Stormwater runoff and export changes with development in a traditional and low impact subdivision.

Development continues at a rapid pace throughout the country. Runoff from the impervious surfaces in these watersheds continues to be a major cause of degradation to freshwater bodies and estuaries. Low impact development techniques have been recommended to reduce these impacts. In this study, stormwater runoff and pollutant concentrations were measured as development progressed in both a traditional development, and a development that used low impact development techniques. Increases in total impervious area in each watershed were also measured. Regression relationships were developed between total impervious area and stormwater runoff/pollutant export. Significant, logarithmic increases in stormwater runoff and nitrogen and phosphorus export were found as development occurred in the traditional subdivision. The increases in stormwater runoff and pollutant export were more than two orders of magnitude. TN and TP export after development was 10 and 1 kg ha(-1) yr(-1), respectively, which was consistent with export from other urban/developed areas. In contrast, stormwater runoff and pollutant export from the low impact subdivision remained unchanged from pre-development levels. TN and TP export from the low impact subdivision were consistent with export values from forested watersheds. The results of this study indicate that the use of low impact development techniques on a watershed scale can greatly reduce the impacts of development on local waterways.

Saturation to improve pollutant retention in a rain garden.

Rain gardens have been recommended as a best management practice to treat stormwater runoff. Replicate rain gardens were constructed in Haddam, CT, to treat roof runoff. The objective of this study was to assess whether the creation of a saturated zone in a rain garden improved retention of pollutants. The gardens were sized to store 2.54 cm (1 in) of runoff. Results show high retention of flow; only 0.8% overflowed. Overall, concentrations of nitrite+ nitrate-N, ammonia-N, and total-N (TN) in roof runoff were reduced significantly by the rain gardens. Total-P concentrations were significantly increased by both rain gardens. ANCOVA results show significant reductions in TN (18%) due to saturation. Redox potential also decreased in the saturated garden. Rain garden mulch was found to be a sink for metals, nitrogen, and phosphorus, but rain garden soils were a source for these pollutants. The design used for these rain gardens was effective for flow retention, but did not reduce concentrations of all pollutants even when modified. These findings suggest that high flow and pollutant retention could be achieved with the 2.54 cm design method, but the use of an underdrain could reduce overall pollutant retention.

Stormwater runoff quality and quantity from asphalt, paver, and crushed stone driveways in Connecticut.

This study compared the quality and quantity of stormwater runoff from replicated asphalt, permeable paver, and crushed-stone driveways. Rainfall was measured on-site and runoff was recorded using tipping buckets. Flow-weighted composite runoff samples were analyzed weekly for total suspended solids, total Kjeldahl nitrogen, nitrate-nitrogen, ammonia-nitrogen, total phosphorus (TP), zinc, lead, and copper. Infiltration rate was determined on each driveway annually. Repeated measures analysis of variance indicated that stormwater runoff was significantly different among each driveway type; the order of decreasing runoff was asphalt> paver> stone. Average infiltration rates were 0, 11.2 and 9.0 cm/h for asphalt, paver, and crushed stone driveways, respectively. Both paver and crushed stone driveways reduced stormwater runoff as compared to asphalt driveways. Runoff from paver driveways contained significantly lower concentrations of all pollutants measured than runoff from asphalt driveways. However, runoff from crushed stone driveways was similar in concentrations to runoff from asphalt driveways, except for TP concentrations, which were lower in runoff from crushed stone driveways than runoff from asphalt driveways. The mass export of measured pollutants followed the relative differences in stormwater runoff, rather than differences in concentrations.

Education and changes in residential nonpoint source pollution.

Urban areas contribute pollutants such as excess nitrogen and bacteria to receiving water bodies. The objective of this project was to determine if stormwater quality could be improved by educating homeowners and implementing best management practices (BMPs) in a suburban neighborhood. The paired watershed design was used, where a control and treatment watershed are monitored during a calibration and treatment period. Treatment consisted of the education of homeowners and structural changes designed to minimize nonpoint pollution. Some changes in measured behavior were reported. According to the treatment period survey, 11% of respondents in the treatment watershed began fertilizing their lawn based on the results of a soil test, whereas none had done so previously. In addition, 82% of respondents in the treatment watershed stated that they left clippings on the lawn compared to 62% from the initial survey. Twelve of 34 lots (35%) adopted some BMPs following education efforts, indicating a significant (P = 0.001) increase in BMP use overall. However, a chi2 analysis of survey data indicated no significant changes in measured behavior with regard to specific questions. Analysis of covariance (ANCOVA) results indicated that a 75% reduction in nitrite + nitrate - N (change in intercept, P = 0.001) and a 127% reduction in fecal coliform bacteria (change in slope, P = 0.05) concentrations occurred. However, the treatment period regression was non-significant for bacteria. Total nitrogen, total phosphorus, and ammonia-N concentrations did not change significantly. Intensive education efforts produced BMP implementation and measurable water quality improvements.

Treatment of parking lot stormwater using a StormTreat system.

The effectiveness of a StormTreat system in treating stormwater from a commercial parking lot in Connecticut was evaluated. Flow-weighted composite samples were collected from StormTreat inflow and outflow during a 2-yr study. Bypass flow was not monitored. The StormTreat significantly (P < 0.05) reduced total suspended solids, total phosphorus, total Kjeldahl-N, total zinc, total copper, and fecal coliform bacteria on a concentration basis. The StormTreat system retained 49% total suspended solids, 74% total phosphorus, 44% total Kjeldahl-N, 45% total zinc, 29% total copper, 2% total lead on a mass basis, and 99% fecal coliform on a concentration basis. Treatment efficiency was not associated with storm size, chamber stage, discharge rate, or hydraulic retention time (r < 0.355). The system retained ammonia-N more efficiently during the summer than during the winter (P < 0.01) and retained total zinc less efficiently during the summer than during the winter (P < 0.05). Season did not significantly (P > 0.05) affect the treatment of other monitored water quality variables. The StormTreat system reduced the concentrations of stormwater pollutants commonly found in parking lot runoff.