Runoff Water Quality

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Draft of an article by Bob Brobst, USEPA, and Charles Caudill, L/E WWTP

Why Should Runoff Water Quality be a problem?

Biosolids or its constituents as with any other fertilizer or soil conditioner has the potential to be carried from applied areas during rainfall events. This runoff may cause contamination of surface waters and impact its uses.

What Does the Research say?

Rainfall of enough magnitude and duration on agricultural sites will cause runoff to form. The question is, will the runoff be contaminated enough to cause pollution problems downstream of the application site? Runoff studies to be of value must be conducted in a manner so that one study can be compared with another. The standard test storm is represented by a 10 cm (4-inch) per hour storm event, in practice 5 cm (2 inches) per 30 minutes-using specific sprinkler heads. The following are findings from studies conducted on agricultural as well as grassland sites.

Effects on Surface Water from Dryland Agricultural Sites

In practice, the surface water pollution potential from application of biosolids is greatest on surface-applied biosolids on bare soil, followed by injected and/or incorporated biosolids. Agriculture practices are changing to more sustainable operations, leaving the surface of the soil covered with organic matter. Studies (Mostaghimi 1989) were completed utilizing a rainfall simulator to measure the effects of different tilling systems at different biosolids application rates. The application method having the least potential for causing off-site contamination from surface water is surface-applied under a no-till farming program. The TKN (total nitrogen) in the runoff for conventional tillage/surface-applied biosolids was 1.5 times that of the no-till. The NO3-N (nitrate nitrogen) in the runoff for the conventional tillage/surface-applied biosolids was 3.6 times that of the no-till systems.

Effects on Surface Water from Irrigated Agricultural Sites

The City of Fort Collins, Colorado operates a resource recovery farm east of the city. The city, to control nitrogen, has set up a nutrient management plan. The farm is a working farm raising corn as its primary crop. The farm was laser leveled in 1985 to aid in surface irrigation. Biosolids were applied to the farm at agronomic rates. In monitoring upstream irrigation water quality as well as downstream irrigation water quality the city found no significant change in all forms of nitrogen; NO3-N, NO2-N, NH3-N and TKN-N. (Houck 1987).

Effects on Surface Water from Grasslands

Runoff and erosion generally increase with decreased vegetation and increased slope. Studies (Harris-Pierce 1995, Aguilar 1992) on arid and semiarid lands have shown that, of the constituents measured in runoff, all were less than the drinking water standards and below the recommended levels for livestock waters. Several papers found that with each successive runoff event the concentration of the constituents of concern was reduced by 55 percent to 80 percent (McLead et al 1984) with each successive storm event. Significant reductions in both surface water runoff and erosion, even under simulated severe precipitation conditions on 10 percent slopes, were confirmed in US Forest Service/City of Albuquerque trials (Aguilar 1992) at Sevilltea LTER Area (see photograph 5). Runoff yields from the non-applied control plots increased progressively with increased precipitation and storm duration. The biosolids applied plots did not follow this pattern. The runoff from the treated plots remained 2 percent of the precipitation input. (See figure 13). Several reasons have been suggested for the lack of runoff, one being the even distribution of the organic matter on the biosolids application sites. The other is that the biosolids together with the high infiltration rates reduced the site runoff.

Effects on Soil Stability

Application of biosolids can reduce erosion through stabilizing the soil surface and promoting infiltration. Studies (Epstein et al 1975, Kelling et al 1977 and Kladivko et al 1979) have shown that this was accomplished through protection of the soil surface against rain drop impact and the associated erosion.

What Best Management Practices can be used to Minimize the Potential for Runoff

  • Surface application to no-till fields or fields with vegetative growth
  • Injection to bare fields or application followed by incorporation
  • Selection of fields with minimal slope
  • Use of vegetative buffer strips on the perimeter of applied areas as well as many other soil erosion control management practices.


Aguilar, R., J.R. Gosz, and T.W. Ward. 1992. Sewage Sludge Application in Semiarid Grasslands: Effects on Vegetation and Water Quality, Annual Report of Attainment Project Number 1423645 New Mexico Water Resources Research Institute, May 31, 1992 pp.1-15.

Epstein, E., J.M. Taylor, and R.L. Chaney. 1975. Effects of Sewage Sludge and Sludge Compost Applied to Soil on the Soil Physical and Chemical Properties. J. Environ. Qual.. Vol. 5 No. 4, pp. 422-426.

Harris-Pierce, R.L., Redente, E.F., and Barbarick, K.A.. 1995. Sewage Sludge Application Effects on Runoff Water Quality in a Semiarid Grassland. J. Environ. Qual.. Vol. 24. pp. 112-115.

Houck, C.P., S.P. Putnam, and F. Loehr. 1987. Initial Operation Report of Sludge Farm, Journal of Environmental Engineering. Vol. 113. No. 5. October pp. 970-978.

Kelling, K.A., A.E. Peterson, and L.M. Walsh. 1977. Effect of Wastewater Sludge on Soil Moisture Relationships and Surface Runoff. Journal WPCF. pp. 1698-1703.

Kladivko, E.J. and, D.W. Nelson. 1979. Surface Runoff from Sludge-amended Soils. Journal WPCF. Vol. 51. No.1. pp. 100-110.

McLeod, R.V. and R.O. Hegg. 1984. Pasture Runoff Water Quality from Application of Inorganic and Organic Nitrogen Sources. J. Environ. Qual. Vol. 13, No. 1 pp. 122-126.

Mostaghimi, S., et al. 1989. Impacts of Land Application of Sewage Sludge on Runoff Water Quality. Transactions of the ASAE, Vol. 12, No. 2, pp.491-496.

*Peer Reviewed Articles. Peer review means that the listed references have gone through a separate detailed scientific review before the article could be published. All of the listed references have gone through that additional review process.