Response to Comments (July 28, 2010 Oregon City Determination of Application Completeness Memo)

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Crystal Reeves
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1 Environmental Science & Assessment, LLC MEMORANDUM DATE: August 13, 2010 TO: Oregon City Planning CC: Jill Long Lane Powell FROM: RE: Jack Dalton Response to Comments (July 28, 2010 Oregon City Determination of Application Completeness Memo) Responses for Code Section Natural Resource Overlay District Comment 1 - Waterway versus wetland comment: As was documented from the field determination, the NROD resource is primarily a waterway along the southern edge of the site has been channelized and flows west to east. The eastern end of the waterway ends at a pair of 36-inch culverts under the southern entry road of the Hilltop Commercial Center The extent of the drainage way is defined by the ordinary high water line (OHWL), which was determined in the field to be approximately 1.5 feet above the channel bottom. The OHWL is clearly defined in the field by a transition from hydrophytic vegetation to upland grasses along the banks. The constrained channel morphology dictates that the hydrology present in the resource is strictly from the perennial flow and wetland soil saturation does not extend outside the channel OHWL. The waterway provides primarily stormwater conveyance, which is only periodically at the OHWL during storm events. The site is located near the top of the surrounding drainage basin so stormwater flows in the waterway are low enough to allow the herbaceous vegetation to persist. The vegetative cover in the channel bottom is dominated by reed canarygrass with the other emergent species established along the upper edge of the OHWL. This is typical of low flow ditched or channelized systems. Historically, the waterway was altered with the development of the intersection of Beaver Creek Road and Molalla Avenue. According to the property owners and confirmed with city staff, a drainage feature was located south of the site and was channelized along the southern edge of the Hilltop property as part of the Beaver 838 SW First Avenue, Ste. 410 Portland, OR v f

2 Creek Road improvements. The resource was not a larger wetland at that time, but rather drainage feature moving surface water to the east and a likely connection to Newell Creek, which indicates the existing waterway did not convert a pre-existing wetland to waterway. Comment 2 - Mitigation Requirements under : The mitigation requirements of are being met under the current proposal. The disturbance area will be mitigated within the additional buffer area at greater than the required 2:1 ratio and the proposed site development will allow for an expanded buffer beyond that currently on site. An analysis was conducted to further document the proposed site plan and the resulting buffer area proposed within the 50-foot NROD overlay. Currently the existing asphalt roadway, sidewalk and maintained landscaping limits the existing buffer (Figure 6). The proposed site plan mitigates for the entire disturbance area, including the buffer and wetland impacts totaling 1302 sf, by providing 2604 sf of mitigation landscape planting within the proposed 4774 additional buffer area (Figure 7). The existing buffer area is 5482 sf. By reconfiguring the parking and pedestrian trail in the southern end of the site, the area of buffer will be expand by 4007 sf for a total buffer area of 9489 sf. Instead of a narrow 8-9 foot buffer along the northern edge of the waterway, the buffer will be expanded to between 22 and 28 feet north of the existing drainage (Figure 7). Proposed parking and sidewalk (impervious) will remain within the 50-foot NROD overlay, but the proposed site plan converts a portion of the existing landscaping and sidewalk to a native planted buffer, resulting a net increase of pervious area of 298 sf (Figure 8). The impact acreage analysis is provided in Attachment A. It should be noted that a small error in the impact calculation was discovered along the existing culvert headwall and the revised impact acreages are provided in Table 1. The mitigation will be increased to the required minimum, which will include the addition of 8 tree and shrub plantings in the mitigation landscape plan. Table 1: Permanent NROD Encroachment Summary NROD Impact Type Total Encroachment (sf) Proposed Mitigation (sf) Access Road (buffer) 551 Bridge/trail (buffer) 120 2,380 (on-site) Culvert/headwall (waterway) 631 TBD (on-site) TOTAL 1,302 2,604 (2:1) Attachments Page 2

3 Attachment A PROPOSED SITE PLAN Existing Buffer 5482 Existing Waterway 5435 All NROD Proposed Impacts 671 Proposed Impacts 631 Proposed Impacts 1302 Remaining Buffer 4811 Remaining Waterway 4804 Remaining NROD 9615 Remaining Buffer 4715 Proposed Addl Buffer 4774 Proposed Addl Buffer 4774 Proposed Buffer Total 9489 Proposed NROD Total PROP BUFFER INCREASE Proposed 9489 Existing 5482 Increase 4007 Increase Total NROD 3472 PROP IMPERVIOUS INCREASE Proposed Addl Buffer 4774 Existing Lawn/Landscape 4476 Increase 298 MITIGATION FOR DISTURBANCE Buffer Impacts 671 Total Impacts 1302 Mitigation Planting Area Ratio Hilltop Commercial Center (ES&A project No ) August 13, 2010

4 STUDY AREA KEY WATERWAY (OHW) - Ordinary High Water NROD BOUNDARY 1 PHOTO POINT ORIENTATION NROD Resource Boundaries: Base 50-ft NROD boundary limited by existing development. Existing buffer extends up to adjacent impervious surfaces. Wetland boundary mapped from field measurements from known locations by ES&A staff. Wetland 5,418 s.f. Buffer 5,482 s.f. Total: 10,900 s.f N TOP OF BANK/EDGE OF LAWN Two 36-in Culverts Existing Driveway Source: Compass Engineering; Modified by ES&A, LLC, June Environmental Science & Assessment, LLC Wetland Delineation/NROD Map Hilltop Commercial Center Road/Culvert Improvements Oregon City, Oregon Figure 6 Scale: 1in. = 50 ft.

5 Project Limits N Source: Rommel Architectural Group, LLP; Modified by ES&A, LLC, June Environmental Science & Assessment, LLC NROD Impact/Mitigation Plan Hilltop Commercial Center Road/Culvert Improvements Oregon City, Oregon Figure 7 Scale: 1in. = 50 ft.

6 STUDY AREA N KEY WATERWAY (OHW) - Ordinary High Water NROD BOUNDARY EXISTING AREAS CONVERTED TO NROD BUFFER: ASPHALT/SIDEWALK LANDSCAPE/LAWN NOTE: See Figure 7 for NROD impact areas TOP OF BANK/EDGE OF LAWN Two 36-in Culverts Existing Driveway Source: Rommel Architecture, 2010; Modified by ES&A, LLC, June Environmental Science & Assessment, LLC NROD Expansion/Mitigation Plan Hilltop Commercial Center Road/Culvert Improvements Oregon City, Oregon Figure 8 Scale: 1in. = 50 ft.

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