CONVERSION FACTORS Temperature in degrees Celsius (ο C) may be converted to degrees Fahrenheit (ο F) as follows: o F=1.8 o C+32. Specific conductance is given microsiemens per centimeter at degrees Celsius (µS/cm at 25 ο C). Concentrations of chemical constituents in water are given either in milligrams per liter (mg/L) or micrograms per liter (µg/L). DATUM Sea level: In this report, "sea level" refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929)-a geodetic datum derived from a general adjustment of the first-order level nets of both the United States and Canada, formerly called Sea Level Datum of 1929. ABBREVIATIONS ABI Applied Biosystems bp base pairs CaCO 3 calcium carbonate CFU/100mL colony forming units per 100 milliliters CH 4 methane CM-1 absorbance per centimeter length CO 2 carbon dioxide DDMMSS degrees, minutes, seconds different in this study than DOC collected during wetter periods. Samples of shallow ground water collected during stormflow from beneath recharge facilities along the Santa Ana River show that most fecal indicator bacteria and DOC were removed as water infiltrated into the streambed. Health Department from 1986 to 1994 (Orange County Health Department, written commun., 1999), the rapid, short-term changes in microbial quality resulting from stormflow runoff in the Santa Ana River previously have not been studied. To address potential public health effects, the chemical and microbiological quality of water recharged from the Santa Ana River to aquifers underlying Orange County that are used for public supply also has been studied as part of the SARWQH study. Similar studies have been done in parts of Los Angeles County (Leenheer and others, 2001; Schroeder and Anders, 2002) and other areas where treated wastewater is used to recharge aquifers pumped for public supply. Introduction 5 Basin boundary County line LAND USE Open space, recreation, vacant or undeveloped Agriculture-Cropland and pasture Agriculture-Livestock Surface water Urban-Industrial, transportation and military Urban-Commercial Urban-Residential