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HomeMy WebLinkAboutWPO201900039 Correspondence 2020-04-03Engineeringfeverde &. Design Studio 4/3/2020 Seth Roderick, PE Monteverde Engineering & Design Studio 250 E Elizabeth St, Suite 114 Harrisonburg, VA 22801 Frank Pohl, PE Albemarle County Community Development 401 McIntire Rd Charlottesville, VA 22902 RE: Hillcrest Vineyard - Erosion & Sediment Control Status / Review Mr. Pohl, On the morning of April 2, 2020, I visited the Hillcrest Vineyard Tasting & Venue (WPO 2019- 00039) work site, in order to observe and denote work completed on the project to date. My visit was attended by the site developer, Michael McGinnis. As you aware, significant (nearly all) site work related to the referenced project number has apparently been completed prior to the issuance of a Grading Permit; while plans were deemed approved on Nov 22, 2019, outstanding items including easement dedication / recordation, posting of bond, and procurement of a DEQ Coverage Letter are required prior to issuance of the Grading Permit. This letter is being sent to document my findings and recommendations for Erosion & Sediment Control treatment / mitigation, as well as provide recommendations for future treatment / review of Stormwater Management particulars. Notations on Work Complete Grading on site was found to be significantly complete, save for 1) relatively small amount of mass grading and fine grading in vicinity of two buildings and parking area, 2) modifications to the SWM pond's principal spillway. The access road and associated cut -fill slopes are complete, save for construction of the pond's spillway. The parking area was largely at proposed grade, save for flattening of the northern slope (requiring borrow from the area just west of the parking area). Building pads were established, with vertical construction well underway. Fill slopes to the south of the two buildings still require flattening in some areas. Hillcrest Vineyard - Erosion & Sediment Control Status / Review April 3, 2020 Notations on Erosion & Sediment Control Measures By and large, the site work appears to have incorporated the Erosion & Sediment Control measures specified by the plans. Silt fence was in place around the project's perimeter, cut - fill slopes were stabilized with seed and blanket matting, and stormwater conveyance channels were lined with either blanket matting or armored with rock. Absent from my observations include the prescribed sediment basin (shown on plans as being located between two buildings) and the sediment trap (shown on plans as being located just above pond). The purpose of the prescribed sediment trap was to filter stormwater from the eastern side of the access road where silt fence would have otherwise been largely ineffective. On -site observations show these areas as being either fully stabilized or nearly so, as shown in the figure below. As such, construction of the sediment trap at this point in time is deemed unnecessary. Figure 1- Access Road Crossing New Pond Embankment Recommendations for Future Erosion & Sediment Control Treatment A. Parking Area Mr. McGinnis indicated that stone was going to be spread upon the parking area that has been brought to final grade beginning today, April 3, 2020 (delay to April 6 possible, depending upon material availability). It is recommended that this stone be spread upon disturbed areas to receive stone/asphalt as soon as possible, in order to achieve stabilization. O/Who, Page 2 of 7 Hillcrest Vineyard - Erosion & Sediment Control Status / Review April 3, 2020 Fill slopes to the north of the parking area, draining off -site, are protected by perimeter -control silt fence. As per typical standard, these slopes need to be seeded immediately upon completion of finished grade. Silt fence shall be maintained after each significant rainfall event, so that siltation deposits do not overwhelm their integrity. Cut slopes for the borrow area immediately west of the parking area needs to be seeded immediately upon completion of finished grade / cessation of earthwork activities. Areas adjacent to the parking area that are not to receive stone need to either be brough to finished grade and seeded as quickly as possible, or be treated with temporary seeding to stabilize in the interim. Figure 2 - Parking Area B. Fill Slopes South of Buildings The fill slopes lying immediately to the south of the two buildings are currently protected by perimeter -control silt fence. As with the grassed areas adjacent to the parking area, these slopes need to either be brought to finished grade and seeded asap, or be treated with temporary seeding to stabilize in the interim. Relocation of the silt fence to the immediate toe of finished slope is also recommended, in order to minimize the upstream drainage area. 'oorth, Page 3 of 7 Hillcrest Vineyard - Erosion & Sediment Control Status / Review April 3, 2020 C. Sediment Basin 'f �.'. '-t. �' ,• lam. As previously stated, the plans prescribed the use a sediment basin between the buildings to filter stormwater deriving from both the parking area and building areas until they could be stabilized. As stone is scheduled to be delivered and spread in the coming days, the need of the sediment basin is largely diminished; silt fence, upon relocation to the toe of slope, can be expected to provide adequate perimeter control until an adequate stand of grass is established on non-stone/building areas. It should also be noted that the area downhill of the silt fence and previously prescribed sediment basin has been largely denuded for agricultural purposes (vine plantings). In such a scenario, the sediment basin at its previously prescribed location would serve little benefit. As it stands, this entire drainage area drains to the existing wet pool/pond at the bottom of the hill, just upstream of the newly constructed pond embankment. Visual observations indicate that sediment has transported to this wet pool and is collecting there before pond overflow continues downstream. As such, this wet pool is serving as a natural sediment basin, and largely accomplishing the intended goals of the one prescribed by the plans. In lieu of building the prescribed sediment basin at this juncture, it is recommended instead that the wet pool be dredged immediately after full stabilization of upstream measures. In this scenario, the wet pool shall not be drained until full stabilization upstream has been accomplished. 'oor,Nm Page 4 of 7 Hillcrest Vineyard - Erosion & Sediment Control Status / Review April 3, 2020 D. Conveyance Channels As previously indicated, on -site conveyance channels were found to either be lined with blanket matting or armored with rock. The channel adjacent to the access road, which had been lined with blanket matting, appeared to be largely stabilized. The area upstream of the culvert, however, was found to be experiencing some erosion, however. It is recommended that stone inlet protection be added immediately to this location to prevent further erosion and undermining of the culvert. Figure 3 - Roadside Channel & Culvert Inlet O/w3h, Page 5 of 7 Hillcrest Vineyard — Erosion & Sediment Control Status / Review April 3, 2020 E. Fuel Storage On -site fuel storage was found to be located in a location different than shown on the plans and without the specified spill protection countermeasure. While on -site location is adequate, it is recommended that spill prevention secondary containment system be implemented, as prescribed by the plans, as soon as possible. Figure 5 — On -Site Fuel Storage F. Maintenance Maintenance of most stabilization efforts and perimeter controls appeared to be adequate. In at least one location, however, it was apparent that heavy rains led to the washout of a seeded slope. All mitigated areas and control measures need to be reviewed after significant rainfall events, as prescribed in the plans. It is recommended that this slope be redressed asap, and that other measures are checked for adequacy now and after each subsequent event. Figure 6 - Roadside Fill Slope Requiring Maintenance for9NhI., Page 6 of 7 Hillcrest Vineyard - Erosion & Sediment Control Status / Review April 3, 2020 Recommendations for Stormwater Management Treatment (Next Steps) While the site has predominantly been constructed within the general parameters outlined in the plans, it was noted (and communicated by Mr. McGinnis) that field changes were made to the precise locations of buildings, and width/slope of the parking lot. These changes will have stormwater management implications that will need to be addressed prior to the release of any related stormwater management bonds. It is my opinion that most effective treatment would be for Mr. McGinnis to commission a surveyed as -built of on -site conditions immediately following the establishment of final grade within the top -of -hill vicinity (improved portions). At that time, Mr. McGinnis should also commission an engineering review (by myself or another qualified professional engineer licensed to perform such duties) of the established conveyance channels, to ensure that capacity and erosive properties are property safeguarded. Recommendations for mitigation will be made for conveyance on an as -needed basis. The pond should be re-evaluated based upon final upstream conditions to ensure the prescribed spillway is adequate prior to its incorporation. If any changes are needed, a revised design would be submitted. As-builts with modified design (if/as necessary) and supporting calculations would then be submitted for County review and concurrence. Upon County approval, Mr. McGinnis would be tasked with performing the necessary mitigation along with construction of the pond's spillway and buffer enhancement precisely as depicted on the plan set. A secondary as -built should be required to ensure mitigation and stormwater management procedures were incorporated as prescribed. County release of associated bond amounts would follow review and acceptance of the final as -built. I hope that this letter and its recommendations are adequate to your present and future needs regarding this site. If you should have any suggestions for further mitigation and/or procedural modifications looking forward, please review with me as soon as possible. Sincerely, K____ Seth Roderick, PE Managing Partner Monteverde Engineering & Design Studio 'oortNoc' Page 7 of 7