HomeMy WebLinkAboutSUB201000119 Review Comments Critical Slope Waiver 2011-08-30OF ALBS
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County of Albemarle
Department of Community Development
Memorandum
To: Megan Yaniglos, Current Development planning and zoning review
From: Phil Custer, Current Development engineering review
Date: 30 August 2011
Subject: Granger Preliminary Plat (SUB- 2010 - 00119) Critical Slope Waiver Request
The critical slope waiver request has been reviewed. The engineering analysis of the request follows:
Description of critical slope area and proposed disturbance:
Disturbances to critical slopes shown in this preliminary plat exist throughout the parcel. There is also
considerable disturbance shown on adjacent parcels which is necessary for the construction of Sunset Ave.
Extended north of the Moore's Creek stream crossing. The majority of the critical slope disturbance
occurs with the construction of Lot 69, stream crossing 1, Sunset Avenue Extended north of Moore's
Creek, and Pond 2. Other disturbance are scattered throughout the site and are needed for lot grading,
drainage pipes /channels, utility lines, and house construction.
Areas
Acres
Total site
69.4 acres approximately
Critical slopes
17.4 acres*
25% of site
Critical slopes disturbed
3.52 acres*
20.2% of critical slopes
*These are the numbers provided by the applicant. However, the offsite work to construct Sunset Avenue
and Stribling north of Moore's Creek does not appear to be included in the applicant's request.
Exemptions to critical slopes waivers for driveways, roads and utilities without reasonable
alternative locations:
The disturbance necessary to construct the Sunset Avenue Connector is exempt from the prohibition to
disturb critical slopes because any development of this parcel will require this connector road to be built to
the property line.
Stormwater management facilities may be considered exempt if there is no reasonable alternative to critical
slope disturbances. In most cases with this project, the alternative to the disturbance shown in this plan
regarding the construction of SWM facilities is a reduction to the total number of proposed lots. The
Planning Commission's review of the critical slope waiver should not consider the disturbance necessary
to construct the stormwater facilities shown on the plan to be exempt.
Similarly to the disturbance necessary to construct SWM facilities, public utilities may be considered
exempt if there is no reasonable alternative to the critical slope disturbances. The disturbances to critical
slopes shown in this plan for utility construction can be reduced or eliminated by a decrease in the number
of lots. The Planning Commission's review of the critical slope waiver should not consider the disturbance
necessary to construct the public utilities shown on the plan to be exempt.
Compliance with Zoning Ordinance 18 -4.2:
Albemarle County Community Development
Engineering Review comments
Page 2 of 2
,'movement of soil and rock"
An erosion and sediment control plan will be required for the proposed disturbance. Developments of
this size will require sediment traps and basins along the stream buffer and floodplain. The stormwater
facilities as shown can likely be designed as a sediment basins and meet state ESC standards.
Sediment loss can be further minimized with a comprehensive, overlot grading plan.
"excessive stormwater runoff'
Stormwater management is required for this project. However, due to the size of the watershed, the
county engineer may look favorably on a detention waiver. In which case, the additional stormwater
runoff from the site will be insignificant when compared to the amount of water flowing through
Moore's Creek. Then again, the 1996 study of the Moore's Creek watershed noted the history of
flooding along this stream and advised against future detention waivers.
"siltation"
Inspection and bonding by the County will ensure siltation control during construction. Proper
stabilization and maintenance will ensure long term stability.
"loss of aesthetic resource"
A significant portion of the disturbed slopes are shown on the county's open space plan.
"septic effluent"
This development will be serviced by public sewer.
Engineering Recommendation:
The construction of the Granger Property disturbs a significant amount of critical slopes. The plans seems
to encroach along the fringes of bands of critical slopes. If development were pulled slightly back a
considerable portion of critical slopes could be spared. In some cases, design changes to avoid critical
slope disturbances are obvious and should be made by the applicant. For instance, the pipe at the end of
Granger Way could be redirected to Pond 3 down the fill slope at the elbow of the alley since this area is
already being disturbed. Another example is the relocation of the sewer line in the middle of lots 22 -26
farther up the hill, above the band of critical slope, so the area in between is not disturbed by the
homebuilder or lot owner in the future.
The Planning Commission will need to weigh the benefits of the Granger application, primarily the
greenway dedication and the connector road against the disturbances to critical slopes. Should the
Planning Commission decide to approve the critical slope waiver request, engineering recommends a
condition be placed on the approval that requires the applicant to provide an overlot grading plan to be
approved with the road, ESC, and SWM plans so that the construction of each lot will be under the grading
permit of just one plan and that the applicant redesigns the aspects of the plan mentioned in the previous
paragraph. All of the standard aspects of an overlot grading plan condition/proffer should be duplicated
for this application.
file: E2_csw_PBC_Cranger Preliminary Plat CSW.doc