HomeMy WebLinkAboutWPO201700011 Plan - E&S WPO VSMP 2017-12-21 EROSION AND SEDIMENT CONTROL NARRATIVE
FOR
MEADE BUILDERS OFFICE BUILDING
September 18, 2017
LOCATION: , r; /
TM 78-15C3 0� � �;f,
Albemarle Count Virginia Y� 9 t o• r•��`
MICH/F.MYERS '��.
L. .No.33028 4
•
OWNER: ' , o �'��g'`
Ballif Investments, LLC
170 South Pantops Drive SSioNAL ,
Charlottesville, Virginia 22911
PREPARED BY:
Dominion Engineering & Design, LLC
172 South Pantops Drive
Charlottesville, VA 22911
P: 434.979.8121
F: 434.979.1681
Total disturbed area = 0.71 acres
APPROVED
by the Albemarle County
Community Development Department
Date It i
File__ 1✓h�nu oaog
At PROJECT DESCRIPTION:
The purpose of this plan is to build parking and circulation areas for an existing building
(2,000 sf) and a proposed building (2,200 sf).
A2. EXISTING SITE CONDITIONS:
The site is paved and wooded with an existing 2,000 sf building. The back 0.30 Ac
wooded area is to be preserved.
B3. ADJACENT AREAS:
The site is bounded on the North by South Pantops Dr, on the East by Parcel 78-15C3, on
the South by the Rivanna River, and on the West by Parcel 78-20.
B4. SOIL DESCRIPTIONS:
The site consists of B soils, specifically 71D, 13E and 88.
1. Catoctin very stony silt loam, 25 to 45 percent slopes, (13E)
Permeability is well drained, runoff is medium.
2. Rabun clay loam, 15 to 25 percent slopes, (71E)
Permeability is well drained, runoff is high.
3. Udorthents, (88)
B5. CRITICAL AREAS:
There are steep slopes in the back portion of the site that will be preserved.
B6. EROSION AND SEDIMENT CONTROL MEASURES:
Unless otherwise indicated, all erosion and sediment control practices will be constructed
and maintained according to the minimum standards and specifications as set forth in the
Virginia Erosion and Sediment Control Handbook, latest edition. The minimum standards
of the Virginia Erosion and Sediment Control Regulations shall be adhered to unless
otherwise waived or approved by variance.
TEMPORARY CONSTRUCTION ENTRANCE (CE) —3.02
A construction entrance shall be provided at the entrance of the project site to provide a
means of removing sediment from the tires of construction vehicles leaving the work site.
The Contractor shall remove any mud from the existing road surface by means of
sweeping and shoveling, in the event the wash area is not adequate in sediment removal.
Sediment-laden runoff is to be directed towards the sediment basin.
SILT FENCE (SF) —3.05
Silt fencing will be installed as a first step in construction activities. Location and details
are shown on the plans.
TEMPORARY DIVERSION DIKE (DD) — 3.09
A temporary diversion dike will be installed before site grading begins, for the purposes of
diverting storm and sediment-laden runoff to the appropriate outlet or trapping facility.
Location and details are shown on the plans.
1
TEMPORARY SEDIMENT TRAP (ST)— 3.13
A temporary sediment trap will be installed before site grading begins on Phase 3, for the
purpose of detaining sediment-laden runoff from disturbed areas. Location and details of
the sediment traps are shown on the plans.
OUTLET PROTECTION (OP) — 3.18
Structurally lined aprons or other acceptable energy dissipating devices placed at the
outlets of pipes or paved channel sections.
TREE PROTECTION (TP) —3.38
Tree protection will be installed as a first step in construction activities to serve to protect
offsite trees from injury during land disturbing activities. Please note that tree protection
will not be provided for the existing trees onsite that are within the construction area so
that the archaeologist can successfully perform his analysis without impediment from tree
protection fencing. Great care is to be taken in clearing under drip lines as discussed in
the archaeological study work plan.
B7. PERMANENT AND TEMPORARY STABILIZATION:
TEMPORARY SEEDING — 3.31
Temporary soil stabilization shall be applied within 7 days to denuded areas that may not
be at final grade, but will remain dormant (undisturbed) for longer than 30 days and less
than 1 year. This includes, but is not limited to areas such as soil stockpiles. Seeded
areas shall be limed when necessary at a rate of 2 tons per acre, and fertilized at a rate of
450 lbs. per acre of 10-20-20 (10 lbs. per 1,000 square feet) or equivalent. Contractor
may use a 50/50 mix of Annual Ryegrass and Cereal (Winter) Rye spread at a rate of 100
lb/acre, or choose an alternate from Table 3.31-C of the Virginia Erosion and Sediment
Control Handbook.
MULCHING — 3.35
All seeded areas shall be mulched with straw immediately following seeding operations.
Straw mulch shall be applied at a rate of two tons per acre.
PERMANENT SEEDING —3.32 (OPTIONAL)
A perennial vegetative covering shall be established on disturbed areas within 7 days of
being brought to final grade on areas not otherwise protected. Selection of the seed
mixture shall depend on the time of year it is to be applied according to the Permanent
Seed Schedule as shown on the drawing. Seeded areas shall be limed when necessary
at a rate of 2 tons per acres, and fertilized at a rate of 1,000 lbs. per acre of 10-20-10 (10
lbs. per 1,000 square feet) or equivalent. Use a mixture of Kentucky 31 Fescue (108 lbs),
Red Top Grass (2 lbs), Annual Rye (20 lbs) and Crown vetch (20 lbs) or other approved
permanent seeding mixture in Specification 3.32.
B8. SOIL STOCKPILES AND BORROW AREAS
A designated area for soil stockpiling within the limits of construction has been identified
and will be coordinated prior to commencement of construction.
2
B9. OFF-SITE AREAS:
It is not anticipated that off-site soil disposal areas will be needed for this project. Existing
vegetation that is cleared will be transported to a suitable offsite location.
B10. STORM WATER MANAGEMENT:
The Contractor is fulfilling the Stormwater management water quality portion by
purchasing offsite nutrient credits. The one year energy balance option has been used to
satisfy the stormwater quantity.
B11. MAINTENANCE SCHEDULE:
A program of maintenance for the erosion and sediment controls specified in this narrative
and shown on the plans will be the responsibility of the landowner and are recommended
as follows:
1. The Site Superintendent or his representative shall make a visual inspection of all
erosion and sediment controls on a daily basis until the site is stabilized and especially
after a rainfall runoff producing event to assure that all controls are in place and that
none have been damaged. Any damaged control shall be repaired prior to the end of
each workday to include re-seeding if necessary.
2. All silt trapping devices shall be cleaned out at 50 percent capacity and sediment shall
be disposed of by spreading on site. For any sediment that is to be spread on site,
contractor to ensure the spread location contains the sediment such that it does not
readily flow back to control structures or off-site.
3. Gravel outlets, if provided, shall be checked regularly for sediment buildup that may
prevent drainage. Controls shall be inspected and repaired after each rainfall and
cleaned if sediment has accumulated to half of the device's original height.
4. All earthen structures such as diversion dikes and berms shall be checked daily during
construction for breaching by equipment. Repairs shall be made immediately.
5. Silt fences shall be checked after each rainstorm to assure they have not fallen or
become clogged with silt. All repairs shall be made immediately.
6. All seeded areas shall be inspected regularly to see that good stand is maintained.
Areas will be re-fertilized and re-seeded as necessary.
7. After construction operations have ended and disturbed areas have been stabilized, all
berms and sediment-trapping devices, including the temporary culvert crossing may be
removed, after removal the ground shall be restored to its natural or proposed
condition to include establishment of permanent vegetation. Removal of any control is
contingent upon approval of the County E&SC Inspector.
B12. CONSTRUCTION SEQUENCE:
Anticipated Start Date: May, 2018
Anticipated Completion Date: May, 2019
Meade Builders Office Building Construction Sequence
NOTE: The contractor is allowed to deviate from the construction sequence per
unanticipated site conditions. The contractor must notify Albemarle County Site
Inspectors in the event that significant changes are to occur.
3
CONSTRUCTION SEQUENCE
Phase 1
1. Perform demolition operations.
2. Provide perimeter controls to include construction entrance with water source, sediment trap
(ST1), diversion dikes, silt fence, tree protection fence.
3. Contractor to exercise caution when working near the steep slopes (preserved) along the
rear of the property. Establish diversion dikes, silt fence, and tree protection at the top of
the slope as one of the first measures. Inspect and repair these controls diligently
throughout construction.
4. Direct wash water from construction entrance to diversion dikes that lead to ST1.
5. Once Phase 1 controls are installed to the satisfaction of Albemarle County, proceed to
Phase 2.
Phase 2
1. Grade pad site for new office and provide domestic utility connections and fire line
connection. Stub utilities to at least within 5' of the building. Building construction may
commence once the permit has been issued and the pad is ready for delivery.
2. Throughout Phase 2, contractor to inspect controls at the top of the steep slope area and
repair these controls diligently throughout completion of construction.
3. At the same time, contractor may begin sitework to include installation of retaining wall
adjacent on the east side of the existing building prior to excavating for SWM system.
Bottom of footer of retaining wall adjacent to SWM pipes to extend at least to below the
invert of the SWM pipes. Maintain positive flow to the sediment trap (ST1) as long as
possible prior to installation of structures 1 and 2 and level spreader. Provide a watertight
cover over the orifice and weir in the weir wall until system is operational to keep sediment
contained.
4. Provide inlet protection over the DI grate in Junction Box Structure 2 once sediment trap is
phased out.
5. Complete retaining wall construction and bring parking lot sub-grade.
6. Install curb as shown on plans.
7. Begin base stone for parking lot area.
8. Provide landscaping as shown on the landscape plan and plant any slopes steeper than 3:1
with low-maintenance ground cover such as monkey grass.
9. Provide final stabilization for all areas not built or paved on.
4
10. Remove E+S Controls with permission of County E+S Inspector.
LEVEL SPREADER NARRATIVE
In order to address adequate outfall for the proposed construction, the developer is proposing to
provide storage to meet the energy balance for the 1-year storm. In order to provide a non-
erosive outfall for the 2-year and 10-year storms, a level spreader is being proposed.
By way of background information, the drainage divide runs from East to West such that the
front 1/4 to 1/3 of the site drains by means of sheet flow to the curb and gutter along South
Pantops Drive. This outfall direction is not feasible since there is no storm drain outfall in the
vicinity of the project and flow over the sidewalk is not acceptable to VDOT due to safety and
maintenance concerns. The closest storm drain inlet is approximately 200 feet down South
Pantops Drive at an inlet in front of Advance Auto Parts. The site is bounded along the entire
rear perimeter with preserved slopes, and a piped outfall through these would be a last resort. In
order to develop a solution, the existing drainage pattern is to be mimicked and the 2 and 10-
year storm runoff will leave the site via sheet flow where it does today along the southeastern
property line.
Today, there is an existing detention trench at the rear of the site which is controlled by a 4"
PVC outfall pipe. From there, the water travels by sheet flow across the property line with the
adjacent County-owned property. There is no evidence of significant erosion at the 4" pipe
outfall and the system has been in place for at least 10 years. Our intention with the level
spreader is to mimic predevelopment conditions and provide sheet flow on to the adjacent
property.
We have proposed a 10' long concrete level spreader just downstream of the 15" outfall pipe
from the proposed SWM pipe detention system. The maximum flow from the outfall pipe will be
approximately 4 cfs. 10' is the maximum length that can be provided without significant impact
to existing water and sewer facilities and adjacent site constraints. There is an existing 10"
ACSA-waterline and an existing 24"-ASCA "AC" pipe within easements that run across the site
and through the sheet flow area. The ACSA has indicated their tentative approval of the level
spreader location due to its shallow design. Final ACSA approval will be provided prior to plan
approval.
To provide additional erosion control measures, the concrete level spreader turns to provide
additional sheet flow length to minimize scour and provide an overflow. Runoff that goes over
the concrete level spreader in any location will sheet flow into or across a 2'-wide strip of sod.
We have also provided a 65-sf pool that is 1' deep and filled with river rock to promote
infiltration of runoff into the soil. The use of concrete allows the contractor to construct the level
spreader to design elevations.
No weep holes are proposed to the level spreader due to invert. Runoff will either infiltrate or
evaporate from the pool during dry periods.
LEVEL SPREADER MAINTENANCE NOTES
1. Check for and redirect flows from the outfall pipe as needed so they do not short-circuit the
level spreader.
5
2. Check for and remove debris and sediment build up in the pool.
3. Inspect condition of rip-rap in pool.
4. Check for and address scour and erosion do not occur at the level spreader.
5. Vegetative density exceeds a 90% cover below the level spreader.
6. Once level spreader is established, there will be minimal maintenance except for: Spring
clean-up, minimum twice a year mowing, and repair of the rip-rap pool
STORMWATER MANAGEMENT NARRATIVE
Stormwater Management is provided for this site in accordance with the Technical
Requirements of Part IIB of the state drainage code. The developer is proposing to increase
the impervious area of the site to provide additional parking and a new building. For the
proposed development, channel protection and flood control is provided by means of 344' of 36"
drainage pipe with a control structure that provides detention for the 1-yr Energy Balance, 2-yr
and 10-yr storms. In order to provide a non-erosive outfall condition from the detention pipe
outfall, a level spreader curb is proposed which will re-create the current condition of sheet flow
at the rear of the property. In the event of a 100-year storm, overflow will travel safely offsite
without impacting any buildings. For water quality control, the developer is proposing to
purchase nutrient credits for the site.
SWM SYSTEM MAINTENANCE NOTES
1. Check junction box control structure weirs and any connecting or outgoing storm pipes for
sediment buildup and structural damage. Note if any sediment needs to be removed.
2. Check that no vegetation forms an overhead canopy that may drop leaf litter, fruits and other
vegetative materials that could clog the inlet.
3. Generally inspect the upland contributing drainage area for any controllable sources of
sediment or erosion.
4. Ensure maintenance access is clear and unobstructed.
5. Check to see that manhole covers can be opened and operated.
6. Based on inspection results, specific maintenance tasks will be triggered.
7. Ensure junction box and 36" detention pipes are free from sediment. Perform periodic
vacuum or manual cleaning.
8. Check weir wall to ensure weirs, openings, trash racks are not clogged and flow freely.
B. MINIMUM STANDARDS (MS):
All applicable Virginia Erosion and Sediment Control Regulations and Minimum Standards
shall be adhered to during all phases of construction. These include, but are not limited to
the following:
6
1. STABLIZATION OF DENUDED AREAS:
Permanent or temporary soil stabilization shall be applied to bare areas within seven days
after final grade is reached on any portion of the site. Temporary soil stabilization shall be
applied within seven days to denuded areas that may not be at final grade, but will remain
dormant or undisturbed for longer than 30 days. Permanent stabilization shall be applied
at areas that are to be left dormant for more than 1 year.
2. STABILIZATION OF SOIL STOCKPILES:
During construction of the project, soil stockpiles shall be stabilized or protected with
sediment trapping measures. The applicant is responsible for temporary protection and
permanent stabilization of all soil stockpiles on site as well as soil intentionally transported
from the project site.
3. PERMANENT VEGETATIVE COVER
A permanent vegetative cover shall be established on denuded areas not otherwise
permanently stabilized. Permanent vegetation shall not be considered established until a
ground cover is achieve that, in the opinion of the County Inspector, is uniform and mature
enough to survive to inhibit erosion.
4. TIMING & STABILIZATION OF SILT TRAPPING MEASURES:
Sediment basins and traps, perimeter dikes, sediment barriers and other measures
intended to trap sediment shall be constructed as a first step in any land disturbing activity
and shall be made functional before upslope land disturbance takes place.
5. STABILIZATION OF EARTHEN STRUCTURES:
Stabilization measures shall be applied to earthen structures such as dams, dikes and
diversions immediately after installation.
6. SEDIMENT TRAPS AND BASINS:
A sediment basin shall control surface runoff from disturbed areas that is comprised of
flow from drainage areas greater than or equal to three acres. The sediment basin shall
be designed and constructed to accommodate the anticipated sediment loading for the
land disturbing activity. The outfall device or system device shall take into account the
total drainage area flowing through the disturbed area to be served by the basin.
7. CUT AND FILL SLOPES:
Cut and fill slopes shall be designed and constructed in a manner that will minimize
erosion. Slopes that are found to be eroding excessively within one year of permanent
stabilization shall be provided with additional slope stabilizing measures until the problem
is corrected.
8. CONCENTRATED RUN-OFF DOWN CUT OR FILL SLOPES:
Concentrated runoff shall not flow down cut or fill slopes unless contained within an
adequate temporary or permanent channel, flume, or slope drain structure.
9. WATER SEEPS FROM A SLOPE FACE:
Whenever water seeps from a slope face, adequate drainage or other protection shall be
provided.
7
10. STORM SEWER INLET PROTECTION:
All storm sewer inlets that are made operable during construction shall be protected so
that sediment-laden water cannot enter the conveyance system without first being filtered
or otherwise treated to remove sediment.
11. STABILIZATION OF OUTLETS:
Before newly constructed stormwater conveyance channels are made operational,
adequate outlet protection and any required temporary or permanent channel lining shall
be installed in both the conveyance channel and receiving channel.
12. WORK IN LIVE WATERCOURSES:
When work in a live watercourse is performed, precautions shall be taken to minimize
encroachment, control sediment transport and stabilize the work area to the greatest
extent possible during construction. Nonerodible material shall be used for the
construction of causeways and cofferdams. Earthen fill may be used for these structures if
armored by nonerodible cover materials.
13. CROSSING A LIVE WATERCOURSE:
When a live watercourse must be crossed by construction vehicles more than twice in any
six month period, a temporary stream crossing constructed of nonerodible materials shall
be provided.
14. APPLICABLE REGULATIONS:
All applicable federal, state and local regulations pertaining to working in or crossing live
watercourses shall be met.
15. STABILIZATION OF BED AND BANKS
The bed and banks of a watercourse shall be stabilized immediately after work in the
watercourse is completed.
16. UNDERGROUND UTILITIES:
Underground utilities shall be installed in accordance with the following standards in
addition to other criteria:
a. No more than 500 linear feet of trench may be opened at one time.
b. Excavated material shall be placed on the uphill side of trenches
c. Effluent for dewatering operations shall be filtered or passed through approved
sediment trapping device, or both, and discharged in a manner that does not adversely
affect flowing streams or offsite property.
d. Material used for backfilling trenches shall be properly compacted in order to minimize
erosion and promote stabilization.
e. Restabilization shall be accomplished in accordance with these regulations.
f. Applicable safety regulations shall be complied with.
17. CONSTRUCTION ACCESS ROUTES:
Where construction vehicle access routes intersect paved public roads, provisions shall be
made to minimize the transport of sediment by vehicular tracking onto paved surfaces.
Where sediment is transported on to a public road surface, the road shall be cleaned
thoroughly at the end of each day. Sediment shall be removed by shoveling or sweeping
and transported to a sediment control disposal area. Street washing shall be allowed only
after sediment is removed in this manner. This provision shall apply to individual lots as
well as to larger land disturbing activities.
8
18. TEMPORARY E&S CONTROL MEASURE REMOVAL:
All temporary erosion and sediment control measures shall be removed within 30 days
after final site stabilization or after temporary measures are no longer needed, unless
otherwise authorized by the local program authority. Trapped sediment and the disturbed
soil areas resulting from the disposition of temporary measures shall be permanently
stabilized to prevent further erosion and sediment.
19. ADEQUACY OF RECEIVING CHANNELS:
Properties and waterways downstream from the development site shall be protected from
sediment deposition, erosion and damage, due to increases in volume, velocity and peak
flow rates of stormwater runoff for the stated frequency storm of 24-hour duration. For this
project, no impervious area is proposed and therefore no increase in runoff is anticipated
following completion of the archaeological survey.
9