Water levels are measured in the designated monitoring wells on a monthly and/or quarterly basis when possible.

Transcription

1 The Washoe County Department of Water Resources (WCDWR) operated an artificial recharge pilot system in Golden Valley, Washoe County, Nevada, from December 199 through March 199. The pilot system was returned to service on October 3,, after new funding sources were established. Annual reports are available upon request. Field work is completed according to requirements outlined in the Nevada Division of Environmental Protection (NDEP) Permit No. UNEV9 when possible. Activities include: 1) collecting and analyzing injection water and ground water samples during artificial recharge; and ) measuring water levels in four () designated monitoring wells and approximately thirty (3) additional domestic wells. Injection water and ground water from the four () monitoring wells are collected and analyzed monthly when possible. Analyses are performed by a state certified laboratory and in the field when equipment is available. Laboratory analyses include chloride, total dissolved solids (TDS), electric conductivity (EC), and ph. The analytical laboratory also performs routine domestic (including nitrate) and total trihalomethanes (TTHM) analyses on a quarterly basis for the monitoring wells and injection water according to NDEP permit requirements. Field analyses include TDS, EC, ph, sample and ambient temperatures, turbidity, salinity, free available chlorine, total residual chlorine, and combined chlorine. Dissolved oxygen (not a permit requirement) also is analyzed in the field. Water levels are measured in the designated monitoring wells on a monthly and/or quarterly basis when possible. Injection quantities and flow rates are tracked by reading flow meters at each injection wellhead. The amount of water injected is reported as gallons. Injection pressures were determined by attaching a removable pressure gauge to a fitting on each injection wellhead. Flow rates (Q) are reported as gallons per minute (gpm) and pressures (P) are reported as pounds per square inch (psi). Historic nitrate-n (mg/l) analyses from this injection program are summarized in the attached graphs (Figures 1 through ). Nitrate-N concentrations in the injected water and in water collected from monitor well GV1 are less than mg/l and are well below the maximum contaminant level (MCL) of mg/l. Nitrate-N in monitoring well GV3 fluctuate seasonally, but have shown an overall decreasing trend from 1 mg/l in 3 to just below the MCL at 9.7 mg/l in. Concentrations of nitrate-n in the Pendill domestic well fluctuate seasonally as well, but remain within a fairly constrained range below the MCL between 1. and.3 mg/l. Previous investigations into the nitrate with respect to groundwater quality concerns have been conducted by WCDWR. A 199 study found that concentrations of nitrate in several domestic wells in the Lemmon Valley basin

2 were above the MCL of ppm for nitrate-n (Widmer and McKay, 199). The two sub-areas most affected by septic effluent were Golden Valley and the Heppner Subdivision. Both areas have experienced groundwater mining resulting in water level declines of as much as feet from 197 to 199, with an estimated continued decline of one to three feet per year. Groundwater pumping could affect water quality by vertically mixing shallow contaminated water with deeper water within the aquifer system. Studies in Lemmon Valley, Golden Valley, and other areas throughout Nevada indicate that pumping effects may draw down contamination into cones of depression under the influence of pumping (Widmer and McKay, 199; Seiler, ; Lopes, ). The 199 WCDWR study also found that groundwater withdrawals in Golden Valley have resulted in pumping exceeding natural recharge by as much as % at the time of publication in 199. Maximum concentrations of nitrate-n in Golden Valley increased from 1 mg/l In 19 to 19 mg/l in The study also noted an increasingly pervasive spreading of above background-level nitrate-n occurrences in Golden Valley (Widmer and McKay, 199). The study observed that the ISDS effluent contamination is largely controlled by soil conditions, especially where fast draining soils exist. A 7 study by the WCDWR into the potential risk associated with septic tanks to groundwater throughout Washoe County reiterated the potential for septic tank effluent impacts (especially nitrate) to groundwater in Golden Valley. As depicted in Figure, septic tank densities in the Golden Valley area are as high as septics per square mile (Kropf and Thomas, 7). Although domestic wells that were sampled for the 199 have not been resampled since that time, there are data available from State and other sources that have allowed for isocontour plots of nitrate to be completed. Figure depicts nitrate-n in various wells in 1993 and Figure 7 depicts nitrate in various domestic wells in 7. The Golden Valley Park well is situated within the HDI and has shown elevated nitrate concentrations (as high as. mg/l). The other water supply wells (LV,, and ) appear to be outside of the highly affected groundwater area.

3 WASHOE COUNTY ARTIFICIAL RECHARGE PROJECT FIGURE 1. NITRATE-N CONCENTRATIONS IN INJECTION WATER/INJECTATE 9 7 NITRATE (mg/l) 3 1 9/1/ 9/1/3 /31/ /31/ 9/1/ 9/1/7 /31/ /31/9 SAMPLING DATE

4 WASHOE COUNTY ARTIFICIAL RECHARGE PROJECT FIGURE. NITRATE-N CONCENTRATIONS IN MONITORING WELL GV1 9 7 NITRATE (mg/l) 3 1 1// 1//3 1/9/ 1/9/ 1// 1//7 1/9/ 1/9/9 SAMPLING DATE

5 WASHOE COUNTY ARTIFICIAL RECHARGE PROJECT FIGURE 3. NITRATE-N CONCENTRATIONS IN MONITORING WELL GV NITRATE (mg/l) 1 1// //3 1// 3 // 1// // 1// /11/ 1/11/ /11/7 1/11/ 7 /11/ 1/11/ /11/9 1/11/ 9 /1/ SAMPLING DATE

6 WASHOE COUNTY ARTIFICIAL RECHARGE PROJECT FIGURE. NITRATE-N CONCENTRATIONS IN PENDILL (PURYEAR) DOMESTIC WELL 9 7 NITRATE (mg/l) 3 1 9/1/ 9/1/3 /31/ /31/ 9/1/ 9/1/7 /31/ /31/9 SAMPLING DATE

7 s:\gis\goldenvalley\rwpc_septicstudy_goldenvalley_septicdensity.mxd Golden Valley LV LV 9 Military Rd Lemmon Dr LV 3 GV PARK Estates Rd 39 Golden Valley Rd N Virginia St Study Area Boudary.. 1 Miles Septics/Sq mile WCDWR Well Other Agency Well Parcel on Septic Hydrobasin Boundary Septic Density - Golden Valley Area Regional Water Planning Commision Septic Nitrate Baseline Data and Risk Assessment Study for Washoe County Notes: The Scale and configuration of all Information shown heron are approximate only and are not intended as a guide for design or survey work. Reproduction is not permitted without prior written permission from the Washoe County Department of Water Resources. November 7 Department of Water Resources Washoe County Nevada 93 Energy Way Reno, Nevada 9 (77) 9- N

8 s:\gis\goldenvalley\rwpc_septicstudy_goldenvalley_nitrate7.mxd LV Golden Valley 1.1 LV 9 1. Military Rd Lemmon Dr LV 3.3 GV PARK. Estates Rd 39 Golden Valley Rd N Virginia St Study Area Boudary.. 1 Miles Nitrate Concentrations (PPM) DS1.1 Monitoring Well Municipal Well Name WCDWR Well Other Agency Well N3 Concentration (ppm) Parcel on Septic Nitrate Concentration - Golden Valley Area (7) Regional Water Planning Commision Septic Nitrate Baseline Data and Risk Assessment Study for Washoe County Notes: The Scale and configuration of all Information shown heron are approximate only and are not intended as a guide for design or survey work. Reproduction is not permitted without prior written permission from the Washoe County Department of Water Resources. November 7 Department of Water Resources Washoe County Nevada 93 Energy Way Reno, Nevada 9 (77) 9- N

9 LV Golden Valley 1.1 LV 9 1. Military Rd Lemmon Dr LV 3.3 GV PARK. Estates Rd 39 Golden Valley Rd N Virginia St Study Area Boudary.. 1 Miles Nitrate Concentrations (PPM) 1 DS1.1 Monitoring Well Municipal Well Name WCDWR Well Other Agency Well N3 Concentration (ppm) Parcel on Septic Nitrate Concentration - Golden Valley Area (1993) Regional Water Planning Commision Septic Nitrate Baseline Data and Risk Assessment Study for Washoe County Notes: The Scale and configuration of all Information shown heron are approximate only and are not intended as a guide for design or survey work. Reproduction is not permitted without prior written permission from the Washoe County Department of Water Resources. November 7 Department of Water Resources Washoe County Nevada 93 Energy Way Reno, Nevada 9 (77) 9- s:\gis\goldenvalley\rwpc_septicstudy_goldenvalley_nitrate1993.mxd N