INTERSTATE 90 235 INTERSTATE 90 205 205 D D D D D D D D D D D D D INSTALL NEW 54" x 88" ARCP FESINVERT IN = 4593.6528 INSTALL NEW 54" x 88" ARCP FESINVERT OUT = 4592.0877 INSTALL ±156.0000 LF (TOTAL - 140 LF BID QTY)54" x 88" ARCP CULVERT @ ±1.0033% SLOPE INSTALL NEW 54" x 88" ARCP FESINVERT IN = 4587.1132 INSTALL NEW 54" x 88" ARCP FESINVERT OUT = 4585.9345INSTALL ±120.0000 LF (TOTAL - 104 LF BID QTY)54" x 88" ARCP CULVERT @ ±0.9822% SLOPE DD D D D D D NelsonRdV a l l e y C e n t e r E R d Fr o n t a g e R d WELL #4 WELL #3 WELL #5 WELL #11 WELL #12 WELL #6 WELL #2 WELL #7 WELL #1 WELL #8 WELL #9 WELL #10 engineerssurveyorsplannersscientists 2880 Technology Boulevard West Bozeman, MT 59718 Phone: (406) 587-0721 Fax: (406) 922-6702 STORM DRAIN FIG. 4:GROUNDWATER MONITORING WELLS SCALE:1" = 500' SUNSET MEMORI A L PARK MONTAN A DEPART M E N T OF TRANSP O R T A T I O N APPENDIX D EXCERPTS FROM NELSON MEADOWS SUBDIVISION STORMWATER DESIGN REPORT (2019) APPENDIX E STORMWATER FACILITIES INSPECTION AND MAINTENANCE PLAN INSPECTION AND MAINTENANCE FOR STORMWATER MANAGEMENT FACILITIES The owner shall be responsible for the maintenance of the stormwater drainage facilities within The Midwest Welding and Machine development. Storm Water Facilities: 1. Underground Stormtech SC-310 Infiltration System collect storm water runoff and store the water until it infiltrates into the ground. 2. Pipe Networks convey storm water to different discharge locations underground. 3. Inlets are facilities where storm water runoff enters a pipe network. Inlets include storm water manholes and drains. 4. Catch Basins are sumps typically located directly below storm water inlets and allow sediment to settle before storm water enters the pipe network. 5. Outlets are points where storm water exits a pipe network. Post Construction Inspection: 1. Use the attached Stormtech Isolator Row Operation & Maintenance manual to determine if maintenance is required on the system after construction is completed. 2. Observe that catch basins are clear of any material or obstructions in the drainage slots. Inspect these structures to ensure proper drainage following a storm event. Immediately identify and remove objects responsible for clogging if not draining properly. Semi-Annual Inspection: 1. Use the attached Stormtech Isolator Row Operation & Maintenance manual to determine if maintenance is required on the system semi-annually. 2. Check for grass clippings, litter, sediment, and/or debris in inlets and catch basins. Flush and/or vacuum storm water pipes if excessive material is observed in the facilities. Standard Maintenance: 1. Inspect and remove debris from catch basins. Use a vacuum truck to clean catch basins and Stormtech system. 2. Inspect for the following issues: differential accumulation of sediment, drain time, signs of petroleum hydrocarbon contamination (odors, oil sheen in pond water), standing water, trash and debris. Sediment accumulation: In most cases, sediment in a catch basin or a retention system does not contain toxins at levels posing a hazardous concern. However, sediments should be tested for toxicants in compliance with current disposal requirements and if land uses in the drainage area include commercial or industrial zones, or if visual or olfactory indications of pollution are noticed. Sediments containing high levels of pollutants should be disposed of in accordance with applicable regulations and the potential sources of contamination should be investigated and contamination practices terminated. Cost Estimate: Depending on the amount of rainfall in the given year, the cost to maintain the stormwater infrastructure will vary. The underground Stormtech system will need to be cleaned according to the attached Stormtech Isolator Row Operation & Maintenance manual. Cost of maintenance will be dependent on the frequency and estimates should be obtained from a local vacuum truck company. The applicant will be responsible for financing the maintenance of the stormwater infrastructure An company 2 THE MOST ADVANCED NAME IN WATER MANAGEMENT SOLUTIONS TM ECCENTRICHEADER MANHOLEWITHOVERFLOWWEIR STORMTECHISOLATOR ROW OPTIONAL PRE-TREATMENT OPTIONAL ACCESS STORMTECH CHAMBERS )(