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The effects of terracing on the quantity and quality of surface runoff and ground water were investigated by the U.S. Geological Survey, in cooperation with the Pennsylvania Department of Environmental Protection, during 1983-89 at a 23.1-acre agricultural site in Lancaster County, Pa., as part of the 1982 Rural Clean Water Program. The site, underlain by carbonate rock, was primarily corn and alfalfa fields; the median slope was 6 percent. Normal precipitation was about 42 inches per year. Average annual runoff was 11 percent, and ground-water recharge was 37 percent of precipitation. Runoff quantity, suspended-sediment and nutrient data, ground-water level and nutrient data, and precipitation-quantity data were collected for 21 months prior to, and 58 months after, construction of pipe-outlet terraces. Data were analyzed by use of graphical, regression, covariate, cluster, Mann-Whitney Rank Sum test, and double-mass curve techniques. Terracing changed runoff characteristics. Storm characteristics were similar throughout the study period. However, after terracing, storms producing less than 0.4 inch of precipitation rarely produced runoff. Total storm discharge as a function of precipitation did not change significantly throughout the range of runoff-producing storms after terracing. Multiple discharge peaks on hydrographs before terracing did not occur after terracing when hydrographs reflected the stepwise draining of each terrace through the pipe outlet. After an initial 2-year period of terrace stabilization, suspended-sediment yield in runoff decreased significantly as a function of runoff. This result was expected because terracing decreased runoff energy and because terrace ponding allowed time for sediment redeposition. Nitrate plus nitrite yields increased proportionally throughout the range of runoff during the post-terracing period relative to the pre-terracing period. After terracing, a combination of increased soil contact time and increased nitrification caused by wetter soils is believed to have increased nitrate concentrations in runoff. No significant change was found in yields of total nitrogen, ammonia plus organic nitrogen, or total phosphorus relative to runoff before and after terracing. Limited data suggest that fine-sediment particles (less than 0.62 micrometers in diameter), which continued to be discharged from the site, transported most of the phosphorus. Terracing did not significantly change the quantity of recharge to the carbonate aquifer. The mean annual water-table altitude did not change after terracing. Nitrate concentrations of ground water increased significantly at four of the site wells after terracing, probably because of increased contact time of the recharge with nutrient-rich soils in ponded terrace water. Qualitative evidence indicates that large decreases in nutrient requirements and nitrogen applications because of a crop change from corn to alfalfa upgradient of two site wells resulted in either no detectable change or a significant decrease in nitrate concentrations of ground water after terracing. INTRODUCTION The U.S. Geological Survey (USGS), in cooperation with the Pennsylvania Department of Environmental Protection (PaDEP)1 , conducted a study to determine the effects of agricultural best-management practices (BMP's) on surface-water and ground-water quality. This study is one of five comprehensive monitoring and evaluation projects in the U.S. Department of Agriculture's (USDA) Rural Clean Waters Program (RCWP). The RCWP, enacted by the U.S. Congress in 1979, designated the Conestoga River Headwaters Basin in Pennsylvania as 1 of 20 project areas approved for remedial action to improve streamand ground-water quality. This area was chosen because it had previously been designated as the top priority watershed in Pennsylvania's Agricultural 208 Plan. This designation had been made because the project area contains 132 mi of streams that have considerable existing or potential use for water supply, livestock watering, fish, wildlife, and recreation as well as significant ground-water use for public water supplies. Also, previous studies (U.S. Department of Agriculture, 1982; Lancaster County Conservation District, 1982; Pennsylvania Department of Environmental Resources, 1983) have demonstrated increasing degradation of surfaceand ground-water quality caused by large nonpoint discharges of suspended sediment and nutrients. The major water-quality problems include nutrients from manure, pesticides from applications to cropland, and sediment from erosion of intensively cropped land. The objective of the RCWP was to improve surface-water and ground-water quality by voluntary implementation of BMP's, such as construction of terraces, manure storage facilities, and grassy waterways and management of nutrients and pesticides. Funds were allocated to the selected project areas to implement these practices with cost-sharing as an incentive and to monitor the effects of implementation on water quality. Water-quality monitoring in the 188-mi2 Conestoga River Headwaters Basin was conducted over a 10-year period (1982-91) at three scales: regional, small watershed, and field. These areas were being monitored before and after implementation of BMP's to determine the effects of BMP's on surface-water and ground-water quality. A detailed description of the overall study can be found in "Evaluation of Agricultural Best-Management Practices in the Conestoga River Headwaters, Pennsylvania: Methods of Data Collection and Analysis, and Description of Study Areas" (Chichester, 1988). Field-Site 1, discussed in this report, was located in the Conestoga River Headwaters Basin, between Churchtown and Goodville, Lancaster County, Pa. (fig. 1). The site, underlain by carbonate rock, was conventionally tilled cropland, planted primarily in corn and alfalfa. A detailed characterization of Field-Site 1 can be found in "Evaluation of Agricultural Best-Management Practices in the Conestoga River Headwaters, Pennsylvania: Characterization of Surface-Runoff and Ground-Water Quantity and Quality in a Small Carbonate Basin Near Churchtown, Pennsylvania, Prior to Terracing and Implementation of Nutrient Management" (Lietman and others, 1996). Purpose and Scope This report documents the effects of terracing and nutrient management on surface-water and ground-water quantity and quality of a 23.1-acre field site, Field-Site 1, in the Conestoga River Headwaters project area. Climatological, agricultural-activity, and soil data as well as surfaceand ground-water quantity and quality data collected after implementation of BMP's (October 1984 through September 1989) are compared to the same type of data collected at the site before the implementation of BMP's. The pre-BMP period, from January 1983 through September 1984, is referred to as Period 1. Data from the post-BMP phase of the study is grouped into three time periods October 1984 through September 1986 is Period 2, October 1986 through September 1988 is Period 3, and October 1988 through July 1989 is Period 4. As documented in the following sections, Period 3 1 Prior to 1995, the Pennsylvania Department of Environmental Protection was the Pennsylvania Department of Environmental Resources. COMESTOGA HEADWATERS AREA Goodville 1"1 x~<>Churchtown.. Field-Site 1

water-resources investigations report

Evaluation of agricultural best-management practices in the Conestoga River headwaters, Pennsylvania: Effects of pipe-outlet terracing on quantity and quality of surface runoff and ground water in a small carbonate-rock basin near Churchtown, Pennsylvania, 1983-89