SIMPLIED STORMWATER MANAGEMENT PROCEDURES FOR EXISTING SINGLE FAMILY DWELLING LOTS

Projects eligible for this procedure

Individual home construction projects on single family lots which result in less than two thousand (2,000) square feet of impervious area (including the building footprint, driveway, sidewalks, and parking areas) and less than five thousand (5,000) square feet of earth disturbance but do not meet exemption criteria of Section 105.B may utilize the simplified procedure contained in this Appendix to meet requirements of this Ordinance and are not required to submit formal drainage plans to the Township.

Are professional services necessary to meet these requirements?

This Appendix has been developed to assist the individual homeowner in meeting the water quality and groundwater recharge goals of the Stormwater Management Ordinance. If the guidelines are followed, the individual homeowner will not require professional services to comply with these water quality and groundwater recharge goals.

What do I need to send to the Solebury Township?

Even though a formal drainage plan is not required for individual lot owners, a brief description of the proposed infiltration facilities, including types of material to be used, total impervious areas and volume calculations, and a simple sketch plan showing the following information shall be submitted to the Township prior to construction:

Location of proposed structures, driveways or other paved areas with approximate surface area in square feet.

Location of any existing or proposed onsite septic system and/or potable water wells showing proximity to infiltration facilities.

Bucks County Conservation District erosion and sediment control "Adequacy" letter.

Determination of Recharge Volume

The amount of recharge volume that must be provided is determined by following the simple steps below. Impervious area calculations must include all areas on the lot proposed to be covered by roof area or pavement which would prevent rain from naturally percolating into the ground, including sidewalks, driveways or parking areas. Sidewalks, driveways or patios that are constructed with turf pavers and are not included in this calculation.

Example Recharge Volume:

STEP 1 Determine Total Impervious Surfaces:

STEP 2 Determine Required Infiltration Volume (Rv) Using the Following Equation

STEP 3 Sizing of Selected Infiltration Method

The following pages identify several methods to infiltrate stormwater runoff. Their appropriateness depends on the amount of required infiltration volume and amount of available land. More than one method may be implemented on a site, depending on site constraints. Dry wells may be used only for receiving runoff from roof drains. Infiltration trenches are appropriate for receiving runoff from driveways, sidewalk or parking areas. Other methods may be appropriate, but these must be reviewed with the Township Engineer prior to installation.

Dry Wells

Dry wells are effective methods to infiltrate runoff from roof leaders. These facilities must be located based upon a determination by the design professional to reduce potential basement seepage problems but not less than a minimum of twenty (20) feet from the building foundation. A dry well maybe either a structural prefabricated chamber or an excavated pit filled with aggregate. Dry well shall not be constructed until all other areas of the site are stabilized, to avoid clogging. During construction, compaction of the subgrade soil shall be avoided, and construction may be performed with only light machinery. Depth of dry wells in excess of three and one-half (3 1/2) feet should be avoided unless warranted by soil conditions. "Clean" gravel fill should average one and one half to three (1.5 - 3.0) inches in diameter. Dry wells should be inspected at least four (4) times annually as well as after large storm events.

Example Sizing For Drywells:

STEP 1 Determine Total Impervious Surfaces

House Roof Area:12 ft. x 48 ft. = 576 sq. ft.

STEP 2 Determine Required Infiltration Volume using Equation

(2.04 in. x 576 sq. ft.) / 12 = 98 cu. ft.

(98 Cu. ft.) / 0.4* = 245 cu. ft. (*assumes 40% void ratio in gravel bed)

STEP 3 Sizing of Selected Infiltration Method

Volume of facility = Depth x Width x Length

Set D = 3.5 ft; Set W = L for a square chamber

245 cu. ft. = 3.5 x L X L; L= 8.4 ft.

Final Facility Dimensions: 3.5 ft. (D) x 8.4 ft. (W) x 8.4 ft. (L)

Infiltration Trenches

An infiltration trench is a long, narrow, rock-filled trench with no outlet that receives stormwater runoff. Runoff is stored in the void space between the stones and infiltrates through the bottom and into the soil matrix. Infiltration trenches perform well for removal of fine sediment and associated pollutants. Pretreatment using buffer strips, swales, or detention basins is important for limiting amounts of coarse sediment entering the trench which can clog and render the trench ineffective.