FIELD DOCUMENTS - Laserfiche WebLink

Home Browse Search

WASTE DISCHARGE REQUI*VIENTS ORDER NO. R5-2004-0028 t"i CITY OF MANTECA, CITY OF LATHROP AND DUTRA FARMS WASTEWATER QUALITY CONTROL FACILITY SAN JOAQUIN COUNTY 34. Arsenic: Arsenic is an inorganic priority pollutant that produces human health effects and is considered a carcinogen. Data, submitted by the discharger between January 2002 and December 2002, indicates arsenic is present in the effluent at levels that exceed the water quality objective for arsenic contained in the Basin Plan (Table III-1). The Basin Plan numeric objective for the San Joaquin-Sacramento Delta is 10 ug/1. Also,the new USEPA Primary MCL for arsenic is 10 ug/l. The maximum concentration in the effluent is 14 ug/l. The Regional Board finds that there is a reasonable potential for the discharge to cause or contribute to an excursion above the numeric water quality objective for arsenic. An effluent limitation for arsenic is included in this Order based on the Basin Plan numeric objective and the calculations outlined in Section 5.4.4 of the TSD. The effluent limitation for arsenic is 10 ug/l as a monthly average (see Table 11 of the Information Sheet). 35. Total Tribalomethanes and Chloroform: Information submitted by the Discharger indicate that the effluent contains trihalomethanes (THMs) and chloroform. The Basin Plan contains the "Chemical Constituent" objective that requires, at a minimum, that waters with a designated MUN use not exceed California MCLS. In addition, the Chemical Constituent objective prohibits chemical constituents in concentrations that adversely affect beneficial uses. The California's Drinking Water Standard primary MCL for total THMs is 100 ug/1. The USEPA primary MCL for total THMs is 80 ug/l,which was effective on 1 January 2002 for surface water systems that serve more than 10,000 people. Pursuant to the Safe Drinking Water Act, DHS must revise the current total THMs MCL in Title 22 CCR to be as low or lower than the USEPA MCL. The State Board, in WQO No 2003-0002, stated that the Drinking Water Standard primary MCL for total THMs,which includes chloroform, of 80 ug/1 could be applied to address chloroform in the discharge regulated in that Order. In addition, the Cal/EPA Office of Environmental Health Hazard Assessment(OEHHA)has published the Toxicity Criteria Database,which contains cancer potency factors for chemicals, including chloroform, that have been used as a basis for regulatory actions by the regional boards, departments and offices within Cal/EPA. This cancer potency factor is equivalent to a concentration in drinking water of 1.1 ug/l (ppb) at the 1-in-a-million cancer risk level with the consumption of the drinking water over a 70-year lifetime. This risk level is consistent with that used by the Department of Health Services (DHS)to set de minimis risks from involuntary exposure to carcinogens in drinking water in developing MCLs and Action Levels and by OEHHA to set negligible cancer risks in developing Public Health Goals for drinking water. The one-in-a-million cancer risk level is also mandated by USEPA in applying human health protective criteria contained in the National Taxies Rule and the California Toxics Rule to priority toxic pollutants in California surface waters. Municipal and domestic supply is a designated beneficial use of the receiving water. However, there are no known drinking water intakes on the San Joaquin River within several miles downstream of the discharge, and chloroform is a non-conservative pollutant. Therefore,to protect the MUN use of the receiving waters,the Regional Board finds that, in this specific circumstance, application of the USEPA MCL for total THMs for the effluent is appropriate, as long as the receiving water does not exceed the OEHHA cancer potency factor's equivalent receiving water concentration at a reasonable distance from the outfall(e.g., before reaching the drinking water intakes). A review of effluent data collected from January 2002 through