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EVALUATION OF DEQ RULE AUTHORIZATION CRITERION G FOR SANTA CLARA STORMWATER BASIN DRY WELLS INTRODUCTION In 1974, the U.S. Environmental Protection Agency (EPA) enacted the Underground Injection Control (UIC) program under the Safe Drinking Water Act. The Oregon Department of Environmental Quality (DEQ) was delegated primacy in Oregon by the EPA in 1984, and re- authorized in 1991. DEQ regulates the program under Oregon Administrative Rules (OAR) Chapter 340, Division 44. The intent of the UIC program is to protect groundwater quality by regulating the injection of fluids into the ground. Dry wells area type of injection system installed and used by the City of Eugene and Lane County to manage stormwater runoff from roads, parking lots, roofs, and other impervious surfaces by injecting the stormwater into the ground. Dry wells are regulated by the DEQ UIC program. DEQ developed a set of criteria, known as "rule authorization criteria" to assess whether use of an injection system is authorizable by DEQ. The criteria define certain conditions that must be met in order for the injection system to be authorizable. Criterion G specifies the condition that a dry well shall not discharge directly into groundwater or below the highest seasonal groundwater level. This technical memorandum presents the methods, results, and conclusions for assessing whether dry wells within the Santa Clara Stormwater Basin (SCSB) have a reasonable likelihood of discharging to groundwater. PROJECT LOCATION AND DRY WELL DESCRIPTION The SCSB is located in the northern portion of the City of Eugene, primarily with Sections 1 through 16, 23, and 24 in Township 17 South, Range 4 West, in Lane County, Oregon. Dry wells are typically constructed as approximately 4- foot - diameter perforated concrete pipes installed vertically within the ground. Installation steps typically include excavation of a pit, placement of the dry well pipe into the pit, and backfilling of the pit with drain rock. The depths of the dry wells are typically in the range of 10 to 15 feet. Stormwater catch basins collect stormwater runoff from curbs and gutters, and convey the stormwater to the dry wells via drainpipes. Less commonly the dry well may contain a perforated lid through which stormwater may directly discharge to the dry well. METHODS The Oregon Water Resources Department (OWRD) maintains a database of water wells installed within the state of Oregon. The database consists of copies of "well logs ", which are forms completed by well installers (drillers) to record pertinent data regarding well location, method of well construction, and hydrogeologic observations such as the water level. To assess the depth to groundwater in the SCSB, the well log database was searched to identify well logs within the township, range, and sections described above that contained useful water level information. RESULTS A search of the OWRD well log database resulted in 1,447 well log records, of which 1,187 records contained water level information. The water levels for these 1,187 records ranged from 0.7 to 230 feet below ground surface (bgs), and spanned the time from 1914 to 2006. Of these, only seven records contained water levels that were below 50 feet bgs. The mean water level for all 1,187 records was 11.6 feet bgs. Figure 1 is a time -sorted plot of the 1,187 water level records.