PRELIMINARY TARGETED DRAINAGE REPORT DRURY LANE DEVELOPMENT 704 1ST STREET SULTAN, WA 98294-94240 PARCEL #28083200305500 AUDITOR’S FILE NO. 1090255
CITY OF SULTAN SNOHOMISH COUNTY, WASHINGTON
PREPARED FOR: STACY MACGREGOR PO BOX 80 GOLD BAR, WA 98251
PREPARED BY: MICHAEL GIESEKE
DATE: January 5th, 2018 RAIN CITY DEVELOPMENT DRURY LANE DEVELOPMENT PROJECT NO. RCD #001 4841 NE 45TH ST, SEATTLE, WA 98105 (425) 443 - 1060
PRELIMINARY TARGETED DRAINAGE REPORT DRURY LANE DEVELOPMENT 704 1ST STREET SULTAN, WA 98294-94240 PARCEL #28083200305500 AUDITOR’S FILE NO. 1090255
CITY OF SULTAN SNOHOMISH COUNTY, WASHINGTON
PREPARED FOR: STACY MACGREGOR PO BOX 80 GOLD BAR, WA 98251
PREPARED BY: MICHAEL GIESEKE
DATE: January 5th, 2018 RAIN CITY DEVELOPMENT DRURY LANE DEVELOPMENT PROJECT NO. RCD #001 4841 NE 45TH ST, SEATTLE, WA 98105 (425) 443 - 1060
Table of Contents 1)
Project Overview: ................................................................................................................ 3 Figure I.2.4.1 Minimum Requirements (MRs) for New Development Projects ................... 5
2)
Existing Conditions Summary: ............................................................................................ 6 Vicinity Map ........................................................................................................................ 7
3)
Offsite Analysis and Mitigation ............................................................................................ 8 Upstream Analysis:................................................................................................................. 8 Downstream Analysis: ............................................................................................................ 8 Existing Drainage Basin Map .............................................................................................10 Developed Drainage Basin Map .........................................................................................11 Downstream Drainage Path Exhibits ..................................................................................12
4)
SWPPP Narrative ..............................................................................................................13 Site Grading / Erosion Control Risk Assessment................................................................13 Minimum Elements: ...........................................................................................................13
5)
Source Control ...................................................................................................................15
6)
Preservation of Natural Downstream System .....................................................................15
7)
Onsite Stormwater Management ........................................................................................15
8)
Run-Off Treatment .............................................................................................................15
9)
Flow Control.......................................................................................................................16
10)
Wetland Protection .........................................................................................................16
11)
Operation and Maintenance Manual ...............................................................................16
Appendix A – Stormwater Calculations .....................................................................................17 Appendix B – Geotechnical Report ...........................................................................................18 Geotechnical Engineering Report ......................................................................................18 Appendix C – Environmental Assement ....................................................................................20 Environmental Study: .........................................................................................................20 Appendix D – O&M Checklist: ...................................................................................................22
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1)
Project Overview:
The project name is the Drury Lane Development. This document is intended to provide engineering information necessary to support the preliminary plat application to the City of Sultan for the Drury Lane Development. The site consists of a single parcel and is located at 704 1st St, within Snohomish County and specifically the City of Sultan, Washington; refer to figure 1 for the project location and vicinity map. The parcel, #28083200305500, total area is approximately 1.91 acres. The existing site contains one single family residence and other sheds and outbuildings, driveway, landscaping, fencing, trees, brush and other vegetation. The stormwater from the existing property infiltrates onsite with no overflows present. The project will consist of 10 new parcels: One existing single-family residence will remain in a new parcel, 1 new storm and open space tract, and 8 parcels for 8 new single single-family residential lots that will be constructed as part of the development. The project proposes to route the storm runoff to the existing low point onsite and utilize the infiltrative nature of the existing soils. The conveyance systems will route the stormwater runoff from the site for pre-treatment/water quality treatment upstream of final infiltration basin. The project will construct minor frontage improvements along the northwesternly boundary of the subject property along 1st Street for access to the proposed short plat. Other work will include a new road, driveways, and an overall and tight line conveyance systems. The project proposes to construct 1.2 ± acres of new and replaced impervious surfaces including roof, driveway, roadway and other landscaping surfaces. Therefore, Minimum requirements 1-9 apply to all of the new impervious surfaces for this project along with all the disturbed pervious surfaces. This proposal does not meet any of the land-use criteria that require specific source control for the final use. A SWPPP will be prepared to address the runoff from the site during construction. Refer to Sections 7 & 9 for a detailed discussion of how the runoff from the new impervious surfaces will be mitigated. Figures 2 & 3 are provided to show the existing and developed basin and runoff conditions for the subject property. This project has two areas that are a single on-site basin that drains to a low point within the site. Therefore, the project will be modeled as one discharge area from both areas within the same point of compliance. In the proposed conditions the areas will be collected and detained within a single system prior to infiltration onsite. The runoff in the existing condition from both areas spread over the pervious surfaces as sheet flow to the low point on site within the middle portion of subject property. During the site visit there were no signs of erosion, flooding, plugging or capacity issues within the low point onsite, or within the local drainage system adjacent to the property up to ¼ mile downstream point within the observed downstream systems. The soils assessment for this project shows the onsite soils to be suitable for infiltration. The soils resulted as infiltrative with infiltration as a viable option per the professional soils engineer for this project Gerry D. Bautista, Jr.,, P.E. As a result, the stormwater impacts will be mitigated using infiltration trenches with perforated stub out connections for each lot for individual lot
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infiltration along with overflow piped to the roadway conveyance system that convey the overall site flows to the proposed water quality, detention & infiltration basin systems for the project. Due to the size of this project, Minimum requirements 1-9 apply to the proposed drainage design as noted above. Included on the following page is a copy of the Minimum Requirements Flow chart out of the Snohomish County Drainage Manual showing how the applicable minimum requirements were determined.
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Figure I.2.4.1 Minimum Requirements (MRs) for New Development Projects
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2)
Existing Conditions Summary:
The existing subject property covers approximately 2.02± acres before any ROW dedication or area vacancies. All of the proposed disturbance area of the existing site contain one existing single family residence and other outbuildings / shed, driveway, landscaping, trees, bushes and other vegetation. All of the proposed impervious surfaces will be considered new Non-Pollution generation impervious surfaces (NPGIS) and Pollution generating impervious surfaces (PGIS) for stormwater modeling. Approximately 1.14 acres of the site will be impacted by new and existing impervious surfaces with approximately 1.91 acres of the total site and adjacent ROW being disturbed as needed for utilities, clearing and grubbing and restoration of the existing site landscaping of other disturbed pervious surfaces. The northern portion of the site sits higher than the existing subject property but is graded to drain into the central southerly low point within the site. The eastern portion of the subject property slopes westerly towards the sites existing low point, and the western portion of the subject property slopes easterly towards the same low point both with soft slopes averaging 15%. There is an existing curb on 1st Street and no roadway flows are tributary to the site. Roadway runoff flows northerly to the City of Sultan’s existing conveyance system on High Street that will be utilized for emergency overflow in the developed conditions. Due to the existing topography of the site no noticeable areas appear tributary to this parcel. The soils have been reviewed by Gerry D. Bautista, Jr., P.E., the Geotest Geotechnical Engineer for this project who found the soils to be viable for water quality and infiltration. Refer to the Geotechnical Report contained in Appendix B of this report for more information. The central low point portion of the site have moderate slopes of approximately 10-15%. Based on the existing soil information and setbacks of the proposed improvements from any of the property lines and existing structures there is little potential for erosion or sedimentation during construction assuming the basic BMPs including in the SWPPP are installed and maintained properly. Refer to Figure 2 for an Existing Site Exhibit.
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Vicinity Map
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3)
Offsite Analysis and Mitigation
The development proposes construction of approximately 1.91 acres with 1.14 acres of new and existing impervious surfaces within the Drury Lane Development. This area will consist of roofs, driveways, public roadway and other impervious surfaces for a single-family residential development. The existing single family residence will remain as part of the development, with its runoff being collected and conveyed within the proposed collection and conveyance system. All other existing impervious surfaces onsite will be removed and the pervious areas outside of the stormwater detention and infiltration areas and setbacks will be converted to landscaping. The following table summarizes the new pervious and impervious proposed surfaces for the 9lot short plat development BASIN TOTAL
IMPERVIOUS (AC) 1.14
PERVIOUS (AC) 0.77
TOTAL (AC) 1.91
The new impervious surfaces will be mitigated using detention and infiltration basin with an overflow control structure manhole tied to the City of Sultan’s existing conveyance system downstream of the subject property along High Street.
Upstream Analysis: During the site visit it was observed that there was no offsite runoff draining towards the subject property. Additionally, since this project will include frontage improvements the ROW runoff will be collected and conveyed towards the City of Sultans existing stormwater conveyance system on High Street. The runoff from the existing parcel will be detained and infiltrated onsite matching the existing conditions. Based on the location of the proposed improvements, and the existing site contours this project will not adversely affect any upstream or downstream flows.
Downstream Analysis: Since this project has two drainage areas but one downstream infiltration point within the site, the subject property will be reviewed and analyzed as one basin. The eastern basin flows westerly and drains to the low point, central portion of the site. The western basin flows easterly and drains to the low point, central portion of the site. The runoff infiltrates onsite with no apparent overflow. Additionally, the existing City of Sultan conveyance system, of which the subject property does not tie into due to topography restraints and the low point on site, but is downstream of the subject property. The existing single-family-residence on site has a small portion of its existing driveway that drains into the 1st Street roadway which flows northerly into the City of Sultan’s existing conveyance system. Therefore the proposed system will have emergency overflow ties to this system. This system flows north by northeast into a drainage swale within the Sultan Osprey park through a series of closed conveyance systems consisting of pipe and catch basins. The SE corner of High Street, the closed conveyance systems flows north to another catch basin that turns north into the parking lot. From the parking lot the pipe outlets into a grass lined ditch within the park that eventually lead into small drainage swale which is considered a state body RCD # 001 January, 2018
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of water which concluded the offsite downstream analysis. This is near the 1/4 mile downstream point from the project. The site visit was conducted on July 29th, at approximately 12:00 P. M., with temperatures at approximately 70-degrees and clear skies. During the site visit no flows were observed on-site. The only flows observed were within the Skykomish River northwest of the site 1/8-miles downstream of the subject property. Based on the Snohomish County Code, Skykomish River would be considered the receiving waters for this project even though the majority portion of the existing property infiltrates on site and no flows were observed leaving the subject property. Based on the fact that all of the runoff from the new on-site and frontage improvements will be detained and infiltrated onsite with portions of high-emergency overflows tied to the existing City’s conveyance system, this project will not increase the peak flows or durations of runoff from the site to the existing city’s system or proposed infiltration basin on site. During the site visit and review of the downstream system no portion of the system appeared to be inadequate and there were no signs of erosion or on or off-site or in any of the downstream areas visited.
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Developed Drainage Basin Map This section will be revised following preliminary plat submittal.
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4)
SWPPP Narrative
The intent of this section is to provide the information necessary to support the engineering plans in order to implement a design that will; reduce, eliminate or prevent the discharge of stormwater pollutants, meet or exceed the water quality and sediment management standards for the City, County and State, and prevent adverse impacts to the receiving waters for this project. Note; this narrative is intended so support the SWPPP that is included with the Drainage Plans also a part of this submittal package to the City. Site Grading / Erosion Control Risk Assessment Area proposed to be cleared / worked: Average slope for the Site: Erosion Hazard of Soil: Critical Areas downslope
1.91 Acres 1-5% (Excluding low point central portion of site) Low No
Based on the above information and with collection and treatment within the stormwater systems onsit, and the standard BMPs will be implemented, the Risk Category for this site is Low Risk.
Minimum Elements: 1: Preserve Vegetation and Mark Clearing Limits The first step in the construction process is for the contractor to flag or fence the limits of clearing/disturbance prior to any other construction activity. 2: Establish Construction Access The SWPPP calls for the proposed construction entrance to be installed as the second step after the staking of clearing limits. Since this project will utilize the proposed access for the construction access, this feature will be installed as the main access and as the second order of work and may require some maintenance so ensure proper function during the site work. 3: Control Flow Rates The site will be filled and the runoff from the construction site will be directed toward low point onsite within the central portion of the site with the stormwater control facilities for the project. This system will be in place to aid in the removal of sediment within the runoff as well as meter out the release of the runoff from the site to the infiltration basin during construction. 4: Install Sediment Controls This site SWPPP proposes to construct/maintain construction entrance, silt fencing, sediment retention within the existing vegetation that will provide a vegetated strip between the cleared areas and any property line. The construction of these features should be completed before the clearing and grading of the site. Mulch will also be used on the exposed soil as necessary to limit erosion. 5: Stabilize Soils The “Construction Sequence” calls for the stabilization of soils that remain unworked for certain lengths of time based on the time of year. Stabilization techniques may include but not limited to mulching, plastic sheeting or hydro seeding. Notes have been added to the plan regarding protection for the stock pile area as necessary. Stockpile areas have been identified on the SWPPP. 6:
Protect Slopes
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All disturbed slopes on site during construction are required to be protected with mulch or other means as specified in the construction sequence. The low point with moderate slopes will be filled during construction to gentle sloping low point. No concentrated runoff or significant amount of sheet flow will be directed to new cut or fill slopes during construction. 7: Protect Drain Inlets All existing catch basins adjacent to this project and immediately downstream will be protected with inlet protection. All new catch basins will also be installed with silt socks. 8: Stabilize Channels and Outlets The detention and infiltration basin for the proposed drainage system will be graded and constructed to be completely infiltrated onsite with any emergency overflows being conveyed within a closed conveyance system to the City of Sultan’s existing piped conveyance system along High Street. 9: Control Pollutants No outside chemicals are expected to be necessary for the construction of this project. All vehicles working on and around the site would need to meet the State requirements for emissions. Vehicle fueling locations will be used to limit the potential impacts from any spills and concrete washout areas will also be provided will away from any critical areas. 10: Control DeWatering DeWatering may be necessary for this project. However, the existing vegetation retained on site would be available to spread any water from construction for filtration and disposal via infiltration onsite. 11: Maintain BMPs The construction supervisor will be responsible for maintaining all BMPs during construction and working with the City to relocate or add BMPs as necessary as site conditions change. 12: Manage the Project It will be the responsibility of the Contractor and Developer to manage this project and coordinate with the City Inspector and Engineer. Inspection and Monitoring: Site inspections shall be done by a person who is knowledgeable in the principles and practices of erosion and sediment control. The person must have skills to first assess the site conditions and construction activities that could impact the quality of stormwater, and second assess the effectiveness of erosion and sediment control measures used to control the quality of stormwater discharges. Whenever inspection and/or monitoring reveals that the BMPs identified in the Construction SWPPP are inadequate, due to the actual discharge of or potential to discharge a significant amount of any pollutant, appropriate BMPs or design changes shall be implemented as soon as possible. Maintaining an Updated Construction SWPPP The construction SWPPP shall be retained on-site or within reasonable access to the site. The SWPPP shall be modified whenever there is a change in the design, construction operation or maintenance at the construction site that has, or could have, a significant effect on the discharge of pollutants to waters of the state. The SWPPP shall be modified if, during inspections or investigations conducted by the owner/operator, or the applicable local or state regulatory authority, it is determined that the SWPPP is ineffective in eliminating or significantly minimizing pollutants in stormwater discharges from the site. The SWPPP shall be modified as necessary to include additional or modified BMPs designed to correct problems identified. Revisions to the SWPPP shall be completed within seven days following inspection.
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5)
Source Control
This project proposes to construct 8 new single-family-residences while maintaining the existing residence, along with paved roads and minor frontage improvements. All runoff from the future paved and pervious surfaces will be collected and conveyed for treatment and infiltration on site. Any emergency overflows will be directed to the existing City of Sultan’s existing piped conveyance system just north of the subject property on High Street. No site-specific source control BMPs are required for this land use.
6)
Preservation of Natural Downstream System
The runoff from the site improvements will be either collected, detained, treated and dispersed through the infiltration basin. This will mimic the existing conditions by maintaining the condition of flow and the existing infiltration basin within the low point onsite.
7)
Onsite Stormwater Management
The soils for this project were found to be viable for water quality and infiltration at varying depths. Gerry D. Bautista, Jr., P.E., the Geotest Geotechnical Engineer prepared the geotechnical report for this project; refer to Appendix B. Since the soils are infiltrative in nature below the existing top soil layer, all single-family-residences will provide infiltration trenches with stub-out connections to act as limited infiltration with stub-out connections for overflow connecting to the on-site conveyance to the main detention and infiltration system to be contained with the storm tract as part of the development. BMP T5.13 will be applied to all areas of landscaping on this site to further provide filtration and shall infiltration of site pervious runoff.
8)
Run-Off Treatment
As noted throughout this report this project will require conveyance, treatment, detention and infiltration systems to maintain the existing basin infiltrative nature. The runoff from the northern basin will be collected and conveyed to a detention and infiltration basin. This design will therefore treat all of the pollution generating runoff from this site prior infiltration. Basic Treatment is required on this project since none of the high level controls are required on the Snohomish County Drainage Manual, Volume 1, Chapter 4, BMP and Facility Selection Process for Permanent Stormwater Control Plans. Oil control is not required since this is a residential project and none of the roads exceed the minimum ADTs. Phosphorus Control is not requires since this project does not drain toward to waters under section 305(b) or 319(a) of the Clean Water Act or a peat wetland or infiltrate with a ¼ mile of a lake. Enhanced treatment is not required since this is a residential project with roads that do not exceed 7,500 ADT. Therefore, this project must meet the Basic Treatment requirements. Within the approved options for water quality treatment under Basic Treatment menu, combined detention/wet pond/pre-settling basin will be included.
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9)
Flow Control
For this project, a single detention and infiltration facility will be used. This system has been laid out to collect the entire portion of the site and will be designed with one main infiltration location to provide an equivalent discharge for the combined basins. The design will maintain equivalent discharge areas matching existing conditions. In order to provide the required infiltration for the total site, the entire project site was analyzed. The existing conditions for the project site were modeled as forested. The total infiltration basin discharges onsite. Since the basin was designed, sized and passed the flow control standard using the WWHM3 software this approach is valid. The maximum flow rates for the project site are as follows: Total Site: 0.21 cfs (100-year) In addition, during the full drainage review process a flow control structure will be designed to ensure the basin has an overflow to the City of Sultan’s existing piped conveyance system downstream of the site. Therefore the proposed design will infiltrate the required flows onsite and any overflows will match or be less than the existing condition. Refer to Appendix A for the WWHM3 output showing how the systems meet the design requirements for all the storm events.
10)
Wetland Protection
There are no existing wetlands onsite.
11)
Operation and Maintenance Manual
The property owners & HOA will be responsible for maintaining the stormwater and landscaping facilities within this development. Included in the future full drainage report will be checklists for each feature specific to this project. Copies should be made of the checklists as necessary for use during routine inspections and required maintenance. Specific problems can be recorded along with the appropriate action taken. Routine inspections and maintenance will improve the long-term performance of the stormwater facilities. If at any time you are unsure if a problem exists or how to address a specific problem contact a Professional Engineer. Refer to Appendix C for a list of each facility to be maintained and the appropriate maintenance checklist.
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Project Sultan 9 Lot Short Plat Date 9/4/2017 Description: Individual Lot - Roof and Footing Conveyance System
C-Value (1-Lot, roof tightline conveyance) Type of Land Cover
C-Value
Area
Dense Forest
0.10
0.00
Light Forest
0.15
0.00
Pasture
0.20
0.00
Lawns Heavy Soil (Flat)
0.17
0.000
Lawns Heavy Soil (Rolling)
0.22
0.000
Playgrounds
0.30
0.000
Gravel Areas
0.80
0.000
Pavements and Roofs
0.90
0.040
1.00
0.000
0.900
0.040
Open Water (pond, lakes, wetlands) Total
Law
Storm Event
IR - Peak Rainfall Intensity PR AR BR
TC
IR
Total Precipitation
Coefficient
Coefficient
Time of Concentration
25-year
3.24
2.66
0.65
6.30
2.605
50-year
4.47
2.61
0.63
6.30
3.659
Rational Method IR A
Storm Event
C
25-year
0.900
2.605
0.04
0.09
QR
50-year
0.900
3.659
0.04
0.13
Project Sultan 9 Lot Short Plat Date 9/4/2017 Description: Individual Lot - Yard Conveyance System
C-Value (1-Lot, conveyance) Type of Land Cover
C-Value
Area
Dense Forest
0.10
0.00
Light Forest
0.15
0.00
Pasture
0.20
0.00
Lawns Heavy Soil (Flat)
0.17
0.045
Lawns Heavy Soil (Rolling)
0.22
0.010
Playgrounds
0.30
0.000
Gravel Areas
0.80
0.000
Pavements and Roofs
0.90
0.070
Open Water (pond, lakes, wetlands)
1.00
0.000
0.565
0.125
Total
Storm Event
IR - Peak Rainfall Intensity PR AR BR
TC
IR
Total Precipitation
Coefficient
Coefficient
Time of Concentration
25-year
3.24
2.66
0.65
6.30
2.605
50-year
4.47
2.61
0.63
6.30
3.659
Rational Method IR A
Storm Event
C
QR
25-year
0.565
2.605
0.13
0.18
50-year
0.565
3.659
0.13
0.26
Project Date Description:
Sultan 9 Lot Short Plat 9/4/2017 3-Lots - Yard Conveyance System
C-Value (3-Lot conveyance) Type of Land Cover
C-Value
Area
Dense Forest
0.10
0.00
Light Forest
0.15
0.00
Pasture
0.20
0.00
Lawns Heavy Soil (Flat)
0.17
0.135
Lawns Heavy Soil (Rolling)
0.22
0.030
Playgrounds
0.30
0.000
Gravel Areas
0.80
0.000
Pavements and Roofs
0.90
0.210
Open Water (pond, lakes, wetlands)
1.00
0.000
0.565
0.375
Total
Storm Event
IR - Peak Rainfall Intensity PR AR BR
TC
IR
Total Precipitation
Coefficient
Coefficient
Time of Concentration
25-year
3.24
2.66
0.65
6.30
2.605
50-year
4.47
2.61
0.63
6.30
3.659
Storm Event
C
Rational Method IR
A
QR
25-year
0.565
2.605
0.38
0.55
50-year
0.565
3.659
0.38
0.78
Project Date Description:
Sultan 9 Lot Short Plat 9/4/2017 Roadway Conveyance System - Total basin area tributary to pond, not including storm tract
C-Value (Roadway conveyance) Type of Land Cover
C-Value
Area
Dense Forest
0.10
0.00
Light Forest
0.15
0.00
Pasture
0.20
0.00
Lawns Heavy Soil (Flat)
0.17
0.480
Lawns Heavy Soil (Rolling)
0.22
0.080
Playgrounds
0.30
0.000
Gravel Areas
0.80
0.000
Pavements and Roofs
0.90
0.900
1.00
0.000
0.611
1.460
Open Water (pond, lakes, wetlands) Total
Storm Event
IR - Peak Rainfall Intensity PR AR BR
TC
IR
Total Precipitation
Coefficient
Coefficient
Time of Concentration
25-year
3.24
2.66
0.65
6.30
2.605
50-year
4.47
2.61
0.63
6.30
3.659
Storm Event
C
Rational Method IR
A
QR
25-year
0.611
2.605
1.46
2.32
50-year
0.611
3.659
1.46
3.26
Project Date Description:
Sultan 9 Lot Short Plat 9/4/2017 Total Site Area
C-Value (Total Project Conveyance) Type of Land Cover
C-Value
Area
Dense Forest
0.10
0.00
Light Forest
0.15
0.00
Pasture
0.20
0.00
Lawns Heavy Soil (Flat)
0.17
0.500
Lawns Heavy Soil (Rolling)
0.22
0.266
Playgrounds
0.30
0.000
Gravel Areas
0.80
0.000
Pavements and Roofs
0.90
1.140
Open Water (pond, lakes, wetlands)
1.00
0.000
0.583
1.906
Total
Storm Event
IR - Peak Rainfall Intensity PR AR BR
TC
IR
Total Precipitation
Coefficient
Coefficient
Time of Concentration
25-year
3.24
2.66
0.65
6.30
2.605
50-year
4.47
2.61
0.63
6.30
3.659
Storm Event
C
Rational Method IR
A
QR
25-year
0.583
2.605
1.91
2.89
50-year
0.583
3.659
1.91
4.07
Appendix B – Geotechnical Report Geotechnical Engineering Report: Onsite Analysis of Soils Prepared by: Geotest: Date: June 16, 2017 Summary: Infiltration feasible. Design rate 12 in/hr Recommended. (Pit test recommended for final design rate). Use Import Structural fill for foundation soils. Native re-use OK for lawn/other fill. Footing Drains 12” below floor slab grade. Road Section: Light Duty: 2-1/2” HMA over 6” CSBC(or 2”CSTC & 10” Gravel borrow) Heavy Duty: 4” HMA over 8” CSBC(or 2”CSTC & 12” Gravel borrow) Stormwater Pollutant Treatment: Near-surface soils suitable for onsite pollutant treatment. (poor infiltration in WQ soils).
The full Geotechnical report can be found on the following page.
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GEOTECHNICAL REPORT THIS PAGE INTENTIONALLY LEFT BLANK – REPLACE THIS PAGE IN PDF WITH FULL GETECHNICAL REPORT
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Appendix C – Environmental Assement Environmental Study: Wetland Delineation Prepared by: Blue Heron Services Date: April 25th, 2017 Summary: No wetlands onsite. The Environmental Study can be found on the following page.
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B lue H eron Services Blue Heron Services Inc PO 393 Index WA 98256 360 793 7767 (phone)
[email protected]
4 25 2017 On site review Prepared for Stacy MacGregor 704 First Street, Sultan Tax # 28083200305500 Property Description SEC 32 TWP 28 RGE 08 BEG SE COR N1/2 SW1/4 NW1/4 SW1/4 TH W 180FT TPB TH N 180FT TH W 290FT M/L TH N 150FT M/L TO N LN SUB TH W 20FT TH S 150FT TH W 160FTTO W LN SUB TH S 180FT TO SW COR SD SUB TH EALG S LN SD SUB TO TPB LESS RDS & LESS R/W TO CITY OF SULTAN PER QCD AFN 200510200776 Size (gross)
2.02
To whom this may concern, On April 16, 2017 I visited the site at 704 1st Street in Sultan with the landowner to check for the presence of wetland identifying conditions. The site is an existing single family home with portions of the lot set aside for grazing in addition to the home and yard area. The site has a unique feature, defined in this topo map (below) from the Snohomish County map folio. An old historical swale in the center of the lot runs north to south with an elevation change of about 4 or 5 feet at the north line but only a few inches at the south. This preliminary site assessment included soil pits in areas of possible wetland conditions (hydric soils) based on the visual topography and vegetation. In this site the swale what attracts the first attention is the dense vegetation of buttercup (ranunculus repens). While the overall vegetation is FAC and FAC+ the soils do not bear any of the identifying criteria required for a wetland soil determination.
Stacy MacGregor Sultan WA
1
The soils pits were dug in three locations, at the bottom of the swale, from north to south. There were no reducing features, concretions or the other features which would indicate anaerobic soil conditions required to define a wetland. Soil pit #1 near the North lot line 10YR 5/2, 4/2 to a depth of 14” Soils were sandy loam to silty loam Vegetation was limited to Ranunculus repens, Rubus armeniacus (an invasive species rooting throughout the swale) a Acer circinatum, a dead Alnus rubra, and a holly (Ilex ssp) which are found in within the lot also.
Soil pit #2 mid lot near a debris pile 10YR 2/2, 3/1 to a depth of 14” No redox or reducing conditions were noted of any shade or color The matrix was consistent and even colored Vegetation did include a small shrub: Symphoricarpos albus, Prunus laurocerasus (invasive), holly (Ilex ssp)invasive. Also an Alnus rubra and Oemleria cerasiformis. No water was noted standing anywhere in the swale and the rains of the last days, weeks months have been record breaking throughout the winter.
Soil pit #3 south lot line area / swale is less defined 2.5YR 3/1, 4/2 to a depth of 14” Consistent silty loam, dry and loose This south half of the lot had more native trees then the rest of the lot as well as several orchard trees. Pseudotsuga menziesii, Tsuga heterophylla, Thuja plicata were all trees present in the general area (though none rooting in the base of the swale. The main issues with this lot will be the elevation change and required grading to fill the site. It does not appear this has been an active flood channel at any time in modern history, and the soils are very well draining. Sultan City Code: 17.10.130 Critical area study content requirements for streams or wetlands. This code defines the delineation of a wetland to be that system which identifies the edge of the wetland based on the State Manual for Identifying and Delineating Jurisdictional Wetlands. As such this site does not meet the criteria for a wetland.
Stacy MacGregor Sultan WA
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As added information This map indicates the low laying feature, while not 100% accurately mapped, this does portray the elevation change on the lot.
NWI data
Site:
Off-site wetland related to the Sultan River to the west.
Stacy MacGregor Sultan WA
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Flood Hazard Data Snohomish County Lidar folio Site
If you have any questions please feel free to contact me Kim Peterson Blue Heron Services Inc. PO 393 Index WA 98256 360 793 7767 (o) 425 327 5799 (c )
[email protected]
Stacy MacGregor Sultan WA
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Appendix D – O&M Checklist: This section will be revised following the preliminary plat submittal.
RCD # 001 January, 2018
Page 22 Drury Lane Development
