SR0085711_SSNL - Laserfiche WebLink

Home Browse Search

Soil Suitability /Nitrate Loading Study Irerracon JPM o Lathrop, Califomia May 24, 2022 im Terracon Project No. NA227026 2.3.6 Impact of Nitrate Loading to Nearby Water Sources The nearest surface water source is the San Joaquin River which is located to the adjoining west of the site. The site is situated lower than the river and the proposed septic systems are proposed to be developed greater than 1,000 feet east; therefore, percolating effluent is not anticipated to affect the surface water source. 2.4 Discussion of Nitrate Loading Results 2.4.1 Total Nitrate Impact Based on the method and assumptions described, the result of the nitrate loading balance indicate that the proposed development is anticipated to be below the MCL. 2.4.2 Methods of Mitigation Nitrate mitigation measures appears unwarranted. 3.0 CONCLUSIONS AND RECOMMENDATIONS Three percolation tests (131 at 6.5 feet, B3 at 3.5 feet and B6 at 3.0 feet bgs) were conducted on the site. The soils encountered in the percolation test borings consisted primarily of silty sand and/or sand with silt. The soil borings demonstrated rapid percolation rates of 1.04 (B1), 1.14 (133), and 1.43 (136) minutes per inch; therefore, the EHD recommends a minimum 20 -foot separation between the bottom of the dispersal system to groundwater. Groundwater was encountered at approximately 3.83 feet bgs within Terracon's soil profile boring (B5) located east of the pond. Groundwater was not encountered in our soil profile / percolation test boring (B1) located north of the pond. Terracon recommends groundwater elevation be verified at various locations across the site. Two groundwater samples collected from the existing trailer (GW -1) and residence (GW -2) were reported below laboratory reporting limits for nitrate as N and DBCP. The client has indicated the existing trailers and residence will not be occupied or utilized in the proposed development. If the two existing septic systems will not be used, these systems should be abandoned in accordance with EHD recommendations. The total maximum daily flow rate for Phase I - Septic System 1 is 1,275 gpd. Peak flow rates are anticipated between 11:00 AM and 1:30 PM during shift overlap. Based on the nitrate loading balance, nitrate levels for the proposed development are anticipated to increase nitrate levels up to 3.3 mg/L-N which is below the MCL of 10 mg/L-N. The result of Responsive ■ Resourceful ■ Reliable 18