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HomeMy WebLinkAboutSUB200800287 Review Comments Preliminary Plat 2011-03-04*-&A County of Albemarle Department of Community Development Memorandum To: Gerald Gatobu, Current Development Project Planner From: Phil Custer, Current Development engineering review Date: 4 March 2011 Subject: Fontana Phase 4C, Section 1 Preliminary Plat (SUB- 2008 - 00287) The fourth submittal of the preliminary plat for Fontana Phase 4c, received on 24 January 2011, has been reviewed. Engineering can recommend approval to the plan after the following comments are addressed. 1. The applicant should clarify what exactly this application is. It appears to be a preliminary plat for Sections 1, 2, and 3, but the title says the plan is just for Section 1. (Rev. 1) The applicant has clarified that this application is intended to be a preliminary plat for Section 1. However, I strongly recommend that this submittal become a preliminary plat for all three sections because, in order to receive a grading permit, the ESC plan must match the grading plan. And, a grading permit can only be granted when a preliminary plat (or final site plan) is approved for the land to be disturbed. In other words, an ESC plan cannot be approved unless the preliminary plats for all three sections are valid. (Rev. 2) The applicant has amended the application to be a preliminary plat for all three sections. 2. A critical slope waiver appears to be necessary. The applicant should provide a request for a waiver to the agent before the next submittal. (Rev. 1) Comment has not been addressed. Once the county has received the critical slope waiver request, we will need to schedule the application for new Site Review Committee and Planning Commission meeting dates. (Rev. 2) Waiver request has been received. Engineering review will provide an analysis of the critical slope disturbance to the planner in a separate document. (Rev. 3) This critical slope waiver was approved at the Planning Commission Meeting held on the 19`h of October. 3. If this plan is intended to be a preliminary plat for section 2, a curb and gutter waiver is required for Cortina Way and Belluno Lane. The applicant should provide a request for a waiver of these standards to the agent before the next submittal. A waiver of sidewalks is also required for these roads as well. (Rev. 1) A waiver is not needed for the lack of curb, gutter, and sidewalk on Cortina Way and Belluno Lane because the sections were approved by the Board of Supervisors as part of the rezoning plan. However, the width of Brunello Court must be increased to the current VDOT standard of 29ft if parking on both sides of the street is desired. (Rev. 2) A waiver is not needed for lack of curb, gutter, and sidewalk for Cortina Way and Belluno Lane because the sections were approved by the Board of Supervisors as part of the rezoning plan. If parking on both sides of the street is not desired, please show "No Parking" signs on the road plans when they are submitted for review with the ESC and SWM plans. 4. Please remove sheets 8.0 and 8.1 from the set. These erosion and sediment control sheets will not be reviewed with the preliminary plat. The erosion and sediment control plan will be reviewed once a WPO application and fee is submitted. For this project, an application cannot be submitted until all off -site improvements have been completed to the County Engineer's satisfaction. (Proffer #8) Current Development Engineering Review Comments Page 2 of 7 (Rev. I) Comment has been addressed. 5. Please provide the date of the topographic survey on the plan. The survey does not appear to be accurate. Lots from previous phases, which have been built out, appear to show before - development grades. The grades on Via Florence appear to be from design drawings from a previous plan. Please show accurate topography. (Rev. I) Comment has been addressed. 6. The plan is lacking analysis of SWM solutions for quality and quantity of runoff. On the next submittal, please supply the County's Modified Simple spreadsheet for each drainage area. SWM facilities should be sited to capture as much runoff as practicable. All lots should be captured. (Rev. 1) The applicant has responded to this comment by stating that half of the new runoff from this development will drain to a private regional pond. After checking the design file for these ponds, I discovered that the impervious area in the Fontana development is likely underestimated. The previous plan (WPO- 2007 - 00087) assumed that Fontana would be developed with 1/2 lots with an average impervious area of 25 %. After examining the maps of the previous Fontana phases draining to the facility, it is clear Fontana is an R -4 development with a much higher impervious area. To rectify this likely shortfall, engineering review sees three options the applicant may pursue: - Provide complete stormwater management for the new development on site; - Supply an agreement that demonstrates the owner of TMP 78F -A permits the pond to serve this development's stormwater management requirements AND provide updated calculations for the pond showing that it is large enough to accommodate the Fontana development; or, - Supply an agreement that demonstrates the owner of TMP 78F -A permits the pond to serve this development's stormwater management requirements AND provide supplemental stormwater management on site to account for the SWM shortfall to the satisfaction of engineering review Also, the rear half of the Section I Lots are not shown as draining to a SWM facility. If this plan became a preliminary plat for all three sections, the SWM facility on the open space parcel could serve all of the development that drains to the north and east. (Rev. 2) The response regarding the SWM aspects of the plan are not sufficient. For the on -site facility adjacent to lot 34, the county's modified simple spreadsheet was not provided so it's impossible to know what removal rate this facility is required to be. Also, the facility is described as a pond, but it appears to be much too small for the drainage area to it and the areas of the contours on Sheet 4.0 do not match the Hydraflow printout on page 5. Please update the page 5 of the comps and compare the volume to the Water Quality Volume that is an output of the county's modified simple spreadsheet. The applicant's response stated that an agreement with the downstream pond owner was provided with the resubmittal but I was notable to find it. The applicant's response also indicated it would supplement the watershed draining to the suspected undersized facility with onsite measures but none were proposed other than the SWM facility adjacent to lot 34, which does not treat any water draining towards the undersized pond. I recommend providing a water quality swale along Via Florrence and converting a sediment trap to a biofilter in Lot 1. (Rev. 3) A modified simple spreadsheet was provided for the stormwater facility adjacent to lot 34. In reviewing this facility from a conceptual standpoint, the basin appears to be appropriately sized. However, there is a portion of the downstream side of the embankment Current Development Engineering Review Comments Page 3 of 7 that is steeper than 3:1. This must be revised so a 3:1 downstream slope is uniform. The other watershed for this project is a little more complicated. Only one modified simple spreadsheet has been provided for the 1.7 acre drainage area to the biofilter facility. The remainder of the development appears to be directed towards water quality swales within the VDOT ROW. No modified simple spreadsheet has been provided for these facilities, so it is unclear whether these facilities meet the required removal rate. Also, it would be impractical to provide a water quality swale on Belluno Lane because of the steep slope; the design standards for this facility cannot be easily met. The SWM plan could be more easily approved if the agreement from the owner of the private regional facility on TMP 78F -A, which states the facility will provide the required stormwater quality and detention (though supplemental facilities will still be necessary as detailed in previous reviews), is received. In the response letter for the third submittal, the applicant stated that the agreement had been provided, but it was not included with the submittal package. If this exists, please resend. The grading plan is not adequate. Please address the following items regarding the grading plan: a. The retaining walls are steeper than the maximum allowed grade of 2:1. (Rev. 1) A low maintenance, non -grass groundcover is required on all slopes steeper than 3:1. Please show this groundcover in all required locations on the landscape plan and identify the quantity needed in the Landscape Schedule. (Rev. 2) With the current grading, a retaining wall is necessary in the back of Lot 30. Retaining walls are not permitted per the Grading Plan Proffer. Please revise the grading plan to eliminate the need for a retaining wall. The roadway should be lowered as much as possible to provide some relief in this area, which will also be difficult to provide adequate ESC protection for. The downstream site of the embankment for the SWM facility cannot be steeper than 3:1. [VSMH 3.011 The landscape plan is missing the low maintenance groundcover on the slope between the houses for lots 5 and 6. (Rev. 3) The need for a retaining wall has been eliminated adjacent to lots 29 and 30. It should be noted at this time that these two lots will need to be constructed as the last phase so that a sediment trap can be placed there when most of the earthwork and road construction is happening. There are still some sections of the downstream side of the SWM embankment where a 2:1 slope is proposed. On lots 19 and 28, there are some slopes shown steeper than 2:1. Please make the necessary grading changes and provide the low maintenance groundcover on Lot 19 if a slope steeper than 3:1 is employed. b. The building sizes are not representative of what will be constructed. After looking at the aerial photographs for the existing Fontana neighborhood, only about 20% have footprints the size shown in the plan. The grading plan should be representative of what the final buildout of the subdivision will be. Please include walkways, house entrances, wider driveways (show side loaded garages if desired), porches, attached garages, and decks on the grading plan for each building site. (Proffer #2A and #2G) (Rev. 1) The building sizes shown in this latest plan have been designed to match typical Current Development Engineering Review Comments Page 4 of 7 units of the Fontana development. However, the applicant has not provided walkways, located house entrances, or specified any small stairway needed for access to homes. Until this is provided, engineering review cannot confirm or comment on the plan's compliance with Proffer 2.G. Preliminarily, it appears as though lots 2, 3, 4, 11, 26, 28, and 29 do not comply with proffer 2G. (Rev. 2) The grading plan shows grades slightly steeper than 10% in front of houses in many lots. But, overall, the grading concept is sufficient so that the contractors will be able to adjust grades in the field to provide reasonable entrances. No adjustment to the plan is necessary. It does not appear that Proffer #2E has been met. Storm sewers through some of the lots south of Brunello Court are required. For instance, it appears a storm sewer is needed between lots 25 and 26. (Rev. 1) Comment has not been addressed. Swales, at least two feet deeper than the elevations adjacent to the houses, are needed between the property lines of lots 19 -27. At the end of each swale, 5-1 Oft off of the Brunello Court ROW, provide yard drains and a pipe system that runs parallel to Brunello Court until it reaches the inlet at the intersection with Fontana Drive. Where necessary, the swales should be riprapped. A IOft private drainage easement will be needed over each swale and drainage pipe. (Rev. 2) After further review, it appears as Proffer 2E has been met. This grading plan must match exactly what will be constructed. Deviations from the approved grading plan will not be granted by the county. (Rev. 1) Deviations will be allowed but each revision to the final grading plan will require an amendment to the ESC plan (with review fee) and will be given no precedence over other applications in the workload of the engineers. The first revision of grading plan requires the following corrections: d. A yard inlet appears to be needed on Lot 19 to pick up the swale adjacent to the Fontana Drive Extension. (Rev. 2) Comment has been addressed. e. The grading of lot 18 must be corrected. It does not look like a 596 contour should be drawn. (Rev. 2) Comment has been addressed. f. Driveways cannot be sloped greater than 10% per Proffer 2G. (Rev. 2) Comment has not been addressed. After a quick review, the driveways to lots 1, 2, 3, 4, 5, and 19 -27 are above 10% in some areas. Please review all driveway slopes again. There may be other instances where a driveway is above 10 %. (Rev. 3) The 612 contour in the driveway for Lot 4 should be modified slightly. g. Please provide spot elevations between lots 13 -18 to assure positive drainage into the Via Florence roadside ditch and to the rear of the lots. (Rev. 2) Comment has been addressed. h. Please provide spot elevations in the roadside ditch of Via Florence to assure positive drainage. (Rev. 2) Comment has been addressed. i. The house on Lot 9 should be moved so that it matches the grading. (Rev. 2) Comment has been addressed. j. Please show the trail and all necessary grading for the trail in Sections II and III. (Rev. 2) Comment has not been addressed. The construction of the path is not shown throughout sections 1, 2, and 3 as graphically shown in Attachment IM of the ZMA Current Development Engineering Review Comments Page 5 of 7 application. Also, culverts for the crossing of roadside ditches and the ditches adjacent to the path as shown in the detail on Attachment IIB of the ZMA application are necessary. (Rev. 3) Comment has not been addressed, though the grading for the path is much improved from the last submittal. The following adjustments and additions are needed to the trail. • Crib ladder stairways are needed between lots 3 and 4 • Crib ladder stairways are needed along the inside of Belluno Court • More detail is needed on the crossing of the swale between lots 3 and 4 • Grading must be shown for the construction of the trail behind lots 104, 105, and 106 (if grading and trailway easements are necessary on existing lots, these must be provided before the approval of the grading plan) • The storm drain line behind lot 12 appears to disturb critical slopes that were not accounted for in the waiver request please eliminate this disturbance and add more culverts along this ditch (from lots 13 and 104) so the discharge is more evenly distributed (one small culvert every 25 -35ft should be sufficient) k. The grading of the roundabouts in Section 2 must be redone to establish a crown and to flatten the slope to no steeper than 6 %. (Rev. 2) Comment has been addressed. This item will be check again when the road, ESC, and SWM plans are submitted for review. 1. Extend the ditch from Lot I to the northern corner of Lot 5. This ditch will require a private easement. (Rev. 2) Comment has not been addressed. This ditch is needed for ESC and SWM purposes to collect water at the rear of the lots. (Rev. 3) Comment has not been addressed. The ditch must be graded all the way to the stormwater facility. Currently, the ditch is shown as directing water over the existing sanitary sewer line on the south end of lots 101 through 97. Please provide a detail for this ditch as well and provide a calculation showing the ditch is sufficiently large enough to carry the 10 year storm and will not erode during the 2-year storm. Please also show an arrow within the ditch (similar to the arrows used in lots 19 -26) to more clearly indicate this Swale. m. The grading plan does not assure positive drainage away from each structure which is good, common practice among builders. For instance, the houses on lots 19 -27 all have the proposed topography directing water to their south walls. Please correct the grading plan so that every lot meets R401.3 of the Virginia Residential Building Code. (Rev. 2) Comment has not been addressed. Water is flowing directly against the houses of lots 19 -28. Clearly defined swales are needed to bring water from behind these units around the sides. In addition, the grading at the sides of many houses direct water into the foundation. Water must slope away from the house. (Rev. 3) Comment has been addressed. n. The grading plan does not show the house on Lot 34 or the grading needed for the SWM facility. Both of these features must be accurately depicted on the final grading plan. Preliminary SWM calculations are needed to confirm the schematic size of the facility. It appears that the open space parcel may need to be increased to accommodate the SWM facility for this development. (Rev. 2) The house has been shown. Please refer to the SWM comment for a response to the grading shown around the facility. o. Please designate the garage FFEs if they differ from the rest of the house. (Rev. 2) Please see comment 7f. p. Please show all necessary road and driveway culverts with inverts and sizes labeled. Current Development Engineering Review Comments Page 6 of 7 (Rev. 2) Comment has been addressed. Though, when the road plans are submitted, the engineer will need to provide hydraulic calculations showing that the culverts as proposed are sized correctly. (Rev. 3) Hydraulic calculations are needed for each culvert. q. It appears more walkout basements could be offered than shown in the design. No revision to the plan is currently needed though. However, if a builder wishes to provide a walkout basement in the future on a lot where one was not shown, an amendment to the plan will be needed. r. (Rev. 2) Please show revised grading at the rear of lot 11 because the house appears to be shown on a waste /stockpile area with unsuitable slopes. (Rev. 3) Comment has been addressed. s. (Rev. 3) More detail regarding the storm drainage system will be needed on the next submittal. Drainage computations, a specification for the type of each yard inlet, and profiles for the yard drainage system will be necessary on the next submittal. The grading plan relies on several drop inlets within swales where bypassing of the inlets may occur. Please provide spot elevations (showing a sump condition) and head calculations showing the sump depth is adequate for the discharge to it. Also, the drainage area map provided must identify each inlet corresponding to the calculations and profile, as well as the acreage and hydrologic coefficient. The drainage area map that was last submitted simply showed the limits of the drainage area of each structure without any other information. 8. The new pedestrian paths must be Class A Type I according to proffer #5. Please update the detail and the plan to show a path 5ft in width with a section of 2" of asphalt overlayed on 4" of gravel. Please also note on the detail that the path is not to have a cross slope of greater than 2 %. The path also appears to be placed on grades steeper than 10 %. (Rev. 1) In detail 7 on sheet 6. 1, please remove the following text: Trail material to be gravel or other approved material. In its place, please specify the following standard: 2 inches of asphalt over a 4" aggregate base at a cross slope no greater than 2 %. (Rev. I) Comment has been addressed. 9. The path east of lot 12 must be shown in a l Oft wide easement. This path also appears to violate the 10% maximum grade requirement of a Class A Type I trail. (Rev. 1) Comment has not been addressed. The path must be contained within a 10ft easement. The easement should be Ift off the edge of the trail and lft off the edge of the ditch. The grading of the ditch must be shown on the plan. Please also show the location of the stairway on the plan with spot elevations at the top and bottom of the stairs. A detail of the stairway is also needed. (Rev. 2) Comment has not been addressed, though an acceptable detail for the stairs has been provided. The grading for the path and ditch adjacent to the path is not shown. Also, the construction of the path is not shown throughout sections 1, 2, and 3 as graphically shown in Attachment IIB. (Rev. 3) This pathway has been removed since it was not shown on the sketch approved with the rezoning plan. 10. Please dimension the horizontal roadway alignment to check for compliance with VDOT standards. (Rev. 1) A review of the horizontal road alignment has not been performed because it has not been dimensioned by the applicant. The horizontal dimensions are necessary in order for a Current Development Engineering Review Comments Page 7 of 7 preliminary plat to be approved for sections 2 and 3. (Rev. 2) The horizontal alignment for Brunello Court is acceptable. However, the horizontal alignment of Belluno Lane must be adjusted. This can be done during the review of the road plans, if necessary. (Rev. 3) The revised horizontal alignment of Brunello Court appears to be acceptable. However, Belluno Lane must be adjusted. Road and SWM plans should be submitted as soon as possible. 11. On the landscape plan please show non - grassed, low maintenance groundcover over all slopes steeper than 3:1. (Rev. 1) The applicant must graphically designate these 2:1 areas on the plan and specify species. Examples of acceptable low maintenance, non - grassed groundcovers can be found in Table 3.37C of the VESCH. The number of plantings needed must also be included in the Landscape Schedule on Sheet C4.4. (Rev. 2) The landscape plan is missing the low maintenance groundcover on the slope between the houses for lots 5 and 6. (Rev. 3) Low maintenance, non - grassed groundcover is needed on Lot 19. 12. (Rev. 1) It appears that the future WPO plan will have problems addressing state adequate channel requirements. The construction of a channel from the outlet of the SWM facility to the existing stream may be necessary. This will require a drainage easement if one does not already exist. This is simply an advisory comment. (Rev. 3) The applicant has shown an offsite easement and the construction of a rip- rapped channel to the stream. Please provide the deedbook and page number for this easement. Otherwise, a letter of intent from the adjacent property is necessary. 13. (Rev. 1) Please show the existing inlets along Fontana Drive correctly. If there is not an inlet placed just above the entrance of Brunello Court, one will likely need to be provided to prevent discharge across the entrance when the street plans are reviewed. This is simply an advisory comment. (Rev. 3) The road and SWM plans should be submitted as soon as possible. File: E4_ppt_PBC_sub200800287.doc