A. Sediment Control Measures: On site sediment control measures, as specified by the following criteria, shall be constructed and functional prior to initiating clearing, grading, stripping, excavating or fill activities on the site:
1. For disturbed areas draining less than one acre, filter barriers (including filter fences, straw bales or equivalent control measures) shall be constructed to control all off site runoff as specified in the referenced handbooks. Vegetated filter strips, with a minimum width of twenty five feet (25'), may be used as an alternative only where runoff in sheet flow is expected.
2. For disturbed areas draining more than one but less than five (5) acres, a sediment trap or equivalent control measure shall be constructed at the downslope point of the disturbed area.
3. For disturbed areas draining more than five (5) acres, a sediment basin or equivalent control measure shall be constructed at the downslope point of the disturbed area.
4. Sediment basin and sediment trap designs shall provide for both detention storage and sediment storage and shall be composed of equal volumes of “wet” detention storage and “dry” detention storage and each shall be sized for the 2-year, 24-hour runoff from the site under maximum runoff conditions during construction. The release rate of the basin shall be that rate required to achieve minimum detention times of at least ten (10) hours. The elevation of the outlet structure shall be placed such that it only drains the dry detention storage.
5. The sediment storage shall be sized to store the estimated sediment load generated from the site over the duration of the construction period with a minimum storage equivalent to the volume of sediment generated in one year. For construction periods exceeding one year, the 1-year sediment load and a sediment removal schedule may be substituted.
B. Stormwater: Stormwater conveyance channels, including ditches, swales and diversions, and the outlets of all channels and pipes, shall be designed and constructed to withstand the expected flow velocity from the 10-year frequency storm without erosion. All constructed or modified channels shall be stabilized within forty eight (48) hours, consistent with the following standards:
1. For grades up to four percent (4%), seeding in combination with mulch, erosion blanket, or an equivalent control measure shall be applied. Sod or erosion blanket or mat shall be applied to the bottom of the channel.
2. For grades of four percent (4%) to eight percent (8%), permanent ditch checks and sod, or an equivalent control measure, shall be applied in the channel.
3. For grades greater than eight percent (8%), rock, riprap or an equivalent control measure shall be applied, or the grade shall be effectively reduced using drop structures.
C. Stabilization Of Disturbed Areas: Disturbed areas shall be stabilized with temporary or permanent measures within seven (7) calendar days following the end of active disturbance, or redisturbance, consistent with the following criteria:
1. Appropriate temporary or permanent stabilization measures shall include seeding, mulching, sodding and/or nonvegetative measures.
2. Areas having slopes greater than twelve percent (12%) shall be stabilized with sod, mat or blanket in combination with seeding, or equivalent.
D. Land Disturbance Activities: Land disturbance activities in stream channels shall be avoided, where possible. If disturbance activities are unavoidable, the following requirements shall be met:
1. Construction vehicles shall be kept out of the stream channel to the maximum extent practicable. Where construction crossings are necessary, temporary crossings shall be constructed of nonerosive material, such as riprap or gravel.
2. The time and area of disturbance of stream channels shall be kept to a minimum. The stream channel, including bed and banks, shall be restabilized within forty eight (48) hours after channel disturbance is completed, interrupted or stopped.
3. Whenever channel relocation is necessary, the new channel shall be constructed and fully stabilized before flow is diverted.
E. Storm Sewer Protection: Storm sewer inlets and culverts shall be protected by sediment traps or filter barriers meeting accepted design standards and specifications.
F. Soil Storage Piles: Soil storage piles containing more than ten (10) cubic yards of material shall not be located with a downslope drainage length of less than twenty five feet (25') to a roadway or drainage channel. Filter barriers, including straw bales, filter fence, or equivalent, shall be installed immediately on the downslope side of the piles.
G. Dewatering Devices: If dewatering devices are used, discharge locations shall be protected from erosion. All pumped discharges shall be routed through appropriately designed sediment traps or basins, or equivalent.
H. Roadway Protection: Each site shall have a graveled (or equivalent) entrance road, access drive and parking area of sufficient length and width to prevent sediment from being tracked onto public or private roadways. Any sediment reaching a public or private road shall be removed by shoveling or street cleaning (not flushing) before the end of each workday and transported to a controlled sediment disposal area.
I. Maintenance Of Erosion And Sediment Control: All temporary and permanent erosion and sediment control practices must be maintained and repaired as needed to assure effective performance of their intended function.
J. Disposal Of Temporary Erosion And Sediment Control: All temporary erosion and sediment control measures shall be disposed of within thirty (30) days after final site stabilization is achieved with permanent soil stabilization measures. Trapped sediment and other disturbed soils resulting from the disposition of temporary measures should be permanently stabilized to prevent further erosion and sedimentation.
(1987 Code § 18.50-12)