HomeMy WebLinkAbout012 OxbowPH2_Stormwater ReportSTORMWATER DRAINAGE REPORT The Oxbow – Phase 2 The Oxbow Phase 2, Bozeman, Montana 59718
Block 2 – Lots 1, Cottonwood Subdivision (Site Plan P ackage E)
Block 1 – Lot 1, Cottonwood Subdivision (Site Plan Pa ckage F)
Block 1 – Lot 2, Cottonwood Subdivision (Site Plan Pa ckage G) Prepared For: Oxbow Land Holding LLC
Attn: Patrick Boel
Director of Development & Construction 1100 Main Idaho Street, Ste. 630 Boise, ID 83703 Prepared By: Cushing Terrell 411 E. Main Street, Ste. 101 Bozeman, MT 59715 www.cushingterrell.com Cushing Terrell Project No. Cottonwood_P2 October 18, 2024 Adam Schlegel, PE
Stormwater Drainage Report The Oxbow – Phase 2 Project No. Cottonwood_P2 cushingterrell.com i TABLE OF CONTENTS 1.0 INTRODUCTION ................................................................................................................................................. 1 1.1 Zoning ............................................................................................................................................................... 1 1.2 Existing Ground Cover and Vegetation ................................................................................................ 2 1.3 Topographic Features, and Slopes ......................................................................................................... 2 1.4 FEMA Floodplain Classification................................................................................................................ 2 1.5 Major Drainage Ways and Receiving Channels ................................................................................. 2 1.6 Existing Drainage Facilities ........................................................................................................................ 2 1.7 Wetlands .......................................................................................................................................................... 2 1.8 Geologic Features and Geotechnical Data .......................................................................................... 2 2.0 STORM DRAINAGE DESIGN .......................................................................................................................... 3 2.1 Methodology .................................................................................................................................................. 3 2.2 Pre-Development Conditions................................................................................................................... 4 2.3 Post-Development Conditions ................................................................................................................ 4 2.4 Post-Development Conveyance .............................................................................................................. 5 2.5 Post-Development BMP Design .............................................................................................................. 6 3.0 CONCLUSION ..................................................................................................................................................... 6 4.0 OPERATIONS AND MAINTENANCE ........................................................................................................... 6 4.1 HYDRODYNAMIC SEPARATOR (Annual) .............................................................................................. 6 4.2 PARKING/PAVEMENT AREAS (Bi-Annual) ........................................................................................... 7 4.3 LANDSCAPING/GROUNDS MAINTENANCE (Monthly) .................................................................. 7 4.4 CATCH BASIN/MANHOLES/INLETS ....................................................................................................... 7 4.5 PIPES .................................................................................................................................................................. 7 LIST OF FIGURES Figure 1.1: Location Map .............................................................................................................................................. 1 LIST OF TABLES Table 2.1: Site Plan Package E Runoff Coefficient ............................................................................................... 5 Table 2.2: Site Plan Package F & G Runoff Coefficient ..................................................................................... 5
Stormwater Drainage Report The Oxbow – Phase 2 Project No. Cottonwood_P2 cushingterrell.com ii APPENDICES Appendix A: Geotechnical Report Excerpts & Wetlands Appendix B: Pre-Development Conditions Appendix C: Post-Development Conditions Appendix D: Stormwater Treatment BMP
Stormwater Drainage Report The Oxbow – Phase 2 Project No. Cottonwood_P2 cushingterrell.com 1 1.0 INTRODUCTION Oxbow Land Holding proposes a multifamily housing development on Lots 1 and 2 of Block 1, and Lot 1 of Block 2 of the Cottonwood Subdivision, Phase 2, generally located east of Cottonwood Road and south of Huffine Lane. The housing development will utilize the existing subdivision stormwater detention facilities and connect to the existing stormwater infrastructure in Stafford Avenue and in an existing utility easement along the north of the property. The development has been separated into three different site plan packages (E, F, & G) which are a continuation from the recently completed Phase 1 packages (A, B, C, and D). Site plan package E covers Lot 1, Block 2. Package F covers Lot 1, Block 1. Package G covers Lot 2, Block 1. The following location map figure shows the boundaries the different site plan packages. The intent and purpose of this design report is to cover all three site plan package areas. Per the Cottonwood Subdivision stormwater management report prepared by Madison Engineering, dated March 2020, on-site developments are responsible for on-site stormwater conveyance and treatment of the first 0.5” of a 24-hour event. Additionally, on-site developments are required to maintain an overall runoff coefficient no greater than 0.7, without having to provide additional on-site stormwater detention facilities. Figure 1.1: Location Map 1.1 Zoning The subject properties are zoned R5: Residential Mixed-Use High Density District.
Stormwater Drainage Report The Oxbow – Phase 2 Project No. Cottonwood_P2 cushingterrell.com 2 1.2 Existing Ground Cover and Vegetation The subject properties are serviced by the existing subdivision streets and City utilities (water, sewer, and storm). Internal lot areas are bare and roughly graded, as a result of the construction of the off-site infrastructure some portions of the existing internal lot areas contain soil stockpiles from Phase 1 construction. 1.3 Topographic Features, and Slopes The subject properties slope from the south boundary along West Garfield Street toward the north property line. There are no known significant topographic features and/or steep slopes aside from the temporary soil stockpile areas that will be removed. 1.4 FEMA Floodplain Classification Per FEMA FIRM Panel #30031C0811D, there are no FEMA determined floodplains on or near the subject property. 1.5 Major Drainage Ways and Receiving Channels The major drainage way/ receiving channel of subdivision stormwater is Baxter Creek. An existing 18-inch RCP stormwater collection system in Cottonwood Road. 1.6 Existing Drainage Facilities The existing drainage facilities consist of the existing subdivision stormwater conveyance piping, inlets, and detention systems. 1.7 Wetlands Wetlands were previously located within the subdivision, but have since been mitigated as part of the subdivision infrastructure work (Corps No. NWO-2017-02234-MTH, Type: NWP 29). See Appendix A. 1.8 Geologic Features and Geotechnical Data See Appendix A for the geotechnical investigation excerpts from the report prepared by Allied Engineering Services, Inc. titled, “Cottonwood Subdivision Southeast Side of Huffine Ln/Cottonwood Rd Bozeman MT” dated January 2019. The full report can be provided upon request. Soils Overall, the report indicates the soils in the area consist of topsoil in the upper ten inches, underlain by eight inches of native silt/clay, underlain by approximately ten feet of a native sandy gravel. Borehole logs and an excerpt on subsurface conditions are located in Appendix A.
Stormwater Drainage Report The Oxbow – Phase 2 Project No. Cottonwood_P2 cushingterrell.com 3 Groundwater The report does indicate the presence of groundwater in the project area. The borehole logs indicate varying levels throughout the site from 3.7’ to 5.1’ below the ground surface. See Appendix A for excerpts. Infiltration Infiltration was not measured as part of the geotechnical investigation. 2.0 STORM DRAINAGE DESIGN The site storm drainage improvements are designed using the most recent edition of the “Design Standards And Specifications Policy, City of Bozeman, Montana (DSSP), dated March 2004, with last addendum being approved March 13, 2020” and the “Montana Post-Construction Storm Water BMP Design Guidance Manual (MPCSW),” dated September 2017. The MPCSW was developed for use to design water quality facilities for Montana’s MS4 Municipalities. The City of Bozeman maintains a MS4 permit for storm water runoff from the City. Overall, the new stormwater improvements will include new stormwater piping to convey site runoff from parking lots, landscape areas, and roof tops to a stormwater treatment unit to treat site runoff from the development. Stormwater will ultimately be conveyed from stormwater treatment unit(s) to the existing storm sewer network and ultimately existing stormwater detention facilities. 2.1 Methodology • Peak Runoff Rates (DSSP II-E): The rational method is used to calculate peak runoff rates for the sizing of storm pipes and other conveyance facilities. Table I-1 of the DSSP and DEQ8 are being referenced for the selection of runoff coefficients. o Landscaping cover (DEQ8): C=0.1 o Impervious (DEQ8): C=0.9 • Time of concentration is calculated per the DSSP and is limited to a minimum of five minutes. Runoff intensities are selected using the provided tables in the DSSP. • Conveyance Structures: Storm drain pipes and other conveyance facilities are sized for the 25-year event in accordance with the DSSP. Additionally, water quality volumes and water quality treatment flow rates are calculated using the methodology set forth in Sections 3.2 and 3.3 of the MPCSW. It should be noted that it is intended to separate runoff generated by non-pollutant generating surfaces (NPGS) from pollutant generating surfaces (PGS) prior to treatment facilities. Asphalt, concrete, and gravel areas are assumed to be PGS. Rooftops and landscaped areas are considered to be NPGS. Any
Stormwater Drainage Report The Oxbow – Phase 2 Project No. Cottonwood_P2 cushingterrell.com 4 NPGS surface flow that mixes with PGS surface flow, prior to the WQ BMP, will need to be treated and accommodated for in the BMP sizing. The following curve numbers (Table 3-6 HEC22) assume Type ‘B’ soils and were utilized in the water quality volume calculations. See Appendix A for site soils data. • Roofs, concrete, and asphalt surfaces: o CN = 98 • Gravel surfaces: o CN = 85 • Landscaped surfaces: o CN = 61 (Good condition) 2.2 Pre-Development Conditions As previously indicated, existing stormwater conveyance pipes are located in the adjacent subdivision streets and easements. Additionally, storm pipe service stubs are provided to the subdivision lots for future connection points to the various site developments. The existing piping conveys stormwater to the subdivision detention facilities. See Appendix B for pre-development conditions exhibit and other data pertaining to the subdivision stormwater system. In summary, the subdivision design and installation provides detention for the internal lots as long as the runoff coefficient is less than or equal to 0.7. Storm water quality treatment is to be provided for the proposed development upstream of the existing detention facilities. See Appendix B for excerpts from the Cottonwood Subdivision stormwater report relating to the internal lot runoff coefficient. 2.3 Post-Development Conditions See Appendix C for a post-development drainage basin map. Overall, there are multiple developed drainage basins that drain to on-site stormwater conveyance systems that ultimately connect to stormwater stub off of Stafford Avenue and to the storm drain just upstream of the existing stormwater detention facility. The following tables indicate that site plan packages E, F, and G all maintain an overall runoff coefficient below 0.7. As the total impervious requirement is within the overall Cottonwood Subdivision stormwater management plan, which assumed a runoff coefficient of 0.7, additional stormwater detention facilities are not required.
Stormwater Drainage Report The Oxbow – Phase 2 Project No. Cottonwood_P2 cushingterrell.com 5 Site Plan Package E Table 2.1: Site Plan Package E Runoff Coefficient Site Plan Package F & G Table 2.2: Site Plan Package F & G Runoff Coefficient 2.4 Post-Development Conveyance Site conveyance piping is sized for the 25-year event. Calculations are provided in Appendix C. The following lists indicate the conveyance piping details. Pipes are sufficiently to convey the 25 year, 24-hour event peak runoff events. • Material = PVC • Roughness Coefficient = 0.013 • Minimum Cleansing Velocity = 3 fps • Full Flow Capacity o 12” @ 0.5% = 2.5 cfs (3.2 fps) o 15” @ 0.5% = 4.6 cfs (3.7 fps) Site combination inlets are located at low points in the various drainage areas. Neenah R-3067 with bi-directional vane grates will be utilized to capture the runoff. According to the manufactures specification, the bi-directional vane grate has an open area of 2.7 square feet. Assuming a clogging factor of 50 percent and maximum runoff depth of six inches, the orifice BasinLandscape (sf) (C=.2)Asphalt/ Concrete/Roof (sf) (C=.9)Total (sf)Total (ac)Weighted Coefficent% ImperviousDEV-01E 29211 49177 78388 1.80 0.64 63%DEV-02E 10464 4050 14514 0.33 0.40 28%Total: 39675 53227 92902 2.13 0.60 57%POST-DEVELOPMENT BASINS - SITE PLAN PACKAGE EBasinLandscape (sf) (C=.2)Asphalt/ Concrete (sf) (C=.9)Total (sf)Total (ac)Weighted Coefficent% ImperviousDEV-01F&G 33564 97715 131279 3.01 0.72 74%DEV-02F&G 27462 4499 31961 0.73 0.30 14%Total: 61026 102214 163240 3.75 0.64 63%POST-DEVELOPMENT BASINS - SITE PLAN PACKAGE F&G
Stormwater Drainage Report The Oxbow – Phase 2 Project No. Cottonwood_P2 cushingterrell.com 6 equation (Q=0.6*A*sqrt(2*g*h) indicates a flow capacity of 4.5 cfs. The combination inlet located at drainage area low points has sufficient capacity to capture the various basin peak flows. 2.5 Post-Development BMP Design In order to provide the Owner with an effective and long-term solution, we are proposing a hydrodynamic separators for treatment of stormwater. Site plan package area E, F, and G will each require a hydrodynamic separator at the downstream end of the stormwater system, prior to connection to the existing storm drain / detention system. See Appendix C for stormwater treatment calculations. Package E Water Quality Treatment Unit Contech CDS 2014-C Required treatment flowrate = 0.40 cfs Treatment flow rate capacity = 0.70 cfs Package F&G Water Quality Treatment Unit #1 Contech CDS 2014-C Required treatment flowrate = 0.60 cfs Treatment flow rate capacity = 0.70 cfs Package E Water Quality Treatment Unit #2 Contech CDS 2014-C Required treatment flowrate = 0.24 cfs Treatment flow rate capacity = 0.70 cfs 3.0 CONCLUSION In conclusion, the proposed project will not increase peak runoff rates and volumes over what was estimated in the original subdivision stormwater management report. The proposed hydrodynamic separators will be sized to accommodate treatment of the first 0.5” of a 24-hour event meeting the on-site treatment requirement indicated in the subdivision stormwater management report. 4.0 OPERATIONS AND MAINTENANCE 4.1 HYDRODYNAMIC SEPARATOR (Annual) Clean and maintain as per the manufacture’s recommendations. In general, the structure should be inspected once a year for sediment loading in the sump. If the sediments and debris are at the removal level, a vactor truck should be utilized to clean out the structure.
Stormwater Drainage Report The Oxbow – Phase 2 Project No. Cottonwood_P2 cushingterrell.com 7 4.2 PARKING/PAVEMENT AREAS (Bi-Annual) Parking area is to be swept twice annually to remove excess sediment. Recommended sweeping should take place once after spring melt and prior to May 1, and once after August 15 and prior to October 15. 4.3 LANDSCAPING/GROUNDS MAINTENANCE (Monthly) Regular site maintenance should consist of removal of garbage and fallen debris from the parking lot on an as needed basis. Routine site maintenance will prevent debris from entering the storm water system and will improve storm water runoff quality over the long term. 4.4 CATCH BASIN/MANHOLES/INLETS Each catch basin/inlet includes a sump to allow sediments suspended in runoff to settle prior to entering storm pipes. These sumps should be annually inspected to ensure that inlets and piping inverts are free from blockage. Clean as required, or at least every three years. Vacuum trucks are commonly utilized to remove sediments and debris from catch basins, manholes, and inlets. 4.5 PIPES During annual inspections, the storm drain lines should also be examined to ensure that sediments are not impacting system performance. At a minimum, each structure should be cleaned out every three years or as required.
cushingterrell.com Appendix A: Geotechnical Report Excerpts & Wetlands
Cottonwood Subdivision
Huffine Lane / Cottonwood Road – Bozeman, MT
Project: 17-170
January 9, 2019
Allied Engineering Services, Inc. Page 6
Soil Conditions
The site can simply be characterized as being underlain by good, dense, clean sandy gravel beginning at
depths of 1.5 to 2.5 feet across the entire property. The gravels in this part of Bozeman are expected to
extend at least 100 feet deep and were confirmed to the 50-foot depth during the borehole drilling that
was conducted at the Bozeman Health Ambulatory Care Facility. The presence of the shallow gravel is
not surprising and has been pretty consistent in the other nearby areas we have recently investigated,
including the Town Pump site to the north, the Bozeman Health ACF to the northwest, and the
Cottonwood Road corridor to the north of Huffine Lane. Based on the eight test pits, the gravels have a
“clean” and sandy composition and are relatively small in size. Most of the gravel is a 3” to 4”-minus
material, but it does contain scattered cobbles up to 6 to 8 inches. The gravels were uniform through-
out the 10 to 11-foot test pit depths. See Figure 4 for the distribution of gravel depth across the site.
No random/foreign surface fill material was found in any of the test pits. All soils were native and in-
place. The site is blanketed by 9 to 12 inches of organic topsoil. Underlying the topsoil and overlying
the sandy gravel is a thin, intermediate layer of silt/clay. In most locations, the silt/clay was stiff to very
stiff and the lowermost 0.5-foot of the silt/clay contained some scattered small gravels (as the interface
with the alluvial sandy gravel was neared). Really, the only anomalies were found in TP-7, which was
located on the south side of the site. At this location, the same soil stratigraphy is present, but the
topsoil was more gravelly and the silt/clay was not only more gravelly, but very moist and much less
stiff. Provided in Table 3 is a summary of the soil conditions that were observed in the eight test pits.
The material descriptions and soil depths in the table match the data shown on the logs.
Table 3. Summary of Soil Conditions in Test Pits 1 - 8
TP # TP LOCATION NATIVE
TOPSOIL
NATIVE
SILT/CLAY
NATIVE
SANDY GRAVEL
1 N1/2 of Site, NW Corner 0.0’ - 1.0’ 1.0’ - 1.7’ 1.7’ - 10.0’
2 N1/2 of Site, NE Corner 0.0’ - 0.8’ 0.8’ - 2.0’ 2.0’ - 11.0’
3 N1/2 of Site, Center 0.0’ - 0.8’ 0.8’ - 1.8’ 1.8’ - 11.0’
4 Middle of Site, Center 0.0’ - 0.8’ 0.8’ - 1.5’ 1.5’ - 11.0’
5 Middle of Site, East Side 0.0’ - 0.8’ 0.8’ - 2.2’ 2.2’ - 11.0’
6 S1/2 of Site, SE Corner 0.0’ - 1.0’ 1.0’ - 2.3’ 2.3’ - 10.0’
7 S1/2 of Site, South Side 0.0’ - 1.0’ 1.0’ - 2.0’ 2.0’ - 10.0’
8 S1/2 of Site, West Side 0.0’ - 0.8’ 0.8’ - 2.2’ 2.2’ - 10.0’
Notes: 1) All soil measurements are depths below existing ground. 2) The native silt/clay is an unsuitable bearing material and shall be removed from under all footing locations.
3) The “target” bearing material for all foundation elements is the dense, native sandy gravel starting at 1.5’ to 2.5’.
4) Generally, the lower 0.5-foot of silt/clay (in all test pits) contained some scattered, small gravels. 5) In TP-7, the silt/clay was more gravelly, more moist, and less stiff (as compared to the other seven pits).
6) PVC monitoring wells were installed in TP-1 through TP-8 for future groundwater monitoring purposes.
Cottonwood Subdivision
Huffine Lane / Cottonwood Road – Bozeman, MT
Project: 17-170
January 9, 2019
Allied Engineering Services, Inc. Page 7
Provided below is a general description of the soil conditions encountered in the test pits. Following
each soil description is a statement regarding foundation bearing potential for the particular soil type.
• Native Topsoil: Generally consists of moist; medium stiff; black to dark brown; organic clayey
SILT with abundant roots.
The native topsoil is an unsuitable foundation bearing material that must be removed
from under all footings. In addition, all organic topsoil must be stripped/removed from
building footprints, utility trench locations, and under exterior slabs and asphalt areas.
• Native Silt/Clay: Generally consists of moist; stiff to very stiff; brown to orangish brown; sandy
SILT to sandy lean CLAY. The lower six inches (+/-) of silt/clay directly above the underlying
sandy gravel contains some scattered gravels. This transitional zone does not constitute clean
sandy gravel. In most pits, the silt/clay was on the dry side (due to relatively deep groundwater)
and consequently these soils were in a stiff to very stiff condition. Really the only exception was
in TP-7, which is located on the south side of the property and closest to the Farmers Canal. At
this location, the silt/clay was very moist and hence less stiff (ie. little softer than other areas).
The native silt/clay is an unsuitable foundation bearing material that must be removed
from under all footings.
• Native Sandy Gravel: Generally consists of slightly moist to wet; dense; brown; clean sandy
GRAVEL with abundant 3” to 4”-minus gravels and scattered 6” to 8”-minus cobbles. The on-site
gravel is a very good reserve of high-quality, sandy pitrun gravel and can be re-used as granular
structural fill under buildings or as sub-base gravel under asphalt areas.
The native, clean sandy gravel is the “target” foundation bearing material for all footings,
including perimeter, interior, and exterior footings.
Groundwater Conditions
During our test pits in January, groundwater was encountered at depths of 7.0 to 9.0 feet in the north,
central, and eastern parts of the site. Two pits (TP-7 and TP-8) were dug in the southwest portion of the
property where the surface terrain appeared to be a little lower. In both of these pits, the groundwater
table was shallower and found at 5.0 feet. The depth of the water relative to the top of the native sandy
gravel was generally 5.0 to 7.0 feet below the gravel in most areas, but decreased to 2.8 to 3.0 feet in
the southwest corner. See Figure 5 for the distribution of groundwater depth across the site.
Provided in Table 4 (on the following page) is a summary of the groundwater measurements in each of
the test pits, along with its positon relative to the top of the sandy gravel. As stated previously, all test
pits were backfilled with PVC monitoring wells. The approximate casing height of each well is also listed
in the table.
DEPARTMENT OF THE ARMY CORPS OF ENGINEERS, OMAHA DISTRICT HELENA REGULATORY OFFICE 10 WEST 15TH STREET, SUITE 2200 HELENA, MONTANA 59626 REPLY TO ATTENTION OF
Printed on Recycled Paper
January 19, 2018 Regulatory Branch
Montana State Program Corps No. NWO-2017-02234-MTH
Subject: TKO Enterprises (Vaughn Environmental Services) - Cottonwood Subdivision - Farmer's Canal - (Gallatin County)
Tyson Olsen TKO Enterprises Po Box 10303 Bozeman, Montana 59719 Dear Mr. Olsen: We are responding to your request for Nationwide Permit (NWP) verification for the above-mentioned project. The project is located at Latitude 45.665522°, Longitude -111.101588°, on or near Farmers Canal, within Section 15, Township 2 S, Range 5 E, Gallatin County, Montana.
Specifically, you requested authorization for the following work in waters of the U.S.:
Work Item Description
a.
Approximately 1,095 cubic yards (cy3) of native fill, 361 cy3 of 6-inch minus of uncrushed subbase course, 123 cy3 of 1.5-inch crushed gravel and 96 cy3 of
asphalt will be used to fill 0.307 acre of jurisdictional wetland in preparation to develop are for a residential subdivision. In addition, a 30-inch reinforced concrete culvert will be placed across Cottonwood road and will be extended 22 linear feet.
Based on the information you provided, the proposed activity, permanently affecting approximately 0.307 acre of jurisdictional Wetlands, is authorized by NWP 29, found in the
January 6, 2017, Federal Register (82 FR 1860), Reissuance of Nationwide Permits. Enclosed is a fact sheet that fully describes this NWP and lists the General and Regional Conditions that must be adhered to for this authorization to remain valid. Please note that deviations from the
original plans and specifications of your project could require additional authorization from this office.
In addition to conditions referenced above, the following special conditions apply: Condition Description
1.
Compensatory mitigation will be required for the 0.307 acre of unavoidable impacts to the wetlands adjacent to Farmers Canal. It has been determined that a practicable alternative to compensate for the aquatic resource functions that will be lost as a result of the permitted activity is mitigation by a third party provider. You have selected the Upper Missouri Mitigation Bank (SRI Missouri Headwaters,
-2-
Printed on Recycled Paper
LLC and Eco-Asset Management, LLC) as the party or parties responsible for the implementation, performance, and long-term management of the compensatory
mitigation project (332.3[l][1]) and so the following specific provisions apply: 1. Credits must be secured from a third party provider authorized by the U.S. Army Corps of Engineers to provide the mitigation;
2. Credits must come from the same service area as the permitted impacts, as specified in the authorized third party provider’s mitigation strategy or executed Banking Agreement; and The applicant must use the authorized third party provider’s credit multipliers in determining the amount of credits to be purchased (for Upper Missouri Mitigation Bank the multipliers are the same as for the Omaha District) namely (i) released credits are secured on a 1:1 ratio (1 impact debit to 1 mitigation credit), and (ii) after-the-fact credits are secured on a 1:1.5 ratio. In this case 0.307 acres of wetland mitigation credits will be required prior to working in Waters of the U.S., provide this office with documentation of completion of the transaction for securing credits. This can be a letter from the third party provider stating its acceptance of
responsibility for the specified mitigation.
You are responsible for ensuring that all work is performed in accordance with the terms and conditions of the NWP. If a contractor or other authorized representative will be conducting work on your behalf it is strongly recommended that they be provided a copy of this letter and the enclosed conditions. Failure to comply with the General and Regional Conditions of this NWP, or the project-specific special conditions of this authorization, may result in the suspension or revocation of your authorization and may be subject to appropriate enforcement action. The Montana Department of Environmental Quality has provided the enclosed CWA
Section 401 water quality certification for this NWP which includes General Conditions, all of which must be complied with for that certification to remain valid. This does not eliminate the need to obtain other permits that may be required by that agency. This verification is valid until March 18, 2022, when the existing NWPs are scheduled to be modified, reissued, or revoked. Furthermore, if you commence or are under contract to
commence this activity before the date that the relevant NWP is modified, reissued or revoked, you will have twelve (12) months from the date of the modification, reissuance or revocation of the NWP to complete the activity under the present terms and conditions unless discretionary authority has been exercised on a case-by-case basis to modify, suspend, or revoke the authorization in accordance with 33 CFR 330.4(e) and 33 CFR 330.5 (c) or (d). Project specific special conditions listed in this letter continue to remain in effect after the NWP verification expires, unless the district engineer removes those conditions. Activities completed under the authorization of an NWP which was in effect at the time the activity was completed continue to
be authorized by that NWP. In compliance with General Condition 30, we have enclosed a "compliance certification"
form, which must be signed and returned within 30 days of completion of the project, including
-3-
Printed on Recycled Paper
any required mitigation. Your signature on this form certifies that you have completed the work in accordance with the terms and conditions of the NWP. The Omaha District, Regulatory Branch is committed to providing quality and timely service to our customers. In an effort to improve customer service, please take a moment to complete our Customer Service Survey found on our website at: http://corpsmapu.usace.army.mil/cm_apex/f?p=regulatory_survey. If you do not have Internet access, you may call and request a paper copy of the survey that you can complete and return to us by mail or fax.
Please refer to identification number NWO-2017-02234-MTH in any correspondence concerning this project. If you have any questions, please contact Timothy McNew at Helena
Regulatory Office 10 West 15 Street, Suite 2200 Helena, Montana 59626, by email at
Timothy.M.McNew@usace.army.mil, or telephone at (406) 441-1375.
Sincerely, Todd N. Tillinger P.E. Montana Program Manager Enclosures: Compliance Certification NWP 29 Fact Sheet with Regional Conditions
Montana DEQ CWA Section 401 Water Quality Certification cc:
Barb Vaughn via e-mail: bvaughn@montana.com
-4-
Printed on Recycled Paper
COMPLIANCE CERTIFICATION Corps File Number: NWO-2017-02234-MTH Permit Type: NWP 29
Name of Permittee: Tyson Olsen County: Gallatin County, Montana Date of Issuance: January 18, 2018
Corps Project Manager: Timothy McNew Upon completion of the activity authorized by this permit and any mitigation required by the permit, sign this certification and return it to the following address: US Army Corps of Engineers Omaha District Helena Regulatory Office 10 West 15 Street, Suite 2200 Helena, Montana 59626 Please note that your permitted activity is subject to a compliance inspection by a U.S. Army
Corps of Engineers representative. If you fail to comply with the conditions of this permit, you are subject to permit suspension, modification, or revocation.
- - - - - - - - - - - - - - - - - - - - - - - - - - - I hereby certify that the work authorized by the above referenced permit has been completed in accordance with the terms and conditions of the said permit, and required mitigation was completed in accordance with the permit conditions. _______________________________________ Signature of Permittee
___________________ Date
cushingterrell.com Appendix B: Pre-Development Conditions
LP
PHNPHN
PHN
BASIN 2
BASIN 1
MADISON ENGINEERING
895 TECHNOLOGY BLVD SUITE 203
BOZEMAN, MT 59718
(406) 586-0262
SHEET
SD1.0
Pre-development
Cottonwood Subd.COTTONWOOD SUBDIVISION
BOZEMAN, MT
STORM WATER DRAINAGE EXHIBIT
PRE-DEVELOPMENT DELINEATION
SUMMARY TABLE
1 inch =
0
SCALE
200'
400100200
LPLP
PHNPHN
PHN
DA 4DA 1DA 2DA 3DA 7
DA 6
DA 5
DA 8
COTTONWOOD ROADALPHA DR.
W. GARFIELD ST.STAFFORDRESORT DR.LOY
A
L
D
RI
V
E
PARK BLVD.AVENUEMADISON ENGINEERING
895 TECHNOLOGY BLVD SUITE 203
BOZEMAN, MT 59718
(406) 586-0262
SHEET
SD1.1
Post-development
Cottonwood Subd.COTTONWOOD SUBDIVISION
BOZEMAN, MT
STORM WATER DRAINAGE EXHIBIT
POST-DEVELOPMENT DELINEATION
1 inch =
0
SCALE
200'
400100200
cushingterrell.com Appendix C: Post-Development Conditions
ststst st st st st ststststststXXXXXXXXXXXXXXXXXXXXXXXBUILDING #18APARTMENTTYPE A3,895 SFFFE = 4,853.43BUILDING #15APARTMENTTYPE C8,234 SFFFE = 4,854.76BUILDING #16
GARAGE
BUILDING #17
GARAGE S89° 50' 18"E 319.32'S0° 05' 08"E 247.25'N89° 54' 58"E 367.84'L=165.82,R=275.00D=34°32'51"S0° 04' 45"E 92.68'CONNECT TO EXISTING STORMDRAIN STUBSTSTSTSTSTSTST48
55 48544853485348544855ABCDABCD1234512345COPYRIGHT GGLO. ALL RIGHTS RESERVED.ORIGINAL SHEET SIZE IS 24"x36"SHEET NO.SHEET TITLEGGLO PROJECT MANAGER:GGLO PRINCIPAL IN CHARGE:PROJECT NO.:OWNER APPROVAL:MARKDATEDESCRIPTIONISSUE INFORMATIONPROJECT:OWNER:PROJECT ADDRESS:OXBOW APARTMENTS4650 W GARFIELD STBOZEMAN, MT 59718OXBOW APARTMENTSPHASE IIOXBOW LAND HOLDING LLC3112 LOS FELIZ BOULEVARDBOISE, ID 847032023075®REVISIONSA10.18.2024FORMAL SITE DEVELOPMENTREVIEWMARKDATEDESCRIPTION0102040SCALE: 1" = 20'NORTH1D.1EDEVELOPED DRAINAGE BASIN-EEXISTING SUBDIVISION STORMWATER SYSTEM (TYP.)D.1EDEVELOPEDDRAINAGE BASINSSITE PLAN PACKAGE 'E'BASIN DESIGNATIONPERCENT IMPERVIOUSBASIN AREA IN ACRESDEV-######DEV-01E1.863DEV-02E0.3328NEW STORMDRAININLETS AND PIPING, TYP
oh oh oh oh oh oh oh oh oh oh oh ohst
stststststststststgas gas gas gas gas gas gas gas gas gas
gas gas gas gas gas gas gas gas gas gas
bpbpbpbpbpbp
st
st ststststbtbtbtbtbtbt bt bt bt bt bt bt bt bt
st
st
st
st st
ststststststMag Nail with1.5" Disk 14535OPEN SPACE LOT 3STORM WATERFACILITY EASEMENTbtbpL=165.82,R=275.00
D=34°32'N89° 58' 35"E 382.39'L=77.93,R=195.00D=22°53'50"
S0° 05' 02"E 195.73'N89° 54' 58"E 222.02'S0° 05' 02"E 78.53'S89° 54' 58"W 145.00'N00° 05' 02"W 193.47'N00° 05' 02"W 78.53'BUILDING #19APARTMENTTYPE C8,234 SFFFE = 4854.40BUILDING #23APARTMENTTYPE A3,895 SFFFE = 4857.10BUILDING #20APARTMENTTYPE A3,895 SFFFE = 4853.50BUILDING #22APARTMENTTYPE C8,234 SFFFE = 4857.00BUILDING #21APARTMENTTYPE C8,234 SFFFE = 4854.60CCCCCCCCCCCCCC C C C C
ST ST ST DST D-2.8%-2.9%-1.0%-1.8%4854485348564855485
7
485
6
4854
4854.404853.504854.604857.104857.00STCI-01GRIM:4854.30IE OUT (N):4851.13 12"STMH-01FRIM:4853.38IE IN (S):4850.13 12"IE OUT (NW):4850.03 15"STORMWATER TREATMENT UNITSTCI-01FRIM:4851.88IE OUT (SW):4850.00 12"STORMWATER TREATMENT UNITSTMH-02FRIM:4851.51IE IN (NE):4849.50 12"IE IN (SE):4848.28 15"201 LF of 12" @ 0.50%91 LF of 15" @ 1.93%25 LF of 12" @ 2.00%ABCDABCD1234512345COPYRIGHT GGLO. ALL RIGHTS RESERVED.ORIGINAL SHEET SIZE IS 24"x36"SHEET NO.SHEET TITLEGGLO PROJECT MANAGER:GGLO PRINCIPAL IN CHARGE:PROJECT NO.:OWNER APPROVAL:MARKDATEDESCRIPTIONISSUE INFORMATIONPROJECT:OWNER:PROJECT ADDRESS:OXBOW APARTMENTS4650 W GARFIELD STBOZEMAN, MT 59718OXBOW APARTMENTSPHASE IIOXBOW LAND HOLDING LLC3112 LOS FELIZ BOULEVARDBOISE, ID 847032023075®REVISIONSA10.18.2024FORMAL SITE DEVELOPMENTREVIEWMARKDATEDESCRIPTION0153060SCALE: 1" = 30'NORTH1D.1FGDEVELOPED DRAINAGE BASINS F & GDEV-01FG2.2870EXISTING SUBDIVISION STORMWATER SYSTEM (TYP.)D.1 F&GDEVELOPEDDRAINAGE BASINSSITE PLAN PACKAGE 'F&G'BASIN DESIGNATIONPERCENT IMPERVIOUSBASIN AREA IN ACRESDEV-######DEV-03F&G0.7314DEV-02FG0.7489
Basin
Landscape
(sf)
(C=.2)
Asphalt/
Concrete/Roof (sf)
(C=.9)
Total
(sf)
Total
(ac)
Weighted
Coefficent
%
Impervious
DEV-01E 29211 49177 78388 1.80 0.64 63%
DEV-02E 10464 4050 14514 0.33 0.40 28%
Total: 39675 53227 92902 2.13 0.60 57%
Basin
Landscape
(sf)
(C=.2)
Asphalt/ Concrete
(sf) (C=.9)
Total
(sf)
Total
(ac)
Weighted
Coefficent
%
Impervious
DEV-01F&G 29974 69210 99184 2.28 0.69 70%
DEV-02F&G 3590 28505 32095 0.74 0.82 89%
DEV-03F&G 27462 4499 31961 0.73 0.30 14%
Total: 61026 102214 163240 3.75 0.64 63%
POST-DEVELOPMENT BASINS - SITE PLAN PACKAGE E
POST-DEVELOPMENT BASINS - SITE PLAN PACKAGE F&G
Area
(ac)P (in) Imperv.RvRRV
(ac-ft)
RRV
(cf)Q (in)CN Tc
(min)Ia Ia/P
qu
(csm/in)RTF (cfs)
Area
(ac)P (in) Imperv.RvRRV
(ac-ft)
RRV
(cf)Q (in)CN Tc
(min)Ia Ia/P
qu
(csm/in)RTF (cfs)
2.28 0.5 70% 0.68 0.06 2802 0.34 98.64 5 0.03 0.06 500 0.60
0.74 0.5 89%0.85 0.03 1136 0.42 985 0.04 0.08 500 0.24
Water Quality Treatment-01
Water Quality Treatment-02
SITE PLAN PACKAGE 'E'
50096.86 5 0.06 0.13
BASIN
Water Quality Flow Rate (RTF)
*WQV is calculated per Section 3.2.1 of Montana Post-Construction Storm Water
BMP Manual. Dated 2017.
*RTF is calculated per Section 3.3 of Montana Post-
Construction Storm Water BMP Manual. Dated 2017.
Water Quality Treatment (Basin
01E)1.80 0.5 57% 0.57 0.04 1847 0.40
BASIN
Runoff Reduction Volume (RRV/WQV)
0.28
Water Quality Flow Rate (RTF)Runoff Reduction Volume (RRV/WQV)
SITE PLAN PACKAGE 'F&G'
BASIN C Area
(ac)Tc (min)(i) in/hr Qcfs
DEV-01E 0.64 1.80 5.0 3.83 4.4
DEV-02E 0.40 0.33 5.0 3.83 0.5
BASIN C Area
(ac)Tc (min)(i) in/hr Qcfs
DEV-01F&G 0.69 2.28 5.0 3.83 6.0
DEV-02F&G 0.82 0.74 5.0 3.83 2.3
DEV-03F&G 0.30 0.73 5.0 3.83 0.8
Peak Runoff (25-yr/24-hr storm) - SITE PLAN PACKAGE 'E'
Peak Runoff (25-yr/24-hr storm) - SITE PLAN PACKAGE 'F&G'
Project Description
Friction Method Manning Formula
Solve For Full Flow Capacity
Input Data
Roughness Coefficient 0.013
Channel Slope 0.00500 ft/ft
Normal Depth 1.00 ft
Diameter 1.00 ft
Discharge 2.52 ft³/s
Results
Discharge 2.52 ft³/s
Normal Depth 1.00 ft
Flow Area 0.79 ft²
Wetted Perimeter 3.14 ft
Hydraulic Radius 0.25 ft
Top Width 0.00 ft
Critical Depth 0.68 ft
Percent Full 100.0 %
Critical Slope 0.00770 ft/ft
Velocity 3.21 ft/s
Velocity Head 0.16 ft
Specific Energy 1.16 ft
Froude Number 0.00
Maximum Discharge 2.71 ft³/s
Discharge Full 2.52 ft³/s
Slope Full 0.00500 ft/ft
Flow Type SubCritical
GVF Input Data
Downstream Depth 0.00 ft
Length 0.00 ft
Number Of Steps 0
GVF Output Data
Upstream Depth 0.00 ft
Profile Description
Profile Headloss 0.00 ft
Average End Depth Over Rise 0.00 %
Worksheet for 12" & 0.5%
10/29/2020 2:27:33 PM
Bentley Systems, Inc. Bentley FlowMaster V8i (SELECTseries 1) [08.11.01.03]
27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666 2of1Page
GVF Output Data
Normal Depth Over Rise 100.00 %
Downstream Velocity Infinity ft/s
Upstream Velocity Infinity ft/s
Normal Depth 1.00 ft
Critical Depth 0.68 ft
Channel Slope 0.00500 ft/ft
Critical Slope 0.00770 ft/ft
Worksheet for 12" & 0.5%
10/29/2020 2:27:33 PM
Bentley Systems, Inc. Bentley FlowMaster V8i (SELECTseries 1) [08.11.01.03]
27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666 2of2Page
Project Description
Friction Method Manning Formula
Solve For Full Flow Capacity
Input Data
Roughness Coefficient 0.013
Channel Slope 0.00500 ft/ft
Normal Depth 1.25 ft
Diameter 1.25 ft
Discharge 4.57 ft³/s
Results
Discharge 4.57 ft³/s
Normal Depth 1.25 ft
Flow Area 1.23 ft²
Wetted Perimeter 3.93 ft
Hydraulic Radius 0.31 ft
Top Width 0.00 ft
Critical Depth 0.87 ft
Percent Full 100.0 %
Critical Slope 0.00732 ft/ft
Velocity 3.72 ft/s
Velocity Head 0.22 ft
Specific Energy 1.47 ft
Froude Number 0.00
Maximum Discharge 4.91 ft³/s
Discharge Full 4.57 ft³/s
Slope Full 0.00500 ft/ft
Flow Type SubCritical
GVF Input Data
Downstream Depth 0.00 ft
Length 0.00 ft
Number Of Steps 0
GVF Output Data
Upstream Depth 0.00 ft
Profile Description
Profile Headloss 0.00 ft
Average End Depth Over Rise 0.00 %
Worksheet for 15" & 0.5%
11/4/2020 10:01:00 AM
Bentley Systems, Inc. Bentley FlowMaster V8i (SELECTseries 1) [08.11.01.03]
27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666 2of1Page
GVF Output Data
Normal Depth Over Rise 100.00 %
Downstream Velocity Infinity ft/s
Upstream Velocity Infinity ft/s
Normal Depth 1.25 ft
Critical Depth 0.87 ft
Channel Slope 0.00500 ft/ft
Critical Slope 0.00732 ft/ft
Worksheet for 15" & 0.5%
11/4/2020 10:01:00 AM
Bentley Systems, Inc. Bentley FlowMaster V8i (SELECTseries 1) [08.11.01.03]
27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666 2of2Page
cushingterrell.com Appendix D: Stormwater Treatment BMP
July 2016
GENERAL USE LEVEL DESIGNATION FOR PRETREATMENT (TSS) AND
CONDITIONAL USE LEVEL DESIGNATION FOR OIL CONTROL
For
CONTECH Engineered Solutions CDS® System
Ecology’s Decision:
Based on the CONTECH Engineered Solutions (CONTECH) application submissions for
the CDS® System, Ecology hereby issues the following use designations for the CDS storm
water treatment system:
1. General Use Level Designation (GULD) for pretreatment use, as defined in Ecology’s
2011 Technical Guidance Manual for Evaluating Emerging Stormwater Treatment
Technologies Technology Assessment Protocol – Ecology (TAPE) Table 2, (a) ahead of
infiltration treatment, or (b) to protect and extend the maintenance cycle of a basic,
enhanced, or phosphorus treatment device (e.g., sand or media filter). This GULD
applies to 2,400 micron screen CDS® units sized per the table below.
2. Conditional Use Level Designation (CULD) for oil and grease treatment. This CULD
applies to 2400 micron screen CDS units sized per the table above at the water quality
design flowrate as determined using the Western Washington Hydrology Model
(WWHM).
3. The following table shows flowrates associated with various CDS models:
CDS Model Water Quality Flow
cfs L/s Precast** Inline or Offline CDS 2015-4 0.7 19.8
CDS 2015-5 0.7 19.8
CDS 2020-5 1.1 31.2
CDS2025-5 1.6 45.3
CDS3020-6 2 56.6
CDS3030-6 3 85.0
CDS3035-6 3.8 106.2
CDS4030-8 4.5 127.4
CDS4040-8 6 169.9
CDS4045-8 7.5 212.4
CDS5640-10 9 254.9
CDS5653-10 14 396.5
CDS5668-10 19 538.1
CDS5678-10 25 7.08
Offline Only CDS3030-V 3 85 Precast** CDS4030-7 4.5 127.4
CDS4040-7 6 169.9
CDS4045-7 7.5 212.4
CDS5640-8 9 254.9
CDS5653-8 14 396.5
CDS5668-8 19 538.1
CDS5678-8 25 708
CDS5042 9 254.9
CDS5050 11 311.5
CDS7070 26 736.3
CDS10060 30 849.6
CDS10080 50 1416
CDS100100 64 1812.5
Cast
In
Place
CDS150134-22 148 4191.4
CDS200164-26 270 7646.6
CDS240160-32 300 8496.2
*Specially Designed CDS Units may be approved by Ecology on a on a site-by-site basis.
**Contact Contech for updated model numbers if PMIU, PMSU, PSW, PSWC are specified.
4. The water quality design flow rates are calculated using the following procedures:
Western Washington: For treatment installed upstream of detention or retention,
the water quality design flow rate is the peak 15-minute flow rate as calculated using
the latest version of the Western Washington Hydrology Model or other Ecology-
approved continuous runoff model.
Eastern Washington: For treatment installed upstream of detention or retention,
the water quality design flow rate is the peak 15-minute flow rate as calculated using
one of the three methods described in Chapter 2.2.5 of the Stormwater Management
Manual for Eastern Washington (SWMMEW) or local manual.
Entire State: For treatment installed downstream of detention, the water quality
design flow rate is the full 2-year release rate of the detention facility.
5. The pretreatment GULD has no expiration date; however, Ecology may amend or
revoke the designation.
6. The oil and grease CULD expires on December 31, 2017 unless extended by Ecology.
7. All designations are subject to the conditions specified below.
8. Properly designed and operated CDS systems may also have applicability in other
situations (example: low-head situations such as bridges or ferry docks), for TSS and
oil/grease removal where, on a case-by-case basis, it is found to be infeasible or
impracticable to use any other approved practice. Jurisdictions covered under the
Phase I or II municipal stormwater permits should use variance/exception procedures
and criteria as required by their NPDES permit.
9. Ecology finds that the CDS, sized according to the table above, could also provide water
quality benefits in retrofit situations.
Ecology’s Conditions of Use:
CDS systems shall comply with these conditions:
1. Design, assemble, install, operate, and maintain CDS Systems in accordance with
Contech’s applicable manuals and documents and the Ecology decision and conditions
specified herein. Ecology recommends use of the inspection and maintenance schedule
included as Attachment 1.
2. Discharges from the CDS System shall not cause or contribute to water quality
standards violations in receiving waters.
3. Contech commits to testing the QAPP accepted by Ecology on September 17, 2014 for
attaining a GULD for Oil Treatment. Ecology must review and approve additional
QAPPs for each CULD field site in Washington State. Choose sites to reflect the
product’s treatment intent.
4. Contech shall complete all required testing and submit a TER on pretreatment and oil
and grease removal for Ecology review by September 15, 2017.
5. Contech may request Ecology to grant deadline or expiration date extensions, upon
showing cause for such extensions.
Applicant: Contech Engineered Solutions
Applicant’s Address: 11835 NE Glen Widing Drive
Portland, OR 97220
Application Documents:
Contech Stormwater Solutions Application to: Washington State Department of Ecology
Water Quality Program for General Use Level Designation – Pretreatment Applications
and Conditional Use Level Designation – Oil Treatment of the Continuous Deflective
Separation (CDS™) Technology (June 2007)
Strynchuk, Royal, and England, The Use of a CDS Unit for Sediment Control in Brevard
County.
Walker, Allison, Wong, and Wootton, Removal of Suspended Solids and Associated
Pollutants by a CDS Gross Pollutant Trap, Cooperative Research Centre for Catchment
Hydrology, Report 99/2, February 1999
Allison, Walker, Chiew, O’Neill, McMahon, From Roads to Rivers Gross Pollutant
Removal from Urban Waterways, Cooperative Research Centre for Catchment Hydrology,
Report 98/6, May 1998
Quality Assurance Project Plan CDS® for Oil Treatment Performance Evaluation received
by Ecology January 15th 2013.
CDS with Sorbents Preliminary Report received by Ecology October 15, 2015.
Applicant’s Use Level Request:
General use level designation as a pretreatment device and conditional use level
designation as an oil and grease device in accordance with Ecology’s Stormwater
Management Manual for Western Washington.
Applicant’s Performance Claims:
Based on laboratory trials, the CDS™ System will achieve 50% removal of total suspended
solids with d50 of 50-μm and 80% removal of total suspended solids with d50 of 125-μm at 100%
design flowrate with typical influent concentration of 200-mg/L.
Contech can design the CDS™ system to achieve the effluent concentration less than 10 mg/L
for total petroleum hydrocarbons.
The CDS system equipped with standard oil baffle and addition of oil sorbent is effective in
control of oil and maintain the TPH level below the Ecology-specified level (<10-mg/L) for
applications in typical urban runoff pollution control.
Ecology’s Recommendation:
Ecology finds that:
The CDS™ system, sized per the table above, should provide, at a minimum, equivalent
performance to a presettling basin as defined in the most recent Stormwater Management
Manual for Western Washington, Volume V, Chapter 6.
Findings of Fact:
1. Laboratory testing was completed on a CDS 2020 unit equipped with 2400-m screen using
OK-110 sand (d50 of 106-μm) at flowrates ranging from 100 to 125% of the design flowrate
(1.1 cfs) with a target influent of 200 mg/L. Laboratory results for the OK-110 sand showed
removal rates from about 65% to 99% removal with 80% removal occurring near 70% of the
design flowrate.
2. Laboratory testing was completed on a CDS 2020 unit equipped with 2400-m screen using
“UF” sediment (d50 of 20 to 30-μm) at flowrates ranging from 100 to 125% of the design
flowrate (1.1 cfs) with a target influent of 200 mg/L. Laboratory results for the “UF”
sediment showed removal rates from about 42% to 94% removal with 80% removal
occurring at 5% of the design flowrate.
3. Laboratory testing was completed on a CDS 2020 unit equipped with 4700-m screen using
OK-110 sand (d50 of 106-μm) at flowrates ranging from 100 to 125% of the design flowrate
(1.1 cfs) with a target influent of 200 mg/L. Laboratory results for the OK-110 sand showed
removal rates from about 45% to 99% removal with an average removal of 83.1%.
4. Laboratory testing was completed on a CDS 2020 unit equipped with 4700-m screen using
“UF” sediment (d50 of 20 to 30-μm) at flowrates ranging from 100 to 125% of the design
flowrate (1.1 cfs) with a target influent of 200 mg/L. Laboratory results for the “UF”
sediment showed removal rates from about 39% to 88% removal with an average removal of
56.1%.
5. Contech completed laboratory testing on a CDS2020 unit using motor oil at flowrates
ranging from 25% to 75% of the design flowrate (1.1 cfs) with influents ranging from 7 to 47
mg/L. Laboratory results showed removal rates from 27% to 92% removal. A spill test was
also run at 10% of the design flowrate with an influent of 82,000 mg/L with an average
percent capture of 94.5%
6. Independent parties in California, Florida, and Australia completed various field studies.
Field studies showed the potential for the unit to remove oils and grease and total suspended
solids, and capture 100% gross solids greater than the aperture size of the screen under
treatment flow rate.
7. Contech is conducting a field evaluation of a CDS2015 with Sorbents for oil and grease
removal. To date, the unit has been evaluated at flow rates ranging from 42% to 119% of the
design flow rate (0.28cfs) with influent motor oil concentrations ranging from 0.46 to 64.8
mg/L (median of 4.5 mg/L; mean of 12.6 mg/L). A preliminary report showed a mean motor
oil removal efficiency of 72%, with a UCL95 for effluent concentration of 0.75 mg/L.
8. CDS Technology has been widely accepted with over 6,200 installations in the United States
and Canada. There are over 1,380 installations in Washington and Oregon.
Technology Description:
Engineers can download a technology description from the company’s website.
www.conteches.com
Recommended Research and Development:
Ecology encourages Contech to pursue continuous improvements to the CDS system. To that
end, Ecology makes the following recommendations:
1. Conduct testing to quantify the flowrate at which resuspension occurs.
2. Conduct testing on various sized CDS units to verify the sizing technique is appropriate.
3. Test the system under normal operating conditions, pollutants partially filling the swirl
concentrator. Results obtained for “clean” systems may not be representative of typical
performance.
Contact Information:
Applicant Contact: Sean Darcy
Contech Engineered Solutions
(800) 548-4667
sdarcy@conteches.com
Applicant website: http://www.conteches.com/
Ecology web link: http://www.ecy.wa.gov/programs/wq/stormwater/newtech/index.html
Ecology: Douglas C. Howie. P.E.
Department of Ecology
Water Quality Program
(360) 407-6444
douglas.howie@ecy.wa.gov
Revision History
Date Revision
July 2008 Original use-level-designation document
February 2010 Reinstate Contech’s Oil Control PULD
August 2012 Revised design storm criteria, revised oil control QAPP, TER, and
Expiration dates
December 2012 Revised Contech Engineered Solutions Contact Information; Added
QAPP for Oil Treatment
May 2013 Revised model numbers in Attachment 1
April 2014 Revised Due dates for QAPP and TER and changed Expiration date
August 2014 Revised Due dates for QAPP and TER and changed Expiration date
July 2016 Updated Oil Control PULD to a CULD based on preliminary field
monitoring results
Attachment 1
CDS Stormwater Treatment Unit Checklist
Frequency Drainage System Feature Problem Conditions to Check For Recommended Action
Date Inspected*
J F M A M J J A S O N D
M & S Inlet Chamber
Accumulation of
trash, debris and
sediment
Trash blocking inlet throat
opening & sediment
accumulation exceeds 2 inches
Remove trash, debris, and
sediments. Inlet throat
opening should not be
blocked by any materials.
A Screen Blockage/Damage
Biological growth on the
surface of the screen; broken
screen or loose screen
Powerwash screen to clean
the surface and Contact
CSS for screen repair
(broken or loose)
M
Separation
Chamber
Trash and floatable
debris
accumulation
Excessive trash and floatable
debris accumulation on the
surface in separation chamber
Remove trash or other
floatable debris in
separation chamber to
minimum level
A Oil Baffle** Damaged
Baffles corroding, cracking,
warping, and/or showing signs
of failure as determined by
maintenance/inspection
person.
Baffles repaired or replaced
to design specifications.
M & S Oil sorbent** Consumed
Change of color in sorbents
(fresh sorbents typically
appears to be white or light
yellow)
Remove spent oil sorbent
and replace with new
sorbent
M
Sediment Depth
in the Sump
Sediment
accumulation
Sediment accumulation
exceeds 75-85% sump depth
(varies depending on the
Model, see attached Table)
Sediment in sump should
be removed using vactor
truck.
M
Sediment Depth behind the
screen
Sediment
accumulation
Sediment accumulation exceeds 2 inches behind the
screen
Sediment behind the screen should be removed
using vactor truck.
Frequency
Drainage
System Feature Problem Conditions to Check For Recommended Action
Date Inspected*
J F M A M J J A S O N D
M
Access Cover
(MH, Grate,
cleanout)
Access cover
Damaged/ Not
working
One maintenance person
cannot remove lid after
applying 80 pounds of lift,
corrosion of deformation of
cover.
Cover repaired to proper
working specifications or
replaced.
A
Inlet and Outlet
Piping
Damaged
Piping/Leaking
Any part of the pipes are
crushed or damaged due to
corrosion and/or settlement. Pipe repaired or replaced.
A
Concrete
Structure
Concrete structure
(MH or diversion
vault) has cracks in
wall, bottom, and
damage to frame
and/or top slab.
Cracks wider than ½ inch or
evidence of soil particles
entering the structure through
the cracks, or
maintenance/inspection
personnel determine that the
structure is not structurally
sound.
Structure repaired so that
no cracks exist wider than
0.25 inch at the joint of
inlet/outlet pipe.
A Access Ladder
Ladder rungs
unsafe
Maintenance person judges
that ladder is unsafe due to
missing rungs, misalignment,
rust, or cracks. Ladder must
be fixed or secured
immediately.
Ladder meets design
standards and allows
maintenance persons safe
access.
*Note dates when maintenance was performed and type of maintenance performed in notes section below.
**May not be present on all units.
(M) Monthly from November through April.
(A) Once in late summer (preferable September)
(S) After any major storm (use 1-inch in 24 hours as a guideline).
If you are unsure whether a problem exists, please contact a Professional Engineer.
Notes:
Maintenance of CDS stormwater treatment unit typically does not require confined space entry. Visual inspections should be
performed above ground. If entry is required, it should be performed by qualified personnel.
Refer to CDS Unit Operation & Maintenance Guideline for maintenance details. Typically the CDS unit needs to be inspected before
and after the rainfall seasons (November to April), after any major storms (>1-inch within 24 hour) and in the event of chemical spills.
Contact Contech Engineered Solutions (CSS) (800-548-4667) if there is any damage to the internal components of CDS Unit.
CDS Maintenance Indicators and Sediment Storage Capacities
CDS
Model
Diameter Distance from Water
Surface to Top of
Sediment Pile
Sediment Storage
Capacity
ft m ft m yd3 m3
CDS2015 5 1.5 3.0 0.9 1.3 1.0
CDS2020 5 1.5 3.5 1.1 1.3 1.0
CDS2025 5 1.5 4.0 1.2 1.3 1.0
CDS3020 6 1.8 4.0 1.2 2.1 1.6
CDS3030 6 1.8 4.6 1.4 2.1 1.6
CDS3035 6 1.8 5.0 1.5 2.1 1.6
CDS4030 8 2.4 4.6 1.4 5.6 4.3
CDS4040 8 2.4 5.7 1.7 5.6 4.3
CDS4045 8 2.4 6.2 1.9 5.6 4.3