Impact of Residential Soil Disturbance on Infiltration Rate and Stormwater Runoff1

Soil disturbances such as excavation and compaction in residential developments affect lawn infiltration rates and stormwater runoff. These effects were investigated via measuring saturated infiltration rates at 108 residential sites and 18 agricultural sites near Shippensburg, south-central Pennsylvania, using a double-ring infiltrometer. Residential sites included four neighborhoods distributed across three soil series classified as hydrologic soil group (HSG) B. Additional parcel data included date of house construction, percentage impervious area, lawn condition, and woody vegetation condition. Measured infiltration rates ranged from 0 to > 40 cm/hour. Analysis of variance indicated significantly different mean infiltration rates (p < 0.001) for lots constructed pre-2000 (9.0 cm/hour) and those constructed post-2000 (2.8 cm/hour). Test results were used to determine a "field-tested" HSG for each site, representing disturbed soil conditions. Stormwater runoff was estimated from residential lots for a range of 24-hour design storms using the TR-55 model and several alternative methods of determining curve numbers, including five different representations of soil conditions. Curve numbers and stormwater runoff were substantially higher when based on field-tested HSGs for lots constructed post-2000 compared with lots built pre-2000 and when based on the HSG for undisturbed soils, documenting the magnitude of possible error in stormwater runoff models that neglect soil disturbance.