Warrenton Chase Attachment 3  

TECHNICAL MEMORANDUM

TO:                  Robert C. Counts, Assistant Chief of Planning

                        Deirdre B. Clark, Senior Planner

FROM:             Christer P. Carshult, P.E., County Engineer

DATE:             April 15, 2003

SUBJECT:        Toll Brothers, Inc., Warrenton Chase

Warrenton  Service District

SE03-C-20, SE03-C-21, SE03-C-22, and PP03-C-17

A technical review of the above referenced special exception requests and preliminary plan has been performed.  Revised information addressing the review performed for the February Planning Commission meeting was received on April 2, 2003 .  A post submission meeting was performed on April 8, 2003 at the request of the applicant to review the revised information.  A supplemental SWM Concept Plan was received on April 11, 2003 as a result of that meeting.  The main thrust of this review is to assess the revised SWM Concept Plan.  See Comments #5 and 6 under the heading of “Floodplain Uses”.  Other items identified with previous reviews are included with this review as they apply to the current submission.  There may still be the need for certain lots to be adjusted during the final plan development stage to accommodate preservation of natural drainage features and steep topographic constraints once more detailed information becomes available.  The following items are provided for your consideration prior to recommendation for final approval:

SPECIAL EXCEPTIONS:

Water Storage Facility

1.       Water supply to the proposed storage facility should be investigated to determine the feasibility of the proposed water distribution approach.  The current proposal requires that a new waterline be extended along Frytown Road from the Route 605 location to the site.  This requires crossing multiple parcels of land along what appears to be a 30’ prescriptive easement.

2.       No further technical comments at this time on the proposed storage tank itself.

3.       A water model will be required at final design to demonstrate adequate domestic supply as well as fire protection with the proposed system.  The model should be designed to introduce looping and redundancy in the system.

Private Sewage Facility

It is the opinion of the engineering department that this development should occur on public sewer service, however, the following comments are provided.

1.       The location and extents of the mass drainfield must be identified on the plan.  It appears as though it will be adjacent to the existing 100-year floodplain.  Drainfields should be contiguous and connected.  Primary and Reserve areas should be clearly identified.

2.       A draft ordinance addressing these types of facilities was received in early April of this year.  It does not appear as though the proposed sewage facility, drainfield(s), and preliminary plan cannot meet the requirements of the WSA draft ordinance as currently designed.  (Open Space requirements, reserve fields, performance standards with respect to design specifications, etc.)

3.       Detailed soils analysis will be required to determine feasibility.  A considerable portion of the site is characterized by soils that are classified as marginal to not suited for development utilizing conventional septic tank and drainfield sewerage.  It appears as though a significant area that will be used for the mass drainfield adjoins an existing FEMA floodplain and will ultimately propose drainfields adjacent to it.  An approved drainfield plat should be required prior to preliminary plat approval.

Floodplain Uses

1.       The FEMA regulatory floodplain must be reflected on the preliminary plan.  The floodplain represented is one that has not been submitted to and revised by FEMA.  Until a floodplain revision has been received and processed by FEMA, the review of this request must be based on the existing regulatory maps on file with Fauquier County .

2.       All applicable Federal, State, and Local (i.e. – USACOE, DEQ, VMRC, etc.) permit requirements will need to be met prior to final approval of the construction plans.

3.       The plan reflects one SWM Facility and only two crossings of the 100-year floodplain.  The statement of justification references “several lines” necessary to cross the floodplain.  All crossings must be identified to allow for full consideration of the proposed impacts.

4.       The SE request was to be revised to allow for potential impacts along Duhollow Road as a result of a realigned entrance configuration.  Additionally, the proposed trails were to be included in the request if necessary, it does not appear as though those have been incorporated as previously discussed.

5.       The revised SWM Concept Plan indicates that SWM/BMP requirements of the development are capable of being achieved outside of what is being represented as the “revised” floodplain limits.  All SWM/BMP facilities should be designed outside of the FEMA defined floodplain limits.

6.       Preliminary BMP calculations indicate that open space credit is being claimed in the proposed drainfield locations.  This is not permitted and will need to be revised when final calculations are prepared.

PRELIMINARY PLAN

All comments from the special exception request apply to this portion of the review also.

1.       The conceptual layout and final design should honor the natural terrain of the site with respect to the roadway network and future house sites.  Many of the proposed lots have slopes approaching 25% in the location of the ultimate house pad.  The following lots may need to be revisited at the final construction plan stage to meet ordinance requirements:  Lots 102 and 103 and others that are not as severe.)

2.       The conceptual layout and final design should honor natural drainage and water features such as existing wetlands, drainage swales, and springs.  Many of the proposed lots have these features across them in the location of the ultimate house pad.  The following lots may need to be revisited at the final construction plan stage to meet ordinance requirements:  Lots 20, 27, 34, 38, 57, 65, 66, 67, 69, 70, 73, 74, 75, 76, 77, 128, 135, 140, 143, 144, 147, and others that are not as severe.)

3.       A detailed overlot grading plan will be required at final construction plan preparation.

4.       The identified wetlands will need to be verified by the US Army Corps of Engineers (COE).  Any impacts will need to be approved and permitted by the COE prior to final construction plan approval.

5.       At all existing Inter-parcel connections, the applicant will be required to perform all final construction and remedial work offsite within the provided temporary construction easements to make the final connection functional and permanent.

6.       A detail of the transition from the proposed curb and gutter street section to existing ditch section will be required at all Inter-parcel connections.

7.       Sidewalks must be 5’ in width or other ADA requirements must be accommodated.

It is recommended that written correspondence be obtained addressing the above items prior to recommendation for approval of the preliminary plat.

Please note that additional technical issues may arise at the final design stages that are not readily apparent with this submittal.

Should you have any questions regarding this review, please contact me.