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Home My WebLink AboutWPO201000074 Review Comments Stormwater Management Plan 2010-12-30� OF AL ,. vIRGI1`IZP COUNTY OF ALBEMARLE Department of Community Development 401 McIntire Road Charlottesville, Virginia 22902 -4596 Phone (434) 296 -5832 Fax (434) 972 -4126 Project: North Pointe Phase 3 Road Improvements [WPO- 2010 - 00074] Plan preparer: David Jensen, PE; WW Associates Owner or rep.: Richard Spurzem; Neighborhood Investments — NP LLC Plan received date: 2 November 2010 Date of comments: 30 December 2010 Reviewer: Phil Custer The Stormwater Management and Road Plans for the North Pointe Phase 3 Road Improvements project, submitted on 2 November 2010, have been reviewed. The letter from the county review of the ESC plan has been provided in a separate document. County engineering can approve the ESC and road plans after the following comments have been addressed. A. General Review 1. All bonds must be posted prior to the approval of the site plan for the northwest residential area. 2. To be in general accord with the application plan, the applicant must include a "pedestrian tunnel" underneath North Pointe Blvd. in approximately the same location. 3. To be in general accord with the application plan, the applicant must include a "picnic area" at the outlet of the culvert at Sta. 23 +30 in approximately the same location with the same square footage. 4. To be in general accord with the application plan, the applicant must include a flat 1Oft (or wider if a path greater than 5ft is desired by the property owner) wide shelf in the roadway embankment, above the culvert endsections, between Sta. 22 +30 and 24 +50 so that a Class A pedestrian path and appropriate drainage swales and culverts can be established when future site plans are submitted for the park and clubhouse. 5. The plan shows a stream at Sta. 23 +30. Please provide the county with approval from the Army Corps of Engineers or the Virginia DEQ. Please also provide the county with a copy of the application submitted to the Army Corps of Engineers. Any required Army Corps mitigation must occur on site. If on -site ACE mitigation cannot be provided, the applicant must contact the county for a list of off -site opportunities. [Proffer 4.4] B. SWM Plan Review Comments In light of the ESC comment B.3 on the county engineering memo dated 17 December 2010, the stormwater management concept will likely be modified so that Pond 3 is constructed with this application. However, a review of the applicant's current proposal was still performed and the following comments are provided for the calculations and design of the biofilter. 1. The use of a biofilter sized for a phosphorous removal rate of 50% as specified by the Virginia Stormwater Management Handbook is acceptable with regard to Proffer 4.3(b) which requires an 80% removal rate of suspended solids. However, the sizing method used by the applicant that designs the bed area equal to 2.5% of the impervious area draining to the biofilter assumes a lft ponding depth, not 6 ". The concept for a biofilter (50% removal rate) is to treat the water quality Albemarle County Community Development Engineering Review Comments Page 2 of 3 volume through the special media. The only way this can come close to being achieved with a 2.5% bed area is by providing lft of ponding. Please either raise the 4" orifice by 0.5ft and update all calculations or provide a biofilter (of 6" ponding) with a bed area of 4968sf, update the landscape plan, and update the calculations. 2. Please specify an anti -vortex device on the 48" riser structure. 3. Please provide a detail for the trashrack over the 4" orifice and specify it on the cross - section detail. 4. Please replace all references to the Luckstone Mix with "State- Approved Mix ". 5. Please provide the latest edition of the county's General Construction Notes for Stormwater Management Plans on Sheet C -18. 6. Please complete a Stormwater Facility Maintenance Agreement and submit it to the county with a $17 fee after reviewing the instructions. 7. After all technical comments have been addressed, the applicant must request that a SWM bond be computed. To request a bond, please complete the bond estimate request form and submit it to the County Engineer. C. Road Plan Review Comments I understand that a variation request was provided to the Planning Department without any detail of what was to be varied. The applicant's letter simply asked the Planning Department to accept the proposed cross - sections as designed. I have reviewed the cross - sections on Sheet C -10 of this set and compared those with the cross - sections on D1 and D2 of the application plan. I have listed all of the discrepancies between the two plans below. If I have missed any differences, the applicant must inform me and the Planning Department before any variation is granted. • increasing the planting strip in the NPBS cross - section from 6ft to l lft • increasing the planting strip in all other cross - sections, except for North Pointe Blvd. north of the intersection and Lewis and Clark Drive east of the intersection, from 6ft to 8ft. • decreasing the median of Lewis and Clark Drive from Sta. 28 +27.99 to Sta. 28 +37.27 from 12ft to 4ft • increasing the sidewalk on both sides of Lewis and Clark Drive between Sta. 28 +27.99 and Sta. 28 +37.27 from 5ft to 8ft • decreasing the median of Lewis and Clark Drive between Sta. 29 +01.27 and Sta. 30 +49.38 from 12ft to 8ft • decreasing the planting strip on North Pointe Blvd. north of the intersection with Lewis and Clark Drive from 6ft to 5.5ft • decreasing the planning strip on Lewis and Clark Drive east of the intersection with North Pointe Blvd. from 6ft to 5.5ft A copy of my comment letter will be sent to the Planning Department for their records. For reconsideration of this variation request please provide another letter to the Planning Department with these listed variations and any other variation I might have missed as well as any change requested or required by County Engineering or VDOT. 2. Between Sta. 27 +75 and Sta. 31 +25 of Lewis and Clark Drive, the alignments of the through lanes are not smooth and appear to connect at angles. The applicant is proposing to modify the median from 8ft down to 4ft, up to 8ft again, and finally up to 16ft all in a span of 350ft. Please provide curve radii and stations of the centerline of each through lane and reduce the number of median variations the road is subjected to. I recommend maintaining the 8ft wide median to Sta. 28 +37.27 and transitioning from the 8ft median to 16ft median between Sta. 29 +01.27 and Sta. 30 +49.38. Per the cross - section on D1 of the Application Plan, the sidewalks in the first cross - section of Albemarle County Community Development Engineering Review Comments Page 3 of 3 Lewis and Clark Drive can be 5ft, rather than 8ft. If VDOT requires 8ft sidewalks in this section, ROW from TMP 32 -22P will be needed or the road will need to be shifted to the northeast. 3. The 50ft wide park and exercise path is shown on the road cross - section on sheet D1 of the Application Plan and must be constructed with the roadway. Though the cross - section on D1 appears to imply that this 50ft wide section is to be placed within the ROW of the North Pointe Blvd., it is to be a park maintained by the Homeowners Association per Sheet G. The hydraulic calculations for the drainage system must be adjusted accordingly. It is expected that the exercise path will be used by bicycles and pedestrians, so the trail should be designed to meet Class A Type 2 standard of the Albemarle County Design Manual. 4. The left turn lanes between Sta. 14 +44.65 and Sta. 15 +40.55 of North Pointe Blvd. are much too short. The entrances as shown on the application plan are too close together and create many conflict points in this area. I recommend moving the school's entrance across from the street at Sta. 15 +62.38 and either eliminating the entrance to the clubhouse or making it a right - in/right -out. Input from VDOT and the County Planning Department should be considered before making any changes. 5. Please expand the limits of grading to provide adequate sight distance for the school entrance. It's much easier to perform this work now without the concern of damaging existing sidewalks or street trees in the future. Sediment loss will also be minimized because the efficiency of the downhill sediment basin is higher than silt fence, which would be necessary if the sight distance was established after construction. 6. The R9x7 sign only works in one direction. Can a sign directing pedestrians to the left and bicycles to the right be easily obtained? If not, alternate signage should be proposed. 7. The length of the shared use path around the school is relatively small when compared to most other bicycle and pedestrian facilities. I anticipate a few riders will opt to stay within the roadway since there will be available space (17ft curb to curb width). Please maintain the automobile and bicycle lane markings through the roadway sections with the shared use path. Maintaining the 17ft curb -to -curb width for the NPBS section might have been an oversight during the rezoning of the property. Elaine Echols had informed me that onstreet parking had been discussed around the school when the bicycle traffic was diverted to the shared use path. This should be clarified during the variation discussion. 8. All drainage structures deeper than 12ft must be equipped with a safety slab (SL -1). 9. All drainage structures with a flow drop of greater than 4ft, including a drop from the throat, must use inlet shaping (IS -1). A general note on each drainage profile sheet will suffice. 10. Please provide a landscaping plan for the street showing ornamental plants within the median and street trees within the buffer strip. 11. After all technical comments have been addressed, the applicant must request that a road bond be computed. To request a bond, please complete the bond estimate request form and submit it and a $250 fee to the County Engineer. E1_swm rp_PBC_North Pointe Phase 3 Road Improvements.doc