Sec. 32-162. On-Site Drainage

Drainage facilities, including but not limited to sump pumps, foundation drains, trench drains and under drains, shall be provided and shall be discharged into a publicly maintained drainage system or continuously flowing natural water course to safely convey surface and ground water in such a manner to prevent detrimental erosion, overflow, ponding or nuisance of any kind in accordance with applicable design criteria, standards and procedures as contained herein and as required by approved standards and regulations of the Prince George's County Department of Permitting, Inspections, and Enforcement.

Unless intended by design for water quality and quantity purposes, the ponding of water shall not be permitted particularly above cut or fill slopes or on drainage terraces, nor shall new development cause water to be impounded on adjacent property. Adequate drainage facilities shall be provided to prevent such ponding. Existing ponding (ponding not created by development) may remain in undisturbed, undeveloped, forested areas, unless it has objectionable effects.

Cut and fill slopes shall be terraced wherever the vertical interval (height) of any 2:1 slope exceeds twenty (20) feet; for 3:1 slope it shall be increased to thirty (30) feet; and for 4:1 to forty (40) feet. Benches shall be located to divide the slope face as equally as possible and shall convey the water to a stable outlet. Drainage terraces shall be a minimum of six (6) feet wide with an absolute minimum invert gradient of between two percent (2%) and a maximum invert gradient of three percent (3%), unless accompanied by appropriate design and calculations, and with a ten to one (10:1) lateral slope toward the toe of the upper bank, and must convey water with minimum six (6) inch freeboard to a safe disposal area.

The permittee and the owner shall make adequate provisions to prevent any surface waters from materially damaging the face of any and all earth surfaces, excavation or fill. All such earth surfaces shall be temporarily and/or permanently protected from surface water runoff from above by interceptor and diversion berms, swales brow or berm ditches, and shall be sodded, seeded and/or planted unless, upon the recommendation of the Prince George's Soil Conservation District, the Director determines such treatment is unnecessary and specifically waives this requirement pursuant to Section 32-132.

All areas designed for buildings pads shall be graded to slope away from the building in conformance with the limitations in Section 32-151.

All drainage terraces, interceptor and diversion berms, swales and ditches shall be designed and constructed in accordance with standards contained elsewhere herein and when required, shall be piped or paved or otherwise improved. In order for drainage to discharge into natural watercourses such natural ground shall be protected from erosion by an adequate amount of riprap or by other measures. Flows exceeding three (3) cubic feet per second will not be permitted in open facilities such as swales and ditches, but shall be conveyed in enclosed storm drain systems. Concentrated flow in driveways, parking lots and access lanes shall not exceed one-half (1/2) the width of paving, or ten (10) feet, whichever is less.

Overflows from one hundred (100) year storm shall be traced through the site and intervening area to their locations of discharge into a natural stream and, at critical locations, their hydraulic gradient determined to ascertain that the proposed construction does not flood or damage existing and proposed buildings or structures along the trace, as required by Division 4 of this Subtitle.

Springs and surface seeps and other ground waters having objectionable effects shall be capped with stone and/or sand with interlaced tile drains or perforated pipes connecting into a piped outfall to a public storm drainage system or continuously flowing natural watercourse.

Unless otherwise permitted by Federal, State or local regulations, or the provisions of this Division, the discharge of pollutants onto land, to a drainage system, or to a watercourse within the County is prohibited.

All drainage system rights-of-way and easements shall be used by the County for the purposes of the administration of this Division to conduct activities related to enforcement, compliance, investigation and surveillance.

Downspout discharge may discharge to a properly graded area provided the point of discharge at the Building Restriction Line (BRL) or ten (10) feet from any property line and conveyed by splash block oriented parallel to said line. If the downspouts are connected into an underground drainage system, a cleanout valve and air gap for blockage overflow is required.