HomeMy WebLinkAboutSUB200800287 Review Comments Critical Slope Waiver 2010-09-216-&A
County of Albemarle
Department of Community Development
Memorandum
To: Summer Frederick, Current Development planning and zoning review
From: Phil Custer, Current Development engineering review
Date: 21 September 2010
Subject: Fontana Phase 4C critical slope waiver request (SUB- 2008 - 00287)
The critical slope waiver request has been reviewed. The engineering analysis of the request follows:
Description of critical slope area and proposed disturbance:
The applicant is requesting a waiver to disturb critical slopes to develop his parcel in accordance with
ZMA- 2004 - 00018. The disturbance is needed to construct the roadways, pedestrian paths, SWM facility( -
ies), ESC measures, and the general mass grading required by Proffer 2. The alignment of the roadways
and lot layout match the approved rezoning plan. It should also be noted that the overlot grading plan is
still under review and will need to be modified, especially around lots 28 -31 where a retaining wall is still
shown. For further information regarding the status of the overlot grading plan, please refer to the
engineering comment memo dated 13 August 2010.
Areas
Acres
Total site
17.146 acres approximately
Critical slopes
2.4 ac.
14% of site
Critical slopes disturbed
1.7 ac.*
70% of critical slopes
*This number was not provided by the applicant in his request letter. I generated this number after
reviewing the grading plan and assuming that the slope at the rear of lots 12 -13 was the only area of the
parcel that would remain undisturbed, except for the construction of the trail across this slope. This
number is also subject to change because a full construction set (ESC, SWM, and road plans) has not been
reviewed.
Exemptions to critical slopes waivers for driveways, roads and utilities without reasonable
alternative locations:
The disturbance to critical slopes to construct the roadways, SWM facility, and pedestrian paths could be
considered exempt per 18- 4.2.6.c. Disturbances to critical slopes necessary to construct the offsite
drainage conveyance will be considered exempt per 18- 4.2.6.c
Compliance with Zoning Ordinance 18 -4.2:
"movement of soil and rock"
Given the existing topography on site, the ESC plan for this phase of Fontana will be challenging. Not
only is a significant portion of the property a critical slope (14% of the acreage), the average slope is
close to 19 %. Standard ESC measures will likely be employed: a sediment basin, sediment traps,
diversion dikes, and silt fence. However, because of the slopes of the existing and proposed
topography, soil loss will be greater than the average site.
"excessive stormwater runoff'
A stormwater management plan must be approved for this project prior to construction. The plan will
collect as much of the runoff as possible and direct it to Stormwater Management facilities.
Albemarle County Community Development
Engineering Review comments
Page 2 of 2
"siltation"
Please refer to the "movement of soil and rock" section.
"loss of aesthetic resource"
The critical slopes located within Sections 1 and 2 are not an aesthetic resource in my opinion. Nearly
all of the critical slopes in these sections were created when other phases of the Fontana Development
were constructed. However, the critical slopes within Section 3 appear to be natural and are associated
with an intermittent stream on TMP 78 -57. This tract is somewhat screened by the existing forest on
TMP 78 -57.
"septic effluent"
This development must be by public sewer.
Concluding Remarks:
In light of the erosion challenges facing this site, engineering review recommends approval of the waiver
with the condition that one WPO plan is submitted for all of Phase 4C and that the site is constructed at
one time. It is my understanding that this was the original intention of the Overlot Grading Proffer but it
was not expressed clearly.
File: E csvN PBC Fontana Phase 4C.doc